China Railways High-Speed (CRH) "Harmony" train in Shanghai, ChinaThere are three types of modern locomotive—electric, diesel-electric and diesel. High-speed trains, such as the French Train à Grande Vitesse (TGV) or the China Railways High-Speed "Harmony", are normally electrically powered with a power car at each end and specially designed carriages. Diesel locomotives are normally used only for shunting and on low-speed local trains.
How trains work
On an electric locomotive, the wheels are moved by electric motors. The electricity comes either from overhead cables or from an electrified third rail. On a diesel-electric locomotive, the wheels are also driven by electric motors, but the electricity is generated by a diesel engine. On a diesel locomotive, a diesel engine drives the wheels via a mechanical transmission.Cutaway illustration of an electric power carHigh-speed trains are powered by electric current, collected from an overhead cable by a pantograph. A transformer converts the very high-voltage electricity in the overhead cable to the lower voltage needed by the motors in the power car. Electronic circuits in the locomotive control how the electricity flows to the motors, and thus the speed of the train. An auxiliary power unit supplies power for utilities such as lighting and air conditioning.
Cross-section of a flat-bottomed rail
Tracks and wheels
There are more than 1,187,000 km (737,000 miles) of railway lines across the world. If they were placed end-to-end, they would circle Earth more than 30 times.
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