Abstract: A first static commutator including a first controllable thyristor rectifier and a first thyristor inverter and a second static commutator including a second controllable thyristor rectifier and a second thyristor inverter are provided. First three-phase AC voltage is supplied to the first controllable rectifier, and second three-phase AC voltage 30 degrees out of phase with said first three-phase AC voltage is supplied to the second controllable rectifier. A brushless motor includes first star-connected three-phase windings receiving the output of the first inverter and second star-connected three-phase windings and 30 degrees out of phase with said first three phase windings. During the starting period of the brushless motor the conduction of the first and second satic commutators is switched for every 30-degree rotation of the brushless motor.

Abstract: A rotary transformer includes rotor and stator cores arranged apart from each other. The rotor core is made of a plurality of U-shaped core plates which are laminated around a rotary shaft and supported by a pair of plates engaged with the opposite side ends of the rotor core and by an insulative band winding the bottom of the annular recess for receiving a rotor coil.