diff options
Diffstat (limited to 'old/50068-h/50068-h.htm')
| -rw-r--r-- | old/50068-h/50068-h.htm | 14361 |
1 files changed, 0 insertions, 14361 deletions
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 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 />&<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 & CO. 72 FIFTH AVE. NEW YORK</b>.</p> - -<p class="center space-above2">COPYRIGHTED, 1915,<br />BY<br />THEO. AUDEL & 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 to 1,868</a></td> - </tr><tr> - <td class="tdl"><br /></td> - <td class="tdl"><br /> -Importance of wave form measurement—<b>methods</b>: -step by step; constantly recording—<b>classes of -apparatus</b>: wave indication; <i>oscillographs</i>—<b>step -by step methods</b>—Joubert's; four part commutator; -modified four part commutator; ballistic galvanometer; -zero; Hospitalier ondograph—<b>constantly recording -methods</b>: cathode ray; glow light; moving iron; moving -coil; hot wire—<b>oscillographs</b>—moving coil type; -construction and operation; production of the time scale; -oscillograms—falling plate camera; its use.</td> - <td class="tdr"><br /></td> - </tr><tr> - <td colspan="3" class="tdc"> </td> - </tr><tr> - <td colspan="2" class="tdl_toc"><b>SWITCHBOARDS</b></td> - <td class="tdr"><a href="#Page_1869">1,869 to 1,884</a></td> - </tr><tr> - <td class="tdl"><br /></td> - <td class="tdl"><br /> -<b>General principles</b>: diagram—small plant a.c. -switchboard—<b>switchboard panels</b>; <b>generator -panel</b>; diagram of connections—simple method of -determining bus bar capacity—feeder panel—diagrams of -connection for two phase and three phase installations.</td> - </tr><tr> - <td colspan="3" class="tdc"> </td> - </tr><tr> - <td colspan="2" class="tdl_toc"><b>ALTERNATING CURRENT WIRING</b></td> - <td class="tdr"><a href="#Page_1885">1,885 to 1,914</a></td> - </tr><tr> - <td class="tdl"><br /></td> - <td class="tdl"><br />Effects to be considered in making -calculations—<b>induction</b>; self- and mutual; mutual -induction, how caused—<b>transpositions</b>—inductance -per mile of three phase circuit, table—<b>capacity</b>; -table—<b>frequency—skin effect</b>; calculation; -table—<b>corona effect</b>; its manifestation; -critical voltage; spacing of wires—<b>resistance of -wires—impedance—power factor</b>; apparent current; -usual power factors encountered; example—<b>wire -calculations—sizes of wire—table of the property of -copper wire—drop</b>; example—current—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"> </td> - </tr><tr> - <td colspan="2" class="tdl_toc"><b>POWER STATIONS</b></td> - <td class="tdr"><a href="#Page_1915">1,915 to 1,988</a></td> - </tr><tr> - <td class="tdl"><br /></td> - <td class="tdl"><br /> -Classification—<b>central stations</b>; types: a.c., -d.c., and a.c. and d.c.; reciprocating engine vs. -turbine—<b>location of central stations</b>; price of -land; trouble after erection; water supply; service -requiring direct current—<b>size of plant</b>; nature -of load; peak load; load factor; machinery required; -example; factors of evaporation; grate surface per -horse power—<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—<b>station -construction</b>—<b>foundations</b>—<b>walls</b>— -<b>roofs</b>—<b>floors</b>—<b>chimneys</b>; -cost of chimneys and mechanical draft; high chimneys -ill advised—<b>steam turbine</b>; types: impulse -and reaction; why high vacuum is necessary; the -working pressure—<b>hydro-electric plants</b>—water -turbines; types: impulse, reaction—<b>isolated -plants</b>—<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"> </td> - </tr><tr> - <td colspan="2" class="tdl_toc"><b>MANAGEMENT</b></td> - <td class="tdr"><a href="#Page_1989">1,989 to 2,114</a></td> - </tr><tr> - <td class="tdl"><br /></td> - <td class="tdl"><br /> -The term "management"—<b>selection</b>; general -considerations—<b>selection of generators</b>; -efficiency of generators; size and number; -regulation—<b>installation</b>; precautions; -handling of armatures; assembling a machine; speed -of generators; calculation of pulley sizes; gear -wheels—<b>belts</b>; various belt drives; horse -power transmitted by belts; velocity of belt; endless -belts—<b>switchboards</b>; essential points of difference -between single phase and three phase switchboard wiring; -assembling a switchboard; usual equipment. - -<b>Operation of Alternators—alternators in parallel</b>; -synchronizing; lamp methods; action of amortisseur winding; -synchronizing three phase alternators; disadvantage of -lamp method—<b>cutting out alternator</b>; precautions; -hunting—<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—<b>motor -generators</b>; various types and conditions requiring -same—<b>dynamotors</b>; precautions—<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—<b>how to test generators</b>; commercial -efficiency; various tests. - -<b>Station Testing:</b> resistance measurement by "drop" -method—methods of connecting ammeter voltmeter and -wattmeter for measurement of power—<b>motor testing:</b> -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—<b>three phase alternator testing:</b> excitation -or magnetization curve test—synchronous impedance -test—load test—three phase alternator or synchronous -motor temperature test—<b>direct current motor</b> or -<b>generator testing:</b> magnetization curve—(shunt) -external characteristic—direct current motor testing; -load and speed tests—temperature test, "loading back" -method—<b>compound dynamo testing</b>: external -characteristic, adjustable load—<b>transformer testing</b>: -external characteristic, adjustable load—<b>transformer -testing</b>: 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.</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.—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"> -  1. Wave indicators;<br /> -  2. Oscillographs.<br /><br /> - -and the methods employed with these two species of apparatus -may be described respectively as,<br /><br /> - -  1. Step by step;<br /> -  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.—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.—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"> </td> - <td class="tdl">❴ Joubert's method;</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdl">❴ Four part commutator method;</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdl">❴ Modified four part commutator method;</td> - </tr><tr> - <td class="tdl">1. Step by step  </td> - <td class="tdl">❴ Ballistic galvanometer method;</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdl">❴ Zero method;</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdl">❴ 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>—<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"> </td> - <td class="tdl"> </td> - <td class="tdl">❴ cathode ray;</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdl">❴ by use of various types  </td> - <td class="tdl">❴ glow light;</td> - </tr><tr> - <td class="tdl">2. constantly recording  </td> - <td class="tdl">❴ of <b>oscillograph</b>,</td> - <td class="tdl">❴ moving iron;</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdl">❴ such as</td> - <td class="tdl">❴ moving coil;</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdl"> </td> - <td class="tdl">❴ hot wire.</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdl"> </td> - <td class="tdl"> </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>—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>—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>—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>—<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>—<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>—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>—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.—<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>—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>—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>—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>—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>—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>—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>—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>—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>—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>—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>—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>—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>—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>—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>—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>—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.—<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.—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.—<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.—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.—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.—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>—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.—<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>—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.—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.—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.—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.—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.—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.—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.—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.—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.—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.—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.—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.—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.—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>—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.—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.—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.—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.—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>—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">  1. Generator panel;<br /> -  2. Feeder panel;<br /> -  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,—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>—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.—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.—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.—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.—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.—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>—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.—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.—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.—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.—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.</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">  1. Self-induction;<br /> -  2. Mutual-induction;<br /> -  3. Power factor;<br /> -  4. Skin effect;<br /> -  5. Corona effect;<br /> -  6. Frequency;<br /> -  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>—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.—<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.—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> ÷ 2π <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"> 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> ÷ 2π <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>—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.—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.—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.—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"> Size B.&S. </th> - <th class="tdr">Diam. <br /> (inches) </th> - <th class="tdc"><br /> Distance <br /><i>d</i><br />(inches)</th> - <th class="tdc"><br /> Self Inductance <br />L<br />(henrys)</th> - </tr><tr class="tr_grey"> - <td class="tdr">0000 </td> <td class="tdr">.46 </td> - <td class="tdc">12</td> <td class="tdc">.00234</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00256</td> - </tr><tr class="tr_grey"> - <td class="tdr"></td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00270</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.00312</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">000 </td> <td class="tdr">.41 </td> - <td class="tdc">12</td> <td class="tdc">.00241</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00262</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00277</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.00318</td> - </tr><tr class="tr_grey"> - <td class="tdr">00 </td> <td class="tdr">.365 </td> - <td class="tdc">12</td> <td class="tdc">.00248</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00269</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00285</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.00330</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">0 </td> <td class="tdr">.325 </td> - <td class="tdc">12</td> <td class="tdc">.00254</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00276</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00293</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.00331</td> - </tr><tr class="tr_grey"> - <td class="tdr">1 </td> <td class="tdr">.289 </td> - <td class="tdc">12</td> <td class="tdc">.00260</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00281</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00308</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.00338</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">2 </td> <td class="tdr">.258 </td> - <td class="tdc">12</td> <td class="tdc">.00267</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00288</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00304</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.00314</td> - </tr><tr class="tr_grey"> - <td class="tdr">3 </td> <td class="tdr">.229 </td> - <td class="tdc">12</td> <td class="tdc">.00274</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00294</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00310</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.00351</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">4 </td> <td class="tdr">.204 </td> - <td class="tdc">12</td> <td class="tdc">.00280</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00300</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00315</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.00358</td> - </tr><tr class="tr_grey"> - <td class="tdr">5 </td> <td class="tdr">.182 </td> - <td class="tdc">12</td> <td class="tdc">.00286</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00307</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00323</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.00356</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">6 </td> <td class="tdr">.162 </td> - <td class="tdc">12</td> <td class="tdc">.00291</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00313</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00329</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.00369</td> - </tr><tr class="tr_grey"> - <td class="tdr">7 </td> <td class="tdr">.144 </td> - <td class="tdc">12</td> <td class="tdc">.00298</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00310</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00336</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.00377</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">8 </td> <td class="tdr">.128 </td> - <td class="tdc">12</td> <td class="tdc">.00303</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00325</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00341</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.00384</td> - </tr><tr class="tr_grey"> - <td class="tdr">9 </td> <td class="tdr">.114 </td> - <td class="tdc">12</td> <td class="tdc">.00310</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00332</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00348</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.00389</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">10 </td> <td class="tdr">.102 </td> - <td class="tdc">12</td> <td class="tdc">.00318</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.00340</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.00355</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </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.