WHAT MAKES THE TROLLEY CAR GO. 



419 



Electric generators for railway work are made in all sizes, from 

 those only large enough to operate fonr or five cars to others 

 capable of furnishing sufiicient current for thirty or forty or even 

 more. Small generators are made so as to be driven by a belt run- 

 ning over a pulley mounted on the end of the armature shaft, or 

 they may be arranged to be connected to the end of a steam-engine 

 shaft, and thus become what is called direct connected machines. 

 Large generators are almost invariably of the latter type. A ma- 

 chine of this class is illustrated in Fig. 23. The driving engine is 

 shown at E, the cylinder being in the background and the crank 

 toward the front, the shaft being clearly seen at 8, while F is the 



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]lllti 



Kli 



vY Generator. 



fly wheel. The generator is mounted directly upon the engine 

 shaft, between the bearing at the crank end and the fly wheel. 

 The large ring marked G is the field magnet ring, and ai D D D the 

 field coils are shown. These coils are equally spaced all the way 

 around the circle. The commutator is marked C, and the com- 

 mutator brushes are located at B B. The armature can not be 

 seen very well, as it is covered by the brush holders and their sup- 

 porting frames, but it is located within the ring G in the position 

 designated by A. This machine is one of a number used to oper- 

 ate the roads of Troy, IST. Y., and is of about one-thousand-horse- 

 power capacity, which is enough to furnish all the current required 

 to run sixty or seventy cars. 



The switches a a and & h, shown in Fig. 22, and the bus bars 



