NormalizeHEADmain

249 files changed, 17 insertions, 24729 deletions

diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..d7b82bc
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1,4 @@
+*.txt text eol=lf
+*.htm text eol=lf
+*.html text eol=lf
+*.md text eol=lf
diff --git a/LICENSE.txt b/LICENSE.txt
new file mode 100644
index 0000000..6312041
--- /dev/null
+++ b/LICENSE.txt
@@ -0,0 +1,11 @@
+This eBook, including all associated images, markup, improvements,
+metadata, and any other content or labor, has been confirmed to be
+in the PUBLIC DOMAIN IN THE UNITED STATES.
+
+Procedures for determining public domain status are described in
+the "Copyright How-To" at https://www.gutenberg.org.
+
+No investigation has been made concerning possible copyrights in
+jurisdictions other than the United States. Anyone seeking to utilize
+this eBook outside of the United States should confirm copyright
+status under the laws that apply to them.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..7db1436
--- /dev/null
+++ b/README.md
@@ -0,0 +1,2 @@
+Project Gutenberg (https://www.gutenberg.org) public repository for
+eBook #50068 (https://www.gutenberg.org/ebooks/50068)
diff --git a/old/50068-0.txt b/old/50068-0.txt
deleted file mode 100644
index cc810d4..0000000
--- a/old/50068-0.txt
+++ /dev/null
@@ -1,10368 +0,0 @@
-The Project Gutenberg EBook of Hawkins Electrical Guide Vol. 8 (of 10), by 
-Nehemiah Hawkins
-
-This eBook is for the use of anyone anywhere in the United States and most
-other parts of the world at no cost and with almost no restrictions
-whatsoever.  You may copy it, give it away or re-use it under the terms of
-the Project Gutenberg License included with this eBook or online at
-www.gutenberg.org.  If you are not located in the United States, you'll have
-to check the laws of the country where you are located before using this ebook.
-
-Title: Hawkins Electrical Guide Vol. 8 (of 10)
-       A Progressive Course of Study for Engineers, Electricians,
-       Students, and Those Desiring to Acquire a Working Knowledge
-       of Electricity and Its Applications
-
-Author: Nehemiah Hawkins
-
-Release Date: September 28, 2015 [EBook #50068]
-
-Language: English
-
-Character set encoding: UTF-8
-
-*** START OF THIS PROJECT GUTENBERG EBOOK HAWKINS ELECTRICAL GUIDE, VOL 8 ***
-
-
-
-
-Produced by Juliet Sutherland, Paul Marshall and the Online
-Distributed Proofreading Team at http://www.pgdp.net
-
-
-
-
-
-
-Transcriber's Notes:
-
-  Underscores "_" before and after a word or phrase indicate _italics_
-    in the original text.
-
-  Equal signs "=" before and after a word or phrase indicate =bold=
-    in the original text.
-
-  Small capitals have been converted to SOLID capitals.
-
-  Illustrations have been moved so they do not break up paragraphs.
-
-  Misprints in the table SAVING DUE TO HEATING THE FEED WATER, Pg. 1936
-    have been corrected, they are:
-
-         Init. Temp.     Pressure     Old Value      New Value
-            130            40            .0954          .0934
-            200            40            .0900          .0999
-            210            40            .1000          .1010
-            230           100            .0117          .1012
-
- In the original text, there are two Fig. 2769's and two Fig. 2770's.
- The second of each has had an "a" suffix added, i.e. 2769a and 2770a.
-
- On line 7397 the word "impedence" was corrected to "impedance".
-
- Superscripts are shown as ^{d} and subscripts are shown as _{d}, where
- "d" is an integer.
-
- Inconsistent spelling and hyphenation has been left as in the original.
-
-
-
-
-       THE THOUGHT IS IN THE QUESTION
-      THE INFORMATION IS IN THE ANSWER
-
-    HAWKINS ELECTRICAL GUIDE NUMBER EIGHT
-
-     QUESTIONS ANSWERS & ILLUSTRATIONS
-
-  A PROGRESSIVE COURSE OF STUDY FOR ENGINEERS,
-  ELECTRICIANS, STUDENTS AND THOSE DESIRING TO
-        ACQUIRE A WORKING KNOWLEDGE OF
-
-       ELECTRICITY AND ITS APPLICATIONS
-
-   A PRACTICAL TREATISE by HAWKINS AND STAFF
-
-   THEO AUDEL & CO. 72 FIFTH AVE. NEW YORK.
-
-   COPYRIGHTED, 1915, BY THEO. AUDEL & CO.,
-
-               NEW YORK.
-          Printed in the United States.
-
-
-
-
-                   TABLE OF CONTENTS
-                      GUIDE No. 8
-
-
-  =WAVE FORM MEASUREMENT=                            1,839 to 1,868
-
-   Importance of wave form measurement--=methods=:
-   step by step; constantly recording--=classes of
-   apparatus=: wave indication; _oscillographs_--=step
-   by step methods=--Joubert's; four part commutator;
-   modified four part commutator; ballistic galvanometer;
-   zero; Hospitalier ondograph--=constantly recording
-   methods=: cathode ray; glow light; moving iron; moving
-   coil; hot wire--=oscillographs=--moving coil type;
-   construction and operation; production of the time scale;
-   oscillograms--falling plate camera; its use.
-
-  =SWITCHBOARDS=                                     1,869 to 1,884
-
-   =General principles=: diagram--small plant a.c.
-   switchboard--=switchboard panels=; =generator
-   panel=; diagram of connections--simple method of
-   determining bus bar capacity--feeder panel--diagrams of
-   connection for two phase and three phase installations.
-
-  =ALTERNATING CURRENT WIRING=                       1,885 to 1,914
-
-   Effects to be considered in making
-   calculations--=induction=; self- and mutual; mutual
-   induction, how caused--=transpositions=--inductance
-   per mile of three phase circuit, table--=capacity=;
-   table--=frequency--skin effect=; calculation;
-   table--=corona effect=; its manifestation;
-   critical voltage; spacing of wires--=resistance of
-   wires--impedance--power factor=; apparent current;
-   usual power factors encountered; example--=wire
-   calculations--sizes of wire--table of the property of
-   copper wire--drop=; example--current--example covering
-   horse power, watts, apparent load, current, size of wire,
-   drop, voltage at the alternator, and electrical horse power.
-
-  =POWER STATIONS=                                   1,915 to 1,988
-
-   Classification--=central stations=; types: a.c.,
-   d.c., and a.c. and d.c.; reciprocating engine vs.
-   turbine--=location of central stations=; price of
-   land; trouble after erection; water supply; service
-   requiring direct current--=size of plant=; nature
-   of load; peak load; load factor; machinery required;
-   example; factors of evaporation; grate surface per
-   horse power--=general arrangement of station=;
-   belt drive with counter shaft; desirable features of
-   belt drive; conditions, suitable for counter shaft
-   drive; location of engine and boilers; the steam pipe;
-   piping between engine and condenser; number and type
-   of engine; superheated steam; switchboard location;
-   individual belt drive; direct drive--=station
-   construction=--=foundations=--=walls=--
-   =roofs=--=floors=--=chimneys=;
-   cost of chimneys and mechanical draft; high chimneys
-   ill advised--=steam turbine=; types: impulse
-   and reaction; why high vacuum is necessary; the
-   working pressure--=hydro-electric plants=--water
-   turbines; types: impulse, reaction--=isolated
-   plants=--=sub-stations=; arrangement; three phase
-   installations; reactance coils in sub-stations; portable
-   sub-stations.
-
-  =MANAGEMENT=                                       1,989 to 2,114
-
-   The term "management"--=selection=; general
-   considerations--=selection of generators=;
-   efficiency of generators; size and number;
-   regulation--=installation=; precautions;
-   handling of armatures; assembling a machine; speed
-   of generators; calculation of pulley sizes; gear
-   wheels--=belts=; various belt drives; horse
-   power transmitted by belts; velocity of belt; endless
-   belts--=switchboards=; essential points of difference
-   between single phase and three phase switchboard wiring;
-   assembling a switchboard; usual equipment.
-
-   =Operation of Alternators--alternators in parallel=;
-   synchronizing; lamp methods; action of amortisseur winding;
-   synchronizing three phase alternators; disadvantage of
-   lamp method--=cutting out alternator=; precautions;
-   hunting--=alternators in series=.
-
-   =Transformers=; selection; efficiency; kind of oil
-   used; detection of moisture; drying oil; regulation;
-   transformers in parallel; polarity test--=motor
-   generators=; various types and conditions requiring
-   same--=dynamotors=; precautions--=rotary
-   converters=; objections to single phase type; operation
-   when driven by direct current, by alternating current; most
-   troublesome part; efficiency; overload; starting; starting
-   current.
-
-   =Electrical measuring instruments=; location;
-   readings; station voltmeters; points relating to
-   ammeters; attention necessary; usual remedies to correct
-   voltmeter--=how to test generators=; commercial
-   efficiency; various tests.
-
-   =Station Testing:= resistance measurement by "drop"
-   method--methods of connecting ammeter voltmeter and
-   wattmeter for measurement of power--=motor testing:=
-   single phase motor--three phase motor, voltmeter and
-   ammeter method; two wattmeter method; polyphase wattmeter
-   method; one wattmeter method; one wattmeter and Y box
-   method--three phase motor with neutral brought out; single
-   wattmeter method--temperature test, three phase induction
-   motor--=three phase alternator testing:= excitation
-   or magnetization curve test--synchronous impedance
-   test--load test--three phase alternator or synchronous
-   motor temperature test--=direct current motor= or
-   =generator testing:= magnetization curve--(shunt)
-   external characteristic--direct current motor testing;
-   load and speed tests--temperature test, "loading back"
-   method--=compound dynamo testing=: external
-   characteristic, adjustable load--=transformer testing=:
-   external characteristic, adjustable load--=transformer
-   testing=: core loss and leakage or exciting current
-   test--copper loss--copper loss by wattmeter measurement
-   and impedance--temperature--insulation--internal
-   insulation--insulation resistance--polarity--winding
-   or ratio tests.
-
-
-
-
-CHAPTER LXIII
-
-WAVE FORM MEASUREMENT
-
-
-The great importance of the wave form in alternating current work
-is never denied, though it has sometimes been overlooked. The
-application of large gas engines to the driving of alternators
-operated in parallel requires an accurate knowledge of the wave form,
-and a close conformation to a sine wave if parallel operation is
-to be satisfactory. It is also important that the fluctuations in
-magnetism of the field poles should be known, especially if solid
-steel pole faces be used.
-
-     If an alternator armature winding be connected in delta, the
-   presence of a third harmonic becomes objectionable, as it gives
-   rise to circulating currents in the winding itself, which increase
-   the heating and lowers the efficiency of the machine.
-
-     That the importance of having a good wave form is being
-   realized, is proved by the increasing prevalence in alternator
-   specifications of a clause specifying the maximum divergence
-   allowable from a true sine wave. It is however perhaps not always
-   realized that an alternator which gives a good pressure wave on
-   no load may give a very bad one under certain loads, and the
-   ability of the machine to maintain a good wave form under severe
-   conditions of load is a better criterion of its good design than
-   is the shape of its wave at no load.
-
-     The question of wave form is of special interest to the power
-   station engineer. Upon it depends the answer to the questions:
-   whether he may ground his neutral wires without getting large
-   circulating currents; whether he may safely run any combination
-   of his alternators in parallel; whether the constants of his
-   distributing circuit are of an order liable to cause dangerous
-   voltage surges due to resonance with the harmonics of his
-   pressure wave; what stresses he is getting in his insulation due
-   to voltage surges when switching on or off, etc. It has been
-   shown by Rossler and Welding that the luminous efficiency of the
-   alternating current arc may be 44 per cent. higher with a flat
-   topped than with a peaked pressure wave, while on the other hand
-   it is well known that transformers are more efficient on a peaked
-   wave. Also the accuracy of many alternating current instruments
-   depends upon the wave shape.
-
-     In making insulation breakdown tests on cables, insulators, or
-   machinery, large errors may be introduced unless the wave form at
-   the time of the test be known. It is not sufficient even to know
-   that the testing alternator gives a close approximation to a sine
-   wave at no load; since if the capacity current of the apparatus
-   under test be moderately large compared with the full load current
-   of the testing alternator, the charging current taken may be
-   sufficient to distort the wave form considerably, thus giving
-   wrong results to the disadvantage of either the manufacturer or
-   purchaser.
-
-[Illustration: FIG. 2,583.--General Electric simultaneous record of
-three waves with common zero.]
-
-The desirability of a complete knowledge of the manner in which the
-pressure and current varies during the cycle, has resulted in various
-methods and apparatus being devised for obtaining this knowledge.
-The apparatus in use for such purpose may be divided into two general
-classes,
-
-  1. Wave indicators;
-  2. Oscillographs.
-
-and the methods employed with these two species of apparatus may be
-described respectively as,
-
-  1. Step by step;
-  2. Constantly recording.
-
-that is to say, in the first instance, a number of instantaneous
-values are obtained at various points of the cycle, which are plotted
-and a curve traced through the several points thus obtained. A
-constantly recording method is one in which an infinite number of
-values are determined and recorded by the machine, thus giving a
-complete record of the cycle, leaving no portion of the wave to be
-filled in.
-
-[Illustration: FIG. 2,584.--General Electric simultaneous record of
-three waves with separate zeros.]
-
-[Illustration: Figs. 2,585 and 2,586.--Oscillograms (from paper by
-Morris and Catterson-Smith, Proc. I. E. E., Vol. XXXIII, page 1,023),
-showing _how the current varies_ =in one of the armature coils of
-a direct current motor=. Fig. 2,585 was obtained with the brushes
-in the neutral position, and fig. 2,586 with the brushes shifted
-forward.]
-
-
-The various methods of determining the wave form may be further
-classified as:
-
-                  { Joubert's method;
-                  { Four part commutator method;
-                  { Modified four part commutator method;
-  1. Step by step { Ballistic galvanometer method;
-                  { Zero method;
-                  { By Hospitalier ondograph.
-
-[Illustration: FIG. 2,587.--=Oscillogram= by Bailey and Cleghorne
-(Proc. I.E.E., Vol. XXXVIII), =showing= _the sparking pressure or
-pressure between the brush and the commutator segment at the moment
-of separation_. The waves fall into groups of three owing to the fact
-that there were three armature coils in each slot.]
-
-                                                     { cathode ray;
-                          { by use of various types  { glow light;
-  2. constantly recording { of =oscillograph=,       { moving iron;
-                          { such as                  { moving coil;
-                                                     { hot wire.
-
-
-[Illustration: FIG. 2,588.--Various wave forms. The sine wave
-represents a current or pressure which varies according to the sine
-law. A distorted wave is due to the properties of the circuit, for
-instance, the effect of hysteresis in an iron core introduced into a
-coil is to distort the current wave by adding harmonics so that the
-ascending and descending portions may not be symmetrical. A peaked
-wave has a large maximum as compared with its virtual value. A peaked
-wave is produced by a machine with concentrated winding.]
-
-=Joubert's Method.=--The apparatus required for determining the
-wave form by this step by step method, consists of a galvanometer,
-condenser, two, two way switches, resistance and adjustable contact
-maker, as shown in fig. =2,589=.
-
-     The contact maker is attached to the alternator shaft so that
-   it will rotate synchronously with the latter. By means of the
-   adjustable contact, the instant of "making" that is, of "closing"
-   the testing circuit may be varied, and the angular position of the
-   armature, at which the testing circuit is closed, determined from
-   the scale, which is divided into degrees.
-
-     A resistance is placed in series with one of the alternator
-   leads, such that the drop across it, gives sufficient pressure for
-   testing.
-
-=Ques. Describe the method of making the test.=
-
-[Illustration: FIG. 2,589.--Diagram illustrating Joubert's =step by
-step method= of wave form measurement.]
-
-Ans. For current wave measurement switch No. 1 is placed on contact
-F, and for pressure wave measurement, on contact G, switch No. 2 is
-now turned to M and the drop across the resistance (assuming switch
-No. 1 to be turned to contact F) measured by charging the condenser,
-and then discharging it through the galvanometer by turning the
-switch to S. This is repeated for a number of positions of the
-contact maker, noting each time the galvanometer reading and position
-of the contact maker. By plotting the positions of contact maker as
-abscissæ, and the galvanometer readings as ordinates, the curve drawn
-through them will represent the wave form.
-
-[Illustration: FIG. 2,590.--=Four part commutator method= of wave
-form measurement. The contact device consists of two slip rings and
-a four part commutator. One slip ring is connected to one terminal
-of the source, the other to the voltmeter, and the commutator to the
-condenser. By adjusting R when a known direct current pressure is
-impressed across the terminals, the voltmeter can be rendered direct
-reading.]
-
-[Illustration: FIG. 2,591.--=Modified four part commutator method=
-of wave form measurement (Duncan's modification). By this method
-one contact maker can be used for any number of waves having the
-same frequency. Electro-dynamometers are used and the connections
-are made as here shown. The moving coils are connected in series to
-the contact maker, and the fixed coils are connected to the various
-sources to be investigated, then the deflection will be steady and
-by calibration with direct current can be made to read directly in
-volts.]
-
-
-     The apparatus is calibrated by passing a known constant current
-   through the resistance.
-
-[Illustration: FIG. 2,592.--Diagram illustrating the =ballistic
-galvanometer method= of wave form measurement. =The test may be made=
-as described in the accompanying text, or in case the contact breaker
-is belted instead of attached rigidly to the shaft, it could be
-arranged to run slightly out of synchronism, then by taking readings
-at regular intervals, points will be obtained along the curve without
-moving the contact breaker. If this method be used, a non-adjustable
-contact breaker suffices. =In arranging the belt drive= so as to run
-slightly out of synchronism, if the pulleys be of the same size, the
-desired result is obtained by pasting a thin strip of paper around
-the face of one of the pulleys thus altering the velocity ratio of
-the drive slightly from unity.]
-
-=Ballistic Galvanometer Method.=--This method, which is due to
-Kubber, employs a _contact breaker_ instead of a _contact maker_.
-The distinction between these two devices should be noted: A contact
-maker keeps the circuit _closed_ during each revolution for a short
-interval only, whereas, a contact breaker keeps the circuit _open_
-for a short interval only.
-
-     Fig. 2,592, shows the necessary apparatus and connections for
-   applying the ballistic galvanometer method. The contact breaker
-   consists of a commutator having an ebonite or insulating segment
-   and two brushes.
-
-     _In operation_ the contact breaker keeps the circuit closed
-   during all of each revolution, except the brief interval in which
-   the brushes pass over the ebonite segment.
-
-     The contact breaker is adjustable and has a scale enabling its
-   various positions of adjustment to be noted.
-
-=Ques. Describe the test.=
-
-[Illustration: FIGS.. 2,593 and 2,594.--=Two curves= _representing
-pressure and current respectively of a rotary converter._ Fig. 2,593,
-pressure wave V, fig. 2,594 current wave C. These waves were obtained
-from a converter which was being driven by an alternator by means of
-an independent motor. The rotary converter was supplying idle current
-to some unloaded transformers and the ripples clearly visible in the
-pressure wave V, correspond to the number of teeth in the armature of
-the rotary converter.]
-
-Ans. The contact breaker is placed in successive positions and
-galvanometer readings taken, the switch being turned to F, fig.
-2,592, in measuring the current wave, and to G in measuring the
-pressure wave. The results thus obtained are plotted giving
-respectively current and pressure waves.
-
-=Ques. How is the apparatus calibrated?=
-
-Ans. By sending a constant current of known value through the
-resistance R.
-
-=Zero Method.=--In electrical measurements, a zero method is one _in
-which the arrangement of the testing devices is such that the value
-of the quantity being measured is shown when the galvanometer needle
-points to_ =zero=.
-
-In the zero method either a contact maker or contact breaker may be
-used in connection with a galvanometer and slide wire bridge, as
-shown in figs. 2,595 and 2,596.
-
-[Illustration: FIG. 2,595.--Diagram illustrating zero method of wave
-measurement with _contact_ =maker=. The voltage of the battery must
-be at least as great as the maximum pressure to be measured and must
-be kept constant.]
-
-=Ques. What capacity of battery should be used?=
-
-Ans. Its voltage should be as great as the maximum pressure to be
-measured.
-
-=Ques. What necessary condition must be maintained in the battery?=
-
-Ans. Its pressure must be kept constant.
-
-=Ques. How are instantaneous values measured?=
-
-Ans. The bridge contact A is adjusted till the galvanometer shows no
-deflection, then the length AS is a measure of the pressure.
-
-     The drop between these points can be directly measured with a
-   voltmeter if desired.
-
-=Ques. How did Mershon modify the test?=
-
-Ans. He used a telephone instead of the galvanometer to determine the
-correct placement of the bridge contact A.
-
-[Illustration: FIG. 2,596.--Diagram illustrating zero method of wave
-measurement with _contact_ =breaker=. The voltage of the battery must
-be at least as great as the maximum pressure to be measured and must
-be kept constant.]
-
-=Ques. How can the instantaneous values be recorded?=
-
-Ans. By attaching to the contact A, a pencil controlled by an
-electro-magnet arranged to strike a revolving paper card at the
-instant of no deflection, the paper being carried on a drum.
-
-=Hospitalier Ondograph.=--The device known by this name is a
-development of the Joubert step by step method of wave form
-measurement, that is to say, the principle on which its =action is
-based=, consists in _automatically charging a condenser from each
-100th wave, and discharging it through a recording galvanometer, each
-successive charge of the condenser being automatically taken from a
-point a little farther along the wave._
-
-[Illustration: FIG. 2,597.--Diagram of Hospitalier ondograph showing
-mechanism and connections. It represents a development of Joubert's
-step by step method of wave form measurement.]
-
-     As shown in the diagram, fig. 2,597, the ondograph consists of
-   a synchronous motor A, operated from the source of the wave form
-   to be measured, connected by gears B to a commutator D, in such a
-   manner that while the motor makes a certain number of revolutions,
-   the commutator makes a like number diminished by unity; that is to
-   say, if the speed of the motor be 900 revolutions per minute, the
-   commutator will have a speed of 899.
-
-     The commutator has three contacts, arranged to automatically
-   charge the condenser _cc'_ from the line, and discharge it through
-   the galvanometer E, the deflection of which will be proportional
-   to the pressure at any particular instant when contact is made.
-
-     In fig. 2,597, GG' are the motor terminals, HH' are connected to
-   the condenser _cc'_ through a resistance (to prevent sparking at
-   the commutator) and I, I' are the connections to the service to be
-   measured.
-
-     A permanent magnet type of recording galvanometer is employed.
-   Its moving coil E receives the discharges of the condenser in
-   rapid succession and turns slowly from one side to the other.
-
-[Illustration: FIG. 2,598.--View of Hospitalier ondograph. =In
-operation=, a long pivoted pointer carrying a pen and actuated by
-electro-magnets, records on a revolving drum a wave form representing
-the alternating current, pressure or current wave.]
-
-     The movable part operates a long needle (separately mounted)
-   carrying a pen F, which traces the curve on the rotating cylinder
-   C. This cylinder is geared to the synchronous motor to run at such
-   a speed as to register three complete waves upon its circumference.
-
-     By substituting an electromagnetic galvanometer for the
-   permanent magnet galvanometer, and by using the magnet coils as
-   current coils and the moving coil as the volt coil, the instrument
-   can be made to draw watt curves. Fig. 2,598 shows the general
-   appearance of the ondograph.
-
-=Cathode Ray Oscillograph.=--This type of apparatus for measuring
-wave form was devised by Braun, and consists of a cathode ray tube
-having a fluorescent screen at one end, a small diaphragm with a
-hole in it at its middle, and two coils of a few turns each, placed
-outside it at right angles to one another. These coils carry currents
-_proportional to the_ =pressure= _and_ =current= _respectively_ of
-the circuit under observation.
-
-[Illustration: FIG. 2,599.--General Electric =moving coil
-oscillograph= complete =with tracing table=. The tracing table is
-employed for observing the waves, and by using a piece of transparent
-paper, the waves under observation appear as a continuous band of
-light which can be traced, thus making a permanent record. This is
-not, however, to be regarded as a recording attachment, and can not
-be used where instantaneous phenomena are being investigated. =The
-synchronous motor= for operating the synchronous mirror in connection
-with tracing and viewing attachment is wound for 100 to 115 volts, 25
-to 125 cycles, and should, of course, be run from the same machine
-which furnishes power to the circuit under observation. A rheostat
-for steadying and adjusting the current should be connected in series
-with the motor. =The beam from the vibrator mirrors= _striking this
-synchronous mirror moves back and forth over the curved glass, and
-gives the length of the wave; the movement of the vibrator mirror
-gives the amplitude, and the combination gives the wave complete_. An
-arc lamp or projection lantern produces the image reflected by the
-mirrors upon the film, tracing table or screen. For the rotation of
-the photographic film, a small direct current shunt wound motor is
-ordinarily used.]
-
-The ray then moves so as to produce an energy diagram on the
-fluorescent screen.
-
-[Illustration: FIG. 2,600.--General Electric moving coil
-oscillograph. =The moving elements= _consist of single loops of flat
-wire carrying a small mirror and held in tension by small spiral
-springs_. The current passing down one side and up the other, forces
-one side forward and the other backward, thus causing the mirror to
-vibrate on a vertical axis. The vibrator elements fit into chambers
-between the poles of electro-magnets, and are adjustable, so as to
-move the beam from the mirror, both vertically and horizontally. A
-sensitized photographic film is wrapped around a drum and held by
-spring clamps. The drum, with film, is placed in a case and a cap
-then placed over the end, making the case light, when the index is
-either up or down. The loading is done in a dark room. A driving dog
-is screwed into the drum shaft, and which, when the drum and case are
-in place, revolves the film past a slot. =When an exposure is to be
-made=, the index is moved from the closed position, thus opening the
-slot in the case and exposing the film to the beam of light from the
-vibrating mirrors when the electrically operated shutter is open. The
-slot is then closed by moving the index to "=Exposed=." A slide with
-ground glass can be inserted in place of the film case or roll holder
-to arrange the optical system when making adjustments. The shutter
-operating mechanism is arranged so as to hold the shutter open during
-exactly one revolution of the film drum. There are two devices
-connected to the shutter operating mechanism; one opens the shutter
-at the instant the end of the film passes the slot; the other opens
-immediately, at any part of the film, and both give exposure during
-one revolution. The first is useful when making investigations in
-which the events are either recurring, or their beginnings known or
-under control, and the second when the time of the event is not under
-control, such as the blowing of fuses or opening of circuit breakers.]
-
-The instrument is much used in wireless telegraphy, as it is capable
-of showing the characteristics of currents of very high frequency.
-
-[Illustration: FIG. 2,601.--General Electric =moving coil
-oscillograph= _with case removed_, =showing= _interior construction
-and arrangement of parts_. The oscillograph is furnished complete
-with a three element electro-magnet galvanometer, optical system,
-shutter and shutter operating mechanism, film driving motor and cone
-pulleys, photographic and tracing attachments, 6 film holders, and
-the following repair parts, for vibrators: 6 extra suspension strips;
-6 vibrator mirrors; 1 box gold leaf fuses; 1 bottle mirror cement; 1
-bottle damping liquid.]
-
-[Illustration: FIG. 2,602.--Oscillogram showing the direct current
-pressure of a 25 cycle rotary converter (below), and (above) the
-pressure wave taken between one collector ring and one commutator
-brush. The 12 ripples per cycles in the direct current voltage are
-due to a 13th harmonic in the alternating current supply.]
-
-=Glow Light Oscillograph.=--This device consists of two aluminum rods
-in a partially evacuated tube, their ends being about two millimeters
-apart. When an alternating current of any frequency passes between
-them a sheath of violet light forms on one of the electrodes, passing
-over to the other when the current reverses during each cycle. The
-phenomenon may be observed or photographed by means of a revolving
-mirror.
-
-[Illustration: FIG. 2,603.--Curves by Morris, _illustrating the_
-=dangerous rush of current which may occur when switching on a
-transformer=. The circuit was broken at F and made again at G. The
-current was so great as to carry the spot of light right off the
-photographic plate due to the fact that a residual field was left in
-the core after switching off, and on closing the switch again the
-direction of the current was such as to tend to build up the full
-flux in the same direction as this residual flux. =The dotted lines=
-have been drawn in _to show how the actual waves were distorted from
-the normal_.]
-
-=Moving Iron Oscillograph.=--This type is due to Blondel, to whom
-belongs the credit of working out and describing in considerable
-detail the principles underlying the construction of oscillographs.
-
-     The moving iron type of oscillograph consists of a very thin
-   vane of iron suspended in a powerful magnetic field, thus forming
-   a polarized magnet. Near this strip are placed two small coils
-   which carry the current whose wave form is to be measured.
-
-     The moving iron vane has a very short period of vibration and
-   can therefore follow every variation in the current.
-
-[Illustration: FIG. 2,604.--Siemens-Blondel =moving coil type=
-oscillograph. The coil is in the shape of a loop of thin wire, which
-is suspended in the field of an electro-magnet excited by continuous
-current. The current to be investigated is sent through this loop,
-which in consequence of the interaction of current and magnetic
-field, begins to vibrate. The oscillations are rendered visible by
-directing a beam of light from a continuous current arc lamp onto a
-small mirror fixed to the loop. The light reflected by the mirror is
-in the form of a light strip, but by suitable means this is drawn
-out in respect of time, so that a curve truly representing the
-current is obtained. The loop of fine wire is stretched between two
-supports and is kept in tension by a spring. As the spring tension
-is considerable, the directive force of the vibrating system is
-large, and its natural periodicity very high. The mirror is fixed in
-the center of the loop, and has an area of 1 square mm. In order to
-protect the loops from mechanical injury they are built into special
-frames. The mirrors are of various sizes, the loop for demonstration
-purposes (projection device) being provided with the largest
-mirror and the most sensitive loop with a mirror of the smallest
-dimensions.]
-
-     Attached to the vane is a small mirror which reflects a beam of
-   light upon some type of receiving device.
-
-     The Siemens-Blondel oscillograph shown in fig. 2,604, is of
-   the _moving coil_ type, being a development of the moving iron
-   principle.
-
-=Moving Coil Oscillograph.=--The operation of this form of
-oscillograph is based _on the behaviour of a movable coil in a
-magnetic field_.
-
-[Illustration: FIGS. 2,605 and 2,606.--=Oscillograms= reproduced from
-a paper by M. B. Field on "A Study of the =Phenomena of Resonance=
-by the Aid of Oscillograms" (_Journal_ of _E. E._, Vol. XXXII). =The
-effect of resonance= on the wave forms of alternators has been the
-subject of much investigation and discussion; it is a matter of vital
-importance to the engineer in charge of a large alternating current
-power distribution system. Fig. 2,605 shows the pressure curve of an
-alternator running on a length of unloaded cable, the 11th harmonic
-being very prominent. Fig. 2,606 shows the striking alteration
-produced by reducing the length of cable in the circuit and thus
-causing resonance with the 13th harmonic.]
-
-     It consists essentially of a modified moving coil galvanometer
-   combined with a rotating or vibrating mirror, a moving
-   photographic film, or a falling photographic plate. The
-   galvanometer portion of the outfit is usually referred to as the
-   oscillograph as illustrated in figs. 2,608 to 2,612, representing
-   diagrammatically the moving system.
-
-     In the narrow gap between the poles S, S of a powerful magnet
-   are stretched two parallel conductors formed by bending a thin
-   strip of phosphor bronze back on itself over an ivory pulley P.
-   A spiral spring attached to this pulley serves to keep a uniform
-   tension on the strips, and a guide piece L limits the length of
-   the vibrating portion to the part actually in the magnetic field.
-
-     A small mirror M bridges across the two strips as shown. The
-   effect of passing a current through such a "vibrator" is to cause
-   one of the strips to advance while the other recedes, and the
-   mirror is thus turned about a vertical axis.
-
-[Illustration: FIG. 2,607.--General view of electro-magnet
-form of Duddell moving coil oscillograph, showing oil bath and
-electro-magnet. This instrument is specially designed to have a very
-high natural period of vibration (about 1/10,000 of a second) so as
-to be suitable for accurate research work. It is quite accurate for
-frequencies up to 300 per second. In the figure, A is the brass oil
-bath in which two vibrators are fixed; B, core of electro-magnet
-which is excited by two coils, one of which, C, is seen. The ends of
-these two coils are brought out to four terminals at D, so that the
-coils may be connected in series for 200 volt, or in parallel for 100
-volt circuits. The bolts, E,E, hold the oil bath in position between
-the poles of the magnet. F,F,F (one not seen), are levelling screws;
-G,G, terminals of one vibrator; H, fuse; K, thermometer with bulb in
-center of oil bath.]
-
-[Illustration: FIGS. 2,608 to 2,612.--=Vibrator= of Duddell moving
-coil oscillograph and =section through oil bath= of electro-magnet
-oscillograph. =The vibrator consists of= a brass frame W, which
-supports two soft iron pole pieces P,P. Between these, a long narrow
-groove is divided into two parts by a thin soft iron partition,
-which runs up the center. The current being led in by the brass wire
-U, passes from an insulated brass plate to the strip, which is led
-over an ivory guide block, down one of the narrow grooves and over
-another guide block, the loops round the ivory pulley O, which puts
-tension on the strip by the spring N, back to the guide block again,
-up the other narrow groove, and out by way of the insulated brass
-plate and lead U. Halfway up the grooves the center iron partition R
-is partially cut away to permit of a small mirror M, bridging across
-from one strip to the other, being stuck to the strips by a dot of
-shellac at each corner. The figure illustrates one type of vibrator
-in which P is removable from W for ease in repairing. In type 1,
-these pole pieces P,P are not removable. =The vibrators= are placed
-side by side in the gap between the poles S,S of the electro-magnet,
-see fig. 2,610. Each vibrator is pivoted about vertical centers, the
-bottom center fitting in the base of the oil bath, and the one at
-the top being formed by a screw in the cock piece Y. It can thus be
-easily turned in azimuth, its position being fixed by the adjusting
-screw L, a spiral spring serving to keep the vibrator always in
-contact with this screw. Since each cock piece can be independently
-moved forward or backward, each vibrator can be tipped slightly in
-either of these directions so that complete control over the mirrors
-is obtained and reflected spots of light may be made to coincide with
-that reflected from the fixed zero mirror, which latter is fixed to a
-brass tongue in between the two vibrators. =A plano-convex lens= of
-50 cm. focal length is fixed on the oil bath in front of the vibrator
-mirrors to converge the reflected beams of light. It will be noticed
-that this lens is slightly inclined so that no trouble will be given
-by reflections from its own surface. The normal distance from the
-vibrator mirrors to the scale of photographic plate is 50 cm., and
-at this distance, a convenient working deflection on each side of
-the zero line is 3 to 4 cm. This is obtained with a R.M.S. current
-through the strips of from .05 to .1 of an ampere according to wave
-form, etc. =The maximum deflection= on each side of the zero line
-should not exceed 5 cm. while the maximum R.M.S. current through the
-strips should in no case exceed .1 ampere.]
-
-     Each strip of the loop passes through a separate gap (not shown
-   in the figure). The whole of the "vibrator," as this part of the
-   instrument is called, is immersed in an oil bath, the object
-   of the oil being to damp the movement of the strips, and make
-   the instrument dead beat. It also has the additional advantage
-   of increasing by refraction the movement of the spot of light
-   reflected from the vibrating mirrors.
-
-     The beam of light reflected from the mirror M is received on
-   a screen or photographic plate, the instantaneous value of the
-   current being proportional to the linear displacement of the spot
-   of light so formed.
-
-     With alternating currents, the spot of light oscillates to and
-   fro as the current varies and would thus trace a straight line.
-
-     To obtain an image of the wave form, it is necessary to traverse
-   the photographic plate or film in a direction at right angles to
-   the direction of the movement of the spot of light.
-
-[Illustration: FIG. 2,613.--Duddell =moving coil oscillograph= _with
-projection and tracing desk outfit_. The outfit is designed for
-teaching and lecture purposes. =In operation=, _after the beam of
-light from the arc lamp has been reflected from the oscillograph
-mirrors, it falls on a vibrating mirror which gives it a deflection
-proportional to time in a direction at right angles to the deflection
-it already has and which is proportional to the current passing
-through the oscillograph_. It is therefore only necessary to place a
-screen in the path of the reflected beam of light to obtain a trace
-of the wave form. Since the vibrating mirror is vibrated by means
-of a cam on the shaft of a synchronous motor, which motor is driven
-from, or synchronously with, the source of supply whose wave form is
-being investigated, the wave form is repeated time after time in the
-same place on the screen, and owing to the "persistence" of vision,
-the whole wave appears stationary on the screen. The synchronous
-motor with its vibrating mirror, mentioned above, is located
-underneath the "tracing desk." When used in this position a wave a
-few centimeters in amplitude is seen through a sheet of tracing paper
-which is bent round a curved sheet of glass. A permanent record of
-the wave form can thus easily be traced on the paper. A _dark box_
-which is designed to hold a sheet of sensitized paper in place of
-the tracing paper, can be fitted in place of the tracing desk. Thus
-an actual photographic record of the wave form is obtained. If the
-synchronous motor be transferred from its position underneath the
-tracing desk to the space reserved for it close to the oscillograph,
-the beam of light is then received on a large mirror which is placed
-at an angle of about 45 degrees to the horizontal and so projects the
-wave form onto a large vertical screen which should be fixed about
-two and a half meters distant. Under these conditions a wave form of
-amplitude 50 cm. each side the zero line may be obtained which is
-therefore visible to a large audience.]
-
-=Ques. How are the oscillograms obtained in the Duddell moving coil
-oscillograph?=
-
-Ans. In all cases the oscillograms are obtained by a spot of light
-tracing out the curve connecting current or voltage with time. The
-source of light is an arc lamp, the light from which passes first
-through a lens, and then, excepting when projecting on a screen,
-through a rectangular slit about 10 mm. long by 1 mm. wide. The
-position of the lamp from the lens is adjusted till an image of the
-arc is obtained covering the three (two moving, one fixed) small
-oscillograph mirrors. The light is reflected back from these mirrors
-and, being condensed by a lens which is immediately in front of them,
-it converges till an image of the slit is formed on the surface where
-the record is desired. All that is necessary now to obtain a bright
-spot of light instead of this line image is to introduce in the path
-of the beam of light a cylindrical lens of short focal length.
-
-[Illustration: FIGS. 2,614 and 2,615.--Sectional view of =permanent
-magnet form= of Duddell =moving coil oscillograph.= This instrument
-has a lower natural period of vibration (1/3000 second) than the
-type shown in fig. 2,612, and therefore is not capable of accurately
-following wave forms of such high frequency, but it is sufficiently
-quick acting to follow wave forms of all ordinary frequencies with
-perfect accuracy. It is easier to repair, and more portable owing to
-the fact that the magnetic field is produced by a permanent magnet
-instead of an electro-magnet. This also renders the instrument
-suitable for use on high tension circuits without earth connection,
-as, owing to the fact that no direct current excitation is required,
-the instrument is more easily insulated than other types.]
-
-=Ques. What is the function of the mirrors on the vibrating vane?=
-
-[Illustration: FIG. 2,616.--Diagram of connections of Duddell
-oscillograph =to high pressure circuit.= The modification necessary
-for high pressure circuit only applies to the vibrator which gives
-the pressure wave and consists in adding two more resistances, R_{4}
-and R_{5}. Referring to fig. 2,617, it will be seen that in case fuse
-f_{2} blows, or the vibrator be accidentally broken, the full supply
-voltage is immediately thrown on the instrument itself. This is not
-permissible in high voltage work and therefore the resistance R_{5}
-is introduced as a permanent shunt to the oscillograph vibrator.
-The resistance R_{4} is an exact duplicate of R_{2} being a 21 ohm
-plug resistance box for adjusting the sensitivity of the vibrator
-to an even figure. =In practice= R_{5} is usually a part of R_{1},
-and in most of the high voltage resistances, two taps are brought
-out near one end to serve as R_{5}. One of these taps is usually 50
-ohms distant from the end terminal and the other only 5 ohms from
-the end. =The use of these taps is as follows:= The large resistance
-consisting of R_{1} + R_{5} is so chosen with respect to the voltage
-of the circuit under investigation that the current through R_{1} is
-about .1 ampere. _It should never be more than this continuously._
-Then R_{4} is connected to the 50 ohm tap, and since the resistance
-of the oscillograph vibrator circuit is variable from about 5 to
-26 ohms by means of R_{4}, the current can be controlled through
-the oscillograph from about .066 to .091 of an ampere, enabling an
-open wave form to a convenient scale to be obtained. =If it now
-be desired to record large rises of pressure,= such as may occur
-in cases of resonance, _the height of the wave must be reduced in
-order to keep these rises on the plate_. This is accomplished by
-disconnecting R_{4} from the 50 ohm tap and connecting it to the 5
-ohm tap, when the current through the vibrator will be from .05 to
-.016 of an ampere according to whether the resistance R_{4} is in
-or out of circuit. When, instead of using the _falling plate_, the
-_cinematograph_ camera is being used, it becomes necessary always
-to work on the 5 ohm tap since the width of the film is much less
-than that of the plate, and the current must therefore be less.
-=In experiments where sudden rises of voltage are expected= _it is
-often advisable to keep_ R_{1} _as great as possible._ That end of
-the resistance R_{1} referred to as R_{5} in the diagram should be
-securely connected to the supply main and no switch or fuse used. A
-switch may, if desired, be used in series with R_{1}, provided it be
-inserted at the point where R_{1} joins the supply main remote from
-R_{5}. It will be seen that fuses f_{1} and f_{2} are shown. Provided
-that the connections are always made in accordance with the diagram,
-and the vibrators are always shunted by R_{5} or R_{3} respectively,
-there is not much objection to the use of these fuses, but on general
-principles it is wise to avoid fuses in high tension work and
-accordingly with each permanent magnet oscillograph, dummy fuses are
-supplied, which can be inserted in place of the ordinary fuses when
-desired. _The remark previously made about keeping both vibrators
-and the frame of the instrument at approximately the same pressure
-applies with additional emphasis in high pressure work._]
-
-Ans. They simply control the direction of a beam of light in a
-horizontal plane in such a manner that its deflection from a zero
-position depends on the current passing through the instrument, and
-it is therefore evident that the oscillograph is not complete without
-means of producing a time scale.
-
-[Illustration: FIG. 2,617.--Diagram of connections of Duddell
-oscillograph =to low pressure circuit=, R_{1} is a high non-inductive
-resistance connected across the mains in series with one of
-the vibrators. S_{2} is a switch, and f_{2}, the fuse (on the
-oscillograph in this circuit). The resistance of R_{1} in ohms
-should be rather more than ten times the voltage of the circuit,
-so that a current of a little less than .1 of an ampere will pass
-through it. The vibrator will then give the curve of the circuit
-on an open scale. (For the projection oscillograph, the resistance
-R_{1} should be only twice the supply voltage, since .5 of an ampere
-is required to give full scale deflection on a large screen.) =To
-obtain the current wave form=, _the shunt_ R_{3} _is connected in
-series with the circuit under investigation and the second vibrator
-is connected across this shunt_. Here also f_{1} is a fuse, S_{1} a
-switch, and R_{2} an adjustable resistance box. The switch S_{1} is
-however unnecessary if the plug resistance box supplied for R_{2}
-be used, since an infinity plug is included in this box. The shunt
-R_{3} should have a drop of about 1 volt across it in order to give
-a suitable working current through the vibrator. The resistance
-R_{2} is not absolutely essential, but it is a great convenience in
-adjusting the current through the vibrator. It is a plug resistance
-box, the smallest coil being .04 of an ohm and the total 21 ohms.
-Being designed to carry .5 ampere continuously it can be used
-with any other type of Duddell oscillograph, and by its use the
-sensitiveness of the vibrator can be adjusted so that a round number
-of amperes in the shunt gives 1 mm. deflection. This adjustment is
-best made with direct current. =It should be noted= in connecting
-the oscillograph in circuit, that _the two vibrators should be so
-connected to the circuit that it is impossible that a higher pressure
-difference than_ 50 _volts should exist between one vibrator and the
-other, or between either vibrator and the frame_. To ensure attention
-to this important point, a brass strap is provided which connects
-the two vibrators together and to the frame of the instrument. This
-does not mean that this point must necessarily be earthed since the
-frame of the instrument is insulated from the earth. It is advisable,
-however, to earth it when possible.]
-
-[Illustration: FIGS. 2,618 and 2,619.--=Two curves= _obtained with
-the_ =falling plate camera= and illustrating _the discharge of a
-condenser through an inductive circuit_. =When taking curve A= the
-resistance in the circuit was very small compared to the inductance,
-while =before taking curve B= an additional non-inductive resistance
-was inserted in the circuit so that the oscillations were damped out
-much more rapidly although the periodic time remained approximately
-constant.]
-
-=Ques. How is the time scale produced?=
-
-Ans. Either the surface on which the beam of light falls may be
-caused to move in a vertical plane with a certain velocity, so that
-the intersection of the beam and the plane surface traces out a curve
-connecting current with time (a curve which becomes a permanent
-record if a sensitized surface be used); or, the surface may remain
-stationary and in the path of the horizontally vibrating beam may be
-introduced a mirror which rotates or vibrates about a horizontal
-axis, thus superposing a vertical motion proportional to time on the
-horizontal vibration which is proportional to current, and causing
-the beam of light to trace out a curve connecting current and time on
-the stationary surface.
-
-=Ques. What kind of recording apparatus is used with the Duddell
-oscillograph?=
-
-Ans. A falling plate camera, or a cinematograph film camera.
-
-[Illustration: FIG. 2,620.--Synchronous motor with vibrating mirror
-as used with Duddell moving coil oscillograph. =Since the motor must
-run synchronously= with the wave form it is required to investigate,
-_it should be supplied with current from the same source_. The motor
-can be used over a wide range of frequencies (from 20 to 120). When
-working at frequencies below 40, it is advisable to increase the
-moment of inertia of the armature, and for this purpose a suitable
-brass disc is used. =The armature carries a sector=, _which cuts off
-the light from the arc lamp during a fraction of each revolution, and
-a cam which rocks the vibrating mirror_. =It makes one revolution
-during two complete periods=, and the cam and sector are so arranged
-that during 1½ periods, the mirror is turning with uniform angular
-velocity, while during the remaining half period, the mirror is
-brought back quickly to its angular position, the light being cut off
-by the sector during this half period.]
-
-=Ques. Explain the operation of the falling plate camera.=
-
-Ans. In this arrangement a photographic plate is allowed to fall
-freely by the force of gravity down a dark slide. At a certain point
-in its fall it passes a horizontal slit through which the beams of
-light from the oscillograph pass, tracing out the curves on the plate
-as it falls.
-
-[Illustration: FIGS. 2,621 to 2,623.--Interior of cinematograph
-camera as used on Duddell moving coil oscillograph =for obtaining
-long records=. The loose side of case is shown removed and one of
-the reels which carry the film lying in front. =The spool of film=
-which is placed on the loose reel A, passes over the guide pulley
-B, then vertically downward between the brass gate D (shown open in
-the figure), and the brass plate C. =The exposure aperture= is in
-the plate C and can be opened or closed by a shutter controlled by
-the lever M. The groove in the plate C, and the springs which press
-the gate D flat on the plate C, prevent the film having any but a
-vertical motion as it passes the exposure slit. E is the sprocket
-driving pulley which engages with the perforations on the film and
-unwinds it from the reel A to reel H. Outside the case on the far
-side of it is secured to the axle G a three speed cone pulley. This
-is driven by a motor of about 1/7 horse power, which also drives,
-through the gears shown, the sprocket pulley E. Close to the grooved
-cone pulley is a lever carrying a jockey pulley L, and a brake, which
-latter is normally held onto the cone pulley by a spring and so
-causes the loose belt to slip. By pressing a lever which is attached
-to the falling plate camera case, the brake can be suddenly released
-and at the same time the jockey pulley caused to tighten the belt
-onto the grooved cone pulley, so that the starting and stopping of
-the film is controlled independently of the driving motor, and being
-quickly accomplished avoids waste of film. =Both reels= are alike and
-each is made in two pieces. =The upper reel= is loose on its axle and
-its motion is retarded slightly by a friction brake. =The lower reel=
-is also loose on its axle, but it is driven by means of a friction
-clutch, the clutch always rotating faster than the reel so that the
-used film delivered by the sprocket pulley E is wound up as fast as
-delivered. K is the front face of one reel, the boss on it pushes
-into the tube on the other half H, which serves not only to unite the
-two halves, but also to secure the end of the film which is doubled
-through J.]
-
-     The mean speed of the plate at the moment of exposure is about
-   13 feet per second. This speed is very suitable for use with
-   frequencies of from 40 to 60 periods per second. A cloth bag is
-   used to introduce the plate to the slide.
-
-     A catch holds the plate until it is desired to let it fall.
-   Inside the case, is a small motor, 100 or 200 volts direct
-   current, driving four mirrors which are fixed about a common axis
-   with their planes parallel to it.
-
-[Illustration: FIG. 2,624.--Portion of oscillograph record taken with
-cinematograph film camera, =showing the rush of current= and =sudden
-rise of voltage= _at the moment of switching on a high pressure
-feeder_.]
-
-     By looking through a small slot in the end of the camera into
-   these rotating mirrors, the observer sees the wave form which the
-   oscillograph is tracing out and is thus able to make sure that
-   he is obtaining the particular wave form or other curve desired
-   before exposing the plate.
-
-[Illustration: FIG. 2,625.--Portion of oscillograph record taken with
-a cinematograph film camera =showing the effect of switching off
-a high pressure feeder= and illustrating the violent fluctuations
-produced by sparking at the switch contacts.]
-
-     The plate falls into a second red cloth bag which is placed on
-   the bottom of the slide. The plates used are "stereoscopic size",
-   6¾" × 3¼" (17.1 × 8.3 cm.).
-
-=Ques. For what use is the cinematograph camera adapted?=
-
-Ans. For long records.
-
-     For instance, in investigations, such as observation on the
-   paralleling of alternators, the running up to speed of motors,
-   and the surges which may occur in switching on and off cable,
-   etc. The cinematograph camera fits on to the falling plate case
-   and by means of which a roll of cinematograph film can be driven
-   at a uniform speed past the exposure aperture, enabling records
-   up to 50 metres in length to be obtained. An interior view of the
-   cinematograph camera is shown in fig. 2,621.
-
-[Illustration: FIG. 2,626.--Curves reproduced from an article by J.
-T. Morris in the _Electrician_. "On recording transitory phenomena by
-the oscillograph."]
-
-[Illustration: FIG. 2,627.--First rush of current from an alternator
-when short circuited, showing unsymmetrical initial wave of current,
-becoming symmetrical after a few cycles. 25 cycles.]
-
-[Illustration: FIG. 2,628.--Pressure wave obtained from narrow
-exploring coil on alternator armature, indicating distribution of
-field flux. The terminal voltage of the alternator is very nearly a
-sine wave, 60 cycles; about 17 volts.]
-
-SOME OSCILLOGRAPH RECORDS
-
-[Illustration: FIG. 2,629.--The waves of voltage and current of an
-alternating arc. A, voltage wave; B, current wave showing low power
-factor of the arc without apparent phase displacement. 60 cycles.]
-
-[Illustration: FIG. 2,630.--Rupturing 650 volt circuit. A, current
-wave; B, 25 cycle wave to mark time scale.]
-
-[Illustration: FIG. 2,631.--First rush of current from alternator
-when short circuited, showing unsymmetrical current wave, also wave
-of field current caused by short circuit current in armature. Upper
-curve, armature current; lower curve, field current.]
-
-[Illustration: FIG. 2,632.--Mazda (tungsten) lamp, showing rapid
-decrease to normal current as filament heats up. 25 cycles.]
-
-[Illustration: FIG. 2,633.--Current wave in telephone line
-corresponding to sustained vowel sound "_i_," as in machine; voice
-pitched at A 110.]
-
-[Illustration: FIG. 2,634.--Carbon lamp, showing rapid increase to
-normal current as filament heats up. 25 cycles.]
-
-[Illustration: FIG. 2,635.--Short circuit current on direct current
-end of rotary converter, 21,500 amperes maximum. Upper curve, direct
-current voltage; lower curve, direct current amperage. Duration of
-short circuit about .1 second.]
-
-
-
-
-CHAPTER LXIV
-
-SWITCHBOARDS
-
-
-=General Principles of Switchboard Connections.=--The interconnection
-of generators, transformers, lines, bus bars, and switches with
-their relays, in modern switchboard practice is shown by the
-diagrams, figs. 2,636 to 2,645. The figures being lettered A to J
-for simplicity, the generators are indicated by black discs, and the
-switches by open circles, while each heavy line represents a set of
-bus bars consisting of two or more bus bars according to the system
-of distribution. It will be understood, also, in this connection,
-that the number of pole of the switches and the type of switch will
-depend upon the particular system of distribution employed.
-
-     Diagram A, shows the simplest system, or one in which a single
-   generator feeds directly into the line. There are no transformers
-   or bus bars and only one switch is sufficient.
-
-     In B, a single generator supplies two or more feeders through a
-   single set of bus bars, requiring a switch for each feeder, and a
-   single generator switch.
-
-     In C, two generators are employed and required and the addition
-   of a bus section switch.
-
-     D, represents a number of generators supplying two independent
-   circuits. The additional set of bus bars employed for this purpose
-   necessitates an additional bus section switch, and also additional
-   selector switches for both feeders and generators.
-
-     E, shows a standard system of connection for a city street
-   railway system having a large number of feeders.
-
-[Illustration: FIGS. 2,645 and 2,646.--Diagrams illustrating general
-principles of switchboard connections.]
-
-     This arrangement allows any group of feeders to be supplied from
-   any group of generators.
-
-[Illustration: FIG. 2,646.--Fort Wayne switchboard panel for one
-alternator and one transfer circuit. Diagram giving dimensions,
-arrangement of instruments of board, and method of wiring. The
-different forms of standard alternating current switchboard panels
-for single phase circuits made by the Fort Wayne Electric Works are
-designed to fulfill all the usual requirements of switchboards for
-this class of work. The line includes panels equipped for a single
-generator; for one generator and two circuits; one generator and one
-transfer circuit; one generator, an incandescent and an arc lighting
-circuit; and also feeder panels of different kinds.]
-
-     It also permits the addition of a generator switch for each
-   generator.
-
-     F, represents the simplest system with transformers.
-
-     It requires a single generator transformer bank, switch and
-   line. The arrangement as show at F is used where a number of
-   plants supply the same system.
-
-     G, represents a system having more than one line.
-
-     In this case a bus bar and transformer switch is used on the
-   high tension side.
-
-     H, shows a number of generators connected to a set of low
-   tension bus bars through generator switches, and employing a low
-   tension transformer switch.
-
-     I, shows the connections of a system having a large number of
-   feeders supplied by several small generators. In this case, the
-   plant is divided into two parts, each of which may be operated
-   independently.
-
-[Illustration: FIG. 2,647.--General Electric =small plant alternating
-current switchboard=, _designed for use in small central stations and
-isolated plants_. They are for use with one set of bus bars, to which
-all generators and feeders are connected by means of single throw
-lever switches or circuit breakers, suitable provision being made for
-the parallel operation of the generators.]
-
-     J, represents the arrangement usually employed in modern plants
-   where the generator capacity is large enough to permit of a
-   generator transformer unit combination with two outgoing lines. By
-   operating in parallel on the high tension side only, any generator
-   can be run with any transformer. The whole plant can be run in
-   parallel, or the two parts can be run separately.
-
-[Illustration: FIG. 2,648.--Crouse-Hinds =voltmeter and ground
-detector radial switch=, arranged for mounting on the switchboard.
-The switch proper is placed on the rear of the board with hand wheel,
-dial, and indicator only on the front side. The current carrying
-parts are of hard brass, with contact surfaces machined after
-assembling. The contact parts are of the plunger spring type, and the
-cross bar has fuse connections. Ground detector circuits are marked
-G+ and G- for two wire system, and G+, G-, GN+ and GN- for three wire
-system. When the voltmeter switch is to be used as a ground detector,
-two circuits are required for a two wire system, and four circuits
-for a three wire system, that is, a six circuit voltmeter and ground
-detector switch for use on a two wire system has two circuits for
-ground detector and four circuits for voltmeter readings. A six
-circuit voltmeter and ground detector switch, for use on a three wire
-system, has four circuits for ground detector and two circuits for
-voltmeter readings.]
-
-=Switchboard Panels.=--The term "panel" means the slab of marble or
-slate upon which is mounted the switches, and the indicating and
-controlling devices. There are usually several panels comprising
-switchboards of moderate or large size, these panels being classified
-according to the division of the system that they control, as for
-instance:
-
-  1. Generator panel;
-  2. Feeder panel;
-  3. Regulator panel, etc.
-
-     In construction, the marble or slate should be free from
-   metallic veins, and for pressures above, say, 600 volts, live
-   connections, terminals, etc., should preferably be insulated from
-   the panels by ebonite, mica, or removed from them altogether, as
-   is generally the case with the alternating gear where the switches
-   are of the oil type.
-
-[Illustration: FIGS. 2,649 and 2,650,--Wiring diagrams of
-Crouse-Hinds voltmeter and ground detector switches. Fig. 2,649
-voltmeter switch; fig. 2,650 voltmeter and ground detector switch. A
-view of the switch is shown in fig. 2,648; it is designed for use on
-two or three wire systems up to 300 volts.]
-
-     The bus bars and connections should be supported by the
-   framework at the back of the board, or in separate cells, and the
-   instruments should be operated at low pressure through instrument
-   transformers.
-
-     The panels are generally held in position by bolting them to an
-   angle iron, or a strip iron framework behind them.
-
-=Generator Panel.=--This section of a switchboard carries the
-instruments and apparatus for measuring and electrically controlling
-the generators. On a well designed switchboard each generator has, as
-a rule, its own panel.
-
-[Illustration: FIGS. 2,651 to 2,653.--Diagrams of connections for
-generator panels. =Key to symbols=: =A=, ammeter; =A.S.=, ammeter
-switch; =C.T.=, current transformer; =F.=, fuse; =F.A.=, direct
-current field ammeter; =F.S.=, field switch; =G.C.S.=, governor
-control switch; =L.S.=, limit switch (included with governor motor);
-=O.S.=, oil switch; =P.I.W.=, polyphase indicating wattmeter;
-=P.W.M.=, polyphase watthour meter; =P.R.=, pressure receptacle;
-=P.P.=, pressure plug; =Rheo.=, rheostat; =S.=, shunt; =S.R.=,
-synchronizing receptacle; =S.P.=, synchronizing plugs; =T.B.=,
-terminal board for instrument leads; =V=, alternating current
-voltmeter.]
-
-[Illustration: FIGS. 2,654 and 2,655.--Diagrams illustrating =a
-simple method of determining bus capacity= as suggested by the
-General Electric Co. Fig. 2,654 relates to any panel; the method is
-as follows: =1.= Make a rough plan of the _entire board_, regardless
-of the number of panels to be ordered. _The order of panels_
-shown is recommended, it being most economical of copper and best
-adapted to future extensions. =2.= To avoid confusion keep on one
-side of board everything pertaining to exciter buses, and on other
-side everything pertaining to A. C. buses. =3.= With single lines
-represent the exciter and A. C. buses across such panels as they
-actually extend and by means of arrows indicate that portion of each
-bus which is connected to feeders and that portion which is connected
-to generators. _Remember that "Generator" and "Feeder" arrows must
-always point toward each other_, otherwise the rules given below do
-not hold. Note also that the field circuits of alternator panels are
-treated as D. C. feeders for the exciter bus. =4.= On each panel
-mark its ampere rating, that is, the maximum current it supplies
-to or takes from the bus. For A. C. alternator panels the D. C.
-rating is the excitation of the machines. =5.= Apply the following
-rules _consecutively_, and note their application in fig. 2,654.
-(For the sake of clearness ampere ratings are shown in light face
-type and bus capacities in large type.) =A.= _Always begin with the
-tail of the arrow and treat "generator" and "feeder" sections of
-the bus separately._ =B.= _Bus capacity for first panel = ampere
-rating of panel._ =C.= _Bus capacity for each succeeding panel =
-ampere rating of panel plus bus capacity for preceding panel._ (See
-sums marked above the buses in fig. 2,654.) =D.= _For a panel not
-connected to a bus extending across it, use the smaller value of
-the bus capacities already obtained for the two adjoining panels._
-(See exciter bus for panel C.) =E.= _The bus capacity for any feeder
-panel need not exceed the maximum for the generator panels_ (see A.
-C. bus for panel G) _and vice versa_ (see exciter bus for panel B).
-Hence the corrections made in values obtained by applying rules =B=
-and =C=. The arrangement of panels shown in fig. 2,654 is the one
-which is mostly used. The above method may, however, be applied to
-other arrangements, one of which is shown in fig. 2,655. Here the
-generators must feed both ways to the feeders at either end of the
-board so that in determining A. C. bus capacities it is necessary to
-first consider the generators with the feeders at one end, and then
-with the feeders at the other end as shown by the dotted A. C. buses.
-The required bus capacities are then obtained by taking the maximum
-values for the two cases.]
-
-[Illustration: FIG. 2,656.--End view showing =general arrangement of
-switchboards= for 240, 480, and 600 volt alternating current. The cut
-shows a single throw oil switch mounted on the panel.]
-
-In the case of a dynamo, a good representative panel would have
-mounted upon it a reverse current circuit breaker, an ammeter, a
-double pole main switch (or perhaps a single pole switch, since
-the circuit breaker could also be used as a switch) a double pole
-socket into which a plug could be inserted to make connection with
-a voltmeter mounted on a swinging bracket at the end of the board;
-a rheostat handle, the spindle of which operates the shunt rheostat
-of the machine, the rheostat being placed either directly behind
-the spindle, if of small size, or lower down with chain drive from
-the hand wheel spindle, if of larger size, a field discharge switch
-and resistance, a lamp near the top of the panel for illuminating
-purposes, a fuse for the voltmeter socket, and, if desired, a
-watthour meter. If the dynamo be compound wound, the equalizing
-switch will generally be mounted on the frame of the machine, and in
-some cases the field rheostat will be operated from a pillar mounted
-in front of the switchboard gallery. If the generator be for traction
-purposes, the circuit breaker is more often of the maximum current
-type, and a lightning arrester is often added, without a choke coil,
-the latter as well as further lightning arresters being mounted on
-the feeder panels.
-
-[Illustration: FIGS. 2,657 and 2,658.--Two views of a =feeder panel=,
-showing general arrangement of the devices assembled thereon. A,
-circuit breaker; B, ammeter; C, voltmeter; D, switches.]
-
-In the case of a high pressure alternating current plant of
-considerable size, the bus bars oil switches, and the current and
-pressure transformers are generally mounted either in stoneware
-cells, or built on a framework in a space guarded by expanded metal
-walls, and no high pressure apparatus of any sort is brought on to
-the panels themselves.
-
-[Illustration: FIGS. 2,659 to 2,666.--Diagram of connections for
-three phase feeder panels. =Key to symbols=: A, ammeter; A.S.,
-three way ammeter switch; B.A.S., bell alarm switch; C.T., current
-transformer; F, fuse; O.S., oil switch; P.I.W., polyphase indicating
-wattmeter; P.W.M., polyphase watthour meter; T.B., terminal board;
-T.C., trip coils for oil switch.]
-
-=Feeder Panel.=--The indicating and control apparatus for a feeder
-circuit is assembled on a panel called the feeder panel.
-
-The most common equipment in the case of a direct current feeder
-panel comprises an ammeter, a double pole switch, and double pole
-fuses or instead of the fuses, a circuit breaker on one or both
-poles; in the case of a traction feeder a choke coil and a lightning
-arrester are often added.
-
-[Illustration: FIGS. 2,667 and 2,668.--Diagrams of connections for
-two phase and three phase installations: A and A1, ammeter; C.C.,
-constant current transformer; C.T., current transformer; D.R.,
-discharge resistance; F, fuse; F.S., field switch; L.A., lightning
-arrester; O.S., oil switch; P.P., pressure plug; P.R., pressure
-receptacle; P.T., pressure transformer; S and S1, plug switches;
-T.C., oil switch trip coil; V, voltmeter.]
-
-The equipment of a typical high pressure three phase feeder panel is
-an ammeter (sometimes three ammeters, one in each phase) operated
-by a current transformer, and oil break switch with two overload
-release coils, or three if the neutral of the circuit be earthed, the
-releases being operated by current transformers.
-
-[Illustration: FIG. 2,669.--Crouse-Hinds radial ammeter switch,
-arranged for mounting directly on the switchboard. It is designed
-for use with external shunt ammeters of any make or capacity, and in
-connection with the required number of shunts, makes possible the
-taking of current readings of a corresponding number of circuits by
-means of one ammeter. The wiring diagram is shown in fig. 2,670.]
-
-The switch when on a large system is often in a cell some distance
-behind the panel, and is then controlled by a system of levers, or by
-a small motor which is started and stopped by a throw over switch on
-the panel, in which case there is generally a lamp or lamps on the
-panel to show whether the switch is open or closed.
-
-     Air brake switches or links are placed between the bus bars
-   and the oil switch to allow of the latter being isolated for
-   inspection purposes, and as a general rule no apparatus carrying
-   high pressure current is allowed on the front of the panel. With
-   both direct and alternating current feeders, a watthour meter is
-   often added to show the total consumption of the circuit.
-
-[Illustration: FIG. 2,670.--Wiring diagram for Crouse-Hinds radial
-ammeter switch as illustrated in fig. 2,669. The switch proper is on
-the rear of the switchboard, and the hand wheel dial and indicator on
-the front.]
-
-     A typical three phase generator panel is provided with three
-   ammeters, one in each phase, operated from three current
-   transformers, one to each ammeter, a volt meter, a power factor
-   indicator, and an indicating watthour meter, all operated from
-   one or more pressure transformers, and the necessary current
-   transformers, the operating handle of the oil switch, which is
-   connected to the switch itself by means of rods, two maximum
-   releases operated by current transformers, or a reverse relay
-   for automatically tripping the switch, lamps for indicating when
-   the switch is tripped, a socket for taking the plug which makes
-   connection between the secondary of a pressure transformer and
-   the synchronizer on the synchronizing panel, and a lamp for
-   illuminating purposes, while on the base of the panel or on a
-   pillar at the front of the gallery is mounted the gear for the
-   field circuit. This consists of a double pole field switch and a
-   discharge resistance, an ammeter, a handle for the rheostat in
-   the generator field, and (if each alternator have its own direct
-   coupled exciter) possibly also a small rheostat for the exciter
-   field.
-
-            NOTE.--In some cases where the capacity of
-          the plant is not very great, the oil switch
-          is mounted on the back of the panel, and the
-          bus bars, current transformers, &c., on the
-          framework, also just at the back of the panel,
-          but under no circumstances, in good modern
-          practice, is high pressure apparatus permitted
-          on the front of the board. Where the capacity of
-          the plant is very large, the oil switches are
-          operated electrically by means of small motors,
-          and in this case the small switch gear for
-          starting and stopping this motor is mounted on
-          the generator panel, also the lamp or lamps to
-          indicate when the switch is open, and when closed.
-
-
-
-
-CHAPTER LXV
-
-=ALTERNATING CURRENT WIRING=
-
-
-In the case of alternating current, because of its peculiar
-behaviour, there are several effects which must be considered in
-making wiring calculations, which do not enter into the problem with
-direct current.
-
-Accordingly, in determining the size of wires, allowance must be made
-for
-
-  1. Self-induction;
-  2. Mutual-induction;
-  3. Power factor;
-  4. Skin effect;
-  5. Corona effect;
-  6. Frequency;
-  7. Resistance.
-
-     Most of these items have already been explained at such length,
-   that only a brief summary of facts need be added, to point out
-   their connection and importance with alternating current wiring.
-
-=Induction.=--The effect of induction, whether self-induction
-or mutual induction, is to set up a back pressure of _spurious
-resistance_, which must be considered, as it sometimes materially
-affects the calculation of circuits even in interior wiring.
-
-     _Self-induction is the effect produced by the action of the
-   electric current upon itself during variations in strength._
-
-=Ques. What conditions besides variations of current strength governs
-the amount of self-induction in a circuit?=
-
-Ans. The shape of the circuit, and the character of the surrounding
-medium.
-
-     If the circuit be straight, there will be little self-induction,
-   but if coiled, the effect will become pronounced. If the
-   surrounding medium be air, the self-induction is small, but if it
-   be iron, the self-induction is considerable.
-
-[Illustration: FIGS. 2,671 to 2,676.--=The effect of self-induction.=
-In a non-inductive circuit, as in fig. 2,672, the whole of the
-virtual pressure is available to cause current to flow through the
-lamp filament, hence it will glow with maximum brilliancy. If an
-inductive coil be inserted in the circuit as in fig. 2,674, the
-reverse pressure due to self-induction will oppose the virtual
-pressure, hence the effective pressure (which is the difference
-between the virtual and reverse pressures), will be reduced and
-the current flow through the lamp diminished, thus reducing the
-brilliancy of the illumination. The effect may be intensified to such
-degree by interposing an iron core in the coil as in fig. 2,676, as
-to extinguish the lamp.]
-
-=Ques. With respect to self-induction, what method should be followed
-in wiring?=
-
-Ans. When iron conduits are used, the wires of each circuit should
-not be installed in separate conduits, because such arrangement will
-cause excessive self-induction.
-
-     The importance of this may be seen from the experience of one
-   contractor, who installed feeders and mains in separate iron
-   pipes. When the current was turned on, it was found that the
-   self-induction was so great as to reduce the pressure to such an
-   extent that the lamps, instead of giving full candle power, were
-   barely red. This necessitated the removal of the feeders and main
-   and re-installing them, so that those of the same circuit were in
-   the same pipe.
-
-=Ques. What is mutual induction?=
-
-Ans. Mutual induction is the effect of one alternating current
-circuit upon another.
-
-[Illustration: FIG. 2,677.--Measurement of self induction when
-the frequency is known. The apparatus required consists of a high
-resistance or electrostatic a.c. voltmeter, d.c. ammeter, and a
-non-inductive resistance. Connect the inductive resistance to be
-measured as shown, and close switch M, short circuiting the ammeter.
-Connect alternator in circuit and measure drop across R and across
-X_{_i_}. Disconnect alternator and connect battery in circuit, then
-open switch M and vary the continuous current until the drop across R
-is the same as with the alternating current, both measurements being
-made with the same voltmeter; read ammeter, and measure drop across
-X_{_i_}. Call the drop across X_{_i_} with alternating current E, and
-with direct current E_{_i_}, and the reading of the ammeter J. Then
-     ____________________
-L = √E^{2} + E_{_i_}^{2} ÷ 2π _f_ I. If the resistance X_{_i_}
-be known, and the ammeter be suitable for use with alternating
-current, the switch and R may be dispensed with.
-
-          ______________________________
-Then L = √E^{2} - X_{_i_}^{2} I_{_i_}^{2} ÷ 2π _f_ I,
-where I_{_i_} is the value of the alternating current. The resistance
-of the voltmeter should be high enough to render its current
-negligible as compared with that through X_{_i_}.]
-
-=Ques. How is it caused?=
-
-Ans. It is due to the magnetic field surrounding a conductor cutting
-adjacent conductors and inducing back pressures therein.
-
-     This effect as a rule in ordinary installations is negligible.
-
-=Transpositions.=--The effect of mutual induction between two
-circuits is proportional to the inter-linkage of the magnetic fluxes
-of the two lines. This in turn depends upon the proximity of the
-lines and upon the general relative arrangement of the conductors.
-
-[Illustration: FIG. 2,678.--Transposition diagram for two parallel
-lines consisting of two wires each.]
-
-[Illustration: FIG. 2,679.--Transposition diagram for three phase,
-three wire line, transposing at the vertices of an equilateral
-triangle. The line is originally balanced and becomes unbalanced on
-transposing, a procedure which should be resorted to only to prevent
-_mutual induction_.]
-
-[Illustration: FIG. 2,680.--Transposition diagram of three phase,
-three wire line, with center arranged in a straight line.]
-
-The inductive effect of one line upon another is equal to the
-algebraic sum of the fluxes due to the different conductors of the
-first line, considered separately, which link the secondary line.
-
-The effect of mutual induction is to induce surges in the line where
-a difference of frequency exists between the two currents, and to
-induce high electrostatic charges in lines carrying little or no
-current, such as telephone lines.
-
-  INDUCTANCE PER MILE OF THREE PHASE CIRCUIT
-
-  ---------+-------+----------+------------
-           | Diam. | Distance |    Self
-    Size   |  in   |  _d_ in  | Inductance
-   B. & S. | inch. |  inches. |  L henrys.
-  ---------+-------+----------+------------
-    0000   |  .46  |    12    |   .00234
-           |       |    18    |   .00256
-           |       |    24    |   .00270
-           |       |    48    |   .00312
-           |       |          |
-     000   |  .41  |    12    |   .00241
-           |       |    18    |   .00262
-           |       |    24    |   .00277
-           |       |    48    |   .00318
-           |       |          |
-      00   |  .365 |    12    |   .00248
-           |       |    18    |   .00269
-           |       |    24    |   .00285
-           |       |    48    |   .00330
-           |       |          |
-       0   |  .325 |    12    |   .00254
-           |       |    18    |   .00276
-           |       |    24    |   .00293
-           |       |    48    |   .00331
-           |       |          |
-       1   |  .289 |    12    |   .00260
-           |       |    18    |   .00281
-           |       |    24    |   .00308
-           |       |    48    |   .00338
-           |       |          |
-       2   |  .258 |    12    |   .00267
-           |       |    18    |   .00288
-           |       |    24    |   .00304
-           |       |    48    |   .00314
-           |       |          |
-       3   |  .229 |    12    |   .00274
-           |       |    18    |   .00294
-           |       |    24    |   .00310
-           |       |    48    |   .00351
-           |       |          |
-       4   |  .204 |    12    |   .00280
-           |       |    18    |   .00300
-           |       |    24    |   .00315
-           |       |    48    |   .00358
-           |       |          |
-       5   |  .182 |    12    |   .00286
-           |       |    18    |   .00307
-           |       |    24    |   .00323
-           |       |    48    |   .00356
-           |       |          |
-       6   |  .162 |    12    |   .00291
-           |       |    18    |   .00313
-           |       |    24    |   .00329
-           |       |    48    |   .00369
-           |       |          |
-       7   |  .144 |    12    |   .00298
-           |       |    18    |   .00310
-           |       |    24    |   .00336
-           |       |    48    |   .00377
-           |       |          |
-       8   |  .128 |    12    |   .00303
-           |       |    18    |   .00325
-           |       |    24    |   .00341
-           |       |    48    |   .00384
-           |       |          |
-       9   |  .114 |    12    |   .00310
-           |       |    18    |   .00332
-           |       |    24    |   .00348
-           |       |    48    |   .00389
-           |       |          |
-      10   |  .102 |    12    |   .00318
-           |       |    18    |   .00340
-           |       |    24    |   .00355
-           |       |    48    |   .00396
-  ---------+-------+----------+------------
-
-This effect may be nullified by separating the lines and by
-transposing the wires of one of the lines so that the effect produced
-in one section is opposed by that in another. Of two parallel lines
-consisting of two wires each, one may be transposed to neutralize the
-mutual inductance.
-
-     Fig. 2,678 shows this method. The length L' should be an even
-   factor of L so that to every section of the line transposed there
-   corresponds an opposing section.
-
-[Illustration: FIG. 2,681.--Capacity effect in single phase
-transmission line. The effect is the same as would be produced by
-shunting across the line at each point an infinitesimal condenser
-having a capacity equal to that of an infinitesimal length of
-circuit. For the purpose of calculating the charging current, a very
-simple and sufficiently accurate method is to determine the current
-taken by a condenser having a capacity equal to that of the entire
-line when charged to the pressure on the line at the generating end.
-The effect of capacity of the line is to reduce the pressure drop,
-that is, improve the regulation, and to decrease or increase the
-power loss depending on the load and power factor of the receiver.]
-
-[Illustration: FIG. 2,682.--Capacity effect in a three phase
-transmission line. It is the same as would be produced by shunting
-the line at each point by three infinitesimal condensers connected in
-star with the neutral point grounded, the capacity of each condenser
-being twice that of a condenser of infinitesimal length formed by
-any two of the wires. The effect of capacity on the regulation and
-efficiency of the line can be determined with sufficient accuracy
-in most cases by considering the line shunted at each end by three
-condensers connected in star, the capacity of each condenser being
-equal to that formed by any two wires of the line. An approximate
-value for the charging current per wire is the current required to
-charge a condenser, equal in capacity to that of any two of the
-wires, to the pressure at the generating end of the line between any
-one wire and the neutral point.]
-
-
-     The self inductance of lines is readily calculated from the
-   following formula:
-
-  L = .000558 {2.303 log (2A ÷ _d_) + .25} per mile of circuit
-
-where
-
-   L = inductance of a loop of a three phase circuit in henrys.
-       _Note._--The inductance of a complete single phase
-                    circuit = L × 2 ÷ √3.
-   A = distance between wires;
-  _d_ = diameter of wire.
-
-
-  CAPACITY IN MICRO-FARADS PER MILE OF CIRCUIT
-            FOR THREE PHASE SYSTEM
-
-  ---------+-------+----------+--------------
-           | Diam. | Distance |   Capacity
-    Size   |  in   |   A in   |     C in
-   B. & S. | inch. |  inches. | micro-farads
-  ---------+-------+----------+--------------
-    0000   | .46   |    12    |    .0226
-           |       |    18    |    .0204
-           |       |    24    |    .01922
-           |       |    48    |    .01474
-           |       |          |
-     000   | .41   |    12    |    .0218
-           |       |    18    |    .01992
-           |       |    24    |    .01876
-           |       |    48    |    .01638
-           |       |          |
-      00   | .365  |    12    |    .0124
-           |       |    18    |    .01946
-           |       |    24    |    .01832
-           |       |    48    |    .01604
-           |       |          |
-       0   | .325  |    12    |    .02078
-           |       |    18    |    .01898
-           |       |    24    |    .01642
-           |       |    48    |    .01570
-           |       |          |
-       1   | .289  |    12    |    .02022
-           |       |    18    |    .01952
-           |       |    24    |    .01748
-           |       |    48    |    .0154
-           |       |          |
-       2   | .258  |    12    |    .01972
-           |       |    18    |    .01818
-           |       |    24    |    .01710
-           |       |    48    |    .01510
-           |       |          |
-       3   | .229  |    12    |    .01938
-           |       |    18    |    .01766
-           |       |    24    |    .01672
-           |       |    48    |    .01480
-           |       |          |
-       4   | .204  |    12    |    .01874
-           |       |    18    |    .01726
-           |       |    24    |    .01636
-           |       |    48    |    .01452
-           |       |          |
-       5   | .182  |    12    |    .01830
-           |       |    18    |    .01690
-           |       |    24    |    .01602
-           |       |    48    |    .01426
-           |       |          |
-       6   | .162  |    12    |    .01788
-           |       |    18    |    .01654
-           |       |    24    |    .01560
-           |       |    48    |    .0140
-           |       |          |
-       7   | .144  |    12    |    .01746
-           |       |    18    |    .01618
-           |       |    24    |    .01538
-           |       |    48    |    .01374
-           |       |          |
-       8   | .128  |    12    |    .01708
-           |       |    18    |    .01586
-           |       |    24    |    .01508
-           |       |    48    |    .01350
-           |       |          |
-       9   | .114  |    12    |    .01660
-           |       |    18    |    .01552
-           |       |    24    |    .01478
-           |       |    48    |    .01326
-           |       |          |
-      10   | .102  |    12    |    .01636
-           |       |    18    |    .01522
-           |       |    24    |    .01452
-           |       |    48    |    .01304
-  ---------+-------+----------+--------------
-
-=Capacity.=--In any given system of electrical conductors, a
-pressure difference between two of them corresponds to the presence
-of a quantity of electricity on each. With the same charges, the
-difference of pressure may be varied by varying the geometrical
-arrangement and magnitudes and also by introducing various
-dielectrics. The constant connecting the charge and the resulting
-pressure is called the capacity of the system.
-
-     All circuits have a certain capacity, because each conductor
-   acts like the plate of a condenser, and the insulating medium,
-   acts as the dielectric. The capacity depends upon the insulation.
-
-     For a given grade of insulation, the capacity is proportional
-   to the surface of the conductors, and universally to the distance
-   between them.
-
-     A three phase three wire transmission line spaced at the corners
-   of an equilateral triangle as regards capacity acts precisely
-   as though the neutral line were situated at the center of the
-   triangle.
-
-     The capacity of circuits is readily calculated by applying the
-   following formulae:
-
-  C = 38.83 sc 10^{-3} / log (D ÷ d) per mile,
-         insulated cable with lead sheath;
-  C = 38.83 × 10^{-3} / log (4h ÷ d) per mile,
-         single conductor with earth return;
-  C = 19.42 × 10^{-3} / log (2A ÷ d) per mile of
-         parallel conductors forming metallic circuit;
-
-     in which
-
-     C = Capacity in micro-farads; for a metallic circuit, C =
-   capacity between wires;
-
-     sc = Specific inductive capacity of insulating material; = 1 for
-   air, and 2.25 to 3.7 for rubber;
-
-     D = Inside diameter of lead sheath;
-     d = Diameter of conductor;
-     h = Distance of conductors above ground;
-     A = Distance between wires.
-
-=Frequency.=--The number of cycles per second, or the frequency,
-has a direct effect upon the inductance reactance in an alternating
-current circuit, as is plainly seen from the formula.
-
-          X_{i} = 2π_f_L
-
-     In the case of a transmission line alone; the lower frequencies
-   are the more desirable, in that they tend to reduce the inductance
-   drop and charging current. The inductance drop is proportional to
-   the frequency.
-
-     The natural period of a line, with distributed inductance and
-   capacity, is approximately given by
-               __
-  P = 7,900 / √LC
-
-     where L is the total inductance in millihenrys, and C, the total
-   capacity in micro-farads. Accordingly some lower odd harmonic of
-   the impressed frequency may be present which corresponds with the
-   natural period of the line. When this obtains, oscillations of
-   dangerous magnitude may occur. Such coincidences are less likely
-   with the lower harmonics than with the higher.
-
-=Skin Effect.=--The tendency of alternating current to confine itself
-to the _outer_ portions of a conductor, instead of passing uniformly
-through the cross section, is called _skin effect_. The effect is
-proportional to the size of the conductor and the frequency.
-
-=Ques. What effect has "skin effect" on the current?=
-
-Ans. It is equivalent to an increase of ohmic resistance and
-therefore opposes the current.
-
-[Illustration: FIGS. 2,683 to 2,687.--Skin effect and shield effect.
-Fig. 2,683, section of conductor illustrating skin effect or tendency
-of the alternating current to distribute itself unequally through the
-cross section of a conductor as shown by the varied shading, which
-represents the current flowing most strongly in the outer portions
-of the conductor. For this reason it has been proposed to use hollow
-or flat instead of solid round conductors; however, with frequency
-not exceeding 100, the skin effect is negligibly small in copper
-conductors of the sizes usually employed. In figs. 2,684 and 2,685,
-or 2,686 and 2,687, if two adjacent conductors be carrying current
-in the same direction, concentration will occur on those parts of
-the two conductors remote from one another, and the nearer parts
-will have less current, that is to say, they will be =shielded=.
-In this case, the induction due to one conductor will exert its
-opposing effect to the greatest extent on those parts of the other
-conductor nearest to it; this effect decreasing the deeper the latter
-is penetrated. After crossing the current axis, the induction will
-still decrease in magnitude, but will now aid the current in the
-conductor. Hence, the effect of these two conductors on one another
-will make the current density more uniform than is the case where
-the two conductors adjacent to one another are carrying current in
-opposite directions, as in figs. 2,685 and 2,686, therefore, the
-resistance and the heating for a given current will be smaller. If
-the two return conductors be situated on the line passing through
-the center of the conductors just considered, the effect will be to
-still further concentrate the current; the distribution symmetry will
-be further disturbed, and the resistance of the conductor system
-increased. It is therefore difficult to say which of the two cases
-considered holds the advantage so far as increasing the resistance is
-concerned. The case, however, in which the phases are mixed has much
-the smaller reactive drop.]
-
-     If the conductor be large, or the frequency high, the central
-   portion of the conductor carries little if any current, hence the
-   resistance is therefore greater for alternating current than for
-   direct current.
-
-=Ques. For what condition may "skin effect" be neglected?=
-
-Ans. For frequencies of 60 or less, with conductors having a diameter
-not greater than 0000 B. & S. gauge.
-
-=Ques. How is the "skin effect" calculated for a given wire?=
-
-Ans. Its area in circular mils multiplied by the frequency, gives the
-ratio of the wire's ohmic resistance to its combined resistance.
-
-     That is to say, the factor thus obtained multiplied by the
-   resistance of the wire to direct current will give its combined
-   resistance or resistance to alternating current.
-
-     The following table gives these ratio factors for large
-   conductors.
-
-          RATIO FACTOR FOR COMBINED RESISTANCE
-
-  +---------------+---------+---------------+---------+
-  |  Cir. mils.   |  Ratio  |  Cir. mils.   |  Ratio  |
-  |  × frequency  |  factor |  × frequency  |  factor |
-  +---------------+---------+---------------+---------+
-  |   10,000,000  |  1.00   |   70,000,000  |  1.13   |
-  |   20,000,000  |  1.01   |   80,000,000  |  1.17   |
-  |   30,000,000  |  1.03   |   90,000,000  |  1.20   |
-  |   40,000,000  |  1.05   |  100,000,000  |  1.25   |
-  |   50,000,000  |  1.08   |  125,000,000  |  1.34   |
-  |   60,000,000  |  1.10   |  150,000,000  |  1.43   |
-  +---------------+---------+---------------+---------+
-
-=Corona Effect.=--When two wires, having a great difference of
-pressure are placed near each other, a certain phenomenon occurs,
-which is called _corona effect_. When the spacing or distance
-between the wires is small and the difference of pressure in the
-wires very great, a continuous passage of energy takes place through
-the dielectric or atmosphere, the amount of this energy may be an
-appreciable percentage of the power transmitted. Therefore in laying
-out high pressure transmission lines, this effect must be considered
-in the spacing of the wires.
-
-=Ques. How does the corona effect manifest itself?=
-
-Ans. It is visible at night as a bluish luminous envelope and audible
-as a hissing sound.
-
-=Ques. What is the critical voltage?=
-
-Ans. The voltage at which the corona effect loss takes place.
-
-=Ques. Upon what does the critical voltage depend?=
-
-Ans. Upon the radius of the wires, the spacing, and the atmospheric
-conditions.
-
-[Illustration: FIG. 2,688.--Electromagnetic and electrostatic
-fields surrounding the conductors of a transmission line. The
-electromagnetic field is represented by lines of magnetic force
-that surround the conductors in circles, (the solid lines), and
-the electrostatic field by (dotted) circles passing from conductor
-to conductor across at right angles to the magnetic circles. For
-any given size of wire and distance apart of wires there is a
-certain voltage at which the critical density or critical gradient
-is reached, where the air breaks down and luminosity begins--the
-critical voltage where corona manifests itself. At still higher
-voltages corona spreads to further distances from the conductor
-and a greater volume of air becomes luminous. Incidentally, it
-produces noise. Now to produce light requires power and to produce
-noise requires power. Air is broken down and is heated in breaking
-down, and to heat also requires power; therefore, as soon as corona
-forms, power is consumed or dissipated in its formation. When this
-phenomenon occurs on the conductors of an alternating current circuit
-a change takes place in relation to current and voltage. On the
-wires of an alternating current transmission line, at a voltage
-below that where corona forms--at a voltage where wires are not
-luminous--considerable current, more or less depending on voltage
-and length of wire, flows into the circuit as capacity current or
-charging current.]
-
-     The critical voltage increases with both the diameter of the
-   wires, and the spacing.
-
-     The losses due to corona effect increase very rapidly with
-   increasing pressure beyond the critical voltage.
-
-     The magnitude of the losses as well as the critical voltage is
-   affected, by atmospheric conditions, hence they probably vary with
-   the particular locality, and the season of the year. Therefore,
-   for a given locality, a voltage which is normally below the
-   critical point, may at times be above it, depending upon changes
-   in the weather.
-
-     Such elements as smoke, fog, moisture, or other particles (dust,
-   snow, etc.) floating in the air, increase the losses; rain,
-   however, apparently has no appreciable effect upon the losses.
-   It follows then that in the design of a transmission line, the
-   atmospheric conditions of the particular locality through which
-   the line passes should be considered.
-
-=Ques. How should live wires be spaced?=
-
-Ans. They should be so spaced as to lessen the tendency to leakage
-and to prevent the wires swinging together or against towers. The
-spacing should be only sufficient for safety, since increased spacing
-increases the self-induction of the line, and while it lessens the
-capacity, it does so only in a slight degree.
-
-     The following spacing is in accordance with average practice.
-
-  SPACING FOR VARIOUS VOLTAGES
-
-     +---------+----------+
-     |  Volts  | Spacing  |
-     +---------+----------+
-     |   5,000 |  28 ins. |
-     |  15,000 |  40 ins. |
-     |  30,000 |  48 ins. |
-     |  45,000 |  60 ins. |
-     |  60,000 |  60 ins. |
-     |  75,000 |  84 ins. |
-     |  90,000 |  96 ins. |
-     | 105,000 | 108 ins. |
-     | 120,000 | 120 ins. |
-     +---------+----------+
-
-=Resistance of Wires.=--For quick calculation the following method
-of obtaining the resistance (approximately) of wires will be found
-convenient:
-
-1,000 feet No. 10 B. & S. wire, which is about .1 inch in diameter
-(.1019), has a resistance of one ohm, at a temperature of 68° F. and
-weighs 31.4 pounds. A wire three sizes larger, that is No. 7, has
-twice the cross section and therefore one-half the resistance. A wire
-three sizes smaller than No. 10, that is No. 13, has one-half the
-cross section and therefore twice the resistance.
-
-Thus, starting with No. 10, any number three sizes larger will double
-the cross sectional area and any wire three sizes smaller will halve
-the cross sectional area of the preceding wire. This is true to the
-extreme limits of the table, so that the area, weight and resistance
-of any wire may be at once calculated to a close approximation from
-this rule, intermediate sizes being obtained by interpolation.
-
-For alternating current, the combined resistance, that is, the total
-resistance, including skin effect, is obtained by multiplying the
-resistance, as found above by the "ratio factor" (see table page
-1,894).
-
-[Illustration: FIGS. 2,689 to 2,692.--Triangles for obtaining
-graphically, impedance, impressed pressure, etc., in alternating
-current circuits. For a full explanation of this method the reader is
-referred to Guide 5, Chapter XLVII on Alternating Current Diagrams. A
-thorough study of this chapter is recommended.]
-
-=Impedance.=--_The total opposition to the flow of electricity in an
-alternating current circuit_, or the impedance may be resolved into
-two components representing the ohmic resistance and the spurious
-resistance; these components have a phase difference of 90°, and
-they may be represented graphically by the two legs of a right angle
-triangle, of which the hypothenuse represents the impedance.
-
-Similarly, the volts lost or "drop" in an alternating circuit may be
-resolved into two components representing respectively
-
-1. The loss due to resistance.
-
-2. The loss due to reactance.
-
-These components have a phase difference of 90° and are represented
-graphically similar to the impedance components. This has been
-explained at considerable length in Chapter XLVII (Guide V).
-
-[Illustration: FIG. 2,693.--Mechanical analogy of power factor, as
-exemplified by a locomotive "poling" a car off a siding. The car and
-locomotive are shown moving in parallel directions, and the pole
-AB, inclined at an angle ϕ. Now, if the length of AB be taken to
-represent the pressure exerted on the pole by the locomotive, then
-the imaginary lines AC and BC, drawn respectively parallel and at
-right angles to the direction of motion will represent respectively
-the useful and no energy (wattless) components; that is to say, if
-the pressure AB be applied to the car at an angle ϕ, only part of it,
-AC, is useful in propelling the car, the other component, BC, being
-wasted in tending to push the car off the track at right angles to
-the rails, being resisted by the flanges of the outer wheels.]
-
-=Power Factor.=--When the current falls out of step with the
-pressure, as on inductive loads, the power factor becomes less than
-unity, and the effect is to increase the current required for a
-given load. Accordingly, this must be considered in calculating the
-size of the wires. As has been explained, the current flowing in
-an alternating current circuit, as measured by an ammeter, can be
-resolved into two components, representing respectively the _active
-component_ and the _wattless component_ or idle current. These are
-graphically represented by the two legs of a right triangle, of which
-the hypothenuse represents the current measured by the ammeter.
-
-This _apparent_ current, as is evident from the triangle, exceeds
-the _active_ current and lags behind the pressure by an amount
-represented by the angle ϕ between the hypothenuse and leg
-representing the energy current as shown in fig. 2,694.
-
-[Illustration: FIG. 2,694.--Diagram showing that the apparent current
-is more than the active current, the excess depending upon the angle
-of phase difference.]
-
-[Illustration: FIG. 2,695.--Diagram showing components of impedance
-volts. Compare this diagram with figs. 2,689 and 2,671, and note that
-the term "reactance" is the difference between the inductance drop
-and the capacity drop if the circuit contain capacity, for instance,
-if inductance drop be 10 volts and capacity drop be 7 volts then
-reactance 10-7 = 3 volts.]
-
-=Ques. What determines the heating of the wires on alternating
-current circuits with inductive loads?=
-
-Ans. The apparent current, as represented by the hypothenuse of the
-triangle in fig. 2,694.
-
-=Ques. How is the apparent current obtained?=
-
-Ans. Divide the true watts by the product of the power factor
-multiplied by the voltage.
-
-     Example.--A certain circuit supplies 20 kw. to motors at 220
-   volts and .8 power factor. What is the apparent current?
-
-                          true watts         20,000
-  Apparent Current = -------------------- = -------- = 113.6 amperes
-                     power factor × volts   .8 × 220
-
-=Ques. What else, besides power factor, should be considered in
-making wire calculations for motor circuits?=
-
-Ans. The efficiency of the motor, and the heavy starting current.
-
-     The product of the efficiency of the motor multiplied by the
-   power factor gives the _apparent efficiency_, which governs the
-   size of the wires, apparatus, etc., necessary to feed the motors.
-
-     Allowance should be made for the heavy starting current required
-   for some motors to avoid undue drop.
-
-           TABLE OF APPROXIMATE AMPERES PER TERMINAL
-                    FOR INDUCTION MOTORS
-
-  Column headings:  A-110 volts  B-220 volts  C-440 volts  D-550 volts
-
-  +-----+----------------+------------------+------------------------+
-  |     |                |    Two phase     |      Three phase       |
-  |Horse|  Single phase  |    four wire     |      three wire        |
-  |power+----+-----+-----+-----+-----+------+-----+-----+------+-----+
-  |     | A  |  B  |  C  |  A  |  B  |  C   |  A  |  B  |  C   |  D  |
-  +-----+----+-----+-----+-----+-----+------+-----+-----+------+-----+
-  |   .5| 6.6| 3.4 |  1.8| 3.3 | 1.7 |   .9 | 3.7 | 1.8 |  1   |     |
-  |   1 | 14 | 7   |  3.5| 6.4 | 3.2 |  1.6 | 7.4 | 3.7 |  1.9 |     |
-  |   2 | 24 | 12  |  6  |  11 | 5.7 |  2.9 |  13 | 6.6 |  3.3 | 2.5 |
-  |   3 | 34 | 17  |  8.5|  16 | 8.1 |  4.1 |  19 | 9.3 |  4.7 | 3.5 |
-  |   4 | 52 | 26  | 13  |  26 |  13 |  6.5 |  30 |  15 |  7.5 |   6 |
-  |   5 | 74 | 37  | 18.5|  38 |  19 |  9.5 |  44 |  22 | 11   |   9 |
-  |  10 | 94 | 47  | 23.5|  44 |  22 | 11   |  50 |  25 | 12.5 |  11 |
-  |  15 |    |     |     |  66 |  33 | 16.5 |  76 |  38 | 19   |  16 |
-  |  20 |    |     |     |  88 |  44 | 22   | 102 |  51 | 25.5 |  22 |
-  |  25 |    |     |     | 111 |  55 | 28   | 129 |  64 | 32   |  25 |
-  |  30 |    |     |     | 134 |  67 | 33.5 | 154 |  77 | 38.5 |  32 |
-  |  40 |    |     |     | 178 |  89 | 44.5 | 204 | 107 | 53.5 |  44 |
-  |  50 |    |     |     | 204 | 102 | 51   | 236 | 118 | 59   |  52 |
-  |  75 |    |     |     | 308 | 154 | 77   | 356 | 178 | 89   |  77 |
-  | 100 |    |     |     | 408 | 204 | 102  | 472 | 236 | 118  | 100 |
-  +-----+----+-----+-----+-----+-----+------+-----+-----+------+-----+
-
-=Ques. What are the usual power factors encountered on commercial
-circuits?=
-
-Ans. A mixed load of incandescent lamps and induction motors will
-have a power factor of from .8 to .85; induction motors above .8 to
-.85; incandescent and Nernst lamps .98; arc lamps, .85.
-
-=Wire Calculations.=--In the calculation of alternating current
-circuits, the two chief factors which make the computation different
-from that for direct current circuits, is _induction_ and _power
-factor_. The first depends on the frequency, and physical condition
-of the circuit, and the second upon the character of the load.
-
-=Ques. Under what conditions may inductance be neglected?=
-
-[Illustration: FIGS. 2,696 to 2,698.--Example of wiring showing where
-inductance is negligible, and where it must be considered in wire
-calculations.]
-
-Ans. In cases where the wires of a circuit are not spaced over an
-inch apart, or in conduit work, where both wires are in the same
-conduit.
-
-     Under these conditions the calculation is the same as for direct
-   current after making proper allowance for power factor.
-
-=Ques. Under what conditions must induction be considered?=
-
-Ans. On exposed circuits with wires separated several inches,
-particularly in the case of large wires.
-
-=Sizes of Wire.=--The size of wire for any alternating circuit may be
-determined by slightly modifying the formula used in direct current
-work, and which, as derived in Guide No. 4, page 748, is
-
-                  amperes × feet × 21.6
-  circular mils = ---------------------  (1)
-                            drop
-
-     The quantity 21.6, is twice the resistance (10.8) of a foot of
-   copper wire one mil in diameter (_mil foot_). This resistance
-   (10.8) is multiplied by 2, giving the quantity 21.6, because the
-   length of a circuit, or feet in the formula, is given as the "run"
-   or distance one way, that is, one-half the total length of wire in
-   the circuit, must be multiplied by 2 to get the total drop, viz.:
-
-                  amperes × feet × 10.8 × 2   amperes × feet × 21.6
-  circular mils = ------------------------- = ---------------------
-                             drop                       drop
-
-It is sometimes however convenient to make the calculation in terms
-of watts. Formula (1) may be modified for such calculation.
-
-In modifying the formula, the "drop" should be expressed in
-percentage instead of actual volts lost, that is, instead of the
-difference in pressure between the beginning and the end of the
-circuit.
-
-In any circuit the loss in percentage, or
-
-                  drop
-  % loss = ------------------ × 100
-           impressed pressure
-
-from which
-
-         % loss × impressed pressure
-  drop = ---------------------------  (2)
-                     100
-
-Substituting equation (2) in equation (1)
-
-                      amperes × feet × 21.6
-  circular mils = -----------------------------
-                     % loss × imp. pressure
-                    ------------------------
-                              100
-
-                    amperes × feet × 2,160
-                = --------------------------  (3)
-                    % loss × imp. pressure
-
-Equation (3) is modified for calculation in terms of watts as
-follows: The power in watts is equal to the _applied voltage_
-multiplied by the current, that is to say, the power is equal to
-the _volts at the consumer's end of the circuit_ multiplied by the
-current, or simply
-
-  watts = volts × amperes
-
-from which
-
-            watts
-  amperes = -----  (4)
-            volts
-
-[Illustration: FIGS. 2,699 to 2,703.--Stranded copper cables. For
-conductors of large areas and in the smaller sizes where extra
-flexibility is required it becomes necessary to employ stranded
-cables made by grouping a number of wires together in either
-concentric or rope form. The concentric cable as here illustrated is
-formed by grouping six wires around a central wire thereby forming
-a seven wire cable. The next step is the application in a reverse
-direction of another layer of 12 wires and a nineteen wire cable is
-produced. This is again increased by a third layer of eighteen wires
-for a 37 wire cable and a fourth layer of 24 wires for a 61 wire
-cable. Successive layers, each containing 6 more wires than that
-preceding, may be applied until the desired capacity is obtained. The
-cuts show sectional views of concentric cables each formed from No.
-10 B. & S. gauge wires.]
-
-Substituting this value for the current in equation (3) and
-remembering that the pressure taken is the volts at the consumer's
-end of the line
-
-                  watts
-                  -----  × feet × 2,160
-                  volts
-  circular mils = ---------------------
-                  % loss × volts
-
-                  watts × feet × 2,160
-                = --------------------    (5)
-                   % loss × volts^{2}
-
-This formula (5) applies to a direct current two wire circuit, and to
-adapt it to any alternating current circuit it is only necessary to
-use the letter M instead of the number 2,160, thus
-
-                    watts × feet × M
-  circular mils =  ------------------  (6)
-                   % loss × volts^{2}
-
-in which M is a coefficient which has various values according to the
-kind of circuit and value of the power factor. These values are given
-in the following table:
-
-                          =VALUES OF M=
-
-  --------+-----------------------------------------------------------
-          |                     POWER FACTOR
-   SYSTEM +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
-          | 1.00|  .98|  .95|  .90|  .85|  .80|  .75|  .70|  .65|  .60
-  --------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
-   Single |2,160|2,249|2,400|2,660|3,000|3,380|3,840|4,400|5,112|6,000
-    phase |     |     |     |     |     |     |     |     |     |
-  --------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
-    Two   |1,080|1,125|1,200|1,330|1,500|1,690|1,920|2,200|2,556|3,000
-   phase  |     |     |     |     |     |     |     |     |     |
-  (4 wire)|     |     |     |     |     |     |     |     |     |
-  --------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
-   Three  |1,080|1,125|1,200|1,330|1,500|1,690|1,920|2,200|2,556|3,000
-   phase  |     |     |     |     |     |     |     |     |     |
-  (3 wire)|     |     |     |     |     |     |     |     |     |
-  --------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
-
-            NOTE.--The above table is calculated as
-          follows: For =single phase= M = 2,160 ÷ power
-          factor^{2} × 100; for =two phase= four wire, or
-          three phase three wire, M = ½ (2,160 ÷ power
-          factor^{2})× 100. Thus the value of M for a
-          single phase line with power factor .95 = 2,160 ÷
-          .95^{2} × 100 = 2,400.
-
-It must be evident that when 2,160 is taken as the value of M,
-formula (6) applies to a two wire direct current circuit and also to
-a single phase alternating current circuit when the power factor is
-unity.
-
-In the table the value of M for any particular power factor is found
-by dividing 2,160 by the square of that power factor for single phase
-and twice the square of the power factor for two phase and three
-phase.
-
-=Ques. For a given load and voltage how do the wires of a single and
-two phase system compare in size and weight, the power factor being
-the same in each case?=
-
-Ans. Since the two phase system is virtually two single phase
-systems, the four wires of the two phase systems are half the size of
-the two wires of the single phase system, and accordingly, the weight
-is the same for either system.
-
-                       =VALUES OF T=
-
-  +-------------------+--------------------------------------------+
-  |                   |                POWER FACTOR                |
-  |      SYSTEM       +--------+--------+--------+--------+--------+
-  |                   |  1.00  |   .98  |   .90  |   .80  |   .70  |
-  +-------------------+--------+--------+--------+--------+--------+
-  |   Single phase    |  1.00  |   .98  |   .90  |   .80  |   .70  |
-  +-------------------+--------+--------+--------+--------+--------+
-  | Two phase, 4 wire |  2.00  |  1.96  |  1.80  |  1.60  |  1.40  |
-  +-------------------+--------+--------+--------+--------+--------+
-  |Three phase, 3 wire|  1.73  |  1.70  |  1.55  |  1.38  |  1.21  |
-  +-------------------+--------+--------+--------+--------+--------+
-
-            NOTE.--This table is for finding the value
-          of the current in line, using the formula I =
-          W ÷ (E × T), in which I = current in line; E =
-          voltage between main conductors at receiving or
-          consumers' end; W = watts. For instance, what
-          is the current in a two phase line transmitting
-          1,000 watts at 550 volts, power factor .80? I =
-          1,000 ÷ (550 × 1.60) = 1.13.
-
-=Ques. Since there is no saving in copper in using two phases, what
-advantage has the two phase system over the one phase system?=
-
-Ans. It is more desirable on power circuits, because two phase motors
-are self-starting.
-
-     That is to say, the rotating magnetic field that can be
-   produced by a two phase current, permits an induction motor to
-   start without being equipped with any special phase splitting
-   devices which are necessary on single phase motors, because the
-   oscillating field produced by a single phase current does not
-   produce any torque on a squirrel cage armature at rest.
-
-=Ques. For equal working conditions, what is the comparison between
-the single, two and three phase system as to size and weight of
-wires?=
-
-Ans. Each wire of the three phase system is half the size of one of
-the wires of the single phase system, hence the weight of copper
-required for the three phase system is 75% of that required for the
-single phase system. Since in the two phase system half of the load
-is carried by each phase, each wire of the three phase system is the
-same size as one of the wires of the two phase system, hence, the
-copper required by the three phase system is 75% of that required by
-the two phase system.
-
-          =MISCELLANEOUS FORMULÆ FOR COPPER WIRES=
-
-  Diameter squared                            = circular mils
-  Circular mils          × .7854              = square mils
-          .000003027     × circular mils      = pounds per foot
-          .003027        × circular mils      = pounds per 1,000 feet
-          .0159847       × circular mils      = pounds per mile
-          .003879        × square mils        = pounds per 1,000 feet
-          .33033         ÷ circular mils      = feet per pound
-          .0000002924    × circular mils      = pounds per ohm
-          .342           ÷ circular mils      = ohms per pound
-          .096585        × circular mils      = feet per ohm
-        10.353568        ÷ circular mils      = ohms per foot
-
-Breaking weight of wire ÷ area = breaking weight per square inch.
-
-Breaking weight per square inch × area = breaking weight of wire.
-
-The weight of copper wire is 1-1/7 times the weight of iron wire of
-same diameter.
-
-     EXAMPLE.--What size wires must be used on a single phase circuit
-   2,000 feet in length to supply 30 kw. at 220 volts with loss of
-   4%, the power factor being .9?
-
-     The formula for circular mils is
-
-                   watts × feet × M
-  circular mils = ------------------     (1)
-                  % loss × volts^{2}
-
-     Substituting the given values and the proper value of M from the
-   table, in (1)
-
-                  30,000 × 2,000 × 2,660
-  circular mils = ---------------------- = 82,438
-                       4 × 220^{2}
-
-     Referring to the accompanying table of the properties of copper
-   wire, the nearest _larger_ size wire is No. 1 B. & S. gauge having
-   an area of 83,690 circular mils.
-
-
-            =TABLE OF THE PROPERTIES OF COPPER WIRE=
-
-     Giving weights, length and resistances of wires of Matthiessen's
-   Standard Conductivity for both B. & S. G. (Brown & Sharpe Gauge)
-   and B. W. G. (Birmingham Wire Gauge) from Transactions October
-   1903, of the American Institute of Electrical Engineers.
-
-    __________________________________________________________________
-                                         |         |        |
-      Gauges. To the nearest fourth      |         | Length.|Resistance.
-            significant digit.           |         |        |
-    _____________________________________|         |________|_________
-          |       |           |          | Weight. |        |
-          |       | Diameter. | Area.    |   Lbs.  |  Feet  | Ohms per
-          |       |           |          |   per   | per lb.|1,000 ft.
-    ______|_______|___________|__________|  1,000  |________|__________
-          |       |           |          |  feet.  |        |
-          |       |           | Circular |         |        |
-    B.& S.| B.W.G.|  Inches.  |  mils.   |         |        | @ 68° F.
-    ______|______ |___________|__________|_________|________|_________
-          |       |           |          |         |        |
-     0000 |       |  0.460    |  211,600 |  640.5  |  1.561 | .04893
-          |  0000 |  0.454    |  206,100 |  623.9  |  1.603 | .05023
-          |   000 |  0.425    |  180,600 |  546.8  |  1.829 | .05732
-          |       |           |          |         |        |
-     000  |       |  0.4096   |  167,800 |  508.0  |  1.969 | .06170
-          |    00 |  0.380    |  144,400 |  437.1  |  2.288 | .07170
-      00  |       |  0.3648   |  133,100 |  402.8  |  2.482 | .07780
-          |       |           |          |         |        |
-          |     0 |  0.340    |  115,600 |  349.9  |  2.858 | .08957
-       0  |       |  0.3249   |  105,500 |  319.5  |  3.130 | .09811
-          |     1 |  0.3000   |   90,000 |  272.4  |  3.671 | .1150
-          |       |           |          |         |        |
-       1  |       |  0.2893   |   83,690 |  253.3  |  3.947 | .1237
-          |     2 |  0.2840   |   80,660 |  244.1  |  4.096 | .1284
-          |     3 |  0.2590   |   67,080 |  203.1  |  4.925 | .1543
-          |       |           |          |         |        |
-       2  |       |  0.2576   |   66,370 |  200.9  |  4.977 | .1560
-          |     4 |  0.2380   |   56,640 |  171.5  |  5.832 | .1828
-       3  |       |  0.2294   |   52,630 |  159.3  |  6.276 | .1967
-          |       |           |          |         |        |
-          |     5 |  0.2200   |   48,400 |  146.5  |  6.826 | .2139
-       4  |       |  0.2043   |   41,740 |  126.4  |  7.914 | .2480
-          |     6 |  0.2030   |   41,210 |  124.7  |  8.017 | .2513
-          |       |           |          |         |        |
-      5   |       |  0.1819   | 33,100   |100.2    |  9.98  | .3128
-          |     7 |  0.1800   | 32,400   | 98.08   | 10.20  | .3196
-          |     8 |  0.1650   | 27,230   | 82.41   | 12.13  | .3803
-          |       |           |          |         |        |
-      6   |       |  0.1620   | 26,250   | 79.46   | 12.58  | .3944
-          |     9 |  0.1480   | 21,900   | 66.30   | 15.08  | .4727
-      7   |       |  0.1443   | 20,820   | 63.02   | 15.87  | .4973
-          |       |           |          |         |        |
-          |    10 |  0.1340   | 17,960   | 54.35   | 18.40  | .5766
-      8   |       |  0.1285   | 16,510   | 49.98   | 20.01  | .6271
-          |    11 |  0.1200   | 14,400   | 43.59   | 22.94  | .7190
-          |       |           |          |         |        |
-      9   |       |  0.1144   | 13,090   | 39.63   | 25.23  | .7908
-          |    12 |  0.1090   | 11,880   | 35.96   | 27.81  | .8715
-     10   |       |  0.1019   | 10,380   | 31.43   | 31.82  | .9972
-          |       |           |          |         |        |
-          |    13 |  0.0950   |  9,025   | 27.32   | 36.60  | 1.147
-     11   |       |  0.09074  |  8,234   | 24.93   | 40.12  | 1.257
-          |    14 |  0.08300  |  6,889   | 20.85   | 47.95  | 1.503
-          |       |           |          |         |        |
-     12   |       |  0.08081  |  6,530   | 19.77   | 50.59  | 1.586
-          |    15 |  0.07200  |  5,184   | 15.69   | 63.73  | 1.997
-     13   |       |  0.07196  |  5,178   | 15.68   | 63.79  | 1.999
-          |       |           |          |         |        |
-          |    16 |  0.06500  |  4,225   | 12.79   | 78.19  | 2.451
-     14   |       |  0.06408  |  4,107   | 12.43   | 80.44  | 2.521
-          |    17 |  0.0580   |  3,364   | 10.18   | 98.23  | 3.078
-          |       |           |          |         |        |
-     15   |       |  0.05707  |  3,257   |  9.858  | 101.4  | 3.179
-     16   |       |  0.05082  |  2,583   |  7.818  | 127.9  | 4.009
-          |    18 |  0.04900  |  2,401   |  7.268  | 137.6  | 4.312
-          |       |           |          |         |        |
-     17   |       |  0.045260 |  2,048   |  6.200  | 161.3  | 5.055
-          |    19 |  0.042000 |  1,764   |  5.340  | 187.3  | 5.870
-     18   |       |  0.040300 |  1,624   |  4.917  | 203.4  | 6.374
-          |       |           |          |         |        |
-     19   |       |  0.035890 |  1,288   |  3.899  | 256.5  | 8.038
-          |    20 |  0.035000 |  1,225   |  3.708  | 269.7  | 8.452
-          |    21 |  0.032000 |  1,024   |  3.100  | 322.6  | 10.11
-          |       |           |          |         |        |
-     20   |       |  0.031960 |  1,022   |  3.092  | 323.4  | 10.14
-     21   |       |  0.028460 |    810.1 |  2.452  | 407.8  | 12.78
-          |    22 |  0.028000 |    784.0 |  2.373  | 421.4  | 13.21
-     22   |       |  0.025350 |    642.4 |  1.945  | 514.2  | 16.12
-          |    23 |  0.025000 |    625.0 |  1.892  | 528.6  | 16.57
-     23   |       |  0.022570 |    509.5 |  1.542  | 648.4  | 20.32
-          |       |           |          |         |        |
-          |    24 |  0.022000 |    484.0 |  1.465  | 682.6  | 21.39
-     24   |       |  0.020100 |    404.0 |  1.223  | 817.6  | 25.63
-          |    25 |  0.020000 |    400.0 |  1.211  | 825.9  | 25.88
-          |       |           |          |         |        |
-          |    26 |  0.018000 |    324.0 |  .9808  | 1,020  |  31.96
-     25   |       |  0.017900 |    320.4 |  .9699  | 1,031  |  32.31
-          |    27 |  0.016000 |    256.0 |  .7749  | 1,290  |  40.45
-          |       |           |          |         |        |
-     26   |       |  0.015940 |    254.1 |  .7692  | 1,300  |  40.75
-     27   |       |  0.014200 |    201.5 |  .6100  | 1,639  |  51.38
-          |    28 |  0.014000 |    196.0 |  .5933  | 1,685  |  52.83
-          |       |           |          |         |        |
-          |    29 |  0.013000 |    169.0 |  .5116  | 1,955  |  61.27
-     28   |       |  0.012640 |    159.8 |  .4837  | 2,067  |  64.79
-          |    30 |  0.012000 |    144.0 |  .4359  | 2,294  |  71.90
-          |       |           |          |         |        |
-     29   |       |  0.011260 |  126.7   |  .3836  | 2,607  |  81.70
-     30   |       |  0.010030 |  100.5   |  .3042  | 3,287  | 103.0
-          |    31 |  0.010000 |  100.0   |  .3027  | 3,304  | 103.5
-          |       |           |          |         |        |
-          |    32 |  0.009000 |   81.0   |  .2452  | 4,078  | 127.8
-     31   |       |  0.008928 |   79.70  |  .2413  | 4,145  | 129.9
-          |    33 |  0.008000 |   64.0   |  .1937  | 5,162  | 161.8
-          |       |           |          |         |        |
-     32   |       |  0.007950 |   63.21  |  .1913  | 5,227  | 163.8
-     33   |       |  0.007080 |   50.13  |  .1517  | 6,591  | 206.6
-          |    34 |  0.007000 |   49.0   |  .1483  | 6,742  | 211.3
-          |       |           |          |         |        |
-     34   |       |  0.006305 |   39.75  |  .1203  | 8,311  | 260.5
-     35   |       |  0.005615 |   31.52  |  .09543 |10,480  | 328.4
-     36   |    35 |  0.005000 |   25.0   |  .07568 |13,210  | 414.2
-          |       |           |          |         |        |
-     37   |       |  0.004453 |   19.83  |  .06001 |16,660  | 522.2
-          |    36 |  0.004000 |   16.    |  .04843 |20,650  | 647.1
-     38   |       |  0.003965 |   15.72  |  .04759 |21,010  | 658.5
-          |       |           |          |         |        |
-     39   |       |  0.003531 |   12.47  |  .03774 |26,500  | 830.4
-     40   |       |  0.003145 |    9.888 |  .02993 |33,410  |1047.
-  --------------------------------------------------------------------
-
-=Drop.=--In order to determine the drop or volts lost in the line,
-the following formula may be used
-
-drop = ((% loss × volts) / 100) × S (1)
-
-in which the % loss is a percentage of the applied power, that is,
-the power delivered to the consumer and not a percentage of the power
-at the alternator. "Volts" is the pressure at the consumer's end of
-the circuit.
-
-                     =VALUE OF "S" FOR 60 CYCLES=
-
-  -----------------+------------------------+------------------------+
-                   |   .98 power factor     |    .90 power factor    |
-  --------+--------+------------------------+------------------------+
-  Size of | Area   |   Spacing of           | Spacing of             |
-   wire   |  in    |   conductors           | conductors             |
-   B.&S.  |circular|                        |                        |
-   gauge  | mils.  |                        |                        |
-          |        +----+----+----+----+----+----+----+----+----+----+
-          |        | 1" | 3" | 6" | 12"| 24"| 1" | 3" | 6" | 12"| 24"|
-  --------+--------+----+----+----+----+----+----+----+----+----+----+
-  500,000 |500,000 |1.21|1.45|1.61|1.77|1.92|1.32|1.80|2.11|2.44|2.75|
-  300,000 |300,000 |1.15|1.29|1.38|1.48|1.57|1.19|1.47|1.66|1.84|2.02|
-    0,000 |211,600 |1.12|1.22|1.28|1.34|1.41|1.13|1.33|1.45|1.58|1.63|
-      000 |167,800 |1.09|1.18|1.22|1.28|1.29|1.08|1.23|1.33|1.44|1.53|
-       00 |133,100 |1.07|1.14|1.18|1.21|1.25|1.03|1.16|1.24|1.32|1.40|
-        0 |105,500 |1.05|1.10|1.14|1.17|1.20|1.00|1.09|1.16|1.22|1.28|
-        1 | 83,690 |1.04|1.08|1.10|1.13|1.15|1.00|1.05|1.09|1.14|1.19|
-        2 | 66,370 |1.02|1.05|1.08|1.10|1.12|1.00|1.00|1.04|1.08|1.12|
-        3 | 52,630 |1.02|1.04|1.06|1.07|1.09|1.00|1.00|1.00|1.03|1.06|
-          |        |    |    |    |    |    |    |    |    |    |    |
-        4 | 41,740}|1.00|1.02|1.03|1.04|1.07|1.00|1.00|1.00|1.00|1.00|
-        5 | 33,100}|    |    |    |    |    |    |    |    |    |    |
-          |        |    |    |    |    |    |    |    |    |    |    |
-        6 | 26,250}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-        7 | 20,820}|    |    |    |    |    |    |    |    |    |    |
-          |        |    |    |    |    |    |    |    |    |    |    |
-        8 | 16,510}|    |    |    |    |    |    |    |    |    |    |
-        9 | 13,090}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-       10 | 10,380}|    |    |    |    |    |    |    |    |    |    |
-  --------+--------+----+----+----+----+----+----+----+----+----+----+
-  --------+--------+----+----+----+----+----+----+----+----+----+----+
-   Size   |        |    .80 power factor    |    .70 power factor    |
-    of    |  Area  +------------------------+------------------------+
-   wire   |   in   |       Spacing of       |        Spacing of      |
-   B.&S.  |circular|       conductors       |        conductors      |
-   gauge  |  mils. +----+----+----+----+----+----+----+----+----+----+
-          |        | 1" | 3" | 6" | 12"| 24"| 1" | 3" | 6" | 12"| 24"|
-  --------+--------+----+----+----+----+----+----+----+----+----+----+
-  500,000 | 500,000|1.27|1.89|2.25|2.64|3.03|1.14|1.72|2.12|2.53|2.92|
-  300,000 | 300,000|1.11|1.46|1.68|1.90|2.12|1.00|1.33|1.56|1.78|2.01|
-    0,000 | 211,600|1.03|1.27|1.43|1.58|1.75|1.00|1.14|1.29|1.45|1.69|
-      000 | 167,800|1.00|1.16|1.28|1.41|1.53|1.00|1.02|1.15|1.28|1.50|
-       00 | 133,100|1.00|1.07|1.15|1.22|1.00|1.00|1.00|1.03|1.13|1.21|
-        0 | 105,500|1.00|1.00|1.07|1.15|1.00|1.00|1.00|1.00|1.01|1.09|
-        1 | 83,690}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-        2 | 66,370}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-        3 | 52,630}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-          |        |    |    |    |    |    |    |    |    |    |    |
-        4 | 41,740}|    |    |    |    |    |    |    |    |    |    |
-        5 | 33,100}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-          |        |    |    |    |    |    |    |    |    |    |    |
-        6 | 26,250}|    |    |    |    |    |    |    |    |    |    |
-        7 | 20,820}|    |    |    |    |    |    |    |    |    |    |
-          |        |    |    |    |    |    |    |    |    |    |    |
-        8 | 16,510}|    |    |    |    |    |    |    |    |    |    |
-        9 | 13,090}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-       10 | 10,380}|    |    |    |    |    |    |    |    |    |    |
-  --------+--------+----+----+----+----+----+----+----+----+----+----+
-The coefficient S has various values as given in the accompanying
-tables. As will be seen from the table, the value of S to be used
-depends upon the size of wire, spacing, power factor and frequency.
-
-These values are accurate enough for all practical purposes, and may
-be used for distances of 20 miles or less and for voltages up to
-25,000.
-
-The capacity effect on very long high voltage lines, makes this
-method of determining the drop somewhat inaccurate beyond the limits
-above mentioned.
-
-                     =VALUE OF "S" FOR 25 CYCLES=
-
-  ---------+--------+------------------------+------------------------+
-    Size   |        |    .98 power factor    |    .90 power factor    |
-     of    | Area   +------------------------+------------------------+
-    wire   |  in    |       Spacing of       |       Spacing of       |
-    B.&S.  |circular|       conductors       |       conductors       |
-    gauge  | mils.  +----+----+----+----+----+----+----+----+----+----+
-           |        | 1" | 2" | 6" | 12"| 24"| 1" | 3" | 6" | 12"| 24"|
-  ---------+--------+----+----+----+----+----+----+----+----+----+----+
-   500,000 |500,000 |1.01|1.17|1.23|1.29|1.36|1.02|1.22|1.35|1.43|1.61|
-   300,000 |300,000 |1.04|1.10|1.13|1.18|1.21|1.00|1.08|1.16|1.25|1.31|
-     0,000 |211,600 |1.03|1.07|1.09|1.11|1.14|1.00|1.02|1.07|1.13|1.15|
-       000 |167,800 |1.00|1.05|1.06|1.09|1.10|1.00|1.00|1.02|1.07|1.11|
-        00 |133,100 |1.00|1.03|1.05|1.06|1.08|1.00|1.00|1.00|1.02|1.05|
-         0 |105,500 |1.00|1.01|1.02|1.03|1.04|1.00|1.00|1.00|1.00|1.00|
-           |        |    |    |    |    |    |    |    |    |    |    |
-         1 | 83,690}|    |    |    |    |    |    |    |    |    |    |
-         2 | 66,370}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-         3 | 52,630}|    |    |    |    |    |    |    |    |    |    |
-           |        |    |    |    |    |    |    |    |    |    |    |
-         4 | 41,740}|    |    |    |    |    |    |    |    |    |    |
-         5 | 33,100}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-         6 | 26,250}|    |    |    |    |    |    |    |    |    |    |
-           |        |    |    |    |    |    |    |    |    |    |    |
-         7 | 20,820}|    |    |    |    |    |    |    |    |    |    |
-         8 | 16,510}|    |    |    |    |    |    |    |    |    |    |
-         9 | 13,090}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-        10 | 10,380}|    |    |    |    |    |    |    |    |    |    |
-  ---------+--------+----+----+----+----+----+----+----+----+----+----+
-    Size   |        |    .80 power factor    |    .70 power factor    |
-     of    |  Area  +------------------------+------------------------+
-    wire   |   in   |       Spacing of       |        Spacing of      |
-    B.&S.  |circular|       conductors       |        conductors      |
-    gauge  |  mils. +----+----+----+----+----+----+----+----+----+----+
-           |        | 1" | 3" | 6" | 12"| 24"| 1" | 3" | 6" | 12"| 24"|
-  ---------+--------+----+----+----+----+----+----+----+----+----+----+
-   500,000 | 500,000|1.00|1.15|1.30|1.47|1.62|1.00|1.00|1.16|1.33|1.49|
-   300,000 | 300,000|1.00|1.00|1.09|1.16|1.25|1.00|1.00|1.00|1.02|1.12|
-     0,000 | 211,600|1.00|1.00|1.00|1.03|1.10|1.00|1.00|1.00|1.00|1.00|
-       000 | 167,800|1.00|1.00|1.00|1.00|1.01|1.00|1.00|1.00|1.00|1.00|
-        00 | 133,100|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-         0 | 105,500|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-           |        |    |    |    |    |    |    |    |    |    |    |
-         1 | 83,690}|    |    |    |    |    |    |    |    |    |    |
-         2 | 66,370}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-         3 | 52,630}|    |    |    |    |    |    |    |    |    |    |
-           |        |    |    |    |    |    |    |    |    |    |    |
-         4 | 41,740}|    |    |    |    |    |    |    |    |    |    |
-         5 | 33,100}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-         6 | 26,250}|    |    |    |    |    |    |    |    |    |    |
-           |        |    |    |    |    |    |    |    |    |    |    |
-         7 | 20,820}|    |    |    |    |    |    |    |    |    |    |
-         8 | 16,510}|    |    |    |    |    |    |    |    |    |    |
-         9 | 13,090}|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|1.00|
-        10 | 10,380}|    |    |    |    |    |    |    |    |    |    |
-  ---------+--------+----+----+----+----+----+----+----+----+----+----+
-
-     EXAMPLE.--A circuit supplying current at 440 volts, 60
-   frequency, with 5% loss and .8 power factor is composed of No. 2
-   B. & S. gauge wires spaced one foot apart. What is the drop in the
-   line?
-
-     According to the formula
-
-         % loss × volts
-  drop = -------------- × S
-               100
-
-     Substituting the given values, and value of S as obtained from
-   the table for frequency 60
-
-         5 × 440
-  drop = ------- × 1 = 22 volts
-           100
-
-
-=Current=.--As has been stated, the effect of power factor less than
-unity, is to increase the current; hence, in inductive circuit
-calculations, the first step is to determine the current flowing in a
-circuit. This is done as follows:
-
-                          apparent load
-                current = -------------              (1)
-                              volts
-
-  and
-
-                             watts
-          apparent load = ------------               (2)
-                          power factor
-
-  Substituting (2) in (1)
-
-                 watts
-              ------------
-              power factor          watts
-    current = ------------ = ---------------------   (3)
-                 volts       power factor × volts
-
-
-[Illustration: FIG. 2,704.--Rope type of stranded copper cable
-which is used when a high degree of flexibility is required. The
-construction of this cable is the stranding together of seven groups,
-each containing seven wires and producing a total of 49 wires.
-In cases when a greater carrying capacity is desired than can be
-obtained through the use of the 7 × 7 or 49 wire cable, the number of
-groups is increased to nineteen thereby making a total of 133 wires
-(19 × 7).]
-
-     EXAMPLE.--A 50 horse power 440 volt motor has a full load
-   efficiency of .9 and power factor of .8. How much current is
-   required?
-
-     Since the brake horse power of the motor is given, it is
-   necessary to obtain the electrical horse power, thus
-
-                  brake horse power   50
-         E.H.P. = ----------------- = -- = 55.5
-                     efficiency       .9
-
-  which in watts is
-
-                    55.5 × 746 = 41,403
-
-  which is the actual load, and from which
-
-                        actual load    41,403
-       apparent load = ------------  = ------ = 51,754
-                       power factor      .8
-
-     The current therefore at 440 volts is
-
-  apparent load   51,754
-  ------------- = ------ = 117.6 amperes
-      volts        440
-
-     EXAMPLE.--A 50 horse power single phase 440 volt motor, having
-   a full load efficiency of .92 and power factor of .8, is to be
-   operated at a distance of 1,000 feet from the alternator. The
-   wires are to be spaced 6 inches apart and the frequency is 60, and
-   % loss 5. Determine: =A=, _electrical horse power_; =B=, _watts_;
-   =C=, _apparent load_; =D=, _current_; =E=, _size of wires_; =F=,
-   _drop_; =G=, _voltage at the alternator_.
-
-     =A=. _Electrical horse power_
-
-                  brake horse power    50
-       E. H. P. = ----------------- × --- = 54.3
-                     efficiency       .92
-
-  or,
-
-               54.3 × 746 = 40,508 watts
-
-                =TABLE OF WIRE EQUIVALENTS=
-                    (Brown and Sharpe gauge)
-  ------+--------+--------+--------+---------+---------+---------
-   0000 | 2 #  0 | 4 #  3 | 8 #  6 | 16 #  9 | 32 # 12 | 64 # 15
-    000 | 2 "  1 | 4 "  4 | 8 "  7 | 16 " 10 | 32 " 13 | 64 " 16
-     00 | 2 "  2 | 4 "  5 | 8 "  8 | 16 " 11 | 32 " 14 | 64 " 17
-      0 | 2 "  3 | 4 "  6 | 8 "  9 | 16 " 12 | 32 " 15 | 64 " 18
-      1 | 2 "  4 | 4 "  7 | 8 " 10 | 16 " 13 | 32 " 16 | 64 " 19
-      2 | 2 "  5 | 4 "  8 | 8 " 11 | 16 " 14 | 32 " 17 | 64 " 20
-      3 | 2 "  6 | 4 "  9 | 8 " 12 | 16 " 15 | 32 " 18 | 64 " 21
-      4 | 2 "  7 | 4 " 10 | 8 " 13 | 16 " 16 | 32 " 19 | 64 " 22
-      5 | 2 "  8 | 4 " 11 | 8 " 14 | 16 " 17 | 32 " 20 | 64 " 23
-      6 | 2 "  9 | 4 " 12 | 8 " 15 | 16 " 18 | 32 " 21 | 64 " 24
-      7 | 2 " 10 | 4 " 13 | 8 " 16 | 16 " 19 | 32 " 22 | 64 " 25
-      8 | 2 " 11 | 4 " 14 | 8 " 17 | 16 " 20 | 32 " 23 | 64 " 26
-      9 | 2 " 12 | 4 " 15 | 8 " 18 | 16 " 21 | 32 " 24 | 64 " 27
-     10 | 2 " 13 | 4 " 16 | 8 " 19 | 16 " 22 | 32 " 25 | 64 " 28
-     11 | 2 " 14 | 4 " 17 | 8 " 20 | 16 " 23 | 32 " 26 | 64 " 29
-     12 | 2 " 15 | 4 " 18 | 8 " 21 | 16 " 24 | 32 " 27 | 64 " 30
-     13 | 2 " 16 | 4 " 19 | 8 " 22 | 16 " 25 | 32 " 28 |
-     14 | 2 " 17 | 4 " 20 | 8 " 23 | 16 " 26 | 32 " 29 |
-     15 | 2 " 18 | 4 " 21 | 8 " 24 | 16 " 27 | 32 " 30 |
-     16 | 2 " 19 | 4 " 22 | 8 " 25 | 16 " 28 |         |
-     17 | 2 " 20 | 4 " 23 | 8 " 26 | 16 " 29 |         |
-     18 | 2 " 21 | 4 " 24 | 8 " 27 | 16 " 30 |         |
-     19 | 2 " 22 | 4 " 25 | 8 " 28 |         |         |
-     20 | 2 " 23 | 4 " 26 | 8 " 29 |         |         |
-     21 | 2 " 24 | 4 " 27 | 8 " 30 |         |         |
-  ------+--------+--------+--------+---------+---------+---------
-
-=B.= _Watts_
-
-  watts = E.H.P. × 746 = 54.3 × 746 = 40,508
-
-=C.= _Apparent load_
-
-  apparent load or kva = (actual load or watts ÷ power factor)
-
-                       = 40,508 ÷ .8 = 50,635
-
-=D.= _Current_
-
-  current = (apparent load or kva ÷ volts)
-          = 50,635 ÷ 440
-          = 115 amperes
-
-=E.= _Size of wires_
-
-  cir. mils = (watts × feet × M) ÷ (% loss × volts^{2})
-            = (40,508 × 1,000 × 3,380) ÷ (5 × 440^{2})
-            = 141,443
-
-From table page 1,907, nearest size _larger_ wire is No. 00 B.&S.
-gauge.
-
-=F.= _Drop_
-
-  drop = ((% loss × volts) ÷ 100) × S
-       = ((5 × 440) ÷ 100) × 1.17
-       = 25.74 volts
-
-NOTE.--Values of S are given on page 1910.
-
-=G.= _Voltage at alternator_
-
-  alternator pressure = (volts at motor + drop)
-                      = 440 + 25.74
-                      = 465.7 volts.
-
-
-
-
-CHAPTER LXVI
-
-POWER STATIONS
-
-
-The term _power station_ is usually applied to any building
-containing an installation of machinery for the conversion of energy
-from one form into another form. There are three general classes of
-station:
-
-  1. Central stations;
-  2. Sub-stations;
-  3. Isolated plants.
-
-These may also be classified with respect to their function as
-
-  1. Generating stations;
-  2. Distributing stations;
-  3. Converting stations.
-
-and with respect to the form of power used in generating the electric
-current, generating stations may be classed as
-
-  1. Steam electric;
-  2. Hydro-electric;
-  3. Gas electric, etc.
-
-=Central Stations.=--It must be evident that the general type of
-central station to be adapted to a given case, that is to say, the
-general character of the machinery to be installed depends upon the
-kind of natural energy available for conversion into electrical
-energy, and the character of the electrical energy required by the
-consumers.
-
-This gives rise to a further classification, as
-
-  1. Alternating current stations;
-  2. Direct current stations;
-  3. Alternating and direct current stations.
-
-The alternators or dynamos may be driven by steam or water turbines,
-reciprocating engines, or gas engines, according to the character of
-the natural energy available.
-
-[Illustration: FIG. 2,705.--Elevation of small station with direct
-drive, showing arrangement of the boiler and engine, piping, etc.]
-
-=Ques. Why is the reciprocating engine being largely replaced by the
-steam turbine, especially for large units?=
-
-Ans. Because of its higher rotative speed, and absence of a
-multiplicity of bearings which in the case of a high speed,
-reciprocating engine must be maintained in close adjustment for the
-proper operation of the engine.
-
-     The higher speed of rotation results in a more compact unit,
-   desirable for driving high frequency alternators.
-
-=Ques. Is the steam turbine more economical than a high duty
-reciprocating engine?=
-
-Ans. No.
-
-=Location of Central Stations.=--As a rule, central stations should
-be so located that the average loss of voltage in overcoming the
-resistance of the lines is a minimum, and this point is located
-at the center of gravity of the system. In fig. 2,706 is shown a
-graphical method of locating this important spot.
-
-[Illustration: Fig. 2,706.--Diagram illustrating graphical method
-of determining the _center of gravity_ of a system in locating the
-central station.]
-
-     Suppose a rough canvass of prospective consumers in a district
-   to be supplied with electric light or power shows the principal
-   loads to be located at A, B, C, D, E, etc., and for simplicity
-   assume that these loads will be approximately equal, so that each
-   may be denoted by 1 for example:
-
-The relative locations of A, B, C, D, E, etc., should be drawn to
-scale (say 1 inch to the 1,000 feet) after which the problem resolves
-itself into finding the location of the station with respect to this
-scale.
-
-[Illustration: FIG. 2,707.--Exterior of central station at Lewis,
-Ia.; example of very small station located in the principal business
-section of a town. It also illustrates the use of a direct connected
-gasoline electric set. The central station is located on Main Street,
-which is the principal thoroughfare, and is installed in a low one
-story building for which a mere nominal rental charge is paid, the
-company having the option to buy the property later at the value of
-the land plus the cost of the improvements and simple interest on
-the same. To the front of an old frame building about 16 feet by
-28 feet has been built a neat, well lighted concrete block room,
-about 16 feet by 16 feet, carrying the building to the lot line and
-affording ample space for the generating set and switchboards, and
-such desk room as is needed for the ordinary office business of
-the company. In this room, which is finished in natural pine with
-plastered walls, has been installed a standard General Electric 25
-kw. gasoline electric generating set consisting of a four cylinder,
-four cycle, vertical water cooled, 43-54 H.P. gasoline engine, direct
-connected to a three phase, 2,300 volt, 600 R.P.M. alternator with
-a 125 volt exciter mounted on the same shaft and in the same frame.
-With the generating set is a slate switchboard panel equipped with
-three ammeters, one voltmeter, an instrument plug switch for voltage
-indication, one single pole carbon break switch, one automatic oil
-circuit breaker line switch and rheostats. Instrument transformers
-are mounted above and back of the board. For street lighting service
-a 4 kw. constant current transformer has been installed, and with
-it a gray marble switchboard panel mounted on iron frames and
-carrying an ammeter and a four point plug switch. On a board near
-the generator set are mounted in convenient reach suitable wrenches,
-spanners, and repair parts and tools. To cool the engine cylinders
-five 6 × 8 steel tanks have been installed in the old building, a
-pump on engine giving forced circulation.]
-
-     The solution consists in first finding the center of gravity
-   of any two of the loads, such as those at A and B. Since each of
-   these is 1, they will together have the same effect on the system
-   as the resultant load of 1 and 1, or 2, located at their center of
-   gravity, this point being so chosen that the product of the loads
-   by their respective distances from this point will in both cases
-   be equal.
-
-     The loads being equal in this case the distances must be equal
-   in order that the products be the same, so that the center of
-   gravity of A + B is at G, which point is midway between A and B.
-
-     Considering, next, the resultant load of 2 at G and the load of
-   1 at C, the resultant load at the center or gravity of these will
-   be 3, and this must be situated at a distance of two units from C
-   and one unit from G so that the distance 2 times the load 1 at C
-   equals the distance 1 times the load 2 at G. Having thus located
-   the load 3 at H, the same method is followed in finding the load 4
-   at I. Then in like manner the resultant load 4 and the load 1 at E
-   gives a load 5 at S.
-
-     The point S being the last to be determined represents,
-   therefore, the position of the center of gravity of the entire
-   system, and consequently the proper position of the plant in order
-   to give the minimum loss of voltage on the lines.
-
-=Ques. Is the center of gravity of the system, as obtained in fig.
-2,706, the proper location for the central station?=
-
-Ans. It is very rarely the best location.
-
-=Ques. Why?=
-
-Ans. Other conditions, such as the price of land, difficulty of
-obtaining water, facilities for delivery of coal and removal of
-ashes, etc., may more than offset the minimum line losses and copper
-cost due to locating the station at the center of gravity of the
-system.
-
-[Illustration: FIG. 2,708.--Map of Cia Docas de Santos hydro-electric
-system; an example of station location remote from the center of
-distribution. In the figure A is the intake; B, flume; C, forebay;
-D, penstocks; E, power house; F, narrow gauge railway; G, general
-store; H, point of debarkation; I, transmission line; J, dead ends;
-K, sub-station. Santos, in the republic of Brazil, is one of the
-great coffee shipping ports of the world, and for the development of
-its water front has required an elaborate system of quays. These have
-been developed by the Santos Dock Company, which holds a concession
-for the whole water front. The company, needing electric power for
-its own use, has developed a system deriving its power from a point
-about thirty miles from the city, where a small stream plunges
-down the sea coast from the mountain range that runs along it. The
-engineers have estimated that 100,000 horse power can be obtained
-from this source.]
-
-=Ques. How then should the station be located?=
-
-Ans. The more practical experience the designer has had, and the
-more common sense he possesses, the better is he equipped to handle
-the problem, as the solution is generally such that it cannot be
-worked out by any rule of thumb method.
-
-[Illustration: FIG. 2,709.--Station location. The figure shows
-two distribution centers as a town A and suburb B supplied with
-electricity from one station. For minimum cost of copper the location
-of the station would be at G, the center of gravity. However, it is
-very rarely that this is the best location. For instance at C, land
-is cheaper than at G, and there is room for future extension to the
-station, as shown by the dotted lines, whereas at G, only enough
-land is available for present requirements. Moreover C is near the
-railroad where coal may be obtained without the expense of cartage,
-and being located at the river, the plant may be run condensing thus
-effecting considerable economy. The conditions may sometimes be such
-that any one of the advantages to be secured by locating the station
-at C may more than offset the additional cost of copper.]
-
-=Ques. What are the general considerations with respect to the price
-of land?=
-
-Ans. The cost for the station site may be so high as to necessitate
-building or renting room at a considerable distance from the district
-to be supplied.
-
-     If the price of land selected for the station be high, the
-   running expenses will be similarly affected, inasmuch as more
-   interest must then be paid on the capital invested.
-
-     The price or rent of real estate might also in certain
-   instances alter the proposed interior arrangement of the station,
-   particularly so in the case of a company with small capital
-   operating in a city where high prices prevail. In general,
-   however, it may be stated that whatever effect the price of real
-   estate would have upon the arrangement, operation and location
-   of a central station it can quite readily and accurately be
-   determined in advance.
-
-=Ques. With respect to the cost of the land what should be especially
-considered?=
-
-Ans. Room for the future extension of the plant.
-
-     Although such additional space need not be purchased at the time
-   of the original installation it is well, if possible, to make
-   provision whereby it can be obtained at a reasonable figure when
-   desired. The preliminary canvass of consumers will aid in deciding
-   the amount of space advisable to allow for future extensions; as a
-   rule, however, it is wise to count on the plant enlarging to not
-   less than twice its original size, as often the dimensions have to
-   be increased four and even six times those found sufficient at the
-   beginning.
-
-[Illustration: FIG. 2,710.--Section of the central station or
-"electricity works" at Derby, showing boiler and engine room and
-arrangement of bunkers, conveyor, ash pit, grates, boilers (drum,
-heating surface and superheater), economizer, flue, turbines,
-condenser pumps, etc.; also location of switchboard gallery and
-system of piping.]
-
-=Ques. What trouble is likely to be encountered with an illy located
-plant after it is in operation?=
-
-Ans. It may be considered a nuisance by those residing in the
-vicinity, occasioning many complaints.
-
-[Illustration: FIG. 2,711.--View of old and new Waterside stations.
-The new station at the right has an all turbine equipment of ten
-units, some Curtis and some Parsons machines, two have a capacity of
-14,000 kw., and the remaining eight are of 12,000 kw. each. The old
-Riverside station, seen at the left is described on page 1940.]
-
-     Thus, if the plant be placed in a residential section of the
-   community the smoke, noise and vibration of the machines may
-   become a nuisance to the surrounding inhabitants, and eventually
-   end in suits for damage against the company responsible for the
-   same. For these and the other reasons just given a company is
-   sometimes forced to disregard entirely the location of a central
-   station near the center of gravity of the system, and build at a
-   considerable distance; such a proceeding would, if the distance be
-   great, necessitate the installation of a high pressure system.
-
-     There might, however, be certain local laws in force restricting
-   the use of high pressure currents on account of the danger
-   resulting to life, that would prevent this solution of the
-   problem. In such cases there could undoubtedly be found some site
-   where the objections previously noted would be tolerated; thus,
-   there would naturally be little objection to locating next to a
-   stable, a brewery, or a factory of any description.
-
-=Ques. Why is the matter of water supply important for a central
-station?=
-
-Ans. Because, in a steam driven plant, water is used in the boilers
-for the production of steam by boiling, and if the engines be of the
-condensing type it is also used in them for creating a vacuum into
-which the exhaust steam passes so as to increase the efficiency of
-the engine above what it would be if the exhaust steam were obliged
-to discharge into the comparatively high pressure of the atmosphere.
-
-     The force of this will be apparent by considering that the
-   water consumption of the engine ordinarily is from 15 to 25 lbs.
-   of "feed water" per horse power per hour, and the amount of
-   "circulating water" required to maintain the vacuum is about 25 to
-   30 times the feed water, and in the case of turbines with their 28
-   or 29 inch vacuum, much more. For instance, a 1,000 horse power
-   plant running on 15 lbs. of feed water and 30 to 1 circulating
-   water would require (1,000 × 15) × (30 + 1) = 465,000 lbs. or
-   55,822 gals. per hour at full capacity.
-
-=Ques. Besides price what other considerations are important with
-respect to water?=
-
-Ans. Its quality and the possibility of a scarcity of supply.
-
-It is quite necessary that the water used in the boilers should be
-as free as possible from impurities, so as to prevent the deposition
-within them of any scale or sediments. The quality of the water used
-for condensing purposes, however, is not quite so important, although
-the purer it is the better.
-
-If the plant is to be located in a city, the matter of water supply
-need not generally be considered, because, as a rule, it can be
-obtained from the waterworks; there will then, of course, be a water
-tax to consider and this, if large, may warrant an effort being
-made to obtain the water in some other way. In any event, however,
-the possibility of a scarcity in the supply should be reduced to a
-minimum.
-
-If the plant be located in the country, some natural source of water
-would be utilized unless the place be supplied with waterworks, which
-is not generally the case. It is usual, however, to find a stream,
-lake or pond in the vicinity, but if none such be conveniently near,
-an artesian or other form of well must be sunk.
-
-If abundance of water exist in the vicinity of the proposed
-installation, not only would the location of the plant be governed
-thereby, but the kind of power to be used for its operation would
-depend thereon. Thus, if the quantity of the water were sufficient
-throughout the entire year to supply the necessary power, water
-wheels might be installed and used in place of boilers and steam
-engines for driving the generators. The station would then, of
-course, be situated close to the waterfall, regardless of the center
-of gravity of the system.
-
-[Illustration: FIG. 2,712.--View illustrating the location of a
-station as governed by the presence of a water falls. In such cases
-the natural water power may be at a considerable distance from the
-center of gravity of the distribution system because of the saving
-in generation. In the case of long distance transmission very
-high pressure may be used and a transformer step down sub-station
-be located at or near the center of gravity of the system, thus
-considerably reducing the cost of copper for the transmission line.]
-
-=Ques. What should be noted with respect to the coal supply?=
-
-Ans. The facility for transporting the coal from the supply point to
-the boiler room.
-
-     In this connection, an admirable location, other conditions
-   permitting, is adjacent to a railway line or water front so that
-   coal delivered by car or boat may be unloaded directly into the
-   bins supplying the boilers.
-
-     If the coal be brought by train, a side or branch track will
-   usually be found convenient, and this will usually render any
-   carting of the fuel entirely unnecessary.
-
-     In whatever way the coal is to be supplied, the liability of a
-   shortage due to traffic or navigation being closed at any time of
-   the year should be well looked into, as should also the facility
-   for the removal of ashes, before deciding upon the final location
-   for the plant.
-
-[Illustration: FIG. 2,713.--View of a station admirably located with
-respect to transportation of the coal supply. As shown, the coal may
-be obtained either by boat or rail, and with modern machinery for
-conveying the coal to the interior of the station, the transportation
-cost is reduced to a minimum.]
