The electrical circuit between the power supply line and each motor or motor pair has an apparatus for re-transferring power from one mechanically driven and/or electrically braked motor to another of the motors. This apparatus includes a levelling or equalizing circuit and a plurality of back coupling devices such as diodes arranged in opposition in series. Each back coupling device electrically connects the intermediate DC circuit loosely to the levelling circuit. Upon braking of a motor, the power flows back through the associated intermediate circuit and then via the back coupling devices and levelling circuit to the other motors.