A voltage lowering device includes at least one pair of forced commutation single-phase rectifiers connected to secondary windings of a main traction transformer. The power drawn from a direct current mains power supply passes through the main traction transformer and is recovered at a secondary winding by means of a forced commutation single-phase rectifier operating as a voltage increasing controlled rectifier. The other forced commutation single-phase rectifiers operate as synchronous voltage inverters. An asynchronous traction system supplied by a single-phase mains power supply includes a voltage lowering device as previously described.