-
-[Illustration: FIG. 2,714.--Floor plan of part of the turbine central
-station erected by the Boston Edison Co., showing two 5,000 kw.
-Curtis steam turbines in place. The complete installation contains
-twelve 5,000 kw. Curtis steam turbines, a sectional elevation being
-shown in fig. 2,758, page 1,971.]
-
-=Choice of System.=--The chief considerations in the design of a
-central station are economy and capacity. When the current has to be
-transmitted long distances for either lighting or power purposes,
-economy is attainable only by reducing the weight of the copper
-conductors. This can be accomplished only by the use of the high
-voltage currents obtainable from alternators.
-
-Again, where the consumers are located within a radius of two miles
-from the central station, thereby requiring a transmission voltage of
-550 volts or less, dynamos may be employed with greater economy.
-
-Alternating current possesses serious disadvantages for certain
-important applications.
-
-For instance, in operating electric railways and for lighting it is
-often necessary to transmit direct current at 500 volts a distance
-of five or ten miles. In such cases, the excessive drop cannot be
-economically reduced by increasing the sizes of the line wire, while
-a sufficient increase of the voltage would cause serious variations
-under changes of load. Hence, it is common practice to employ some
-form of auxiliary generator or booster, which when connected in
-series with the feeder, automatically maintains the required pressure
-in the most remote districts so long as the main generators continue
-to furnish the normal or working voltage.
-
-The advantage of a direct current installation in such cases over a
-similar plant supplying alternating current line is the fact that a
-storage battery may be used in connection with the former for taking
-up the fluctuations of the current, thereby permitting the dynamo to
-run with a less variable load, and consequently at higher efficiency.
-
-=Ques. Name some services requiring direct current.=
-
-Ans. Direct current is required for certain kinds of electrolytic
-work, such as electro-plating, the electrical separation of
-metals, etc., also the charging of storage batteries for electric
-automobiles.
-
-[Illustration: FIG. 2,715.--Example of central station located
-remote from the distributing center and furnishing alternating
-current at high pressure to a sub-station where the current is passed
-through step down transformers and supplied at moderate pressure
-to the distribution system. In some cases the sub-station contains
-also converters supplying direct current for battery charging,
-electro-plating, etc.]
-
-=Ques. How is direct current supplied?=
-
-Ans. Sometimes the central station is equipped with suitable
-apparatus for supplying both direct and alternating current. This may
-be accomplished in several different ways: By installing both direct
-and alternating current generators in the central station; by the use
-of double current generators or dynamotors, from which direct current
-may be taken from one side and alternating current from the other
-side; or by installing, in the sub-station of an alternating current
-central station, in addition to the transformers usually placed
-therein, a rotary converter for changing or converting alternating
-current into direct current.
-
-     Thus, it is evident that the character of a central station
-   will be governed to a great extent by the class of services to be
-   supplied.
-
-     An exception to this is where the entire output has to be
-   transmitted a long distance to the point of utilization.
-
-     In such cases a copper economy demands the use of high tension
-   alternating current, and its distribution to consumers may be made
-   directly by means of step down transformers mounted near by or
-   within the consumers' premises, or it may be transformed into low
-   voltage alternating current by a conveniently located sub-station.
-
-     Where the current is to be used chiefly for lighting and there
-   are only a few or no motors to be supplied, the choice between
-   direct current and alternating current will depend greatly upon
-   the size of the installation, direct current being preferable
-   for small installations and alternating current for large
-   installations.
-
-     If the current is to be used primarily for operating machinery,
-   such as elevators, travelling cranes, machine tools and other
-   devices of a similar character, which have to be operated
-   intermittently and at varying speeds and loads, direct current is
-   the more suitable; but if the motors performing such work can be
-   operated continuously for many hours at a time under practically
-   constant loads, as, for instance in the general work of a pumping
-   station, alternating current may be employed with advantage.
-
-[Illustration: FIG. 2,716.--Diagram illustrating diversity factor.
-By definition _diversity factor = combined actual maximum demand of
-a group of customers divided by the sum of their individual maximum
-demands_. Example, a customer has fifty (50) watt lamps and, of
-course, the sum of the individual maximum demands of the lamps is 2.5
-kw. watts ("connected load"). The customer's maximum demand, however,
-is 1.5 kw. Hence, the diversity factor[A] of the customer's group of
-lamps is 1.5 ÷ 2.5 = .6. In the diagram the ordinates of the curves
-show the ratio _maximum demand_ to _connected load_ for various kinds
-of electric lighting service in Chicago.]
-
-[A] NOTE.--The diversity factor of a customer's group of lamps,
-namely, the ratio of maximum demand to connected load is usually
-called the _demand factor_ of the customer.
-
-=Size of Plant.=--Before any definite calculation can be made, or
-plans drawn, the engineer must determine the probable load. This is
-usually ascertained in terms of the number and distances of lamps
-that will be required, by making a thorough canvass of the city or
-town, or that portion for which electrical energy is to be supplied.
-The probable load that the station is to carry when it begins
-operation, the nature of this load, and the probable rate of increase
-are matters upon which the design and construction chiefly depend.
-
-[Illustration: FIG. 2,717.--Load curve for one day.]
-
-=Ques. What is the nature of the load carried by a central station?=
-
-Ans. It fluctuates with the time of day and also with the time of
-year.
-
-=Ques. How is a fluctuating load best represented?=
-
-Ans. Graphically, that is to say by means of a curve plotted on
-coordinate paper of which ordinates represent load values and the
-corresponding abscissæ time values, as in the accompanying curves.
-
-=What is the nature of a power load?=
-
-Ans. Where electricity is supplied for power purposes to a number of
-factories, the load is fairly steady, dropping, of course, during
-meal hours. In the case of traction, the average value of the load is
-fairly steady but there are momentarily violent fluctuations due to
-starting cars or trains.
-
-[Illustration: FIG. 2,718.--Load curve for one year.]
-
-=Ques. What is the peak load?=
-
-Ans. The maximum load which has to be carried by the station at any
-time of day or night as shown by the highest point of the load curve.
-
-=Ques. Define the load factor.=
-
-Ans. The machinery of the station evidently must be large enough to
-carry the peak load, and therefore considerably in excess of that
-required for the average demand. The ratio of the average to the
-maximum load is called the load factor.
-
-     There are two kinds of load factor: the annual, and the daily.
-
-     The annual load factor is obtained as a percentage by
-   multiplying the number of units sold (per year) by 100, and
-   dividing by the product of the maximum load and the number of
-   hours in the year. The daily load factor is obtained by taking the
-   figures for 24 hours instead of a year.
-
-[Illustration: FIG. 2,719.--Load curve of plant supplying power for
-the operation of motors in a manufacturing district. The horizontal
-dotted lines show suitable power ratings. A properly designed steam
-plant has a large overload capacity, a hydraulic plant has a small
-overload capacity, and a gasoline engine plant has no overload
-capacity. Accordingly, the peak of the load (maximum load) may be 25
-or 30 per cent. in excess of the rated capacity of a steam plant,
-not more than 5 or 10 per cent. in excess of the rated capacity of a
-hydraulic plant, not at all in excess of the rated capacity of a gas
-engine plant.]
-
-=Ques. What must be provided in addition to the machinery required to
-supply the peak load?=
-
-Ans. Additional units must be installed for use in case of repairs or
-break down of some of the other units.
-
-     EXAMPLE.--What would be the boiler horse power required to
-   generate 5,000 kw. under the following conditions: Efficiency of
-   generators 85%; efficiency of engines 90%; feed water of engines
-   and auxiliaries 15 lbs. per I. H. P.; boiler pressure 175 lbs.;
-   temperature of feed water 150° Fahr? With a rate of combustion of
-   15 lbs. of coal per sq. foot of grate per hour and an evaporation
-   (from and at 212°) of 8 lbs. of water per lb. of coal, what area
-   of grate would be required and how much heating surface?
-
-           5,000 kw. = 5,000 ÷ .746 = 6,702= electrical horse power
-
-     To obtain this electrical horse power with alternators whose
-   efficiency is 85% requires
-
-           6,702 ÷ .85 = 7,885 brake horse power at the engine
-
-     This, with mechanical efficiency of 90% is equivalent to
-
-           7,885 ÷ .9 = 8,761 indicated horse power
-
-     Since 15 lbs. of feed water are required for the engines and
-   auxiliaries per indicated horse power per hour, the total feed
-   water or evaporation required to generate 5,000 kw. is
-
-           15 × 8,761 = 131,415 lbs. per hour.
-
-     that is to say, the boilers must be of sufficient capacity
-   to generate 131,415 lbs. of steam per hour from water at a
-   temperature of 150° Fahr. This must be multiplied by the _factor
-   of evaporation_ for steam at 175 lbs. pressure from feed water at
-   a temperature of 150°, in order to get the equivalent evaporation
-   "_from and at 212_°."
-
-     The formula for the factor of evaporation is
-
-                           H - _h_
-           factor of evaporation = -------    (1)
-                           965.7
-
-     in which
-
-         H = total heat of steam at the observed pressure;
-       _h_ = total heat of feed water of the observed temperature;
-     965.7 = latent heat, of steam at atmospheric pressure.
-
-     Substituting in (1) values for the observed pressure and
-   temperature as obtained from the steam table
-
-                                    1,197 - 118
-           factor of evaporation = ------------ = 1.117
-                                       965.7
-
-     for which the equivalent evaporation "_from and at 212_°" is
-
-           131,415 × 1.117 = 146,791 lbs.= per hour
-
-
-                         =FACTORS OF EVAPORATION=
-
-  -------------+-----------------------------------------------------+
-   Temp of     |        STEAM PRESSURE BY GAUGE             |
-   feed water. +-----+-----+-----+-----+-----+-----+-----+-----+-----+
-   Deg. Fahr.  |  50 |  60 |  70 |  80 |  90 | 100 | 110 | 120 | 130 |
-  -------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
-        32     |1.214|1.216|1.220|1.222|1.225|1.227|1.229|1.231|1.232|
-        40     |1.206|1.209|1.212|1.214|1.216|1.219|1.220|1.222|1.224|
-        50     |1.195|1.197|1.201|1.204|1.206|1.208|1.210|1.212|1.214|
-        60     |1.185|1.188|1.191|1.193|1.196|1.198|1.200|1.202|1.203|
-        70     |1.175|1.178|1.180|1.183|1.185|1.187|1.189|1.191|1.193|
-        80     |1.164|1.167|1.170|1.173|1.175|1.177|1.179|1.181|1.183|
-        90     |1.154|1.157|1.160|1.162|1.165|1.167|1.169|1.170|1.172|
-       100     |1.144|1.147|1.150|1.152|1.154|1.156|1.158|1.160|1.162|
-       110     |1.133|1.136|1.139|1.142|1.144|1.146|1.148|1.150|1.152|
-       120     |1.123|1.126|1.129|1.131|1.133|1.136|1.138|1.140|1.141|
-       130     |1.113|1.116|1.118|1.121|1.123|1.125|1.127|1.129|1.130|
-       140     |1.102|1.105|1.108|1.110|1.113|1.115|1.117|1.119|1.120|
-       150     |1.091|1.095|1.098|1.100|1.102|1.104|1.106|1.108|1.110|
-       160     |1.081|1.084|1.087|1.090|1.092|1.094|1.096|1.098|1.100|
-       170     |1.070|1.074|1.077|1.079|1.081|1.083|1.085|1.087|1.089|
-       180     |1.060|1.063|1.066|1.069|1.071|1.073|1.075|1.077|1.079|
-       190     |1.050|1.053|1.056|1.058|1.060|1.063|1.065|1.066|1.068|
-       200     |1.039|1.043|1.045|1.048|1.050|1.052|1.054|1.056|1.058|
-       210     |1.029|1.032|1.035|1.037|1.040|1.042|1.044|1.046|1.047|
-  -------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
-   Temp of     |        STEAM PRESSURE BY GAUGE             |
-   feed water. +-----+-----+-----+-----+-----+-----+-----+-----+-----+
-   Deg. Fahr.  | 140 | 150 | 160 | 170 | 180 | 190 | 200 | 210 | 220 |
-  -------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
-        32     |1.234|1.236|1.237|1.239|1.240|1.241|1.243|1.244|1.245|
-        40     |1.226|1.227|1.229|1.230|1.232|1.233|1.234|1.236|1.237|
-        50     |1.215|1.217|1.218|1.220|1.221|1.223|1.224|1.225|1.226|
-        60     |1.205|1.207|1.208|1.210|1.211|1.212|1.214|1.215|1.216|
-        70     |1.194|1.196|1.197|1.199|1.200|1.202|1.203|1.205|1.206|
-        80     |1.184|1.186|1.187|1.189|1.190|1.192|1.193|1.194|1.195|
-        90     |1.174|1.176|1.177|1.179|1.180|1.181|1.183|1.184|1.185|
-       100     |1.164|1.165|1.167|1.168|1.170|1.171|1.172|1.174|1.175|
-       110     |1.153|1.155|1.156|1.158|1.159|1.160|1.162|1.163|1.164|
-       120     |1.143|1.145|1.146|1.147|1.149|1.150|1.151|1.153|1.154|
-       130     |1.132|1.134|1.136|1.137|1.138|1.140|1.141|1.142|1.144|
-       140     |1.122|1.124|1.125|1.127|1.128|1.129|1.131|1.132|1.133|
-       150     |1.111|1.113|1.115|1.116|1.118|1.119|1.120|1.121|1.123|
-       160     |1.101|1.103|1.104|1.106|1.107|1.108|1.110|1.111|1.112|
-       170     |1.091|1.092|1.094|1.095|1.097|1.098|1.099|1.101|1.102|
-       180     |1.080|1.082|1.083|1.085|1.086|1.088|1.089|1.090|1.091|
-       190     |1.070|1.071|1.073|1.074|1.076|1.077|1.078|1.080|1.081|
-       200     |1.059|1.061|1.063|1.064|1.065|1.067|1.068|1.069|1.071|
-       210     |1.049|1.051|1.052|1.053|1.055|1.056|1.057|1.059|1.060|
-  -------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
-   Temp. of    |        STEAM PRESSURE BY GAUGE             |
-   feed water. +-----+-----+-----+-----+-----+-----+-----+-----+-----+
-   Deg. Fahr.  | 230 | 240 | 250 | 260 | 270 | 280 | 290 | 300 |     |
-  -------------+-----+-----+-----+-----+-----+-----+-----+----+------+
-        32     |1.246|1.247|1.248|1.250|1.251|1.252|1.253|1.254|
-        40     |1.238|1.239|1.240|1.241|1.242|1.243|1.244|1.245|
-        50     |1.228|1.229|1.230|1.231|1.232|1.233|1.234|1.235|
-        60     |1.217|1.218|1.219|1.220|1.221|1.222|1.223|1.224|
-        70     |1.207|1.208|1.209|1.210|1.211|1.212|1.213|1.214|
-        80     |1.196|1.198|1.199|1.200|1.201|1.202|1.203|1.204|
-        90     |1.186|1.187|1.188|1.189|1.190|1.191|1.192|1.193|
-       100     |1.176|1.177|1.178|1.179|1.180|1.181|1.182|1.183|
-       110     |1.166|1.167|1.168|1.169|1.170|1.171|1.172|1.173|
-       120     |1.155|1.156|1.157|1.158|1.159|1.160|1.161|1.162|
-       130     |1.145|1.146|1.147|1.148|1.149|1.150|1.151|1.152|
-       140     |1.134|1.135|1.136|1.137|1.138|1.139|1.140|1.141|
-       150     |1.124|1.125|1.126|1.127|1.128|1.129|1.130|1.131|
-       160     |1.113|1.115|1.116|1.117|1.118|1.119|1.120|1.121|
-       170     |1.103|1.104|1.105|1.106|1.107|1.108|1.109|1.110|
-       180     |1.093|1.094|1.095|1.096|1.097|1.098|1.099|1.100|
-       190     |1.082|1.083|1.084|1.085|1.086|1.087|1.088|1.089|
-       200     |1.072|1.073|1.074|1.075|1.076|1.077|1.078|1.079|
-       210     |1.061|1.062|1.063|1.064|1.065|1.066|1.067|1.068|
-  -------------+-----+-----+-----+-----+-----+-----+-----+-----+
-
-     One boiler horse power being equal to _an evaporation of_ 34½
-   _lbs. of water from a feed water temperature of 212° Fahr., into
-   steam at the same temperature_, the boiler capacity is accordingly
-
-           148,105 ÷ 34.5 = 4,293 boiler horse power.
-
-     The rate of evaporation is given at 8 lbs. of water (from and at
-   212° Fahr.), for which the fuel required is
-
-           148,105 ÷ 8 = 18,513 lbs. of coal per hour.
-
-     For a rate of combustion of 15 lbs. of coal per hour per square
-   foot of grate,
-
-           grate area = 18,513 ÷ 15 = 1,234 sq. ft.
-
-     For stationary boilers the usual ratio of heating surface to
-   grate area is 35:1, accordingly the heating surface corresponding
-   to this ratio is
-
-           1,234 × 35 = 43,190 sq.ft.
-
-     The above calculation is based on a rate of evaporation of 8
-   lbs. of water per lb. of coal and a rate of combustion of 15 lbs.
-   of coal per sq. ft. of grate. For other rates the required grate
-   area may be obtained from the following table:
-
-  ----------------------------------------------------------------------
-                  GRATE SURFACE  PER HORSE  POWER  (KENT)
-  ------------+------+-----+--------------------------------------------
-              |Pounds|     |
-              | of   | Lbs.|  Pounds of coal burned per square foot of
-              |water |  of |              grate per hour
-              | from | coal+----+----+----+----+----+----+----+----+----
-              |and at| per |    |    |    |    |    |    |    |    |
-              | 212° | h.p.|  8 | 10 | 12 | 15 | 20 | 25 | 30 | 35 | 40
-              | per  | per |    |    |    |    |    |    |    |    |
-              |pound | hour+----+----+----+----+----+----+----+----+----
-              | of   |     |      Square feet grate per horse power
-              | coal |     |
-  ------------+------+-----+----+----+----+----+----+----+----+----+----
-   Good coal  | }10  | 3.45| .43|.35 | .28| .23| .17| .14| .11| .10| .09
-   and boiler | } 9  | 3.83| .48| .38| .32| .25| .19| .15| .13| .11| .10
-              |      |     |    |    |    |    |    |    |    |    |
-   Fair coal  |{8.61 | 4.  | .50| .40| .33| .26| .20| .16| .13| .12| .10
-   or boiler  |{8    | 4.31| .54| .43| .36| .29| .22| .17| .14| .13| .11
-              |{7    | 4.93| .62| .49| .41| .33| .24| .20| .17| .14| .12
-              |      |     |    |    |    |    |    |    |    |    |
-   Poor coal  |{6.9  | 5.  | .63| .50| .42| .34| .25| .20| .17| .15| .13
-   or boiler  |{6    | 5.75| .72| .58| .48| .38| .29| .23| .19| .17| .14
-              |{5    | 6.9 | .86| .69| .58| .46| .35| .28| .23| .22| .17
-              |      |     |    |    |    |    |    |    |    |    |
-   Lignite and|}3.45 |10.  |1.25|1.00| .83| .67| .50| .40| .33| .29| .25
-   poor boiler|}     |     |    |    |    |    |    |    |    |    |
-  ------------+------+-----+----+----+----+----+----+----+----+----+----
-
-=General Arrangement of Station.=--In designing an electrical
-station, it is preferable that whatever rooms or divisions of the
-interior space are desired should determine the total outside
-dimensions of the plant in the original plans of the building than
-that these latter dimensions be fixed and the rooms, etc., be fitted
-in afterward.
-
-              =SAVING DUE TO HEATING THE FEED WATER=
-
- Table showing the percentage of saving for each degree of increase in
-         temperature of feed water heated by waste steam.
-
-  ----------------------------------------------------------------------
-  Init| Pressure of steam in boiler, lbs. per sq. inch above atmosphere
-  temp|-----------------------------------------------------------------
-   of |
-  feed|  0  |  20 |  40 |  60 |  80 | 100 | 120 | 140 | 160 | 180 | 200
-  ----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
-   32°|.0872|.0861|.0855|.0851|.0847|.0844|.0841|.0839|.0837|.0835|.0833
-   40 |.0878|.0867|.0861|.0856|.0853|.0850|.0847|.0845|.0843|.0841|.0839
-   50 |.0886|.0875|.0868|.0864|.0860|.0857|.0854|.0852|.0850|.0848|.0846
-   60 |.0894|.0883|.0876|.0872|.0867|.0864|.0862|.0859|.0856|.0855|.0853
-   70 |.0902|.0890|.0884|.0879|.0875|.0872|.0869|.0867|.0864|.0862|.0860
-   80 |.0910|.0898|.0891|.0887|.0883|.0879|.0877|.0874|.0872|.0870|.0868
-   90 |.0919|.0907|.0900|.0895|.0888|.0887|.0884|.0883|.0879|.0877|.0875
-  100 |.0927|.0915|.0908|.0903|.0899|.0895|.0892|.0890|.0887|.0885|.0883
-  110 |.0936|.0923|.0916|.0911|.0907|.0903|.0900|.0898|.0895|.0893|.0891
-  120 |.0945|.0932|.0925|.0919|.0915|.0911|.0908|.0906|.0903|.0901|.0899
-  130 |.0954|.0941|.0934|.0928|.0924|.0920|.0917|.0914|.0912|.0909|.0907
-  140 |.0963|.0950|.0943|.0937|.0932|.0929|.0925|.0923|.0920|.0918|.0916
-  150 |.0973|.0959|.0951|.0946|.0941|.0937|.0934|.0931|.0929|.0926|.0924
-  160 |.0982|.0968|.0961|.0955|.0950|.0946|.0943|.0940|.0937|.0935|.0933
-  170 |.0992|.0978|.0970|.0964|.0959|.0955|.0952|.0949|.0946|.0944|.0941
-  180 |.1002|.0988|.0981|.0973|.0969|.0965|.0961|.0958|.0955|.0953|.0951
-  190 |.1012|.0998|.0989|.0983|.0978|.0974|.0971|.0968|.0964|.0062|.0960
-  200 |.1022|.1008|.0999|.0993|.0988|.0984|.0980|.0977|.0974|.0972|.0969
-  210 |.1033|.1018|.1010|.1003|.0998|.0994|.0990|.0987|.0984|.0981|.0979
-  220 |  -- |.1029|.1019|.1013|.1008|.1004|.1000|.0997|.0994|.0991|.0989
-  230 |  -- |.1039|.1031|.1024|.1018|.1012|.1010|.1007|.1003|.1001|.0999
-  240 |  -- |.1050|.1041|.1034|.1029|.1024|.1020|.1017|.1014|.1011|.1009
-  250 |  -- |.1062|.1052|.1045|.1040|.1035|.1031|.1027|.1025|.1022|.1019
-  ----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
-
-     NOTE.--An approximate rule for the conditions of ordinary
-   practice is a saving of 1 per cent. made by each increase of
-   11° in the temperature of the feed water. This corresponds to
-   .0909 per cent. per degree. The calculation of saving is made as
-   follows: Boiler pressure, 100 lbs. gauge; total heat in steam
-   above 32° = 1,185 B.T.U. feed water, original temperature 60°,
-   final temperature 209°F. Increase in heat units, 150. Heat units
-   above 32° in feed water of original temperature = 28. Heat units
-   in steam above that in cold feed water, 1,185-28 = 1,157. Saving
-   by the feed water heater = 150 ÷ 1,157 = 12.96 per cent. The
-   same result is obtained by the use of the table. Increase in
-   temperature 150° × tabular figure .0864 = 12.96 per cent. Let
-   total heat of 1 lb. of steam at the boiler pressure = H; total
-   heat of 1 lb. of feed water before entering the heater = _h'_, and
-   after passing through the heater = _h''_; then the saving made by
-   the heater is (_h''_-_h'_) ÷ (H-_h'_).
-
-Under usual conditions the plans of an electrical station are readily
-drawn, as they are generally of a simple nature. The engines and
-generators will occupy the majority of the space, and these are
-usually placed in one large room; in some stations, however, they are
-located respectively in two adjacent rooms. The boilers are generally
-located in a room apart from the engines and dynamos, and in some
-cases a separate building is provided for them; the pumps, etc., must
-be installed not far from the boilers, and space must also be allowed
-near the boilers for coal and ashes.
-
-[Illustration: FIG. 2,720.--Floor plan of an electrical station
-having a belted drive with counter shaft.]
-
-     Fig. 2,720 shows the floor plan of an electrical station, in
-   which a countershaft and belted connections are used between
-   the engines and generators. Referring first to the plan of the
-   building itself, A represents the engine and dynamo room, B
-   denotes the boiler room, C the office, D the store room, and E the
-   chimney connected with the boilers by means of the uptake _w_.
-   Referring next to the apparatus installed, S, S, S, S represents
-   a battery of four boilers; these are connected by steam piping
-   VV to the two steam engines, M and M, which are belted to the
-   countershaft O. Belted to the countershaft are the generators,
-   T, T, T, T, the circuits from which are controlled on the
-   switchboard, H.
-
-=Ques. What are the objections to the arrangement shown in
-fig. 2,720.=?
-
-Ans. The large space required by the belt drive especially in
-locations where land is expensive. Another objection is the
-frictional loss due to the belt drive with its countershaft, etc.
-
-[Illustration: FIG. 2,721.--Elevation of station having a belted
-drive with countershaft, as shown in plan in fig. 2,720.]
-
-=Ques. What are the desirable features of the belt drive?=
-
-Ans. High speed generators may be used, thus reducing the first
-cost, and the multiplicity of speeds and flexibility of the system
-resulting from the use of a friction clutch.
-
-     Thus in fig. 2,720, each pulley may be mounted on the counter
-   shaft O with a friction clutch. A jaw clutch may also be provided
-   at Z, thus permitting the shaft O to be divided into two sections.
-   It is therefore possible by this arrangement to cause either of
-   the engines to drive any one of the generators, or all of them, or
-   both of the engines to drive all of the generators simultaneously.
-
-=Ques. Under what condition is the counter shaft belt drive
-particularly valuable?=
-
-Ans. In case of a break down of any one of the engines or generators,
-and also when it becomes necessary to clean them without interrupting
-the service.
-
-[Illustration: FIG. 2,722.--Plan of station arranged for extension.
-The space required for a central station depends upon the number and
-kind of lights to be supplied, and upon the character and arrangement
-of the machinery. In calculating the size of building required, two
-things must be carefully considered: first, the building must be
-adapted to the plant to be installed in the beginning; and second, it
-must be arranged so that enlargement can be made without disarranging
-or interfering with the plant already in existence. This is usually
-best secured by providing for expansion in one or two definite
-directions, the building being made large enough to accommodate
-additional units that will be necessary at some future time because
-of the growth of the community and consequent increased demand for
-electric current.]
-
-=Ques. How may the design in fig. 2,720 be modified for the
-installation of a storage battery?=
-
-Ans. If a storage battery be necessary, a partition may be
-constructed across the room A, as indicated by the dotted lines, and
-the battery installed in the room thus formed.
-
-[Illustration: FIG. 2,723.--Interior of old Riverside station
-showing at the right, seven 6,000 horse power alternators driven by
-reciprocating engines, and at the left, a number of turbine units
-aggregating 90,000 horse power.]
-
-=Ques. Mention a few details in the general arrangement of the
-building fig. 2,720.=
-
-Ans. Two doors to the room A may conveniently be provided at K and L,
-the former connecting with the boiler room B, and the latter serving
-as the main entrance to the station. There is little that need be
-added to what has already been stated regarding the boiler room B.
-The door at F provides for the entrance of coal and the removal of
-ashes, while at P, the pump and heaters may conveniently be located.
-In the office C, visitors may be received, the station reports made
-out, bulletins issued from time to time, and whatever engineering
-problems arise may here be solved on paper by the engineer in
-charge of the plant. The store room D will be found convenient for
-various supplies, tools and appliances needed in the operation of
-the station. These may here be kept under lock and key and the daily
-waste and loss resulting from carelessness avoided.
-
-=Ques. What important point should be noted in locating the engines
-and boilers?=
-
-Ans. They should be so placed that the piping between them will be as
-short and direct as possible.
-
-=Ques. Why?=
-
-Ans. The steam pipe should be short to reduce the loss of heat
-between engine and boiler to a minimum, and both short and direct to
-avoid undue friction and consequent drop in pressure of the steam in
-passing through the pipe to the engine.
-
-     Entirely too little attention is given to this matter on the
-   part of designers and it cannot be too strongly emphasized that,
-   for economy, the steam pipe between an engine and boiler should
-   be as short and direct as possible, having regard of course, for
-   proper piping methods.
-
-=Ques. What should be provided for the steam pipe?=
-
-Ans. A heavy covering of approved material should be placed around
-the pipe to reduce the loss of heat by radiation. For this purpose
-hair felt, mineral wool and asbestos are used.
-
-[Illustration: FIG. 2,724.--View of engine and condenser, showing how
-to arrange the piping to secure good vacuum. _Locate the condenser as
-near the engine as possible_; =use easy bends= _instead of elbows;
-place the pump_ =below= _bottom of condenser so the water will
-drain to pump_. At A is a relief valve, for protection in case the
-condenser become flooded through failure of the pump, and at B is
-a gate valve to shut off condenser in case atmospheric exhaust is
-desired to permit repairs to be made to condenser during operation.
-=A water seal= should be maintained on the relief valve and =special
-attention= _should be given to the stuffing box_ of the gate valve
-=to prevent air leakage=. _The discharge valve of the pump should be
-water sealed._]
-
-=Ques. How should the piping be arranged between the engine and
-condenser, and why?=
-
-Ans. It should be as short and direct as possible; especially should
-elbows be avoided so that the back pressure on the engine piston will
-be reduced as near as can be to that of the condenser.
-
-     That is to say, in order to get nearly the full effect of the
-   vacuum in the condenser the frictional resistance of the piping
-   should be reduced to a minimum.
-
-     Where 90° turns are necessary, easy bends should be used instead
-   of sharp elbows. The force of this argument must be apparent by
-   noting the practice of steam turbine builders of placing the
-   turbine right up against the condenser, and remembering that a
-   high vacuum is necessary to the economical working of a turbine.
-   See fig. 1,445, page 1,182.
-
-=Ques. What are the considerations respecting the number and type of
-engine to be used?=
-
-Ans. In the illustration fig. 2,720, two engines M and M' are
-employed, one belted to each end of the countershaft O. These engines
-should be of similar or identical pattern; for a small output
-they may be either simple or compound, as the conditions of fuel
-expenditure may dictate, but if the output be large, triple expansion
-engines or turbines are advisable.
-
-[Illustration: FIG. 2,725.--"Dry pipe" for horizontal boiler: it is
-connected to the main outlet and its upper surface is perforated with
-small holes, the far end being closed. With this arrangement steam is
-taken from the boiler over a large area, so that it will contain very
-little moisture. _All horizontal boilers without a dome should be
-fitted with a dry pipe;_ most engineers do not realize the importance
-of obtaining dry steam for engine operation.]
-
-     Corliss or similar slow speed engines may advantageously be used
-   in either case. In all cases the engine should be run condensing
-   unless the cost for circulating water is prohibitive; even in such
-   cases cooling towers may be installed and effect a saving.
-
-     In operation, during the greater part of the day, one engine
-   running two or perhaps three of the generators, will carry the
-   load, but when the load is particularly heavy, as in the morning
-   and evening, both engines and all the generators may be required
-   to meet the demands.
-
-[Illustration: FIG. 2,726.--Method of connecting a header to a
-battery of boilers. Where two or more boilers are connected to a
-single header, the use of a reliable non-return boiler stop valve is
-necessary, and in some countries their installation is compulsory. A
-non-return boiler stop valve will instantly close should the pressure
-in the boiler to which it is attached suddenly decrease below that
-in the header, and thereby prevent the entrance of steam from the
-other boilers of the battery. This sudden decrease in pressure may be
-caused by a ruptured fitting or the blowing out of a tube, in which
-event an ordinary stop valve taking the place of a non-return boiler
-stop valve would be inadequate, as the loss of steam from the other
-boilers of the battery would be tremendous before an ordinary valve
-could be reached and closed, assuming that it would be possible to do
-so, which in the majority of cases it is not. Should it be desired
-to cut out a boiler for cleaning or repairs, the non-return boiler
-stop valve will not permit steam to enter the boiler from the header,
-even should the handwheel be operated for this purpose, as it cannot
-be opened by hand, but can, however, be closed. A non-return boiler
-stop valve should be attached to each boiler and connected to an
-angle valve on the header. A pipe bend should be used for connecting
-the valves, as this will allow for expansion and contraction. The
-pipe should slope a trifle downward toward the header and a suitable
-drain provided. This drain should be opened and all water permitted
-to escape before the angle valve is opened, thereby preventing any
-damage due to water hammer.]
-
-     By exercising a little ingenuity in shifting the load on
-   different machines at different times, both engines and dynamos,
-   may readily be cleaned and repaired without interrupting the
-   service.
-
-=Ques. For economy what kind of steam should be used?=
-
-Ans. Super-heated steam.
-
-     The saving due to the use of superheated steam is about 1% for
-   every ten degrees Fahr. of super-heat. It should be used in all
-   cases.
-
-=Ques. How should the machines be located?=
-
-Ans. Sufficient space should be allowed between them that cleaning
-and repairing may be done easily, quickly and effectually.
-
-[Illustration: FIGS. 2,727 and 2,728.--Method of preventing vibration
-and of supporting pipes. The figures show top and side views of
-a main header carried in suitable frames fitted with adjustable
-roller. While the pipe is illustrated as resting on the adjustable
-rollers, nevertheless the rollers may also be placed at the sides
-or on top of the pipe to prevent vibration, or in cases where the
-thrust from a horizontal or vertical branch has to be provided for.
-This arrangement will take care of the vibration without in any way
-preventing the free expansion and contraction of the pipe.]
-
-=Ques. How should the switchboard be located?=
-
-Ans. In fig. 2,720, the switchboard H is mounted against the wall
-dividing the room A from the room B, and is in line with the machines.
-
-     The advantages arising from a switchboard thus installed are,
-   that the switchboard attendant working thereon can obtain at any
-   time an unobstructed view of the performance of each individual
-   machine, and he has in consequence a much better control of them;
-   then, too, while he is engaged at the engines or generators he
-   can also see the measuring instruments on the switchboard, and
-   ascertain approximately the readings upon them.
-
-     In cases of emergency it is sometimes necessary for the
-   engineer in charge of a plant to be in several places at the same
-   time in order to prevent an accident, and that this seemingly
-   impossibility may be approximated as nearly as possible, it is
-   essential that the controlling devices be located as closely
-   together as is consistent, and that no moving belt or pulley
-   intervene between them.
-
-     These conditions are well satisfied in fig. 2,720, and owing to
-   the short distances between the generators and the switchboard the
-   drop of voltage in each of the conducting wires between them will
-   be low.
-
-     This latter advantage is worthy of notice in a station
-   generating large currents at a low pressure. To offset the
-   advantages just mentioned, the location of the switchboard in
-   line with the machines introduces an element of danger to the
-   switchboard, its apparatus, and the attendant, on account of the
-   possible bursting of a flywheel or other parts of the machines
-   from centrifugal force.
-
-[Illustration: FIGS. 2,729 and 2,730.--Points on placing stop valves.
-The first and most important feature is to ascertain whether the
-valve will act as a water trap for condensed steam. Fig. 2,729
-illustrates a common error in the placing of valves, as this
-arrangement permits of an accumulation of condensed steam above the
-valve when closed, and should the engineer be careless and open the
-valve suddenly, serious results might follow owing to water-hammer.
-Fig. 2,730 illustrates the correct method of placing the valve. It
-sometimes occurs, however, that it is not convenient to place the
-valve as shown in fig. 2,730 and that fig. 2,729 is the only manner
-in which the valve can be placed. In such cases, the valve should
-have a drain, and this drain should always be opened before the large
-valve is opened.]
-
-     If the switchboard be placed in the dotted position at H', or,
-   in fact, at the opposite end of the room A, the damage to life
-   and property that might result from the effects of centrifugal
-   force would be eliminated, but in place thereof would be the
-   disadvantages of an obstructed view of the machines from the
-   switchboard, an obstructed view of the switchboard from the
-   machines, inaccessibility between these two, and a greater drop
-   of voltage in the majority of the conducting wires between the
-   generators and the switchboard.
-
-=Ques. Describe a second arrangement of station with belt drive and
-compare it with the design shown in fig. 2,720.=
-
-[Illustration: FIG. 2,731.--Plan of electrical station with belt
-drive without counter shaft. The installation here represented
-consists of two boilers, S, etc., and three sets of engines and
-generators, T, M, etc. Sufficient allowance has been made in the
-plans, however, for future increase of business, as additional space
-has been provided for an extra engine and generator set, as indicated
-by the dotted lines.]
-
-Ans. A floor plan somewhat different from that presented in fig.
-2,720 is shown in fig. 2,731. Here a belt drive is employed, but no
-countershaft is used. Each generator, therefore, is dependent upon
-its respective engine, and in consequence the flexibility obtained by
-the use of a countershaft is lost. On the other hand, there is less
-loss of mechanical power between the engines and generators in the
-driving of the latter, and less floor space is necessary in the room
-A. If, however, the floor area of this room be made the same as in
-the previous arrangement and the same number of machines are to be
-installed, they may be spaced further apart, affording in consequence
-considerably more room for cleaning and repairing them.
-
-     In operation, the normal conditions should be such that any two
-   of the engine and generator sets may readily carry the average
-   load, the third set to be used only as a reserve either to aid the
-   other two when the load is unusually heavy or to replace one of
-   the other sets when it becomes necessary to clean or repair the
-   latter.
-
-     The switchboard may perhaps be best located at H, as a similar
-   position on the opposite side of the room A would bring it beneath
-   one or more of the steam pipes and thus endanger it should a
-   possible leakage occur from these pipes. If located at H, however,
-   it will be in line with the machines, and therefore will be
-   subject to the disadvantages previously mentioned for such cases;
-   consequently it might be as well to place it at the further end
-   of the room, either against the partition (shown dotted) of the
-   storage battery room if this be built, or else (if no storage
-   battery is to be installed), against the end wall itself. The
-   nearer end of the room A would not be very desirable for the
-   switchboard installation on account of being so far removed from
-   the machines, and therefore more or less inaccessible from them.
-   Outside of what has now been mentioned, the division of the floor
-   plan and the arrangement therein is practically the same as in
-   fig. 2,720, accordingly what has already been stated regarding the
-   former installation applies, therefore, with equal force to the
-   present installation.
-
-=Ques. Describe a plant with direct drive.=
-
-Ans. This type of drive is shown in fig. 2,732. Each engine is
-directly connected to a generator, that is, the main shafts of both
-are joined together in line so that the generator is driven without
-the aid of a belt.
-
-=Ques. What is the advantage of direct drive?=
-
-Ans. The great saving in floor space, which is plainly shown in fig.
-2,732, the portion A' representing the saving which results over the
-installations previously illustrated in figs. 2,720 and 2,731.
-
-=Ques. How could the floor space be further reduced?=
-
-Ans. By employing vertical instead of horizontal engines.
-
-=Ques. What should be done before drawing the plans for the station?=
-
-Ans. The types of the various machines and apparatus to be installed
-should, as nearly as possible, be selected in advance so that their
-approximate dimensions may serve as a guide in drawing up the plans
-of the building.
-
-[Illustration: FIG. 2,732.--Plan of electrical station containing
-direct connected units. As shown, space is provided for an extra
-boiler and engine and generator set, as indicated by the dotted
-lines. Space also exists for a storage battery room if necessary, and
-the partition dividing this room from the engine and dynamo room is
-shown by a dotted line as in previous cases.]
-
-     Owing to the great difference in these dimensions for the
-   various types, and in fact for the same types as manufactured by
-   different concerns, no definite rules regarding the necessary
-   space required can here be given. In a general way, however, the
-   author has endeavoured to indicate by the drawings the relative
-   amounts of space that ordinarily would be considered sufficient.
-
-=Ques. What is the disadvantage of direct drive?=
-
-Ans. A more expensive generator is required because it must run at
-the same speed as the engine, which is relatively low as compared
-with that of a belted generator.
-
-=Station Construction.=--The construction or rearrangement of the
-building intended for the plant is a problem that under ordinary
-conditions would be solved by an architect, or at least by an
-architect with the assistance of an electrical or mechanical
-engineer, still there are many installations where the electrical
-engineer has been compelled to design the building.
-
-In such instances he should be equipped with a general knowledge of
-the construction of buildings.
-
-=Foundations.=--The foundation may be either natural or artificial;
-that is, it may be composed of rock or soil sufficiently solid
-to serve the purpose unaided, or it may be such as to require
-strengthening by means of wood or iron beams, etc. In either case any
-tendency toward a considerable settling or shifting of the foundation
-due to the action of water, frost, etc., after the station has been
-completed must be well guarded against. To this end special attention
-should be given to the matter of drainage.
-
-=Ques. How should the foundation be constructed for the machines?=
-
-Ans. The foundations constructed for the machines should be entirely
-separate from that built for the walls of the building, so that the
-vibrations of the former will not affect the latter.
-
-     If there be several engines and dynamos to be installed, it is
-   best to construct two foundations, one for the engines and one for
-   the dynamos. If, however, there be considerable distance between
-   the units, it may be advisable to build a separate foundation
-   for each engine and for each dynamo. The material of which these
-   foundations are composed should if the machines be of 20 horse
-   power or over, possess considerable strength and be impervious to
-   moisture. Brick, stone and concrete are desirable for the purpose,
-   and only the best quality of cement mortar should be employed.
-   Care must be taken that lime mortar is not used in place of
-   cement mortar, as the former is not well adapted to withstand the
-   vibrations of the machines without crumbling.
-
-[Illustration: FIG. 2,733.--Angle for foundation footing. In ordinary
-practice the footing courses upon which the walls of the building
-proper rest, consist of blocks or slabs of stone as large as are
-available and convenient to handle. Footings of brick or concrete are
-also used in very soft soils; footings consisting of timber grillage
-are often employed. A grillage of iron or steel beams has also
-been used successfully. The inclination of the angle φ, of footing
-should be about as follows: for metal footings 75°; for stone, 60°;
-for concrete, 45°; for brick, 30°. Damp proof courses of slate, or
-layer of asphalt are laid in or on the foundations or lower walls to
-prevent moisture arising or penetrating by capillary attraction.]
-
-=Ques. Describe a method of constructing foundations.=
-
-Ans. An excavation is made to the desired depth and a form inserted
-corresponding to the desired dimensions for the foundation. A
-template is placed on top locating all the centers, with iron
-pipes suspended from these centers, two or three sizes larger than
-the anchor bolts. At the lower end of the pipes are core boxes.
-Concrete is poured into the mould thus formed, and when hard, the
-forms are removed thus leaving the solid foundation. The anchor
-bolts are inserted through the pipes and passed through iron plates
-at the lower end as shown in fig. 2,734, being secured by nuts. By
-using pipe of two or three bolt diameters a margin is provided for
-adjustment so the bolts will pass through the holes in the frame of
-the machine thus allowing for any slight errors in laying out the
-centers on the template.
-
-[Illustration: FIG. 2,734.--Concrete foundation showing method of
-installing the anchor bolts.]
-
-=Ques. What is the object of the openings in the bottom of the
-foundation?=
-
-Ans. In case of a defective bolt, it may be replaced by a new one
-without injury to the foundation.
-
-=Walls.=--Regarding the material for the walls of the station iron,
-stone, brick and wood may be considered. Of these, iron in the form
-of sheets or plates would be entirely fireproof, but being itself
-a conductor would introduce difficulties in maintaining a high
-insulation resistance of the current carrying circuits; it would
-also make the building difficult to heat in winter and to keep cool
-in summer. Stone in the form of limestone, granite or sandstone, as
-a building material is desirable for solidity and attractiveness;
-it is also fireproof and an insulator, but the high cost of such a
-structure for an electrical station usually prohibits its use except
-in private plants or in electrical stations located in large cities.
-
-[Illustration: FIG. 2,735.--View showing part of template for
-locating anchor bolt centers, pipes through which the bolts pass
-and bolt boxes at lower end of bolts. The completed foundation is
-shown in fig. 2,734, with template removed. The template is made of
-plain boards upon which the center lines are drawn, and bolt center
-located. Holes are bored at the bolt centers to permit insertion of
-the pipes as shown.]
-
-Brick is a good material and is readily obtained in nearly all parts
-of the country; it is comparatively cheap, and is also an insulating
-and fireproof material. The bricks selected for this purpose should
-possess true sharp edges, and be hard burned.
-
-=Ques. What are the features of wood?=
-
-Ans. Wood forms the cheapest material that can be used for the walls
-of electrical stations, and it usually affords satisfaction, but has
-the disadvantage of high fire risk.
-
-=Roofs=.--In fig. 2,736 is shown one form of construction for the
-roof of an electrical station. The end view here presented shows
-the upper portion of the walls at B and D; these support the iron
-trusses C, and the roof proper MN. In many stations there is provided
-throughout the length of the building, a monitor or raised structure
-on the peak of the roof for ventilation and light. The end view of
-the monitor is shown at S in the figure; its sides should be fitted
-with windows adjustable from the floor.
-
-[Illustration: FIG. 2,736.--One form of roof construction.]
-
-=Floors.=--The floor of the station should be so designed that
-it will be capable of supporting a reasonable weight, but as the
-weights of the machines are borne entirely by their respective
-foundations the normal weight upon the floor will not be great; for
-short periods, however, it may be called upon to support one or two
-machines while they are being placed in position or interchanged,
-and due allowance must be made for such occurrences.
-
-Station floors for engine and dynamo rooms are, as a rule,
-constructed of wood. Where very high currents are generated, however,
-insulated floors of special construction mounted on glass are
-necessary as a protection from injurious shocks. Brick, concrete,
-cement, and other substances of a similar nature are objectionable
-as a floor material for engine and dynamo rooms on account of the
-grit from them, caused by constant wear, being liable to get into the
-bearings of the machines.
-
-Where there are no moving parts, however, as in the boiler room, the
-materials just mentioned possess no disadvantages and are preferable
-to wood on account of being fireproof.
-
-           =THEORETICAL DRAFT PRESSURE IN INCHES OF WATER IN=
-                    =A CHIMNEY 100 FEET HIGH=
-
-       (For other heights the draft varies directly as the height)
-
-   Temp. in       TEMP. OF EXTERNAL AIR. (BAROMETER 30 INCHES)
-  Chimney, °F.   0°  10°  20°  30°  40°  50°  60°  70°  80°  90° 100°
-      200°     .453 .419 .384 .353 .321 .292 .263 .234 .209 .182 .157
-      220      .488 .453 .419 .388 .355 .326 .298 .269 .244 .217 .192
-      240      .520 .488 .451 .421 .388 .359 .330 .301 .276 .250 .225
-      260      .555 .528 .484 .453 .420 .392 .363 .334 .309 .282 .257
-      280      .584 .549 .515 .482 .451 .422 .394 .365 .340 .313 .288
-      300      .611 .576 .541 .511 .478 .449 .420 .392 .367 .340 .315
-      320      .637 .603 .568 .538 .505 .476 .447 .419 .394 .367 .342
-      340      .662 .638 .593 .563 .530 .501 .472 .443 .419 .392 .367
-      360      .687 .653 .618 .588 .555 .526 .497 .468 .444 .417 .392
-      380      .710 .676 .641 .611 .578 .549 .520 .492 .467 .440 .415
-      400      .732 .697 .662 .632 .598 .570 .541 .513 .488 .461 .436
-      420      .753 .718 .684 .653 .620 .591 .563 .534 .509 .482 .457
-      440      .774 .739 .705 .674 .641 .612 .584 .555 .530 .503 .478
-      460      .793 .758 .724 .694 .660 .632 .603 .574 .549 .522 .497
-      480      .810 .776 .741 .710 .678 .649 .620 .591 .566 .540 .515
-      500      .829 .791 .760 .730 .697 .669 .639 .610 .586 .559 .534
-
-=Chimneys.=--These are generally constructed of brick and iron,
-sometimes of concrete. Iron chimneys cost less than brick chimneys,
-necessitate less substantial foundations, and are free from the
-liability of cracking. They must be painted to prevent corrosion, are
-less substantial, and lose considerably more heat by radiation than
-do brick chimneys.
-
-[Illustration: FIG. 2,737.--An example of direct connected unit with
-gas engine power. The view shows a Westinghouse 200 kva., 4,000 volt,
-three phase, 60 cycle alternator direct connected to a gas engine.]
-
-[Illustration: FIG. 2,738.--Curves showing comparative costs of
-chimney and mechanical draft. In certain of these, the cost of the
-existing chimney is known, and that of the complete mechanical draft
-plant is estimated, while in others, the cost of mechanical draft
-installation is determined from the contract price, and the expense
-of a chimney to produce equivalent results is calculated. Costs are
-shown for both single, forced and induced engine driven fans and
-for duplex engine driven plants, in which either fan may serve as a
-relay. An apparatus of the latter type is the most expensive, and
-finds its greatest use where economizers are employed.]
-
-Both brick and iron chimneys, require an inner wall or lining of
-brick, which forms the flue proper, and in order that this wall be
-not cracked by sudden cooling an air space is left between it and
-the outer wall. In a brick chimney the inner wall need not extend
-much beyond half the height of the chimney, but when iron is used it
-should reach to the top.
-
-=Ques. Upon what does the force of natural draught in a chimney
-depend?=
-
-Ans. It depends upon the difference between the weight of the column
-of hot gases inside the chimney and the weight of a like column of
-the cold external air.
-
-[Illustration: FIGS. 2,739 and 2,740.--Substituting mechanical
-draught in place of chimney. The relative proportions of a brick
-chimney, and of the smoke pipe required when mechanical draft is
-introduced are forcibly shown in the illustrations, which show the
-works of the B.F. Sturtevant Co., at Jamaica Plain, Mass. The removal
-of the boilers to a position too far distant from the existing
-chimney to permit of its longer fulfilling its office, led to the
-substitution of an induced draft fan and the subsequent removal of
-the chimney. The present stack or smoke pipe, barely visible in fig.
-2,740, extends only 31 feet above the ground, and no trouble is
-experienced from smoke.]
-
-=Ques. How is the intensity of the draught expressed?=
-
-Ans. In terms of the number of inches of a water column sustained by
-the pressure produced.
-
-=Ques. Are high chimneys necessary?=
-
-Ans. No.
-
-     _Chimneys above 150 feet in height are very costly, and their
-   increased cost is not justified by increased efficiency._
-
-[Illustrations: FIGS. 2,741 to 2,744.--Installation of forced draft
-system to old boiler plant. The figures illustrate the simplest
-method. The fan which is of steel plate with direct connected double
-cylinder engine, is placed immediately over the end of a brick duct
-into which the air is discharged. This duct is carried under ground
-across the front of the boilers, to the ash pits of each of which
-connection is made through branch ducts. Each branch duct opening
-is provided with special ash pit damper, operated by notched handle
-bar, as illustrated in the detail. This method of introduction
-serves to distribute the air within the ash pit, and to secure even
-flow through the fuel upon the grate above. Of course, the ash pit
-doors must remain closed in order to bring about this result. A
-chimney of sufficient height to merely discharge the gases above
-objectionable level is all that is absolutely necessary with this
-arrangement. Although the introduction of a fan in an old plant is
-usually evidence of the insufficiency of the existing chimney to meet
-the requirements, such a chimney, will, however, usually serve as a
-discharge pipe for the gases when the fan is employed. The fan thus
-becomes more than a mere auxiliary to the chimney; it practically
-supplants it so far as the method of draught production is concerned.]
-
-     The latest chimney practice is to build two or more small
-   chimneys instead of one large one. A notable example is the
-   Spreckels Sugar Refinery in Philadelphia, where three separate
-   chimneys are used for one boiler plant of 7,500 horse power. The
-   three chimneys are said to have cost several thousand dollars less
-   than an equivalent single chimney.
-
-     =Very tall chimneys= have been characterized by one writer as
-   "_monuments to the folly of their builders._"
-
-[Illustration: FIGS. 2,745 and 2,746.--Comparison of chimney draft
-and mechanical draft. The illustrations show a plant of 2,400 H.P. of
-modern water tube boilers, 12 in number, set in pairs and equipped
-with economizers. Fig. 2,745 indicates the location of a chimney, 9
-feet in internal diameter by 180 feet high, designed to furnish the
-necessary draft; fig. 2,746 represents the same plant with a complete
-duplex induced draught apparatus substituted for the chimney, and
-placed above the economizer connections. Each of the two fans is
-driven by a special engine, direct connected to the fan shaft, and
-each is capable of producing draft for the entire plant. A short
-steel plate stack unites the two fan outlets and discharges the gases
-just above the boiler house roof. All of the room necessary for the
-chimney is saved, and no valuable space is required for the fans.]
-
-=Ques. How is mechanical draft secured?=
-
-Ans. In two ways, known respectively as _induced draught_ and _forced
-draught_.
-
-=Ques. Describe the method of induced draft.=
-
-Ans. A fan is located in the smoke flue, and which in operation
-draws the gases through the furnace and discharges them into a
-_short_ chimney.
-
-=Ques. Describe the method of forced draft.=
-
-Ans. In this method, air is forced into the furnace underneath the
-grate bars by means of a fan or a steam jet blower.
-
-[Illustration: FIG. 2,747.--Forced draft plant with hollow bridge
-wall at the Crystal Water Co., Buffalo, N. Y. The air is delivered to
-the ash pit via the hollow bridge wall, being supplied under pressure
-by the blower seen at the side of the boiler setting. As shown, the
-blower is operated by a small reciprocating engine; however, compact
-blowing units with steam turbine drive can be had and which are
-designed to be placed in the boiler setting.]
-
-=Ques. What is the application of the two systems?=
-
-Ans. Induced draft is installed mostly in new plants, while forced
-draft is better adapted to old plants.
-
-=Steam Turbines=.--It is not the author's intention to discuss at
-length the steam end of the electric plant, because too much space
-would be required, and also because the subject belongs properly
-to the field of mechanical engineering rather than electrical
-engineering. However, because of the recent introduction of the steam
-turbine for the direct driving of large generators, and the fact
-that it is now almost universally used in large central stations, a
-detailed explanation of its principles and construction may not be
-out of place.
-
-[Illustration: FIG. 2,748.--Longitudinal section of elementary
-Parsons type steam turbine. The turbine consists essentially of a
-fixed casing, or cylinder, and a revolving spindle or drum. The ends
-of the spindle are extended in the form of a shaft, carried in two
-bearings A and B, and, excepting the small parts of the governing
-mechanism and the oil pump, these bearings are the only rubbing
-parts in the entire turbine. Steam enters from the steam pipe at C
-and passes through the main throttle or regulating valve D, which,
-as actually constructed, is a balanced valve. This valve is operated
-by the governor through suitable controlling mechanism. The steam
-enters the cylinder through the passage E and, turning to the left
-passes through alternate stationary and revolving rows of blades,
-finally emerging from them at F and flowing through the connection
-G to the condenser or to the atmosphere, depending upon whether the
-turbine is condensing or non-condensing. Each row of blades, both
-stationary and revolving, extends completely around the turbine and
-the steam flows through the full annulus between the spindle and
-the cylinder. In an ideal turbine the lengths of the blades and the
-diameter of the spindle which carries them would continuously and
-gradually increase from the steam inlet to the exhaust. Practically,
-however, the desired effect is produced by making the spindle in
-steps, there being generally three such steps or stages, H, J and K.
-The blades in each step are arranged in groups of increasing length.
-At the beginning of each of the larger steps, the blades are usually
-shorter than at the end of the preceding smaller step, the change
-being made in such a way that the correct relation of blade length
-to spindle diameter is secured. The steam, acting as previously
-described, produces a thrust tending to force the spindle toward
-the left, as seen in the cut. This thrust, however, is counteracted
-by the "balance pistons," L, M and N, which are of the necessary
-diameter to neutralize the thrust on the spindle steps, H, J and K,
-respectively. These elements are called "pistons" for convenience,
-although they do not come in contact with the cylinder, but both
-the pistons and the cylinder are provided with alternate rings
-which form a labyrinth packing to retard the leakage of steam. In
-order that each balance piston may have the proper pressure on both
-sides, equalizing passages O, P and Q are provided connecting the
-balance pistons with the corresponding stages of the blading. The end
-thrust being thus practically neutralized by means of the balance
-pistons, the spindle "floats" so that it can be easily moved in one
-direction or the other. In order to definitely fix the position of
-the spindle, a small adjustable collar bearing is provided at R,
-inside the housing of the main bearing B. This collar bearing is
-adjustable so as to locate and hold the spindle in such position so
-that there will be such a clearance between the rings of the balance
-piston and those of the cylinder, that the leakage of steam will be
-reduced to a minimum and, at the same time, prevent actual contact
-under varying conditions of temperature. Where the shaft passes out
-of the cylinder, at S and T, it is necessary to provide against
-in-leakage of air or out-leakage of steam by means of glands. These
-glands are made tight by water packing without metallic contact. The
-shaft of the turbine is extended at U and coupled to the shaft of
-the alternator by means of a flexible coupling. The high pressure
-turbines are so proportioned that, when using steam as previously
-described, they have enough capacity to take care of the ordinary
-fluctuations of load when controlled by the governor through the
-valve D, thus insuring maximum economy of steam consumption at
-approximately the rated load. To provide for overloads, the valve V
-is supplied to admit steam to an intermediate stage of the turbine.
-This valve shown diagrammatically in the illustration, is arranged
-to be operated by the governor and is, according to circumstances,
-located either as shown by the illustration, or at another stage of
-the turbine.]
-
-[Illustration: FIG. 2,749.--Arrangement of blading in Parsons type
-turbine, consisting of alternate moving and stationary blades. The
-path taken by the steam is indicated by the arrows.]
-
-A turbine is a machine in which a rotary motion is obtained by
-transference of the _momentum_ of a fluid or gas. In general the
-fluid is guided by fixed blades, attached to a casing, and, impinging
-on other blades mounted on a drum or shaft, causing the latter to
-revolve.
-
-Turbines are classed in various ways as: 1, _radial flow_, when the
-steam enters near the center and escapes toward the circumference;
-and 2, _parallel flow_, when the steam travels _axially_ or parallel
-to the length of the turning body.
-
-Turbines are commonly, yet erroneously classed as:
-
-  1. Impulse;
-  2. Reaction.
-
-=Ques. What is the distinction between these two types?=
-
-Ans. In the so called impulse type, _steam enters and leaves the
-passages between the vanes at the same pressure_. In the so called
-reaction type, _the pressure is less on the exit side of the vanes
-than on the entrance side_.
-
-     Fig. 2,750 is a sectional view of the Parsons-Westinghouse
-   parallel flow turbine. Steam from the boiler enters first a
-   receiver in which are the governor controlled admission valves.
-   These valves are actuated by a centrifugal governor.
-
-[Illustration: FIG. 2,750.--Sectional view of Parsons-Westinghouse
-turbine, showing rotor and governor.]
-
-     _Steam does not enter the turbine in a continuous blast, but
-   intermittently, or in puffs._ The speed regulation is therefore
-   accomplished by proportioning the duration of these puffs to the
-   load of the engine, this being effected by the governor, fig.
-   2,752.
-
-     The governor of the turbine has only to move a small pilot
-   valve, or slide, E, which admits steam under the piston F, and
-   lifts the throttle valve proper off its seat.
-
-     As soon as the pilot valve closes, the spring shifts the main
-   throttle valve. Thus, at light loads, the main throttle or
-   admission valve is continually opening and shutting at uniform
-   intervals, the length of time during which it remains open
-   depending upon the load.
-
-     As the load increases, the duration of the valve opening also
-   increases, until at full load the valve does not reach its seat at
-   all and the steam flows steadily through the turbine. The steam
-   thus admitted flows into the annular passage A, fig. 2,750, by the
-   opening S, and then past the blades, revolving the rotor.
-
-     When the load increases above the normal rated amount a
-   secondary pilot valve is moved by the same means, this in turn
-   admitting steam to a piston, similar to F, which lifts another
-   throttle valve. This admits steam into the annular space I, so
-   that it acts upon the larger diameter of the drum or rotor, giving
-   largely increased power for the time being.
-
-     The levers or arms of the governor are mounted upon knife edges
-   instead of pins, making it extremely sensitive. The tension spring
-   may be adjusted by hand while the turbine is running.
-
-[Illustration: FIG. 2,751.--Sectional view of a combination impulse
-and reaction single flow turbine. This is a modification of the
-single flow type, in which the smallest barrel of reaction blading is
-replaced by an impulse wheel. Steam is admitted to the nozzle block
-A, is expanded in the nozzles and discharged against a portion of the
-periphery of the impulse wheel. The intermediate and low pressure
-stages are identical with the corresponding stages in the single flow
-type. The substitution of the impulse element for the high pressure
-section of reaction blading has no influence one way or another on
-the efficiency. That is to say the efficiency of an impulse wheel is
-about the same at the least efficient section of reaction blading.
-This design is attractive, however, in that it shortens the machine
-materially, and gives a stiffer design of rotor. The entering steam
-is confined in the nozzle chamber until its pressure and temperature
-have been materially reduced by expanding through the nozzles.
-As the nozzle chamber is cast separately from the main cylinder,
-the temperature and pressure differences to which the cylinder is
-subjected are correspondingly lessened. However, probably on account
-of its small diameter at the high pressure section, the straight
-Parsons type has always shown itself to be adequate for all of the
-steam pressures and temperatures encountered in ordinary practice.]
-
-     The governor does not actually move the pilot valve, but shifts
-   the point L in fig. 2,752. A reciprocating motion is given to the
-   rod I by a small eccentric on the governor shaft; this is driven
-   by worm gearing shown near O in fig. 2,750, so that the eccentric
-   makes one revolution to about eight of the turbine. Thus, with a
-   turbine running 1,200 revolutions, the rod I would be moved up and
-   down 150 times per minute. As the points A and H are fixed, the
-   motion is conveyed to the small pilot valve E, thus giving 150
-   puffs a minute. The governor in shifting the point L brings the
-   edge of the pilot valve nearer the port and so cuts off the steam
-   earlier.
-
-     The annular diameter or space between the rotor and the stator
-   is gradually increased from inlet to exhaust, the blades being
-   made longer in each ring. When the mechanical limit is reached,
-   the diameter of the rotor is increased as at I and D so as to
-   keep the length of blade within bound.
-
-     Balance pistons as at B, C, F are attached to the rotor,
-   their office being to oppose end thrust upon those blades in
-   corresponding diameter of the rotor. Communication is established
-   through the passage V and pipe M between the eduction pipe and the
-   back of these pistons, thus increasing the efficiency of their
-   balancing and also taking care of any leakage past them.
-
-     A small thrust bearing T prevents end play of the rotor, and is
-   adjustable to maintain the proper clearance between the rings of
-   blades; this varies from ⅛ inch at the admission to 1 inch at the
-   exhaust. This bearing also takes up any extra unbalanced thrust. A
-   turbine should operate with a high vacuum, because without this it
-   does not compare favorably with an ordinary reciprocating engine
-   from the point of economy.
-
-[Illustration: FIG. 2,752.--Sectional view of governor of the
-Parsons-Westinghouse turbine.]
-
-     _Separate air pumps are provided to create the vacuum._
-
-     Where the ordinary type of vertical air pump is employed, a
-   booster or _vacuum increaser_ is added, as nothing below 26 inches
-   is advisable, 28 and 29 inches being always striven for. It is
-   also preferable to use a certain amount of _super-heat_ with steam
-   turbines.
-
-     To assist in producing the high vacuum, exhaust passages are
-   made large, the eduction passage E in fig. 2,750 being nearly
-   twenty-three times the area of the steam pipe.
-
-     Among other details, a noteworthy feature is a small oil pump K,
-   which circulates oil through bearings of the machinery, the oil
-   being drawn from the tank under the governor shaft and gravitating
-   there after use. No pressure of oil is employed. Stuffing rings
-   prevent leakage; these consist of alternate grooves and collars in
-   shaft and bearing, like the grooves in an indicator piston.
-
-=Ques. Why is a high vacuum desirable?=
-
-Ans. Because the turbine is capable of expanding the steam to a very
-low terminal pressure, and this is necessary for economy.
-
-=Ques. What may be said of the working pressures for turbines?=
-
-Ans. To meet the varied conditions of service, turbines are designed
-to operate with: 1, high pressure, 2, low pressure, or 3, mixed
-pressure.
-
-[Illustration: FIG. 2,753.--Sectional view of a double flow turbine.
-The maximum economical capacity of a single flow turbine is limited
-by the rotative speed. The economical velocity at which the steam may
-pass through the blades of the turbine depends on the velocity of
-the moving blades. The capacity of the turbine depends on the weight
-of the steam passed per unit of time, which in turn depends on the
-mean velocity and the height of the blades. For a given rotative
-speed, the mean diameter of blade ring practicable is limited by
-the allowable stresses due to centrifugal force, and there is a
-practical limit for the height of the blades. Now if the rotative
-speed be taken only half as great, the maximum diameter of the rotor
-may be doubled and, without increasing the height of the blades, the
-capacity of the turbine will be doubled. So with the single flow
-steam turbine as well as with the single crank reciprocating engine,
-there is a practical limiting economical capacity for any given
-speed. If this limit be reached with a single crank reciprocating
-engine, a unit of double the power may be produced at the same speed
-by coupling two single crank engines to one shaft. Similar results
-are secured making a double flow turbine which is in effect, as will
-be seen from the figure, two single flow turbines made up in a single
-rotor in a single casing with a common inlet and two exhausts. Steam
-enters the nozzle block, acts on the impulse element, and then the
-current divides, one-half of the steam going through the reaction
-blading at the left of the impulse wheel; the remainder passes over
-the top of the impulse wheel and through the impulse blading at the
-right.]
-
-     High pressure turbines operate at about the same initial
-   pressure as triple expansion engines.
-
-     Low pressure, as here applied, means the exhaust pressure of the
-   reciprocating engine from which the exhaust steam passes through
-   the turbine before entering the condenser.
-
-     Mixed pressure implies that the exhaust steam is supplemented,
-   for heavy loads, by the admission of live steam.
-
-=Ques. What determines the working pressure?=
-
-Ans. When all the power is furnished by the turbine, it is designed
-for high pressure; when operated in combination with a reciprocating
-engine, low pressure is used for constant load, and mixed pressure
-for variable load.
-
-[Illustration: FIG. 2,754.--Sectional view of a semi-double flow
-turbine. This is a modification in which the intermediate section
-of reaction blading is single flow, and the low pressure section
-only is double flow. This would be analogous to a four cylinder
-triple expansion engine, that is, one with one high pressure, one
-intermediate pressure and two low pressure cylinders--a design not at
-all uncommon in very large engines in which the required dimensions
-of a single low pressure cylinder would be prohibitive. Such turbines
-are useful for capacities greater than is desirable for a single
-flow turbine, and which are still below the maximum possibilities of
-a double flow turbine of the same speed. In such machines the best
-efficiency is secured by making the intermediate blading in a single
-section large enough to pass the entire quantity of steam. A "dummy"
-similar to those used on the single flow Parsons type, shown at the
-right of the impulse wheel, compels all of the steam to pass through
-the single intermediate section of the reaction blading, and balances
-the end thrust due to this section. When the steam issues from the
-intermediate section, the current is divided, one-half passing
-directly to the adjacent low pressure section, while the other half
-passes through the holes shown in the periphery of the hollow rotor
-and through the rotor itself, beyond the dummy ring, into the other
-low pressure section at the left hand end of the turbine.]
-
-     NOTE.--There are logical engineering reasons for the existence
-   of the several types of turbine, viz., single flow, double flow,
-   and semi-double flow. The double flow turbine is not inherently
-   superior to the single flow design, but is used under conditions
-   for which the single flow machine is unsuitable. Similarly, the
-   semi-double flow is recommended only for conditions which it can
-   meet more satisfactorily than either of the other types.
-
-     NOTE.--Low pressure turbines use exhaust steam from
-   non-condensing engines and are valuable as an adjunct to existing
-   plants for the purpose of increasing economy and capacity with a
-   minimum outlay for new equipment.
-
-     NOTE.--Bleeder turbines are for use in plants which are required
-   to furnish, not only power, but also considerable and varying
-   quantities of low pressure steam for heating purposes. In these
-   turbines a part of the steam after it has done work in the high
-   pressure stages may be diverted to the heating system, and the
-   remainder expanded through the low pressure blading and exhausted
-   into the condenser. In this way none of the energy of the heating
-   steam, due to the difference of pressure between the boiler and
-   the heating system is wasted. On the other hand if no steam is
-   required for heating purposes, the turbine operates just as
-   efficiently as though the bleeder feature were absent.
-
-[Illustration: FIG. 2,755.--Westinghouse valve gear with steam relay.
-In the smaller turbines, the governor acts directly on the steam
-admission valves, opening first the primary valve, and then, if
-necessary, the secondary valve, after the primary is fully open. In
-turbines of the single flow Parsons type, the governor actuates two
-small valves controlling ports leading to steam relay cylinders which
-operate the admission valves. The little valve controlling the relay
-cylinder for the secondary valve has more lap than the other and
-consequently does not come into action until the primary valve has
-attained its maximum effective opening. The figure shows the general
-design of this type of valve gear.]
-
-     _The De Laval steam turbine_ is termed by its builders a high
-   speed rotary steam engine. It has but a single wheel, fitted with
-   vanes or buckets of such curvature as has been found to be best
-   adapted for receiving the impulse of the steam jet. There are no
-   stationary or guide blades, the angular position of the nozzles
-   giving direction to the jet. The nozzles are placed at an angle
-   of 20 degrees to the plane of motion of the buckets. The best
-   energy in the steam is practically devoted to the production of
-   velocity in the expanding or divergent nozzle, and the velocity
-   thus attained by the issuing jet of steam is about 4,000 feet per
-   second. To attain the maximum efficiency, the buckets attached to
-   the periphery of the wheel against which this jet impinges should
-   have a speed of about 1,900 feet per second, but, owing to the
-   difficulty of producing a material for the wheel strong enough to
-   withstand the strains induced by such a high speed, it has been
-   found necessary to limit the peripheral speed to 1,200 or 1,300
-   feet per second.
-
-     It is well known that in a correctly designed nozzle the
-   adiabatic expansion of the steam from maximum to minimum pressure
-   will convert the entire static energy of the steam into kinetic
-   energy. Theoretically this is what occurs in the De Laval nozzle.
-   The expanding steam acquires great velocity, and the energy
-   of the jet of steam issuing from the nozzle is equal to the
-   amount of energy that would be developed if an equal volume of
-   steam were allowed to adiabatically expand behind the piston
-   of a reciprocating engine, a condition, however, which for
-   obvious reasons has never yet been attained in practice with the
-   reciprocating engine. But with the divergent nozzle the conditions
-   are different.
-
-     _The Curtis turbine_ is built by the General Electric Company at
-   their works in Schenectady, N. Y., and Lynn, Mass. They are of the
-   horizontal and vertical types. In the vertical type the revolving
-   parts are set upon a vertical shaft, the diameter of the shaft
-   corresponding to the size of the machine.
-
-     The shaft is supported by and runs upon a step bearing at the
-   bottom. This step bearing consists of two cylindrical cast iron
-   plates bearing upon each other and having a central recess between
-   them into which lubricating oil is forced under pressure by a
-   steam or electrically driven pump, the oil passing up from beneath.
-
-[Illustration: FIGS. 2,756 and 2,757.--Westinghouse valve gear with
-oil relay. Governors for the larger turbines, particularly those of
-the combination impulse and reaction double, or single double flow
-type, employ an oil relay mechanism, as shown in the figure, for
-operating the steam valves. In these turbines the lubricating oil
-circulating pump, maintains a higher pressure than is required for
-the lubricating system. The governor controls a small relay valve
-A which admits pressure oil to, or exhausts it from the operating
-cylinder. When oil is admitted to the operating cylinder raising the
-piston, the lever C lifts the primary valve E. The lever D moves
-simultaneously with C, but on account of the slotted connection
-with the stem of the secondary valve F, the latter does not begin
-to lift until the primary valve is raised to the point at which its
-effective opening ceases to be increased by further upward travel.
-In the Westinghouse designs, the operating valve, A is connected not
-only to the governor, but also to a vibrator, which gives it a slight
-but continuous reciprocating motion, while the governor controls its
-mean position. The effect of this is manifested in a slight pulsation
-throughout the entire relay system, which, so to speak, keeps it
-"alive" and ready to respond instantly, to the smallest change in
-the position of the governor. The oil relay can be made sufficiently
-powerful to operate valves of any size, and it is also in effect
-a safety device in that any failure of the lubricating oil supply
-will automatically and immediately shut off the steam and stop the
-turbine.]
-
-     A weighted accumulator is sometimes installed in connection with
-   the oil pipe as a convenient device for governing the step bearing
-   pumps, and also as a safety device in case the pumps should fail,
-   but it is seldom required for the latter purpose, as the step
-   bearing pumps have proven after a long service in a number of
-   cases, to be reliable. The vertical shaft is also held in place
-   and kept steady by three sleeve bearings one just above the step,
-   one between the turbine and generator, and the other near the top.
-
-[Illustration: FIG. 2,758.--Elevation of new turbine central station
-erected by the Boston Edison Co. The turbine room is 68 feet, 4
-inches wide and 650 feet long from outside to outside of the walls.
-The boiler room is 149 feet, 6 inches by 640 feet and equipped with
-twelve groups of boiler, one group consisting of eight 512 H.P.
-boilers for each turbine. The switching arrangements are located in
-a separate building as shown in the elevation. The total floor space
-covered by boiler room, turbine room and switchboard room is 2.64
-square feet per kw. The boilers are all on the ground floor. See fig.
-2,714 for plan.]
-
-     These guide bearings are lubricated by a standard gravity feed
-   system. It is apparent that the amount of friction in the machine
-   is very small, and as there is no end thrust caused by the action
-   of the steam, the relation between the revolving and stationary
-   blades may be maintained accurately. As a consequence, therefore,
-   the clearances are reduced to the minimum.
-
-     The Curtis turbine is divided into two or more stages, and each
-   stage has one, two or more sets of revolving blades bolted upon
-   the peripheries of wheels keyed to the shaft. There are also the
-   corresponding sets of stationary blades bolted to the inner walls
-   of the cylinder or casing.
-
-     The governing of speed is accomplished in the first set of
-   nozzles and the control of the admission valves here is effected
-   by means of a centrifugal governor attached to the top end of the
-   shaft. This governor, by a very slight movement, imparts motion
-   to levers, which in turn work the valve mechanism.
-
-     The admission of steam to the nozzles is controlled by piston
-   valves which are actuated by steam from small pilot valves which
-   are in turn under the control of the governor.
-
-[Illustration: FIG. 2,759.--Illustration of a weir. To make a weir,
-place a board across the stream at some point which will allow a
-pond to form above. The board should have a notch cut in it with
-both side edges and the bottom sharply beveled toward the intake,
-as shown in the above cut. The bottom of the notch, which is called
-the "crest" of the weir, should be perfectly level and the sides
-vertical. In the pond back of the weir, at a distance not less than
-the length of the notch, drive a stake near the bank, with its top
-precisely level with the crest. By means of a rule, or a graduated
-stake as shown, measure the depth of water over the top of stake,
-making allowance for capillary attraction of the water against the
-sides of the weir. For extreme accuracy this depth may be measured
-to thousandths of a foot by means of a "hook gauge," familiar to all
-engineers. Having ascertained the depth of water over the stake,
-refer to the accompanying table, from which may be calculated the
-amount of water flowing over the weir. There are certain proportions
-which must be observed in the dimensions of this notch. Its length,
-or width, should be between four and eight times the depth of water
-flowing over the crest of the weir. The pond back of the weir should
-be at least fifty per cent. wider than the notch and of sufficient
-width and depth that the velocity of flow or approach be not over one
-foot per second. In order to obtain these results it is advisable to
-experiment to some extent.]
-
-     Speed regulation is effected by varying the number of nozzles
-   in flow, that is, for light loads fewer nozzles are open and a
-   smaller volume of steam is admitted to the turbine wheel, but the
-   steam that is admitted impinges against the moving blades with the
-   same velocity always, no matter whether the volume be large or
-   small. With a full load and all the nozzle sections in flow, the
-   steam passes to the wheel in a broad belt and steady flow.
-
-                           WEIR TABLE
-    giving cubic feet of water per minute that will flow over a weir
-             one inch wide and from ⅛ to 20⅞ inches deep.
-
-  --------+------+------+------+------+------+------+------+------
-   Depth  |      |      |      |      |      |      |      |
-   inches |      |   ⅛  |   ¼  |   ⅜  |   ½  |   ⅝  |  ¾   |  ⅞
-  --------+------+------+------+------+------+------+------+------
-     =0=  |  .00 |  .01 |  .05 |  .09 |  .14 |  .19 |  .26 |  .32
-     =1=  |  .40 |  .47 |  .55 |  .64 |  .73 |  .82 |  .92 | 1.02
-     =2=  | 1.13 | 1.23 | 1.35 | 1.36 | 1.58 | 1.70 | 1.82 | 1.95
-     =3=  | 2.07 | 2.21 | 2.34 | 2.48 | 2.61 | 2.76 | 2.90 | 3.05
-     =4=  | 3.20 | 3.35 | 3.50 | 3.66 | 3.81 | 3.97 | 4.14 | 4.30
-     =5=  | 4.47 | 4.64 | 4.81 | 4.98 | 5.15 | 5.33 | 5.51 | 5.69
-     =6=  | 5.87 | 6.06 | 6.25 | 6.44 | 6.62 | 6.82 | 7.01 | 7.21
-     =7=  | 7.40 | 7.60 | 7.80 | 8.01 | 8.21 | 8.42 | 8.63 | 8.83
-     =8=  | 9.05 | 9.26 | 9.47 | 9.69 | 9.91 |10.13 |10.35 |10.57
-     =9=  |10.80 |11.02 |11.25 |11.48 |11.71 |11.94 |12.17 |12.41
-    =10=  |12.64 |12.88 |13.12 |13.36 |13.60 |13.85 |14.09 |14.34
-    =11=  |14.59 |14.84 |15.09 |15.34 |15.59 |15.85 |16.11 |16.36
-    =12=  |16.62 |16.88 |17.15 |17.41 |17.67 |17.94 |18.21 |18.47
-    =13=  |18.74 |19.01 |19.29 |19.56 |19.84 |20.11 |20.39 |20.67
-    =14=  |20.95 |21.23 |21.51 |21.80 |22.08 |22.37 |22.65 |22.94
-    =15=  |23.23 |23.52 |23.82 |24.11 |24.40 |24.70 |25.00 |25.30
-    =16=  |25.60 |25.90 |26.20 |26.50 |26.80 |27.11 |27.42 |27.72
-    =17=  |28.03 |28.34 |28.65 |28.97 |29.28 |29.59 |29.91 |30.22
-    =18=  |30.54 |30.86 |31.18 |31.50 |31.82 |32.15 |32.47 |32.80
-    =19=  |33.12 |33.45 |33.78 |34.11 |34.44 |34.77 |35.10 |35.44
-    =20=  |35.77 |36.11 |36.45 |36.78 |37.12 |37.46 |37.80 |38.15
-  --------+------+------+------+------+------+------+------+------
-
-            NOTE.--The weir table on this page contains
-          figures 1, 2, 3, etc., in the first vertical
-          column which indicates the inches depth of water
-          running over weir board notches. Frequently the
-          depths measured represent also fractional inches,
-          between 1 and 2, 2 and 3, etc. The horizontal
-          line of fraction at the top represents these
-          fractional parts, and can be applied between any
-          of the numbers of inches depth, from 1 to 25. The
-          body of the table shows the cubic feet, and the
-          fractional parts of a cubic foot, which will pass
-          each minute for each inch in depth, and for each
-          fractional part of an inch by eighths for all
-          depths from 1 to 25 inches. Each of these results
-          is for only one inch width of weir. To estimate
-          for any width of weir the result obtained for one
-          inch width must be multiplied by the number of
-          inches constituting the whole horizontal length
-          of weir.
-
-[Illustration: FIGS. 2,760 and 2,761.--Samson vertical runner and
-shaft, and complete Samson vertical turbine. The runner is composed
-of two separate and distinct types of wheel, having thereby also
-two diameters. Each wheel or set of buckets receives its separate
-quantity of water from one and the same set of guides, but each set
-acts only once and singly upon the water used, and the water does not
-act twice upon the combined wheel, as some suppose. In construction=,
-the lower or main set of buckets is made of flanged plate steel, and
-cast solidly into a heavy ring surrounding the outer and lower edges,
-and into a heavy diaphragm, separating the two sets of buckets.]
-
-[Illustration: FIG. 2,762.--Water discharging from a needle nozzle
-due to a pressure of 169 lbs. per sq. in.]
-
-=Hydro-Electric Plants.=--The economy with which electricity can be
-transmitted long distances by high tension alternating currents, has
-led to the development of a large number of water powers in more or
-less remote regions.
-
-[Illustration: FIG. 2,763.--Photograph of an operating tangential
-water wheel equipped with Pelton buckets.]
-
-     This economy is possible by the facility with which alternating
-   current can be transformed up and down. Thus at the hydro-electro
-   plant, the current generated by the water wheel driven alternator
-   is transformed to very high pressure and transmitted with economy
-   a long distance to the distributing point where it is transformed
-   down to the proper pressure for distribution.
-
-     A water wheel or turbine is a machine in which a rotary motion
-   is obtained by transference of the momentum of water; broadly
-   speaking, the fluid is guided by fixed blades, attached with a
-   casing, and impinging on other blades mounted on a drum or shaft,
-   causing the latter to revolve.
-
-     There are two general classes of turbine:
-        1. Impulse turbines;
-        2. Reaction turbines.
-
-
-[Illustration: FIG. 2,764.--Sectional elevation of one of the 5,000
-horse power vertical Pelton-Francis turbines directly connected to
-generator, as installed for the Schenectady Power Co.]
-
-=Ques. What is an impulse turbine?=
-
-Ans. One in which the fluid is directed by means of a series of
-nozzles against vanes which it drives.
-
-=Ques. What is a reaction turbine?=
-
-Ans. One in which the pressure or head of the water is employed
-rather than its velocity. The current is deflected upon the wheel by
-the action of suitably disposed guide blades, the passages being full
-of water. Rotary motion is obtained by the change in the direction
-and momentum of the fluid.
-
-[Illustration: Figs. 2,765 to 2,768.--Cross sections of Lowel dam
-power house, and wheel pits containing sixteen Samson turbines: The
-section C-D gives an end view of the generator room showing the
-locations of the generators below the head level water. They are
-secure against flood water, or leakage, by well constructed stuffing
-boxes in the iron bulkheads, through which the turbine wheel shafts
-pass and connect to the generators. Section E-F gives an end view of
-one of these wheel rooms or penstocks, and shows the extension of the
-draft tube from wheel case into tail water. The section A-B shows the
-sub-structure of gravel and macadam under the controlling gates, this
-forming also a portion or extension of the dam proper. These gates
-turn on an axis made of two 15 inch I beams securely riveted together
-with plates and angle irons to which the wooden frame is attached.
-The radius of the gates is 14 feet. They are designed to allow the
-water to pass underneath the gate, thus controlling any height of
-head water. They are intended to take care of an excess of water at
-unusual stages of the river. The whole affair has been well designed
-and executed. This plant furnishes a good example of a secure, and
-level foundation, since the wheel houses and generator room are
-immediately on the rock. It is necessary in all tandem plants to
-provide a very secure, substantial super-structure so that the long
-line of turbines and shaft will always remain straight and in proper
-alignment with the generator and the turbine cases. Users cannot be
-reminded of this too often.]
-
-=Ques. Name three classes of reaction turbines.=
-
-Ans. Parallel flow, inward flow, and outward flow.
-
-     Parallel flow turbines have an efficiency of about 70% and are
-   suited for low falls not over 30 feet. Inward and outward flow
-   turbines have an efficiency of about 85%. Impulse turbines are
-   suitable for high heads.
-
-[Illustration: FIGS. 2,769 and 2,770.--Exterior and interior of
-hydro-electric plant at Harrisburg, Va. It is located on the south
-fork of the Shenandoah River, twelve and one-half miles distant. A
-dam 720 feet long and 15 feet high was built on a limestone ledge
-running across the river; which with a fall of 5 feet from the dam to
-the power house, a quarter of a mile distant, secured an effective
-head pressure of 20 feet. The power house, comprising the generator
-room and the wheel room, also the machinery room, are here shown. The
-wheel room, which is 20 × 40 feet, extends across the head race, and
-rests upon solid concrete walls, forming the sides and ends of the
-wheel pits. The end wall is 6 feet thick at the bottom, and 4½ feet
-at the top. It has three arched openings, each 8 feet wide and 9 feet
-high, through which the water escapes after leaving the turbines.
-The intake is protected by a wrought iron rack 40 feet long. The
-power is obtained by three 50 inch vertical shaft Samson turbines,
-with a 20 inch Samson for an exciter. The three large turbines
-have a rating of 1,350 horse power; and are connected to the main
-horizontal line shaft by bevel mortise gears 7 feet diameter and 15
-inches face. The couplings on the main shaft have 48 inch friction
-clutch hubs, permitting either or each turbine being operated, or
-shut down independently of the others. The main shaft is 85 feet long
-and 6 inches diameter; making 280 revolutions. This shaft carries
-two pulleys 70 inches diameter and 38 inches face for driving the
-generators. The accompanying illustration shows the harness work,
-gears, pulleys, etc., furnished with the turbines. The 20 inch
-horizontal shaft Samson turbine of 72 horse power is direct connected
-to an exciter generator of 20 kw., running 700 rev. per min. The
-two large generators are driven 450 revolutions per minute by belts
-producing a three phase current of 60 cycles of 11,500 volts for the
-twelve and one-half miles transmission. The line consists of three
-strands of No. 4 bare copper wire. This current is used for lighting
-and power purposes, and the plant is of the latest improved design
-and construction.]
-
-=Isolated Plants.=--When electric power transmission from central
-stations first came into commercial use, the distance from the
-station at which current could be obtained at a reasonable cost was
-exceedingly limited.
-
-[Illustration: FIG. 2,769a.--Triumph direct current generator set with
-upright slide valve engine.]
-
-[Illustration: FIG. 2,770a.--Murray alternating current direct
-connected unit with high speed Corliss engine and belt driven
-exciter, 50, 75 and 100 kva. alternator and 150 R.P.M. engine.]
-
-[Illustration: FIG. 2,771.--Direct connected direct current unit with
-Ridgway high speed four valve engine.]
-
-[Illustration: FIG. 2,772.--Buckeye mobile, or self contained unit
-consisting of compound condensing engine, boiler, superheater,
-reheater, feed and air pumps; it produces one horse power on 1½ lbs.
-of coal, built in sizes from 75 to 600 horse power.]
-
-[Illustration: FIG. 2,773.--Westinghouse three cylinder gas engine,
-direct connected to dynamo, showing application of gas engine drive
-for small direct connected units.]
-
-     Consequently, persons desiring electrical power were in the
-   majority of cases forced to install their own apparatus for
-   producing it, this being the origin of isolated plants.
-
-     From the nature of the case it is evident that an isolated
-   plant is as a rule smaller and more simple in construction than
-   a central station, and in consequence much more readily operated
-   and managed. It is generally owned by a private individual or a
-   corporation and operated in conjunction with other affairs of a
-   similar character. A basement or other portion of a building is
-   usually set aside in which the necessary apparatus is installed.
-
-[Illustration: FIG. 2,774.--General Electric 25 kw., gasoline
-electric generating set for lighting and power. The engine has
-four cylinders 7¼ × 7½, and runs at a speed of 560 revolutions per
-minute. The total candle power capacity in Mazda lamps is 20,000. The
-ignition is by low tension magneto, coil and battery. Carburetter is
-of the constant level type to which gasoline is delivered by a pump
-driven by the engine. Forced lubrication; five crank shaft bearings
-babbitted; valves in side; overall dimensions 96 × 34 × 60 high;
-weight 5,000.]
-
-     Although electricity is now transmitted economically to great
-   distances from central stations, there is still a field for the
-   isolated plant.
-
-     The average type of isolated plant has enlarged from a small
-   dynamo driven by a little slide valve engine located in an out
-   of the way corner to direct connected generators and engines of
-   hundreds and even thousands of horse power assembled in a large
-   room specially adapted to the purpose.
-
-     In the more modern of these, the electrical outputs are each
-   frequently equal to that of a town central station of respectable
-   size, and the auxiliary equipments are similar in every
-   particular. As a matter of fact, in certain modern isolated plants
-   the only feature that distinguishes them from central stations
-   is that in the former case the owner of the plant represents the
-   sole consumer and conducts other business in connection with it,
-   whereas in the latter case there are a large number of consumers
-   uninterested financially in the enterprise, which is itself
-   generally owned and operated by a company conducting no other
-   business.
-
-[Illustration: FIG. 2,775.--Plan of sub-station with air blast
-transformers and motor operated oil switches and underground 11,000
-or 13,200 volt high tension lines.]
-
-=Sub-Stations.=--According to the usual meaning of the term, a
-sub-station is a building provided with apparatus for changing high
-pressure alternating current received from the central station into
-direct current of the requisite pressure, which in the case of
-railways is 550 to 600 volts.
-
-Where traffic is heavy and the railway system of considerable
-distance, sub-stations are provided at intervals along the line,
-each receiving high pressure current from one large central station
-and converting it into moderate pressure direct current for their
-districts.
-
-=Ques. Upon what does the arrangement of the sub-station depend?=
-
-Ans. Upon the character of the work and the type of apparatus
-employed for converting the high pressure alternating current into
-direct current.
-
-[Illustration: FIG. 2,776.--Plan of small sub-station with single
-phase oil insulated self-cooling transformers and hand operated oil
-switches 11,000 or 13,200 volts, overhead high tension lines.]
-
-     In general it should be substantial, convenient to install or
-   replace the heavy machines, and the layout arranged so that the
-   apparatus can be readily operated by those in attendance.
-
-     An overhead traveling crane is the most convenient method of
-   handling the heavy machinery, and is frequently used in large
-   sub-stations.
-
-     Fig. 2,776 shows a sectional view, and fig. 2,777, a plan for
-   a small sub-station containing two rotary converters and two
-   banks of three single phase static transformers operating on a
-   three phase system at 11,000 or 13,200 volts, together with the
-   auxiliary apparatus.
-
-[Illustration: FIG. 2,777.--Elevation of small sub-station, as shown
-in plan in Fig. 2,776.]
-
-=Ques. For three phase installations, what are the merits of
-separate and combined transformers?=
-
-Ans. With separate transformer for each phase, repairs are more
-readily made in case of accident or burnouts in the coils. The three
-phase units have the advantage of low first cost.
-
-     Sub-station transformers produce considerable heat, due to the
-   hysteresis and eddy currents, and it is necessary to get rid of it.
-
-     Small transformers radiate the heat from the shell and the
-   medium sizes have corrugated shells which increase the surface and
-   provide more rapid radiation.
-
-     Large transformers are cooled by an air blast supplied by motor
-   driven blowers or by water pumped through a coil of pipe which is
-   immersed in the insulating oil of the transformer. The large size
-   oil insulated, water cooled transformers are used on circuits of
-   33,000 volts or more. In water turbine plants, the water may be
-   piped to the transformer under pressure and the pump omitted which
-   cuts down the cost of operating. Air blast transformers usually
-   have a damper or shutter for air control.
-
-[Illustration: FIG. 2,778.--Marine portable transformer station on
-Los Angeles Aqueduct. The view shows three 20 kva. Westinghouse out
-door transformers installed on a float, 33,000 volts high pressure;
-440 volts low pressure; 50 cycles.]
-
-=Ques. Explain the use of reactance coils in sub-stations.=
-
-Ans. In order that the direct current voltage of the ordinary rotary
-may be regulated by a field rheostat, which calls for a corresponding
-change in the alternating current voltage, a reactance coil is
-provided between the low tension winding and the converter.
-
-     Without such a reactance the maintenance of the same voltage at
-   full load as at no load involves excessive leading and lagging
-   currents and consequently excessive heating in the armature
-   inductors, unless the resistance drop from the source of constant
-   pressure is small, or the natural reactance of the circuit high.
-
-=Ques. What is the effect of weakening the converter field?=
-
-Ans. A lagging current is set up which causes a drop in the reactance
-coil.
-
-[Illustration: FIG. 2,779.--Sectional elevation of portable outdoor
-transformer type sub-station. The high voltage switching and
-protective apparatus is mounted, out of the way, on the roof of the
-car, but is operated from the switchboard with a standard remote
-control handle. The transformer is carried directly over the truck at
-the uncovered end of the car and the low-tension leads from it run in
-conduit beneath the floor and up into the cab, (which contains the
-converter and switchboard) to the converter. The positive lead runs
-through a conduit and ends in a terminal on the roof. The energy thus
-makes a complete circuit of the car leaving at a point close to that
-at which it entered. The low pressure alternating current as well as
-the direct current positive leads are carried below the car floor
-in iron conduit supported from the channel frame. The field wires
-are carried through this conduit to the rheostat. Wiring for the
-lights is arranged to supply two, 5 light clusters. One is fed with
-the 600 volt direct current and the other with 420 volt alternating
-current. All lighting conductors are carried in metal moulding
-carried between the flanges of the channel iron ribs. High wiring
-is carried entirely on the roof of the car where it is entirely out
-of the way and where the operator cannot come in contact with it.
-The switchboard should be of the utmost simplicity. Usually the
-negative and equalizer switches, and the field break-up switch are
-mounted on the frame of the converter. The double throw switch for
-starting and running the converter can be mounted under the floor
-of the car and operated by handle at the switchboard. The rheostat
-can be mounted back of the switchboard on brackets bolted to the car
-super-structure. The switchboard need only carry the positive knife
-switch and circuit breaker, and the alternating current ammeter,
-voltmeter and power factor meter. Sometimes a watthour meter is
-added. The positive lead is brought out through a conduit on the
-roof of the car and is arranged for bolting to the positive feeder.
-The negative and equalizer terminals are located at the cab end of
-the car and are arranged so that connection can be easily made from
-them to the ground and, if necessary, to an equalizer circuit. There
-is usually a sliding door at each end of the cab and two windows on
-each side. Above the doors, transoms, extending the width of the cab,
-are arranged to drop so that a current of air will circulate through
-the cab under the roof, carrying out the heated air. There are also
-several ventilating holes beneath the converter in the floor of the
-car. These provisions insure a constant circulation of air through
-the car which carries away all heated air.]
-
-=Ques. State the effect of strengthening converter field.=
-
-Ans. A leading current is set up which gives a rise of voltage in the
-reactance coil.
-
-     Hence when a heavy current passes through the series coil of a
-   compound wound converter and tends to produce a leading current,
-   the reactance coil will balance it, and improve the power factor
-   of the whole line.
-
-[Illustration: FIG. 2,780.--Westinghouse 300 kw. converter in
-portable sub-station.]
-
-=Portable Sub-Stations.=--A portable sub-station constitutes a spare
-equipment for practically any number of permanent sub-stations and
-renders unnecessary the installation of spare equipment in each.
-
-     It can be used to increase the capacity of a permanent
-   sub-station when the load is unusually heavy, or to provide
-   service while a permanent sub-station is being overhauled or
-   rebuilt.
-
-     The transformer can be used for emergency lighting, the primary
-   being connected to a high pressure line and the secondary to the
-   load, if special provision be made at the time the transformer is
-   built to adapt it for these applications.
-
-[Illustration: FIG. 2,781.--Switchboard end of Westinghouse portable
-sub-station.]
-
-When an electric railway has a portable sub-station, direct current
-can be provided at any point on the system where there is track at
-the high pressure line. The direct current can be made available
-very quickly as its production involves only the transferring of the
-sub-station, and its connection to the high pressure line.
-
-     Portable sub-stations range in capacity from 200 to 500 kw., and
-   for all alternating current voltages up to 66,000, and frequencies
-   of 25 and 60 cycles.
-
-     Although portable sub-stations usually must be of more or
-   less special design to adapt them to the conditions under which
-   they must operate, there are certain general features that are
-   common to all. All members are readily accessible and there are
-   no unnecessary parts. The weight and dimensions are a minimum
-   insuring ease of transportation. Live parts are so protected that
-   the danger of accidental contact with them is minimized.
-
-[Illustration: FIGS. 2,782 and 2,783.--Views of levelling device for
-Westinghouse converter.]
-
-=Ques. What are the advantages of using outdoor transformers on
-portable sub-stations?=
-
-Ans. All high pressure wiring is kept out of the car. The transformer
-is more effectively cooled and the heat dissipated by the transformer
-does not warm the interior of the cab. The transformer is much more
-accessible. The car can be run under a crane and the transformer
-coils pulled out with a hoist.
-
-     Taps for different high and low pressure voltages can be readily
-   provided at the time the transformer is being built.
-
-
-
-
-CHAPTER LXVII
-
-MANAGEMENT
-
-
-The term "management," broadly speaking, includes not only the
-actual skilled attention necessary for the proper operation of the
-machines, after the plant is built, but also other duties which must
-be performed from its inception to completion, and which may be
-classified as
-
-  1. Selection;
-  2. Location;
-  3. Erection;
-  4. Testing;
-  5. Running;
-  6. Care;
-  7. Repair.
-
-That is to say, someone must select the machinery, determine where
-each machine is to be located, install them, and then attend to the
-running of the machines and make any necessary repairs due to the
-ordinary mishaps likely to occur in operation.
-
-These various duties are usually entrusted to more than one
-individual; thus, the selection and location of the machinery is done
-by the designer of the plant, and requires for its proper execution
-the services of an electrical engineer, or one possessing more than
-simply a practical knowledge of power plants.
-
-The erection of the machines is best accomplished by those making a
-specialty of this line of work, who by the nature of the undertaking
-acquire proficiency in methods of precision and an appreciation of
-the value of accuracy which is so essential in the work of aligning
-the machines, and which if poorly done will prove a constant source
-of annoyance afterward.
-
-The attention required for the operation of the machines, embracing
-the running care and repair, is left to the "man in charge," who
-in most cases of small and medium size plants is the chief steam
-engineer. He must therefore, not only understand the steam apparatus,
-but possess sufficient knowledge of electrical machinery to operate
-and maintain it in proper working order.
-
-The present chapter deals chiefly with alternating current machinery,
-the management of direct current machines having been fully explained
-in Guide No. 3, however, some of the matter here presented is common
-to both classes of apparatus.
-
-       *       *       *       *       *
-
-=Selection.=--In order to intelligently select a machine so that it
-will properly harmonize with the conditions under which it is to
-operate, there are several things to be considered.
-
-  1. Type;
-  2. Capacity;
-  3. Efficiency;
-  4. Construction.
-
-The general type of machine to be used is, of course, dependent on
-the system employed, that is, whether it be direct or alternating,
-single or polyphase.
-
-     Thus, the voltage in most cases is fixed except on transformer
-   systems where a choice of voltage may be had by selecting a
-   transformer to suit.
-
-In alternating current constant pressure transmission circuits, an
-average voltage of 2,200 volts with step down transformer ratios of
-1/10 and 1/20 is in general use, and is recommended.
-
-     For long distance, the following average voltages are
-   recommended 6,000; 11,000; 22,000; 33,000; 44,000; 66,000; 88,000;
-   and higher, depending on the length of the line and degree of
-   economy desired.
-
-In alternating circuits the standard frequencies are 25, and 60
-cycles. These frequencies are already in extensive use and it is
-recommended to adhere to them as closely as possible.
-
-[Illustration: FIG. 2,784.--Diagram of connections for testing to
-obtain the saturation curve of an alternator. The saturation curve
-shows the relation between the volts generated in the armature and
-the amperes of field current (or ampere turns of the field) for a
-constant armature current. The armature current may be zero, in which
-case the curve is called _no load saturation curve_, or sometimes the
-_open circuit characteristic curve_. A saturation curve may be taken
-with full load current in the armature; but this is rarely done,
-except in alternators of comparatively small output. If a full load
-saturation curve be desired, it can be approximately calculated from
-the no load saturation curve. The figure shows the connections. If
-the voltage generated is greater than the capacity of the voltmeter,
-a multiplying coil or a step down pressure transformer may be used,
-as shown. A series of observations of the voltage between the
-terminals of one of the phases, is made for different values of the
-field current. Eight or nine points along the curve are usually
-sufficient, the series extending from zero to about fifty per cent.
-above normal rated voltage. The points should be taken more closely
-together in the vicinity of normal voltage than at other portions of
-the curve. Care must be taken that the alternator is run at its rated
-speed, and this speed must be kept constant. Deviations from constant
-speed may be most easily detected by the use of a tachometer. If the
-machine be two phase or three phase, the voltmeter may be connected
-to any one phase throughout a complete series of observations. The
-voltage of all the phases should be observed for normal full load
-excitation by connecting the voltmeter to each phase successively,
-keeping the field current constant at normal voltage. This is done in
-order to see how closely the voltage of the different phases agree.]
-
-     In fixing the capacity of a machine, _careful consideration
-   should be given to the conditions of operation both_ =present=
-   _and_ =future= in order that the resultant efficiency may be
-   maximum.
-
-     Most machines show the best efficiency at or near full load.
-   If the load be always constant, as for instance, a pump forcing
-   water to a given head, it would be a simple matter to specify the
-   proper size of machine, but in nearly all cases, and especially
-   in electrical plants, the load varies widely, not only the daily
-   and hourly fluctuations, but the varying demands depending on
-   the season of the year and growth of the plant's business. All
-   of these conditions tend to complicate the matter, so that
-   intelligent selection of capacity of a machine requires not only
-   calculation but mature judgment, which is only obtained by long
-   experience.
-
-[Illustration: FIG. 2,785.--Saturation curve taken from a 2,000 kw.,
-three phase alternator of the revolving field type, having 16 poles,
-and generating 2,000 volts, and 576 amperes per phase when run at 300
-R.P.M.]
-
-In selecting a machine, or in fact any item connected with the plant
-_its construction should be carefully considered_.
-
-     Standard construction should be insisted upon so that in the
-   event of damage a new part can be obtained with the least possible
-   delay.
-
-     The parts of most machines are _interchangeable_, that is to
-   say, with the refined methods of machinery a duplicate part
-   (usually carried in stock) may be obtained at once to replace a
-   defective or broken part, and made with such precision that little
-   or no fitting will be required.
-
-The importance of standard construction cannot be better illustrated
-than in the matter of steam piping, that is, the kind of fittings
-selected for a given installation.
-
-With the exception of the exhaust line from engine to condenser,
-where other than standard construction may sometimes be used to
-reduce the frictional resistance to the steam, the author would
-adhere to standard construction except in very exceptional cases.
-Those who have had practical experience in pipe fitting will
-appreciate the wisdom of this.
-
-For installations in places remote from large supply houses, the more
-usual forms of standard fittings should be employed, such as ordinary
-T's, 45° and 90° elbows, etc.
-
-In such locations, where designers specify the less usual forms of
-standard fittings such as union fittings, offset reducers, etc.,
-or special fittings made to sketch, it simply means, in the first
-instance that they usually cannot be obtained of the local dealer,
-making it necessary to order from some large supply house and
-resulting in vexatious delays.
-
-As a rule, those who specify special fittings have found that their
-making requires an unreasonable length of time, and the cost to be
-several times that of the equivalent in standard fittings.
-
-An examination of a few installations will usually show numerous
-special and odd shape fittings, which are entirely unnecessary.
-
-Moreover, a standard design, in general, is better than a special
-design, because the former has been tried out, and any imperfection
-or weakness remedied, and where thousands of castings of a kind are
-turned out, a better article is usually the result as compared with a
-special casting.
-
-In the matter of construction, in addition to the items just
-mentioned, it should be considered with respect to
-
-  1. Quality;
-  2. Range;
-  3. Accessibility;
-  4. Proportion;
-  5. Lubrication;
-  6. Adjustment.
-
-It is poor policy, excepting in very rare instances, to buy a "cheap"
-article, as, especially in these days of commercial greed, the best
-is none too good.
-
-[Illustration: FIGS. 2,786 and 2,787.--Wheel and roller pipe cutters
-illustrating =range=. The illustrations show the comparative
-movements necessary with the two types of cutter to perform their
-function. The wheel cutter requiring only a small arc of movement
-will cut a pipe in an inaccessible place as shown, which with a
-roller cutter would be impossible. Accordingly, the wheel cutter is
-said to have a greater _range_ than the roller cutter.]
-
-Perhaps next in importance to quality, at least in most cases,
-is _range_. This may be defined as _scope of operation_,
-_effectiveness_, or _adaptability_. The importance of range is
-perhaps most pronounced in the selection of tools, especially for
-plants remote from repair shops.
-
-     For instance, in selecting a pipe cutter, there are two general
-   classes: wheel cutters, and roller cutters. A wheel cutter has
-   three wheels and a roller cutter one wheel and two rollers, the
-   object of the rollers being to keep the wheel perpendicular to
-   the pipe in starting the cut and to reduce burning. It must be
-   evident that in operation, a roller cutter requires sufficient
-   room around the pipe to permit making a complete revolution of
-   the cutter, whereas, with a wheel cutter, the work may be done
-   by moving the cutter back and forth through a small arc, as
-   illustrated in figs. 2,786 and 2,787. Thus a wheel cutter has a
-   _greater range_ than a roll cutter.
-
-     Range relates not only to ability to operate in inaccessible
-   places but to the various operations that may be performed by one
-   tool.
-
-       PROPERTIES OF STANDARD WROUGHT IRON PIPE
-
-  --------------------------+------+-----------------+
-                            |      |                 |
-                            |      |                 |
-                            |      |                 |
-                            |      |                 |
-           Diameter         |Thick-|  Circumference. |
-                            | ness.|                 |
-  --------+--------+--------+      +--------+--------+
-   Nominal| Actual | Actual |      |External|Internal|
-  internal|external|internal|      |        |        |
-  --------+--------+--------+------+--------+--------+
-   Inches | Inches | Inches |Inches| Inches | Inches |
-  --------+--------+--------+------+--------+--------+
-       ⅛  |   .405 |   .27  | .068 |  1.272 |   .848 |
-       ¼  |   .54  |   .364 | .088 |  1.696 |  1.144 |
-       ⅜  |   .675 |   .494 | .91  |  2.121 |  1.552 |
-       ½  |   .84  |   .623 | .109 |  2.639 |  1.957 |
-       ¾  |  1.05  |   .824 | .113 |  3.299 |  2.589 |
-      1   |  1.315 |  1.048 | .134 |  4.131 |  3.292 |
-      1¼  |  1.66  |  1.38  | .14  |  5.215 |  4.335 |
-      1½  |  1.9   |  1.611 | .145 |  5.969 |  5.061 |
-      2   |  2.375 |  2.067 | .154 |  7.461 |  6.494 |
-      2½  |  2.875 |  2.468 | .204 |  9.032 |  7.753 |
-      3   |  3.5   |  3.067 | .217 | 10.996 |  9.636 |
-      3½  |  4.    |  3.548 | .226 | 12.566 | 11.146 |
-      4   |  4.5   |  4.026 | .237 | 14.137 | 12.648 |
-      4½  |  5.    |  4.508 | .246 | 15.708 | 14.162 |
-      5   |  5.563 |  5.045 | .259 | 17.477 | 15.849 |
-      6   |  6.625 |  6.065 | .28  | 20.813 | 19.054 |
-      7   |  7.625 |  7.023 | .301 | 23.955 | 22.063 |
-      8   |  8.625 |  7.982 | .322 | 27.096 | 25.076 |
-      9   |  9.625 |  8.937 | .344 | 30.238 | 28.076 |
-     10   | 10.75  | 10.019 | .366 | 33.772 | 31.477 |
-     11   | 12.    | 11.25  | .375 | 37.699 | 35.343 |
-     12   | 12.75  | 12.    | .375 | 40.055 | 37.7   |
-  --------+--------+--------+------+--------+--------+
-------+-------------------------+---------------+--------+-------+------
-      |                         |               |        |       |
-      |                         |               |        |       |
-      |                         |               | Length |       |
-      |                         |Length of pipe |of pipe |Nominal|
- Diam.|     Transverse areas.   |  per square   |contain-|weight |Number
-      |                         |    foot of    |ing one | per   |  of
-------+--------+--------+-------+-------+-------+ cubic  | foot. |thread
- Nom. |External|Internal| Metal |Ext'nal|Int'nal|  foot. |       | per
-intern|        |        |       |surface|surface|        |       | inch
-------+--------+--------+-------+-------+-------+--------+-------+ of
-Inches|Sq. ins.|Sq. ins.|Sq.ins.|  Feet |  Feet |  Feet  |Pounds |screw
-------+--------+--------+-------+-------+-------+--------+-------+-----
-    ⅛ |   .129 |   .0573|  .0717| 9.44  |14.15  |2513.   |  .241 | 27
-    ¼ |   .229 |   .1041|  .1249| 7.075 |10.49  |1383.3  |  .42  | 18
-    ⅜ |   .358 |   .1917|  .1663| 5.657 | 7.73  | 751.2  |  .559 | 18
-    ½ |   .554 |   .3048|  .2492| 4.547 | 6.13  | 472.4  |  .837 | 14
-    ¾ |   .866 |   .5333|  .3327| 3.637 | 4.635 | 270.   | 1.115 | 14
-   1  |  1.358 |   .8626|  .4954| 2.904 | 3.645 | 166.9  | 1.668 | 11½
-   1¼ |  2.164 |  1.496 |  .668 | 2.301 | 2.768 |  96.25 | 2.244 | 11½
-   1½ |  2.835 |  2.038 |  .797 | 2.01  | 2.371 |  70.66 | 2.678 | 11½
-   2  |  4.43  |  3.356 | 1.074 | 1.608 | 1.848 |  42.91 | 3.609 | 11½
-   2½ |  6.492 |  4.784 | 1.708 | 1.328 | 1.547 |  30.1  | 5.739 |  8
-   3  |  9.621 |  7.388 | 2.243 | 1.091 | 1.245 |  19.5  | 7.536 |  8
-   3½ | 12.566 |  9.887 | 2.679 |  .955 | 1.077 |  14.57 | 9.001 |  8
-   4  | 15.904 | 12.73  | 3.174 |  .849 |  .949 |  11.31 |10.665 |  8
-   4½ | 19.635 | 15.961 | 3.674 |  .764 |  .848 |   9.02 |12.34  |  8
-   5  | 24.306 | 19.99  | 4.316 |  .687 |  .757 |   7.2  |14.502 |  8
-   6  | 34.472 | 28.888 | 5.584 |  .577 |  .63  |   4.98 |18.762 |  8
-   7  | 45.664 | 38.738 | 6.926 |  .501 |  .544 |   3.72 |23.271 |  8
-   8  | 58.426 | 50.04  | 8.386 |  .443 |  .478 |   2.88 |28.177 |  8
-   9  | 72.76  | 62.73  |10.03  |  .397 |  .427 |   2.29 |33.701 |  8
-  10  | 90.763 | 78.839 |11.924 |  .355 |  .382 |   1.82 |40.065 |  8
-  11  |113.098 | 99.402 |13.696 |  .318 |  .339 |   1.450|45.95  |  8
-  12  |127.677 |113.098 |14.579 |  .299 |  .319 |   1.27 |48.985 |  8
-------+--------+--------+-------+-------+-------+--------+-------+----
-
-Open construction should be employed, wherever possible, so that
-all parts of a machine that require attention, or that may become
-deranged in operation, may be accessible for adjustment or repair.
-
-     The design should be such that there is ample strength, and the
-   bearings for moving parts should be of liberal proportions to
-   avoid heating with minimum attention.
-
-     A comparison of the proportions used by different manufacturers
-   for a machine of given size might profitably be made before a
-   selection is made.
-
-The matter of lubrication is important.
-
-     Fast running machines, such as generators and motors, should be
-   provided with ring oilers and oil reservoirs of ample capacity, as
-   shown in figs. 2,788 to 2,794.
-
-[Illustration: FIG. 2,788.--Sectional view showing a ring oiler or
-self oiling bearing. As shown the pedestal or bearing standard is
-cored out to form a reservoir for the oil. The rings are in rolling
-contact with the shaft, and dip at their lower part into the oil.
-In operation, oil is brought up by the rings which revolve because
-of the frictional contacts with the shaft. The oil is in this way
-brought up to the top of the bearing and distributed along the shaft
-gradually descending by gravity to the reservoir, being thus used
-over and over. A drain cock, is provided in the base so that the oil
-may be periodically removed from the reservoir and strained to remove
-the accumulation of foreign matter. This should be frequently done to
-minimize the wear of the bearing.]
-
-All bearings subject to appreciable wear should be made adjustable so
-that lost motion may be taken up from time to time and thus keep the
-vibration and noise of operation within proper limits.
-
-=Selection of Generators.=--This is governed by the class of work
-to be done and by certain local conditions which are liable to vary
-considerably for different stations.
-
-These variable factors determine whether the generators must be of
-the direct or alternating current type, whether they must be wound
-to develop a high or a low voltage, and whether their outputs in
-amperes must be large or small. Sufficient information has already
-been given to cover these various cases; there are, however, certain
-general rules that may advantageously be observed in the selection of
-generators designed to fill any of the aforementioned conditions, and
-it is well to possess certain facts regarding their construction.
-
-[Illustration: FIGS. 2,789 to 2,794.--Self oiling self aligning
-bearing open. Views showing oil grooves, rings, bolts etc.]
-
-=Ques. Name an important point to be considered in selecting a
-generator.=
-
-Ans. Its efficiency.
-
-=Ques. What are the important points with respect to efficiency?=
-
-Ans. A generator possessing a high efficiency at the average load is
-more desirable than a generator showing a high efficiency at full
-load.
-
-=Ques. Why?=
-
-Ans. The reason is that in station practice the full load limit is
-seldom reached, the usual load carried by a generator ordinarily
-lying between the one-half and three-quarter load points.
-
-=Ques. How do the efficiencies of large and small generators compare?=
-
-Ans. There is little difference.
-
-[Illustration: FIG. 2,795.--Rotor of Westinghouse type T turbine
-dynamo set. The dynamo is of the commutating pole type either shunt
-or compound wound. The turbine is of the single wheel impulse type.
-The wheel is mounted directly on the end of the shaft as shown. Steam
-is used two or more times on the wheel to secure efficiency. A fly
-ball governor is provided with weights hung on hardened steel knife
-edges. In case of over speeding, an automatic safety stop throttle
-valve is tapped shutting off the steam supply. This type of turbine
-dynamo set is especially applicable for exciter service in modern,
-superheated steam generating stations where the steam pressure
-exceeds 125 pounds. Westinghouse Type T turbines operate directly
-(that is, without a reducing valve) on pressures up to 200 pounds per
-square inch with steam superheated to 150 degrees Fahrenheit.]
-
-=Ques. How are the sizes and number of generator determined?=
-
-Ans. The sizes and number of generator to be installed should be
-such as to permit the engines operating them being worked at nearly
-full load, because the efficiencies of the latter machines decrease
-rapidly when carrying less than this amount.
-
-=Ques. What is understood by regulation?=
-
-Ans. The accuracy and reliability with which the pressure or current
-developed in a machine may be controlled.
-
-     It is generally possible if purchasing of a reputable concern,
-   to obtain access to record sheets on which may be found results
-   of tests conducted on the generator in question, and as these are
-   really the only means of ascertaining the values of efficiency and
-   regulation, the purchaser has a right to inspect them. If, for
-   some reason or other, he has not been afforded this privilege, he
-   should order the machine installed in the station on approval, and
-   test its efficiency and regulation before making the purchase.
-
-[Illustration: FIG. 2,796.--Cross section of electrical station
-showing small traveling crane.]
-
-=Installation.=--The installation of machines and apparatus in an
-electrical station is a task which increases in difficulty with
-the size of the plant. When the parts are small and comparatively
-light they may readily be placed in position, either by hand, by
-erecting temporary supports which may be moved from place to place
-as desired, or by rolling the parts along on the floor upon pieces
-of iron pipe. If, however, the parts be large and heavy, a traveling
-crane such as shown in fig. 2,797, becomes necessary.
-
-=Ques. What precaution should be taken in moving the parts of
-machines?=
-
-Ans. Care should be taken not to injure the bearings and shafts, the
-joints in magnetic circuits such as those between frame and pole
-pieces, and the windings on the field and armature.
-
-[Illustration: FIG. 2,797.--Cross section of electrical station
-showing a traveling crane for the installation or removal of large
-and heavy machine parts. A traveling crane consists of an iron beam
-which, being supplied with wheels at the ends, can be made to move
-either mechanically or electrically upon a track running the entire
-length of the station. This track is not supported by the walls
-of the building, but rests upon beams specially provided for the
-purpose. In addition to the horizontal motion thus obtained, another
-horizontal motion at right angles to the former is afforded by means
-of the carriage which, being also mounted on wheels, runs upon a
-track on the top of the beam. Electrical power is generally used to
-move the carriage and also the revolving drums contained thereon,
-the latter of which give a vertical motion to the main hoist or the
-auxiliary hoist, these hoists being used respectively for raising
-or lowering heavy or light loads. In the larger sizes of electric
-traveling crane, a cage is attached to the beam for the operator,
-who, by means of three controllers mounted in the cage, can move a
-load on either the main or auxiliary hoist in any direction.]
-
-     The insulations of the windings are perhaps the most vital parts
-   of a generator, and the most readily injured. The prick of a pin
-   or tack, a bruise, or a bending of the wires by resting their
-   weight upon them or by their coming in contact with some hard
-   substance, will often render a field coil or an armature useless.
-
-     Owing to its costly construction, it is advisable when
-   transporting armatures by means of cranes to use a wooden
-   spreader, as shown in fig. 2,798 to prevent the supporting rope
-   bruising the winding.
-
-[Illustration: FIG. 2,798.--View of armature in transit showing use
-of a wooden spreader as a protection. If a chain be used in place of
-the rope, a padding of cloth should be placed around the armature
-shaft and special care taken that the chain does not scratch the
-commutator.]
-
-=Ques. If an armature cannot be placed at once in its final position
-what should be done?=
-
-Ans. It may be laid temporarily upon the floor, if a sheet of
-cardboard or cloth be placed underneath the armature as a protection
-for the windings; in case the armature is not to be used for some
-time, it is better practice to place it in a horizontal position on
-two wooden supports near the shaft ends.
-
-=Ques. What kind of base should be used with a belt driven generator
-or motor?=
-
-Ans. The base should be provided with V ways and adjusting screws
-for moving the machine horizontally to take up slack in the belt, as
-shown in fig. 2,799.
-
-     Owing to the normal tension on the belt, there is a moment
-   exerted equal in amount to the distance from the center of gravity
-   of the machine to the center of the belt, multiplied by the
-   effective pull on the belt. This force tends to turn the machine
-   about its center of gravity. By placing the screws as shown, any
-   turning moment, as just mentioned, is prevented.
-
-[Illustration: FIG. 2,799.--Plan of belt drive machine showing V ways
-and adjusting screws for moving the machine forward from the engine
-or counter shaft to take up slack in the belt.]
-
-=Ques. How should a machine be assembled?=
-
-Ans. The assembling should progress by the aid of a blue print, or by
-the information obtained from a photograph of the complete machine
-as it appears when ready for service. Each part should be perfectly
-clean when placed in position, especially those parts between which
-there is friction when the machine is in operation, or across which
-pass lines of magnetic force; in both cases the surfaces in contact
-must be true and slightly oiled before placing in position.
-
-     Contact surfaces forming part of electrical circuits must also
-   be clean and tightly screwed together. An important point to bear
-   in mind when assembling a machine is, to so place the parts that
-   it will not be necessary to remove any one of them in order to get
-   some other part in its proper position. By remembering this simple
-   rule much time will be saved, and in the majority of instances the
-   parts will finally be better fitted together than if the task has
-   to be repeated a number of times.
-
-     When there are two or more parts of the machine similarly
-   shaped, it is often difficult to properly locate them, but in such
-   cases notice should be taken of the factory marks usually stamped
-   upon such pieces and their proper places determined from the
-   instructions sent with the machine.
-
-[Illustration: FIGS. 2,800 to 2,802.--Starrett's improved speed
-indicator. In construction, the working parts are enclosed like a
-watch. The graduations show every revolution, and with two rows of
-figures read both right and left as the shaft may run. While looking
-at the watch, each hundred revolutions may be counted by allowing
-the oval headed pin on the revolving disc to pass under the thumb as
-the instrument is pressed to its work. A late improvement in this
-indicator consists in the rotating disc, which, being carried by
-friction may be moved to the starting point where the raised knobs
-coincide. When the spindle is placed in connection with the revolving
-shaft, pressing the raised knob with the thumb will prevent the disc
-rotating, while the hand of the watch gets to the right position to
-take the time. By releasing the pressure the disc is liberated for
-counting the revolutions of the shaft when every 100 may be noted by
-feeling the knob pass under the thumb lightly pressed against it,
-thus relieving the eye, which has only to look on the watch to note
-the time.]
-
-=Ques. What should be noted with respect to speed of generator?=
-
-Ans. Each generator is designed to be run at a certain speed in
-order to develop the voltage at which the machine is rated. The
-speed, in revolutions per minute, the pressure in volts, and the
-capacity or output in watts (volts × amperes) or in kilowatts
-(thousands of watts) are generally stamped on a nameplate screwed to
-the machine.
-
-     This requirement frequently requires calculations to be made by
-   the erectors to determine the proper size pulleys to employ to
-   obtain the desired speed.
-
-[Illustration: FIG. 2,803.--Home made belt clamp. It is made with
-four pieces of oak of ample size to firmly grip the belt ends where
-the bolts are tightened. The figure shows the clamp complete and
-in position on the belt and clearly illustrates the details of
-construction. In making the long bolts the thread should be cut about
-three-quarter length of bolt and deep enough so that the nuts will
-easily screw on.]
-
-     =Example.=--What diameter of engine pulley is required to run
-   a dynamo at a speed of 1,450 revolutions per minute the dynamo
-   pulley being 10 inches in diameter and the speed of engine, 275
-   revolutions per minute?
-
-The diameter of pulley required on engine is 10 × (1,450 ÷ 275) = 53
-inches, nearly.
-
-     =Rule.=--To find the diameter of the driving pulley, _multiply
-   the speed of the driven pulley by its diameter, divide the product
-   by the speed of the driver and the answer will be the size of the
-   driver required_.
-
-     _Example._--If the speed of an engine be 325 revolutions per
-   minute, diameter of engine pulley 42 inches, and the speed of
-   the dynamo 1,400 revolutions per minute, how large a pulley is
-   required on dynamo?
-
-     The size of the dynamo pulley is
-
-42 × (325 ÷ 1,400) = 9¾ inches.
-
-     =Rule.=--To find the size of dynamo pulley, _multiply the speed
-   of engine by the diameter of engine wheel and divide the product
-   by the speed of the dynamo_.
-
-[Illustration: FIGS. 2,804 and 2,805.--A good method of lacing a
-belt. The view at the left shows outer side of belt, and at the
-right, inner or pulley side.]
-
-     _Example._--If a steam engine, running 300 revolutions per
-   minute, have a belt wheel 48 inches in diameter, and be belted
-   to a dynamo having a pulley 12 inches in diameter, how many
-   revolutions per minute will the dynamo make?
-
-     The speed of dynamo will be 300 × (48 ÷ 12) = 1,200 rev. per min.
-
-     =Rule.=--When the speed of the driving pulley and its diameter
-   are known, and the diameter of the driven pulley is known, the
-   speed of the driven pulley is found by _multiplying the speed of
-   the driver by its diameter in inches and dividing the product by
-   the diameter of the driven pulley_.
-
-     =Example.=--What will be the required speed of an engine
-   having a belt wheel 46 inches in diameter to run a dynamo 1,500
-   revolutions per minute, the dynamo pulley being 11 inches in
-   diameter?
-
-     The speed of the engine is 1,500 × (11 ÷ 46) = 359 rev. per min.
-   nearly.
-
-[Illustration: FIG. 2,806.--Wiring diagram and directions for
-operating Holzer-Cabot single phase self-starting motor. =Location:=
-The motor should be placed in as clear and dry a location as
-possible, away from acid or other fumes which would attack the
-metal parts or insulation, and should be located where it is easily
-accessible for cleaning and oiling. =Erection:= The motor should be
-set so that the shaft is level and parallel with the shaft it is
-to drive so that the belt will run in the middle of the pulleys.
-Do not use a belt which is too heavy or too tight for the work it
-has to do, as it will materially reduce the output of the motor.
-The belt should be from one-half to one inch narrower than the
-pulley. =Rotation:= In order to reverse the direction of rotation,
-interchange leads A and B. =Suspended Motors:= Motors with ring oil
-bearings may be used on the wall or ceiling by taking off end caps
-and revolving 90 or 180 degrees until the oil wells come directly
-below the bearings. =Starting:= Motors are provided with link across
-two terminals on the upper right hand bracket at the front of the
-motor and with this connection should start considerable overloads.
-If the starting current be too great with this connection, it may be
-reduced by removing the link. =Temperatures:= At full load the motor
-will feel hot to the hand, but this is far below the danger point. If
-too hot for touch, measure temperature with a thermometer by placing
-bulb against field winding for 10 minutes, covering thermometer
-with cloth or waste. The temperature should not exceed 75 degrees
-Fahr. above the surrounding air. =Oiling:= Fill the oil wells to the
-overflow before starting and keep them full. See that the oil rings
-turn freely with shaft. =Care:= The motor must be kept clean. Smooth
-collector rings with sandpaper and see that the brushes make good
-contact. When brushes become worn they may be reversed. When fitting
-new brushes or changing them always sandpaper them down until they
-make good contact with the collector rings, by passing a strip of
-sandpaper beneath the brush.]
-
-     =Rule.=--To find the speed of engine when diameter of both
-   pulleys, and speed of dynamo are given, _multiply the dynamo speed
-   by the diameter of its pulley and divide by the diameter of engine
-   pulley_.
-
-=Ques. How are the diameters and speeds of gear wheels figured?=
-
-Ans. The same as belted wheels, using either the pitch circle
-diameters or number of teeth in each gear wheel.
-
-[Illustration: FIGS. 2,807 to 2,809.--Wiring diagrams and directions
-for operating Holzer-Cabot slow speed alternating current motors.
-=Erecting:= In installing the motor, be sure the transformer and
-wiring to the motor are large enough to permit the proper voltage
-at the terminals. If too small, the voltage will drop and reduce
-the capacity of the motor. =Oiling:= Maintain oil in wells to the
-overflow. =Starting: Single phase= motors are started by first
-throwing the starting switch down into the starting position, and
-when the motor is up to speed, throwing it up into the running
-position. _Do not hold the switch in starting position over 10
-seconds._ Starter for single phase motors above ½ H.P. are arranged
-with an adjusting link at the bottom of the panel. The link is shown
-in the position of least starting torque and current. Connect from
-W to 2 or W to 3 for starting heavier loads. _Two or three phase_
-motors are started simply by closing the switch. These motors start
-full load without starters. The motor should start promptly on
-closing the switch. It should be started the first time without
-being coupled to the line shaft. If the motor start free, but will
-not start loaded, it shows either that the load upon the motor is
-too great, the line voltage too low, or the frequency too high. The
-voltage and frequency with the motor running should be within 5% of
-the name plate rating and the voltage with 10 to 15% while starting.
-If the motor do not start free, either it is getting no current or
-something is wrong with the motor. In either case an electrician
-should be consulted. =Solution:= To reverse the direction of rotation
-interchange the leads marked "XX" in the diagrams. =Temperature:= At
-full load the motor should not heat over 75 degrees Fahr. above the
-temperature of the surrounding air; if run in a small enclosed space
-with no ventilation, the temperature will be somewhat higher.]
-
-=Ques. What should be noted with respect to generator pulleys?=
-
-Ans. A pulley of certain size is usually supplied with each generator
-by its manufacturer, and it is not generally advisable to depart much
-from the dimensions of this pulley. Accordingly, the solution of the
-pulley problem usually consists in finding the necessary diameter of
-the driving pulley relative to that of the pulley on the generator in
-order to furnish the required speed.
-
-=Ques. What is the chief objection to belt drive?=
-
-Ans. The large amount of floor space required.
-
-[Illustration: FIG. 2,810.--Tandem drive for economizing floor space
-with belt transmission. Belts of different lengths are used, as
-shown, each of which passes over the driving wheel _d_ of the engine,
-and then over the pulley wheel of one of the generators. In such
-an arrangement the belts would be run lengthwise through the room
-in which the machines are placed, and it is obvious that since the
-width of the room would be governed by the width of the machines thus
-installed, this method is a very efficient one for accomplishing the
-end in view.]
-
-=Ques. How may the amount of space that would ordinarily be required
-for belt drive, be reduced?=
-
-Ans. By driving machines in tandem as in fig. 2,810, or by the double
-pulley drive as in fig. 2,811.
-
-=Ques. What is the objection to the tandem method?=
-
-Ans. The most economical distance between centers cannot be employed
-for all machines.
-
-=Ques. What is the objectionable tendency in resorting to floor
-economy methods with belt transmission?=
-
-Ans. The tendency to place the machines too closely together. This is
-poor economy as it makes the cleaning of the machines a difficult and
-dangerous task; it is therefore advisable to allow sufficient room
-for this purpose regardless of the method of belting employed.
-
-[Illustration: FIG. 2,811.--Double pulley drive for economizing floor
-space with belt transmission. Where a center crank engine is used
-both pulleys may be employed by belting a machine to each as shown.
-Although considerable floor space would be saved by the use of this
-scheme if the generators thus belted were placed at M and G yet still
-more floor space would be saved by having them occupy the positions
-indicated at M and S.]
-
-=Ques. What is the approved location for an alternator exciter?=
-
-Ans. To economize floor space the exciter may be placed between the
-alternator and engine at S in fig. 2,811.
-
-=Belts.=--In the selection of a belt, the quality of the leather
-should be first under consideration. The leather must be firm, yet
-pliable, free from wrinkles on the grain or hair side, and of an even
-thickness throughout.
-
-[Illustration: FIG. 2,812.--Separately excited belt driven alternator
-showing approved location of exciter. In an electrical station where
-alternating current is generated, the alternators for producing
-the current generally require separate excitation for their field
-windings; that is, it is usually necessary to install in conjunction
-with an alternator a small dynamo for supplying current to the
-alternator field. The exciter is a comparatively small machine; in
-fact, it requires only about 1 per cent. of the capacity of the
-alternator which it excites, and so being small is often belted to
-an auxiliary pulley mounted on the alternator shaft. Considerable
-floor space would be occupied by an installation of this nature if
-the exciter be placed at M, and belted to the alternator as indicated
-by the dotted lines. By locating the exciter at S, between the
-alternator and the engine, much floor space will be saved and the
-general appearance of the installation improved.]
-
-If the belt be well selected and properly handled, it should do
-service for twenty years, and even then if the worn part be cut off,
-the remaining portion may be remade and used again as a narrower and
-shorter belt.
-
-     Besides leather belts, there are those made of rubber which
-   withstand moisture much better than leather belts, and which also
-   possess an excellent grip on the pulley; they are, however, more
-   costly and much less durable under normal conditions.
-
-     In addition to leather and rubber belts, there are belts
-   composed of cotton, of a combination of cotton and leather, and
-   of rope. The leather belt, however, is the standard and is to be
-   recommended.
-
-Equally important with the quality of a belt is its size in order to
-transmit the necessary power.
-
-     The average strain under which leather will break has been found
-   by many experiments to be 3,200 pounds per square inch of cross
-   section. A good quality of leather will sustain a somewhat greater
-   strain. In use on the pulleys, belts should not be subjected to a
-   greater strain than one eleventh their tensile strength, or about
-   290 pounds to the square inch or cross section. This will be about
-   55 pounds average strain for every inch in width of single belt
-   three-sixteenths inch thick. The strain allowed for all widths
-   of belting--single, light double, and heavy double--is in direct
-   proportion to the thickness of the belt.
-
-=Ques. How much horse power will a belt transmit?=
-
-Ans. The capacity of a belt depends on, its width, speed, and
-thickness. _A single belt one inch wide and travelling 1,000 feet per
-minute will transmit one horse power; a double belt under the same
-conditions, will transmit two horse power._
-
-[Illustration: FIG. 2,813.--One horse power transmitted by belt to
-illustrate the rule given above. A pulley is driven by a belt by
-means of the friction between the surfaces in contact. Let T be the
-tension on the driving side of the belt, and T', the tension on the
-loose side; then the driving force = T-T'. In the figure T is taken
-at 34 lbs. and T' at 1 lb.; hence driving force = 34-1 = 33 lbs.
-Since the belt is travelling at a velocity of 1,000 feet per minute
-the power transmitted = 33 lbs. × 1,000 ft. = 33,000 ft. lbs. per
-minute = 1 horse power.]
-
-     This corresponds to a working pull of 33 and 66 lbs. per inch of
-   width respectively.
-
-     =Example.=--What width double belt will be required to transmit
-   50 horse power travelling at a speed of 3,000 feet per minute?
-
-     The horse power transmitted by each inch width of double belt
-   travelling at the stated speed is
-
-                3,000
-           1 ×  -----  × 2 = 6,
-                1,000
-
-hence the width of belt required to transmit 50 horse power is
-
-           50 ÷ 6 = 8.33, say 8 inches.
-
-=Ques. At what velocity should a belt be run?=
-
-Ans. At from 3,000 to 5,000 feet per minute.
-
-=Ques. How may the greatest amount of power transmitting capacity be
-obtained from belts?=
-
-Ans. By covering the pulleys with leather.
-
-=Ques. How should belts be run?=
-
-Ans. With the tight side underneath as in fig. 2,814.
-
-[Illustration: FIGS. 2,814 and 2,815.--Right and wrong way to run a
-belt. The tight side should be underneath so as to increase the arc
-of contact and consequently the adhesion, that is to say, a _better
-grip_, is in this way obtained.]
-
-=Ques. What is a good indication of the capacity of a belt in
-operation?=
-
-Ans. Its appearance after a few days' run.
-
-     If the side of the belt coming in contact with the pulley assume
-   a mottled appearance, it is an indication that the capacity of
-   the belt is considerably in excess of the power which it is
-   transmitting, inasmuch as the spotted portions of the belt do not
-   touch the pulley; and in consequence of this there is liable to be
-   more or less slipping.
-
-     Small quantities of a mixture of tallow and fish oil which
-   have previously been melted together in the proportion of two of
-   the former to one of the latter, will, if applied to the belt
-   at frequent intervals, do much toward softening it, and thus
-   by permitting its entire surface to come in contact with the
-   pulley, prevent any tendency toward slipping. The best results
-   are obtained when the smooth side of the belt is used next to the
-   pulley, since tests conducted in the past prove that more power is
-   thus transmitted, and that the belt lasts longer when used in this
-   way.
-
-[Illustration: FIG. 2,816.--The Hill friction clutch pulley for power
-control. The clutch mechanism will start a load equivalent to the
-double belt capacity of the pulley to which the clutch is attached.]
-
-=Ques. What is the comparison between the so called endless belts and
-laced belts?=
-
-Ans. With an endless belt there is no uneven or noisy action as with
-laced belts, when the laced joint passes over the pulleys, and the
-former is free from the liability of breakage at the joint.
-
-=Ques. How should a belt be placed on the pulleys?=
-
-Ans. The belt should first be placed on the pulley at rest, and then
-run on the other pulley while the latter is in motion.
-
-     The best results are obtained, and the strain on the belt is
-   less, when the speed at which the moving pulley revolves is
-   comparatively low. With heavy belts, particular care should be
-   taken to prevent any portion of the clothing being caught either
-   by the moving belt or pulleys, as many serious accidents have
-   resulted in the past from carelessness in regard to this important
-   detail. The person handling the belt should, therefore, be sure of
-   a firm footing, and when it is impossible to secure this, it is
-   advisable to stop the engine and fit the belt around the engine
-   pulley as well as possible by the aid of a rope looped around the
-   belt.
-
-[Illustration: FIG. 2,817--Sectional view of Hill clutch mechanism.
-In every case the mechanism hub A, and in a clutch coupling the
-ring W, is permanently and rigidly secured to the shaft and need
-not be disturbed when removing the wearing parts. When erected, the
-adjustment should be verified, and always with the clutch and ring
-engaged and at rest. If the jaws do not press equally on the ring, or
-if the pressure required on the cone be abnormal, loosen the upper
-adjusting nuts T´ on eye bolts and set up the lower adjusting nuts
-T´´ until each set of jaws is under the same pressure. Should the
-clutch then slip when started it is evident that the jaw pressure is
-insufficient and a further adjustment will be necessary. All clutches
-are equipped throughout with split lock washers. Vibration or shock
-will not loosen the nuts if properly set up. The jaws can be removed
-parallel to the shaft as follows: Remove the gibs V, and withdraw the
-jaw pins P, then pull out the levers D. Do not disturb the eye bolt
-nuts T´ and T´´. The outside jaws B can now be taken out. Remove the
-bolt nuts I allowing the fulcrum plates R to be taken off. On the
-separable hub pattern the clamping bolts must be taken out before
-fulcrum plate is removed. The inside jaws C may now be withdrawn.
-Always set the clutch operating lever in the position as shown in
-fig. 2,816 to avoid interference with mechanism parts. Oil the moving
-parts of the clutch. Keep it clean. Examine at regular intervals.]
-
-=Ques. Under what conditions does a belt drive give the best results?=
-
-Ans. When the two pulleys are at the same level.
-
-     If the belt must occupy an inclined position it should not form
-   a greater angle than 45 degrees with the horizontal.
-
-=Ques. What is a characteristic feature in the operation of belts,
-and why?=
-
-Ans. Belts in motion will always run to the highest side of a
-pulley; this is due partially to the greater speed in feet per minute
-developed at that point owing to the greater circumference of the
-pulley, and also to the effects of centrifugal force.
-
-     If, therefore, the highest sides of both pulleys be in line with
-   each other, and the shafts of the respective pulleys be parallel
-   to each other, there will be no tendency for the belt to leave
-   the pulleys when once in its proper position. In order that these
-   conditions be maintained, the belt should be no more than tight
-   enough to prevent slipping, and the distance between the centers
-   of the pulleys should be approximately 3.5 times the diameter of
-   the larger one.
-
-[Illustration: FIG. 2,818.--Hill clutch mechanism Smith type. The
-friction surfaces are wood to iron, the wood shoes being made from
-maple. All parts of the toggle gear are of steel and forgings with
-the exception of the connection lever which is of cast iron.]
-
-=Ques. What minor appurtenances should be provided in a station?=
-
-Ans. Apparatus should be installed as a prevention against accidents,
-such as fire, and protection of attendants from danger.
-
-     In every electrical station there should be a pump, pipes
-   and hose; the pump may be either directly connected to a small
-   electric motor or belted to a countershaft, while the pipes
-   and hose should be so placed that no water can accidentally
-   reach the generators and electrical circuits. A number of fire
-   bucket filled with water should be placed on brackets around the
-   station, and with these there should be an equal number of bucket
-   containing dry sand, the water being used for extinguishing fire
-   occurring at a distance from the machines and conductors, and the
-   sand for extinguishing fire in current carrying circuits where
-   water would cause more harm than benefit. To prevent the sand
-   being blown about the station, each sand bucket, when not in use,
-   should be provided with a cover.
-
-     Neat cans and boxes should be mounted in convenient places for
-   greasy rags, waste, nuts, screws, etc., which are used continually
-   and which therefore cannot be kept in the storeroom.
-
-     While it is important to guard against fire in the station,
-   it is equally necessary to provide for personal safety. All
-   passages and dark pits should therefore be thoroughly lighted
-   both day and night, and obstacles of any nature that are not
-   absolutely necessary in the operation of the station, should be
-   removed. Moving belts, and especially those passing through the
-   floor, should be enclosed in iron railings. If high voltages be
-   generated, it is well to place a railing about the switchboard to
-   prevent accidental contact with current carrying circuits, and in
-   such cases it is also advisable to construct an insulated platform
-   on the floor in front of the switchboard.
-
-[Illustration: FIG. 2,819.--Method of joining adjacent switchboard
-panels.]
-
-=Switchboards.=--The plan of switchboard wiring for alternating
-current work depends upon the system in use and this latter may be
-either of the single phase, two phase, three phase, or monocyclic
-types. The general principles in all these cases, however, are
-practically identical.
-
-     Fig. 2,820 shows the switchboard wiring for a single phase
-   alternator. As an aid in reading the diagram, the conductors
-   carrying alternating current are represented by solid lines, and
-   those carrying direct current, by dotted lines.
-
-[Illustration: FIG. 2,820.--Switchboard wiring for a single phase
-separately excited alternator. The direct current circuits are
-represented by dotted lines, and the alternating current circuit, by
-solid lines.]
-
-     The exciter shown at the right is a shunt wound machine. By
-   means of the exciter rheostat, the voltage for exciting the field
-   winding of the alternator is varied; this, in turn, varies the
-   voltage developed in the alternator since the main leads of the
-   exciter are connected through a double pole switch G to the field
-   winding of the alternator.
-
-[Illustration: FIGS. 2,821 to 2,825.--General Electric diagrams of
-connections. A, ammeter; C.B, circuit breaker; C.P, candle power;
-C.T, current transformer; D.R, discharge resistance; F, fuse; F.S,
-field switch; L, lamp; O.C, overload coil; P.P, pressure plug;
-P.R, pressure receptacle; R.C, reactance; rheo, rheostat; R.P,
-synchronizing plug, running; R.S, resistance; S, switch; S.I,
-synchronism indicator; S.P, synchronizing plug, starting; S.R,
-synchronizing receptacle; V, voltmeter.]
-
-     A rheostat is also introduced in the alternator field winding
-   circuit to adjust the alternator pressure. It may seem unnecessary
-   to employ a rheostat in each of two separate field circuits to
-   regulate the voltage of the alternator, but these rheostats are
-   not both used to produce the same result. When a considerable
-   variation of pressure is required, the exciter rheostat is
-   manipulated, whereas for a fine adjustment of voltage the
-   alternator rheostat is preferably employed.
-
-     Sometimes a direct current ammeter is introduced in the
-   alternator's field circuit to aid in the adjustment.
-
-     The main circuit of alternator after being protected on both
-   sides by fuses, runs to the double pole switch K. These fuses
-   serve as a protection to the alternator in case of a short circuit
-   at the main switch. It will be noticed the fuses are of the single
-   pole type and are mounted a considerable distance apart; this is
-   to prevent any liability of a short circuit between them in case
-   of action. Enclosed fuses are now used entirely for such work,
-   since in these there is no danger of heated metal being thrown
-   about and causing damage when the fuse wire is melted. Enclosed
-   fuses are also more readily and quickly replaced than open fuses,
-   the containing tube of each being easy to adjust in circuit, and
-   when the fuse wire within is once melted the tube is discarded for
-   a new one.
-
-     The main circuit after passing through the main switch is
-   further protected on both sides by circuit breakers. Leaving these
-   protective devices, the left hand side of the circuit includes
-   the alternating current ammeter, and then connects with one of
-   the bus bars. The right hand side of the circuit runs from the
-   circuit breaker to the other bus bar. As many feeder circuits
-   may be connected to the bus bars and supplied with current by
-   the alternator as the capacity of this machine will permit. If,
-   however, there be more than one feeder circuit, each must be wired
-   through a double pole switch.
-
-     In alternating current work the pressures dealt with are much
-   greater than those in direct current installations, so that
-   proportionate care must be taken in the wiring to remove all
-   possibility of grounds.
-
-     To locate such troubles, however, should they occur, a ground
-   detector is provided. For this class of work the ground detector
-   must be an instrument especially designed for high pressure
-   circuits. Two of its terminals should be connected to the line
-   wires and the third, to ground; in case of a leak on the line, a
-   current will then flow through the detector and by the position of
-   the pointer the location and seriousness of the leak may be judged.
-
-     A step down transformer is also rendered necessary for the
-   voltmeter and the pilot lamps, owing to the high voltage in use.
-   The primary winding of the transformer is connected across the
-   main circuit of the alternator. This connection should never be
-   made so that it will be cut out of circuit when the main switch is
-   open, for it is always advisable to consult the voltmeter before
-   throwing on the load by closing this switch.
-
-[Illustration: FIGS. 2,826 to 2,829.--General Electric diagrams of
-connections. A, ammeter; C.B, circuit breaker; C.P, candle power;
-C.T, current transformer; D.R, discharge resistance; F, fuse; F.S,
-field switch; L, lamp; O.C, overload coil; P.P, pressure plug;
-P.R, pressure receptacle; R.C, reactance; rheo, rheostat; R.P,
-synchronizing plug, running; R.S, resistance; S, switch; S.I,
-synchronous indicator: S.P, synchronizing plug, starting; S.R,
-synchronizing receptacle: V, voltmeter.]
-
-=Ques. How does the switchboard wiring for a two phase system differ
-from the single phase arrangement shown in fig. 2,820?=
-
-Ans. It is practically the same, except for the introduction of an
-extra ammeter and a compensator in each of the outside wires, and in
-the use of a four pole switch in place of the two pole main switch.
-
-     The ammeters, of course, are for measuring the alternating
-   currents in each of the two phases or legs of the system, and the
-   compensators are two transformers with their primary coils in
-   series with the outside wires and their secondary coils in series
-   with each other across the outside wires. The transformers thus
-   connected are known as compensators or pressure regulators, and
-   as such compensate for the drop in pressure on either side of the
-   system.
-
-=Ques. How is the four pole main switch wired?=
-
-Ans. Its two central terminals which connect directly with the line
-wires, are joined together by a conductor, and from this point one
-wire is led off. This wire, together with the two outside wires, form
-the feeders of the system.
-
-=Ques. How many voltmeters are required for the two phase system?=
-
-Ans. One voltmeter is sufficient on the board if a proper switching
-device be employed to shift its connections across either of the two
-circuits; otherwise, two voltmeters will be necessary, one bridged
-across each of these respective circuits.
-
-     The same reasoning holds true in regard to ground detectors,
-   so that one or two of these will be required, depending upon the
-   aforementioned conditions.
-
-=Ques. What are the essential points of difference between the single
-phase switchboard wiring as shown in fig. 2,820, and that required
-for a three wire three phase system?=
-
-Ans. The three phase system requires the use of a three pole switch
-in place of the two pole switch; the insertion of an ammeter, a
-circuit breaker, and a compensator in each of the three wires of the
-system; the presence of two ground detectors instead of one, and the
-addition of a voltmeter switch if but one voltmeter be provided, or
-else the installation of two voltmeters, connected the one between
-the middle wire and outer right hand wire, and the other between the
-middle wire and outer left hand wire.
-
-[Illustration: FIG. 2,830.--Diagram of switchboard connections for
-General Electric automatic voltage regulator with two exciters and
-two alternators.]
-
-=Ques. Mention a few points relating to lightning arresters.=
-
-Ans. In most cases where direct current is used they are mounted
-on the walls of the station near the place at which the line wires
-enter. If they be mounted outside the station at this point, special
-precautions should be taken to keep them free from moisture by
-enclosing them in iron cases, but no matter where they are located it
-is necessary that they be dry in order to work properly.
