Traction Substation

part of the traction system used by electrified railroads, streetcar and trolleybus lines, and subways. The equipment in a traction substation transforms electric current and changes its frequency, and also distributes the power to the system.

For general-use railroad main lines, and in industrial transport lines operating on standard industrial-frequency alternating current, traction substations are designed as transformer substations. In this case they are used to step down the three-phase current obtained from the power-supply system to the required value, which is 27.5 kilovolts (kV) for railroad main lines and 6–10 kV for industrial transport lines. On electrified sectors of railroads that operate on low-frequency alternating current (16⅔ or 25 hertz), the traction substation must either step down the voltage of a single-phase current obtained from special power plants or convert the standard industrial-frequency three-phase current obtained from a power transmission system into single-phase current of lower frequency. In DC lines, the substation converts the three-phase alternating current to a direct current at 257 volts (V) for mine haulage locomotives, 600 and 825 V for urban and industrial transport, 1,650 V for industrial transport, or 3,300 V for railroad main lines.

In the USSR, railroad traction substations usually also provide power for nontraction users, such as various railroad services, industrial and farm consumers, and public utilities that are located in areas adjacent to the railroad.

In the case of railroad main lines, subways, and streetcar and trolleybus lines, traction substations may be unattended, with automatic or remote control. Stations in industrial transport systems are continuously attended by service personnel.

Traction substations may be of the outdoor type, with all their main equipment located outdoors, or the indoor type, with all main equipment located in a building. There are also mobile traction substations, with all main equipment mounted on railroad cars. Mobile substations are mainly for standby use, to provide emergency service if a regular substation breaks down.