—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.—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>—The inductance of a complete -single phase circuit = L × 2 ÷ √<span class="rad">3</span>.</p> - -<p>A = distance between wires;<br /> -  <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"> Size B.&S. </th> - <th class="tdr">Diam. <br /> (inches) </th> - <th class="tdc"> Distance <br /><i>d</i><br />(inches)</th> - <th class="tdc"> Capacity <br />C<br />(μfarads)</th> - </tr><tr class="tr_grey"> - <td class="tdr">0000 </td> <td class="tdr">.46 </td> - <td class="tdc">12</td> <td class="tdc">.0226 </td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.0204 </td> - </tr><tr class="tr_grey"> - <td class="tdr"></td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01922</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.01474</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">000 </td> <td class="tdr">.41 </td> - <td class="tdc">12</td> <td class="tdc">.0218 </td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.01992</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01876</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.01638</td> - </tr><tr class="tr_grey"> - <td class="tdr">00 </td> <td class="tdr">.365 </td> - <td class="tdc">12</td> <td class="tdc">.0124 </td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.01946</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01832</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.01604</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">0 </td> <td class="tdr">.325 </td> - <td class="tdc">12</td> <td class="tdc">.02078</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.01898</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01642</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.01570</td> - </tr><tr class="tr_grey"> - <td class="tdr">1 </td> <td class="tdr">.289 </td> - <td class="tdc">12</td> <td class="tdc">.02022</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.01952</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01748</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.0154 </td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">2 </td> <td class="tdr">.258 </td> - <td class="tdc">12</td> <td class="tdc">.01972</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.01818</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01710</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.01510</td> - </tr><tr class="tr_grey"> - <td class="tdr">3 </td> <td class="tdr">.229 </td> - <td class="tdc">12</td> <td class="tdc">.01938</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.01766</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01672</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.01480</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">4 </td> <td class="tdr">.204 </td> - <td class="tdc">12</td> <td class="tdc">.01874</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.01726</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01636</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.01452</td> - </tr><tr class="tr_grey"> - <td class="tdr">5 </td> <td class="tdr">.182 </td> - <td class="tdc">12</td> <td class="tdc">.01830</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.01690</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01602</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.01426</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">6 </td> <td class="tdr">.162 </td> - <td class="tdc">12</td> <td class="tdc">.01788</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.01654</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01560</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.0140 </td> - </tr><tr class="tr_grey"> - <td class="tdr">7 </td> <td class="tdr">.144 </td> - <td class="tdc">12</td> <td class="tdc">.01746</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.01618</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01538</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.01374</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">8 </td> <td class="tdr">.128 </td> - <td class="tdc">12</td> <td class="tdc">.01708</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.01586</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01508</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.01350</td> - </tr><tr class="tr_grey"> - <td class="tdr">9 </td> <td class="tdr">.114 </td> - <td class="tdc">12</td> <td class="tdc">.01660</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.01552</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01478</td> - </tr><tr class="tr_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.01326</td> - - </tr><tr class="tr_lt_grey"> - <td class="tdr">10 </td> <td class="tdr">.102 </td> - <td class="tdc">12</td> <td class="tdc">.01636</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">18</td> <td class="tdc">.01522</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">24</td> <td class="tdc">.01452</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr"> </td> <td class="tdr"> </td> - <td class="tdc">48</td> <td class="tdc">.01304</td> - </tr> - </tbody> -</table> - -<p class="space-above1"><b>Capacity.</b>—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"> </td> - <td class="tdc">38.83 <i>sc</i> 10<sup>-3</sup></td> - <td class="tdl"> </td> - </tr><tr> - <td class="tdr">C = </td> - <td class="tdc">——————</td> - <td class="tdl">  per mile, insulated cable with lead sheath;</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdc">log (D ÷ d)</td> - <td class="tdl"> </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 = </td> - <td class="tdc">——————</td> - <td class="tdl">  per mile, single conductor with earth return;</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdc">log (4<i>h</i> ÷ <i>d</i>)</td> - <td class="tdl"> </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 = </td> - <td class="tdc">——————</td> - <td class="tdl">  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 /> -    for a metallic circuit, C = capacity between wires;</p> - -<p><i>sc</i> = Specific inductive capacity of insulating material;<br /> -   = 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>—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> = 2π <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>—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.—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. & 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. <br />× frequency </th> - <th class="tdc">Ratio<br /> factor </th> - <th class="tdr">Cir. mils. <br />× frequency </th> - <th class="tdc">Ratio<br /> factor </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>—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.—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.</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"> 5,000</td> <td class="tdc"> 28 ins.</td> - </tr><tr> - <td class="tdc"> 15,000</td> <td class="tdc"> 40 ins.</td> - </tr><tr> - <td class="tdc"> 30,000</td> <td class="tdc"> 48 ins.</td> - </tr><tr> - <td class="tdc"> 45,000</td> <td class="tdc"> 60 ins.</td> - </tr><tr> - <td class="tdc"> 60,000</td> <td class="tdc"> 60 ins.</td> - </tr><tr> - <td class="tdc"> 75,000</td> <td class="tdc"> 84 ins.</td> - </tr><tr> - <td class="tdc"> 90,000</td> <td class="tdc"> 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>—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. & 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.—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>—<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 /> -  1. The loss due to resistance.<br /> -  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.—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.</p> -</div> - -<p><b>Power Factor.</b>—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 ϕ 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.—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.—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.—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"> </td> - <td class="tdc">true watts</td> - <td class="tdl"> 20,000</td> - <td class="tdr"> </td> - </tr><tr> - <td class="tdr">Apparent Current = </td> - <td class="tdc">————————— = </td> - <td class="tdl">———— = </td> - <td class="tdr"> 113.6 amperes</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdl"> power factor × volts</td> - <td class="tdl"> .8 × 220</td> - <td class="tdr"> </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 <br /> power </td> - <td class="tdc">110<br /> volts </td> <td class="tdc">220<br /> volts </td> - <td class="tdc">440<br /> volts </td> <td class="tdc">110<br /> volts </td> - <td class="tdc">220<br /> volts </td> <td class="tdc">440<br /> volts </td> - <td class="tdc">110<br /> volts </td> <td class="tdc">220<br /> volts </td> - <td class="tdc">440<br /> volts </td> <td class="tdc">550<br /> volts </td> - </tr><tr> - <td class="tdr">.5  </td> - <td class="tdl"> 6.6</td> <td class="tdl"> 3.4</td> - <td class="tdl"> 1.8</td> <td class="tdl"> 3.3</td> - <td class="tdl"> 1.7</td> <td class="tdl"> .9</td> - <td class="tdl"> 3.7</td> <td class="tdl"> 1.8</td> - <td class="tdl"> 1</td> <td class="tdl"> </td> - </tr><tr> - <td class="tdr">1  </td> - <td class="tdl"> 14</td> <td class="tdl"> 7</td> - <td class="tdl"> 3.5</td> <td class="tdl"> 6.4</td> - <td class="tdl"> 3.2</td> <td class="tdl"> 1.6</td> - <td class="tdl"> 7.4</td> <td class="tdl"> 3.7</td> - <td class="tdl"> 1.9</td> <td class="tdl"> </td> - </tr><tr> - <td class="tdr">2  </td> - <td class="tdl"> 24</td> <td class="tdl"> 12</td> - <td class="tdl"> 6</td> <td class="tdl"> 11</td> - <td class="tdl"> 5.7</td> <td class="tdl"> 2.9</td> - <td class="tdl"> 13</td> <td class="tdl"> 6.6</td> - <td class="tdl"> 3.3</td> <td class="tdl"> 2.5</td> - </tr><tr> - <td class="tdr">3  </td> - <td class="tdl"> 34</td> <td class="tdl"> 17</td> - <td class="tdl"> 8.5</td> <td class="tdl"> 16</td> - <td class="tdl"> 8.1</td> <td class="tdl"> 4.1</td> - <td class="tdl"> 19</td> <td class="tdl"> 9.3</td> - <td class="tdl"> 4.7</td> <td class="tdl"> 3.5</td> - </tr><tr> - <td class="tdr">4  </td> - <td class="tdl"> 52</td> <td class="tdl"> 26</td> - <td class="tdl"> 13</td> <td class="tdl"> 26</td> - <td class="tdl"> 13</td> <td class="tdl"> 6.5</td> - <td class="tdl"> 30</td> <td class="tdl"> 15</td> - <td class="tdl"> 7.5</td> <td class="tdl"> 6</td> - </tr><tr> - <td class="tdr">5  </td> - <td class="tdl"> 74</td> <td class="tdl"> 37</td> - <td class="tdl"> 18.5</td> <td class="tdl"> 38</td> - <td class="tdl"> 19</td> <td class="tdl"> 9.5</td> - <td class="tdl"> 44</td> <td class="tdl"> 22</td> - <td class="tdl"> 11</td> <td class="tdl"> 9</td> - </tr><tr> - <td class="tdr">10  </td> - <td class="tdl"> 94</td> <td class="tdl"> 47</td> - <td class="tdl"> 23.5</td> <td class="tdl"> 44</td> - <td class="tdl"> 22</td> <td class="tdl"> 11</td> - <td class="tdl"> 50</td> <td class="tdl"> 25</td> - <td class="tdl"> 12.5</td> <td class="tdl"> 11</td> - </tr><tr> - <td class="tdr">15  </td> - <td class="tdl"> </td> <td class="tdl"> </td> - <td class="tdl"> </td> <td class="tdl"> 66</td> - <td class="tdl"> 33</td> <td class="tdl"> 16.5</td> - <td class="tdl"> 76</td> <td class="tdl"> 38</td> - <td class="tdl"> 19</td> <td class="tdl"> 16</td> - </tr><tr> - <td class="tdr">20  </td> - <td class="tdl"> </td> <td class="tdl"> </td> - <td class="tdl"> </td> <td class="tdl"> 88</td> - <td class="tdl"> 44</td> <td class="tdl"> 22</td> - <td class="tdl"> 102</td> <td class="tdl"> 51</td> - <td class="tdl"> 25.5</td> <td class="tdl"> 22</td> - </tr><tr> - <td class="tdr">25  </td> - <td class="tdl"> </td> <td class="tdl"> </td> - <td class="tdl"> </td> <td class="tdl"> 111</td> - <td class="tdl"> 55</td> <td class="tdl"> 28</td> - <td class="tdl"> 129</td> <td class="tdl"> 64</td> - <td class="tdl"> 32</td> <td class="tdl"> 25</td> - </tr><tr> - <td class="tdr">30  </td> - <td class="tdl"> </td> <td class="tdl"> </td> - <td class="tdl"> </td> <td class="tdl"> 134</td> - <td class="tdl"> 67</td> <td class="tdl"> 33.5</td> - <td class="tdl"> 154</td> <td class="tdl"> 77</td> - <td class="tdl"> 38.5</td> <td class="tdl"> 32</td> - </tr><tr> - <td class="tdr">40  </td> - <td class="tdl"> </td> <td class="tdl"> </td> - <td class="tdl"> </td> <td class="tdl"> 178</td> - <td class="tdl"> 89</td> <td class="tdl"> 44.5</td> - <td class="tdl"> 204</td> <td class="tdl"> 107</td> - <td class="tdl"> 53.5</td> <td class="tdl"> 44</td> - </tr><tr> - <td class="tdr">50  </td> - <td class="tdl"> </td> <td class="tdl"> </td> - <td class="tdl"> </td> <td class="tdl"> 204</td> - <td class="tdl"> 102</td> <td class="tdl"> 51</td> - <td class="tdl"> 236</td> <td class="tdl"> 118</td> - <td class="tdl"> 59</td> <td class="tdl"> 52</td> - </tr><tr> - <td class="tdr">75  </td> - <td class="tdl"> </td> <td class="tdl"> </td> - <td class="tdl"> </td> <td class="tdl"> 308</td> - <td class="tdl"> 154</td> <td class="tdl"> 77</td> - <td class="tdl"> 356</td> <td class="tdl"> 178</td> - <td class="tdl"> 89</td> <td class="tdl"> 77</td> - </tr><tr> - <td class="tdr">100  </td> - <td class="tdl"> </td> <td class="tdl"> </td> - <td class="tdl"> </td> <td class="tdl"> 408</td> - <td class="tdl"> 204</td> <td class="tdl"> 102</td> - <td class="tdl"> 472</td> <td class="tdl"> 236</td> - <td class="tdl"> 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>—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.