-
-[Illustration: FIGS. 2,831 and 2,832.--Garton-Daniels alternating
-current lightning arrester; diagram showing connections. A lightning
-discharge takes the path indicated by the dotted line, across the
-upper air gap A, through resistance rod B, C, D, across copper strip
-R on the base, thence flowing to ground through the movable plunger
-M, lower on gap N, and ground binding post L. The discharge path is
-practically straight, contains an air gap, distance of but 3/32 inch,
-a series resistance averaging but 225 ohms. The lightning discharge
-does not flow through the flexible lead connecting band D on the
-lower end of the resistance rod with the top of the movable plunger.
-These two points are electrically connected by the heavy copper
-strip R, and lightning discharges generally, if not always, take the
-path across this copper strip in preference to flowing through the
-inductance of the one turn of flexible cable. When a discharge occurs
-from line to ground through any lightning arrester, the air gaps arc
-over, and so there is offered a path from line to ground for the line
-current. This flow of line current following the lightning discharge
-to ground may vary anywhere from a small capacity current where
-the arrester is installed on an ungrounded circuit, a moderately
-heavy flow on a partially grounded circuit, to a very heavy flow on
-a grounded circuit--either a circuit operated as a dead grounded
-circuit, or a circuit which has become accidentally grounded during
-a storm. The path taken by this flow of line current from line to
-ground may be traced by following the path shown by the dashed line.
-It, as seen, crosses upper air gap A, flows through section B of the
-resistance rod to band C. Leaving band C it flows through the magnet
-winding H, thence to band D on the resistance rod, through flexible
-lead to upper end of movable plunger, through movable plunger, across
-lower air gap N, to ground binding post L, thence to ground. The
-function of the short length of resistance rod CD is as follows: It
-has an ohmic resistance of about 30 ohms but is _non-inductive_.
-Magnet winding H, connected to bands C and D on the ends of this
-short length of rod has an ohmic resistance of 3 ohms, but is _highly
-inductive_. Lightning discharges being of _high frequency_ take the
-higher resistance _but non-inductive_ path CD in their passage from
-line to ground. The flow of normal current from line to ground being
-of a very low frequency, 25 or 60 cycles in ordinary alternating
-current circuits, zero in direct current circuits--takes the _low
-resistance_ path through coil H in its path to ground. Section CD of
-the rod is used therefore simply to shunt the inductance of winding
-H to high frequency lightning discharges, leaving the lightning
-discharge path in the arrester a _non-inductive_ highly efficient
-path. In all Garton-Daniels A. C. lightning arresters operating on
-non-grounded or partially grounded circuits, the action of the air
-gaps and series resistance are together sufficient to extinguish the
-flow of normal current to ground at the zero point of the generator
-voltage wave. If, however, as frequently happens, the line grounds
-accidentally during a storm, then the arrester does not have to
-depend for its proper operation on the arc extinguishing properties
-of the air gaps and resistance, but the heavier flow of line current
-through the arrester energizes the movable plunger, which raises
-upward in the coil, opening the circuit between the discharge point M
-and the lower end of the plunger. To limit the flow of line current
-to ground the resistance rod B is provided, there being approximately
-225 ohms between the discharge point A and clamp C in the 2,500 volt
-arrester. This feature is particularly effective where the circuit is
-temporarily or accidentally grounded. The series resistance prevents
-a heavy short circuit through the arrester and limits the current to
-a value that is readily broken by the cut out and is not enough to
-impede the passage of the discharge.]
-
-
-[Illustration: FIG. 2,833.--Diagram of switchboard connections for
-General Electric automatic voltage regulator with three exciters and
-three alternators.]
-
-     If possible, one place should be set aside for them and a marble
-   or slate panel provided on which they may be mounted.
-
-     Wooden supports are undesirable for lightning arresters on
-   account of the fire risk incurred; this, however, may be reduced
-   to a minimum by employing skeleton boards and using sheets of
-   asbestos between the arresters and the wood.
-
-     In parts of the country where lightning is of common occurrence
-   and where overhead circuits are installed which carry high
-   pressures, heavy currents, and extend over considerable territory,
-   it is advisable to have the station well equipped with lightning
-   arresters of the most improved types.
-
-     In each side of the main circuit, between the lightning arrester
-   connections and the switchboard apparatus there should be
-   connected a choke coil or else each of the main conductors at this
-   point should be tightly coiled up part of its length to answer the
-   same purpose.
-
-     A quick and effective way of coiling up a wire consists in
-   wrapping around a cylindrical piece of iron or wood that part
-   of the conductor in which it is desired to have the coils, the
-   desired number of times, and then withdrawing the cylindrical
-   piece. The coils, each of which may contain 50 or 200 turns,
-   thus inserted in the main circuit introduce a high resistance or
-   reluctance to a lightning current, and thus prevent it passing
-   to the generator; there will, however, be an easy path to earth
-   afforded it through the lightning arrester, and so no damage will
-   be done. Coils of the nature just mentioned may advantageously be
-   introduced between the generator and switchboard to take up the
-   reactive current developed upon the opening of the circuit, and in
-   the case of suspended conductors, the coils may be used to take up
-   the slack by the spring-like effect produced by them.
-
-     The safety of the operator should be especially considered in
-   the design of high pressure alternating current switchboards.
-
-     Such protection may be secured by screening all the exposed
-   terminals, or preferably by mounting all the switch mechanism on
-   the back of the board with simply the switch handle projecting
-   through to the front; by pushing or pulling the switch handle, the
-   connections can thus be shifted either to one side of the system
-   or to the other.
-
-=Ques. Upon what does the work of assembling a switchboard depend?=
-
-Ans. It depends almost entirely upon the size of the plant, varying
-from the simple task of mounting a single panel in the case of an
-isolated plant, to the more difficult problem of supporting a large
-number of panels in a central station.
-
-=Ques. When the material chosen for a switchboard must be shipped a
-considerable distance, what form of board should be used?=
-
-Ans. The board units or "slabs" should be of small dimensions, to
-avoid the liability of breakage and expense of renewal when a unit
-becomes cracked or machine injured.
-
-[Illustration: FIGS. 2,834 and 2,835.--Front and rear views showing
-General Electric automatic voltage regulator mounted on switchboard
-panel.]
-
-     Ordinarily, switchboards vary from five to eight feet in
-   height and the widths of the panels vary from five to six feet.
-   In some boards the seams between the slabs run vertically, and
-   in others horizontally. In order to render the assembling of
-   the switchboard as simple as possible, and its appearance when
-   finished the most artistic, these seams should run horizontally
-   rather than vertically. The edges of each of the slabs should also
-   be chamfered so that there will be less danger of their breaking
-   out when being mounted on the framework.
-
-=Ques. In assembling a switchboard, how should the lower slabs be
-placed, and why?=
-
-Ans. They should be suspended a little distance from the floor to
-prevent contact with any oil, dirt, water or rubbish that might be on
-the floor.
-
-=Ques. How are the slabs or panels supported?=
-
-Ans. They are carried on an iron or wooden framework with braces to
-give stability.
-
-     The braces should be securely fastened at one end to the wall of
-   the station, and at the other end to the framework of the board,
-   as shown in fig. 2,836.
-
-     To fasten the switchboard end of the brace directly to the
-   slate, marble or other material composing the board is poor
-   practice and should never be attempted.
-
-     If the station be constructed of iron, these switchboard braces
-   must be such that they will thoroughly insulate the board and its
-   contents from the adjoining wall.
-
-[Illustration: FIG. 2,836.--Method of supporting the framework of a
-switchboard.]
-
-=Ques. What is the usual equipment of a switchboard?=
-
-Ans. It comprises switching devices, current or pressure limiting
-devices, indicating devices, and fuses for protecting the apparatus
-and circuits.
-
-[Illustration: FIG. 2,837.--Diagram showing elementary connections of
-General Electric automatic regulator for direct current. It consists
-essentially of a main control magnet with two independent windings
-and a differentially wound relay magnet. One winding, known as the
-pressure winding, of the main control magnet is connected across the
-dynamo terminals, the other across a shunt in one of the load mains.
-The latter is the "compensating winding" and it opposes the action
-of the pressure winding so that as the load increases, a higher
-pressure at the dynamo is necessary to "over compound" for line drop.
-In ordinary practice, the voltage terminals are connected to the bus
-bars, and the compensating shunt inserted in one of the principal
-feeders of the system. In operation the shunt circuit across the
-dynamo field rheostat is first opened by means of a switch provided
-for that purpose on the base of the regulator and the rheostat turned
-to a point that will reduce the generator voltage 35 per cent below
-normal. The main control magnet is at once weakened and allows the
-spring to pull out the movable core until the main contacts are
-closed. This closes the second circuit of the differential relay,
-thus neutralizing its windings. The relay spring then lifts the
-armature and closes the relay contacts. The switch in the shunt
-circuit across the dynamo field rheostat is now closed, practically
-short circuiting the rheostat, and the dynamo voltage at once rises.
-As soon as it reaches the point for which the regulator has been
-adjusted, the main control magnet is strengthened, which causes the
-main contacts to open, which in turn open the relay contacts across
-the rheostat. The rheostat is now in the field circuit, the voltage
-at once falls off, the main contacts are closed, and relay armature
-released, and shunt circuit across the rheostat again completed. The
-voltage then starts to rise and this cycle of operation is continued
-at a high rate of vibration, maintaining not a constant but a steady
-voltage at the bus bars. When neither the compensating winding nor
-pressure wires are used, there will be no "over compounding" effect
-due to increase of load and a constant voltage will be maintained at
-the bus bars. The compensating winding on the control magnet, which
-opposes the pressure winding is connected across an adjustable shunt
-in the principal feeder circuit. As the load increases the voltage
-drop across the shunt increases and the effect of the compensating
-winding becomes greater. This will require a higher voltage on the
-pressure winding to open the main contacts and the regulator will
-therefore cause the dynamo to compensate for line drop, maintaining
-at the bus bars a steady voltage without fluctuations, which rises
-and falls with a load on the feeders, giving a constant voltage at
-the lamps or center of distribution. The compensating shunt may be
-adjusted so as to compensate for any desired line drop up to 15 per
-cent; it is preferably placed in the principal lighting feeder, but
-may be connected to the bus bars so that the total current will pass
-through it. The latter method, however, is sometimes desirable, as
-large fluctuating power loads on separate feeders might disturb the
-regulation of the lighting feeders. Adjustment is made by sliding
-the movable contact at the center of the shunt. This contact may be
-clamped at any desired point and determines the pressure across the
-compensating winding of the regulator's main control magnet. Where
-pressure wires are run back to the central station from the center
-of distribution they may be connected directly to the pressure
-winding of the main control magnet, and it is unnecessary to use the
-compensating shunt. The pressure wires take the place of the leads
-from the control magnet to the bus bars and maintain a constant
-voltage at the center of distribution.]
-
-     On some switchboards are also mounted small transformers for
-   raising or lowering the voltages, and lightning arresters as a
-   protection from lightning. In addition to the apparatus previously
-   mentioned nearly all switchboards carry at or near their top two
-   or more incandescent lamps provided with shades or reflectors, for
-   lighting the board.
-
-=Ques. What should be done before wiring a switchboard?=
-
-Ans. The electrical connections between the various apparatus
-mounted on the face or front of the board, are made on the back of
-the board. It is necessary that these connections be properly made
-else considerable electrical power will be wasted at this point. The
-wiring on the back of the board should therefore be planned out on
-paper before commencing the work.
-
-[Illustration: FIG. 2,838.--Diagram showing connections of General
-Electric automatic voltage regulator for direct current as connected
-for maintaining balanced voltage on both sides of a three wire system
-using a balancer set. In operation, should the voltage on the upper
-bus bars become greater than that on the lower ones, the middle and
-upper contacts on the regulator will close, thus opening the relay
-contacts to the left and closing those to the right. This inserts all
-the resistance in the field of balancer A, and short circuits the
-resistance in the field of balancer B. A will then be running as a
-motor, and B as a dynamo, thereby equalizing the two voltages until
-that on the lower bus bars becomes greater than that of the upper
-ones; then the regulator contacts operate in the opposite direction
-and balancer A is run as a dynamo, and balancer B as a motor. This
-cycle of operation is repeated at the rate of from three to four
-hundred times per minute, thus maintaining a balanced voltage on the
-system.]
-
-     In laying out the plan of wiring care must be taken to allow
-   sufficient contact surface at each connection; there should be not
-   less than one square inch of contact surface allowed for each 160
-   amperes of current transmitted.
-
-[Illustration: FIG. 2,839.--Diagram of connections of General
-Electric voltage regulators for one or more alternators using one
-exciter.]
-
-     For the bus bars, which, by the way are always of copper, one
-   square inch per 1,000 amperes is the usual allowance; this is
-   equal to 1,000 circular mils of cross sectional area per ampere.
-
-     Every effort should be made to give the bus bars the greatest
-   amount of radiation consistent with other conditions, in order
-   that their resistances may not become excessive owing to the heat
-   developed by the large currents they are forced to carry. Suppose,
-   for instance, the number of amperes to be generated is such as
-   to require bus bars having each a cross sectional area of one
-   square inch. If the end dimensions of these bars were each 1 inch
-   by 1 inch, there would be less radiating surface than if their
-   dimensions were each 2 inches by ½ inch.
-
-=Operation of Alternators.=--The operation of an alternator when run
-singly differs but little from that for a dynamo.
-
-     As to the preliminaries, the exciter must first be started.
-   This is done in the same way as for any shunt dynamo. At first
-   only a small current should be sent through the field winding of
-   the alternator; then, if the exciter operates satisfactorily and
-   the field magnetism of the operator show up well, the load may
-   gradually be thrown on until the normal current is carried, the
-   same method of procedure being followed as in the similar case of
-   a dynamo.
-
-[Illustration: FIGS. 2,840 and 2,841.--General Electric equalizer
-regulator designed to equalize the load on two machines, and diagram
-of connections.]
-
-On loading an alternator, a noticeable drop in voltage occurs
-across its terminals. This drop in voltage is caused in part by the
-demagnetization of the field magnets due to the armature current,
-and so depends in a measure upon the position and form of the pole
-pieces as well as upon those of the teeth in the armature core. The
-resistance of the armature winding also causes a drop in voltage
-under an increase of load.
-
-     Another cause which may be mentioned is the inductance of the
-   armature winding, which is in turn due to the positions of the
-   armature coils with respect to each other and also with respect to
-   the field magnets.
-
-[Illustration: FIG. 2,842.--Connection of General Electric equalizing
-regulator for equalizing loads on an engine driven dynamo and rotary
-converter running in parallel. Should the load on the dynamo become
-greater than that on the rotary converter, the middle and upper
-contacts on the regulator close, and thus by means of the relay
-switch and control motor, cause the feeder regulator to boost the
-voltage on the rotary until the loads again become equal. Should
-the load on the rotary converter become greater than that on the
-generator, the regulator contacts operate in the reverse direction
-and the feeder regulator is caused to buck the rotary voltage.]
-
-=Alternators in Parallel.=--When the load on a station increases
-beyond that which can conveniently be carried by one alternator, it
-becomes necessary to connect other alternators in parallel with it.
-To properly switch in a new machine in parallel with one already in
-operation and carrying load, requires a complete knowledge of the
-situation on the part of the attendant, and also some experience.
-
-     The connections for operating alternators in parallel are
-   shown in fig. 2,843. In the illustration the alternator A is in
-   operation and is supplying current to the bus bars. The alternator
-   B is at rest. The main pole switch B' by means of which this
-   machine can be connected into circuit is therefore open.
-
-[Illustration: FIG. 2,843.--Method of synchronizing with one lamp;
-_dark lamp method_. Assuming A to be in operation, B, may be brought
-up to approximately the proper speed, and voltage. Then if B, be
-run a little slower or faster than A, the synchronizing lamp will
-glow for one moment and be dark the next. At the instant when the
-pressures are equal and the machines in phase, the lamp will become
-dark, but when the phases are in quadrature, the lamp will glow at
-its maximum brilliancy. Since the flickering of the lamp is dependent
-upon the difference in frequency, the machines should not be thrown
-in parallel while this flickering exists. The nearer alternator
-approaches synchronism, in adjusting its speed, the slower the
-flickering, and when the flickering becomes very slow, the incoming
-machine may be thrown in the moment the lamp is dark by closing the
-switch. The machines are then in phase and tend to remain so, since
-if one slow down, the other will drive it as a motor.]
-
-     Now, if the load increase to such extent as to require the
-   service of the second alternator B, it must be switched in
-   parallel with A. In order that both machines may operate properly
-   in parallel, three conditions must be satisfied before they are
-   connected together, or else the one alternator will be short
-   circuited through the other, and serious results will undoubtedly
-   follow.
-
-Accordingly before closing main switch B, it is necessary that
-
-  1. The frequencies of both machines be the same;
-  2. The machines must be in synchronism;
-  3. The voltages must be the same.
-
-=Ques. How are the frequencies made the same?=
-
-Ans. By speeding up the alternator to be cut in, or change the speed
-of both until frequency of both machines is the same.
-
-[Illustration: FIG. 2,844.--Diagram of connections of General
-Electric automatic voltage regulator for several alternators running
-in parallel with exciters in parallel.]
-
-=Ques. How are the alternators synchronized or brought in phase?=
-
-Ans. The synchronism of the alternators is determined by employing
-some form of synchronizer, as by the single lamp method of fig.
-2,843, or the two lamp method of fig. 2,845.
-
-=Ques. In synchronizing by the one lamp method, when should the
-incoming machine be thrown in?=
-
-Ans. It is advisable to close the switch when the machines are
-approaching synchronism rather than when they are receding from it,
-that is to say, the instant the lamp becomes dark.
-
-[Illustration: FIG. 2,845.--Method of synchronizing with two lamps;
-_dark lamp method_. The two synchronizing lamps are connected as
-shown, and each must be designed to supply its rated candle power
-at the normal voltage developed by the alternators. Now since the
-alternators are both running under normal field excitation the left
-hand terminals of each of them will alternately be positive and
-negative in polarity, while the right hand terminals are respectively
-negative and positive in polarity. If, however, the alternators be
-in phase with each other, the left hand terminals of both of them
-will be positive while the right hand terminals are negative, and
-when the left hand terminals of both machines are negative the right
-hand terminals will be positive. Hence, when the machines are in
-phase there will be no difference of pressure between the left hand
-terminals or between the right hand terminals of the two machines.
-Hence, if the synchronizing lamps be connected as shown, both will
-be dark. The instant there is a difference of phase, both lamps
-will glow attaining full candle power when the difference of phase
-has reached a maximum. As the alternators continue to come closer
-in step, the red glow will gradually fade away until the lamps
-become dark. Then the switch may be closed, thereby throwing the
-two machines in parallel. If the intervals between the successive
-lighting up of the lamps are of short duration it is advisable to
-wait until these become longer even though the other conditions are
-satisfied, because where the phases pass each other rapidly there is
-a greater possibility of not bringing them together at the proper
-instant. An interval of not less than five seconds should therefore
-be allowed between the successive lighting up of the lamps, before
-closing the switch.]
-
-[Illustration: FIG. 2,846.--Inductor type synchroscope. This type
-is especially applicable where pressure transformers are already
-installed for use with other meters. As it requires only about ten
-apparent watts it may be used on the same transformers with other
-meters. There are three stationary coils, N, M and C, and a moving
-system, comprising an iron armature, A, rigidly attached to a shaft
-suitably pivoted and mounted in bearings. A pointer is also attached
-to the shaft. The moving system is balanced and is not subjected
-to any restraining force, such as a spring or gravity control. The
-axes of the coils N and M are in the same vertical plane, but 90
-degrees apart, while the axis of C is in a horizontal plane. The
-coils N and M are connected in "split phase" relation through an
-inductive resistance P and non-inductive resistance Q, and these two
-circuits are parallel across the bus bar terminals 3 and 4 of the
-synchroscope. Coil C is connected through a non-inductive resistance
-across the upper machine terminals 1 and 2 of the synchroscope. =In
-operation=, current in the coil C magnetizes the iron core carried
-by the shaft and the two projections, marked A and "iron armature."
-There is however, no tendency to rotate the shaft. If current be
-passed through one of the other coils, say M, a magnetic field will
-be produced parallel with its axis. This will act on the projections
-of the iron armature, causing it to turn so that the positive and
-negative projections assume their appropriate position in the field
-of the coil M. A reversal of the direction in both coils will
-obviously not affect the position of the armature, hence alternating
-current of the same frequency and phase in the coils C and M cause
-the same directional effect upon the armature as if direct current
-were passed through the coils. If current lagging 90 degrees behind
-that in the coils M and C be passed through the coil N, it will cause
-no rotative effect upon the armature, because the maximum value of
-the field which it produces will occur at the instant when the pole
-strength of the armature is zero. The two currents in the coils M and
-N produce a shifting magnetic field which rotates about the shaft as
-an axis. As all currents are assumed to be of the same frequency, the
-rate of rotation of this field is such that its direction corresponds
-with that of the armature projections at the instant when the poles
-induced in them by the current in the coil C are at maximum value,
-and the field shifts through 180 degrees in the same interval as is
-required for reversal of the poles. This is the essential feature of
-the instrument, namely, that the armature projections take a position
-in the rotating magnetic field which corresponds to the direction of
-the field at the instant when the projections are magnetized to their
-maximum strength by their current in the coil C. If the frequency
-of the currents in the coils which produce the shifting field be
-less than that in the coil which magnetized the armature, then the
-armature must turn in order that it may be parallel with the field
-when its poles are at maximum strength.]
-
-=Ques. What are the objections to the one lamp method?=
-
-Ans. The filament of the lamp may break, and cause darkness, or the
-lamp may be dark with considerable voltage as it takes over 20 volts
-to cause a 100 volt lamp to glow.
-
-=Ques. What capacity of single lamp must be used?=
-
-Ans. It must be good for twice the voltage of either machine.
-
-[Illustration: FIG. 2,847.--Brilliant lamp method of synchronizing.
-The synchronizing lamps are connected as shown, and must be of the
-alternator voltage. When the voltages are equal and the machines in
-phase, the difference of pressure between _a_ and a given point is
-the same as that between _a'_ and the same point; this obtains for
-_b_ and _b'_. Accordingly, a lamp connected across _a b'_ will burn
-with the same brilliancy as across _a' b_; the same holds for the
-other lamp. When the voltages are the same and the phase difference
-is 180° the lamps are dark, and as the phase difference is decreased,
-the lamps glow with increasing brightness until at synchronism they
-glow with maximum brilliancy. Hence the incoming alternator should be
-thrown in at the instant of maximum brilliancy.]
-
-=Ques. What modification of the synchronizing methods shown in
-the accompanying illustrations is necessary when high pressure
-alternators are used?=
-
-Ans. Step down transformers must be used between the alternators and
-the lamps to obtain the proper working voltages for the lamps.
-
-[Illustration: FIG. 2,848.--Synchronizing with high pressure
-alternators; dark and brilliant lamp methods. In both methods the
-primaries of the transformers are connected in the same way across
-the terminals of the alternators as shown. In the dark lamp method,
-the connections between the secondary coils of the transformers must
-be made so that when each is subjected to the same conditions the
-action of the one coil opposes that of the other as in the dark lamp
-method; then, if the transformers be both of the same design, there
-will be no voltage across the lamps when the alternators are in phase
-with each other. If the ratio of each transformer is such as to give,
-for example, 100 volts across its secondary terminals, then the two
-incandescent lamps since they are joined together in series must
-each be designed for 100 volts. One 200 volt lamp could be used in
-either method in place of the two 100 volt lamps. When, therefore,
-the alternators are directly opposite in phase to each other, both
-the lamps will burn brightly; as the alternators come together in
-phase the lamps will produce less and less light, until when the
-machines are exactly in phase no light will be emitted at all, at
-which instant the incoming alternator should be thrown in. It must
-be evident, if the transformer secondary connections are arranged as
-in the brilliant lamp method, so that they do not oppose each other,
-the lamps will be at maximum brilliancy when the alternators are in
-phase and dark when the phase difference is 180°, assuming of course
-equalized voltage.]
-
-=Ques. How is the voltage of an incoming machine adjusted so that it
-will be the same as the one already in operation?=
-
-Ans. By varying the field excitation with a rheostat in the
-alternator field circuit.
-
-=Ques. How may two or more alternators be started simultaneously?=
-
-Ans. After bringing each of them up to its proper speed so as to
-obtain equal frequencies, the main switches may be closed, thereby
-joining their armature circuits in parallel. As yet, however, their
-respective field windings have not been supplied with current, so
-that no harm can result in doing this. The exciters of these machines
-after being joined in parallel, should then be made to send direct
-current simultaneously through the field windings of the alternators,
-and from this stage on the directions previously given may be
-followed in detail.
-
-=Ques. What are the conditions when two or more alternators are
-directly connected together?=
-
-Ans. If rigidly connected together, or directly connected to the same
-engine, they must necessarily run in the same manner at all times.
-
-     When machines connected in this way are once properly adjusted
-   so that they are in phase with each other, their operation in
-   parallel is even a simpler task than when they are all started
-   together but are not directly connected.
-
-=Ques. When an alternator is driven by a gas engine, what provision
-is sometimes made to insure successful operation in parallel?=
-
-Ans. An amortisseur winding is provided to counteract the tendency to
-"hunting."
-
-[Illustration: FIG. 2,849.--Diagram of Lincoln Synchronizer. =In
-construction=, a stationary coil F, has suspended within it a coil A,
-free to move about an axis in the planes of both coils and including
-a diameter of each. If an alternating current be passed through both
-coils, A, will take a position with its plane parallel to F. If now
-the currents in A and F be reversed with respect to each other, coil
-A will take up a position 180° from its former position. Reversal
-of the relative directions of currents in A and F is equivalent to
-changing their phase relation by 180°, and therefore this change
-of 180° in phase relation is followed by a corresponding change of
-180° in their mechanical relation. Suppose now, instead of reversing
-the relative direction of currents in A and F, the change in phase
-relation between them be made gradually and without disturbing the
-current strength in either coil. It is evident that when the phase
-difference between A and F reaches 90°, the force between A and F
-will become reduced to zero, and a movable system, of which A may
-be made a part, is in condition to take up any position demanded
-by any other force. Let a second number of this movable system
-consist of coil B, which may be fastened rigidly to coil A, with its
-plane 90° from that of coil A, and the axis of A passing through
-diameter of B. Further, suppose a current to circulate through B,
-whose difference in phase relation to that in A, is always 90°. It
-is evident under these conditions that when the difference in phase
-between A and F is 90°, the movable system will take up a position,
-such that B is parallel to F, because the force between A and F is
-zero, and the force between B and F is a maximum; similarly when the
-difference in phase between B and F is 90°, A will be parallel to F.
-That is, beginning with a phase difference between A and F of zero
-a phase change of 90° will be followed by a mechanical change on a
-movable system of 90°, and each successive change of 90° in phase
-will be followed by a corresponding mechanical change of 90°. For
-intermediate phase relation, it can be proved that under certain
-conditions the position of equilibrium assumed by the movable element
-will exactly represent the phase relations. That is, with proper
-design, the mechanical angle between the plane of F and that of A
-and also between the plane of F and that of B, is always equal to
-the phase angle between the current flowing in F and those in A and
-B respectively. =As commercially constructed= coil F consists of a
-small laminated iron field magnet with a winding whose terminals
-are connected with binding posts. The coils A and B are windings
-practically 90° apart on a laminated iron armature pivoted between
-the poles of the magnet. These two windings are joined, and a tap
-from the junction is brought out through a slip ring to one of two
-other binding posts. The two remaining ends are brought out through
-two more slip rings, one of which is connected to the remaining
-binding post, through a non-inductive resistance, and the other
-to the same binding post through an inductive resistance. A light
-aluminum hand attached to the armature shaft marks the position
-assumed by the armature.]
-
-=Ques. What is the action of the amortisseur winding?=
-
-Ans. Any sudden change in the speed of the field, generates a current
-in the amortisseur winding which resists the change of velocity that
-caused the current.
-
-     The appearance of an amortisseur winding is shown in the cut
-   below (fig. 2,850) illustrating the field of a synchronous
-   condenser equipped with amortisseur winding.
-
-[Illustration: FIG. 2,850.--General Electric field of synchronous
-condenser provided with amortisseur winding. Hunting is accompanied
-by a shifting of flux across the face of the pole pieces due to the
-variation in the effect of armature reaction on the main field flux
-as the current varies and the angular displacement between the field
-and armature poles is changed. Copper short circuited collars placed
-around the pole face have currents induced in them by this shifting
-flux, which have such a direction as to exert a torque tending to
-oppose any change in the relative position of the field and armature.
-This action is similar to that of the running torque of an induction
-motor and the damping device has been still further developed until
-in its best form it resembles the armature winding of a "squirrel
-cage" induction motor. The pole pieces are in ducts, and low
-resistance copper bars placed in them with their ends joined by means
-of a continuous short circuiting ring extending around the field.
-Such a device has proven very effective in damping out oscillations
-started from any cause, the same winding doing duty as a damping
-device and to assist the starting characteristics.]
-
-=Ques. How are three phase alternators synchronized?=
-
-Ans. In a manner similar to the single phase method.
-
-     Thus the synchronizing lamps may be arranged as in fig. 2,581,
-   which is simply an extension of the single phase method.
-
-=Ques. Are three lamps necessary?=
-
-Ans. Only to insure that the connections are properly made, after
-which one lamp is all that is required.
-
-=Ques. How is it known that the connections of fig. 2,851 are
-correct?=
-
-Ans. If, in operation, the three lamps become bright or dark
-_simultaneously_, the connections are correct; if this action takes
-place _successively_, the connections are wrong.
-
-     If wrong, transpose the leads of one machine until simultaneous
-   action of the lamps is secured.
-
-[Illustration: FIG. 2,851.--Method of synchronizing three phase
-alternators with, three lamps, being an extension of the single phase
-method.]
-
-=Ques. What is the disadvantage of the lamp method of synchronizing?=
-
-Ans. Lack of sensitiveness.
-
-=Ques. Which is the accepted lamp method, dark or brilliant?=
-
-Ans. In the United States it is usual to make the connections for
-a dark lamp at synchronism, while in England the opposite practice
-obtains.
-
-     With the dark lamp method, the breaking of a filament might
-   cause the machines to be connected with a great phase difference,
-   whereas, with the brilliant lamp it is difficult to determine the
-   point of maximum brilliancy. This latter method, therefore may be
-   called the safer.
-
-=Ques. What may be used in place of lamps for synchronizing?=
-
-Ans. Some form of synchroscopes, or synchronizers.
-
-=Ques. How does the Lincoln synchronizer work?=
-
-Ans. The construction is such that a hand moves around a dial so
-that the angle between the hand and the vertical is always the phase
-angle between the two sources of electric pressure to which the
-synchronizer is connected.
-
-     If the incoming alternator be running too slow, the hand
-   deflects in one direction, if too fast, in the other direction.
-   When the hand shows no deflection, that is, when it stands
-   vertical, the machines are in phase. A complete revolution of the
-   hand indicates a gain or loss of one cycle in the frequency of the
-   incoming machine, as referred to the bus bars.
-
-=Cutting Out Alternator.=--When it is desired to cut out of circuit
-an alternator running in parallel with others, the method of
-procedure is as follows:
-
-  1. Reduce driving power until the load has been transferred
-      to the other alternators, adjusting field rheostat to obtain
-      minimum current;
-  2. Open main switch;
-  3. Open field switch.
-
-=Ques. What precaution should be taken?=
-
-Ans. _Never_ open field switch before main switch.
-
-[Illustration: FIG. 2,852.--General Electric 500 kw., horizontal
-mixed pressure Curtis turbine connected to a 500 kw. dynamo. In
-a Curtis turbine it is not necessary to use the whole periphery
-of the first stage for low pressure steam nozzles. A section can
-be partitioned off and equipped with special expanding nozzles to
-receive steam at high pressure direct from the boilers. Such nozzles
-deliver their steam against the same wheel as do the low pressure
-nozzles, but occupy only a small portion of its periphery. The steam
-is expanded in these nozzles from high pressure all the way down
-to the normal pressure of the first stage, and in such expansion
-acquires a high velocity and consequently contains a great deal
-of energy--much more than does an equal quantity of low pressure
-steam. In consequence of this, high pressure steam is used with
-a far lower water rate than is obtained with low pressure steam,
-or with high pressure steam reduced to low pressure in a reducing
-valve. This construction is called "mixed pressure." Its function
-is the same as that of the reducing valve, that is, it makes up
-for a deficiency of low pressure steam by drawing direct on the
-boilers. With this construction, the full power of the turbine can be
-developed with: All low-pressure steam, all high pressure steam, or,
-any necessary proportion of steam of each pressure. Furthermore, the
-transition from all low pressure to all high pressure, through all
-the conditions intermediate between these extremes, is provided for
-automatically by the turbine governor; a deficiency of low pressure
-steam causes the high pressure nozzles to open automatically.]
-
-=Ques. What is the ordinary method of cutting out an alternator?=
-
-Ans. The main switch is usually opened without any preliminaries.
-
-=Ques. What is the objection to this procedure?=
-
-Ans. It suddenly throws all the load on the other alternators, and
-causes "hunting."
-
-=Ques. What forms of drive are especially desirable for running
-alternators in parallel, and why?=
-
-Ans. Water turbine or steam turbine because of the uniform torque,
-thus giving uniform motion of rotation.
-
-     With reciprocating engines, the crank effect is very variable
-   during the revolution, resulting in pulsations driving the
-   alternator too fast or too slow, and causing cross current between
-   the alternators.
-
-=Ques. Is a sluggish, or a too sensitive governor preferable on an
-engine driving alternators in parallel?=
-
-Ans. A sluggish governor.
-
-=Alternators in Series.=--Alternators are seldom if ever connected
-in series, for the reason that the synchronizing tendency peculiar
-to these machines causes them to oppose each other and fall out of
-phase when they are joined together in this way. If, however, they
-be directly connected to each other, or to an engine, so that they
-necessarily keep in phase at all times, and thus add their respective
-voltages instead of counteracting them, series operation is possible.
-
-            NOTE.--According to the practice of the General
-          Electric Co., 2½ degrees of phase difference
-          from a mean is the limit allowable in ordinary
-          cases. It will, in certain cases, be possible to
-          operate satisfactorily in parallel, or to run
-          synchronous apparatus from machines whose angular
-          variation exceeds this amount, and in other cases
-          it will be easy and desirable to obtain a better
-          speed control. The 2½ degree limit is intended to
-          imply that the maximum departure from the mean
-          position during any revolution shall not exceed
-          2½ ÷ 360 of an angle corresponding to two poles
-          of a machine. The angle of circumference which
-          corresponds to the 2½ degree of phase variation
-          can be ascertained by dividing 2½ by ½ the
-          number of pole; thus, in a 20 pole machine, the
-          allowable angular variation from the mean would
-          be 2½ ÷ 10 = ¼ of one degree.
-
-[Illustration: FIG. 2,853.--Diagram of connections for synchronizing
-two compound wound three phase alternators. A and A' are the
-armatures of the two machines, the fields of which are partly
-separately excited, the amount of excitation current being controlled
-by the series compounding rheostats B and B', which form a stationary
-shunt. It is assumed that the alternator A is connected to the
-bus bars 1, 2, and 3, by the switch 1S. If an increase make it
-necessary to introduce the alternator A', it is first run up to
-speed and excited to standard pressure by its exciter, and then
-the double plug switch 3S is closed, connecting the primary of the
-station transformer T and T' with the bus bars through the secondary
-coil, so that the synchronizing lamps light up when the secondary
-circuit is closed through the single pole switch 4S. The primary of
-the station transformer T is thus excited through the double pole
-switch 5S, connecting it with the outer terminals of the armature
-A'. The two alternators will now work in opposition to each other
-upon the synchronizing lamps, the transformer T being operated by
-the new alternator A' through the switch 2S, and the transformer
-T' being operated by the working alternator A, from the bus bars.
-If the new alternator be not in step with the working alternator,
-the synchronizing lamps will glow, growing brighter and dimmer
-alternately with greater or lesser rapidity. In this case, the
-armature speed of the new alternator must be controlled in such a
-manner that the brightening and dimming will occur more and more
-slowly, until the lamps cease to glow or remain extinguished for
-a decided interval of time. The extinction of the light is due to
-the disappearance of the secondary current, and indicates that
-the alternators are in step. The switch 2S should now be thrown,
-thus coupling the two machines electrically, and both of them will
-continue to operate in step. The double pole equalizer switch 6S
-should now be closed, connecting the two field windings in parallel
-and equalizing the compounding, so that any variations of load will
-affect the two alternators equally. After the alternators have been
-connected in parallel, the switches 4S and 5S, may be opened leaving
-the switch 3S closed, to operate the switchboard lamps K, K, as pilot
-lights from the bus bars.]
-
-=Transformers.=--These, as a whole, are simple in construction, high
-in efficiency, and comparatively inexpensive. Their principles of
-operation are also readily understood.
-
-The efficiency of a transformer, that is, the ratio between full
-load primary and full load secondary is greatest when the load on it
-is such that the sum of the constant losses equals the sum of the
-variable losses.
-
-     In general, transformers designed for high frequencies and
-   large capacities are more efficient than those designed for
-   low frequencies and small capacities. As a whole, however, a
-   transformer leaves but little to be desired as regards efficiency,
-   a modern 60 cycle transformer of 50 kilowatts capacity or more
-   possesses an efficiency of approximately 98 per cent. at full load
-   and an efficiency of about 97 per cent. at half load.
-
-=Ques. How should a transformer be selected, with respect to
-efficiency?=
-
-Ans. One should be chosen, whose parts are so proportioned that the
-point of maximum efficiency occurs at that load which the transformer
-usually carries in service.
-
-     In many alternating current installations, comparatively light
-   loads are carried the greater part of the time, the rated full
-   load or an overload being occurrences of short durations. For such
-   purposes special attention should be given to the designing or
-   selecting of transformers having low core losses rather than low
-   resistance losses, because the latter are then of relatively small
-   importance.
-
-=Ques. What kind of efficiency is the station manager interested in?=
-
-Ans. The "all day efficiency."
-
-     This expression, as commonly met with in practice, denotes
-   _the percentage that the amount of energy actually used by the
-   consumer is of the total energy supplied to his transformer during
-   24 hours_. The formula for calculating the all day efficiency of
-   a transformer is based upon the supposition that the amount of
-   energy used by the consumer during 24 hours is equivalent to full
-   load on his transformer during five hours and is as follows:
-
-                  5w
-         E = -------------
-             24c + 5r + 5w
-  where
-        E = the all day efficiency of the transformer,
-        w = the full load in watts on the primary,
-        c = the core loss in watts,
-        r = the resistance loss in watts.
-
-[Illustration: FIG. 2,854.--Performance curves of Westinghouse air
-blast 550 kw, 10,500 volt transformer, 3,000 alternations.]
-
-=Ques. What are the usual all day efficiencies?=
-
-Ans. The average is about 85 per cent. for those of 1 kilowatt
-capacity, 92 per cent. for those of 5 kilowatts capacity, 94 per
-cent. for those of 10 kilowatts capacity, and about 94.5 per cent.
-for those of 15 kilowatts capacity.
-
-=Ques. What becomes of the energy lost by a transformer?=
-
-Ans. It reappears as heat in the windings and core.
-
-     This heat not only increases the resistances of the windings and
-   core, producing thereby a further increase of their respective
-   losses, but in addition causes in time a peculiar effect on the
-   iron core which is intensified by the reversals of magnetism
-   constantly going on within it.
-
-     After about two years' service, the iron apparently becomes
-   fatigued or tired, and this phenomenon is called aging of the
-   iron. Since the life of the transformer depends to a great extent
-   upon this factor, the conditions responsible for its existence
-   should as far as possible be removed. Means must therefore be
-   provided in the construction to radiate the heat as quickly as it
-   is generated.
-
-=Ques. What kind of oil is used in oil cooled transformers?=
-
-Ans. Mineral oil.
-
-[Illustration: FIG. 2,855.--General arrangement of air blast
-transformers and blowers.]
-
-=Ques. How is it obtained?=
-
-Ans. By fractional distillations of petroleum unmixed with any other
-substances and without subsequent chemical treatment.
-
-=Ques. What is the important requirement for transformer oil?=
-
-Ans. It should be free from moisture, acid, alkali or sulphur
-compounds.
-
-=Ques. How may the presence of moisture be determined?=
-
-Ans. By thrusting a red hot iron rod in the oil; if it "crackle,"
-moisture is present.
-
-=Ques. Describe the Westinghouse method of drying oil.=
-
-Ans. It is circulated through a tank containing lime, and afterwards,
-through a dry sand filter.
-
-=Ques. What is the objection to heating the oil (raising its
-temperature slightly above boiling point of water) to remove the
-moisture?=
-
-Ans. The time consumed (several days) is excessive.
-
-[Illustration: FIG. 2,856.--Small Curtis turbine generator set as
-made by the General Electric Co., in sizes from 5 kw., to 300 kw.
-It can be arranged to operate either condensing or non-condensing,
-and at any steam pressure above 80 lbs. for the smaller sizes and
-100 lbs. for the larger. There are only two main bearings. A thrust
-bearing, consisting of roller bearings and running between hardened
-steel face washers located at either end of the main bearings is
-provided solely for centering the rotor so as to equalize the
-clearance. A centrifugal governor is provided (in the smaller sizes)
-completely housed, and mounted directly on the main shaft end. It
-controls a balanced poppet valve through a bell crank. In the larger
-sizes (75 kw. and above) the governor is mounted on a vertical
-secondary shaft geared to the main shaft and controls a cam shaft
-which opens or closes a series of valves in rotation, admitting the
-steam to different sections of the first stage nozzles. In this
-way throttling of the steam is avoided. There is also an emergency
-governor which closes the throttle valve in the event of the speed
-reaching a predetermined limit. The speeds of operation range from
-5,000 R.P.M. for the smallest size to 1,500 R.P.M. for the largest.
-The lubrication system is enclosed and is automatic. Air leakage
-where the shaft passes through the wheel casing is prevented by steam
-seal.]
-
-=Ques. What effect has moisture?=
-
-Ans. It reduces the insulation value of the oil. .06 per cent. of
-moisture has been found to reduce the dielectric strength of oil
-about 50 per cent. "dry" oil will withstand a pressure of 25,000
-volts between two 9½ inch knobs separated .15 inch.
-
-=Ques. What is understood by transformer regulation?=
-
-Ans. It is the difference between the secondary voltage at no load
-and at full load, and is generally expressed as a percentage of the
-secondary voltage at no load.
-
-=Ques. What governs its value?=
-
-Ans. The resistance and reactance of the windings.
-
-[Illustration: FIG. 2,857.--Cut off coupling for power transmission
-by line shafting. It is used to cut off a driving shaft from a driven
-shaft. Its use obviates the use of a _quill_, such as is shown in
-fig. 2,858.]
-
-=Ques. How may the regulation be improved?=
-
-Ans. By decreasing the resistances of the windings by employing
-conductors of greater cross section, or decreasing their reactance by
-dividing the coils into sections and closely interspersing those of
-the primary between those of the secondary.
-
-            NOTE.--_The term_ ="regulation"= as here used
-          is synonymous with "drop." The _voltage drop_
-          in a transformer denotes the drop of voltage
-          occurring across the secondary terminals of a
-          transformer with load. This drop is due to two
-          causes: 1, the resistance of the windings; and
-          2, the reactance or magnetic leakage of the
-          windings. On non-inductive load, the reactive
-          drop, being in quadrature, produces but a slight
-          effect, but on inductive loads it causes the
-          voltage to drop, and on _leading current loads_
-          it causes the voltage to rise. As the voltage
-          drop of a good transformer is very small even
-          on inductive load, direct accurate measurement
-          is difficult. It is best to measure the copper
-          loss with short circuited secondary by means of
-          a wattmeter, and at the same time the voltage
-          required to drive full load current through. From
-          the watts, the resistance drop can be found, and
-          from this and the impedance voltage, the reactive
-          drop may be calculated. From these data a simple
-          vector diagram will give, near enough for all
-          practical purposes, the drop for any power
-          factor, or the following formula may be used
-          which has been deduced from the vector diagram.
-               _________________________
-          D = √(W + X)^{2} + (R + P)^{2} - 100 where R
-          = % resistance drop; X = % reactive drop; P = %
-          power factor of load; W = % wattless factor of
-                 ________
-          load (√1 - P^{2}); D = % resultant secondary
-          drop. For non-inductive loads where P = 100 and W
-                    _____________________
-          = 0, D = √X^{2} + (100 + R)^{2} - 100. In the
-          case of leading currents it should be considered
-          negative.
-
-     In transformers where there is a great difference in voltage
-   between the primary and secondary windings, however, this remedy
-   has its limitations on account of the great amount of insulation
-   which must necessarily be used between the windings, and which
-   therefore causes the distances between them to become such as to
-   cause considerable leakage of the lines of force.
-
-=Ques. How does the regulation vary for different transformers, and
-what should be the limit?=
-
-Ans. Those of large capacity usually have a better regulation than
-those of small capacity, but in no case should its value exceed 2 per
-cent.
-
-[Illustration: FIG. 2,858.--Quill drive. This is the proper
-transmission arrangement substitute for heavy service, requiring
-large pulleys, sheaves, gears, rotors, etc. It is a hollow shaft
-supported by independent bearings. The main driving shaft running
-through the quill is thus relieved of all transverse stresses. The
-power is transmitted to the quill by means of a friction or jaw
-clutch. When the clutch is thrown out the pulley or sheave stands
-idle and the driving shaft revolves freely within the quill. As there
-is no contact between moving parts there is no wear. Jaw clutches
-should be used for drives demanding positive angular displacement.
-They can only be thrown in and out of engagement when at rest. All
-very large clutch pulleys, sheaves, or gears designed to run loose on
-the line shaft are preferably mounted on quills. The letters A, B, C,
-etc., indicate the dimensions to be specified in ordering a quill.]
-
-=Ques. What advantages have shell type transformers over those of the
-core type?=
-
-Ans. They have a larger proportion of core surface exposed for
-radiation of heat, and a shorter magnetic circuit which reduces the
-tendency for a leakage of the lines of force into the air.
-
-     Both types have advantages and disadvantages as compared with
-   the other. In the shell type, there is less magnetic leakage, but
-   also less surface exposed for radiation, and greater difficulty in
-   providing efficient insulation between the two circuits; in the
-   core type there is more surface exposed for radiation and less
-   difficulty in insulating the windings, but there is also a great
-   leakage of the lines of magnetic force into the outer air.
-
-=Ques. How are the windings usually arranged?=
-
-Ans. As a rule, there is only one primary winding but the secondary
-winding is generally divided into two equal sections, the four
-terminals of which are permanently wired to four connection blocks
-which may be connected so as to throw the secondary sections either
-in parallel or in series with each other at will.
-
-=Ques. What is necessary for satisfactory operation of transformers
-in parallel?=
-
-Ans. They must be designed for the same pressures and capacities,
-their percentages of regulation should be the same and they must have
-the same polarity at a given instant.
-
-     One may satisfy himself as to the first of these conditions by
-   examining the name plates fastened to the transformers, whereon
-   are stamped the values of the respective pressures and capacities
-   of each.
-
-     Although equal values of regulation is given as one of the
-   conditions to be satisfied, transformers may be operated in
-   parallel when their percentages of regulation are not the same.
-   Ideal operation, however, can be attained only under the former
-   state of affairs. Suppose, for instance, a transformer having a
-   regulation of two per cent. be operated in parallel with another
-   of similar size and design but having a regulation of one per
-   cent. The secondary pressures of these transformers at no load
-   will of course be the same, but at full load if the secondary
-   pressure of the one be 98 volts, that of the other will be 99
-   volts. There will, therefore, be a difference of pressure of one
-   volt between them which will tend to force a current backward
-   through the secondary winding of the transformer delivering 98
-   volts. This reversed current, although comparatively small in
-   value, lowers the efficiency of the installation by causing a
-   displacement of phase and a decrease in the combined power factor
-   of the transformers.
-
-=Ques. Describe the polarity test.=
-
-Ans. The test for polarity consists in joining together by means of a
-fuse wire, a terminal of the secondary winding of each transformer,
-and then with the primary windings supplied with normal voltage,
-connecting temporarily the remaining terminals of the secondary
-windings. The melting of the fuse wire thus connected indicates that
-the secondary terminals joined together are of opposite polarities,
-and that the connections must therefore be reversed, whereas if the
-fuse wire do not melt, it shows that the proper terminals have been
-joined and that the connections may be made permanent.
-
-[Illustration: FIG. 2,859.--Single overhung tangential water wheel
-equipped with Doble ellipsoidal buckets. The central position of the
-front entering wedge or lip of the bucket is cut away in the form of
-a semi-circular notch, which allows a solid circular water jet to
-discharge upon the central dividing wedge of the bucket without being
-split in a horizontal plane.]
-
-     The object of this test is, obviously, not to determine the
-   exact polarity of each secondary terminal, but merely to indicate
-   which of them are of the same polarity.
-
-[Illustration: FIG. 2,860.--Motor generator exciter set driven by
-a Pelton-Doble tangential water wheel. The water wheel runner is
-mounted on the shaft overhung and the jet is regulated by either a
-hand actuated or governor controlled needle nozzle. The speed of the
-water wheel is equivalent to the synchronous speed of the induction
-motor, hence, the latter floats on the line, and under certain
-conditions may perform the functions of an alternator by feeding into
-the circuit, should the water wheel tend to operate above synchronous
-speed. Should any interruption to the operation of the wheel occur,
-causing a diminution of speed, the induction motor would drop back
-to full load speed and take up the exciter load, resulting in no
-appreciable drop of exciter voltage. The only variation of speed
-possible is dependent upon the "slip" of the motor. Where two or more
-exciter sets are employed in the station, an advantageous arrangement
-embraces the installation of a water wheel driven motor generator set
-and an exciter set, consisting of merely the direct current generator
-and water wheel. The induction motor being electrically tied into
-the circuit, the possibility of a runaway of the water wheel is
-eliminated, since its speed can only slightly exceed the synchronous
-speed of the system.]
-
-=Motor Generators.=--In motor generator sets, either the shunt or
-series wound type of motor may be employed at the power producing
-end of the set, but the field of the generator is either shunt
-or compound wound, depending upon whether or not it is desired
-to maintain or to raise the secondary voltage near full load. In
-either case a rheostat introduced in the shunt field winding of the
-generator will be found very essential. Both generator and motor are
-so mounted on the base that their respective commutators are at the
-outer ends of the set. By this means ample space surrounds all of the
-working parts, and repairs can readily be made.
-
-Motor generators are frequently used as boosters to raise or boost
-the voltage near the extremities of long distance, direct current
-transmission lines. Of these, electric railway systems in which it is
-desired to extend certain of the longer lines, form a typical example.
-
-[Illustration: FIG. 2,861.--Automatically governed Pelton-Doble
-tangential water wheel driving exciter dynamo. The water wheel is
-mounted on one end of the shaft, while the opposite end is extended
-to carry a fly wheel of suitable design to compensate for the low fly
-wheel effect of the direct current armature. Two bearings support
-the shaft which carries the rotating elements of the unit. A needle
-nozzle actuated by a direct motion Pelton-Doble governor (designed
-for operation by either oil or water pressure) maintains constant
-speed.]
-
-Owing to the great cost of changing such a system over to one
-employing alternating current, or storage batteries, or of
-constructing an additional power station, these solutions of the
-problem are usually at variance with good judgment and the amount
-of money at hand. The choice then remains between the purchase of
-additional wire for feeders, the connection of a booster in the old
-feeders, or the installation of both larger feeders and a booster.
-Of these, it is generally found that either the second or the third
-mentioned alternative meets the conditions most satisfactorily.
-
-     A booster installed in a railway system for the purpose just
-   mentioned, would have a series wound motor, and the conditions
-   to which it must conform would be as follows: The motor having a
-   series winding must provide for the full feeder current passing
-   through both armature and field windings.
-
-     Owing to the varying loads on a railway system, due to the
-   frequent starting and stopping of cars, the feeder current varies
-   between zero and some such value as 150 amperes. This fluctuation
-   of current through the field winding will, in ordinary cases, vary
-   the magnetization of the pole pieces from zero almost to the point
-   of saturation; that is, the maximum feeder current will so nearly
-   fill the magnet cores with lines of force that it would be quite
-   difficult to cause more lines of magnetic force to pass through
-   them.
-
-     So long as the point of saturation is not reached, however, the
-   proportion of current to field strength remains constant, and
-   therefore the ratio of amperes to volts will not vary.
-
-     The severe fluctuations of the feeder current would, if the
-   motor were shunt or compound wound, cause most serious sparking
-   and various other troubles, but in a series motor where the back
-   ampere turns on the armature that react on the field vary in
-   precisely the same proportion as the ampere turns in the field,
-   there exists at all times a tendency to balance the active forces
-   and produce satisfactory operation. If, however, the field magnet
-   cores be very large, they cannot so quickly respond, magnetically,
-   to changes in the strength of the current, and there is then
-   greater liability of the armature reaction momentarily weakening
-   the field and thereby producing temporary sparking.
-
-=Ques. Are motor generators always composed of direct current sets?=
-
-Ans. No.
-
-=Ques. Describe conditions requiring a different combination.=
-
-Ans. For purposes where for instance direct currents of widely
-different voltages are to be obtained from an alternating current
-circuit, and it is desired to install but one set, a motor generator
-consisting of an alternating current motor such as an induction
-motor, and a dynamo must necessarily be employed.
-
-     In such sets, it is common to find both motor and dynamo
-   armatures mounted on a common shaft, and the respective field
-   frames resting on a single base, although for connection on a
-   very high pressure alternating current circuit, separate armature
-   shafts insulated from each other but directly connected together,
-   and separate bases resting on a single foundation, are usually
-   employed to afford the highest degree of insulation between the
-   respective circuits of the two machines.
-
-=Ques. What is the objection to a set composed of alternating current
-motor and alternator?=
-
-Ans. The commercial field that would be naturally covered by such a
-set is better supplied by a transformer.
-
-=Ques. Why?=
-
-Ans. Because a transformer contains no moving parts, and is therefore
-simpler in construction, cheaper in price, and less liable to get out
-of order.
-
-=Dynamotors.=--A dynamotor differs from a motor generator in that
-the motor armature and the generator armature are combined into one,
-thereby requiring but one field frame. Since the motor and generator
-armature windings are mounted on a single core, the armature reaction
-due to the one winding is neutralized by the reaction caused by the
-other winding. There is, consequently, little or no tendency for
-sparking to occur at the brushes, and they therefore need not be
-shifted on this account for different loads.
-
-=Ques. How is a dynamotor usually constructed?=
-
-Ans. It is usually built with two pole pieces which are shunt wound.
-
-=Ques. Why does the voltage developed fall off slightly under an
-increase of load?=
-
-Ans. Because a compound winding cannot be provided.
-
-[Illustration: FIGS. 2,862 and 2,863.--Method of putting on belts
-when the driver is in motion, and device used. The latter is called a
-_belt slipper_, and consists, as shown in fig. 2,862, of a cone and
-shield, which revolve upon the stem, B, thus yielding easily to the
-pull of the belt. A staff or handle C of any convenient length can be
-fastened to the socket. The mode of operation is illustrated in fig.
-2,863, which is self explanatory.]
-
-=Ques. Describe the armature construction and operation.=
-
-Ans. It consists of two separate windings; one of which is joined to
-a commutator mounted on one side of the armature for motor purposes,
-and the other to the commutator on the other side of the armature for
-generator purposes.
-
-     By means of two studs of brushes pressing on the motor
-   commutator, current from the service wires is fed into the winding
-   connected to this commutator, and since the shunt field winding
-   is also excited by the current from the service wires, there is
-   developed in the generator winding on the rotating armature a
-   direct voltage which is proportional to the speed of rotation of
-   the armature in revolutions per second, the number of conductors
-   in series which constitute the generator winding, and the total
-   strength of the field in which the armature revolves. This
-   pressure causes current to pass through the generator winding and
-   the distributing circuit when the distributing circuit to which
-   this winding is connected by means of its respective commutator,
-   brushes, etc., is closed.
-
-[Illustration: FIGS. 2,864 to 2,866.--Converter connections; fig.
-2,864 double delta connection; fig. 2,865 diametrical connection;
-fig. 2,866 two circuit single phase connection. For six phase
-synchronous converter, two different arrangements of the connections
-are generally used. One is called the _double delta_, and the other
-the _diametrical_ connection. Let the armature winding of the
-converter be represented by a circle as in figs. 2,864 and 2,865,
-and let the six equidistant points on the circumference represent
-collector rings, then the secondary of the supply transformers can
-be connected to the collector rings in a _double delta_ as in fig.
-2,864, or across diametrical pairs of pointer as in fig. 2,865.
-In the first instance, the voltage ratio is the same as for the
-three phase synchronous converter and simply consists of two delta
-systems. The transformers can also be connected in double star, and
-in such a case the ratio between the three phase voltage between
-the terminals of each star, and the direct voltage will be the same
-as for double delta, while the voltage of each transformer coil,
-or voltage to neutral, is 1 ÷ √3 times as much. With the
-diametrical connection, the ratio is the same as for the two ring
-single phase converter, it being analogous to three such systems.
-                                      _      _
-Hence six phase double delta E_{1} = √3E ÷ 2√2 = .612E.
-Six phase diametrical, E_{1} = E ÷ √2 = .707E. The ratio of the
-virtual_voltage E_{0} between any collector ring and the neutral
-point is always E_{0} = (E ÷ 2) √2 = .354E. For single phase
-synchronous converters, consisting of a closed circuit armature
-winding tapped at two equidistant points to the two collector rings
-the virtual voltage is 1 ÷ √2 × the direct current voltage. While
-such an arrangement of the single phase converter is the simplest,
-requiring only two collector rings, it is undesirable, especially
-for larger machines, on account of excessive heating of the armature
-conductors. In fig. 2,866, which represents the armature winding of a
-single phase converter, the supply circuits from two secondaries of
-the step down transformers are connected to four collector rings, so
-that the two circuits are in phase with each other, but each spreads
-over an arc of 120 electrical degrees instead of over 180 degrees
-as in the single phase circuit converter. To distinguish the two
-types, it is generally called a two circuit single phase synchronous
-converter. The virtual voltage E_{2} bears to the direct voltage the
-same relation as in the three phase converter, that is single phase
-two circuit, E_{1} = √3 ÷ 2√2 =.612E.]
-
-=Ques. How is a dynamotor started?=
-
-Ans. It is connected at its motor end and started in the same manner
-as any shunt wound motor on a constant pressure circuit.
-
-=Ques. What precautions should be taken in starting a dynamotor?=
-
-Ans. The necessary precautions are, to have the poles strongly
-magnetized before passing current through the motor winding on the
-armature; to increase gradually the current through this winding, and
-not to close the generating circuit until normal conditions regarding
-speed, etc., are established in the motor circuit.
-
-=Ques. How is the current developed in the machine regulated?=
-
-Ans. It can be regulated by the introduction of resistance in one or
-the other of the armature circuits, or by a shifting of the brushes
-around the commutator.
-
-=Ques. Are dynamotors less efficient than motor generators of a
-similar type?=
-
-Ans. No, they are more efficient.
-
-=Ques. Why?=
-
-Ans. Because they have only one field circuit and at least one
-bearing less than a motor generator.
-
-     A motor generator has at least three bearings, and occasionally,
-   four, where the set consists of two independent machines directly
-   connected together.
-
-=Rotary Converters.=--An important modification of the dynamotor
-is the rotary converter. This machine forms, as it were, a link
-between alternating and direct current systems, being in general a
-combination of an alternating current motor and a dynamo.
-
-[Illustration: FIG. 2,867.--Skeleton diagram showing wiring of
-alternator, exciter, transformer and converter. The cut also shows
-switchboard and connections.]
-
-It has practically become a fixture in all large electric railway
-systems and in other installations where heavy direct currents of
-constant pressure are required at a considerable distance from the
-generating plant. In such cases a rotary converter is installed
-in the sub-station, and being simpler in construction, higher in
-efficiency, more economical of floor space, and lower in price than
-a motor generator set consisting of an alternating current motor and
-a dynamo which might be used in its place, it has almost entirely
-superseded the latter machine for the class of work mentioned.
-
-=Ques. What is the objection to the single phase rotary converter?=
-
-Ans. It is not self-starting.
-
-=Ques. What feature of operation is inherent in a rotary converter?=
-
-Ans. A rotary converter is a "reversible machine."
-
-     That is to say, if it be supplied with direct current of the
-   proper voltage at its commutator end, it will run as a direct
-   current motor and deliver alternating current to the collector
-   rings. While this feature is sometimes taken advantage of in
-   starting the converter from rest, the machine is not often used
-   permanently in this way, its commercial application being usually
-   the conversion of alternating currents into direct currents.
-
-=Ques. How does a rotary converter operate when driven by direct
-current?=
-
-Ans. The same as a direct current motor, its speed of rotation
-depending upon the relation existing between the strength of the
-field and the direct current voltage applied.
-
-     If the field be weak with respect to the armature magnetism
-   resulting from the applied voltage, the armature will rotate at a
-   high speed, increasing until the conductors on the armature cut
-   the lines of force in the field so as to develop a voltage which
-   will be equal to that applied.
-
-     Again, if the field be strong with respect to the armature
-   magnetism, resulting from the applied voltage, the armature will
-   rotate at a low speed. If, therefore, it be desired to operate the
-   converter in this manner and maintain an alternating current of
-   constant frequency, the speed of rotation must be kept constant by
-   supplying a constant voltage not only to the brushes pressing on
-   the commutator, but also to the terminals of the field winding.
-
-[Illustration: FIG. 2,868.--General Electric synchronous converter
-with series booster. This type of converter generally consists of
-an alternator with revolving field mounted on the same shaft as the
-converter armature. The armature of the alternator, or booster, as it
-is usually called, is stationary and connected electrically in series
-between the supply circuit and the collector rings of the synchronous
-converter. The booster field has the same number of pole as the
-converter and is generally shunt wound. A change in the booster
-voltage will correspondingly change the alternating voltage impressed
-on the converter and this regulation can, of course, be made so as
-to either increase or decrease the impressed voltage by means of
-strengthening or weakening the booster field. The voltage variation
-can be made either non-automatic or automatic, and in the latter
-case, it becomes necessary to provide a motor operated rheostat
-controlled by suitable relays, or the booster can be provided with
-a series field. By means of a booster, it is possible to vary the
-direct voltage of the converter with a constant alternating supply
-voltage, and this voltage regulation is obtained without disturbance
-of the power factor or wave shape of the system. Synchronous
-converters are frequently installed in connection with Edison
-systems, where three wire direct current is required. The three wire
-feature is obtained either by providing extra collector rings and
-compensator, as with ordinary direct current generators, or also by
-connecting the neutral wire directly to the neutral point of the
-secondary winding of step down transformers, if such be furnished.]
-
-=Ques. How does it operate with alternating current drive?=
-
-Ans. The same as a synchronous motor.
-
-=Ques. What is the most troublesome part and why?=
-
-Ans. The commutator, because of the many pieces of which it is
-composed and the necessary lines along which it is constructed, its
-peripheral speed must be kept within reasonable limits.
-
-=Ques. What should be the limit of the commutator speed?=
-
-Ans. The commutator speed, or tangential speed at the brushes should
-not exceed 3,000 feet per minute.
-
-[Illustration: FIG. 2,869.--Wiring diagram for General Electric
-synchronous converter with series booster as illustrated in fig.
-2,868.]
-
-=Ques. Name another limitation necessary for satisfactory operation.=
-
-Ans. The pressure between adjacent commutator bars should not exceed
-eight or ten volts.
-
-     If the commutator bars be made narrow in order to obtain
-   the necessary number for the desired voltage with the minimum
-   circumference and therefore low commutator speed, the brushes
-   employed to collect the current are liable to require excessive
-   width in order to provide the proper cross section and yet not
-   cover more than two bars at once.
-
-=Ques. How can the commutator speed be kept within reasonable limits,
-other than by reducing the width of the commutator bars?=
-
-Ans. By using alternating current of comparatively low frequency.
-
-     For a rotary converter delivering 500 volt direct current, the
-   proper frequency for the alternating current circuit has been
-   found to be 25 cycles per second.
-
-=Ques. When a rotary converter is operated in this usual manner on an
-alternating current circuit, how can the direct current be varied?=
-
-Ans. It may be varied (from zero to a maximum) by changing the value
-of the alternating pressure supplied to the machine, or it may be
-altered within a limited range by moving the brushes around the
-commutator, or in a compound wound converter by changing the amount
-of compounding.
-
-     Under ordinary conditions, varying the voltage developed by
-   changing the voltage at the motor end is not practical, hence
-   the voltage developed can be varied only over a limited range.
-   In addition to this, the voltage developed at the direct current
-   end bears always a certain constant proportion to the alternating
-   current voltage applied at the motor end; this is due to the same
-   winding being used both for motor and generator purposes. In all
-   cases the proportion is such that the alternating current voltage
-   is the lower, being in the single phase and in the two phase
-   converters about .707 of the direct current voltage, and in the
-   three phase converter about .612 of the direct current voltage.
-   It is thus seen that whatever value of direct current voltage be
-   desired, the value of the applied alternating current voltage must
-   be lower, requiring in consequence the installation of step down
-   transformers at the sub-station for reducing the line wire voltage
-   to conform to the direct current pressure required.
-
-=Ques. What is the efficiency of a rotary converter?=
-
-Ans. It may be said to have approximately the same efficiency as that
-in the average of the same output, although in reality the converter
-is a trifle more efficient on account of affording a somewhat shorter
-average path for the current in the armature, reducing in consequence
-the resistance loss and the armature reaction.
-
-=Ques. May a converter be overloaded more than a dynamo of the same
-output, and why?=
-
-Ans. Yes, because there is usually less resistance loss in the
-armature of the converter than in the armature of the dynamo.
-
-[Illustration: FIG. 2,870.--Wiring diagram for three wire synchronous
-converter with delta-Y connected step down transformer with the
-neutral brought out. It is evident that in this case each transformer
-secondary receives ⅓ of the neutral current, and if this current
-be not so small, as compared with the exciting current of the
-transformer, it will cause an increase in the magnetic density.]
-
-     Thus, a two phase converter may be overloaded approximately 60
-   per cent., and a three phase converter may be overloaded about 30
-   per cent. above their respective outputs if operated as dynamos.
-
-=Ques. Describe how a converter is started.=
-
-Ans. There are several methods any one of which may be employed, the
-choice in any given case depending upon which of them may best be
-followed under the existing conditions.
-
-     If it be found advisable to start the converter with direct
-   current, the same connections would be made between the source of
-   the direct current and the armature terminals on the commutator
-   side of the converter as would be the case were a direct current
-   shunt motor of considerable size to be started; this naturally
-   means that a starting rheostat and a circuit breaker will be
-   introduced in the armature circuit.
-
-     The shunt field winding alone is used, and this part of the
-   wiring may be made permanent if, as is usually the case, the same
-   source of direct current is used normally for separate field
-   excitation.
-
-[Illustration: FIG. 2,871.--Wiring diagram of three wire synchronous
-converter with distributed Y secondary. This system eliminates the
-flux distortion due to the unbalanced direct current in the neutral.
-Two separate interconnected windings are used for each leg of the Y.
-The unbalanced neutral current flowing in this system may be compared
-in action to the effect of a magnetizing current in a transformer.
-The effect of the main transformer currents in the primary and
-secondary is balanced with regard to the flux in the transformer
-core, which depends upon the magnetic current. When a direct current
-is passed through the transformer, unless the fluxes produced by
-the same neutralize one another, its effect on the transformer iron
-varies as the magnetizing current. For example, assume a transformer
-having a normal ampere capacity of 100 and, approximately, 6 amperes
-magnetizing current, and assume that three such transformers are
-used with Y connected secondaries for operating a synchronous
-converter connected to a three wire Edison system. Allowing 25 per
-cent. unbalancing, the current will divide equally among the three
-legs giving 8.33 amperes per leg, which is more than the normal
-magnetizing current. The loss due to this current is, however,
-inappreciable, but the increased core losses may be considerable.
-If a distributed winding be used, the direct current flows in the
-opposite direction, around the halves of each core thus entirely
-neutralizing the flux distortion. Whether the straight Y connection
-is to be used is merely a question of balancing the increased core
-loss of the straight Y connection against the increased copper loss
-and the greater cost of the interconnected Y system. The straight
-Y connection is much simpler, and it would be quite permissible to
-use it for transformers of small capacities where the direct current
-circulating in the neutral is less than 30 per cent. of the rated
-transformer current.]
-
-     The direct current may be derived from a storage battery, from a
-   separate converter, or from a motor generator set installed in the
-   sub-station for the purpose.
-
-     An adjustable rheostat will, of course, be connected in the
-   field circuit for regulation. Before starting the converter,
-   however, it is necessary to do certain wiring between the
-   terminals on the collector side of the machine and the alternating
-   current supply wires, in order that the change over from direct
-   current motive power to alternating current motive power may be
-   made when the proper phase relations are established between
-   the alternating current in the supply wires and the alternating
-   current in the armature winding of the converter.
-
-     In order that proper phase relations exist, the armature
-   of the converter must rotate at such a speed that each coil
-   thereon passes its proper reversal point at the same time as the
-   alternating current reverses in the supply wires. This speed may
-   be calculated by doubling the frequency of the supply current and
-   then dividing by the number of pole pieces on the converter, but a
-   far more accurate method of judging when the converter is in step
-   or in synchronism with the supply current consists in employing
-   incandescent lamps as shown in fig. 2,872.
-
-=Ques. How is a polyphase converter started with alternating current?=
-
-Ans. This may be done by applying the alternating pressure directly
-to the collector rings while the armature is at rest. There need
-be no field excitation; in fact the field windings on the separate
-pole pieces should be disconnected from each other before the
-alternating voltage is applied to the armature, else a high voltage
-will be induced in the field windings which may prove injurious to
-their insulation. The passage of the alternating current through the
-armature winding produces a magnetic field that rotates about the
-armature core, and induces in the pole pieces eddy currents, which,
-reacting on the armature, exert a sufficient torque to start the
-converter from rest and cause it to speed up to synchronism.
-
-=Ques. How much alternating current is required to start a polyphase
-converter?=
-
-Ans. About 100 per cent. more than that required for full load.
-
-=Ques. How may this starting current be reduced?=
-
-Ans. Transformers may be switched into circuit temporarily to reduce
-the line wire voltage until the speed become normal.
-
-[Illustration: FIG. 2,872.--Wiring diagram showing arrangement of
-incandescent lamps for determining the proper phase relations in
-starting a rotary converter. The alternating current side of a
-three phase converter is shown at C. The three brushes, D, T and G
-pressing on its collector rings are joined in order to the three
-single pole switches H, L and B which can be made to connect with
-the respective wires M, R, and V, of the alternating current supply
-circuit. Across one of the outside switches, H, for example, a number
-of incandescent lamps are joined in series as indicated at E, while
-the three pole switch (not shown) in the main circuit, between the
-alternator and the single pole switches is open. If then the main
-switch just mentioned and the middle switch L be both closed, and
-the armature of the alternator be brought up to normal speed by
-running it as a direct current motor, the lamps at E will light up
-and darken in rapid succession; the lighting and darkening of the
-lamps will continue until, by a proper adjustment of the speed,
-the correct phase relations be established between the alternating
-current in the supply circuit and the alternating current developed
-in the armature of the converter. As this condition is approached,
-the intervals between the successive lighting up and darkening of
-the lamps will increase until they remain perfectly dark. There is
-then no difference of pressure between the supply circuit M R V and
-the rotary converter armature circuit, so the source of the direct
-current may at that instant be disconnected from the machine, and the
-switches H and B, closed. If the change over has been accomplished
-before the phase relations of the two circuits differed, the
-converter will at once conform itself to the supply circuit and run
-thereon as a synchronous motor without further trouble. The opening
-of the direct current circuit and the closing of the alternating
-current supply circuit may be done by hand, but preferably by
-employing a device that will automatically trip the circuit breaker
-in the direct current circuit at the instant the switches in the
-alternating current circuit are closed.]
-
-     In conjunction with this method, the method of synchronizing
-   shown in fig. 2,872 may be used, thus, in starting, there is
-   an alternating current between the brushes which pulsates very
-   rapidly, but when synchronism is approached, the pulsations
-   become less rapid until finally with the converter in step with
-   the alternator the pulsations entirely disappear.
-
-     The light given by the lamps thus connected indicates accurately
-   the condition of affairs at any one time, varying from a rapidly
-   fluctuating light at the beginning to one of constant brilliancy
-   at synchronism.
-
-[Illustration: FIG. 2,873.--Diagram of motor converter. This machine
-which is only to be used for converting from alternating to direct
-current, consists of an ordinary induction motor with phase wound
-armature, and a dynamo. The revolving parts of both machines are
-mounted on the same shaft and from the figure it is seen that the
-armature of the motor and the armature of the dynamo are also
-electrically connected. The motor converter is a synchronous machine,
-but the dynamo receives the current from the armature of the motor at
-a frequency much reduced from that impressed upon the field winding
-of the motor. Assuming that the motor and the converter have the same
-number of pole, the motor will rotate at a speed corresponding to
-one-half the frequency of the supply circuit. The motor will operate
-half as a motor and half as a transformer, and the converter, half
-as a dynamo and half as a synchronous converter, in that one-half of
-the electrical energy supplied to the motor will be converted into
-mechanical power for driving the converter, while the other one-half
-is transferred to the secondary motor windings and thereby to the
-converter armature in the form of electrical power. The capacity of
-the motor is theoretically only half what it would be if it were to
-convert the whole of the electrical energy into mechanical power
-because the rating depends upon the speed of the rotating field and
-not on that of the rotor. If the two machines have a different number
-of pole, or are connected to run at different speeds, the division of
-power is at a different but constant ratio. The machine starts up as
-an ordinary polyphase induction motor and the field of the converter
-is built up as though it were an ordinary dynamo. Motor converters
-are occasionally used on high frequency systems, as their commutating
-component is of half frequency, and thus permits better commutator
-design than a high frequency converter. The advantage of this type
-of machine is that for phase control it requires no extra reactive
-coils, the motor itself having sufficient reactance. It is, however,
-larger than standard converters, but smaller than motor generators,
-as half the power is converted in each machine. Its efficiency is
-less than for synchronous converters, and the danger of reaching
-double speed in case of a short circuit on the direct current side
-is very great. It has been used abroad to some extent for 60 cycle
-work, in preference to synchronous converters, but with the present
-reliable design of 60 cycle converters, and the general use of 25
-cycles, where severe service conditions are met, as in railroading,
-motor converters should not be recommended.]
-
-=Ques. If the armature of the starting motor have a starting
-resistance, how must this be connected?=
-
-Ans. It should be connected in series with the armature inductors
-before the alternating voltage is applied.
-
-     As the motor increases in speed, the starting resistance is
-   gradually short circuited until it is entirely cut out of circuit.
-
-[Illustration: FIG. 2,874.--Sectional view of General Electric
-vertical synchronous converter. In this construction, the field frame
-carrying the poles is mounted on cast iron pedestals and is split
-vertically. This allows the two halves of the frame to be separated
-for inspection or repairs of the armature. The armature, including
-commutator and collector rings, is mounted on a vertical stationary
-shaft, which is rigidly supported from the foundation. The thrust
-of the armature is carried on a roller bearing attached to the top
-of the shaft and upper side of the armature spider. The under side
-of the lower plate of the roller bearing is made spherical and fits
-into a corresponding spherical cup on the end of the shaft, making
-the bearing self aligning. The armature spider has a babbitted sleeve
-along the fit of the vertical shaft, which acts as a guide bearing
-and has to take only the thrust due to the unbalancing effect of
-the rotating parts. A circulating pump furnishes oil to the roller
-bearing, the oil draining off through the guide bearing. A marked
-advantage of this type of construction is the accessibility of the
-commutator for adjustment of the brushes, etc., as there is no pit or
-pedestal bearing to interfere.]
-
-            NOTE.--Some converters are provided
-          with a small induction motor for starting
-          mounted on an iron bracket cast in the converter
-          frame, and whose shaft is keyed to that of the
-          converter. Allowing for a certain amount of
-          slip in the induction motor, the field of this
-          machine must possess a less number of magnet
-          poles than the converter in order to enable the
-          latter machine to be brought to full synchronism.
-          To start the induction motor, it is simply
-          necessary to apply to its field terminals the
-          proper alternating voltage. The bracket, and
-          therefore the motor, is usually mounted outside
-          the armature bearing on the collector side of the
-          converter.
-
-[Illustration: FIG. 2,875.--Resistance measurement by "drop" method.
-The circuit whose resistance is to be measured, is connected in
-series with an ammeter and an adjustable resistance to vary the
-flow of current. A voltmeter is connected directly across the
-terminals of the resistance to be measured, as shown in the figure.
-According to Ohm's law I = E ÷ R, from which, R = E ÷ I. If then the
-current flowing in the circuit through the unknown resistance be
-measured, and also the drop or difference of pressure, the resistance
-can be calculated by above formula. In order to secure accurate
-determination of the resistance such value of current must be used
-as will give large deflections of the needle on the instruments
-employed. A number of independent readings should be taken with some
-variation of the current and necessarily a corresponding variation
-in voltage. The resistance should then be figured from each set
-of readings and the average of all readings taken for the correct
-resistance. Great care must be taken, however, in the readings, and
-the instruments must be fairly accurate. For example, suppose that
-the combined instrument error and the error of the reading in the
-voltmeter should be 1 per cent., the reading being high, while the
-corresponding error of the ammeter is 1 per cent. low. This would
-cause an error of approximately 2 per cent. in the reading of the
-resistance. In making careful measurements of the resistance, it is
-also necessary to determine the temperature of the resistance being
-measured, as the resistance of copper increases approximately .4
-of 1 per cent. for each degree rise in temperature. Use is made of
-this fact for determining the increase in temperature of a piece of
-apparatus when operating under load. The resistance of the apparatus
-at some known temperature is measured, this being called the cold
-resistance of the apparatus. At the end of the temperature test the
-hot resistance is taken. Assume the resistance has increased by 15
-per cent. This would indicate a rise in temperature of 37½ degrees
-above the original or cold temperature of the apparatus. Suppose then
-that in measuring the cold resistance, results are obtained which are
-2 per cent. low, and that in measuring the hot resistance, there be
-2 per cent. error in the opposite direction. This would mean that a
-total error of 4 per cent. had been made in the difference between
-the hot and cold resistances, or an error of 10 degrees. The correct
-rise in temperature is, therefore, about 27½ instead of 37½ degrees.
-In other words, an error of 2 per cent. in measuring each resistance
-has caused an error of approximately 36½ per cent. in the measurement
-of the rise in temperature. The constant .4 which has been used above
-is only approximate and should not be used for exact work. For detail
-instructions of making calculations of resistance and temperature,
-see "Standardization Rules of the A.I.E.E."]
-
-=Ques. Describe the usual wiring for the installation of a rotary
-converter in a sub-station.=
-
-Ans. Commencing at the entrance of the high pressure cables, first
-there is the wiring for the lightning arresters, then for the
-connection in circuit of the high tension switching devices, from
-which the conductors are led to bus bars, and thence to the step down
-transformers.
-
-[Illustration: Figs. 2,876 to 2,879.--How to connect instruments
-for power measurement. There are several ways of connecting an
-ammeter, voltmeter and wattmeter in the circuit for the measurement
-of power. A few of the methods are discussed below. With some of the
-connections it is necessary to correct the readings of the wattmeter
-for the losses in the coil, or coils, of the wattmeter, or for losses
-in ammeter or voltmeter. This is necessary since the instruments may
-be so connected that the wattmeter not only measures the load but
-includes in its indications some of the instrument losses. If the
-load measured be small, or considerable accuracy is required, these
-instrument losses may be calculated as follows: Loss in pressure
-coils is E^{2} ÷ R, in which E is the voltage at the terminals of
-the pressure coil and R is the resistance. Loss in current coil is
-I^{2} R in which I is the current flowing and R the resistance of the
-current coil. In general let E_{v} = voltage across terminals of the
-voltmeter; E_{_w_} = voltage across the terminals of the pressure
-coil of the wattmeter; I_{_w_} = current through current coil of
-wattmeter; I_{_a_} = current through current coil of ammeter; R_{_v_}
-= resistance of pressure coil of voltmeter; R_{_w_} = resistance of
-pressure coil of wattmeter; R^{1}_{w} = resistance of current coil
-of wattmeter; R_{_a_} = resistance of current coil of ammeter. Then
-the losses in the various coils will be as follows: E^{2}_{_v_} ÷
-R_{_v_} = loss in pressure coil of voltmeter. E^{2}_{_w_} ÷ R_{_w_}
-= loss in pressure coil of wattmeter. I^{2}_{_w_} ÷ R_{_v_} = loss
-in current coil of wattmeter. I^{2}_{_a_}R_{_a_} = loss in current
-coil of ammeter. If connection be made as in fig. 2,876, the correct
-power of the circuit will be the wattmeter reading W-(E^{2}_{_v_} ÷
-R_{_v_} + E^{2}_{_w_} ÷ R_{_w_}) in which E_{_v_} = E_{_w_}. In fig.
-2,877, the power is W-E^{2}_{_w_} ÷ R_{_w_}. In fig. 2,878, the power
-is W-I^{2}_{_w_}R^{1}_{_w_}, or the correct power is the wattmeter
-reading minus the loss in the current coil of the wattmeter. In fig.
-2,879, the power is W-(E^{2}_{_w_} ÷ R_{_w_} + I^{2}_{_a_}R_{_a_})·
-The usual method of connection is either as in fig. 2,876 or fig.
-2,877. In either case the current reading is that of the load plus
-the currents in the pressure coils of the voltmeter and wattmeter.
-Unless the current being measured, however, is very small, or extreme
-accuracy is desired, it is unnecessary to correct ammeter readings.
-In fig. 2,877 a small error is introduced due to the fact that the
-actual voltage applied to the load is that given by the voltmeter
-minus the small drop in voltage through the current coil of the
-wattmeter. If an accurate measure of the current in connection with
-the power consumed by the load be required, the connections shown
-in fig. 2,879 are used, and if extreme accuracy is required, the
-wattmeter reading is reduced by the losses in the ammeter and in
-the pressure coil of the wattmeter. The loss in the pressure coil
-of a wattmeter or voltmeter may be as high as 12 or 15 watts at 220
-volts. The loss in the current coil of a wattmeter with 10 amperes
-flowing may be 6 or 8 watts. It can be easily seen that if the core
-or copper losses of small transformers are being measured, it is
-quite necessary to correct the wattmeter readings, for the instrument
-losses. In measuring the losses of a 25 or 50 H.P. induction motor,
-the instrument losses may be neglected. A careful study of the above
-will show when it becomes necessary to correct for instrument losses
-and the method of making these corrections. Connections are seldom
-used which make it necessary to correct for the losses in the current
-coils of either ammeter or wattmeter, as the losses vary with the
-change in the current. On the other hand, the voltages generally
-used are fairly constant at 110 or 220, and when the losses of the
-pressure coils at these voltages have once been calculated, the
-necessary instrument correction can be readily made.]
-
-     On a three phase system the transformers should be joined in
-   delta connection, as a considerable advantage is thereby gained
-   over the star connection, in that should one of the transformers
-   become defective, the remaining two will carry the load without
-   change except more or less additional heating. Between the
-   transformers and rotary converter the circuits should be as short
-   and simple as possible, switches, fuses, and other instruments
-   being entirely excluded. The direct current from the converter is
-   led to the direct current switchboard, and from there distributed
-   to the feeder circuits.
-
-    =WATTMETER ERROR FOR A LOAD OF 1,000 VOLT-AMPERES=
-      (For a lag of 1 degree in the pressure coil)
-
-  +------------+----------+-------+-------------------+
-  |            |          |       |Error of indication|
-  |Power factor|True watts| Error |    in per cent    |
-  |            |          |       |   of true value   |
-  +------------+----------+-------+-------------------+
-  |   1.       |  1,000   |   .3  |      0.03         |
-  |    .9      |    900   |  7.6  |      0.85         |
-  |    .8      |    800   | 10.5  |      1.31         |
-  |    .7      |    700   | 12.5  |      1.78         |
-  |    .6      |    600   | 13.9  |      2.32         |
-  |    .5      |    500   | 15.1  |      3.02         |
-  |    .4      |    400   | 15.9  |      3.98         |
-  |    .3      |    300   | 16.6  |      5.54         |
-  |    .2      |    200   | 17.1  |      8.55         |
-  |    .1      |    100   | 17.3  |     17.30         |
-  +------------+----------+-------+-------------------+
-
-            NOTE.--In the iron vane type instrument when
-          used as a wattmeter, the current of the series
-          coil always remains in perfect phase with
-          the current of the circuit, provided series
-          transformers are not introduced. The error,
-          then, is entirely due to the lag of the current
-          in the pressure coil, and this error in high
-          power factor is exceedingly small, increasing as
-          the power factor decreases. In the above table
-          it should be noted that the value of the error
-          as distinguished from the per cent. of error,
-          instead of indefinitely increasing as the power
-          factor diminishes, rapidly attains a maximum
-          value which is less than 2 per cent. of the power
-          delivered under the same current and without
-          inductance. It should also be noted that the
-          above tabulation is on the assumption of a lag of
-          1 degree in the pressure coil. The actual lag in
-          Wagner instruments for instance, is approximately
-          .085 of a degree, and the error due to the lag
-          of the pressure coil in Wagner instruments is,
-          therefore, proportionally reduced from the
-          figures shown in the above tabulation.
-
-=Ques. In large sub-stations containing several rotary converters how
-are they operated?=
-
-Ans. Frequently they are installed to receive their respective
-currents from the same set of bus bars; that is, they may be operated
-as alternating current motors in parallel. They are also frequently
-operated independently from single bus bars, but very seldom in
-series with each other.
-
-[Illustration: FIG. 2,880.--Single phase motor test. In this method
-of measuring the input of a single phase motor of any type, the
-ammeter, voltmeter and wattmeter are connected as shown in the
-illustration. The ammeter measures the current flowing through the
-motor, the voltmeter, the pressure across the terminals of the motor,
-and the wattmeter the total power which flows through the motor
-circuit. With the connections as shown, the wattmeter would also
-measure the slight losses in the voltmeter and the pressure coil of
-the wattmeter, but for motors of ¼ H.P. and larger, this loss is so
-small that it may be neglected. The power factor may be calculated by
-dividing the true watts as indicated by the wattmeter, by the product
-of the volts and amperes.]
-
-=Ques. How may the direct current circuit be connected?=
-
-Ans. In parallel.
-
-            NOTE.--In motor testing, by the methods
-          illustrated in the accompanying cuts, it is
-          assumed that the motor is loaded in the ordinary
-          way by belting or direct connecting the motor
-          to some form of load, and that the object is to
-          determine whether the motor is over or under
-          loaded, and approximately what per cent. of full
-          load it is carrying. All commercial motors have
-          name plates, giving the rating of the motor and
-          the full load current in amperes. Hence the
-          per cent. of load carried can be determined
-          approximately by measuring the current input
-          and the voltage. If an efficiency test of the
-          apparatus be required, it becomes necessary to
-          use some form of absorption by dynamometer, such
-          as a Prony or other form of brake. The output of
-          the motor can then be determined from the brake
-          readings. The scope of the present treatment
-          is, however, too limited to go into the subject
-          of different methods of measuring the output of
-          the apparatus, and is confined rather to methods
-          of measuring current input, voltage, and watts.
-          The accuracy of all tests is obviously dependent
-          upon the accuracy of the instruments employed.
-          Before accepting the result obtained by any test,
-          especially under light or no load, correction
-          should be made for wattmeter error. See table of
-          wattmeter error on page 2,075.
-
-[Illustration: FIG. 2,881.--Three phase motor test; voltmeter and
-ammeter method. If it be desired to determine the approximate load
-on a three phase motor, this may be done by means of the connections
-as shown in the figure, and the current through one of the three
-lines and the voltage across the phase measured. If the voltage be
-approximately the rated voltage of the motor and the amperes the
-rated current of the motor (as noted on the name plate) it may be
-assumed that the motor is carrying approximately full load. If, on
-the other hand, the amperes show much in excess of full load rating,
-the motor is carrying an overload. The heat generated in the copper
-varies as the square of the current. That generated in the iron
-varies anywhere from the 1.6 power, to the square. This method is
-very convenient if a wattmeter be not available, although, it is, of
-course, of no value for the determination of the efficiency or power
-factor of the apparatus. This method gives fairly accurate results,
-providing the load on the three phases of the motor be fairly well
-balanced. If there be much difference, however, in the voltage of
-the three phases, the ammeter should be switched from one circuit to
-another, and the current measured in each phase. If the motor be very
-lightly loaded and the voltage of the different phases vary by 2 or 3
-per cent., the current in the three legs of the circuit will vary 20
-to 30 per cent.]
-
-=Ques. What provision should be made against interruption of service
-in sub-stations?=
-
-Ans. There should be one reserve rotary converter to every three or
-four converters actually required.
-
-=Ques. Why does a rotary converter operate with greater efficiency,
-and require less attention than does a dynamo of the same output?=
-
-Ans. There is less friction, and less armature resistance, the
-latter because the alternating current at certain portions of each
-revolution passes directly to the commutator bars without traversing
-the entire armature winding as it does in a dynamo; there is no
-distortion of the field and consequently no sparking, or shifting of
-the brushes, since the armature reaction resulting from the current
-fed into the machine and that due to the current generated in the
-armature completely neutralizes each other.
-
-[Illustration: FIG. 2,882.--Three phase motor test by the two
-wattmeter method. If an accurate test of a three phase motor be
-required, it is necessary to use the method here indicated. Assume
-the motor to be loaded with a brake so that its output can be
-determined. This method gives correct results even with considerable
-unbalancing in the voltages of the three phases. With the connections
-as shown, the sum of the two wattmeter readings gives the total power
-in the circuit. Neither meter by itself measures the power in any
-one of the three phases. In fact, with light load one of the meters
-will probably give a negative reading, and it will then be necessary
-to either reverse its current or pressure leads in order that the
-deflection may be noted. In such cases the algebraic sums of the two
-readings must be taken. In, other words, if one read plus 500 watts
-and the other, minus 300 watts, the total power in the circuit will
-be 500 minus 300, or 200 watts. As the load comes on, the readings of
-the instrument which gave the negative deflection will decrease until
-the reading drops to zero, and it will then be necessary to again
-reverse the pressure leads on this wattmeter. Thereafter the readings
-of both instruments will be positive, and the numerical sum of the
-two should be taken as the measurement of the load. If one set of the
-instruments be removed from the circuit, the reading of the remaining
-wattmeter will have no meaning. As stated above, it will not indicate
-the power under these conditions in any one phase of the circuit. The
-power factor is obtained by dividing the actual watts input by the
-product of the average of the voltmeter readings × the average of the
-ampere readings × 1.73.]
-
-=What electrical difficulty is experienced with a rotary converter?=
-
-Ans. Regulation of the direct current voltage.
-
-=Ques. How is this done?=
-
-Ans. It can be maintained constant only by preserving uniform
-conditions of inductance in the alternating current circuit, and
-uniform conditions in the alternator.
-
-     While changes in either of these may be compensated to a certain
-   extent by adjustment of the field strength of the converter, they
-   cannot be entirely neutralized in this manner; it is therefore
-   necessary that both the line circuit and the alternator be
-   given attention if the best results are to be obtained from the
-   converter.
-
-=Ques. What mechanical difficulty is experienced with rotary
-converters?=
-
-Ans. Hunting.
-
-=Ques. What is the cause of this?=
-
-Ans. It is due to a variation in frequency.
-
-     The inertia of the converter armature tends to maintain a
-   constant speed; variations in the frequency of the supply circuit
-   will cause a displacement of phase between the current in the
-   armature and that in the line wires, which displacement, however,
-   the synchronizing current strives to decrease. The synchronizing
-   current, although beneficial in remedying the trouble after it
-   occurs, exerts but little effort in preventing it, and many
-   attempts have been made to devise a plan to eliminate this trouble.
-
-            NOTE.--Three phase motor test; polyphase
-          wattmeter method. This is identical with the test
-          of fig. 2,882, except that the wattmeter itself
-          combines the movement of the two wattmeters.
-          Otherwise the method of making the measurements
-          is identical. If the power factor be known to be
-          less than 50 per cent., connect one movement so
-          as to give a positive deflection; then disconnect
-          movement one and connect movement two so as to
-          give a positive deflection. Then reverse either
-          the pressure or current leads of the movement,
-          giving the smaller deflection, leaving the
-          remaining movement with the original connections.
-          The readings now obtained will be the correct
-          total watts delivered to the motor. If the power
-          factor be known to be over 50 per cent., the same
-          methods should be employed, except that both
-          movements should be independently connected to
-          give positive readings. An unloaded induction
-          motor has a power factor of less than 50 per
-          cent., and may, therefore, be used as above
-          for determining the correct connections. For a
-          better understanding of the reasons for the above
-          method of procedure, the explanation of the two
-          wattmeter method, fig. 2,882, should be read. The
-          power factor may be calculated as explained under
-          fig. 2,882. Connect as shown in fig 2,882. The
-          following check on connection may be made. Let
-          the polyphase induction motor run idle, that is,
-          with no load. The motor will then operate with a
-          power factor less than 50 per cent. The polyphase
-          meter should give a positive indication, but
-          if each movement be tried separately one will
-          be found to give a negative reading, the other
-          movement will give a positive reading. This can
-          be done by disconnecting one of the pressure
-          leads from the binding post of one movement. When
-          the power factor is above 50 per cent. then both
-          movements will give positive deflection.
-
-=Ques. What are the methods employed to prevent hunting?=
-
-Ans. 1, the employment of a strongly magnetized field relative to
-that developed by the armature; 2, a heavy flywheel effect in the
-converter; 3, the increasing of the inductance of the armature by
-sinking the windings thereon in deep slots in the core, the slots
-being provided with extended heads; and 4, the employment of damping
-devices or amortisseur winding on the pole pieces of the converter.
-
-[Illustration: FIG. 2,883.--Three phase motor test; one wattmeter
-method. This method is equivalent to the two wattmeter method with
-the following difference. A single voltmeter (as shown above) with
-a switch, A, can be used to connect the voltmeter across either one
-of the two phases. Three switches, B, C and D, are employed for
-changing the connection of the ammeter and wattmeter in either one
-of the two lines. With the switches B and D in the position shown,
-the ammeter and wattmeter series coils are connected in the left hand
-line. The switch C must be closed under these conditions in order to
-have the middle line closed. Another reading should then be taken
-before any change of load has occurred, with switch A thrown to the
-right, switch B closed, switch D thrown to the right and switch C
-opened. The ammeter and the current coil of the wattmeter will then
-be connected to the middle line of the motor. In order to prevent
-any interruption of the circuit, the switches B, D and C should be
-operated in the order given above. With very light load on the motor
-the wattmeter will probably give a negative deflection in one phase
-or the other, and it will be necessary to reverse its connections
-before taking the readings. For this purpose a double pole, double
-throw switch is sometimes inserted in the circuit of the pressure
-coil of the wattmeter so that the indications can be reversed
-without disturbing any of the connections. It is suggested, before
-undertaking this test, that the instructions for test by the two
-wattmeter and by the polyphase wattmeter methods be read.]
-
-=Ques. What method is the best?=
-
-Ans. The damping method.
-
-     The devices employed for the purpose are usually copper shields
-   placed between or around the pole pieces, although in some
-   converters the copper is embedded in the poles, and in others it
-   is made simply to surround a portion of the pole tips.
-
-     In any case its action is as follows: The armature rotating at a
-   variable speed has a field developed therein which is assumed to
-   be also rotating at a variable speed; the magnetism of this rotary
-   field induces currents in the copper which, however, react on the
-   armature and oppose any tendency toward a further shifting of the
-   magnetism in the armature and therefore prevent the development
-   of additional currents in the copper. Since copper is of low
-   resistance, the induced currents are sufficient in strength to
-   thus dampen any tendency toward phase displacement, and so exert a
-   steadying influence upon the installation as a whole.
-
-[Illustration: FIG. 2,884.--Three phase motor, one wattmeter and Y
-box method. This method is of service, only, provided the voltages of
-the three phases are the same. A slight variation of the voltage of
-the different phases may cause a very large error in the readings of
-the wattmeter, and inasmuch as the voltage of all commercial three
-phase circuits is more or less unbalanced, this method is not to be
-recommended for motor testing. With balanced voltage in all three
-phases, the power is that indicated by the wattmeter, multiplied by
-three. Power factor may be calculated as before.]
-
-=Electrical Measuring Instruments.=--In the manufacture of most
-measuring instruments, the graduations of the scale are made at the
-factory, by comparing the deflections of the pointer with voltages
-as measured on standard apparatus. The voltmeters in most common
-use have capacities of 5, 15, 75, 150, 300, 500 and 750 volts each,
-although in the measurement of very low resistances such as those of
-armatures, heavy cables, or bus bars, voltmeters having capacities as
-low as .02 volt are employed.
-
-[Illustration: FIG. 2,885.--Test of three phase motor with neutral
-brought out; single wattmeter method. Some star connected motors
-have the connection brought out from the neutral of the winding. In
-this case the circuit may be connected, as here shown. The voltmeter
-now measures voltage between the neutral and one of the lines, and
-the wattmeter the power in one of the three phases of the motor.
-Therefore, the total power taken by the motor will be three times the
-wattmeter readings. By this method, just as accurate results can be
-obtained as with the two wattmeter method. The power factor will be
-the indicated watts divided by the product of the indicated amperes
-and volts.]
-
-The difference between the design of direct current voltmeters of
-different capacities lies simply in the high resistance joined in
-series with the fine wire coil. This resistance is usually about 100
-ohms per volt capacity of the meter, and is composed of fine silk
-covered copper wire wound non-inductively on a wooden spool.
-
-In the operation of an instrument, if the pointer when deflected do
-not readily come to a position of rest owing to friction in the
-moving parts, it may be aided in this respect by gently tapping
-the case of the instrument with the hand; this will often enable
-the obstruction, if not of a serious nature, to be overcome and an
-accurate reading to be obtained.
-
-[Illustration: FIG. 2,886.--Temperature test of a large three
-phase induction motor. Temperature tests are usually made on small
-induction motors by belting the motor to a generator and loading the
-generator with a lamp bank or resistance until the motor input is
-equal to the full load. If, however, the motor be of considerable
-size, such that the cost of power becomes a considerable item in
-the cost of testing, the method here shown may be employed. For
-this purpose, however, two motors, preferably of the same size and
-type, are required. One is driven as a motor and runs slightly below
-synchronism, due to its slip when operating with load. This motor is
-belted to a second machine. If the pulley of the second machine be
-smaller than the pulley of the first machine, the second machine will
-then operate as an induction generator, and will return to the line
-as much power as the first motor draws from the line, less the losses
-of the second machine. By properly selecting the ratio of pulleys,
-the first machine can be caused to draw full load current and full
-load energy from the line. In this way, the total energy consumed
-is equivalent to the total of the losses of both machines, which is
-approximately twice the losses of a single machine. The figure shows
-the connection of the wattmeters, without necessary switches, for
-reading the total energy by two wattmeter method. Detailed connection
-of the wattmeter is shown in fig. 2,883. It is usual, in making
-temperature tests, to insert one or more thermometers in what is
-supposed to be the hottest part of the winding, one on the surface
-of the laminae and one in the air duct between the iron laminae. The
-test should be continued until the difference in temperature between
-any part of the motor and the air reaches a steady value. The motor
-should then be stopped and the temperature of the armature also
-measured. For the method of testing wound armature type induction
-motors of very large size, see fig. 2,890. For the approved way
-of taking temperature readings and interpreting results, see the
-"Standardization Rules of the A.I.E.E."]
-
-=Ques. Describe a two scale voltmeter.=
-
-Ans. In this type of instrument, one scale is for low voltage
-readings and the other for high voltage readings; on these scales
-the values of the graduations for low voltages are usually marked
-with red figures, while those for high voltages are marked with
-black figures. A voltmeter carrying two scales must also contain two
-resistances in place of one; a terminal from each of these coils must
-be connected with a separate binding post, but the remaining terminal
-of each resistance is joined to a wire which connects through the
-fine wire coil with the third binding post of the meter. The two
-first mentioned binding posts are usually mounted at the left hand
-side of the meter and the last mentioned binding post and key at the
-right hand side.
-
-[Illustration: FIG. 2,887.--Alternator excitation or magnetization
-curve test. The object of this test is to determine the change of
-the armature voltage due to the variation of the field current when
-the external circuit is kept open. As here shown, the field circuit
-is connected with an ammeter and an adjustable resistance in series
-with a direct current source of supply. The adjustable resistance is
-varied, and readings of the voltmeter across the armature, and of
-the ammeter, are recorded. The speed of the generator must be kept
-constant, preferably at the speed which is given on the name plate.
-The excitation or magnetization curve of the machine is obtained by
-plotting the current and the voltage.]
-
-     The resistance corresponding to the high reading scale is
-   composed of copper wire having the same diameter as that
-   constituting the resistance for the low reading scale, but as the
-   capacity of the former scale is generally a whole number of times
-   greater than that of the latter scale, the resistances for the two
-   must bear the same proportion.
-
-[Illustration: FIG. 2,888.--Three phase alternator synchronous
-impedance test. In determining the regulation of an alternator, it
-is necessary to obtain what is called the _synchronous impedance_ of
-the machine. To obtain this, the field is connected, as shown above.
-Voltmeters are removed and the armature short circuited with the
-ammeters in circuit. The field current is then varied, the armature
-driven at synchronous speed, and the armature current measured by
-the ammeters in circuit. The relation between field and armature
-amperes are then plotted. The combination of the results of this
-test, with those obtained from the test shown in fig. 2,887, are used
-in the determination of the regulation of an alternator. Engineers
-differ widely in the application of the above to the determination
-of regulation, and employ many empirical formulae and constants for
-different lines of design.]
-
-=Ques. How is a two scale voltmeter connected?=
-
-Ans. In the connection of a two scale voltmeter in circuit, the
-single binding post is always employed regardless of which scale is
-desired. If, then, the voltage be such that it may be measured on the
-low reading scale, the other binding post employed is that connected
-to the lower of the two resistances contained within; if, however,
-the pressure be higher than those recorded on the low reading scale,
-the binding post connected to the higher of the two resistances
-contained within is used.
-
-            NOTE.--Three phase alternator load test. By
-          means of the connection shown in fig. 2,888,
-          readings of armature current and field amperes
-          can be obtained with any desired load. The field
-          current can be varied also so as to maintain
-          constant armature voltage irrespective of load;
-          or the field current may be kept constant and
-          the armature voltage allowed to vary as the load
-          increases. The connections may also be used to
-          make a temperature test on the alternator by
-          loading it with an artificial load. In some cases
-          after the alternator is installed the connection
-          may be used to make a temperature test, using
-          the actual commercial load the alternator is
-          furnishing.
-
-            Inasmuch as the capacities of the scales are
-          usually marked on or near the corresponding
-          binding posts, there will generally be no
-          difficulty in selecting the proper one of the two
-          left hand binding posts.
-
-[Illustration: FIG. 2,889.--Three phase alternator or synchronous
-motor temperature test. In this test two alternators or synchronous
-motors of same size and type are used, and are belted together, one
-to be driven as a synchronous motor and the other as an alternator.
-The method employed is to synchronize the synchronous motor with
-the alternator or alternators on the three phase circuit, and then
-connect to the line by means of a three pole single throw switch.
-The alternator is then similarly synchronized with the alternator
-of the three phase circuit and thrown onto the line. By varying the
-field of the alternator it can be made to carry approximately full
-load, and the motor will then be also approximately fully loaded.
-The usual method is to have the motor carry slightly in excess of
-full load, and the alternator slightly less than full load. Under
-these conditions the motor will run a little warmer than it should
-with normal load, while the alternator will run slightly cooler.
-Temperature measurements are made in the same way as discussed
-under three phase motors. The necessary ammeters, voltmeters and
-wattmeters for adjusting the loads on the motors and generator are
-shown in above figure. If pulleys be of sufficient size to transmit
-the full load, with, say one per cent. slip, the pulley on the motor
-should be one per cent. larger in diameter than the pulley on the
-alternator, so as to enable the alternator to remain in synchronism
-and at the same time deliver power to the circuit. With very large
-machines under test, it is inadvisable to use the above method as
-it is sometimes difficult to so adjust the pulleys and belt tension
-that the belt slip will be just right to make up for the difference
-in diameter of the pulleys, and very violent flapping of the belt
-results. To meet such cases, various other methods have been devised.
-One which gives consistent results is shown in fig. 2,890.]
-
-=Ques. How is a two scale voltmeter connected when the binding posts
-are not marked?=
-
-Ans. If only an approximate idea is possessed of the voltage to be
-measured, it is always advisable to connect to the binding post
-corresponding to the high reading scale of the meter in order
-to determine if the measurement may not be made safely and more
-accurately on the low reading scale. In any case, some knowledge must
-be had of the voltage at hand, else the high reading portion of the
-instrument may be endangered.
-
-[Illustration: FIG. 2,890.--Three phase alternator or synchronous
-motor temperature test. Supply the field with normal field current.
-The armature is connected in open delta as illustrated, and full load
-current sent through it from an external source of direct current,
-care being taken to ground one terminal of the dynamo so as to avoid
-danger of shock due to the voltage on the armature winding. The field
-is then driven at synchronous speed. If the armature be designed to
-be connected star for 2,300 volts, the voltage generated in each leg
-of the delta will be 1,330 volts, and unless one leg of the dynamo
-were grounded, the tester might receive a severe shock by coming
-in contact with the direct current circuit. The insulation of the
-dynamo would also be subjected to abnormal strain unless one terminal
-were grounded. By the above method the field is subjected to its
-full copper loss and the armature to full copper loss and core loss.
-Temperature readings are taken as per standardization rules of the
-A.I.E.E. This method may also be used with satisfactory results on
-large three phase motors of the wound rotor type. If the alternator
-pressure be above 600 volts, a pressure transformer should be used in
-connection with the voltmeter.]
-
-     _Too much care cannot be taken to observe these precautions_
-   whenever the voltmeter is used, for the burning out or charring
-   of the insulation either in the fine wire coil or in the high
-   resistance of the meter by an excessive current, is one of the
-   most serious accidents that can befall the instrument.
-
-     If a voltmeter has been subjected to a voltage higher than that
-   for which it was designed, yet not sufficiently high to injure the
-   insulation, but high enough to cause the pointer to pass rapidly
-   over the entire scale, damage has been done in another way. The
-   pointer being forced against the side of the case in this manner,
-   bends it more or less and so introduces an error in the readings
-   that are afterward taken.
-
-     The same damage will be done if the meter be connected in
-   circuit so the current does not pass through it in the proper
-   direction, although in this case the pointer is not liable to
-   be bent so much as when it is forced to the opposite side of
-   the meter by an abnormal current, since then it has gained
-   considerable momentum which causes a severer impact. The extent
-   of the damage may be ascertained by noting how far away from the
-   zero mark the pointer lies when no current is passing through
-   the instrument. If this distance be more than two-tenths of a
-   division, the metal case enclosing the working part should be
-   removed and the pointer straightened by the careful use of a pair
-   of pinchers.
-
-[Illustration: FIG. 2,891.--Direct motor or dynamo magnetization
-test. The object of this test is to determine the variation of
-armature voltage without load, with the current flowing through the
-field circuit. The armature should be driven at normal speed. The
-adjustment resistance in the field circuit is varied and the voltage
-across the armature measured. The curve obtained by plotting these
-two figures is usually called magnetization curve of the dynamo. It
-is usual to start with the higher resistance in the field circuit so
-that very small current flows, gradually increasing this current by
-cutting out the field resistance. When the highest no load voltage
-required is reached, the field current is then diminished, and what
-is called the descending (as opposed to the ascending) magnetization
-curves are obtained. The difference in the two curves is due to the
-lag of the magnetization behind the magnetizing current, and is
-caused by the hysteresis of the iron of the armature core.]
-
-=Ques. What should be noted with respect to location of instruments?=
-
-Ans. If they be placed near conductors carrying large currents,
-the magnetic field developed thereby will produce a change in the
-magnetism of the instruments and so introduce an error in the
-readings.
-
-[Illustration: FIG. 2,892.--Shunt dynamo external characteristic
-test. The external characteristic of a shunt dynamo is a curve
-showing the relation between the current and voltage of the external
-circuit. This is obtained by the connection as here shown. The shunt
-field is so adjusted that the machine gives normal voltage when
-the external circuit is open. The field current is then maintained
-constant and the external current varied by varying the resistance
-in the circuit. By plotting voltage along the vertical, against the
-corresponding amperes represented along the horizontal, the external
-characteristic is obtained.]
-
-=Ques. How should portable instruments be wired?=
-
-Ans. The wires must be firmly secured to the supports on which they
-rest, so as to reduce the possibility of their being pulled by
-accident, and so causing the instruments to fall.
-
-     A fall or a rough handling of the meter at once shows its effect
-   on the readings, for as much harm is done as would result from a
-   similar treatment of a watch.
-
-     The hardened steel pivots used in all high grade voltmeters are
-   ground and polished with extreme care so as to secure and maintain
-   a high degree of sensitiveness. The jewels on which the moving
-   parts revolve are of sapphire, and they too must necessarily be
-   made with skill and carefulness; if, therefore, the jewels become
-   cracked and the pivots dulled by careless handling, the meter at
-   once becomes useless as a measuring instrument.
-
-=Ques. How should readings be taken?=
-
-Ans. The deflection of the pointer should be read to tenths of a
-division; this can be done with considerable accuracy, especially
-after a little practice.
-
-[Illustration: FIG. 2,893.--Load and speed test of direct current
-shunt motor. The object of this test is to maintain the voltage
-applied to the motor constant, and to vary the load by means of a
-brake and find the corresponding variation in speed of the machine
-and the current drawn from the circuit. If the motor be a constant
-speed motor, the field resistance is maintained constant. The above
-indicates the method of connecting instruments for the test alone;
-for starting the machine the ordinary starting box, should, of
-course, be inserted.]
-
-     For very accurate results, a temperature correction should be
-   applied to compensate the effect which the temperature of the
-   atmosphere has upon the resistance of the meter when measurements
-   are being taken. In ordinary station practice the temperature
-   correction is negligible, being for resistance corresponding to
-   the high scale in first class meters, less than one-quarter of 1
-   per cent. for a range of 35 degrees above or 35 degrees below 70
-   degrees Fahrenheit.
-
-=Ques. What attachment is sometimes provided on station voltmeters
-used for constant pressure service?=
-
-Ans. A normal index.
-
-[Illustration: FIG. 2,894.--Temperature test of direct current
-motor or dynamo; loading back method. In making temperature tests
-on a small dynamo it is usual to drive the dynamo with a motor and
-load the dynamo by means of a lamp bank or resistance, the voltage
-across the dynamo being maintained constant, and the current through
-the external circuit adjusted to full load value. The temperatures
-are then recorded, and when they reach a constant value above the
-temperature of the atmosphere, the test is discontinued. Similarly,
-in making a test on a small motor, the motor is loaded with a dynamo
-and the load increased until the input current reaches the normal
-full load value of the motor, the test being conducted as for a small
-dynamo. When, however, the apparatus, either motor or dynamo, reaches
-a certain size, it becomes necessary, in order to economize energy,
-to use what is called the =loading back method=, as here illustrated.
-The motor is started in the usual way, with the dynamo belted to it,
-the circuit of the dynamo being open. The field of the dynamo is then
-adjusted so that the dynamo voltage is equal to that of the line.
-The dynamo is then connected to the circuit and its field resistance
-varied until it carries normal full load current. Under these
-conditions, if the motor and dynamo be of the same size and type,
-the motor will carry slightly in excess of full load, the difference
-being approximately twice the losses of the machines. Under these
-conditions the total power drawn from the line is equal to twice the
-loss of either machine. Temperature readings are taken as in other
-temperature tests.]
-
-=Ques. What precaution must be taken in connecting station
-voltmeters?=
-
-Ans. Care must be taken to guard against any short circuiting of the
-voltmeter, which, would mean a short circuiting of the generator, and
-as a result the probable burning out of its armature.
-
-     The high resistance of the voltmeter prevents any such
-   occurrence when it is connected in the proper way, but should one
-   side of the circuit be grounded to the metal case or frame of the
-   meter, a careless handling of the lead connected with the other
-   side of the circuit would produce the result just mentioned.
-
-[Illustration: FIG. 2,895.--Compound dynamo external characteristics
-test; adjustable load. The object of this test is to determine the
-relation between armature voltage and armature current. Shunt field
-is adjusted to give normal secondary voltage when the external
-circuit is open. The load is then applied by means of an adjustable
-resistance or lamp bank, and readings of external voltage and current
-recorded. If the machine be normally compounded, the external voltage
-will remain practically constant throughout the load range. If the
-machine be under-compounded, the external voltage will drop with
-load, while if over-compounded, there will be a rise in voltage with
-increase in load.]
-
-=Ques. Why do station voltmeters indicate a voltage slightly lower
-than actually exists across the leads?=
-
-Ans. Since they are usually connected permanently in circuit; a
-certain amount of heat is developed in the wiring of the instrument.
-
-[Illustration: FIGS. 2,896 and 2,897.--Transformer core loss and
-leakage, or exciting current test. With the primary circuit open,
-the ammeter indicates the exciting or no load current. It should
-be noted that all instruments are inserted on the low voltage
-side, for both safety of the operator and because the measurements
-are more accurate. The no load primary current, if the ratio of
-transformation be 10: 1, will be one-tenth of the measured secondary
-current. The wattmeter connected, as shown, measures the sum of the
-losses, in the transformer, in the pressure coil of the wattmeter,
-and in the voltmeter. On all standard makes of portable instruments,
-the resistance of the wattmeter pressure coil and of the voltmeter
-is given, and the loss in either instrument is the square of the
-voltage at its terminals, divided by its resistance. Subtracting
-these losses from the total indicated upon the wattmeter, gives the
-true core or iron loss. It should be noted that in this diagram is
-shown an auxiliary transformer with a number of taps for obtaining
-the exact rated voltage of the transformer under test. In fig. 2,897
-is shown, in general, the same connections as in fig. 2,896, except
-that the auto-transformer has been replaced by a resistance. If the
-line voltage available be not much in excess of the rated voltage of
-the transformer under test, very little error is introduced by the
-use of the resistance method. However, if the difference be 10 per
-cent. or more the auxiliary transformer shown in fig. 2,896 should be
-used. Measurements made under the resistance method always give lower
-results than those obtained with the auxiliary transformer.]
-
-     The effect of this heat increases the voltmeter resistance and
-   consequently reduces the current below that which otherwise would
-   pass through the meter; since the deflections of the pointer
-   are governed by the strength of the current, station voltmeters
-   invariably indicate a voltage slightly lower than that which
-   actually exists across their leads.
-
-[Illustration: FIG. 2,898.--Diagram of connections for calibrating a
-wattmeter. The calibration of a portable wattmeter is accomplished
-with direct current of constant value which is passed through the
-series winding by connecting the source thereof with the current
-terminals. A direct current voltage which may be varied throughout
-the range of the wattmeter is also applied to the instrument
-between the middle and right hand pressure terminals A and E the
-wiring in the meter between these terminals being such that its
-differential winding is then cut out of circuit. The method of
-procedure consists in comparing the deflections on the wattmeter at
-five of six approximately equidistant points over its scale with the
-corresponding products of volts and amperes used to obtain them. The
-changes in the wattmeter deflections are effected by merely varying
-the voltage, the value of the current being maintained constant at a
-value which represents the full current capacity of the meter.]
-
-            NOTE.--=Checking up of a recording wattmeter.=
-          This may conveniently be done by noting the
-          deflections at short intervals on an ammeter
-          connected in circuit, and also the readings
-          on the dial of the recording wattmeter during
-          this period. If this test be continued for an
-          appreciable time, the product of the pressure
-          in volts, the current in amperes, and the time
-          in hours, should equal the number of watthours
-          recorded on the counters of the dial.
-
-            NOTE.--=Transformer testing.= In the early
-          days of transformer building, before the
-          commercial wattmeter had been perfected, leakage
-          or exciting current was the criterion of good
-          design. After the introduction of the wattmeter,
-          core loss became the all important factor, and
-          for a long time the question of leakage current
-          was lost sight of. With the introduction of
-          silicon steel, leakage or exciting current again
-          assumed prominence. Keeping in mind the fact
-          that all characteristics of a transformer are of
-          more or less importance, it is essential that
-          the user of such apparatus have at hand the
-          necessary facilities for making tests of all such
-          variable quantities. The tests which all users
-          of transformers should make, are given in this
-          chapter.
-
-=Ques. Can direct current be measured by an alternating current
-voltmeter?=
-
-Ans. Yes.
-
-[Illustration: FIG. 2,899.--Transformer copper loss by wattmeter
-measurement and impedance. At first glance, this method would
-seem better than the calculation of loss after measurement of the
-resistance. However, it should be noted that the wattmeter is, in
-itself, subject to considerable error under the low power factor
-that will exist in this test. The secondary of the transformer is
-short circuited, and a voltage applied to the primary which is just
-sufficient to cause full load primary current. If full current pass
-through the primary of the transformer with the secondary short
-circuited, the secondary will also carry full load current. With
-connections as shown, and with the full load current, the voltmeter
-indicates the impedance volts of the transformer. This divided by
-the rated voltage gives what is called the _per cent. impedance of
-the transformer_. In a commercial transformer of 5 kw., this should
-be approximately 3 per cent. The iron loss of the transformer under
-approximately 3 per cent. of the normal voltage will be negligible,
-and the losses measured will be the sum of the primary and secondary
-copper losses. As in the discussion of the core loss measurements,
-the wattmeter readings must be corrected for the loss in its pressure
-coil, the method of correction being the same as that discussed under
-the core loss measurement. If the impedance volts, as measured, be
-divided by the primary current, the impedance of the transformer
-is obtained. The reciprocal of this quantity is known by the term
-"admittance." _When two or more transformers are connected in
-parallel they divide the load in proportion to their admittance._
-It is, therefore, important that the users of transformers know the
-impedance of the apparatus used, in order to determine whether two
-or more transformers will operate satisfactorily in parallel. For
-discussion of wattmeter error on low power factor, see note on page
-2,075. For accurate measurement of impedance, the voltmeter should
-be connected directly across the terminals of the transformer rather
-than as shown in the diagram.]
-
-            NOTE.--=Transformer copper loss test.= The
-          usual and best method of obtaining copper
-          losses is to separately measure the primary and
-          secondary resistance and calculate from these
-          the primary and secondary copper losses. For
-          general diagram of connections and discussion
-          of the drop method, see fig. 2,875. The current
-          should be kept well within the load current of
-          the transformer to avoid temperature rise during
-          the test. In other words, the resistance of the
-          coil is the voltage across its terminals divided
-          by the current. The resistance of the primary
-          coil can be measured similarly. The copper loss
-          in watts in each coil will then be the product
-          of the resistance and the square of the rated
-          current for that coil. The total copper loss will
-          be the sum.
-
-=Ques. What would be the effect of placing a direct voltmeter across
-an alternating current circuit, and why?=
-
-Ans. There would be no deflection of the pointer owing to the rapid
-reversals of the alternating current.
-
-=Ques. What are the usual capacities of alternating current
-voltmeters?=
-
-Ans. They are 3, 7.5, 10, 12, 15, 20, 60, 75, 120, 150, 300 and 600
-volts, but these capacities may each be increased by the use of a
-multiplier.
-
-[Illustration: FIG. 2,900.--Temperature test of transformer with
-non-inductive load. The figure shows the simplest way of making the
-test. Connect the primary of the transformer to the line as shown,
-and carry normal secondary load by means of a bank of lamps or other
-suitable resistance, until full load secondary current is shown by
-the ammeter in the secondary circuit. The transformer should then be
-allowed to run at its rated load for the desired interval of time,
-temperature readings being made of the oil in its hottest part, and
-also of the surrounding air. Where temperatures of the coil rather
-than temperatures of the oil are desired, it is necessary to use the
-resistance method. This is obtained by first carefully measuring the
-resistance of both primary and secondary coils at the temperature
-of the room, and then, after the transformer has been under heat
-test for the desired time, disconnect it from the circuit and again
-measure the resistance of primary and secondary. For proper method
-of calculating the temperature rise from resistance measurements,
-the reader is referred to the standardization rules of the A.I.E.E.
-In making resistance measurements of large transformers by the drop
-method care should be taken to allow both ammeter and voltmeter
-indications to settle down to steady values before readings are
-taken. This may require several minutes. Each time the current is
-changed it is necessary in order to obtain check values on resistance
-measurements, to wait until the current is again settled to its
-permanent value before taking readings. All resistance measurements
-must be taken with great care, as small errors in the measurement of
-the resistance may make very large errors in the determination of
-the temperature rise. The method above described is satisfactory for
-small transformers. Where large units are to be tested, the cost of
-current for testing becomes an important item. The "bucking test" as
-in fig. 2,901, is more economical.]
-
-=Ques. How are station voltmeters usually attached to the
-switchboard?=
-
-Ans. They are usually bolted to the switchboard by means of four
-iron supports mounted on the back of the instrument; two of these are
-fastened near each side of the case.
-
-     Under certain conditions, however, as in paralleling of
-   alternators, it is convenient to have the alternating current
-   voltmeter mounted on a swinging bracket at the side of the
-   switchboard. The voltmeter may then be swung around in any desired
-   direction so as to enable the attendant to keep informed of the
-   voltage while switching in each additional alternator.
-
-[Illustration: FIG. 2,901.--Transformer temperature "bucking test."
-For this purpose two transformers of the same size and ratio are
-required. The connections are as shown. Full secondary voltage is
-applied, and rheostats or auxiliary auto-transformers are inserted
-in the circuit to properly regulate the voltage. The primaries
-are connected with one bucking the other, and a voltage equal to
-twice the impedance voltage of either transformer inserted in the
-primary circuit. It should be noted that when the secondaries are
-subjected to the full secondary voltage, a full primary voltage
-exists across either primary, but with the primaries connected so
-that the voltage of one is bucked against the voltage of the other,
-the resultant voltage in the circuit will be zero. By applying to the
-primary circuit twice the impedance voltage of either transformer,
-full primary and secondary current will circulate through both
-transformers. On the other hand, by subjecting the secondaries to
-the full secondary voltage, the iron of the transformer will be
-magnetized as under its regular operating conditions, and the full
-iron loss of the transformer introduced. This method permits the
-operation of two transformers under temperature test with their
-full losses, without taking energy from the line equal to the rated
-capacity. Measurements of temperature are taken in exactly the
-same way as above. This method is successfully employed for making
-temperature tests on transformers of all sizes.]
-
-=Ques. How should an ammeter be operated to get accurate readings,
-and why?=
-
-Ans. It should be cut out of circuit except while taking a reading,
-because of the error introduced by the heating effect of the current.
-
-[Illustration: FIG. 2,902.--Transformer insulation test. In applying
-a 10,000 volt insulation test between the primary and secondary of
-a transformer, the testing leads should be disconnected from the
-transformer under test, and a spark gap introduced as shown, with the
-test needle set at a proper sparking distance for 10,000 volts. A
-high resistance should be connected in the secondary before closing
-its circuit, and the voltage gradually increased by cutting out
-this secondary resistance until a spark jumps across the spark gap.
-When the spark jumps across the spark gap, the voltmeter reading
-should be recorded and the testing transformer disconnected. The
-spark gap should then be increased about 10 per cent. and the high
-tension leads connected to the transformer under test as indicated
-in the diagram. In order to equalize the insulation strains, all
-primary leads should be connected together, all secondary leads not
-only connected together, but to the core as well. All resistance
-in the rheostat in the low tension circuit should then be inserted
-and the switch closed. Gradually cut out secondary resistance until
-the voltmeter shows the same voltage as was recorded previously
-when the spark jumped across the gap, and apply this voltage to the
-transformer for one minute. Insulation tests for a period of over
-one minute are very unadvisable, as transformers with excellent
-insulation may be seriously damaged by prolonged insulation tests.
-The longer the strain to which any insulation is subjected, the
-shorter the subsequent life of the insulation. Also the greater the
-applied voltage above the actual operating voltage of the apparatus,
-the shorter the subsequent life of the insulation. In testing small
-transformers, the spark gap may be omitted and the voltage of the low
-pressure coil of the testing transformer measured. This multiplied by
-the ratio of transformation gives the testing voltage.]
-
-     In an ammeter having a capacity of 50 amperes, the error thus
-   introduced will be less than 1 per cent. if connected continuously
-   in circuit with a current not exceeding three-quarters this
-   capacity.
-
-     An ammeter of 100 amperes capacity may be used indefinitely
-   in circuit with less than 1 per cent. error up to one-half its
-   capacity, and for five minutes at three-quarters capacity without
-   exceeding the 1 per cent. limit.
-
-[Illustration: FIG. 2,903.--Transformer insulation test as made
-when a special high tension transformer be not available. In this
-method a number of standard transformers, connected as shown may be
-employed, but great care should be taken to have such transformer
-cases thoroughly insulated from the ground and from one another, in
-order to minimize the insulation strains in the testing transformers.
-Care should be taken to insert in the circuit of each testing
-transformer a fuse, not in excess of the transformer capacity, which
-will blow, in case of a break down in the apparatus under test.
-In testing insulation between secondary and core, disconnect the
-primary entirely, apply one terminal of the testing transformer to
-the secondary terminals of the transformer under test, and the other
-terminal of the testing transformer to the core of the transformer
-under test. This test should also not be in excess of one minute.]
-
-     The 150 scale ammeter may be left in circuit for an indefinite
-   length of time at one-third its full capacity, and for three
-   minutes at one-half its full capacity, with a negligible error.
-
-     Ammeters of 200 and of 300 ampere capacities must not
-   continuously carry more than one-quarter of these loads
-   respectively if the readings are to have an accuracy within 1 per
-   cent. nor more than one-half these respective number of amperes
-   for three minutes if the same degree of accuracy be desired.
-
-     In order to cut or shunt the ammeter out of circuit when not
-   in use, it is customary when wiring the instrument in place, to
-   introduce a switch as a shunt across it; this switch is kept
-   closed except when a measurement is being taken.
-
-     When currents larger than 300 amperes have to be measured,
-   ammeter shunts are generally employed, although ammeters up to
-   500 amperes capacity are manufactured.
-
-[Illustration: FIG. 2,904.--Transformer internal insulation test,
-sometimes called double normal voltage test, from the fact that most
-transformers are tested with double normal voltage across their
-terminals. If either the primary or secondary of the transformer
-be connected to some source of current with voltage double that of
-the voltage of the transformer under test, the insulation between
-adjacent turns, and also the insulation between adjacent layers
-will be subjected to twice the normal operating voltage. It is good
-practice to employ high frequency for this test in order to prevent
-an abnormal current from passing through the transformer. Sixty
-cycle transformers are usually tested on 133 cycles, and 25 cycle
-transformers on 60 cycle circuits for this double normal voltage
-test. It is necessary to insert the resistance in the circuit of the
-transformer and bring the voltage up gradually, the same as applying
-other high insulation tests in order to prevent abnormal rises in
-pressure at the instant of closing the circuit.]
-
-=Ques. What is used in place of instrument shunts for high pressure
-alternating current measurements?=
-
-Ans. Instrument transformers.
-
-=Ques. What important attention should be periodically given to
-measuring instruments?=
-
-Ans. They should be frequently tested by comparison with standards
-that are known to be correct.
-
-     Electrical measuring instruments, owing to the nature of their
-   construction and the conditions under which they must necessarily
-   be used, are subject to variations in accuracy. This feature is an
-   annoying one on account of the difficulty of detecting it; a meter
-   may, as far as appearances go, be in excellent working order and
-   yet give readings which are not to be relied upon.
-
-     Ridiculous as it may appear, the average station attendant
-   may frequently be seen straining his eyes to read to tenths of
-   a division on the scale of a meter which, if subjected to test,
-   would show an inaccuracy of over 2 per cent.
-
-     In testing a meter, by comparing it with a standard, in order to
-   obtain the best results there should be one man at each meter so
-   that simultaneous readings may be taken on both instruments, and
-   the man at the standard meter should maintain the voltage constant
-   while a reading is being taken, by means of a rheostat in the
-   field circuit of the generator supplying the current.
-
-[Illustration: FIG. 2,905.--Transformer insulation resistance
-test. The insulation, besides being able to resist puncture, due
-to increased voltage, must also have sufficient resistance to
-prevent any appreciable amount of current flowing between primary
-and secondary coils. It is, therefore, sometimes important that the
-insulation resistance between primary and secondary be measured. This
-can be done, as here shown. Great care should be taken to have all
-wires thoroughly insulated from the ground, and to have an ammeter
-placed as near as possible to the terminals of the transformer under
-test, in order that current leaking from one side of the line to the
-other, external to the transformer, may not be measured. Great care
-is required in making this measurement, in order to obtain consistent
-results.]
-
-     Each meter should be checked or calibrated at five or six
-   approximately equidistant points over its scale; the adjustable
-   resistance being varied each time to give a deflection on the
-   standard meter of an even number of divisions and the deflection
-   on the other meter recorded at whatever it may be. Having obtained
-   the necessary readings, the calculation of the constant or
-   multiplying factor of the meter undergoing test is next in order.
-
-     This may best be shown by taking an actual case in which a 150
-   scale voltmeter is being tested to determine its accuracy. The
-   data and calculations are as follows:
-
-   Readings on     Readings on        Constant
-  standard meter   meter tested
-       150            149.2        150 ÷ 149.2 = 1.005
-       125            125.0        125 ÷ 125.0 = 1.000
-       100             98.9        100 ÷  98.9 = 1.011
-        75             73.6         75 ÷  73.6 = 1.019
-        50             50.0         50 ÷  50.0 = 1.000
-        25             24.8         25 ÷  24.8 = 1.008
-                                                ------
-                                                 6.043
-
-  Average constant for six readings, 6.043 ÷ 6 = 1.007.
-
-[Illustration: FIG. 2,906.--Transformer winding or ratio test. The
-object of this test is to check the ratio between the primary and
-the secondary windings. For this purpose a transformer of known
-ratio is used as a standard. Connect the transformer under test with
-a standard transformer as shown. Leave switch S_{2} open. With the
-single pole double throw switch in position S_{1}B, the voltmeter
-is thrown across the terminals of the standard transformer. With
-the switch in position S_{1}A, the voltmeter is thrown across the
-terminals of the transformer under test. The voltmeter should be read
-with the switch in each position. If the winding ratio be the same as
-that of the standard transformer, the two voltmeter readings will be
-identical.]
-
-     It may be stated in general that before taking the readings for
-   this test, the zero position of the pointer on the meter tested
-   should be noted, and if it be more than two-tenths of a division
-   off the zero mark, the case of the meter should be removed and the
-   pointer straightened.
-
-     Furthermore, it will be noticed from the readings here recorded
-   that the test is started at the high reading end of the scale;
-   this is done in order that the pointer may gradually be brought
-   up to this spot, by slowly cutting out of circuit the adjustable
-   resistance, and thus show whether or not the pointer has a
-   tendency to stick at any part of the scale. If the meter seem to
-   be defective in this respect, it should be remedied either by
-   bending the pointer or scale, or by renewing one or both of the
-   jewels, before the comparison with the standard is commenced.
-
-     It is obvious from the readings recorded for the 150 scale
-   voltmeter, that as compared with the corresponding deflections of
-   the standard, the former are a trifle low.
-
-     In order to determine for each observation how much too low
-   they are, it is necessary to divide each reading on the standard
-   by the corresponding reading on the meter tested. The result is
-   the amount by which a deflection of this size on the meter tested
-   must be multiplied in order to obtain the exact reading. This
-   multiplier is called a constant, and as shown, a constant is
-   determined for each of the six observations.
-
-     The average constant for the six readings is then found, and
-   this is taken as the constant for the meter as a whole; that is,
-   whenever this 150-scale voltmeter is used, each reading taken
-   thereon must be multiplied by 1.007 in order to correct for its
-   inaccuracy.
-
-     The most convenient and systematic way of registering the
-   constant of a meter is to write it, together with the number of
-   the meter and the date of its calibration, in ink on a cardboard
-   tag and loop the same by means of a string to the handle or some
-   other convenient part of the meter.
-
-            NOTE.--=Transformer polarity test.= A test of
-          importance in the manufacture of transformers,
-          and sometimes necessary for the user, is the
-          so called _banking_ or _polarity_ test. The
-          transformers from any particular manufacturer
-          have the leads brought out in such a manner that
-          a transformer of any size can be connected to
-          primary and secondary lines in a given order
-          without danger of blowing the fuses due to
-          incorrect connections. All manufacturers of
-          transformers, however, do not bank transformers
-          in the same way, so that it is necessary in
-          placing transformers of different makes to test
-          for polarity. This is done as shown in fig.
-          2,906. One transformer is selected as a standard
-          and the leads of the second transformer connected
-          as indicated in the diagram. If the transformers
-          be 1,100-2,200 volts to 110-220, two 110 volt
-          lamps are connected in the secondaries of the
-          transformers as indicated, while the primary of
-          the transformer is connected across the line.
-          In transformers built for two primary and two
-          secondary voltages, it is necessary to test each
-          primary and each secondary. The diagram shows the
-          method of connecting one 2,200 volt coil and one
-          110 volt coil to the transformer to be tested.
-          When the primary circuit of the transformer under
-          test is closed, and if the secondary leads of
-          the 110 volt coil under test be brought out of
-          the case properly, the two 110 volt lamps should
-          be brightly illuminated. If, on the other hand,
-          the two 110 volt terminals have been reversed,
-          no current will flow through the lamps. If
-          these two terminals be found to be brought out
-          correctly, transfer the secondary leads of the
-          transformer under test to the second 110 volt
-          coil. Upon closing the primary circuit, the lamp
-          should again be brightly illuminated. Repeat this
-          process with each of the secondary coils and the
-          other primary coil, and if the lamps show up
-          brightly in every case on closing the primary
-          circuit, all leads have been properly brought
-          out. If on any tests the lamps do not light up
-          brightly, the leads on the transformer must be so
-          changed as to produce the proper banking.
-
-=Ques. What are the usual remedies applied to a voltmeter to correct
-a 3 or 4 per cent. error?=
-
-Ans. They consist of straightening the pointer, varying the tension
-of the spiral springs, renewing the jewels in the bearings, altering
-the value of the high resistance, and, in the case of a direct
-current instrument, strengthening the permanent magnet.
-
-=Ques. How is the permanent magnet strengthened?=
-
-Ans. After detaching it from the instrument, wrap around several
-turns of insulated wire, and pass through this wire for a short time
-3 or 4 amperes of direct current in such a direction as to reinforce
-the magnet magnetism.
-
-=Ques. How may the value of the high resistance of a voltmeter be
-altered?=
-
-Ans. Determine the resistance of the voltmeter and add or subtract,
-according as the reading is high or low, a certain length of wire
-whose resistance is in per cent. of the voltmeter resistance the same
-as the per cent. of error.
-
-            NOTE.--The complete calibration of a two
-          scale voltmeter does not, as might be supposed,
-          necessitate that the readings on both scales be
-          checked with standards, for since the resistance
-          corresponding to the one scale is always some
-          multiple of the resistance of the other, the
-          constants of the two scales are proportional. For
-          instance, if S = the reading at the end of the
-          high scale of the voltmeter; S^{1} = the reading
-          at the end of the low scale of the voltmeter; R =
-          the resistance in the meter corresponding to the
-          high scale; R^{1} = the resistance in the meter
-          corresponding to the low scale; K = the constant
-          for the high scale, and K^{1} = the constant for
-          the low scale. Then
-
-           SK ÷ R = S^{1}K^{1} ÷ R^{1}
-
-from which
-
-           K^{1} = SKR ÷ S^{1}R
-
-     That is to say, if the respective resistances corresponding to
-   the two scales be known, and the constant of the high scale be
-   determined by comparison with a standard, then by aid of these
-   known values and the maximum readings on the two scales, the
-   constant of the low scale may be calculated. It is also possible
-   to calculate the constant of the high scale if the constant of the
-   low scale be known, together with the values of the resistances
-   corresponding to the two scales; for from the equation previously
-   given.
-
-           K = RS^{1}K^{1} ÷ R^{1}S
-
-=Ques. What is a frequent cause of error in an alternating current
-meter, and why?=
-
-Ans. The deterioration of its insulation, which permits the working
-parts of the instrument coming in contact with the surrounding metal
-case.
-
-     A convenient method of testing for deterioration of insulation
-   is shown in fig. 2,905.
-
-[Illustration: FIG. 2,907.--Diagrams showing various synchronous
-converter transformer connections. The diametrical connection is
-used most frequently as it requires only one secondary coil on each
-transformer, this being connected to diametrically opposite points on
-the armature winding. The middle points can be connected together and
-a neutral obtained the unbalanced three wire direct current having no
-distorting effect. With diametrical secondaries, the primaries should
-preferably be connected delta, except with regulating pole converters
-where they must be connected Y. Diametrical secondaries with delta
-primaries should not be used with regulating pole converters. Double
-star connection of secondaries may, however, be used with delta
-primaries, and is free from the trouble of the triple harmonic of the
-transformer appearing in the primary. In this case, however, the two
-secondary neutrals must not be connected with each other.]
-
-=How to Test Generators.=--In the operation of electrical stations,
-many problems dealing with the generators installed therein can be
-readily solved by the aid of characteristic curves, which bear a
-relation to the generators similarly as do indicator diagrams to
-steam engines.
-
-[Illustration: FIG. 2,908.--General form of characteristic curves
-for a series dynamo. The general curve that may be expected is OA.
-It is obtained practically in the same manner as for the shunt
-characteristic curve, except that no field rheostat is employed.
-Commencing with no load or amperes, there will probably be a
-small deflection noticeable on the voltmeter, due to the residual
-magnetism. The other readings are taken with successive reductions
-of main current resistance. The curve OA thus obtained for a certain
-series generator is practically a straight line at the beginning,
-representing thereby a proportional increase of voltage with
-increase of current, but after a certain current is reached (about
-20 amperes in this case) the curve flattens and takes a downward
-direction. The turning point occurs in the characteristic curves
-of all series generators, and it denotes the stage at which the
-iron magnet cores become so saturated with lines of magnetic force
-that they will not readily allow more to pass through them; this
-turning point is technically known as the point of saturation, and
-the current corresponding (20 amperes in this case) is called the
-critical current of the dynamo. The point of saturation in any given
-series machine is governed by the amount of iron in the magnetic
-circuit; its position in the curve therefore varies according to
-the design of the generator as does also the critical current. The
-value of the latter is important inasmuch as the valuable features
-of a series generator assert themselves only when the machine is
-supplying a greater number of amperes than that of the critical
-current, for if the series generator be worked along that part M A of
-the curve to the right of the point of saturation it becomes nearly
-self-regulating as regards current, because as the current increases
-the voltage drops. In the diagram in addition to the characteristic
-curve O A, which may more definitely be called an external
-characteristic curve on account of representing the conditions
-external to the generator, there is shown a total characteristic
-curve, O C B. The latter curve represents the relation between the
-current and the total voltage developed in the armature, and may be
-plotted from the external characteristic curve if the resistance of
-the armature between brushes and the resistance of the series field
-winding be known. For example, assume these combined resistances
-amount to .6 ohm. At 30 amperes there would be required 30 × .6 = 18
-volts to force this current through the armature and field windings.
-At 30 amperes the external pressure is 65 volts, as shown by the
-curve O A; the total voltage developed for 30 amperes is, therefore,
-the external voltage plus the internal voltage or 65 + 18 = 83
-volts. Plotting 83 volts for 30 amperes will give one point for the
-external characteristic curve of this machine, and by determining in
-like manner the total voltages developed for six or eight different
-currents over the scale, sufficient data will be at hand for plotting
-and drawing in the curve O C B.]
-
-In steam engineering, a man who did not fully understand the method
-of taking an indicator diagram would be considered not in touch with
-his profession, and in electrical engineering the same would be true
-of one ignorant of the method of obtaining characteristic curves.
-
-     The necessary arrangement or connection of the generator from
-   which it is desired to obtain a characteristic curve, consists in
-   providing a constant motive power so that the machine may be run
-   at a uniform speed, and when the field magnets of the generator
-   are separately excited the field current from the outside source
-   must also be maintained constant, preferably by a rheostat
-   connected in the field of the auxiliary exciting machine. It is
-   also necessary in every case that means be provided for varying
-   the main current of the generator step by step from zero to
-   maximum. This may best be done by employing a water rheostat, as
-   shown in fig. 2,909.
-
-=Ques. What instruments are needed in making a test of dynamo
-characteristics?=
-
-Ans. A voltmeter, ammeter, speed indicator, the usual switches and
-rheostats.
-
-=Ques. How is the apparatus connected?=
-
-Ans. It is connected as shown in fig. 2,910.
-
-=Ques. Describe the test.=
-
-Ans. Having completed the preliminaries as in fig. 2,910, the test
-should be started with the main circuit of the generator open. Then,
-in the case of the shunt machine, the speed should be made normal and
-the field rheostat adjusted until the voltmeter reading indicates
-the rated voltage of the machine at no load and readings taken. The
-electrodes of the water rheostat should be adjusted for maximum
-resistance and main circuit closed, and a second set of readings
-taken. Several sets of readings are taken, with successive reductions
-of water rheostat resistance. The results are then plotted on
-coordinate paper giving the characteristic curve shown in fig. 2,908.
-
-[Illustration: FIG. 2,909.--Water rheostat. It consists essentially
-of a tank of suitable size containing salt water into which are
-placed two electrodes having means of adjustment of the distance
-separating them. The solution depends on the voltage. Pure water is
-seldom used for pressures under 1,000 volts. The size of the tank is
-determined by the size of the electrodes, and roughly the size of the
-latter equal the number of amperes. With a current density of one
-ampere per square inch, a water solution gives a drop of 2,500 to
-3,000 volts per inch distance between the plates. Where high voltage
-is used, the water must be circulated through and from the tank by
-rubber hose allowing for 2,500 volts, a length of 15 to 20 feet of
-1 inch hose to prevent grounding. In place of the arrangement shown
-above, a barrel may be used for the tank, and for the electrodes,
-coils of galvanized iron wire. This is the simplest form and is
-satisfactory.]
-
-=Ques. What does the characteristic curve (fig. 2,911) show?=
-
-Ans. An examination of the curve shows that the highest point of
-the curve occurs at no load or 0 amperes; that as the current is
-increased, the voltage drops, first slightly to the point B and then
-rapidly until the point E is reached, when any further lowering of
-resistance in the main circuit to increase the current causes not
-only a rapid decline in the voltage but also of the current until
-both voltage and current become approximately zero.
-
-[Illustration: FIG. 2,910.--Connections for test of dynamo. During
-the test, one man should be assigned to the tachometer, another man
-to the water rheostat, and there should preferably be one man at
-each of the electrical measuring instruments. In order to enable the
-man at the tachometer to keep the speed constant, he should be in
-communication either directly or indirectly with the source of the
-driving power, and the man at the water rheostat should be in plain
-view of the man reading the ammeter so that the latter party may
-signal him for the proper adjustment of the rheostat in order that
-the desired increase of current be obtained for each set of readings.]
-
-     In some generators, a very slight current results even when the
-   terminals of the machine are actually short circuited; that is,
-   due to residual magnetism in the pole pieces, the lower portion of
-   the curve often terminates, not exactly at zero, but at a point
-   some distance along the current line.
-
-     The working portion of the curve is from A to C, at which time
-   the machine is supplying a fairly constant voltage. From C to E
-   shows a critical condition of affairs, while the straight portion
-   D O represents the unstable part of the curve caused by the field
-   current being below its proper value.
-
-     The position of the point C determines the maximum power the
-   machine is capable of developing, being in this case (47.5 × 25) ÷
-   746 = 1.59 horse power.
-
-=Ques. How may the commercial efficiency of a generator be
-determined?=
-
-Ans. To obtain the commercial efficiency, the _input_ and _output_
-must be found for different loads.
-
-     The input may be found by running the generator as a motor
-   at its rated speed, loading it by means of a Prony brake. The
-   generator must be stripped of all belting or other mechanical
-   connections, supplied with its normal voltage and full load
-   current, and the pressure of the Prony brake upon its armature
-   shaft or pulley adjusted until the rated speed of the armature is
-   obtained. The data thus obtained is substituted in the formula.
-
-                                         2π L W R
-           input in brake horse power = ----------      (1)
-                                          33,000
-
-in which
-
-           L = length of Prony brake lever;
-           W = pounds pull at end of lever;
-           R = revolutions per minute.
-
-The output or electrical horse power for the same load is easily
-calculated from the formula
-
-                                     amperes × volts
-           output in electrical horse power = ---------------  (2)
-                                          746
-
-After obtaining value for (1) and (2) the commercial efficiency for
-the load taken is obtained from the formula
-
-                                   output
-           commercial efficiency = ------      (3)
-                                    input
-
-Having obtained the commercial efficiency, the difference between the
-ideal 100 per cent. and the efficiency found will be due to certain
-losses in the generator. These losses may be classified as
-
-  1. Mechanical.
-  2. Electrical.
-
-     The mechanical losses are the friction of the bearings and
-   brushes, and air friction. The electrical losses consist of the
-   eddy current loss, hysteresis loss, armature resistance loss, and
-   field resistance loss.
-
-     In testing for these losses, the generator to be tested should
-   be belted to a calibrated motor which latter machine should
-   preferably be of the constant pressure, shunt wound type.
-
-     The friction of the bearings and belt of the generator are
-   determined together by raising the brushes off its commutator and
-   running it at the rated speed by means of the calibrated motor.
-
-[Illustration: FIG. 2,911.--Characteristic curve of shunt dynamo.
-Suppose in making the test, the deflections on the meters for the
-first readings be 63 volts and 0 amperes, the plotting of these
-values will give the first point on the curve. Similarly, the second
-readings with main circuit closed and maximum resistance in the water
-rheostat may be assumed to be 62.5 volts and 7.5 amperes, which
-plotted gives the second point B. A still further lowering of the
-plate will permit a stronger current in the main circuit, and the
-value of this together with its corresponding voltage will give a
-third point for the curve. Neither for this reading, however, nor
-for the following readings of the test should the field rheostat be
-altered. When six or eight points ranging from zero to a maximum
-current have been obtained and plotted, a curved line should be drawn
-through them such as shown through ABCDEFG0, the _characteristic
-curve_ of the dynamo. While the curve may be sketched in free hand,
-it should preferably be drawn by the aid of French curves. In case
-the French curve cannot be exactly made to coincide with all the
-points as for instance C and D, it should be run in between giving an
-average result, and smoothing out irregularities, or small errors due
-to the "personal equation." The meter of course must be correct or
-calibrated and the readings corrected by the calibration coefficient.]
-
-     The amount of power as ascertained from the calibration curve of
-   the motor for the voltage and current used therein when driving
-   the generator as just explained, is a measure of these two losses.
