A rotary converter uses a rotating electromechanical assembly to convert electrical power, whereas a static converter (such as a rectifier or inverter) has no moving parts. This mechanical distinction is the key classification boundary — units with rotating components belong under the rotary converter heading, while solid-state devices fall elsewhere.

Rail traction systems, industrial process plants requiring precise frequency conversion, and older utility substations are the primary end-use sectors. Some specialized military and marine applications also rely on rotary converters where static alternatives cannot meet harmonic or isolation requirements.