—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>—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"> </td> - <td class="tdc">amperes × feet × 21.6</td> - <td class="tdl"> </td> - </tr><tr> - <td class="tdr">circular mils = </td> - <td class="tdc"> —————————— </td> - <td class="tdl">  (1)</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdc">drop</td> - <td class="tdl"> </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"> </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 = </td> - <td class="tdc"> ———————————— =</td> - <td class="tdl"> ——————————</td> - </tr><tr> - <td class="tdr"> </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"> </td> - <td class="tdc">drop</td> - <td class="tdl"> </td> - </tr><tr> - <td class="tdr">% loss = </td> - <td class="tdc"> ———————— </td> - <td class="tdl"> × 100</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdc">impressed pressure</td> - <td class="tdl"> </td> - </tr> - </tbody> -</table> - -<p class="no-indent">from which</p> - -<table border="0" cellspacing="2" summary="_" cellpadding="0"> - <tbody><tr> - <td class="tdr"> </td> - <td class="tdc">% loss × impressed pressure</td> - <td class="tdl"> </td> - </tr><tr> - <td class="tdr">drop = </td> - <td class="tdc"> ———————————— </td> - <td class="tdl">  (2)</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdc">100</td> - <td class="tdl"> </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"> </td> - <td class="tdc">amperes × feet × 21.6</td> - </tr><tr> - <td class="tdr">circular mils = </td> - <td class="tdc"> ———————————— </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdc">% loss × imp. pressure</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdc"> ———————— </td> - </tr><tr> - <td class="tdr"> </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"> = </td> - <td class="tdc"> ————————————  (3)</td> - </tr><tr> - <td class="tdr"> </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"> </td> - <td class="tdc">watts</td> - <td class="tdl"> </td> - </tr><tr> - <td class="tdr">amperes = </td> - <td class="tdc"> ——— </td> - <td class="tdl">  (4)</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdc">volts</td> - <td class="tdl"> </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdc"> </td> - <td class="tdl"> </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.—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.</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"> </td> - <td class="tdc">(watts/volts) × feet × 2,160 </td> - </tr><tr> - <td class="tdr">circular mils = </td> - <td class="tdc"> ———————————— </td> - </tr><tr> - <td class="tdr"> </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"> = </td> - <td class="tdc"> ————————————  (5)</td> - </tr><tr> - <td class="tdr"> </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"> </td> - <td class="tdc">watts × feet × M </td> - </tr><tr> - <td class="tdr">circular mils = </td> - <td class="tdc">  ——————————  (6)</td> - </tr><tr> - <td class="tdr"> </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"> 2,160 </td> <td class="tdc"> 2,249 </td> - <td class="tdc"> 2,400 </td> <td class="tdc"> 2,660 </td> - <td class="tdc"> 3,000 </td> <td class="tdc"> 3,380 </td> - <td class="tdc"> 3,840 </td> <td class="tdc"> 4,400 </td> - <td class="tdc"> 5,112 </td> <td class="tdc"> 6,000 </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.—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"> 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">Two phase<br />(4 wire)</td> - <td class="tdc_top"> 2.00 </td> <td class="tdc_top"> 1.96 </td> - <td class="tdc_top"> 1.80 </td> <td class="tdc_top"> 1.60 </td> - <td class="tdc_top"> 1.40 </td> - </tr><tr> - <td class="tdc">Three phase<br />(3 wire)</td> - <td class="tdc_top"> 1.73 </td> <td class="tdc_top"> 1.70 </td> - <td class="tdc_top"> 1.55 </td> <td class="tdc_top"> 1.38 </td> - <td class="tdc_top"> 1.21 </td> - </tr> - </tbody> -</table> - -<div class="blockquot"> -<p>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.</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 FORMULÆ FOR COPPER WIRES</b></caption> - <tbody><tr> - <td class="tdl">Diameter squared</td> - <td class="tdl"> </td> - <td class="tdl"> = circular mils</td> - </tr><tr> - <td class="tdl">Circular mils</td> - <td class="tdl"> × .7854</td> - <td class="tdl"> = square mils</td> - </tr><tr> - <td class="tdl">  .000003027</td> - <td class="tdl"> × circular mils</td> - <td class="tdl"> = pounds per foot</td> - </tr><tr> - <td class="tdl">  .003027</td> - <td class="tdl"> × circular mils</td> - <td class="tdl"> = pounds per 1,000 feet</td> - </tr><tr> - <td class="tdl">  .0159847</td> - <td class="tdl"> × circular mils</td> - <td class="tdl"> = pounds per mile</td> - </tr><tr> - <td class="tdl">  .003879</td> - <td class="tdl"> × square mils</td> - <td class="tdl"> = pounds per 1,000 feet</td> - </tr><tr> - <td class="tdl">  .33033</td> - <td class="tdl"> ÷ circular mils</td> - <td class="tdl"> = feet per pound</td> - </tr><tr> - <td class="tdl">  .0000002924</td> - <td class="tdl"> × circular mils</td> - <td class="tdl"> = pounds per ohm</td> - </tr><tr> - <td class="tdl">  .342</td> - <td class="tdl"> ÷ circular mils</td> - <td class="tdl"> = ohms per pound</td> - </tr><tr> - <td class="tdl">  .096585</td> - <td class="tdl"> × circular mils</td> - <td class="tdl"> = feet per ohm</td> - </tr><tr> - <td class="tdl"> 10.353568</td> - <td class="tdl"> ÷ circular mils</td> - <td class="tdl"> = 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.—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"> </td> - <td class="tdc">watts × feet × M </td> - </tr><tr> - <td class="tdr">circular mils = </td> - <td class="tdc">  ——————————  (1)</td> - </tr><tr> - <td class="tdr"> </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"> </td> - <td class="tdc">30,000 × 2,000 × 2,660</td> - </tr><tr> - <td class="tdr">circular mils = </td> - <td class="tdc">  ——————————</td> - </tr><tr> - <td class="tdr"> </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. & 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. & S. G. (Brown & 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"> </td> - <td class="tdc"> </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.& 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 </td> - <td class="tdr"> </td> <td class="tdl"> 0.460</td> - <td class="tdl"> 211,600</td> <td class="tdl"> 640.5</td> - <td class="tdr">1.561 </td> <td class="tdr">.04893 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">0000 </td> <td class="tdl"> 0.454</td> - <td class="tdl"> 206,100</td> <td class="tdl"> 623.9</td> - <td class="tdr">1.603 </td> <td class="tdr"> .05023</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">000 </td> <td class="tdl"> 0.425</td> - <td class="tdl"> 180,600</td> <td class="tdl"> 546.8</td> - <td class="tdr">1.829 </td> <td class="tdr">.05732 </td> - </tr><tr> - <td class="tdr">000 </td> - <td class="tdr"> </td> <td class="tdl"> 0.4096</td> - <td class="tdl"> 167,800</td> <td class="tdl"> 508.0</td> - <td class="tdr">1.969 </td> <td class="tdr">.06170 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">00 </td> <td class="tdl"> 0.380</td> - <td class="tdl"> 144,400</td> <td class="tdl"> 437.1</td> - <td class="tdr">2.288 </td> <td class="tdr">.07170 </td> - </tr><tr> - <td class="tdr">00 </td> - <td class="tdr"> </td> <td class="tdl"> 0.3648</td> - <td class="tdl"> 133,100</td> <td class="tdl"> 402.8</td> - <td class="tdr">2.482 </td> <td class="tdr">.07780 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">0 </td> <td class="tdl"> 0.340</td> - <td class="tdl"> 115,600</td> <td class="tdl"> 349.9</td> - <td class="tdr">2.858 </td> <td class="tdr">.08957 </td> - </tr><tr> - <td class="tdr">0 </td> - <td class="tdr"> </td> <td class="tdl"> 0.3249</td> - <td class="tdl"> 105,500</td> <td class="tdl"> 319.5</td> - <td class="tdr">3.130 </td> <td class="tdr">.09811 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">1 </td> <td class="tdl"> 0.3000</td> - <td class="tdl"> 90,000</td> <td class="tdl"> 272.4</td> - <td class="tdr">3.671 </td> <td class="tdr">.1150 </td> - </tr><tr> - <td class="tdr">1 </td> - <td class="tdr"> </td> <td class="tdl"> 0.2893</td> - <td class="tdl"> 83,690</td> <td class="tdl"> 253.3</td> - <td class="tdr">3.947 </td> <td class="tdr">.1237 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">2 </td> <td class="tdl"> 0.2840</td> - <td class="tdl"> 80,660</td> <td class="tdl"> 244.1</td> - <td class="tdr">4.096 </td> <td class="tdr">.1284 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">3 </td> <td class="tdl"> 0.2590</td> - <td class="tdl"> 67,080</td> <td class="tdl"> 203.1</td> - <td class="tdr">4.925 </td> <td class="tdr">.1543 </td> - </tr><tr> - <td class="tdr">2 </td> - <td class="tdr"> </td> <td class="tdl"> 0.2576</td> - <td class="tdl"> 66,370</td> <td class="tdl"> 200.9</td> - <td class="tdr">4.977 </td> <td class="tdr">.1560 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">4 </td> <td class="tdl"> 0.2380</td> - <td class="tdl"> 56,640</td> <td class="tdl"> 171.5</td> - <td class="tdr">5.832 </td> <td class="tdr">.1828 </td> - </tr><tr> - <td class="tdr">3 </td> - <td class="tdr"> </td> <td class="tdl"> 0.2294</td> - <td class="tdl"> 52,630</td> <td class="tdl"> 159.3</td> - <td class="tdr">6.276 </td> <td class="tdr">.1967 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">5 </td> <td class="tdl"> 0.2200</td> - <td class="tdl"> 48,400</td> <td class="tdl"> 146.5</td> - <td class="tdr">6.826 </td> <td class="tdr">.2139 </td> - </tr><tr> - <td class="tdr">4 <span class="pagenum"><a name="Page_1908" id="Page_1908">1908</a></span></td> - <td class="tdr"> </td> <td class="tdl"> 0.2043</td> - <td class="tdl"> 41,740</td> <td class="tdl"> 126.4</td> - <td class="tdr">7.914 </td> <td class="tdr">.2480 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">6 </td> <td class="tdl"> 0.2030</td> - <td class="tdl"> 41,210</td> <td class="tdl"> 124.7</td> - <td class="tdr">8.017 </td> <td class="tdr">.2513 </td> - </tr><tr> - <td class="tdr">5 </td> - <td class="tdr"> </td> <td class="tdl"> 0.1819</td> - <td class="tdl"> 33,100</td> <td class="tdl"> 100.2</td> - <td class="tdr">9.98  </td> <td class="tdr">.3128 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">7 </td> <td class="tdl"> 0.1800</td> - <td class="tdl"> 32,400</td> <td class="tdl"> 98.08</td> - <td class="tdr">10.20  </td> <td class="tdr">.3196 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">8 </td> <td class="tdl"> 0.1650</td> - <td class="tdl"> 27,230</td> <td class="tdl"> 82.41</td> - <td class="tdr">12.13  </td> <td class="tdr">.3803 </td> - </tr><tr> - <td class="tdr">6 </td> - <td class="tdr"> </td> <td class="tdl"> 0.1620</td> - <td class="tdl"> 26,250</td> <td class="tdl"> 79.46</td> - <td class="tdr">12.58  </td> <td class="tdr">.3944 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">9 </td> <td class="tdl"> 0.1480</td> - <td class="tdl"> 21,900</td> <td class="tdl"> 66.30</td> - <td class="tdr">15.08  </td> <td class="tdr">.4727 </td> - </tr><tr> - <td class="tdr">7 </td> - <td class="tdr"> </td> <td class="tdl"> 0.1443</td> - <td class="tdl"> 20,820</td> <td class="tdl"> 63.02</td> - <td class="tdr">15.87  </td> <td class="tdr">.4973 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">10 </td> <td class="tdl"> 0.1340</td> - <td class="tdl"> 17,960</td> <td class="tdl"> 54.35</td> - <td class="tdr">18.40  </td> <td class="tdr">.5766 </td> - </tr><tr> - <td class="tdr">8 </td> - <td class="tdr"> </td> <td class="tdl"> 0.1285</td> - <td class="tdl"> 16,510</td> <td class="tdl"> 49.98</td> - <td class="tdr">20.01  </td> <td class="tdr">.6271 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">11 </td> <td class="tdl"> 0.1200</td> - <td class="tdl"> 14,400</td> <td class="tdl"> 43.59</td> - <td class="tdr">22.94  </td> <td class="tdr">.7190 </td> - </tr><tr> - <td class="tdr">9 </td> - <td class="tdr"> </td> <td class="tdl"> 0.1144</td> - <td class="tdl"> 13,090</td> <td class="tdl"> 39.63</td> - <td class="tdr">25.23  </td> <td class="tdr">.7908 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">12 </td> <td class="tdl"> 0.1090</td> - <td class="tdl"> 11,880</td> <td class="tdl"> 35.96</td> - <td class="tdr">27.81  </td> <td class="tdr">.8715 </td> - </tr><tr> - <td class="tdr">10 </td> - <td class="tdr"> </td> <td class="tdl"> 0.1019</td> - <td class="tdl"> 10,380</td> <td class="tdl"> 31.43</td> - <td class="tdr">31.82  </td> <td class="tdr">.9972 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">13 </td> <td class="tdl"> 0.0950</td> - <td class="tdl">  9,025</td> <td class="tdl"> 27.32</td> - <td class="tdr">36.60  </td> <td class="tdr">1.147 </td> - </tr><tr> - <td class="tdr">11 </td> - <td class="tdr"> </td> <td class="tdl"> 0.09074</td> - <td class="tdl">  8,234</td> <td class="tdl"> 24.93</td> - <td class="tdr">40.12  </td> <td class="tdr">1.257 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">14 </td> <td class="tdl"> 0.08300</td> - <td class="tdl">  6,889</td> <td class="tdl"> 20.85</td> - <td class="tdr">47.95  </td> <td class="tdr">1.503 </td> - </tr><tr> - <td class="tdr">12 </td> - <td class="tdr"> </td> <td class="tdl"> 0.08081</td> - <td class="tdl">  6,530</td> <td class="tdl"> 19.77</td> - <td class="tdr">50.59  </td> <td class="tdr">1.586 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">15 </td> <td class="tdl"> 0.07200</td> - <td class="tdl">  5,184</td> <td class="tdl"> 15.69</td> - <td class="tdr">63.73  </td> <td class="tdr">1.997 </td> - </tr><tr> - <td class="tdr">13 </td> - <td class="tdr"> </td> <td class="tdl"> 0.07196</td> - <td class="tdl">  5,178</td> <td class="tdl"> 15.68</td> - <td class="tdr">63.79  </td> <td class="tdr">1.999 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">16 </td> <td class="tdl"> 0.06500</td> - <td class="tdl">  