-   The power thus used is practically constant at all loads and is
-   about 2 per cent. of that necessary to drive the generator at full
-   load.
-
-[Illustration: FIG. 2,912.--Characteristic curves for a compound
-dynamo. If the machine be over compounded, the characteristic curve
-has the form of the curve A B, which curve was obtained from a
-machine over-compounded from 118 to 123 volts, and designed to give
-203 amperes at full load. The preliminary arrangements for testing
-a compound dynamo are similar to those for a shunt generator, and
-if the shunt across the series field winding be already made up and
-in position, the readings are taken precisely in the same manner.
-It is generally considered sufficient if observations be recorded
-at zero, ¼, ½, ¾ and full load. If it be desired to ascertain the
-effect which residual magnetism has upon the field magnets the
-current is decreased after the full load point is reached without
-opening the circuit, and readings are taken in succession at ¾,
-½, ¼ and zero load giving in this case the curve B C D E S. It is
-thus seen that residual magnetism exerts no small effect upon the
-voltage obtained at the different loads, for had there been no
-residual magnetism in the field magnets the curve B C D E S would
-have coincided with the curve A B. The curve A B, and the straight
-line A X drawn through the points A and B, are almost identical,
-and as A X represents the theoretical characteristic curve for the
-machine, it is seen that compounding is practically perfect. In
-order to insure such accurate results being obtained, providing
-the machinery be correctly designed, requires considerable care in
-taking the readings; for example, each step or load on the ascending
-curve should not be exceeded before the corresponding deflection is
-taken, else the residual magnetism will cause the pressure reading
-to be higher than it actually should be, and the following pressure
-readings will also be affected in the same manner. In case the shunt
-to be employed across the series field has not been made up, it is
-advisable to perform a trial test before taking the readings for the
-curve as previously described. The trial test consists in taking
-two readings,--one at no load and the other at full load, the shunt
-being so adjusted as to length and section that the desired amount
-of compounding will be obtained in the latter reading with normal
-voltage at no load. If the first trial fail to produce the desired
-result by giving too low a voltage at full load, the length of the
-shunt across the series field should be increased, or its section
-should be reduced by employing a less number of strips in its makeup;
-again, if the voltage at full load be higher than that desired, there
-must be made a decrease in length or an increase of section in the
-shunt employed.]
-
-     The friction of the brushes can very conveniently be determined
-   next by lowering them on the commutator and giving them the proper
-   tension.
-
-     The increase in power resulting from the greater current that
-   will now be taken by the motor to run the dynamo at its rated
-   speed, will be a measure of this loss. In general, its value will
-   be about .5 per cent. of the total power required to drive the
-   dynamo at full load, and this also will remain constant at all
-   loads.
-
-     The friction of the air upon the moving armature of the dynamo
-   cannot be determined experimentally, but theoretically this loss
-   is small and may be estimated as .5 per cent.; it is also constant
-   at all loads.
-
-     The core loss may be determined experimentally by exciting
-   the field magnets of the dynamo with the normal full load field
-   current through the magnet coils, and noting the increase of power
-   required by the motor to maintain the rated speed of the dynamo
-   thus excited under no load, over that necessary under the same
-   conditions with no field excitation. This increase of power will
-   be the value of the core loss. The core loss is approximately 3
-   per cent. of the power required to operate the dynamo at full
-   load, and it is constant at varying loads. If it be desired to
-   divide the core loss into its component parts, it is necessary
-   also to run the dynamo under the same conditions as before with
-   field excitation but at half its rated speed. If, then,
-
-  H = the power lost in hysteresis at rated speed,
-  E = the power lost in eddy currents at rated speed,
-  T = the power lost in hysteresis and eddy currents at rated speed,
-  S = the power lost in hysteresis and eddy currents at half speed.
-
-there may be formed the two following equations:
-
-                               H     E
-           T = H + E, and S = --- + ---,
-                               2     2
-
-     from which the elimination of H will give E = 2T - 4S.
-
-     The value of the eddy current loss thus found will be about 1½
-   per cent., and constant at all loads.
-
-     Having previously ascertained the power lost in both eddy
-   currents and hysteresis, and knowing now the power lost in eddy
-   currents alone, it is easy to find that lost in hysteresis by
-   simply subtracting the latter known value from the former. The
-   value of the hysteresis loss is therefore approximately 1½ per
-   cent., and it is constant at different loads.
-
-     There yet remains to be determined the armature resistance
-   loss and the field resistance loss. As for the calibrated motor,
-   this may be disconnected from the dynamo, as it need not be used
-   further in the test.
-
-     The armature resistance is the resistance of the armature
-   winding of the dynamo, between the commutator bars upon which
-   press the positive and negative brushes. Assume that the value
-   of the armature resistance be known, call this value R ohms,
-   together with that of the full load armature current, which is
-   also known and which call I amperes, this is sufficient data for
-   calculating the armature resistance loss at full load. It is
-   evident that to force the full load current I through the armature
-   resistance R will require a pressure of R volts, and that the
-   watts lost in doing so will be the voltage multiplied by the
-   current. The armature resistance is consequently
-
-           IR × I = I^{2}R watts
-
-or, expressed in horse power it is
-
-           I^{2}R ÷ 746
-
-     At full load it is usually about 2 per cent. of the total
-   power required to drive the generator fully loaded. The armature
-   resistance loss varies in proportion to the load, in fact, as the
-   last expression shows, it increases as the square of the armature
-   current.
-
-     The field resistance loss is calculated in the same manner as
-   just explained for the armature resistance loss, it being equal
-   in horse power to the square of the full load field current
-   multiplied by the resistance of the field winding and divided by
-   746. In a shunt dynamo it is practically constant at 2 per cent.
-   of the total power at full load, but in a series or in a compound
-   generator it will vary in proportion to the load.
-
-
-
-
-   HAWKINS PRACTICAL LIBRARY OF ELECTRICITY
-
-   IN HANDY POCKET FORM       PRICE $1 EACH
-
-
-_They are not only the best, but the cheapest work published on
-Electricity. Each number being complete in itself. Separate numbers
-sent postpaid to any address on receipt of price. They are guaranteed
-in every way or your money will be returned. Complete catalog of
-series will be mailed free on request._
-
-=ELECTRICAL GUIDE, NO. 1=
-     Containing the principles of Elementary Electricity, Magnetism,
-   Induction, Experiments, Dynamos, Electric Machinery.
-
-=ELECTRICAL GUIDE, NO. 2=
-     The construction of Dynamos, Motors, Armatures, Armature
-   Windings, Installing of Dynamos.
-
-=ELECTRICAL GUIDE, NO. 3=
-     Electrical Instruments, Testing, Practical Management of Dynamos
-   and Motors.
-
-=ELECTRICAL GUIDE, NO. 4=
-     Distribution Systems, Wiring, Wiring Diagrams, Sign Flashers,
-   Storage Batteries.
-
-=ELECTRICAL GUIDE, NO. 5=
-     Principles of Alternating Currents and Alternators.
-
-=ELECTRICAL GUIDE, NO. 6=
-     Alternating Current Motors, Transformers, Converters, Rectifiers.
-
-=ELECTRICAL GUIDE, NO. 7=
-     Alternating Current Systems, Circuit Breakers, Measuring
-   Instruments.
-
-=ELECTRICAL GUIDE, NO. 8=
-     Alternating Current Switch Boards, Wiring, Power Stations,
-   Installation and Operation.
-
-=ELECTRICAL GUIDE, NO. 9=
-     Telephone, Telegraph, Wireless, Bells, Lighting, Railways.
-
-=ELECTRICAL GUIDE, NO. 10=
-     Modern Practical Applications of Electricity and Ready Reference
-   Index of the 10 Numbers.
-
-  =Theo. Audel & Co., Publishers.     72 FIFTH AVENUE=,
-                                        =NEW YORK.=
-
-
-
-
-
-End of the Project Gutenberg EBook of Hawkins Electrical Guide Vol. 8 (of 10), by 
-Nehemiah Hawkins
-
-*** END OF THIS PROJECT GUTENBERG EBOOK HAWKINS ELECTRICAL GUIDE, VOL 8 ***
-
-***** This file should be named 50068-0.txt or 50068-0.zip *****
-This and all associated files of various formats will be found in:
-        http://www.gutenberg.org/5/0/0/6/50068/
-
-Produced by Juliet Sutherland, Paul Marshall and the Online
-Distributed Proofreading Team at http://www.pgdp.net
-
-Updated editions will replace the previous one--the old editions will
-be renamed.
-
-Creating the works from print editions not protected by U.S. copyright
-law means that no one owns a United States copyright in these works,
-so the Foundation (and you!) can copy and distribute it in the United
-States without permission and without paying copyright
-royalties. Special rules, set forth in the General Terms of Use part
-of this license, apply to copying and distributing Project
-Gutenberg-tm electronic works to protect the PROJECT GUTENBERG-tm
-concept and trademark. Project Gutenberg is a registered trademark,
-and may not be used if you charge for the eBooks, unless you receive
-specific permission. If you do not charge anything for copies of this
-eBook, complying with the rules is very easy. You may use this eBook
-for nearly any purpose such as creation of derivative works, reports,
-performances and research. They may be modified and printed and given
-away--you may do practically ANYTHING in the United States with eBooks
-not protected by U.S. copyright law. Redistribution is subject to the
-trademark license, especially commercial redistribution.
-
-START: FULL LICENSE
-
-THE FULL PROJECT GUTENBERG LICENSE
-PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK
-
-To protect the Project Gutenberg-tm mission of promoting the free
-distribution of electronic works, by using or distributing this work
-(or any other work associated in any way with the phrase "Project
-Gutenberg"), you agree to comply with all the terms of the Full
-Project Gutenberg-tm License available with this file or online at
-www.gutenberg.org/license.
-
-Section 1. General Terms of Use and Redistributing Project
-Gutenberg-tm electronic works
-
-1.A. By reading or using any part of this Project Gutenberg-tm
-electronic work, you indicate that you have read, understand, agree to
-and accept all the terms of this license and intellectual property
-(trademark/copyright) agreement. If you do not agree to abide by all
-the terms of this agreement, you must cease using and return or
-destroy all copies of Project Gutenberg-tm electronic works in your
-possession. If you paid a fee for obtaining a copy of or access to a
-Project Gutenberg-tm electronic work and you do not agree to be bound
-by the terms of this agreement, you may obtain a refund from the
-person or entity to whom you paid the fee as set forth in paragraph
-1.E.8.
-
-1.B. "Project Gutenberg" is a registered trademark. It may only be
-used on or associated in any way with an electronic work by people who
-agree to be bound by the terms of this agreement. There are a few
-things that you can do with most Project Gutenberg-tm electronic works
-even without complying with the full terms of this agreement. See
-paragraph 1.C below. There are a lot of things you can do with Project
-Gutenberg-tm electronic works if you follow the terms of this
-agreement and help preserve free future access to Project Gutenberg-tm
-electronic works. See paragraph 1.E below.
-
-1.C. The Project Gutenberg Literary Archive Foundation ("the
-Foundation" or PGLAF), owns a compilation copyright in the collection
-of Project Gutenberg-tm electronic works. Nearly all the individual
-works in the collection are in the public domain in the United
-States. If an individual work is unprotected by copyright law in the
-United States and you are located in the United States, we do not
-claim a right to prevent you from copying, distributing, performing,
-displaying or creating derivative works based on the work as long as
-all references to Project Gutenberg are removed. Of course, we hope
-that you will support the Project Gutenberg-tm mission of promoting
-free access to electronic works by freely sharing Project Gutenberg-tm
-works in compliance with the terms of this agreement for keeping the
-Project Gutenberg-tm name associated with the work. You can easily
-comply with the terms of this agreement by keeping this work in the
-same format with its attached full Project Gutenberg-tm License when
-you share it without charge with others.
-
-1.D. The copyright laws of the place where you are located also govern
-what you can do with this work. Copyright laws in most countries are
-in a constant state of change. If you are outside the United States,
-check the laws of your country in addition to the terms of this
-agreement before downloading, copying, displaying, performing,
-distributing or creating derivative works based on this work or any
-other Project Gutenberg-tm work. The Foundation makes no
-representations concerning the copyright status of any work in any
-country outside the United States.
-
-1.E. Unless you have removed all references to Project Gutenberg:
-
-1.E.1. The following sentence, with active links to, or other
-immediate access to, the full Project Gutenberg-tm License must appear
-prominently whenever any copy of a Project Gutenberg-tm work (any work
-on which the phrase "Project Gutenberg" appears, or with which the
-phrase "Project Gutenberg" is associated) is accessed, displayed,
-performed, viewed, copied or distributed:
-
-  This eBook is for the use of anyone anywhere in the United States and
-  most other parts of the world at no cost and with almost no
-  restrictions whatsoever. You may copy it, give it away or re-use it
-  under the terms of the Project Gutenberg License included with this
-  eBook or online at www.gutenberg.org. If you are not located in the
-  United States, you'll have to check the laws of the country where you
-  are located before using this ebook.
-
-1.E.2. If an individual Project Gutenberg-tm electronic work is
-derived from texts not protected by U.S. copyright law (does not
-contain a notice indicating that it is posted with permission of the
-copyright holder), the work can be copied and distributed to anyone in
-the United States without paying any fees or charges. If you are
-redistributing or providing access to a work with the phrase "Project
-Gutenberg" associated with or appearing on the work, you must comply
-either with the requirements of paragraphs 1.E.1 through 1.E.7 or
-obtain permission for the use of the work and the Project Gutenberg-tm
-trademark as set forth in paragraphs 1.E.8 or 1.E.9.
-
-1.E.3. If an individual Project Gutenberg-tm electronic work is posted
-with the permission of the copyright holder, your use and distribution
-must comply with both paragraphs 1.E.1 through 1.E.7 and any
-additional terms imposed by the copyright holder. Additional terms
-will be linked to the Project Gutenberg-tm License for all works
-posted with the permission of the copyright holder found at the
-beginning of this work.
-
-1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm
-License terms from this work, or any files containing a part of this
-work or any other work associated with Project Gutenberg-tm.
-
-1.E.5. Do not copy, display, perform, distribute or redistribute this
-electronic work, or any part of this electronic work, without
-prominently displaying the sentence set forth in paragraph 1.E.1 with
-active links or immediate access to the full terms of the Project
-Gutenberg-tm License.
-
-1.E.6. You may convert to and distribute this work in any binary,
-compressed, marked up, nonproprietary or proprietary form, including
-any word processing or hypertext form. However, if you provide access
-to or distribute copies of a Project Gutenberg-tm work in a format
-other than "Plain Vanilla ASCII" or other format used in the official
-version posted on the official Project Gutenberg-tm web site
-(www.gutenberg.org), you must, at no additional cost, fee or expense
-to the user, provide a copy, a means of exporting a copy, or a means
-of obtaining a copy upon request, of the work in its original "Plain
-Vanilla ASCII" or other form. Any alternate format must include the
-full Project Gutenberg-tm License as specified in paragraph 1.E.1.
-
-1.E.7. Do not charge a fee for access to, viewing, displaying,
-performing, copying or distributing any Project Gutenberg-tm works
-unless you comply with paragraph 1.E.8 or 1.E.9.
-
-1.E.8. You may charge a reasonable fee for copies of or providing
-access to or distributing Project Gutenberg-tm electronic works
-provided that
-
-* You pay a royalty fee of 20% of the gross profits you derive from
-  the use of Project Gutenberg-tm works calculated using the method
-  you already use to calculate your applicable taxes. The fee is owed
-  to the owner of the Project Gutenberg-tm trademark, but he has
-  agreed to donate royalties under this paragraph to the Project
-  Gutenberg Literary Archive Foundation. Royalty payments must be paid
-  within 60 days following each date on which you prepare (or are
-  legally required to prepare) your periodic tax returns. Royalty
-  payments should be clearly marked as such and sent to the Project
-  Gutenberg Literary Archive Foundation at the address specified in
-  Section 4, "Information about donations to the Project Gutenberg
-  Literary Archive Foundation."
-
-* You provide a full refund of any money paid by a user who notifies
-  you in writing (or by e-mail) within 30 days of receipt that s/he
-  does not agree to the terms of the full Project Gutenberg-tm
-  License. You must require such a user to return or destroy all
-  copies of the works possessed in a physical medium and discontinue
-  all use of and all access to other copies of Project Gutenberg-tm
-  works.
-
-* You provide, in accordance with paragraph 1.F.3, a full refund of
-  any money paid for a work or a replacement copy, if a defect in the
-  electronic work is discovered and reported to you within 90 days of
-  receipt of the work.
-
-* You comply with all other terms of this agreement for free
-  distribution of Project Gutenberg-tm works.
-
-1.E.9. If you wish to charge a fee or distribute a Project
-Gutenberg-tm electronic work or group of works on different terms than
-are set forth in this agreement, you must obtain permission in writing
-from both the Project Gutenberg Literary Archive Foundation and The
-Project Gutenberg Trademark LLC, the owner of the Project Gutenberg-tm
-trademark. Contact the Foundation as set forth in Section 3 below.
-
-1.F.
-
-1.F.1. Project Gutenberg volunteers and employees expend considerable
-effort to identify, do copyright research on, transcribe and proofread
-works not protected by U.S. copyright law in creating the Project
-Gutenberg-tm collection. Despite these efforts, Project Gutenberg-tm
-electronic works, and the medium on which they may be stored, may
-contain "Defects," such as, but not limited to, incomplete, inaccurate
-or corrupt data, transcription errors, a copyright or other
-intellectual property infringement, a defective or damaged disk or
-other medium, a computer virus, or computer codes that damage or
-cannot be read by your equipment.
-
-1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right
-of Replacement or Refund" described in paragraph 1.F.3, the Project
-Gutenberg Literary Archive Foundation, the owner of the Project
-Gutenberg-tm trademark, and any other party distributing a Project
-Gutenberg-tm electronic work under this agreement, disclaim all
-liability to you for damages, costs and expenses, including legal
-fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT
-LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE
-PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE
-TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE
-LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR
-INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH
-DAMAGE.
-
-1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a
-defect in this electronic work within 90 days of receiving it, you can
-receive a refund of the money (if any) you paid for it by sending a
-written explanation to the person you received the work from. If you
-received the work on a physical medium, you must return the medium
-with your written explanation. The person or entity that provided you
-with the defective work may elect to provide a replacement copy in
-lieu of a refund. If you received the work electronically, the person
-or entity providing it to you may choose to give you a second
-opportunity to receive the work electronically in lieu of a refund. If
-the second copy is also defective, you may demand a refund in writing
-without further opportunities to fix the problem.
-
-1.F.4. Except for the limited right of replacement or refund set forth
-in paragraph 1.F.3, this work is provided to you 'AS-IS', WITH NO
-OTHER WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
-LIMITED TO WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PURPOSE.
-
-1.F.5. Some states do not allow disclaimers of certain implied
-warranties or the exclusion or limitation of certain types of
-damages. If any disclaimer or limitation set forth in this agreement
-violates the law of the state applicable to this agreement, the
-agreement shall be interpreted to make the maximum disclaimer or
-limitation permitted by the applicable state law. The invalidity or
-unenforceability of any provision of this agreement shall not void the
-remaining provisions.
-
-1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the
-trademark owner, any agent or employee of the Foundation, anyone
-providing copies of Project Gutenberg-tm electronic works in
-accordance with this agreement, and any volunteers associated with the
-production, promotion and distribution of Project Gutenberg-tm
-electronic works, harmless from all liability, costs and expenses,
-including legal fees, that arise directly or indirectly from any of
-the following which you do or cause to occur: (a) distribution of this
-or any Project Gutenberg-tm work, (b) alteration, modification, or
-additions or deletions to any Project Gutenberg-tm work, and (c) any
-Defect you cause.
-
-Section 2. Information about the Mission of Project Gutenberg-tm
-
-Project Gutenberg-tm is synonymous with the free distribution of
-electronic works in formats readable by the widest variety of
-computers including obsolete, old, middle-aged and new computers. It
-exists because of the efforts of hundreds of volunteers and donations
-from people in all walks of life.
-
-Volunteers and financial support to provide volunteers with the
-assistance they need are critical to reaching Project Gutenberg-tm's
-goals and ensuring that the Project Gutenberg-tm collection will
-remain freely available for generations to come. In 2001, the Project
-Gutenberg Literary Archive Foundation was created to provide a secure
-and permanent future for Project Gutenberg-tm and future
-generations. To learn more about the Project Gutenberg Literary
-Archive Foundation and how your efforts and donations can help, see
-Sections 3 and 4 and the Foundation information page at
-www.gutenberg.org
-
-
-
-Section 3. Information about the Project Gutenberg Literary Archive Foundation
-
-The Project Gutenberg Literary Archive Foundation is a non profit
-501(c)(3) educational corporation organized under the laws of the
-state of Mississippi and granted tax exempt status by the Internal
-Revenue Service. The Foundation's EIN or federal tax identification
-number is 64-6221541. Contributions to the Project Gutenberg Literary
-Archive Foundation are tax deductible to the full extent permitted by
-U.S. federal laws and your state's laws.
-
-The Foundation's principal office is in Fairbanks, Alaska, with the
-mailing address: PO Box 750175, Fairbanks, AK 99775, but its
-volunteers and employees are scattered throughout numerous
-locations. Its business office is located at 809 North 1500 West, Salt
-Lake City, UT 84116, (801) 596-1887. Email contact links and up to
-date contact information can be found at the Foundation's web site and
-official page at www.gutenberg.org/contact
-
-For additional contact information:
-
-    Dr. Gregory B. Newby
-    Chief Executive and Director
-    gbnewby@pglaf.org
-
-Section 4. Information about Donations to the Project Gutenberg
-Literary Archive Foundation
-
-Project Gutenberg-tm depends upon and cannot survive without wide
-spread public support and donations to carry out its mission of
-increasing the number of public domain and licensed works that can be
-freely distributed in machine readable form accessible by the widest
-array of equipment including outdated equipment. Many small donations
-($1 to $5,000) are particularly important to maintaining tax exempt
-status with the IRS.
-
-The Foundation is committed to complying with the laws regulating
-charities and charitable donations in all 50 states of the United
-States. Compliance requirements are not uniform and it takes a
-considerable effort, much paperwork and many fees to meet and keep up
-with these requirements. We do not solicit donations in locations
-where we have not received written confirmation of compliance. To SEND
-DONATIONS or determine the status of compliance for any particular
-state visit www.gutenberg.org/donate
-
-While we cannot and do not solicit contributions from states where we
-have not met the solicitation requirements, we know of no prohibition
-against accepting unsolicited donations from donors in such states who
-approach us with offers to donate.
-
-International donations are gratefully accepted, but we cannot make
-any statements concerning tax treatment of donations received from
-outside the United States. U.S. laws alone swamp our small staff.
-
-Please check the Project Gutenberg Web pages for current donation
-methods and addresses. Donations are accepted in a number of other
-ways including checks, online payments and credit card donations. To
-donate, please visit: www.gutenberg.org/donate
-
-Section 5. General Information About Project Gutenberg-tm electronic works.
-
-Professor Michael S. Hart was the originator of the Project
-Gutenberg-tm concept of a library of electronic works that could be
-freely shared with anyone. For forty years, he produced and
-distributed Project Gutenberg-tm eBooks with only a loose network of
-volunteer support.
-
-Project Gutenberg-tm eBooks are often created from several printed
-editions, all of which are confirmed as not protected by copyright in
-the U.S. unless a copyright notice is included. Thus, we do not
-necessarily keep eBooks in compliance with any particular paper
-edition.
-
-Most people start at our Web site which has the main PG search
-facility: www.gutenberg.org
-
-This Web site includes information about Project Gutenberg-tm,
-including how to make donations to the Project Gutenberg Literary
-Archive Foundation, how to help produce our new eBooks, and how to
-subscribe to our email newsletter to hear about new eBooks.
-
diff --git a/old/50068-0.zip b/old/50068-0.zip
deleted file mode 100644
index c7ea617..0000000
--- a/old/50068-0.zip
+++ /dev/null
diff --git a/old/50068-h.zip b/old/50068-h.zip
deleted file mode 100644
index 3f11155..0000000
--- a/old/50068-h.zip
+++ /dev/null
diff --git a/old/50068-h/50068-h.htm b/old/50068-h/50068-h.htm
deleted file mode 100644
index 540d7e7..0000000
--- a/old/50068-h/50068-h.htm
+++ /dev/null
@@ -1,14361 +0,0 @@
-<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
-    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
-<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
-  <head>
-    <meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
-    <meta http-equiv="Content-Style-Type" content="text/css" />
-    <title>
-      The Project Gutenberg eBook of Hawkins Electrical Guide Number 8, by Nehemiah Hawkins.
-    </title>
-    <link rel="coverpage" href="images/cover.jpg" />
-    <style type="text/css">
-
-body {
-    margin-left: 10%;
-    margin-right: 10%;
-}
-
-    h1,h2 {
-    text-align: center;
-    clear: both;
-}
-
-.h_subtitle{font-weight: normal; font-size: smaller;}
-
-p { margin-top: .51em; text-align: justify; text-indent: 1.5em; margin-bottom: .49em; }
-p.no-indent { margin-top: .51em; text-align: justify; text-indent: 0em; margin-bottom: .49em;}
-p.author    { margin-top: 1em; margin-right: 5%; text-align: right;}
-p.f90       { font-size: 90%;  text-align: center; text-indent: 0em; }
-p.f90_left  { font-size: 90%;  text-align: left; text-indent: 0em; }
-p.f110      { font-size: 110%; text-align: center; text-indent: 0em; }
-p.f150      { font-size: 150%; text-align: center; text-indent: 0em; }
-p.f200      { font-size: 200%; text-align: center; text-indent: 0em; }
-
-.space-above1 { margin-top: 1em; }
-.space-above2 { margin-top: 2em; }
-.space-above3 { margin-top: 3em; }
-
-.space-below1 { margin-bottom: 1em; }
-.space-below2 { margin-bottom: 2em; }
-
-.center   {text-align: center;
-           text-indent: 0; }
-p {
-    margin-top: .51em;
-    text-align: justify;
-    margin-bottom: .49em;
-}
-
-img {max-width: 100%; height: auto;}
-sup {vertical-align: top; font-size: 70%;}
-
-hr.r5     {width: 5%; margin-top: 1em; margin-bottom: 1em;
-                      margin-left: 47.5%; margin-right: 47.5%; }
-hr.chap {width: 65%; margin-left: 17.5%; margin-right: 17.5%; }
-
-table {
-    margin-left: auto;
-    margin-right: auto;
-}
-
-    .tr_grey    {background-color: #C0C0C0;}
-    .tr_lt_grey {background-color: #E8E8E8;}
-
-    .tdl      {text-align: left;}
-    .tdr      {text-align: right;}
-    .tdc      {text-align: center;}
-    .tdl_toc  {text-align: left; text-indent: -1em;}
-    .tdc_top    {text-align: center;  vertical-align: top;}
-    .tdc_bott   {text-align: center;  vertical-align: bottom;}
-
-.pagenum {
-    /*  visibility: hidden;  */
-    position: absolute;
-    left: 92%;
-    font-size: smaller;
-    text-align: right;
-}
-
-.blockquot {
-    margin-left: 10%;
-    margin-right: 10%;
-    font-size: 90%;
-}
-
-.bbox     {border: solid 2px;}
-.smcap    {font-variant: small-caps;}
-.u        {text-decoration: underline;}
-.rad {border-top: thin black solid;}
-
-.figcenter   {
-    margin: auto;
-    text-align: center;
-}
-
-.footnote         {margin-left: 10%; margin-right: 10%; font-size: 0.9em;}
-.footnote .label  {position: absolute; right: 84%; text-align: right;}
-
-.fnanchor {
-    vertical-align: super;
-    font-size: .8em;
-    text-decoration:
-    none;
-}
-
-.transnote {background-color: #E6E6FA;
-    color: black;
-     font-size:smaller;
-     padding:0.5em;
-     margin-bottom:5em;
-     font-family:sans-serif, serif; }
-    </style>
-  </head>
-
-<body>
-
-
-<pre>
-
-The Project Gutenberg EBook of Hawkins Electrical Guide Vol. 8 (of 10), by 
-Nehemiah Hawkins
-
-This eBook is for the use of anyone anywhere in the United States and most
-other parts of the world at no cost and with almost no restrictions
-whatsoever.  You may copy it, give it away or re-use it under the terms of
-the Project Gutenberg License included with this eBook or online at
-www.gutenberg.org.  If you are not located in the United States, you'll have
-to check the laws of the country where you are located before using this ebook.
-
-Title: Hawkins Electrical Guide Vol. 8 (of 10)
-       A Progressive Course of Study for Engineers, Electricians,
-              Students, and Those Desiring to Acquire a Working Knowledge
-              of Electricity and Its Applications
-
-Author: Nehemiah Hawkins
-
-Release Date: September 28, 2015 [EBook #50068]
-
-Language: English
-
-Character set encoding: UTF-8
-
-*** START OF THIS PROJECT GUTENBERG EBOOK HAWKINS ELECTRICAL GUIDE, VOL 8 ***
-
-
-
-
-Produced by Juliet Sutherland, Paul Marshall and the Online
-Distributed Proofreading Team at http://www.pgdp.net
-
-
-
-
-
-
-</pre>
-
-<div class="bbox">
-<p class="center space-below1">
-THE THOUGHT IS IN THE QUESTION&emsp;THE INFORMATION IS IN THE ANSWER</p>
-
-<h1>HAWKINS ELECTRICAL GUIDE<br />NUMBER EIGHT</h1>
-<hr class="r5" />
-<p class="f200 space-above1"><b>QUESTIONS<br />ANSWERS<br />&amp;<br />ILLUSTRATIONS</b></p>
-
-<p class="center">A PROGRESSIVE COURSE OF STUDY FOR ENGINEERS,<br />
-ELECTRICIANS, STUDENTS AND THOSE DESIRING TO<br />
-ACQUIRE A WORKING KNOWLEDGE OF</p>
-
-<p class="f150 space-above1"><b>ELECTRICITY AND ITS APPLICATIONS</b></p>
-<p class="f110 space-above2">A PRACTICAL TREATISE<br />by<br />HAWKINS AND STAFF</p>
-<p class="center space-above2"><b>THEO AUDEL &amp; CO. 72 FIFTH AVE. NEW YORK</b>.</p>
-
-<p class="center space-above2">COPYRIGHTED, 1915,<br />BY<br />THEO. AUDEL &amp; CO.,<br /><span class="smcap">New York.</span></p>
-<p class="center space-above3">Printed in the United States.</p>
-</div>
-<p class="f150 space-above2 space-below2"><b>TABLE OF CONTENTS<br />GUIDE No. 8</b></p>
-
-<table border="0" cellspacing="2" summary="Table of Contents." cellpadding="0">
-  <tbody><tr>
-      <td colspan="2" class="tdl_toc"><b>WAVE FORM MEASUREMENT</b></td>
-      <td class="tdr"><a href="#Page_1839">1,839&nbsp;to&nbsp;1,868</a></td>
-    </tr><tr>
-      <td class="tdl"><br /></td>
-      <td class="tdl"><br />
-Importance of wave form measurement&mdash;<b>methods</b>:
-step by step; constantly recording&mdash;<b>classes of
-apparatus</b>: wave indication; <i>oscillographs</i>&mdash;<b>step
-by step methods</b>&mdash;Joubert's; four part commutator;
-modified four part commutator; ballistic galvanometer;
-zero; Hospitalier ondograph&mdash;<b>constantly recording
-methods</b>: cathode ray; glow light; moving iron; moving
-coil; hot wire&mdash;<b>oscillographs</b>&mdash;moving coil type;
-construction and operation; production of the time scale;
-oscillograms&mdash;falling plate camera; its use.</td>
-      <td class="tdr"><br /></td>
-    </tr><tr>
-      <td colspan="3" class="tdc">&nbsp;</td>
-    </tr><tr>
-      <td colspan="2" class="tdl_toc"><b>SWITCHBOARDS</b></td>
-      <td class="tdr"><a href="#Page_1869">1,869&nbsp;to&nbsp;1,884</a></td>
-    </tr><tr>
-      <td class="tdl"><br /></td>
-      <td class="tdl"><br />
-<b>General principles</b>: diagram&mdash;small plant a.c.
-switchboard&mdash;<b>switchboard panels</b>; <b>generator
-panel</b>; diagram of connections&mdash;simple method of
-determining bus bar capacity&mdash;feeder panel&mdash;diagrams of
-connection for two phase and three phase installations.</td>
-    </tr><tr>
-      <td colspan="3" class="tdc">&nbsp;</td>
-    </tr><tr>
-      <td colspan="2" class="tdl_toc"><b>ALTERNATING CURRENT WIRING</b></td>
-      <td class="tdr"><a href="#Page_1885">1,885&nbsp;to&nbsp;1,914</a></td>
-    </tr><tr>
-      <td class="tdl"><br /></td>
-      <td class="tdl"><br />Effects to be considered in making
-calculations&mdash;<b>induction</b>; self- and mutual; mutual
-induction, how caused&mdash;<b>transpositions</b>&mdash;inductance
-per mile of three phase circuit, table&mdash;<b>capacity</b>;
-table&mdash;<b>frequency&mdash;skin effect</b>; calculation;
-table&mdash;<b>corona effect</b>; its manifestation;
-critical voltage; spacing of wires&mdash;<b>resistance of
-wires&mdash;impedance&mdash;power factor</b>; apparent current;
-usual power factors encountered; example&mdash;<b>wire
-calculations&mdash;sizes of wire&mdash;table of the property of
-copper wire&mdash;drop</b>; example&mdash;current&mdash;example
-covering horse power, watts, apparent load, current, size of wire,
-drop, voltage at the alternator, and electrical horse power.</td>
-      <td class="tdr"><br /></td>
-    </tr><tr>
-      <td colspan="3" class="tdc">&nbsp;</td>
-    </tr><tr>
-      <td colspan="2" class="tdl_toc"><b>POWER STATIONS</b></td>
-      <td class="tdr"><a href="#Page_1915">1,915&nbsp;to&nbsp;1,988</a></td>
-    </tr><tr>
-      <td class="tdl"><br /></td>
-      <td class="tdl"><br />
-Classification&mdash;<b>central stations</b>; types: a.c.,
-d.c., and a.c. and d.c.; reciprocating engine vs.
-turbine&mdash;<b>location of central stations</b>; price of
-land; trouble after erection; water supply; service
-requiring direct current&mdash;<b>size of plant</b>; nature
-of load; peak load; load factor; machinery required;
-example; factors of evaporation; grate surface per
-horse power&mdash;<b>general arrangement of station</b>;
-belt drive with counter shaft; desirable features of
-belt drive; conditions, suitable for counter shaft
-drive; location of engine and boilers; the steam pipe;
-piping between engine and condenser; number and type
-of engine; superheated steam; switchboard location;
-individual belt drive; direct drive&mdash;<b>station
-construction</b>&mdash;<b>foundations</b>&mdash;<b>walls</b>&mdash;
-<b>roofs</b>&mdash;<b>floors</b>&mdash;<b>chimneys</b>;
-cost of chimneys and mechanical draft; high chimneys
-ill advised&mdash;<b>steam turbine</b>; types: impulse
-and reaction; why high vacuum is necessary; the
-working pressure&mdash;<b>hydro-electric plants</b>&mdash;water
-turbines; types: impulse, reaction&mdash;<b>isolated
-plants</b>&mdash;<b>sub-stations</b>; arrangement; three phase
-installations; reactance coils in sub-stations; portable
-sub-stations.</td>
-      <td class="tdr"><br /></td>
-    </tr><tr>
-      <td colspan="3" class="tdc">&nbsp;</td>
-    </tr><tr>
-      <td colspan="2" class="tdl_toc"><b>MANAGEMENT</b></td>
-      <td class="tdr"><a href="#Page_1989">1,989&nbsp;to&nbsp;2,114</a></td>
-    </tr><tr>
-      <td class="tdl"><br /></td>
-      <td class="tdl"><br />
-The term "management"&mdash;<b>selection</b>; general
-considerations&mdash;<b>selection of generators</b>;
-efficiency of generators; size and number;
-regulation&mdash;<b>installation</b>; precautions;
-handling of armatures; assembling a machine; speed
-of generators; calculation of pulley sizes; gear
-wheels&mdash;<b>belts</b>; various belt drives; horse
-power transmitted by belts; velocity of belt; endless
-belts&mdash;<b>switchboards</b>; essential points of difference
-between single phase and three phase switchboard wiring;
-assembling a switchboard; usual equipment.
-
-<b>Operation of Alternators&mdash;alternators in parallel</b>;
-synchronizing; lamp methods; action of amortisseur winding;
-synchronizing three phase alternators; disadvantage of
-lamp method&mdash;<b>cutting out alternator</b>; precautions;
-hunting&mdash;<b>alternators in series</b>.
-
-<b>Transformers</b>; selection; efficiency; kind of oil
-used; detection of moisture; drying oil; regulation;
-transformers in parallel; polarity test&mdash;<b>motor
-generators</b>; various types and conditions requiring
-same&mdash;<b>dynamotors</b>; precautions&mdash;<b>rotary
-converters</b>; objections to single phase type; operation
-when driven by direct current, by alternating current; most
-troublesome part; efficiency; overload; starting; starting
-current.
-
-<b>Electrical measuring instruments</b>; location;
-readings; station voltmeters; points relating to
-ammeters; attention necessary; usual remedies to correct
-voltmeter&mdash;<b>how to test generators</b>; commercial
-efficiency; various tests.
-
-<b>Station Testing:</b> resistance measurement by "drop"
-method&mdash;methods of connecting ammeter voltmeter and
-wattmeter for measurement of power&mdash;<b>motor testing:</b>
-single phase motor&mdash;three phase motor, voltmeter and
-ammeter method; two wattmeter method; polyphase wattmeter
-method; one wattmeter method; one wattmeter and Y box
-method&mdash;three phase motor with neutral brought out; single
-wattmeter method&mdash;temperature test, three phase induction
-motor&mdash;<b>three phase alternator testing:</b> excitation
-or magnetization curve test&mdash;synchronous impedance
-test&mdash;load test&mdash;three phase alternator or synchronous
-motor temperature test&mdash;<b>direct current motor</b> or
-<b>generator testing:</b> magnetization curve&mdash;(shunt)
-external characteristic&mdash;direct current motor testing;
-load and speed tests&mdash;temperature test, "loading back"
-method&mdash;<b>compound dynamo testing</b>: external
-characteristic, adjustable load&mdash;<b>transformer testing</b>:
-external characteristic, adjustable load&mdash;<b>transformer
-testing</b>: core loss and leakage or exciting current
-test&mdash;copper loss&mdash;copper loss by wattmeter measurement
-and impedance&mdash;temperature&mdash;insulation&mdash;internal
-insulation&mdash;insulation resistance&mdash;polarity&mdash;winding
-or ratio tests.</td>
-      <td class="tdr"><br /></td>
-    </tr>
- </tbody>
-</table>
-
-<p><span class="pagenum"><a name="Page_1839" id="Page_1839">1839</a></span></p>
-<hr class="chap" />
-<h2><span class="h_subtitle">CHAPTER LXIII</span><br /><b>WAVE FORM MEASUREMENT</b></h2>
-
-<p>The great importance of the wave form in alternating current work
-is never denied, though it has sometimes been overlooked. The
-application of large gas engines to the driving of alternators
-operated in parallel requires an accurate knowledge of the wave form,
-and a close conformation to a sine wave if parallel operation is
-to be satisfactory. It is also important that the fluctuations in
-magnetism of the field poles should be known, especially if solid
-steel pole faces be used.</p>
-
-<div class="blockquot">
-<p>If an alternator armature winding be connected in delta, the presence
-of a third harmonic becomes objectionable, as it gives rise to
-circulating currents in the winding itself, which increase the
-heating and lowers the efficiency of the machine.</p>
-
-<p>That the importance of having a good wave form is being realized, is
-proved by the increasing prevalence in alternator specifications of a
-clause specifying the maximum divergence allowable from a true sine
-wave. It is however perhaps not always realized that an alternator
-which gives a good pressure wave on no load may give a very bad one
-under certain loads, and the ability of the machine to maintain a
-good wave form under severe conditions of load is a better criterion
-of its good design than is the shape of its wave at no load.</p>
-
-<p>The question of wave form is of special interest to the power station
-engineer. Upon it depends the answer to the questions: whether he may
-ground his neutral wires without getting large circulating currents;
-whether he may safely run any combination of his alternators in
-parallel; whether the constants of his distributing circuit are of an
-order liable to cause dangerous voltage surges due to resonance with
-the harmonics of his pressure wave; what stresses he is getting in
-his insulation due to voltage surges when switching on or off, etc.
-<span class="pagenum"><a name="Page_1840" id="Page_1840">1840</a></span>
-It has been shown by Rossler and Welding that the luminous efficiency
-of the alternating current arc may be 44 per cent. higher with a flat
-topped than with a peaked pressure wave, while on the other hand it
-is well known that transformers are more efficient on a peaked wave.
-Also the accuracy of many alternating current instruments depends
-upon the wave shape.</p>
-
-<p class="space-below1">In making insulation breakdown tests on cables, insulators,
-or machinery, large errors may be introduced unless the wave form at the
-time of the test be known. It is not sufficient even to know that
-the testing alternator gives a close approximation to a sine wave
-at no load; since if the capacity current of the apparatus under
-test be moderately large compared with the full load current of the
-testing alternator, the charging current taken may be sufficient to
-distort the wave form considerably, thus giving wrong results to the
-disadvantage of either the manufacturer or purchaser.</p></div>
-
-<div class="figcenter">
-  <a name="fig2583"></a>
-  <img src="images/i-0284.jpg" alt="_" width="600" height="493" />
-  <p class="f90 space-below1"><span class="smcap">Fig.</span> 2,583.&mdash;General
-     Electric simultaneous record of three waves with common zero.</p>
-</div>
-
-<p>The desirability of a complete knowledge of the manner in
-which the pressure and current varies during the cycle, has
-resulted in various methods and apparatus being devised for
-<span class="pagenum"><a name="Page_1841" id="Page_1841">1841</a></span>
-obtaining this knowledge. The apparatus in use for such purpose
-may be divided into two general classes,</p>
-
-<p class="no-indent">
-&emsp;&emsp;1. Wave indicators;<br />
-&emsp;&emsp;2. Oscillographs.<br /><br />
-
-and the methods employed with these two species of apparatus
-may be described respectively as,<br /><br />
-
-&emsp;&emsp;1. Step by step;<br />
-&emsp;&emsp;2. Constantly recording.<br /><br />
-
-that is to say, in the first instance, a number of instantaneous
-<span class="pagenum"><a name="Page_1842" id="Page_1842">1842</a></span>
-values are obtained at various points of the cycle, which are
-plotted and a curve traced through the several points thus
-obtained. A constantly recording method is one in which an
-infinite number of values are determined and recorded by the
-machine, thus giving a complete record of the cycle, leaving no
-portion of the wave to be filled in.</p>
-
-<div class="figcenter">
-  <a name="fig2584"></a>
-  <img src="images/i-0285.jpg" alt="_" width="600" height="630" />
-  <p class="f90 space-below1"><span class="smcap">Fig.</span> 2,584.&mdash;General
-          Electric simultaneous record of three waves with separate zeros.</p>
-</div>
-
-<div class="figcenter">
-  <a name="fig2585"></a>
-  <img src="images/i010.jpg" alt="_" width="600" height="586" />
-  <p class="f90_left space-below1">Figs. 2,585 and 2,586.&mdash;Oscillograms (from paper by
-    Morris and Catterson-Smith, Proc. I. E. E., Vol. XXXIII, page 1,023),
-    showing <i>how the current varies</i> <b>in one of the armature coils
-    of a direct current motor</b>. Fig. 2,585 was obtained with the
-    brushes in the neutral position, and fig. 2,586 with the brushes
-    shifted forward.</p>
-</div>
-
-<p>The various methods of determining the wave form may be further classified as:
-<span class="pagenum"><a name="Page_1843" id="Page_1843">1843</a></span></p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&#10100;&ensp;Joubert's method;</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&#10100;&ensp;Four part commutator method;</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&#10100;&ensp;Modified four part commutator method;</td>
-    </tr><tr>
-      <td class="tdl">1. Step by step&emsp;&nbsp;</td>
-      <td class="tdl">&#10100;&ensp;Ballistic galvanometer method;</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&#10100;&ensp;Zero method;</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&#10100;&ensp;By Hospitalier ondograph.</td>
-    </tr>
- </tbody>
-</table>
-
-<div class="figcenter">
-  <a name="fig2587"></a>
-  <img src="images/i011a.jpg" alt="_" width="600" height="123" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,587.</span>&mdash;<b>Oscillogram</b>
-by Bailey and Cleghorne (Proc. I.E.E., Vol. XXXVIII), <b>showing</b>
-<i>the sparking pressure or pressure between the brush and the
-commutator segment at the moment of separation</i>. The waves fall into
-groups of three owing to the fact that there were three armature
-coils in each slot.</p>
-</div>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&#10100;&ensp;cathode ray;</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&#10100;&ensp;by use of various types&emsp;&nbsp;</td>
-      <td class="tdl">&#10100;&ensp;glow light;</td>
-    </tr><tr>
-      <td class="tdl">2. constantly recording&emsp;&nbsp;</td>
-      <td class="tdl">&#10100;&ensp;of <b>oscillograph</b>,</td>
-      <td class="tdl">&#10100;&ensp;moving iron;</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&#10100;&ensp;such as</td>
-      <td class="tdl">&#10100;&ensp;moving coil;</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&#10100;&ensp;hot wire.</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td>
-    </tr>
- </tbody>
-</table>
-
-<div class="figcenter">
-  <a name="fig2588"></a>
-  <img src="images/i011b.jpg" alt="_" width="600" height="321" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,588.</span>&mdash;Various
-wave forms. The sine wave represents a current or pressure which
-varies according to the sine law. A distorted wave is due to the
-properties of the circuit, for instance, the effect of hysteresis in
-an iron core introduced into a coil is to distort the current wave by
-adding harmonics so that the ascending and descending portions may
-not be symmetrical. A peaked wave has a large maximum as compared
-with its virtual value. A peaked wave is produced by a machine with
-concentrated winding.</p>
-</div>
-
-<p><b>Joubert's Method.</b>&mdash;The apparatus required for
-determining the wave form by this step by step method, consists of
-a galvanometer, condenser, two, two way switches, resistance and
-adjustable contact maker, as shown in <a href="#fig2589">fig. <b>2,589</b></a>.
-<span class="pagenum"><a name="Page_1844" id="Page_1844">1844</a></span></p>
-
-<div class="blockquot">
-<p>The contact maker is attached to the alternator shaft so that it will
-rotate synchronously with the latter. By means of the adjustable
-contact, the instant of "making" that is, of "closing" the testing
-circuit may be varied, and the angular position of the armature, at
-which the testing circuit is closed, determined from the scale, which
-is divided into degrees.</p>
-
-<p class="space-below1">A resistance is placed in series with one of the alternator
-leads, such that the drop across it, gives sufficient pressure for testing.</p>
-</div>
-
-<div class="figcenter">
-  <a name="fig2589"></a>
-  <img src="images/i012.jpg" alt="_" width="600" height="368" />
-  <p class="f90 space-below1"><span class="smcap">Fig. 2,589.</span>&mdash;Diagram
-illustrating Joubert's <b>step by step method</b> of wave form measurement.</p>
-</div>
-
-<p><b>Ques. Describe the method of making the test.</b></p>
-
-<p>Ans. For current wave measurement switch No. 1 is placed on
-contact F, and for pressure wave measurement, on contact G, switch
-No. 2 is now turned to M and the drop across the resistance (assuming
-switch No. 1 to be turned to contact F) measured by charging the
-condenser, and then discharging it through the galvanometer by
-turning the switch to S. This is repeated for a number of positions
-of the contact maker, noting each time the galvanometer reading and
-position of the contact maker. By plotting the positions of contact
-maker as abscissæ, and the galvanometer readings as ordinates, the
-curve drawn through them will represent the wave form.
-<span class="pagenum"><a name="Page_1845" id="Page_1845">1845</a></span></p>
-
-<div class="blockquot">
-<p>The apparatus is calibrated by passing a known constant current
-through the resistance.</p></div>
-
-<div class="figcenter">
-  <a name="fig2590"></a>
-  <img src="images/i013a.jpg" alt="_" width="600" height="263" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,590.</span>&mdash;<b>Four
-part commutator method</b> of wave form measurement. The contact
-device consists of two slip rings and a four part commutator. One
-slip ring is connected to one terminal of the source, the other to
-the voltmeter, and the commutator to the condenser. By adjusting
-R when a known direct current pressure is impressed across the
-terminals, the voltmeter can be rendered direct reading.</p>
-</div>
-
-<div class="figcenter">
-  <a name="fig2591"></a>
-  <img src="images/i013b.jpg" alt="_" width="600" height="418" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,591.</span>&mdash;<b>Modified
-four part commutator method</b> of wave form measurement (Duncan's
-modification). By this method one contact maker can be used for any
-number of waves having the same frequency. Electro-dynamometers are
-used and the connections are made as here shown. The moving coils
-are connected in series to the contact maker, and the fixed coils
-are connected to the various sources to be investigated, then the
-deflection will be steady and by calibration with direct current can
-be made to read directly in volts.</p>
-</div>
-<p><span class="pagenum"><a name="Page_1846" id="Page_1846">1846</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2592"></a>
-  <img src="images/i014.jpg" alt="_" width="600" height="364" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,592.</span>&mdash;Diagram
-illustrating the <b>ballistic galvanometer method</b> of wave
-form measurement. <b>The test may be made</b> as described in the
-accompanying text, or in case the contact breaker is belted instead
-of attached rigidly to the shaft, it could be arranged to run
-slightly out of synchronism, then by taking readings at regular
-intervals, points will be obtained along the curve without moving the
-contact breaker. If this method be used, a non-adjustable contact
-breaker suffices. <b>In arranging the belt drive</b> so as to run
-slightly out of synchronism, if the pulleys be of the same size, the
-desired result is obtained by pasting a thin strip of paper around
-the face of one of the pulleys thus altering the velocity ratio of
-the drive slightly from unity.</p>
-</div>
-
-<p><b>Ballistic Galvanometer Method.</b>&mdash;This method, which is
-due to Kubber, employs a <i>contact breaker</i> instead of a <i>contact
-maker</i>. The distinction between these two devices should be
-noted: A contact maker keeps the circuit <i>closed</i> during each
-revolution for a short interval only, whereas, a contact breaker
-keeps the circuit <i>open</i> for a short interval only.</p>
-
-<div class="blockquot">
-
-<p><a href="#fig2592">Fig. 2,592</a>, shows the necessary apparatus and connections
-for applying the ballistic galvanometer method. The contact breaker consists of a
-commutator having an ebonite or insulating segment and two brushes.
-<span class="pagenum"><a name="Page_1847" id="Page_1847">1847</a></span></p>
-
-<p><i>In operation</i> the contact breaker keeps the circuit closed during
-all of each revolution, except the brief interval in which the
-brushes pass over the ebonite segment.</p>
-
-<p>The contact breaker is adjustable and has a scale enabling its
-various positions of adjustment to be noted.</p></div>
-
-<p><b>Ques. Describe the test.</b></p>
-
-<p class="space-below1">Ans. The contact breaker is placed in successive
-positions and galvanometer readings taken, the switch being turned to F,
-<a href="#fig2592">fig. 2,592</a>, in measuring the current wave, and to G
-in measuring the pressure wave. The results thus obtained are plotted
-giving respectively current and pressure waves.</p>
-
-<div class="figcenter">
-  <a name="fig2593"></a>
-  <img src="images/i-0286.jpg" alt="_" width="600" height="380" />
-  <p class="f90_left space-below1"><span class="smcap">Figs.</span>. 2,593 and
-2,594.&mdash;<b>Two curves</b> <i>representing pressure and current
-respectively of a rotary converter.</i> Fig. 2,593, pressure wave V,
-fig. 2,594 current wave C. These waves were obtained from
-a converter which was being driven by an alternator by means of an independent
-motor. The rotary converter was supplying idle current to some
-unloaded transformers and the ripples clearly visible in the pressure
-wave V, correspond to the number of teeth in the armature of the
-rotary converter.</p>
-</div>
-
-<p><b>Ques. How is the apparatus calibrated?</b></p>
-
-<p>Ans. By sending a constant current of known value through the resistance R.
-<span class="pagenum"><a name="Page_1848" id="Page_1848">1848</a></span></p>
-
-<p><b>Zero Method.</b>&mdash;In electrical measurements, a zero method is
-one <i>in which the arrangement of the testing devices is such that the
-value of the quantity being measured is shown when the galvanometer
-needle points to</i> <b>zero</b>.</p>
-
-<p>In the zero method either a contact maker or contact breaker may
-be used in connection with a galvanometer and slide wire bridge, as
-shown in <a href="#fig2595">figs. 2,595</a> and <a href="#fig2596">2,596</a>.</p>
-
-<div class="figcenter">
-  <a name="fig2595"></a>
-  <img src="images/i016.jpg" alt="_" width="600" height="361" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,595.</span>&mdash;Diagram
-illustrating zero method of wave measurement with <i>contact</i>
-<b>maker</b>. The voltage of the battery must be at least as great as
-the maximum pressure to be measured and must be kept constant.</p>
-</div>
-
-<p><b>Ques. What capacity of battery should be used?</b></p>
-
-<p>Ans. Its voltage should be as great as the maximum pressure
-to be measured.</p>
-
-<p><b>Ques. What necessary condition must be maintained in the
-battery?</b></p>
-
-<p>Ans. Its pressure must be kept constant.</p>
-
-<p><b>Ques. How are instantaneous values measured?</b></p>
-
-<p>Ans. The bridge contact A is adjusted till the galvanometer
-<span class="pagenum"><a name="Page_1849" id="Page_1849">1849</a></span>
-shows no deflection, then the length AS is a measure of the pressure.</p>
-
-<p class="blockquot">
-The drop between these points can be directly measured with a
-voltmeter if desired.</p>
-
-<p><b>Ques. How did Mershon modify the test?</b></p>
-
-<p>Ans. He used a telephone instead of the galvanometer to
-determine the correct placement of the bridge contact A.</p>
-
-<div class="figcenter">
-  <a name="fig2596"></a>
-  <img src="images/i017.jpg" alt="_" width="600" height="346" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,596.</span>&mdash;Diagram
-illustrating zero method of wave measurement with <i>contact</i>
-<b>breaker</b>. The voltage of the battery must be at least as great
-as the maximum pressure to be measured and must be kept constant.</p>
-</div>
-
-<p><b>Ques. How can the instantaneous values be recorded?</b></p>
-
-<p>Ans. By attaching to the contact A, a pencil controlled by an
-electro-magnet arranged to strike a revolving paper card at the
-instant of no deflection, the paper being carried on a drum.</p>
-
-<p><b>Hospitalier Ondograph.</b>&mdash;The device known by this name is
-a development of the Joubert step by step method of wave form
-measurement, that is to say, the principle on which its
-<span class="pagenum"><a name="Page_1850" id="Page_1850">1850</a></span>
-<b>action is based</b>, consists in <i>automatically charging a
-condenser from each 100th wave, and discharging it through a
-recording galvanometer, each successive charge of the condenser being
-automatically taken from a point a little farther along the wave.</i></p>
-
-<div class="figcenter">
-  <a name="fig2597"></a>
-  <img src="images/i018.jpg" alt="_" width="600" height="717" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,597.</span>&mdash;Diagram
-of Hospitalier ondograph showing mechanism and connections. It
-represents a development of Joubert's step by step method of wave
-form measurement.</p>
-</div>
-
-<div class="blockquot">
-<p>As shown in the diagram, <a href="#fig2597">fig. 2,597</a>, the ondograph
-consists of a synchronous motor A, operated from the source of the wave form
-to be measured, connected by gears B to a commutator D, in such a
-manner that while the motor makes a certain number of revolutions,
-the commutator makes a like number diminished by unity; that is to
-say, if the speed of the motor be 900 revolutions per minute, the
-commutator will have a speed of 899.
-<span class="pagenum"><a name="Page_1851" id="Page_1851">1851</a></span></p>
-
-<p>The commutator has three contacts, arranged to automatically charge
-the condenser <i>cc'</i> from the line, and discharge it through the
-galvanometer E, the deflection of which will be proportional to the
-pressure at any particular instant when contact is made.</p>
-
-<p>In <a href="#fig2597">fig. 2,597</a>, GG' are the motor terminals, HH' are
-connected to the condenser <i>cc'</i> through a resistance (to prevent sparking
-at the commutator) and I, I' are the connections to the service to
-be measured.</p>
-
-<p>A permanent magnet type of recording galvanometer is employed.
-Its moving coil E receives the discharges of the condenser in
-rapid succession and turns slowly from one side to the other.</p>
-</div>
-
-<div class="figcenter">
-  <a name="fig2598"></a>
-  <img src="images/i-0287.jpg" alt="_" width="600" height="404" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,598.</span>&mdash;View
-of Hospitalier ondograph. <b>In operation</b>, a long pivoted
-pointer carrying a pen and actuated by electro-magnets, records on
-a revolving drum a wave form representing the alternating current,
-pressure or current wave.</p>
-</div>
-
-<div class="blockquot">
-<p>The movable part operates a long needle (separately mounted) carrying
-a pen F, which traces the curve on the rotating cylinder C. This
-cylinder is geared to the synchronous motor to run at such a speed
-as to register three complete waves upon its circumference.</p>
-
-<p>By substituting an electromagnetic galvanometer for the permanent
-magnet galvanometer, and by using the magnet coils as current coils
-and the moving coil as the volt coil, the instrument can be made to
-draw watt curves. <a href="#fig2598">Fig. 2,598</a> shows the general
-appearance of the ondograph.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1852" id="Page_1852">1852</a></span>
-<b>Cathode Ray Oscillograph.</b>&mdash;This type of apparatus for
-measuring wave form was devised by Braun, and consists of a cathode
-ray tube having a fluorescent screen at one end, a small diaphragm
-with a hole in it at its middle, and two coils of a few turns each,
-placed outside it at right angles to one another. These coils carry
-currents <i>proportional to the</i> <b>pressure</b> <i>and</i>
-<b>current</b> <i>respectively</i> of the circuit under observation.</p>
-
-<div class="figcenter">
-  <a name="fig2599"></a>
-  <img src="images/i-0288.jpg" alt="_" width="600" height="627" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,599.</span>&mdash;General
-Electric <b>moving coil oscillograph</b> complete <b>with tracing
-table</b>. The tracing table is employed for observing the waves, and
-by using a piece of transparent paper, the waves under observation
-appear as a continuous band of light which can be traced, thus
-making a permanent record. This is not, however, to be regarded as
-a recording attachment, and can not be used where instantaneous
-phenomena are being investigated. <b>The synchronous motor</b> for
-operating the synchronous mirror in connection with tracing and
-viewing attachment is wound for 100 to 115 volts, 25 to 125 cycles,
-and should, of course, be run from the same machine which furnishes
-power to the circuit under observation. A rheostat for steadying
-and adjusting the current should be connected in series with the
-motor. <b>The beam from the vibrator mirrors</b> <i>striking this
-synchronous mirror moves back and forth over the curved glass, and
-gives the length of the wave; the movement of the vibrator mirror
-gives the amplitude, and the combination gives the wave complete</i>. An
-arc lamp or projection lantern produces the image reflected by the
-mirrors upon the film, tracing table or screen. For the rotation of
-the photographic film, a small direct current shunt wound motor is
-ordinarily used.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1853" id="Page_1853">1853</a></span>
-The ray then moves so as to produce an energy diagram on
-the fluorescent screen.</p>
-
-<div class="figcenter">
-  <a name="fig2600"></a>
-  <img src="images/i-0289.jpg" alt="_" width="600" height="380" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,600.</span>&mdash;General
-Electric moving coil oscillograph. <b>The moving elements</b>
-<i>consist of single loops of flat wire carrying a small mirror and
-held in tension by small spiral springs</i>. The current passing
-down one side and up the other, forces one side forward and the
-other backward, thus causing the mirror to vibrate on a vertical
-axis. The vibrator elements fit into chambers between the poles of
-electro-magnets, and are adjustable, so as to move the beam from the
-mirror, both vertically and horizontally. A sensitized photographic
-film is wrapped around a drum and held by spring clamps. The drum,
-with film, is placed in a case and a cap then placed over the end,
-making the case light, when the index is either up or down. The
-loading is done in a dark room. A driving dog is screwed into the
-drum shaft, and which, when the drum and case are in place, revolves
-the film past a slot. <b>When an exposure is to be made</b>, the
-index is moved from the closed position, thus opening the slot in the
-case and exposing the film to the beam of light from the vibrating
-mirrors when the electrically operated shutter is open. The slot
-is then closed by moving the index to "<b>Exposed</b>." A slide
-with ground glass can be inserted in place of the film case or roll
-holder to arrange the optical system when making adjustments. The
-shutter operating mechanism is arranged so as to hold the shutter
-open during exactly one revolution of the film drum. There are two
-devices connected to the shutter operating mechanism; one opens the
-shutter at the instant the end of the film passes the slot; the other
-opens immediately, at any part of the film, and both give exposure
-during one revolution. The first is useful when making investigations
-in which the events are either recurring, or their beginnings known
-or under control, and the second when the time of the event is not
-under control, such as the blowing of fuses or opening of circuit
-breakers.</p></div>
-
-<p>The instrument is much used in wireless telegraphy, as it is capable
-of showing the characteristics of currents of very high frequency.
-<span class="pagenum"><a name="Page_1854" id="Page_1854">1854</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2601"></a>
-  <img src="images/i-0290-1.jpg" alt="_" width="600" height="297" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,601.</span>&mdash;General
-Electric <b>moving coil oscillograph</b> <i>with case removed</i>,
-<b>showing</b> <i>interior construction and arrangement of parts</i>.
-The oscillograph is furnished complete with a three element
-electro-magnet galvanometer, optical system, shutter and shutter
-operating mechanism, film driving motor and cone pulleys,
-photographic and tracing attachments, 6 film holders, and the
-following repair parts, for vibrators: 6 extra suspension strips;
-6 vibrator mirrors; 1 box gold leaf fuses; 1 bottle mirror cement;
-1 bottle damping liquid.</p>
-</div>
-
-<div class="figcenter">
-  <a name="fig2602"></a>
-  <img src="images/i-0290-2.jpg" alt="_" width="600" height="416" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,602.</span>&mdash;Oscillogram
-showing the direct current pressure of a 25 cycle rotary converter
-(below), and (above) the pressure wave taken between one collector
-ring and one commutator brush. The 12 ripples per cycles in the
-direct current voltage are due to a 13th harmonic in the alternating
-current supply.</p>
-</div>
-
-<p class="space-below1"><span class="pagenum"><a name="Page_1855" id="Page_1855">1855</a></span>
-<b>Glow Light Oscillograph.</b>&mdash;This device consists of two aluminum
-rods in a partially evacuated tube, their ends being about two
-millimeters apart. When an alternating current of any frequency
-passes between them a sheath of violet light forms on one of the
-electrodes, passing over to the other when the current reverses
-during each cycle. The phenomenon may be observed or photographed by
-means of a revolving mirror.</p>
-
-<div class="figcenter">
-  <a name="fig2603"></a>
-  <img src="images/i-0291.jpg" alt="_" width="600" height="322" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,603.</span>&mdash;Curves
-by Morris, <i>illustrating the</i> <b>dangerous rush of current which may
-occur when switching on a transformer</b>. The circuit was broken
-at F and made again at G. The current was so great as to carry the
-spot of light right off the photographic plate due to the fact that
-a residual field was left in the core after switching off, and on
-closing the switch again the direction of the current was such as to
-tend to build up the full flux in the same direction as this residual
-flux. <b>The dotted lines</b> have been drawn in <i>to show how the
-actual waves were distorted from the normal</i>.</p>
-</div>
-
-<p><b>Moving Iron Oscillograph.</b>&mdash;This type is due to Blondel, to
-whom belongs the credit of working out and describing in considerable
-detail the principles underlying the construction of oscillographs.</p>
-
-<div class="blockquot">
-<p>The moving iron type of oscillograph consists of a very thin vane of
-iron suspended in a powerful magnetic field, thus forming a polarized
-magnet. Near this strip are placed two small coils which carry the
-current whose wave form is to be measured.</p>
-
-<p>The moving iron vane has a very short period of vibration and can
-therefore follow every variation in the current.</p>
-</div>
-<p class="space-below1"><span class="pagenum"><a name="Page_1856" id="Page_1856">1856</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2604"></a>
-  <img src="images/i-0292.jpg" alt="_" width="600" height="328" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,604.</span>&mdash;Siemens-Blondel
-<b>moving coil type</b> oscillograph. The coil is in the shape
-of a loop of thin wire, which is suspended in the field of an
-electro-magnet excited by continuous current. The current to be
-investigated is sent through this loop, which in consequence of the
-interaction of current and magnetic field, begins to vibrate. The
-oscillations are rendered visible by directing a beam of light from
-a continuous current arc lamp onto a small mirror fixed to the loop.
-The light reflected by the mirror is in the form of a light strip,
-but by suitable means this is drawn out in respect of time, so that
-a curve truly representing the current is obtained. The loop of fine
-wire is stretched between two supports and is kept in tension by a
-spring. As the spring tension is considerable, the directive force of
-the vibrating system is large, and its natural periodicity very high.
-The mirror is fixed in the center of the loop, and has an area of 1
-square mm. In order to protect the loops from mechanical injury they
-are built into special frames. The mirrors are of various sizes, the
-loop for demonstration purposes (projection device) being provided
-with the largest mirror and the most sensitive loop with a mirror of
-the smallest dimensions.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1857" id="Page_1857">1857</a></span></p>
-
-<div class="blockquot">
-<p>Attached to the vane is a small mirror which reflects a beam of light
-upon some type of receiving device.</p>
-
-<p>The Siemens-Blondel oscillograph shown in <a href="#fig2604">fig. 2,604</a>,
-is of the <i>moving coil</i> type, being a development of the moving iron
-principle.</p></div>
-
-<p><b>Moving Coil Oscillograph.</b>&mdash;The operation of this form of
-oscillograph is based <i>on the behaviour of a movable coil in a
-magnetic field</i>.</p>
-
-<div class="figcenter">
-  <a name="fig2605"></a>
-  <img src="images/i025.jpg" alt="_" width="600" height="266" />
-  <p class="f90_left space-below1"><span class="smcap">Figs.</span> 2,605
-and 2,606.&mdash;<b>Oscillograms</b> reproduced from a paper by M.
-B. Field on "A Study of the <b>Phenomena of Resonance</b> by the Aid
-of Oscillograms" (<i>Journal</i> of <i>E. E.</i>, Vol. XXXII). <b>The effect
-of resonance</b> on the wave forms of alternators has been the
-subject of much investigation and discussion; it is a matter of vital
-importance to the engineer in charge of a large alternating current
-power distribution system. Fig. 2,605 shows the pressure
-curve of an alternator running on a length of unloaded cable, the 11th harmonic
-being very prominent. Fig. 2,606 shows the striking alteration
-produced by reducing the length of cable in the circuit and thus
-causing resonance with the 13th harmonic.</p>
-</div>
-
-<div class="blockquot">
-<p>It consists essentially of a modified moving coil galvanometer combined
-with a rotating or vibrating mirror, a moving photographic film, or a
-falling photographic plate. The galvanometer portion of the outfit is
-usually referred to as the oscillograph as illustrated in <a href="#fig2608">figs. 2,608 to
-2,612</a>, representing diagrammatically the moving system.</p>
-
-<p>In the narrow gap between the poles S, S of a powerful magnet are
-stretched two parallel conductors formed by bending a thin strip of
-phosphor bronze back on itself over an ivory pulley P. A spiral spring
-attached to this pulley serves to keep a uniform tension on the strips,
-and a guide piece L limits the length of the vibrating portion to the part
-actually in the magnetic field.
-<span class="pagenum"><a name="Page_1858" id="Page_1858">1858</a></span></p>
-
-<p class="space-below1">A small mirror M bridges across the two strips as shown.
-The effect of passing a current through such a "vibrator" is to cause one of the
-strips to advance while the other recedes, and the mirror is thus
-turned about a vertical axis.</p></div>
-
-<div class="figcenter">
-  <a name="fig2607"></a>
-  <img src="images/i-0293.jpg" alt="_" width="600" height="580" />
-  <p class="f90_left space-below1"><span class="smcap">Fig.</span> 2,607.&mdash;General
-view of electro-magnet form of Duddell moving coil oscillograph,
-showing oil bath and electro-magnet. This instrument is specially
-designed to have a very high natural period of vibration (about
-1/10,000 of a second) so as to be suitable for accurate research
-work. It is quite accurate for frequencies up to 300 per second.
-In the figure, A is the brass oil bath in which two vibrators are
-fixed; B, core of electro-magnet which is excited by two coils, one
-of which, C, is seen. The ends of these two coils are brought out to
-four terminals at D, so that the coils may be connected in series for
-200 volt, or in parallel for 100 volt circuits. The bolts, E,E, hold
-the oil bath in position between the poles of the magnet. F,F,F (one
-not seen), are levelling screws; G,G, terminals of one vibrator; H,
-fuse; K, thermometer with bulb in center of oil bath.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1859" id="Page_1859">1859</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2608"></a>
-  <img src="images/i027.jpg" alt="_" width="600" height="461" />
-  <p class="f90_left space-below1"><span class="smcap">Figs.</span> 2,608
-to 2,612.&mdash;<b>Vibrator</b> of Duddell moving coil oscillograph
-and <b>section through oil bath</b> of electro-magnet oscillograph.
-<b>The vibrator consists of</b> a brass frame W, which supports two
-soft iron pole pieces P,P. Between these, a long narrow groove is
-divided into two parts by a thin soft iron partition, which runs up
-the center. The current being led in by the brass wire U, passes from
-an insulated brass plate to the strip, which is led over an ivory
-guide block, down one of the narrow grooves and over another guide
-block, the loops round the ivory pulley O, which puts tension on the
-strip by the spring N, back to the guide block again, up the other
-narrow groove, and out by way of the insulated brass plate and lead
-U. Halfway up the grooves the center iron partition R is partially
-cut away to permit of a small mirror M, bridging across from one
-strip to the other, being stuck to the strips by a dot of shellac at
-each corner. The figure illustrates one type of vibrator in which
-P is removable from W for ease in repairing. In type 1, these pole
-pieces P,P are not removable. <b>The vibrators</b> are placed side by
-side in the gap between the poles S,S of the electro-magnet, <a href="#fig2608">
-see fig. 2,610</a>. Each vibrator is pivoted about vertical centers, the bottom
-center fitting in the base of the oil bath, and the one at the top
-being formed by a screw in the cock piece Y. It can thus be easily
-turned in azimuth, its position being fixed by the adjusting screw L,
-a spiral spring serving to keep the vibrator always in contact with
-this screw. Since each cock piece can be independently moved forward
-or backward, each vibrator can be tipped slightly in either of these
-directions so that complete control over the mirrors is obtained and
-reflected spots of light may be made to coincide with that reflected
-from the fixed zero mirror, which latter is fixed to a brass tongue
-in between the two vibrators. <b>A plano-convex lens</b> of 50 cm.
-focal length is fixed on the oil bath in front of the vibrator
-mirrors to converge the reflected beams of light. It will be noticed
-that this lens is slightly inclined so that no trouble will be given
-by reflections from its own surface. The normal distance from the
-vibrator mirrors to the scale of photographic plate is 50 cm., and
-at this distance, a convenient working deflection on each side of
-the zero line is 3 to 4 cm. This is obtained with a R.M.S. current
-through the strips of from .05 to .1 of an ampere according to wave
-form, etc. <b>The maximum deflection</b> on each side of the zero
-line should not exceed 5 cm. while the maximum R.M.S. current through
-the strips should in no case exceed .1 ampere.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1860" id="Page_1860">1860</a></span></p>
-
-<div class="blockquot">
-<p>Each strip of the loop passes through a separate gap (not shown
-in the figure). The whole of the "vibrator," as this part of the
-instrument is called, is immersed in an oil bath, the object of the
-oil being to damp the movement of the strips, and make the instrument
-dead beat. It also has the additional advantage of increasing by
-refraction the movement of the spot of light reflected from the
-vibrating mirrors.</p>
-
-<p>The beam of light reflected from the mirror M is received on a screen
-or photographic plate, the instantaneous value of the current being
-proportional to the linear displacement of the spot of light so formed.</p>
-
-<p>With alternating currents, the spot of light oscillates to and fro as
-the current varies and would thus trace a straight line.</p>
-
-<p class="space-below1">To obtain an image of the wave form, it is necessary
-to traverse the photographic plate or film in a direction at right angles
-to the direction of the movement of the spot of light.</p></div>
-
-<div class="figcenter">
-  <a name="fig2613"></a>
-  <img src="images/i-0294.jpg" alt="_" width="600" height="285" />
-  <p class="f90_left space-below1"><span class="smcap">Fig.</span> 2,613.&mdash;Duddell
-<b>moving coil oscillograph</b> <i>with projection and tracing desk
-outfit</i>. The outfit is designed for teaching and lecture purposes.
-<b>In operation</b>, <i>after the beam of light from the arc lamp has
-been reflected from the oscillograph mirrors, it falls on a vibrating
-mirror which gives it a deflection proportional to time in a
-direction at right angles to the deflection it already has and which
-is proportional to the current passing through the oscillograph</i>.
-It is therefore only necessary to place a screen in the path of the
-reflected beam of light to obtain a trace of the wave form. Since
-the vibrating mirror is vibrated by means of a cam on the shaft of a
-synchronous motor, which motor is driven from, or synchronously with,
-the source of supply whose wave form is being investigated, the wave
-form is repeated time after time in the same place on the screen,
-and owing to the "persistence" of vision, the whole wave appears
-stationary on the screen. The synchronous motor with its vibrating
-mirror, mentioned above, is located underneath the "tracing desk."
-When used in this position a wave a few centimeters in amplitude is
-seen through a sheet of tracing paper which is bent round a curved
-sheet of glass. A permanent record of the wave form can thus easily
-be traced on the paper. A <i>dark box</i> which is designed to hold a
-sheet of sensitized paper in place of the tracing paper, can be
-fitted in place of the tracing desk. Thus an actual photographic
-record of the wave form is obtained. If the synchronous motor be
-transferred from its position underneath the tracing desk to the
-space reserved for it close to the oscillograph, the beam of light
-is then received on a large mirror which is placed at an angle of
-about 45 degrees to the horizontal and so projects the wave form
-onto a large vertical screen which should be fixed about two and a
-half meters distant. Under these conditions a wave form of amplitude
-50 cm. each side the zero line may be obtained which is therefore
-visible to a large audience.</p>
-</div>
-
-<p><b>Ques. How are the oscillograms obtained in the Duddell moving
-coil oscillograph?</b></p>
-
-<p class="space-below1">Ans. In all cases the oscillograms are obtained by a
-spot of light tracing out the curve connecting current or voltage with time.
-<span class="pagenum"><a name="Page_1861" id="Page_1861">1861</a></span>
-The source of light is an arc lamp, the light from which passes first
-through a lens, and then, excepting when projecting on a screen,
-through a rectangular slit about 10 mm. long by 1 mm. wide. The
-position of the lamp from the lens is adjusted till an image of the
-arc is obtained covering the three (two moving, one fixed) small
-oscillograph mirrors. The light is reflected back from these mirrors
-and, being condensed by a lens which is immediately in front of them,
-it converges till an image of the slit is formed on the surface where
-the record is desired. All that is necessary now to obtain a bright
-spot of light instead of this line image is to introduce in the path
-of the beam of light a cylindrical lens of short focal length.</p>
-
-<div class="figcenter">
-  <a name="fig2614"></a>
-  <img src="images/i029.jpg" alt="_" width="600" height="352" />
-  <p class="f90_left space-below1"><span class="smcap">Figs.</span>
-2,614 and 2,615.&mdash;Sectional view of <b>permanent magnet form</b>
-of Duddell <b>moving coil oscillograph.</b> This instrument has a
-lower natural period of vibration (1/3000 second) than the type shown
-in <a href="#fig2608">fig. 2,612</a>, and therefore is not capable of accurately
-following wave forms of such high frequency, but it is sufficiently quick
-acting to follow wave forms of all ordinary frequencies with perfect
-accuracy. It is easier to repair, and more portable owing to the fact
-that the magnetic field is produced by a permanent magnet instead of
-an electro-magnet. This also renders the instrument suitable for use
-on high tension circuits without earth connection, as, owing to the
-fact that no direct current excitation is required, the instrument is
-more easily insulated than other types.</p>
-</div>
-
-<p><b>Ques. What is the function of the mirrors on the vibrating vane?</b>
-<span class="pagenum"><a name="Page_1862" id="Page_1862">1862</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2616"></a>
-  <img src="images/i030.jpg" alt="_" width="600" height="384" />
-  <p class="f90_left space-below1"><span class="smcap">Fig.</span> 2,616.&mdash;Diagram
-of connections of Duddell oscillograph <b>to high pressure
-circuit.</b> The modification necessary for high pressure circuit
-only applies to the vibrator which gives the pressure wave and
-consists in adding two more resistances, R<sub>4</sub> and
-R<sub>5</sub>. Referring to <a href="#fig2617">fig. 2,617</a>, it will be seen
-that in case fuse f<sub>2</sub> blows, or the vibrator be accidentally broken,
-the full supply voltage is immediately thrown on the instrument
-itself. This is not permissible in high voltage work and therefore
-the resistance R<sub>5</sub> is introduced as a permanent shunt to
-the oscillograph vibrator. The resistance R<sub>4</sub> is an exact
-duplicate of R<sub>2</sub> being a 21 ohm plug resistance box for
-adjusting the sensitivity of the vibrator to an even figure. <b>In
-practice</b> R<sub>5</sub> is usually a part of R<sub>1</sub>, and in
-most of the high voltage resistances, two taps are brought out near
-one end to serve as R<sub>5</sub>. One of these taps is usually 50
-ohms distant from the end terminal and the other only 5 ohms from the
-end. <b>The use of these taps is as follows:</b> The large resistance
-consisting of R<sub>1</sub> + R<sub>5</sub> is so chosen with
-respect to the voltage of the circuit under investigation that the
-current through R<sub>1</sub> is about .1 ampere. <i>It should never
-be more than this continuously.</i> Then R<sub>4</sub> is connected
-to the 50 ohm tap, and since the resistance of the oscillograph
-vibrator circuit is variable from about 5 to 26 ohms by means of
-R<sub>4</sub>, the current can be controlled through the oscillograph
-from about .066 to .091 of an ampere, enabling an open wave form
-to a convenient scale to be obtained. <b>If it now be desired to
-record large rises of pressure,</b> such as may occur in cases of
-resonance, <i>the height of the wave must be reduced in order to keep
-these rises on the plate</i>. This is accomplished by disconnecting
-R<sub>4</sub> from the 50 ohm tap and connecting it to the 5 ohm
-tap, when the current through the vibrator will be from .05 to .016
-of an ampere according to whether the resistance R<sub>4</sub> is in
-or out of circuit. When, instead of using the <i>falling plate</i>, the
-<i>cinematograph</i> camera is being used, it becomes necessary always to
-work on the 5 ohm tap since the width of the film is much less than
-that of the plate, and the current must therefore be less. <b>In
-experiments where sudden rises of voltage are expected</b> <i>it is
-often advisable to keep</i> R<sub>1</sub> <i>as great as possible.</i> That
-end of the resistance R<sub>1</sub> referred to as R<sub>5</sub> in
-the diagram should be securely connected to the supply main and no
-switch or fuse used. A switch may, if desired, be used in series
-with R<sub>1</sub>, provided it be inserted at the point where
-R<sub>1</sub> joins the supply main remote from R<sub>5</sub>. It
-will be seen that fuses f<sub>1</sub> and f<sub>2</sub> are shown.
-Provided that the connections are always made in accordance with the
-diagram, and the vibrators are always shunted by R<sub>5</sub> or
-R<sub>3</sub> respectively, there is not much objection to the use
-of these fuses, but on general principles it is wise to avoid fuses
-in high tension work and accordingly with each permanent magnet
-oscillograph, dummy fuses are supplied, which can be inserted in
-place of the ordinary fuses when desired. <i>The remark previously
-made about keeping both vibrators and the frame of the instrument at
-approximately the same pressure applies with additional emphasis in
-high pressure work.</i></p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1863" id="Page_1863">1863</a></span>
-Ans. They simply control the direction of a beam of light in a
-horizontal plane in such a manner that its deflection from a zero
-position depends on the current passing through the instrument, and
-it is therefore evident that the oscillograph is not complete without
-means of producing a time scale.</p>
-
-<div class="figcenter">
-  <a name="fig2617"></a>
-  <img src="images/i031.jpg" alt="_" width="600" height="383" />
-  <p class="f90_left space-below1"><span class="smcap">Fig. 2,617.</span>&mdash;Diagram
-of connections of Duddell oscillograph <b>to low pressure
-circuit</b>, R<sub>1</sub> is a high non-inductive resistance
-connected across the mains in series with one of the vibrators.
-S<sub>2</sub> is a switch, and f<sub>2</sub>, the fuse (on the
-oscillograph in this circuit). The resistance of R<sub>1</sub> in
-ohms should be rather more than ten times the voltage of the circuit,
-so that a current of a little less than .1 of an ampere will pass
-through it. The vibrator will then give the curve of the circuit
-on an open scale. (For the projection oscillograph, the resistance
-R<sub>1</sub> should be only twice the supply voltage, since .5 of an
-ampere is required to give full scale deflection on a large screen.)
-<b>To obtain the current wave form</b>, <i>the shunt</i> R<sub>3</sub>
-<i>is connected in series with the circuit under investigation and
-the second vibrator is connected across this shunt</i>. Here also
-f<sub>1</sub> is a fuse, S<sub>1</sub> a switch, and R<sub>2</sub>
-an adjustable resistance box. The switch S<sub>1</sub> is however
-unnecessary if the plug resistance box supplied for R<sub>2</sub>
-be used, since an infinity plug is included in this box. The shunt
-R<sub>3</sub> should have a drop of about 1 volt across it in
-order to give a suitable working current through the vibrator. The
-resistance R<sub>2</sub> is not absolutely essential, but it is a
-great convenience in adjusting the current through the vibrator. It
-is a plug resistance box, the smallest coil being .04 of an ohm and
-the total 21 ohms. Being designed to carry .5 ampere continuously
-it can be used with any other type of Duddell oscillograph, and by
-its use the sensitiveness of the vibrator can be adjusted so that
-a round number of amperes in the shunt gives 1 mm. deflection.
-This adjustment is best made with direct current. <b>It should be
-noted</b> in connecting the oscillograph in circuit, that <i>the two
-vibrators should be so connected to the circuit that it is impossible
-that a higher pressure difference than</i> 50 <i>volts should exist
-between one vibrator and the other, or between either vibrator and
-the frame</i>. To ensure attention to this important point, a brass
-strap is provided which connects the two vibrators together and to
-the frame of the instrument. This does not mean that this point
-must necessarily be earthed since the frame of the instrument is
-insulated from the earth. It is advisable, however, to earth it when
-possible.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1864" id="Page_1864">1864</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2618"></a>
-  <img src="images/i-0295-1.jpg" alt="_" width="450" height="560" />
-  <img src="images/i-0295-2.jpg" alt="_" width="450" height="404" />
-  <p class="f90_left space-below1"><span class="smcap">Figs.</span> 2,618
-and 2,619.&mdash;<b>Two curves</b> <i>obtained with the</i> <b>falling
-plate camera</b> and illustrating <i>the discharge of a condenser
-through an inductive circuit</i>. <b>When taking curve A</b> the
-resistance in the circuit was very small compared to the inductance,
-while <b>before taking curve B</b> an additional non-inductive
-resistance was inserted in the circuit so that the oscillations were
-damped out much more rapidly although the periodic time remained
-approximately constant.</p>
-</div>
-
-<p><b>Ques. How is the time scale produced?</b></p>
-
-<p>Ans. Either the surface on which the beam of light falls may be
-caused to move in a vertical plane with a certain velocity, so that
-the intersection of the beam and the plane surface traces out a curve
-connecting current with time (a curve which becomes a permanent
-record if a sensitized surface be used); or, the surface may remain
-stationary and in the path of the horizontally vibrating beam may
-be introduced a mirror which rotates or vibrates about a horizontal
-<span class="pagenum"><a name="Page_1865" id="Page_1865">1865</a></span>
-axis, thus superposing a vertical motion proportional to time on the
-horizontal vibration which is proportional to current, and causing
-the beam of light to trace out a curve connecting current and time on
-the stationary surface.</p>
-
-<p><b>Ques. What kind of recording apparatus is used with
-the Duddell oscillograph?</b></p>
-
-<p>Ans. A falling plate camera, or a cinematograph film camera.</p>
-
-<div class="figcenter">
-  <a name="fig2620"></a>
-  <img src="images/i-0296.jpg" alt="_" width="600" height="536" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig. 2,620.</span>&mdash;Synchronous motor with
-vibrating mirror as used with Duddell moving coil oscillograph.
-<b>Since the motor must run synchronously</b> with the wave form
-it is required to investigate, <i>it should be supplied with current
-from the same source</i>. The motor can be used over a wide range of
-frequencies (from 20 to 120). When working at frequencies below 40,
-it is advisable to increase the moment of inertia of the armature,
-and for this purpose a suitable brass disc is used. <b>The armature
-carries a sector</b>, <i>which cuts off the light from the arc lamp
-during a fraction of each revolution, and a cam which rocks the
-vibrating mirror</i>. <b>It makes one revolution during two complete
-periods</b>, and the cam and sector are so arranged that during 1½
-periods, the mirror is turning with uniform angular velocity, while
-during the remaining half period, the mirror is brought back quickly
-to its angular position, the light being cut off by the sector during
-this half period.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1866" id="Page_1866">1866</a></span>
-<b>Ques. Explain the operation of the falling plate camera.</b></p>
-
-<p class="space-below1">Ans. In this arrangement a photographic plate is allowed
-to fall freely by the force of gravity down a dark slide. At a certain point
-in its fall it passes a horizontal slit through which the beams of
-light from the oscillograph pass, tracing out the curves on the plate
-as it falls.</p>
-
-<div class="figcenter">
-  <a name="fig2621"></a>
-  <img src="images/i-0297.jpg" alt="_" width="400" height="618" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,621 to 2,623.&mdash;Interior of
-cinematograph camera as used on Duddell moving coil oscillograph
-<b>for obtaining long records</b>. The loose side of case is shown
-removed and one of the reels which carry the film lying in front.
-<b>The spool of film</b> which is placed on the loose reel A,
-passes over the guide pulley B, then vertically downward between
-the brass gate D (shown open in the figure), and the brass plate C.
-<b>The exposure aperture</b> is in the plate C and can be opened or
-closed by a shutter controlled by the lever M. The groove in the
-plate C, and the springs which press the gate D flat on the plate
-C, prevent the film having any but a vertical motion as it passes
-the exposure slit. E is the sprocket driving pulley which engages
-with the perforations on the film and unwinds it from the reel A
-to reel H. Outside the case on the far side of it is secured to
-the axle G a three speed cone pulley. This is driven by a motor of
-about 1/7 horse power, which also drives, through the gears shown,
-the sprocket pulley E. Close to the grooved cone pulley is a lever
-carrying a jockey pulley L, and a brake, which latter is normally
-held onto the cone pulley by a spring and so causes the loose belt
-to slip. By pressing a lever which is attached to the falling plate
-camera case, the brake can be suddenly released and at the same time
-the jockey pulley caused to tighten the belt onto the grooved cone
-pulley, so that the starting and stopping of the film is controlled
-independently of the driving motor, and being quickly accomplished
-avoids waste of film. <b>Both reels</b> are alike and each is made in
-two pieces. <b>The upper reel</b> is loose on its axle and its motion
-is retarded slightly by a friction brake. <b>The lower reel</b> is
-also loose on its axle, but it is driven by means of a friction
-clutch, the clutch always rotating faster than the reel so that the
-used film delivered by the sprocket pulley E is wound up as fast as
-delivered. K is the front face of one reel, the boss on it pushes
-into the tube on the other half H, which serves not only to unite the
-two halves, but also to secure the end of the film which is doubled
-through J.</p>
-</div>
-
-<div class="blockquot">
-<p>The mean speed of the plate at the moment of exposure is about 13
-feet per second. This speed is very suitable for use with frequencies
-<span class="pagenum"><a name="Page_1867" id="Page_1867">1867</a></span>
-of from 40 to 60 periods per second. A cloth bag is used to introduce
-the plate to the slide.</p>
-
-<p class="space-below1">A catch holds the plate until it is desired to let it fall.
-Inside the case, is a small motor, 100 or 200 volts direct current, driving
-four mirrors which are fixed about a common axis with their planes parallel to it.</p></div>
-
-<div class="figcenter">
-  <a name="fig2624"></a>
-  <img src="images/i-0298-1.jpg" alt="_" width="600" height="243" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,624.&mdash;Portion of oscillograph
-record taken with cinematograph film camera, <b>showing the rush
-of current</b> and <b>sudden rise of voltage</b> <i>at the moment
-of switching on a high pressure feeder</i>.</p>
-</div>
-
-<p class="blockquot space-below1">
-By looking through a small slot in the end of the camera into these
-rotating mirrors, the observer sees the wave form which the oscillograph
-is tracing out and is thus able to make sure that he is obtaining the
-particular wave form or other curve desired before exposing the plate.</p>
-
-<div class="figcenter">
-  <a name="fig2625"></a>
-  <img src="images/i-0298-2.jpg" alt="_" width="600" height="280" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,625.&mdash;Portion of oscillograph record
-taken with a cinematograph film camera <b>showing the effect of
-switching off a high pressure feeder</b> and illustrating the violent
-fluctuations produced by sparking at the switch contacts.</p>
-</div>
-
-<p class="blockquot">
-The plate falls into a second red cloth bag which is placed on the
-bottom of the slide. The plates used are "stereoscopic size", 6¾" ×
-3¼" (17.1 × 8.3 cm.).</p>
-
-<p><b>Ques. For what use is the cinematograph camera adapted?</b></p>
-
-<p>Ans. For long records.
-<span class="pagenum"><a name="Page_1868" id="Page_1868">1868</a></span></p>
-
-<p class="blockquot space-below1">
-For instance, in investigations, such as observation on the
-paralleling of alternators, the running up to speed of motors, and
-the surges which may occur in switching on and off cable, etc. The
-cinematograph camera fits on to the falling plate case and by means
-of which a roll of cinematograph film can be driven at a uniform
-speed past the exposure aperture, enabling records up to 50 metres in
-length to be obtained. An interior view of the cinematograph camera
-is shown in <a href="#fig2621">fig. 2,621</a>.</p>
-
-<div class="figcenter">
-  <a name="fig2626"></a>
-  <img src="images/i036.jpg" alt="_" width="600" height="328" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,626.&mdash;Curves reproduced from an article
-by J. T. Morris in the <i>Electrician</i>. "On recording transitory
-phenomena by the oscillograph."</p>
-</div>
-
-<div class="figcenter">
-  <a name="fig2627"></a>
-  <img src="images/i-0299.jpg" alt="_" width="600" height="184" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,627.&mdash;First rush of current from an
-alternator when short circuited, showing unsymmetrical initial wave
-of current, becoming symmetrical after a few cycles. 25 cycles.</p>
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,628.&mdash;Pressure wave obtained from
-narrow exploring coil on alternator armature, indicating distribution
-of field flux. The terminal voltage of the alternator is very nearly
-a sine wave, 60 cycles; about 17 volts.</p>
-</div>
-
-<p class="center space-above2">
-<span class="pagenum"><a name="Page_1869" id="Page_1869">1869</a></span>
-<b>SOME OSCILLOGRAPH RECORDS</b></p>
-
-<div class="figcenter">
-  <a name="fig2629"></a>
-  <img src="images/i-0300-1.jpg" alt="_" width="600" height="300" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,629.&mdash;The waves of voltage and current
-of an alternating arc. A, voltage wave; B, current wave showing low
-power factor of the arc without apparent phase displacement. 60 cycles.</p>
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,630.&mdash;Rupturing 650 volt circuit.
-A, current wave; B, 25 cycle wave to mark time scale.</p>
-</div>
-
-<div class="figcenter">
-  <a name="fig2631"></a>
-  <img src="images/i-0300-2.jpg" alt="_" width="600" height="454" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,631.&mdash;First rush of current from
-alternator when short circuited, showing unsymmetrical current
-wave, also wave of field current caused by short circuit current in
-armature. Upper curve, armature current; lower curve, field current.</p>
-</div>
-
-<div class="figcenter">
-  <a name="fig2632"></a>
-  <img src="images/i-0300-3.jpg" alt="_" width="600" height="224" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,632.&mdash;Mazda (tungsten) lamp, showing
-rapid decrease to normal current as filament heats up. 25 cycles.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1870" id="Page_1870">1870</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2633"></a>
-  <img src="images/i-0301-1.jpg" alt="_" width="600" height="150" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,633.&mdash;Current wave in telephone line
-corresponding to sustained vowel sound "<i>i</i>," as in machine; voice
-pitched at A 110.</p>
-</div>
-
-<div class="figcenter">
-  <a name="fig2634"></a>
-  <img src="images/i-0301-2.jpg" alt="_" width="600" height="458" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,634.&mdash;Carbon lamp, showing rapid
-increase to normal current as filament heats up. 25 cycles.</p>
-</div>
-
-<div class="figcenter">
-  <a name="fig2635"></a>
-  <img src="images/i-0301-3.jpg" alt="_" width="600" height="267" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,635.&mdash;Short circuit current on direct
-current end of rotary converter, 21,500 amperes maximum. Upper
-curve, direct current voltage; lower curve, direct current amperage.
-Duration of short circuit about .1 second.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1871" id="Page_1871">1871</a></span></p>
-
-<hr class="chap" />
-<h2><span class="h_subtitle">CHAPTER LXIV</span><br />SWITCHBOARDS</h2>
-
-<p><b>General Principles of Switchboard Connections.</b>&mdash;The
-interconnection of generators, transformers, lines, bus bars, and
-switches with their relays, in modern switchboard practice is shown
-by the diagrams, figs. 2,636 to <a href="#fig2645">2,645</a>. The figures being
-lettered A to J for simplicity, the generators are indicated by black discs,
-and the switches by open circles, while each heavy line represents
-a set of bus bars consisting of two or more bus bars according to
-the system of distribution. It will be understood, also, in this
-connection, that the number of pole of the switches and the type
-of switch will depend upon the particular system of distribution
-employed.</p>
-
-<div class="blockquot">
-<p>Diagram A, shows the simplest system, or one in which a single
-generator feeds directly into the line. There are no transformers or
-bus bars and only one switch is sufficient.</p>
-
-<p>In B, a single generator supplies two or more feeders through a
-single set of bus bars, requiring a switch for each feeder, and a
-single generator switch.</p>
-
-<p>In C, two generators are employed and required and the addition of a
-bus section switch.</p>
-
-<p>D, represents a number of generators supplying two independent
-circuits. The additional set of bus bars employed for this purpose
-necessitates an additional bus section switch, and also additional
-selector switches for both feeders and generators.</p>
-
-<p>E, shows a standard system of connection for a city street railway
-system having a large number of feeders.</p></div>
-
-<p><span class="pagenum"><a name="Page_1872" id="Page_1872">1872</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2645"></a>
-  <img src="images/i040.jpg" alt="_" width="500" height="687" />
-  <p class="f90 space-below1">
-<span class="smcap">Figs.</span> 2,645 and 2,646.&mdash;Diagrams illustrating
-general principles of switchboard connections.</p>
-</div>
-
-<p>
-<span class="pagenum"><a name="Page_1873" id="Page_1873">1873</a></span>
-This arrangement allows any group of feeders to be supplied from any
-group of generators.</p>
-
-<div class="figcenter">
-  <a name="fig2646"></a>
-  <img src="images/i041.jpg" alt="_" width="600" height="305" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,646.&mdash;Fort Wayne switchboard panel for
-one alternator and one transfer circuit. Diagram giving dimensions,
-arrangement of instruments of board, and method of wiring. The
-different forms of standard alternating current switchboard panels
-for single phase circuits made by the Fort Wayne Electric Works are
-designed to fulfill all the usual requirements of switchboards for
-this class of work. The line includes panels equipped for a single
-generator; for one generator and two circuits; one generator and one
-transfer circuit; one generator, an incandescent and an arc lighting
-circuit; and also feeder panels of different kinds.</p>
-</div>
-
-<div class="blockquot">
-<p>It also permits the addition of a generator switch for each generator.</p>
-
-<p>F, represents the simplest system with transformers.</p>
-
-<p>It requires a single generator transformer bank, switch and line. The
-arrangement as show at F is used where a number of plants supply the
-same system.</p>
-
-<p>G, represents a system having more than one line.</p>
-
-<p>In this case a bus bar and transformer switch is used on the high
-tension side.</p>
-
-<p>H, shows a number of generators connected to a set of low tension
-bus bars through generator switches, and employing a low tension transformer switch.
-<span class="pagenum"><a name="Page_1874" id="Page_1874">1874</a></span></p>
-
-<p>I, shows the connections of a system having a large number of feeders
-supplied by several small generators. In this case, the plant is
-divided into two parts, each of which may be operated independently.</p>
-
-<p>J, represents the arrangement usually employed in modern plants
-where the generator capacity is large enough to permit of a generator
-transformer unit combination with two outgoing lines. By operating
-in parallel on the high tension side only, any generator can be run with
-any transformer. The whole plant can be run in parallel, or the two
-parts can be run separately.</p></div>
-
-<div class="figcenter">
-  <a name="fig2647"></a>
-  <img src="images/i-0302.jpg" alt="_" width="500" height="640" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,647.&mdash;General Electric <b>small plant
-alternating current switchboard</b>, <i>designed for use in small
-central stations and isolated plants</i>. They are for use with one set
-of bus bars, to which all generators and feeders are connected by
-means of single throw lever switches or circuit breakers, suitable
-provision being made for the parallel operation of the generators.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1875" id="Page_1875">1875</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2648"></a>
-  <img src="images/i-0303.jpg" alt="_" width="600" height="664" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,648.&mdash;Crouse-Hinds <b>voltmeter and
-ground detector radial switch</b>, arranged for mounting on the
-switchboard. The switch proper is placed on the rear of the board
-with hand wheel, dial, and indicator only on the front side. The
-current carrying parts are of hard brass, with contact surfaces
-machined after assembling. The contact parts are of the plunger
-spring type, and the cross bar has fuse connections. Ground detector
-circuits are marked G+ and G- for two wire system, and G+, G-,
-GN+ and GN- for three wire system. When the voltmeter switch is to
-be used as a ground detector, two circuits are required for a two
-wire system, and four circuits for a three wire system, that is, a
-six circuit voltmeter and ground detector switch for use on a two
-wire system has two circuits for ground detector and four circuits
-for voltmeter readings. A six circuit voltmeter and ground detector
-switch, for use on a three wire system, has four circuits for ground
-detector and two circuits for voltmeter readings.</p>
-</div>
-
-<p><b>Switchboard Panels.</b>&mdash;The term "panel" means the slab
-of marble or slate upon which is mounted the switches, and the
-indicating and controlling devices. There are usually several
-panels comprising switchboards of moderate or large size, these
-panels being classified according to the division of the system
-that they control, as for instance:
-<span class="pagenum"><a name="Page_1876" id="Page_1876">1876</a></span></p>
-
-<p class="no-indent">&emsp;&emsp;1. Generator panel;<br />
-&emsp;&emsp;2. Feeder panel;<br />
-&emsp;&emsp;3. Regulator panel, etc.</p>
-
-<p class="blockquot space-below1">
-In construction, the marble or slate should be free from metallic
-veins, and for pressures above, say, 600 volts, live connections,
-terminals, etc., should preferably be insulated from the panels by
-ebonite, mica, or removed from them altogether, as is generally the
-case with the alternating gear where the switches are of the oil type.</p>
-
-<div class="figcenter">
-  <a name="fig2649"></a>
-  <img src="images/i044.jpg" alt="_" width="600" height="456" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,649 and 2,650,&mdash;Wiring
-diagrams of Crouse-Hinds voltmeter and ground detector switches.
-Fig. 2,649 voltmeter switch; fig. 2,650 voltmeter and ground detector
-switch. A view of the switch is shown in <a href="#fig2648">fig. 2,648</a>;
-it is designed for use on two or three wire systems up to 300 volts.</p>
-</div>
-
-<div class="blockquot">
-<p>The bus bars and connections should be supported by the framework
-at the back of the board, or in separate cells, and the instruments
-should be operated at low pressure through instrument transformers.</p>
-
-<p>The panels are generally held in position by bolting them to an angle
-iron, or a strip iron framework behind them.</p></div>
-
-<p><span class="pagenum"><a name="Page_1877" id="Page_1877">1877</a></span>
-<b>Generator Panel.</b>&mdash;This section of a switchboard carries the
-instruments and apparatus for measuring and electrically controlling
-the generators. On a well designed switchboard each generator has, as
-a rule, its own panel.</p>
-
-<div class="figcenter">
-  <a name="fig2651"></a>
-  <img src="images/i045.jpg" alt="_" width="600" height="622" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,651 to 2,653.&mdash;Diagrams of
-connections for generator panels. <b>Key to symbols</b>: <b>A</b>,
-ammeter; <b>A.S.</b>, ammeter switch; <b>C.T.</b>, current
-transformer; <b>F.</b>, fuse; <b>F.A.</b>, direct current field
-ammeter; <b>F.S.</b>, field switch; <b>G.C.S.</b>, governor control
-switch; <b>L.S.</b>, limit switch (included with governor motor);
-<b>O.S.</b>, oil switch; <b>P.I.W.</b>, polyphase indicating
-wattmeter; <b>P.W.M.</b>, polyphase watthour meter; <b>P.R.</b>,
-pressure receptacle; <b>P.P.</b>, pressure plug; <b>Rheo.</b>,
-rheostat; <b>S.</b>, shunt; <b>S.R.</b>, synchronizing receptacle;
-<b>S.P.</b>, synchronizing plugs; <b>T.B.</b>, terminal board for
-instrument leads; <b>V</b>, alternating current voltmeter.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1878" id="Page_1878">1878</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2654"></a>
-  <img src="images/i-0304.jpg" alt="_" width="600" height="381" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,654 and 2,655.&mdash;Diagrams illustrating
-<b>a simple method of determining bus capacity</b> as suggested by
-the General Electric Co. Fig. 2,654 relates to any panel; the method
-is as follows: <b>1.</b> Make a rough plan of the <i>entire board</i>,
-regardless of the number of panels to be ordered. <i>The order of
-panels</i> shown is recommended, it being most economical of copper
-and best adapted to future extensions. <b>2.</b> To avoid confusion
-keep on one side of board everything pertaining to exciter buses,
-and on other side everything pertaining to A. C. buses. <b>3.</b>
-With single lines represent the exciter and A. C. buses across such
-panels as they actually extend and by means of arrows indicate that
-portion of each bus which is connected to feeders and that portion
-which is connected to generators. <i>Remember that "Generator" and
-"Feeder" arrows must always point toward each other</i>, otherwise the
-rules given below do not hold. Note also that the field circuits of
-alternator panels are treated as D. C. feeders for the exciter bus.
-<b>4.</b> On each panel mark its ampere rating, that is, the maximum
-current it supplies to or takes from the bus. For A. C. alternator
-panels the D. C. rating is the excitation of the machines. <b>5.</b>
-Apply the following rules <i>consecutively</i>, and note their application
-in fig. 2,654. (For the sake of clearness ampere ratings are shown
-in light face type and bus capacities in large type.) <b>A.</b>
-<i>Always begin with the tail of the arrow and treat "generator" and
-"feeder" sections of the bus separately.</i> <b>B.</b> <i>Bus capacity for
-first panel = ampere rating of panel.</i> <b>C.</b> <i>Bus capacity for
-each succeeding panel = ampere rating of panel plus bus capacity for
-preceding panel.</i> (See sums marked above the buses in fig. 2,654.)
-<b>D.</b> <i>For a panel not connected to a bus extending across it,
-use the smaller value of the bus capacities already obtained for the
-two adjoining panels.</i> (See exciter bus for panel C.) <b>E.</b> <i>The
-bus capacity for any feeder panel need not exceed the maximum for
-the generator panels</i> (see A. C. bus for panel G) <i>and vice versa</i>
-(see exciter bus for panel B). Hence the corrections made in values
-obtained by applying rules <b>B</b> and <b>C</b>. The arrangement of
-panels shown in fig. 2,654 is the one which is mostly used. The above
-method may, however, be applied to other arrangements, one of which
-is shown in fig. 2,655. Here the generators must feed both ways to
-the feeders at either end of the board so that in determining A. C.
-bus capacities it is necessary to first consider the generators with
-the feeders at one end, and then with the feeders at the other end as
-shown by the dotted A. C. buses. The required bus capacities are then
-obtained by taking the maximum values for the two cases.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1879" id="Page_1879">1879</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2656"></a>
-  <img src="images/i047.jpg" alt="_" width="500" height="830" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,656.&mdash;End view showing
-<b>general arrangement of switchboards</b> for 240, 480, and 600 volt
-alternating current. The cut shows a single throw oil switch mounted
-on the panel.</p>
-</div>
-
-<p class="space-below1">In the case of a dynamo, a good
-representative panel would have mounted upon it a reverse current
-circuit breaker, an ammeter, a double pole main switch (or perhaps a
-single pole switch, since the circuit breaker could also be used as
-a switch) a double pole socket into which a plug could be inserted
-to make connection with a voltmeter mounted on a swinging bracket at
-the end of the board; a <span class="pagenum"><a name="Page_1880"
-id="Page_1880">1880</a></span> rheostat handle, the spindle of which
-operates the shunt rheostat of the machine, the rheostat being placed
-either directly behind the spindle, if of small size, or lower down
-with chain drive from the hand wheel spindle, if of larger size, a
-field discharge switch and resistance, a lamp near the top of the
-panel for illuminating purposes, a fuse for the voltmeter socket,
-and, if desired, a watthour meter. If the dynamo be compound wound,
-the equalizing switch will generally be mounted on the frame of
-the machine, and in some cases the field rheostat will be operated
-from a pillar mounted in front of the switchboard gallery. If the
-generator be for traction purposes, the circuit breaker is more
-often of the maximum current type, and a lightning arrester is often
-added, without a choke coil, the latter as well as further lightning
-arresters being mounted on the feeder panels.</p>
-
-<div class="figcenter">
-  <a name="fig2657"></a>
-  <img src="images/i048.jpg" alt="_" width="500" height="844" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,657 and 2,658.&mdash;Two views of
-a <b>feeder panel</b>, showing general arrangement of the devices
-assembled thereon. A, circuit breaker; B, ammeter; C, voltmeter; D,
-switches.</p>
-</div>
-
-<p>In the case of a high pressure alternating current plant of
-considerable size, the bus bars oil switches, and the current and
-<span class="pagenum"><a name="Page_1881" id="Page_1881">1881</a></span>
-pressure transformers are generally mounted either in stoneware
-cells, or built on a framework in a space guarded by expanded metal
-walls, and no high pressure apparatus of any sort is brought on to
-the panels themselves.</p>
-
-<div class="figcenter">
-  <a name="fig2659"></a>
-  <img src="images/i049.jpg" alt="_" width="600" height="469" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,659 to 2,666.&mdash;Diagram of
-connections for three phase feeder panels. <b>Key to symbols</b>:
-A, ammeter; A.S., three way ammeter switch; B.A.S., bell alarm
-switch; C.T., current transformer; F, fuse; O.S., oil switch; P.I.W.,
-polyphase indicating wattmeter; P.W.M., polyphase watthour meter;
-T.B., terminal board; T.C., trip coils for oil switch.</p>
-</div>
-
-<p><b>Feeder Panel.</b>&mdash;The indicating and control apparatus for
-a feeder circuit is assembled on a panel called the feeder panel.</p>
-
-<p>The most common equipment in the case of a direct current
-feeder panel comprises an ammeter, a double pole switch, and
-double pole fuses or instead of the fuses, a circuit breaker on one
-or both poles; in the case of a traction feeder a choke coil and
-a lightning arrester are often added.
-<span class="pagenum"><a name="Page_1882" id="Page_1882">1882</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2667"></a>
-  <img src="images/i050.jpg" alt="_" width="600" height="744" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,667 and 2,668.&mdash;Diagrams of
-connections for two phase and three phase installations: A and
-A1, ammeter; C.C., constant current transformer; C.T., current
-transformer; D.R., discharge resistance; F, fuse; F.S., field switch;
-L.A., lightning arrester; O.S., oil switch; P.P., pressure plug;
-P.R., pressure receptacle; P.T., pressure transformer; S and S1, plug
-switches; T.C., oil switch trip coil; V, voltmeter.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1883" id="Page_1883">1883</a></span></p>
-
-<p class="space-below1">The equipment of a typical high pressure
-three phase feeder panel is an ammeter (sometimes three ammeters,
-one in each phase) operated by a current transformer, and oil break
-switch with two overload release coils, or three if the neutral
-of the circuit be earthed, the releases being operated by current
-transformers.</p>
-
-<div class="figcenter">
-  <a name="fig2669"></a>
-  <img src="images/i-0305.jpg" alt="_" width="600" height="602" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,669.&mdash;Crouse-Hinds radial
-ammeter switch, arranged for mounting directly on the switchboard.
-It is designed for use with external shunt ammeters of any make or
-capacity, and in connection with the required number of shunts, makes
-possible the taking of current readings of a corresponding number of
-circuits by means of one ammeter. The wiring diagram is shown in
-<a href="#fig2670">fig. 2,670</a>.</p>
-</div>
-
-<p>The switch when on a large system is often in a cell some distance
-behind the panel, and is then controlled by a system of levers, or by
-a small motor which is started and stopped by a throw over switch on
-the panel, in which case there is generally a lamp or lamps on the
-panel to show whether the switch is open or closed.
-<span class="pagenum"><a name="Page_1884" id="Page_1884">1884</a></span></p>
-
-<p class="blockquot">
-Air brake switches or links are placed between the bus bars and the
-oil switch to allow of the latter being isolated for inspection
-purposes, and as a general rule no apparatus carrying high pressure
-current is allowed on the front of the panel. With both direct and
-alternating current feeders, a watthour meter is often added to show
-the total consumption of the circuit.</p>
-
-<div class="figcenter">
-  <a name="fig2670"></a>
-  <img src="images/i052.jpg" alt="_" width="600" height="336" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,670.&mdash;Wiring diagram for Crouse-Hinds
-radial ammeter switch as illustrated in <a href="#fig2669">fig. 2,669</a>.
-The switch proper is on the rear of the switchboard, and the hand wheel
-dial and indicator on the front.</p>
-</div>
-
-<div class="blockquot">
-<p>A typical three phase generator panel is provided with three
-ammeters, one in each phase, operated from three current
-transformers, one to each ammeter, a volt meter, a power factor
-indicator, and an indicating watthour meter, all operated from one or
-more pressure transformers, and the necessary current transformers,
-the operating handle of the oil switch, which is connected to the
-switch itself by means of rods, two maximum releases operated by
-current transformers, or a reverse relay for automatically tripping
-the switch, lamps for indicating when the switch is tripped, a socket
-for taking the plug which makes connection between the secondary of a
-pressure transformer and the synchronizer on the synchronizing panel,
-and a lamp for illuminating purposes, while on the base of the panel
-or on a pillar at the front of the gallery is mounted the gear for
-the field circuit. This consists of a double pole field switch and a
-discharge resistance, an ammeter, a handle for the rheostat in the
-generator field, and (if each alternator have its own direct coupled
-exciter) possibly also a small rheostat for the exciter field.</p></div>
-<hr class="r5" />
-<p class="blockquot">
-NOTE.&mdash;In some cases where the capacity of the plant is not very
-great, the oil switch is mounted on the back of the panel, and the
-bus bars, current transformers, &amp;c., on the framework, also just at
-the back of the panel, but under no circumstances, in good modern
-practice, is high pressure apparatus permitted on the front of
-the board. Where the capacity of the plant is very large, the oil
-switches are operated electrically by means of small motors, and in
-this case the small switch gear for starting and stopping this motor
-is mounted on the generator panel, also the lamp or lamps to indicate
-when the switch is open, and when closed.</p>
-
-<p><span class="pagenum"><a name="Page_1885" id="Page_1885">1885</a></span></p>
-<hr class="chap" />
-<h2><span class="h_subtitle">CHAPTER LXV</span><br />ALTERNATING CURRENT WIRING</h2>
-
-<p>In the case of alternating current, because of its peculiar
-behaviour, there are several effects which must be considered in
-making wiring calculations, which do not enter into the problem with
-direct current.</p>
-
-<p>Accordingly, in determining the size of wires, allowance must be made for</p>
-
-<p class="no-indent">&emsp;&emsp;1. Self-induction;<br />
-&emsp;&emsp;2. Mutual-induction;<br />
-&emsp;&emsp;3. Power factor;<br />
-&emsp;&emsp;4. Skin effect;<br />
-&emsp;&emsp;5. Corona effect;<br />
-&emsp;&emsp;6. Frequency;<br />
-&emsp;&emsp;7. Resistance.</p>
-
-<p class="blockquot">
-Most of these items have already been explained at such length, that
-only a brief summary of facts need be added, to point out their
-connection and importance with alternating current wiring.</p>
-
-<p><b>Induction.</b>&mdash;The effect of induction, whether self-induction
-or mutual induction, is to set up a back pressure of <i>spurious
-resistance</i>, which must be considered, as it sometimes materially
-affects the calculation of circuits even in interior wiring.</p>
-
-<div class="blockquot">
-<p><i>Self-induction is the effect produced by the action of the electric
-current upon itself during variations in strength.</i></p></div>
-
-<p><span class="pagenum"><a name="Page_1886" id="Page_1886">1886</a></span>
-<b>Ques. What conditions besides variations of current
-strength governs the amount of self-induction in a circuit?</b></p>
-
-<p>Ans. The shape of the circuit, and the character of the surrounding medium.</p>
-
-<p class="blockquot">
-If the circuit be straight, there will be little self-induction, but
-if coiled, the effect will become pronounced. If the surrounding
-medium be air, the self-induction is small, but if it be iron, the
-self-induction is considerable.</p>
-
-<div class="figcenter">
-  <a name="fig2671"></a>
-  <img src="images/i054.jpg" alt="_" width="600" height="403" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs</span>. 2,671 to 2,676.&mdash;<b>The effect of
-self-induction.</b> In a non-inductive circuit, as in fig. 2,672,
-the whole of the virtual pressure is available to cause current to
-flow through the lamp filament, hence it will glow with maximum
-brilliancy. If an inductive coil be inserted in the circuit as in
-fig. 2,674, the reverse pressure due to self-induction will oppose
-the virtual pressure, hence the effective pressure (which is the
-difference between the virtual and reverse pressures), will be
-reduced and the current flow through the lamp diminished, thus
-reducing the brilliancy of the illumination. The effect may be
-intensified to such degree by interposing an iron core in the coil
-as in fig. 2,676, as to extinguish the lamp.</p>
-</div>
-
-<p><b>Ques. With respect to self-induction, what method should be
-followed in wiring?</b></p>
-
-<p>Ans. When iron conduits are used, the wires of each circuit should
-not be installed in separate conduits, because such arrangement will
-cause excessive self-induction.</p>
-
-<p class="blockquot">
-The importance of this may be seen from the experience of one
-contractor, who installed feeders and mains in separate iron pipes.
-<span class="pagenum"><a name="Page_1887" id="Page_1887">1887</a></span>
-When the current was turned on, it was found that the self-induction
-was so great as to reduce the pressure to such an extent that the
-lamps, instead of giving full candle power, were barely red. This
-necessitated the removal of the feeders and main and re-installing
-them, so that those of the same circuit were in the same pipe.</p>
-
-<p><b>Ques. What is mutual induction?</b></p>
-
-<p>Ans. Mutual induction is the effect of one alternating current
-circuit upon another.</p>
-
-<div class="figcenter">
-  <a name="fig2677"></a>
-  <img src="images/i055.jpg" alt="_" width="600" height="350" />
-  <p class="f90_left">
-<span class="smcap">Fig.</span> 2,677.&mdash;Measurement of self induction
-when the frequency is known. The apparatus required consists of a
-high resistance or electrostatic a.c. voltmeter, d.c. ammeter, and
-a non-inductive resistance. Connect the inductive resistance to be
-measured as shown, and close switch M, short circuiting the ammeter.
-Connect alternator in circuit and measure drop across R and across
-X<sub><i>i</i></sub>. Disconnect alternator and connect battery in circuit, then
-open switch M and vary the continuous current until the drop across R
-is the same as with the alternating current, both measurements being
-made with the same voltmeter; read ammeter, and measure drop across
-X<sub><i>i</i></sub>. Call the drop across X<sub><i>i</i></sub> with alternating current E,
-and with direct current E<sub><i>i</i></sub>, and the reading of the ammeter J.
-Then L = √<span class="rad">E<sup>2</sup> + E<sub><i>i</i></sub><sup>2</sup></span> ÷ 2&#960; <i>f</i> I. If the resistance
-X<sub><i>i</i></sub> be known, and the ammeter be suitable for use with alternating
-current, the switch and R may be dispensed with.</p>
-
-<p class="f90_left space-below1">&emsp;Then L = √<span class="rad">E<sup>2</sup>
-- X<sub><i>i</i></sub><sup>2</sup> I<sub><i>i</i></sub><sup>2</sup></span> ÷ 2&#960; <i>f</i> I,
-where I<sub><i>i</i></sub> is the value of the alternating current.
-The resistance of the voltmeter should be high enough to render
-its current negligible as compared with that through X<sub><i>i</i></sub>.</p>
-</div>
-
-<p><b>Ques. How is it caused?</b></p>
-
-<p>Ans. It is due to the magnetic field surrounding a conductor
-cutting adjacent conductors and inducing back pressures therein.</p>
-
-<p class="blockquot">
-This effect as a rule in ordinary installations is negligible.
-<span class="pagenum"><a name="Page_1888" id="Page_1888">1888</a></span></p>
-
-<p><b>Transpositions.</b>&mdash;The effect of mutual induction between two
-circuits is proportional to the inter-linkage of the magnetic fluxes
-of the two lines. This in turn depends upon the proximity of the
-lines and upon the general relative arrangement of the conductors.</p>
-
-<div class="figcenter">
-  <a name="fig2678"></a>
-  <img src="images/i056a.jpg" alt="_" width="600" height="173" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,678.&mdash;Transposition diagram for two
-parallel lines consisting of two wires each.</p>
-</div>
-
-<div class="figcenter">
-  <a name="fig2679"></a>
-  <img src="images/i056b.jpg" alt="_" width="600" height="153" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,679.&mdash;Transposition diagram for three
-phase, three wire line, transposing at the vertices of an equilateral
-triangle. The line is originally balanced and becomes unbalanced on
-transposing, a procedure which should be resorted to only to prevent
-<i>mutual induction</i>.</p>
-</div>
-
-<div class="figcenter">
-  <a name="fig2680"></a>
-  <img src="images/i056c.jpg" alt="_" width="600" height="163" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,680.&mdash;Transposition diagram of three
-phase, three wire line, with center arranged in a straight line.</p>
-</div>
-
-<p>The inductive effect of one line upon another is equal to the
-algebraic sum of the fluxes due to the different conductors of the
-first line, considered separately, which link the secondary line.
-<span class="pagenum"><a name="Page_1889" id="Page_1889">1889</a></span></p>
-
-<p>The effect of mutual induction is to induce surges in the line where
-a difference of frequency exists between the two currents, and to
-induce high electrostatic charges in lines carrying little or no
-current, such as telephone lines.</p>
-
-<table border="1" cellspacing="2" summary="Inductance" cellpadding="0">
-  <caption class="tr_grey bbox"><b>INDUCTANCE PER MILE OF THREE PHASE CIRCUIT</b></caption>
-  <tbody><tr class="tr_lt_grey">
-      <th class="tdr">&nbsp;Size&nbsp;B.&amp;S.&nbsp;</th>
-      <th class="tdr">Diam.&nbsp;<br />&nbsp;(inches)&nbsp;</th>
-      <th class="tdc"><br />&nbsp;Distance&nbsp;<br /><i>d</i><br />(inches)</th>
-      <th class="tdc"><br />&nbsp;Self&nbsp;Inductance&nbsp;<br />L<br />(henrys)</th>
-   </tr><tr class="tr_grey">
-      <td class="tdr">0000&nbsp;</td> <td class="tdr">.46&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00234</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00256</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr"></td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00270</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00312</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">000&nbsp;</td> <td class="tdr">.41&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00241</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00262</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00277</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00318</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">00&nbsp;</td> <td class="tdr">.365&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00248</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00269</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00285</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00330</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">0&nbsp;</td> <td class="tdr">.325&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00254</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00276</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00293</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00331</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">1&nbsp;</td> <td class="tdr">.289&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00260</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00281</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00308</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00338</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">2&nbsp;</td> <td class="tdr">.258&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00267</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00288</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00304</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00314</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">3&nbsp;</td> <td class="tdr">.229&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00274</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00294</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00310</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00351</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">4&nbsp;</td> <td class="tdr">.204&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00280</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00300</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00315</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00358</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">5&nbsp;</td> <td class="tdr">.182&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00286</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00307</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00323</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00356</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">6&nbsp;</td> <td class="tdr">.162&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00291</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00313</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00329</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00369</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">7&nbsp;</td> <td class="tdr">.144&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00298</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00310</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00336</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00377</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">8&nbsp;</td> <td class="tdr">.128&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00303</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00325</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00341</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00384</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">9&nbsp;</td> <td class="tdr">.114&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00310</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00332</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00348</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00389</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">10&nbsp;</td> <td class="tdr">.102&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.00318</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.00340</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.00355</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.00396</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="space-above1"><span class="pagenum"><a name="Page_1890" id="Page_1890">1890</a></span>
-This effect may be nullified by separating the lines and by
-transposing the wires of one of the lines so that the effect produced
-in one section is opposed by that in another. Of two parallel lines
-consisting of two wires each, one may be transposed to neutralize the
-mutual inductance.</p>
-
-<p class="blockquot">
-<a href="#fig2678">Fig. 2,678</a> shows this method. The length L' should be
-an even factor of L so that to every section of the line transposed there
-corresponds an opposing section.</p>
-
-<div class="figcenter">
-  <a name="fig2681"></a>
-  <img src="images/i058.jpg" alt="_" width="600" height="206" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,681.&mdash;Capacity effect in single phase
-transmission line. The effect is the same as would be produced by
-shunting across the line at each point an infinitesimal condenser
-having a capacity equal to that of an infinitesimal length of
-circuit. For the purpose of calculating the charging current, a very
-simple and sufficiently accurate method is to determine the current
-taken by a condenser having a capacity equal to that of the entire
-line when charged to the pressure on the line at the generating end.
-The effect of capacity of the line is to reduce the pressure drop,
-that is, improve the regulation, and to decrease or increase the
-power loss depending on the load and power factor of the receiver.</p>
-
-<p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,682.&mdash;Capacity effect in a
-three phase transmission line. It is the same as would be produced
-by shunting the line at each point by three infinitesimal condensers
-connected in star with the neutral point grounded, the capacity of
-each condenser being twice that of a condenser of infinitesimal
-length formed by any two of the wires. The effect of capacity on
-the regulation and efficiency of the line can be determined with
-sufficient accuracy in most cases by considering the line shunted at
-each end by three condensers connected in star, the capacity of each
-condenser being equal to that formed by any two wires of the line. An
-approximate value for the charging current per wire is the current
-required to charge a condenser, equal in capacity to that of any
-two of the wires, to the pressure at the generating end of the line
-between any one wire and the neutral point.</p>
-</div>
-
-<p>The self inductance of lines is readily calculated from the following
-formula:</p>
-
-<p class="center">L = .000558 {2.303 log (2A ÷ <i>d</i>) + .25} per mile of circuit</p>
-
-<p class="no-indent">where</p>
-
-<p>L = inductance of a loop of a three phase circuit in henrys.</p>
-
-<p class="blockquot"><i>Note.</i>&mdash;The inductance of a complete
-single phase circuit = L × 2 ÷ √<span class="rad">3</span>.</p>
-
-<p>A = distance between wires;<br />
-&emsp;&ensp;<i>d</i> = diameter of wire.</p>
-
-<p><span class="pagenum"><a name="Page_1891" id="Page_1891">1891</a></span></p>
-
-<table border="1" cellspacing="2" summary="Capacitance" cellpadding="0">
-  <caption class="tr_grey bbox"><b>CAPACITY IN MICRO-FARADS PER MILE OF CIRCUIT FOR THREE PHASE SYSTEM</b></caption>
-  <tbody><tr class="tr_lt_grey">
-      <th class="tdr">&nbsp;Size&nbsp;B.&amp;S.&nbsp;</th>
-      <th class="tdr">Diam.&nbsp;<br />&nbsp;(inches)&nbsp;</th>
-      <th class="tdc">&nbsp;Distance&nbsp;<br /><i>d</i><br />(inches)</th>
-      <th class="tdc">&nbsp;Capacity&nbsp;<br />C<br />(μfarads)</th>
-   </tr><tr class="tr_grey">
-      <td class="tdr">0000&nbsp;</td> <td class="tdr">.46&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.0226&nbsp;</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.0204&nbsp;</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr"></td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01922</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.01474</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">000&nbsp;</td> <td class="tdr">.41&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.0218&nbsp;</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.01992</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01876</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.01638</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">00&nbsp;</td> <td class="tdr">.365&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.0124&nbsp;</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.01946</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01832</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.01604</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">0&nbsp;</td> <td class="tdr">.325&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.02078</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.01898</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01642</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.01570</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">1&nbsp;</td> <td class="tdr">.289&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.02022</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.01952</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01748</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.0154&nbsp;</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">2&nbsp;</td> <td class="tdr">.258&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.01972</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.01818</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01710</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.01510</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">3&nbsp;</td> <td class="tdr">.229&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.01938</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.01766</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01672</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.01480</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">4&nbsp;</td> <td class="tdr">.204&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.01874</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.01726</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01636</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.01452</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">5&nbsp;</td> <td class="tdr">.182&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.01830</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.01690</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01602</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.01426</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">6&nbsp;</td> <td class="tdr">.162&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.01788</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.01654</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01560</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.0140&nbsp;</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">7&nbsp;</td> <td class="tdr">.144&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.01746</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.01618</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01538</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.01374</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">8&nbsp;</td> <td class="tdr">.128&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.01708</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.01586</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01508</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.01350</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">9&nbsp;</td> <td class="tdr">.114&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.01660</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.01552</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01478</td>
-   </tr><tr class="tr_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.01326</td>
-
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">10&nbsp;</td> <td class="tdr">.102&nbsp;</td>
-      <td class="tdc">12</td> <td class="tdc">.01636</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">18</td> <td class="tdc">.01522</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">24</td> <td class="tdc">.01452</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">&nbsp;</td> <td class="tdr">&nbsp;</td>
-      <td class="tdc">48</td> <td class="tdc">.01304</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="space-above1"><b>Capacity.</b>&mdash;In any given
-system of electrical conductors, a pressure difference between
-two of them corresponds to the presence <span class="pagenum"><a
-name="Page_1892" id="Page_1892">1892</a></span> of a quantity of
-electricity on each. With the same charges, the difference of
-pressure may be varied by varying the geometrical arrangement and
-magnitudes and also by introducing various dielectrics. The constant
-connecting the charge and the resulting pressure is called the
-capacity of the system.</p>
-
-<div class="blockquot">
-<p>All circuits have a certain capacity, because each conductor acts
-like the plate of a condenser, and the insulating medium, acts as the
-dielectric. The capacity depends upon the insulation.</p>
-
-<p>For a given grade of insulation, the capacity is proportional to the
-surface of the conductors, and universally to the distance between
-them.</p>
-
-<p>A three phase three wire transmission line spaced at the corners of
-an equilateral triangle as regards capacity acts precisely as though
-the neutral line were situated at the center of the triangle.</p>
-
-<p>The capacity of circuits is readily calculated by applying the
-following formulae:</p></div>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">38.83 <i>sc</i> 10<sup>-3</sup></td>
-      <td class="tdl">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">C =&nbsp;</td>
-      <td class="tdc">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</td>
-      <td class="tdl">&nbsp;&emsp;per mile, insulated cable with lead sheath;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">log (D ÷ d)</td>
-      <td class="tdl">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><br /></td>
-      <td class="tdc"><br />38.83 × 10<sup>-3</sup></td>
-      <td class="tdl"><br /></td>
-   </tr><tr>
-      <td class="tdr">C =&nbsp;</td>
-      <td class="tdc">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</td>
-      <td class="tdl">&nbsp;&emsp;per mile, single conductor with earth return;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">log (4<i>h</i> ÷ <i>d</i>)</td>
-      <td class="tdl">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><br /></td>
-      <td class="tdc"><br />19.42 × 10<sup>-3</sup></td>
-      <td class="tdl"><br /></td>
-   </tr><tr>
-      <td class="tdr">C =&nbsp;</td>
-      <td class="tdc">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</td>
-      <td class="tdl">&nbsp;&emsp;per mile of parallel conductors forming metallic circuit;</td>
-   </tr><tr>
-      <td class="tdr"></td>
-      <td class="tdc">log (2A ÷ <i>d</i></td>
-      <td class="tdl"></td>
-    </tr>
- </tbody>
-</table>
-
-<p class="no-indent">in which</p>
-
-<p>C = Capacity in micro-farads;<br />
-&emsp;&emsp;&emsp;&emsp;for a metallic circuit, C = capacity between wires;</p>
-
-<p><i>sc</i> = Specific inductive capacity of insulating material;<br />
-&emsp;&emsp;&emsp;= 1 for air, and 2.25 to 3.7 for rubber;</p>
-
-<p>D = Inside diameter of lead sheath;</p>
-<p><i>d</i> = Diameter of conductor;</p>
-<p><i>h</i> = Distance of conductors above ground;</p>
-<p class="space-below2">A = Distance between wires.</p>
-
-<p><b>Frequency.</b>&mdash;The number of cycles per second, or the frequency,
-has a direct effect upon the inductance reactance in an alternating
-current circuit, as is plainly seen from the formula.</p>
-
-<p class="f150">X<sub>i</sub> = 2&#960; <i>f</i> L</p>
-
-<div class="blockquot">
-<p>In the case of a transmission line alone; the lower frequencies are
-the more desirable, in that they tend to reduce the inductance drop
-and charging current. The inductance drop is proportional to the
-frequency.</p>
-
-<p>The natural period of a line, with distributed inductance and
-capacity, is approximately given by</p></div>
-
-<p class="f150">P = 7,900 / √<span class="rad">LC</span></p>
-
-<p class="blockquot no-indent">where L is the total inductance in millihenrys,
-and C, the total capacity in micro-farads. Accordingly some lower odd
-harmonic of the impressed frequency may be present which corresponds
-with the natural period of the line. When this obtains, oscillations
-of dangerous magnitude may occur. Such coincidences are less likely
-with the lower harmonics than with the higher.</p>
-
-<p><span class="pagenum"><a name="Page_1893" id="Page_1893">1893</a></span>
-<b>Skin Effect.</b>&mdash;The tendency of alternating current to confine
-itself to the <i>outer</i> portions of a conductor, instead of passing
-uniformly through the cross section, is called <i>skin effect</i>. The
-effect is proportional to the size of the conductor and the frequency.</p>
-
-<p><b>Ques. What effect has "skin effect" on the current?</b></p>
-
-<p>Ans. It is equivalent to an increase of ohmic resistance and
-therefore opposes the current.</p>
-
-<div class="figcenter">
-  <a name="fig2683"></a>
-  <img src="images/i061.jpg" alt="_" width="600" height="299" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,683 to 2,687.&mdash;Skin effect and shield
-effect. Fig. 2,683, section of conductor illustrating skin effect or
-tendency of the alternating current to distribute itself unequally
-through the cross section of a conductor as shown by the varied
-shading, which represents the current flowing most strongly in the
-outer portions of the conductor. For this reason it has been proposed
-to use hollow or flat instead of solid round conductors; however,
-with frequency not exceeding 100, the skin effect is negligibly
-small in copper conductors of the sizes usually employed. In figs.
-2,684 and 2,685, or 2,686 and 2,687, if two adjacent conductors be
-carrying current in the same direction, concentration will occur on
-those parts of the two conductors remote from one another, and the
-nearer parts will have less current, that is to say, they will be
-<b>shielded</b>. In this case, the induction due to one conductor
-will exert its opposing effect to the greatest extent on those parts
-of the other conductor nearest to it; this effect decreasing the
-deeper the latter is penetrated. After crossing the current axis,
-the induction will still decrease in magnitude, but will now aid the
-current in the conductor. Hence, the effect of these two conductors
-on one another will make the current density more uniform than
-is the case where the two conductors adjacent to one another are
-carrying current in opposite directions, as in figs. 2,685 and 2,686,
-therefore, the resistance and the heating for a given current will be
-smaller. If the two return conductors be situated on the line passing
-through the center of the conductors just considered, the effect
-will be to still further concentrate the current; the distribution
-symmetry will be further disturbed, and the resistance of the
-conductor system increased. It is therefore difficult to say which of
-the two cases considered holds the advantage so far as increasing the
-resistance is concerned. The case, however, in which the phases are
-mixed has much the smaller reactive drop.</p>
-</div>
-
-<p class="blockquot">
-If the conductor be large, or the frequency high, the central portion
-of the conductor carries little if any current, hence the resistance is
-therefore greater for alternating current than for direct current.</p>
-
-<p><b>Ques. For what condition may "skin effect" be neglected?</b></p>
-
-<p>Ans. For frequencies of 60 or less, with conductors having
-a diameter not greater than 0000 B. &amp; S. gauge.
-<span class="pagenum"><a name="Page_1894" id="Page_1894">1894</a></span></p>
-
-<p><b>Ques. How is the "skin effect" calculated for a given wire?</b></p>
-
-<p>Ans. Its area in circular mils multiplied by the frequency, gives the
-ratio of the wire's ohmic resistance to its combined resistance.</p>
-
-<div class="blockquot">
-<p>That is to say, the factor thus obtained multiplied by the resistance
-of the wire to direct current will give its combined resistance or
-resistance to alternating current.</p>
-
-<p class="space-below1">The following table gives these ratio factors for large conductors.</p></div>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-<caption><b>RATIO FACTOR FOR COMBINED RESISTANCE</b></caption>
-  <tbody><tr>
-      <th class="tdr">Cir. mils.&nbsp;&nbsp;<br />× frequency&nbsp;</th>
-      <th class="tdc">Ratio<br />&nbsp;&nbsp;factor&nbsp;&nbsp;</th>
-      <th class="tdr">Cir. mils.&nbsp;&nbsp;<br />× frequency&nbsp;</th>
-      <th class="tdc">Ratio<br />&nbsp;&nbsp;factor&nbsp;&nbsp;</th>
-    </tr><tr>
-      <td class="tdr">10,000,000</td>  <td class="tdc">1.00</td>
-      <td class="tdr">70,000,000</td>  <td class="tdc">1.13</td>
-    </tr><tr>
-      <td class="tdr">20,000,000</td>  <td class="tdc">1.01</td>
-      <td class="tdr">80,000,000</td>  <td class="tdc">1.17</td>
-    </tr><tr>
-      <td class="tdr">30,000,000</td>  <td class="tdc">1.03</td>
-      <td class="tdr">90,000,000</td>  <td class="tdc">1.20</td>
-    </tr><tr>
-      <td class="tdr">40,000,000</td>  <td class="tdc">1.05</td>
-      <td class="tdr">100,000,000</td> <td class="tdc">1.25</td>
-    </tr><tr>
-      <td class="tdr">50,000,000</td>  <td class="tdc">1.08</td>
-      <td class="tdr">125,000,000</td> <td class="tdc">1.34</td>
-    </tr><tr>
-      <td class="tdr">60,000,000</td>  <td class="tdc">1.10</td>
-      <td class="tdr">150,000,000</td> <td class="tdc">1.43</td>
-    </tr>
- </tbody>
-</table>
-
-<p><b>Corona Effect.</b>&mdash;When two wires, having a great difference
-of pressure are placed near each other, a certain phenomenon occurs,
-which is called <i>corona effect</i>. When the spacing or distance
-between the wires is small and the difference of pressure in the
-wires very great, a continuous passage of energy takes place through
-the dielectric or atmosphere, the amount of this energy may be an
-appreciable percentage of the power transmitted. Therefore in laying
-out high pressure transmission lines, this effect must be considered
-in the spacing of the wires.</p>
-
-<p><b>Ques. How does the corona effect manifest itself?</b></p>
-
-<p>Ans. It is visible at night as a bluish luminous envelope
-and audible as a hissing sound.
-<span class="pagenum"><a name="Page_1895" id="Page_1895">1895</a></span></p>
-
-<p><b>Ques. What is the critical voltage?</b></p>
-
-<p>Ans. The voltage at which the corona effect loss takes place.</p>
-
-<p><b>Ques. Upon what does the critical voltage depend?</b></p>
-
-<p class="space-below1">Ans. Upon the radius of the wires,
-the spacing, and the atmospheric conditions.</p>
-
-<div class="figcenter">
-  <a name="fig2688"></a>
-  <img src="images/i063.jpg" alt="_" width="600" height="441" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,688.&mdash;Electromagnetic and
-electrostatic fields surrounding the conductors of a transmission
-line. The electromagnetic field is represented by lines of magnetic
-force that surround the conductors in circles, (the solid lines), and
-the electrostatic field by (dotted) circles passing from conductor
-to conductor across at right angles to the magnetic circles. For
-any given size of wire and distance apart of wires there is a
-certain voltage at which the critical density or critical gradient
-is reached, where the air breaks down and luminosity begins&mdash;the
-critical voltage where corona manifests itself. At still higher
-voltages corona spreads to further distances from the conductor
-and a greater volume of air becomes luminous. Incidentally, it
-produces noise. Now to produce light requires power and to produce
-noise requires power. Air is broken down and is heated in breaking
-down, and to heat also requires power; therefore, as soon as corona
-forms, power is consumed or dissipated in its formation. When this
-phenomenon occurs on the conductors of an alternating current circuit
-a change takes place in relation to current and voltage. On the
-wires of an alternating current transmission line, at a voltage
-below that where corona forms&mdash;at a voltage where wires are not
-luminous&mdash;considerable current, more or less depending on voltage
-and length of wire, flows into the circuit as capacity current or
-charging current.</p>
-</div>
-
-<div class="blockquot">
-<p>The critical voltage increases with both the diameter of the wires,
-and the spacing.</p>
-
-<p>The losses due to corona effect increase very rapidly with increasing
-pressure beyond the critical voltage.</p>
-
-<p>The magnitude of the losses as well as the critical voltage is
-affected, by atmospheric conditions, hence they probably vary with
-the particular locality, and the season of the year. Therefore, for a
-given locality, a voltage which is normally below the critical point,
-may at times be above it, depending upon changes in the weather.
-<span class="pagenum"><a name="Page_1896" id="Page_1896">1896</a></span></p>
-
-<p>Such elements as smoke, fog, moisture, or other particles (dust,
-snow, etc.) floating in the air, increase the losses; rain, however,
-apparently has no appreciable effect upon the losses. It follows then
-that in the design of a transmission line, the atmospheric conditions
-of the particular locality through which the line passes should be
-considered.</p></div>
-
-<p><b>Ques. How should live wires be spaced?</b></p>
-
-<p>Ans. They should be so spaced as to lessen the tendency to
-leakage and to prevent the wires swinging together or against
-towers. The spacing should be only sufficient for safety, since
-increased spacing increases the self-induction of the line, and
-while it lessens the capacity, it does so only in a slight degree.</p>
-
-<p class="blockquot">The following spacing is in accordance with average practice.</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-     <th colspan="4"><b>SPACING FOR VARIOUS VOLTAGES</b></th>
-    </tr><tr>
-     <th class="tdc">Volts</th>   <th class="tdc">Spacing</th>
-    </tr><tr>
-      <td class="tdc">&nbsp;&nbsp;5,000</td>   <td class="tdc">&nbsp;28 ins.</td>
-    </tr><tr>
-      <td class="tdc">&nbsp;15,000</td>  <td class="tdc">&nbsp;40 ins.</td>
-    </tr><tr>
-      <td class="tdc">&nbsp;30,000</td>  <td class="tdc">&nbsp;48 ins.</td>
-    </tr><tr>
-      <td class="tdc">&nbsp;45,000</td>  <td class="tdc">&nbsp;60 ins.</td>
-    </tr><tr>
-      <td class="tdc">&nbsp;60,000</td>  <td class="tdc">&nbsp;60 ins.</td>
-    </tr><tr>
-      <td class="tdc">&nbsp;75,000</td>  <td class="tdc">&nbsp;84 ins.</td>
-    </tr><tr>
-      <td class="tdc">&nbsp;90,000</td>  <td class="tdc">&nbsp;96 ins.</td>
-    </tr><tr>
-      <td class="tdc">105,000</td> <td class="tdc">108 ins.</td>
-    </tr><tr>
-      <td class="tdc">120,000</td> <td class="tdc">120 ins.</td>
-    </tr>
- </tbody>
-</table>
-
-<p><b>Resistance of Wires.</b>&mdash;For quick calculation the following
-method of obtaining the resistance (approximately) of wires will be
-found convenient:</p>
-
-<p>1,000 feet No. 10 B. &amp; S. wire, which is about .1 inch in diameter
-(.1019), has a resistance of one ohm, at a temperature of 68° F. and
-weighs 31.4 pounds. A wire three sizes larger, that is No. 7, has
-twice the cross section and therefore one-half the resistance. A wire
-three sizes smaller than No. 10, that is No. 13, has one-half the
-cross section and therefore twice the resistance.</p>
-
-<p>Thus, starting with No. 10, any number three sizes larger will double
-the cross sectional area and any wire three sizes smaller will halve
-<span class="pagenum"><a name="Page_1897" id="Page_1897">1897</a></span>
-the cross sectional area of the preceding wire. This is true to the
-extreme limits of the table, so that the area, weight and resistance
-of any wire may be at once calculated to a close approximation from
-this rule, intermediate sizes being obtained by interpolation.</p>
-
-<p class="space-below1">For alternating current, the combined
-resistance, that is, the total resistance, including skin effect, is
-obtained by multiplying the resistance, as found above by the "ratio
-factor" (<a href="#Page_1894">see table page 1,894</a>).</p>
-
-<div class="figcenter">
-  <a name="fig2689"></a>
-  <img src="images/i065.jpg" alt="_" width="600" height="384" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,689 to 2,692.&mdash;Triangles for
-obtaining graphically, impedance, impressed pressure, etc., in
-alternating current circuits. For a full explanation of this method
-the reader is referred to Guide 5, Chapter XLVII on Alternating
-Current Diagrams. A thorough study of this chapter is recommended.</p>
-</div>
-
-<p><b>Impedance.</b>&mdash;<i>The total opposition to the flow of electricity
-in an alternating current circuit</i>, or the impedance may be resolved
-into two components representing the ohmic resistance and the
-spurious resistance; these components have a phase difference of 90°,
-and they may be represented graphically by the two legs of a right
-angle triangle, of which the hypothenuse represents the impedance.
