Electrified railway, which is also called electrochemical railway, is to use electric locomotive for railway traction power of electrified railway traction is electric locomotives, but the locomotive itself does not take energy, the energy needed to provided by the electric traction power supply system of traction power supply system is mainly refers to two substation general mostly in railway traction substation and catenary nearby, it will be the current from high voltage transmission line from the plant, to contact the Internet over the rail.

The catenary is a device that delivers electricity directly to the electric locomotive. And you can see along the sides of the railway line, there are a row of stilts with wires suspended on them. These wires are called catenary. The electric locomotive USES the pantograph on the roof of the car to get electricity from the catenary, so that it can pull the train.

Traction power supply system is divided into dc system and ac system according to the current system of the catenary two dc system is the high voltage three-phase power in the traction substation voltage reduction and rectifier, and then to the catenary for direct current, this is the earliest development of a current system, to the 1950s after rarely used.

Ac system is a high pressure after step-down substation and become a single-phase three-phase electricity, to contact line for alternating current power supply voltage ac system is higher, the development quickly in our country of electrified railway traction power supply system is used in single phase power frequency from the beginning (50 hz) 25 kv ac system, the choice is very beneficial to the development of electrified railway in the future.

Compared with traditional steam locomotive or diesel locomotive, electrified railway has the advantages of large transportation capacity, fast running speed, less energy consumption, low operating cost, good working conditions, less maintenance and less pollution. Therefore, it has obvious advantages in technology and economy