4,225</td> <td class="tdl"> 12.79</td> - <td class="tdr">78.19  </td> <td class="tdr">2.451 </td> - </tr><tr> - <td class="tdr">14 </td> - <td class="tdr"> </td> <td class="tdl"> 0.06408</td> - <td class="tdl">  4,107</td> <td class="tdl"> 12.43</td> - <td class="tdr">80.44  </td> <td class="tdr">2.521 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">17 </td> <td class="tdl"> 0.0580</td> - <td class="tdl">  3,364</td> <td class="tdl"> 10.18</td> - <td class="tdr">98.23  </td> <td class="tdr">3.078 </td> - </tr><tr> - <td class="tdr">15 </td> - <td class="tdr"> </td> <td class="tdl"> 0.05707</td> - <td class="tdl">  3,257</td> <td class="tdl"> 9.858</td> - <td class="tdr">101.4  </td> <td class="tdr">3.179 </td> - </tr><tr> - <td class="tdr">16 </td> - <td class="tdr"> </td> <td class="tdl"> 0.05082</td> - <td class="tdl">  2,583</td> <td class="tdl"> 7.818</td> - <td class="tdr">127.9  </td> <td class="tdr">4.009 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">18 </td> <td class="tdl"> 0.04900</td> - <td class="tdl">  2,401</td> <td class="tdl"> 7.268</td> - <td class="tdr">137.6  </td> <td class="tdr">4.312 </td> - </tr><tr> - <td class="tdr">17 </td> - <td class="tdr"> </td> <td class="tdl"> 0.045260</td> - <td class="tdl">  2,048</td> <td class="tdl"> 6.200</td> - <td class="tdr">161.3  </td> <td class="tdr">5.055 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">19 </td> <td class="tdl"> 0.042000</td> - <td class="tdl">  1,764</td> <td class="tdl"> 5.340</td> - <td class="tdr">187.3  </td> <td class="tdr">5.870 </td> - </tr><tr> - <td class="tdr">18 </td> - <td class="tdr"> </td> <td class="tdl"> 0.040300</td> - <td class="tdl">  1,624</td> <td class="tdl"> 4.917</td> - <td class="tdr">203.4  </td> <td class="tdr">6.374 </td> - </tr><tr> - <td class="tdr">19 </td> - <td class="tdr"> </td> <td class="tdl"> 0.035890</td> - <td class="tdl">  1,288</td> <td class="tdl"> 3.899</td> - <td class="tdr">256.5  </td> <td class="tdr">8.038 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">20 </td> <td class="tdl"> 0.035000</td> - <td class="tdl">  1,225</td> <td class="tdl"> 3.708</td> - <td class="tdr">269.7  </td> <td class="tdr">8.452 </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">21 </td> <td class="tdl"> 0.032000</td> - <td class="tdl">  1,024</td> <td class="tdl"> 3.100</td> - <td class="tdr">322.6  </td> <td class="tdr">10.11  </td> - </tr><tr> - <td class="tdr">20 </td> - <td class="tdr"> </td> <td class="tdl"> 0.031960</td> - <td class="tdl">  1,022</td> <td class="tdl"> 3.092</td> - <td class="tdr">323.4  </td> <td class="tdr">10.14  </td> - </tr><tr> - <td class="tdr">21 </td> - <td class="tdr"> </td> <td class="tdl"> 0.028460</td> - <td class="tdl">  810.1</td> <td class="tdl"> 2.452</td> - <td class="tdr">407.8  </td> <td class="tdr">12.78  </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">22 </td> <td class="tdl"> 0.028000</td> - <td class="tdl">  784.0</td> <td class="tdl"> 2.373</td> - <td class="tdr">421.4  </td> <td class="tdr">13.21  </td> - </tr><tr> - <td class="tdr">22 </td> - <td class="tdr"> </td> <td class="tdl"> 0.025350</td> - <td class="tdl">  642.4</td> <td class="tdl"> 1.945</td> - <td class="tdr">514.2  </td> <td class="tdr">16.12  </td> - </tr><tr> - <td class="tdr"><span class="pagenum"><a name="Page_1909" id="Page_1909">1909</a></span></td> - <td class="tdr">23 </td> <td class="tdl"> 0.025000</td> - <td class="tdl">  625.0</td> <td class="tdl"> 1.892</td> - <td class="tdr">528.6  </td> <td class="tdr">16.57  </td> - </tr><tr> - <td class="tdr">23 </td> - <td class="tdr"> </td> <td class="tdl"> 0.022570</td> - <td class="tdl">  509.5</td> <td class="tdl"> 1.542</td> - <td class="tdr">648.4  </td> <td class="tdr">20.32  </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">24 </td> <td class="tdl"> 0.022000</td> - <td class="tdl">  484.0</td> <td class="tdl"> 1.465</td> - <td class="tdr">682.6  </td> <td class="tdr">21.39  </td> - </tr><tr> - <td class="tdr">24 </td> - <td class="tdr"> </td> <td class="tdl"> 0.020100</td> - <td class="tdl">  404.0</td> <td class="tdl"> 1.223</td> - <td class="tdr">817.6  </td> <td class="tdr">25.63  </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">25 </td> <td class="tdl"> 0.020000</td> - <td class="tdl">  400.0</td> <td class="tdl"> 1.211</td> - <td class="tdr">825.9  </td> <td class="tdr">25.88  </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">26 </td> <td class="tdl"> 0.018000</td> - <td class="tdl">  324.0</td> <td class="tdl">  .9808</td> - <td class="tdr"> 1,020  </td> <td class="tdr">31.96  </td> - </tr><tr> - <td class="tdr">25 </td> - <td class="tdr"> </td> <td class="tdl"> 0.017900</td> - <td class="tdl">  320.4</td> <td class="tdl">  .9699</td> - <td class="tdr">1,031  </td> <td class="tdr">32.31  </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">27 </td> <td class="tdl"> 0.016000</td> - <td class="tdl">  256.0</td> <td class="tdl">  .7749</td> - <td class="tdr">1,290  </td> <td class="tdr">40.45  </td> - </tr><tr> - <td class="tdr">26 </td> - <td class="tdr"> </td> <td class="tdl"> 0.015940</td> - <td class="tdl">  254.1</td> <td class="tdl">  .7692</td> - <td class="tdr">1,300  </td> <td class="tdr">40.75  </td> - </tr><tr> - <td class="tdr">27 </td> - <td class="tdr"> </td> <td class="tdl"> 0.014200</td> - <td class="tdl">  201.5</td> <td class="tdl">  .6100</td> - <td class="tdr">1,639  </td> <td class="tdr">51.38  </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">28 </td> <td class="tdl"> 0.014000</td> - <td class="tdl">  196.0</td> <td class="tdl">  .5933</td> - <td class="tdr">1,685  </td> <td class="tdr">52.83  </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">29 </td> <td class="tdl"> 0.013000</td> - <td class="tdl">  169.0</td> <td class="tdl">  .5116</td> - <td class="tdr">1,955  </td> <td class="tdr">61.27  </td> - </tr><tr> - <td class="tdr">28 </td> - <td class="tdr"> </td> <td class="tdl"> 0.012640</td> - <td class="tdl">  159.8</td> <td class="tdl">  .4837</td> - <td class="tdr">2,067  </td> <td class="tdr">64.79  </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">30 </td> <td class="tdl"> 0.012000</td> - <td class="tdl">  144.0</td> <td class="tdl">  .4359</td> - <td class="tdr">2,294  </td> <td class="tdr">71.90  </td> - </tr><tr> - <td class="tdr">29 </td> - <td class="tdr"> </td> <td class="tdl"> 0.011260</td> - <td class="tdl">  126.7</td> <td class="tdl">  .3836</td> - <td class="tdr">2,607  </td> <td class="tdr">81.70  </td> - </tr><tr> - <td class="tdr">30 </td> - <td class="tdr"> </td> <td class="tdl"> 0.010030</td> - <td class="tdl">  100.5</td> <td class="tdl">  .3042</td> - <td class="tdr">3,287  </td> <td class="tdr">103.0  </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">31 </td> <td class="tdl"> 0.010000</td> - <td class="tdl">  100.0</td> <td class="tdl">  .3027</td> - <td class="tdr">3,304  </td> <td class="tdr">103.5  </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">32 </td> <td class="tdl"> 0.009000</td> - <td class="tdl">  81.0</td> <td class="tdl">  .2452</td> - <td class="tdr">4,078  </td> <td class="tdr">127.8  </td> - </tr><tr> - <td class="tdr">31 </td> - <td class="tdr"> </td> <td class="tdl"> 0.008928</td> - <td class="tdl">  79.70</td> <td class="tdl">  .2413</td> - <td class="tdr">4,145  </td> <td class="tdr">129.9  </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">33 </td> <td class="tdl"> 0.008000</td> - <td class="tdl">  64.0</td> <td class="tdl">  .1937</td> - <td class="tdr">5,162  </td> <td class="tdr">161.8  </td> - </tr><tr> - <td class="tdr">32 </td> - <td class="tdr"> </td> <td class="tdl"> 0.007950</td> - <td class="tdl">  63.21</td> <td class="tdl">  .1913</td> - <td class="tdr">5,227  </td> <td class="tdr">163.8  </td> - </tr><tr> - <td class="tdr">33 </td> - <td class="tdr"> </td> <td class="tdl"> 0.007080</td> - <td class="tdl">  50.13</td> <td class="tdl">  .1517</td> - <td class="tdr">6,591  </td> <td class="tdr">206.6  </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">34 </td> <td class="tdl"> 0.007000</td> - <td class="tdl">  49.0</td> <td class="tdl">  .1483</td> - <td class="tdr">6,742  </td> <td class="tdr">211.3  </td> - </tr><tr> - <td class="tdr">34 </td> - <td class="tdr"> </td> <td class="tdl"> 0.006305</td> - <td class="tdl">  39.75</td> <td class="tdl">  .1203</td> - <td class="tdr">8,311  </td> <td class="tdr">260.5  </td> - </tr><tr> - <td class="tdr">35 </td> - <td class="tdr"> </td> <td class="tdl"> 0.005615</td> - <td class="tdl">  31.52</td> <td class="tdl">  .09543</td> - <td class="tdr">10,480  </td> <td class="tdr">328.4  </td> - </tr><tr> - <td class="tdr">36 </td> - <td class="tdr">35 </td> <td class="tdl"> 0.005000</td> - <td class="tdl">  25.0</td> <td class="tdl">  .07568</td> - <td class="tdr">13,210  </td> <td class="tdr">414.2  </td> - </tr><tr> - <td class="tdr">37 </td> - <td class="tdr"> </td> <td class="tdl"> 0.004453</td> - <td class="tdl">  19.83</td> <td class="tdl">  .06001</td> - <td class="tdr">16,660  </td> <td class="tdr">522.2  </td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdr">36 </td> <td class="tdl"> 0.004000</td> - <td class="tdl">  16.</td> <td class="tdl">  .04843</td> - <td class="tdr">20,650  </td> <td class="tdr">647.1  </td> - </tr><tr> - <td class="tdr">38 </td> - <td class="tdr"> </td> <td class="tdl"> 0.003965</td> - <td class="tdl">  15.72</td> <td class="tdl">  .04759</td> - <td class="tdr">21,010  </td> <td class="tdr">658.5  </td> - </tr><tr> - <td class="tdr">39 </td> - <td class="tdr"> </td> <td class="tdl"> 0.003531</td> - <td class="tdl">  12.47</td> <td class="tdl">  .03774</td> - <td class="tdr">26,500  </td> <td class="tdr">830.4  </td> - </tr><tr> - <td class="tdr">40 </td> - <td class="tdr"> </td> <td class="tdl"> 0.003145</td> - <td class="tdl">   9.888</td> <td class="tdl">  .02993</td> - <td class="tdr">33,410  </td> <td class="tdr">1047.  </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>—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"> </td> - <td class="tdl">  % loss × volts</td> - </tr><tr> - <td class="tdr">drop =</td> - <td class="tdc"> —————— × S   (1)</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdl">   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. & 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"> 1" </td> <td class="tdc"> 3" </td> <td class="tdc"> 6" </td> - <td class="tdc">12"</td> <td class="tdc">24"</td> <td class="tdc"> 1" </td> - <td class="tdc"> 3" </td> <td class="tdc"> 6" </td> <td class="tdc">12"</td> - <td class="tdc">24"</td> - </tr><tr> - <td class="tdr">500,000 </td> <td class="tdr">500,000 </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 </td> <td class="tdr">300,000 </td> <td class="tdc"> 1.15 </td> - <td class="tdc"> 1.29 </td> <td class="tdc"> 1.38 </td> <td class="tdc"> 1.48 </td> - <td class="tdc"> 1.57 </td> <td class="tdc"> 1.19 </td> <td class="tdc"> 1.47 </td> - <td class="tdc"> 1.66 </td> <td class="tdc"> 1.84 </td> <td class="tdc"> 2.02 </td> - </tr><tr> - <td class="tdr">0,000 </td> <td class="tdr">211,600 </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 </td> <td class="tdr">167,800 </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 </td> <td class="tdr">133,100 </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 </td> <td class="tdr">105,500 </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 </td> <td class="tdr">83,690 </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 </td> <td class="tdr">66,370 </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 </td> <td class="tdr u">52,630 </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} </td> <td class="tdr">41,740 </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} </td> <td class="tdr">33,100 </td> - </tr><tr> - <td class="tdr">6} </td> <td class="tdr">26,250 </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"} </td> <td class="tdr">20,820 </td> - </tr><tr> - <td class="tdr">8} </td> <td class="tdr">16,510 </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} </td> <td class="tdr">13,090 </td> - </tr><tr> - <td class="tdr">10} </td> <td class="tdr">10,380 </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. & 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"> 1" </td> <td class="tdc"> 3" </td> <td class="tdc"> 6" </td> - <td class="tdc">12"</td> <td class="tdc">24"</td> <td class="tdc"> 1" </td> - <td class="tdc"> 3" </td> <td class="tdc"> 6" </td> <td class="tdc">12"</td> - <td class="tdc">24"</td> - </tr><tr> - <td class="tdr">500,000 </td> <td class="tdr">500,000 </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 </td> <td class="tdr">300,000 </td> <td class="tdc"> 1.11 </td> - <td class="tdc"> 1.46 </td> <td class="tdc"> 1.68 </td> <td class="tdc"> 1.90 </td> - <td class="tdc"> 2.12 </td> <td class="tdc"> 1.00 </td> <td class="tdc"> 1.33 </td> - <td class="tdc"> 1.56 </td> <td class="tdc"> 1.78 </td> <td class="tdc"> 2.01 </td> - </tr><tr> - <td class="tdr">0,000 </td> <td class="tdr">211,600 </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 </td> <td class="tdr">167,800 </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 </td> <td class="tdr">133,100 </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 </td> <td class="tdr">105,500 </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 </td> <td class="tdr">83,690 </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 </td> <td class="tdr">66,370 </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 </td> <td class="tdr u">52,630 </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} </td> <td class="tdr">41,740 </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} </td> <td class="tdr">33,100 </td> - </tr><tr> - <td class="tdr">6} </td> <td class="tdr">26,250 </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} </td> <td class="tdr">20,820 </td> - </tr><tr> - <td class="tdr">8} </td> <td class="tdr">16,510 </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} </td> <td class="tdr">13,090 </td> - </tr><tr> - <td class="tdr">10} </td> <td class="tdr">10,380 </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. & 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"> 1" </td> <td class="tdc"> 3" </td> <td class="tdc"> 6" </td> - <td class="tdc">12"</td> <td class="tdc">24"</td> <td class="tdc"> 1" </td> - <td class="tdc"> 3" </td> <td class="tdc"> 6" </td> <td class="tdc">12"</td> - <td class="tdc">24"</td> - </tr><tr> - <td class="tdr">500,000 </td> <td class="tdr">500,000 </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 </td> <td class="tdr">300,000 </td> <td class="tdc"> 1.04 </td> - <td class="tdc"> 1.10 </td> <td class="tdc"> 1.13 </td> <td class="tdc"> 1.18 </td> - <td