Electric locomotives are a type of traction equipment for rail vehicle transportation. They are powered by driving the wheels with a traction motor, utilizing the friction between the wheels and the rail surface to propel the locomotive along the tracks. This mode of operation is limited by both the power of the traction motor (or internal combustion engine) and the friction between the wheels and the rail surface. The transportable gradient for locomotive operation is restricted, with the general rail gradient being 3‰ and the local gradient not exceeding 30‰. They are categorized structurally into overhead wire locomotives and battery-powered locomotives.

Overhead traveling trolley motor

The working process of overhead line electric locomotives involves the high-voltage AC power being stepped down and rectified in the traction converter, with the positive terminal connected to the overhead wire and the negative terminal to the rail. The locomotive's collector arm contacts the overhead wire, introducing the current into the train. It then passes through an air-operated switch, controller, and resistor box to the traction motor, powering its operation. The motor drives the wheels through a transmission system, propelling the train forward. The current exiting the motor flows back to the converter via the rail.