-<span class="pagenum"><a name="Page_1898" id="Page_1898">1898</a></span></p>
-
-<p>Similarly, the volts lost or "drop" in an alternating circuit may
-be resolved into two components representing respectively<br />
-&emsp;&emsp;1. The loss due to resistance.<br />
-&emsp;&emsp;2. The loss due to reactance.</p>
-
-<p>These components have a phase difference of 90° and are represented
-graphically similar to the impedance components. This has been
-explained at considerable length in Chapter XLVII (Guide V).</p>
-
-<div class="figcenter">
-  <a name="fig2693"></a>
-  <img src="images/i066.jpg" alt="_" width="600" height="135" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,693.&mdash;Mechanical analogy of
-power factor, as exemplified by a locomotive "poling" a car off
-a siding. The car and locomotive are shown moving in parallel
-directions, and the pole AB, inclined at an angle &#981;. Now, if the
-length of AB be taken to represent the pressure exerted on the
-pole by the locomotive, then the imaginary lines AC and BC, drawn
-respectively parallel and at right angles to the direction of motion
-will represent respectively the useful and no energy (wattless)
-components; that is to say, if the pressure AB be applied to the car
-at an angle &#981;, only part of it, AC, is useful in propelling the car,
-the other component, BC, being wasted in tending to push the car off
-the track at right angles to the rails, being resisted by the flanges
-of the outer wheels.</p>
-</div>
-
-<p><b>Power Factor.</b>&mdash;When the current falls out of step with the
-pressure, as on inductive loads, the power factor becomes less than
-unity, and the effect is to increase the current required for a
-given load. Accordingly, this must be considered in calculating the
-size of the wires. As has been explained, the current flowing in
-an alternating current circuit, as measured by an ammeter, can be
-<span class="pagenum"><a name="Page_1899" id="Page_1899">1899</a></span>
-resolved into two components, representing respectively the <i>active
-component</i> and the <i>wattless component</i> or idle current. These
-are graphically represented by the two legs of a right triangle, of
-which the hypothenuse represents the current measured by the ammeter.</p>
-
-<p>This <i>apparent</i> current, as is evident from the triangle, exceeds
-the <i>active</i> current and lags behind the pressure by an amount
-represented by the angle &#981; between the hypothenuse and leg
-representing the energy current as shown in <a href="#fig2694">fig. 2,694</a>.</p>
-
-<div class="figcenter">
-  <a name="fig2694"></a>
-  <img src="images/i067.jpg" alt="_" width="600" height="209" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,694.&mdash;Diagram showing that the
-apparent current is more than the active current, the excess
-depending upon the angle of phase difference.</p>
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,695.&mdash;Diagram showing components
-of impedance volts. Compare this diagram with <a href="#fig2689">figs. 2,689</a> and
-<a href="#fig2671">2,671</a>, and note that the term "reactance" is the difference between
-the inductance drop and the capacity drop if the circuit contain
-capacity, for instance, if inductance drop be 10 volts and capacity
-drop be 7 volts then reactance 10-7 = 3 volts.</p>
-</div>
-
-<p><b>Ques. What determines the heating of the wires on alternating
-current circuits with inductive loads?</b></p>
-
-<p>Ans. The apparent current, as represented by the hypothenuse of the
-triangle in <a href="#fig2694">fig. 2,694</a>.</p>
-
-<p><b>Ques. How is the apparent current obtained?</b></p>
-
-<p>Ans. Divide the true watts by the product of the power factor
-multiplied by the voltage.</p>
-
-<p class="blockquot">
-Example.&mdash;A certain circuit supplies 20 kw. to motors at 220 volts
-and .8 power factor. What is the apparent current?</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">true watts</td>
-      <td class="tdl">&nbsp;&nbsp;20,000</td>
-      <td class="tdr">&nbsp;</td>
-     </tr><tr>
-      <td class="tdr">Apparent Current =&nbsp;</td>
-      <td class="tdc">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;&nbsp;=&nbsp;&nbsp;</td>
-      <td class="tdl">&mdash;&mdash;&mdash;&mdash;&nbsp;&nbsp;=&nbsp;&nbsp;</td>
-      <td class="tdr">&nbsp;113.6 amperes</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;&nbsp;power factor × volts</td>
-      <td class="tdl">&nbsp;&nbsp;.8 × 220</td>
-      <td class="tdr">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-<p><span class="pagenum"><a name="Page_1900" id="Page_1900">1900</a></span></p>
-
-<p class="space-above2"><b>Ques. What else, besides power factor, should be
-considered in making wire calculations for motor circuits?</b></p>
-
-<p>Ans. The efficiency of the motor, and the heavy starting current.</p>
-
-<div class="blockquot space-below2">
-<p>The product of the efficiency of the motor multiplied by the power
-factor gives the <i>apparent efficiency</i>, which governs the size of
-the wires, apparatus, etc., necessary to feed the motors.</p>
-
-<p>Allowance should be made for the heavy starting current required for
-some motors to avoid undue drop.</p></div>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-<caption><b>TABLE OF APPROXIMATE AMPERES PER TERMINAL FOR INDUCTION MOTORS</b></caption>
-  <tbody><tr class="tr_lt_grey">
-      <td class="tdr"><br /></td>
-      <td colspan="3" class="tdc"><br />Single phase</td>
-      <td colspan="3" class="tdc">Two phase<br />four wire</td>
-      <td colspan="4" class="tdc">Three phase<br />three wire</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">Horse&nbsp;<br />&nbsp;power&nbsp;</td>
-      <td class="tdc">110<br />&nbsp;volts&nbsp;</td> <td class="tdc">220<br />&nbsp;volts&nbsp;</td>
-      <td class="tdc">440<br />&nbsp;volts&nbsp;</td> <td class="tdc">110<br />&nbsp;volts&nbsp;</td>
-      <td class="tdc">220<br />&nbsp;volts&nbsp;</td> <td class="tdc">440<br />&nbsp;volts&nbsp;</td>
-      <td class="tdc">110<br />&nbsp;volts&nbsp;</td> <td class="tdc">220<br />&nbsp;volts&nbsp;</td>
-      <td class="tdc">440<br />&nbsp;volts&nbsp;</td> <td class="tdc">550<br />&nbsp;volts&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">.5&ensp;&nbsp;</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;6.6</td> <td class="tdl">&nbsp;&nbsp;3.4</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;1.8</td> <td class="tdl">&nbsp;&nbsp;&nbsp;3.3</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;1.7</td> <td class="tdl">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;.9</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;3.7</td> <td class="tdl">&nbsp;&nbsp;&nbsp;1.8</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;1</td> <td class="tdl">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">1&ensp;&nbsp;&nbsp;</td>
-      <td class="tdl">&nbsp;14</td> <td class="tdl">&nbsp;&nbsp;7</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;3.5</td> <td class="tdl">&nbsp;&nbsp;&nbsp;6.4</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;3.2</td> <td class="tdl">&nbsp;&nbsp;&nbsp;1.6</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;7.4</td> <td class="tdl">&nbsp;&nbsp;&nbsp;3.7</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;1.9</td> <td class="tdl">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">2&ensp;&nbsp;&nbsp;</td>
-      <td class="tdl">&nbsp;24</td> <td class="tdl">&nbsp;12</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;6</td> <td class="tdl">&nbsp;&nbsp;11</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;5.7</td> <td class="tdl">&nbsp;&nbsp;&nbsp;2.9</td>
-      <td class="tdl">&nbsp;&nbsp;13</td> <td class="tdl">&nbsp;&nbsp;&nbsp;6.6</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;3.3</td> <td class="tdl">&nbsp;&nbsp;&nbsp;2.5</td>
-   </tr><tr>
-      <td class="tdr">3&ensp;&nbsp;&nbsp;</td>
-      <td class="tdl">&nbsp;34</td> <td class="tdl">&nbsp;17</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;8.5</td> <td class="tdl">&nbsp;&nbsp;16</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;8.1</td> <td class="tdl">&nbsp;&nbsp;&nbsp;4.1</td>
-      <td class="tdl">&nbsp;&nbsp;19</td> <td class="tdl">&nbsp;&nbsp;&nbsp;9.3</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;4.7</td> <td class="tdl">&nbsp;&nbsp;&nbsp;3.5</td>
-   </tr><tr>
-      <td class="tdr">4&ensp;&nbsp;&nbsp;</td>
-      <td class="tdl">&nbsp;52</td> <td class="tdl">&nbsp;26</td>
-      <td class="tdl">&nbsp;&nbsp;13</td> <td class="tdl">&nbsp;&nbsp;26</td>
-      <td class="tdl">&nbsp;&nbsp;13</td> <td class="tdl">&nbsp;&nbsp;6.5</td>
-      <td class="tdl">&nbsp;&nbsp;30</td> <td class="tdl">&nbsp;&nbsp;15</td>
-      <td class="tdl">&nbsp;&nbsp;&nbsp;7.5</td> <td class="tdl">&nbsp;&nbsp;&nbsp;6</td>
-   </tr><tr>
-      <td class="tdr">5&ensp;&nbsp;&nbsp;</td>
-      <td class="tdl">&nbsp;74</td> <td class="tdl">&nbsp;37</td>
-      <td class="tdl">&nbsp;&nbsp;18.5</td> <td class="tdl">&nbsp;&nbsp;38</td>
-      <td class="tdl">&nbsp;&nbsp;19</td> <td class="tdl">&nbsp;&nbsp;9.5</td>
-      <td class="tdl">&nbsp;&nbsp;44</td> <td class="tdl">&nbsp;&nbsp;22</td>
-      <td class="tdl">&nbsp;&nbsp;11</td> <td class="tdl">&nbsp;&nbsp;&nbsp;9</td>
-   </tr><tr>
-      <td class="tdr">10&ensp;&nbsp;&nbsp;</td>
-      <td class="tdl">&nbsp;94</td> <td class="tdl">&nbsp;47</td>
-      <td class="tdl">&nbsp;&nbsp;23.5</td> <td class="tdl">&nbsp;&nbsp;44</td>
-      <td class="tdl">&nbsp;&nbsp;22</td> <td class="tdl">&nbsp;&nbsp;11</td>
-      <td class="tdl">&nbsp;&nbsp;50</td> <td class="tdl">&nbsp;&nbsp;25</td>
-      <td class="tdl">&nbsp;&nbsp;12.5</td> <td class="tdl">&nbsp;11</td>
-   </tr><tr>
-      <td class="tdr">15&ensp;&nbsp;&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;&nbsp;66</td>
-      <td class="tdl">&nbsp;&nbsp;33</td> <td class="tdl">&nbsp;&nbsp;16.5</td>
-      <td class="tdl">&nbsp;&nbsp;76</td> <td class="tdl">&nbsp;&nbsp;38</td>
-      <td class="tdl">&nbsp;&nbsp;19</td> <td class="tdl">&nbsp;16</td>
-   </tr><tr>
-      <td class="tdr">20&ensp;&nbsp;&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;&nbsp;88</td>
-      <td class="tdl">&nbsp;&nbsp;44</td> <td class="tdl">&nbsp;&nbsp;22</td>
-      <td class="tdl">&nbsp;102</td> <td class="tdl">&nbsp;&nbsp;51</td>
-      <td class="tdl">&nbsp;&nbsp;25.5</td> <td class="tdl">&nbsp;22</td>
-   </tr><tr>
-      <td class="tdr">25&ensp;&nbsp;&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;111</td>
-      <td class="tdl">&nbsp;&nbsp;55</td> <td class="tdl">&nbsp;&nbsp;28</td>
-      <td class="tdl">&nbsp;129</td> <td class="tdl">&nbsp;&nbsp;64</td>
-      <td class="tdl">&nbsp;&nbsp;32</td> <td class="tdl">&nbsp;25</td>
-   </tr><tr>
-      <td class="tdr">30&ensp;&nbsp;&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;134</td>
-      <td class="tdl">&nbsp;&nbsp;67</td> <td class="tdl">&nbsp;&nbsp;33.5</td>
-      <td class="tdl">&nbsp;154</td> <td class="tdl">&nbsp;&nbsp;77</td>
-      <td class="tdl">&nbsp;&nbsp;38.5</td> <td class="tdl">&nbsp;32</td>
-   </tr><tr>
-      <td class="tdr">40&ensp;&nbsp;&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;178</td>
-      <td class="tdl">&nbsp;&nbsp;89</td> <td class="tdl">&nbsp;&nbsp;44.5</td>
-      <td class="tdl">&nbsp;204</td> <td class="tdl">&nbsp;107</td>
-      <td class="tdl">&nbsp;&nbsp;53.5</td> <td class="tdl">&nbsp;44</td>
-   </tr><tr>
-      <td class="tdr">50&ensp;&nbsp;&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;204</td>
-      <td class="tdl">&nbsp;102</td> <td class="tdl">&nbsp;&nbsp;51</td>
-      <td class="tdl">&nbsp;236</td> <td class="tdl">&nbsp;118</td>
-      <td class="tdl">&nbsp;&nbsp;59</td> <td class="tdl">&nbsp;52</td>
-   </tr><tr>
-      <td class="tdr">75&ensp;&nbsp;&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;308</td>
-      <td class="tdl">&nbsp;154</td> <td class="tdl">&nbsp;&nbsp;77</td>
-      <td class="tdl">&nbsp;356</td> <td class="tdl">&nbsp;178</td>
-      <td class="tdl">&nbsp;&nbsp;89</td> <td class="tdl">&nbsp;77</td>
-   </tr><tr>
-      <td class="tdr">100&ensp;&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td> <td class="tdl">&nbsp;408</td>
-      <td class="tdl">&nbsp;204</td> <td class="tdl">&nbsp;&nbsp;102</td>
-      <td class="tdl">&nbsp;472</td> <td class="tdl">&nbsp;236</td>
-      <td class="tdl">&nbsp;118</td> <td class="tdl">100</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="space-above1"><b>Ques. What are the usual power factors
-encountered on commercial circuits?</b></p>
-
-<p>Ans. A mixed load of incandescent lamps and induction motors will
-have a power factor of from .8 to .85; induction motors above .8 to
-.85; incandescent and Nernst lamps .98; arc lamps, .85.
-<span class="pagenum"><a name="Page_1901" id="Page_1901">1901</a></span></p>
-
-<p><b>Wire Calculations.</b>&mdash;In the calculation of alternating current
-circuits, the two chief factors which make the computation different
-from that for direct current circuits, is <i>induction</i> and <i>power
-factor</i>. The first depends on the frequency, and physical condition
-of the circuit, and the second upon the character of the load.</p>
-
-<p><b>Ques. Under what conditions may inductance be neglected?</b></p>
-
-<div class="figcenter">
-  <a name="fig2696"></a>
-  <img src="images/i069.jpg" alt="_" width="600" height="269" />
-  <p class="f90_left space-below1"><span class="smcap">Figs.</span>
-2,696 to 2,698.&mdash;Example of wiring showing where inductance is
-negligible, and where it must be considered in wire calculations.</p>
-</div>
-
-<p>Ans. In cases where the wires of a circuit are not spaced over an
-inch apart, or in conduit work, where both wires are in the same
-conduit.</p>
-
-<p class="blockquot">
-Under these conditions the calculation is the same as for direct current
-after making proper allowance for power factor.</p>
-
-<p><b>Ques. Under what conditions must induction be considered?</b></p>
-
-<p>Ans. On exposed circuits with wires separated several inches,
-particularly in the case of large wires.
-<span class="pagenum"><a name="Page_1902" id="Page_1902">1902</a></span></p>
-
-<p><b>Sizes of Wire.</b>&mdash;The size of wire for any alternating circuit
-may be determined by slightly modifying the formula used in direct
-current work, and which, as derived in Guide No. 4, page 748, is</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">amperes × feet × 21.6</td>
-      <td class="tdl">&nbsp;</td>
-     </tr><tr>
-      <td class="tdr">circular mils =&nbsp;</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
-      <td class="tdl">&emsp;&nbsp;(1)</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">drop</td>
-      <td class="tdl">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="blockquot">
-The quantity 21.6, is twice the resistance (10.8) of a foot of copper
-wire one mil in diameter (<i>mil foot</i>). This resistance (10.8) is
-multiplied by 2, giving the quantity 21.6, because the length of a
-circuit, or feet in the formula, is given as the "run" or distance
-one way, that is, one-half the total length of wire in the circuit,
-must be multiplied by 2 to get the total drop, viz.:</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">amperes × feet × 10.8 × 2</td>
-      <td class="tdc">amperes × feet × 21.6</td>
-     </tr><tr>
-      <td class="tdr">circular mils =&nbsp;</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;=</td>
-      <td class="tdl">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">drop</td>
-      <td class="tdc">drop</td>
-   </tr>
- </tbody>
-</table>
-
-<p>It is sometimes however convenient to make the calculation in terms
-of watts. Formula (1) may be modified for such calculation.</p>
-
-<p>In modifying the formula, the "drop" should be expressed in
-percentage instead of actual volts lost, that is, instead of the
-difference in pressure between the beginning and the end of the
-circuit.</p>
-
-<p>In any circuit the loss in percentage, or</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">drop</td>
-      <td class="tdl">&nbsp;</td>
-     </tr><tr>
-      <td class="tdr">% loss = </td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
-      <td class="tdl">&nbsp;× 100</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">impressed pressure</td>
-      <td class="tdl">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="no-indent">from which</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">% loss × impressed pressure</td>
-      <td class="tdl">&nbsp;</td>
-     </tr><tr>
-      <td class="tdr">drop = </td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
-      <td class="tdl">&emsp;&nbsp;(2)</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">100</td>
-      <td class="tdl">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<p>Substituting equation (2) in equation (1)</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">amperes × feet × 21.6</td>
-     </tr><tr>
-      <td class="tdr">circular mils = </td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">% loss × imp. pressure</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">100</td>
-     </tr><tr>
-      <td class="tdr"><br /></td>
-      <td class="tdc"><br />amperes × feet × 2,160</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;=&nbsp; </td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&emsp;&nbsp;(3)</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">% loss × imp. pressure</td>
-   </tr>
- </tbody>
-</table>
-
-<p><span class="pagenum"><a name="Page_1903" id="Page_1903">1903</a></span></p>
-
-<p>Equation (3) is modified for calculation in terms of watts as
-follows: The power in watts is equal to the <i>applied voltage</i>
-multiplied by the current, that is to say, the power is equal to
-the <i>volts at the consumer's end of the circuit</i> multiplied by the
-current, or simply</p>
-
-<p class="center">watts = volts × amperes</p>
-
-<p class="no-indent">from which</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">watts</td>
-      <td class="tdl">&nbsp;</td>
-     </tr><tr>
-      <td class="tdr">amperes = </td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&nbsp;</td>
-      <td class="tdl">&emsp;&nbsp;(4)</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">volts</td>
-      <td class="tdl">&nbsp;</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdl">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<div class="figcenter">
-  <a name="fig2699"></a>
-  <img src="images/i071.jpg" alt="_" width="600" height="135" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs</span>. 2,699 to 2,703.&mdash;Stranded copper
-cables. For conductors of large areas and in the smaller sizes
-where extra flexibility is required it becomes necessary to employ
-stranded cables made by grouping a number of wires together in either
-concentric or rope form. The concentric cable as here illustrated is
-formed by grouping six wires around a central wire thereby forming
-a seven wire cable. The next step is the application in a reverse
-direction of another layer of 12 wires and a nineteen wire cable is
-produced. This is again increased by a third layer of eighteen wires
-for a 37 wire cable and a fourth layer of 24 wires for a 61 wire
-cable. Successive layers, each containing 6 more wires than that
-preceding, may be applied until the desired capacity is obtained. The
-cuts show sectional views of concentric cables each formed from No.
-10 B. &amp; S. gauge wires.</p>
-</div>
-
-<p>Substituting this value for the current in equation (3) and
-remembering that the pressure taken is the volts at the consumer's
-end of the line</p>
-
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">(watts/volts) × feet × 2,160 </td>
-     </tr><tr>
-      <td class="tdr">circular mils = </td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">% loss × volts</td>
-     </tr><tr>
-      <td class="tdr"><br /></td>
-      <td class="tdc"><br />watts × feet × 2,160</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;=&nbsp;</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&emsp;&nbsp;(5)</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">% loss × volts<sup>2</sup></td>
-   </tr>
- </tbody>
-</table>
-
-<p><span class="pagenum"><a name="Page_1904" id="Page_1904">1904</a></span>
-This formula (5) applies to a direct current two wire circuit, and to
-adapt it to any alternating current circuit it is only necessary to
-use the letter M instead of the number 2,160, thus</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">watts × feet × M </td>
-     </tr><tr>
-      <td class="tdr">circular mils = </td>
-      <td class="tdc">&nbsp;&emsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&emsp;&nbsp;(6)</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">% loss × volts<sup>2</sup></td>
-     </tr>
- </tbody>
-</table>
-
-<p class="no-indent">in which M is a coefficient which has various
-values according to the kind of circuit and value of the power
-factor. These values are given in the following table:</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-<caption><b>VALUES OF M</b></caption>
-  <tbody><tr class="tr_lt_grey">
-      <td rowspan="2" class="tdr"><br />SYSTEM</td>
-      <td colspan="10" class="tdc">POWER FACTOR</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">1.00</td> <td class="tdc">.98</td>
-      <td class="tdc">.95</td> <td class="tdc">.90</td>
-      <td class="tdc">.85</td> <td class="tdc">.80</td>
-      <td class="tdc">.75</td> <td class="tdc">.70</td>
-      <td class="tdc">.65</td> <td class="tdc">.60</td>
-   </tr><tr>
-      <td class="tdc">Single phase</td>
-      <td class="tdc">&nbsp;2,160&nbsp;</td> <td class="tdc">&nbsp;2,249&nbsp;</td>
-      <td class="tdc">&nbsp;2,400&nbsp;</td> <td class="tdc">&nbsp;2,660&nbsp;</td>
-      <td class="tdc">&nbsp;3,000&nbsp;</td> <td class="tdc">&nbsp;3,380&nbsp;</td>
-      <td class="tdc">&nbsp;3,840&nbsp;</td> <td class="tdc">&nbsp;4,400&nbsp;</td>
-      <td class="tdc">&nbsp;5,112&nbsp;</td> <td class="tdc">&nbsp;6,000&nbsp;</td>
-   </tr><tr>
-      <td class="tdc">Two phase<br />(4 wire)</td>
-      <td class="tdc_top">1,080</td> <td class="tdc_top">1,125</td>
-      <td class="tdc_top">1,200</td> <td class="tdc_top">1,330</td>
-      <td class="tdc_top">1,500</td> <td class="tdc_top">1,690</td>
-      <td class="tdc_top">1,920</td> <td class="tdc_top">2,200</td>
-      <td class="tdc_top">2,556</td> <td class="tdc_top">3,000</td>
-   </tr><tr>
-      <td class="tdc">Three phase<br />(3 wire)</td>
-      <td class="tdc_top">1,080</td> <td class="tdc_top">1,125</td>
-      <td class="tdc_top">1,200</td> <td class="tdc_top">1,330</td>
-      <td class="tdc_top">1,500</td> <td class="tdc_top">1,690</td>
-      <td class="tdc_top">1,920</td> <td class="tdc_top">2,200</td>
-      <td class="tdc_top">2,556</td> <td class="tdc_top">3,000</td>
-   </tr>
- </tbody>
-</table>
-
-<div class="blockquot">
-<p>NOTE.&mdash;The above table is calculated as follows: For <b>single
-phase</b> M = 2,160 ÷ power factor<sup>2</sup> × 100; for <b>two phase</b>
-four wire, or three phase three wire, M = ½ (2,160 ÷ power
-factor<sup>2</sup>)× 100. Thus the value of M for a single phase line with
-power factor .95 = 2,160 ÷ .95<sup>2</sup> × 100 = 2,400.</p></div>
-
-<p>It must be evident that when 2,160 is taken as the value of M,
-formula (6) applies to a two wire direct current circuit and also to
-a single phase alternating current circuit when the power factor is
-unity.</p>
-
-<p>In the table the value of M for any particular power factor is found
-by dividing 2,160 by the square of that power factor for single phase
-and twice the square of the power factor for two phase and three phase.
-<span class="pagenum"><a name="Page_1905" id="Page_1905">1905</a></span></p>
-
-<p><b>Ques. For a given load and voltage how do the wires of a single
-and two phase system compare in size and weight, the power factor
-being the same in each case?</b></p>
-
-<p>Ans. Since the two phase system is virtually two single phase
-systems, the four wires of the two phase systems are half the size of
-the two wires of the single phase system, and accordingly, the weight
-is the same for either system.</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-<caption><b>VALUES OF T</b></caption>
-  <tbody><tr class="tr_lt_grey">
-      <td rowspan="2" class="tdr"><br />SYSTEM</td>
-      <td colspan="10" class="tdc">POWER FACTOR</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">1.00</td> <td class="tdc">.98</td>
-      <td class="tdc">.90</td> <td class="tdc">.80</td>
-      <td class="tdc">.70</td>
-   </tr><tr>
-      <td class="tdc">Single phase</td>
-      <td class="tdc">&nbsp;1.00&nbsp;</td> <td class="tdc">&nbsp;.98&nbsp;</td>
-      <td class="tdc">&nbsp;.90&nbsp;</td> <td class="tdc">&nbsp;.80&nbsp;</td>
-      <td class="tdc">&nbsp;.70&nbsp;</td>
-   </tr><tr>
-      <td class="tdc">Two phase<br />(4 wire)</td>
-      <td class="tdc_top">&nbsp;2.00&nbsp;</td> <td class="tdc_top">&nbsp;1.96&nbsp;</td>
-      <td class="tdc_top">&nbsp;1.80&nbsp;</td> <td class="tdc_top">&nbsp;1.60&nbsp;</td>
-      <td class="tdc_top">&nbsp;1.40&nbsp;</td>
-   </tr><tr>
-      <td class="tdc">Three phase<br />(3 wire)</td>
-      <td class="tdc_top">&nbsp;1.73&nbsp;</td> <td class="tdc_top">&nbsp;1.70&nbsp;</td>
-      <td class="tdc_top">&nbsp;1.55&nbsp;</td> <td class="tdc_top">&nbsp;1.38&nbsp;</td>
-      <td class="tdc_top">&nbsp;1.21&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<div class="blockquot">
-<p>NOTE.&mdash;This table is for finding the
-value of the current in line, using the formula
-I&nbsp;=&nbsp;W&nbsp;÷&nbsp;(E&nbsp;×&nbsp;T), in which I = current
-in line; E = voltage between main conductors at receiving or
-consumers' end; W = watts. For instance, what is the current in a two
-phase line transmitting 1,000 watts at 550 volts, power factor .80?&emsp;I
-= 1,000 ÷ (550 × 1.60) = 1.13.</p></div>
-
-<p><b>Ques. Since there is no saving in copper in using two phases, what
-advantage has the two phase system over the one phase system?</b></p>
-
-<p>Ans. It is more desirable on power circuits, because two phase motors
-are self-starting.</p>
-
-<p class="blockquot">
-That is to say, the rotating magnetic field that can be produced by a
-two phase current, permits an induction motor to start without being
-equipped with any special phase splitting devices which are necessary
-on single phase motors, because the oscillating field produced by a
-single phase current does not produce any torque on a squirrel cage
-armature at rest.
-<span class="pagenum"><a name="Page_1906" id="Page_1906">1906</a></span></p>
-
-<p><b>Ques. For equal working conditions, what is the comparison
-between the single, two and three phase system as to size and
-weight of wires?</b></p>
-
-<p class="space-below2">Ans. Each wire of the three phase system is half the
-size of one of the wires of the single phase system, hence the weight of copper
-required for the three phase system is 75% of that required for the
-single phase system. Since in the two phase system half of the load
-is carried by each phase, each wire of the three phase system is the
-same size as one of the wires of the two phase system, hence, the
-copper required by the three phase system is 75% of that required by
-the two phase system.</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-<caption><b>MISCELLANEOUS&nbsp;FORMULÆ&nbsp;FOR&nbsp;COPPER&nbsp;WIRES</b></caption>
-  <tbody><tr>
-      <td class="tdl">Diameter squared</td>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;= circular mils</td>
-    </tr><tr>
-      <td class="tdl">Circular mils</td>
-      <td class="tdl">&nbsp;× .7854</td>
-      <td class="tdl">&nbsp;= square mils</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;&emsp;.000003027</td>
-      <td class="tdl">&nbsp;× circular mils</td>
-      <td class="tdl">&nbsp;= pounds per foot</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;&emsp;.003027</td>
-      <td class="tdl">&nbsp;× circular mils</td>
-      <td class="tdl">&nbsp;= pounds per 1,000 feet</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;&emsp;.0159847</td>
-      <td class="tdl">&nbsp;× circular mils</td>
-      <td class="tdl">&nbsp;= pounds per mile</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;&emsp;.003879</td>
-      <td class="tdl">&nbsp;× square mils</td>
-      <td class="tdl">&nbsp;= pounds per 1,000 feet</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;&emsp;.33033</td>
-      <td class="tdl">&nbsp;÷ circular mils</td>
-      <td class="tdl">&nbsp;= feet per pound</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;&emsp;.0000002924</td>
-      <td class="tdl">&nbsp;× circular mils</td>
-      <td class="tdl">&nbsp;= pounds per ohm</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;&emsp;.342</td>
-      <td class="tdl">&nbsp;÷ circular mils</td>
-      <td class="tdl">&nbsp;= ohms per pound</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;&emsp;.096585</td>
-      <td class="tdl">&nbsp;× circular mils</td>
-      <td class="tdl">&nbsp;= feet per ohm</td>
-    </tr><tr>
-      <td class="tdl">&nbsp;10.353568</td>
-      <td class="tdl">&nbsp;÷ circular mils</td>
-      <td class="tdl">&nbsp;= ohms per foot</td>
-    </tr>
- </tbody>
-</table>
-
-<p class="space-above1">Breaking weight of wire ÷ area = breaking weight per square inch.</p>
-
-<p>Breaking weight per square inch × area = breaking weight of wire.</p>
-
-<p>The weight of copper wire is 1-1/7 times the weight of iron wire of same diameter.
-<span class="pagenum"><a name="Page_1907" id="Page_1907">1907</a></span></p>
-
-<div class="blockquot">
-<p>EXAMPLE.&mdash;What size wires must be used on a single phase circuit
-2,000 feet in length to supply 30 kw. at 220 volts with loss of 4%,
-the power factor being .9?</p>
-
-<p>The formula for circular mils is</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">watts × feet × M </td>
-     </tr><tr>
-      <td class="tdr">circular mils = </td>
-      <td class="tdc">&nbsp;&emsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&emsp;&nbsp;(1)</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">% loss × volts<sup>2</sup></td>
-     </tr>
- </tbody>
-</table>
-
-<p class="no-indent">Substituting the given values and the proper value of M from
-the table, in (1)</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">30,000 × 2,000 × 2,660</td>
-     </tr><tr>
-      <td class="tdr">circular mils = </td>
-      <td class="tdc">&nbsp;&emsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">4 × 220<sup>2</sup></td>
-     </tr>
- </tbody>
-</table>
-
-<p>Referring to the accompanying table of the properties of copper wire,
-the nearest <i>larger</i> size wire is No. 1 B. &amp; S. gauge having an area
-of 83,690 circular mils.</p></div>
-
-<p class="center space-above2"><b>TABLE OF THE PROPERTIES OF COPPER WIRE</b></p>
-<p class="blockquot">
-Giving weights, length and resistances of wires of Matthiessen's
-Standard Conductivity for both B. &amp; S. G. (Brown &amp; Sharpe Gauge) and
-B. W. G. (Birmingham Wire Gauge) from Transactions October 1903, of
-the American Institute of Electrical Engineers.</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr class="tr_lt_grey">
-      <td colspan="4" class="tdc">Gauges. To the nearest fourth significant digit.</td>
-      <td rowspan="3" class="tdc">Weight.<br />Lbs. per<br />1,000 ft.</td>
-      <td class="tdc">Length.</td>
-      <td class="tdc">Resistance.</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">&nbsp;</td> <td class="tdc">Diameter.</td>
-      <td class="tdc">Area.</td>
-      <td rowspan="2" class="tdc">Feet<br />per lb.</td>
-      <td rowspan="2" class="tdc">Ohms per<br />1,000 feet.<br />@ 68° F.</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">B.&amp; S.</td>
-      <td class="tdc">B.W.G.</td> <td class="tdc">Inches.</td>
-      <td class="tdc">Circular mils.</td>
-   </tr><tr>
-      <td class="tdr">0000&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.460</td>
-      <td class="tdl">&nbsp;211,600</td> <td class="tdl">&nbsp;640.5</td>
-      <td class="tdr">1.561&nbsp;</td> <td class="tdr">.04893&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">0000&nbsp;</td> <td class="tdl">&nbsp;0.454</td>
-      <td class="tdl">&nbsp;206,100</td> <td class="tdl">&nbsp;623.9</td>
-      <td class="tdr">1.603&nbsp;</td> <td class="tdr">&nbsp;.05023</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">000&nbsp;</td> <td class="tdl">&nbsp;0.425</td>
-      <td class="tdl">&nbsp;180,600</td> <td class="tdl">&nbsp;546.8</td>
-      <td class="tdr">1.829&nbsp;</td> <td class="tdr">.05732&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">000&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.4096</td>
-      <td class="tdl">&nbsp;167,800</td> <td class="tdl">&nbsp;508.0</td>
-      <td class="tdr">1.969&nbsp;</td> <td class="tdr">.06170&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">00&nbsp;</td> <td class="tdl">&nbsp;0.380</td>
-      <td class="tdl">&nbsp;144,400</td> <td class="tdl">&nbsp;437.1</td>
-      <td class="tdr">2.288&nbsp;</td> <td class="tdr">.07170&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">00&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.3648</td>
-      <td class="tdl">&nbsp;133,100</td> <td class="tdl">&nbsp;402.8</td>
-      <td class="tdr">2.482&nbsp;</td> <td class="tdr">.07780&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">0&nbsp;</td> <td class="tdl">&nbsp;0.340</td>
-      <td class="tdl">&nbsp;115,600</td> <td class="tdl">&nbsp;349.9</td>
-      <td class="tdr">2.858&nbsp;</td> <td class="tdr">.08957&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">0&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.3249</td>
-      <td class="tdl">&nbsp;105,500</td> <td class="tdl">&nbsp;319.5</td>
-      <td class="tdr">3.130&nbsp;</td> <td class="tdr">.09811&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">1&nbsp;</td> <td class="tdl">&nbsp;0.3000</td>
-      <td class="tdl">&emsp;90,000</td> <td class="tdl">&nbsp;272.4</td>
-      <td class="tdr">3.671&nbsp;</td> <td class="tdr">.1150&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">1&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.2893</td>
-      <td class="tdl">&emsp;83,690</td> <td class="tdl">&nbsp;253.3</td>
-      <td class="tdr">3.947&nbsp;</td> <td class="tdr">.1237&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">2&nbsp;</td> <td class="tdl">&nbsp;0.2840</td>
-      <td class="tdl">&emsp;80,660</td> <td class="tdl">&nbsp;244.1</td>
-      <td class="tdr">4.096&nbsp;</td> <td class="tdr">.1284&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">3&nbsp;</td> <td class="tdl">&nbsp;0.2590</td>
-      <td class="tdl">&emsp;67,080</td> <td class="tdl">&nbsp;203.1</td>
-      <td class="tdr">4.925&nbsp;</td> <td class="tdr">.1543&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">2&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.2576</td>
-      <td class="tdl">&emsp;66,370</td> <td class="tdl">&nbsp;200.9</td>
-      <td class="tdr">4.977&nbsp;</td> <td class="tdr">.1560&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">4&nbsp;</td> <td class="tdl">&nbsp;0.2380</td>
-      <td class="tdl">&emsp;56,640</td> <td class="tdl">&nbsp;171.5</td>
-      <td class="tdr">5.832&nbsp;</td> <td class="tdr">.1828&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">3&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.2294</td>
-      <td class="tdl">&emsp;52,630</td> <td class="tdl">&nbsp;159.3</td>
-      <td class="tdr">6.276&nbsp;</td> <td class="tdr">.1967&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">5&nbsp;</td> <td class="tdl">&nbsp;0.2200</td>
-      <td class="tdl">&emsp;48,400</td> <td class="tdl">&nbsp;146.5</td>
-      <td class="tdr">6.826&nbsp;</td> <td class="tdr">.2139&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">4&nbsp;<span class="pagenum"><a name="Page_1908" id="Page_1908">1908</a></span></td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.2043</td>
-      <td class="tdl">&emsp;41,740</td> <td class="tdl">&nbsp;126.4</td>
-      <td class="tdr">7.914&nbsp;</td> <td class="tdr">.2480&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">6&nbsp;</td> <td class="tdl">&nbsp;0.2030</td>
-      <td class="tdl">&emsp;41,210</td> <td class="tdl">&nbsp;124.7</td>
-      <td class="tdr">8.017&nbsp;</td> <td class="tdr">.2513&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">5&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.1819</td>
-      <td class="tdl">&emsp;33,100</td> <td class="tdl">&nbsp;100.2</td>
-      <td class="tdr">9.98&ensp;&nbsp;</td> <td class="tdr">.3128&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">7&nbsp;</td> <td class="tdl">&nbsp;0.1800</td>
-      <td class="tdl">&emsp;32,400</td> <td class="tdl">&nbsp;98.08</td>
-      <td class="tdr">10.20&ensp;&nbsp;</td> <td class="tdr">.3196&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">8&nbsp;</td> <td class="tdl">&nbsp;0.1650</td>
-      <td class="tdl">&emsp;27,230</td> <td class="tdl">&nbsp;82.41</td>
-      <td class="tdr">12.13&ensp;&nbsp;</td> <td class="tdr">.3803&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">6&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.1620</td>
-      <td class="tdl">&emsp;26,250</td> <td class="tdl">&nbsp;79.46</td>
-      <td class="tdr">12.58&ensp;&nbsp;</td> <td class="tdr">.3944&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">9&nbsp;</td> <td class="tdl">&nbsp;0.1480</td>
-      <td class="tdl">&emsp;21,900</td> <td class="tdl">&nbsp;66.30</td>
-      <td class="tdr">15.08&ensp;&nbsp;</td> <td class="tdr">.4727&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">7&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.1443</td>
-      <td class="tdl">&emsp;20,820</td> <td class="tdl">&nbsp;63.02</td>
-      <td class="tdr">15.87&ensp;&nbsp;</td> <td class="tdr">.4973&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">10&nbsp;</td> <td class="tdl">&nbsp;0.1340</td>
-      <td class="tdl">&emsp;17,960</td> <td class="tdl">&nbsp;54.35</td>
-      <td class="tdr">18.40&ensp;&nbsp;</td> <td class="tdr">.5766&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">8&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.1285</td>
-      <td class="tdl">&emsp;16,510</td> <td class="tdl">&nbsp;49.98</td>
-      <td class="tdr">20.01&ensp;&nbsp;</td> <td class="tdr">.6271&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">11&nbsp;</td> <td class="tdl">&nbsp;0.1200</td>
-      <td class="tdl">&emsp;14,400</td> <td class="tdl">&nbsp;43.59</td>
-      <td class="tdr">22.94&ensp;&nbsp;</td> <td class="tdr">.7190&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">9&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.1144</td>
-      <td class="tdl">&emsp;13,090</td> <td class="tdl">&nbsp;39.63</td>
-      <td class="tdr">25.23&ensp;&nbsp;</td> <td class="tdr">.7908&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">12&nbsp;</td> <td class="tdl">&nbsp;0.1090</td>
-      <td class="tdl">&emsp;11,880</td> <td class="tdl">&nbsp;35.96</td>
-      <td class="tdr">27.81&ensp;&nbsp;</td> <td class="tdr">.8715&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">10&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.1019</td>
-      <td class="tdl">&emsp;10,380</td> <td class="tdl">&nbsp;31.43</td>
-      <td class="tdr">31.82&ensp;&nbsp;</td> <td class="tdr">.9972&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">13&nbsp;</td> <td class="tdl">&nbsp;0.0950</td>
-      <td class="tdl">&emsp;&ensp;9,025</td> <td class="tdl">&nbsp;27.32</td>
-      <td class="tdr">36.60&ensp;&nbsp;</td> <td class="tdr">1.147&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">11&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.09074</td>
-      <td class="tdl">&emsp;&ensp;8,234</td> <td class="tdl">&nbsp;24.93</td>
-      <td class="tdr">40.12&ensp;&nbsp;</td> <td class="tdr">1.257&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">14&nbsp;</td> <td class="tdl">&nbsp;0.08300</td>
-      <td class="tdl">&emsp;&ensp;6,889</td> <td class="tdl">&nbsp;20.85</td>
-      <td class="tdr">47.95&ensp;&nbsp;</td> <td class="tdr">1.503&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">12&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.08081</td>
-      <td class="tdl">&emsp;&ensp;6,530</td> <td class="tdl">&nbsp;19.77</td>
-      <td class="tdr">50.59&ensp;&nbsp;</td> <td class="tdr">1.586&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">15&nbsp;</td> <td class="tdl">&nbsp;0.07200</td>
-      <td class="tdl">&emsp;&ensp;5,184</td> <td class="tdl">&nbsp;15.69</td>
-      <td class="tdr">63.73&ensp;&nbsp;</td> <td class="tdr">1.997&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">13&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.07196</td>
-      <td class="tdl">&emsp;&ensp;5,178</td> <td class="tdl">&nbsp;15.68</td>
-      <td class="tdr">63.79&ensp;&nbsp;</td> <td class="tdr">1.999&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">16&nbsp;</td> <td class="tdl">&nbsp;0.06500</td>
-      <td class="tdl">&emsp;&ensp;4,225</td> <td class="tdl">&nbsp;12.79</td>
-      <td class="tdr">78.19&ensp;&nbsp;</td> <td class="tdr">2.451&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">14&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.06408</td>
-      <td class="tdl">&emsp;&ensp;4,107</td> <td class="tdl">&nbsp;12.43</td>
-      <td class="tdr">80.44&ensp;&nbsp;</td> <td class="tdr">2.521&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">17&nbsp;</td> <td class="tdl">&nbsp;0.0580</td>
-      <td class="tdl">&emsp;&ensp;3,364</td> <td class="tdl">&nbsp;10.18</td>
-      <td class="tdr">98.23&ensp;&nbsp;</td> <td class="tdr">3.078&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">15&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.05707</td>
-      <td class="tdl">&emsp;&ensp;3,257</td> <td class="tdl">&nbsp;&nbsp;9.858</td>
-      <td class="tdr">101.4&emsp;&nbsp;</td> <td class="tdr">3.179&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">16&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.05082</td>
-      <td class="tdl">&emsp;&ensp;2,583</td> <td class="tdl">&nbsp;&nbsp;7.818</td>
-      <td class="tdr">127.9&emsp;&nbsp;</td> <td class="tdr">4.009&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">18&nbsp;</td> <td class="tdl">&nbsp;0.04900</td>
-      <td class="tdl">&emsp;&ensp;2,401</td> <td class="tdl">&nbsp;&nbsp;7.268</td>
-      <td class="tdr">137.6&emsp;&nbsp;</td> <td class="tdr">4.312&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">17&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.045260</td>
-      <td class="tdl">&emsp;&ensp;2,048</td> <td class="tdl">&nbsp;&nbsp;6.200</td>
-      <td class="tdr">161.3&emsp;&nbsp;</td> <td class="tdr">5.055&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">19&nbsp;</td> <td class="tdl">&nbsp;0.042000</td>
-      <td class="tdl">&emsp;&ensp;1,764</td> <td class="tdl">&nbsp;&nbsp;5.340</td>
-      <td class="tdr">187.3&emsp;&nbsp;</td> <td class="tdr">5.870&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">18&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.040300</td>
-      <td class="tdl">&emsp;&ensp;1,624</td> <td class="tdl">&nbsp;&nbsp;4.917</td>
-      <td class="tdr">203.4&emsp;&nbsp;</td> <td class="tdr">6.374&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">19&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.035890</td>
-      <td class="tdl">&emsp;&ensp;1,288</td> <td class="tdl">&nbsp;&nbsp;3.899</td>
-      <td class="tdr">256.5&emsp;&nbsp;</td> <td class="tdr">8.038&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">20&nbsp;</td> <td class="tdl">&nbsp;0.035000</td>
-      <td class="tdl">&emsp;&ensp;1,225</td> <td class="tdl">&nbsp;&nbsp;3.708</td>
-      <td class="tdr">269.7&emsp;&nbsp;</td> <td class="tdr">8.452&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">21&nbsp;</td> <td class="tdl">&nbsp;0.032000</td>
-      <td class="tdl">&emsp;&ensp;1,024</td> <td class="tdl">&nbsp;&nbsp;3.100</td>
-      <td class="tdr">322.6&emsp;&nbsp;</td> <td class="tdr">10.11&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">20&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.031960</td>
-      <td class="tdl">&emsp;&ensp;1,022</td> <td class="tdl">&nbsp;&nbsp;3.092</td>
-      <td class="tdr">323.4&emsp;&nbsp;</td> <td class="tdr">10.14&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">21&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.028460</td>
-      <td class="tdl">&emsp;&ensp;810.1</td> <td class="tdl">&nbsp;&nbsp;2.452</td>
-      <td class="tdr">407.8&emsp;&nbsp;</td> <td class="tdr">12.78&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">22&nbsp;</td> <td class="tdl">&nbsp;0.028000</td>
-      <td class="tdl">&emsp;&ensp;784.0</td> <td class="tdl">&nbsp;&nbsp;2.373</td>
-      <td class="tdr">421.4&emsp;&nbsp;</td> <td class="tdr">13.21&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">22&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.025350</td>
-      <td class="tdl">&emsp;&ensp;642.4</td> <td class="tdl">&nbsp;&nbsp;1.945</td>
-      <td class="tdr">514.2&emsp;&nbsp;</td> <td class="tdr">16.12&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><span class="pagenum"><a name="Page_1909" id="Page_1909">1909</a></span></td>
-      <td class="tdr">23&nbsp;</td> <td class="tdl">&nbsp;0.025000</td>
-      <td class="tdl">&emsp;&ensp;625.0</td> <td class="tdl">&nbsp;&nbsp;1.892</td>
-      <td class="tdr">528.6&emsp;&nbsp;</td> <td class="tdr">16.57&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">23&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.022570</td>
-      <td class="tdl">&emsp;&ensp;509.5</td> <td class="tdl">&nbsp;&nbsp;1.542</td>
-      <td class="tdr">648.4&emsp;&nbsp;</td> <td class="tdr">20.32&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">24&nbsp;</td> <td class="tdl">&nbsp;0.022000</td>
-      <td class="tdl">&emsp;&ensp;484.0</td> <td class="tdl">&nbsp;&nbsp;1.465</td>
-      <td class="tdr">682.6&emsp;&nbsp;</td> <td class="tdr">21.39&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">24&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.020100</td>
-      <td class="tdl">&emsp;&ensp;404.0</td> <td class="tdl">&nbsp;&nbsp;1.223</td>
-      <td class="tdr">817.6&emsp;&nbsp;</td> <td class="tdr">25.63&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">25&nbsp;</td> <td class="tdl">&nbsp;0.020000</td>
-      <td class="tdl">&emsp;&ensp;400.0</td> <td class="tdl">&nbsp;&nbsp;1.211</td>
-      <td class="tdr">825.9&emsp;&nbsp;</td> <td class="tdr">25.88&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">26&nbsp;</td> <td class="tdl">&nbsp;0.018000</td>
-      <td class="tdl">&emsp;&ensp;324.0</td> <td class="tdl">&ensp; &nbsp;.9808</td>
-      <td class="tdr">&nbsp;1,020&emsp;&nbsp;&nbsp;</td> <td class="tdr">31.96&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">25&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.017900</td>
-      <td class="tdl">&emsp;&ensp;320.4</td> <td class="tdl">&ensp; &nbsp;.9699</td>
-      <td class="tdr">1,031&emsp;&nbsp;&nbsp;</td> <td class="tdr">32.31&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">27&nbsp;</td> <td class="tdl">&nbsp;0.016000</td>
-      <td class="tdl">&emsp;&ensp;256.0</td> <td class="tdl">&ensp; &nbsp;.7749</td>
-      <td class="tdr">1,290&emsp;&nbsp;&nbsp;</td> <td class="tdr">40.45&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">26&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.015940</td>
-      <td class="tdl">&emsp;&ensp;254.1</td> <td class="tdl">&ensp; &nbsp;.7692</td>
-      <td class="tdr">1,300&emsp;&nbsp;&nbsp;</td> <td class="tdr">40.75&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">27&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.014200</td>
-      <td class="tdl">&emsp;&ensp;201.5</td> <td class="tdl">&ensp; &nbsp;.6100</td>
-      <td class="tdr">1,639&emsp;&nbsp;&nbsp;</td> <td class="tdr">51.38&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">28&nbsp;</td> <td class="tdl">&nbsp;0.014000</td>
-      <td class="tdl">&emsp;&ensp;196.0</td> <td class="tdl">&ensp; &nbsp;.5933</td>
-      <td class="tdr">1,685&emsp;&nbsp;&nbsp;</td> <td class="tdr">52.83&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">29&nbsp;</td> <td class="tdl">&nbsp;0.013000</td>
-      <td class="tdl">&emsp;&ensp;169.0</td> <td class="tdl">&ensp; &nbsp;.5116</td>
-      <td class="tdr">1,955&emsp;&nbsp;&nbsp;</td> <td class="tdr">61.27&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">28&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.012640</td>
-      <td class="tdl">&emsp;&ensp;159.8</td> <td class="tdl">&ensp; &nbsp;.4837</td>
-      <td class="tdr">2,067&emsp;&nbsp;&nbsp;</td> <td class="tdr">64.79&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">30&nbsp;</td> <td class="tdl">&nbsp;0.012000</td>
-      <td class="tdl">&emsp;&ensp;144.0</td> <td class="tdl">&ensp; &nbsp;.4359</td>
-      <td class="tdr">2,294&emsp;&nbsp;&nbsp;</td> <td class="tdr">71.90&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">29&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.011260</td>
-      <td class="tdl">&emsp;&ensp;126.7</td> <td class="tdl">&ensp; &nbsp;.3836</td>
-      <td class="tdr">2,607&emsp;&nbsp;&nbsp;</td> <td class="tdr">81.70&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">30&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.010030</td>
-      <td class="tdl">&emsp;&ensp;100.5</td> <td class="tdl">&ensp; &nbsp;.3042</td>
-      <td class="tdr">3,287&emsp;&nbsp;&nbsp;</td> <td class="tdr">103.0&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">31&nbsp;</td> <td class="tdl">&nbsp;0.010000</td>
-      <td class="tdl">&emsp;&ensp;100.0</td> <td class="tdl">&ensp; &nbsp;.3027</td>
-      <td class="tdr">3,304&emsp;&nbsp;&nbsp;</td> <td class="tdr">103.5&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">32&nbsp;</td> <td class="tdl">&nbsp;0.009000</td>
-      <td class="tdl">&emsp;&emsp;81.0</td> <td class="tdl">&ensp; &nbsp;.2452</td>
-      <td class="tdr">4,078&emsp;&nbsp;&nbsp;</td> <td class="tdr">127.8&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">31&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.008928</td>
-      <td class="tdl">&emsp;&emsp;79.70</td> <td class="tdl">&ensp; &nbsp;.2413</td>
-      <td class="tdr">4,145&emsp;&nbsp;&nbsp;</td> <td class="tdr">129.9&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">33&nbsp;</td> <td class="tdl">&nbsp;0.008000</td>
-      <td class="tdl">&emsp;&emsp;64.0</td> <td class="tdl">&ensp; &nbsp;.1937</td>
-      <td class="tdr">5,162&emsp;&nbsp;&nbsp;</td> <td class="tdr">161.8&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">32&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.007950</td>
-      <td class="tdl">&emsp;&emsp;63.21</td> <td class="tdl">&ensp; &nbsp;.1913</td>
-      <td class="tdr">5,227&emsp;&nbsp;&nbsp;</td> <td class="tdr">163.8&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">33&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.007080</td>
-      <td class="tdl">&emsp;&emsp;50.13</td> <td class="tdl">&ensp; &nbsp;.1517</td>
-      <td class="tdr">6,591&emsp;&nbsp;&nbsp;</td> <td class="tdr">206.6&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">34&nbsp;</td> <td class="tdl">&nbsp;0.007000</td>
-      <td class="tdl">&emsp;&emsp;49.0</td> <td class="tdl">&ensp; &nbsp;.1483</td>
-      <td class="tdr">6,742&emsp;&nbsp;&nbsp;</td> <td class="tdr">211.3&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">34&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.006305</td>
-      <td class="tdl">&emsp;&emsp;39.75</td> <td class="tdl">&ensp; &nbsp;.1203</td>
-      <td class="tdr">8,311&emsp;&nbsp;&nbsp;</td> <td class="tdr">260.5&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">35&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.005615</td>
-      <td class="tdl">&emsp;&emsp;31.52</td> <td class="tdl">&ensp; &nbsp;.09543</td>
-      <td class="tdr">10,480&emsp;&nbsp;&nbsp;</td> <td class="tdr">328.4&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">36&nbsp;</td>
-      <td class="tdr">35&nbsp;</td> <td class="tdl">&nbsp;0.005000</td>
-      <td class="tdl">&emsp;&emsp;25.0</td> <td class="tdl">&ensp; &nbsp;.07568</td>
-      <td class="tdr">13,210&emsp;&nbsp;&nbsp;</td> <td class="tdr">414.2&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">37&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.004453</td>
-      <td class="tdl">&emsp;&emsp;19.83</td> <td class="tdl">&ensp; &nbsp;.06001</td>
-      <td class="tdr">16,660&emsp;&nbsp;&nbsp;</td> <td class="tdr">522.2&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">36&nbsp;</td> <td class="tdl">&nbsp;0.004000</td>
-      <td class="tdl">&emsp;&emsp;16.</td> <td class="tdl">&ensp; &nbsp;.04843</td>
-      <td class="tdr">20,650&emsp;&nbsp;&nbsp;</td> <td class="tdr">647.1&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">38&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.003965</td>
-      <td class="tdl">&emsp;&emsp;15.72</td> <td class="tdl">&ensp; &nbsp;.04759</td>
-      <td class="tdr">21,010&emsp;&nbsp;&nbsp;</td> <td class="tdr">658.5&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">39&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.003531</td>
-      <td class="tdl">&emsp;&emsp;12.47</td> <td class="tdl">&ensp; &nbsp;.03774</td>
-      <td class="tdr">26,500&emsp;&nbsp;&nbsp;</td> <td class="tdr">830.4&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">40&nbsp;</td>
-      <td class="tdr">&nbsp;</td> <td class="tdl">&nbsp;0.003145</td>
-      <td class="tdl">&nbsp;&emsp;&emsp;9.888</td> <td class="tdl">&ensp; &nbsp;.02993</td>
-      <td class="tdr">33,410&emsp;&nbsp;&nbsp;</td> <td class="tdr">1047.&emsp;&nbsp;&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-<p><span class="pagenum"><a name="Page_1910" id="Page_1910">1910</a></span></p>
-
-<p class="space-above2"><b>Drop.</b>&mdash;In order to determine the
-drop or volts lost in the line, the following formula may be used</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;&ensp;% loss × volts</td>
-     </tr><tr>
-      <td class="tdr">drop =</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp; × S &emsp;&nbsp;(1)</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;&emsp;&emsp;100</td>
-     </tr>
- </tbody>
-</table>
-
-<p class="no-indent">in which the % loss is a percentage of the
-applied power, that is, the power delivered to the consumer and not a
-percentage of the power at the alternator. "Volts" is the pressure at
-the consumer's end of the circuit.</p>
-
-<table border="0" cellspacing="2" summary="_" rules="cols" cellpadding="0">
-<caption><b>VALUE OF "S" FOR 60 CYCLES</b></caption>
-  <tbody><tr class="tr_lt_grey">
-      <td rowspan="3" class="tdc">Size of<br />wire<br />B. &amp; S.<br />gauge</td>
-      <td rowspan="3" class="tdc">Area<br />in<br />circular<br />mils.</td>
-      <td colspan="5" class="tdc u">.98 power factor</td>
-      <td colspan="5" class="tdc u">.90 power factor</td>
-   </tr><tr class="tr_lt_grey">
-      <td colspan="5" class="tdc">Spacing of<br />conductors</td>
-      <td colspan="5" class="tdc">Spacing of<br />conductors</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">&nbsp;1"&nbsp;</td> <td class="tdc">&nbsp;3"&nbsp;</td> <td class="tdc">&nbsp;6"&nbsp;</td>
-      <td class="tdc">12"</td> <td class="tdc">24"</td> <td class="tdc">&nbsp;1"&nbsp;</td>
-      <td class="tdc">&nbsp;3"&nbsp;</td> <td class="tdc">&nbsp;6"&nbsp;</td> <td class="tdc">12"</td>
-      <td class="tdc">24"</td>
-   </tr><tr>
-      <td class="tdr">500,000&nbsp;&nbsp;</td> <td class="tdr">500,000&nbsp;&nbsp;</td> <td class="tdc">1.21</td>
-      <td class="tdc">1.45</td> <td class="tdc">1.61</td> <td class="tdc">1.77</td>
-      <td class="tdc">1.92</td> <td class="tdc">1.32</td> <td class="tdc">1.80</td>
-      <td class="tdc">2.11</td> <td class="tdc">2.44</td> <td class="tdc">2.75</td>
-   </tr><tr>
-      <td class="tdr">300,000&nbsp;&nbsp;</td> <td class="tdr">300,000&nbsp;&nbsp;</td> <td class="tdc">&nbsp;1.15&nbsp;</td>
-      <td class="tdc">&nbsp;1.29&nbsp;</td> <td class="tdc">&nbsp;1.38&nbsp;</td> <td class="tdc">&nbsp;1.48&nbsp;</td>
-      <td class="tdc">&nbsp;1.57&nbsp;</td> <td class="tdc">&nbsp;1.19&nbsp;</td> <td class="tdc">&nbsp;1.47&nbsp;</td>
-      <td class="tdc">&nbsp;1.66&nbsp;</td> <td class="tdc">&nbsp;1.84&nbsp;</td> <td class="tdc">&nbsp;2.02&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">0,000&nbsp;&nbsp;</td> <td class="tdr">211,600&nbsp;&nbsp;</td> <td class="tdc">1.12</td>
-      <td class="tdc">1.22</td> <td class="tdc">1.28</td> <td class="tdc">1.34</td>
-      <td class="tdc">1.41</td> <td class="tdc">1.13</td> <td class="tdc">1.33</td>
-      <td class="tdc">1.45</td> <td class="tdc">1.58</td> <td class="tdc">1.63</td>
-   </tr><tr>
-      <td class="tdr">000&nbsp;&nbsp;</td> <td class="tdr">167,800&nbsp;&nbsp;</td> <td class="tdc">1.09</td>
-      <td class="tdc">1.18</td> <td class="tdc">1.22</td> <td class="tdc">1.28</td>
-      <td class="tdc">1.29</td> <td class="tdc">1.08</td> <td class="tdc">1.23</td>
-      <td class="tdc">1.33</td> <td class="tdc">1.44</td> <td class="tdc">1.53</td>
-   </tr><tr>
-      <td class="tdr">00&nbsp;&nbsp;</td> <td class="tdr">133,100&nbsp;&nbsp;</td> <td class="tdc">1.07</td>
-      <td class="tdc">1.14</td> <td class="tdc">1.18</td> <td class="tdc">1.21</td>
-      <td class="tdc">1.25</td> <td class="tdc">1.03</td> <td class="tdc">1.16</td>
-      <td class="tdc">1.24</td> <td class="tdc">1.32</td> <td class="tdc">1.40</td>
-   </tr><tr>
-      <td class="tdr">0&nbsp;&nbsp;</td> <td class="tdr">105,500&nbsp;&nbsp;</td> <td class="tdc">1.05</td>
-      <td class="tdc">1.10</td> <td class="tdc">1.14</td> <td class="tdc">1.17</td>
-      <td class="tdc">1.20</td> <td class="tdc">1.00</td> <td class="tdc">1.09</td>
-      <td class="tdc">1.16</td> <td class="tdc">1.22</td> <td class="tdc">1.28</td>
-   </tr><tr>
-      <td class="tdr">1&nbsp;&nbsp;</td> <td class="tdr">83,690&nbsp;&nbsp;</td> <td class="tdc">1.04</td>
-      <td class="tdc">1.08</td> <td class="tdc">1.10</td> <td class="tdc">1.13</td>
-      <td class="tdc">1.15</td> <td class="tdc">1.00</td> <td class="tdc">1.05</td>
-      <td class="tdc">1.09</td> <td class="tdc">1.14</td> <td class="tdc">1.19</td>
-   </tr><tr>
-      <td class="tdr">2&nbsp;&nbsp;</td> <td class="tdr">66,370&nbsp;&nbsp;</td> <td class="tdc">1.02</td>
-      <td class="tdc">1.05</td> <td class="tdc">1.08</td> <td class="tdc">1.10</td>
-      <td class="tdc">1.12</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.04</td> <td class="tdc">1.08</td> <td class="tdc">1.12</td>
-   </tr><tr>
-      <td class="tdr u">3&nbsp;&nbsp;</td> <td class="tdr u">52,630&nbsp;&nbsp;</td> <td class="tdc">1.02</td>
-      <td class="tdc">1.04</td> <td class="tdc">1.06</td> <td class="tdc">1.07</td>
-      <td class="tdc">1.09</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.03</td> <td class="tdc">1.06</td>
-   </tr><tr>
-      <td class="tdr">4}&nbsp;</td> <td class="tdr">41,740&nbsp;&nbsp;</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.02</td> <td rowspan="2" class="tdc">1.03</td> <td rowspan="2" class="tdc">1.04</td>
-      <td rowspan="2" class="tdc">1.07</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-   </tr><tr class="u">
-      <td class="tdr">5}&nbsp;</td> <td class="tdr">33,100&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">6}&nbsp;</td> <td class="tdr">26,250&nbsp;&nbsp;</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-   </tr><tr class="u">
-      <td class="tdr">7"}&nbsp;</td> <td class="tdr">20,820&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">8}&nbsp;</td> <td class="tdr">16,510&nbsp;&nbsp;</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">9}&nbsp;</td> <td class="tdr">13,090&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">10}&nbsp;</td> <td class="tdr">10,380&nbsp;&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-<table border="0" cellspacing="2" summary="_" rules="cols" cellpadding="0">
-  <tbody><tr class="tr_lt_grey">
-      <td rowspan="3" class="tdc">Size of<br />wire<br />B. &amp; S.<br />gauge</td>
-      <td rowspan="3" class="tdc">Area<br />in<br />circular<br />mils.</td>
-      <td colspan="5" class="tdc u">.80 power factor</td>
-      <td colspan="5" class="tdc u">.70 power factor</td>
-   </tr><tr class="tr_lt_grey">
-      <td colspan="5" class="tdc">Spacing of<br />conductors</td>
-      <td colspan="5" class="tdc">Spacing of<br />conductors</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">&nbsp;1"&nbsp;</td> <td class="tdc">&nbsp;3"&nbsp;</td> <td class="tdc">&nbsp;6"&nbsp;</td>
-      <td class="tdc">12"</td> <td class="tdc">24"</td> <td class="tdc">&nbsp;1"&nbsp;</td>
-      <td class="tdc">&nbsp;3"&nbsp;</td> <td class="tdc">&nbsp;6"&nbsp;</td> <td class="tdc">12"</td>
-      <td class="tdc">24"</td>
-   </tr><tr>
-      <td class="tdr">500,000&nbsp;&nbsp;</td> <td class="tdr">500,000&nbsp;&nbsp;</td> <td class="tdc">1.27</td>
-      <td class="tdc">1.89</td> <td class="tdc">2.25</td> <td class="tdc">2.64</td>
-      <td class="tdc">3.03</td> <td class="tdc">1.14</td> <td class="tdc">1.72</td>
-      <td class="tdc">2.12</td> <td class="tdc">2.53</td> <td class="tdc">2.92</td>
-   </tr><tr>
-      <td class="tdr">300,000&nbsp;&nbsp;</td> <td class="tdr">300,000&nbsp;&nbsp;</td> <td class="tdc">&nbsp;1.11&nbsp;</td>
-      <td class="tdc">&nbsp;1.46&nbsp;</td> <td class="tdc">&nbsp;1.68&nbsp;</td> <td class="tdc">&nbsp;1.90&nbsp;</td>
-      <td class="tdc">&nbsp;2.12&nbsp;</td> <td class="tdc">&nbsp;1.00&nbsp;</td> <td class="tdc">&nbsp;1.33&nbsp;</td>
-      <td class="tdc">&nbsp;1.56&nbsp;</td> <td class="tdc">&nbsp;1.78&nbsp;</td> <td class="tdc">&nbsp;2.01&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">0,000&nbsp;&nbsp;</td> <td class="tdr">211,600&nbsp;&nbsp;</td> <td class="tdc">1.03</td>
-      <td class="tdc">1.27</td> <td class="tdc">1.43</td> <td class="tdc">1.58</td>
-      <td class="tdc">1.75</td> <td class="tdc">1.00</td> <td class="tdc">1.14</td>
-      <td class="tdc">1.29</td> <td class="tdc">1.45</td> <td class="tdc">1.69</td>
-   </tr><tr>
-      <td class="tdr">000&nbsp;&nbsp;</td> <td class="tdr">167,800&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.16</td> <td class="tdc">1.28</td> <td class="tdc">1.41</td>
-      <td class="tdc">1.53</td> <td class="tdc">1.00</td> <td class="tdc">1.02</td>
-      <td class="tdc">1.15</td> <td class="tdc">1.28</td> <td class="tdc">1.50</td>
-   </tr><tr>
-      <td class="tdr">00&nbsp;&nbsp;</td> <td class="tdr">133,100&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.07</td> <td class="tdc">1.17</td> <td class="tdc">1.27</td>
-      <td class="tdc">1.36</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.03</td> <td class="tdc">1.13</td> <td class="tdc">1.21</td>
-   </tr><tr>
-      <td class="tdr">0&nbsp;&nbsp;</td> <td class="tdr">105,500&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.07</td> <td class="tdc">1.15</td>
-      <td class="tdc">1.22</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.01</td> <td class="tdc">1.09</td>
-   </tr><tr>
-      <td class="tdr">1&nbsp;&nbsp;</td> <td class="tdr">83,690&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.05</td>
-      <td class="tdc">1.11</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">2&nbsp;&nbsp;</td> <td class="tdr">66,370&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.02</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr u">3&nbsp;&nbsp;</td> <td class="tdr u">52,630&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">4}&nbsp;</td> <td class="tdr">41,740&nbsp;&nbsp;</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-   </tr><tr class="u">
-      <td class="tdr">5}&nbsp;</td> <td class="tdr">33,100&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">6}&nbsp;</td> <td class="tdr">26,250&nbsp;&nbsp;</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-   </tr><tr class="u">
-      <td class="tdr">7}&nbsp;</td> <td class="tdr">20,820&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">8}&nbsp;</td> <td class="tdr">16,510&nbsp;&nbsp;</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-      <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td> <td rowspan="2" class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">9}&nbsp;</td> <td class="tdr">13,090&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">10}&nbsp;</td> <td class="tdr">10,380&nbsp;&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="space-above2">The coefficient S has various values as given
-in the accompanying tables. As will be seen from the table, the value
-of S to be used depends upon the size of wire, spacing, power factor
-and frequency.</p>
-
-<p>These values are accurate enough for all practical purposes, and
-may be used for distances of 20 miles or less and for voltages up to 25,000.
-<span class="pagenum"><a name="Page_1911" id="Page_1911">1911</a></span></p>
-
-<p class="space-below2">The capacity effect on very long high voltage
-lines, makes this method of determining the drop somewhat inaccurate
-beyond the limits above mentioned.</p>
-
-<table border="0" cellspacing="2" summary="_" rules="cols" cellpadding="0">
-<caption><b>VALUE OF "S" FOR 25 CYCLES</b></caption>
-  <tbody><tr class="tr_lt_grey">
-      <td rowspan="3" class="tdc">Size of<br />wire<br />B. &amp; S.<br />gauge</td>
-      <td rowspan="3" class="tdc">Area<br />in<br />circular<br />mils.</td>
-      <td colspan="5" class="tdc u">.98 power factor</td>
-      <td colspan="5" class="tdc u">.90 power factor</td>
-   </tr><tr class="tr_lt_grey">
-      <td colspan="5" class="tdc">Spacing of<br />conductors</td>
-      <td colspan="5" class="tdc">Spacing of<br />conductors</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">&nbsp;1"&nbsp;</td> <td class="tdc">&nbsp;3"&nbsp;</td> <td class="tdc">&nbsp;6"&nbsp;</td>
-      <td class="tdc">12"</td> <td class="tdc">24"</td> <td class="tdc">&nbsp;1"&nbsp;</td>
-      <td class="tdc">&nbsp;3"&nbsp;</td> <td class="tdc">&nbsp;6"&nbsp;</td> <td class="tdc">12"</td>
-      <td class="tdc">24"</td>
-   </tr><tr>
-      <td class="tdr">500,000&nbsp;&nbsp;</td> <td class="tdr">500,000&nbsp;&nbsp;</td> <td class="tdc">1.01</td>
-      <td class="tdc">1.17</td> <td class="tdc">1.23</td> <td class="tdc">1.29</td>
-      <td class="tdc">1.36</td> <td class="tdc">1.02</td> <td class="tdc">1.22</td>
-      <td class="tdc">1.35</td> <td class="tdc">1.43</td> <td class="tdc">1.61</td>
-   </tr><tr>
-      <td class="tdr">300,000&nbsp;&nbsp;</td> <td class="tdr">300,000&nbsp;&nbsp;</td> <td class="tdc">&nbsp;1.04&nbsp;</td>
-      <td class="tdc">&nbsp;1.10&nbsp;</td> <td class="tdc">&nbsp;1.13&nbsp;</td> <td class="tdc">&nbsp;1.18&nbsp;</td>
-      <td class="tdc">&nbsp;1.21&nbsp;</td> <td class="tdc">&nbsp;1.00&nbsp;</td> <td class="tdc">&nbsp;1.08&nbsp;</td>
-      <td class="tdc">&nbsp;1.16&nbsp;</td> <td class="tdc">&nbsp;1.25&nbsp;</td> <td class="tdc">&nbsp;1.31&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">0,000&nbsp;&nbsp;</td> <td class="tdr">211,600&nbsp;&nbsp;</td> <td class="tdc">1.03</td>
-      <td class="tdc">1.07</td> <td class="tdc">1.09</td> <td class="tdc">1.11</td>
-      <td class="tdc">1.14</td> <td class="tdc">1.00</td> <td class="tdc">1.02</td>
-      <td class="tdc">1.07</td> <td class="tdc">1.13</td> <td class="tdc">1.15</td>
-   </tr><tr>
-      <td class="tdr">000&nbsp;&nbsp;</td> <td class="tdr">167,800&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.05</td> <td class="tdc">1.06</td> <td class="tdc">1.09</td>
-      <td class="tdc">1.10</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.02</td> <td class="tdc">1.07</td> <td class="tdc">1.11</td>
-   </tr><tr>
-      <td class="tdr">00&nbsp;&nbsp;</td> <td class="tdr">133,100&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.03</td> <td class="tdc">1.05</td> <td class="tdc">1.06</td>
-      <td class="tdc">1.08</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.02</td> <td class="tdc">1.05</td>
-   </tr><tr>
-      <td class="tdr u">0&nbsp;&nbsp;</td> <td class="tdr u">105,500&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.01</td> <td class="tdc">1.02</td> <td class="tdc">1.03</td>
-      <td class="tdc">1.04</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">1&nbsp;&nbsp;</td> <td class="tdr">83,690&nbsp;&nbsp;</td> <td rowspan="3" class="tdc">1.00</td>
-      <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td>
-      <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td>
-      <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">2&nbsp;&nbsp;</td> <td class="tdr">66,370&nbsp;&nbsp;</td>
-   </tr><tr class="u">
-      <td class="tdr">3&nbsp;&nbsp;</td> <td class="tdr">52,630&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">4}</td> <td class="tdr">41,740&nbsp;&nbsp;</td> <td rowspan="3" class="tdc">1.00</td>
-      <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td>
-      <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td>
-      <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">5}</td> <td class="tdr">33,100&nbsp;&nbsp;</td>
-   </tr><tr class="u">
-      <td class="tdr">6}</td> <td class="tdr">26,250&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">7}</td> <td class="tdr">20,820&nbsp;&nbsp;</td> <td rowspan="4" class="tdc">1.00</td>
-      <td rowspan="4" class="tdc">1.00</td> <td rowspan="4" class="tdc">1.00</td> <td rowspan="4" class="tdc">1.00</td>
-      <td rowspan="4" class="tdc">1.00</td> <td rowspan="4" class="tdc">1.00</td> <td rowspan="4" class="tdc">1.00</td>
-      <td rowspan="4" class="tdc">1.00</td> <td rowspan="4" class="tdc">1.00</td> <td rowspan="4" class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">8}</td> <td class="tdr">16,510&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">9}</td> <td class="tdr">13,090&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">10}</td> <td class="tdr">10,380&nbsp;&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-<table border="0" cellspacing="2" summary="_" rules="cols" cellpadding="0">
-  <tbody><tr class="tr_lt_grey">
-      <td rowspan="3" class="tdc">Size of<br />wire<br />B. &amp; S.<br />gauge</td>
-      <td rowspan="3" class="tdc">Area<br />in<br />circular<br />mils.</td>
-      <td colspan="5" class="tdc u">.80 power factor</td>
-      <td colspan="5" class="tdc u">.70 power factor</td>
-   </tr><tr class="tr_lt_grey">
-      <td colspan="5" class="tdc">Spacing of<br />conductors</td>
-      <td colspan="5" class="tdc">Spacing of<br />conductors</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">&nbsp;1"&nbsp;</td> <td class="tdc">&nbsp;3"&nbsp;</td> <td class="tdc">&nbsp;6"&nbsp;</td>
-      <td class="tdc">12"</td> <td class="tdc">24"</td> <td class="tdc">&nbsp;1"&nbsp;</td>
-      <td class="tdc">&nbsp;3"&nbsp;</td> <td class="tdc">&nbsp;6"&nbsp;</td> <td class="tdc">12"</td>
-      <td class="tdc">24"</td>
-   </tr><tr>
-      <td class="tdr">500,000&nbsp;&nbsp;</td> <td class="tdr">500,000&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.15</td> <td class="tdc">1.30</td> <td class="tdc">1.47</td>
-      <td class="tdc">1.62</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.16</td> <td class="tdc">1.33</td> <td class="tdc">1.49</td>
-   </tr><tr>
-      <td class="tdr">300,000&nbsp;&nbsp;</td> <td class="tdr">300,000&nbsp;&nbsp;</td> <td class="tdc">&nbsp;1.00&nbsp;</td>
-      <td class="tdc">&nbsp;1.00&nbsp;</td> <td class="tdc">&nbsp;1.09&nbsp;</td> <td class="tdc">&nbsp;1.16&nbsp;</td>
-      <td class="tdc">&nbsp;1.25&nbsp;</td> <td class="tdc">&nbsp;1.00&nbsp;</td> <td class="tdc">&nbsp;1.00&nbsp;</td>
-      <td class="tdc">&nbsp;1.00&nbsp;</td> <td class="tdc">&nbsp;1.02&nbsp;</td> <td class="tdc">&nbsp;1.12&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">0,000&nbsp;&nbsp;</td> <td class="tdr">211,600&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.03</td>
-      <td class="tdc">1.10</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">000&nbsp;&nbsp;</td> <td class="tdr">167,800&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.01</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">00&nbsp;&nbsp;</td> <td class="tdr">133,100&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr u">0&nbsp;&nbsp;</td> <td class="tdr u">105,500&nbsp;&nbsp;</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-      <td class="tdc">1.00</td> <td class="tdc">1.00</td> <td class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">1&nbsp;&nbsp;</td> <td class="tdr">83,690&nbsp;&nbsp;</td> <td rowspan="3" class="tdc">1.00</td>
-      <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td>
-      <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td>
-      <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">2&nbsp;&nbsp;</td> <td class="tdr">66,370&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr u">3&nbsp;&nbsp;</td> <td class="tdr u">52,630&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">4}&nbsp;</td> <td class="tdr">41,740&nbsp;&nbsp;</td> <td rowspan="3" class="tdc">1.00</td>
-      <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td>
-      <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td>
-      <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td> <td rowspan="3" class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">5}&nbsp;</td> <td class="tdr">33,100&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr u">6}&nbsp;</td> <td class="tdr u">26,250&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">7}&nbsp;</td> <td class="tdr">20,820&nbsp;&nbsp;</td> <td rowspan="4" class="tdc">1.00</td>
-      <td rowspan="4" class="tdc">1.00</td> <td rowspan="4" class="tdc">1.00</td> <td rowspan="4" class="tdc">1.00</td>
-      <td rowspan="4" class="tdc">1.00</td> <td rowspan="4" class="tdc">1.00</td> <td rowspan="4" class="tdc">1.00</td>
-      <td rowspan="4" class="tdc">1.00</td> <td rowspan="4" class="tdc">1.00</td> <td rowspan="4" class="tdc">1.00</td>
-   </tr><tr>
-      <td class="tdr">8}&nbsp;</td> <td class="tdr">16,510&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">9}&nbsp;</td> <td class="tdr">13,090&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">10}&nbsp;</td> <td class="tdr">10,380&nbsp;&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<div class="blockquot"> <p class="space-above2">EXAMPLE.&mdash;A
-circuit supplying current at 440 volts, 60 frequency, with 5% loss
-and .8 power factor is composed of No. 2 B. &amp; S. gauge wires
-spaced one foot apart. What is the drop in the line?</p>
-
-<p>According to the formula</p></div>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;&ensp;% loss × volts</td>
-     </tr><tr>
-      <td class="tdr">drop =</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp; × S</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;&emsp;&emsp;100</td>
-     </tr>
- </tbody>
-</table>
-
-<p class="blockquot">Substituting the given values, and value of S
-as obtained from the table for frequency 60</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;&ensp;5 × 440</td>
-     </tr><tr>
-      <td class="tdr">drop =</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp; × 1 = 22 volts</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;&emsp;&emsp;100</td>
-     </tr>
- </tbody>
-</table>
-
-<p><b>Current</b>.&mdash;As has been stated, the effect of power factor less
-than unity, is to increase the current; hence, in inductive circuit
-<span class="pagenum"><a name="Page_1912" id="Page_1912">1912</a></span>
-calculations, the first step is to determine the current flowing in a
-circuit. This is done as follows:</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;&ensp;apparent load</td>
-     </tr><tr>
-      <td class="tdr">current =</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&emsp;&nbsp;(1)</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;&emsp;&emsp;volts</td>
-     </tr>
- </tbody>
-</table>
-<p>&emsp;&emsp;and</p>
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;&emsp;watts</td>
-     </tr><tr>
-      <td class="tdr">apparent load =</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&emsp;&nbsp;(2)</td>
-     </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;power factor</td>
-     </tr>
- </tbody>
-</table>
-
-<p>Substituting (2) in (1)</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">watts</td>
-      <td class="tdc">&nbsp;</td>
-     </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;</td>
-      <td class="tdc">&nbsp;</td>
-     </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">power factor</td>
-      <td class="tdc">watts</td>
-     </tr><tr>
-      <td class="tdc">current =</td>
-      <td class="tdc">&nbsp;&emsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&emsp;=</td>
-      <td class="tdc">&nbsp;&emsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&emsp;(3)</td>
-     </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">volts</td>
-      <td class="tdc">&nbsp;power factor × volts</td>
-     </tr>
- </tbody>
-</table>
-
-<div class="figcenter">
-  <a name="fig2704"></a>
-  <img src="images/i080.jpg" alt="_" width="250" height="273" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,704.&mdash;Rope type of stranded
-copper cable which is used when a high degree of flexibility is
-required. The construction of this cable is the stranding together of
-seven groups, each containing seven wires and producing a total of
-49 wires. In cases when a greater carrying capacity is desired than
-can be obtained through the use of the 7 × 7 or 49 wire cable, the
-number of groups is increased to nineteen thereby making a total of
-133 wires (19 × 7).</p>
-</div>
-
-<div class="blockquot">
-<p>EXAMPLE.&mdash;A 50 horse power 440 volt motor has a full load efficiency
-of .9 and power factor of .8. How much current is required?</p>
-
-<p>Since the brake horse power of the motor is given, it is necessary to
-obtain the electrical horse power, thus</p></div>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">brake horse power</td>
-      <td class="tdl">&ensp;50</td>
-     </tr><tr>
-      <td class="tdc">E.H.P. =</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; =</td>
-      <td class="tdc">&mdash;&mdash; = 55.5</td>
-     </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">efficiency</td>
-      <td class="tdl">&ensp;.9</td>
-     </tr>
- </tbody>
-</table>
-
-<div class="blockquot">
-<p class="no-indent">which in watts is</p>
-<p class="center">55.5 × 746 = 41,403</p>
-<p class="no-indent">which is the actual load, and from which</p></div>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">actual load</td>
-      <td class="tdl">&emsp;41,403</td>
-     </tr><tr>
-      <td class="tdc">apparent load =</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; =</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash; = 51,754</td>
-     </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">power factor</td>
-      <td class="tdl">&emsp;&emsp;.8</td>
-     </tr>
- </tbody>
-</table>
-
-<p><span class="pagenum"><a name="Page_1913" id="Page_1913">1913</a></span>
-The current therefore at 440 volts is</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdc">apparent load</td>
-      <td class="tdc">51,754</td>
-      <td class="tdc">&nbsp;</td>
-     </tr><tr>
-      <td class="tdc">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; =</td>
-      <td class="tdc">&mdash;&mdash;&mdash;&mdash;&mdash; =</td>
-      <td class="tdc">117.6 amperes</td>
-     </tr><tr>
-      <td class="tdc">volts</td>
-      <td class="tdc">440</td>
-      <td class="tdc">&nbsp;</td>
-     </tr>
- </tbody>
-</table>
-
-<p class="blockquot">EXAMPLE.&mdash;A 50 horse power single phase
-440 volt motor, having a full load efficiency of .92 and power
-factor of .8, is to be operated at a distance of 1,000 feet from
-the alternator. The wires are to be spaced 6 inches apart and the
-frequency is 60, and % loss 5. Determine: <b>A</b>, <i>electrical horse
-power</i>; <b>B</b>, <i>watts</i>; <b>C</b>, <i>apparent load</i>; <b>D</b>,
-<i>current</i>; <b>E</b>, <i>size of wires</i>; <b>F</b>, <i>drop</i>; <b>G</b>,
-<i>voltage at the alternator</i>.</p>
-
-<p><b>A</b>. <i>Electrical horse power</i></p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">brake horse power</td>
-      <td class="tdl">&ensp; 50</td>
-     </tr><tr>
-      <td class="tdc">E. H. P. =</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; × </td>
-      <td class="tdc">&nbsp;&mdash;&mdash; = 54.3</td>
-     </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">efficiency</td>
-      <td class="tdl">&ensp;.92</td>
-     </tr>
- </tbody>
-</table>
-
-<p>or,</p>
-<p class="center space-below2">54.3 × 746 = 40,508 watts</p>
-
-<table border="0" cellspacing="2" summary="Wire Gauges" rules="cols" cellpadding="0">
-<caption><b>TABLE OF WIRE EQUIVALENTS</b><br />(Brown and Sharpe gauge)</caption>
-  <tbody><tr class="tr_lt_grey">
-      <td class="tdr">0000&nbsp;&nbsp;</td> <td class="tdc">&nbsp;2 No. 0&nbsp;</td>
-      <td class="tdc">&nbsp;4 No. 3&nbsp;</td> <td class="tdc">&nbsp;8 No. 6&nbsp;</td>
-      <td class="tdc">16 No. 9</td> <td class="tdc">&nbsp;32 No. 12&nbsp;</td>
-      <td class="tdc">64 No. 15</td>
-   </tr><tr>
-      <td class="tdr">000&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " &nbsp;1</td>
-      <td class="tdc">4&nbsp; " &nbsp;4</td> <td class="tdc">8&nbsp; " &nbsp; 7</td>
-      <td class="tdc">&nbsp;16&nbsp; " &nbsp;10&nbsp;</td> <td class="tdc">32&nbsp; " &nbsp;13</td>
-      <td class="tdc">64&nbsp; " &nbsp;16</td>
-   </tr><tr>
-      <td class="tdr">00&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " &nbsp;2</td>
-      <td class="tdc">4&nbsp; " &nbsp;5</td> <td class="tdc">8&nbsp; " &nbsp; 8</td>
-      <td class="tdc">16&nbsp; " &nbsp;11</td> <td class="tdc">32&nbsp; " &nbsp;14</td>
-      <td class="tdc">64&nbsp; " &nbsp;17</td>
-   </tr><tr>
-      <td class="tdr">0&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " &nbsp;3</td>
-      <td class="tdc">4&nbsp; " &nbsp;6</td> <td class="tdc">8&nbsp; " &nbsp; 9</td>
-      <td class="tdc">16&nbsp; " &nbsp;12</td> <td class="tdc">32&nbsp; " &nbsp;15</td>
-      <td class="tdc">64&nbsp; " &nbsp;18</td>
-   </tr><tr>
-      <td class="tdr">1&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " &nbsp;4</td>
-      <td class="tdc">4&nbsp; " &nbsp;7</td> <td class="tdc">8&nbsp; " &nbsp;10</td>
-      <td class="tdc">16&nbsp; " &nbsp;13</td> <td class="tdc">32&nbsp; " &nbsp;16</td>
-      <td class="tdc">64&nbsp; " &nbsp;19</td>
-   </tr><tr>
-      <td class="tdr">2&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " &nbsp;5</td>
-      <td class="tdc">4&nbsp; " &nbsp;8</td> <td class="tdc">8&nbsp; " &nbsp;11</td>
-      <td class="tdc">16&nbsp; " &nbsp;14</td> <td class="tdc">32&nbsp; " &nbsp;17</td>
-      <td class="tdc">64&nbsp; " &nbsp;20</td>
-   </tr><tr>
-      <td class="tdr">3&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " &nbsp;6</td>
-      <td class="tdc">4&nbsp; " &nbsp;9</td> <td class="tdc">8&nbsp; " &nbsp;12</td>
-      <td class="tdc">16&nbsp; " &nbsp;15</td> <td class="tdc">32&nbsp; " &nbsp;18</td>
-      <td class="tdc">64&nbsp; " &nbsp;21</td>
-   </tr><tr>
-      <td class="tdr">4&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " &nbsp;7</td>
-      <td class="tdc">4&nbsp; " 10</td> <td class="tdc">8&nbsp; " &nbsp;13</td>
-      <td class="tdc">16&nbsp; " &nbsp;16</td> <td class="tdc">32&nbsp; " &nbsp;19</td>
-      <td class="tdc">64&nbsp; " &nbsp;22</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">5&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " &nbsp;8</td>
-      <td class="tdc">4&nbsp; " 11</td> <td class="tdc">8&nbsp; " &nbsp;14</td>
-      <td class="tdc">16&nbsp; " &nbsp;17</td> <td class="tdc">32&nbsp; " &nbsp;20</td>
-      <td class="tdc">64&nbsp; " &nbsp;23</td>
-   </tr><tr>
-      <td class="tdr">6&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " &nbsp;9</td>
-      <td class="tdc">4&nbsp; " 12</td> <td class="tdc">8&nbsp; " &nbsp;15</td>
-      <td class="tdc">16&nbsp; " &nbsp;18</td> <td class="tdc">32&nbsp; " &nbsp;21</td>
-      <td class="tdc">64&nbsp; " &nbsp;24</td>
-   </tr><tr>
-      <td class="tdr">7&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 10</td>
-      <td class="tdc">4&nbsp; " 13</td> <td class="tdc">8&nbsp; " &nbsp;16</td>
-      <td class="tdc">16&nbsp; " &nbsp;19</td> <td class="tdc">32&nbsp; " &nbsp;22</td>
-      <td class="tdc">64&nbsp; " &nbsp;25</td>
-   </tr><tr>
-      <td class="tdr">8&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 11</td>
-      <td class="tdc">4&nbsp; " 14</td> <td class="tdc">8&nbsp; " &nbsp;17</td>
-      <td class="tdc">16&nbsp; " &nbsp;20</td> <td class="tdc">32&nbsp; " &nbsp;23</td>
-      <td class="tdc">64&nbsp; " &nbsp;26</td>
-   </tr><tr>
-      <td class="tdr">9&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 12</td>
-      <td class="tdc">4&nbsp; " 15</td> <td class="tdc">8&nbsp; " &nbsp;18</td>
-      <td class="tdc">16&nbsp; " &nbsp;21</td> <td class="tdc">32&nbsp; " &nbsp;24</td>
-      <td class="tdc">64&nbsp; " &nbsp;27</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">10&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 13</td>
-      <td class="tdc">4&nbsp; " 16</td> <td class="tdc">8&nbsp; " &nbsp;19</td>
-      <td class="tdc">16&nbsp; " &nbsp;22</td> <td class="tdc">32&nbsp; " &nbsp;25</td>
-      <td class="tdc">64&nbsp; " &nbsp;28</td>
-   </tr><tr>
-      <td class="tdr">11&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 14</td>
-      <td class="tdc">4&nbsp; " 17</td> <td class="tdc">8&nbsp; " &nbsp;20</td>
-      <td class="tdc">16&nbsp; " &nbsp;23</td> <td class="tdc">32&nbsp; " &nbsp;26</td>
-      <td class="tdc">64&nbsp; " &nbsp;29</td>
-   </tr><tr>
-      <td class="tdr">12&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 15</td>
-      <td class="tdc">4&nbsp; " 18</td> <td class="tdc">8&nbsp; " &nbsp;21</td>
-      <td class="tdc">16&nbsp; " &nbsp;24</td> <td class="tdc">32&nbsp; " &nbsp;27</td>
-      <td class="tdc">64&nbsp; " &nbsp;30</td>
-   </tr><tr>
-      <td class="tdr">13&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 16</td>
-      <td class="tdc">4&nbsp; " 19</td> <td class="tdc">8&nbsp; " &nbsp;22</td>
-      <td class="tdc">16&nbsp; " &nbsp;25</td> <td class="tdc">32&nbsp; " &nbsp;28</td>
-      <td class="tdc">&mdash;</td>
-   </tr><tr>
-      <td class="tdr">14&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 17</td>
-      <td class="tdc">4&nbsp; " 20</td> <td class="tdc">8&nbsp; " &nbsp;23</td>
-      <td class="tdc">16&nbsp; " &nbsp;26</td> <td class="tdc">32&nbsp; " &nbsp;29</td>
-      <td class="tdc">&mdash;</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdr">15&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 18</td>
-      <td class="tdc">4&nbsp; " 21</td> <td class="tdc">8&nbsp; " &nbsp;24</td>
-      <td class="tdc">16&nbsp; " &nbsp;27</td> <td class="tdc">32&nbsp; " &nbsp;30</td>
-      <td class="tdc">&mdash;</td>
-   </tr><tr>
-      <td class="tdr">16&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 19</td>
-      <td class="tdc">4&nbsp; " 22</td> <td class="tdc">8&nbsp; " &nbsp;25</td>
-      <td class="tdc">16&nbsp; " &nbsp;28</td> <td class="tdc">&mdash;</td>
-      <td class="tdc">&mdash;</td>
-   </tr><tr>
-      <td class="tdr">17&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 20</td>
-      <td class="tdc">4&nbsp; " 23</td> <td class="tdc">8&nbsp; " &nbsp;26</td>
-      <td class="tdc">16&nbsp; " &nbsp;29</td> <td class="tdc">&mdash;</td>
-      <td class="tdc">&mdash;</td>
-   </tr><tr>
-      <td class="tdr">18&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 21</td>
-      <td class="tdc">4&nbsp; " 24</td> <td class="tdc">8&nbsp; " &nbsp;27</td>
-      <td class="tdc">16&nbsp; " &nbsp;30</td> <td class="tdc">&mdash;</td>
-      <td class="tdc">&mdash;</td>
-   </tr><tr>
-      <td class="tdr">19&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 22</td>
-      <td class="tdc">4&nbsp; " 25</td> <td class="tdc">8&nbsp; " &nbsp;28</td>
-      <td class="tdc">&mdash;</td> <td class="tdc">&mdash;</td>
-      <td class="tdc">&mdash;</td>
-   </tr><tr>
-      <td class="tdr">20&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 23</td>
-      <td class="tdc">4&nbsp; " 26</td> <td class="tdc">8&nbsp; " &nbsp;29</td>
-      <td class="tdc">&mdash;</td> <td class="tdc">&mdash;</td>
-      <td class="tdc">&mdash;</td>
-   </tr><tr>
-      <td class="tdr">21&nbsp;&nbsp;</td> <td class="tdc">2&nbsp; " 24</td>
-      <td class="tdc">4&nbsp; " 27</td> <td class="tdc">8&nbsp; " &nbsp;30</td>
-      <td class="tdc">&mdash;</td> <td class="tdc">&mdash;</td>
-      <td class="tdc">&mdash;</td>
-   </tr>
- </tbody>
-</table>
-<p><span class="pagenum"><a name="Page_1914" id="Page_1914">1914</a></span></p>
-
-<p class="space-above2"><b>B.</b> <i>Watts</i></p>
-<p class="center">watts = E.H.P. × 746 = 54.3 × 746 = 40,508</p>
-
-<p><b>C.</b> <i>Apparent load</i></p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">actual load or watts</td>
-      <td class="tdc">40,508</td>
-      <td class="tdc">&nbsp;</td>
-     </tr><tr>
-      <td class="tdc">apparent load or kva&emsp;=</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; = </td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash; = </td>
-      <td class="tdc">&emsp;50,635</td>
-     </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">power factor</td>
-      <td class="tdc">.8</td>
-      <td class="tdc">&nbsp;</td>
-     </tr>
- </tbody>
-</table>
-
-<p><b>D.</b> <i>Current</i></p>
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">apparent load or kva</td>
-      <td class="tdc">50,635</td>
-      <td class="tdc">&nbsp;</td>
-     </tr><tr>
-      <td class="tdc">current&emsp;=</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; = </td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash; = </td>
-      <td class="tdc">&emsp;115 amperes</td>
-     </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">volts</td>
-      <td class="tdc">440</td>
-      <td class="tdc">&nbsp;</td>
-     </tr>
- </tbody>
-</table>
-
-<p><b>E.</b> <i>Size of wires</i></p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">watts × feet × M</td>
-      <td class="tdc">40,508 × 1,000 × 3,380</td>
-      <td class="tdc">&nbsp;</td>
-     </tr><tr>
-      <td class="tdc">cir. mils&emsp;=</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; = </td>
-      <td class="tdc">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; = </td>
-      <td class="tdc">&emsp;141,443</td>
-     </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">% loss × volts<sup>2</sup></td>
-      <td class="tdc">5 × 440<sup>2</sup></td>
-      <td class="tdc">&nbsp;</td>
-     </tr>
- </tbody>
-</table>
-
-<p>From table page 1,907, nearest size <i>larger</i> wire is No. 00 B. &amp; S. gauge.</p>
-
-<p><b>F.</b> <i>Drop</i></p>
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdl">&emsp;% loss × volts</td>
-      <td class="tdl">&nbsp;5 × 440</td>
-      <td class="tdc">&nbsp;</td>
-     </tr><tr>
-      <td class="tdc">drop&emsp;=</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; × S = </td>
-      <td class="tdc">&mdash;&mdash;&mdash;&mdash; × 1.17 = </td>
-      <td class="tdc">&emsp;25.74 volts</td>
-     </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdl">&emsp;&emsp;&emsp;100</td>
-      <td class="tdl">&emsp;100</td>
-      <td class="tdc">&nbsp;</td>
-     </tr>
- </tbody>
-</table>
-
-<p class="blockquot">NOTE.&mdash;Values of S are given on page 1910.</p>
-
-<p><b>G.</b> <i>Voltage at alternator</i></p>
-
-<p class="center">alternator pressure = (volts at motor + drop) = 440 + 25.74 = 465.7 volts.
-<span class="pagenum"><a name="Page_1915" id="Page_1915">1915</a></span></p>
-
-<hr class="chap" />
-<h2><span class="h_subtitle">CHAPTER LXVI</span><br /><b>POWER STATIONS</b></h2>
-
-<p>The term <i>power station</i> is usually applied to any building
-containing an installation of machinery for the conversion of energy
-from one form into another form. There are three general classes of
-station:</p>
-
-<p class="no-indent">&emsp;&emsp;1. Central stations;<br />
-&emsp;&emsp;2. Sub-stations;<br />&emsp;&emsp;3. Isolated plants.</p>
-
-<p class="no-indent">These may also be classified with respect to their function as</p>
-
-<p class="no-indent">&emsp;&emsp;1. Generating stations;<br />
-&emsp;&emsp;2. Distributing stations;<br />&emsp;&emsp;3. Converting stations.</p>
-
-<p class="no-indent">and with respect to the form of power used in generating
-the electric current, generating stations may be classed as</p>
-
-<p class="no-indent">&emsp;&emsp;1. Steam electric;<br />
-&emsp;&emsp;2. Hydro-electric;<br />&emsp;&emsp;3. Gas electric, etc.</p>
-
-<p><b>Central Stations.</b>&mdash;It must be evident that the general type
-of central station to be adapted to a given case, that is to say, the
-<span class="pagenum"><a name="Page_1916" id="Page_1916">1916</a></span>
-general character of the machinery to be installed depends upon the
-kind of natural energy available for conversion into electrical
-energy, and the character of the electrical energy required by the
-consumers.</p>
-
-<p>This gives rise to a further classification, as</p>
-
-<p class="no-indent">&emsp;&emsp;1. Alternating current stations;<br />
-&emsp;&emsp;2. Direct current stations;<br />&emsp;&emsp;3. Alternating and
-direct current stations.</p>
-
-<p class="space-below1">The alternators or dynamos may be driven by steam
-or water turbines, reciprocating engines, or gas engines, according to the
-character of the natural energy available.</p>
-
-<div class="figcenter">
-  <a name="fig2705"></a>
-  <img src="images/i084.jpg" alt="_" width="600" height="282" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,705.&mdash;Elevation of small
-station with direct drive, showing arrangement of the boiler and
-engine, piping, etc.</p>
-</div>
-
-<p><b>Ques. Why is the reciprocating engine being largely replaced by
-the steam turbine, especially for large units?</b></p>
-
-<p>Ans. Because of its higher rotative speed, and absence of a
-multiplicity of bearings which in the case of a high speed,
-reciprocating engine must be maintained in close adjustment for the
-proper operation of the engine.</p>
-
-<p class="blockquot">
-The higher speed of rotation results in a more compact unit, desirable
-for driving high frequency alternators.
-<span class="pagenum"><a name="Page_1917" id="Page_1917">1917</a></span></p>
-
-<p><b>Ques. Is the steam turbine more economical than a high duty
-reciprocating engine?</b></p>
-
-<p>Ans. No.</p>
-
-<p class="space-below1"><b>Location of Central Stations.</b>&mdash;As a rule,
-central stations should be so located that the average loss of voltage in
-overcoming the resistance of the lines is a minimum, and this point
-is located at the center of gravity of the system. In <a href="#fig2706">fig. 2,706</a>
-is shown a graphical method of locating this important spot.</p>
-
-<div class="figcenter">
-  <a name="fig2706"></a>
-  <img src="images/i-0306.jpg" alt="_" width="600" height="521" />
-  <p class="f90_left space-below1">
-Fig. 2,706.&mdash;Diagram illustrating graphical method of
-determining the <i>center of gravity</i> of a system in locating the
-central station.</p>
-</div>
-
-<p class="blockquot">
-Suppose a rough canvass of prospective consumers in a district to be
-supplied with electric light or power shows the principal loads to be
-located at A, B, C, D, E, etc., and for simplicity assume that these
-loads will be approximately equal, so that each may be denoted by 1
-<span class="pagenum"><a name="Page_1918" id="Page_1918">1918</a></span>
-for example:</p>
-
-<p class="space-below1">The relative locations of A, B, C, D, E, etc., should be
-drawn to scale (say 1 inch to the 1,000 feet) after which the problem resolves
-itself into finding the location of the station with respect to this scale.</p>
-
-<div class="figcenter">
-  <a name="fig2707"></a>
-  <img src="images/i-0307.jpg" alt="_" width="600" height="329" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,707.&mdash;Exterior of central
-station at Lewis, Ia.; example of very small station located in the
-principal business section of a town. It also illustrates the use
-of a direct connected gasoline electric set. The central station is
-located on Main Street, which is the principal thoroughfare, and is
-installed in a low one story building for which a mere nominal rental
-charge is paid, the company having the option to buy the property
-later at the value of the land plus the cost of the improvements and
-simple interest on the same. To the front of an old frame building
-about 16 feet by 28 feet has been built a neat, well lighted concrete
-block room, about 16 feet by 16 feet, carrying the building to
-the lot line and affording ample space for the generating set and
-switchboards, and such desk room as is needed for the ordinary office
-business of the company. In this room, which is finished in natural
-pine with plastered walls, has been installed a standard General
-Electric 25 kw. gasoline electric generating set consisting of a four
-cylinder, four cycle, vertical water cooled, 43-54 H.P. gasoline
-engine, direct connected to a three phase, 2,300 volt, 600 R.P.M.
-alternator with a 125 volt exciter mounted on the same shaft and
-in the same frame. With the generating set is a slate switchboard
-panel equipped with three ammeters, one voltmeter, an instrument
-plug switch for voltage indication, one single pole carbon break
-switch, one automatic oil circuit breaker line switch and rheostats.
-Instrument transformers are mounted above and back of the board. For
-street lighting service a 4 kw. constant current transformer has
-been installed, and with it a gray marble switchboard panel mounted
-on iron frames and carrying an ammeter and a four point plug switch.
-On a board near the generator set are mounted in convenient reach
-suitable wrenches, spanners, and repair parts and tools. To cool the
-engine cylinders five 6 × 8 steel tanks have been installed in the
-old building, a pump on engine giving forced circulation.</p>
-</div>
-
-<div class="blockquot">
-<p>The solution consists in first finding the center of gravity of
-any two of the loads, such as those at A and B. Since each of these
-is 1, they will together have the same effect on the system as the
-resultant load of 1 and 1, or 2, located at their center of gravity,
-this point being so chosen that the product of the loads by their
-respective distances from this point will in both cases be equal.</p>
-
-<p>The loads being equal in this case the distances must be equal in
-order that the products be the same, so that the center of gravity of
-A + B is at G, which point is midway between A and B.</p>
-
-<p>Considering, next, the resultant load of 2 at G and the load of 1
-at C, the resultant load at the center or gravity of these will be 3,
-and this must be situated at a distance of two units from C and one
-unit from G so that the distance 2 times the load 1 at C equals the
-distance 1 times the load 2 at G. Having thus located the load 3 at
-H, the same method is followed in finding the load 4 at I. Then in
-like manner the resultant load 4 and the load 1 at E gives a load 5
-at S.</p>
-
-<p>The point S being the last to be determined represents, therefore,
-the position of the center of gravity of the entire system, and
-consequently the proper position of the plant in order to give the
-minimum loss of voltage on the lines.</p></div>
-
-<p><span class="pagenum"><a name="Page_1919" id="Page_1919">1919</a></span>
-<b>Ques. Is the center of gravity of the system, as obtained in
-<a href="#fig2706">fig. 2,706</a>, the proper location for the central
-station?</b></p>
-
-<p>Ans. It is very rarely the best location.</p>
-
-<p><b>Ques. Why?</b></p>
-
-<p class="space-below1">Ans. Other conditions, such as the price of land,
-difficulty of obtaining water, facilities for delivery of coal and removal
-of ashes, etc., may more than offset the minimum line losses and copper
-cost due to locating the station at the center of gravity of the system.</p>
-
-<div class="figcenter">
-  <a name="fig2708"></a>
-  <img src="images/i-0308.jpg" alt="_" width="600" height="313" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,708.&mdash;Map of Cia Docas de
-Santos hydro-electric system; an example of station location remote
-from the center of distribution. In the figure A is the intake; B,
-flume; C, forebay; D, penstocks; E, power house; F, narrow gauge
-railway; G, general store; H, point of debarkation; I, transmission
-line; J, dead ends; K, sub-station. Santos, in the republic of
-Brazil, is one of the great coffee shipping ports of the world, and
-for the development of its water front has required an elaborate
-system of quays. These have been developed by the Santos Dock
-Company, which holds a concession for the whole water front. The
-company, needing electric power for its own use, has developed a
-system deriving its power from a point about thirty miles from the
-city, where a small stream plunges down the sea coast from the
-mountain range that runs along it. The engineers have estimated that
-100,000 horse power can be obtained from this source.</p>
-</div>
-
-<p><b>Ques. How then should the station be located?</b></p>
-
-<p class="space-below1">Ans. The more practical experience the designer has had, and the more
-<span class="pagenum"><a name="Page_1920" id="Page_1920">1920</a></span>
-common sense he possesses, the better is he equipped to handle the
-problem, as the solution is generally such that it cannot be worked
-out by any rule of thumb method.</p>
-
-<div class="figcenter">
-  <a name="fig2709"></a>
-  <img src="images/i-0309.jpg" alt="_" width="600" height="385" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,709.&mdash;Station location.
-The figure shows two distribution centers as a town A and suburb
-B supplied with electricity from one station. For minimum cost of
-copper the location of the station would be at G, the center of
-gravity. However, it is very rarely that this is the best location.
-For instance at C, land is cheaper than at G, and there is room
-for future extension to the station, as shown by the dotted lines,
-whereas at G, only enough land is available for present requirements.
-Moreover C is near the railroad where coal may be obtained without
-the expense of cartage, and being located at the river, the plant may
-be run condensing thus effecting considerable economy. The conditions
-may sometimes be such that any one of the advantages to be secured by
-locating the station at C may more than offset the additional cost of
-copper.</p>
-</div>
-
-<p><b>Ques. What are the general considerations with respect to the
-price of land?</b></p>
-
-<p>Ans. The cost for the station site may be so high as to necessitate
-building or renting room at a considerable distance from the district
-to be supplied.</p>
-
-<div class="blockquot">
-<p>If the price of land selected for the station be high, the running
-expenses will be similarly affected, inasmuch as more interest must
-then be paid on the capital invested.</p>
-
-<p>The price or rent of real estate might also in certain instances
-alter the proposed interior arrangement of the station, particularly
-so in the case of a company with small capital operating in a city
-where high prices prevail. In general, however, it may be stated
-that whatever effect the price of real estate would have upon the
-arrangement, operation and location of a central station it can quite
-readily and accurately be determined in advance.</p></div>
-
-<p><span class="pagenum"><a name="Page_1921" id="Page_1921">1921</a></span>
-<b>Ques. With respect to the cost of the land what should be especially
-considered?</b></p>
-
-<p>Ans. Room for the future extension of the plant.</p>
-
-<p class="blockquot">
-Although such additional space need not be purchased at the time of
-the original installation it is well, if possible, to make provision
-whereby it can be obtained at a reasonable figure when desired. The
-preliminary canvass of consumers will aid in deciding the amount of
-space advisable to allow for future extensions; as a rule, however,
-it is wise to count on the plant enlarging to not less than twice its
-original size, as often the dimensions have to be increased four and
-even six times those found sufficient at the beginning.</p>
-
-<div class="figcenter">
-  <a name="fig2710"></a>
-  <img src="images/i089.jpg" alt="_" width="600" height="385" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,710.&mdash;Section of the central
-station or "electricity works" at Derby, showing boiler and engine
-room and arrangement of bunkers, conveyor, ash pit, grates, boilers
-(drum, heating surface and superheater), economizer, flue, turbines,
-condenser pumps, etc.; also location of switchboard gallery and
-system of piping.</p>
-</div>
-
-<p><b>Ques. What trouble is likely to be encountered with an illy
-located plant after it is in operation?</b></p>
-
-<p>Ans. It may be considered a nuisance by those residing in the vicinity,
-occasioning many complaints.
-<span class="pagenum"><a name="Page_1922" id="Page_1922">1922</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2711"></a>
-  <img src="images/i-0310.jpg" alt="_" width="600" height="400" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,711.&mdash;View of old and new
-Waterside stations. The new station at the right has an all turbine
-equipment of ten units, some Curtis and some Parsons machines, two
-have a capacity of 14,000 kw., and the remaining eight are of 12,000
-kw. each. The old Riverside station, seen at the left is described on page 1940.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1923" id="Page_1923">1923</a></span></p>
-
-<div class="blockquot">
-<p>Thus, if the plant be placed in a residential section of the
-community the smoke, noise and vibration of the machines may become a
-nuisance to the surrounding inhabitants, and eventually end in suits
-for damage against the company responsible for the same. For these
-and the other reasons just given a company is sometimes forced to
-disregard entirely the location of a central station near the center
-of gravity of the system, and build at a considerable distance;
-such a proceeding would, if the distance be great, necessitate the
-installation of a high pressure system.</p>
-
-<p>There might, however, be certain local laws in force restricting the
-use of high pressure currents on account of the danger resulting to
-life, that would prevent this solution of the problem. In such cases
-there could undoubtedly be found some site where the objections
-previously noted would be tolerated; thus, there would naturally
-be little objection to locating next to a stable, a brewery, or a
-factory of any description.</p></div>
-
-<p><b>Ques. Why is the matter of water supply important for a central station?</b></p>
-
-<p>Ans. Because, in a steam driven plant, water is used in the
-boilers for the production of steam by boiling, and if the engines
-be of the condensing type it is also used in them for creating a
-vacuum into which the exhaust steam passes so as to increase the
-efficiency of the engine above what it would be if the exhaust steam
-were obliged to discharge into the comparatively high pressure of the atmosphere.</p>
-
-<p class="blockquot"> The force of this will be apparent by
-considering that the water consumption of the engine ordinarily is
-from 15 to 25 lbs. of "feed water" per horse power per hour, and the
-amount of "circulating water" required to maintain the vacuum is
-about 25 to 30 times the feed water, and in the case of turbines with
-their 28 or 29 inch vacuum, much more. For instance, a 1,000 horse
-power plant running on 15 lbs. of feed water and 30 to 1 circulating
-water would require (1,000 × 15) × (30 + 1) = 465,000 lbs. or 55,822
-gals. per hour at full capacity.</p>
-
-<p><b>Ques. Besides price what other considerations are important with
-respect to water?</b></p>
-
-<p>Ans. Its quality and the possibility of a scarcity of supply.</p>
-
-<div class="blockquot">
-
-<p>It is quite necessary that the water used in the boilers should be
-as free as possible from impurities, so as to prevent the deposition
-within them of any scale or sediments. The quality of the water used
-<span class="pagenum"><a name="Page_1924" id="Page_1924">1924</a></span>
-for condensing purposes, however, is not quite so important, although
-the purer it is the better.</p>
-
-<p>If the plant is to be located in a city, the matter of water
-supply need not generally be considered, because, as a rule, it can
-be obtained from the waterworks; there will then, of course, be a
-water tax to consider and this, if large, may warrant an effort being
-made to obtain the water in some other way. In any event, however,
-the possibility of a scarcity in the supply should be reduced to a
-minimum.</p>
-
-<p>If the plant be located in the country, some natural source
-of water would be utilized unless the place be supplied with
-waterworks, which is not generally the case. It is usual, however,
-to find a stream, lake or pond in the vicinity, but if none such be
-conveniently near, an artesian or other form of well must be sunk.</p>
-
-<p>If abundance of water exist in the vicinity of the proposed
-installation, not only would the location of the plant be governed
-thereby, but the kind of power to be used for its operation would
-depend thereon. Thus, if the quantity of the water were sufficient
-throughout the entire year to supply the necessary power, water
-wheels might be installed and used in place of boilers and steam
-engines for driving the generators. The station would then, of
-course, be situated close to the waterfall, regardless of the center
-of gravity of the system.</p></div>
-
-<div class="figcenter">
-  <a name="fig2712"></a>
-  <img src="images/i092.jpg" alt="_" width="600" height="390" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,712.&mdash;View illustrating the location
-of a station as governed by the presence of a water falls. In such
-cases the natural water power may be at a considerable distance from
-the center of gravity of the distribution system because of the
-saving in generation. In the case of long distance transmission very
-high pressure may be used and a transformer step down sub-station
-be located at or near the center of gravity of the system, thus
-considerably reducing the cost of copper for the transmission line.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1925" id="Page_1925">1925</a></span>
-<b>Ques. What should be noted with respect to the coal supply?</b></p>
-
-<p>Ans. The facility for transporting the coal from the supply point to
-the boiler room.</p>
-
-<div class="blockquot">
-<p>In this connection, an admirable location, other conditions
-permitting, is adjacent to a railway line or water front so that
-coal delivered by car or boat may be unloaded directly into the bins
-supplying the boilers.</p>
-
-<p>If the coal be brought by train, a side or branch track will usually
-be found convenient, and this will usually render any carting of the
-fuel entirely unnecessary.</p>
-
-<p>In whatever way the coal is to be supplied, the liability of a
-shortage due to traffic or navigation being closed at any time of the
-year should be well looked into, as should also the facility for the
-removal of ashes, before deciding upon the final location for the
-plant.</p></div>
-
-<div class="figcenter">
-  <a name="fig2713"></a>
-  <img src="images/i093.jpg" alt="_" width="600" height="453" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,713.&mdash;View of a station admirably
-located with respect to transportation of the coal supply. As shown,
-the coal may be obtained either by boat or rail, and with modern
-machinery for conveying the coal to the interior of the station, the
-transportation cost is reduced to a minimum.</p>
-</div>
-<p><span class="pagenum"><a name="Page_1926" id="Page_1926">1926</a></span></p>
-<div class="figcenter">
-  <a name="fig2714"></a>
-  <img src="images/i094.jpg" alt="_" width="600" height="406" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,714.&mdash;Floor plan of part of the
-turbine central station erected by the Boston Edison Co., showing two
-5,000 kw. Curtis steam turbines in place. The complete installation
-contains twelve 5,000 kw. Curtis steam turbines, a sectional
-elevation being shown in <a href="#fig2758">fig. 2,758, page 1,971</a>.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1927" id="Page_1927">1927</a></span>
-<b>Choice of System.</b>&mdash;The chief considerations in the design
-of a central station are economy and capacity. When the current
-has to be transmitted long distances for either lighting or power
-purposes, economy is attainable only by reducing the weight of the
-copper conductors. This can be accomplished only by the use of the
-high voltage currents obtainable from alternators.</p>
-
-<p>Again, where the consumers are located within a radius of two
-miles from the central station, thereby requiring a transmission
-voltage of 550 volts or less, dynamos may be employed with greater
-economy.</p>
-
-<p>Alternating current possesses serious disadvantages for certain
-important applications.</p>
-
-<p>For instance, in operating electric railways and for lighting it
-is often necessary to transmit direct current at 500 volts a distance
-of five or ten miles. In such cases, the excessive drop cannot be
-economically reduced by increasing the sizes of the line wire, while
-a sufficient increase of the voltage would cause serious variations
-under changes of load. Hence, it is common practice to employ some
-form of auxiliary generator or booster, which when connected in
-series with the feeder, automatically maintains the required pressure
-in the most remote districts so long as the main generators continue
-to furnish the normal or working voltage.</p>
-
-<p>The advantage of a direct current installation in such cases over a
-similar plant supplying alternating current line is the fact that a
-storage battery may be used in connection with the former for taking
-up the fluctuations of the current, thereby permitting the dynamo to
-run with a less variable load, and consequently at higher efficiency.</p>
-
-<p><b>Ques. Name some services requiring direct current.</b></p>
-
-<p class="space-below1">Ans. Direct current is required for certain kinds of
-electrolytic work, such as electro-plating, the electrical separation of metals,
-etc., also the charging of storage batteries for electric automobiles.
-<span class="pagenum"><a name="Page_1928" id="Page_1928">1928</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2715"></a>
-  <img src="images/i-0311.jpg" alt="_" width="600" height="169" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,715.&mdash;Example of central station
-located remote from the distributing center and furnishing
-alternating current at high pressure to a sub-station where the
-current is passed through step down transformers and supplied at
-moderate pressure to the distribution system. In some cases the
-sub-station contains also converters supplying direct current for
-battery charging, electro-plating, etc.</p>
-</div>
-
-<p><b>Ques. How is direct current supplied?</b></p>
-
-<p>Ans. Sometimes the central station is equipped with suitable
-apparatus for supplying both direct and alternating current. This may
-be accomplished in several different ways: By installing both direct
-and alternating current generators in the central station; by the use
-of double current generators or dynamotors, from which direct current
-may be taken from one side and alternating current from the other
-side; or by installing, in the sub-station of an alternating current
-central station, in addition to the transformers usually placed
-therein, a rotary converter for changing or converting alternating
-current into direct current.</p>
-
-<div class="blockquot">
-<p>Thus, it is evident that the character of a central station
-will be governed to a great extent by the class of services to be
-supplied.</p>
-
-<p>An exception to this is where the entire output has to be
-transmitted a long distance to the point of utilization.</p>
-
-<p>In such cases a copper economy demands the use of high
-<span class="pagenum"><a name="Page_1929" id="Page_1929">1929</a></span>
-tension alternating current, and its distribution to consumers may
-be made directly by means of step down transformers mounted near by
-or within the consumers' premises, or it may be transformed into low
-voltage alternating current by a conveniently located sub-station.</p>
-
-<p>Where the current is to be used chiefly for lighting and there
-are only a few or no motors to be supplied, the choice between
-direct current and alternating current will depend greatly upon the
-size of the installation, direct current being preferable for small
-installations and alternating current for large installations.</p>
-
-<p class="space-below1">If the current is to be used primarily for operating machinery,
-such as elevators, travelling cranes, machine tools and other devices of
-a similar character, which have to be operated intermittently and at
-varying speeds and loads, direct current is the more suitable; but if
-the motors performing such work can be operated continuously for many
-hours at a time under practically constant loads, as, for instance
-in the general work of a pumping station, alternating current may be
-employed with advantage.</p></div>
-
-<div class="figcenter">
-  <a name="fig2716"></a>
-  <img src="images/i097.jpg" alt="_" width="600" height="291" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,716.&mdash;Diagram illustrating diversity
-factor. By definition <i>diversity factor = combined actual maximum
-demand of a group of customers divided by the sum of their individual
-maximum demands</i>. Example, a customer has fifty (50) watt lamps and,
-of course, the sum of the individual maximum demands of the lamps
-is 2.5 kw. watts ("connected load"). The customer's maximum demand,
-however, is 1.5 kw. Hence, the diversity
-factor<a name="FNanchor_A_1" id="FNanchor_A_1"></a><a href="#Footnote_A_1" class="fnanchor">[A]</a>
-of the customer's group of lamps is 1.5 ÷ 2.5 = .6. In the diagram
-the ordinates of the curves show the ratio <i>maximum demand</i> to
-<i>connected load</i> for various kinds of electric lighting service in Chicago.</p>
-</div>
-
-<div class="footnote"><p>
-<a name="Footnote_A_1" id="Footnote_A_1"></a><a href="#FNanchor_A_1">
-<span class="label">[A]</span></a>
-NOTE.&mdash;The diversity factor of a customer's group of
-lamps, namely, the ratio of maximum demand to connected load is
-usually called the <i>demand factor</i> of the customer.</p></div>
-
-<p class="space-below1"><b>Size of Plant.</b>&mdash;Before any definite calculation
-can be made, or plans drawn, the engineer must determine the probable load.
-This is usually ascertained in terms of the number and distances
-<span class="pagenum"><a name="Page_1930" id="Page_1930">1930</a></span>
-of lamps that will be required, by making a thorough canvass of the
-city or town, or that portion for which electrical energy is to be
-supplied. The probable load that the station is to carry when it
-begins operation, the nature of this load, and the probable rate of
-increase are matters upon which the design and construction chiefly depend.</p>
-
-<div class="figcenter">
-  <a name="fig2717"></a>
-  <img src="images/i098.jpg" alt="_" width="600" height="352" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,717.&mdash;Load curve for one day.</p>
-</div>
-
-<p><b>Ques. What is the nature of the load carried by a central station?</b></p>
-
-<p>Ans. It fluctuates with the time of day and also with the time of year.</p>
-
-<p><b>Ques. How is a fluctuating load best represented?</b></p>
-
-<p>Ans. Graphically, that is to say by means of a curve plotted on
-coordinate paper of which ordinates represent load values and the
-corresponding abscissæ time values, as in the accompanying curves.
-<span class="pagenum"><a name="Page_1931" id="Page_1931">1931</a></span></p>
-
-<p><b>What is the nature of a power load?</b></p>
-
-<p>Ans. Where electricity is supplied for power purposes to a number of
-factories, the load is fairly steady, dropping, of course, during
-meal hours. In the case of traction, the average value of the load is
-fairly steady but there are momentarily violent fluctuations due to
-starting cars or trains.</p>
-
-<div class="figcenter">
-  <a name="fig2718"></a>
-  <img src="images/i099.jpg" alt="_" width="600" height="367" />
-  <p class="f90 space-below1">
-  <span class="smcap">Fig.</span> 2,718.&mdash;Load curve for one year.</p>
-</div>
-
-<p><b>Ques. What is the peak load?</b></p>
-
-<p>Ans. The maximum load which has to be carried by the station at any
-time of day or night as shown by the highest point of the load curve.</p>
-
-<p><b>Ques. Define the load factor.</b></p>
-
-<p>Ans. The machinery of the station evidently must be large
-enough to carry the peak load, and therefore considerably in
-<span class="pagenum"><a name="Page_1932" id="Page_1932">1932</a></span>
-excess of that required for the average demand. The ratio of
-the average to the maximum load is called the load factor.</p>
-
-<div class="blockquot">
-<p>There are two kinds of load factor: the annual, and the daily.</p>
-
-<p>The annual load factor is obtained as a percentage by multiplying the
-number of units sold (per year) by 100, and dividing by the product
-of the maximum load and the number of hours in the year. The daily
-load factor is obtained by taking the figures for 24 hours instead of
-a year.</p></div>
-
-<div class="figcenter">
-  <a name="fig2719"></a>
-  <img src="images/i100.jpg" alt="_" width="600" height="288" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,719.&mdash;Load curve of plant supplying
-power for the operation of motors in a manufacturing district. The
-horizontal dotted lines show suitable power ratings. A properly
-designed steam plant has a large overload capacity, a hydraulic
-plant has a small overload capacity, and a gasoline engine plant has
-no overload capacity. Accordingly, the peak of the load (maximum
-load) may be 25 or 30 per cent. in excess of the rated capacity of a
-steam plant, not more than 5 or 10 per cent. in excess of the rated
-capacity of a hydraulic plant, not at all in excess of the rated
-capacity of a gas engine plant.</p>
-</div>
-
-<p><b>Ques. What must be provided in addition to the machinery required
-to supply the peak load?</b></p>
-
-<p>Ans. Additional units must be installed for use in case of repairs or
-break down of some of the other units.</p>
-
-<div class="blockquot">
-<p>EXAMPLE.&mdash;What would be the boiler horse power required to generate
-5,000 kw. under the following conditions: Efficiency of generators
-85%; efficiency of engines 90%; feed water of engines and auxiliaries
-15 lbs. per I. H. P.; boiler pressure 175 lbs.; temperature of feed
-water 150° Fahr? With a rate of combustion of 15 lbs. of coal per sq.
-foot of grate per hour and an evaporation (from and at 212°) of
-8 lbs. of water per lb. of coal, what area of grate would be required
-and how much heating surface?</p>
-
-<p class="center"><b>5,000 kw. = 5,000 ÷ .746 = 6,702</b> electrical horse power
-<span class="pagenum"><a name="Page_1933" id="Page_1933">1933</a></span></p>
-
-<p>To obtain this electrical horse power with alternators whose efficiency is 85% requires</p>
-
-<p class="center"><b>6,702 ÷ .85 = 7,885</b> brake horse power at the engine</p>
-
-<p>This, with mechanical efficiency of 90% is equivalent to</p>
-
-<p class="center"><b>7,885 ÷ .9 = 8,761</b> indicated horse power</p>
-
-<p>Since 15 lbs. of feed water are required for the engines and
-auxiliaries per indicated horse power per hour, the total feed water
-or evaporation required to generate 5,000 kw. is</p>
-
-<p class="center"><b>15 × 8,761 = 131,415</b> lbs. per hour.</p>
-
-<p class="no-indent">that is to say, the boilers must be of sufficient capacity to
-generate 131,415 lbs. of steam per hour from water at a temperature
-of 150° Fahr. This must be multiplied by the <i>factor of evaporation</i>
-for steam at 175 lbs. pressure from feed water at a temperature of
-150°, in order to get the equivalent evaporation "<i>from and at 212</i>°."</p>
-
-<p>The formula for the factor of evaporation is</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">H - <i>h</i></td>
-      <td class="tdl">&nbsp;</td>
-     </tr><tr>
-      <td class="tdc">factor of evaporation =</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;</td>
-      <td class="tdc">&emsp;&emsp;(1)</td>
-     </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">965.7</td>
-      <td class="tdl">&nbsp;</td>
-
-     </tr>
- </tbody>
-</table>
-
-<p class="no-indent">in which<br /><br />
-&emsp;&emsp;H = total heat of steam at the observed pressure;<br /><br />
-&emsp;&emsp;<i>h</i> = total heat of feed water of the observed temperature;<br /><br />
-&emsp;&emsp;965.7 = latent heat, of steam at atmospheric pressure.</p>
-
-<p class="space-above1">Substituting in (1) values for the observed pressure
-and temperature as obtained from the steam table</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">1,197 - 118</td>
-      <td class="tdl">&nbsp;</td>
-     </tr><tr>
-      <td class="tdc">factor of evaporation =</td>
-      <td class="tdc">&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash; =</td>
-      <td class="tdc">&emsp;1.117</td>
-     </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdc">965.7</td>
-      <td class="tdl">&nbsp;</td>
-     </tr>
- </tbody>
-</table>
-
-<p class="no-indent">for which the equivalent evaporation "<i>from and at 212</i>°" is</p>
-
-<p class="center"><b>131,415 × 1.117 = 146,791 lbs.</b> per hour</p>
-</div>
-<p class="space-below1"><span class="pagenum"><a name="Page_1934" id="Page_1934">1934</a></span></p>
-
-<table border="0" cellspacing="2" summary="_" rules="cols" cellpadding="0">
-<caption><b>FACTORS OF EVAPORATION</b></caption>
-  <tbody><tr class="tr_lt_grey">
-      <td class="tdc">Temp of<br />feed water.</td>
-      <td colspan="9" class="tdc"><span class="smcap">Steam Pressure by Gauge</span></td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">Deg. Fahr.</td>
-      <td class="tdc">50</td> <td class="tdc">60</td>
-      <td class="tdc">70</td> <td class="tdc">80</td>
-      <td class="tdc">90</td> <td class="tdc">100</td>
-      <td class="tdc">110</td> <td class="tdc">120</td>
-      <td class="tdc">130</td>
-   </tr><tr>
-      <td class="tdr">32&emsp;&nbsp;&nbsp;</td> <td class="tdc">&nbsp;1.214&nbsp;</td>
-      <td class="tdc">&nbsp;1.216&nbsp;</td> <td class="tdc">&nbsp;1.220&nbsp;</td>
-      <td class="tdc">&nbsp;1.222&nbsp;</td> <td class="tdc">&nbsp;1.225&nbsp;</td>
-      <td class="tdc">&nbsp;1.227&nbsp;</td> <td class="tdc">&nbsp;1.229&nbsp;</td>
-      <td class="tdc">&nbsp;1.231&nbsp;</td> <td class="tdc">&nbsp;1.232&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">40&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.206</td>
-      <td class="tdc">1.209</td> <td class="tdc">1.212</td>
-      <td class="tdc">1.214</td> <td class="tdc">1.216</td>
-      <td class="tdc">1.219</td> <td class="tdc">1.220</td>
-      <td class="tdc">1.222</td> <td class="tdc">1.224</td>
-   </tr><tr>
-      <td class="tdr">50&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.195</td>
-      <td class="tdc">1.197</td> <td class="tdc">1.201</td>
-      <td class="tdc">1.204</td> <td class="tdc">1.206</td>
-      <td class="tdc">1.208</td> <td class="tdc">1.210</td>
-      <td class="tdc">1.212</td> <td class="tdc">1.214</td>
-   </tr><tr>
-      <td class="tdr">60&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.185</td>
-      <td class="tdc">1.188</td> <td class="tdc">1.191</td>
-      <td class="tdc">1.193</td> <td class="tdc">1.196</td>
-      <td class="tdc">1.198</td> <td class="tdc">1.200</td>
-      <td class="tdc">1.202</td> <td class="tdc">1.203</td>
-   </tr><tr>
-      <td class="tdr">70&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.175</td>
-      <td class="tdc">1.178</td> <td class="tdc">1.180</td>
-      <td class="tdc">1.183</td> <td class="tdc">1.185</td>
-      <td class="tdc">1.187</td> <td class="tdc">1.189</td>
-      <td class="tdc">1.191</td> <td class="tdc">1.193</td>
-   </tr><tr>
-      <td class="tdr">80&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.164</td>
-      <td class="tdc">1.167</td> <td class="tdc">1.170</td>
-      <td class="tdc">1.173</td> <td class="tdc">1.175</td>
-      <td class="tdc">1.177</td> <td class="tdc">1.179</td>
-      <td class="tdc">1.181</td> <td class="tdc">1.183</td>
-   </tr><tr>
-      <td class="tdr">90&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.154</td>
-      <td class="tdc">1.157</td> <td class="tdc">1.160</td>
-      <td class="tdc">1.162</td> <td class="tdc">1.165</td>
-      <td class="tdc">1.167</td> <td class="tdc">1.169</td>
-      <td class="tdc">1.170</td> <td class="tdc">1.172</td>
-   </tr><tr>
-      <td class="tdr">100&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.144</td>
-      <td class="tdc">1.147</td> <td class="tdc">1.150</td>
-      <td class="tdc">1.152</td> <td class="tdc">1.154</td>
-      <td class="tdc">1.156</td> <td class="tdc">1.158</td>
-      <td class="tdc">1.160</td> <td class="tdc">1.162</td>
-   </tr><tr>
-      <td class="tdr">110&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.133</td>
-      <td class="tdc">1.136</td> <td class="tdc">1.139</td>
-      <td class="tdc">1.142</td> <td class="tdc">1.144</td>
-      <td class="tdc">1.146</td> <td class="tdc">1.148</td>
-      <td class="tdc">1.150</td> <td class="tdc">1.152</td>
-   </tr><tr>
-      <td class="tdr">120&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.123</td>
-      <td class="tdc">1.126</td> <td class="tdc">1.129</td>
-      <td class="tdc">1.131</td> <td class="tdc">1.133</td>
-      <td class="tdc">1.136</td> <td class="tdc">1.138</td>
-      <td class="tdc">1.140</td> <td class="tdc">1.141</td>
-   </tr><tr>
-      <td class="tdr">130&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.113</td>
-      <td class="tdc">1.116</td> <td class="tdc">1.118</td>
-      <td class="tdc">1.121</td> <td class="tdc">1.123</td>
-      <td class="tdc">1.125</td> <td class="tdc">1.127</td>
-      <td class="tdc">1.129</td> <td class="tdc">1.130</td>
-   </tr><tr>
-      <td class="tdr">140&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.102</td>
-      <td class="tdc">1.105</td> <td class="tdc">1.108</td>
-      <td class="tdc">1.110</td> <td class="tdc">1.113</td>
-      <td class="tdc">1.115</td> <td class="tdc">1.117</td>
-      <td class="tdc">1.119</td> <td class="tdc">1.120</td>
-   </tr><tr>
-      <td class="tdr">150&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.091</td>
-      <td class="tdc">1.095</td> <td class="tdc">1.098</td>
-      <td class="tdc">1.100</td> <td class="tdc">1.102</td>
-      <td class="tdc">1.104</td> <td class="tdc">1.106</td>
-      <td class="tdc">1.108</td> <td class="tdc">1.110</td>
-   </tr><tr>
-      <td class="tdr">160&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.081</td>
-      <td class="tdc">1.084</td> <td class="tdc">1.087</td>
-      <td class="tdc">1.090</td> <td class="tdc">1.092</td>
-      <td class="tdc">1.094</td> <td class="tdc">1.096</td>
-      <td class="tdc">1.098</td> <td class="tdc">1.100</td>
-   </tr><tr>
-      <td class="tdr">170&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.070</td>
-      <td class="tdc">1.074</td> <td class="tdc">1.077</td>
-      <td class="tdc">1.079</td> <td class="tdc">1.081</td>
-      <td class="tdc">1.083</td> <td class="tdc">1.085</td>
-      <td class="tdc">1.087</td> <td class="tdc">1.089</td>
-   </tr><tr>
-      <td class="tdr">180&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.060</td>
-      <td class="tdc">1.063</td> <td class="tdc">1.066</td>
-      <td class="tdc">1.069</td> <td class="tdc">1.071</td>
-      <td class="tdc">1.073</td> <td class="tdc">1.075</td>
-      <td class="tdc">1.077</td> <td class="tdc">1.079</td>
-   </tr><tr>
-      <td class="tdr">190&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.050</td>
-      <td class="tdc">1.053</td> <td class="tdc">1.056</td>
-      <td class="tdc">1.058</td> <td class="tdc">1.060</td>
-      <td class="tdc">1.063</td> <td class="tdc">1.065</td>
-      <td class="tdc">1.066</td> <td class="tdc">1.068</td>
-   </tr><tr>
-      <td class="tdr">200&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.039</td>
-      <td class="tdc">1.043</td> <td class="tdc">1.045</td>
-      <td class="tdc">1.048</td> <td class="tdc">1.050</td>
-      <td class="tdc">1.052</td> <td class="tdc">1.054</td>
-      <td class="tdc">1.056</td> <td class="tdc">1.058</td>
-   </tr><tr>
-      <td class="tdr">210&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.029</td>
-      <td class="tdc">1.032</td> <td class="tdc">1.035</td>
-      <td class="tdc">1.037</td> <td class="tdc">1.040</td>
-      <td class="tdc">1.042</td> <td class="tdc">1.044</td>
-      <td class="tdc">1.046</td> <td class="tdc">1.047</td>
-   </tr>
- </tbody>
-</table>
-<table border="0" cellspacing="2" summary="_" rules="cols" cellpadding="0">
-  <tbody><tr class="tr_lt_grey">
-      <td class="tdc">Temp of<br />feed water.</td>
-      <td colspan="9" class="tdc"><span class="smcap">Steam Pressure by Gauge</span></td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">Deg. Fahr.</td>
-      <td class="tdc">140</td> <td class="tdc">150</td>
-      <td class="tdc">160</td> <td class="tdc">170</td>
-      <td class="tdc">180</td> <td class="tdc">190</td>
-      <td class="tdc">200</td> <td class="tdc">210</td>
-      <td class="tdc">220</td>
-   </tr><tr>
-      <td class="tdr">32&emsp;&nbsp;&nbsp;</td> <td class="tdc">&nbsp;1.234&nbsp;</td>
-      <td class="tdc">&nbsp;1.236&nbsp;</td> <td class="tdc">&nbsp;1.237&nbsp;</td>
-      <td class="tdc">&nbsp;1.239&nbsp;</td> <td class="tdc">&nbsp;1.240&nbsp;</td>
-      <td class="tdc">&nbsp;1.241&nbsp;</td> <td class="tdc">&nbsp;1.243&nbsp;</td>
-      <td class="tdc">&nbsp;1.244&nbsp;</td> <td class="tdc">&nbsp;1.245&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">40&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.226</td>
-      <td class="tdc">1.227</td> <td class="tdc">1.229</td>
-      <td class="tdc">1.230</td> <td class="tdc">1.232</td>
-      <td class="tdc">1.233</td> <td class="tdc">1.234</td>
-      <td class="tdc">1.236</td> <td class="tdc">1.237</td>
-   </tr><tr>
-      <td class="tdr">50&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.215</td>
-      <td class="tdc">1.217</td> <td class="tdc">1.218</td>
-      <td class="tdc">1.220</td> <td class="tdc">1.221</td>
-      <td class="tdc">1.223</td> <td class="tdc">1.224</td>
-      <td class="tdc">1.225</td> <td class="tdc">1.226</td>
-   </tr><tr>
-      <td class="tdr">60&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.205</td>
-      <td class="tdc">1.207</td> <td class="tdc">1.208</td>
-      <td class="tdc">1.210</td> <td class="tdc">1.211</td>
-      <td class="tdc">1.212</td> <td class="tdc">1.214</td>
-      <td class="tdc">1.215</td> <td class="tdc">1.216</td>
-   </tr><tr>
-      <td class="tdr">70&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.194</td>
-      <td class="tdc">1.196</td> <td class="tdc">1.197</td>
-      <td class="tdc">1.199</td> <td class="tdc">1.200</td>
-      <td class="tdc">1.202</td> <td class="tdc">1.203</td>
-      <td class="tdc">1.205</td> <td class="tdc">1.206</td>
-   </tr><tr>
-      <td class="tdr">80&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.184</td>
-      <td class="tdc">1.186</td> <td class="tdc">1.187</td>
-      <td class="tdc">1.189</td> <td class="tdc">1.190</td>
-      <td class="tdc">1.192</td> <td class="tdc">1.193</td>
-      <td class="tdc">1.194</td> <td class="tdc">1.195</td>
-   </tr><tr>
-      <td class="tdr">90&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.174</td>
-      <td class="tdc">1.176</td> <td class="tdc">1.177</td>
-      <td class="tdc">1.179</td> <td class="tdc">1.180</td>
-      <td class="tdc">1.181</td> <td class="tdc">1.183</td>
-      <td class="tdc">1.184</td> <td class="tdc">1.185</td>
-   </tr><tr>
-      <td class="tdr">100&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.164</td>
-      <td class="tdc">1.165</td> <td class="tdc">1.167</td>
-      <td class="tdc">1.168</td> <td class="tdc">1.170</td>
-      <td class="tdc">1.171</td> <td class="tdc">1.172</td>
-      <td class="tdc">1.174</td> <td class="tdc">1.175</td>
-   </tr><tr>
-      <td class="tdr">110&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.153</td>
-      <td class="tdc">1.155</td> <td class="tdc">1.156</td>
-      <td class="tdc">1.158</td> <td class="tdc">1.159</td>
-      <td class="tdc">1.160</td> <td class="tdc">1.162</td>
-      <td class="tdc">1.163</td> <td class="tdc">1.164</td>
-   </tr><tr>
-      <td class="tdr">120&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.143</td>
-      <td class="tdc">1.145</td> <td class="tdc">1.146</td>
-      <td class="tdc">1.147</td> <td class="tdc">1.149</td>
-      <td class="tdc">1.150</td> <td class="tdc">1.151</td>
-      <td class="tdc">1.153</td> <td class="tdc">1.154</td>
-   </tr><tr>
-      <td class="tdr">130&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.132</td>
-      <td class="tdc">1.134</td> <td class="tdc">1.136</td>
-      <td class="tdc">1.137</td> <td class="tdc">1.138</td>
-      <td class="tdc">1.140</td> <td class="tdc">1.141</td>
-      <td class="tdc">1.142</td> <td class="tdc">1.144</td>
-   </tr><tr>
-      <td class="tdr">140&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.122</td>
-      <td class="tdc">1.124</td> <td class="tdc">1.125</td>
-      <td class="tdc">1.127</td> <td class="tdc">1.128</td>
-      <td class="tdc">1.129</td> <td class="tdc">1.131</td>
-      <td class="tdc">1.132</td> <td class="tdc">1.133</td>
-   </tr><tr>
-      <td class="tdr">150&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.111</td>
-      <td class="tdc">1.113</td> <td class="tdc">1.115</td>
-      <td class="tdc">1.116</td> <td class="tdc">1.118</td>
-      <td class="tdc">1.119</td> <td class="tdc">1.120</td>
-      <td class="tdc">1.121</td> <td class="tdc">1.123</td>
-   </tr><tr>
-      <td class="tdr">160&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.101</td>
-      <td class="tdc">1.103</td> <td class="tdc">1.104</td>
-      <td class="tdc">1.106</td> <td class="tdc">1.107</td>
-      <td class="tdc">1.108</td> <td class="tdc">1.110</td>
-      <td class="tdc">1.111</td> <td class="tdc">1.112</td>
-   </tr><tr>
-      <td class="tdr">170&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.091</td>
-      <td class="tdc">1.092</td> <td class="tdc">1.094</td>
-      <td class="tdc">1.095</td> <td class="tdc">1.097</td>
-      <td class="tdc">1.098</td> <td class="tdc">1.099</td>
-      <td class="tdc">1.101</td> <td class="tdc">1.102</td>
-   </tr><tr>
-      <td class="tdr">180&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.080</td>
-      <td class="tdc">1.082</td> <td class="tdc">1.083</td>
-      <td class="tdc">1.085</td> <td class="tdc">1.086</td>
-      <td class="tdc">1.088</td> <td class="tdc">1.089</td>
-      <td class="tdc">1.090</td> <td class="tdc">1.091</td>
-   </tr><tr>
-      <td class="tdr">190&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.070</td>
-      <td class="tdc">1.071</td> <td class="tdc">1.073</td>
-      <td class="tdc">1.074</td> <td class="tdc">1.076</td>
-      <td class="tdc">1.077</td> <td class="tdc">1.078</td>
-      <td class="tdc">1.080</td> <td class="tdc">1.081</td>
-   </tr><tr>
-      <td class="tdr">200&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.059</td>
-      <td class="tdc">1.061</td> <td class="tdc">1.063</td>
-      <td class="tdc">1.064</td> <td class="tdc">1.065</td>
-      <td class="tdc">1.067</td> <td class="tdc">1.068</td>
-      <td class="tdc">1.069</td> <td class="tdc">1.071</td>
-   </tr><tr>
-      <td class="tdr">210&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.049</td>
-      <td class="tdc">1.051</td> <td class="tdc">1.052</td>
-      <td class="tdc">1.053</td> <td class="tdc">1.055</td>
-      <td class="tdc">1.056</td> <td class="tdc">1.057</td>
-      <td class="tdc">1.059</td> <td class="tdc">1.060</td>
-   </tr>
- </tbody>
-</table>
-<table border="0" cellspacing="2" summary="_" rules="cols" cellpadding="0">
-  <tbody><tr class="tr_lt_grey">
-      <td class="tdc">Temp of<br />feed water.</td>
-      <td colspan="9" class="tdc"><span class="smcap">Steam Pressure by Gauge</span></td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">Deg. Fahr.</td>
-      <td class="tdc">230</td> <td class="tdc">240</td>
-      <td class="tdc">250</td> <td class="tdc">260</td>
-      <td class="tdc">270</td> <td class="tdc">280</td>
-      <td class="tdc">290</td> <td class="tdc">300</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">32&emsp;&nbsp;&nbsp;</td> <td class="tdc">&nbsp;1.246&nbsp;</td>
-      <td class="tdc">&nbsp;1.247&nbsp;</td> <td class="tdc">&nbsp;1.248&nbsp;</td>
-      <td class="tdc">&nbsp;1.250&nbsp;</td> <td class="tdc">&nbsp;1.251&nbsp;</td>
-      <td class="tdc">&nbsp;1.252&nbsp;</td> <td class="tdc">&nbsp;1.253&nbsp;</td>
-      <td class="tdc">&nbsp;1.254&nbsp;</td> <td class="tdc">&nbsp;&emsp;&emsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">40&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.238</td>
-      <td class="tdc">1.239</td> <td class="tdc">1.240</td>
-      <td class="tdc">1.241</td> <td class="tdc">1.242</td>
-      <td class="tdc">1.243</td> <td class="tdc">1.244</td>
-      <td class="tdc">1.245</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">50&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.228</td>
-      <td class="tdc">1.229</td> <td class="tdc">1.230</td>
-      <td class="tdc">1.231</td> <td class="tdc">1.232</td>
-      <td class="tdc">1.233</td> <td class="tdc">1.234</td>
-      <td class="tdc">1.235</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">60&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.217</td>
-      <td class="tdc">1.218</td> <td class="tdc">1.219</td>
-      <td class="tdc">1.220</td> <td class="tdc">1.221</td>
-      <td class="tdc">1.222</td> <td class="tdc">1.223</td>
-      <td class="tdc">1.224</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">70&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.207</td>
-      <td class="tdc">1.208</td> <td class="tdc">1.209</td>
-      <td class="tdc">1.210</td> <td class="tdc">1.211</td>
-      <td class="tdc">1.212</td> <td class="tdc">1.213</td>
-      <td class="tdc">1.214</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">80&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.196</td>
-      <td class="tdc">1.198</td> <td class="tdc">1.199</td>
-      <td class="tdc">1.200</td> <td class="tdc">1.201</td>
-      <td class="tdc">1.202</td> <td class="tdc">1.203</td>
-      <td class="tdc">1.204</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">90&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.186</td>
-      <td class="tdc">1.187</td> <td class="tdc">1.188</td>
-      <td class="tdc">1.189</td> <td class="tdc">1.190</td>
-      <td class="tdc">1.191</td> <td class="tdc">1.192</td>
-      <td class="tdc">1.193</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">100&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.176</td>
-      <td class="tdc">1.177</td> <td class="tdc">1.178</td>
-      <td class="tdc">1.179</td> <td class="tdc">1.180</td>
-      <td class="tdc">1.181</td> <td class="tdc">1.182</td>
-      <td class="tdc">1.183</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">110&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.166</td>
-      <td class="tdc">1.167</td> <td class="tdc">1.168</td>
-      <td class="tdc">1.169</td> <td class="tdc">1.170</td>
-      <td class="tdc">1.171</td> <td class="tdc">1.172</td>
-      <td class="tdc">1.173</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">120&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.155</td>
-      <td class="tdc">1.156</td> <td class="tdc">1.157</td>
-      <td class="tdc">1.158</td> <td class="tdc">1.159</td>
-      <td class="tdc">1.160</td> <td class="tdc">1.161</td>
-      <td class="tdc">1.162</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">130&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.145</td>
-      <td class="tdc">1.146</td> <td class="tdc">1.147</td>
-      <td class="tdc">1.148</td> <td class="tdc">1.149</td>
-      <td class="tdc">1.150</td> <td class="tdc">1.151</td>
-      <td class="tdc">1.152</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">140&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.134</td>
-      <td class="tdc">1.135</td> <td class="tdc">1.136</td>
-      <td class="tdc">1.137</td> <td class="tdc">1.138</td>
-      <td class="tdc">1.139</td> <td class="tdc">1.140</td>
-      <td class="tdc">1.141</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">150&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.124</td>
-      <td class="tdc">1.125</td> <td class="tdc">1.126</td>
-      <td class="tdc">1.127</td> <td class="tdc">1.128</td>
-      <td class="tdc">1.129</td> <td class="tdc">1.130</td>
-      <td class="tdc">1.131</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">160&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.113</td>
-      <td class="tdc">1.115</td> <td class="tdc">1.116</td>
-      <td class="tdc">1.117</td> <td class="tdc">1.118</td>
-      <td class="tdc">1.119</td> <td class="tdc">1.120</td>
-      <td class="tdc">1.121</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">170&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.103</td>
-      <td class="tdc">1.104</td> <td class="tdc">1.105</td>
-      <td class="tdc">1.106</td> <td class="tdc">1.107</td>
-      <td class="tdc">1.108</td> <td class="tdc">1.109</td>
-      <td class="tdc">1.110</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">180&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.093</td>
-      <td class="tdc">1.094</td> <td class="tdc">1.095</td>
-      <td class="tdc">1.096</td> <td class="tdc">1.097</td>
-      <td class="tdc">1.098</td> <td class="tdc">1.099</td>
-      <td class="tdc">1.100</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">190&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.082</td>
-      <td class="tdc">1.083</td> <td class="tdc">1.084</td>
-      <td class="tdc">1.085</td> <td class="tdc">1.086</td>
-      <td class="tdc">1.087</td> <td class="tdc">1.088</td>
-      <td class="tdc">1.089</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">200&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.072</td>
-      <td class="tdc">1.073</td> <td class="tdc">1.074</td>
-      <td class="tdc">1.075</td> <td class="tdc">1.076</td>
-      <td class="tdc">1.077</td> <td class="tdc">1.078</td>
-      <td class="tdc">1.079</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">210&emsp;&nbsp;&nbsp;</td> <td class="tdc">1.061</td>
-      <td class="tdc">1.062</td> <td class="tdc">1.063</td>
-      <td class="tdc">1.064</td> <td class="tdc">1.065</td>
-      <td class="tdc">1.066</td> <td class="tdc">1.067</td>
-      <td class="tdc">1.068</td> <td class="tdc">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<p><span class="pagenum"><a name="Page_1935" id="Page_1935">1935</a></span></p>
-
-<div class="blockquot">
-<p class="space-above1">One boiler horse power being equal to <i>an
-evaporation of</i> 34½ <i>lbs. of water from a feed water temperature of
-212° Fahr., into steam at the same temperature</i>, the boiler capacity
-is accordingly</p>
-
-<p class="center">148,105 ÷ 34.5 = 4,293 boiler horse power.</p>
-
-<p>The rate of evaporation is given at 8 lbs. of water (from and at 212°
-Fahr.), for which the fuel required is</p>
-
-<p class="center">148,105 ÷ 8 = 18,513 lbs. of coal per hour.</p>
-
-<p>For a rate of combustion of 15 lbs. of coal per hour per square foot of grate,</p>
-
-<p class="center">grate area = 18,513 ÷ 15 = 1,234 sq. ft.</p>
-
-<p>For stationary boilers the usual ratio of heating surface to grate
-area is 35:1, accordingly the heating surface corresponding to this ratio is</p>
-
-<p class="center">1,234 × 35 = 43,190 sq.ft.</p>
-
-<p class="space-below1">The above calculation is based on a rate of evaporation
-of 8 lbs. of water per lb. of coal and a rate of combustion of 15 lbs. of coal
-per sq. ft. of grate. For other rates the required grate area may be
-obtained from the following table:</p></div>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-<caption><b>GRATE SURFACE PER HORSE POWER (KENT)</b></caption>
-  <tbody><tr class="tr_lt_grey">
-      <td rowspan="3" class="tdc">&nbsp;</td>
-      <td rowspan="3" class="tdc">Pounds<br />of water<br />from and<br />at 212°<br />per pound<br />of coal</td>
-      <td rowspan="3" class="tdc">Pounds<br />of coal<br />per h.p.<br />per hour</td>
-      <td colspan="9" class="tdc">&nbsp;Pounds of coal burned per square foot of grate per hour&nbsp;</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">8</td> <td class="tdc">10</td>
-      <td class="tdc">12</td> <td class="tdc">15</td>
-      <td class="tdc">20</td> <td class="tdc">25</td>
-      <td class="tdc">30</td> <td class="tdc">35</td>
-      <td class="tdc">40</td>
-   </tr><tr class="tr_lt_grey">
-      <td colspan="9" class="tdc">Square feet grate per horse power</td>
-   </tr><tr>
-      <td rowspan="2" class="tdr">Good coal and boiler&nbsp;</td>
-      <td class="tdl">&nbsp;&nbsp;10</td>
-      <td class="tdc">3.45</td> <td class="tdc">.43</td>
-      <td class="tdc">.35</td> <td class="tdc">.28</td>
-      <td class="tdc">.23</td> <td class="tdc">.17</td>
-      <td class="tdc">.14</td> <td class="tdc">.11</td>
-      <td class="tdc">.10</td> <td class="tdc">.09</td>
-   </tr><tr>
-                                <td class="tdl">&nbsp;&nbsp;9</td>
-      <td class="tdc">3.83</td> <td class="tdc">.48</td>
-      <td class="tdc">.38</td> <td class="tdc">.32</td>
-      <td class="tdc">.25</td> <td class="tdc">.19</td>
-      <td class="tdc">.15</td> <td class="tdc">.13</td>
-      <td class="tdc">.11</td> <td class="tdc">.10</td>
-   </tr><tr>
-      <td rowspan="3" class="tdr">Fair coal or boiler&nbsp;</td>
-      <td class="tdl"><br />&nbsp;&nbsp;8.61</td>
-      <td class="tdc"><br />4.&emsp;&nbsp;</td> <td class="tdc"><br />.50</td>
-      <td class="tdc"><br />.40</td> <td class="tdc"><br />.33</td>
-      <td class="tdc"><br />.26</td> <td class="tdc"><br />.20</td>
-      <td class="tdc"><br />.16</td> <td class="tdc"><br />.13</td>
-      <td class="tdc"><br />.12</td> <td class="tdc"><br />.10</td>
-   </tr><tr>
-                            <td class="tdl">&nbsp;&nbsp;8</td>
-      <td class="tdc">4.31</td> <td class="tdc">.54</td>
-      <td class="tdc">.43</td> <td class="tdc">.36</td>
-      <td class="tdc">.29</td> <td class="tdc">.22</td>
-      <td class="tdc">.17</td> <td class="tdc">.14</td>
-      <td class="tdc">.13</td> <td class="tdc">.11</td>
-   </tr><tr>
-                            <td class="tdl">&nbsp;&nbsp;7</td>
-      <td class="tdc">4.93</td> <td class="tdc">.62</td>
-      <td class="tdc">.49</td> <td class="tdc">.41</td>
-      <td class="tdc">.33</td> <td class="tdc">.24</td>
-      <td class="tdc">.20</td> <td class="tdc">.17</td>
-      <td class="tdc">.14</td> <td class="tdc">.12</td>
-   </tr><tr>
-      <td rowspan="3" class="tdr">Poor coal or boiler&nbsp;</td>
-      <td class="tdl"><br />&nbsp;&nbsp;6.9</td>
-      <td class="tdc"><br />5.&emsp;&nbsp;</td> <td class="tdc"><br />.63</td>
-      <td class="tdc"><br />.50</td> <td class="tdc"><br />.42</td>
-      <td class="tdc"><br />.34</td> <td class="tdc"><br />.25</td>
-      <td class="tdc"><br />.20</td> <td class="tdc"><br />.17</td>
-      <td class="tdc"><br />.15</td> <td class="tdc"><br />.13</td>
-   </tr><tr>
-                            <td class="tdl">&nbsp;&nbsp;6</td>
-      <td class="tdc">5.75</td> <td class="tdc">.72</td>
-      <td class="tdc">.58</td> <td class="tdc">.48</td>
-      <td class="tdc">.38</td> <td class="tdc">.29</td>
-      <td class="tdc">.23</td> <td class="tdc">.19</td>
-      <td class="tdc">.17</td> <td class="tdc">.14</td>
-   </tr><tr>
-                            <td class="tdl">&nbsp;&nbsp;5</td>
-      <td class="tdc">6.9&nbsp;&nbsp;</td> <td class="tdc">.86</td>
-      <td class="tdc">.69</td> <td class="tdc">.58</td>
-      <td class="tdc">.46</td> <td class="tdc">.35</td>
-      <td class="tdc">.28</td> <td class="tdc">.23</td>
-      <td class="tdc">.22</td> <td class="tdc">.17</td>
-   </tr><tr>
-      <td class="tdr"><br />Lignite and poor boiler&nbsp;</td> <td class="tdl"><br />&nbsp;&nbsp;3.45</td>
-      <td class="tdc"><br />10.&emsp;&nbsp;</td>
-      <td class="tdc"><br />1.25</td> <td class="tdc"><br />1.00</td>
-      <td class="tdc"><br />.83</td> <td class="tdc"><br />.67</td>
-      <td class="tdc"><br />.50</td> <td class="tdc"><br />.40</td>
-      <td class="tdc"><br />.33</td> <td class="tdc"><br />.29</td> <td class="tdc"><br />.25</td>
-   </tr>
- </tbody>
-</table>
-<p><span class="pagenum"><a name="Page_1936" id="Page_1936">1936</a></span></p>
-
-<p class="space-above1 space-below1"><b>General Arrangement of
-Station.</b>&mdash;In designing an electrical station, it is
-preferable that whatever rooms or divisions of the interior space are
-desired should determine the total outside dimensions of the plant in
-the original plans of the building than that these latter dimensions
-be fixed and the rooms, etc., be fitted in afterward.</p>
-
-<table border="0" cellspacing="2" summary="_" rules="cols" cellpadding="0">
-<caption><b>SAVING DUE TO HEATING THE FEED WATER</b><br /><br />
-Table showing the percentage of saving for each degree of increase in
-temperature of feed water heated by waste steam.</caption>
-  <tbody><tr class="tr_lt_grey">
-      <td rowspan="3" class="tdc">Initial<br />temp.<br />of feed.</td>
-      <td colspan="11" class="tdc">&nbsp;</td>
-      <td rowspan="3" class="tdc">Initial<br />temp.<br />of feed.</td>
-   </tr><tr class="tr_lt_grey">
-      <td colspan="11" class="tdc u">&nbsp;&emsp;Pressure of steam in boiler, lbs. per sq. inch above atmosphere&emsp;&nbsp;</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">0</td> <td class="tdc">20</td>
-      <td class="tdc">40</td> <td class="tdc">60</td>
-      <td class="tdc">80</td> <td class="tdc">100</td>
-      <td class="tdc">120</td> <td class="tdc">140</td>
-      <td class="tdc">160</td> <td class="tdc">180</td>
-      <td class="tdc">200</td>
-   </tr><tr>
-      <td class="tdr">32°&nbsp;&nbsp;</td> <td class="tdc">&nbsp;.0872&nbsp;</td>
-      <td class="tdc">&nbsp;.0861&nbsp;</td> <td class="tdc">&nbsp;.0855&nbsp;</td>
-      <td class="tdc">&nbsp;.0851&nbsp;</td> <td class="tdc">&nbsp;.0847&nbsp;</td>
-      <td class="tdc">&nbsp;.0844&nbsp;</td> <td class="tdc">&nbsp;.0841&nbsp;</td>
-      <td class="tdc">&nbsp;.0839&nbsp;</td> <td class="tdc">&nbsp;.0837&nbsp;</td>
-      <td class="tdc">&nbsp;.0835&nbsp;</td>  <td class="tdc">&nbsp;.0833&nbsp;</td>
-      <td class="tdr">32&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">40&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0878</td>
-      <td class="tdc">.0867</td> <td class="tdc">.0861</td>
-      <td class="tdc">.0856</td> <td class="tdc">.0853</td>
-      <td class="tdc">.0850</td> <td class="tdc">.0847</td>
-      <td class="tdc">.0845</td> <td class="tdc">.0843</td>
-      <td class="tdc">.0841</td> <td class="tdc">.0839</td>
-      <td class="tdr">40&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">50&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0886</td>
-      <td class="tdc">.0875</td> <td class="tdc">.0868</td>
-      <td class="tdc">.0864</td> <td class="tdc">.0860</td>
-      <td class="tdc">.0857</td> <td class="tdc">.0854</td>
-      <td class="tdc">.0852</td> <td class="tdc">.0850</td>
-      <td class="tdc">.0848</td> <td class="tdc">.0846</td>
-      <td class="tdr">50&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">60&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0894</td>
-      <td class="tdc">.0883</td> <td class="tdc">.0876</td>
-      <td class="tdc">.0872</td> <td class="tdc">.0867</td>
-      <td class="tdc">.0864</td> <td class="tdc">.0862</td>
-      <td class="tdc">.0859</td> <td class="tdc">.0856</td>
-      <td class="tdc">.0855</td> <td class="tdc">.0853</td>
-      <td class="tdr">60&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">70&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0902</td>
-      <td class="tdc">.0890</td> <td class="tdc">.0884</td>
-      <td class="tdc">.0879</td> <td class="tdc">.0875</td>
-      <td class="tdc">.0872</td> <td class="tdc">.0869</td>
-      <td class="tdc">.0867</td> <td class="tdc">.0864</td>
-      <td class="tdc">.0862</td> <td class="tdc">.0860</td>
-      <td class="tdr">70&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">80&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0910</td>
-      <td class="tdc">.0898</td> <td class="tdc">.0891</td>
-      <td class="tdc">.0887</td> <td class="tdc">.0883</td>
-      <td class="tdc">.0879</td> <td class="tdc">.0877</td>
-      <td class="tdc">.0874</td> <td class="tdc">.0872</td>
-      <td class="tdc">.0870</td> <td class="tdc">.0868</td>
-      <td class="tdr">80&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">90&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0919</td>
-      <td class="tdc">.0907</td> <td class="tdc">.0900</td>
-      <td class="tdc">.0895</td> <td class="tdc">.0888</td>
-      <td class="tdc">.0887</td> <td class="tdc">.0884</td>
-      <td class="tdc">.0883</td> <td class="tdc">.0879</td>
-      <td class="tdc">.0877</td> <td class="tdc">.0875</td>
-      <td class="tdr">90&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">100&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0927</td>
-      <td class="tdc">.0915</td> <td class="tdc">.0908</td>
-      <td class="tdc">.0903</td> <td class="tdc">.0899</td>
-      <td class="tdc">.0895</td> <td class="tdc">.0892</td>
-      <td class="tdc">.0890</td> <td class="tdc">.0887</td>
-      <td class="tdc">.0885</td> <td class="tdc">.0883</td>
-      <td class="tdr">100&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">110&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0936</td>
-      <td class="tdc">.0923</td> <td class="tdc">.0916</td>
-      <td class="tdc">.0911</td> <td class="tdc">.0907</td>
-      <td class="tdc">.0903</td> <td class="tdc">.0900</td>
-      <td class="tdc">.0898</td> <td class="tdc">.0895</td>
-      <td class="tdc">.0893</td> <td class="tdc">.0891</td>
-      <td class="tdr">110&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">120&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0945</td>
-      <td class="tdc">.0932</td> <td class="tdc">.0925</td>
-      <td class="tdc">.0919</td> <td class="tdc">.0915</td>
-      <td class="tdc">.0911</td> <td class="tdc">.0908</td>
-      <td class="tdc">.0906</td> <td class="tdc">.0903</td>
-      <td class="tdc">.0901</td> <td class="tdc">.0899</td>
-      <td class="tdr">120&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">130&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0954</td>
-      <td class="tdc">.0941</td> <td class="tdc">.0934</td>
-      <td class="tdc">.0928</td> <td class="tdc">.0924</td>
-      <td class="tdc">.0920</td> <td class="tdc">.0917</td>
-      <td class="tdc">.0914</td> <td class="tdc">.0912</td>
-      <td class="tdc">.0909</td> <td class="tdc">.0907</td>
-      <td class="tdr">130&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">140&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0963</td>
-      <td class="tdc">.0950</td> <td class="tdc">.0943</td>
-      <td class="tdc">.0937</td> <td class="tdc">.0932</td>
-      <td class="tdc">.0929</td> <td class="tdc">.0925</td>
-      <td class="tdc">.0923</td> <td class="tdc">.0920</td>
-      <td class="tdc">.0918</td> <td class="tdc">.0916</td>
-      <td class="tdr">140&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">150&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0973</td>
-      <td class="tdc">.0959</td> <td class="tdc">.0951</td>
-      <td class="tdc">.0946</td> <td class="tdc">.0941</td>
-      <td class="tdc">.0937</td> <td class="tdc">.0934</td>
-      <td class="tdc">.0931</td> <td class="tdc">.0929</td>
-      <td class="tdc">.0926</td> <td class="tdc">.0924</td>
-      <td class="tdr">150&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">160&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0982</td>
-      <td class="tdc">.0968</td> <td class="tdc">.0961</td>
-      <td class="tdc">.0955</td> <td class="tdc">.0950</td>
-      <td class="tdc">.0946</td> <td class="tdc">.0943</td>
-      <td class="tdc">.0940</td> <td class="tdc">.0937</td>
-      <td class="tdc">.0935</td> <td class="tdc">.0933</td>
-      <td class="tdr">160&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">170&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.0992</td>
-      <td class="tdc">.0978</td> <td class="tdc">.0970</td>
-      <td class="tdc">.0964</td> <td class="tdc">.0959</td>
-      <td class="tdc">.0955</td> <td class="tdc">.0952</td>
-      <td class="tdc">.0949</td> <td class="tdc">.0946</td>
-      <td class="tdc">.0944</td> <td class="tdc">.0941</td>
-      <td class="tdr">170&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">180&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.1002</td>
-      <td class="tdc">.0988</td> <td class="tdc">.0981</td>
-      <td class="tdc">.0973</td> <td class="tdc">.0969</td>
-      <td class="tdc">.0965</td> <td class="tdc">.0961</td>
-      <td class="tdc">.0958</td> <td class="tdc">.0955</td>
-      <td class="tdc">.0953</td> <td class="tdc">.0951</td>
-      <td class="tdr">180&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">190&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.1012</td>
-      <td class="tdc">.0998</td> <td class="tdc">.0989</td>
-      <td class="tdc">.0983</td> <td class="tdc">.0978</td>
-      <td class="tdc">.0974</td> <td class="tdc">.0971</td>
-      <td class="tdc">.0968</td> <td class="tdc">.0964</td>
-      <td class="tdc">.0062</td> <td class="tdc">.0960</td>
-      <td class="tdr">190&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">200&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.1022</td>
-      <td class="tdc">.1008</td> <td class="tdc">.0999</td>
-      <td class="tdc">.0993</td> <td class="tdc">.0988</td>
-      <td class="tdc">.0984</td> <td class="tdc">.0980</td>
-      <td class="tdc">.0977</td> <td class="tdc">.0974</td>
-      <td class="tdc">.0972</td> <td class="tdc">.0969</td>
-      <td class="tdr">200&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">210&nbsp;&nbsp;&nbsp;</td> <td class="tdc">.1033</td>
-      <td class="tdc">.1018</td> <td class="tdc">.1010</td>
-      <td class="tdc">.1003</td> <td class="tdc">.0998</td>
-      <td class="tdc">.0994</td> <td class="tdc">.0990</td>
-      <td class="tdc">.0987</td> <td class="tdc">.0984</td>
-      <td class="tdc">.0981</td> <td class="tdc">.0979</td>
-      <td class="tdr">210&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">220&nbsp;&nbsp;&nbsp;</td> <td class="tdc">&mdash;</td>
-      <td class="tdc">.1029</td> <td class="tdc">.1019</td>
-      <td class="tdc">.1013</td> <td class="tdc">.1008</td>
-      <td class="tdc">.1004</td> <td class="tdc">.1000</td>
-      <td class="tdc">.0997</td> <td class="tdc">.0994</td>
-      <td class="tdc">.0991</td> <td class="tdc">.0989</td>
-      <td class="tdr">220&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">230&nbsp;&nbsp;&nbsp;</td> <td class="tdc">&mdash;</td>
-      <td class="tdc">.1039</td> <td class="tdc">.1031</td>
-      <td class="tdc">.1024</td> <td class="tdc">.1018</td>
-      <td class="tdc">.1012</td> <td class="tdc">.1010</td>
-      <td class="tdc">.1007</td> <td class="tdc">.1003</td>
-      <td class="tdc">.1001</td> <td class="tdc">.0999</td>
-      <td class="tdr">230&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">240&nbsp;&nbsp;&nbsp;</td> <td class="tdc">&mdash;</td>
-      <td class="tdc">.1050</td> <td class="tdc">.1041</td>
-      <td class="tdc">.1034</td> <td class="tdc">.1029</td>
-      <td class="tdc">.1024</td> <td class="tdc">.1020</td>
-      <td class="tdc">.1017</td> <td class="tdc">.1014</td>
-      <td class="tdc">.1011</td> <td class="tdc">.1009</td>
-      <td class="tdr">240&nbsp;&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">250&nbsp;&nbsp;&nbsp;</td> <td class="tdc">&mdash;</td>
-      <td class="tdc">.1062</td> <td class="tdc">.1052</td>
-      <td class="tdc">.1045</td> <td class="tdc">.1040</td>
-      <td class="tdc">.1035</td> <td class="tdc">.1031</td>
-      <td class="tdc">.1027</td> <td class="tdc">.1025</td>
-      <td class="tdc">.1022</td> <td class="tdc">.1019</td>
-      <td class="tdr">250&nbsp;&nbsp;&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="blockquot">
-NOTE.&mdash;An approximate rule for the conditions of ordinary practice
-is a saving of 1 per cent. made by each increase of 11° in the
-temperature of the feed water. This corresponds to .0909 per cent.
