Railway electrification system

A railway electrification system supplies electrical energy to railway locomotives and multiple units so that they can operate without having an on-board prime mover. Their main advantages are high energy efficiency and low operating cost. Building their wires and other infrastructure is expensive, however.

Electricity may be sent to the train in different ways. Different countries use different systems. The most widely used systems are:

• Alternating current from overhead lines at 15,000 volts, 16.7 Hz
• Alternating current from overhead lines at 25,000 volts, 50 Hz
• Direct current from overhead lines at 1,500 or 3,000 volts
• Direct current from a third rail at 600 or 750 volts

• Electric locomotive

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