class="tdc"> 1.21 </td> <td class="tdc"> 1.00 </td> <td class="tdc"> 1.08 </td> - <td class="tdc"> 1.16 </td> <td class="tdc"> 1.25 </td> <td class="tdc"> 1.31 </td> - </tr><tr> - <td class="tdr">0,000 </td> <td class="tdr">211,600 </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 </td> <td class="tdr">167,800 </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 </td> <td class="tdr">133,100 </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 </td> <td class="tdr u">105,500 </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 </td> <td class="tdr">83,690 </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 </td> <td class="tdr">66,370 </td> - </tr><tr class="u"> - <td class="tdr">3 </td> <td class="tdr">52,630 </td> - </tr><tr> - <td class="tdr">4}</td> <td class="tdr">41,740 </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 </td> - </tr><tr class="u"> - <td class="tdr">6}</td> <td class="tdr">26,250 </td> - </tr><tr> - <td class="tdr">7}</td> <td class="tdr">20,820 </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 </td> - </tr><tr> - <td class="tdr">9}</td> <td class="tdr">13,090 </td> - </tr><tr> - <td class="tdr">10}</td> <td class="tdr">10,380 </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. & 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"> 1" </td> <td class="tdc"> 3" </td> <td class="tdc"> 6" </td> - <td class="tdc">12"</td> <td class="tdc">24"</td> <td class="tdc"> 1" </td> - <td class="tdc"> 3" </td> <td class="tdc"> 6" </td> <td class="tdc">12"</td> - <td class="tdc">24"</td> - </tr><tr> - <td class="tdr">500,000 </td> <td class="tdr">500,000 </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 </td> <td class="tdr">300,000 </td> <td class="tdc"> 1.00 </td> - <td class="tdc"> 1.00 </td> <td class="tdc"> 1.09 </td> <td class="tdc"> 1.16 </td> - <td class="tdc"> 1.25 </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"> 1.12 </td> - </tr><tr> - <td class="tdr">0,000 </td> <td class="tdr">211,600 </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 </td> <td class="tdr">167,800 </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 </td> <td class="tdr">133,100 </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 </td> <td class="tdr u">105,500 </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 </td> <td class="tdr">83,690 </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 </td> <td class="tdr">66,370 </td> - </tr><tr> - <td class="tdr u">3 </td> <td class="tdr u">52,630 </td> - </tr><tr> - <td class="tdr">4} </td> <td class="tdr">41,740 </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 </td> - </tr><tr> - <td class="tdr u">6} </td> <td class="tdr u">26,250 </td> - </tr><tr> - <td class="tdr">7} </td> <td class="tdr">20,820 </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 </td> - </tr><tr> - <td class="tdr">9} </td> <td class="tdr">13,090 </td> - </tr><tr> - <td class="tdr">10} </td> <td class="tdr">10,380 </td> - </tr> - </tbody> -</table> - -<div class="blockquot"> <p class="space-above2">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?</p> - -<p>According to the formula</p></div> - -<table border="0" cellspacing="2" summary="_" cellpadding="0"> - <tbody><tr> - <td class="tdr"> </td> - <td class="tdl">  % loss × volts</td> - </tr><tr> - <td class="tdr">drop =</td> - <td class="tdc"> —————— × S</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdl">   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"> </td> - <td class="tdl">  5 × 440</td> - </tr><tr> - <td class="tdr">drop =</td> - <td class="tdc"> ————— × 1 = 22 volts</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdl">   100</td> - </tr> - </tbody> -</table> - -<p><b>Current</b>.—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"> </td> - <td class="tdl">  apparent load</td> - </tr><tr> - <td class="tdr">current =</td> - <td class="tdc"> ———————  (1)</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdl">   volts</td> - </tr> - </tbody> -</table> -<p>  and</p> -<table border="0" cellspacing="2" summary="_" cellpadding="0"> - <tbody><tr> - <td class="tdr"> </td> - <td class="tdl">  watts</td> - </tr><tr> - <td class="tdr">apparent load =</td> - <td class="tdc"> —————  (2)</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdl"> 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"> </td> - <td class="tdc">watts</td> - <td class="tdc"> </td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc"> —————</td> - <td class="tdc"> </td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">power factor</td> - <td class="tdc">watts</td> - </tr><tr> - <td class="tdc">current =</td> - <td class="tdc">  ——————— =</td> - <td class="tdc">  ————————— (3)</td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">volts</td> - <td class="tdc"> 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.—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.—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"> </td> - <td class="tdc">brake horse power</td> - <td class="tdl"> 50</td> - </tr><tr> - <td class="tdc">E.H.P. =</td> - <td class="tdc"> ———————— =</td> - <td class="tdc">—— = 55.5</td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">efficiency</td> - <td class="tdl"> .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"> </td> - <td class="tdc">actual load</td> - <td class="tdl"> 41,403</td> - </tr><tr> - <td class="tdc">apparent load =</td> - <td class="tdc"> —————— =</td> - <td class="tdc"> ———— = 51,754</td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">power factor</td> - <td class="tdl">  .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"> </td> - </tr><tr> - <td class="tdc">——————— =</td> - <td class="tdc">————— =</td> - <td class="tdc">117.6 amperes</td> - </tr><tr> - <td class="tdc">volts</td> - <td class="tdc">440</td> - <td class="tdc"> </td> - </tr> - </tbody> -</table> - -<p class="blockquot">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: <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"> </td> - <td class="tdc">brake horse power</td> - <td class="tdl">  50</td> - </tr><tr> - <td class="tdc">E. H. P. =</td> - <td class="tdc"> ————————— × </td> - <td class="tdc"> —— = 54.3</td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">efficiency</td> - <td class="tdl"> .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 </td> <td class="tdc"> 2 No. 0 </td> - <td class="tdc"> 4 No. 3 </td> <td class="tdc"> 8 No. 6 </td> - <td class="tdc">16 No. 9</td> <td class="tdc"> 32 No. 12 </td> - <td class="tdc">64 No. 15</td> - </tr><tr> - <td class="tdr">000 </td> <td class="tdc">2 " 1</td> - <td class="tdc">4 " 4</td> <td class="tdc">8 " 7</td> - <td class="tdc"> 16 " 10 </td> <td class="tdc">32 " 13</td> - <td class="tdc">64 " 16</td> - </tr><tr> - <td class="tdr">00 </td> <td class="tdc">2 " 2</td> - <td class="tdc">4 " 5</td> <td class="tdc">8 " 8</td> - <td class="tdc">16 " 11</td> <td class="tdc">32 " 14</td> - <td class="tdc">64 " 17</td> - </tr><tr> - <td class="tdr">0 </td> <td class="tdc">2 " 3</td> - <td class="tdc">4 " 6</td> <td class="tdc">8 " 9</td> - <td class="tdc">16 " 12</td> <td class="tdc">32 " 15</td> - <td class="tdc">64 " 18</td> - </tr><tr> - <td class="tdr">1 </td> <td class="tdc">2 " 4</td> - <td class="tdc">4 " 7</td> <td class="tdc">8 " 10</td> - <td class="tdc">16 " 13</td> <td class="tdc">32 " 16</td> - <td class="tdc">64 " 19</td> - </tr><tr> - <td class="tdr">2 </td> <td class="tdc">2 " 5</td> - <td class="tdc">4 " 8</td> <td class="tdc">8 " 11</td> - <td class="tdc">16 " 14</td> <td class="tdc">32 " 17</td> - <td class="tdc">64 " 20</td> - </tr><tr> - <td class="tdr">3 </td> <td class="tdc">2 " 6</td> - <td class="tdc">4 " 9</td> <td class="tdc">8 " 12</td> - <td class="tdc">16 " 15</td> <td class="tdc">32 " 18</td> - <td class="tdc">64 " 21</td> - </tr><tr> - <td class="tdr">4 </td> <td class="tdc">2 " 7</td> - <td class="tdc">4 " 10</td> <td class="tdc">8 " 13</td> - <td class="tdc">16 " 16</td> <td class="tdc">32 " 19</td> - <td class="tdc">64 " 22</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">5 </td> <td class="tdc">2 " 8</td> - <td class="tdc">4 " 11</td> <td class="tdc">8 " 14</td> - <td class="tdc">16 " 17</td> <td class="tdc">32 " 20</td> - <td class="tdc">64 " 23</td> - </tr><tr> - <td class="tdr">6 </td> <td class="tdc">2 " 9</td> - <td class="tdc">4 " 12</td> <td class="tdc">8 " 15</td> - <td class="tdc">16 " 18</td> <td class="tdc">32 " 21</td> - <td class="tdc">64 " 24</td> - </tr><tr> - <td class="tdr">7 </td> <td class="tdc">2 " 10</td> - <td class="tdc">4 " 13</td> <td class="tdc">8 " 16</td> - <td class="tdc">16 " 19</td> <td class="tdc">32 " 22</td> - <td class="tdc">64 " 25</td> - </tr><tr> - <td class="tdr">8 </td> <td class="tdc">2 " 11</td> - <td class="tdc">4 " 14</td> <td class="tdc">8 " 17</td> - <td class="tdc">16 " 20</td> <td class="tdc">32 " 23</td> - <td class="tdc">64 " 26</td> - </tr><tr> - <td class="tdr">9 </td> <td class="tdc">2 " 12</td> - <td class="tdc">4 " 15</td> <td class="tdc">8 " 18</td> - <td class="tdc">16 " 21</td> <td class="tdc">32 " 24</td> - <td class="tdc">64 " 27</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">10 </td> <td class="tdc">2 " 13</td> - <td class="tdc">4 " 16</td> <td class="tdc">8 " 19</td> - <td class="tdc">16 " 22</td> <td class="tdc">32 " 25</td> - <td class="tdc">64 " 28</td> - </tr><tr> - <td class="tdr">11 </td> <td class="tdc">2 " 14</td> - <td class="tdc">4 " 17</td> <td class="tdc">8 " 20</td> - <td class="tdc">16 " 23</td> <td class="tdc">32 " 26</td> - <td class="tdc">64 " 29</td> - </tr><tr> - <td class="tdr">12 </td> <td class="tdc">2 " 15</td> - <td class="tdc">4 " 18</td> <td class="tdc">8 " 21</td> - <td class="tdc">16 " 24</td> <td class="tdc">32 " 27</td> - <td class="tdc">64 " 30</td> - </tr><tr> - <td class="tdr">13 </td> <td class="tdc">2 " 16</td> - <td class="tdc">4 " 19</td> <td class="tdc">8 " 22</td> - <td class="tdc">16 " 25</td> <td class="tdc">32 " 28</td> - <td class="tdc">—</td> - </tr><tr> - <td class="tdr">14 </td> <td class="tdc">2 " 17</td> - <td class="tdc">4 " 20</td> <td class="tdc">8 " 23</td> - <td class="tdc">16 " 26</td> <td class="tdc">32 " 29</td> - <td class="tdc">—</td> - </tr><tr class="tr_lt_grey"> - <td class="tdr">15 </td> <td class="tdc">2 " 18</td> - <td class="tdc">4 " 21</td> <td class="tdc">8 " 24</td> - <td class="tdc">16 " 27</td> <td class="tdc">32 " 30</td> - <td class="tdc">—</td> - </tr><tr> - <td class="tdr">16 </td> <td class="tdc">2 " 19</td> - <td class="tdc">4 " 22</td> <td class="tdc">8 " 25</td> - <td class="tdc">16 " 28</td> <td class="tdc">—</td> - <td class="tdc">—</td> - </tr><tr> - <td class="tdr">17 </td> <td class="tdc">2 " 20</td> - <td class="tdc">4 " 23</td> <td class="tdc">8 " 26</td> - <td class="tdc">16 " 29</td> <td class="tdc">—</td> - <td class="tdc">—</td> - </tr><tr> - <td class="tdr">18 </td> <td class="tdc">2 " 21</td> - <td class="tdc">4 " 24</td> <td class="tdc">8 " 27</td> - <td class="tdc">16 " 30</td> <td class="tdc">—</td> - <td class="tdc">—</td> - </tr><tr> - <td class="tdr">19 </td> <td class="tdc">2 " 22</td> - <td class="tdc">4 " 25</td> <td class="tdc">8 " 28</td> - <td class="tdc">—</td> <td class="tdc">—</td> - <td class="tdc">—</td> - </tr><tr> - <td class="tdr">20 </td> <td class="tdc">2 " 23</td> - <td class="tdc">4 " 26</td> <td class="tdc">8 " 29</td> - <td class="tdc">—</td> <td class="tdc">—</td> - <td class="tdc">—</td> - </tr><tr> - <td class="tdr">21 </td> <td class="tdc">2 " 24</td> - <td class="tdc">4 " 27</td> <td class="tdc">8 " 30</td> - <td class="tdc">—</td> <td class="tdc">—</td> - <td class="tdc">—</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"> </td> - <td class="tdc">actual load or watts</td> - <td class="tdc">40,508</td> - <td class="tdc"> </td> - </tr><tr> - <td class="tdc">apparent load or kva =</td> - <td class="tdc"> ————————— = </td> - <td class="tdc"> ———— = </td> - <td class="tdc"> 50,635</td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">power factor</td> - <td class="tdc">.8</td> - <td class="tdc"> </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"> </td> - <td class="tdc">apparent load or kva</td> - <td class="tdc">50,635</td> - <td class="tdc"> </td> - </tr><tr> - <td class="tdc">current =</td> - <td class="tdc"> ————————— = </td> - <td class="tdc"> ———— = </td> - <td class="tdc"> 115 amperes</td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">volts</td> - <td class="tdc">440</td> - <td class="tdc"> </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"> </td> - <td class="tdc">watts × feet × M</td> - <td class="tdc">40,508 × 1,000 × 3,380</td> - <td class="tdc"> </td> - </tr><tr> - <td class="tdc">cir. mils =</td> - <td class="tdc"> ————————— = </td> - <td class="tdc">—————————— = </td> - <td class="tdc"> 141,443</td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">% loss × volts<sup>2</sup></td> - <td class="tdc">5 × 440<sup>2</sup></td> - <td class="tdc"> </td> - </tr> - </tbody> -</table> - -<p>From table page 1,907, nearest size <i>larger</i> wire is No. 00 B. & S. gauge.</p> - -<p><b>F.</b> <i>Drop</i></p> -<table border="0" cellspacing="2" summary="_" cellpadding="0"> - <tbody><tr> - <td class="tdc"> </td> - <td class="tdl"> % loss × volts</td> - <td class="tdl"> 5 × 440</td> - <td class="tdc"> </td> - </tr><tr> - <td class="tdc">drop =</td> - <td class="tdc"> ——————— × S = </td> - <td class="tdc">———— × 1.17 = </td> - <td class="tdc"> 25.74 volts</td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdl">   100</td> - <td class="tdl"> 100</td> - <td class="tdc"> </td> - </tr> - </tbody> -</table> - -<p class="blockquot">NOTE.—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">  1. Central stations;<br /> -  2. Sub-stations;<br />  3. Isolated plants.</p> - -<p class="no-indent">These may also be classified with respect to their function as</p> - -<p class="no-indent">  1. Generating stations;<br /> -  2. Distributing stations;<br />  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">  1. Steam electric;<br /> -  2. Hydro-electric;<br />  3. Gas electric, etc.</p> - -<p><b>Central Stations.</b>—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">  1. Alternating current stations;<br /> -  2. Direct current stations;<br />  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.—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>—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.—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.—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.—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.—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.—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.