-per degree. The calculation of saving is made as follows: Boiler
-pressure, 100 lbs. gauge; total heat in steam above 32° = 1,185
-B.T.U. feed water, original temperature 60°, final temperature 209°F.
-Increase in heat units, 150. Heat units above 32° in feed water of
-original temperature = 28. Heat units in steam above that in cold
-feed water, 1,185-28 = 1,157. Saving by the feed water heater =
-150 ÷ 1,157 = 12.96 per cent. The same result is obtained by the use
-of the table. Increase in temperature 150° × tabular figure .0864
-= 12.96 per cent. Let total heat of 1 lb. of steam at the boiler
-pressure = H; total heat of 1 lb. of feed water before entering the
-heater = <i>h'</i>, and after passing through the heater = <i>h"</i>; then
-the saving made by the heater is (<i>h"</i>-<i>h'</i>) ÷ (H-<i>h'</i>).</p>
-
-<p><span class="pagenum"><a name="Page_1937" id="Page_1937">1937</a></span>
-Under usual conditions the plans of an electrical station are readily
-drawn, as they are generally of a simple nature. The engines and
-generators will occupy the majority of the space, and these are
-usually placed in one large room; in some stations, however, they are
-located respectively in two adjacent rooms. The boilers are generally
-located in a room apart from the engines and dynamos, and in some
-cases a separate building is provided for them; the pumps, etc., must
-be installed not far from the boilers, and space must also be allowed
-near the boilers for coal and ashes.</p>
-
-<div class="figcenter">
-  <a name="fig2720"></a>
-  <img src="images/i105.jpg" alt="_" width="600" height="584" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,720.&mdash;Floor plan of an electrical
-station having a belted drive with counter shaft.</p>
-</div>
-
-<p class="blockquot">
-Fig. 2,720 shows the floor plan of an electrical station,
-in which a countershaft and belted connections are used between the engines and
-<span class="pagenum"><a name="Page_1938" id="Page_1938">1938</a></span>
-generators. Referring first to the plan of the building itself, A
-represents the engine and dynamo room, B denotes the boiler room, C
-the office, D the store room, and E the chimney connected with the
-boilers by means of the uptake <i>w</i>. Referring next to the apparatus
-installed, S, S, S, S represents a battery of four boilers; these are
-connected by steam piping VV to the two steam engines, M and M, which
-are belted to the countershaft O. Belted to the countershaft are the
-generators, T, T, T, T, the circuits from which are controlled on the
-switchboard, H.</p>
-
-<p><b>Ques. What are the objections to the arrangement shown in <a href="#fig2720">fig. 2,720</a>.</b>?</p>
-
-<p>Ans. The large space required by the belt drive especially
-in locations where land is expensive. Another objection is the
-frictional loss due to the belt drive with its countershaft, etc.</p>
-
-<div class="figcenter">
-  <a name="fig2721"></a>
-  <img src="images/i106.jpg" alt="_" width="600" height="179" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig</span>. 2,721.&mdash;Elevation of station having a
-belted drive with countershaft, as shown in plan in <a href="#fig2720">fig. 2,720</a>.</p>
-</div>
-
-<p><b>Ques. What are the desirable features of the belt drive?</b></p>
-
-<p>Ans. High speed generators may be used, thus reducing the first
-cost, and the multiplicity of speeds and flexibility of the system
-resulting from the use of a friction clutch.</p>
-
-<p class="blockquot">
-Thus in <a href="#fig2720">fig. 2,720</a>, each pulley may be mounted on the
-counter shaft O with a friction clutch. A jaw clutch may also be provided at Z,
-thus permitting the shaft O to be divided into two sections. It is
-therefore possible by this arrangement to cause either of the engines
-to drive any one of the generators, or all of them, or both of the
-engines to drive all of the generators simultaneously.</p>
-
-<p><b>Ques. Under what condition is the counter shaft belt drive particularly valuable?</b>
-<span class="pagenum"><a name="Page_1939" id="Page_1939">1939</a></span></p>
-
-<p>Ans. In case of a break down of any one of the engines or generators,
-and also when it becomes necessary to clean them without interrupting
-the service.</p>
-
-<div class="figcenter">
-  <a name="fig2722"></a>
-  <img src="images/i107.jpg" alt="_" width="600" height="494" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,722.&mdash;Plan of station arranged for
-extension. The space required for a central station depends upon the
-number and kind of lights to be supplied, and upon the character
-and arrangement of the machinery. In calculating the size of
-building required, two things must be carefully considered: first,
-the building must be adapted to the plant to be installed in the
-beginning; and second, it must be arranged so that enlargement can be
-made without disarranging or interfering with the plant already in
-existence. This is usually best secured by providing for expansion in
-one or two definite directions, the building being made large enough
-to accommodate additional units that will be necessary at some future
-time because of the growth of the community and consequent increased
-demand for electric current.</p>
-</div>
-
-<p><b>Ques. How may the design in <a href="#fig2720">fig. 2,720</a> be modified
-for the installation of a storage battery?</b></p>
-
-<p>Ans. If a storage battery be necessary, a partition may be
-constructed across the room A, as indicated by the dotted lines, and
-the battery installed in the room thus formed.
-<span class="pagenum"><a name="Page_1940" id="Page_1940">1940</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2723"></a>
-  <img src="images/i-0312.jpg" alt="_" width="600" height="407" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,723.&mdash;Interior of old Riverside
-station showing at the right, seven 6,000 horse power alternators
-driven by reciprocating engines, and at the left, a number of turbine
-units aggregating 90,000 horse power.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1941" id="Page_1941">1941</a></span>
-<b>Ques. Mention a few details in the general arrangement of the
-building <a href="#fig2720">fig. 2,720</a>.</b></p>
-
-<p>Ans. Two doors to the room A may conveniently be provided at K
-and L, the former connecting with the boiler room B, and the latter
-serving as the main entrance to the station. There is little that
-need be added to what has already been stated regarding the boiler
-room B. The door at F provides for the entrance of coal and the
-removal of ashes, while at P, the pump and heaters may conveniently
-be located. In the office C, visitors may be received, the station
-reports made out, bulletins issued from time to time, and whatever
-engineering problems arise may here be solved on paper by the
-engineer in charge of the plant. The store room D will be found
-convenient for various supplies, tools and appliances needed in the
-operation of the station. These may here be kept under lock and key
-and the daily waste and loss resulting from carelessness avoided.</p>
-
-<p><b>Ques. What important point should be noted in locating the engines
-and boilers?</b></p>
-
-<p>Ans. They should be so placed that the piping between them will be as
-short and direct as possible.</p>
-
-<p><b>Ques. Why?</b></p>
-
-<p>Ans. The steam pipe should be short to reduce the loss of heat
-between engine and boiler to a minimum, and both short and direct to
-avoid undue friction and consequent drop in pressure of the steam in
-passing through the pipe to the engine.</p>
-
-<p class="blockquot">
-Entirely too little attention is given to this matter on the part of
-designers and it cannot be too strongly emphasized that, for economy,
-the steam pipe between an engine and boiler should be as short and
-direct as possible, having regard of course, for proper piping
-methods.</p>
-
-<p><b>Ques. What should be provided for the steam pipe?</b></p>
-
-<p class="space-below1">Ans. A heavy covering of approved material should be placed around
-<span class="pagenum"><a name="Page_1942" id="Page_1942">1942</a></span>
-the pipe to reduce the loss of heat by radiation. For this purpose
-hair felt, mineral wool and asbestos are used.</p>
-
-<div class="figcenter">
-  <a name="fig2724"></a>
-  <img src="images/i110.jpg" alt="_" width="600" height="515" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,724.&mdash;View of engine and condenser,
-showing how to arrange the piping to secure good vacuum. <i>Locate the
-condenser as near the engine as possible</i>; <b>use easy bends</b>
-<i>instead of elbows; place the pump</i> <b>below</b> <i>bottom of condenser
-so the water will drain to pump</i>. At A is a relief valve, for
-protection in case the condenser become flooded through failure of
-the pump, and at B is a gate valve to shut off condenser in case
-atmospheric exhaust is desired to permit repairs to be made to
-condenser during operation. <b>A water seal</b> should be maintained
-on the relief valve and <b>special attention</b> <i>should be given to
-the stuffing box</i> of the gate valve <b>to prevent air leakage</b>.
-<i>The discharge valve of the pump should be water sealed.</i></p>
-</div>
-
-<p><b>Ques. How should the piping be arranged between the engine and
-condenser, and why?</b></p>
-
-<p>Ans. It should be as short and direct as possible; especially
-should elbows be avoided so that the back pressure on the engine
-piston will be reduced as near as can be to that of the condenser.
-<span class="pagenum"><a name="Page_1943" id="Page_1943">1943</a></span></p>
-
-<div class="blockquot">
-<p>That is to say, in order to get nearly the full effect of the vacuum
-in the condenser the frictional resistance of the piping should be
-reduced to a minimum.</p>
-
-<p>Where 90° turns are necessary, easy bends should be used instead of
-sharp elbows. The force of this argument must be apparent by noting
-the practice of steam turbine builders of placing the turbine right
-up against the condenser, and remembering that a high vacuum is
-necessary to the economical working of a turbine. See fig. 1,445,
-page 1,182.</p></div>
-
-<p><b>Ques. What are the considerations respecting the number and type
-of engine to be used?</b></p>
-
-<p>Ans. In the illustration <a href="#fig2720">fig. 2,720</a>, two engines M
-and M' are employed, one belted to each end of the countershaft O. These
-engines should be of similar or identical pattern; for a small output
-they may be either simple or compound, as the conditions of fuel
-expenditure may dictate, but if the output be large, triple expansion
-engines or turbines are advisable.</p>
-
-<div class="figcenter">
-  <a name="fig2725"></a>
-  <img src="images/i111.jpg" alt="_" width="600" height="205" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,725.&mdash;"Dry pipe" for horizontal
-boiler: it is connected to the main outlet and its upper surface is
-perforated with small holes, the far end being closed. With this
-arrangement steam is taken from the boiler over a large area, so that
-it will contain very little moisture. <i>All horizontal boilers without
-a dome should be fitted with a dry pipe;</i> most engineers do not
-realize the importance of obtaining dry steam for engine operation.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_1944" id="Page_1944">1944</a></span></p>
-
-<div class="blockquot">
-<p>Corliss or similar slow speed engines may advantageously be used in
-either case. In all cases the engine should be run condensing unless
-the cost for circulating water is prohibitive; even in such cases
-cooling towers may be installed and effect a saving.</p>
-
-<p>In operation, during the greater part of the day, one engine running
-two or perhaps three of the generators, will carry the load, but when
-the load is particularly heavy, as in the morning and evening, both
-engines and all the generators may be required to meet the demands.</p></div>
-
-<div class="figcenter">
-  <a name="fig2726"></a>
-  <img src="images/i112.jpg" alt="_" width="600" height="477" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,726.&mdash;Method of connecting a header to
-a battery of boilers. Where two or more boilers are connected to a
-single header, the use of a reliable non-return boiler stop valve is
-necessary, and in some countries their installation is compulsory. A
-non-return boiler stop valve will instantly close should the pressure
-in the boiler to which it is attached suddenly decrease below that
-in the header, and thereby prevent the entrance of steam from the
-other boilers of the battery. This sudden decrease in pressure may be
-caused by a ruptured fitting or the blowing out of a tube, in which
-event an ordinary stop valve taking the place of a non-return boiler
-stop valve would be inadequate, as the loss of steam from the other
-boilers of the battery would be tremendous before an ordinary valve
-could be reached and closed, assuming that it would be possible to do
-so, which in the majority of cases it is not. Should it be desired
-to cut out a boiler for cleaning or repairs, the non-return boiler
-stop valve will not permit steam to enter the boiler from the header,
-even should the handwheel be operated for this purpose, as it cannot
-be opened by hand, but can, however, be closed. A non-return boiler
-stop valve should be attached to each boiler and connected to an
-angle valve on the header. A pipe bend should be used for connecting
-the valves, as this will allow for expansion and contraction. The
-pipe should slope a trifle downward toward the header and a suitable
-drain provided. This drain should be opened and all water permitted
-to escape before the angle valve is opened, thereby preventing any
-damage due to water hammer.</p>
-</div>
-
-<p class="blockquot">
-By exercising a little ingenuity in shifting the load on different
-machines at different times, both engines and dynamos, may readily be
-cleaned and repaired without interrupting the service.
-<span class="pagenum"><a name="Page_1945" id="Page_1945">1945</a></span></p>
-
-<p><b>Ques. For economy what kind of steam should be used?</b></p>
-
-<p>Ans. Super-heated steam.</p>
-
-<p class="blockquot">
-The saving due to the use of superheated steam is about 1% for every
-ten degrees Fahr. of super-heat. It should be used in all cases.</p>
-
-<p><b>Ques. How should the machines be located?</b></p>
-
-<p>Ans. Sufficient space should be allowed between them that cleaning and
-repairing may be done easily, quickly and effectually.</p>
-
-<div class="figcenter">
-  <a name="fig2727"></a>
-  <img src="images/i113.jpg" alt="_" width="600" height="595" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,727 and 2,728.&mdash;Method of preventing
-vibration and of supporting pipes. The figures show top and side
-views of a main header carried in suitable frames fitted with
-adjustable roller. While the pipe is illustrated as resting on the
-adjustable rollers, nevertheless the rollers may also be placed at
-the sides or on top of the pipe to prevent vibration, or in cases
-where the thrust from a horizontal or vertical branch has to be
-provided for. This arrangement will take care of the vibration
-without in any way preventing the free expansion and contraction of the pipe.</p>
-</div>
-
-<p><b>Ques. How should the switchboard be located?</b></p>
-
-<p>Ans. In <a href="#fig2720">fig. 2,720</a>, the switchboard H is mounted against
-the wall dividing the room A from the room B, and is in line with the machines.</p>
-
-<div class="blockquot">
-<p>The advantages arising from a switchboard thus installed are, that
-the switchboard attendant working thereon can obtain at any time an
-unobstructed view of the performance of each individual machine,
-and he has in consequence a much better control of them; then, too,
-while he is engaged at the engines or generators he can also see the
-measuring instruments on the switchboard, and ascertain approximately
-the readings upon them.</p>
-
-<p>In cases of emergency it is sometimes necessary for the engineer in
-charge of a plant to be in several places at the same time in order to
-<span class="pagenum"><a name="Page_1946" id="Page_1946">1946</a></span>
-prevent an accident, and that this seemingly impossibility may
-be approximated as nearly as possible, it is essential that the
-controlling devices be located as closely together as is consistent,
-and that no moving belt or pulley intervene between them.</p>
-
-<p>These conditions are well satisfied in <a href="#fig2720">fig. 2,720</a>, and
-owing to the short distances between the generators and the switchboard the drop
-of voltage in each of the conducting wires between them will be low.</p>
-
-<p>This latter advantage is worthy of notice in a station generating
-large currents at a low pressure. To offset the advantages just
-mentioned, the location of the switchboard in line with the machines
-introduces an element of danger to the switchboard, its apparatus,
-and the attendant, on account of the possible bursting of a flywheel
-or other parts of the machines from centrifugal force.</p></div>
-
-<div class="figcenter">
-  <a name="fig2729"></a>
-  <img src="images/i114.jpg" alt="_" width="600" height="369" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,729 and 2,730.&mdash;Points on placing
-stop valves. The first and most important feature is to ascertain
-whether the valve will act as a water trap for condensed steam. Fig.
-2,729 illustrates a common error in the placing of valves, as this
-arrangement permits of an accumulation of condensed steam above the
-valve when closed, and should the engineer be careless and open the
-valve suddenly, serious results might follow owing to water-hammer.
-Fig. 2,730 illustrates the correct method of placing the valve. It
-sometimes occurs, however, that it is not convenient to place the
-valve as shown in fig. 2,730 and that fig. 2,729 is the only manner
-in which the valve can be placed. In such cases, the valve should
-have a drain, and this drain should always be opened before the large
-valve is opened.</p></div>
-
-<p class="blockquot">
-If the switchboard be placed in the dotted position at H', or, in
-fact, at the opposite end of the room A, the damage to life and
-property that might result from the effects of centrifugal force
-would be eliminated, but in place thereof would be the disadvantages
-of an obstructed view of the machines from the switchboard, an
-obstructed view of the switchboard from the machines, inaccessibility
-between these two, and a greater drop of voltage in the majority of
-the conducting wires between the generators and the switchboard.
-<span class="pagenum"><a name="Page_1947" id="Page_1947">1947</a></span></p>
-
-<p><b>Ques. Describe a second arrangement of station with belt drive and
-compare it with the design shown in <a href="#fig2720">fig. 2,720</a>.</b></p>
-
-<div class="figcenter">
-  <a name="fig2731"></a>
-  <img src="images/i115.jpg" alt="_" width="600" height="593" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,731.&mdash;Plan of electrical station with
-belt drive without counter shaft. The installation here represented
-consists of two boilers, S, etc., and three sets of engines and
-generators, T, M, etc. Sufficient allowance has been made in the
-plans, however, for future increase of business, as additional space
-has been provided for an extra engine and generator set, as indicated
-by the dotted lines.</p></div>
-
-<p>Ans. A floor plan somewhat different from that presented in <a href="#fig2720">fig.
-2,720</a> is shown in <a href="#fig2731">fig. 2,731</a>. Here a belt drive is employed,
-but no countershaft is used. Each generator, therefore, is dependent upon
-its respective engine, and in consequence the flexibility obtained by
-the use of a countershaft is lost. On the other hand, there is less
-<span class="pagenum"><a name="Page_1948" id="Page_1948">1948</a></span>
-loss of mechanical power between the engines and generators in the
-driving of the latter, and less floor space is necessary in the room
-A. If, however, the floor area of this room be made the same as in
-the previous arrangement and the same number of machines are to be
-installed, they may be spaced further apart, affording in consequence
-considerably more room for cleaning and repairing them.</p>
-
-<div class="blockquot">
-<p>In operation, the normal conditions should be such that any two of
-the engine and generator sets may readily carry the average load, the
-third set to be used only as a reserve either to aid the other two
-when the load is unusually heavy or to replace one of the other sets
-when it becomes necessary to clean or repair the latter.</p>
-
-<p>The switchboard may perhaps be best located at H, as a similar
-position on the opposite side of the room A would bring it beneath
-one or more of the steam pipes and thus endanger it should a possible
-leakage occur from these pipes. If located at H, however, it will
-be in line with the machines, and therefore will be subject to the
-disadvantages previously mentioned for such cases; consequently it
-might be as well to place it at the further end of the room, either
-against the partition (shown dotted) of the storage battery room if
-this be built, or else (if no storage battery is to be installed),
-against the end wall itself. The nearer end of the room A would not
-be very desirable for the switchboard installation on account of
-being so far removed from the machines, and therefore more or less
-inaccessible from them. Outside of what has now been mentioned, the
-division of the floor plan and the arrangement therein is practically
-the same as in <a href="#fig2720">fig. 2,720</a>, accordingly what has already
-been stated regarding the former installation applies, therefore, with equal
-force to the present installation.</p></div>
-
-<p><b>Ques. Describe a plant with direct drive.</b></p>
-
-<p>Ans. This type of drive is shown in <a href="#fig2732">fig. 2,732</a>. Each
-engine is directly connected to a generator, that is, the main shafts of both
-are joined together in line so that the generator is driven without
-the aid of a belt.</p>
-
-<p><b>Ques. What is the advantage of direct drive?</b></p>
-
-<p>Ans. The great saving in floor space, which is plainly shown in <a href="#fig2732">fig.
-2,732</a>, the portion A' representing the saving which results over the
-installations previously illustrated in figs. <a href="#fig2720">2,720</a>
-and <a href="#fig2731">2,731</a>.
-<span class="pagenum"><a name="Page_1949" id="Page_1949">1949</a></span></p>
-
-<p><b>Ques. How could the floor space be further reduced?</b></p>
-
-<p>Ans. By employing vertical instead of horizontal engines.</p>
-
-<p><b>Ques. What should be done before drawing the plans for the station?</b></p>
-
-<p>Ans. The types of the various machines and apparatus to be
-installed should, as nearly as possible, be selected in advance so
-that their approximate dimensions may serve as a guide in drawing up
-the plans of the building.</p>
-
-<div class="figcenter">
-  <a name="fig2732"></a>
-  <img src="images/i117.jpg" alt="_" width="600" height="595" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,732.&mdash;Plan of electrical station
-containing direct connected units. As shown, space is provided for an
-extra boiler and engine and generator set, as indicated by the dotted
-lines. Space also exists for a storage battery room if necessary, and
-the partition dividing this room from the engine and dynamo room is
-shown by a dotted line as in previous cases.</p></div>
-
-<p class="blockquot">
-Owing to the great difference in these dimensions for the various
-types, and in fact for the same types as manufactured by different
-concerns, no definite rules regarding the necessary space required can
-<span class="pagenum"><a name="Page_1950" id="Page_1950">1950</a></span>
-here be given. In a general way, however, the author has endeavoured
-to indicate by the drawings the relative amounts of space that
-ordinarily would be considered sufficient.</p>
-
-<p><b>Ques. What is the disadvantage of direct drive?</b></p>
-
-<p>Ans. A more expensive generator is required because it must run
-at the same speed as the engine, which is relatively low as compared
-with that of a belted generator.</p>
-
-<p><b>Station Construction.</b>&mdash;The construction or
-rearrangement of the building intended for the plant is a problem
-that under ordinary conditions would be solved by an architect, or
-at least by an architect with the assistance of an electrical or
-mechanical engineer, still there are many installations where the
-electrical engineer has been compelled to design the building.</p>
-
-<p>In such instances he should be equipped with a general knowledge
-of the construction of buildings.</p>
-
-<p><b>Foundations.</b>&mdash;The foundation may be either natural or
-artificial; that is, it may be composed of rock or soil sufficiently
-solid to serve the purpose unaided, or it may be such as to require
-strengthening by means of wood or iron beams, etc. In either case any
-tendency toward a considerable settling or shifting of the foundation
-due to the action of water, frost, etc., after the station has been
-completed must be well guarded against. To this end special attention
-should be given to the matter of drainage.</p>
-
-<p><b>Ques. How should the foundation be constructed for the machines?</b></p>
-
-<p>Ans. The foundations constructed for the machines should be
-entirely separate from that built for the walls of the building, so
-that the vibrations of the former will not affect the latter.
-<span class="pagenum"><a name="Page_1951" id="Page_1951">1951</a></span></p>
-
-<p class="blockquot">
-If there be several engines and dynamos to be installed, it is best
-to construct two foundations, one for the engines and one for the
-dynamos. If, however, there be considerable distance between the
-units, it may be advisable to build a separate foundation for each
-engine and for each dynamo. The material of which these foundations
-are composed should if the machines be of 20 horse power or over,
-possess considerable strength and be impervious to moisture. Brick,
-stone and concrete are desirable for the purpose, and only the best
-quality of cement mortar should be employed. Care must be taken that
-lime mortar is not used in place of cement mortar, as the former is
-not well adapted to withstand the vibrations of the machines without
-crumbling.</p>
-
-<div class="figcenter">
-  <a name="fig2733"></a>
-  <img src="images/i119.jpg" alt="_" width="600" height="354" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,733.&mdash;Angle for foundation footing.
-In ordinary practice the footing courses upon which the walls of
-the building proper rest, consist of blocks or slabs of stone as
-large as are available and convenient to handle. Footings of brick
-or concrete are also used in very soft soils; footings consisting
-of timber grillage are often employed. A grillage of iron or steel
-beams has also been used successfully. The inclination of the angle
-&#966;, of footing should be about as follows: for metal footings 75°; for
-stone, 60°; for concrete, 45°; for brick, 30°. Damp proof courses
-of slate, or layer of asphalt are laid in or on the foundations or
-lower walls to prevent moisture arising or penetrating by capillary
-attraction.</p></div>
-
-<p><b>Ques. Describe a method of constructing foundations.</b></p>
-
-<p>Ans. An excavation is made to the desired depth and a form inserted
-corresponding to the desired dimensions for the foundation. A
-template is placed on top locating all the centers, with iron pipes
-suspended from these centers, two or three sizes larger than the
-anchor bolts. At the lower end of the pipes are core boxes. Concrete
-<span class="pagenum"><a name="Page_1952" id="Page_1952">1952</a></span>
-is poured into the mould thus formed, and when hard, the forms
-are removed thus leaving the solid foundation. The anchor bolts
-are inserted through the pipes and passed through iron plates at
-the lower end as shown in <a href="#fig2734">fig. 2,734</a>, being secured
-by nuts. By using pipe of two or three bolt diameters a margin is provided
-for adjustment so the bolts will pass through the holes in the frame of
-the machine thus allowing for any slight errors in laying out the
-centers on the template.</p>
-
-<div class="figcenter">
-  <a name="fig2734"></a>
-  <img src="images/i120.jpg" alt="_" width="600" height="473" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,734.&mdash;Concrete foundation showing
-method of installing the anchor bolts.</p></div>
-
-<p><b>Ques. What is the object of the openings in the bottom of the
-foundation?</b></p>
-
-<p>Ans. In case of a defective bolt, it may be replaced by a new one
-without injury to the foundation.</p>
-
-<p><b>Walls.</b>&mdash;Regarding the material for the walls of the station
-iron, stone, brick and wood may be considered. Of these, iron in the
-form of sheets or plates would be entirely fireproof, but
-<span class="pagenum"><a name="Page_1953" id="Page_1953">1953</a></span>
-being itself a conductor would introduce difficulties in maintaining
-a high insulation resistance of the current carrying circuits; it
-would also make the building difficult to heat in winter and to keep
-cool in summer. Stone in the form of limestone, granite or sandstone,
-as a building material is desirable for solidity and attractiveness;
-it is also fireproof and an insulator, but the high cost of such a
-structure for an electrical station usually prohibits its use except
-in private plants or in electrical stations located in large cities.</p>
-
-<div class="figcenter">
-  <a name="fig2735"></a>
-  <img src="images/i121.jpg" alt="_" width="600" height="349" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,735.&mdash;View showing part of template
-for locating anchor bolt centers, pipes through which the bolts pass
-and bolt boxes at lower end of bolts. The completed foundation is
-shown in <a href="#fig2734">fig. 2,734</a>, with template removed. The template
-is made of plain boards upon which the center lines are drawn, and bolt center
-located. Holes are bored at the bolt centers to permit insertion of
-the pipes as shown.</p></div>
-
-<p>Brick is a good material and is readily obtained in nearly all parts
-of the country; it is comparatively cheap, and is also an insulating
-and fireproof material. The bricks selected for this purpose should
-possess true sharp edges, and be hard burned.</p>
-
-<p><b>Ques. What are the features of wood?</b></p>
-
-<p>Ans. Wood forms the cheapest material that can be used for the
-walls of electrical stations, and it usually affords satisfaction,
-but has the disadvantage of high fire risk.
-<span class="pagenum"><a name="Page_1954" id="Page_1954">1954</a></span></p>
-
-<p><b>Roofs</b>.&mdash;In <a href="#fig2736">fig. 2,736</a> is shown one form
-of construction for the roof of an electrical station. The end view here
-presented shows the upper portion of the walls at B and D; these
-support the iron trusses C, and the roof proper MN. In many stations
-there is provided throughout the length of the building, a monitor or
-raised structure on the peak of the roof for ventilation and light.
-The end view of the monitor is shown at S in the figure; its sides
-should be fitted with windows adjustable from the floor.</p>
-
-<div class="figcenter">
-  <a name="fig2736"></a>
-  <img src="images/i122.jpg" alt="_" width="600" height="429" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,736.&mdash;One form of roof construction.</p></div>
-
-<p><b>Floors.</b>&mdash;The floor of the station should be so
-designed that it will be capable of supporting a reasonable weight,
-but as the weights of the machines are borne entirely by their
-respective foundations the normal weight upon the floor will not be
-great; for short periods, however, it may be called upon to support
-one or two machines while they are being placed in position or <span
-class="pagenum"><a name="Page_1955" id="Page_1955">1955</a></span>
-interchanged, and due allowance must be made for such occurrences.</p>
-
-<p>Station floors for engine and dynamo rooms are, as a rule,
-constructed of wood. Where very high currents are generated, however,
-insulated floors of special construction mounted on glass are
-necessary as a protection from injurious shocks. Brick, concrete,
-cement, and other substances of a similar nature are objectionable
-as a floor material for engine and dynamo rooms on account of the
-grit from them, caused by constant wear, being liable to get into the
-bearings of the machines.</p>
-
-<p class="space-below1">Where there are no moving parts, however, as in the boiler room,
-the materials just mentioned possess no disadvantages and are
-preferable to wood on account of being fireproof.</p>
-
-<table border="0" cellspacing="2" summary="_" rules="cols" cellpadding="0">
-<caption><b>THEORETICAL DRAFT PRESSURE IN INCHES OF WATER IN A CHIMNEY 100 FEET HIGH</b><br />
-(For other heights the draft varies directly as the height)</caption>
-  <tbody><tr class="tr_lt_grey">
-      <td rowspan="2" class="tdc">Temp. in<br />Chimney,&nbsp;°F.</td>
-      <td colspan="11" class="tdc u">&nbsp;TEMP. OF EXTERNAL AIR. (BAROMETER 30 INCHES)&nbsp;</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">0°</td> <td class="tdc">10°</td>
-      <td class="tdc">20°</td> <td class="tdc">30°</td>
-      <td class="tdc">40°</td> <td class="tdc">50°</td>
-      <td class="tdc">60°</td> <td class="tdc">70°</td>
-      <td class="tdc">80°</td> <td class="tdc">90°</td>
-      <td class="tdc">100°</td>
-   </tr><tr>
-      <td class="tdc">200°</td> <td class="tdc">&nbsp;.453&nbsp;</td>
-      <td class="tdc">&nbsp;.419&nbsp;</td> <td class="tdc">&nbsp;.384&nbsp;</td>
-      <td class="tdc">&nbsp;.353&nbsp;</td> <td class="tdc">&nbsp;.321&nbsp;</td>
-      <td class="tdc">&nbsp;.292&nbsp;</td> <td class="tdc">&nbsp;.263&nbsp;</td>
-      <td class="tdc">&nbsp;.234&nbsp;</td> <td class="tdc">&nbsp;.209&nbsp;</td>
-      <td class="tdc">&nbsp;.182&nbsp;</td>  <td class="tdc">&nbsp;.157&nbsp;</td>
-   </tr><tr>
-      <td class="tdc">220</td> <td class="tdc">.488</td>
-      <td class="tdc">.453</td> <td class="tdc">.419</td>
-      <td class="tdc">.388</td> <td class="tdc">.355</td>
-      <td class="tdc">.326</td> <td class="tdc">.298</td>
-      <td class="tdc">.269</td> <td class="tdc">.244</td>
-      <td class="tdc">.217</td> <td class="tdc">.192</td>
-   </tr><tr>
-      <td class="tdc">240</td> <td class="tdc">.520</td>
-      <td class="tdc">.488</td> <td class="tdc">.451</td>
-      <td class="tdc">.421</td> <td class="tdc">.388</td>
-      <td class="tdc">.359</td> <td class="tdc">.330</td>
-      <td class="tdc">.301</td> <td class="tdc">.276</td>
-      <td class="tdc">.250</td> <td class="tdc">.225</td>
-   </tr><tr>
-      <td class="tdc">260</td> <td class="tdc">.555</td>
-      <td class="tdc">.528</td> <td class="tdc">.484</td>
-      <td class="tdc">.453</td> <td class="tdc">.420</td>
-      <td class="tdc">.392</td> <td class="tdc">.363</td>
-      <td class="tdc">.334</td> <td class="tdc">.309</td>
-      <td class="tdc">.282</td> <td class="tdc">.257</td>
-   </tr><tr>
-      <td class="tdc">280</td> <td class="tdc">.584</td>
-      <td class="tdc">.549</td> <td class="tdc">.515</td>
-      <td class="tdc">.482</td> <td class="tdc">.451</td>
-      <td class="tdc">.422</td> <td class="tdc">.394</td>
-      <td class="tdc">.365</td> <td class="tdc">.340</td>
-      <td class="tdc">.313</td> <td class="tdc">.288</td>
-   </tr><tr>
-      <td class="tdc">300</td> <td class="tdc">.611</td>
-      <td class="tdc">.576</td> <td class="tdc">.541</td>
-      <td class="tdc">.511</td> <td class="tdc">.478</td>
-      <td class="tdc">.449</td> <td class="tdc">.420</td>
-      <td class="tdc">.392</td> <td class="tdc">.367</td>
-      <td class="tdc">.340</td> <td class="tdc">.315</td>
-   </tr><tr>
-      <td class="tdc">320</td> <td class="tdc">.637</td>
-      <td class="tdc">.603</td> <td class="tdc">.568</td>
-      <td class="tdc">.538</td> <td class="tdc">.505</td>
-      <td class="tdc">.476</td> <td class="tdc">.447</td>
-      <td class="tdc">.419</td> <td class="tdc">.394</td>
-      <td class="tdc">.367</td> <td class="tdc">.342</td>
-   </tr><tr>
-      <td class="tdc">340</td> <td class="tdc">.662</td>
-      <td class="tdc">.638</td> <td class="tdc">.593</td>
-      <td class="tdc">.563</td> <td class="tdc">.530</td>
-      <td class="tdc">.501</td> <td class="tdc">.472</td>
-      <td class="tdc">.443</td> <td class="tdc">.419</td>
-      <td class="tdc">.392</td> <td class="tdc">.367</td>
-   </tr><tr>
-      <td class="tdc">360</td> <td class="tdc">.687</td>
-      <td class="tdc">.653</td> <td class="tdc">.618</td>
-      <td class="tdc">.588</td> <td class="tdc">.555</td>
-      <td class="tdc">.526</td> <td class="tdc">.497</td>
-      <td class="tdc">.468</td> <td class="tdc">.444</td>
-      <td class="tdc">.417</td> <td class="tdc">.392</td>
-   </tr><tr>
-      <td class="tdc">380</td> <td class="tdc">.710</td>
-      <td class="tdc">.676</td> <td class="tdc">.641</td>
-      <td class="tdc">.611</td> <td class="tdc">.578</td>
-      <td class="tdc">.549</td> <td class="tdc">.520</td>
-      <td class="tdc">.492</td> <td class="tdc">.467</td>
-      <td class="tdc">.440</td> <td class="tdc">.415</td>
-   </tr><tr>
-      <td class="tdc">400</td> <td class="tdc">.732</td>
-      <td class="tdc">.697</td> <td class="tdc">.662</td>
-      <td class="tdc">.632</td> <td class="tdc">.598</td>
-      <td class="tdc">.570</td> <td class="tdc">.541</td>
-      <td class="tdc">.513</td> <td class="tdc">.488</td>
-      <td class="tdc">.461</td> <td class="tdc">.436</td>
-   </tr><tr>
-      <td class="tdc">420</td> <td class="tdc">.753</td>
-      <td class="tdc">.718</td> <td class="tdc">.684</td>
-      <td class="tdc">.653</td> <td class="tdc">.620</td>
-      <td class="tdc">.591</td> <td class="tdc">.563</td>
-      <td class="tdc">.534</td> <td class="tdc">.509</td>
-      <td class="tdc">.482</td> <td class="tdc">.457</td>
-   </tr><tr>
-      <td class="tdc">440</td> <td class="tdc">.774</td>
-      <td class="tdc">.739</td> <td class="tdc">.705</td>
-      <td class="tdc">.674</td> <td class="tdc">.641</td>
-      <td class="tdc">.612</td> <td class="tdc">.584</td>
-      <td class="tdc">.555</td> <td class="tdc">.530</td>
-      <td class="tdc">.503</td> <td class="tdc">.478</td>
-   </tr><tr>
-      <td class="tdc">460</td> <td class="tdc">.793</td>
-      <td class="tdc">.758</td> <td class="tdc">.724</td>
-      <td class="tdc">.694</td> <td class="tdc">.660</td>
-      <td class="tdc">.632</td> <td class="tdc">.603</td>
-      <td class="tdc">.574</td> <td class="tdc">.549</td>
-      <td class="tdc">.522</td> <td class="tdc">.497</td>
-   </tr><tr>
-      <td class="tdc">480</td> <td class="tdc">.810</td>
-      <td class="tdc">.776</td> <td class="tdc">.741</td>
-      <td class="tdc">.710</td> <td class="tdc">.678</td>
-      <td class="tdc">.649</td> <td class="tdc">.620</td>
-      <td class="tdc">.591</td> <td class="tdc">.566</td>
-      <td class="tdc">.540</td> <td class="tdc">.515</td>
-   </tr><tr>
-      <td class="tdc">500</td> <td class="tdc">.829</td>
-      <td class="tdc">.791</td> <td class="tdc">.760</td>
-      <td class="tdc">.730</td> <td class="tdc">.697</td>
-      <td class="tdc">.669</td> <td class="tdc">.639</td>
-      <td class="tdc">.610</td> <td class="tdc">.586</td>
-      <td class="tdc">.559</td> <td class="tdc">.534</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="space-above1"><b>Chimneys.</b>&mdash;These are generally
-constructed of brick and iron, sometimes of concrete. Iron chimneys
-cost less than brick chimneys, necessitate less substantial
-foundations, and are free from the liability of cracking. They must
-be painted to prevent corrosion, are less substantial, and lose
-considerably more heat by radiation than do brick chimneys.
-<span class="pagenum"><a name="Page_1956" id="Page_1956">1956</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2737"></a>
-  <img src="images/i-0313.jpg" alt="_" width="500" height="680" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,737.&mdash;An example of direct connected
-unit with gas engine power. The view shows a Westinghouse 200 kva.,
-4,000 volt, three phase, 60 cycle alternator direct connected to a
-gas engine.</p></div>
-<p><span class="pagenum"><a name="Page_1957" id="Page_1957">1957</a></span></p>
-<div class="figcenter">
-  <a name="fig2738"></a>
-  <img src="images/i125.jpg" alt="_" width="600" height="599" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,738.&mdash;Curves showing comparative costs
-of chimney and mechanical draft. In certain of these, the cost of the
-existing chimney is known, and that of the complete mechanical draft
-plant is estimated, while in others, the cost of mechanical draft
-installation is determined from the contract price, and the expense
-of a chimney to produce equivalent results is calculated. Costs are
-shown for both single, forced and induced engine driven fans and
-for duplex engine driven plants, in which either fan may serve as a
-relay. An apparatus of the latter type is the most expensive, and
-finds its greatest use where economizers are employed.</p></div>
-
-<p>Both brick and iron chimneys, require an inner wall or lining of
-brick, which forms the flue proper, and in order that this wall be
-not cracked by sudden cooling an air space is left between it and
-the outer wall. In a brick chimney the inner wall need not extend
-much beyond half the height of the chimney, but when iron is used it
-should reach to the top.</p>
-
-<p><span class="pagenum"><a name="Page_1958" id="Page_1958">1958</a></span>
-<b>Ques. Upon what does the force of natural draught in a chimney depend?</b></p>
-
-<p>Ans. It depends upon the difference between the weight of the column
-of hot gases inside the chimney and the weight of a like column of
-the cold external air.</p>
-
-<div class="figcenter">
-  <a name="fig2739"></a>
-  <img src="images/i-0314-1.jpg" alt="_" width="400" height="687" />
-  <img src="images/i-0314-2.jpg" alt="_" width="400" height="672" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,739 and 2,740.&mdash;Substituting
-mechanical draught in place of chimney. The relative proportions of a
-brick chimney, and of the smoke pipe required when mechanical draft
-is introduced are forcibly shown in the illustrations, which show the
-works of the B.F. Sturtevant Co., at Jamaica Plain, Mass. The removal
-of the boilers to a position too far distant from the existing
-chimney to permit of its longer fulfilling its office, led to the
-substitution of an induced draft fan and the subsequent removal of
-the chimney. The present stack or smoke pipe, barely visible in
-fig. 2,740, extends only 31 feet above the
-ground, and no trouble is experienced from smoke.</p></div>
-
-<p><b>Ques. How is the intensity of the draught expressed?</b></p>
-
-<p>Ans. In terms of the number of inches of a water column sustained by
-the pressure produced.
-<span class="pagenum"><a name="Page_1959" id="Page_1959">1959</a></span></p>
-
-<p><b>Ques. Are high chimneys necessary?</b></p>
-
-<p>Ans. No.</p>
-
-<p class="blockquot">
-<i>Chimneys above 150 feet in height are very costly, and their
-increased cost is not justified by increased efficiency.</i></p>
-
-<div class="figcenter">
-  <a name="fig2741"></a>
-  <img src="images/i127.jpg" alt="_" width="600" height="419" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,741 to 2,744.&mdash;Installation of
-forced draft system to old boiler plant. The figures illustrate
-the simplest method. The fan which is of steel plate with direct
-connected double cylinder engine, is placed immediately over the
-end of a brick duct into which the air is discharged. This duct is
-carried under ground across the front of the boilers, to the ash
-pits of each of which connection is made through branch ducts. Each
-branch duct opening is provided with special ash pit damper, operated
-by notched handle bar, as illustrated in the detail. This method of
-introduction serves to distribute the air within the ash pit, and to
-secure even flow through the fuel upon the grate above. Of course,
-the ash pit doors must remain closed in order to bring about this
-result. A chimney of sufficient height to merely discharge the gases
-above objectionable level is all that is absolutely necessary with
-this arrangement. Although the introduction of a fan in an old plant
-is usually evidence of the insufficiency of the existing chimney
-to meet the requirements, such a chimney, will, however, usually
-serve as a discharge pipe for the gases when the fan is employed.
-The fan thus becomes more than a mere auxiliary to the chimney; it
-practically supplants it so far as the method of draught production
-is concerned.</p></div>
-
-<div class="blockquot">
-<p>The latest chimney practice is to build two or more small chimneys
-instead of one large one. A notable example is the Spreckels Sugar
-Refinery in Philadelphia, where three separate chimneys are used for
-<span class="pagenum"><a name="Page_1960" id="Page_1960">1960</a></span>
-one boiler plant of 7,500 horse power. The three chimneys are said to
-have cost several thousand dollars less than an equivalent single
-chimney.</p>
-
-<p><b>Very tall chimneys</b> have been characterized by one writer as
-"<i>monuments to the folly of their builders.</i>"</p></div>
-
-<div class="figcenter">
-  <a name="fig2745"></a>
-  <img src="images/i128.jpg" alt="_" width="600" height="459" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,745 and 2,746.&mdash;Comparison of chimney
-draft and mechanical draft. The illustrations show a plant of 2,400
-H.P. of modern water tube boilers, 12 in number, set in pairs and
-equipped with economizers. Fig. 2,745 indicates the location of a
-chimney, 9 feet in internal diameter by 180 feet high, designed to
-furnish the necessary draft; fig. 2,746 represents the same plant
-with a complete duplex induced draught apparatus substituted for the
-chimney, and placed above the economizer connections. Each of the
-two fans is driven by a special engine, direct connected to the fan
-shaft, and each is capable of producing draft for the entire plant. A
-short steel plate stack unites the two fan outlets and discharges the
-gases just above the boiler house roof. All of the room necessary for
-the chimney is saved, and no valuable space is required for the fans.</p></div>
-
-<p><b>Ques. How is mechanical draft secured?</b></p>
-
-<p>Ans. In two ways, known respectively as <i>induced draught</i> and
-<i>forced draught</i>.</p>
-
-<p><b>Ques. Describe the method of induced draft.</b></p>
-
-<p>Ans. A fan is located in the smoke flue, and which in operation draws
-<span class="pagenum"><a name="Page_1961" id="Page_1961">1961</a></span>
-the gases through the furnace and discharges them into a <i>short</i>
-chimney.</p>
-
-<p><b>Ques. Describe the method of forced draft.</b></p>
-
-<p>Ans. In this method, air is forced into the furnace underneath
-the grate bars by means of a fan or a steam jet blower.</p>
-
-<div class="figcenter">
-  <a name="fig2747"></a>
-  <img src="images/i-0315.jpg" alt="_" width="600" height="392" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,747.&mdash;Forced draft plant with hollow
-bridge wall at the Crystal Water Co., Buffalo, N. Y. The air is
-delivered to the ash pit via the hollow bridge wall, being supplied
-under pressure by the blower seen at the side of the boiler setting.
-As shown, the blower is operated by a small reciprocating engine;
-however, compact blowing units with steam turbine drive can be had
-and which are designed to be placed in the boiler setting.</p></div>
-
-<p><b>Ques. What is the application of the two systems?</b></p>
-
-<p>Ans. Induced draft is installed mostly in new plants, while forced draft
-is better adapted to old plants.</p>
-
-<p class="space-below1"><b>Steam Turbines</b>.&mdash;It is not the
-author's intention to discuss at length the steam end of the electric
-plant, because too much space would be required, and also because
-the subject belongs properly to the field of mechanical engineering
-rather than electrical engineering. However, because of the recent
-introduction of the steam turbine for the direct driving of large
-generators, and the fact that it is now almost universally used in
-large central stations, a detailed explanation of its principles and
-construction may not be out of place.
-<span class="pagenum"><a name="Page_1962" id="Page_1962">1962</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2748"></a>
-  <img src="images/i-0316.jpg" alt="_" width="600" height="259" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,748.&mdash;Longitudinal section of
-elementary Parsons type steam turbine. The turbine consists
-essentially of a fixed casing, or cylinder, and a revolving spindle
-or drum. The ends of the spindle are extended in the form of a shaft,
-carried in two bearings A and B, and, excepting the small parts of
-the governing mechanism and the oil pump, these bearings are the only
-rubbing parts in the entire turbine. Steam enters from the steam
-pipe at C and passes through the main throttle or regulating valve
-D, which, as actually constructed, is a balanced valve. This valve
-is operated by the governor through suitable controlling mechanism.
-The steam enters the cylinder through the passage E and, turning
-to the left passes through alternate stationary and revolving rows
-of blades, finally emerging from them at F and flowing through the
-connection G to the condenser or to the atmosphere, depending upon
-whether the turbine is condensing or non-condensing. Each row of
-blades, both stationary and revolving, extends completely around
-the turbine and the steam flows through the full annulus between
-the spindle and the cylinder. In an ideal turbine the lengths of
-the blades and the diameter of the spindle which carries them
-would continuously and gradually increase from the steam inlet to
-the exhaust. Practically, however, the desired effect is produced
-by making the spindle in steps, there being generally three such
-steps or stages, H, J and K. The blades in each step are arranged
-in groups of increasing length. At the beginning of each of the
-larger steps, the blades are usually shorter than at the end of the
-preceding smaller step, the change being made in such a way that the
-correct relation of blade length to spindle diameter is secured. The
-steam, acting as previously described, produces a thrust tending to
-force the spindle toward the left, as seen in the cut. This thrust,
-however, is counteracted by the "balance pistons," L, M and N,
-which are of the necessary diameter to neutralize the thrust on the
-spindle steps, H, J and K, respectively. These elements are called
-"pistons" for convenience, although they do not come in contact with
-the cylinder, but both the pistons and the cylinder are provided
-with alternate rings which form a labyrinth packing to retard the
-leakage of steam. In order that each balance piston may have the
-proper pressure on both sides, equalizing passages O, P and Q are
-provided connecting the balance pistons with the corresponding stages
-of the blading. The end thrust being thus practically neutralized by
-means of the balance pistons, the spindle "floats" so that it can be
-easily moved in one direction or the other. In order to definitely
-fix the position of the spindle, a small adjustable collar bearing is
-provided at R, inside the housing of the main bearing B. This collar
-bearing is adjustable so as to locate and hold the spindle in such
-position so that there will be such a clearance between the rings of
-the balance piston and those of the cylinder, that the leakage of
-steam will be reduced to a minimum and, at the same time, prevent
-actual contact under varying conditions of temperature. Where the
-shaft passes out of the cylinder, at S and T, it is necessary to
-provide against in-leakage of air or out-leakage of steam by means of
-glands. These glands are made tight by water packing without metallic
-contact. The shaft of the turbine is extended at U and coupled to
-the shaft of the alternator by means of a flexible coupling. The
-high pressure turbines are so proportioned that, when using steam as
-previously described, they have enough capacity to take care of the
-ordinary fluctuations of load when controlled by the governor through
-the valve D, thus insuring maximum economy of steam consumption at
-approximately the rated load. To provide for overloads, the valve V
-is supplied to admit steam to an intermediate stage of the turbine.
-This valve shown diagrammatically in the illustration, is arranged
-to be operated by the governor and is, according to circumstances,
-located either as shown by the illustration, or at another stage of
-the turbine.</p></div>
-
-<p><span class="pagenum"><a name="Page_1963" id="Page_1963">1963</a></span></p>
-<div class="figcenter">
-  <a name="fig2749"></a>
-  <img src="images/i131.jpg" alt="_" width="600" height="451" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,749.&mdash;Arrangement of blading in
-Parsons type turbine, consisting of alternate moving and stationary
-blades. The path taken by the steam is indicated by the arrows.</p></div>
-
-<p>A turbine is a machine in which a rotary motion is obtained by
-transference of the <i>momentum</i> of a fluid or gas. In general the
-fluid is guided by fixed blades, attached to a casing, and, impinging
-on other blades mounted on a drum or shaft, causing the latter to
-revolve.</p>
-
-<p>Turbines are classed in various ways as: 1, <i>radial flow</i>,
-when the steam enters near the center and escapes toward the
-circumference; and 2, <i>parallel flow</i>, when the steam travels
-<i>axially</i> or parallel to the length of the turning body.</p>
-
-<p>Turbines are commonly, yet erroneously classed as:<br />
-&emsp;&emsp;&emsp;1. Impulse;<br />
-&emsp;&emsp;&emsp;2. Reaction.</p>
-
-<p><span class="pagenum"><a name="Page_1964" id="Page_1964">1964</a></span>
-<b>Ques. What is the distinction between these two types?</b></p>
-
-<p class="space-below1">Ans. In the so called impulse type, <i>steam
-enters and leaves the passages between the vanes at the same
-pressure</i>. In the so called reaction type, <i>the pressure is less on
-the exit side of the vanes than on the entrance side</i>.</p>
-
-<div class="figcenter">
-  <a name="fig2750"></a>
-  <img src="images/i132.jpg" alt="_" width="600" height="457" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,750.&mdash;Sectional view of
-Parsons-Westinghouse turbine, showing rotor and governor.</p></div>
-
-<div class="blockquot">
-<p><a href="#fig2750">Fig. 2,750</a> is a sectional view of the Parsons-Westinghouse
-parallel flow turbine. Steam from the boiler enters first a receiver in which
-are the governor controlled admission valves. These valves are
-actuated by a centrifugal governor.</p>
-
-<p><i>Steam does not enter the turbine in a continuous blast, but
-intermittently, or in puffs.</i> The speed regulation is therefore
-accomplished by proportioning the duration of these puffs to the load
-of the engine, this being effected by the governor, <a href="#fig2752">fig. 2,752</a>.</p>
-
-<p>The governor of the turbine has only to move a small pilot valve,
-or slide, E, which admits steam under the piston F, and lifts the
-throttle valve proper off its seat.</p>
-
-<p>As soon as the pilot valve closes, the spring shifts the main
-throttle valve. Thus, at light loads, the main throttle or admission
-valve is continually opening and shutting at uniform intervals, the
-length of time during which it remains open depending upon the load.</p>
-
-<p>As the load increases, the duration of the valve opening also
-increases, until at full load the valve does not reach its seat at
-all and the steam flows steadily through the turbine. The steam thus
-admitted flows into the annular passage A, <a href="#fig2750">fig. 2,750</a>,
-by the opening S, and then past the blades, revolving the rotor.
-<span class="pagenum"><a name="Page_1965" id="Page_1965">1965</a></span></p>
-
-<p>When the load increases above the normal rated amount a secondary
-pilot valve is moved by the same means, this in turn admitting steam
-to a piston, similar to F, which lifts another throttle valve. This
-admits steam into the annular space I, so that it acts upon the
-larger diameter of the drum or rotor, giving largely increased power
-for the time being.</p>
-
-<p>The levers or arms of the governor are mounted upon knife edges
-instead of pins, making it extremely sensitive. The tension spring
-may be adjusted by hand while the turbine is running.</p></div>
-
-<div class="figcenter">
-  <a name="fig2751"></a>
-  <img src="images/i133.jpg" alt="_" width="600" height="225" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,751.&mdash;Sectional view of a combination
-impulse and reaction single flow turbine. This is a modification
-of the single flow type, in which the smallest barrel of reaction
-blading is replaced by an impulse wheel. Steam is admitted to the
-nozzle block A, is expanded in the nozzles and discharged against a
-portion of the periphery of the impulse wheel. The intermediate and
-low pressure stages are identical with the corresponding stages in
-the single flow type. The substitution of the impulse element for
-the high pressure section of reaction blading has no influence one
-way or another on the efficiency. That is to say the efficiency of
-an impulse wheel is about the same at the least efficient section
-of reaction blading. This design is attractive, however, in that
-it shortens the machine materially, and gives a stiffer design of
-rotor. The entering steam is confined in the nozzle chamber until its
-pressure and temperature have been materially reduced by expanding
-through the nozzles. As the nozzle chamber is cast separately from
-the main cylinder, the temperature and pressure differences to which
-the cylinder is subjected are correspondingly lessened. However,
-probably on account of its small diameter at the high pressure
-section, the straight Parsons type has always shown itself to be
-adequate for all of the steam pressures and temperatures encountered
-in ordinary practice.</p></div>
-
-<div class="blockquot">
-<p>The governor does not actually move the pilot valve, but shifts the
-point L in <a href="#fig2752">fig. 2,752</a>. A reciprocating motion is given
-to the rod I by a small eccentric on the governor shaft; this is driven by worm
-gearing shown near O in <a href="#fig2750">fig. 2,750</a>, so that the eccentric
-makes one revolution to about eight of the turbine. Thus, with a turbine
-running 1,200 revolutions, the rod I would be moved up and down 150
-times per minute. As the points A and H are fixed, the motion is
-conveyed to the small pilot valve E, thus giving 150 puffs a minute.
-The governor in shifting the point L brings the edge of the pilot
-valve nearer the port and so cuts off the steam earlier.</p>
-
-<p>The annular diameter or space between the rotor and the stator is
-gradually increased from inlet to exhaust, the blades being made
-longer in each ring. When the mechanical limit is reached, the
-<span class="pagenum"><a name="Page_1966" id="Page_1966">1966</a></span>
-diameter of the rotor is increased as at I and D so as to keep the
-length of blade within bound.</p>
-
-<p>Balance pistons as at B, C, F are attached to the rotor, their
-office being to oppose end thrust upon those blades in corresponding
-diameter of the rotor. Communication is established through the
-passage V and pipe M between the eduction pipe and the back of these
-pistons, thus increasing the efficiency of their balancing and also
-taking care of any leakage past them.</p>
-
-<p>A small thrust bearing T prevents end play of the rotor, and is
-adjustable to maintain the proper clearance between the rings of
-blades; this varies from &#8539; inch at the admission to 1 inch at the
-exhaust. This bearing also takes up any extra unbalanced thrust. A
-turbine should operate with a high vacuum, because without this it
-does not compare favorably with an ordinary reciprocating engine from
-the point of economy.</p></div>
-
-<div class="figcenter">
-  <a name="fig2752"></a>
-  <img src="images/i134.jpg" alt="_" width="600" height="301" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,752.&mdash;Sectional view of governor of the
-Parsons-Westinghouse turbine.</p></div>
-
-<div class="blockquot">
-<p><i>Separate air pumps are provided to create the vacuum.</i></p>
-
-<p>Where the ordinary type of vertical air pump is employed, a booster
-or <i>vacuum increaser</i> is added, as nothing below 26 inches is
-advisable, 28 and 29 inches being always striven for. It is also
-preferable to use a certain amount of <i>super-heat</i> with steam
-turbines.</p>
-
-<p>To assist in producing the high vacuum, exhaust passages are made
-large, the eduction passage E in <a href="#fig2750">fig. 2,750</a> being nearly
-twenty-three times the area of the steam pipe.</p>
-
-<p>Among other details, a noteworthy feature is a small oil pump K,
-which circulates oil through bearings of the machinery, the oil being
-drawn from the tank under the governor shaft and gravitating there
-after use. No pressure of oil is employed. Stuffing rings prevent
-leakage; these consist of alternate grooves and collars in shaft and
-bearing, like the grooves in an indicator piston.</p></div>
-
-<p><span class="pagenum"><a name="Page_1967" id="Page_1967">1967</a></span>
-<b>Ques. Why is a high vacuum desirable?</b></p>
-
-<p>Ans. Because the turbine is capable of expanding the steam to a very
-low terminal pressure, and this is necessary for economy.</p>
-
-<p><b>Ques. What may be said of the working pressures for turbines?</b></p>
-
-<p class="space-below1">Ans. To meet the varied conditions of
-service, turbines are designed to operate with: 1, high pressure, 2,
-low pressure, or 3, mixed pressure.</p>
-
-<div class="figcenter">
-  <a name="fig2753"></a>
-  <img src="images/i135.jpg" alt="_" width="600" height="171" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,753.&mdash;Sectional view of a double flow
-turbine. The maximum economical capacity of a single flow turbine
-is limited by the rotative speed. The economical velocity at which
-the steam may pass through the blades of the turbine depends on the
-velocity of the moving blades. The capacity of the turbine depends
-on the weight of the steam passed per unit of time, which in turn
-depends on the mean velocity and the height of the blades. For a
-given rotative speed, the mean diameter of blade ring practicable
-is limited by the allowable stresses due to centrifugal force, and
-there is a practical limit for the height of the blades. Now if the
-rotative speed be taken only half as great, the maximum diameter
-of the rotor may be doubled and, without increasing the height of
-the blades, the capacity of the turbine will be doubled. So with
-the single flow steam turbine as well as with the single crank
-reciprocating engine, there is a practical limiting economical
-capacity for any given speed. If this limit be reached with a single
-crank reciprocating engine, a unit of double the power may be
-produced at the same speed by coupling two single crank engines to
-one shaft. Similar results are secured making a double flow turbine
-which is in effect, as will be seen from the figure, two single flow
-turbines made up in a single rotor in a single casing with a common
-inlet and two exhausts. Steam enters the nozzle block, acts on the
-impulse element, and then the current divides, one-half of the steam
-going through the reaction blading at the left of the impulse wheel;
-the remainder passes over the top of the impulse wheel and through
-the impulse blading at the right.</p></div>
-
-<div class="blockquot">
-<p>High pressure turbines operate at about the same initial pressure as
-triple expansion engines.</p>
-
-<p>Low pressure, as here applied, means the exhaust pressure of the
-reciprocating engine from which the exhaust steam passes through the
-turbine before entering the condenser.</p>
-
-<p>Mixed pressure implies that the exhaust steam is supplemented, for
-heavy loads, by the admission of live steam.</p></div>
-
-<p><span class="pagenum"><a name="Page_1968" id="Page_1968">1968</a></span>
-<b>Ques. What determines the working pressure?</b></p>
-
-<p class="space-below1">Ans. When all the power is furnished by
-the turbine, it is designed for high pressure; when operated in
-combination with a reciprocating engine, low pressure is used for
-constant load, and mixed pressure for variable load.</p>
-
-<div class="figcenter">
-  <a name="fig2754"></a>
-  <img src="images/i136.jpg" alt="_" width="600" height="228" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,754.&mdash;Sectional view of a semi-double
-flow turbine. This is a modification in which the intermediate
-section of reaction blading is single flow, and the low pressure
-section only is double flow. This would be analogous to a four
-cylinder triple expansion engine, that is, one with one high
-pressure, one intermediate pressure and two low pressure cylinders&mdash;a
-design not at all uncommon in very large engines in which the
-required dimensions of a single low pressure cylinder would be
-prohibitive. Such turbines are useful for capacities greater than
-is desirable for a single flow turbine, and which are still below
-the maximum possibilities of a double flow turbine of the same
-speed. In such machines the best efficiency is secured by making the
-intermediate blading in a single section large enough to pass the
-entire quantity of steam. A "dummy" similar to those used on the
-single flow Parsons type, shown at the right of the impulse wheel,
-compels all of the steam to pass through the single intermediate
-section of the reaction blading, and balances the end thrust due to
-this section. When the steam issues from the intermediate section,
-the current is divided, one-half passing directly to the adjacent low
-pressure section, while the other half passes through the holes shown
-in the periphery of the hollow rotor and through the rotor itself,
-beyond the dummy ring, into the other low pressure section at the
-left hand end of the turbine.</p></div>
-
-<div class="blockquot">
-<p>NOTE.&mdash;There are logical engineering reasons for the existence of
-the several types of turbine, viz., single flow, double flow, and
-semi-double flow. The double flow turbine is not inherently superior
-to the single flow design, but is used under conditions for which the
-single flow machine is unsuitable. Similarly, the semi-double flow is
-recommended only for conditions which it can meet more satisfactorily
-than either of the other types.</p>
-
-<p>NOTE.&mdash;Low pressure turbines use exhaust steam from non-condensing
-engines and are valuable as an adjunct to existing plants for the
-purpose of increasing economy and capacity with a minimum outlay for
-new equipment.</p>
-
-<p>NOTE.&mdash;Bleeder turbines are for use in plants which are required to
-furnish, not only power, but also considerable and varying quantities
-of low pressure steam for heating purposes. In these turbines a part
-of the steam after it has done work in the high pressure stages may
-be diverted to the heating system, and the remainder expanded through
-the low pressure blading and exhausted into the condenser. In this
-way none of the energy of the heating steam, due to the difference of
-pressure between the boiler and the heating system is wasted. On the
-other hand if no steam is required for heating purposes, the turbine
-operates just as efficiently as though the bleeder feature were
-absent.</p></div>
-
-<p><span class="pagenum"><a name="Page_1969" id="Page_1969">1969</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2755"></a>
-  <img src="images/i137.jpg" alt="_" width="600" height="407" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,755.&mdash;Westinghouse valve gear with
-steam relay. In the smaller turbines, the governor acts directly on
-the steam admission valves, opening first the primary valve, and
-then, if necessary, the secondary valve, after the primary is fully
-open. In turbines of the single flow Parsons type, the governor
-actuates two small valves controlling ports leading to steam relay
-cylinders which operate the admission valves. The little valve
-controlling the relay cylinder for the secondary valve has more lap
-than the other and consequently does not come into action until the
-primary valve has attained its maximum effective opening. The figure
-shows the general design of this type of valve gear.</p></div>
-
-<div class="blockquot">
-<p><i>The De Laval steam turbine</i> is termed by its builders a high speed
-rotary steam engine. It has but a single wheel, fitted with vanes or
-buckets of such curvature as has been found to be best adapted for
-receiving the impulse of the steam jet. There are no stationary or
-guide blades, the angular position of the nozzles giving direction
-to the jet. The nozzles are placed at an angle of 20 degrees to the
-plane of motion of the buckets. The best energy in the steam is
-practically devoted to the production of velocity in the expanding
-or divergent nozzle, and the velocity thus attained by the issuing
-jet of steam is about 4,000 feet per second. To attain the maximum
-efficiency, the buckets attached to the periphery of the wheel
-against which this jet impinges should have a speed of about 1,900
-feet per second, but, owing to the difficulty of producing a material
-for the wheel strong enough to withstand the strains induced by such
-a high speed, it has been found necessary to limit the peripheral
-speed to 1,200 or 1,300 feet per second.</p>
-
-<p>It is well known that in a correctly designed nozzle the adiabatic
-expansion of the steam from maximum to minimum pressure will
-convert the entire static energy of the steam into kinetic energy.
-Theoretically this is what occurs in the De Laval nozzle. The
-<span class="pagenum"><a name="Page_1970" id="Page_1970">1970</a></span>
-expanding steam acquires great velocity, and the energy of the jet
-of steam issuing from the nozzle is equal to the amount of energy
-that would be developed if an equal volume of steam were allowed to
-adiabatically expand behind the piston of a reciprocating engine,
-a condition, however, which for obvious reasons has never yet been
-attained in practice with the reciprocating engine. But with the
-divergent nozzle the conditions are different.</p>
-
-<p><i>The Curtis turbine</i> is built by the General Electric Company at
-their works in Schenectady, N. Y., and Lynn, Mass. They are of the
-horizontal and vertical types. In the vertical type the revolving
-parts are set upon a vertical shaft, the diameter of the shaft
-corresponding to the size of the machine.</p>
-
-<p>The shaft is supported by and runs upon a step bearing at the bottom.
-This step bearing consists of two cylindrical cast iron plates
-bearing upon each other and having a central recess between them
-into which lubricating oil is forced under pressure by a steam or
-electrically driven pump, the oil passing up from beneath.</p></div>
-
-<div class="figcenter">
-  <a name="fig2756"></a>
-  <img src="images/i138.jpg" alt="_" width="600" height="350" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,756 and 2,757.&mdash;Westinghouse valve
-gear with oil relay. Governors for the larger turbines, particularly
-those of the combination impulse and reaction double, or single
-double flow type, employ an oil relay mechanism, as shown in the
-figure, for operating the steam valves. In these turbines the
-lubricating oil circulating pump, maintains a higher pressure than is
-required for the lubricating system. The governor controls a small
-relay valve A which admits pressure oil to, or exhausts it from the
-operating cylinder. When oil is admitted to the operating cylinder
-raising the piston, the lever C lifts the primary valve E. The
-lever D moves simultaneously with C, but on account of the slotted
-connection with the stem of the secondary valve F, the latter does
-not begin to lift until the primary valve is raised to the point
-at which its effective opening ceases to be increased by further
-upward travel. In the Westinghouse designs, the operating valve, A
-is connected not only to the governor, but also to a vibrator, which
-gives it a slight but continuous reciprocating motion, while the
-governor controls its mean position. The effect of this is manifested
-in a slight pulsation throughout the entire relay system, which, so
-to speak, keeps it "alive" and ready to respond instantly, to the
-smallest change in the position of the governor. The oil relay can be
-made sufficiently powerful to operate valves of any size, and it is
-also in effect a safety device in that any failure of the lubricating
-oil supply will automatically and immediately shut off the steam and
-stop the turbine.</p></div>
-
-<p><span class="pagenum"><a name="Page_1971" id="Page_1971">1971</a></span></p>
-<p class="blockquot">
-A weighted accumulator is sometimes installed in connection with
-the oil pipe as a convenient device for governing the step bearing
-pumps, and also as a safety device in case the pumps should fail, but
-it is seldom required for the latter purpose, as the step bearing
-pumps have proven after a long service in a number of cases, to be
-reliable. The vertical shaft is also held in place and kept steady
-by three sleeve bearings one just above the step, one between the
-turbine and generator, and the other near the top.</p>
-
-<div class="figcenter">
-  <a name="fig2758"></a>
-  <img src="images/i139.jpg" alt="_" width="600" height="215" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,758.&mdash;Elevation of new turbine
-central station erected by the Boston Edison Co. The turbine room is
-68 feet, 4 inches wide and 650 feet long from outside to outside of the
-walls. The boiler room is 149 feet, 6 inches by 640 feet and equipped
-with twelve groups of boiler, one group consisting of eight 512 H.P.
-boilers for each turbine. The switching arrangements are located in
-a separate building as shown in the elevation. The total floor space
-covered by boiler room, turbine room and switchboard room is 2.64
-square feet per kw. The boilers are all on the ground floor.
-See <a href="#fig2714">fig. 2,714</a> for plan.</p></div>
-
-<div class="blockquot">
-<p>These guide bearings are lubricated by a standard gravity feed
-system. It is apparent that the amount of friction in the machine is
-very small, and as there is no end thrust caused by the action of the
-steam, the relation between the revolving and stationary blades may
-be maintained accurately. As a consequence, therefore, the clearances
-are reduced to the minimum.</p>
-
-<p>The Curtis turbine is divided into two or more stages, and each
-stage has one, two or more sets of revolving blades bolted upon
-the peripheries of wheels keyed to the shaft. There are also the
-corresponding sets of stationary blades bolted to the inner walls of
-the cylinder or casing.</p>
-
-<p>The governing of speed is accomplished in the first set of nozzles
-and the control of the admission valves here is effected by means of
-a centrifugal governor attached to the top end of the shaft. This
-<span class="pagenum"><a name="Page_1972" id="Page_1972">1972</a></span>
-governor, by a very slight movement, imparts motion to levers, which
-in turn work the valve mechanism.</p>
-
-<p>The admission of steam to the nozzles is controlled by piston valves
-which are actuated by steam from small pilot valves which are in turn
-under the control of the governor.</p></div>
-
-<div class="figcenter">
-  <a name="fig2759"></a>
-  <img src="images/i-0317.jpg" alt="_" width="600" height="481" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,759.&mdash;Illustration of a weir. To
-make a weir, place a board across the stream at some point which will
-allow a pond to form above. The board should have a notch cut in
-it with both side edges and the bottom sharply beveled toward the
-intake, as shown in the above cut. The bottom of the notch, which
-is called the "crest" of the weir, should be perfectly level and
-the sides vertical. In the pond back of the weir, at a distance not
-less than the length of the notch, drive a stake near the bank, with
-its top precisely level with the crest. By means of a rule, or a
-graduated stake as shown, measure the depth of water over the top
-of stake, making allowance for capillary attraction of the water
-against the sides of the weir. For extreme accuracy this depth may
-be measured to thousandths of a foot by means of a "hook gauge,"
-familiar to all engineers. Having ascertained the depth of water
-over the stake, refer to the accompanying table, from which may be
-calculated the amount of water flowing over the weir. There are
-certain proportions which must be observed in the dimensions of this
-notch. Its length, or width, should be between four and eight times
-the depth of water flowing over the crest of the weir. The pond
-back of the weir should be at least fifty per cent. wider than the
-notch and of sufficient width and depth that the velocity of flow or
-approach be not over one foot per second. In order to obtain these
-results it is advisable to experiment to some extent.</p></div>
-
-<p><span class="pagenum"><a name="Page_1973" id="Page_1973">1973</a></span></p>
-<p class="blockquot">
-Speed regulation is effected by varying the number of nozzles in
-flow, that is, for light loads fewer nozzles are open and a smaller
-volume of steam is admitted to the turbine wheel, but the steam that
-is admitted impinges against the moving blades with the same velocity
-always, no matter whether the volume be large or small. With a full
-load and all the nozzle sections in flow, the steam passes to the
-wheel in a broad belt and steady flow.</p>
-
-<table border="0" cellspacing="2" summary="_" rules="cols" cellpadding="0">
-<caption><br /><b>WEIR TABLE</b><br />
-giving cubic feet of water per minute that will flow over a weir
-one inch wide and from ⅛ to 20⅞ inches deep.
-</caption>
-  <tbody><tr class="tr_lt_grey">
-      <td class="tdc">Depth<br />&nbsp;inches&nbsp;</td> <td class="tdc"> </td>
-      <td class="tdc"><big>⅛</big></td> <td class="tdc"><big>¼</big></td>
-      <td class="tdc"><big>⅜</big></td> <td class="tdc"><big>½</big></td>
-      <td class="tdc"><big>⅝</big></td> <td class="tdc"><big>¾</big></td>
-      <td class="tdc"><big>⅞</big></td>
-   </tr><tr>
-      <td class="tdr"><b>0</b>&emsp;&nbsp;</td> <td class="tdr">.00&nbsp;&nbsp;</td>
-      <td class="tdr">.01&nbsp;&nbsp;</td> <td class="tdr">.05&nbsp;&nbsp;</td>
-      <td class="tdr">.09&nbsp;&nbsp;</td> <td class="tdr">.14&nbsp;&nbsp;</td>
-      <td class="tdr">.19&nbsp;&nbsp;</td> <td class="tdr">.26&nbsp;&nbsp;</td>
-      <td class="tdr">.32&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>1</b>&emsp;&nbsp;</td> <td class="tdr">.40&nbsp;&nbsp;</td>
-      <td class="tdr">.47&nbsp;&nbsp;</td> <td class="tdr">.55&nbsp;&nbsp;</td>
-      <td class="tdr">.64&nbsp;&nbsp;</td> <td class="tdr">.73&nbsp;&nbsp;</td>
-      <td class="tdr">.82&nbsp;&nbsp;</td> <td class="tdr">.92&nbsp;&nbsp;</td>
-      <td class="tdr">1.02&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>2</b>&emsp;&nbsp;</td> <td class="tdr">1.13&nbsp;&nbsp;</td>
-      <td class="tdr">1.23&nbsp;&nbsp;</td> <td class="tdr">1.35&nbsp;&nbsp;</td>
-      <td class="tdr">1.36&nbsp;&nbsp;</td> <td class="tdr">1.58&nbsp;&nbsp;</td>
-      <td class="tdr">1.70&nbsp;&nbsp;</td> <td class="tdr">1.82&nbsp;&nbsp;</td>
-      <td class="tdr">1.95&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>3</b>&emsp;&nbsp;</td> <td class="tdr">2.07&nbsp;&nbsp;</td>
-      <td class="tdr">2.21&nbsp;&nbsp;</td> <td class="tdr">2.34&nbsp;&nbsp;</td>
-      <td class="tdr">2.48&nbsp;&nbsp;</td> <td class="tdr">2.61&nbsp;&nbsp;</td>
-      <td class="tdr">2.76&nbsp;&nbsp;</td> <td class="tdr">2.90&nbsp;&nbsp;</td>
-      <td class="tdr">3.05&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>4</b>&emsp;&nbsp;</td> <td class="tdr">3.20&nbsp;&nbsp;</td>
-      <td class="tdr">3.35&nbsp;&nbsp;</td> <td class="tdr">3.50&nbsp;&nbsp;</td>
-      <td class="tdr">3.66&nbsp;&nbsp;</td> <td class="tdr">3.81&nbsp;&nbsp;</td>
-      <td class="tdr">3.97&nbsp;&nbsp;</td> <td class="tdr">4.14&nbsp;&nbsp;</td>
-      <td class="tdr">4.30&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>5</b>&emsp;&nbsp;</td> <td class="tdr">4.47&nbsp;&nbsp;</td>
-      <td class="tdr">4.64&nbsp;&nbsp;</td> <td class="tdr">4.81&nbsp;&nbsp;</td>
-      <td class="tdr">4.98&nbsp;&nbsp;</td> <td class="tdr">5.15&nbsp;&nbsp;</td>
-      <td class="tdr">5.33&nbsp;&nbsp;</td> <td class="tdr">5.51&nbsp;&nbsp;</td>
-      <td class="tdr">5.69&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>6</b>&emsp;&nbsp;</td> <td class="tdr">5.87&nbsp;&nbsp;</td>
-      <td class="tdr">6.06&nbsp;&nbsp;</td> <td class="tdr">6.25&nbsp;&nbsp;</td>
-      <td class="tdr">6.44&nbsp;&nbsp;</td> <td class="tdr">6.62&nbsp;&nbsp;</td>
-      <td class="tdr">6.82&nbsp;&nbsp;</td> <td class="tdr">7.01&nbsp;&nbsp;</td>
-      <td class="tdr">7.21&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>7</b>&emsp;&nbsp;</td> <td class="tdr">7.40&nbsp;&nbsp;</td>
-      <td class="tdr">7.60&nbsp;&nbsp;</td> <td class="tdr">7.80&nbsp;&nbsp;</td>
-      <td class="tdr">8.01&nbsp;&nbsp;</td> <td class="tdr">8.21&nbsp;&nbsp;</td>
-      <td class="tdr">8.42&nbsp;&nbsp;</td> <td class="tdr">8.63&nbsp;&nbsp;</td>
-      <td class="tdr">8.83&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>8</b>&emsp;&nbsp;</td> <td class="tdr">9.05&nbsp;&nbsp;</td>
-      <td class="tdr">9.26&nbsp;&nbsp;</td> <td class="tdr">9.47&nbsp;&nbsp;</td>
-      <td class="tdr">9.69&nbsp;&nbsp;</td> <td class="tdr">9.91&nbsp;&nbsp;</td>
-      <td class="tdr">10.13&nbsp;&nbsp;</td> <td class="tdr">10.35&nbsp;&nbsp;</td>
-      <td class="tdr">10.57&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>9</b>&emsp;&nbsp;</td> <td class="tdr">&nbsp;10.80&nbsp;&nbsp;</td>
-      <td class="tdr">&nbsp;11.02&nbsp;&nbsp;</td> <td class="tdr">&nbsp;11.25&nbsp;&nbsp;</td>
-      <td class="tdr">&nbsp;11.48&nbsp;&nbsp;</td> <td class="tdr">&nbsp;11.71&nbsp;&nbsp;</td>
-      <td class="tdr">&nbsp;11.94&nbsp;&nbsp;</td> <td class="tdr">&nbsp;12.17&nbsp;&nbsp;</td>
-      <td class="tdr">&nbsp;12.41&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>10</b>&emsp;&nbsp;</td> <td class="tdr">12.64&nbsp;&nbsp;</td>
-      <td class="tdr">12.88&nbsp;&nbsp;</td> <td class="tdr">13.12&nbsp;&nbsp;</td>
-      <td class="tdr">13.36&nbsp;&nbsp;</td> <td class="tdr">13.60&nbsp;&nbsp;</td>
-      <td class="tdr">13.85&nbsp;&nbsp;</td> <td class="tdr">14.09&nbsp;&nbsp;</td>
-      <td class="tdr">14.34&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>11</b>&emsp;&nbsp;</td> <td class="tdr">14.59&nbsp;&nbsp;</td>
-      <td class="tdr">14.84&nbsp;&nbsp;</td> <td class="tdr">15.09&nbsp;&nbsp;</td>
-      <td class="tdr">15.34&nbsp;&nbsp;</td> <td class="tdr">15.59&nbsp;&nbsp;</td>
-      <td class="tdr">15.85&nbsp;&nbsp;</td> <td class="tdr">16.11&nbsp;&nbsp;</td>
-      <td class="tdr">16.36&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>12</b>&emsp;&nbsp;</td> <td class="tdr">16.62&nbsp;&nbsp;</td>
-      <td class="tdr">16.88&nbsp;&nbsp;</td> <td class="tdr">17.15&nbsp;&nbsp;</td>
-      <td class="tdr">17.41&nbsp;&nbsp;</td> <td class="tdr">17.67&nbsp;&nbsp;</td>
-      <td class="tdr">17.94&nbsp;&nbsp;</td> <td class="tdr">18.21&nbsp;&nbsp;</td>
-      <td class="tdr">18.47&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>13</b>&emsp;&nbsp;</td> <td class="tdr">18.74&nbsp;&nbsp;</td>
-      <td class="tdr">19.01&nbsp;&nbsp;</td> <td class="tdr">19.29&nbsp;&nbsp;</td>
-      <td class="tdr">19.56&nbsp;&nbsp;</td> <td class="tdr">19.84&nbsp;&nbsp;</td>
-      <td class="tdr">20.11&nbsp;&nbsp;</td> <td class="tdr">20.39&nbsp;&nbsp;</td>
-      <td class="tdr">20.67&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>14</b>&emsp;&nbsp;</td> <td class="tdr">20.95&nbsp;&nbsp;</td>
-      <td class="tdr">21.23&nbsp;&nbsp;</td> <td class="tdr">21.51&nbsp;&nbsp;</td>
-      <td class="tdr">21.80&nbsp;&nbsp;</td> <td class="tdr">22.08&nbsp;&nbsp;</td>
-      <td class="tdr">22.37&nbsp;&nbsp;</td> <td class="tdr">22.65&nbsp;&nbsp;</td>
-      <td class="tdr">22.94&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>15</b>&emsp;&nbsp;</td> <td class="tdr">23.23&nbsp;&nbsp;</td>
-      <td class="tdr">23.52&nbsp;&nbsp;</td> <td class="tdr">23.82&nbsp;&nbsp;</td>
-      <td class="tdr">24.11&nbsp;&nbsp;</td> <td class="tdr">24.40&nbsp;&nbsp;</td>
-      <td class="tdr">24.70&nbsp;&nbsp;</td> <td class="tdr">25.00&nbsp;&nbsp;</td>
-      <td class="tdr">25.30&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>16</b>&emsp;&nbsp;</td> <td class="tdr">25.60&nbsp;&nbsp;</td>
-      <td class="tdr">25.90&nbsp;&nbsp;</td> <td class="tdr">26.20&nbsp;&nbsp;</td>
-      <td class="tdr">26.50&nbsp;&nbsp;</td> <td class="tdr">26.80&nbsp;&nbsp;</td>
-      <td class="tdr">27.11&nbsp;&nbsp;</td> <td class="tdr">27.42&nbsp;&nbsp;</td>
-      <td class="tdr">27.72&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>17</b>&emsp;&nbsp;</td> <td class="tdr">28.03&nbsp;&nbsp;</td>
-      <td class="tdr">28.34&nbsp;&nbsp;</td> <td class="tdr">28.65&nbsp;&nbsp;</td>
-      <td class="tdr">28.97&nbsp;&nbsp;</td> <td class="tdr">29.28&nbsp;&nbsp;</td>
-      <td class="tdr">29.59&nbsp;&nbsp;</td> <td class="tdr">29.91&nbsp;&nbsp;</td>
-      <td class="tdr">30.22&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>18</b>&emsp;&nbsp;</td> <td class="tdr">30.54&nbsp;&nbsp;</td>
-      <td class="tdr">30.86&nbsp;&nbsp;</td> <td class="tdr">31.18&nbsp;&nbsp;</td>
-      <td class="tdr">31.50&nbsp;&nbsp;</td> <td class="tdr">31.82&nbsp;&nbsp;</td>
-      <td class="tdr">32.15&nbsp;&nbsp;</td> <td class="tdr">32.47&nbsp;&nbsp;</td>
-      <td class="tdr">32.80&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>19</b>&emsp;&nbsp;</td> <td class="tdr">33.12&nbsp;&nbsp;</td>
-      <td class="tdr">33.45&nbsp;&nbsp;</td> <td class="tdr">33.78&nbsp;&nbsp;</td>
-      <td class="tdr">34.11&nbsp;&nbsp;</td> <td class="tdr">34.44&nbsp;&nbsp;</td>
-      <td class="tdr">34.77&nbsp;&nbsp;</td> <td class="tdr">35.10&nbsp;&nbsp;</td>
-      <td class="tdr">35.44&nbsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr"><b>20</b>&emsp;&nbsp;</td> <td class="tdr">35.77&nbsp;&nbsp;</td>
-      <td class="tdr">36.11&nbsp;&nbsp;</td> <td class="tdr">36.45&nbsp;&nbsp;</td>
-      <td class="tdr">36.78&nbsp;&nbsp;</td> <td class="tdr">37.12&nbsp;&nbsp;</td>
-      <td class="tdr">37.46&nbsp;&nbsp;</td> <td class="tdr">37.80&nbsp;&nbsp;</td>
-      <td class="tdr">38.15&nbsp;&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="blockquot">
-NOTE.&mdash;The weir table on this page contains figures 1, 2, 3, etc.,
-in the first vertical column which indicates the inches depth of
-water running over weir board notches. Frequently the depths measured
-represent also fractional inches, between 1 and 2, 2 and 3, etc. The
-horizontal line of fraction at the top represents these fractional
-parts, and can be applied between any of the numbers of inches
-depth, from 1 to 25. The body of the table shows the cubic feet, and
-the fractional parts of a cubic foot, which will pass each minute
-for each inch in depth, and for each fractional part of an inch by
-eighths for all depths from 1 to 25 inches. Each of these results is
-for only one inch width of weir. To estimate for any width of weir
-the result obtained for one inch width must be multiplied by the
-number of inches constituting the whole horizontal length of weir.</p>
-
-<p><span class="pagenum"><a name="Page_1974" id="Page_1974">1974</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2760"></a>
-  <img src="images/i-0318-1.jpg" alt="_" width="500" height="763" />
-  <img src="images/i-0318-2.jpg" alt="_" width="500" height="783" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,760 and 2,761.&mdash;Samson vertical
-runner and shaft, and complete Samson vertical turbine. The runner
-is composed of two separate and distinct types of wheel, having
-thereby also two diameters. Each wheel or set of buckets receives
-its separate quantity of water from one and the same set of guides,
-but each set acts only once and singly upon the water used, and the
-water does not act twice upon the combined wheel, as some suppose. <b>In
-construction</b>, the lower or main set of buckets is made of flanged
-plate steel, and cast solidly into a heavy ring surrounding the outer
-and lower edges, and into a heavy diaphragm, separating the two sets
-of buckets.</p></div>
-
-<p><span class="pagenum"><a name="Page_1975" id="Page_1975">1975</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2762"></a>
-  <img src="images/i-0319-1.jpg" alt="_" width="600" height="436" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,762.&mdash;Water discharging from a needle
-nozzle due to a pressure of 169 lbs. per sq. in.</p></div>
-
-<p class="space-above1 space-below1"><b>Hydro-Electric
-Plants.</b>&mdash;The economy with which electricity can be
-transmitted long distances by high tension alternating currents, has
-led to the development of a large number of water powers in more or
-less remote regions.</p>
-
-<div class="figcenter">
-  <a name="fig2763"></a>
-  <img src="images/i-0319-2.jpg" alt="_" width="600" height="201" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,763.&mdash;Photograph of an operating
-tangential water wheel equipped with Pelton buckets.</p></div>
-
-<p><span class="pagenum"><a name="Page_1976" id="Page_1976">1976</a></span></p>
-
-<div class="blockquot">
-<p>This economy is possible by the facility with which alternating
-current can be transformed up and down. Thus at the hydro-electro
-plant, the current generated by the water wheel driven alternator is
-transformed to very high pressure and transmitted with economy a long
-distance to the distributing point where it is transformed down to
-the proper pressure for distribution.</p>
-
-<p>A water wheel or turbine is a machine in which a rotary motion is
-obtained by transference of the momentum of water; broadly speaking,
-the fluid is guided by fixed blades, attached with a casing, and
-impinging on other blades mounted on a drum or shaft, causing the
-latter to revolve.</p>
-
-<p>There are two general classes of turbine:<br />
-&emsp;&emsp;&emsp;1. Impulse turbines;<br />
-&emsp;&emsp;&emsp;2. Reaction turbines.</p>
-</div>
-
-<div class="figcenter">
-  <a name="fig2764"></a>
-  <img src="images/i144.jpg" alt="_" width="450" height="769" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,764.&mdash;Sectional elevation of one of
-the 5,000 horse power vertical Pelton-Francis turbines directly
-connected to generator, as installed for the Schenectady Power Co.</p></div>
-
-<p><b>Ques.</b> <b>What is an impulse turbine?</b></p>
-
-<p>Ans. One in which the fluid is directed by means of a series of
-nozzles against vanes which it drives.</p>
-
-<p><b>Ques.</b> <b>What is a reaction turbine?</b></p>
-
-<p>Ans. One in which the pressure or head of the water is employed
-rather than its velocity. The current is deflected upon the wheel by
-the action of suitably disposed guide blades, the passages being full
-of water. Rotary motion is obtained by the change in the direction
-and momentum of the fluid.
-<span class="pagenum"><a name="Page_1977" id="Page_1977">1977</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2765"></a>
-  <img src="images/i145a.jpg" alt="_" width="600" height="201" />
-  <img src="images/i145b.jpg" alt="_" width="600" height="125" />
-  <p class="f90_left space-below1">
-Figs. 2,765 to 2,768.&mdash;Cross sections of Lowel dam
-power house, and wheel pits containing sixteen Samson turbines: The
-section C-D gives an end view of the generator room showing the
-locations of the generators below the head level water. They are
-secure against flood water, or leakage, by well constructed stuffing
-boxes in the iron bulkheads, through which the turbine wheel shafts
-pass and connect to the generators. Section E-F gives an end view of
-one of these wheel rooms or penstocks, and shows the extension of the
-draft tube from wheel case into tail water. The section A-B shows the
-sub-structure of gravel and macadam under the controlling gates, this
-forming also a portion or extension of the dam proper. These gates
-turn on an axis made of two 15 inch I beams securely riveted together
-with plates and angle irons to which the wooden frame is attached.
-The radius of the gates is 14 feet. They are designed to allow the
-water to pass underneath the gate, thus controlling any height of
-head water. They are intended to take care of an excess of water at
-unusual stages of the river. The whole affair has been well designed
-and executed. This plant furnishes a good example of a secure, and
-level foundation, since the wheel houses and generator room are
-immediately on the rock. It is necessary in all tandem plants to
-provide a very secure, substantial super-structure so that the long
-line of turbines and shaft will always remain straight and in proper
-alignment with the generator and the turbine cases. Users cannot be
-reminded of this too often.</p></div>
-
-<p><span class="pagenum"><a name="Page_1978" id="Page_1978">1978</a></span>
-<b>Ques.</b> <b>Name three classes of reaction turbines.</b></p>
-
-<p>Ans. Parallel flow, inward flow, and outward flow.</p>
-
-<p class="blockquot">
-Parallel flow turbines have an efficiency of about 70% and are suited
-for low falls not over 30 feet. Inward and outward flow turbines have an
-efficiency of about 85%. Impulse turbines are suitable for high heads.</p>
-
-<div class="figcenter">
-  <a name="fig2769"></a>
-  <img src="images/i-0320-1.jpg" alt="_" width="600" height="583" />
-  <img src="images/i-0320-2.jpg" alt="_" width="600" height="525" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,769 and 2,770.&mdash;Exterior and interior
-of hydro-electric plant at Harrisburg, Va. It is located on the south
-fork of the Shenandoah River, twelve and one-half miles distant. A
-dam 720 feet long and 15 feet high was built on a limestone ledge
-running across the river; which with a fall of 5 feet from the dam to
-the power house, a quarter of a mile distant, secured an effective
-head pressure of 20 feet. The power house, comprising the generator
-room and the wheel room, also the machinery room, are here shown.
-The wheel room, which is 20 × 40 feet, extends across the head race,
-and rests upon solid concrete walls, forming the sides and ends of
-the wheel pits. The end wall is 6 feet thick at the bottom, and
-4½ feet at the top. It has three arched openings, each 8 feet
-wide and 9 feet high, through which the water escapes after leaving
-the turbines. The intake is protected by a wrought iron rack 40 feet
-long. The power is obtained by three 50 inch vertical shaft Samson
-turbines, with a 20 inch Samson for an exciter. The three large
-turbines have a rating of 1,350 horse power; and are connected to the
-main horizontal line shaft by bevel mortise gears 7 feet diameter and
-15 inches face. The couplings on the main shaft have 48 inch friction
-clutch hubs, permitting either or each turbine being operated, or
-shut down independently of the others. The main shaft is 85 feet long
-and 6 inches diameter; making 280 revolutions. This shaft carries
-two pulleys 70 inches diameter and 38 inches face for driving the
-generators. The accompanying illustration shows the harness work,
-gears, pulleys, etc., furnished with the turbines. The 20 inch
-horizontal shaft Samson turbine of 72 horse power is direct connected
-to an exciter generator of 20 kw., running 700 rev. per min. The
-two large generators are driven 450 revolutions per minute by belts
-producing a three phase current of 60 cycles of 11,500 volts for the
-twelve and one-half miles transmission. The line consists of three
-strands of No. 4 bare copper wire. This current is used for lighting
-and power purposes, and the plant is of the latest improved design
-and construction.</p></div>
-
-<p><b>Isolated Plants.</b>&mdash;When electric power transmission
-from central stations first came into commercial use, the distance
-from the station at which current could be obtained at a reasonable
-cost was exceedingly limited.
-<span class="pagenum"><a name="Page_1979" id="Page_1979">1979</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2769a"></a>
-  <img src="images/i-0321-1.jpg" alt="_" width="500" height="588" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig. 2,769a.</span>&mdash;Triumph direct current generator
-set with upright slide valve engine.</p>
-
-  <a name="fig2770a"></a>
-  <img src="images/i-0321-2.jpg" alt="_" width="600" height="287" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig. 2,770a.</span>&mdash;Murray alternating current
-direct connected unit with high speed Corliss engine and belt driven
-exciter, 50, 75 and 100 kva. alternator and 150 R.P.M. engine.</p>
-
-  <a name="fig2771"></a>
-  <img src="images/i-0321-3.jpg" alt="_" width="600" height="319" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig. 2,771.</span>&mdash;Direct connected direct current
-unit with Ridgway high speed four valve engine.</p>
-
-  <a name="fig2772"></a>
-  <img src="images/i-0321-4.jpg" alt="_" width="600" height="487" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig. 2,772.</span>&mdash;Buckeye mobile, or self
-contained unit consisting of compound condensing engine, boiler,
-superheater, reheater, feed and air pumps; it produces one horse
-power on 1½ lbs. of coal, built in sizes from 75 to 600 horse power.</p>
-
-  <a name="fig2773"></a>
-  <img src="images/i147.jpg" alt="_" width="600" height="427" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig. 2,773.</span>&mdash;Westinghouse three cylinder gas
-engine, direct connected to dynamo, showing application of gas engine
-drive for small direct connected units.</p></div>
-
-<p><span class="pagenum"><a name="Page_1980" id="Page_1980">1980</a></span></p>
-
-<div class="blockquot">
-<p>Consequently, persons desiring electrical power were in the majority
-of cases forced to install their own apparatus for producing it, this
-being the origin of isolated plants.</p>
-
-<p>From the nature of the case it is evident that an isolated plant is
-as a rule smaller and more simple in construction than a central
-station, and in consequence much more readily operated and managed.
-It is generally owned by a private individual or a corporation and
-operated in conjunction with other affairs of a similar character. A
-basement or other portion of a building is usually set aside in which
-the necessary apparatus is installed.</p></div>
-
-<div class="figcenter">
-  <a name="fig2774"></a>
-  <img src="images/i-0322.jpg" alt="_" width="600" height="498" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig. 2,774.</span>&mdash;General Electric 25 kw.,
-gasoline electric generating set for lighting and power. The engine
-has four cylinders 7¼ × 7½, and runs at a speed of 560 revolutions
-per minute. The total candle power capacity in Mazda lamps is 20,000.
-The ignition is by low tension magneto, coil and battery. Carburetter
-is of the constant level type to which gasoline is delivered by a
-pump driven by the engine. Forced lubrication; five crank shaft
-bearings babbitted; valves in side; overall dimensions 96 × 34 × 60
-high; weight 5,000.</p></div>
-
-<div class="blockquot">
-<p>Although electricity is now transmitted economically to great
-distances from central stations, there is still a field for the
-isolated plant.</p>
-
-<p>The average type of isolated plant has enlarged from a small dynamo
-driven by a little slide valve engine located in an out of the way
-corner to direct connected generators and engines of hundreds and
-even thousands of horse power assembled in a large room specially
-adapted to the purpose.
-<span class="pagenum"><a name="Page_1981" id="Page_1981">1981</a></span></p>
-
-<p>In the more modern of these, the electrical outputs are each
-frequently equal to that of a town central station of respectable
-size, and the auxiliary equipments are similar in every particular.
-As a matter of fact, in certain modern isolated plants the only
-feature that distinguishes them from central stations is that in the
-former case the owner of the plant represents the sole consumer and
-conducts other business in connection with it, whereas in the latter
-case there are a large number of consumers uninterested financially
-in the enterprise, which is itself generally owned and operated by a
-company conducting no other business.</p></div>
-
-<div class="figcenter">
-  <a name="fig2775"></a>
-  <img src="images/i149.jpg" alt="_" width="600" height="566" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig. 2,775.</span>&mdash;Plan of sub-station with air
-blast transformers and motor operated oil switches and underground
-11,000 or 13,200 volt high tension lines.</p></div>
-
-<p><b>Sub-Stations.</b>&mdash;According to the usual meaning of
-the term, a sub-station is a building provided with apparatus for
-changing high pressure alternating current received from the central
-station into direct current of the requisite pressure, which in the
-case of railways is 550 to 600 volts.</p>
-
-<p>Where traffic is heavy and the railway system of
-considerable <span class="pagenum"><a name="Page_1982"
-id="Page_1982">1982</a></span> distance, sub-stations are provided at
-intervals along the line, each receiving high pressure current from
-one large central station and converting it into moderate pressure
-direct current for their districts.</p>
-
-<p><b>Ques.</b> <b>Upon what does the arrangement of the sub-station depend?</b></p>
-
-<p>Ans. Upon the character of the work and the type of apparatus
-employed for converting the high pressure alternating current into
-direct current.</p>
-
-<div class="figcenter">
-  <a name="fig2776"></a>
-  <img src="images/i150.jpg" alt="_" width="600" height="534" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig. 2,776.</span>&mdash;Plan of small sub-station
-with single phase oil insulated self-cooling transformers and hand
-operated oil switches 11,000 or 13,200 volts, overhead high tension lines.</p></div>
-
-<div class="blockquot">
-<p>In general it should be substantial, convenient to install or replace
-the heavy machines, and the layout arranged so that the apparatus can
-be readily operated by those in attendance.
-<span class="pagenum"><a name="Page_1983" id="Page_1983">1983</a></span></p>
-
-<p>An overhead traveling crane is the most convenient method of handling
-the heavy machinery, and is frequently used in large sub-stations.</p>
-
-<p><a href="#fig2776">Fig. 2,776</a> shows a sectional view, and <a href="#fig2777">fig. 2,777</a>,
-a plan for a small sub-station containing two rotary converters and
-two banks of three single phase static transformers operating on
-a three phase system at 11,000 or 13,200 volts, together with the
-auxiliary apparatus.</p></div>
-
-<div class="figcenter">
-  <a name="fig2777"></a>
-  <img src="images/i151.jpg" alt="_" width="600" height="471" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig. 2,777.</span>&mdash;Elevation of small sub-station,
-as shown in plan in <a href="#fig2776">Fig. 2,776</a>.</p></div>
-
-<p><b>Ques.</b> <b>For three phase installations, what are the merits of
-separate and combined transformers?</b></p>
-
-<p>Ans. With separate transformer for each phase, repairs are more
-readily made in case of accident or burnouts in the coils. The three
-phase units have the advantage of low first cost.</p>
-
-<div class="blockquot">
-<p>Sub-station transformers produce considerable heat, due to the
-hysteresis and eddy currents, and it is necessary to get rid of it.</p>
-
-<p>Small transformers radiate the heat from the shell and the medium
-sizes have corrugated shells which increase the surface and provide
-more rapid radiation.
-<span class="pagenum"><a name="Page_1984" id="Page_1984">1984</a></span></p>
-
-<p>Large transformers are cooled by an air blast supplied by motor
-driven blowers or by water pumped through a coil of pipe which is
-immersed in the insulating oil of the transformer. The large size oil
-insulated, water cooled transformers are used on circuits of 33,000
-volts or more. In water turbine plants, the water may be piped to the
-transformer under pressure and the pump omitted which cuts down the
-cost of operating. Air blast transformers usually have a damper or
-shutter for air control.</p></div>
-
-<div class="figcenter">
-  <a name="fig2778"></a>
-  <img src="images/i-0323.jpg" alt="_" width="600" height="398" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig. 2,778.</span>&mdash;Marine portable transformer
-station on Los Angeles Aqueduct. The view shows three 20 kva.
-Westinghouse out door transformers installed on a float, 33,000 volts
-high pressure; 440 volts low pressure; 50 cycles.</p><div>
-
-<p><b>Ques.</b> <b>Explain the use of reactance coils in sub-stations.</b></p>
-
-<p>Ans. In order that the direct current voltage of the ordinary rotary
-may be regulated by a field rheostat, which calls for a corresponding
-change in the alternating current voltage, a reactance coil is
-provided between the low tension winding and the converter.</p>
-
-<p class="blockquot">
-Without such a reactance the maintenance of the same voltage at full
-load as at no load involves excessive leading and lagging currents
-and consequently excessive heating in the armature inductors, unless
-<span class="pagenum"><a name="Page_1985" id="Page_1985">1985</a></span>
-the resistance drop from the source of constant pressure is small, or
-the natural reactance of the circuit high.</p>
-
-<p><b>Ques.</b> <b>What is the effect of weakening the converter field?</b></p>
-
-<p class="space-below1">Ans. A lagging current is set up which causes
-a drop in the reactance coil.</p>
-
-<div class="figcenter">
-  <a name="fig2779"></a>
-  <img src="images/i153.jpg" alt="_" width="600" height="292" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig. 2,779.</span>&mdash;Sectional elevation of portable
-outdoor transformer type sub-station. The high voltage switching and
-protective apparatus is mounted, out of the way, on the roof of the
-car, but is operated from the switchboard with a standard remote
-control handle. The transformer is carried directly over the truck at
-the uncovered end of the car and the low-tension leads from it run in
-conduit beneath the floor and up into the cab, (which contains the
-converter and switchboard) to the converter. The positive lead runs
-through a conduit and ends in a terminal on the roof. The energy thus
-makes a complete circuit of the car leaving at a point close to that
-at which it entered. The low pressure alternating current as well as
-the direct current positive leads are carried below the car floor
-in iron conduit supported from the channel frame. The field wires
-are carried through this conduit to the rheostat. Wiring for the
-lights is arranged to supply two, 5 light clusters. One is fed with
-the 600 volt direct current and the other with 420 volt alternating
-current. All lighting conductors are carried in metal moulding
-carried between the flanges of the channel iron ribs. High wiring
-is carried entirely on the roof of the car where it is entirely out
-of the way and where the operator cannot come in contact with it.
-The switchboard should be of the utmost simplicity. Usually the
-negative and equalizer switches, and the field break-up switch are
-mounted on the frame of the converter. The double throw switch for
-starting and running the converter can be mounted under the floor
-of the car and operated by handle at the switchboard. The rheostat
-can be mounted back of the switchboard on brackets bolted to the car
-super-structure. The switchboard need only carry the positive knife
-switch and circuit breaker, and the alternating current ammeter,
-voltmeter and power factor meter. Sometimes a watthour meter is
-added. The positive lead is brought out through a conduit on the
-roof of the car and is arranged for bolting to the positive feeder.
-The negative and equalizer terminals are located at the cab end of
-the car and are arranged so that connection can be easily made from
-them to the ground and, if necessary, to an equalizer circuit. There
-is usually a sliding door at each end of the cab and two windows on
-each side. Above the doors, transoms, extending the width of the cab,
-are arranged to drop so that a current of air will circulate through
-the cab under the roof, carrying out the heated air. There are also
-several ventilating holes beneath the converter in the floor of the
-car. These provisions insure a constant circulation of air through
-the car which carries away all heated air.</p></div>
-
-<p><span class="pagenum"><a name="Page_1986" id="Page_1986">1986</a></span>
-<b>Ques.</b> <b>State the effect of strengthening converter field.</b></p>
-
-<p>Ans. A leading current is set up which gives a rise of voltage
-in the reactance coil.</p>
-
-<p class="blockquot">
-Hence when a heavy current passes through the series coil of a compound
-wound converter and tends to produce a leading current, the reactance
-coil will balance it, and improve the power factor of the whole line.</p>
-
-<div class="figcenter">
-  <a name="fig2780"></a>
-  <img src="images/i-0324.jpg" alt="_" width="500" height="534" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig. 2,780.</span>&mdash;Westinghouse 300 kw. converter in
-portable sub-station.</p></div>
-
-<p><b>Portable Sub-Stations.</b>&mdash;A portable sub-station constitutes a
-spare equipment for practically any number of permanent sub-stations
-and renders unnecessary the installation of spare equipment in each.
-<span class="pagenum"><a name="Page_1987" id="Page_1987">1987</a></span></p>
-
-<div class="blockquot">
-<p>It can be used to increase the capacity of a permanent sub-station
-when the load is unusually heavy, or to provide service while a
-permanent sub-station is being overhauled or rebuilt.</p>
-
-<p>The transformer can be used for emergency lighting, the primary being
-connected to a high pressure line and the secondary to the load, if
-special provision be made at the time the transformer is built to
-adapt it for these applications.</p></div>
-
-<div class="figcenter">
-  <a name="fig2781"></a>
-  <img src="images/i-0325.jpg" alt="_" width="500" height="546" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig. 2,781.</span>&mdash;Switchboard end of Westinghouse
-portable sub-station.</p></div>
-
-<p>When an electric railway has a portable sub-station, direct current
-can be provided at any point on the system where there is track at
-the high pressure line. The direct current can be made available very
-<span class="pagenum"><a name="Page_1988" id="Page_1988">1988</a></span>
-quickly as its production involves only the transferring of the
-sub-station, and its connection to the high pressure line.</p>
-
-<div class="blockquot">
-<p>Portable sub-stations range in capacity from 200 to 500 kw., and for
-all alternating current voltages up to 66,000, and frequencies of 25
-and 60 cycles.</p>
-
-<p>Although portable sub-stations usually must be of more or less
-special design to adapt them to the conditions under which they must
-operate, there are certain general features that are common to all.
-All members are readily accessible and there are no unnecessary
-parts. The weight and dimensions are a minimum insuring ease of
-transportation. Live parts are so protected that the danger of
-accidental contact with them is minimized.</p></div>
-
-<div class="figcenter">
-  <a name="fig2782"></a>
-  <img src="images/i156.jpg" alt="_" width="600" height="451" />
-  <p class="f90 space-below1">
-<span class="smcap">Figs.</span> 2,782 and 2,783.&mdash;Views of levelling
-device for Westinghouse converter.</p></div>
-
-<p><b>Ques.</b> <b>What are the advantages of using outdoor transformers
-on portable sub-stations?</b></p>
-
-<p>Ans. All high pressure wiring is kept out of the car. The transformer
-is more effectively cooled and the heat dissipated by the transformer
-does not warm the interior of the cab. The transformer is much more
-accessible. The car can be run under a crane and the transformer
-coils pulled out with a hoist.</p>
-
-<p class="blockquot">
-Taps for different high and low pressure voltages can be readily
-provided at the time the transformer is being built.</p>
-
-<p><span class="pagenum"><a name="Page_1989" id="Page_1989">1989</a></span></p>
-<hr class="chap" />
-<h2><span class="h_subtitle">CHAPTER LXVII</span><br /><b>MANAGEMENT</b></h2>
-
-<p>The term "management," broadly speaking, includes not only the
-actual skilled attention necessary for the proper operation of the
-machines, after the plant is built, but also other duties which must
-be performed from its inception to completion, and which may be
-classified as</p>
-
-<p class="no-indent">
-&emsp;&emsp;&emsp;1. Selection;<br />
-&emsp;&emsp;&emsp;2. Location;<br />
-&emsp;&emsp;&emsp;3. Erection;<br />
-&emsp;&emsp;&emsp;4. Testing;<br />
-&emsp;&emsp;&emsp;5. Running;<br />
-&emsp;&emsp;&emsp;6. Care;<br />
-&emsp;&emsp;&emsp;7. Repair.</p>
-
-<p>That is to say, someone must select the machinery, determine where
-each machine is to be located, install them, and then attend to the
-running of the machines and make any necessary repairs due to the
-ordinary mishaps likely to occur in operation.</p>
-
-<p>These various duties are usually entrusted to more than one
-individual; thus, the selection and location of the machinery is done
-by the designer of the plant, and requires for its proper execution
-the services of an electrical engineer, or one possessing more than
-simply a practical knowledge of power plants.
-<span class="pagenum"><a name="Page_1990" id="Page_1990">1990</a></span></p>
-
-<p>The erection of the machines is best accomplished by those
-making a specialty of this line of work, who by the nature of the
-undertaking acquire proficiency in methods of precision and an
-appreciation of the value of accuracy which is so essential in the
-work of aligning the machines, and which if poorly done will prove a
-constant source of annoyance afterward.</p>
-
-<p>The attention required for the operation of the machines,
-embracing the running care and repair, is left to the "man in
-charge," who in most cases of small and medium size plants is the
-chief steam engineer. He must therefore, not only understand the
-steam apparatus, but possess sufficient knowledge of electrical
-machinery to operate and maintain it in proper working order.</p>
-
-<p>The present chapter deals chiefly with alternating current
-machinery, the management of direct current machines having been
-fully explained in Guide No. 3, however, some of the matter here
-presented is common to both classes of apparatus.</p>
-
-<p><br /><br /><b>Selection.</b>&mdash;In order to intelligently select a
-machine so that it will properly harmonize with the conditions under
-which it is to operate, there are several things to be considered.</p>
-
-<p class="no-indent">
-&emsp;&emsp;&emsp;1. Type;<br />
-&emsp;&emsp;&emsp;2. Capacity;<br />
-&emsp;&emsp;&emsp;3. Efficiency;<br />
-&emsp;&emsp;&emsp;4. Construction.</p>
-
-<p>The general type of machine to be used is, of course, dependent
-on the system employed, that is, whether it be direct or alternating,
-single or polyphase.</p>
-
-<p class="blockquot">
-Thus, the voltage in most cases is fixed except on transformer systems
-where a choice of voltage may be had by selecting a transformer to suit.
-<span class="pagenum"><a name="Page_1991" id="Page_1991">1991</a></span></p>
-
-<p>In alternating current constant pressure transmission circuits,
-an average voltage of 2,200 volts with step down transformer
-ratios of <sup>1</sup>&frasl;<sub>10</sub> and
-<sup>1</sup>&frasl;<sub>20</sub> is in general use, and is recommended.</p>
-
-<p class="blockquot">
-For long distance, the following average voltages are recommended
-6,000; 11,000; 22,000; 33,000; 44,000; 66,000; 88,000; and higher,
-depending on the length of the line and degree of economy desired.</p>
-
-<p>In alternating circuits the standard frequencies are 25, and 60
-cycles. These frequencies are already in extensive use and it is
-recommended to adhere to them as closely as possible.</p>
-
-<div class="figcenter">
-  <a name="fig2784"></a>
-  <img src="images/i-0326.jpg" alt="_" width="600" height="196" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig. 2,784.</span>&mdash;Diagram of connections for
-testing to obtain the saturation curve of an alternator. The
-saturation curve shows the relation between the volts generated in
-the armature and the amperes of field current (or ampere turns of the
-field) for a constant armature current. The armature current may be
-zero, in which case the curve is called <i>no load saturation curve</i>,
-or sometimes the <i>open circuit characteristic curve</i>. A saturation
-curve may be taken with full load current in the armature; but this
-is rarely done, except in alternators of comparatively small output.
-If a full load saturation curve be desired, it can be approximately
-calculated from the no load saturation curve. The figure shows the
-connections. If the voltage generated is greater than the capacity of
-the voltmeter, a multiplying coil or a step down pressure transformer
-may be used, as shown. A series of observations of the voltage
-between the terminals of one of the phases, is made for different
-values of the field current. Eight or nine points along the curve are
-usually sufficient, the series extending from zero to about fifty per
-cent. above normal rated voltage. The points should be taken more
-closely together in the vicinity of normal voltage than at other
-portions of the curve. Care must be taken that the alternator is run
-at its rated speed, and this speed must be kept constant. Deviations
-from constant speed may be most easily detected by the use of a
-tachometer. If the machine be two phase or three phase, the voltmeter
-may be connected to any one phase throughout a complete series of
-observations. The voltage of all the phases should be observed for
-normal full load excitation by connecting the voltmeter to each phase
-successively, keeping the field current constant at normal voltage.
-This is done in order to see how closely the voltage of the different
-phases agree.</p></div>
-
-<div class="blockquot">
-<p>In fixing the capacity of a machine, <i>careful consideration should
-be given to the conditions of operation both</i> <b>present</b> <i>and</i>
-<b>future</b> in order that the resultant efficiency may be maximum.</p>
-
-<p>Most machines show the best efficiency at or near full load. If the
-load be always constant, as for instance, a pump forcing water to a
-<span class="pagenum"><a name="Page_1992" id="Page_1992">1992</a></span>
-given head, it would be a simple matter to specify the proper size
-of machine, but in nearly all cases, and especially in electrical
-plants, the load varies widely, not only the daily and hourly
-fluctuations, but the varying demands depending on the season of the
-year and growth of the plant's business. All of these conditions tend
-to complicate the matter, so that intelligent selection of capacity
-of a machine requires not only calculation but mature judgment, which
-is only obtained by long experience.</p></div>
-
-<div class="figcenter">
-  <a name="fig2785"></a>
-  <img src="images/i-0327.jpg" alt="_" width="500" height="666" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig. 2,785.</span>&mdash;Saturation curve taken from
-a 2,000 kw., three phase alternator of the revolving field type, having
-16 poles, and generating 2,000 volts, and 576 amperes per phase when
-run at 300 R.P.M.</p></div>
-
-<p>In selecting a machine, or in fact any item connected with the plant
-<i>its construction should be carefully considered</i>.</p>
-
-<div class="blockquot">
-<p>Standard construction should be insisted upon so that in the event of
-damage a new part can be obtained with the least possible delay.</p>
-
-<p>The parts of most machines are <i>interchangeable</i>, that is to say,
-with the refined methods of machinery a duplicate part (usually
-carried in stock) may be obtained at once to replace a defective or
-broken part, and made with such precision that little or no fitting
-will be required.</p></div>
-
-<p><span class="pagenum"><a name="Page_1993" id="Page_1993">1993</a></span>
-The importance of standard construction cannot be better illustrated
-than in the matter of steam piping, that is, the kind of fittings
-selected for a given installation.</p>
-
-<p>With the exception of the exhaust line from engine to condenser,
-where other than standard construction may sometimes be used to
-reduce the frictional resistance to the steam, the author would
-adhere to standard construction except in very exceptional cases.
-Those who have had practical experience in pipe fitting will
-appreciate the wisdom of this.</p>
-
-<p>For installations in places remote from large supply houses, the
-more usual forms of standard fittings should be employed, such as
-ordinary T's, 45° and 90° elbows, etc.</p>
-
-<p>In such locations, where designers specify the less usual forms
-of standard fittings such as union fittings, offset reducers, etc.,
-or special fittings made to sketch, it simply means, in the first
-instance that they usually cannot be obtained of the local dealer,
-making it necessary to order from some large supply house and
-resulting in vexatious delays.</p>
-
-<p>As a rule, those who specify special fittings have found that
-their making requires an unreasonable length of time, and the cost to
-be several times that of the equivalent in standard fittings.</p>
-
-<p>An examination of a few installations will usually show numerous
-special and odd shape fittings, which are entirely unnecessary.</p>
-
-<p>Moreover, a standard design, in general, is better than a special
-design, because the former has been tried out, and any imperfection
-or weakness remedied, and where thousands of castings of a kind are
-turned out, a better article is usually the result as compared with a
-special casting.
-<span class="pagenum"><a name="Page_1994" id="Page_1994">1994</a></span></p>
-
-<p>In the matter of construction, in addition to the items just mentioned,
-it should be considered with respect to</p>
-
-<p class="no-indent">
-&emsp;&emsp;&emsp;1. Quality;<br />
-&emsp;&emsp;&emsp;2. Range;<br />
-&emsp;&emsp;&emsp;3. Accessibility;<br />
-&emsp;&emsp;&emsp;4. Proportion;<br />
-&emsp;&emsp;&emsp;5. Lubrication;<br />
-&emsp;&emsp;&emsp;6. Adjustment.</p>
-
-<p>It is poor policy, excepting in very rare instances, to buy a "cheap"
-article, as, especially in these days of commercial greed, the best
-is none too good.</p>
-
-<div class="figcenter">
-  <a name="fig2786"></a>
-  <img src="images/i162.jpg" alt="_" width="600" height="243" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,786 and 2,787.&mdash;Wheel and roller
-pipe cutters illustrating <b>range</b>. The illustrations show the
-comparative movements necessary with the two types of cutter to
-perform their function. The wheel cutter requiring only a small arc
-of movement will cut a pipe in an inaccessible place as shown, which
-with a roller cutter would be impossible. Accordingly, the wheel
-cutter is said to have a greater <i>range</i> than the roller cutter.</p></div>
-
-<p>Perhaps next in importance to quality, at least in most
-cases, is <i>range</i>. This may be defined as <i>scope of operation</i>,
-<i>effectiveness</i>, or <i>adaptability</i>. The importance of range is
-perhaps most pronounced in the selection of tools, especially for
-plants remote from repair shops.</p>
-
-<div class="blockquot"> <p>For instance, in selecting a pipe cutter,
-there are two general classes: wheel cutters, and roller cutters. A
-wheel cutter has three wheels and a roller cutter one wheel and two
-rollers, the object of <span class="pagenum"><a name="Page_1995"
-id="Page_1995">1995</a></span> the rollers being to keep the
-wheel perpendicular to the pipe in starting the cut and to reduce
-burning. It must be evident that in operation, a roller cutter
-requires sufficient room around the pipe to permit making a complete
-revolution of the cutter, whereas, with a wheel cutter, the work may
-be done by moving the cutter back and forth through a small arc,
-as illustrated in <a href="#fig2786">figs. 2,786</a> and <a href="#fig2786">2,787</a>.
-Thus a wheel cutter has a <i>greater range</i> than a roll cutter.</p>
-
-<p>Range relates not only to ability to operate in inaccessible
-places but to the various operations that may be performed by one tool.</p></div>
-
-<table border="0" cellspacing="2" summary="_" rules="cols" cellpadding="0">
-<caption><br /><b>PROPERTIES OF STANDARD WROUGHT IRON PIPE</b></caption>
-  <tbody><tr class="tr_lt_grey">
-      <td colspan="3" class="tdc">Diameter.</td> <td class="tdc">Thick-<br />ness.</td>
-      <td colspan="2" class="tdc">Circumference.</td>
-      <td colspan="3" class="tdc">Transverse areas.</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">&nbsp;Nominal&nbsp;<br />internal.</td> <td class="tdc">Actual<br />&nbsp;external.&nbsp;</td>
-      <td class="tdc">Actual<br />&nbsp;internal.&nbsp;</td> <td class="tdc">&nbsp;</td>
-      <td class="tdc">&nbsp;External.&nbsp;</td> <td class="tdc">&nbsp;Internal.&nbsp;</td>
-      <td class="tdc">&nbsp;External.&nbsp;</td> <td class="tdc">&nbsp;Internal.&nbsp;</td>
-      <td class="tdc">&nbsp;Metal.&nbsp;</td>
-   </tr><tr class="tr_grey">
-      <td class="tdc">Inches</td> <td class="tdc">Inches</td>
-      <td class="tdc">Inches</td> <td class="tdc">&nbsp;Inches&nbsp;</td>
-      <td class="tdc">Inches</td> <td class="tdc">Inches</td>
-      <td class="tdc">Sq. ins.</td> <td class="tdc">Sq. ins.</td>
-      <td class="tdc">Sq. ins.</td>
-   </tr><tr>
-      <td class="tdr">⅛&nbsp;&nbsp;</td> <td class="tdr">.405&nbsp;</td>
-      <td class="tdr">.27&ensp;&nbsp;</td> <td class="tdc">.068</td>
-      <td class="tdr">1.272&nbsp;</td> <td class="tdr">.848&nbsp;</td>
-      <td class="tdr">.129&nbsp;</td> <td class="tdr">.0573&nbsp;</td>
-      <td class="tdr">.0717</td>
-   </tr><tr>
-      <td class="tdr">¼&nbsp;&nbsp;</td> <td class="tdr">.54&ensp;&nbsp;</td>
-      <td class="tdr">.364&nbsp;</td> <td class="tdc">.088</td>
-      <td class="tdr">1.696&nbsp;</td> <td class="tdr">1.144&nbsp;</td>
-      <td class="tdr">.229&nbsp;</td> <td class="tdr">.1041&nbsp;</td>
-      <td class="tdr">.1249</td>
-   </tr><tr>
-      <td class="tdr">⅜&nbsp;&nbsp;</td> <td class="tdr">.675&nbsp;</td>
-      <td class="tdr">.494&nbsp;</td> <td class="tdc">.091</td>
-      <td class="tdr">2.121&nbsp;</td> <td class="tdr">1.552&nbsp;</td>
-      <td class="tdr">.358&nbsp;</td> <td class="tdr">.1917&nbsp;</td>
-      <td class="tdr">.1663</td>
-   </tr><tr>
-      <td class="tdr">½&nbsp;&nbsp;</td> <td class="tdr">.84&ensp;&nbsp;</td>
-      <td class="tdr">.623&nbsp;</td> <td class="tdc">.109</td>
-      <td class="tdr">2.639&nbsp;</td> <td class="tdr">1.957&nbsp;</td>
-      <td class="tdr">.554&nbsp;</td> <td class="tdr">.3048&nbsp;</td>
-      <td class="tdr">.2492</td>
-   </tr><tr>
-      <td class="tdr">¾&nbsp;&nbsp;</td> <td class="tdr">1.05&ensp;&nbsp;</td>
-      <td class="tdr">.824&nbsp;</td> <td class="tdc">.113</td>
-      <td class="tdr">3.299&nbsp;</td> <td class="tdr">2.589&nbsp;</td>
-      <td class="tdr">.866&nbsp;</td> <td class="tdr">.5333&nbsp;</td>
-      <td class="tdr">.3327</td>
-   </tr><tr>
-      <td class="tdr">1&emsp;&nbsp;</td> <td class="tdr">1.315&nbsp;</td>
-      <td class="tdr">1.048&nbsp;</td> <td class="tdc">.134</td>
-      <td class="tdr">4.131&nbsp;</td> <td class="tdr">3.292&nbsp;</td>
-      <td class="tdr">1.358&nbsp;</td> <td class="tdr">.8626&nbsp;</td>
-      <td class="tdr">.4954</td>
-   </tr><tr>
-      <td class="tdr">1¼&nbsp;&nbsp;</td> <td class="tdr">1.66&ensp;&nbsp;</td>
-      <td class="tdr">1.38&ensp;&nbsp;</td> <td class="tdc">&nbsp;.14&nbsp;&nbsp;</td>
-      <td class="tdr">5.215&nbsp;</td> <td class="tdr">4.335&nbsp;</td>
-      <td class="tdr">2.164&nbsp;</td> <td class="tdr">1.496&nbsp;&nbsp;</td>
-      <td class="tdr">.668&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">1½&nbsp;&nbsp;</td> <td class="tdr">1.9&emsp;&nbsp;</td>
-      <td class="tdr">1.611&nbsp;</td> <td class="tdc">.145</td>
-      <td class="tdr">5.969&nbsp;</td> <td class="tdr">5.061&nbsp;</td>
-      <td class="tdr">2.835&nbsp;</td> <td class="tdr">2.038&nbsp;&nbsp;</td>
-      <td class="tdr">.797&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">2&emsp;&nbsp;</td> <td class="tdr">2.375&nbsp;</td>
-      <td class="tdr">2.067&nbsp;</td> <td class="tdc">.154</td>
-      <td class="tdr">7.461&nbsp;</td> <td class="tdr">6.494&nbsp;</td>
-      <td class="tdr">4.43&ensp;&nbsp;</td> <td class="tdr">3.356&nbsp;&nbsp;</td>
-      <td class="tdr">1.074&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">2½&nbsp;&nbsp;</td> <td class="tdr">2.875&nbsp;</td>
-      <td class="tdr">2.468&nbsp;</td> <td class="tdc">.204</td>
-      <td class="tdr">9.032&nbsp;</td> <td class="tdr">7.753&nbsp;</td>
-      <td class="tdr">6.492&nbsp;</td> <td class="tdr">4.784&nbsp;&nbsp;</td>
-      <td class="tdr">1.708&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">3&emsp;&nbsp;</td> <td class="tdr">3.5&emsp;&nbsp;</td>
-      <td class="tdr">3.067&nbsp;</td> <td class="tdc">.217</td>
-      <td class="tdr">10.996&nbsp;</td> <td class="tdr">9.636&nbsp;</td>
-      <td class="tdr">9.621&nbsp;</td> <td class="tdr">7.388&nbsp;&nbsp;</td>
-      <td class="tdr">2.243&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">3½&nbsp;&nbsp;</td> <td class="tdr">4.&ensp;&emsp;&nbsp;</td>
-      <td class="tdr">3.548&nbsp;</td> <td class="tdc">.226</td>
-      <td class="tdr">12.566&nbsp;</td> <td class="tdr">11.146&nbsp;</td>
-      <td class="tdr">12.566&nbsp;</td> <td class="tdr">9.887&nbsp;&nbsp;</td>
-      <td class="tdr">2.679&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">4&emsp;&nbsp;</td> <td class="tdr">4.5&emsp;&nbsp;</td>
-      <td class="tdr">4.026&nbsp;</td> <td class="tdc">.237</td>
-      <td class="tdr">14.137&nbsp;</td> <td class="tdr">12.648&nbsp;</td>
-      <td class="tdr">15.904&nbsp;</td> <td class="tdr">12.73&nbsp;&nbsp;&nbsp;&nbsp;</td>
-      <td class="tdr">3.174&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">4½&nbsp;&nbsp;</td> <td class="tdr">5.&emsp;&ensp;&nbsp;</td>
-      <td class="tdr">4.508&nbsp;</td> <td class="tdc">.246</td>
-      <td class="tdr">15.708&nbsp;</td> <td class="tdr">14.162&nbsp;</td>
-      <td class="tdr">19.635&nbsp;</td> <td class="tdr">15.961&nbsp;&nbsp;</td>
-      <td class="tdr">3.674&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">5&emsp;&nbsp;</td> <td class="tdr">5.563&nbsp;</td>
-      <td class="tdr">5.045&nbsp;</td> <td class="tdc">.259</td>
-      <td class="tdr">17.477&nbsp;</td> <td class="tdr">15.849&nbsp;</td>
-      <td class="tdr">24.306&nbsp;</td> <td class="tdr">19.99&ensp;&nbsp;&nbsp;</td>
-      <td class="tdr">4.316&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">6&emsp;&nbsp;</td> <td class="tdr">6.625&nbsp;</td>
-      <td class="tdr">6.065&nbsp;</td> <td class="tdc">.28 &nbsp;</td>
-      <td class="tdr">20.813&nbsp;</td> <td class="tdr">19.054&nbsp;</td>
-      <td class="tdr">34.472&nbsp;</td> <td class="tdr">28.888&nbsp;&nbsp;</td>
-      <td class="tdr">5.584&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">7&emsp;&nbsp;</td> <td class="tdr">7.625&nbsp;</td>
-      <td class="tdr">7.023&nbsp;</td> <td class="tdc">.301</td>
-      <td class="tdr">23.955&nbsp;</td> <td class="tdr">22.063&nbsp;</td>
-      <td class="tdr">45.664&nbsp;</td> <td class="tdr">38.738&nbsp;&nbsp;</td>
-      <td class="tdr">6.926&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">8&emsp;&nbsp;</td> <td class="tdr">8.625&nbsp;</td>
-      <td class="tdr">7.982&nbsp;</td> <td class="tdc">.322</td>
-      <td class="tdr">27.096&nbsp;</td> <td class="tdr">25.076&nbsp;</td>
-      <td class="tdr">58.426&nbsp;</td> <td class="tdr">50.04&ensp;&nbsp;</td>
-      <td class="tdr">8.386&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">9&emsp;&nbsp;</td> <td class="tdr">9.625&nbsp;</td>
-      <td class="tdr">8.937&nbsp;</td> <td class="tdc">.344</td>
-      <td class="tdr">30.238&nbsp;</td> <td class="tdr">28.076&nbsp;</td>
-      <td class="tdr">72.76 &nbsp;&nbsp;</td> <td class="tdr">62.73&ensp;&nbsp;</td>
-      <td class="tdr">10.03&ensp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">10&emsp;&nbsp;</td> <td class="tdr">10.75 &nbsp;&nbsp;</td>
-      <td class="tdr">10.019&nbsp;</td> <td class="tdc">.366</td>
-      <td class="tdr">33.772&nbsp;</td> <td class="tdr">31.477&nbsp;</td>
-      <td class="tdr">90.763&nbsp;</td> <td class="tdr">78.839&nbsp;&nbsp;</td>
-      <td class="tdr">11.924&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">11&emsp;&nbsp;</td> <td class="tdr">12. &emsp;&nbsp;&nbsp;</td>
-      <td class="tdr">11.25 &nbsp;&nbsp;</td> <td class="tdc">.375</td>
-      <td class="tdr">37.699&nbsp;</td> <td class="tdr">35.343&nbsp;</td>
-      <td class="tdr">113.098&nbsp;</td> <td class="tdr">99.402&nbsp;&nbsp;</td>
-      <td class="tdr">13.696&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">12&emsp;&nbsp;</td> <td class="tdr">12.75 &nbsp;&nbsp;</td>
-      <td class="tdr">12.&emsp;&ensp;&nbsp;</td> <td class="tdc">.375</td>
-      <td class="tdr">40.055&nbsp;</td> <td class="tdr">37.7&emsp;&nbsp;</td>
-      <td class="tdr">127.677&nbsp;</td> <td class="tdr">113.098&nbsp;&nbsp;</td>
-      <td class="tdr">&nbsp;14.579&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-<table border="0" cellspacing="2" summary="_" rules="cols" cellpadding="0">
-<caption><br /><b>PROPERTIES OF STANDARD WROUGHT IRON PIPE</b><br />(Continued)</caption>
-  <tbody><tr class="tr_lt_grey">
-      <td class="tdc">Diam.</td>
-      <td colspan="2" class="tdc">Length of<br />pipe per<br />square<br />foot of</td>
-      <td rowspan="2" class="tdc">Length of<br />pipe per<br />&nbsp;containing&nbsp;<br />one cubic<br />foot.</td>
-      <td rowspan="2" class="tdc">&nbsp;Nominal&nbsp;<br />weight<br />per foot.</td>
-      <td rowspan="2" class="tdc">&nbsp;Number of&nbsp;<br />threads<br />per inch.</td>
-   </tr><tr class="tr_lt_grey">
-      <td class="tdc">&nbsp;Nominal&nbsp;<br />internal.</td>
-      <td class="tdc">&nbsp;External&nbsp;<br />surface</td> <td class="tdc">&nbsp;Internal&nbsp;<br />surface</td>
-   </tr><tr class="tr_grey">
-      <td class="tdc">Inches</td>  <td class="tdc">Feet.</td>
-      <td class="tdc">Feet.</td>   <td class="tdc">Feet.</td>
-      <td class="tdc">Pounds.</td> <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">⅛&nbsp;&nbsp;</td> <td class="tdr">9.44 &nbsp;&nbsp;</td>
-      <td class="tdr">14.15&ensp;&nbsp;</td> <td class="tdl">&nbsp;2513.</td>
-      <td class="tdr">.241&nbsp;</td> <td class="tdl">&nbsp;&nbsp;27</td>
-   </tr><tr>
-      <td class="tdr">¼&nbsp;&nbsp;</td> <td class="tdr">7.075&nbsp;</td>
-      <td class="tdr">10.49&ensp;&nbsp;</td> <td class="tdl">&nbsp;1383.3</td>
-      <td class="tdr">.42 &nbsp;&nbsp;</td> <td class="tdl">&nbsp;&nbsp;18</td>
-   </tr><tr>
-      <td class="tdr">⅜&nbsp;&nbsp;</td> <td class="tdr">5.657&nbsp;</td>
-      <td class="tdr">7.73&ensp;&nbsp;</td> <td class="tdl">&nbsp;&nbsp;&nbsp;751.2</td>
-      <td class="tdr">.559&nbsp;</td> <td class="tdl">&nbsp;&nbsp;18</td>
-   </tr><tr>
-      <td class="tdr">½&nbsp;&nbsp;</td> <td class="tdr">4.547&nbsp;</td>
-      <td class="tdr">6.13&ensp;&nbsp;</td> <td class="tdl">&nbsp;&nbsp;&nbsp;472.4</td>
-      <td class="tdr">.837&nbsp;</td> <td class="tdl">&nbsp;&nbsp;14</td>
-   </tr><tr>
-      <td class="tdr">¾&nbsp;&nbsp;</td> <td class="tdr">3.637&nbsp;</td>
-      <td class="tdr">4.635&nbsp;</td> <td class="tdl">&nbsp;&nbsp;&nbsp;270.</td>
-      <td class="tdr">1.115&nbsp;</td> <td class="tdl">&nbsp;&nbsp;14</td>
-   </tr><tr>
-      <td class="tdr">1&emsp;&nbsp;</td> <td class="tdr">2.904&nbsp;</td>
-      <td class="tdr">3.645&nbsp;</td> <td class="tdl">&nbsp;&nbsp;&nbsp;166.9</td>
-      <td class="tdr">1.668&nbsp;</td> <td class="tdl">&nbsp;&nbsp;11½</td>
-   </tr><tr>
-      <td class="tdr">1¼&nbsp;&nbsp;</td> <td class="tdr">2.301&nbsp;</td>
-      <td class="tdr">2.768&nbsp;</td> <td class="tdl">&emsp;&nbsp;96.25</td>
-      <td class="tdr">2.244&nbsp;</td> <td class="tdl">&nbsp;&nbsp;11½</td>
-   </tr><tr>
-      <td class="tdr">1½&nbsp;&nbsp;</td> <td class="tdr">2.01 &nbsp;&nbsp;</td>
-      <td class="tdr">2.371&nbsp;</td> <td class="tdl">&emsp;&nbsp;70.66</td>
-      <td class="tdr">2.678&nbsp;</td> <td class="tdl">&nbsp;&nbsp;11½</td>
-   </tr><tr>
-      <td class="tdr">2&emsp;&nbsp;</td> <td class="tdr">1.608&nbsp;</td>
-      <td class="tdr">1.848&nbsp;</td> <td class="tdl">&emsp;&nbsp;42.91</td>
-      <td class="tdr">3.609&nbsp;</td> <td class="tdl">&nbsp;&nbsp;11½</td>
-   </tr><tr>
-      <td class="tdr">2½&nbsp;&nbsp;</td> <td class="tdr">1.328&nbsp;</td>
-      <td class="tdr">1.547&nbsp;</td> <td class="tdl">&emsp;&nbsp;30.1</td>
-      <td class="tdr">5.739&nbsp;</td> <td class="tdl">&emsp;&nbsp;8</td>
-   </tr><tr>
-      <td class="tdr">3&emsp;&nbsp;</td> <td class="tdr">1.091&nbsp;</td>
-      <td class="tdr">1.245&nbsp;</td> <td class="tdl">&emsp;&nbsp;19.5</td>
-      <td class="tdr">7.536&nbsp;</td> <td class="tdl">&emsp;&nbsp;8</td>
-   </tr><tr>
-      <td class="tdr">3½&nbsp;&nbsp;</td> <td class="tdr">.955&nbsp;</td>
-      <td class="tdr">1.077&nbsp;</td> <td class="tdl">&emsp;&nbsp;14.57</td>
-      <td class="tdr">9.001&nbsp;</td> <td class="tdl">&emsp;&nbsp;8</td>
-   </tr><tr>
-      <td class="tdr">4&emsp;&nbsp;</td> <td class="tdr">.849&nbsp;</td>
-      <td class="tdr">.949&nbsp;</td> <td class="tdl">&emsp;&nbsp;11.31</td>
-      <td class="tdr">10.665&nbsp;</td> <td class="tdl">&emsp;&nbsp;8</td>
-   </tr><tr>
-      <td class="tdr">4½&nbsp;&nbsp;</td> <td class="tdr">.764&nbsp;</td>
-      <td class="tdr">.848&nbsp;</td> <td class="tdl">&emsp;&nbsp; &nbsp;9.02</td>
-      <td class="tdr">12.34 &nbsp;&nbsp;</td> <td class="tdl">&emsp;&nbsp;8</td>
-   </tr><tr>
-      <td class="tdr">5&emsp;&nbsp;</td> <td class="tdr">.687&nbsp;</td>
-      <td class="tdr">.757&nbsp;</td> <td class="tdl">&emsp;&nbsp; &nbsp;7.2</td>
-      <td class="tdr">14.502&nbsp;</td> <td class="tdl">&emsp;&nbsp;8</td>
-   </tr><tr>
-      <td class="tdr">6&emsp;&nbsp;</td> <td class="tdr">.577&nbsp;</td>
-      <td class="tdr">.63 &nbsp;&nbsp;</td> <td class="tdl">&emsp;&nbsp; &nbsp;4.98</td>
-      <td class="tdr">18.762&nbsp;</td> <td class="tdl">&emsp;&nbsp;8</td>
-   </tr><tr>
-      <td class="tdr">7&emsp;&nbsp;</td> <td class="tdr">.501&nbsp;</td>
-      <td class="tdr">.544&nbsp;</td> <td class="tdl">&emsp;&nbsp; &nbsp;3.72</td>
-      <td class="tdr">23.271&nbsp;</td> <td class="tdl">&emsp;&nbsp;8</td>
-   </tr><tr>
-      <td class="tdr">8&emsp;&nbsp;</td> <td class="tdr">.443&nbsp;</td>
-      <td class="tdr">.478&nbsp;</td> <td class="tdl">&emsp;&nbsp; &nbsp;2.88</td>
-      <td class="tdr">28.177&nbsp;</td> <td class="tdl">&emsp;&nbsp;8</td>
-   </tr><tr>
-      <td class="tdr">9&emsp;&nbsp;</td> <td class="tdr">.397&nbsp;</td>
-      <td class="tdr">.427&nbsp;</td> <td class="tdl">&emsp;&nbsp; &nbsp;2.29</td>
-      <td class="tdr">33.701&nbsp;</td> <td class="tdl">&emsp;&nbsp;8</td>
-   </tr><tr>
-      <td class="tdr">10&emsp;&nbsp;</td> <td class="tdr">.355&nbsp;</td>
-      <td class="tdr">.382&nbsp;</td> <td class="tdl">&emsp;&nbsp; &nbsp;1.82</td>
-      <td class="tdr">40.065&nbsp;</td> <td class="tdl">&emsp;&nbsp;8</td>
-   </tr><tr>
-      <td class="tdr">11&emsp;&nbsp;</td> <td class="tdr">.318&nbsp;</td>
-      <td class="tdr">.339&nbsp;</td> <td class="tdl">&emsp;&nbsp; &nbsp;1.450</td>
-      <td class="tdr">45.95&nbsp;</td> <td class="tdl">&emsp;&nbsp;8</td>
-   </tr><tr>
-      <td class="tdr">12&emsp;&nbsp;</td> <td class="tdr">.299&nbsp;</td>
-      <td class="tdr">.319&nbsp;</td> <td class="tdl">&emsp;&nbsp; &nbsp;1.27</td>
-      <td class="tdr">48.985&nbsp;</td> <td class="tdl">&emsp;&nbsp;8</td>
-   </tr>
- </tbody>
-</table>
-
-<p>Open construction should be employed, wherever possible, so that
-all parts of a machine that require attention, or that may become
-deranged in operation, may be accessible for adjustment or repair.
