Electric locomotives are traction devices used for transporting rail vehicles. They operate by utilizing a traction motor to rotate the wheels, which then rely on the friction between the wheels and the rail surface to move 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. The locomotive's ability to traverse slopes is also limited, with typical track gradients being 3‰ and local gradients not exceeding 30‰. They are categorized structurally into overhead-catenary locomotives and battery-powered locomotives.

Overhead Trolley Motor Vehicle

The process of the overhead-line electric locomotive: The high-voltage AC power is stepped down and rectified by the traction converter, with the positive terminal connected to the overhead wire and the negative terminal to the rail. The locomotive's pantograph contacts the overhead wire, introducing the current into the train. It then passes through the air automatic switch, controller, and resistor box to the traction motor, driving the motor to operate. The motor drives the wheels through a transmission mechanism, thus propelling the train. The current flowing out of the motor returns to the converter via the rail.