25kV overhead line is an alternating current (AC) system, typically operating at a frequency of 50 or 60 Hz. This specific voltage is a global standard for mainline railway electrification and high-speed rail systems. The relatively high voltage allows for efficient power transmission over long distances, reducing the need for numerous substations and minimizing power loss.

Unlike a typical power distribution line, a 25kV system often uses a catenary system, which is a complex network of wires that ensures the pantograph on top of an electric train maintains constant and reliable contact with the energized contact wire.