The Transmission of Electrical Energy
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-431
2025-12-15
29
The function of a transmission line is to transmit electrical energy to a distance. There is always a certain loss in transmission, due chiefly to the heating of the line. As the heating of a conductor is proportional to the square of the current, it is plain that the current sent should be as small as possible. To transmit 10,000 watts of electrical power by using 1 ampere at a pressure of 10,000 volts is much more economical than to send 10 amperes at a pressure of 1000 volts. For this reason transmission lines are high tension lines, and require only a small wire to carry the current.
For instance, the alternators of the electric road from Philadelphia to Atlantic City give 6600 volts, but this current is changed to one of 33,000 volts by the use of step-up transformers. It is sent over the line at this voltage to the substations where the voltage is reduced to 430 volts by step-down transformers and then fed into the alternating side of a rotary converter, from the direct current side of which a direct current of 650 volts is taken. This is fed into the third rail which feeds the motors on the cars.
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