For years now, the field of train traction has been powered by switch mode inverters, driving the motor or auxiliary power circuits. There are two main application for aluminium electrolytic capacitors, as traction drives used to control the speed of large electrical motors and as auxiliary power supplies in rolling stock ( air conditioning).

Aside from functioning as a filter to block high-frequency components from disturbing the board net, they are used as an energy buffer to guarantee stable operation of the switch mode inverter driving the motor or supplementary power circuit.