The electrified railway traction power supply system refers to a power supply system that supplies electric traction to the electric locomotive. Mainly composed of traction substation and contact network. The traction substation converts the 110kV or 220kV three-phase AC power sent by the power plant via the pressure transmission line into a current and voltage suitable for the electric locomotive, and then sends it to the contact network, and then supplies power to the locomotive from the contact network. According to the current system that supplies power to the locomotive, it is divided into DC and AC.

The DC system contact network voltage is relatively low, generally 1500V, 3000V, which is difficult to improve. A traction substation must be installed every 10~30km along the line. The exchange system is divided into a power frequency single-phase communication system and a low-frequency single-phase communication system. China adopts 50Hz 25kV power frequency single-phase AC system. With the increase of AC network voltage and the simplified structure of the contact network, the spacing set by the traction substation has been expanded to 30~70km.