Electric generators for railway work are made in all sizes, from those only large enough to operate four or five cars to others capable of furnishing sufficient current for thirty or forty or even more. Small generators are made so as to be driven by a belt running 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 machine 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 S, while F is the
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 at 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 commutator brushes are located at B B. The armature can not be seen very well, as it is covered by the brush holders and their supporting frames, but it is located within the ring G in the position designated by A. This machine is one of a number used to operate the roads of Troy, N. Y., and is of about one-thousand-horsepower capacity, which is enough to furnish all the current required to run sixty or seventy cars.
The switches a a and b b, shown in Fig. 22, and the bus bars