—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.—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.—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.—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>—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.—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.—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.—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>—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.—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.—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.—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.—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"> </td> - <td class="tdc">H - <i>h</i></td> - <td class="tdl"> </td> - </tr><tr> - <td class="tdc">factor of evaporation =</td> - <td class="tdc"> ———</td> - <td class="tdc">  (1)</td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">965.7</td> - <td class="tdl"> </td> - - </tr> - </tbody> -</table> - -<p class="no-indent">in which<br /><br /> -  H = total heat of steam at the observed pressure;<br /><br /> -  <i>h</i> = total heat of feed water of the observed temperature;<br /><br /> -  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"> </td> - <td class="tdc">1,197 - 118</td> - <td class="tdl"> </td> - </tr><tr> - <td class="tdc">factor of evaporation =</td> - <td class="tdc"> —————— =</td> - <td class="tdc"> 1.117</td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdc">965.7</td> - <td class="tdl"> </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  </td> <td class="tdc"> 1.214 </td> - <td class="tdc"> 1.216 </td> <td class="tdc"> 1.220 </td> - <td class="tdc"> 1.222 </td> <td class="tdc"> 1.225 </td> - <td class="tdc"> 1.227 </td> <td class="tdc"> 1.229 </td> - <td class="tdc"> 1.231 </td> <td class="tdc"> 1.232 </td> - </tr><tr> - <td class="tdr">40  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </td> <td class="tdc"> 1.234 </td> - <td class="tdc"> 1.236 </td> <td class="tdc"> 1.237 </td> - <td class="tdc"> 1.239 </td> <td class="tdc"> 1.240 </td> - <td class="tdc"> 1.241 </td> <td class="tdc"> 1.243 </td> - <td class="tdc"> 1.244 </td> <td class="tdc"> 1.245 </td> - </tr><tr> - <td class="tdr">40  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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  </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"> </td> - </tr><tr> - <td class="tdr">32  </td> <td class="tdc"> 1.246 </td> - <td class="tdc"> 1.247 </td> <td class="tdc"> 1.248 </td> - <td class="tdc"> 1.250 </td> <td class="tdc"> 1.251 </td> - <td class="tdc"> 1.252 </td> <td class="tdc"> 1.253 </td> - <td class="tdc"> 1.254 </td> <td class="tdc">    </td> - </tr><tr> - <td class="tdr">40  </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"> </td> - </tr><tr> - <td class="tdr">50  </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"> </td> - </tr><tr> - <td class="tdr">60  </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"> </td> - </tr><tr> - <td class="tdr">70  </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"> </td> - </tr><tr> - <td class="tdr">80  </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"> </td> - </tr><tr> - <td class="tdr">90  </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"> </td> - </tr><tr> - <td class="tdr">100  </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"> </td> - </tr><tr> - <td class="tdr">110  </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"> </td> - </tr><tr> - <td class="tdr">120  </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"> </td> - </tr><tr> - <td class="tdr">130  </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"> </td> - </tr><tr> - <td class="tdr">140  </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"> </td> - </tr><tr> - <td class="tdr">150  </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"> </td> - </tr><tr> - <td class="tdr">160  </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"> </td> - </tr><tr> - <td class="tdr">170  </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"> </td> - </tr><tr> - <td class="tdr">180  </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"> </td> - </tr><tr> - <td class="tdr">190  </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"> </td> - </tr><tr> - <td class="tdr">200  </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"> </td> - </tr><tr> - <td class="tdr">210  </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"> </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"> </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"> Pounds of coal burned per square foot of grate per hour </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 </td> - <td class="tdl"> 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"> 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 </td> - <td class="tdl"><br /> 8.61</td> - <td class="tdc"><br />4.  </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"> 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"> 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 </td> - <td class="tdl"><br /> 6.9</td> - <td class="tdc"><br />5.  </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"> 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"> 5</td> - <td class="tdc">6.9 </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 </td> <td class="tdl"><br /> 3.45</td> - <td class="tdc"><br />10.  </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>—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"> </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">  Pressure of steam in boiler, lbs. per sq. inch above atmosphere  </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° </td> <td class="tdc"> .0872 </td> - <td class="tdc"> .0861 </td> <td class="tdc"> .0855 </td> - <td class="tdc"> .0851 </td> <td class="tdc"> .0847 </td> - <td class="tdc"> .0844 </td> <td class="tdc"> .0841 </td> - <td class="tdc"> .0839 </td> <td class="tdc"> .0837 </td> - <td class="tdc"> .0835 </td> <td class="tdc"> .0833 </td> - <td class="tdr">32 </td> - </tr><tr> - <td class="tdr">40 </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 </td> - </tr><tr> - <td class="tdr">50 </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 </td> - </tr><tr> - <td class="tdr">60 </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 </td> - </tr><tr> - <td class="tdr">70 </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 </td> - </tr><tr> - <td class="tdr">80 </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 </td> - </tr><tr> - <td class="tdr">90 </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 </td> - </tr><tr> - <td class="tdr">100 </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 </td> - </tr><tr> - <td class="tdr">110 </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 </td> - </tr><tr> - <td class="tdr">120 </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 </td> - </tr><tr> - <td class="tdr">130 </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 </td> - </tr><tr> - <td class="tdr">140 </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 </td> - </tr><tr> - <td class="tdr">150 </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 </td> - </tr><tr> - <td class="tdr">160 </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 </td> - </tr><tr> - <td class="tdr">170 </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 </td> - </tr><tr> - <td class="tdr">180 </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 </td> - </tr><tr> - <td class="tdr">190 </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 </td> - </tr><tr> - <td class="tdr">200 </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 </td> - </tr><tr> - <td class="tdr">210 </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 </td> - </tr><tr> - <td class="tdr">220 </td> <td class="tdc">—</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 </td> - </tr><tr> - <td class="tdr">230 </td> <td class="tdc">—</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 </td> - </tr><tr> - <td class="tdr">240 </td> <td class="tdc">—</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 </td> - </tr><tr> - <td class="tdr">250 </td> <td class="tdc">—</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 </td> - </tr> - </tbody> -</table> - -<p class="blockquot"> -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 = <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.—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.—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.—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.—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.—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.—"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.—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.—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.—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.—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.—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>—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>—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.—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.</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.—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>—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.—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>.—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.—One form of roof construction.</p></div> - -<p><b>Floors.</b>—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, °F.</td> - <td colspan="11" class="tdc u"> TEMP. OF EXTERNAL AIR. (BAROMETER 30 INCHES) </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"> .453 </td> - <td class="tdc"> .419 </td> <td class="tdc"> .384 </td> - <td class="tdc"> .353 </td> <td class="tdc"> .321 </td> - <td class="tdc"> .292 </td> <td class="tdc"> .263 </td> - <td class="tdc"> .234 </td> <td class="tdc"> .209 </td> - <td class="tdc"> .182 </td> <td class="tdc"> .157 </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>—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.—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.—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.—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.—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.—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.—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>.—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.—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.—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 /> -   1. Impulse;<br /> -   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.—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.—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 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.</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.—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.—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.—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.</p></div> - -<div class="blockquot"> -<p>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.</p> - -<p>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.</p> - -<p>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.</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.—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.—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.—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.—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 /> inches </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>  </td> <td class="tdr">.00 </td> - <td class="tdr">.01 </td> <td class="tdr">.05 </td> - <td class="tdr">.09 </td> <td class="tdr">.14 </td> - <td class="tdr">.19 </td> <td class="tdr">.26 </td> - <td class="tdr">.32 </td> - </tr><tr> - <td class="tdr"><b>1</b>  </td> <td class="tdr">.40 </td> - <td class="tdr">.47 </td> <td class="tdr">.55 </td> - <td class="tdr">.64 </td> <td class="tdr">.73 </td> - <td class="tdr">.82 </td> <td class="tdr">.92 </td> - <td class="tdr">1.02 </td> - </tr><tr> - <td class="tdr"><b>2</b>  </td> <td class="tdr">1.13 </td> - <td class="tdr">1.23 </td> <td class="tdr">1.35 </td> - <td class="tdr">1.36 </td> <td class="tdr">1.58 </td> - <td class="tdr">1.70 </td> <td class="tdr">1.82 </td> - <td class="tdr">1.95 </td> - </tr><tr> - <td class="tdr"><b>3</b>  </td> <td class="tdr">2.07 </td> - <td class="tdr">2.21 </td> <td class="tdr">2.34 </td> - <td class="tdr">2.48 </td> <td class="tdr">2.61 </td> - <td class="tdr">2.76 </td> <td class="tdr">2.90 </td> - <td class="tdr">3.05 </td> - </tr><tr> - <td class="tdr"><b>4</b>  </td> <td class="tdr">3.20 </td> - <td class="tdr">3.35 </td> <td class="tdr">3.50 </td> - <td class="tdr">3.66 </td> <td class="tdr">3.81 </td> - <td class="tdr">3.97 </td> <td class="tdr">4.14 </td> - <td class="tdr">4.30 </td> - </tr><tr> - <td class="tdr"><b>5</b>  </td> <td class="tdr">4.47 </td> - <td class="tdr">4.64 </td> <td class="tdr">4.81 </td> - <td class="tdr">4.98 </td> <td class="tdr">5.15 </td> - <td class="tdr">5.33 </td> <td class="tdr">5.51 </td> - <td class="tdr">5.69 </td> - </tr><tr> - <td class="tdr"><b>6</b>  </td> <td class="tdr">5.87 </td> - <td class="tdr">6.06 </td> <td class="tdr">6.25 </td> - <td class="tdr">6.44 </td> <td class="tdr">6.62 </td> - <td class="tdr">6.82 </td> <td class="tdr">7.01 </td> - <td class="tdr">7.21 </td> - </tr><tr> - <td class="tdr"><b>7</b>  </td> <td class="tdr">7.40 </td> - <td class="tdr">7.60 </td> <td class="tdr">7.80 </td> - <td class="tdr">8.01 </td> <td class="tdr">8.21 </td> - <td class="tdr">8.42 </td> <td class="tdr">8.63 </td> - <td class="tdr">8.83 </td> - </tr><tr> - <td class="tdr"><b>8</b>  </td> <td class="tdr">9.05 </td> - <td class="tdr">9.26 </td> <td class="tdr">9.47 </td> - <td class="tdr">9.69 </td> <td class="tdr">9.91 </td> - <td class="tdr">10.13 </td> <td class="tdr">10.35 </td> - <td class="tdr">10.57 </td> - </tr><tr> - <td class="tdr"><b>9</b>  </td> <td class="tdr"> 10.80 </td> - <td class="tdr"> 11.02 </td> <td class="tdr"> 11.25 </td> - <td class="tdr"> 11.48 </td> <td class="tdr"> 11.71 </td> - <td class="tdr"> 11.94 </td> <td class="tdr"> 12.17 </td> - <td class="tdr"> 12.41 </td> - </tr><tr> - <td class="tdr"><b>10</b>  </td> <td class="tdr">12.64 </td> - <td class="tdr">12.88 </td> <td class="tdr">13.12 </td> - <td class="tdr">13.36 </td> <td class="tdr">13.60 </td> - <td class="tdr">13.85 </td> <td class="tdr">14.09 </td> - <td class="tdr">14.34 </td> - </tr><tr> - <td class="tdr"><b>11</b>  </td> <td class="tdr">14.59 </td> - <td class="tdr">14.84 </td> <td