-<span class="pagenum"><a name="Page_1996" id="Page_1996">1996</a></span></p>
-
-<div class="blockquot">
-<p>The design should be such that there is ample strength, and the
-bearings for moving parts should be of liberal proportions to avoid
-heating with minimum attention.</p>
-
-<p>A comparison of the proportions used by different manufacturers for a
-machine of given size might profitably be made before a selection is
-made.</p></div>
-
-<p>The matter of lubrication is important.</p>
-
-<p class="blockquot">
-Fast running machines, such as generators and motors, should be
-provided with ring oilers and oil reservoirs of ample capacity, as
-shown in <a href="#fig2788">figs. 2,788</a> to <a href="#fig2789">2,794</a>.</p>
-
-<div class="figcenter">
-  <a name="fig2788"></a>
-  <img src="images/i164.jpg" alt="_" width="600" height="440" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,788.&mdash;Sectional view showing a ring
-oiler or self oiling bearing. As shown the pedestal or bearing
-standard is cored out to form a reservoir for the oil. The rings are
-in rolling contact with the shaft, and dip at their lower part into
-the oil. In operation, oil is brought up by the rings which revolve
-because of the frictional contacts with the shaft. The oil is in this
-way brought up to the top of the bearing and distributed along the
-shaft gradually descending by gravity to the reservoir, being thus
-used over and over. A drain cock, is provided in the base so that the
-oil may be periodically removed from the reservoir and strained to
-remove the accumulation of foreign matter. This should be frequently
-done to minimize the wear of the bearing.</p></div>
-
-<p>All bearings subject to appreciable wear should be made adjustable
-so that lost motion may be taken up from time to time and thus keep
-the vibration and noise of operation within proper limits.
-<span class="pagenum"><a name="Page_1997" id="Page_1997">1997</a></span></p>
-
-<p><b>Selection of Generators.</b>&mdash;This is governed by the
-class of work to be done and by certain local conditions which are
-liable to vary considerably for different stations.</p>
-
-<p class="space-below1">These variable factors determine whether
-the generators must be of the direct or alternating current type,
-whether they must be wound to develop a high or a low voltage, and
-whether their outputs in amperes must be large or small. Sufficient
-information has already been given to cover these various cases;
-there are, however, certain general rules that may advantageously be
-observed in the selection of generators designed to fill any of the
-aforementioned conditions, and it is well to possess certain facts
-regarding their construction.</p>
-
-<div class="figcenter">
-  <a name="fig2789"></a>
-  <img src="images/i165.jpg" alt="_" width="600" height="207" />
-  <p class="f90 space-below1">
-<span class="smcap">Figs.</span> 2,789 to 2,794.&mdash;Self oiling self
-aligning bearing open. Views showing oil grooves, rings, bolts etc.</p></div>
-
-<p><b>Ques. Name an important point to be considered in selecting a generator.</b></p>
-
-<p>Ans. Its efficiency.</p>
-
-<p><b>Ques. What are the important points with respect to efficiency?</b></p>
-
-<p>Ans. A generator possessing a high efficiency at the average load is
-more desirable than a generator showing a high efficiency at full load.
-<span class="pagenum"><a name="Page_1998" id="Page_1998">1998</a></span></p>
-
-<p><b>Ques. Why?</b></p>
-
-<p>Ans. The reason is that in station practice the full load limit
-is seldom reached, the usual load carried by a generator ordinarily
-lying between the one-half and three-quarter load points.</p>
-
-<p><b>Ques. How do the efficiencies of large and small generators compare?</b></p>
-
-<p class="space-below1">Ans. There is little difference.</p>
-
-<div class="figcenter">
-  <a name="fig2795"></a>
-  <img src="images/i-0328.jpg" alt="_" width="600" height="235" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,795.&mdash;Rotor of Westinghouse type
-T turbine dynamo set. The dynamo is of the commutating pole type
-either shunt or compound wound. The turbine is of the single wheel
-impulse type. The wheel is mounted directly on the end of the shaft
-as shown. Steam is used two or more times on the wheel to secure
-efficiency. A fly ball governor is provided with weights hung on
-hardened steel knife edges. In case of over speeding, an automatic
-safety stop throttle valve is tapped shutting off the steam supply.
-This type of turbine dynamo set is especially applicable for exciter
-service in modern, superheated steam generating stations where the
-steam pressure exceeds 125 pounds. Westinghouse Type T turbines
-operate directly (that is, without a reducing valve) on pressures up
-to 200 pounds per square inch with steam superheated to 150 degrees
-Fahrenheit.</p></div>
-
-<p><b>Ques. How are the sizes and number of generator determined?</b></p>
-
-<p>Ans. The sizes and number of generator to be installed should be
-such as to permit the engines operating them being worked at nearly
-full load, because the efficiencies of the latter machines decrease
-rapidly when carrying less than this amount.
-<span class="pagenum"><a name="Page_1999" id="Page_1999">1999</a></span></p>
-
-<p><b>Ques. What is understood by regulation?</b></p>
-
-<p>Ans. The accuracy and reliability with which the pressure or current
-developed in a machine may be controlled.</p>
-
-<p class="blockquot">
-It is generally possible if purchasing of a reputable concern, to
-obtain access to record sheets on which may be found results of tests
-conducted on the generator in question, and as these are really the
-only means of ascertaining the values of efficiency and regulation,
-the purchaser has a right to inspect them. If, for some reason or
-other, he has not been afforded this privilege, he should order the
-machine installed in the station on approval, and test its efficiency
-and regulation before making the purchase.</p>
-
-<div class="figcenter">
-  <a name="fig2796"></a>
-  <img src="images/i167.jpg" alt="_" width="600" height="437" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,796.&mdash;Cross section of electrical
-station showing small traveling crane.</p></div>
-
-<p><b>Installation.</b>&mdash;The installation of machines and apparatus in
-an electrical station is a task which increases in difficulty with
-the size of the plant. When the parts are small and comparatively
-light they may readily be placed in position, either by hand, by
-erecting temporary supports which may be moved from place to place as
-<span class="pagenum"><a name="Page_2000" id="Page_2000">2000</a></span>
-desired, or by rolling the parts along on the floor upon pieces of
-iron pipe. If, however, the parts be large and heavy, a traveling
-crane such as shown in <a href="#fig2797">fig. 2,797</a>, becomes necessary.</p>
-
-<p><b>Ques. What precaution should be taken in moving the parts of machines?</b></p>
-
-<p>Ans. Care should be taken not to injure the bearings and shafts, the
-joints in magnetic circuits such as those between frame and pole
-pieces, and the windings on the field and armature.</p>
-
-<div class="figcenter">
-  <a name="fig2797"></a>
-  <img src="images/i168.jpg" alt="_" width="600" height="362" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,797.&mdash;Cross section of electrical
-station showing a traveling crane for the installation or removal of
-large and heavy machine parts. A traveling crane consists of an iron
-beam which, being supplied with wheels at the ends, can be made to
-move either mechanically or electrically upon a track running the
-entire length of the station. This track is not supported by the
-walls of the building, but rests upon beams specially provided for
-the purpose. In addition to the horizontal motion thus obtained,
-another horizontal motion at right angles to the former is afforded
-by means of the carriage which, being also mounted on wheels, runs
-upon a track on the top of the beam. Electrical power is generally
-used to move the carriage and also the revolving drums contained
-thereon, the latter of which give a vertical motion to the main
-hoist or the auxiliary hoist, these hoists being used respectively
-for raising or lowering heavy or light loads. In the larger sizes
-of electric traveling crane, a cage is attached to the beam for the
-operator, who, by means of three controllers mounted in the cage, can
-move a load on either the main or auxiliary hoist in any direction.</p></div>
-
-<div class="blockquot">
-<p>The insulations of the windings are perhaps the most vital parts of
-a generator, and the most readily injured. The prick of a pin or tack,
-<span class="pagenum"><a name="Page_2001" id="Page_2001">2001</a></span>
-a bruise, or a bending of the wires by resting their weight upon them
-or by their coming in contact with some hard substance, will often
-render a field coil or an armature useless.</p>
-
-<p>Owing to its costly construction, it is advisable when transporting
-armatures by means of cranes to use a wooden spreader, as shown in
-<a href="#fig2798">fig. 2,798</a> to prevent the supporting rope bruising
-the winding.</p></div>
-
-<div class="figcenter">
-  <a name="fig2798"></a>
-  <img src="images/i169.jpg" alt="_" width="600" height="448" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,798.&mdash;View of armature in transit
-showing use of a wooden spreader as a protection. If a chain be used
-in place of the rope, a padding of cloth should be placed around the
-armature shaft and special care taken that the chain does not scratch
-the commutator.</p></div>
-
-<p><b>Ques. If an armature cannot be placed at once in its final
-position what should be done?</b></p>
-
-<p>Ans. It may be laid temporarily upon the floor, if a sheet of
-cardboard or cloth be placed underneath the armature as a protection
-for the windings; in case the armature is not to be used for some
-time, it is better practice to place it in a horizontal position on
-two wooden supports near the shaft ends.
-<span class="pagenum"><a name="Page_2002" id="Page_2002">2002</a></span></p>
-
-<p><b>Ques. What kind of base should be used with a belt driven
-generator or motor?</b></p>
-
-<p>Ans. The base should be provided with V ways and adjusting screws
-for moving the machine horizontally to take up slack in the belt, as
-shown in <a href="#fig2799">fig. 2,799</a>.</p>
-
-<p class="blockquot">
-Owing to the normal tension on the belt, there is a moment exerted
-equal in amount to the distance from the center of gravity of the
-machine to the center of the belt, multiplied by the effective pull
-on the belt. This force tends to turn the machine about its center of
-gravity. By placing the screws as shown, any turning moment, as just
-mentioned, is prevented.</p>
-
-<div class="figcenter">
-  <a name="fig2799"></a>
-  <img src="images/i170.jpg" alt="_" width="600" height="521" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,799.&mdash;Plan of belt drive machine
-showing V ways and adjusting screws for moving the machine forward
-from the engine or counter shaft to take up slack in the belt.</p></div>
-
-<p><b>Ques. How should a machine be assembled?</b></p>
-
-<p>Ans. The assembling should progress by the aid of a blue print, or by
-the information obtained from a photograph of the complete machine
-as it appears when ready for service. Each part should be perfectly
-<span class="pagenum"><a name="Page_2003" id="Page_2003">2003</a></span>
-clean when placed in position, especially those parts between which
-there is friction when the machine is in operation, or across which
-pass lines of magnetic force; in both cases the surfaces in contact
-must be true and slightly oiled before placing in position.</p>
-
-<div class="blockquot space-below1">
-<p>Contact surfaces forming part of electrical circuits must also be
-clean and tightly screwed together. An important point to bear in
-mind when assembling a machine is, to so place the parts that it will
-not be necessary to remove any one of them in order to get some other
-part in its proper position. By remembering this simple rule much
-time will be saved, and in the majority of instances the parts will
-finally be better fitted together than if the task has to be repeated
-a number of times.</p>
-
-<p>When there are two or more parts of the machine similarly shaped, it
-is often difficult to properly locate them, but in such cases notice
-should be taken of the factory marks usually stamped upon such pieces
-and their proper places determined from the instructions sent with
-the machine.</p></div>
-
-<div class="figcenter">
-  <a name="fig2800"></a>
-  <img src="images/i-0329.jpg" alt="_" width="600" height="261" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,800 to 2,802.&mdash;Starrett's improved
-speed indicator. In construction, the working parts are enclosed like
-a watch. The graduations show every revolution, and with two rows of
-figures read both right and left as the shaft may run. While looking
-at the watch, each hundred revolutions may be counted by allowing
-the oval headed pin on the revolving disc to pass under the thumb as
-the instrument is pressed to its work. A late improvement in this
-indicator consists in the rotating disc, which, being carried by
-friction may be moved to the starting point where the raised knobs
-coincide. When the spindle is placed in connection with the revolving
-shaft, pressing the raised knob with the thumb will prevent the disc
-rotating, while the hand of the watch gets to the right position to
-take the time. By releasing the pressure the disc is liberated for
-counting the revolutions of the shaft when every 100 may be noted by
-feeling the knob pass under the thumb lightly pressed against it,
-thus relieving the eye, which has only to look on the watch to note
-the time.</p></div>
-
-<p><b>Ques. What should be noted with respect to speed of generator?</b></p>
-
-<p>Ans. Each generator is designed to be run at a certain speed
-<span class="pagenum"><a name="Page_2004" id="Page_2004">2004</a></span>
-in order to develop the voltage at which the machine is rated.
-The speed, in revolutions per minute, the pressure in volts, and
-the capacity or output in watts (volts × amperes) or in kilowatts
-(thousands of watts) are generally stamped on a nameplate
-screwed to the machine.</p>
-
-<p class="blockquot">
-This requirement frequently requires calculations to be made by the
-erectors to determine the proper size pulleys to employ to obtain the
-desired speed.</p>
-
-<div class="figcenter">
-  <a name="fig2803"></a>
-  <img src="images/i172.jpg" alt="_" width="600" height="366" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,803.&mdash;Home made belt clamp. It is made
-with four pieces of oak of ample size to firmly grip the belt ends
-where the bolts are tightened. The figure shows the clamp complete
-and in position on the belt and clearly illustrates the details of
-construction. In making the long bolts the thread should be cut about
-three-quarter length of bolt and deep enough so that the nuts will
-easily screw on.</p></div>
-
-<p class="blockquot">
-<b>Example.</b>&mdash;What diameter of engine pulley is required to run a
-dynamo at a speed of 1,450 revolutions per minute the dynamo pulley
-being 10 inches in diameter and the speed of engine, 275 revolutions
-per minute?</p>
-
-<p class="no-indent">The diameter of pulley required on engine is
-<b>10 × (1,450 ÷ 275) = 53</b> inches, nearly.</p>
-
-<div class="blockquot">
-<p><b>Rule.</b>&mdash;To find the diameter of the driving pulley, <i>multiply
-the speed of the driven pulley by its diameter, divide the product by
-the speed of the driver and the answer will be the size of the driver required</i>.
-<span class="pagenum"><a name="Page_2005" id="Page_2005">2005</a></span></p>
-
-<p><i>Example.</i>&mdash;If the speed of an engine be 325 revolutions per minute,
-diameter of engine pulley 42 inches, and the speed of the dynamo
-1,400 revolutions per minute, how large a pulley is required on dynamo?</p></div>
-
-<p class="no-indent">The size of the dynamo pulley is <b>42 × (325 ÷ 1,400) = 9¾</b> inches.</p>
-
-<p class="blockquot">
-<b>Rule.</b>&mdash;To find the size of dynamo pulley, <i>multiply the speed
-of engine by the diameter of engine wheel and divide the product by
-the speed of the dynamo</i>.</p>
-
-<div class="figcenter">
-  <a name="fig2804"></a>
-  <img src="images/i173.jpg" alt="_" width="600" height="395" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,804 and 2,805.&mdash;A good method of
-lacing a belt. The view at the left shows outer side of belt, and at
-the right, inner or pulley side.</p></div>
-
-<p class="blockquot">
-<i>Example.</i>&mdash;If a steam engine, running 300 revolutions per minute,
-have a belt wheel 48 inches in diameter, and be belted to a dynamo
-having a pulley 12 inches in diameter, how many revolutions per
-minute will the dynamo make?</p>
-
-<p class="no-indent">The speed of dynamo will be <b>300 × (48 ÷ 12) = 1,200</b> rev. per min.</p>
-
-<div class="blockquot">
-<p><b>Rule.</b>&mdash;When the speed of the driving pulley and its diameter
-are known, and the diameter of the driven pulley is known, the speed
-of the driven pulley is found by <i>multiplying the speed of the driver
-by its diameter in inches and dividing the product by the diameter of
-the driven pulley</i>.
-<span class="pagenum"><a name="Page_2006" id="Page_2006">2006</a></span></p>
-
-<p><b>Example.</b>&mdash;What will be the required speed of an engine having
-a belt wheel 46 inches in diameter to run a dynamo 1,500 revolutions
-per minute, the dynamo pulley being 11 inches in diameter?</p></div>
-
-<p class="no-indent">The speed of the engine is <b>1,500 × (11 ÷ 46) = 359</b> rev. per min. nearly.</p>
-
-<div class="figcenter">
-  <a name="fig2806"></a>
-  <img src="images/i174.jpg" alt="_" width="600" height="405" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,806.&mdash;Wiring diagram and directions
-for operating Holzer-Cabot single phase self-starting motor.
-<b>Location:</b> The motor should be placed in as clear and dry a
-location as possible, away from acid or other fumes which would
-attack the metal parts or insulation, and should be located where it
-is easily accessible for cleaning and oiling. <b>Erection:</b> The
-motor should be set so that the shaft is level and parallel with the
-shaft it is to drive so that the belt will run in the middle of the
-pulleys. Do not use a belt which is too heavy or too tight for the
-work it has to do, as it will materially reduce the output of the
-motor. The belt should be from one-half to one inch narrower than
-the pulley. <b>Rotation:</b> In order to reverse the direction of
-rotation, interchange leads A and B. <b>Suspended Motors:</b> Motors
-with ring oil bearings may be used on the wall or ceiling by taking
-off end caps and revolving 90 or 180 degrees until the oil wells come
-directly below the bearings. <b>Starting:</b> Motors are provided
-with link across two terminals on the upper right hand bracket at the
-front of the motor and with this connection should start considerable
-overloads. If the starting current be too great with this connection,
-it may be reduced by removing the link. <b>Temperatures:</b> At full
-load the motor will feel hot to the hand, but this is far below
-the danger point. If too hot for touch, measure temperature with a
-thermometer by placing bulb against field winding for 10 minutes,
-covering thermometer with cloth or waste. The temperature should not
-exceed 75 degrees Fahr. above the surrounding air. <b>Oiling:</b>
-Fill the oil wells to the overflow before starting and keep them
-full. See that the oil rings turn freely with shaft. <b>Care:</b> The
-motor must be kept clean. Smooth collector rings with sandpaper and
-see that the brushes make good contact. When brushes become worn they
-may be reversed. When fitting new brushes or changing them always
-sandpaper them down until they make good contact with the collector
-rings, by passing a strip of sandpaper beneath the brush.</p></div>
-
-<p><span class="pagenum"><a name="Page_2007" id="Page_2007">2007</a></span></p>
-
-<p class="blockquot">
-<b>Rule.</b>&mdash;To find the speed of engine when diameter of both
-pulleys, and speed of dynamo are given, <i>multiply the dynamo speed
-by the diameter of its pulley and divide by the diameter of engine
-pulley</i>.</p>
-
-<p><b>Ques. How are the diameters and speeds of gear wheels figured?</b></p>
-
-<p>Ans. The same as belted wheels, using either the pitch circle
-diameters or number of teeth in each gear wheel.</p>
-
-<div class="figcenter">
-  <a name="fig2807"></a>
-  <img src="images/i175.jpg" alt="_" width="600" height="350" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,807 to 2,809.&mdash;Wiring diagrams
-and directions for operating Holzer-Cabot slow speed alternating
-current motors. <b>Erecting:</b> In installing the motor, be sure
-the transformer and wiring to the motor are large enough to permit
-the proper voltage at the terminals. If too small, the voltage will
-drop and reduce the capacity of the motor. <b>Oiling:</b> Maintain
-oil in wells to the overflow. <b>Starting: Single phase</b> motors
-are started by first throwing the starting switch down into the
-starting position, and when the motor is up to speed, throwing it
-up into the running position. <i>Do not hold the switch in starting
-position over 10 seconds.</i> Starter for single phase motors above
-½ H.P. are arranged with an adjusting link at the bottom of the
-panel. The link is shown in the position of least starting torque
-and current. Connect from W to 2 or W to 3 for starting heavier
-loads. <i>Two or three phase</i> motors are started simply by closing the
-switch. These motors start full load without starters. The motor
-should start promptly on closing the switch. It should be started
-the first time without being coupled to the line shaft. If the motor
-start free, but will not start loaded, it shows either that the
-load upon the motor is too great, the line voltage too low, or the
-frequency too high. The voltage and frequency with the motor running
-should be within 5% of the name plate rating and the voltage with 10
-to 15% while starting. If the motor do not start free, either it is
-getting no current or something is wrong with the motor. In either
-case an electrician should be consulted. <b>Solution:</b> To reverse
-the direction of rotation interchange the leads marked "XX" in the
-diagrams. <b>Temperature:</b> At full load the motor should not heat
-over 75 degrees Fahr. above the temperature of the surrounding air;
-if run in a small enclosed space with no ventilation, the temperature
-will be somewhat higher.</p></div>
-
-<p><span class="pagenum"><a name="Page_2008" id="Page_2008">2008</a></span>
-<b>Ques. What should be noted with respect to generator pulleys?</b></p>
-
-<p>Ans. A pulley of certain size is usually supplied with each generator
-by its manufacturer, and it is not generally advisable to depart much
-from the dimensions of this pulley. Accordingly, the solution of the
-pulley problem usually consists in finding the necessary diameter of
-the driving pulley relative to that of the pulley on the generator in
-order to furnish the required speed.</p>
-
-<p><b>Ques. What is the chief objection to belt drive?</b></p>
-
-<p>Ans. The large amount of floor space required.</p>
-
-<div class="figcenter">
-  <a name="fig2810"></a>
-  <img src="images/i176.jpg" alt="_" width="600" height="165" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,810.&mdash;Tandem drive for economizing
-floor space with belt transmission. Belts of different lengths are
-used, as shown, each of which passes over the driving wheel <i>d</i> of
-the engine, and then over the pulley wheel of one of the generators.
-In such an arrangement the belts would be run lengthwise through the
-room in which the machines are placed, and it is obvious that since
-the width of the room would be governed by the width of the machines
-thus installed, this method is a very efficient one for accomplishing
-the end in view.</p></div>
-
-<p><b>Ques. How may the amount of space that would ordinarily be
-required for belt drive, be reduced?</b></p>
-
-<p>Ans. By driving machines in tandem as in <a href="#fig2810">fig. 2,810</a>, or by the double
-pulley drive as in <a href="#fig2811">fig. 2,811</a>.
-<span class="pagenum"><a name="Page_2009" id="Page_2009">2009</a></span></p>
-
-<p><b>Ques. What is the objection to the tandem method?</b></p>
-
-<p>Ans. The most economical distance between centers cannot be employed
-for all machines.</p>
-
-<p><b>Ques. What is the objectionable tendency in resorting to floor
-economy methods with belt transmission?</b></p>
-
-<p>Ans. The tendency to place the machines too closely together. This is
-poor economy as it makes the cleaning of the machines a difficult and
-dangerous task; it is therefore advisable to allow sufficient room
-for this purpose regardless of the method of belting employed.</p>
-
-<div class="figcenter">
-  <a name="fig2811"></a>
-  <img src="images/i177.jpg" alt="_" width="600" height="166" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,811.&mdash;Double pulley drive for
-economizing floor space with belt transmission. Where a center crank
-engine is used both pulleys may be employed by belting a machine to
-each as shown. Although considerable floor space would be saved by
-the use of this scheme if the generators thus belted were placed at M
-and G yet still more floor space would be saved by having them occupy
-the positions indicated at M and S.</p></div>
-
-<p><b>Ques. What is the approved location for an alternator exciter?</b></p>
-
-<p>Ans. To economize floor space the exciter may be placed between the
-alternator and engine at S in <a href="#fig2811">fig. 2,811</a>.</p>
-
-<p><b>Belts.</b>&mdash;In the selection of a belt, the quality of
-the leather should be first under consideration. The leather must be
-firm, yet pliable, free from wrinkles on the grain or hair side, and
-of an even thickness throughout.
-<span class="pagenum"><a name="Page_2010" id="Page_2010">2010</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2812"></a>
-  <img src="images/i178.jpg" alt="_" width="600" height="119" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,812.&mdash;Separately excited
-belt driven alternator showing approved location of exciter. In
-an electrical station where alternating current is generated, the
-alternators for producing the current generally require separate
-excitation for their field windings; that is, it is usually necessary
-to install in conjunction with an alternator a small dynamo for
-supplying current to the alternator field. The exciter is a
-comparatively small machine; in fact, it requires only about 1 per
-cent. of the capacity of the alternator which it excites, and so
-being small is often belted to an auxiliary pulley mounted on the
-alternator shaft. Considerable floor space would be occupied by an
-installation of this nature if the exciter be placed at M, and belted
-to the alternator as indicated by the dotted lines. By locating the
-exciter at S, between the alternator and the engine, much floor
-space will be saved and the general appearance of the installation
-improved.</p></div>
-
-<p>If the belt be well selected and properly handled, it should do
-service for twenty years, and even then if the worn part be cut off,
-the remaining portion may be remade and used again as a narrower and
-shorter belt.</p>
-
-<div class="blockquot">
-<p>Besides leather belts, there are those made of rubber which withstand
-moisture much better than leather belts, and which also possess an
-excellent grip on the pulley; they are, however, more costly and much
-less durable under normal conditions.</p>
-
-<p>In addition to leather and rubber belts, there are belts composed
-of cotton, of a combination of cotton and leather, and of rope. The
-leather belt, however, is the standard and is to be recommended.</p></div>
-
-<p>Equally important with the quality of a belt is its size in order to
-transmit the necessary power.</p>
-
-<p class="blockquot">
-The average strain under which leather will break has been found by
-many experiments to be 3,200 pounds per square inch of cross section.
-A good quality of leather will sustain a somewhat greater strain. In
-use on the pulleys, belts should not be subjected to a greater strain
-than one eleventh their tensile strength, or about 290 pounds to the
-square inch or cross section. This will be about 55 pounds average
-strain for every inch in width of single belt three-sixteenths inch
-<span class="pagenum"><a name="Page_2011" id="Page_2011">2011</a></span>
-thick. The strain allowed for all widths of belting&mdash;single, light
-double, and heavy double&mdash;is in direct proportion to the thickness of
-the belt.</p>
-
-<p><b>Ques. How much horse power will a belt transmit?</b></p>
-
-<p>Ans. The capacity of a belt depends on, its width, speed, and
-thickness. <i>A single belt one inch wide and travelling 1,000 feet per
-minute will transmit one horse power; a double belt under the same
-conditions, will transmit two horse power.</i></p>
-
-<div class="figcenter">
-  <a name="fig2813"></a>
-  <img src="images/i-0331.jpg" alt="_" width="600" height="269" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,813.&mdash;One horse power transmitted by
-belt to illustrate the rule given above. A pulley is driven by a belt
-by means of the friction between the surfaces in contact. Let T be
-the tension on the driving side of the belt, and T', the tension on
-the loose side; then the driving force = T-T'. In the figure T is
-taken at 34 lbs. and T' at 1 lb.; hence driving force = 34-1 = 33
-lbs. Since the belt is travelling at a velocity of 1,000 feet per
-minute the power transmitted = 33 lbs. × 1,000 ft. = 33,000 ft. lbs.
-per minute = 1 horse power.</p></div>
-
-<div class="blockquot">
-<p>This corresponds to a working pull of 33 and 66 lbs. per inch of
-width respectively.</p>
-
-<p><b>Example.</b>&mdash;What width double belt will be required to transmit
-50 horse power travelling at a speed of 3,000 feet per minute?</p>
-
-<p>The horse power transmitted by each inch width of double belt travelling
-at the stated speed is</p></div>
-
-<p class="center"><b>( 1 × 3,000 / 1,000 ) × 2 = 6</b>,</p>
-
-<p class="no-indent">hence the width of belt required to transmit 50 horse power is</p>
-
-<p class="center"><b>50 ÷ 6 = 8.33</b>, say 8 inches.
-<span class="pagenum"><a name="Page_2012" id="Page_2012">2012</a></span></p>
-
-<p><b>Ques. At what velocity should a belt be run?</b></p>
-
-<p>Ans. At from 3,000 to 5,000 feet per minute.</p>
-
-<p><b>Ques. How may the greatest amount of power transmitting capacity
-be obtained from belts?</b></p>
-
-<p>Ans. By covering the pulleys with leather.</p>
-
-<p><b>Ques. How should belts be run?</b></p>
-
-<p>Ans. With the tight side underneath as in <a href="#fig2814">fig. 2,814</a>.</p>
-
-<div class="figcenter">
-  <a name="fig2814"></a>
-  <img src="images/i180.jpg" alt="_" width="600" height="406" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,814 and 2,815.&mdash;Right and wrong way
-to run a belt. The tight side should be underneath so as to increase
-the arc of contact and consequently the adhesion, that is to say, a
-<i>better grip</i>, is in this way obtained.</p></div>
-
-<p><b>Ques. What is a good indication of the capacity of a belt in operation?</b></p>
-
-<p>Ans. Its appearance after a few days' run.</p>
-
-<div class="blockquot">
-<p>If the side of the belt coming in contact with the pulley assume a
-mottled appearance, it is an indication that the capacity of the belt
-is considerably in excess of the power which it is transmitting,
-<span class="pagenum"><a name="Page_2013" id="Page_2013">2013</a></span>
-inasmuch as the spotted portions of the belt do not touch the pulley;
-and in consequence of this there is liable to be more or less
-slipping.</p>
-
-<p>Small quantities of a mixture of tallow and fish oil which have
-previously been melted together in the proportion of two of the
-former to one of the latter, will, if applied to the belt at frequent
-intervals, do much toward softening it, and thus by permitting its
-entire surface to come in contact with the pulley, prevent any
-tendency toward slipping. The best results are obtained when the
-smooth side of the belt is used next to the pulley, since tests
-conducted in the past prove that more power is thus transmitted, and
-that the belt lasts longer when used in this way.</p></div>
-
-<div class="figcenter">
-  <a name="fig2816"></a>
-  <img src="images/i-0332.jpg" alt="_" width="600" height="591" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,816.&mdash;The Hill friction clutch pulley
-for power control. The clutch mechanism will start a load equivalent
-to the double belt capacity of the pulley to which the clutch is attached.</p></div>
-
-<p><b>Ques. What is the comparison between the so called endless belts
-and laced belts?</b></p>
-
-<p>Ans. With an endless belt there is no uneven or noisy action as with
-laced belts, when the laced joint passes over the pulleys, and the
-former is free from the liability of breakage at the joint.</p>
-
-<p><b>Ques. How should a belt be placed on the pulleys?</b></p>
-
-<p>Ans. The belt should first be placed on the pulley at rest, and then
-run on the other pulley while the latter is in motion.
-<span class="pagenum"><a name="Page_2014" id="Page_2014">2014</a></span></p>
-
-<p class="blockquot">
-The best results are obtained, and the strain on the belt is less,
-when the speed at which the moving pulley revolves is comparatively
-low. With heavy belts, particular care should be taken to prevent
-any portion of the clothing being caught either by the moving belt
-or pulleys, as many serious accidents have resulted in the past from
-carelessness in regard to this important detail. The person handling
-the belt should, therefore, be sure of a firm footing, and when it is
-impossible to secure this, it is advisable to stop the engine and fit
-the belt around the engine pulley as well as possible by the aid of a
-rope looped around the belt.</p>
-
-<div class="figcenter">
-  <a name="fig2817"></a>
-  <img src="images/i182.jpg" alt="_" width="600" height="220" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,817&mdash;Sectional view of Hill
-clutch mechanism. In every case the mechanism hub A, and in a clutch
-coupling the ring W, is permanently and rigidly secured to the shaft
-and need not be disturbed when removing the wearing parts. When
-erected, the adjustment should be verified, and always with the
-clutch and ring engaged and at rest. If the jaws do not press equally
-on the ring, or if the pressure required on the cone be abnormal,
-loosen the upper adjusting nuts T´ on eye bolts and set up the lower
-adjusting nuts T´´ until each set of jaws is under the same pressure.
-Should the clutch then slip when started it is evident that the jaw
-pressure is insufficient and a further adjustment will be necessary.
-All clutches are equipped throughout with split lock washers.
-Vibration or shock will not loosen the nuts if properly set up. The
-jaws can be removed parallel to the shaft as follows: Remove the gibs
-V, and withdraw the jaw pins P, then pull out the levers D. Do not
-disturb the eye bolt nuts T´ and T´´. The outside jaws B can now be
-taken out. Remove the bolt nuts I allowing the fulcrum plates R to be
-taken off. On the separable hub pattern the clamping bolts must be
-taken out before fulcrum plate is removed. The inside jaws C may now
-be withdrawn. Always set the clutch operating lever in the position
-as shown in <a href="#fig2816">fig. 2,816</a> to avoid interference with mechanism
-parts. Oil the moving parts of the clutch. Keep it clean. Examine at regular
-intervals.</p></div>
-
-<p><b>Ques. Under what conditions does a belt drive give the best results?</b></p>
-
-<p>Ans. When the two pulleys are at the same level.</p>
-
-<p class="blockquot">
-If the belt must occupy an inclined position it should not form a
-greater angle than 45 degrees with the horizontal.</p>
-
-<p><b>Ques. What is a characteristic feature in the operation of
-belts, and why?</b></p>
-
-<p>Ans. Belts in motion will always run to the highest side of a
-<span class="pagenum"><a name="Page_2015" id="Page_2015">2015</a></span>
-pulley; this is due partially to the greater speed in feet per
-minute developed at that point owing to the greater circumference
-of the pulley, and also to the effects of centrifugal force.</p>
-
-<p class="blockquot">
-If, therefore, the highest sides of both pulleys be in line with each
-other, and the shafts of the respective pulleys be parallel to each
-other, there will be no tendency for the belt to leave the pulleys
-when once in its proper position. In order that these conditions be
-maintained, the belt should be no more than tight enough to prevent
-slipping, and the distance between the centers of the pulleys should
-be approximately 3.5 times the diameter of the larger one.</p>
-
-<div class="figcenter">
-  <a name="fig2818"></a>
-  <img src="images/i-0333.jpg" alt="_" width="600" height="573" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,818.&mdash;Hill clutch mechanism Smith
-type. The friction surfaces are wood to iron, the wood shoes being
-made from maple. All parts of the toggle gear are of steel and
-forgings with the exception of the connection lever which is of cast iron.</p></div>
-
-<p><b>Ques. What minor appurtenances should be provided in a station?</b></p>
-
-<p>Ans. Apparatus should be installed as a prevention against accidents,
-such as fire, and protection of attendants from danger.</p>
-
-<div class="blockquot space-below1">
-<p>In every electrical station there should be a pump, pipes and hose;
-the pump may be either directly connected to a small electric motor
-or belted to a countershaft, while the pipes and hose should be
-so placed that no water can accidentally reach the generators and
-<span class="pagenum"><a name="Page_2016" id="Page_2016">2016</a></span>
-electrical circuits. A number of fire bucket filled with water should
-be placed on brackets around the station, and with these there should
-be an equal number of bucket containing dry sand, the water being
-used for extinguishing fire occurring at a distance from the machines
-and conductors, and the sand for extinguishing fire in current
-carrying circuits where water would cause more harm than benefit. To
-prevent the sand being blown about the station, each sand bucket,
-when not in use, should be provided with a cover.</p>
-
-<p>Neat cans and boxes should be mounted in convenient places for greasy
-rags, waste, nuts, screws, etc., which are used continually and which
-therefore cannot be kept in the storeroom.</p>
-
-<p>While it is important to guard against fire in the station, it is
-equally necessary to provide for personal safety. All passages and
-dark pits should therefore be thoroughly lighted both day and night,
-and obstacles of any nature that are not absolutely necessary in
-the operation of the station, should be removed. Moving belts, and
-especially those passing through the floor, should be enclosed in
-iron railings. If high voltages be generated, it is well to place
-a railing about the switchboard to prevent accidental contact with
-current carrying circuits, and in such cases it is also advisable
-to construct an insulated platform on the floor in front of the switchboard.</p></div>
-
-<div class="figcenter">
-  <a name="fig2819"></a>
-  <img src="images/i184.jpg" alt="_" width="600" height="360" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,819.&mdash;Method of joining adjacent
-switchboard panels.</p></div>
-
-<p><b>Switchboards.</b>&mdash;The plan of switchboard wiring for alternating
-<span class="pagenum"><a name="Page_2017" id="Page_2017">2017</a></span>
-current work depends upon the system in use and this latter may be
-either of the single phase, two phase, three phase, or monocyclic
-types. The general principles in all these cases, however, are
-practically identical.</p>
-
-<p class="blockquot">
-<a href="#fig2820">Fig. 2,820</a> shows the switchboard wiring for a single
-phase alternator. As an aid in reading the diagram, the conductors carrying
-alternating current are represented by solid lines, and those
-carrying direct current, by dotted lines.</p>
-
-<div class="figcenter">
-  <a name="fig2820"></a>
-  <img src="images/i-0334.jpg" alt="_" width="600" height="1105" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,820.&mdash;Switchboard wiring for a single
-phase separately excited alternator. The direct current circuits are
-represented by dotted lines, and the alternating current circuit, by
-solid lines.</p></div>
-
-<p class="blockquot">
-The exciter shown at the right is a shunt wound machine. By means of
-the exciter rheostat, the voltage for exciting the field winding of
-the alternator is varied; this, in turn, varies the voltage developed
-in the alternator since the main leads of the exciter are connected
-through a double pole switch G to the field winding of the alternator.
-<span class="pagenum"><a name="Page_2018" id="Page_2018">2018</a></span></p></div>
-
-<div class="figcenter">
-  <a name="fig2821"></a>
-  <img src="images/i186.jpg" alt="_" width="600" height="362" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,821 to 2,825.&mdash;General Electric
-diagrams of connections. A, ammeter; C.B, circuit breaker; C.P,
-candle power; C.T, current transformer; D.R, discharge resistance; F,
-fuse; F.S, field switch; L, lamp; O.C, overload coil; P.P, pressure
-plug; P.R, pressure receptacle; R.C, reactance; rheo, rheostat;
-R.P, synchronizing plug, running; R.S, resistance; S, switch; S.I,
-synchronism indicator; S.P, synchronizing plug, starting; S.R,
-synchronizing receptacle; V, voltmeter.</p></div>
-
-<p><span class="pagenum"><a name="Page_2019" id="Page_2019">2019</a></span></p>
-
-<div class="blockquot">
-<p>A rheostat is also introduced in the alternator field winding circuit
-to adjust the alternator pressure. It may seem unnecessary to employ
-a rheostat in each of two separate field circuits to regulate the
-voltage of the alternator, but these rheostats are not both used to
-produce the same result. When a considerable variation of pressure
-is required, the exciter rheostat is manipulated, whereas for a fine
-adjustment of voltage the alternator rheostat is preferably employed.</p>
-
-<p>Sometimes a direct current ammeter is introduced in the alternator's
-field circuit to aid in the adjustment.</p>
-
-<p>The main circuit of alternator after being protected on both sides
-by fuses, runs to the double pole switch K. These fuses serve as a
-protection to the alternator in case of a short circuit at the main
-switch. It will be noticed the fuses are of the single pole type and
-are mounted a considerable distance apart; this is to prevent any
-liability of a short circuit between them in case of action. Enclosed
-fuses are now used entirely for such work, since in these there is no
-danger of heated metal being thrown about and causing damage when the
-fuse wire is melted. Enclosed fuses are also more readily and quickly
-replaced than open fuses, the containing tube of each being easy to
-adjust in circuit, and when the fuse wire within is once melted the
-tube is discarded for a new one.</p>
-
-<p>The main circuit after passing through the main switch is further
-protected on both sides by circuit breakers. Leaving these protective
-devices, the left hand side of the circuit includes the alternating
-current ammeter, and then connects with one of the bus bars. The
-right hand side of the circuit runs from the circuit breaker to the
-other bus bar. As many feeder circuits may be connected to the bus
-bars and supplied with current by the alternator as the capacity of
-this machine will permit. If, however, there be more than one feeder
-circuit, each must be wired through a double pole switch.</p>
-
-<p>In alternating current work the pressures dealt with are much greater
-than those in direct current installations, so that proportionate
-care must be taken in the wiring to remove all possibility of grounds.</p>
-
-<p>To locate such troubles, however, should they occur, a ground
-detector is provided. For this class of work the ground detector must
-be an instrument especially designed for high pressure circuits. Two
-of its terminals should be connected to the line wires and the third,
-to ground; in case of a leak on the line, a current will then flow
-through the detector and by the position of the pointer the location
-and seriousness of the leak may be judged.</p>
-
-<p>A step down transformer is also rendered necessary for the voltmeter
-and the pilot lamps, owing to the high voltage in use. The primary
-winding of the transformer is connected across the main circuit of
-the alternator. This connection should never be made so that it will
-be cut out of circuit when the main switch is open, for it is always
-advisable to consult the voltmeter before throwing on the load by closing this switch.
-<span class="pagenum"><a name="Page_2020" id="Page_2020">2020</a></span></p></div>
-
-<div class="figcenter">
-  <a name="fig2826"></a>
-  <img src="images/i188.jpg" alt="_" width="600" height="360" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,826 to 2,829.&mdash;General Electric
-diagrams of connections. A, ammeter; C.B, circuit breaker; C.P,
-candle power; C.T, current transformer; D.R, discharge resistance; F,
-fuse; F.S, field switch; L, lamp; O.C, overload coil; P.P, pressure
-plug; P.R, pressure receptacle; R.C, reactance; rheo, rheostat;
-R.P, synchronizing plug, running; R.S, resistance; S, switch; S.I,
-synchronous indicator: S.P, synchronizing plug, starting; S.R,
-synchronizing receptacle: V, voltmeter.</p></div>
-
-<p><span class="pagenum"><a name="Page_2021" id="Page_2021">2021</a></span>
-<b>Ques. How does the switchboard wiring for a two phase system
-differ from the single phase arrangement shown in <a href="#fig2820">fig. 2,820?</a></b></p>
-
-<p>Ans. It is practically the same, except for the introduction of an
-extra ammeter and a compensator in each of the outside wires, and in
-the use of a four pole switch in place of the two pole main switch.</p>
-
-<p class="blockquot">
-The ammeters, of course, are for measuring the alternating currents
-in each of the two phases or legs of the system, and the compensators
-are two transformers with their primary coils in series with the
-outside wires and their secondary coils in series with each other
-across the outside wires. The transformers thus connected are known
-as compensators or pressure regulators, and as such compensate for
-the drop in pressure on either side of the system.</p>
-
-<p><b>Ques. How is the four pole main switch wired?</b></p>
-
-<p>Ans. Its two central terminals which connect directly with the line
-wires, are joined together by a conductor, and from this point one
-wire is led off. This wire, together with the two outside wires, form
-the feeders of the system.</p>
-
-<p><b>Ques. How many voltmeters are required for the two phase system?</b></p>
-
-<p>Ans. One voltmeter is sufficient on the board if a proper switching
-device be employed to shift its connections across either of the two
-circuits; otherwise, two voltmeters will be necessary, one bridged
-across each of these respective circuits.</p>
-
-<p class="blockquot">
-The same reasoning holds true in regard to ground detectors, so
-that one or two of these will be required, depending upon the
-aforementioned conditions.</p>
-
-<p><b>Ques. What are the essential points of difference between the
-single phase switchboard wiring as shown in <a href="#fig2820">fig. 2,820</a>,
-and that required for a three wire three phase system?</b></p>
-
-<p>Ans. The three phase system requires the use of a three pole
-<span class="pagenum"><a name="Page_2022" id="Page_2022">2022</a></span>
-switch in place of the two pole switch; the insertion of an ammeter,
-a circuit breaker, and a compensator in each of the three wires of
-the system; the presence of two ground detectors instead of one, and
-the addition of a voltmeter switch if but one voltmeter be provided,
-or else the installation of two voltmeters, connected the one between
-the middle wire and outer right hand wire, and the other between the
-middle wire and outer left hand wire.</p>
-
-<div class="figcenter">
-  <a name="fig2830"></a>
-  <img src="images/i190.jpg" alt="_" width="600" height="431" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,830.&mdash;Diagram of switchboard
-connections for General Electric automatic voltage regulator with
-two exciters and two alternators.</p></div>
-
-<p><b>Ques. Mention a few points relating to lightning arresters.</b></p>
-
-<p>Ans. In most cases where direct current is used they are mounted
-on the walls of the station near the place at which the line wires
-enter. If they be mounted outside the station at this point, special
-precautions should be taken to keep them free from moisture by
-enclosing them in iron cases, but no matter where they are located it
-is necessary that they be dry in order to work properly.
-<span class="pagenum"><a name="Page_2023" id="Page_2023">2023</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2831"></a>
-  <img src="images/i191.jpg" alt="_" width="400" height="701" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,831 and 2,832.&mdash;Garton-Daniels
-alternating current lightning arrester; diagram showing connections.
-A lightning discharge takes the path indicated by the dotted line,
-across the upper air gap A, through resistance rod B, C, D, across
-copper strip R on the base, thence flowing to ground through the
-movable plunger M, lower on gap N, and ground binding post L.
-The discharge path is practically straight, contains an air gap,
-distance of but 3/32 inch, a series resistance averaging but 225
-ohms. The lightning discharge does not flow through the flexible
-lead connecting band D on the lower end of the resistance rod with
-the top of the movable plunger. These two points are electrically
-connected by the heavy copper strip R, and lightning discharges
-generally, if not always, take the path across this copper strip
-in preference to flowing through the inductance of the one turn
-of flexible cable. When a discharge occurs from line to ground
-through any lightning arrester, the air gaps arc over, and so there
-is offered a path from line to ground for the line current. This
-flow of line current following the lightning discharge to ground
-may vary anywhere from a small capacity current where the arrester
-is installed on an ungrounded circuit, a moderately heavy flow on
-a partially grounded circuit, to a very heavy flow on a grounded
-circuit&mdash;either a circuit operated as a dead grounded circuit, or a
-circuit which has become accidentally grounded during a storm. The
-path taken by this flow of line current from line to ground may be
-traced by following the path shown by the dashed line. It, as seen,
-crosses upper air gap A, flows through section B of the resistance
-rod to band C. Leaving band C it flows through the magnet winding
-H, thence to band D on the resistance rod, through flexible lead to
-upper end of movable plunger, through movable plunger, across lower
-air gap N, to ground binding post L, thence to ground. The function
-of the short length of resistance rod CD is as follows: It has an
-ohmic resistance of about 30 ohms but is <i>non-inductive</i>. Magnet
-winding H, connected to bands C and D on the ends of this short
-length of rod has an ohmic resistance of 3 ohms, but is <i>highly
-inductive</i>. Lightning discharges being of <i>high frequency</i> take the
-higher resistance <i>but non-inductive</i> path CD in their passage from
-line to ground. The flow of normal current from line to ground being
-of a very low frequency, 25 or 60 cycles in ordinary alternating
-current circuits, zero in direct current circuits&mdash;takes the <i>low
-resistance</i> path through coil H in its path to ground. Section CD of
-the rod is used therefore simply to shunt the inductance of winding
-H to high frequency lightning discharges, leaving the lightning
-discharge path in the arrester a <i>non-inductive</i> highly efficient
-path. In all Garton-Daniels A. C. lightning arresters operating on
-non-grounded or partially grounded circuits, the action of the air
-gaps and series resistance are together sufficient to extinguish the
-flow of normal current to ground at the zero point of the generator
-voltage wave. If, however, as frequently happens, the line grounds
-accidentally during a storm, then the arrester does not have to
-depend for its proper operation on the arc extinguishing properties
-of the air gaps and resistance, but the heavier flow of line current
-through the arrester energizes the movable plunger, which raises
-upward in the coil, opening the circuit between the discharge point M
-and the lower end of the plunger. To limit the flow of line current
-to ground the resistance rod B is provided, there being approximately
-225 ohms between the discharge point A and clamp C in the 2,500 volt
-arrester. This feature is particularly effective where the circuit is
-temporarily or accidentally grounded. The series resistance prevents
-a heavy short circuit through the arrester and limits the current to
-a value that is readily broken by the cut out and is not enough to
-impede the passage of the discharge.</p></div>
-
-<p><span class="pagenum"><a name="Page_2024" id="Page_2024">2024</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2833"></a>
-  <img src="images/i192.jpg" alt="_" width="600" height="358" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,833.&mdash;Diagram of switchboard
-connections for General Electric automatic voltage regulator with
-three exciters and three alternators.</p></div>
-
-<p><span class="pagenum"><a name="Page_2025" id="Page_2025">2025</a></span></p>
-
-<div class="blockquot">
-<p>If possible, one place should be set aside for them and a marble or
-slate panel provided on which they may be mounted.</p>
-
-<p>Wooden supports are undesirable for lightning arresters on account of
-the fire risk incurred; this, however, may be reduced to a minimum by
-employing skeleton boards and using sheets of asbestos between the
-arresters and the wood.</p>
-
-<p>In parts of the country where lightning is of common occurrence and
-where overhead circuits are installed which carry high pressures,
-heavy currents, and extend over considerable territory, it is
-advisable to have the station well equipped with lightning arresters
-of the most improved types.</p>
-
-<p>In each side of the main circuit, between the lightning arrester
-connections and the switchboard apparatus there should be connected a
-choke coil or else each of the main conductors at this point should
-be tightly coiled up part of its length to answer the same purpose.</p>
-
-<p>A quick and effective way of coiling up a wire consists in wrapping
-around a cylindrical piece of iron or wood that part of the conductor
-in which it is desired to have the coils, the desired number of
-times, and then withdrawing the cylindrical piece. The coils, each of
-which may contain 50 or 200 turns, thus inserted in the main circuit
-introduce a high resistance or reluctance to a lightning current, and
-thus prevent it passing to the generator; there will, however, be an
-easy path to earth afforded it through the lightning arrester, and
-so no damage will be done. Coils of the nature just mentioned may
-advantageously be introduced between the generator and switchboard
-to take up the reactive current developed upon the opening of the
-circuit, and in the case of suspended conductors, the coils may be
-used to take up the slack by the spring-like effect produced by them.</p>
-
-<p>The safety of the operator should be especially considered in the
-design of high pressure alternating current switchboards.</p>
-
-<p>Such protection may be secured by screening all the exposed
-terminals, or preferably by mounting all the switch mechanism on the
-back of the board with simply the switch handle projecting through to
-the front; by pushing or pulling the switch handle, the connections
-can thus be shifted either to one side of the system or to the other.</p></div>
-
-<p><b>Ques. Upon what does the work of assembling a switchboard depend?</b></p>
-
-<p>Ans. It depends almost entirely upon the size of the plant,
-<span class="pagenum"><a name="Page_2026" id="Page_2026">2026</a></span>
-varying from the simple task of mounting a single panel in the case
-of an isolated plant, to the more difficult problem of supporting a
-large number of panels in a central station.</p>
-
-<p><b>Ques. When the material chosen for a switchboard must be shipped a
-considerable distance, what form of board should be used?</b></p>
-
-<p>Ans. The board units or "slabs" should be of small dimensions, to
-avoid the liability of breakage and expense of renewal when a unit
-becomes cracked or machine injured.</p>
-
-<div class="figcenter">
-  <a name="fig2834"></a>
-  <img src="images/i-0335.jpg" alt="_" width="500" height="710" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,834 and 2,835.&mdash;Front and rear views
-showing General Electric automatic voltage regulator mounted on switchboard panel.</p></div>
-
-<p class="blockquot">
-Ordinarily, switchboards vary from five to eight feet in height
-and the widths of the panels vary from five to six feet. In some
-boards the seams between the slabs run vertically, and in others
-horizontally. In order to render the assembling of the switchboard
-as simple as possible, and its appearance when finished the most
-artistic, these seams should run horizontally rather than vertically.
-The edges of each of the slabs should also be chamfered so that there
-<span class="pagenum"><a name="Page_2027" id="Page_2027">2027</a></span>
-will be less danger of their breaking out when being mounted on the framework.</p>
-
-<p><b>Ques. In assembling a switchboard, how should the lower slabs be
-placed, and why?</b></p>
-
-<p>Ans. They should be suspended a little distance from the floor to
-prevent contact with any oil, dirt, water or rubbish that might be on
-the floor.</p>
-
-<p><b>Ques. How are the slabs or panels supported?</b></p>
-
-<p>Ans. They are carried on an iron or wooden framework with braces to
-give stability.</p>
-
-<div class="blockquot">
-<p>The braces should be securely fastened at one end to the wall of the
-station, and at the other end to the framework of the board, as shown
-in <a href="#fig2836">fig. 2,836</a>.</p>
-
-<p>To fasten the switchboard end of the brace directly to the slate,
-marble or other material composing the board is poor practice and
-should never be attempted.</p>
-
-<p>If the station be constructed of iron, these switchboard braces must
-be such that they will thoroughly insulate the board and its contents
-from the adjoining wall.</p></div>
-
-<div class="figcenter">
-  <a name="fig2836"></a>
-  <img src="images/i195.jpg" alt="_" width="350" height="894" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,836.&mdash;Method of supporting the framework
-of a switchboard.</p></div>
-
-<p><b>Ques. What is the usual equipment of a switchboard?</b></p>
-
-<p>Ans. It comprises switching devices, current or pressure limiting
-devices, indicating devices, and fuses for protecting the apparatus and circuits.
-<span class="pagenum"><a name="Page_2028" id="Page_2028">2028</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2837"></a>
-  <img src="images/i-0336.jpg" alt="_" width="600" height="355" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,837.&mdash;Diagram showing elementary
-connections of General Electric automatic regulator for direct
-current. It consists essentially of a main control magnet with two
-independent windings and a differentially wound relay magnet. One
-winding, known as the pressure winding, of the main control magnet
-is connected across the dynamo terminals, the other across a shunt
-in one of the load mains. The latter is the "compensating winding"
-and it opposes the action of the pressure winding so that as the
-load increases, a higher pressure at the dynamo is necessary to
-"over compound" for line drop. In ordinary practice, the voltage
-terminals are connected to the bus bars, and the compensating shunt
-inserted in one of the principal feeders of the system. In operation
-the shunt circuit across the dynamo field rheostat is first opened
-by means of a switch provided for that purpose on the base of the
-regulator and the rheostat turned to a point that will reduce the
-generator voltage 35 per cent below normal. The main control magnet
-is at once weakened and allows the spring to pull out the movable
-core until the main contacts are closed. This closes the second
-circuit of the differential relay, thus neutralizing its windings.
-The relay spring then lifts the armature and closes the relay
-contacts. The switch in the shunt circuit across the dynamo field
-rheostat is now closed, practically short circuiting the rheostat,
-and the dynamo voltage at once rises. As soon as it reaches the
-point for which the regulator has been adjusted, the main control
-magnet is strengthened, which causes the main contacts to open,
-which in turn open the relay contacts across the rheostat. The
-rheostat is now in the field circuit, the voltage at once falls
-off, the main contacts are closed, and relay armature released, and
-shunt circuit across the rheostat again completed. The voltage then
-starts to rise and this cycle of operation is continued at a high
-rate of vibration, maintaining not a constant but a steady voltage
-at the bus bars. When neither the compensating winding nor pressure
-wires are used, there will be no "over compounding" effect due to
-increase of load and a constant voltage will be maintained at the
-bus bars. The compensating winding on the control magnet, which
-opposes the pressure winding is connected across an adjustable shunt
-in the principal feeder circuit. As the load increases the voltage
-drop across the shunt increases and the effect of the compensating
-winding becomes greater. This will require a higher voltage on the
-pressure winding to open the main contacts and the regulator will
-therefore cause the dynamo to compensate for line drop, maintaining
-at the bus bars a steady voltage without fluctuations, which rises
-and falls with a load on the feeders, giving a constant voltage at
-the lamps or center of distribution. The compensating shunt may be
-adjusted so as to compensate for any desired line drop up to 15 per
-cent; it is preferably placed in the principal lighting feeder, but
-may be connected to the bus bars so that the total current will pass
-through it. The latter method, however, is sometimes desirable, as
-large fluctuating power loads on separate feeders might disturb the
-regulation of the lighting feeders. Adjustment is made by sliding
-the movable contact at the center of the shunt. This contact may be
-clamped at any desired point and determines the pressure across the
-compensating winding of the regulator's main control magnet. Where
-pressure wires are run back to the central station from the center
-of distribution they may be connected directly to the pressure
-winding of the main control magnet, and it is unnecessary to use the
-compensating shunt. The pressure wires take the place of the leads
-from the control magnet to the bus bars and maintain a constant
-voltage at the center of distribution.</p></div>
-
-<p><span class="pagenum"><a name="Page_2029" id="Page_2029">2029</a></span></p>
-
-<p class="blockquot">
-On some switchboards are also mounted small transformers for raising
-or lowering the voltages, and lightning arresters as a protection
-from lightning. In addition to the apparatus previously mentioned
-nearly all switchboards carry at or near their top two or more
-incandescent lamps provided with shades or reflectors, for lighting
-the board.</p>
-
-<p><b>Ques. What should be done before wiring a switchboard?</b></p>
-
-<p>Ans. The electrical connections between the various apparatus
-mounted on the face or front of the board, are made on the back of
-the board. It is necessary that these connections be properly made
-else considerable electrical power will be wasted at this point. The
-wiring on the back of the board should therefore be planned out on
-paper before commencing the work.</p>
-
-<div class="figcenter">
-  <a name="fig2838"></a>
-  <img src="images/i197.jpg" alt="_" width="600" height="350" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,838.&mdash;Diagram showing connections
-of General Electric automatic voltage regulator for direct current as
-connected for maintaining balanced voltage on both sides of a three
-wire system using a balancer set. In operation, should the voltage on
-the upper bus bars become greater than that on the lower ones, the
-middle and upper contacts on the regulator will close, thus opening
-the relay contacts to the left and closing those to the right. This
-inserts all the resistance in the field of balancer A, and short
-circuits the resistance in the field of balancer B. A will then
-be running as a motor, and B as a dynamo, thereby equalizing the
-two voltages until that on the lower bus bars becomes greater than
-that of the upper ones; then the regulator contacts operate in the
-opposite direction and balancer A is run as a dynamo, and balancer B
-as a motor. This cycle of operation is repeated at the rate of from
-three to four hundred times per minute, thus maintaining a balanced
-voltage on the system.</p></div>
-
-<p><span class="pagenum"><a name="Page_2030" id="Page_2030">2030</a></span></p>
-
-<p class="blockquot">
-In laying out the plan of wiring care must be taken to allow
-sufficient contact surface at each connection; there should be not
-less than one square inch of contact surface allowed for each 160
-amperes of current transmitted.</p>
-
-<div class="figcenter">
-  <a name="fig2839"></a>
-  <img src="images/i198.jpg" alt="_" width="600" height="512" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,839.&mdash;Diagram of connections of General
-Electric voltage regulators for one or more alternators using one exciter.</p></div>
-
-<div class="blockquot">
-<p>For the bus bars, which, by the way are always of copper, one square
-inch per 1,000 amperes is the usual allowance; this is equal to 1,000
-circular mils of cross sectional area per ampere.</p>
-
-<p>Every effort should be made to give the bus bars the greatest amount
-of radiation consistent with other conditions, in order that their
-resistances may not become excessive owing to the heat developed by
-the large currents they are forced to carry. Suppose, for instance,
-the number of amperes to be generated is such as to require bus bars
-having each a cross sectional area of one square inch. If the end
-<span class="pagenum"><a name="Page_2031" id="Page_2031">2031</a></span>
-dimensions of these bars were each 1 inch by 1 inch, there would be
-less radiating surface than if their dimensions were each 2 inches by
-½ inch.</p></div>
-
-<p><b>Operation of Alternators.</b>&mdash;The operation of an alternator
-when run singly differs but little from that for a dynamo.</p>
-
-<p class="blockquot">
-As to the preliminaries, the exciter must first be started. This is
-done in the same way as for any shunt dynamo. At first only a small
-current should be sent through the field winding of the alternator;
-then, if the exciter operates satisfactorily and the field magnetism
-of the operator show up well, the load may gradually be thrown on
-until the normal current is carried, the same method of procedure
-being followed as in the similar case of a dynamo.</p>
-
-<div class="figcenter">
-  <a name="fig2840"></a>
-  <img src="images/i-0337.jpg" alt="_" width="600" height="522" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,840 and 2,841.&mdash;General Electric
-equalizer regulator designed to equalize the load on two machines,
-and diagram of connections.</p></div>
-
-<p>On loading an alternator, a noticeable drop in voltage occurs across
-<span class="pagenum"><a name="Page_2032" id="Page_2032">2032</a></span>
-its terminals. This drop in voltage is caused in part by the
-demagnetization of the field magnets due to the armature current,
-and so depends in a measure upon the position and form of the pole
-pieces as well as upon those of the teeth in the armature core. The
-resistance of the armature winding also causes a drop in voltage
-under an increase of load.</p>
-
-<p class="blockquot">
-Another cause which may be mentioned is the inductance of the
-armature winding, which is in turn due to the positions of the
-armature coils with respect to each other and also with respect to
-the field magnets.</p>
-
-<div class="figcenter">
-  <a name="fig2842"></a>
-  <img src="images/i200.jpg" alt="_" width="600" height="368" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,842.&mdash;Connection of General Electric
-equalizing regulator for equalizing loads on an engine driven dynamo
-and rotary converter running in parallel. Should the load on the
-dynamo become greater than that on the rotary converter, the middle
-and upper contacts on the regulator close, and thus by means of the
-relay switch and control motor, cause the feeder regulator to boost
-the voltage on the rotary until the loads again become equal. Should
-the load on the rotary converter become greater than that on the
-generator, the regulator contacts operate in the reverse direction
-and the feeder regulator is caused to buck the rotary voltage.</p></div>
-
-<p><b>Alternators in Parallel.</b>&mdash;When the load on a station increases
-beyond that which can conveniently be carried by one alternator, it
-becomes necessary to connect other alternators in parallel with it.
-To properly switch in a new machine in parallel with one already in
-<span class="pagenum"><a name="Page_2033" id="Page_2033">2033</a></span>
-operation and carrying load, requires a complete knowledge of the
-situation on the part of the attendant, and also some experience.</p>
-
-<p class="blockquot">
-The connections for operating alternators in parallel are shown in
-<a href="#fig2843">fig. 2,843</a>. In the illustration the alternator A is
-in operation and is supplying current to the bus bars. The alternator B is
-at rest. The main pole switch B' by means of which this machine can be
-connected into circuit is therefore open.</p>
-
-<div class="figcenter">
-  <a name="fig2843"></a>
-  <img src="images/i201.jpg" alt="_" width="500" height="536" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,843.&mdash;Method of synchronizing with one
-lamp; <i>dark lamp method</i>. Assuming A to be in operation, B, may be
-brought up to approximately the proper speed, and voltage. Then if B,
-be run a little slower or faster than A, the synchronizing lamp will
-glow for one moment and be dark the next. At the instant when the
-pressures are equal and the machines in phase, the lamp will become
-dark, but when the phases are in quadrature, the lamp will glow at
-its maximum brilliancy. Since the flickering of the lamp is dependent
-upon the difference in frequency, the machines should not be thrown
-in parallel while this flickering exists. The nearer alternator
-approaches synchronism, in adjusting its speed, the slower the
-flickering, and when the flickering becomes very slow, the incoming
-machine may be thrown in the moment the lamp is dark by closing the
-switch. The machines are then in phase and tend to remain so, since
-if one slow down, the other will drive it as a motor.</p></div>
-
-<p class="blockquot">
-Now, if the load increase to such extent as to require the service
-of the second alternator B, it must be switched in parallel with A.
-In order that both machines may operate properly in parallel, three
-conditions must be satisfied before they are connected together, or
-else the one alternator will be short circuited through the other,
-and serious results will undoubtedly follow.</p></div>
-
-<p><span class="pagenum"><a name="Page_2034" id="Page_2034">2034</a></span>
-Accordingly before closing main switch B, it is necessary that</p>
-
-<p class="no-indent">
-&emsp;&emsp;&emsp;1. The frequencies of both machines be the same;<br />
-&emsp;&emsp;&emsp;2. The machines must be in synchronism;<br />
-&emsp;&emsp;&emsp;3. The voltages must be the same.</p>
-
-<p><b>Ques. How are the frequencies made the same?</b></p>
-
-<p>Ans. By speeding up the alternator to be cut in, or change the speed
-of both until frequency of both machines is the same.</p>
-
-<div class="figcenter">
-  <a name="fig2844"></a>
-  <img src="images/i202.jpg" alt="_" width="600" height="460" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,844.&mdash;Diagram of connections of
-General Electric automatic voltage regulator for several alternators
-running in parallel with exciters in parallel.</p></div>
-
-<p><b>Ques. How are the alternators synchronized or brought in phase?</b></p>
-
-<p>Ans. The synchronism of the alternators is determined by employing
-some form of synchronizer, as by the single lamp method of <a href="#fig2843">fig. 2,843</a>,
-or the two lamp method of <a href="#fig2845">fig. 2,845</a>.
-<span class="pagenum"><a name="Page_2035" id="Page_2035">2035</a></span></p>
-
-<p><b>Ques. In synchronizing by the one lamp method, when should the
-incoming machine be thrown in?</b></p>
-
-<p>Ans. It is advisable to close the switch when the machines are
-approaching synchronism rather than when they are receding from it,
-that is to say, the instant the lamp becomes dark.</p>
-
-<div class="figcenter">
-  <a name="fig2845"></a>
-  <img src="images/i203.jpg" alt="_" width="500" height="534" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,845.&mdash;Method of synchronizing with two
-lamps; <i>dark lamp method</i>. The two synchronizing lamps are connected
-as shown, and each must be designed to supply its rated candle power
-at the normal voltage developed by the alternators. Now since the
-alternators are both running under normal field excitation the left
-hand terminals of each of them will alternately be positive and
-negative in polarity, while the right hand terminals are respectively
-negative and positive in polarity. If, however, the alternators be
-in phase with each other, the left hand terminals of both of them
-will be positive while the right hand terminals are negative, and
-when the left hand terminals of both machines are negative the right
-hand terminals will be positive. Hence, when the machines are in
-phase there will be no difference of pressure between the left hand
-terminals or between the right hand terminals of the two machines.
-Hence, if the synchronizing lamps be connected as shown, both will
-be dark. The instant there is a difference of phase, both lamps
-will glow attaining full candle power when the difference of phase
-has reached a maximum. As the alternators continue to come closer
-in step, the red glow will gradually fade away until the lamps
-become dark. Then the switch may be closed, thereby throwing the
-two machines in parallel. If the intervals between the successive
-lighting up of the lamps are of short duration it is advisable to
-wait until these become longer even though the other conditions are
-satisfied, because where the phases pass each other rapidly there is
-a greater possibility of not bringing them together at the proper
-instant. An interval of not less than five seconds should therefore
-be allowed between the successive lighting up of the lamps, before
-closing the switch.</p></div>
-
-<p><span class="pagenum"><a name="Page_2036" id="Page_2036">2036</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2846"></a>
-  <img src="images/i204.jpg" alt="_" width="400" height="538" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,846.&mdash;Inductor type synchroscope.
-This type is especially applicable where pressure transformers are already
-installed for use with other meters. As it requires only about ten
-apparent watts it may be used on the same transformers with other
-meters. There are three stationary coils, N, M and C, and a moving
-system, comprising an iron armature, A, rigidly attached to a shaft
-suitably pivoted and mounted in bearings. A pointer is also attached
-to the shaft. The moving system is balanced and is not subjected
-to any restraining force, such as a spring or gravity control. The
-axes of the coils N and M are in the same vertical plane, but 90
-degrees apart, while the axis of C is in a horizontal plane. The
-coils N and M are connected in "split phase" relation through an
-inductive resistance P and non-inductive resistance Q, and these two
-circuits are parallel across the bus bar terminals 3 and 4 of the
-synchroscope. Coil C is connected through a non-inductive resistance
-across the upper machine terminals 1 and 2 of the synchroscope. <b>In
-operation</b>, current in the coil C magnetizes the iron core carried
-by the shaft and the two projections, marked A and "iron armature."
-There is however, no tendency to rotate the shaft. If current be
-passed through one of the other coils, say M, a magnetic field will
-be produced parallel with its axis. This will act on the projections
-of the iron armature, causing it to turn so that the positive and
-negative projections assume their appropriate position in the field
-of the coil M. A reversal of the direction in both coils will
-obviously not affect the position of the armature, hence alternating
-current of the same frequency and phase in the coils C and M cause
-the same directional effect upon the armature as if direct current
-were passed through the coils. If current lagging 90 degrees behind
-that in the coils M and C be passed through the coil N, it will cause
-no rotative effect upon the armature, because the maximum value of
-the field which it produces will occur at the instant when the pole
-strength of the armature is zero. The two currents in the coils M and
-N produce a shifting magnetic field which rotates about the shaft as
-an axis. As all currents are assumed to be of the same frequency, the
-rate of rotation of this field is such that its direction corresponds
-with that of the armature projections at the instant when the poles
-induced in them by the current in the coil C are at maximum value,
-and the field shifts through 180 degrees in the same interval as is
-required for reversal of the poles. This is the essential feature of
-the instrument, namely, that the armature projections take a position
-in the rotating magnetic field which corresponds to the direction of
-the field at the instant when the projections are magnetized to their
-maximum strength by their current in the coil C. If the frequency
-of the currents in the coils which produce the shifting field be
-less than that in the coil which magnetized the armature, then the
-armature must turn in order that it may be parallel with the field
-when its poles are at maximum strength.</p></div>
-
-<p><b>Ques. What are the objections to the one lamp method?</b>
-<span class="pagenum"><a name="Page_2037" id="Page_2037">2037</a></span></p>
-
-<p>Ans. The filament of the lamp may break, and cause darkness, or the
-lamp may be dark with considerable voltage as it takes over 20 volts
-to cause a 100 volt lamp to glow.</p>
-
-<p><b>Ques. What capacity of single lamp must be used?</b></p>
-
-<p>Ans. It must be good for twice the voltage of either machine.</p>
-
-<div class="figcenter">
-  <a name="fig2847"></a>
-  <img src="images/i205.jpg" alt="_" width="600" height="467" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,847.&mdash;Brilliant lamp method of
-synchronizing. The synchronizing lamps are connected as shown, and
-must be of the alternator voltage. When the voltages are equal and
-the machines in phase, the difference of pressure between <i>a</i> and a
-given point is the same as that between <i>a'</i> and the same point; this
-obtains for <i>b</i> and <i>b'</i>. Accordingly, a lamp connected across
-<i>a b'</i> will burn with the same brilliancy as across <i>a' b</i>; the
-same holds for the other lamp. When the voltages are the same and
-the phase difference is 180° the lamps are dark, and as the phase
-difference is decreased, the lamps glow with increasing brightness
-until at synchronism they glow with maximum brilliancy. Hence the
-incoming alternator should be thrown in at the instant of maximum brilliancy.</p></div>
-
-<p><b>Ques. What modification of the synchronizing methods shown in
-the accompanying illustrations is necessary when high pressure
-alternators are used?</b></p>
-
-<p>Ans. Step down transformers must be used between the alternators and
-the lamps to obtain the proper working voltages for the lamps.
-<span class="pagenum"><a name="Page_2038" id="Page_2038">2038</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2848"></a>
-  <img src="images/i206.jpg" alt="_" width="600" height="325" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,848.&mdash;Synchronizing with high pressure
-alternators; dark and brilliant lamp methods. In both methods the
-primaries of the transformers are connected in the same way across
-the terminals of the alternators as shown. In the dark lamp method,
-the connections between the secondary coils of the transformers must
-be made so that when each is subjected to the same conditions the
-action of the one coil opposes that of the other as in the dark lamp
-method; then, if the transformers be both of the same design, there
-will be no voltage across the lamps when the alternators are in phase
-with each other. If the ratio of each transformer is such as to give,
-for example, 100 volts across its secondary terminals, then the two
-incandescent lamps since they are joined together in series must
-each be designed for 100 volts. One 200 volt lamp could be used in
-either method in place of the two 100 volt lamps. When, therefore,
-the alternators are directly opposite in phase to each other, both
-the lamps will burn brightly; as the alternators come together in
-phase the lamps will produce less and less light, until when the
-machines are exactly in phase no light will be emitted at all, at
-which instant the incoming alternator should be thrown in. It must
-be evident, if the transformer secondary connections are arranged as
-in the brilliant lamp method, so that they do not oppose each other,
-the lamps will be at maximum brilliancy when the alternators are in
-phase and dark when the phase difference is 180°, assuming of course
-equalized voltage.</p></div>
-
-<p><span class="pagenum"><a name="Page_2039" id="Page_2039">2039</a></span>
-<b>Ques. How is the voltage of an incoming machine adjusted so that
-it will be the same as the one already in operation?</b></p>
-
-<p>Ans. By varying the field excitation with a rheostat in the
-alternator field circuit.</p>
-
-<p><b>Ques. How may two or more alternators be started
-simultaneously?</b></p>
-
-<p>Ans. After bringing each of them up to its proper speed so as to
-obtain equal frequencies, the main switches may be closed, thereby
-joining their armature circuits in parallel. As yet, however, their
-respective field windings have not been supplied with current, so
-that no harm can result in doing this. The exciters of these machines
-after being joined in parallel, should then be made to send direct
-current simultaneously through the field windings of the alternators,
-and from this stage on the directions previously given may be
-followed in detail.</p>
-
-<p><b>Ques. What are the conditions when two or more alternators are
-directly connected together?</b></p>
-
-<p>Ans. If rigidly connected together, or directly connected to the same
-engine, they must necessarily run in the same manner at all times.</p>
-
-<p class="blockquot">
-When machines connected in this way are once properly adjusted so
-that they are in phase with each other, their operation in parallel
-is even a simpler task than when they are all started together but
-are not directly connected.</p>
-
-<p><b>Ques. When an alternator is driven by a gas engine, what provision
-is sometimes made to insure successful operation in parallel?</b></p>
-
-<p>Ans. An amortisseur winding is provided to counteract the tendency to "hunting."
-<span class="pagenum"><a name="Page_2040" id="Page_2040">2040</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2849"></a>
-  <img src="images/i208.jpg" alt="_" width="600" height="386" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,849.&mdash;Diagram of Lincoln Synchronizer.
-<b>In construction</b>, a stationary coil F, has suspended within
-it a coil A, free to move about an axis in the planes of both coils
-and including a diameter of each. If an alternating current be
-passed through both coils, A, will take a position with its plane
-parallel to F. If now the currents in A and F be reversed with
-respect to each other, coil A will take up a position 180° from its
-former position. Reversal of the relative directions of currents in
-A and F is equivalent to changing their phase relation by 180°, and
-therefore this change of 180° in phase relation is followed by a
-corresponding change of 180° in their mechanical relation. Suppose
-now, instead of reversing the relative direction of currents in A
-and F, the change in phase relation between them be made gradually
-and without disturbing the current strength in either coil. It is
-evident that when the phase difference between A and F reaches 90°,
-the force between A and F will become reduced to zero, and a movable
-system, of which A may be made a part, is in condition to take up
-any position demanded by any other force. Let a second number of
-this movable system consist of coil B, which may be fastened rigidly
-to coil A, with its plane 90° from that of coil A, and the axis
-of A passing through diameter of B. Further, suppose a current to
-circulate through B, whose difference in phase relation to that in
-A, is always 90°. It is evident under these conditions that when the
-difference in phase between A and F is 90°, the movable system will
-take up a position, such that B is parallel to F, because the force
-between A and F is zero, and the force between B and F is a maximum;
-similarly when the difference in phase between B and F is 90°, A
-will be parallel to F. That is, beginning with a phase difference
-between A and F of zero a phase change of 90° will be followed by a
-mechanical change on a movable system of 90°, and each successive
-change of 90° in phase will be followed by a corresponding mechanical
-change of 90°. For intermediate phase relation, it can be proved that
-under certain conditions the position of equilibrium assumed by the
-movable element will exactly represent the phase relations. That is,
-with proper design, the mechanical angle between the plane of F and
-that of A and also between the plane of F and that of B, is always
-equal to the phase angle between the current flowing in F and those
-in A and B respectively. <b>As commercially constructed</b> coil F
-consists of a small laminated iron field magnet with a winding whose
-terminals are connected with binding posts. The coils A and B are
-windings practically 90° apart on a laminated iron armature pivoted
-between the poles of the magnet. These two windings are joined,
-and a tap from the junction is brought out through a slip ring to
-one of two other binding posts. The two remaining ends are brought
-out through two more slip rings, one of which is connected to the
-remaining binding post, through a non-inductive resistance, and the
-other to the same binding post through an inductive resistance. A
-light aluminum hand attached to the armature shaft marks the position
-assumed by the armature.</p></div>
-
-<p><span class="pagenum"><a name="Page_2041" id="Page_2041">2041</a></span>
-<b>Ques. What is the action of the amortisseur winding?</b></p>
-
-<p>Ans. Any sudden change in the speed of the field, generates a current
-in the amortisseur winding which resists the change of velocity that
-caused the current.</p>
-
-<p class="blockquot">
-The appearance of an amortisseur winding is shown in the cut below
-(<a href="#fig2850">fig. 2,850</a>) illustrating the field of a synchronous
-condenser equipped with amortisseur winding.</p>
-
-<div class="figcenter">
-  <a name="fig2850"></a>
-  <img src="images/i-0338.jpg" alt="_" width="600" height="313" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,850.&mdash;General Electric field of
-synchronous condenser provided with amortisseur winding. Hunting is
-accompanied by a shifting of flux across the face of the pole pieces
-due to the variation in the effect of armature reaction on the main
-field flux as the current varies and the angular displacement between
-the field and armature poles is changed. Copper short circuited
-collars placed around the pole face have currents induced in them by
-this shifting flux, which have such a direction as to exert a torque
-tending to oppose any change in the relative position of the field
-and armature. This action is similar to that of the running torque
-of an induction motor and the damping device has been still further
-developed until in its best form it resembles the armature winding
-of a "squirrel cage" induction motor. The pole pieces are in ducts,
-and low resistance copper bars placed in them with their ends joined
-by means of a continuous short circuiting ring extending around
-the field. Such a device has proven very effective in damping out
-oscillations started from any cause, the same winding doing duty as a
-damping device and to assist the starting characteristics.</p></div>
-
-<p><b>Ques. How are three phase alternators synchronized?</b></p>
-
-<p>Ans. In a manner similar to the single phase method.</p>
-
-<p class="blockquot">
-Thus the synchronizing lamps may be arranged as in <a href="#fig2851">fig. 2,581</a>,
-which is simply an extension of the single phase method.</p>
-
-<p><b>Ques. Are three lamps necessary?</b></p>
-
-<p>Ans. Only to insure that the connections are properly made, after which
-one lamp is all that is required.
-<span class="pagenum"><a name="Page_2042" id="Page_2042">2042</a></span></p>
-
-<p><b>Ques. How is it known that the connections of <a href="#fig2851">fig. 2,851</a>
-are correct?</b></p>
-
-<p>Ans. If, in operation, the three lamps become bright or dark
-<i>simultaneously</i>, the connections are correct; if this action takes
-place <i>successively</i>, the connections are wrong.</p>
-
-<p class="blockquot space-below1">
-If wrong, transpose the leads of one machine until simultaneous
-action of the lamps is secured.</p>
-
-<div class="figcenter">
-  <a name="fig2851"></a>
-  <img src="images/i210.jpg" alt="_" width="600" height="443" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,851.&mdash;Method of synchronizing three
-phase alternators with, three lamps, being an extension of the single
-phase method.</p></div>
-
-<p><b>Ques. What is the disadvantage of the lamp method of synchronizing?</b></p>
-
-<p>Ans. Lack of sensitiveness.</p>
-
-<p><b>Ques. Which is the accepted lamp method, dark or brilliant?</b></p>
-
-<p>Ans. In the United States it is usual to make the connections
-<span class="pagenum"><a name="Page_2043" id="Page_2043">2043</a></span>
-for a dark lamp at synchronism, while in England the opposite
-practice obtains.</p>
-
-<p class="blockquot">
-With the dark lamp method, the breaking of a filament might cause the
-machines to be connected with a great phase difference, whereas, with
-the brilliant lamp it is difficult to determine the point of maximum
-brilliancy. This latter method, therefore may be called the safer.</p>
-
-<p><b>Ques. What may be used in place of lamps for synchronizing?</b></p>
-
-<p>Ans. Some form of synchroscopes, or synchronizers.</p>
-
-<p><b>Ques. How does the Lincoln synchronizer work?</b></p>
-
-<p>Ans. The construction is such that a hand moves around a dial so
-that the angle between the hand and the vertical is always the phase
-angle between the two sources of electric pressure to which the
-synchronizer is connected.</p>
-
-<p class="blockquot">
-If the incoming alternator be running too slow, the hand deflects in
-one direction, if too fast, in the other direction. When the hand
-shows no deflection, that is, when it stands vertical, the machines
-are in phase. A complete revolution of the hand indicates a gain
-or loss of one cycle in the frequency of the incoming machine, as
-referred to the bus bars.</p>
-
-<p><b>Cutting Out Alternator.</b>&mdash;When it is desired to cut out of
-circuit an alternator running in parallel with others, the method of
-procedure is as follows:</p>
-
-<table border="0" style="max-width: 25em;" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdc_top"><br />1.</td>
-      <td class="tdl"><br />Reduce driving power until the load has been transferred
-                            to the other alternators, adjusting field rheostat to obtain
-                            minimum current;</td>
-    </tr><tr>
-      <td class="tdc">2.</td>
-      <td class="tdl">Open main switch;</td>
-    </tr><tr>
-      <td class="tdc">3.</td>
-      <td class="tdl">Open field switch.</td>
-    </tr>
- </tbody>
-</table>
-
-<p><b>Ques. What precaution should be taken?</b></p>
-
-<p>Ans. <i>Never</i> open field switch before main switch.
-<span class="pagenum"><a name="Page_2044" id="Page_2044">2044</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2852"></a>
-  <img src="images/i-0339.jpg" alt="_" width="600" height="320" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig</span>. 2,852.&mdash;General Electric 500 kw.,
-horizontal mixed pressure Curtis turbine connected to a 500 kw.
-dynamo. In a Curtis turbine it is not necessary to use the whole
-periphery of the first stage for low pressure steam nozzles. A
-section can be partitioned off and equipped with special expanding
-nozzles to receive steam at high pressure direct from the boilers.
-Such nozzles deliver their steam against the same wheel as do
-the low pressure nozzles, but occupy only a small portion of its
-periphery. The steam is expanded in these nozzles from high pressure
-all the way down to the normal pressure of the first stage, and in
-such expansion acquires a high velocity and consequently contains
-a great deal of energy&mdash;much more than does an equal quantity of
-low pressure steam. In consequence of this, high pressure steam is
-used with a far lower water rate than is obtained with low pressure
-steam, or with high pressure steam reduced to low pressure in a
-reducing valve. This construction is called "mixed pressure." Its
-function is the same as that of the reducing valve, that is, it makes
-up for a deficiency of low pressure steam by drawing direct on the
-boilers. With this construction, the full power of the turbine can be
-developed with: All low-pressure steam, all high pressure steam, or,
-any necessary proportion of steam of each pressure. Furthermore, the
-transition from all low pressure to all high pressure, through all
-the conditions intermediate between these extremes, is provided for
-automatically by the turbine governor; a deficiency of low pressure
-steam causes the high pressure nozzles to open automatically.</p></div>
-
-<p><span class="pagenum"><a name="Page_2045" id="Page_2045">2045</a></span>
-<b>Ques. What is the ordinary method of cutting out an alternator?</b></p>
-
-<p>Ans. The main switch is usually opened without any preliminaries.</p>
-
-<p><b>Ques. What is the objection to this procedure?</b></p>
-
-<p>Ans. It suddenly throws all the load on the other alternators, and
-causes "hunting."</p>
-
-<p><b>Ques. What forms of drive are especially desirable for running
-alternators in parallel, and why?</b></p>
-
-<p>Ans. Water turbine or steam turbine because of the uniform torque,
-thus giving uniform motion of rotation.</p>
-
-<p class="blockquot">
-With reciprocating engines, the crank effect is very variable during
-the revolution, resulting in pulsations driving the alternator too
-fast or too slow, and causing cross current between the alternators.</p>
-
-<p><b>Ques. Is a sluggish, or a too sensitive governor preferable
-on an engine driving alternators in parallel?</b></p>
-
-<p>Ans. A sluggish governor.</p>
-
-<p><b>Alternators in Series.</b>&mdash;Alternators are seldom if ever
-connected in series, for the reason that the synchronizing tendency
-peculiar to these machines causes them to oppose each other and fall
-out of phase when they are joined together in this way. If, however,
-they be directly connected to each other, or to an engine, so that
-they necessarily keep in phase at all times, and thus add their
-respective voltages instead of counteracting them, series operation is possible.</p>
-
-<p class="blockquot">
-NOTE.&mdash;According to the practice of the General Electric Co.,
-2½ degrees of phase difference from a mean is the limit allowable in
-ordinary cases. It will, in certain cases, be possible to operate
-satisfactorily in parallel, or to run synchronous apparatus from
-machines whose angular variation exceeds this amount, and in other
-cases it will be easy and desirable to obtain a better speed control.
-The 2½ degree limit is intended to imply that the maximum departure
-from the mean position during any revolution shall not exceed 2½ ÷
-360 of an angle corresponding to two poles of a machine. The angle of
-circumference which corresponds to the 2½ degree of phase variation
-can be ascertained by dividing 2½ by ½ the number of pole; thus, in a
-20 pole machine, the allowable angular variation from the mean would
-be 2½ ÷ 10 = ¼ of one degree.
-<span class="pagenum"><a name="Page_2046" id="Page_2046">2046</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2853"></a>
-  <img src="images/i214.jpg" alt="_" width="600" height="446" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig</span>. 2,853.&mdash;Diagram of connections for
-synchronizing two compound wound three phase alternators. A and
-A' are the armatures of the two machines, the fields of which are
-partly separately excited, the amount of excitation current being
-controlled by the series compounding rheostats B and B', which form
-a stationary shunt. It is assumed that the alternator A is connected
-to the bus bars 1, 2, and 3, by the switch 1S. If an increase make
-it necessary to introduce the alternator A', it is first run up to
-speed and excited to standard pressure by its exciter, and then
-the double plug switch 3S is closed, connecting the primary of the
-station transformer T and T' with the bus bars through the secondary
-coil, so that the synchronizing lamps light up when the secondary
-circuit is closed through the single pole switch 4S. The primary of
-the station transformer T is thus excited through the double pole
-switch 5S, connecting it with the outer terminals of the armature
-A'. The two alternators will now work in opposition to each other
-upon the synchronizing lamps, the transformer T being operated by
-the new alternator A' through the switch 2S, and the transformer
-T' being operated by the working alternator A, from the bus bars.
-If the new alternator be not in step with the working alternator,
-the synchronizing lamps will glow, growing brighter and dimmer
-alternately with greater or lesser rapidity. In this case, the
-armature speed of the new alternator must be controlled in such a
-manner that the brightening and dimming will occur more and more
-slowly, until the lamps cease to glow or remain extinguished for
-a decided interval of time. The extinction of the light is due to
-the disappearance of the secondary current, and indicates that
-the alternators are in step. The switch 2S should now be thrown,
-thus coupling the two machines electrically, and both of them will
-continue to operate in step. The double pole equalizer switch 6S
-should now be closed, connecting the two field windings in parallel
-and equalizing the compounding, so that any variations of load will
-affect the two alternators equally. After the alternators have been
-connected in parallel, the switches 4S and 5S, may be opened leaving
-the switch 3S closed, to operate the switchboard lamps K, K, as pilot
-lights from the bus bars.</p></div>
-
-<p><span class="pagenum"><a name="Page_2047" id="Page_2047">2047</a></span>
-<b>Transformers.</b>&mdash;These, as a whole, are simple in construction,
-high in efficiency, and comparatively inexpensive. Their principles
-of operation are also readily understood.</p>
-
-<p>The efficiency of a transformer, that is, the ratio between full
-load primary and full load secondary is greatest when the load on it
-is such that the sum of the constant losses equals the sum of the
-variable losses.</p>
-
-<p class="blockquot">
-In general, transformers designed for high frequencies and large
-capacities are more efficient than those designed for low frequencies
-and small capacities. As a whole, however, a transformer leaves
-but little to be desired as regards efficiency, a modern 60 cycle
-transformer of 50 kilowatts capacity or more possesses an efficiency
-of approximately 98 per cent. at full load and an efficiency of about
-97 per cent. at half load.</p>
-
-<p><b>Ques. How should a transformer be selected, with respect to efficiency?</b></p>
-
-<p>Ans. One should be chosen, whose parts are so proportioned that the
-point of maximum efficiency occurs at that load which the transformer
-usually carries in service.</p>
-
-<p class="blockquot">
-In many alternating current installations, comparatively light loads
-are carried the greater part of the time, the rated full load or an
-overload being occurrences of short durations. For such purposes
-special attention should be given to the designing or selecting
-of transformers having low core losses rather than low resistance
-losses, because the latter are then of relatively small importance.</p>
-
-<p><b>Ques. What kind of efficiency is the station manager interested in?</b></p>
-
-<p>Ans. The "all day efficiency."</p>
-
-<p class="blockquot">
-This expression, as commonly met with in practice, denotes <i>the
-percentage that the amount of energy actually used by the consumer
-is of the total energy supplied to his transformer during 24 hours</i>.
-The formula for calculating the all day efficiency of a transformer
-is based upon the supposition that the amount of energy used by the
-<span class="pagenum"><a name="Page_2048" id="Page_2048">2048</a></span>
-consumer during 24 hours is equivalent to full load on his
-transformer during five hours and is as follows:</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&emsp;&emsp;&nbsp;5w</td>
-   </tr><tr>
-      <td class="tdr">E =&nbsp;</td>
-      <td class="tdl">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</td>
-   </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdl">24c + 5r + 5w</td>
-   </tr><tr>
-      <td class="tdr">where&emsp;&emsp;&nbsp;</td>
-      <td class="tdc">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">E =&nbsp;</td>
-      <td class="tdl">&nbsp;the all day efficiency of the transformer,</td>
-   </tr><tr>
-      <td class="tdr">w =&nbsp;</td>
-      <td class="tdl">&nbsp;the full load in watts on the primary,</td>
-   </tr><tr>
-      <td class="tdr">c =&nbsp;</td>
-      <td class="tdl">&nbsp;the core loss in watts,</td>
-   </tr><tr>
-      <td class="tdr">r =&nbsp;</td>
-      <td class="tdl">&nbsp;the resistance loss in watts.</td>
-   </tr>
- </tbody>
-</table>
-
-<div class="figcenter">
-  <a name="fig2854"></a>
-  <img src="images/i216.jpg" alt="_" width="600" height="390" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,854.&mdash;Performance curves of
-Westinghouse air blast 550 kw, 10,500 volt transformer, 3,000
-alternations.</p></div>
-
-<p class="space-above1"><b>Ques. What are the usual all day efficiencies?</b></p>
-
-<p>Ans. The average is about 85 per cent. for those of 1 kilowatt
-capacity, 92 per cent. for those of 5 kilowatts capacity, 94 per
-cent. for those of 10 kilowatts capacity, and about 94.5 per cent.
-for those of 15 kilowatts capacity.</p>
-
-<p><b>Ques. What becomes of the energy lost by a transformer?</b></p>
-
-<p>Ans. It reappears as heat in the windings and core.
-<span class="pagenum"><a name="Page_2049" id="Page_2049">2049</a></span></p>
-
-<div class="blockquot">
-<p>This heat not only increases the resistances of the windings and
-core, producing thereby a further increase of their respective
-losses, but in addition causes in time a peculiar effect on the iron
-core which is intensified by the reversals of magnetism constantly
-going on within it.</p>
-
-<p>After about two years' service, the iron apparently becomes fatigued
-or tired, and this phenomenon is called aging of the iron. Since
-the life of the transformer depends to a great extent upon this
-factor, the conditions responsible for its existence should as far
-as possible be removed. Means must therefore be provided in the
-construction to radiate the heat as quickly as it is generated.</p></div>
-
-<p><b>Ques. What kind of oil is used in oil cooled transformers?</b></p>
-
-<p>Ans. Mineral oil.</p>
-
-<div class="figcenter">
-  <a name="fig2855"></a>
-  <img src="images/i217.jpg" alt="_" width="600" height="188" />
-  <p class="f90 space-below1">
-<span class="smcap">Fig.</span> 2,855.&mdash;General arrangement of air blast
-transformers and blowers.</p></div>
-
-<p><b>Ques. How is it obtained?</b></p>
-
-<p>Ans. By fractional distillations of petroleum unmixed with any other
-substances and without subsequent chemical treatment.</p>
-
-<p><b>Ques. What is the important requirement for transformer oil?</b></p>
-
-<p>Ans. It should be free from moisture, acid, alkali or sulphur compounds.</p>
-
-<p><b>Ques. How may the presence of moisture be determined?</b></p>
-
-<p>Ans. By thrusting a red hot iron rod in the oil; if it "crackle,"
-moisture is present.
-<span class="pagenum"><a name="Page_2050" id="Page_2050">2050</a></span></p>
-
-<p><b>Ques. Describe the Westinghouse method of drying oil.</b></p>
-
-<p>Ans. It is circulated through a tank containing lime, and afterwards,
-through a dry sand filter.</p>
-
-<p><b>Ques. What is the objection to heating the oil (raising its
-temperature slightly above boiling point of water) to remove the
-moisture?</b></p>
-
-<p>Ans. The time consumed (several days) is excessive.</p>
-
-<div class="figcenter">
-  <a name="fig2856"></a>
-  <img src="images/i-0340.jpg" alt="_" width="600" height="297" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,856.&mdash;Small Curtis turbine generator
-set as made by the General Electric Co., in sizes from 5 kw.,
-to 300 kw. It can be arranged to operate either condensing or
-non-condensing, and at any steam pressure above 80 lbs. for the
-smaller sizes and 100 lbs. for the larger. There are only two main
-bearings. A thrust bearing, consisting of roller bearings and running
-between hardened steel face washers located at either end of the
-main bearings is provided solely for centering the rotor so as to
-equalize the clearance. A centrifugal governor is provided (in the
-smaller sizes) completely housed, and mounted directly on the main
-shaft end. It controls a balanced poppet valve through a bell crank.
-In the larger sizes (75 kw. and above) the governor is mounted on a
-vertical secondary shaft geared to the main shaft and controls a cam
-shaft which opens or closes a series of valves in rotation, admitting
-the steam to different sections of the first stage nozzles. In this
-way throttling of the steam is avoided. There is also an emergency
-governor which closes the throttle valve in the event of the speed
-reaching a predetermined limit. The speeds of operation range from
-5,000 R.P.M. for the smallest size to 1,500 R.P.M. for the largest.
-The lubrication system is enclosed and is automatic. Air leakage
-where the shaft passes through the wheel casing is prevented by steam
-seal.</p></div>
-
-<p><b>Ques. What effect has moisture?</b></p>
-
-<p>Ans. It reduces the insulation value of the oil. .06 per cent. of
-moisture has been found to reduce the dielectric strength of oil
-about 50 per cent. "dry" oil will withstand a pressure of 25,000
-volts between two 9½ inch knobs separated .15 inch.
-<span class="pagenum"><a name="Page_2051" id="Page_2051">2051</a></span></p>
-
-<p><b>Ques. What is understood by transformer regulation?</b></p>
-
-<p>Ans. It is the difference between the secondary voltage at no load
-and at full load, and is generally expressed as a percentage of the
-secondary voltage at no load.</p>
-
-<p><b>Ques. What governs its value?</b></p>
-
-<p>Ans. The resistance and reactance of the windings.</p>
-
-<div class="figcenter">
-  <a name="fig2857"></a>
-  <img src="images/i219.jpg" alt="_" width="600" height="211" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,857.&mdash;Cut off coupling for power
-transmission by line shafting. It is used to cut off a driving shaft
-from a driven shaft. Its use obviates the use of a <i>quill</i>, such as
-is shown in <a href="#fig2858">fig. 2,858</a>.</p></div>
-
-<p><b>Ques. How may the regulation be improved?</b></p>
-
-<p>Ans. By decreasing the resistances of the windings by employing
-conductors of greater cross section, or decreasing their
-reactance by dividing the coils into sections and closely interspersing
-those of the primary between those of the secondary.</p>
-
-<div class="blockquot">
-<p>NOTE.&mdash;<i>The term</i> <b>"regulation"</b> as here used is synonymous
-with "drop." The <i>voltage drop</i> in a transformer denotes the drop of
-voltage occurring across the secondary terminals of a transformer
-with load. This drop is due to two causes: 1, the resistance of the
-windings; and 2, the reactance or magnetic leakage of the windings.
-On non-inductive load, the reactive drop, being in quadrature,
-produces but a slight effect, but on inductive loads it causes the
-voltage to drop, and on <i>leading current loads</i> it causes the voltage
-to rise. As the voltage drop of a good transformer is very small even
-on inductive load, direct accurate measurement is difficult. It is
-best to measure the copper loss with short circuited secondary by
-means of a wattmeter, and at the same time the voltage required to
-drive full load current through. From the watts, the resistance drop
-can be found, and from this and the impedance voltage, the reactive
-drop may be calculated. From these data a simple vector diagram will
-give, near enough for all practical purposes, the drop for any power
-factor, or the following formula may be used which has been deduced
-from the vector diagram.</p>
-
-<p class="center">D = √<span class="rad">(W + X)<sup>2</sup> + (R + P)<sup>2</sup></span> - 100</p>
-
-<p class="no-indent">where R = % resistance drop; X = % reactive drop; P = % power factor
-of load; W = % wattless factor of load (√<span class="rad">1 - P<sup>2</sup></span>); D = %
-resultant secondary drop. For non-inductive loads where P = 100 and W = 0,</p>
-
-<p class="center">D = √<span class="rad">X<sup>2</sup> + (100 + R)<sup>2</sup></span> - 100.</p>
-
-<p class="no-indent">In the case of leading currents it should be considered negative.
-<span class="pagenum"><a name="Page_2052" id="Page_2052">2052</a></span></p>
-
-<p>In transformers where there is a great difference in voltage between
-the primary and secondary windings, however, this remedy has its
-limitations on account of the great amount of insulation which must
-necessarily be used between the windings, and which therefore causes
-the distances between them to become such as to cause considerable
-leakage of the lines of force.</p></div>
-
-<p><b>Ques. How does the regulation vary for different transformers, and
-what should be the limit?</b></p>
-
-<p>Ans. Those of large capacity usually have a better regulation than
-those of small capacity, but in no case should its value exceed 2 per
-cent.</p>
-
-<div class="figcenter">
-  <a name="fig2858"></a>
-  <img src="images/i220.jpg" alt="_" width="600" height="210" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,858.&mdash;Quill drive. This is the
-proper transmission arrangement substitute for heavy service, requiring
-large pulleys, sheaves, gears, rotors, etc. It is a hollow shaft
-supported by independent bearings. The main driving shaft running
-through the quill is thus relieved of all transverse stresses. The
-power is transmitted to the quill by means of a friction or jaw
-clutch. When the clutch is thrown out the pulley or sheave stands
-idle and the driving shaft revolves freely within the quill. As there
-is no contact between moving parts there is no wear. Jaw clutches
-should be used for drives demanding positive angular displacement.
-They can only be thrown in and out of engagement when at rest. All
-very large clutch pulleys, sheaves, or gears designed to run loose on
-the line shaft are preferably mounted on quills. The letters A, B, C,
-etc., indicate the dimensions to be specified in ordering a quill.</p></div>
-
-<p><b>Ques. What advantages have shell type transformers over those of
-the core type?</b></p>
-
-<p>Ans. They have a larger proportion of core surface exposed for
-radiation of heat, and a shorter magnetic circuit which reduces the
-tendency for a leakage of the lines of force into the air.
-<span class="pagenum"><a name="Page_2053" id="Page_2053">2053</a></span></p>
-
-<p class="blockquot">
-Both types have advantages and disadvantages as compared with the
-other. In the shell type, there is less magnetic leakage, but also
-less surface exposed for radiation, and greater difficulty in
-providing efficient insulation between the two circuits; in the core
-type there is more surface exposed for radiation and less difficulty
-in insulating the windings, but there is also a great leakage of the
-lines of magnetic force into the outer air.</p>
-
-<p><b>Ques. How are the windings usually arranged?</b></p>
-
-<p>Ans. As a rule, there is only one primary winding but the secondary
-winding is generally divided into two equal sections, the four
-terminals of which are permanently wired to four connection blocks
-which may be connected so as to throw the secondary sections either
-in parallel or in series with each other at will.</p>
-
-<p><b>Ques. What is necessary for satisfactory operation of transformers
-in parallel?</b></p>
-
-<p>Ans. They must be designed for the same pressures and capacities,
-their percentages of regulation should be the same and they must have
-the same polarity at a given instant.</p>
-
-<div class="blockquot">
-<p>One may satisfy himself as to the first of these conditions by
-examining the name plates fastened to the transformers, whereon are
-stamped the values of the respective pressures and capacities of each.</p>
-
-<p>Although equal values of regulation is given as one of the conditions
-to be satisfied, transformers may be operated in parallel when their
-percentages of regulation are not the same. Ideal operation, however,
-can be attained only under the former state of affairs. Suppose,
-for instance, a transformer having a regulation of two per cent. be
-operated in parallel with another of similar size and design but
-having a regulation of one per cent. The secondary pressures of these
-transformers at no load will of course be the same, but at full load
-if the secondary pressure of the one be 98 volts, that of the other
-will be 99 volts. There will, therefore, be a difference of pressure
-of one volt between them which will tend to force a current backward
-through the secondary winding of the transformer delivering 98 volts.
-This reversed current, although comparatively small in value, lowers
-the efficiency of the installation by causing a displacement of phase
-and a decrease in the combined power factor of the transformers.
-<span class="pagenum"><a name="Page_2054" id="Page_2054">2054</a></span></p></div>
-
-<p><b>Ques. Describe the polarity test.</b></p>
-
-<p>Ans. The test for polarity consists in joining together by means of a
-fuse wire, a terminal of the secondary winding of each transformer,
-and then with the primary windings supplied with normal voltage,
-connecting temporarily the remaining terminals of the secondary
-windings. The melting of the fuse wire thus connected indicates that
-the secondary terminals joined together are of opposite polarities,
-and that the connections must therefore be reversed, whereas if the
-fuse wire do not melt, it shows that the proper terminals have been
-joined and that the connections may be made permanent.</p>
-
-<div class="figcenter">
-  <a name="fig2859"></a>
-  <img src="images/i-0341.jpg" alt="_" width="600" height="359" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,859.&mdash;Single overhung tangential water
-wheel equipped with Doble ellipsoidal buckets. The central position
-of the front entering wedge or lip of the bucket is cut away in the
-form of a semi-circular notch, which allows a solid circular water
-jet to discharge upon the central dividing wedge of the bucket
-without being split in a horizontal plane.</p></div>
-
-<p class="blockquot">
-The object of this test is, obviously, not to determine the exact
-polarity of each secondary terminal, but merely to indicate which of
-them are of the same polarity.
-<span class="pagenum"><a name="Page_2055" id="Page_2055">2055</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2860"></a>
-  <img src="images/i-0342.jpg" alt="_" width="600" height="361" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,860.&mdash;Motor generator exciter
-set driven by a Pelton-Doble tangential water wheel. The water wheel
-runner is mounted on the shaft overhung and the jet is regulated by
-either a hand actuated or governor controlled needle nozzle. The
-speed of the water wheel is equivalent to the synchronous speed of
-the induction motor, hence, the latter floats on the line, and under
-certain conditions may perform the functions of an alternator by
-feeding into the circuit, should the water wheel tend to operate
-above synchronous speed. Should any interruption to the operation
-of the wheel occur, causing a diminution of speed, the induction
-motor would drop back to full load speed and take up the exciter
-load, resulting in no appreciable drop of exciter voltage. The only
-variation of speed possible is dependent upon the "slip" of the
-motor. Where two or more exciter sets are employed in the station,
-an advantageous arrangement embraces the installation of a water
-wheel driven motor generator set and an exciter set, consisting of
-merely the direct current generator and water wheel. The induction
-motor being electrically tied into the circuit, the possibility of a
-runaway of the water wheel is eliminated, since its speed can only
-slightly exceed the synchronous speed of the system.</p></div>
-
-<p><b>Motor Generators.</b>&mdash;In motor generator sets, either the
-shunt or series wound type of motor may be employed at the power
-producing end of the set, but the field of the generator is either
-shunt or compound wound, depending upon whether or not it is desired
-to maintain or to raise the secondary voltage near full load. In
-either case a rheostat introduced in the shunt field winding of the
-generator will be found very essential. Both generator and motor are
-so mounted on the base that their respective commutators are at the
-<span class="pagenum"><a name="Page_2056" id="Page_2056">2056</a></span>
-outer ends of the set. By this means ample space surrounds all of the
-working parts, and repairs can readily be made.</p>
-
-<p>Motor generators are frequently used as boosters to raise or boost
-the voltage near the extremities of long distance, direct current
-transmission lines. Of these, electric railway systems in which it is
-desired to extend certain of the longer lines, form a typical example.</p>
-
-<div class="figcenter">
-  <a name="fig2861"></a>
-  <img src="images/i-0343.jpg" alt="_" width="600" height="384" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,861.&mdash;Automatically governed
-Pelton-Doble tangential water wheel driving exciter dynamo. The water
-wheel is mounted on one end of the shaft, while the opposite end is
-extended to carry a fly wheel of suitable design to compensate for
-the low fly wheel effect of the direct current armature. Two bearings
-support the shaft which carries the rotating elements of the unit.
-A needle nozzle actuated by a direct motion Pelton-Doble governor
-(designed for operation by either oil or water pressure) maintains
-constant speed.</p></div>
-
-<p>Owing to the great cost of changing such a system over to one
-employing alternating current, or storage batteries, or of
-constructing an additional power station, these solutions of the
-problem are usually at variance with good judgment and the amount
-of money at hand. The choice then remains between the purchase of
-<span class="pagenum"><a name="Page_2057" id="Page_2057">2057</a></span>
-additional wire for feeders, the connection of a booster in the old
-feeders, or the installation of both larger feeders and a booster.
-Of these, it is generally found that either the second or the third
-mentioned alternative meets the conditions most satisfactorily.</p>
-
-<div class="blockquot">
-<p>A booster installed in a railway system for the purpose just
-mentioned, would have a series wound motor, and the conditions to
-which it must conform would be as follows: The motor having a series
-winding must provide for the full feeder current passing through both
-armature and field windings.</p>
-
-<p>Owing to the varying loads on a railway system, due to the frequent
-starting and stopping of cars, the feeder current varies between
-zero and some such value as 150 amperes. This fluctuation of
-current through the field winding will, in ordinary cases, vary the
-magnetization of the pole pieces from zero almost to the point of
-saturation; that is, the maximum feeder current will so nearly fill
-the magnet cores with lines of force that it would be quite difficult
-to cause more lines of magnetic force to pass through them.</p>
-
-<p>So long as the point of saturation is not reached, however, the
-proportion of current to field strength remains constant, and
-therefore the ratio of amperes to volts will not vary.</p>
-
-<p>The severe fluctuations of the feeder current would, if the motor
-were shunt or compound wound, cause most serious sparking and
-various other troubles, but in a series motor where the back ampere
-turns on the armature that react on the field vary in precisely
-the same proportion as the ampere turns in the field, there exists
-at all times a tendency to balance the active forces and produce
-satisfactory operation. If, however, the field magnet cores be very
-large, they cannot so quickly respond, magnetically, to changes in
-the strength of the current, and there is then greater liability of
-the armature reaction momentarily weakening the field and thereby
-producing temporary sparking.</p></div>
-
-<p><b>Ques. Are motor generators always composed of direct current sets?</b></p>
-
-<p>Ans. No.</p>
-
-<p><b>Ques. Describe conditions requiring a different combination.</b></p>
-
-<p>Ans. For purposes where for instance direct currents of widely
-different voltages are to be obtained from an alternating current
-circuit, and it is desired to install but one set, a motor generator
-<span class="pagenum"><a name="Page_2058" id="Page_2058">2058</a></span>
-consisting of an alternating current motor such as an induction
-motor, and a dynamo must necessarily be employed.</p>
-
-<p class="blockquot">
-In such sets, it is common to find both motor and dynamo armatures
-mounted on a common shaft, and the respective field frames resting
-on a single base, although for connection on a very high pressure
-alternating current circuit, separate armature shafts insulated
-from each other but directly connected together, and separate bases
-resting on a single foundation, are usually employed to afford the
-highest degree of insulation between the respective circuits of the
-two machines.</p>
-
-<p><b>Ques. What is the objection to a set composed of alternating
-current motor and alternator?</b></p>
-
-<p>Ans. The commercial field that would be naturally covered by such a
-set is better supplied by a transformer.</p>
-
-<p><b>Ques. Why?</b></p>
-
-<p>Ans. Because a transformer contains no moving parts, and is therefore
-simpler in construction, cheaper in price, and less liable to get out
-of order.</p>
-
-<p><b>Dynamotors.</b>&mdash;A dynamotor differs from a motor generator in
-that the motor armature and the generator armature are combined
-into one, thereby requiring but one field frame. Since the motor
-and generator armature windings are mounted on a single core, the
-armature reaction due to the one winding is neutralized by the
-reaction caused by the other winding. There is, consequently, little
-or no tendency for sparking to occur at the brushes, and they
-therefore need not be shifted on this account for different loads.</p>
-
-<p><b>Ques. How is a dynamotor usually constructed?</b></p>
-
-<p>Ans. It is usually built with two pole pieces which are shunt wound.
-<span class="pagenum"><a name="Page_2059" id="Page_2059">2059</a></span></p>
-
-<p><b>Ques. Why does the voltage developed fall off slightly under an
-increase of load?</b></p>
-
-<p>Ans. Because a compound winding cannot be provided.</p>
-
-<table border="0" cellspacing="2" summary="Table of Contents." cellpadding="0">
-  <tbody><tr>
-      <td class="tdc_bott"><div class="figcenter">
-  <a name="fig2862"></a>
-  <img src="images/i-0344-1.jpg" alt="_" width="100" height="269" /></div></td>
-      <td class="tdc"><div class="figcenter">
-  <img src="images/i-0344-2.jpg" alt="_" width="400" height="615" /></div></td>
-    </tr><tr>
-      <td colspan="2" class="tdc"><p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,862 and 2,863.&mdash;Method of putting on
-belts when the driver is in motion, and device used. The latter is
-called a <i>belt slipper</i>, and consists, as shown in fig. 2,862,
-of a cone and shield, which revolve upon the stem, B, thus yielding easily
-to the pull of the belt. A staff or handle C of any convenient length
-can be fastened to the socket. The mode of operation is illustrated
-in fig. 2,863, which is self explanatory.</p></td>
-    </tr>
- </tbody>
-</table>
-
-<p><b>Ques. Describe the armature construction and operation.</b></p>
-
-<p>Ans. It consists of two separate windings; one of which is joined to
-a commutator mounted on one side of the armature for motor purposes, and the
-other to the commutator on the other side of the armature for generator purposes.
-<span class="pagenum"><a name="Page_2060" id="Page_2060">2060</a></span></p>
-
-<p class="blockquot space-below2">
-By means of two studs of brushes pressing on the motor commutator,
-current from the service wires is fed into the winding connected to
-this commutator, and since the shunt field winding is also excited
-by the current from the service wires, there is developed in the
-generator winding on the rotating armature a direct voltage which is
-proportional to the speed of rotation of the armature in revolutions
-per second, the number of conductors in series which constitute the
-generator winding, and the total strength of the field in which the
-armature revolves. This pressure causes current to pass through the
-generator winding and the distributing circuit when the distributing
-circuit to which this winding is connected by means of its respective
-commutator, brushes, etc., is closed.</p>
-
-<div class="figcenter">
-  <a name="fig2864"></a>
-  <img src="images/i-0345.jpg" alt="_" width="600" height="191" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,864 to 2,866.&mdash;Converter connections;
-fig. 2,864 double delta connection; fig. 2,865 diametrical
-connection; fig. 2,866 two circuit single phase connection. For
-six phase synchronous converter, two different arrangements of the
-connections are generally used. One is called the <i>double delta</i>, and
-the other the <i>diametrical</i> connection. Let the armature winding of
-the converter be represented by a circle as in figs. 2,864 and 2,865,
-and let the six equidistant points on the circumference represent
-collector rings, then the secondary of the supply transformers can
-be connected to the collector rings in a <i>double delta</i> as in fig.
-2,864, or across diametrical pairs of pointer as in fig. 2,865.
-In the first instance, the voltage ratio is the same as for the
-three phase synchronous converter and simply consists of two delta
-systems. The transformers can also be connected in double star, and
-in such a case the ratio between the three phase voltage between
-the terminals of each star, and the direct voltage will be the same
-as for double delta, while the voltage of each transformer coil,
-or voltage to neutral, is 1 ÷ √<span class="rad">3</span> times as much.
-With the diametrical connection, the ratio is the same as for the two ring
-single phase converter, it being analogous to three such systems.
-Hence six phase double delta
-E<sub>1</sub> = √<span class="rad">3</span> E ÷ 2√<span class="rad">2</span> = .612E.
-Six phase diametrical, E<sub>1</sub> = E ÷ √<span class="rad">2</span> = .707E. The ratio of the
-virtual_voltage E<sub>0</sub> between any collector ring and the neutral
-point is always E<sub>0</sub> = (E ÷ 2) √<span class="rad">2</span> = .354E. For single phase
-synchronous converters, consisting of a closed circuit armature
-winding tapped at two equidistant points to the two collector rings
-the virtual voltage is 1 ÷ √<span class="rad">2</span> × the direct current voltage. While
-such an arrangement of the single phase converter is the simplest,
-requiring only two collector rings, it is undesirable, especially
-for larger machines, on account of excessive heating of the armature
-conductors. In fig. 2,866, which represents the armature winding of a
-single phase converter, the supply circuits from two secondaries of
-the step down transformers are connected to four collector rings, so
-that the two circuits are in phase with each other, but each spreads
-over an arc of 120 electrical degrees instead of over 180 degrees
-as in the single phase circuit converter. To distinguish the two
-types, it is generally called a two circuit single phase synchronous
-converter. The virtual voltage E<sub>2</sub> bears to the direct voltage the
-same relation as in the three phase converter, that is single phase
-<span class="pagenum"><a name="Page_2061" id="Page_2061">2061</a></span>
-two circuit, E<sub>1</sub> = √<span class="rad">3</span> ÷ 2√<span class="rad">2</span> =.612E.</p></div>
-
-<p><b>Ques. How is a dynamotor started?</b></p>
-
-<p>Ans. It is connected at its motor end and started in the same manner
-as any shunt wound motor on a constant pressure circuit.</p>
-
-<p><b>Ques. What precautions should be taken in starting a dynamotor?</b></p>
-
-<p>Ans. The necessary precautions are, to have the poles strongly
-magnetized before passing current through the motor winding on the
-armature; to increase gradually the current through this winding, and
-not to close the generating circuit until normal conditions regarding
-speed, etc., are established in the motor circuit.</p>
-
-<p><b>Ques. How is the current developed in the machine regulated?</b></p>
-
-<p>Ans. It can be regulated by the introduction of resistance in one or
-the other of the armature circuits, or by a shifting of the brushes
-around the commutator.</p>
-
-<p><b>Ques. Are dynamotors less efficient than motor generators of a
-similar type?</b></p>
-
-<p>Ans. No, they are more efficient.</p>
-
-<p><b>Ques. Why?</b></p>
-
-<p>Ans. Because they have only one field circuit and at least one bearing
-less than a motor generator.</p>
-
-<p class="blockquot">
-A motor generator has at least three bearings, and occasionally,
-four, where the set consists of two independent machines directly
-connected together.</p>
-
-<p><b>Rotary Converters.</b>&mdash;An important modification of the dynamotor
-is the rotary converter. This machine forms, as it were, a link
-between alternating and direct current systems, being in general a
-combination of an alternating current motor and a dynamo.
-<span class="pagenum"><a name="Page_2062" id="Page_2062">2062</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2867"></a>
-  <img src="images/i230.jpg" alt="_" width="600" height="391" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,867.&mdash;Skeleton diagram showing wiring
-of alternator, exciter, transformer and converter. The cut also shows
-switchboard and connections.</p></div>
-
-<p><span class="pagenum"><a name="Page_2063" id="Page_2063">2063</a></span>
-It has practically become a fixture in all large electric railway
-systems and in other installations where heavy direct currents of
-constant pressure are required at a considerable distance from the
-generating plant. In such cases a rotary converter is installed
-in the sub-station, and being simpler in construction, higher in
-efficiency, more economical of floor space, and lower in price than
-a motor generator set consisting of an alternating current motor and
-a dynamo which might be used in its place, it has almost entirely
-superseded the latter machine for the class of work mentioned.</p>
-
-<p><b>Ques. What is the objection to the single phase rotary converter?</b></p>
-
-<p>Ans. It is not self-starting.</p>
-
-<p><b>Ques. What feature of operation is inherent in a rotary converter?</b></p>
-
-<p>Ans. A rotary converter is a "reversible machine."</p>
-
-<p class="blockquot">
-That is to say, if it be supplied with direct current of the proper
-voltage at its commutator end, it will run as a direct current motor
-and deliver alternating current to the collector rings. While this
-feature is sometimes taken advantage of in starting the converter
-from rest, the machine is not often used permanently in this way, its
-commercial application being usually the conversion of alternating
-currents into direct currents.</p>
-
-<p><b>Ques. How does a rotary converter operate when driven by
-direct current?</b></p>
-
-<p>Ans. The same as a direct current motor, its speed of rotation
-depending upon the relation existing between the strength of the
-field and the direct current voltage applied.</p>
-
-<div class="blockquot">
-<p>If the field be weak with respect to the armature magnetism
-resulting from the applied voltage, the armature will rotate at a
-high speed, increasing until the conductors on the armature cut the
-lines of force in the field so as to develop a voltage which will be
-equal to that applied.
-<span class="pagenum"><a name="Page_2064" id="Page_2064">2064</a></span></p>
-
-<p>Again, if the field be strong with respect to the armature magnetism,
-resulting from the applied voltage, the armature will rotate at a low
-speed. If, therefore, it be desired to operate the converter in this
-manner and maintain an alternating current of constant frequency,
-the speed of rotation must be kept constant by supplying a constant
-voltage not only to the brushes pressing on the commutator, but also
-to the terminals of the field winding.</p></div>
-
-<div class="figcenter">
-  <a name="fig2868"></a>
-  <img src="images/i-0346.jpg" alt="_" width="600" height="342" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,868.&mdash;General Electric synchronous
-converter with series booster. This type of converter generally
-consists of an alternator with revolving field mounted on the
-same shaft as the converter armature. The armature of the alternator,
-or booster, as it is usually called, is stationary and connected
-electrically in series between the supply circuit and the collector
-rings of the synchronous converter. The booster field has the same
-number of pole as the converter and is generally shunt wound. A
-change in the booster voltage will correspondingly change the
-alternating voltage impressed on the converter and this regulation
-can, of course, be made so as to either increase or decrease the
-impressed voltage by means of strengthening or weakening the booster
-field. The voltage variation can be made either non-automatic or
-automatic, and in the latter case, it becomes necessary to provide a
-motor operated rheostat controlled by suitable relays, or the booster
-can be provided with a series field. By means of a booster, it is
-possible to vary the direct voltage of the converter with a constant
-alternating supply voltage, and this voltage regulation is obtained
-without disturbance of the power factor or wave shape of the system.
-Synchronous converters are frequently installed in connection with
-Edison systems, where three wire direct current is required. The
-three wire feature is obtained either by providing extra collector
-rings and compensator, as with ordinary direct current generators,
-or also by connecting the neutral wire directly to the neutral point
-of the secondary winding of step down transformers, if such be furnished.</p></div>
-
-<p><b>Ques. How does it operate with alternating current drive?</b></p>
-
-<p>Ans. The same as a synchronous motor.</p>
-
-<p><b>Ques. What is the most troublesome part and why?</b>
-<span class="pagenum"><a name="Page_2065" id="Page_2065">2065</a></span></p>
-
-<p>Ans. The commutator, because of the many pieces of which it is
-composed and the necessary lines along which it is constructed, its
-peripheral speed must be kept within reasonable limits.</p>
-
-<p><b>Ques. What should be the limit of the commutator speed?</b></p>
-
-<p>Ans. The commutator speed, or tangential speed at the
-brushes should not exceed 3,000 feet per minute.</p>
-
-<div class="figcenter">
-  <a name="fig2869"></a>
-  <img src="images/i233.jpg" alt="_" width="600" height="371" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,869.&mdash;Wiring diagram for General
-Electric synchronous converter with series booster as illustrated in
-<a href="#fig2868">fig. 2,868</a>.</p></div>
-
-<p><b>Ques. Name another limitation necessary for satisfactory
-operation.</b></p>
-
-<p>Ans. The pressure between adjacent commutator bars should not exceed
-eight or ten volts.</p>
-
-<p class="blockquot">
-If the commutator bars be made narrow in order to obtain the
-necessary number for the desired voltage with the minimum
-circumference and therefore low commutator speed, the brushes
-employed to collect the current are liable to require excessive width
-in order to provide the proper cross section and yet not cover more
-than two bars at once.
-<span class="pagenum"><a name="Page_2066" id="Page_2066">2066</a></span></p>
-
-<p><b>Ques. How can the commutator speed be kept within reasonable
-limits, other than by reducing the width of the commutator bars?</b></p>
-
-<p>Ans. By using alternating current of comparatively low frequency.</p>
-
-<p class="blockquot">
-For a rotary converter delivering 500 volt direct current, the proper
-frequency for the alternating current circuit has been found to be 25
-cycles per second.</p>
-
-<p><b>Ques. When a rotary converter is operated in this usual manner
-on an alternating current circuit, how can the direct current be varied?</b></p>
-
-<p>Ans. It may be varied (from zero to a maximum) by changing the value
-of the alternating pressure supplied to the machine, or it may be
-altered within a limited range by moving the brushes around the
-commutator, or in a compound wound converter by changing the amount
-of compounding.</p>
-
-<p class="blockquot">
-Under ordinary conditions, varying the voltage developed by changing
-the voltage at the motor end is not practical, hence the voltage
-developed can be varied only over a limited range. In addition to
-this, the voltage developed at the direct current end bears always
-a certain constant proportion to the alternating current voltage
-applied at the motor end; this is due to the same winding being used
-both for motor and generator purposes. In all cases the proportion
-is such that the alternating current voltage is the lower, being
-in the single phase and in the two phase converters about .707 of
-the direct current voltage, and in the three phase converter about
-.612 of the direct current voltage. It is thus seen that whatever
-value of direct current voltage be desired, the value of the applied
-alternating current voltage must be lower, requiring in consequence
-the installation of step down transformers at the sub-station for
-reducing the line wire voltage to conform to the direct current
-pressure required.</p>
-
-<p><b>Ques. What is the efficiency of a rotary converter?</b></p>
-
-<p>Ans. It may be said to have approximately the same efficiency as that
-in the average of the same output, although in reality the converter
-<span class="pagenum"><a name="Page_2067" id="Page_2067">2067</a></span>
-is a trifle more efficient on account of affording a somewhat shorter
-average path for the current in the armature, reducing in consequence
-the resistance loss and the armature reaction.</p>
-
-<p><b>Ques. May a converter be overloaded more than a dynamo of the same
-output, and why?</b></p>
-
-<p>Ans. Yes, because there is usually less resistance loss in the
-armature of the converter than in the armature of the dynamo.</p>
-
-<div class="figcenter">
-  <a name="fig2870"></a>
-  <img src="images/i235.jpg" alt="_" width="600" height="349" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,870.&mdash;Wiring diagram for three wire
-synchronous converter with delta-Y connected step down transformer
-with the neutral brought out. It is evident that in this case each
-transformer secondary receives &#8531; of the neutral current, and
-if this current be not so small, as compared with the exciting
-current of the transformer, it will cause an increase in the magnetic
-density.</p></div>
-
-<p class="blockquot">
-Thus, a two phase converter may be overloaded approximately 60 per
-cent., and a three phase converter may be overloaded about 30 per
-cent. above their respective outputs if operated as dynamos.</p>
-
-<p><b>Ques. Describe how a converter is started.</b></p>
-
-<p>Ans. There are several methods any one of which may be employed, the
-choice in any given case depending upon which of them may best be
-followed under the existing conditions.
-<span class="pagenum"><a name="Page_2068" id="Page_2068">2068</a></span></p>
-
-<div class="blockquot">
-<p>If it be found advisable to start the converter with direct current,
-the same connections would be made between the source of the direct
-current and the armature terminals on the commutator side of the
-converter as would be the case were a direct current shunt motor of
-considerable size to be started; this naturally means that a starting
-rheostat and a circuit breaker will be introduced in the armature
-circuit.</p>
-
-<p>The shunt field winding alone is used, and this part of the wiring
-may be made permanent if, as is usually the case, the same source of
-direct current is used normally for separate field excitation.</p></div>
-
-<div class="figcenter">
-  <a name="fig2871"></a>
-  <img src="images/i236.jpg" alt="_" width="600" height="350" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,871.&mdash;Wiring diagram of three
-wire synchronous converter with distributed Y secondary. This system
-eliminates the flux distortion due to the unbalanced direct current
-in the neutral. Two separate interconnected windings are used for
-each leg of the Y. The unbalanced neutral current flowing in this
-system may be compared in action to the effect of a magnetizing
-current in a transformer. The effect of the main transformer currents
-in the primary and secondary is balanced with regard to the flux
-in the transformer core, which depends upon the magnetic current.
-When a direct current is passed through the transformer, unless
-the fluxes produced by the same neutralize one another, its effect
-on the transformer iron varies as the magnetizing current. For
-example, assume a transformer having a normal ampere capacity of 100
-and, approximately, 6 amperes magnetizing current, and assume that
-three such transformers are used with Y connected secondaries for
-operating a synchronous converter connected to a three wire Edison
-system. Allowing 25 per cent. unbalancing, the current will divide
-equally among the three legs giving 8.33 amperes per leg, which
-is more than the normal magnetizing current. The loss due to this
-current is, however, inappreciable, but the increased core losses
-may be considerable. If a distributed winding be used, the direct
-current flows in the opposite direction, around the halves of each
-core thus entirely neutralizing the flux distortion. Whether the
-straight Y connection is to be used is merely a question of balancing
-the increased core loss of the straight Y connection against the
-increased copper loss and the greater cost of the interconnected Y
-system. The straight Y connection is much simpler, and it would be
-quite permissible to use it for transformers of small capacities
-where the direct current circulating in the neutral is less than 30
-per cent. of the rated transformer current.</p></div>
-
-<p><span class="pagenum"><a name="Page_2069" id="Page_2069">2069</a></span></p>
-
-<div class="blockquot">
-<p>The direct current may be derived from a storage battery, from a
-separate converter, or from a motor generator set installed in the
-sub-station for the purpose.</p>
-
-<p>An adjustable rheostat will, of course, be connected in the field
-circuit for regulation. Before starting the converter, however,
-it is necessary to do certain wiring between the terminals on the
-collector side of the machine and the alternating current supply
-wires, in order that the change over from direct current motive power
-to alternating current motive power may be made when the proper phase
-relations are established between the alternating current in the
-supply wires and the alternating current in the armature winding of
-the converter.</p>
-
-<p>In order that proper phase relations exist, the armature of the
-converter must rotate at such a speed that each coil thereon passes
-its proper reversal point at the same time as the alternating
-current reverses in the supply wires. This speed may be calculated
-by doubling the frequency of the supply current and then dividing by
-the number of pole pieces on the converter, but a far more accurate
-method of judging when the converter is in step or in synchronism
-with the supply current consists in employing incandescent lamps as
-shown in <a href="#fig2872">fig. 2,872</a>.</p></div>
-
-<p><b>Ques. How is a polyphase converter started with alternating
-current?</b></p>
-
-<p>Ans. This may be done by applying the alternating pressure directly
-to the collector rings while the armature is at rest. There need
-be no field excitation; in fact the field windings on the separate
-pole pieces should be disconnected from each other before the
-alternating voltage is applied to the armature, else a high voltage
-will be induced in the field windings which may prove injurious to
-their insulation. The passage of the alternating current through the
-armature winding produces a magnetic field that rotates about the
-armature core, and induces in the pole pieces eddy currents, which,
-reacting on the armature, exert a sufficient torque to start the
-converter from rest and cause it to speed up to synchronism.</p>
-
-<p><b>Ques. How much alternating current is required to start a
-polyphase converter?</b></p>
-
-<p>Ans. About 100 per cent. more than that required for full load.
-<span class="pagenum"><a name="Page_2070" id="Page_2070">2070</a></span></p>
-
-<p><b>Ques. How may this starting current be reduced?</b></p>
-
-<p>Ans. Transformers may be switched into circuit temporarily to reduce
-the line wire voltage until the speed become normal.</p>
-
-<div class="figcenter">
-  <a name="fig2872"></a>
-  <img src="images/i238.jpg" alt="_" width="600" height="376" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,872.&mdash;Wiring diagram showing
-arrangement of incandescent lamps for determining the proper phase
-relations in starting a rotary converter. The alternating current
-side of a three phase converter is shown at C. The three brushes, D,
-T and G pressing on its collector rings are joined in order to the
-three single pole switches H, L and B which can be made to connect
-with the respective wires M, R, and V, of the alternating current
-supply circuit. Across one of the outside switches, H, for example, a
-number of incandescent lamps are joined in series as indicated at E,
-while the three pole switch (not shown) in the main circuit, between
-the alternator and the single pole switches is open. If then the
-main switch just mentioned and the middle switch L be both closed,
-and the armature of the alternator be brought up to normal speed
-by running it as a direct current motor, the lamps at E will light
-up and darken in rapid succession; the lighting and darkening of
-the lamps will continue until, by a proper adjustment of the speed,
-the correct phase relations be established between the alternating
-current in the supply circuit and the alternating current developed
-in the armature of the converter. As this condition is approached,
-the intervals between the successive lighting up and darkening of
-the lamps will increase until they remain perfectly dark. There is
-then no difference of pressure between the supply circuit M R V and
-the rotary converter armature circuit, so the source of the direct
-current may at that instant be disconnected from the machine, and the
-switches H and B, closed. If the change over has been accomplished
-before the phase relations of the two circuits differed, the
-converter will at once conform itself to the supply circuit and run
-thereon as a synchronous motor without further trouble. The opening
-of the direct current circuit and the closing of the alternating
-current supply circuit may be done by hand, but preferably by
-employing a device that will automatically trip the circuit breaker
-in the direct current circuit at the instant the switches in the
-alternating current circuit are closed.</p></div>
-
-<div class="blockquot">
-<p>In conjunction with this method, the method of synchronizing shown in
-<a href="#fig2872">fig. 2,872</a> may be used, thus, in starting, there is an
-alternating current between the brushes which pulsates very rapidly, but when
-<span class="pagenum"><a name="Page_2071" id="Page_2071">2071</a></span>
-synchronism is approached, the pulsations become less rapid until
-finally with the converter in step with the alternator the pulsations
-entirely disappear.</p>
-
-<p>The light given by the lamps thus connected indicates accurately
-the condition of affairs at any one time, varying from a rapidly
-fluctuating light at the beginning to one of constant brilliancy at
-synchronism.</p></div>
-
-<div class="figcenter">
-  <a name="fig2873"></a>
-  <img src="images/i239.jpg" alt="_" width="600" height="381" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,873.&mdash;Diagram of motor converter.
-This machine which is only to be used for converting from alternating to
-direct current, consists of an ordinary induction motor with phase
-wound armature, and a dynamo. The revolving parts of both machines
-are mounted on the same shaft and from the figure it is seen that
-the armature of the motor and the armature of the dynamo are also
-electrically connected. The motor converter is a synchronous machine,
-but the dynamo receives the current from the armature of the motor at
-a frequency much reduced from that impressed upon the field winding
-of the motor. Assuming that the motor and the converter have the same
-number of pole, the motor will rotate at a speed corresponding to
-one-half the frequency of the supply circuit. The motor will operate
-half as a motor and half as a transformer, and the converter, half
-as a dynamo and half as a synchronous converter, in that one-half of
-the electrical energy supplied to the motor will be converted into
-mechanical power for driving the converter, while the other one-half
-is transferred to the secondary motor windings and thereby to the
-converter armature in the form of electrical power. The capacity of
-the motor is theoretically only half what it would be if it were to
-convert the whole of the electrical energy into mechanical power
-because the rating depends upon the speed of the rotating field and
-not on that of the rotor. If the two machines have a different number
-of pole, or are connected to run at different speeds, the division of
-power is at a different but constant ratio. The machine starts up as
-an ordinary polyphase induction motor and the field of the converter
-is built up as though it were an ordinary dynamo. Motor converters
-are occasionally used on high frequency systems, as their commutating
-component is of half frequency, and thus permits better commutator
-design than a high frequency converter. The advantage of this type
-of machine is that for phase control it requires no extra reactive
-coils, the motor itself having sufficient reactance. It is, however,
-larger than standard converters, but smaller than motor generators,
-as half the power is converted in each machine. Its efficiency is
-less than for synchronous converters, and the danger of reaching
-double speed in case of a short circuit on the direct current side
-is very great. It has been used abroad to some extent for 60 cycle
-work, in preference to synchronous converters, but with the present
-reliable design of 60 cycle converters, and the general use of 25
-cycles, where severe service conditions are met, as in railroading,
-motor converters should not be recommended.</p></div>
-
-<p><span class="pagenum"><a name="Page_2072" id="Page_2072">2072</a></span>
-<b>Ques. If the armature of the starting motor have a starting
-resistance, how must this be connected?</b></p>
-
-<p>Ans. It should be connected in series with the armature inductors
-before the alternating voltage is applied.</p>
-
-<p class="blockquot">
-As the motor increases in speed, the starting resistance is gradually
-short circuited until it is entirely cut out of circuit.</p>
-
-<div class="figcenter">
-  <a name="fig2874"></a>
-  <img src="images/i240.jpg" alt="_" width="600" height="719" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,874.&mdash;Sectional view of General
-Electric vertical synchronous converter. In this construction, the
-field frame carrying the poles is mounted on cast iron pedestals and
-is split vertically. This allows the two halves of the frame to be
-separated for inspection or repairs of the armature. The armature,
-including commutator and collector rings, is mounted on a vertical
-stationary shaft, which is rigidly supported from the foundation.
-The thrust of the armature is carried on a roller bearing attached
-to the top of the shaft and upper side of the armature spider. The
-under side of the lower plate of the roller bearing is made spherical
-and fits into a corresponding spherical cup on the end of the shaft,
-making the bearing self aligning. The armature spider has a babbitted
-sleeve along the fit of the vertical shaft, which acts as a guide
-bearing and has to take only the thrust due to the unbalancing effect
-of the rotating parts. A circulating pump furnishes oil to the roller
-bearing, the oil draining off through the guide bearing. A marked
-advantage of this type of construction is the accessibility of the
-commutator for adjustment of the brushes, etc., as there is no pit or
-pedestal bearing to interfere.</p></div>
-
-<p class="blockquot">
-NOTE.&mdash;Some converters are provided with a small induction motor for
-starting mounted on an iron bracket cast in the converter frame, and
-whose shaft is keyed to that of the converter. Allowing for a certain
-amount of slip in the induction motor, the field of this machine must
-possess a less number of magnet poles than the converter in order to
-enable the latter machine to be brought to full synchronism. To start
-the induction motor, it is simply necessary to apply to its field
-terminals the proper alternating voltage. The bracket, and therefore
-the motor, is usually mounted outside the armature bearing on the
-collector side of the converter.
-<span class="pagenum"><a name="Page_2073" id="Page_2073">2073</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2875"></a>
-  <img src="images/i241.jpg" alt="_" width="600" height="266" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,875.&mdash;Resistance measurement by "drop"
-method. The circuit whose resistance is to be measured, is connected
-in series with an ammeter and an adjustable resistance to vary
-the flow of current. A voltmeter is connected directly across the
-terminals of the resistance to be measured, as shown in the figure.
-According to Ohm's law I = E ÷ R, from which, R = E ÷ I. If then the
-current flowing in the circuit through the unknown resistance be
-measured, and also the drop or difference of pressure, the resistance
-can be calculated by above formula. In order to secure accurate
-determination of the resistance such value of current must be used
-as will give large deflections of the needle on the instruments
-employed. A number of independent readings should be taken with some
-variation of the current and necessarily a corresponding variation
-in voltage. The resistance should then be figured from each set
-of readings and the average of all readings taken for the correct
-resistance. Great care must be taken, however, in the readings, and
-the instruments must be fairly accurate. For example, suppose that
-the combined instrument error and the error of the reading in the
-voltmeter should be 1 per cent., the reading being high, while the
-corresponding error of the ammeter is 1 per cent. low. This would
-cause an error of approximately 2 per cent. in the reading of the
-resistance. In making careful measurements of the resistance, it is
-also necessary to determine the temperature of the resistance being
-measured, as the resistance of copper increases approximately .4
-of 1 per cent. for each degree rise in temperature. Use is made of
-this fact for determining the increase in temperature of a piece of
-apparatus when operating under load. The resistance of the apparatus
-at some known temperature is measured, this being called the cold
-resistance of the apparatus. At the end of the temperature test the
-hot resistance is taken. Assume the resistance has increased by 15
-per cent. This would indicate a rise in temperature of 37½ degrees
-above the original or cold temperature of the apparatus. Suppose then
-that in measuring the cold resistance, results are obtained which are
-2 per cent. low, and that in measuring the hot resistance, there be
-2 per cent. error in the opposite direction. This would mean that a
-total error of 4 per cent. had been made in the difference between
-the hot and cold resistances, or an error of 10 degrees. The correct
-rise in temperature is, therefore, about 27½ instead of 37½
-degrees. In other words, an error of 2 per cent. in measuring each
-resistance has caused an error of approximately 36½ per cent. in
-the measurement of the rise in temperature. The constant .4 which has
-been used above is only approximate and should not be used for exact
-work. For detail instructions of making calculations of resistance
-and temperature, see "Standardization Rules of the A.I.E.E."</p></div>
-
-<p><b>Ques. Describe the usual wiring for the installation of a rotary
-converter in a sub-station.</b></p>
-
-<p>Ans. Commencing at the entrance of the high pressure cables, first
-there is the wiring for the lightning arresters, then for the
-connection in circuit of the high tension switching devices, from
-which the conductors are led to bus bars, and thence to the step down transformers.
