Electric Railways
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-431
2025-12-15
33
The trolley lines and third-rail railways of the United States have for their essential parts the generating stations and generators, feed wires, trolley wires or third rails, the cars, and the road bed. The generators are usually direct-current dynamos producing current at a pressure of about 500 volts. The positive poles of these dynamos are connected to the feed wires, trolley wires, or third rails, while the negative poles are connected to the rails, which serve as return conductors.
Feed wires are used when the line is a long one; they are connected to different sections of the trolley wire. The current goes from the trolley wire to the wheel in contact with it, down the conductor carried by the pole, to the motor, then through the car wheels to the track and then to the dynamo. The cars are in parallel, like incandescent lamps on a lighting circuit, and each takes its own current, independent of the rest. The amount of current taken by each car depends largely upon the load in the car and the grade of the road. Since the motors are subject to the severest kind of usage, they are protected with water-tight cases.
Hundreds of electric railways transport people to and from their places of business in large cities. Figure 3 shows a transcontinental passenger train on an electric railway. Another important use of motors is their application to individual machines such as printing presses, lathes, band saws, etc. Each machine can then be run separately without large waste of power through the friction of shafts and belting.
Fsubject to the severest kind of usage, they are protected with water-tight cases. IG. 3. -Electric Locomotive and Transcontinental Passenger Train in the Cascade Mountains subject to the severest kind of usage, they are protected with water-tight cases.
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