class="tdr">15.09 </td> - <td class="tdr">15.34 </td> <td class="tdr">15.59 </td> - <td class="tdr">15.85 </td> <td class="tdr">16.11 </td> - <td class="tdr">16.36 </td> - </tr><tr> - <td class="tdr"><b>12</b>  </td> <td class="tdr">16.62 </td> - <td class="tdr">16.88 </td> <td class="tdr">17.15 </td> - <td class="tdr">17.41 </td> <td class="tdr">17.67 </td> - <td class="tdr">17.94 </td> <td class="tdr">18.21 </td> - <td class="tdr">18.47 </td> - </tr><tr> - <td class="tdr"><b>13</b>  </td> <td class="tdr">18.74 </td> - <td class="tdr">19.01 </td> <td class="tdr">19.29 </td> - <td class="tdr">19.56 </td> <td class="tdr">19.84 </td> - <td class="tdr">20.11 </td> <td class="tdr">20.39 </td> - <td class="tdr">20.67 </td> - </tr><tr> - <td class="tdr"><b>14</b>  </td> <td class="tdr">20.95 </td> - <td class="tdr">21.23 </td> <td class="tdr">21.51 </td> - <td class="tdr">21.80 </td> <td class="tdr">22.08 </td> - <td class="tdr">22.37 </td> <td class="tdr">22.65 </td> - <td class="tdr">22.94 </td> - </tr><tr> - <td class="tdr"><b>15</b>  </td> <td class="tdr">23.23 </td> - <td class="tdr">23.52 </td> <td class="tdr">23.82 </td> - <td class="tdr">24.11 </td> <td class="tdr">24.40 </td> - <td class="tdr">24.70 </td> <td class="tdr">25.00 </td> - <td class="tdr">25.30 </td> - </tr><tr> - <td class="tdr"><b>16</b>  </td> <td class="tdr">25.60 </td> - <td class="tdr">25.90 </td> <td class="tdr">26.20 </td> - <td class="tdr">26.50 </td> <td class="tdr">26.80 </td> - <td class="tdr">27.11 </td> <td class="tdr">27.42 </td> - <td class="tdr">27.72 </td> - </tr><tr> - <td class="tdr"><b>17</b>  </td> <td class="tdr">28.03 </td> - <td class="tdr">28.34 </td> <td class="tdr">28.65 </td> - <td class="tdr">28.97 </td> <td class="tdr">29.28 </td> - <td class="tdr">29.59 </td> <td class="tdr">29.91 </td> - <td class="tdr">30.22 </td> - </tr><tr> - <td class="tdr"><b>18</b>  </td> <td class="tdr">30.54 </td> - <td class="tdr">30.86 </td> <td class="tdr">31.18 </td> - <td class="tdr">31.50 </td> <td class="tdr">31.82 </td> - <td class="tdr">32.15 </td> <td class="tdr">32.47 </td> - <td class="tdr">32.80 </td> - </tr><tr> - <td class="tdr"><b>19</b>  </td> <td class="tdr">33.12 </td> - <td class="tdr">33.45 </td> <td class="tdr">33.78 </td> - <td class="tdr">34.11 </td> <td class="tdr">34.44 </td> - <td class="tdr">34.77 </td> <td class="tdr">35.10 </td> - <td class="tdr">35.44 </td> - </tr><tr> - <td class="tdr"><b>20</b>  </td> <td class="tdr">35.77 </td> - <td class="tdr">36.11 </td> <td class="tdr">36.45 </td> - <td class="tdr">36.78 </td> <td class="tdr">37.12 </td> - <td class="tdr">37.46 </td> <td class="tdr">37.80 </td> - <td class="tdr">38.15 </td> - </tr> - </tbody> -</table> - -<p class="blockquot"> -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.</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.—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.—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>—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.—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 /> -   1. Impulse turbines;<br /> -   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.—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.—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.—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>—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>—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>—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>—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>—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>—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>—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>—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>—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>—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>—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>—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>—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>—Westinghouse 300 kw. converter in -portable sub-station.</p></div> - -<p><b>Portable Sub-Stations.</b>—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>—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.—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"> -   1. Selection;<br /> -   2. Location;<br /> -   3. Erection;<br /> -   4. Testing;<br /> -   5. Running;<br /> -   6. Care;<br /> -   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>—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"> -   1. Type;<br /> -   2. Capacity;<br /> -   3. Efficiency;<br /> -   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>⁄<sub>10</sub> and -<sup>1</sup>⁄<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>—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>—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"> -   1. Quality;<br /> -   2. Range;<br /> -   3. Accessibility;<br /> -   4. Proportion;<br /> -   5. Lubrication;<br /> -   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.—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"> Nominal <br />internal.</td> <td class="tdc">Actual<br /> external. </td> - <td class="tdc">Actual<br /> internal. </td> <td class="tdc"> </td> - <td class="tdc"> External. </td> <td class="tdc"> Internal. </td> - <td class="tdc"> External. </td> <td class="tdc"> Internal. </td> - <td class="tdc"> Metal. </td> - </tr><tr class="tr_grey"> - <td class="tdc">Inches</td> <td class="tdc">Inches</td> - <td class="tdc">Inches</td> <td class="tdc"> Inches </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 </td> <td class="tdr">.405 </td> - <td class="tdr">.27  </td> <td class="tdc">.068</td> - <td class="tdr">1.272 </td> <td class="tdr">.848 </td> - <td class="tdr">.129 </td> <td class="tdr">.0573 </td> - <td class="tdr">.0717</td> - </tr><tr> - <td class="tdr">¼ </td> <td class="tdr">.54  </td> - <td class="tdr">.364 </td> <td class="tdc">.088</td> - <td class="tdr">1.696 </td> <td class="tdr">1.144 </td> - <td class="tdr">.229 </td> <td class="tdr">.1041 </td> - <td class="tdr">.1249</td> - </tr><tr> - <td class="tdr">⅜ </td> <td class="tdr">.675 </td> - <td class="tdr">.494 </td> <td class="tdc">.091</td> - <td class="tdr">2.121 </td> <td class="tdr">1.552 </td> - <td class="tdr">.358 </td> <td class="tdr">.1917 </td> - <td class="tdr">.1663</td> - </tr><tr> - <td class="tdr">½ </td> <td class="tdr">.84  </td> - <td class="tdr">.623 </td> <td class="tdc">.109</td> - <td class="tdr">2.639 </td> <td class="tdr">1.957 </td> - <td class="tdr">.554 </td> <td class="tdr">.3048 </td> - <td class="tdr">.2492</td> - </tr><tr> - <td class="tdr">¾ </td> <td class="tdr">1.05  </td> - <td class="tdr">.824 </td> <td class="tdc">.113</td> - <td class="tdr">3.299 </td> <td class="tdr">2.589 </td> - <td class="tdr">.866 </td> <td class="tdr">.5333 </td> - <td class="tdr">.3327</td> - </tr><tr> - <td class="tdr">1  </td> <td class="tdr">1.315 </td> - <td class="tdr">1.048 </td> <td class="tdc">.134</td> - <td class="tdr">4.131 </td> <td class="tdr">3.292 </td> - <td class="tdr">1.358 </td> <td class="tdr">.8626 </td> - <td class="tdr">.4954</td> - </tr><tr> - <td class="tdr">1¼ </td> <td class="tdr">1.66  </td> - <td class="tdr">1.38  </td> <td class="tdc"> .14 </td> - <td class="tdr">5.215 </td> <td class="tdr">4.335 </td> - <td class="tdr">2.164 </td> <td class="tdr">1.496 </td> - <td class="tdr">.668 </td> - </tr><tr> - <td class="tdr">1½ </td> <td class="tdr">1.9  </td> - <td class="tdr">1.611 </td> <td class="tdc">.145</td> - <td class="tdr">5.969 </td> <td class="tdr">5.061 </td> - <td class="tdr">2.835 </td> <td class="tdr">2.038 </td> - <td class="tdr">.797 </td> - </tr><tr> - <td class="tdr">2  </td> <td class="tdr">2.375 </td> - <td class="tdr">2.067 </td> <td class="tdc">.154</td> - <td class="tdr">7.461 </td> <td class="tdr">6.494 </td> - <td class="tdr">4.43  </td> <td class="tdr">3.356 </td> - <td class="tdr">1.074 </td> - </tr><tr> - <td class="tdr">2½ </td> <td class="tdr">2.875 </td> - <td class="tdr">2.468 </td> <td class="tdc">.204</td> - <td class="tdr">9.032 </td> <td class="tdr">7.753 </td> - <td class="tdr">6.492 </td> <td class="tdr">4.784 </td> - <td class="tdr">1.708 </td> - </tr><tr> - <td class="tdr">3  </td> <td class="tdr">3.5  </td> - <td class="tdr">3.067 </td> <td class="tdc">.217</td> - <td class="tdr">10.996 </td> <td class="tdr">9.636 </td> - <td class="tdr">9.621 </td> <td class="tdr">7.388 </td> - <td class="tdr">2.243 </td> - </tr><tr> - <td class="tdr">3½ </td> <td class="tdr">4.   </td> - <td class="tdr">3.548 </td> <td class="tdc">.226</td> - <td class="tdr">12.566 </td> <td class="tdr">11.146 </td> - <td class="tdr">12.566 </td> <td class="tdr">9.887 </td> - <td class="tdr">2.679 </td> - </tr><tr> - <td class="tdr">4  </td> <td class="tdr">4.5  </td> - <td class="tdr">4.026 </td> <td class="tdc">.237</td> - <td class="tdr">14.137 </td> <td class="tdr">12.648 </td> - <td class="tdr">15.904 </td> <td class="tdr">12.73 </td> - <td class="tdr">3.174 </td> - </tr><tr> - <td class="tdr">4½ </td> <td class="tdr">5.   </td> - <td class="tdr">4.508 </td> <td class="tdc">.246</td> - <td class="tdr">15.708 </td> <td class="tdr">14.162 </td> - <td class="tdr">19.635 </td> <td class="tdr">15.961 </td> - <td class="tdr">3.674 </td> - </tr><tr> - <td class="tdr">5  </td> <td class="tdr">5.563 </td> - <td class="tdr">5.045 </td> <td class="tdc">.259</td> - <td class="tdr">17.477 </td> <td class="tdr">15.849 </td> - <td class="tdr">24.306 </td> <td class="tdr">19.99  </td> - <td class="tdr">4.316 </td> - </tr><tr> - <td class="tdr">6  </td> <td class="tdr">6.625 </td> - <td class="tdr">6.065 </td> <td class="tdc">.28 </td> - <td class="tdr">20.813 </td> <td class="tdr">19.054 </td> - <td class="tdr">34.472 </td> <td class="tdr">28.888 </td> - <td class="tdr">5.584 </td> - </tr><tr> - <td class="tdr">7  </td> <td class="tdr">7.625 </td> - <td class="tdr">7.023 </td> <td class="tdc">.301</td> - <td class="tdr">23.955 </td> <td class="tdr">22.063 </td> - <td class="tdr">45.664 </td> <td class="tdr">38.738 </td> - <td class="tdr">6.926 </td> - </tr><tr> - <td class="tdr">8  </td> <td class="tdr">8.625 </td> - <td class="tdr">7.982 </td> <td class="tdc">.322</td> - <td class="tdr">27.096 </td> <td class="tdr">25.076 </td> - <td class="tdr">58.426 </td> <td class="tdr">50.04  </td> - <td class="tdr">8.386 </td> - </tr><tr> - <td class="tdr">9  </td> <td class="tdr">9.625 </td> - <td class="tdr">8.937 </td> <td class="tdc">.344</td> - <td class="tdr">30.238 </td> <td class="tdr">28.076 </td> - <td class="tdr">72.76 </td> <td class="tdr">62.73  </td> - <td class="tdr">10.03  </td> - </tr><tr> - <td class="tdr">10  </td> <td class="tdr">10.75 </td> - <td class="tdr">10.019 </td> <td class="tdc">.366</td> - <td class="tdr">33.772 </td> <td class="tdr">31.477 </td> - <td class="tdr">90.763 </td> <td class="tdr">78.839 </td> - <td class="tdr">11.924 </td> - </tr><tr> - <td class="tdr">11  </td> <td class="tdr">12.   </td> - <td class="tdr">11.25 </td> <td class="tdc">.375</td> - <td class="tdr">37.699 </td> <td class="tdr">35.343 </td> - <td class="tdr">113.098 </td> <td class="tdr">99.402 </td> - <td class="tdr">13.696 </td> - </tr><tr> - <td class="tdr">12  </td> <td class="tdr">12.75 </td> - <td class="tdr">12.   </td> <td class="tdc">.375</td> - <td class="tdr">40.055 </td> <td class="tdr">37.7  </td> - <td class="tdr">127.677 </td> <td class="tdr">113.098 </td> - <td class="tdr"> 14.579 </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 /> containing <br />one cubic<br />foot.</td> - <td rowspan="2" class="tdc"> Nominal <br />weight<br />per foot.</td> - <td rowspan="2" class="tdc"> Number of <br />threads<br />per inch.</td> - </tr><tr class="tr_lt_grey"> - <td class="tdc"> Nominal <br />internal.</td> - <td class="tdc"> External <br />surface</td> <td class="tdc"> Internal <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"> </td> - </tr><tr> - <td class="tdr">⅛ </td> <td class="tdr">9.44 </td> - <td class="tdr">14.15  </td> <td class="tdl"> 2513.</td> - <td class="tdr">.241 </td> <td class="tdl"> 27</td> - </tr><tr> - <td class="tdr">¼ </td> <td class="tdr">7.075 </td> - <td class="tdr">10.49  </td> <td class="tdl"> 1383.3</td> - <td class="tdr">.42 </td> <td class="tdl"> 18</td> - </tr><tr> - <td class="tdr">⅜ </td> <td class="tdr">5.657 </td> - <td class="tdr">7.73  </td> <td class="tdl"> 751.2</td> - <td class="tdr">.559 </td> <td class="tdl"> 18</td> - </tr><tr> - <td class="tdr">½ </td> <td class="tdr">4.547 </td> - <td class="tdr">6.13  </td> <td class="tdl"> 472.4</td> - <td class="tdr">.837 </td> <td class="tdl"> 14</td> - </tr><tr> - <td class="tdr">¾ </td> <td class="tdr">3.637 </td> - <td class="tdr">4.635 </td> <td class="tdl"> 270.</td> - <td class="tdr">1.115 </td> <td class="tdl"> 14</td> - </tr><tr> - <td class="tdr">1  </td> <td class="tdr">2.904 </td> - <td class="tdr">3.645 </td> <td class="tdl"> 166.9</td> - <td class="tdr">1.668 </td> <td class="tdl"> 11½</td> - </tr><tr> - <td class="tdr">1¼ </td> <td class="tdr">2.301 </td> - <td class="tdr">2.768 </td> <td class="tdl">  96.25</td> - <td class="tdr">2.244 </td> <td class="tdl"> 11½</td> - </tr><tr> - <td class="tdr">1½ </td> <td class="tdr">2.01 </td> - <td class="tdr">2.371 </td> <td class="tdl">  70.66</td> - <td class="tdr">2.678 </td> <td class="tdl"> 11½</td> - </tr><tr> - <td class="tdr">2  </td> <td class="tdr">1.608 </td> - <td class="tdr">1.848 </td> <td class="tdl">  42.91</td> - <td class="tdr">3.609 </td> <td class="tdl"> 11½</td> - </tr><tr> - <td class="tdr">2½ </td> <td class="tdr">1.328 </td> - <td class="tdr">1.547 </td> <td class="tdl">  30.1</td> - <td class="tdr">5.739 </td> <td class="tdl">  8</td> - </tr><tr> - <td class="tdr">3  </td> <td class="tdr">1.091 </td> - <td class="tdr">1.245 </td> <td class="tdl">  19.5</td> - <td class="tdr">7.536 </td> <td class="tdl">  8</td> - </tr><tr> - <td class="tdr">3½ </td> <td class="tdr">.955 </td> - <td class="tdr">1.077 </td> <td class="tdl">  14.57</td> - <td class="tdr">9.001 </td> <td class="tdl">  8</td> - </tr><tr> - <td class="tdr">4  </td> <td class="tdr">.849 </td> - <td class="tdr">.949 </td> <td class="tdl">  11.31</td> - <td class="tdr">10.665 </td> <td class="tdl">  8</td> - </tr><tr> - <td class="tdr">4½ </td> <td class="tdr">.764 </td> - <td class="tdr">.848 </td> <td class="tdl">  9.02</td> - <td class="tdr">12.34 </td> <td class="tdl">  8</td> - </tr><tr> - <td class="tdr">5  </td> <td class="tdr">.687 </td> - <td class="tdr">.757 </td> <td class="tdl">  7.2</td> - <td class="tdr">14.502 </td> <td class="tdl">  8</td> - </tr><tr> - <td class="tdr">6  </td> <td class="tdr">.577 </td> - <td class="tdr">.63 </td> <td class="tdl">  4.98</td> - <td class="tdr">18.762 </td> <td class="tdl">  8</td> - </tr><tr> - <td class="tdr">7  </td> <td class="tdr">.501 </td> - <td class="tdr">.544 </td> <td class="tdl">  3.72</td> - <td class="tdr">23.271 </td> <td class="tdl">  8</td> - </tr><tr> - <td class="tdr">8  </td> <td class="tdr">.443 </td> - <td class="tdr">.478 </td> <td class="tdl">  2.88</td> - <td class="tdr">28.177 </td> <td class="tdl">  8</td> - </tr><tr> - <td class="tdr">9  </td> <td class="tdr">.397 </td> - <td class="tdr">.427 </td> <td class="tdl">  2.29</td> - <td class="tdr">33.701 </td> <td class="tdl">  8</td> - </tr><tr> - <td class="tdr">10  </td> <td class="tdr">.355 </td> - <td class="tdr">.382 </td> <td class="tdl">  1.82</td> - <td class="tdr">40.065 </td> <td class="tdl">  8</td> - </tr><tr> - <td class="tdr">11  </td> <td class="tdr">.318 </td> - <td class="tdr">.339 </td> <td class="tdl">  1.450</td> - <td class="tdr">45.95 </td> <td class="tdl">  8</td> - </tr><tr> - <td class="tdr">12  </td> <td class="tdr">.299 </td> - <td class="tdr">.319 </td> <td class="tdl">  1.27</td> - <td class="tdr">48.985 </td> <td class="tdl">  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.