-<span class="pagenum"><a name="Page_2074" id="Page_2074">2074</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2876"></a>
-  <img src="images/i242.jpg" alt="_" width="600" height="297" />
-  <p class="f90_left space-below1">
-Figs. 2,876 to 2,879.&mdash;How to connect instruments
-for power measurement. There are several ways of connecting an
-ammeter, voltmeter and wattmeter in the circuit for the measurement
-of power. A few of the methods are discussed below. With some of the
-connections it is necessary to correct the readings of the wattmeter
-for the losses in the coil, or coils, of the wattmeter, or for losses
-in ammeter or voltmeter. This is necessary since the instruments may
-be so connected that the wattmeter not only measures the load but
-includes in its indications some of the instrument losses. If the
-load measured be small, or considerable accuracy is required, these
-instrument losses may be calculated as follows: Loss in pressure
-coils is E<sup>2</sup> ÷ R, in which E is the voltage at the terminals of
-the pressure coil and R is the resistance. Loss in current coil is
-I<sup>2</sup> R in which I is the current flowing and R the resistance of the
-current coil. In general let E<sub>v</sub> = voltage across terminals of the
-voltmeter; E<sub><i>w</i></sub> = voltage across the terminals of the pressure
-coil of the wattmeter; I<sub><i>w</i></sub> = current through current coil of
-wattmeter; I<sub><i>a</i></sub> = current through current coil of ammeter; R<sub><i>v</i></sub>
-= resistance of pressure coil of voltmeter; R<sub><i>w</i></sub> = resistance of
-pressure coil of wattmeter; R<sup>1</sup><sub>w</sub> = resistance of current coil of
-wattmeter; R<sub><i>a</i></sub> = resistance of current coil of ammeter. Then the
-losses in the various coils will be as follows: E<sup>2</sup><sub><i>v</i></sub> ÷ R<sub><i>v</i></sub>
-= loss in pressure coil of voltmeter. E<sup>2</sup><sub><i>w</i></sub> ÷ R<sub><i>w</i></sub> = loss in
-pressure coil of wattmeter. I<sup>2</sup><sub><i>w</i></sub> ÷ R<sub><i>v</i></sub> = loss in current
-coil of wattmeter. I<sup>2</sup><sub><i>a</i></sub>R<sub><i>a</i></sub> = loss in current coil of
-ammeter. If connection be made as in fig. 2,876, the correct power of
-the circuit will be the wattmeter reading W-(E<sup>2</sup><sub><i>v</i></sub> ÷ R<sub><i>v</i></sub>
-+ E<sup>2</sup><sub><i>w</i></sub> ÷ R<sub><i>w</i></sub>) in which E<sub><i>v</i></sub> = E<sub><i>w</i></sub>. In fig. 2,877,
-the power is W-E<sup>2</sup><sub><i>w</i></sub> ÷ R<sub><i>w</i></sub>. In fig. 2,878, the power is
-W-I<sup>2</sup><sub><i>w</i></sub>R<sup>1</sup><sub><i>w</i></sub>, or the correct power is the wattmeter
-reading minus the loss in the current coil of the wattmeter. In fig.
-2,879, the power is W-(E<sup>2</sup><sub><i>w</i></sub> ÷ R<sub><i>w</i></sub> + I<sup>2</sup><sub><i>a</i></sub>R<sub><i>a</i></sub>)·
-The usual method of connection is either as in fig. 2,876 or fig.
-2,877. In either case the current reading is that of the load plus
-the currents in the pressure coils of the voltmeter and wattmeter.
-Unless the current being measured, however, is very small, or extreme
-accuracy is desired, it is unnecessary to correct ammeter readings.
-In fig. 2,877 a small error is introduced due to the fact that the
-actual voltage applied to the load is that given by the voltmeter
-minus the small drop in voltage through the current coil of the
-wattmeter. If an accurate measure of the current in connection with
-the power consumed by the load be required, the connections shown
-in fig. 2,879 are used, and if extreme accuracy is required, the
-wattmeter reading is reduced by the losses in the ammeter and in
-the pressure coil of the wattmeter. The loss in the pressure coil
-of a wattmeter or voltmeter may be as high as 12 or 15 watts at 220
-volts. The loss in the current coil of a wattmeter with 10 amperes
-flowing may be 6 or 8 watts. It can be easily seen that if the core
-or copper losses of small transformers are being measured, it is
-quite necessary to correct the wattmeter readings, for the instrument
-losses. In measuring the losses of a 25 or 50 H.P. induction motor,
-the instrument losses may be neglected. A careful study of the above
-will show when it becomes necessary to correct for instrument losses
-and the method of making these corrections. Connections are seldom
-used which make it necessary to correct for the losses in the current
-coils of either ammeter or wattmeter, as the losses vary with the
-change in the current. On the other hand, the voltages generally
-used are fairly constant at 110 or 220, and when the losses of the
-pressure coils at these voltages have once been calculated, the
-necessary instrument correction can be readily made.</p></div>
-
-<p><span class="pagenum"><a name="Page_2075" id="Page_2075">2075</a></span></p>
-
-<p class="blockquot">
-On a three phase system the transformers should be joined in delta
-connection, as a considerable advantage is thereby gained over the
-star connection, in that should one of the transformers become
-defective, the remaining two will carry the load without change
-except more or less additional heating. Between the transformers
-and rotary converter the circuits should be as short and simple as
-possible, switches, fuses, and other instruments being entirely
-excluded. The direct current from the converter is led to the direct
-current switchboard, and from there distributed to the feeder
-circuits.</p>
-
-<table border="0" cellspacing="2" summary="_" rules="cols" cellpadding="0">
-<caption><br /><b>WATTMETER ERROR FOR A LOAD OF 1,000 VOLT-AMPERES</b><br />
-(For a lag of 1 degree in the pressure coil)</caption>
-  <tbody><tr class="tr_lt_grey">
-      <td class="tdc">&nbsp;Power factor&nbsp;</td>
-      <td class="tdc">&nbsp;True watts&nbsp;</td>
-      <td class="tdc">&nbsp;Error&nbsp;</td>
-      <td class="tdc">&nbsp;Error of indication&nbsp;<br />in per cent<br />of true value</td>
-    </tr><tr>
-      <td class="tdc">1.&nbsp;&nbsp;&nbsp;&nbsp;</td>
-      <td class="tdc">1,000&nbsp;&nbsp;&nbsp;</td>
-      <td class="tdr">.3&nbsp;&nbsp;</td>
-      <td class="tdc">0.03</td>
-    </tr><tr>
-      <td class="tdc">.9</td>
-      <td class="tdc">900</td>
-      <td class="tdr">7.6&nbsp;&nbsp;</td>
-      <td class="tdc">0.85</td>
-    </tr><tr>
-      <td class="tdc">.8</td>
-      <td class="tdc">800</td>
-      <td class="tdr">10.5&nbsp;&nbsp;</td>
-      <td class="tdc">1.31</td>
-    </tr><tr>
-      <td class="tdc">.7</td>
-      <td class="tdc">700</td>
-      <td class="tdr">12.5&nbsp;&nbsp;</td>
-      <td class="tdc">1.78</td>
-    </tr><tr>
-      <td class="tdc">.6</td>
-      <td class="tdc">600</td>
-      <td class="tdr">13.9&nbsp;&nbsp;</td>
-      <td class="tdc">2.32</td>
-    </tr><tr>
-      <td class="tdc">.5</td>
-      <td class="tdc">500</td>
-      <td class="tdr">15.1&nbsp;&nbsp;</td>
-      <td class="tdc">3.02</td>
-    </tr><tr>
-      <td class="tdc">.4</td>
-      <td class="tdc">400</td>
-      <td class="tdr">15.9&nbsp;&nbsp;</td>
-      <td class="tdc">3.98</td>
-    </tr><tr>
-      <td class="tdc">.3</td>
-      <td class="tdc">300</td>
-      <td class="tdr">16.6&nbsp;&nbsp;</td>
-      <td class="tdc">5.54</td>
-    </tr><tr>
-      <td class="tdc">.2</td>
-      <td class="tdc">200</td>
-      <td class="tdr">17.1&nbsp;&nbsp;</td>
-      <td class="tdc">8.55</td>
-    </tr><tr>
-      <td class="tdc">.1</td>
-      <td class="tdc">100</td>
-      <td class="tdr">17.3&nbsp;&nbsp;</td>
-      <td class="tdc">17.30&nbsp;&nbsp;</td>
-    </tr>
- </tbody>
-</table>
-
-<p class="blockquot">
-NOTE.&mdash;In the iron vane type instrument when used as a wattmeter,
-the current of the series coil always remains in perfect phase
-with the current of the circuit, provided series transformers are
-not introduced. The error, then, is entirely due to the lag of the
-current in the pressure coil, and this error in high power factor
-is exceedingly small, increasing as the power factor decreases. In
-the above table it should be noted that the value of the error as
-distinguished from the per cent. of error, instead of indefinitely
-increasing as the power factor diminishes, rapidly attains a maximum
-value which is less than 2 per cent. of the power delivered under the
-same current and without inductance. It should also be noted that the
-above tabulation is on the assumption of a lag of 1 degree in the
-pressure coil. The actual lag in Wagner instruments for instance, is
-approximately .085 of a degree, and the error due to the lag of the
-pressure coil in Wagner instruments is, therefore, proportionally
-reduced from the figures shown in the above tabulation.
-<span class="pagenum"><a name="Page_2076" id="Page_2076">2076</a></span></p>
-
-<p><b>Ques. In large sub-stations containing several rotary converters
-how are they operated?</b></p>
-
-<p class="space-below1">Ans. Frequently they are installed to receive
-their respective currents from the same set of bus bars; that is,
-they may be operated as alternating current motors in parallel. They
-are also frequently operated independently from single bus bars, but
-very seldom in series with each other.</p>
-
-<div class="figcenter">
-  <a name="fig2880"></a>
-  <img src="images/i244.jpg" alt="_" width="600" height="195" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,880.&mdash;Single phase motor test.
-In this method of measuring the input of a single phase motor of any
-type, the ammeter, voltmeter and wattmeter are connected as shown in
-the illustration. The ammeter measures the current flowing through the
-motor, the voltmeter, the pressure across the terminals of the motor,
-and the wattmeter the total power which flows through the motor
-circuit. With the connections as shown, the wattmeter would also
-measure the slight losses in the voltmeter and the pressure coil of
-the wattmeter, but for motors of ¼ H.P. and larger, this loss is so
-small that it may be neglected. The power factor may be calculated by
-dividing the true watts as indicated by the wattmeter, by the product
-of the volts and amperes.</p></div>
-
-<p><b>Ques. How may the direct current circuit be connected?</b></p>
-
-<p>Ans. In parallel.</p>
-
-<p class="blockquot space-below1">
-NOTE.&mdash;In motor testing, by the methods illustrated in the
-accompanying cuts, it is assumed that the motor is loaded in the
-ordinary way by belting or direct connecting the motor to some form
-of load, and that the object is to determine whether the motor is
-over or under loaded, and approximately what per cent. of full load
-it is carrying. All commercial motors have name plates, giving the
-rating of the motor and the full load current in amperes. Hence
-the per cent. of load carried can be determined approximately by
-measuring the current input and the voltage. If an efficiency test
-of the apparatus be required, it becomes necessary to use some form
-of absorption by dynamometer, such as a Prony or other form of
-brake. The output of the motor can then be determined from the brake
-readings. The scope of the present treatment is, however, too limited
-to go into the subject of different methods of measuring the output
-of the apparatus, and is confined rather to methods of measuring
-current input, voltage, and watts. The accuracy of all tests is
-obviously dependent upon the accuracy of the instruments employed.
-Before accepting the result obtained by any test, especially under
-light or no load, correction should be made for wattmeter error. See
-table of wattmeter error on page 2,075.
-<span class="pagenum"><a name="Page_2077" id="Page_2077">2077</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2881"></a>
-  <img src="images/i245.jpg" alt="_" width="600" height="305" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,881.&mdash;Three phase motor test;
-voltmeter and ammeter method. If it be desired to determine the
-approximate load on a three phase motor, this may be done by means
-of the connections as shown in the figure, and the current through
-one of the three lines and the voltage across the phase measured. If
-the voltage be approximately the rated voltage of the motor and the
-amperes the rated current of the motor (as noted on the name plate)
-it may be assumed that the motor is carrying approximately full load.
-If, on the other hand, the amperes show much in excess of full load
-rating, the motor is carrying an overload. The heat generated in the
-copper varies as the square of the current. That generated in the
-iron varies anywhere from the 1.6 power, to the square. This method
-is very convenient if a wattmeter be not available, although, it
-is, of course, of no value for the determination of the efficiency
-or power factor of the apparatus. This method gives fairly accurate
-results, providing the load on the three phases of the motor be
-fairly well balanced. If there be much difference, however, in the
-voltage of the three phases, the ammeter should be switched from
-one circuit to another, and the current measured in each phase. If
-the motor be very lightly loaded and the voltage of the different
-phases vary by 2 or 3 per cent., the current in the three legs of the
-circuit will vary 20 to 30 per cent.</p></div>
-
-<p><b>Ques. What provision should be made against interruption of
-service in sub-stations?</b></p>
-
-<p>Ans. There should be one reserve rotary converter to every three or
-four converters actually required.</p>
-
-<p><b>Ques. Why does a rotary converter operate with greater efficiency,
-and require less attention than does a dynamo of the same output?</b></p>
-
-<p>Ans. There is less friction, and less armature resistance, the
-latter because the alternating current at certain portions of each
-revolution passes directly to the commutator bars without
-<span class="pagenum"><a name="Page_2078" id="Page_2078">2078</a></span>
-traversing the entire armature winding as it does in a dynamo;
-there is no distortion of the field and consequently no sparking,
-or shifting of the brushes, since the armature reaction resulting
-from the current fed into the machine and that due to the current
-generated in the armature completely neutralizes each other.</p>
-
-<div class="figcenter">
-  <a name="fig2882"></a>
-  <img src="images/i246.jpg" alt="_" width="600" height="319" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,882.&mdash;Three phase motor test by
-the two wattmeter method. If an accurate test of a three phase motor
-be required, it is necessary to use the method here indicated.
-Assume the motor to be loaded with a brake so that its output can be
-determined. This method gives correct results even with considerable
-unbalancing in the voltages of the three phases. With the connections
-as shown, the sum of the two wattmeter readings gives the total power
-in the circuit. Neither meter by itself measures the power in any
-one of the three phases. In fact, with light load one of the meters
-will probably give a negative reading, and it will then be necessary
-to either reverse its current or pressure leads in order that the
-deflection may be noted. In such cases the algebraic sums of the two
-readings must be taken. In, other words, if one read plus 500 watts
-and the other, minus 300 watts, the total power in the circuit will
-be 500 minus 300, or 200 watts. As the load comes on, the readings of
-the instrument which gave the negative deflection will decrease until
-the reading drops to zero, and it will then be necessary to again
-reverse the pressure leads on this wattmeter. Thereafter the readings
-of both instruments will be positive, and the numerical sum of the
-two should be taken as the measurement of the load. If one set of the
-instruments be removed from the circuit, the reading of the remaining
-wattmeter will have no meaning. As stated above, it will not indicate
-the power under these conditions in any one phase of the circuit. The
-power factor is obtained by dividing the actual watts input by the
-product of the average of the voltmeter readings × the average of the
-ampere readings × 1.73.</p></div>
-
-<p><b>What electrical difficulty is experienced with a rotary
-converter?</b></p>
-
-<p>Ans. Regulation of the direct current voltage.
-<span class="pagenum"><a name="Page_2079" id="Page_2079">2079</a></span></p>
-
-<p><b>Ques. How is this done?</b></p>
-
-<p>Ans. It can be maintained constant only by preserving uniform
-conditions of inductance in the alternating current circuit, and
-uniform conditions in the alternator.</p>
-
-<p class="blockquot">
-While changes in either of these may be compensated to a certain
-extent by adjustment of the field strength of the converter, they
-cannot be entirely neutralized in this manner; it is therefore
-necessary that both the line circuit and the alternator be given
-attention if the best results are to be obtained from the converter.</p>
-
-<p><b>Ques. What mechanical difficulty is experienced with rotary converters?</b></p>
-
-<p>Ans. Hunting.</p>
-
-<p><b>Ques. What is the cause of this?</b></p>
-
-<p>Ans. It is due to a variation in frequency.</p>
-
-<div class="blockquot">
-<p>The inertia of the converter armature tends to maintain a constant
-speed; variations in the frequency of the supply circuit will cause
-a displacement of phase between the current in the armature and that
-in the line wires, which displacement, however, the synchronizing
-current strives to decrease. The synchronizing current, although
-beneficial in remedying the trouble after it occurs, exerts but
-little effort in preventing it, and many attempts have been made to
-devise a plan to eliminate this trouble.</p>
-
-<p>NOTE.&mdash;Three phase motor test; polyphase wattmeter method.
-This is identical with the test of <a href="#fig2882">fig. 2,882</a>, except
-that the wattmeter itself combines the movement of the two wattmeters.
-Otherwise the method of making the measurements is identical. If
-the power factor be known to be less than 50 per cent., connect
-one movement so as to give a positive deflection; then disconnect
-movement one and connect movement two so as to give a positive
-deflection. Then reverse either the pressure or current leads of
-the movement, giving the smaller deflection, leaving the remaining
-movement with the original connections. The readings now obtained
-will be the correct total watts delivered to the motor. If the power
-factor be known to be over 50 per cent., the same methods should
-be employed, except that both movements should be independently
-connected to give positive readings. An unloaded induction motor has
-a power factor of less than 50 per cent., and may, therefore, be
-used as above for determining the correct connections. For a better
-understanding of the reasons for the above method of procedure, the
-explanation of the two wattmeter method, <a href="#fig2882">fig. 2,882</a>, should be read.
-The power factor may be calculated as explained under <a href="#fig2882">fig. 2,882</a>.
-Connect as shown in <a href="#fig2882">fig 2,882</a>. The following check on connection may
-be made. Let the polyphase induction motor run idle, that is, with
-no load. The motor will then operate with a power factor less than
-50 per cent. The polyphase meter should give a positive indication,
-but if each movement be tried separately one will be found to give a
-negative reading, the other movement will give a positive reading.
-This can be done by disconnecting one of the pressure leads from the
-binding post of one movement. When the power factor is above 50 per
-cent. then both movements will give positive deflection.</p></div>
-
-<p><span class="pagenum"><a name="Page_2080" id="Page_2080">2080</a></span>
-<b>Ques. What are the methods employed to prevent hunting?</b></p>
-
-<p>Ans. 1, the employment of a strongly magnetized field relative to
-that developed by the armature; 2, a heavy flywheel effect in the
-converter; 3, the increasing of the inductance of the armature by
-sinking the windings thereon in deep slots in the core, the slots
-being provided with extended heads; and 4, the employment of damping
-devices or amortisseur winding on the pole pieces of the converter.</p>
-
-<div class="figcenter">
-  <a name="fig2883"></a>
-  <img src="images/i248.jpg" alt="_" width="600" height="314" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,883.&mdash;Three phase motor test;
-one wattmeter method. This method is equivalent to the two wattmeter
-method with the following difference. A single voltmeter (as shown
-above) with a switch, A, can be used to connect the voltmeter across
-either one of the two phases. Three switches, B, C and D, are
-employed for changing the connection of the ammeter and wattmeter
-in either one of the two lines. With the switches B and D in the
-position shown, the ammeter and wattmeter series coils are connected
-in the left hand line. The switch C must be closed under these
-conditions in order to have the middle line closed. Another reading
-should then be taken before any change of load has occurred, with
-switch A thrown to the right, switch B closed, switch D thrown to the
-right and switch C opened. The ammeter and the current coil of the
-wattmeter will then be connected to the middle line of the motor.
-In order to prevent any interruption of the circuit, the switches
-B, D and C should be operated in the order given above. With very
-light load on the motor the wattmeter will probably give a negative
-deflection in one phase or the other, and it will be necessary to
-reverse its connections before taking the readings. For this purpose
-a double pole, double throw switch is sometimes inserted in the
-circuit of the pressure coil of the wattmeter so that the indications
-can be reversed without disturbing any of the connections. It is
-suggested, before undertaking this test, that the instructions for
-test by the two wattmeter and by the polyphase wattmeter methods be read.</p></div>
-
-<p><span class="pagenum"><a name="Page_2081" id="Page_2081">2081</a></span>
-<b>Ques. What method is the best?</b></p>
-
-<p>Ans. The damping method.</p>
-
-<div class="blockquot">
-<p>The devices employed for the purpose are usually copper shields
-placed between or around the pole pieces, although in some converters
-the copper is embedded in the poles, and in others it is made simply
-to surround a portion of the pole tips.</p>
-
-<p>In any case its action is as follows: The armature rotating at a
-variable speed has a field developed therein which is assumed to
-be also rotating at a variable speed; the magnetism of this rotary
-field induces currents in the copper which, however, react on the
-armature and oppose any tendency toward a further shifting of the
-magnetism in the armature and therefore prevent the development of
-additional currents in the copper. Since copper is of low resistance,
-the induced currents are sufficient in strength to thus dampen
-any tendency toward phase displacement, and so exert a steadying
-influence upon the installation as a whole.</p></div>
-
-<div class="figcenter">
-  <a name="fig2884"></a>
-  <img src="images/i249.jpg" alt="_" width="600" height="308" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,884.&mdash;Three phase motor, one
-wattmeter and Y box method. This method is of service, only, provided
-the voltages of the three phases are the same. A slight variation of
-the voltage of the different phases may cause a very large error in
-the readings of the wattmeter, and inasmuch as the voltage of all
-commercial three phase circuits is more or less unbalanced, this
-method is not to be recommended for motor testing. With balanced
-voltage in all three phases, the power is that indicated by the
-wattmeter, multiplied by three. Power factor may be calculated as
-before.</p></div>
-
-<p><b>Electrical Measuring Instruments.</b>&mdash;In the manufacture of most
-measuring instruments, the graduations of the scale are made at the
-<span class="pagenum"><a name="Page_2082" id="Page_2082">2082</a></span>
-factory, by comparing the deflections of the pointer with voltages
-as measured on standard apparatus. The voltmeters in most common
-use have capacities of 5, 15, 75, 150, 300, 500 and 750 volts each,
-although in the measurement of very low resistances such as those of
-armatures, heavy cables, or bus bars, voltmeters having capacities as
-low as .02 volt are employed.</p>
-
-<div class="figcenter">
-  <a name="fig2885"></a>
-  <img src="images/i250.jpg" alt="_" width="600" height="307" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,885.&mdash;Test of three phase motor with
-neutral brought out; single wattmeter method. Some star connected
-motors have the connection brought out from the neutral of the
-winding. In this case the circuit may be connected, as here shown.
-The voltmeter now measures voltage between the neutral and one of
-the lines, and the wattmeter the power in one of the three phases
-of the motor. Therefore, the total power taken by the motor will be
-three times the wattmeter readings. By this method, just as accurate
-results can be obtained as with the two wattmeter method. The power
-factor will be the indicated watts divided by the product of the
-indicated amperes and volts.</p></div>
-
-<p>The difference between the design of direct current voltmeters of
-different capacities lies simply in the high resistance joined in
-series with the fine wire coil. This resistance is usually about 100
-ohms per volt capacity of the meter, and is composed of fine silk
-covered copper wire wound non-inductively on a wooden spool.</p>
-
-<p>In the operation of an instrument, if the pointer when deflected
-do not readily come to a position of rest owing to friction in the
-<span class="pagenum"><a name="Page_2083" id="Page_2083">2083</a></span>
-moving parts, it may be aided in this respect by gently tapping
-the case of the instrument with the hand; this will often enable
-the obstruction, if not of a serious nature, to be overcome and an
-accurate reading to be obtained.</p>
-
-<div class="figcenter">
-  <a name="fig2886"></a>
-  <img src="images/i251.jpg" alt="_" width="600" height="356" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,886.&mdash;Temperature test of a
-large three phase induction motor. Temperature tests are usually made
-on small induction motors by belting the motor to a generator and
-loading the generator with a lamp bank or resistance until the
-motor input is equal to the full load. If, however, the motor be of
-considerable size, such that the cost of power becomes a considerable
-item in the cost of testing, the method here shown may be employed.
-For this purpose, however, two motors, preferably of the same size
-and type, are required. One is driven as a motor and runs slightly
-below synchronism, due to its slip when operating with load. This
-motor is belted to a second machine. If the pulley of the second
-machine be smaller than the pulley of the first machine, the second
-machine will then operate as an induction generator, and will return
-to the line as much power as the first motor draws from the line,
-less the losses of the second machine. By properly selecting the
-ratio of pulleys, the first machine can be caused to draw full
-load current and full load energy from the line. In this way, the
-total energy consumed is equivalent to the total of the losses of
-both machines, which is approximately twice the losses of a single
-machine. The figure shows the connection of the wattmeters, without
-necessary switches, for reading the total energy by two wattmeter
-method. Detailed connection of the wattmeter is shown in <a href="#fig2883">fig. 2,883</a>.
-It is usual, in making temperature tests, to insert one or
-more thermometers in what is supposed to be the hottest part of
-the winding, one on the surface of the laminae and one in the air
-duct between the iron laminae. The test should be continued until
-the difference in temperature between any part of the motor and the
-air reaches a steady value. The motor should then be stopped and
-the temperature of the armature also measured. For the method of
-testing wound armature type induction motors of very large size, see
-<a href="#fig2890">fig. 2,890</a>. For the approved way of taking temperature readings
-and interpreting results, see the "Standardization Rules of the A.I.E.E."</p></div>
-
-<p><b>Ques. Describe a two scale voltmeter.</b></p>
-
-<p>Ans. In this type of instrument, one scale is for low voltage
-<span class="pagenum"><a name="Page_2084" id="Page_2084">2084</a></span>
-readings and the other for high voltage readings; on these
-scales the values of the graduations for low voltages are usually
-marked with red figures, while those for high voltages are marked
-with black figures. A voltmeter carrying two scales must also
-contain two resistances in place of one; a terminal from each
-of these coils must be connected with a separate binding post,
-but the remaining terminal of each resistance is joined to a wire
-which connects through the fine wire coil with the third binding
-post of the meter. The two first mentioned binding posts are
-usually mounted at the left hand side of the meter and the
-last mentioned binding post and key at the right hand side.</p>
-
-<div class="figcenter">
-  <a name="fig2887"></a>
-  <img src="images/i252.jpg" alt="_" width="600" height="302" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,887.&mdash;Alternator excitation or
-magnetization curve test. The object of this test is to determine
-the change of the armature voltage due to the variation of the field
-current when the external circuit is kept open. As here shown,
-the field circuit is connected with an ammeter and an adjustable
-resistance in series with a direct current source of supply. The
-adjustable resistance is varied, and readings of the voltmeter across
-the armature, and of the ammeter, are recorded. The speed of the
-generator must be kept constant, preferably at the speed which is
-given on the name plate. The excitation or magnetization curve of the
-machine is obtained by plotting the current and the voltage.</p></div>
-
-<p class="blockquot">
-The resistance corresponding to the high reading scale is composed
-of copper wire having the same diameter as that constituting the
-resistance for the low reading scale, but as the capacity of the
-former scale is generally a whole number of times greater than that
-of the latter scale, the resistances for the two must bear the same proportion.
-<span class="pagenum"><a name="Page_2085" id="Page_2085">2085</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2888"></a>
-  <img src="images/i253.jpg" alt="_" width="600" height="380" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,888.&mdash;Three phase alternator
-synchronous impedance test. In determining the regulation of an
-alternator, it is necessary to obtain what is called the <i>synchronous
-impedance</i> of the machine. To obtain this, the field is connected, as
-shown above. Voltmeters are removed and the armature short circuited
-with the ammeters in circuit. The field current is then varied,
-the armature driven at synchronous speed, and the armature current
-measured by the ammeters in circuit. The relation between field and
-armature amperes are then plotted. The combination of the results of
-this test, with those obtained from the test shown in <a href="#fig2887">fig. 2,887</a>,
-are used in the determination of the regulation of an alternator.
-Engineers differ widely in the application of the above to the
-determination of regulation, and employ many empirical formulae and
-constants for different lines of design.</p></div>
-
-<p><b>Ques. How is a two scale voltmeter connected?</b></p>
-
-<p>Ans. In the connection of a two scale voltmeter in circuit, the
-single binding post is always employed regardless of which scale is
-desired. If, then, the voltage be such that it may be measured on the
-low reading scale, the other binding post employed is that connected
-to the lower of the two resistances contained within; if, however,
-the pressure be higher than those recorded on the low reading scale,
-the binding post connected to the higher of the two resistances
-contained within is used.</p>
-
-<div class="blockquot">
-<p>NOTE.&mdash;Three phase alternator load test. By means of the connection
-shown in <a href="#fig2888">fig. 2,888</a>, readings of armature current and
-field amperes can be obtained with any desired load. The field current can be
-varied also so as to maintain constant armature voltage irrespective
-of load; or the field current may be kept constant and the armature
-voltage allowed to vary as the load increases. The connections may
-also be used to make a temperature test on the alternator by loading
-it with an artificial load. In some cases after the alternator is
-installed the connection may be used to make a temperature test,
-using the actual commercial load the alternator is furnishing.
-<span class="pagenum"><a name="Page_2086" id="Page_2086">2086</a></span></p>
-
-<p>Inasmuch as the capacities of the scales are usually marked on or
-near the corresponding binding posts, there will generally be no
-difficulty in selecting the proper one of the two left hand binding
-posts.</p></div>
-
-<div class="figcenter">
-  <a name="fig2889"></a>
-  <img src="images/i254.jpg" alt="_" width="600" height="330" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,889.&mdash;Three phase alternator
-or synchronous motor temperature test. In this test two alternators
-or synchronous motors of same size and type are used, and are
-belted together, one to be driven as a synchronous motor and the
-other as an alternator. The method employed is to synchronize the
-synchronous motor with the alternator or alternators on the three
-phase circuit, and then connect to the line by means of a three pole
-single throw switch. The alternator is then similarly synchronized
-with the alternator of the three phase circuit and thrown onto
-the line. By varying the field of the alternator it can be made
-to carry approximately full load, and the motor will then be also
-approximately fully loaded. The usual method is to have the motor
-carry slightly in excess of full load, and the alternator slightly
-less than full load. Under these conditions the motor will run a
-little warmer than it should with normal load, while the alternator
-will run slightly cooler. Temperature measurements are made in
-the same way as discussed under three phase motors. The necessary
-ammeters, voltmeters and wattmeters for adjusting the loads on the
-motors and generator are shown in above figure. If pulleys be of
-sufficient size to transmit the full load, with, say one per cent.
-slip, the pulley on the motor should be one per cent. larger in
-diameter than the pulley on the alternator, so as to enable the
-alternator to remain in synchronism and at the same time deliver
-power to the circuit. With very large machines under test, it is
-inadvisable to use the above method as it is sometimes difficult to
-so adjust the pulleys and belt tension that the belt slip will be
-just right to make up for the difference in diameter of the pulleys,
-and very violent flapping of the belt results. To meet such cases,
-various other methods have been devised. One which gives consistent
-results is shown in <a href="#fig2890">fig. 2,890</a>.</p></div>
-
-<p><span class="pagenum"><a name="Page_2087" id="Page_2087">2087</a></span>
-<b>Ques. How is a two scale voltmeter connected when the binding
-posts are not marked?</b></p>
-
-<p>Ans. If only an approximate idea is possessed of the voltage to be
-measured, it is always advisable to connect to the binding post
-corresponding to the high reading scale of the meter in order
-to determine if the measurement may not be made safely and more
-accurately on the low reading scale. In any case, some knowledge must
-be had of the voltage at hand, else the high reading portion of the
-instrument may be endangered.</p>
-
-<div class="figcenter">
-  <a name="fig2890"></a>
-  <img src="images/i-0347.jpg" alt="_" width="600" height="304" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,890.&mdash;Three phase alternator
-or synchronous motor temperature test. Supply the field with
-normal field current. The armature is connected in open delta as
-illustrated, and full load current sent through it from an external
-source of direct current, care being taken to ground one terminal of
-the dynamo so as to avoid danger of shock due to the voltage on the
-armature winding. The field is then driven at synchronous speed. If
-the armature be designed to be connected star for 2,300 volts, the
-voltage generated in each leg of the delta will be 1,330 volts, and
-unless one leg of the dynamo were grounded, the tester might receive
-a severe shock by coming in contact with the direct current circuit.
-The insulation of the dynamo would also be subjected to abnormal
-strain unless one terminal were grounded. By the above method the
-field is subjected to its full copper loss and the armature to full
-copper loss and core loss. Temperature readings are taken as per
-standardization rules of the A.I.E.E. This method may also be used
-with satisfactory results on large three phase motors of the wound
-rotor type. If the alternator pressure be above 600 volts, a pressure
-transformer should be used in connection with the voltmeter.</p></div>
-
-<div class="blockquot">
-<p><i>Too much care cannot be taken to observe these precautions</i> whenever
-the voltmeter is used, for the burning out or charring of the
-insulation either in the fine wire coil or in the high resistance of
-<span class="pagenum"><a name="Page_2088" id="Page_2088">2088</a></span>
-the meter by an excessive current, is one of the most serious
-accidents that can befall the instrument.</p>
-
-<p>If a voltmeter has been subjected to a voltage higher than that
-for which it was designed, yet not sufficiently high to injure the
-insulation, but high enough to cause the pointer to pass rapidly over
-the entire scale, damage has been done in another way. The pointer
-being forced against the side of the case in this manner, bends it
-more or less and so introduces an error in the readings that are
-afterward taken.</p>
-
-<p>The same damage will be done if the meter be connected in circuit
-so the current does not pass through it in the proper direction,
-although in this case the pointer is not liable to be bent so much as
-when it is forced to the opposite side of the meter by an abnormal
-current, since then it has gained considerable momentum which causes
-a severer impact. The extent of the damage may be ascertained by
-noting how far away from the zero mark the pointer lies when no
-current is passing through the instrument. If this distance be more
-than two-tenths of a division, the metal case enclosing the working
-part should be removed and the pointer straightened by the careful
-use of a pair of pinchers.</p></div>
-
-<div class="figcenter">
-  <a name="fig2891"></a>
-  <img src="images/i256.jpg" alt="_" width="600" height="330" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,891.&mdash;Direct motor or dynamo
-magnetization test. The object of this test is to determine the
-variation of armature voltage without load, with the current flowing
-through the field circuit. The armature should be driven at normal
-speed. The adjustment resistance in the field circuit is varied and
-the voltage across the armature measured. The curve obtained by
-plotting these two figures is usually called magnetization curve
-of the dynamo. It is usual to start with the higher resistance
-in the field circuit so that very small current flows, gradually
-increasing this current by cutting out the field resistance. When
-the highest no load voltage required is reached, the field current
-is then diminished, and what is called the descending (as opposed
-to the ascending) magnetization curves are obtained. The difference
-in the two curves is due to the lag of the magnetization behind the
-magnetizing current, and is caused by the hysteresis of the iron of
-the armature core.</p></div>
-
-<p><span class="pagenum"><a name="Page_2089" id="Page_2089">2089</a></span>
-<b>Ques. What should be noted with respect to location of instruments?</b></p>
-
-<p>Ans. If they be placed near conductors carrying large currents,
-the magnetic field developed thereby will produce a change in the
-magnetism of the instruments and so introduce an error in the readings.</p>
-
-<div class="figcenter">
-  <a name="fig2892"></a>
-  <img src="images/i257.jpg" alt="_" width="600" height="371" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,892.&mdash;Shunt dynamo external
-characteristic test. The external characteristic of a shunt dynamo
-is a curve showing the relation between the current and voltage of
-the external circuit. This is obtained by the connection as here
-shown. The shunt field is so adjusted that the machine gives normal
-voltage when the external circuit is open. The field current is then
-maintained constant and the external current varied by varying the
-resistance in the circuit. By plotting voltage along the vertical,
-against the corresponding amperes represented along the horizontal,
-the external characteristic is obtained.</p></div>
-
-<p><b>Ques. How should portable instruments be wired?</b></p>
-
-<p>Ans. The wires must be firmly secured to the supports on which they
-rest, so as to reduce the possibility of their being pulled by
-accident, and so causing the instruments to fall.</p>
-
-<div class="blockquot">
-<p>A fall or a rough handling of the meter at once shows its effect on
-the readings, for as much harm is done as would result from a similar
-treatment of a watch.
-<span class="pagenum"><a name="Page_2090" id="Page_2090">2090</a></span></p>
-
-<p>The hardened steel pivots used in all high grade voltmeters are
-ground and polished with extreme care so as to secure and maintain a
-high degree of sensitiveness. The jewels on which the moving parts
-revolve are of sapphire, and they too must necessarily be made with
-skill and carefulness; if, therefore, the jewels become cracked and
-the pivots dulled by careless handling, the meter at once becomes
-useless as a measuring instrument.</p></div>
-
-<p><b>Ques. How should readings be taken?</b></p>
-
-<p>Ans. The deflection of the pointer should be read to tenths of a
-division; this can be done with considerable accuracy, especially
-after a little practice.</p>
-
-<div class="figcenter">
-  <a name="fig2893"></a>
-  <img src="images/i258.jpg" alt="_" width="600" height="376" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,893.&mdash;Load and speed test of direct
-current shunt motor. The object of this test is to maintain the
-voltage applied to the motor constant, and to vary the load by means
-of a brake and find the corresponding variation in speed of the
-machine and the current drawn from the circuit. If the motor be a
-constant speed motor, the field resistance is maintained constant.
-The above indicates the method of connecting instruments for the test
-alone; for starting the machine the ordinary starting box, should, of
-course, be inserted.</p></div>
-
-<p class="blockquot">
-For very accurate results, a temperature correction should be applied
-to compensate the effect which the temperature of the atmosphere
-has upon the resistance of the meter when measurements are being
-taken. In ordinary station practice the temperature correction is
-negligible, being for resistance corresponding to the high scale in
-<span class="pagenum"><a name="Page_2091" id="Page_2091">2091</a></span>
-first class meters, less than one-quarter of 1 per cent. for a range
-of 35 degrees above or 35 degrees below 70 degrees Fahrenheit.</p>
-
-<p><b>Ques. What attachment is sometimes provided on station voltmeters
-used for constant pressure service?</b></p>
-
-<p>Ans. A normal index.</p>
-
-<div class="figcenter">
-  <a name="fig2894"></a>
-  <img src="images/i259.jpg" alt="_" width="600" height="380" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,894.&mdash;Temperature test of direct
-current motor or dynamo; loading back method. In making temperature
-tests on a small dynamo it is usual to drive the dynamo with a
-motor and load the dynamo by means of a lamp bank or resistance,
-the voltage across the dynamo being maintained constant, and the
-current through the external circuit adjusted to full load value. The
-temperatures are then recorded, and when they reach a constant value
-above the temperature of the atmosphere, the test is discontinued.
-Similarly, in making a test on a small motor, the motor is loaded
-with a dynamo and the load increased until the input current reaches
-the normal full load value of the motor, the test being conducted
-as for a small dynamo. When, however, the apparatus, either motor
-or dynamo, reaches a certain size, it becomes necessary, in order
-to economize energy, to use what is called the <b>loading back
-method</b>, as here illustrated. The motor is started in the usual
-way, with the dynamo belted to it, the circuit of the dynamo being
-open. The field of the dynamo is then adjusted so that the dynamo
-voltage is equal to that of the line. The dynamo is then connected to
-the circuit and its field resistance varied until it carries normal
-full load current. Under these conditions, if the motor and dynamo be
-of the same size and type, the motor will carry slightly in excess of
-full load, the difference being approximately twice the losses of the
-machines. Under these conditions the total power drawn from the line
-is equal to twice the loss of either machine. Temperature readings
-are taken as in other temperature tests.</p></div>
-
-<p><span class="pagenum"><a name="Page_2092" id="Page_2092">2092</a></span>
-<b>Ques. What precaution must be taken in connecting station voltmeters?</b></p>
-
-<p>Ans. Care must be taken to guard against any short circuiting of the
-voltmeter, which, would mean a short circuiting of the generator, and
-as a result the probable burning out of its armature.</p>
-
-<p class="blockquot">
-The high resistance of the voltmeter prevents any such occurrence
-when it is connected in the proper way, but should one side of the
-circuit be grounded to the metal case or frame of the meter, a
-careless handling of the lead connected with the other side of the
-circuit would produce the result just mentioned.</p>
-
-<div class="figcenter">
-  <a name="fig2895"></a>
-  <img src="images/i260.jpg" alt="_" width="600" height="356" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,895.&mdash;Compound dynamo external
-characteristics test; adjustable load. The object of this test is to
-determine the relation between armature voltage and armature current.
-Shunt field is adjusted to give normal secondary voltage when the
-external circuit is open. The load is then applied by means of an
-adjustable resistance or lamp bank, and readings of external voltage
-and current recorded. If the machine be normally compounded, the
-external voltage will remain practically constant throughout the load
-range. If the machine be under-compounded, the external voltage will
-drop with load, while if over-compounded, there will be a rise in
-voltage with increase in load.</p></div>
-
-<p><b>Ques. Why do station voltmeters indicate a voltage slightly lower
-than actually exists across the leads?</b>
-<span class="pagenum"><a name="Page_2093" id="Page_2093">2093</a></span></p>
-
-<p>Ans. Since they are usually connected permanently in circuit; a
-certain amount of heat is developed in the wiring of the instrument.</p>
-
-<div class="figcenter">
-  <a name="fig2896"></a>
-  <img src="images/i-0348-1.jpg" alt="_" width="600" height="239" />
-  <img src="images/i-0348-2.jpg" alt="_" width="600" height="245" />
-  <p class="f90_left space-below1">
-<span class="smcap">Figs.</span> 2,896 and 2,897.&mdash;Transformer core
-loss and leakage, or exciting current test. With the primary circuit
-open, the ammeter indicates the exciting or no load current. It
-should be noted that all instruments are inserted on the low voltage
-side, for both safety of the operator and because the measurements
-are more accurate. The no load primary current, if the ratio of
-transformation be 10: 1, will be one-tenth of the measured secondary
-current. The wattmeter connected, as shown, measures the sum of the
-losses, in the transformer, in the pressure coil of the wattmeter,
-and in the voltmeter. On all standard makes of portable instruments,
-the resistance of the wattmeter pressure coil and of the voltmeter
-is given, and the loss in either instrument is the square of the
-voltage at its terminals, divided by its resistance. Subtracting
-these losses from the total indicated upon the wattmeter, gives the
-true core or iron loss. It should be noted that in this diagram is
-shown an auxiliary transformer with a number of taps for obtaining
-the exact rated voltage of the transformer under test. In fig. 2,897
-is shown, in general, the same connections as in fig. 2,896,
-except that the auto-transformer has been replaced by a resistance. If the
-line voltage available be not much in excess of the rated voltage of
-the transformer under test, very little error is introduced by the
-use of the resistance method. However, if the difference be 10 per
-cent. or more the auxiliary transformer shown in fig. 2,896
-should be used. Measurements made under the resistance method always give lower
-results than those obtained with the auxiliary transformer.</p></div>
-
-<p><span class="pagenum"><a name="Page_2094" id="Page_2094">2094</a></span></p>
-
-<p class="blockquot">
-The effect of this heat increases the voltmeter resistance and
-consequently reduces the current below that which otherwise would
-pass through the meter; since the deflections of the pointer
-are governed by the strength of the current, station voltmeters
-invariably indicate a voltage slightly lower than that which actually
-exists across their leads.</p>
-
-<div class="figcenter">
-  <a name="fig2898"></a>
-  <img src="images/i262.jpg" alt="_" width="600" height="563" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,898.&mdash;Diagram of connections for
-calibrating a wattmeter. The calibration of a portable wattmeter
-is accomplished with direct current of constant value which is
-passed through the series winding by connecting the source thereof
-with the current terminals. A direct current voltage which may be
-varied throughout the range of the wattmeter is also applied to the
-instrument between the middle and right hand pressure terminals A and
-E the wiring in the meter between these terminals being such that
-its differential winding is then cut out of circuit. The method of
-procedure consists in comparing the deflections on the wattmeter at
-five of six approximately equidistant points over its scale with the
-corresponding products of volts and amperes used to obtain them. The
-changes in the wattmeter deflections are effected by merely varying
-the voltage, the value of the current being maintained constant at a
-value which represents the full current capacity of the meter.</p></div>
-
-<div class="blockquot">
-<p>NOTE.&mdash;<b>Checking up of a recording wattmeter.</b> This may
-conveniently be done by noting the deflections at short intervals on
-an ammeter connected in circuit, and also the readings on the dial of
-the recording wattmeter during this period. If this test be continued
-for an appreciable time, the product of the pressure in volts, the
-current in amperes, and the time in hours, should equal the number of
-watthours recorded on the counters of the dial.</p>
-
-<p>NOTE.&mdash;<b>Transformer testing.</b> In the early days of transformer
-building, before the commercial wattmeter had been perfected, leakage
-or exciting current was the criterion of good design. After the
-introduction of the wattmeter, core loss became the all important
-factor, and for a long time the question of leakage current was
-lost sight of. With the introduction of silicon steel, leakage or
-exciting current again assumed prominence. Keeping in mind the
-fact that all characteristics of a transformer are of more or less
-importance, it is essential that the user of such apparatus have at
-hand the necessary facilities for making tests of all such variable
-quantities. The tests which all users of transformers should make,
-are given in this chapter.
-<span class="pagenum"><a name="Page_2095" id="Page_2095">2095</a></span></p></div>
-
-<p><b>Ques. Can direct current be measured by an alternating current
-voltmeter?</b></p>
-
-<p>Ans. Yes.</p>
-
-<div class="figcenter">
-  <a name="fig2899"></a>
-  <img src="images/i-0349.jpg" alt="_" width="600" height="231" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,899.&mdash;Transformer copper loss
-by wattmeter measurement and impedance. At first glance, this method
-would seem better than the calculation of loss after measurement of
-the resistance. However, it should be noted that the wattmeter is,
-in itself, subject to considerable error under the low power factor
-that will exist in this test. The secondary of the transformer is
-short circuited, and a voltage applied to the primary which is just
-sufficient to cause full load primary current. If full current pass
-through the primary of the transformer with the secondary short
-circuited, the secondary will also carry full load current. With
-connections as shown, and with the full load current, the voltmeter
-indicates the impedance volts of the transformer. This divided by
-the rated voltage gives what is called the <i>per cent. impedance of
-the transformer</i>. In a commercial transformer of 5 kw., this should
-be approximately 3 per cent. The iron loss of the transformer under
-approximately 3 per cent. of the normal voltage will be negligible,
-and the losses measured will be the sum of the primary and secondary
-copper losses. As in the discussion of the core loss measurements,
-the wattmeter readings must be corrected for the loss in its pressure
-coil, the method of correction being the same as that discussed under
-the core loss measurement. If the impedance volts, as measured, be
-divided by the primary current, the impedance of the transformer
-is obtained. The reciprocal of this quantity is known by the term
-"admittance." <i>When two or more transformers are connected in
-parallel they divide the load in proportion to their admittance.</i>
-It is, therefore, important that the users of transformers know the
-impedance of the apparatus used, in order to determine whether two
-or more transformers will operate satisfactorily in parallel. For
-discussion of wattmeter error on low power factor, see note on page
-2,075. For accurate measurement of impedance, the voltmeter should
-be connected directly across the terminals of the transformer rather
-than as shown in the diagram.</p></div>
-
-<p class="blockquot">
-NOTE.&mdash;<b>Transformer copper loss test.</b> The usual and best method
-of obtaining copper losses is to separately measure the primary
-and secondary resistance and calculate from these the primary and
-secondary copper losses. For general diagram of connections and
-discussion of the drop method, <a href="#fig2875">see fig. 2,875</a>. The current
-should be kept well within the load current of the transformer to avoid
-temperature rise during the test. In other words, the resistance of
-the coil is the voltage across its terminals divided by the current.
-The resistance of the primary coil can be measured similarly. The
-copper loss in watts in each coil will then be the product of the
-resistance and the square of the rated current for that coil. The
-total copper loss will be the sum.
-<span class="pagenum"><a name="Page_2096" id="Page_2096">2096</a></span></p>
-
-<p><b>Ques. What would be the effect of placing a direct voltmeter
-across an alternating current circuit, and why?</b></p>
-
-<p>Ans. There would be no deflection of the pointer owing to the rapid
-reversals of the alternating current.</p>
-
-<p><b>Ques. What are the usual capacities of alternating current voltmeters?</b></p>
-
-<p>Ans. They are 3, 7.5, 10, 12, 15, 20, 60, 75, 120, 150, 300 and 600
-volts, but these capacities may each be increased by the use of a
-multiplier.</p>
-
-<div class="figcenter">
-  <a name="fig2900"></a>
-  <img src="images/i264.jpg" alt="_" width="600" height="154" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,900.&mdash;Temperature test of transformer
-with non-inductive load. The figure shows the simplest way of making
-the test. Connect the primary of the transformer to the line as
-shown, and carry normal secondary load by means of a bank of lamps or
-other suitable resistance, until full load secondary current is shown
-by the ammeter in the secondary circuit. The transformer should then
-be allowed to run at its rated load for the desired interval of time,
-temperature readings being made of the oil in its hottest part, and
-also of the surrounding air. Where temperatures of the coil rather
-than temperatures of the oil are desired, it is necessary to use the
-resistance method. This is obtained by first carefully measuring the
-resistance of both primary and secondary coils at the temperature
-of the room, and then, after the transformer has been under heat
-test for the desired time, disconnect it from the circuit and again
-measure the resistance of primary and secondary. For proper method
-of calculating the temperature rise from resistance measurements,
-the reader is referred to the standardization rules of the A.I.E.E.
-In making resistance measurements of large transformers by the drop
-method care should be taken to allow both ammeter and voltmeter
-indications to settle down to steady values before readings are
-taken. This may require several minutes. Each time the current is
-changed it is necessary in order to obtain check values on resistance
-measurements, to wait until the current is again settled to its
-permanent value before taking readings. All resistance measurements
-must be taken with great care, as small errors in the measurement of
-the resistance may make very large errors in the determination of
-the temperature rise. The method above described is satisfactory for
-small transformers. Where large units are to be tested, the cost of
-current for testing becomes an important item. The "bucking test" as
-in <a href="#fig2901">fig. 2,901</a>, is more economical.</p></div>
-
-<p><b>Ques. How are station voltmeters usually attached to the switchboard?</b></p>
-
-<p>Ans. They are usually bolted to the switchboard by means
-<span class="pagenum"><a name="Page_2097" id="Page_2097">2097</a></span>
-of four iron supports mounted on the back of the instrument;
-two of these are fastened near each side of the case.</p>
-
-<p class="blockquot space-below1">
-Under certain conditions, however, as in paralleling of alternators,
-it is convenient to have the alternating current voltmeter mounted
-on a swinging bracket at the side of the switchboard. The voltmeter
-may then be swung around in any desired direction so as to enable the
-attendant to keep informed of the voltage while switching in each
-additional alternator.</p>
-
-<div class="figcenter">
-  <a name="fig2901"></a>
-  <img src="images/i265.jpg" alt="_" width="600" height="399" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,901.&mdash;Transformer temperature "bucking
-test." For this purpose two transformers of the same size and ratio
-are required. The connections are as shown. Full secondary voltage is
-applied, and rheostats or auxiliary auto-transformers are inserted
-in the circuit to properly regulate the voltage. The primaries
-are connected with one bucking the other, and a voltage equal to
-twice the impedance voltage of either transformer inserted in the
-primary circuit. It should be noted that when the secondaries are
-subjected to the full secondary voltage, a full primary voltage
-exists across either primary, but with the primaries connected so
-that the voltage of one is bucked against the voltage of the other,
-the resultant voltage in the circuit will be zero. By applying to the
-primary circuit twice the impedance voltage of either transformer,
-full primary and secondary current will circulate through both
-transformers. On the other hand, by subjecting the secondaries to
-the full secondary voltage, the iron of the transformer will be
-magnetized as under its regular operating conditions, and the full
-iron loss of the transformer introduced. This method permits the
-operation of two transformers under temperature test with their
-full losses, without taking energy from the line equal to the rated
-capacity. Measurements of temperature are taken in exactly the
-same way as above. This method is successfully employed for making
-temperature tests on transformers of all sizes.</p></div>
-
-<p><span class="pagenum"><a name="Page_2098" id="Page_2098">2098</a></span>
-<b>Ques. How should an ammeter be operated to get accurate readings, and why?</b></p>
-
-<p>Ans. It should be cut out of circuit except while taking a reading,
-because of the error introduced by the heating effect of the current.</p>
-
-<div class="figcenter">
-  <a name="fig2902"></a>
-  <img src="images/i-0350.jpg" alt="_" width="600" height="306" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,902.&mdash;Transformer insulation test.
-In applying a 10,000 volt insulation test between the primary and
-secondary of a transformer, the testing leads should be disconnected
-from the transformer under test, and a spark gap introduced as shown,
-with the test needle set at a proper sparking distance for 10,000
-volts. A high resistance should be connected in the secondary before
-closing its circuit, and the voltage gradually increased by cutting
-out this secondary resistance until a spark jumps across the spark
-gap. When the spark jumps across the spark gap, the voltmeter reading
-should be recorded and the testing transformer disconnected. The
-spark gap should then be increased about 10 per cent. and the high
-tension leads connected to the transformer under test as indicated
-in the diagram. In order to equalize the insulation strains, all
-primary leads should be connected together, all secondary leads not
-only connected together, but to the core as well. All resistance
-in the rheostat in the low tension circuit should then be inserted
-and the switch closed. Gradually cut out secondary resistance until
-the voltmeter shows the same voltage as was recorded previously
-when the spark jumped across the gap, and apply this voltage to the
-transformer for one minute. Insulation tests for a period of over
-one minute are very unadvisable, as transformers with excellent
-insulation may be seriously damaged by prolonged insulation tests.
-The longer the strain to which any insulation is subjected, the
-shorter the subsequent life of the insulation. Also the greater the
-applied voltage above the actual operating voltage of the apparatus,
-the shorter the subsequent life of the insulation. In testing small
-transformers, the spark gap may be omitted and the voltage of the low
-pressure coil of the testing transformer measured. This multiplied by
-the ratio of transformation gives the testing voltage.</p></div>
-
-<div class="blockquot">
-<p>In an ammeter having a capacity of 50 amperes, the error thus
-introduced will be less than 1 per cent. if connected continuously in
-circuit with a current not exceeding three-quarters this capacity.</p>
-
-<p>An ammeter of 100 amperes capacity may be used indefinitely in
-circuit with less than 1 per cent. error up to one-half its capacity,
-<span class="pagenum"><a name="Page_2099" id="Page_2099">2099</a></span>
-and for five minutes at three-quarters capacity without exceeding the
-1 per cent. limit.</p></div>
-
-<div class="figcenter">
-  <a name="fig2903"></a>
-  <img src="images/i-0352.jpg" alt="_" width="600" height="184" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,903.&mdash;Transformer insulation test
-as made when a special high tension transformer be not available.
-In this method a number of standard transformers, connected as
-shown may be employed, but great care should be taken to have such
-transformer cases thoroughly insulated from the ground and from one
-another, in order to minimize the insulation strains in the testing
-transformers. Care should be taken to insert in the circuit of
-each testing transformer a fuse, not in excess of the transformer
-capacity, which will blow, in case of a break down in the apparatus
-under test. In testing insulation between secondary and core,
-disconnect the primary entirely, apply one terminal of the testing
-transformer to the secondary terminals of the transformer under test,
-and the other terminal of the testing transformer to the core of the
-transformer under test. This test should also not be in excess of one minute.</p></div>
-
-<div class="blockquot space-below1">
-
-<p>The 150 scale ammeter may be left in circuit for an indefinite length
-of time at one-third its full capacity, and for three minutes at
-one-half its full capacity, with a negligible error.</p>
-
-<p>Ammeters of 200 and of 300 ampere capacities must not continuously
-carry more than one-quarter of these loads respectively if the
-readings are to have an accuracy within 1 per cent. nor more than
-one-half these respective number of amperes for three minutes if the
-same degree of accuracy be desired.</p>
-
-<p>In order to cut or shunt the ammeter out of circuit when not in use,
-it is customary when wiring the instrument in place, to introduce a
-switch as a shunt across it; this switch is kept closed except when a
-measurement is being taken.</p>
-
-<p>When currents larger than 300 amperes have to be measured, ammeter
-<span class="pagenum"><a name="Page_2100" id="Page_2100">2100</a></span>
-shunts are generally employed, although ammeters up to 500 amperes
-capacity are manufactured.</p></div>
-
-<div class="figcenter">
-  <a name="fig2904"></a>
-  <img src="images/i-0351.jpg" alt="_" width="600" height="218" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,904.&mdash;Transformer internal insulation
-test, sometimes called double normal voltage test, from the fact that
-most transformers are tested with double normal voltage across their
-terminals. If either the primary or secondary of the transformer
-be connected to some source of current with voltage double that of
-the voltage of the transformer under test, the insulation between
-adjacent turns, and also the insulation between adjacent layers
-will be subjected to twice the normal operating voltage. It is good
-practice to employ high frequency for this test in order to prevent
-an abnormal current from passing through the transformer. Sixty
-cycle transformers are usually tested on 133 cycles, and 25 cycle
-transformers on 60 cycle circuits for this double normal voltage
-test. It is necessary to insert the resistance in the circuit of the
-transformer and bring the voltage up gradually, the same as applying
-other high insulation tests in order to prevent abnormal rises in
-pressure at the instant of closing the circuit.</p></div>
-
-<p><b>Ques. What is used in place of instrument shunts for high pressure
-alternating current measurements?</b></p>
-
-<p>Ans. Instrument transformers.</p>
-
-<p><b>Ques. What important attention should be periodically given to
-measuring instruments?</b></p>
-
-<p>Ans. They should be frequently tested by comparison with standards
-that are known to be correct.
-<span class="pagenum"><a name="Page_2101" id="Page_2101">2101</a></span></p>
-
-<div class="blockquot">
-<p>Electrical measuring instruments, owing to the nature of their
-construction and the conditions under which they must necessarily
-be used, are subject to variations in accuracy. This feature is an
-annoying one on account of the difficulty of detecting it; a meter
-may, as far as appearances go, be in excellent working order and yet
-give readings which are not to be relied upon.</p>
-
-<p>Ridiculous as it may appear, the average station attendant may
-frequently be seen straining his eyes to read to tenths of a division
-on the scale of a meter which, if subjected to test, would show an
-inaccuracy of over 2 per cent.</p>
-
-<p>In testing a meter, by comparing it with a standard, in order to
-obtain the best results there should be one man at each meter so that
-simultaneous readings may be taken on both instruments, and the man
-at the standard meter should maintain the voltage constant while a
-reading is being taken, by means of a rheostat in the field circuit
-of the generator supplying the current.</p></div>
-
-<div class="figcenter">
-  <a name="fig2905"></a>
-  <img src="images/i269.jpg" alt="_" width="600" height="182" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,905.&mdash;Transformer insulation
-resistance test. The insulation, besides being able to resist
-puncture, due to increased voltage, must also have sufficient
-resistance to prevent any appreciable amount of current flowing
-between primary and secondary coils. It is, therefore, sometimes
-important that the insulation resistance between primary and
-secondary be measured. This can be done, as here shown. Great care
-should be taken to have all wires thoroughly insulated from the
-ground, and to have an ammeter placed as near as possible to the
-terminals of the transformer under test, in order that current
-leaking from one side of the line to the other, external to the
-transformer, may not be measured. Great care is required in making
-this measurement, in order to obtain consistent results.]</p>
-
-<div class="blockquot">
-<p>Each meter should be checked or calibrated at five or six
-approximately equidistant points over its scale; the adjustable
-resistance being varied each time to give a deflection on the
-standard meter of an even number of divisions and the deflection on
-the other meter recorded at whatever it may be. Having obtained the
-necessary readings, the calculation of the constant or multiplying
-factor of the meter undergoing test is next in order.</p>
-
-<p>This may best be shown by taking an actual case in which a 150 scale
-voltmeter is being tested to determine its accuracy. The data and
-calculations are as follows:
-<span class="pagenum"><a name="Page_2102" id="Page_2102">2102</a></span></p></div>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr class="tr_lt_grey">
-      <td class="tdc">Readings on<br />&nbsp;standard meter&nbsp;</td>
-      <td class="tdc">&nbsp;Readings on&nbsp;<br />meter tested</td>
-      <td class="tdc">Constant</td>
-    </tr><tr>
-      <td class="tdc">150</td>
-      <td class="tdr">149.2&nbsp;&nbsp;</td>
-      <td class="tdr">&emsp;150 ÷ 149.2 = 1.005</td>
-    </tr><tr>
-      <td class="tdc">125</td>
-      <td class="tdr">125.0&nbsp;&nbsp;</td>
-      <td class="tdr">125 ÷ 125.0 = 1.000</td>
-    </tr><tr>
-      <td class="tdc">100</td>
-      <td class="tdr">98.9&nbsp;&nbsp;</td>
-      <td class="tdr">100 ÷ &nbsp; 98.9 = 1.011</td>
-    </tr><tr>
-      <td class="tdc">&nbsp;&nbsp;75</td>
-      <td class="tdr">73.6&nbsp;&nbsp;</td>
-      <td class="tdr">75 ÷ &nbsp; 73.6 = 1.019</td>
-    </tr><tr>
-      <td class="tdc">&nbsp;&nbsp;50</td>
-      <td class="tdr">50.0&nbsp;&nbsp;</td>
-      <td class="tdr">50 ÷ &nbsp; 50.0 = 1.000</td>
-    </tr><tr>
-      <td class="tdc">&nbsp;&nbsp;25</td>
-      <td class="tdr">24.8&nbsp;&nbsp;</td>
-      <td class="tdr u">25 ÷ &nbsp; 24.8 = 1.008</td>
-    </tr><tr>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">6.043</td>
-    </tr><tr class="tr_lt_grey">
-      <td colspan="3" class="tdc"><br />Average constant for six readings, 6.043 ÷ 6 = 1.007.</td>
-    </tr>
- </tbody>
-</table>
-<hr class="chap" />
-<div class="figcenter">
-  <a name="fig2906"></a>
-  <img src="images/i-0353.jpg" alt="_" width="600" height="340" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,906.&mdash;Transformer winding or ratio
-test. The object of this test is to check the ratio between the
-primary and the secondary windings. For this purpose a transformer of
-known ratio is used as a standard. Connect the transformer under test
-with a standard transformer as shown. Leave switch S<sub>2</sub> open. With
-the single pole double throw switch in position S<sub>1</sub>B, the voltmeter
-is thrown across the terminals of the standard transformer. With
-the switch in position S<sub>1</sub>A, the voltmeter is thrown across the
-terminals of the transformer under test. The voltmeter should be read
-with the switch in each position. If the winding ratio be the same as
-that of the standard transformer, the two voltmeter readings will be identical.</p></div>
-
-<div class="blockquot">
-<p>It may be stated in general that before taking the readings for this
-test, the zero position of the pointer on the meter tested should
-be noted, and if it be more than two-tenths of a division off the
-zero mark, the case of the meter should be removed and the pointer
-straightened.</p>
-
-<p>Furthermore, it will be noticed from the readings here recorded that
-the test is started at the high reading end of the scale; this is
-done in order that the pointer may gradually be brought up to this
-<span class="pagenum"><a name="Page_2103" id="Page_2103">2103</a></span>
-spot, by slowly cutting out of circuit the adjustable resistance, and
-thus show whether or not the pointer has a tendency to stick at any
-part of the scale. If the meter seem to be defective in this respect,
-it should be remedied either by bending the pointer or scale, or by
-renewing one or both of the jewels, before the comparison with the
-standard is commenced.</p>
-
-<p>It is obvious from the readings recorded for the 150 scale voltmeter,
-that as compared with the corresponding deflections of the standard,
-the former are a trifle low.</p>
-
-<p>In order to determine for each observation how much too low they
-are, it is necessary to divide each reading on the standard by the
-corresponding reading on the meter tested. The result is the amount
-by which a deflection of this size on the meter tested must be
-multiplied in order to obtain the exact reading. This multiplier is
-called a constant, and as shown, a constant is determined for each of
-the six observations.</p>
-
-<p>The average constant for the six readings is then found, and this is
-taken as the constant for the meter as a whole; that is, whenever
-this 150-scale voltmeter is used, each reading taken thereon must be
-multiplied by 1.007 in order to correct for its inaccuracy.</p>
-
-<p>The most convenient and systematic way of registering the constant of
-a meter is to write it, together with the number of the meter and the
-date of its calibration, in ink on a cardboard tag and loop the same
-by means of a string to the handle or some other convenient part of
-the meter.</p>
-
-<p>NOTE.&mdash;<b>Transformer polarity test.</b> A test of importance
-in the manufacture of transformers, and sometimes necessary for the
-user, is the so called <i>banking</i> or <i>polarity</i> test. The transformers
-from any particular manufacturer have the leads brought out in
-such a manner that a transformer of any size can be connected to
-primary and secondary lines in a given order without danger of
-blowing the fuses due to incorrect connections. All manufacturers
-of transformers, however, do not bank transformers in the same
-way, so that it is necessary in placing transformers of different
-makes to test for polarity. This is done as shown in <a href="#fig2906">fig. 2,906</a>.
-One transformer is selected as a standard and the leads of the
-second transformer connected as indicated in the diagram. If the
-transformers be 1,100-2,200 volts to 110-220, two 110 volt lamps
-are connected in the secondaries of the transformers as indicated,
-while the primary of the transformer is connected across the line.
-In transformers built for two primary and two secondary voltages, it
-is necessary to test each primary and each secondary. The diagram
-shows the method of connecting one 2,200 volt coil and one 110 volt
-coil to the transformer to be tested. When the primary circuit of the
-transformer under test is closed, and if the secondary leads of the
-110 volt coil under test be brought out of the case properly, the two
-110 volt lamps should be brightly illuminated. If, on the other hand,
-the two 110 volt terminals have been reversed, no current will flow
-through the lamps. If these two terminals be found to be brought out
-correctly, transfer the secondary leads of the transformer under test
-to the second 110 volt coil. Upon closing the primary circuit, the
-lamp should again be brightly illuminated. Repeat this process with
-each of the secondary coils and the other primary coil, and if the
-lamps show up brightly in every case on closing the primary circuit,
-all leads have been properly brought out. If on any tests the lamps
-do not light up brightly, the leads on the transformer must be so
-changed as to produce the proper banking.
-<span class="pagenum"><a name="Page_2104" id="Page_2104">2104</a></span></p></div>
-
-<p><b>Ques. What are the usual remedies applied to a voltmeter to
-correct a 3 or 4 per cent. error?</b></p>
-
-<p>Ans. They consist of straightening the pointer, varying the tension
-of the spiral springs, renewing the jewels in the bearings, altering
-the value of the high resistance, and, in the case of a direct
-current instrument, strengthening the permanent magnet.</p>
-
-<p><b>Ques. How is the permanent magnet strengthened?</b></p>
-
-<p>Ans. After detaching it from the instrument, wrap around several
-turns of insulated wire, and pass through this wire for a short time
-3 or 4 amperes of direct current in such a direction as to reinforce
-the magnet magnetism.</p>
-
-<p><b>Ques. How may the value of the high resistance of a voltmeter
-be altered?</b></p>
-
-<p>Ans. Determine the resistance of the voltmeter and add or subtract,
-according as the reading is high or low, a certain length of wire
-whose resistance is in per cent. of the voltmeter resistance the same
-as the per cent. of error.</p>
-
-<p class="blockquot">
-NOTE.&mdash;The complete calibration of a two scale voltmeter does not,
-as might be supposed, necessitate that the readings on both scales
-be checked with standards, for since the resistance corresponding to
-the one scale is always some multiple of the resistance of the other,
-the constants of the two scales are proportional. For instance, if S
-= the reading at the end of the high scale of the voltmeter; S<sup>1</sup>
-= the reading at the end of the low scale of the voltmeter; R = the
-resistance in the meter corresponding to the high scale; R<sup>1</sup> =
-the resistance in the meter corresponding to the low scale; K = the
-constant for the high scale, and K<sup>1</sup> = the constant for the low
-scale. Then</p>
-
-<p class="center"><b>SK ÷ R = S<sup>1</sup>K<sup>1</sup> ÷ R<sup>1</sup></b></p>
-
-<p class="no-indent">from which</p>
-
-<p class="center"><b>K<sup>1</sup> = SKR ÷ S<sup>1</sup>R</b></p>
-
-<p class="blockquot">
-That is to say, if the respective resistances corresponding to the
-two scales be known, and the constant of the high scale be determined
-by comparison with a standard, then by aid of these known values and
-the maximum readings on the two scales, the constant of the low scale
-may be calculated. It is also possible to calculate the constant of
-the high scale if the constant of the low scale be known, together
-with the values of the resistances corresponding to the two scales;
-for from the equation previously given.</p>
-
-<p class="center space-below1"><b>K = RS<sup>1</sup>K<sup>1</sup> ÷ R<sup>1</sup>S</b></p>
-<span class="pagenum"><a name="Page_2105" id="Page_2105">2105</a></span>
-
-<p><b>Ques. What is a frequent cause of error in an alternating current meter, and why?</b></p>
-
-<p>Ans. The deterioration of its insulation, which permits the working
-parts of the instrument coming in contact with the surrounding metal
-case.</p>
-
-<p class="blockquot">
-A convenient method of testing for deterioration of insulation is
-shown in <a href="#fig2905">fig. 2,905</a>.</p>
-
-<div class="figcenter">
-  <a name="fig2907"></a>
-  <img src="images/i273.jpg" alt="_" width="600" height="539" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,907.&mdash;Diagrams showing various
-synchronous converter transformer connections. The diametrical
-connection is used most frequently as it requires only one secondary
-coil on each transformer, this being connected to diametrically
-opposite points on the armature winding. The middle points can be
-connected together and a neutral obtained the unbalanced three
-wire direct current having no distorting effect. With diametrical
-secondaries, the primaries should preferably be connected delta,
-except with regulating pole converters where they must be connected
-Y. Diametrical secondaries with delta primaries should not be
-used with regulating pole converters. Double star connection of
-secondaries may, however, be used with delta primaries, and is free
-from the trouble of the triple harmonic of the transformer appearing
-in the primary. In this case, however, the two secondary neutrals
-must not be connected with each other.</p></div>
-
-<p><b>How to Test Generators.</b>&mdash;In the operation of electrical
-stations, many problems dealing with the generators installed therein
-can be readily solved by the aid of characteristic curves, which bear
-a relation to the generators similarly as do indicator diagrams to steam engines.
-<span class="pagenum"><a name="Page_2106" id="Page_2106">2106</a></span></p>
-
-<div class="figcenter">
-  <a name="fig2908"></a>
-  <img src="images/i-0354.jpg" alt="_" width="600" height="824" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,908.&mdash;General form of characteristic
-curves for a series dynamo. The general curve that may be expected is
-OA. It is obtained practically in the same manner as for the shunt
-characteristic curve, except that no field rheostat is employed.
-Commencing with no load or amperes, there will probably be a
-small deflection noticeable on the voltmeter, due to the residual
-magnetism. The other readings are taken with successive reductions
-of main current resistance. The curve OA thus obtained for a certain
-series generator is practically a straight line at the beginning,
-representing thereby a proportional increase of voltage with
-increase of current, but after a certain current is reached (about
-20 amperes in this case) the curve flattens and takes a downward
-direction. The turning point occurs in the characteristic curves
-of all series generators, and it denotes the stage at which the
-iron magnet cores become so saturated with lines of magnetic force
-that they will not readily allow more to pass through them; this
-turning point is technically known as the point of saturation, and
-the current corresponding (20 amperes in this case) is called the
-critical current of the dynamo. The point of saturation in any given
-series machine is governed by the amount of iron in the magnetic
-circuit; its position in the curve therefore varies according to
-the design of the generator as does also the critical current. The
-value of the latter is important inasmuch as the valuable features
-of a series generator assert themselves only when the machine is
-supplying a greater number of amperes than that of the critical
-current, for if the series generator be worked along that part M A of
-the curve to the right of the point of saturation it becomes nearly
-self-regulating as regards current, because as the current increases
-the voltage drops. In the diagram in addition to the characteristic
-curve O A, which may more definitely be called an external
-characteristic curve on account of representing the conditions
-external to the generator, there is shown a total characteristic
-curve, O C B. The latter curve represents the relation between the
-current and the total voltage developed in the armature, and may be
-plotted from the external characteristic curve if the resistance of
-the armature between brushes and the resistance of the series field
-winding be known. For example, assume these combined resistances
-amount to .6 ohm. At 30 amperes there would be required 30 × .6 = 18
-volts to force this current through the armature and field windings.
-At 30 amperes the external pressure is 65 volts, as shown by the
-curve O A; the total voltage developed for 30 amperes is, therefore,
-the external voltage plus the internal voltage or 65 + 18 = 83
-volts. Plotting 83 volts for 30 amperes will give one point for the
-external characteristic curve of this machine, and by determining in
-like manner the total voltages developed for six or eight different
-currents over the scale, sufficient data will be at hand for plotting
-and drawing in the curve O C B.</p></div>
-
-<p><span class="pagenum"><a name="Page_2107" id="Page_2107">2107</a></span>
-In steam engineering, a man who did not fully understand the method
-of taking an indicator diagram would be considered not in touch with
-his profession, and in electrical engineering the same would be true
-of one ignorant of the method of obtaining characteristic curves.</p>
-
-<p class="blockquot">
-The necessary arrangement or connection of the generator from which
-it is desired to obtain a characteristic curve, consists in providing
-a constant motive power so that the machine may be run at a uniform
-speed, and when the field magnets of the generator are separately
-excited the field current from the outside source must also be
-maintained constant, preferably by a rheostat connected in the field
-of the auxiliary exciting machine. It is also necessary in every case
-that means be provided for varying the main current of the generator
-step by step from zero to maximum. This may best be done by employing
-a water rheostat, as shown in <a href="#fig2909">fig. 2,909</a>.</p>
-
-<p><b>Ques. What instruments are needed in making a test of dynamo characteristics?</b></p>
-
-<p>Ans. A voltmeter, ammeter, speed indicator, the usual switches and rheostats.</p>
-
-<p><b>Ques. How is the apparatus connected?</b></p>
-
-<p>Ans. It is connected as shown in <a href="#fig2910">fig. 2,910</a>.</p>
-
-<p><b>Ques. Describe the test.</b></p>
-
-<p><span class="pagenum"><a name="Page_2108" id="Page_2108">2108</a></span>
-Ans. Having completed the preliminaries as in <a href="#fig2910">fig. 2,910</a>,
-the test should be started with the main circuit of the generator open. Then,
-in the case of the shunt machine, the speed should be made normal and
-the field rheostat adjusted until the voltmeter reading indicates
-the rated voltage of the machine at no load and readings taken. The
-electrodes of the water rheostat should be adjusted for maximum
-resistance and main circuit closed, and a second set of readings
-taken. Several sets of readings are taken, with successive reductions
-of water rheostat resistance. The results are then plotted on
-coordinate paper giving the characteristic curve shown in <a href="#fig2908">fig. 2,908</a>.</p>
-
-<div class="figcenter">
-  <a name="fig2909"></a>
-  <img src="images/i276.jpg" alt="_" width="600" height="335" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,909.&mdash;Water rheostat. It consists
-essentially of a tank of suitable size containing salt water into
-which are placed two electrodes having means of adjustment of the
-distance separating them. The solution depends on the voltage. Pure
-water is seldom used for pressures under 1,000 volts. The size of
-the tank is determined by the size of the electrodes, and roughly
-the size of the latter equal the number of amperes. With a current
-density of one ampere per square inch, a water solution gives a
-drop of 2,500 to 3,000 volts per inch distance between the plates.
-Where high voltage is used, the water must be circulated through and
-from the tank by rubber hose allowing for 2,500 volts, a length of
-15 to 20 feet of 1 inch hose to prevent grounding. In place of the
-arrangement shown above, a barrel may be used for the tank, and for
-the electrodes, coils of galvanized iron wire. This is the simplest
-form and is satisfactory.</p></div>
-
-<p><b>Ques. What does the characteristic curve (<a href="#fig2911">fig. 2,911</a>) show?</b></p>
-
-<p>Ans. An examination of the curve shows that the highest
-<span class="pagenum"><a name="Page_2109" id="Page_2109">2109</a></span>
-point of the curve occurs at no load or 0 amperes; that as the
-current is increased, the voltage drops, first slightly to the point
-B and then rapidly until the point E is reached, when any further
-lowering of resistance in the main circuit to increase the current
-causes not only a rapid decline in the voltage but also of the
-current until both voltage and current become approximately zero.</p>
-
-<div class="figcenter">
-  <a name="fig2910"></a>
-  <img src="images/i277.jpg" alt="_" width="600" height="451" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,910.&mdash;Connections for test of dynamo.
-During the test, one man should be assigned to the tachometer,
-another man to the water rheostat, and there should preferably be
-one man at each of the electrical measuring instruments. In order
-to enable the man at the tachometer to keep the speed constant, he
-should be in communication either directly or indirectly with the
-source of the driving power, and the man at the water rheostat should
-be in plain view of the man reading the ammeter so that the latter
-party may signal him for the proper adjustment of the rheostat in
-order that the desired increase of current be obtained for each set
-of readings.</p></div>
-
-<p class="blockquot">
-In some generators, a very slight current results even when the
-terminals of the machine are actually short circuited; that is, due
-to residual magnetism in the pole pieces, the lower portion of the
-curve often terminates, not exactly at zero, but at a point some
-distance along the current line.
-<span class="pagenum"><a name="Page_2110" id="Page_2110">2110</a></span></p>
-
-<p>The working portion of the curve is from A to C, at which time the
-machine is supplying a fairly constant voltage. From C to E shows
-a critical condition of affairs, while the straight portion D O
-represents the unstable part of the curve caused by the field current
-being below its proper value.</p>
-
-<p>The position of the point C determines the maximum power the machine
-is capable of developing, being in this case (47.5 × 25) ÷ 746 = 1.59
-horse power.</p></div>
-
-<p><b>Ques. How may the commercial efficiency of a generator be determined?</b></p>
-
-<p>Ans. To obtain the commercial efficiency, the <i>input</i> and
-<i>output</i> must be found for different loads.</p>
-
-<p class="blockquot">
-The input may be found by running the generator as a motor at its
-rated speed, loading it by means of a Prony brake. The generator must
-be stripped of all belting or other mechanical connections, supplied with
-its normal voltage and full load current, and the pressure of the Prony
-brake upon its armature shaft or pulley adjusted until the rated speed
-of the armature is obtained. The data thus obtained is substituted
-in the formula.</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">2&#960; L W R</td>
-      <td class="tdl">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">input in brake horse power =&nbsp;</td>
-      <td class="tdc">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</td>
-      <td class="tdl">&emsp;&emsp;&emsp;(1)</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">33,000</td>
-      <td class="tdl">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="no-indent">in which<br />
-&emsp;&emsp;&emsp;L = length of Prony brake lever;<br />
-&emsp;&emsp;&emsp;W = pounds pull at end of lever;<br />
-&emsp;&emsp;&emsp;R = revolutions per minute.</p>
-
-<p>The output or electrical horse power for the same load is easily
-calculated from the formula</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">amperes × volts</td>
-      <td class="tdl">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">output in electrical horse power =&nbsp;</td>
-      <td class="tdc">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</td>
-      <td class="tdl">&emsp;&emsp;&emsp;(2)</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">746</td>
-      <td class="tdl">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<p>After obtaining value for (1) and (2) the commercial efficiency for
-the load taken is obtained from the formula</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">output</td>
-      <td class="tdl">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">commercial efficiency =&nbsp;</td>
-      <td class="tdc">&mdash;&mdash;&mdash;&mdash;</td>
-      <td class="tdl">&emsp;&emsp;&emsp;(3)</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdc">input</td>
-      <td class="tdl">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<p>Having obtained the commercial efficiency, the difference between the
-ideal 100 per cent. and the efficiency found will be due to certain
-losses in the generator. These losses may be classified as</p>
-
-<p class="no-indent">
-&emsp;&emsp;&emsp;1. Mechanical.<br />
-&emsp;&emsp;&emsp;2. Electrical.
-<span class="pagenum"><a name="Page_2111" id="Page_2111">2111</a></span></p>
-
-<div class="blockquot space-below1">
-<p>The mechanical losses are the friction of the bearings and brushes,
-and air friction. The electrical losses consist of the eddy current
-loss, hysteresis loss, armature resistance loss, and field resistance
-loss.</p>
-
-<p>In testing for these losses, the generator to be tested should be
-belted to a calibrated motor which latter machine should preferably
-be of the constant pressure, shunt wound type.</p>
-
-<p>The friction of the bearings and belt of the generator are determined
-together by raising the brushes off its commutator and running it at
-the rated speed by means of the calibrated motor.</p></div>
-
-<div class="figcenter">
-  <a name="fig2911"></a>
-  <img src="images/i-0355.jpg" alt="_" width="600" height="779" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,911.&mdash;Characteristic curve of shunt
-dynamo. Suppose in making the test, the deflections on the meters
-for the first readings be 63 volts and 0 amperes, the plotting of
-these values will give the first point on the curve. Similarly, the
-second readings with main circuit closed and maximum resistance in
-the water rheostat may be assumed to be 62.5 volts and 7.5 amperes,
-which plotted gives the second point B. A still further lowering of
-the plate will permit a stronger current in the main circuit, and
-the value of this together with its corresponding voltage will give
-a third point for the curve. Neither for this reading, however, nor
-for the following readings of the test should the field rheostat be
-altered. When six or eight points ranging from zero to a maximum
-current have been obtained and plotted, a curved line should be drawn
-through them such as shown through ABCDEFG0, the <i>characteristic
-curve</i> of the dynamo. While the curve may be sketched in free hand,
-it should preferably be drawn by the aid of French curves. In case
-the French curve cannot be exactly made to coincide with all the
-points as for instance C and D, it should be run in between giving an
-average result, and smoothing out irregularities, or small errors due
-to the "personal equation." The meter of course must be correct or
-calibrated and the readings corrected by the calibration coefficient.</p></div>
-
-<p class="blockquot space-below1">
-The amount of power as ascertained from the calibration curve of
-the motor for the voltage and current used therein when driving the
-generator as just explained, is a measure of these two losses. The
-<span class="pagenum"><a name="Page_2112" id="Page_2112">2112</a></span>
-power thus used is practically constant at all loads and is about 2
-per cent. of that necessary to drive the generator at full load.</p>
-
-<div class="figcenter">
-  <a name="fig2912"></a>
-  <img src="images/i280.jpg" alt="_" width="600" height="398" />
-  <p class="f90_left space-below1">
-<span class="smcap">Fig.</span> 2,912.&mdash;Characteristic curves
-for a compound dynamo. If the machine be over compounded, the
-characteristic curve has the form of the curve A B, which curve
-was obtained from a machine over-compounded from 118 to 123 volts,
-and designed to give 203 amperes at full load. The preliminary
-arrangements for testing a compound dynamo are similar to those
-for a shunt generator, and if the shunt across the series field
-winding be already made up and in position, the readings are taken
-precisely in the same manner. It is generally considered sufficient
-if observations be recorded at zero, ¼, ½, ¾ and full load. If it be
-desired to ascertain the effect which residual magnetism has upon
-the field magnets the current is decreased after the full load point
-is reached without opening the circuit, and readings are taken in
-succession at ¾, ½, ¼ and zero load giving in this case the curve
-B C D E S. It is thus seen that residual magnetism exerts no small
-effect upon the voltage obtained at the different loads, for had
-there been no residual magnetism in the field magnets the curve B C
-D E S would have coincided with the curve A B. The curve A B, and
-the straight line A X drawn through the points A and B, are almost
-identical, and as A X represents the theoretical characteristic curve
-for the machine, it is seen that compounding is practically perfect.
-In order to insure such accurate results being obtained, providing
-the machinery be correctly designed, requires considerable care in
-taking the readings; for example, each step or load on the ascending
-curve should not be exceeded before the corresponding deflection is
-taken, else the residual magnetism will cause the pressure reading
-to be higher than it actually should be, and the following pressure
-readings will also be affected in the same manner. In case the shunt
-to be employed across the series field has not been made up, it is
-advisable to perform a trial test before taking the readings for the
-curve as previously described. The trial test consists in taking
-two readings,&mdash;one at no load and the other at full load, the shunt
-being so adjusted as to length and section that the desired amount
-of compounding will be obtained in the latter reading with normal
-voltage at no load. If the first trial fail to produce the desired
-result by giving too low a voltage at full load, the length of the
-shunt across the series field should be increased, or its section
-should be reduced by employing a less number of strips in its makeup;
-again, if the voltage at full load be higher than that desired, there
-must be made a decrease in length or an increase of section in the
-shunt employed.</p></div>
-
-<p><span class="pagenum"><a name="Page_2113" id="Page_2113">2113</a></span></p>
-
-<div class="blockquot">
-<p>The friction of the brushes can very conveniently be determined next
-by lowering them on the commutator and giving them the proper tension.</p>
-
-<p>The increase in power resulting from the greater current that will
-now be taken by the motor to run the dynamo at its rated speed, will
-be a measure of this loss. In general, its value will be about .5 per
-cent. of the total power required to drive the dynamo at full load,
-and this also will remain constant at all loads.</p>
-
-<p>The friction of the air upon the moving armature of the dynamo cannot
-be determined experimentally, but theoretically this loss is small
-and may be estimated as .5 per cent.; it is also constant at all
-loads.</p>
-
-<p>The core loss may be determined experimentally by exciting the
-field magnets of the dynamo with the normal full load field current
-through the magnet coils, and noting the increase of power required
-by the motor to maintain the rated speed of the dynamo thus excited
-under no load, over that necessary under the same conditions with no
-field excitation. This increase of power will be the value of the
-core loss. The core loss is approximately 3 per cent. of the power
-required to operate the dynamo at full load, and it is constant at
-varying loads. If it be desired to divide the core loss into its
-component parts, it is necessary also to run the dynamo under the
-same conditions as before with field excitation but at half its rated
-speed. If, then,</p></div>
-
-<p class="no-indent">
-&emsp;&emsp;H = the power lost in hysteresis at rated speed,<br />
-&emsp;&emsp;E = the power lost in eddy currents at rated speed,<br />
-&emsp;&emsp;T = the power lost in hysteresis and eddy currents at rated speed,<br />
-&emsp;&emsp;S = the power lost in hysteresis and eddy currents at half speed.</p>
-
-<p class="no-indent">there may be formed the two following equations:</p>
-
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;H &nbsp;&emsp;E</td>
-   </tr><tr>
-      <td class="tdr">T &nbsp;= &nbsp;H + E, &nbsp;and S =&nbsp;</td>
-      <td class="tdl">&mdash; + &mdash;,</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;2&nbsp; &nbsp;&emsp;2</td>
-   </tr>
- </tbody>
-</table>
-
-<div class="blockquot">
-<p class="no-indent">from which the elimination of H will give &nbsp; <b>E = 2T - 4S</b>.</p>
-
-<p>The value of the eddy current loss thus found will be about 1½ per
-cent., and constant at all loads.</p>
-
-<p>Having previously ascertained the power lost in both eddy currents
-and hysteresis, and knowing now the power lost in eddy currents
-alone, it is easy to find that lost in hysteresis by simply
-subtracting the latter known value from the former. The value of the
-hysteresis loss is therefore approximately 1½ per cent., and it is
-constant at different loads.</p>
-
-<p>There yet remains to be determined the armature resistance loss and
-the field resistance loss. As for the calibrated motor, this may be
-disconnected from the dynamo, as it need not be used further in the test.</p>
-
-<p>The armature resistance is the resistance of the armature winding of
-the dynamo, between the commutator bars upon which press the positive
-and negative brushes. Assume that the value of the armature
-<span class="pagenum"><a name="Page_2114" id="Page_2114">2114</a></span>
-resistance be known, call this value R ohms, together with that of
-the full load armature current, which is also known and which call
-I amperes, this is sufficient data for calculating the armature
-resistance loss at full load. It is evident that to force the full
-load current I through the armature resistance R will require a
-pressure of R volts, and that the watts lost in doing so will be
-the voltage multiplied by the current. The armature resistance is
-consequently</p></div>
-
-<p class="center"><b>I&nbsp;R × I = I<sup>2</sup>R</b> watts</p>
-
-<p>or, expressed in horse power it is</p>
-
-<p class="center"><b>I<sup>2</sup>R ÷ 746</b></p>
-
-<div class="blockquot">
-<p>At full load it is usually about 2 per cent. of the total power
-required to drive the generator fully loaded. The armature resistance
-loss varies in proportion to the load, in fact, as the last
-expression shows, it increases as the square of the armature current.</p>
-
-<p>The field resistance loss is calculated in the same manner as just
-explained for the armature resistance loss, it being equal in horse
-power to the square of the full load field current multiplied by the
-resistance of the field winding and divided by 746. In a shunt dynamo
-it is practically constant at 2 per cent. of the total power at full
-load, but in a series or in a compound generator it will vary in
-proportion to the load.</p></div>
-
-<hr class="chap" />
-<p class="f200">HAWKINS PRACTICAL LIBRARY<br />OF ELECTRICITY</p>
-<p class="center"><b>IN HANDY POCKET FORM&nbsp;&emsp;&nbsp;&emsp;&nbsp;&emsp;&nbsp;PRICE $1 EACH</b></p>
-
-<p class="no-indent"><i>They are not only the best, but the cheapest
-work published on Electricity. Each number being complete in itself.
-Separate numbers sent postpaid to any address on receipt of price.
-They are guaranteed in every way or your money will be returned.
-Complete catalog of series will be mailed free on request.</i></p>
-
-<p><b>ELECTRICAL GUIDE, NO. 1</b></p>
-<p class="blockquot no-indent">
-Containing the principles of Elementary Electricity, Magnetism,
-Induction, Experiments, Dynamos, Electric Machinery.</p>
-
-<p><b>ELECTRICAL GUIDE, NO. 2</b></p>
-<p class="blockquot no-indent">
-The construction of Dynamos, Motors, Armatures, Armature
-Windings, Installing of Dynamos.</p>
-
-<p><b>ELECTRICAL GUIDE, NO. 3</b></p>
-<p class="blockquot no-indent">
-Electrical Instruments, Testing, Practical Management of Dynamos
-and Motors.</p>
-
-<p><b>ELECTRICAL GUIDE, NO. 4</b></p>
-<p class="blockquot no-indent">
-Distribution Systems, Wiring, Wiring Diagrams, Sign Flashers,
-Storage Batteries.</p>
-
-<p><b>ELECTRICAL GUIDE, NO. 5</b></p>
-<p class="blockquot no-indent">
-Principles of Alternating Currents and Alternators.</p>
-
-<p><b>ELECTRICAL GUIDE, NO. 6</b></p>
-<p class="blockquot no-indent">
-Alternating Current Motors, Transformers, Converters, Rectifiers.</p>
-
-<p><b>ELECTRICAL GUIDE, NO. 7</b></p>
-<p class="blockquot no-indent">
-Alternating Current Systems, Circuit Breakers, Measuring
-Instruments.</p>
-
-<p><b>ELECTRICAL GUIDE, NO. 8</b></p>
-<p class="blockquot no-indent">
-Alternating Current Switch Boards, Wiring, Power Stations,
-Installation and Operation.</p>
-
-<p><b>ELECTRICAL GUIDE, NO. 9</b></p>
-<p class="blockquot no-indent">
-Telephone, Telegraph, Wireless, Bells, Lighting, Railways.</p>
-
-<p><b>ELECTRICAL GUIDE, NO. 10</b></p>
-<p class="blockquot no-indent">
-Modern Practical Applications of Electricity and Ready Reference
-Index of the 10 Numbers.</p>
-
-<p class="space-above2"><big><b>Theo. Audel &amp; Co., Publishers</b>.</big></p>
-
-<p class="author space-below1"><b>72 FIFTH AVENUE,</b><br />
-<b>NEW YORK.&nbsp;&nbsp;</b></p>
-<hr class="chap" />
-<div class="transnote bbox space-above2">
-<p class="f110 space-above1">Transcriber Notes:</p>
-<hr class="r5" />
-<p>The illustrations have been moved so that they do not break up
-   paragraphs and so that they are near to the text they illustrate.</p>
-<p>
-  Misprints in the table SAVING DUE TO HEATING THE FEED WATER, Pg. 1936
-    have been corrected, they are:</p>
-<table border="0" cellspacing="2" summary="_" cellpadding="0">
-  <tbody><tr>
-      <td class="tdc">Init. Temp.&nbsp;</td>
-      <td class="tdc">&nbsp;Pressure&nbsp;</td>
-      <td class="tdc">&nbsp;Old Value&nbsp;</td>
-      <td class="tdc">&nbsp;New Value</td>
-   </tr><tr>
-      <td class="tdc">130</td> <td class="tdc">&nbsp;40</td>
-      <td class="tdc">.0954</td> <td class="tdc">.0934</td>
-   </tr><tr>
-      <td class="tdc">200</td> <td class="tdc">&nbsp;40</td>
-      <td class="tdc">.0900</td> <td class="tdc">.0999</td>
-   </tr><tr>
-      <td class="tdc">210</td> <td class="tdc">&nbsp;40</td>
-      <td class="tdc">.1000</td> <td class="tdc">.1010</td>
-   </tr><tr>
-      <td class="tdc">230</td> <td class="tdc">100</td>
-      <td class="tdc">.0017</td> <td class="tdc">.1012</td>
-   </tr>
- </tbody>
-</table>
-<p>In the original text, there are two Fig. 2769's and two Fig. 2770's.
-   The second of each has had an "A" suffix added, i.e. 2769A and 2770A.</p>
-<p> On line 10984 the word "impedence" was corrected to "impedance".</p>
-<p> Inconsistent spelling and hyphenation has been left as in the original.</p>
-</div>
-
-
-
-
-
-
-
-<pre>
-
-
-
-
-
-End of the Project Gutenberg EBook of Hawkins Electrical Guide Vol. 8 (of 10), by 
-Nehemiah Hawkins
-
-*** END OF THIS PROJECT GUTENBERG EBOOK HAWKINS ELECTRICAL GUIDE, VOL 8 ***
-
-***** This file should be named 50068-h.htm or 50068-h.zip *****
-This and all associated files of various formats will be found in:
-        http://www.gutenberg.org/5/0/0/6/50068/
-
-Produced by Juliet Sutherland, Paul Marshall and the Online
-Distributed Proofreading Team at http://www.pgdp.net
-
-Updated editions will replace the previous one--the old editions will
-be renamed.
-
-Creating the works from print editions not protected by U.S. copyright
-law means that no one owns a United States copyright in these works,
-so the Foundation (and you!) can copy and distribute it in the United
-States without permission and without paying copyright
-royalties. Special rules, set forth in the General Terms of Use part
-of this license, apply to copying and distributing Project
-Gutenberg-tm electronic works to protect the PROJECT GUTENBERG-tm
-concept and trademark. Project Gutenberg is a registered trademark,
-and may not be used if you charge for the eBooks, unless you receive
-specific permission. If you do not charge anything for copies of this
-eBook, complying with the rules is very easy. You may use this eBook
-for nearly any purpose such as creation of derivative works, reports,
-performances and research. They may be modified and printed and given
-away--you may do practically ANYTHING in the United States with eBooks
-not protected by U.S. copyright law. Redistribution is subject to the
-trademark license, especially commercial redistribution.
-
-START: FULL LICENSE
-
-THE FULL PROJECT GUTENBERG LICENSE
-PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK
-
-To protect the Project Gutenberg-tm mission of promoting the free
-distribution of electronic works, by using or distributing this work
-(or any other work associated in any way with the phrase "Project
-Gutenberg"), you agree to comply with all the terms of the Full
-Project Gutenberg-tm License available with this file or online at
-www.gutenberg.org/license.
-
-Section 1. General Terms of Use and Redistributing Project
-Gutenberg-tm electronic works
-
-1.A. By reading or using any part of this Project Gutenberg-tm
-electronic work, you indicate that you have read, understand, agree to
-and accept all the terms of this license and intellectual property
-(trademark/copyright) agreement. If you do not agree to abide by all
-the terms of this agreement, you must cease using and return or
-destroy all copies of Project Gutenberg-tm electronic works in your
-possession. If you paid a fee for obtaining a copy of or access to a
-Project Gutenberg-tm electronic work and you do not agree to be bound
-by the terms of this agreement, you may obtain a refund from the
-person or entity to whom you paid the fee as set forth in paragraph
-1.E.8.
-
-1.B. "Project Gutenberg" is a registered trademark. It may only be
-used on or associated in any way with an electronic work by people who
-agree to be bound by the terms of this agreement. There are a few
-things that you can do with most Project Gutenberg-tm electronic works
-even without complying with the full terms of this agreement. See
-paragraph 1.C below. There are a lot of things you can do with Project
-Gutenberg-tm electronic works if you follow the terms of this
-agreement and help preserve free future access to Project Gutenberg-tm
-electronic works. See paragraph 1.E below.
-
-1.C. The Project Gutenberg Literary Archive Foundation ("the
-Foundation" or PGLAF), owns a compilation copyright in the collection
-of Project Gutenberg-tm electronic works. Nearly all the individual
-works in the collection are in the public domain in the United
-States. If an individual work is unprotected by copyright law in the
-United States and you are located in the United States, we do not
-claim a right to prevent you from copying, distributing, performing,
-displaying or creating derivative works based on the work as long as
-all references to Project Gutenberg are removed. Of course, we hope
-that you will support the Project Gutenberg-tm mission of promoting
-free access to electronic works by freely sharing Project Gutenberg-tm
-works in compliance with the terms of this agreement for keeping the
-Project Gutenberg-tm name associated with the work. You can easily
-comply with the terms of this agreement by keeping this work in the
-same format with its attached full Project Gutenberg-tm License when
-you share it without charge with others.
-
-1.D. The copyright laws of the place where you are located also govern
-what you can do with this work. Copyright laws in most countries are
-in a constant state of change. If you are outside the United States,
-check the laws of your country in addition to the terms of this
-agreement before downloading, copying, displaying, performing,
-distributing or creating derivative works based on this work or any
-other Project Gutenberg-tm work. The Foundation makes no
-representations concerning the copyright status of any work in any
-country outside the United States.
-
-1.E. Unless you have removed all references to Project Gutenberg:
-
-1.E.1. The following sentence, with active links to, or other
-immediate access to, the full Project Gutenberg-tm License must appear
-prominently whenever any copy of a Project Gutenberg-tm work (any work
-on which the phrase "Project Gutenberg" appears, or with which the
-phrase "Project Gutenberg" is associated) is accessed, displayed,
-performed, viewed, copied or distributed:
-
-  This eBook is for the use of anyone anywhere in the United States and
-  most other parts of the world at no cost and with almost no
-  restrictions whatsoever. You may copy it, give it away or re-use it
-  under the terms of the Project Gutenberg License included with this
-  eBook or online at www.gutenberg.org. If you are not located in the
-  United States, you'll have to check the laws of the country where you
-  are located before using this ebook.
-
-1.E.2. If an individual Project Gutenberg-tm electronic work is
-derived from texts not protected by U.S. copyright law (does not
-contain a notice indicating that it is posted with permission of the
-copyright holder), the work can be copied and distributed to anyone in
-the United States without paying any fees or charges. If you are
-redistributing or providing access to a work with the phrase "Project
-Gutenberg" associated with or appearing on the work, you must comply
-either with the requirements of paragraphs 1.E.1 through 1.E.7 or
-obtain permission for the use of the work and the Project Gutenberg-tm
-trademark as set forth in paragraphs 1.E.8 or 1.E.9.
-
-1.E.3. If an individual Project Gutenberg-tm electronic work is posted
-with the permission of the copyright holder, your use and distribution
-must comply with both paragraphs 1.E.1 through 1.E.7 and any
-additional terms imposed by the copyright holder. Additional terms
-will be linked to the Project Gutenberg-tm License for all works
-posted with the permission of the copyright holder found at the
-beginning of this work.
-
-1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm
-License terms from this work, or any files containing a part of this
-work or any other work associated with Project Gutenberg-tm.
-
-1.E.5. Do not copy, display, perform, distribute or redistribute this
-electronic work, or any part of this electronic work, without
-prominently displaying the sentence set forth in paragraph 1.E.1 with
-active links or immediate access to the full terms of the Project
-Gutenberg-tm License.
-
-1.E.6. You may convert to and distribute this work in any binary,
-compressed, marked up, nonproprietary or proprietary form, including
-any word processing or hypertext form. However, if you provide access
-to or distribute copies of a Project Gutenberg-tm work in a format
-other than "Plain Vanilla ASCII" or other format used in the official
-version posted on the official Project Gutenberg-tm web site
-(www.gutenberg.org), you must, at no additional cost, fee or expense
-to the user, provide a copy, a means of exporting a copy, or a means
-of obtaining a copy upon request, of the work in its original "Plain
-Vanilla ASCII" or other form. Any alternate format must include the
-full Project Gutenberg-tm License as specified in paragraph 1.E.1.
-
-1.E.7. Do not charge a fee for access to, viewing, displaying,
-performing, copying or distributing any Project Gutenberg-tm works
-unless you comply with paragraph 1.E.8 or 1.E.9.
-
-1.E.8. You may charge a reasonable fee for copies of or providing
-access to or distributing Project Gutenberg-tm electronic works
-provided that
-
-* You pay a royalty fee of 20% of the gross profits you derive from
-  the use of Project Gutenberg-tm works calculated using the method
-  you already use to calculate your applicable taxes. The fee is owed
-  to the owner of the Project Gutenberg-tm trademark, but he has
-  agreed to donate royalties under this paragraph to the Project
-  Gutenberg Literary Archive Foundation. Royalty payments must be paid
-  within 60 days following each date on which you prepare (or are
-  legally required to prepare) your periodic tax returns. Royalty
-  payments should be clearly marked as such and sent to the Project
-  Gutenberg Literary Archive Foundation at the address specified in
-  Section 4, "Information about donations to the Project Gutenberg
-  Literary Archive Foundation."
-
-* You provide a full refund of any money paid by a user who notifies
-  you in writing (or by e-mail) within 30 days of receipt that s/he
-  does not agree to the terms of the full Project Gutenberg-tm
-  License. You must require such a user to return or destroy all
-  copies of the works possessed in a physical medium and discontinue
-  all use of and all access to other copies of Project Gutenberg-tm
-  works.
-
-* You provide, in accordance with paragraph 1.F.3, a full refund of
-  any money paid for a work or a replacement copy, if a defect in the
-  electronic work is discovered and reported to you within 90 days of
-  receipt of the work.
-
-* You comply with all other terms of this agreement for free
-  distribution of Project Gutenberg-tm works.
-
-1.E.9. If you wish to charge a fee or distribute a Project
-Gutenberg-tm electronic work or group of works on different terms than
-are set forth in this agreement, you must obtain permission in writing
-from both the Project Gutenberg Literary Archive Foundation and The
-Project Gutenberg Trademark LLC, the owner of the Project Gutenberg-tm
-trademark. Contact the Foundation as set forth in Section 3 below.
-
-1.F.
-
-1.F.1. Project Gutenberg volunteers and employees expend considerable
-effort to identify, do copyright research on, transcribe and proofread
-works not protected by U.S. copyright law in creating the Project
-Gutenberg-tm collection. Despite these efforts, Project Gutenberg-tm
-electronic works, and the medium on which they may be stored, may
-contain "Defects," such as, but not limited to, incomplete, inaccurate
-or corrupt data, transcription errors, a copyright or other
-intellectual property infringement, a defective or damaged disk or
-other medium, a computer virus, or computer codes that damage or
-cannot be read by your equipment.
-
-1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right
-of Replacement or Refund" described in paragraph 1.F.3, the Project
-Gutenberg Literary Archive Foundation, the owner of the Project
-Gutenberg-tm trademark, and any other party distributing a Project
-Gutenberg-tm electronic work under this agreement, disclaim all
-liability to you for damages, costs and expenses, including legal
-fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT
-LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE
-PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE
-TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE
-LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR
-INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH
-DAMAGE.
-
-1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a
-defect in this electronic work within 90 days of receiving it, you can
-receive a refund of the money (if any) you paid for it by sending a
-written explanation to the person you received the work from. If you
-received the work on a physical medium, you must return the medium
-with your written explanation. The person or entity that provided you
-with the defective work may elect to provide a replacement copy in
-lieu of a refund. If you received the work electronically, the person
-or entity providing it to you may choose to give you a second
-opportunity to receive the work electronically in lieu of a refund. If
-the second copy is also defective, you may demand a refund in writing
-without further opportunities to fix the problem.
-
-1.F.4. Except for the limited right of replacement or refund set forth
-in paragraph 1.F.3, this work is provided to you 'AS-IS', WITH NO
-OTHER WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
-LIMITED TO WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PURPOSE.
-
-1.F.5. Some states do not allow disclaimers of certain implied
-warranties or the exclusion or limitation of certain types of
-damages. If any disclaimer or limitation set forth in this agreement
-violates the law of the state applicable to this agreement, the
-agreement shall be interpreted to make the maximum disclaimer or
-limitation permitted by the applicable state law. The invalidity or
-unenforceability of any provision of this agreement shall not void the
-remaining provisions.
-
-1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the
-trademark owner, any agent or employee of the Foundation, anyone
-providing copies of Project Gutenberg-tm electronic works in
-accordance with this agreement, and any volunteers associated with the
-production, promotion and distribution of Project Gutenberg-tm
-electronic works, harmless from all liability, costs and expenses,
-including legal fees, that arise directly or indirectly from any of
-the following which you do or cause to occur: (a) distribution of this
-or any Project Gutenberg-tm work, (b) alteration, modification, or
-additions or deletions to any Project Gutenberg-tm work, and (c) any
-Defect you cause.
-
-Section 2. Information about the Mission of Project Gutenberg-tm
-
-Project Gutenberg-tm is synonymous with the free distribution of
-electronic works in formats readable by the widest variety of
-computers including obsolete, old, middle-aged and new computers. It
-exists because of the efforts of hundreds of volunteers and donations
-from people in all walks of life.
-
-Volunteers and financial support to provide volunteers with the
-assistance they need are critical to reaching Project Gutenberg-tm's
-goals and ensuring that the Project Gutenberg-tm collection will
-remain freely available for generations to come. In 2001, the Project
-Gutenberg Literary Archive Foundation was created to provide a secure
-and permanent future for Project Gutenberg-tm and future
-generations. To learn more about the Project Gutenberg Literary
-Archive Foundation and how your efforts and donations can help, see
-Sections 3 and 4 and the Foundation information page at
-www.gutenberg.org
-
-
-
-Section 3. Information about the Project Gutenberg Literary Archive Foundation
-
-The Project Gutenberg Literary Archive Foundation is a non profit
-501(c)(3) educational corporation organized under the laws of the
-state of Mississippi and granted tax exempt status by the Internal
-Revenue Service. The Foundation's EIN or federal tax identification
-number is 64-6221541. Contributions to the Project Gutenberg Literary
-Archive Foundation are tax deductible to the full extent permitted by
-U.S. federal laws and your state's laws.
-
-The Foundation's principal office is in Fairbanks, Alaska, with the
-mailing address: PO Box 750175, Fairbanks, AK 99775, but its
-volunteers and employees are scattered throughout numerous
-locations. Its business office is located at 809 North 1500 West, Salt
-Lake City, UT 84116, (801) 596-1887. Email contact links and up to
-date contact information can be found at the Foundation's web site and
-official page at www.gutenberg.org/contact
-
-For additional contact information:
-
-    Dr. Gregory B. Newby
-    Chief Executive and Director
-    gbnewby@pglaf.org
-
-Section 4. Information about Donations to the Project Gutenberg
-Literary Archive Foundation
-
-Project Gutenberg-tm depends upon and cannot survive without wide
-spread public support and donations to carry out its mission of
-increasing the number of public domain and licensed works that can be
-freely distributed in machine readable form accessible by the widest
-array of equipment including outdated equipment. Many small donations
-($1 to $5,000) are particularly important to maintaining tax exempt
-status with the IRS.
-
-The Foundation is committed to complying with the laws regulating
-charities and charitable donations in all 50 states of the United
-States. Compliance requirements are not uniform and it takes a
-considerable effort, much paperwork and many fees to meet and keep up
-with these requirements. We do not solicit donations in locations
-where we have not received written confirmation of compliance. To SEND
-DONATIONS or determine the status of compliance for any particular
-state visit www.gutenberg.org/donate
-
-While we cannot and do not solicit contributions from states where we
-have not met the solicitation requirements, we know of no prohibition
-against accepting unsolicited donations from donors in such states who
-approach us with offers to donate.
-
-International donations are gratefully accepted, but we cannot make
-any statements concerning tax treatment of donations received from
-outside the United States. U.S. laws alone swamp our small staff.
-
-Please check the Project Gutenberg Web pages for current donation
-methods and addresses. Donations are accepted in a number of other
-ways including checks, online payments and credit card donations. To
-donate, please visit: www.gutenberg.org/donate
-
-Section 5. General Information About Project Gutenberg-tm electronic works.
-
-Professor Michael S. Hart was the originator of the Project
-Gutenberg-tm concept of a library of electronic works that could be
-freely shared with anyone. For forty years, he produced and
-distributed Project Gutenberg-tm eBooks with only a loose network of
-volunteer support.
-
-Project Gutenberg-tm eBooks are often created from several printed
-editions, all of which are confirmed as not protected by copyright in
-the U.S. unless a copyright notice is included. Thus, we do not
-necessarily keep eBooks in compliance with any particular paper
-edition.
-
-Most people start at our Web site which has the main PG search
-facility: www.gutenberg.org
-
-This Web site includes information about Project Gutenberg-tm,
-including how to make donations to the Project Gutenberg Literary
-Archive Foundation, how to help produce our new eBooks, and how to
-subscribe to our email newsletter to hear about new eBooks.
-
-
-
-</pre>
-
-</body>
-</html>
diff --git a/old/50068-h/images/cover.jpg b/old/50068-h/images/cover.jpg
deleted file mode 100644
index 597bf22..0000000
--- a/old/50068-h/images/cover.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0284.jpg b/old/50068-h/images/i-0284.jpg
deleted file mode 100644
index 9944126..0000000
--- a/old/50068-h/images/i-0284.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0285.jpg b/old/50068-h/images/i-0285.jpg
deleted file mode 100644
index 59f2123..0000000
--- a/old/50068-h/images/i-0285.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0286.jpg b/old/50068-h/images/i-0286.jpg
deleted file mode 100644
index 9f7271b..0000000
--- a/old/50068-h/images/i-0286.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0287.jpg b/old/50068-h/images/i-0287.jpg
deleted file mode 100644
index 2697da6..0000000
--- a/old/50068-h/images/i-0287.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0288.jpg b/old/50068-h/images/i-0288.jpg
deleted file mode 100644
index f342612..0000000
--- a/old/50068-h/images/i-0288.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0289.jpg b/old/50068-h/images/i-0289.jpg
deleted file mode 100644
index 867a10a..0000000
--- a/old/50068-h/images/i-0289.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0290-1.jpg b/old/50068-h/images/i-0290-1.jpg
deleted file mode 100644
index d3b2550..0000000
--- a/old/50068-h/images/i-0290-1.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0290-2.jpg b/old/50068-h/images/i-0290-2.jpg
deleted file mode 100644
index 7fc243a..0000000
--- a/old/50068-h/images/i-0290-2.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0291.jpg b/old/50068-h/images/i-0291.jpg
deleted file mode 100644
index 875b8a6..0000000
--- a/old/50068-h/images/i-0291.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0292.jpg b/old/50068-h/images/i-0292.jpg
deleted file mode 100644
index 6fd037e..0000000
--- a/old/50068-h/images/i-0292.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0293.jpg b/old/50068-h/images/i-0293.jpg
deleted file mode 100644
index c05a0de..0000000
--- a/old/50068-h/images/i-0293.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0294.jpg b/old/50068-h/images/i-0294.jpg
deleted file mode 100644
index b358191..0000000
--- a/old/50068-h/images/i-0294.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0295-1.jpg b/old/50068-h/images/i-0295-1.jpg
deleted file mode 100644
index 38b362f..0000000
--- a/old/50068-h/images/i-0295-1.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0295-2.jpg b/old/50068-h/images/i-0295-2.jpg
deleted file mode 100644
index 07314ca..0000000
--- a/old/50068-h/images/i-0295-2.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0296.jpg b/old/50068-h/images/i-0296.jpg
deleted file mode 100644
index 32cc8ce..0000000
--- a/old/50068-h/images/i-0296.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0297.jpg b/old/50068-h/images/i-0297.jpg
deleted file mode 100644
index 2cd0154..0000000
--- a/old/50068-h/images/i-0297.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0298-1.jpg b/old/50068-h/images/i-0298-1.jpg
deleted file mode 100644
index 22d7bd9..0000000
--- a/old/50068-h/images/i-0298-1.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0298-2.jpg b/old/50068-h/images/i-0298-2.jpg
deleted file mode 100644
index 4d57d5c..0000000
--- a/old/50068-h/images/i-0298-2.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0299.jpg b/old/50068-h/images/i-0299.jpg
deleted file mode 100644
index 102bfed..0000000
--- a/old/50068-h/images/i-0299.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0300-1.jpg b/old/50068-h/images/i-0300-1.jpg
deleted file mode 100644
index 3c58703..0000000
--- a/old/50068-h/images/i-0300-1.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0300-2.jpg b/old/50068-h/images/i-0300-2.jpg
deleted file mode 100644
index 11181dd..0000000
--- a/old/50068-h/images/i-0300-2.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0300-3.jpg b/old/50068-h/images/i-0300-3.jpg
deleted file mode 100644
index 3c42e03..0000000
--- a/old/50068-h/images/i-0300-3.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0301-1.jpg b/old/50068-h/images/i-0301-1.jpg
deleted file mode 100644
index f4f5f21..0000000
--- a/old/50068-h/images/i-0301-1.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0301-2.jpg b/old/50068-h/images/i-0301-2.jpg
deleted file mode 100644
index 94db21c..0000000
--- a/old/50068-h/images/i-0301-2.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0301-3.jpg b/old/50068-h/images/i-0301-3.jpg
deleted file mode 100644
index f19e63d..0000000
--- a/old/50068-h/images/i-0301-3.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0302.jpg b/old/50068-h/images/i-0302.jpg
deleted file mode 100644
index 8f0069f..0000000
--- a/old/50068-h/images/i-0302.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0303.jpg b/old/50068-h/images/i-0303.jpg
deleted file mode 100644
index 44ebc73..0000000
--- a/old/50068-h/images/i-0303.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0304.jpg b/old/50068-h/images/i-0304.jpg
deleted file mode 100644
index ecdf177..0000000
--- a/old/50068-h/images/i-0304.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0305.jpg b/old/50068-h/images/i-0305.jpg
deleted file mode 100644
index 5534974..0000000
--- a/old/50068-h/images/i-0305.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0306.jpg b/old/50068-h/images/i-0306.jpg
deleted file mode 100644
index 272a705..0000000
--- a/old/50068-h/images/i-0306.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0307.jpg b/old/50068-h/images/i-0307.jpg
deleted file mode 100644
index dda87c9..0000000
--- a/old/50068-h/images/i-0307.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0308.jpg b/old/50068-h/images/i-0308.jpg
deleted file mode 100644
index e4fc20c..0000000
--- a/old/50068-h/images/i-0308.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0309.jpg b/old/50068-h/images/i-0309.jpg
deleted file mode 100644
index 67bc161..0000000
--- a/old/50068-h/images/i-0309.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0310.jpg b/old/50068-h/images/i-0310.jpg
deleted file mode 100644
index d712333..0000000
--- a/old/50068-h/images/i-0310.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0311.jpg b/old/50068-h/images/i-0311.jpg
deleted file mode 100644
index be4d76c..0000000
--- a/old/50068-h/images/i-0311.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0312.jpg b/old/50068-h/images/i-0312.jpg
deleted file mode 100644
index 19a5189..0000000
--- a/old/50068-h/images/i-0312.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0313.jpg b/old/50068-h/images/i-0313.jpg
deleted file mode 100644
index 76a9ce4..0000000
--- a/old/50068-h/images/i-0313.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0314-1.jpg b/old/50068-h/images/i-0314-1.jpg
deleted file mode 100644
index a7bed8b..0000000
--- a/old/50068-h/images/i-0314-1.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0314-2.jpg b/old/50068-h/images/i-0314-2.jpg
deleted file mode 100644
index bbca191..0000000
--- a/old/50068-h/images/i-0314-2.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0315.jpg b/old/50068-h/images/i-0315.jpg
deleted file mode 100644
index 44a1800..0000000
--- a/old/50068-h/images/i-0315.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0316.jpg b/old/50068-h/images/i-0316.jpg
deleted file mode 100644
index 2272e31..0000000
--- a/old/50068-h/images/i-0316.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0317.jpg b/old/50068-h/images/i-0317.jpg
deleted file mode 100644
index 50aac6b..0000000
--- a/old/50068-h/images/i-0317.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0318-1.jpg b/old/50068-h/images/i-0318-1.jpg
deleted file mode 100644
index 1e68a0b..0000000
--- a/old/50068-h/images/i-0318-1.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0318-2.jpg b/old/50068-h/images/i-0318-2.jpg
deleted file mode 100644
index 5648372..0000000
--- a/old/50068-h/images/i-0318-2.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0319-1.jpg b/old/50068-h/images/i-0319-1.jpg
deleted file mode 100644
index 86c6c9f..0000000
--- a/old/50068-h/images/i-0319-1.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0319-2.jpg b/old/50068-h/images/i-0319-2.jpg
deleted file mode 100644
index 888d77b..0000000
--- a/old/50068-h/images/i-0319-2.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0320-1.jpg b/old/50068-h/images/i-0320-1.jpg
deleted file mode 100644
index 3bc1ef2..0000000
--- a/old/50068-h/images/i-0320-1.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0320-2.jpg b/old/50068-h/images/i-0320-2.jpg
deleted file mode 100644
index 3dbdd39..0000000
--- a/old/50068-h/images/i-0320-2.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0321-1.jpg b/old/50068-h/images/i-0321-1.jpg
deleted file mode 100644
index 3e9213d..0000000
--- a/old/50068-h/images/i-0321-1.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0321-2.jpg b/old/50068-h/images/i-0321-2.jpg
deleted file mode 100644
index 9716a8f..0000000
--- a/old/50068-h/images/i-0321-2.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0321-3.jpg b/old/50068-h/images/i-0321-3.jpg
deleted file mode 100644
index 1771d8f..0000000
--- a/old/50068-h/images/i-0321-3.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0321-4.jpg b/old/50068-h/images/i-0321-4.jpg
deleted file mode 100644
index 8e48398..0000000
--- a/old/50068-h/images/i-0321-4.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0322.jpg b/old/50068-h/images/i-0322.jpg
deleted file mode 100644
index b332247..0000000
--- a/old/50068-h/images/i-0322.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0323.jpg b/old/50068-h/images/i-0323.jpg
deleted file mode 100644
index fee8cfd..0000000
--- a/old/50068-h/images/i-0323.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0324.jpg b/old/50068-h/images/i-0324.jpg
deleted file mode 100644
index 2bbd264..0000000
--- a/old/50068-h/images/i-0324.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0325.jpg b/old/50068-h/images/i-0325.jpg
deleted file mode 100644
index 7c55352..0000000
--- a/old/50068-h/images/i-0325.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0326.jpg b/old/50068-h/images/i-0326.jpg
deleted file mode 100644
index 049887d..0000000
--- a/old/50068-h/images/i-0326.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0327.jpg b/old/50068-h/images/i-0327.jpg
deleted file mode 100644
index 27a0d83..0000000
--- a/old/50068-h/images/i-0327.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0328.jpg b/old/50068-h/images/i-0328.jpg
deleted file mode 100644
index 35d9787..0000000
--- a/old/50068-h/images/i-0328.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0329.jpg b/old/50068-h/images/i-0329.jpg
deleted file mode 100644
index ce41096..0000000
--- a/old/50068-h/images/i-0329.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0331.jpg b/old/50068-h/images/i-0331.jpg
deleted file mode 100644
index 63e291e..0000000
--- a/old/50068-h/images/i-0331.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0332.jpg b/old/50068-h/images/i-0332.jpg
deleted file mode 100644
index 1e3d896..0000000
--- a/old/50068-h/images/i-0332.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0333.jpg b/old/50068-h/images/i-0333.jpg
deleted file mode 100644
index d7eb2ff..0000000
--- a/old/50068-h/images/i-0333.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0334.jpg b/old/50068-h/images/i-0334.jpg
deleted file mode 100644
index dd5d18b..0000000
--- a/old/50068-h/images/i-0334.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0335.jpg b/old/50068-h/images/i-0335.jpg
deleted file mode 100644
index 3e45ad0..0000000
--- a/old/50068-h/images/i-0335.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0336.jpg b/old/50068-h/images/i-0336.jpg
deleted file mode 100644
index 7222300..0000000
--- a/old/50068-h/images/i-0336.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0337.jpg b/old/50068-h/images/i-0337.jpg
deleted file mode 100644
index 8514099..0000000
--- a/old/50068-h/images/i-0337.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0338.jpg b/old/50068-h/images/i-0338.jpg
deleted file mode 100644
index 861fa3f..0000000
--- a/old/50068-h/images/i-0338.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0339.jpg b/old/50068-h/images/i-0339.jpg
deleted file mode 100644
index 3b27730..0000000
--- a/old/50068-h/images/i-0339.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0340.jpg b/old/50068-h/images/i-0340.jpg
deleted file mode 100644
index 8ecedc0..0000000
--- a/old/50068-h/images/i-0340.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0341.jpg b/old/50068-h/images/i-0341.jpg
deleted file mode 100644
index ebfe871..0000000
--- a/old/50068-h/images/i-0341.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0342.jpg b/old/50068-h/images/i-0342.jpg
deleted file mode 100644
index aad1812..0000000
--- a/old/50068-h/images/i-0342.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0343.jpg b/old/50068-h/images/i-0343.jpg
deleted file mode 100644
index be9877c..0000000
--- a/old/50068-h/images/i-0343.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0344-1.jpg b/old/50068-h/images/i-0344-1.jpg
deleted file mode 100644
index 8181417..0000000
--- a/old/50068-h/images/i-0344-1.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0344-2.jpg b/old/50068-h/images/i-0344-2.jpg
deleted file mode 100644
index 77530f4..0000000
--- a/old/50068-h/images/i-0344-2.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0345.jpg b/old/50068-h/images/i-0345.jpg
deleted file mode 100644
index 96d0377..0000000
--- a/old/50068-h/images/i-0345.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0346.jpg b/old/50068-h/images/i-0346.jpg
deleted file mode 100644
index 175965b..0000000
--- a/old/50068-h/images/i-0346.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0347.jpg b/old/50068-h/images/i-0347.jpg
deleted file mode 100644
index e63c749..0000000
--- a/old/50068-h/images/i-0347.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0348-1.jpg b/old/50068-h/images/i-0348-1.jpg
deleted file mode 100644
index cbdea9b..0000000
--- a/old/50068-h/images/i-0348-1.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0348-2.jpg b/old/50068-h/images/i-0348-2.jpg
deleted file mode 100644
index 935f695..0000000
--- a/old/50068-h/images/i-0348-2.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0349.jpg b/old/50068-h/images/i-0349.jpg
deleted file mode 100644
index d269ed6..0000000
--- a/old/50068-h/images/i-0349.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0350.jpg b/old/50068-h/images/i-0350.jpg
deleted file mode 100644
index b6e286c..0000000
--- a/old/50068-h/images/i-0350.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0351.jpg b/old/50068-h/images/i-0351.jpg
deleted file mode 100644
index c6d1fe9..0000000
--- a/old/50068-h/images/i-0351.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0352.jpg b/old/50068-h/images/i-0352.jpg
deleted file mode 100644
index e5726c2..0000000
--- a/old/50068-h/images/i-0352.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0353.jpg b/old/50068-h/images/i-0353.jpg
deleted file mode 100644
index 3284d87..0000000
--- a/old/50068-h/images/i-0353.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0354.jpg b/old/50068-h/images/i-0354.jpg
deleted file mode 100644
index 6b5301a..0000000
--- a/old/50068-h/images/i-0354.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i-0355.jpg b/old/50068-h/images/i-0355.jpg
deleted file mode 100644
index 682592c..0000000
--- a/old/50068-h/images/i-0355.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i010.jpg b/old/50068-h/images/i010.jpg
deleted file mode 100644
index 0e35820..0000000
--- a/old/50068-h/images/i010.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i011a.jpg b/old/50068-h/images/i011a.jpg
deleted file mode 100644
index ba634eb..0000000
--- a/old/50068-h/images/i011a.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i011b.jpg b/old/50068-h/images/i011b.jpg
deleted file mode 100644
index 054a36c..0000000
--- a/old/50068-h/images/i011b.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i012.jpg b/old/50068-h/images/i012.jpg
deleted file mode 100644
index 9bbf0d6..0000000
--- a/old/50068-h/images/i012.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i013a.jpg b/old/50068-h/images/i013a.jpg
deleted file mode 100644
index a964ea7..0000000
--- a/old/50068-h/images/i013a.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i013b.jpg b/old/50068-h/images/i013b.jpg
deleted file mode 100644
index 9ab9821..0000000
--- a/old/50068-h/images/i013b.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i014.jpg b/old/50068-h/images/i014.jpg
deleted file mode 100644
index 94d55a3..0000000
--- a/old/50068-h/images/i014.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i016.jpg b/old/50068-h/images/i016.jpg
deleted file mode 100644
index 45a3293..0000000
--- a/old/50068-h/images/i016.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i017.jpg b/old/50068-h/images/i017.jpg
deleted file mode 100644
index 997047c..0000000
--- a/old/50068-h/images/i017.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i018.jpg b/old/50068-h/images/i018.jpg
deleted file mode 100644
index d08c44c..0000000
--- a/old/50068-h/images/i018.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i025.jpg b/old/50068-h/images/i025.jpg
deleted file mode 100644
index fb706be..0000000
--- a/old/50068-h/images/i025.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i027.jpg b/old/50068-h/images/i027.jpg
deleted file mode 100644
index 21b69a8..0000000
--- a/old/50068-h/images/i027.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i029.jpg b/old/50068-h/images/i029.jpg
deleted file mode 100644
index 374bf81..0000000
--- a/old/50068-h/images/i029.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i030.jpg b/old/50068-h/images/i030.jpg
deleted file mode 100644
index a0d50b8..0000000
--- a/old/50068-h/images/i030.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i031.jpg b/old/50068-h/images/i031.jpg
deleted file mode 100644
index b3e2a6f..0000000
--- a/old/50068-h/images/i031.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i036.jpg b/old/50068-h/images/i036.jpg
deleted file mode 100644
index a44988f..0000000
--- a/old/50068-h/images/i036.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i040.jpg b/old/50068-h/images/i040.jpg
deleted file mode 100644
index 662ef54..0000000
--- a/old/50068-h/images/i040.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i041.jpg b/old/50068-h/images/i041.jpg
deleted file mode 100644
index adae317..0000000
--- a/old/50068-h/images/i041.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i044.jpg b/old/50068-h/images/i044.jpg
deleted file mode 100644
index a10080f..0000000
--- a/old/50068-h/images/i044.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i045.jpg b/old/50068-h/images/i045.jpg
deleted file mode 100644
index d40547e..0000000
--- a/old/50068-h/images/i045.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i047.jpg b/old/50068-h/images/i047.jpg
deleted file mode 100644
index 529240f..0000000
--- a/old/50068-h/images/i047.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i048.jpg b/old/50068-h/images/i048.jpg
deleted file mode 100644
index fc910e9..0000000
--- a/old/50068-h/images/i048.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i049.jpg b/old/50068-h/images/i049.jpg
deleted file mode 100644
index 19ba327..0000000
--- a/old/50068-h/images/i049.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i050.jpg b/old/50068-h/images/i050.jpg
deleted file mode 100644
index cfd8fb0..0000000
--- a/old/50068-h/images/i050.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i052.jpg b/old/50068-h/images/i052.jpg
deleted file mode 100644
index 0c60f46..0000000
--- a/old/50068-h/images/i052.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i054.jpg b/old/50068-h/images/i054.jpg
deleted file mode 100644
index dd86bc0..0000000
--- a/old/50068-h/images/i054.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i055.jpg b/old/50068-h/images/i055.jpg
deleted file mode 100644
index c172fa9..0000000
--- a/old/50068-h/images/i055.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i056a.jpg b/old/50068-h/images/i056a.jpg
deleted file mode 100644
index 2215441..0000000
--- a/old/50068-h/images/i056a.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i056b.jpg b/old/50068-h/images/i056b.jpg
deleted file mode 100644
index 0f98404..0000000
--- a/old/50068-h/images/i056b.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i056c.jpg b/old/50068-h/images/i056c.jpg
deleted file mode 100644
index ce0f576..0000000
--- a/old/50068-h/images/i056c.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i058.jpg b/old/50068-h/images/i058.jpg
deleted file mode 100644
index df1ed1d..0000000
--- a/old/50068-h/images/i058.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i061.jpg b/old/50068-h/images/i061.jpg
deleted file mode 100644
index 0f24bd3..0000000
--- a/old/50068-h/images/i061.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i063.jpg b/old/50068-h/images/i063.jpg
deleted file mode 100644
index 0aab3fb..0000000
--- a/old/50068-h/images/i063.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i065.jpg b/old/50068-h/images/i065.jpg
deleted file mode 100644
index b4c7249..0000000
--- a/old/50068-h/images/i065.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i066.jpg b/old/50068-h/images/i066.jpg
deleted file mode 100644
index 16cad8f..0000000
--- a/old/50068-h/images/i066.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i067.jpg b/old/50068-h/images/i067.jpg
deleted file mode 100644
index 291f329..0000000
--- a/old/50068-h/images/i067.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i069.jpg b/old/50068-h/images/i069.jpg
deleted file mode 100644
index e2e95b5..0000000
--- a/old/50068-h/images/i069.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i071.jpg b/old/50068-h/images/i071.jpg
deleted file mode 100644
index 78c0d64..0000000
--- a/old/50068-h/images/i071.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i080.jpg b/old/50068-h/images/i080.jpg
deleted file mode 100644
index 615ffda..0000000
--- a/old/50068-h/images/i080.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i084.jpg b/old/50068-h/images/i084.jpg
deleted file mode 100644
index 558d84b..0000000
--- a/old/50068-h/images/i084.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i089.jpg b/old/50068-h/images/i089.jpg
deleted file mode 100644
index e1cc446..0000000
--- a/old/50068-h/images/i089.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i092.jpg b/old/50068-h/images/i092.jpg
deleted file mode 100644
index 62be531..0000000
--- a/old/50068-h/images/i092.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i093.jpg b/old/50068-h/images/i093.jpg
deleted file mode 100644
index 5bb1487..0000000
--- a/old/50068-h/images/i093.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i094.jpg b/old/50068-h/images/i094.jpg
deleted file mode 100644
index edf99f0..0000000
--- a/old/50068-h/images/i094.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i097.jpg b/old/50068-h/images/i097.jpg
deleted file mode 100644
index abbe930..0000000
--- a/old/50068-h/images/i097.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i098.jpg b/old/50068-h/images/i098.jpg
deleted file mode 100644
index ac76d18..0000000
--- a/old/50068-h/images/i098.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i099.jpg b/old/50068-h/images/i099.jpg
deleted file mode 100644
index 00eb281..0000000
--- a/old/50068-h/images/i099.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i100.jpg b/old/50068-h/images/i100.jpg
deleted file mode 100644
index 4fc711d..0000000
--- a/old/50068-h/images/i100.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i105.jpg b/old/50068-h/images/i105.jpg
deleted file mode 100644
index 1f2098b..0000000
--- a/old/50068-h/images/i105.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i106.jpg b/old/50068-h/images/i106.jpg
deleted file mode 100644
index 14ed8ab..0000000
--- a/old/50068-h/images/i106.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i107.jpg b/old/50068-h/images/i107.jpg
deleted file mode 100644
index f67d298..0000000
--- a/old/50068-h/images/i107.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i110.jpg b/old/50068-h/images/i110.jpg
deleted file mode 100644
index 03f344e..0000000
--- a/old/50068-h/images/i110.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i111.jpg b/old/50068-h/images/i111.jpg
deleted file mode 100644
index bdb79ee..0000000
--- a/old/50068-h/images/i111.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i112.jpg b/old/50068-h/images/i112.jpg
deleted file mode 100644
index 34bf1bf..0000000
--- a/old/50068-h/images/i112.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i113.jpg b/old/50068-h/images/i113.jpg
deleted file mode 100644
index 5136111..0000000
--- a/old/50068-h/images/i113.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i114.jpg b/old/50068-h/images/i114.jpg
deleted file mode 100644
index c52a875..0000000
--- a/old/50068-h/images/i114.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i115.jpg b/old/50068-h/images/i115.jpg
deleted file mode 100644
index 729dce1..0000000
--- a/old/50068-h/images/i115.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i117.jpg b/old/50068-h/images/i117.jpg
deleted file mode 100644
index 825d306..0000000
--- a/old/50068-h/images/i117.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i119.jpg b/old/50068-h/images/i119.jpg
deleted file mode 100644
index cd87d30..0000000
--- a/old/50068-h/images/i119.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i120.jpg b/old/50068-h/images/i120.jpg
deleted file mode 100644
index 3a6155d..0000000
--- a/old/50068-h/images/i120.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i121.jpg b/old/50068-h/images/i121.jpg
deleted file mode 100644
index c85f896..0000000
--- a/old/50068-h/images/i121.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i122.jpg b/old/50068-h/images/i122.jpg
deleted file mode 100644
index a4fb90e..0000000
--- a/old/50068-h/images/i122.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i125.jpg b/old/50068-h/images/i125.jpg
deleted file mode 100644
index 06d47b8..0000000
--- a/old/50068-h/images/i125.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i127.jpg b/old/50068-h/images/i127.jpg
deleted file mode 100644
index d2df30e..0000000
--- a/old/50068-h/images/i127.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i128.jpg b/old/50068-h/images/i128.jpg
deleted file mode 100644
index 326f206..0000000
--- a/old/50068-h/images/i128.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i131.jpg b/old/50068-h/images/i131.jpg
deleted file mode 100644
index f088bdc..0000000
--- a/old/50068-h/images/i131.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i132.jpg b/old/50068-h/images/i132.jpg
deleted file mode 100644
index 127f0f7..0000000
--- a/old/50068-h/images/i132.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i133.jpg b/old/50068-h/images/i133.jpg
deleted file mode 100644
index c2cdef3..0000000
--- a/old/50068-h/images/i133.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i134.jpg b/old/50068-h/images/i134.jpg
deleted file mode 100644
index 4197536..0000000
--- a/old/50068-h/images/i134.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i135.jpg b/old/50068-h/images/i135.jpg
deleted file mode 100644
index 1a1556f..0000000
--- a/old/50068-h/images/i135.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i136.jpg b/old/50068-h/images/i136.jpg
deleted file mode 100644
index 6bcbd54..0000000
--- a/old/50068-h/images/i136.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i137.jpg b/old/50068-h/images/i137.jpg
deleted file mode 100644
index fe2335a..0000000
--- a/old/50068-h/images/i137.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i138.jpg b/old/50068-h/images/i138.jpg
deleted file mode 100644
index a8f7d92..0000000
--- a/old/50068-h/images/i138.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i139.jpg b/old/50068-h/images/i139.jpg
deleted file mode 100644
index 95fc398..0000000
--- a/old/50068-h/images/i139.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i144.jpg b/old/50068-h/images/i144.jpg
deleted file mode 100644
index 089758e..0000000
--- a/old/50068-h/images/i144.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i145a.jpg b/old/50068-h/images/i145a.jpg
deleted file mode 100644
index f218fdf..0000000
--- a/old/50068-h/images/i145a.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i145b.jpg b/old/50068-h/images/i145b.jpg
deleted file mode 100644
index c331f75..0000000
--- a/old/50068-h/images/i145b.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i147.jpg b/old/50068-h/images/i147.jpg
deleted file mode 100644
index 20e40c0..0000000
--- a/old/50068-h/images/i147.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i149.jpg b/old/50068-h/images/i149.jpg
deleted file mode 100644
index 49ebd88..0000000
--- a/old/50068-h/images/i149.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i150.jpg b/old/50068-h/images/i150.jpg
deleted file mode 100644
index ea3edd2..0000000
--- a/old/50068-h/images/i150.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i151.jpg b/old/50068-h/images/i151.jpg
deleted file mode 100644
index 3e9c0d5..0000000
--- a/old/50068-h/images/i151.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i153.jpg b/old/50068-h/images/i153.jpg
deleted file mode 100644
index dacfec6..0000000
--- a/old/50068-h/images/i153.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i156.jpg b/old/50068-h/images/i156.jpg
deleted file mode 100644
index 5814fae..0000000
--- a/old/50068-h/images/i156.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i162.jpg b/old/50068-h/images/i162.jpg
deleted file mode 100644
index 4f2cf1a..0000000
--- a/old/50068-h/images/i162.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i164.jpg b/old/50068-h/images/i164.jpg
deleted file mode 100644
index 31ffb2b..0000000
--- a/old/50068-h/images/i164.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i165.jpg b/old/50068-h/images/i165.jpg
deleted file mode 100644
index 810205a..0000000
--- a/old/50068-h/images/i165.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i167.jpg b/old/50068-h/images/i167.jpg
deleted file mode 100644
index c86b191..0000000
--- a/old/50068-h/images/i167.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i168.jpg b/old/50068-h/images/i168.jpg
deleted file mode 100644
index b4c47af..0000000
--- a/old/50068-h/images/i168.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i169.jpg b/old/50068-h/images/i169.jpg
deleted file mode 100644
index 79d2f5e..0000000
--- a/old/50068-h/images/i169.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i170.jpg b/old/50068-h/images/i170.jpg
deleted file mode 100644
index 0647bed..0000000
--- a/old/50068-h/images/i170.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i172.jpg b/old/50068-h/images/i172.jpg
deleted file mode 100644
index a17205e..0000000
--- a/old/50068-h/images/i172.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i173.jpg b/old/50068-h/images/i173.jpg
deleted file mode 100644
index df4515d..0000000
--- a/old/50068-h/images/i173.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i174.jpg b/old/50068-h/images/i174.jpg
deleted file mode 100644
index c400f98..0000000
--- a/old/50068-h/images/i174.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i175.jpg b/old/50068-h/images/i175.jpg
deleted file mode 100644
index 8a013d0..0000000
--- a/old/50068-h/images/i175.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i176.jpg b/old/50068-h/images/i176.jpg
deleted file mode 100644
index 1aab5c6..0000000
--- a/old/50068-h/images/i176.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i177.jpg b/old/50068-h/images/i177.jpg
deleted file mode 100644
index 85dd92b..0000000
--- a/old/50068-h/images/i177.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i178.jpg b/old/50068-h/images/i178.jpg
deleted file mode 100644
index cf2139a..0000000
--- a/old/50068-h/images/i178.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i180.jpg b/old/50068-h/images/i180.jpg
deleted file mode 100644
index 6b41fff..0000000
--- a/old/50068-h/images/i180.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i182.jpg b/old/50068-h/images/i182.jpg
deleted file mode 100644
index 5ea0cae..0000000
--- a/old/50068-h/images/i182.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i184.jpg b/old/50068-h/images/i184.jpg
deleted file mode 100644
index ba19200..0000000
--- a/old/50068-h/images/i184.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i186.jpg b/old/50068-h/images/i186.jpg
deleted file mode 100644
index bd4d9da..0000000
--- a/old/50068-h/images/i186.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i188.jpg b/old/50068-h/images/i188.jpg
deleted file mode 100644
index c376ca1..0000000
--- a/old/50068-h/images/i188.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i190.jpg b/old/50068-h/images/i190.jpg
deleted file mode 100644
index 8d45e3b..0000000
--- a/old/50068-h/images/i190.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i191.jpg b/old/50068-h/images/i191.jpg
deleted file mode 100644
index 39883f1..0000000
--- a/old/50068-h/images/i191.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i192.jpg b/old/50068-h/images/i192.jpg
deleted file mode 100644
index 5eec599..0000000
--- a/old/50068-h/images/i192.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i195.jpg b/old/50068-h/images/i195.jpg
deleted file mode 100644
index 0f576dc..0000000
--- a/old/50068-h/images/i195.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i197.jpg b/old/50068-h/images/i197.jpg
deleted file mode 100644
index 4c36253..0000000
--- a/old/50068-h/images/i197.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i198.jpg b/old/50068-h/images/i198.jpg
deleted file mode 100644
index 2bf1897..0000000
--- a/old/50068-h/images/i198.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i200.jpg b/old/50068-h/images/i200.jpg
deleted file mode 100644
index 2170d74..0000000
--- a/old/50068-h/images/i200.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i201.jpg b/old/50068-h/images/i201.jpg
deleted file mode 100644
index 7d01bbe..0000000
--- a/old/50068-h/images/i201.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i202.jpg b/old/50068-h/images/i202.jpg
deleted file mode 100644
index e65d3a8..0000000
--- a/old/50068-h/images/i202.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i203.jpg b/old/50068-h/images/i203.jpg
deleted file mode 100644
index ac22f81..0000000
--- a/old/50068-h/images/i203.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i204.jpg b/old/50068-h/images/i204.jpg
deleted file mode 100644
index 2b2f414..0000000
--- a/old/50068-h/images/i204.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i205.jpg b/old/50068-h/images/i205.jpg
deleted file mode 100644
index 3904570..0000000
--- a/old/50068-h/images/i205.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i206.jpg b/old/50068-h/images/i206.jpg
deleted file mode 100644
index 0df0f21..0000000
--- a/old/50068-h/images/i206.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i208.jpg b/old/50068-h/images/i208.jpg
deleted file mode 100644
index ed93045..0000000
--- a/old/50068-h/images/i208.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i210.jpg b/old/50068-h/images/i210.jpg
deleted file mode 100644
index f42bf86..0000000
--- a/old/50068-h/images/i210.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i214.jpg b/old/50068-h/images/i214.jpg
deleted file mode 100644
index e9840b7..0000000
--- a/old/50068-h/images/i214.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i216.jpg b/old/50068-h/images/i216.jpg
deleted file mode 100644
index 709a654..0000000
--- a/old/50068-h/images/i216.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i217.jpg b/old/50068-h/images/i217.jpg
deleted file mode 100644
index 2277505..0000000
--- a/old/50068-h/images/i217.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i219.jpg b/old/50068-h/images/i219.jpg
deleted file mode 100644
index 70e33c0..0000000
--- a/old/50068-h/images/i219.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i220.jpg b/old/50068-h/images/i220.jpg
deleted file mode 100644
index 4596750..0000000
--- a/old/50068-h/images/i220.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i230.jpg b/old/50068-h/images/i230.jpg
deleted file mode 100644
index 8522271..0000000
--- a/old/50068-h/images/i230.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i233.jpg b/old/50068-h/images/i233.jpg
deleted file mode 100644
index 3c46cc7..0000000
--- a/old/50068-h/images/i233.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i235.jpg b/old/50068-h/images/i235.jpg
deleted file mode 100644
index 0b34128..0000000
--- a/old/50068-h/images/i235.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i236.jpg b/old/50068-h/images/i236.jpg
deleted file mode 100644
index a51689f..0000000
--- a/old/50068-h/images/i236.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i238.jpg b/old/50068-h/images/i238.jpg
deleted file mode 100644
index b2a2d1e..0000000
--- a/old/50068-h/images/i238.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i239.jpg b/old/50068-h/images/i239.jpg
deleted file mode 100644
index c912cd5..0000000
--- a/old/50068-h/images/i239.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i240.jpg b/old/50068-h/images/i240.jpg
deleted file mode 100644
index 8c5feb6..0000000
--- a/old/50068-h/images/i240.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i241.jpg b/old/50068-h/images/i241.jpg
deleted file mode 100644
index d8b4026..0000000
--- a/old/50068-h/images/i241.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i242.jpg b/old/50068-h/images/i242.jpg
deleted file mode 100644
index d2f4f3d..0000000
--- a/old/50068-h/images/i242.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i244.jpg b/old/50068-h/images/i244.jpg
deleted file mode 100644
index 2172559..0000000
--- a/old/50068-h/images/i244.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i245.jpg b/old/50068-h/images/i245.jpg
deleted file mode 100644
index 1fed440..0000000
--- a/old/50068-h/images/i245.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i246.jpg b/old/50068-h/images/i246.jpg
deleted file mode 100644
index a5d03b2..0000000
--- a/old/50068-h/images/i246.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i248.jpg b/old/50068-h/images/i248.jpg
deleted file mode 100644
index 7e52ff7..0000000
--- a/old/50068-h/images/i248.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i249.jpg b/old/50068-h/images/i249.jpg
deleted file mode 100644
index de61cb3..0000000
--- a/old/50068-h/images/i249.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i250.jpg b/old/50068-h/images/i250.jpg
deleted file mode 100644
index b1acbcd..0000000
--- a/old/50068-h/images/i250.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i251.jpg b/old/50068-h/images/i251.jpg
deleted file mode 100644
index b7d5393..0000000
--- a/old/50068-h/images/i251.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i252.jpg b/old/50068-h/images/i252.jpg
deleted file mode 100644
index 3102589..0000000
--- a/old/50068-h/images/i252.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i253.jpg b/old/50068-h/images/i253.jpg
deleted file mode 100644
index d8e460e..0000000
--- a/old/50068-h/images/i253.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i254.jpg b/old/50068-h/images/i254.jpg
deleted file mode 100644
index 67fbaa6..0000000
--- a/old/50068-h/images/i254.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i256.jpg b/old/50068-h/images/i256.jpg
deleted file mode 100644
index 93a6ad0..0000000
--- a/old/50068-h/images/i256.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i257.jpg b/old/50068-h/images/i257.jpg
deleted file mode 100644
index 6be791f..0000000
--- a/old/50068-h/images/i257.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i258.jpg b/old/50068-h/images/i258.jpg
deleted file mode 100644
index 0ea6a8e..0000000
--- a/old/50068-h/images/i258.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i259.jpg b/old/50068-h/images/i259.jpg
deleted file mode 100644
index b1b6b25..0000000
--- a/old/50068-h/images/i259.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i260.jpg b/old/50068-h/images/i260.jpg
deleted file mode 100644
index f4bfbd8..0000000
--- a/old/50068-h/images/i260.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i262.jpg b/old/50068-h/images/i262.jpg
deleted file mode 100644
index edc533a..0000000
--- a/old/50068-h/images/i262.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i264.jpg b/old/50068-h/images/i264.jpg
deleted file mode 100644
index c85d40e..0000000
--- a/old/50068-h/images/i264.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i265.jpg b/old/50068-h/images/i265.jpg
deleted file mode 100644
index e8bf1e6..0000000
--- a/old/50068-h/images/i265.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i269.jpg b/old/50068-h/images/i269.jpg
deleted file mode 100644
index d87ec7b..0000000
--- a/old/50068-h/images/i269.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i273.jpg b/old/50068-h/images/i273.jpg
deleted file mode 100644
index 438d9da..0000000
--- a/old/50068-h/images/i273.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i276.jpg b/old/50068-h/images/i276.jpg
deleted file mode 100644
index 7023e14..0000000
--- a/old/50068-h/images/i276.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i277.jpg b/old/50068-h/images/i277.jpg
deleted file mode 100644
index fe02b75..0000000
--- a/old/50068-h/images/i277.jpg
+++ /dev/null
diff --git a/old/50068-h/images/i280.jpg b/old/50068-h/images/i280.jpg
deleted file mode 100644
index 2c835af..0000000
--- a/old/50068-h/images/i280.jpg
+++ /dev/null