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 transport of locomotives is restricted by the gradient they can travel, with the general gradient of the transport tracks being 3‰, and local gradients not exceeding 30‰. They are categorized structurally into overhead wire-powered electric locomotives and battery-powered electric locomotives.

Track-mounted electric locomotive

The working process of overhead line electric locomotives involves high-voltage AC power being stepped down and rectified at the traction converter. The positive pole is connected to the overhead wire, while the negative pole is connected to the rail. The locomotive's collector arm 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, via a transmission device, rotates the wheels, thus propelling the train. The current flowing out of the motor returns to the converter via the rail.

Track-mounted electric trolley

Trolley locomotives are powered by the current supplied to the overhead lines from the traction converter, which then enters the circuitry and the motor of the trolley, and returns to the converter via the tracks. In China, the direct current voltage for underground overhead power grids is either 250V or 550V, while for outdoor grids, it is either 550V or 750V.

Advantages: The overhead trolley is structurally simple, cost-effective, easy to maintain, with high transport capacity and speed, high electrical efficiency, low transportation costs, and wide application.

Disadvantages: Requires rectification and wiring facilities, lacks flexibility; wiring can affect tunnel dimensions and pedestrian safety; there is a risk of sparks between the collector and the wiring, making it unsuitable for mines with severe gas presence; initial construction investment is high, but in the long run, the total cost of using trolley wire locomotives is significantly lower than that of battery-powered locomotives. Therefore, if the mine conditions permit, the main transportation in the mine should use trolley wire locomotives.