—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>—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.—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.—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.—Cross section of electrical -station showing small traveling crane.</p></div> - -<p><b>Installation.</b>—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.—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.—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.—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.—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.—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>—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>—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>—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>—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.—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>—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>—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>—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.—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>—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.—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.—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.—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>—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.—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—single, light -double, and heavy double—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.—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>—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.—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.—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—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.—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.—Method of joining adjacent -switchboard panels.</p></div> - -<p><b>Switchboards.</b>—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.—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.—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.—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.—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.—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 <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—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.—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.—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.—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.—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.—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.—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>—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.—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.—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>—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.—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"> -   1. The frequencies of both machines be the same;<br /> -   2. The machines must be in synchronism;<br /> -   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.—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.—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.—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.—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.—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.—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.—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.—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>—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.—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.</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>—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.—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.—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>—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"> </td> - <td class="tdl">   5w</td> - </tr><tr> - <td class="tdr">E = </td> - <td class="tdl">——————</td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdl">24c + 5r + 5w</td> - </tr><tr> - <td class="tdr">where   </td> - <td class="tdc"> </td> - </tr><tr> - <td class="tdr">E = </td> - <td class="tdl"> the all day efficiency of the transformer,</td> - </tr><tr> - <td class="tdr">w = </td> - <td class="tdl"> the full load in watts on the primary,</td> - </tr><tr> - <td class="tdr">c = </td> - <td class="tdl"> the core loss in watts,</td> - </tr><tr> - <td class="tdr">r = </td> - <td class="tdl"> 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.—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.—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.—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.—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.—<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.—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.—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.—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>—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.—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>—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.—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.—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>—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.—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.—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.—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.—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.</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.—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.—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.—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.—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.—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.—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.—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"> Power factor </td> - <td class="tdc"> True watts </td> - <td class="tdc"> Error </td> - <td class="tdc"> Error of indication <br />in per cent<br />of true value</td> - </tr><tr> - <td class="tdc">1. </td> - <td class="tdc">1,000 </td> - <td class="tdr">.3 </td> - <td class="tdc">0.03</td> - </tr><tr> - <td class="tdc">.9</td> - <td class="tdc">900</td> - <td class="tdr">7.6 </td> - <td class="tdc">0.85</td> - </tr><tr> - <td class="tdc">.8</td> - <td class="tdc">800</td> - <td class="tdr">10.5 </td> - <td class="tdc">1.31</td> - </tr><tr> - <td class="tdc">.7</td> - <td class="tdc">700</td> - <td class="tdr">12.5 </td> - <td class="tdc">1.78</td> - </tr><tr> - <td class="tdc">.6</td> - <td class="tdc">600</td> - <td class="tdr">13.9 </td> - <td class="tdc">2.32</td> - </tr><tr> - <td class="tdc">.5</td> - <td class="tdc">500</td> - <td class="tdr">15.1 </td> - <td class="tdc">3.02</td> - </tr><tr> - <td class="tdc">.4</td> - <td class="tdc">400</td> - <td class="tdr">15.9 </td> - <td class="tdc">3.98</td> - </tr><tr> - <td class="tdc">.3</td> - <td class="tdc">300</td> - <td class="tdr">16.6 </td> - <td class="tdc">5.54</td> - </tr><tr> - <td class="tdc">.2</td> - <td class="tdc">200</td> - <td class="tdr">17.1 </td> - <td class="tdc">8.55</td> - </tr><tr> - <td class="tdc">.1</td> - <td class="tdc">100</td> - <td class="tdr">17.3 </td> - <td class="tdc">17.30 </td> - </tr> - </tbody> -</table> - -<p class="blockquot"> -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. -<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.—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.—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.—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.—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.—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.—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.—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>—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.—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.—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.—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.—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.—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.—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.—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.—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.—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.—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.—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.—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.—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.—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.—<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.—<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.—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.—<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.—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.—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.—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.—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.—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.—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 /> standard meter </td> - <td class="tdc"> Readings on <br />meter tested</td> - <td class="tdc">Constant</td> - </tr><tr> - <td class="tdc">150</td> - <td class="tdr">149.2 </td> - <td class="tdr"> 150 ÷ 149.2 = 1.005</td> - </tr><tr> - <td class="tdc">125</td> - <td class="tdr">125.0 </td> - <td class="tdr">125 ÷ 125.0 = 1.000</td> - </tr><tr> - <td class="tdc">100</td> - <td class="tdr">98.9 </td> - <td class="tdr">100 ÷ 98.9 = 1.011</td> - </tr><tr> - <td class="tdc"> 75</td> - <td class="tdr">73.6 </td> - <td class="tdr">75 ÷ 73.6 = 1.019</td> - </tr><tr> - <td class="tdc"> 50</td> - <td class="tdr">50.0 </td> - <td class="tdr">50 ÷ 50.0 = 1.000</td> - </tr><tr> - <td class="tdc"> 25</td> - <td class="tdr">24.8 </td> - <td class="tdr u">25 ÷ 24.8 = 1.008</td> - </tr><tr> - <td class="tdc"> </td> - <td class="tdr"> </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.—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.—<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.—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.—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>—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.—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.—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.—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"> </td> - <td class="tdc">2π L W R</td> - <td class="tdl"> </td> - </tr><tr> - <td class="tdr">input in brake horse power = </td> - <td class="tdc">——————</td> - <td class="tdl">   (1)</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdc">33,000</td> - <td class="tdl"> </td> - </tr> - </tbody> -</table> - -<p class="no-indent">in which<br /> -   L = length of Prony brake lever;<br /> -   W = pounds pull at end of lever;<br /> -   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"> </td> - <td class="tdc">amperes × volts</td> - <td class="tdl"> </td> - </tr><tr> - <td class="tdr">output in electrical horse power = </td> - <td class="tdc">————————</td> - <td class="tdl">   (2)</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdc">746</td> - <td class="tdl"> </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"> </td> - <td class="tdc">output</td> - <td class="tdl"> </td> - </tr><tr> - <td class="tdr">commercial efficiency = </td> - <td class="tdc">————</td> - <td class="tdl">   (3)</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdc">input</td> - <td class="tdl"> </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"> -   1. Mechanical.<br /> -   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.—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.—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.</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"> -  H = the power lost in hysteresis at rated speed,<br /> -  E = the power lost in eddy currents at rated speed,<br /> -  T = the power lost in hysteresis and eddy currents at rated speed,<br /> -  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"> </td> - <td class="tdl"> H  E</td> - </tr><tr> - <td class="tdr">T = H + E, and S = </td> - <td class="tdl">— + —,</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdl"> 2  2</td> - </tr> - </tbody> -</table> - -<div class="blockquot"> -<p class="no-indent">from which the elimination of H will give <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 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       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 & Co., Publishers</b>.</big></p> - -<p class="author space-below1"><b>72 FIFTH AVENUE,</b><br /> -<b>NEW YORK. </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. </td> - <td class="tdc"> Pressure </td> - <td class="tdc"> Old Value </td> - <td class="tdc"> New Value</td> - </tr><tr> - <td class="tdc">130</td> <td class="tdc"> 40</td> - <td class="tdc">.0954</td> <td class="tdc">.0934</td> - </tr><tr> - <td class="tdc">200</td> <td class="tdc"> 40</td> - <td class="tdc">.0900</td> <td class="tdc">.0999</td> - </tr><tr> - <td class="tdc">210</td> <td class="tdc"> 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> |