Identifier: electricengineer03inte (find matches)
Title: (Electric engineering.)
Year: 1902 (1900s)
Authors: International Library of Technology
Subjects: Electrical engineering
Publisher: Scranton, International Textbook Co.
Contributing Library: UMass Amherst Libraries
Digitizing Sponsor: Boston Library Consortium Member Libraries

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st toa limited extent for the operation of synchronous motors.The ordinary single-phase synchronous motor, i. e., a motorconstructed in the same way as an alternator, will not startup even if it is not loaded; it has to be brought up to speedfrom some outside source; this is a great drawback to its use,and the single-phase system is now seldom, if ever, installedwhere power is to be transmitted for the operation of alterna-ting-current motors of large size. The motor M shown inFig. 15 is the same in construction as an alternator, but itwould have to be provided with some arrangement forbringing it up to speed. This could be done by means of asmall single-phase induction motor or by using the exciterof the synchronous motor, running it as a motor from stor-age batteries. This difficulty of getting single-phase syn-chronous motors started has kept them from being used toany great extent, and even in those places where they wereinstalled, they are being replaced by multiphase synchronous
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§ 14 ELECTRIC TRANSMISSION. 51 motors, which will run up to speed of their own accordwhen not loaded. If the amount of power required is not large, say under10 horsepower, special self-starting single-phase synchronousmotors may be used. Induction motors are also made tooperate on single-phase circuits by using special startingdevices, but in general it may be stated that the single-phasesystem is not well adapted for motor operation, at least notin those cases Avhere large motors are required. TWO-PHASE POWER TRANSMISSION. 64. A two-phase alternator delivers two currents differ-ing in phase by 90°, so that when the current in one phaseis at its maximum value, the current in the other phase is atzero. The great advantage of the tAvo-phase system overthe single-phase is that it allows the operation of rotary-field induction motors and two-phase synchronous motors.Two-phase induction motors will start up under full load.The synchronous motors will not start up under load, butthey will

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