File:A textbook on electric lighting and railways. International correspondence schools, Scranton, Pa. v. 1-3, 5 (1901) (14738343586).jpg

Identifier: textbookonelectr03inte (find matches)
Title: A textbook on electric lighting and railways. International correspondence schools, Scranton, Pa. v. 1-3, 5
Year: 1901 (1900s)
Authors: International Correspondence Schools
Subjects: Electric engineering Electric lighting Electric railroads
Publisher: Scranton, International Textbook co.
Contributing Library: Northeastern University, Snell Library
Digitizing Sponsor: Northeastern University, Snell Library

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is providedwith two windings, a series and a shunt, as indicated in thefigure. The brush holders, of which there are as many setsas there are poles, are carried by the frame A A, which isfitted into the field casting so that it may be revolved througha small arc by turning the wheel B, thus allowing thebrushes to be adjusted to the point on the commutatorthat gives the least amount of sparking. Alternate sets ofbrushes connect to the rings A, A, and to these rings themain armature cables 1\ T are attached. 37. Fig. 13 (a) and (b) gives two views of a typicalarmature for a direct-driven railway generator. It will benoticed that the construction is very substantial and thatthe commutator A is of ample proportions. The conductorson the armature are in the shape of rectangular copper bars,which are sunk into slots in the i)eriphcry of the iron core.The ends of these bars, seen projecting at a, a on the com-mutator end, are connected to the ccnnmutator bars by the 30 ELECTRIC RAILWAYS. 20
Text Appearing After Image:
§20 ELECTRIC RAILWAYS. 31 strips h, b. The laminated iron core on which the con-ductors are carried is mounted on the heavy spider Z>,which is keyed to the engine shaft. In these large multi-polar armatures there are a number of paths in parallel;i. c., when the current enters at one side, it has the choiceof several parallel paths through the armature. If theE. M. F.s generated in these armature sections, as theymight be called, were all exactly equal, the currents flowingin the dififerent parts of the armature would also be equal.It is very difficult to have the magnetic field exactly equalall around the armature, because some of the poles may beslightly closer to the armature than are others, due to wearin the bearings or other causes. This causes the E. M. F.sin some parts of the armature to overbalance those in otherparts, giving rise to local currents that may cause the arma-ture to heat considerably. In order to balance the currents in the various parts of thearmature, equa

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