GB610382A - Improvements relating to electric motor controlling systems - Google Patents

Abstract

610,382. Control of A.C. motors. WADKIN, Ltd., and SIMS, W. L. April 3, 1946, No. 10331. [Class 38 (iii)] A three-phase induction motor providing an intermittently operating drive for a machine tool such as a wood moulding cutter is arranged for D.C. injection braking by supplying the motor through a continuously energized rotary frequency-changer which has a winding or windings arranged to form the primary of a step-down transformer feeding a rectifier through switching means adapted to operate to break the A.C. supply to the induction motor stator and connect the rectifier thereto. In the example, a 50-cycle supply from lines 2-4 is converted to 125 cycles by a motor-driven frequency-changer comprising a delta connected motor winding 1, star-connected exciter winding 5 and a star-connected rotor 6 which, in the driving position is connected over contacts j-r, l-o and k-t of a switch 7 to the deltaconnected stator winding 8 of the motor driving a cutter. In the braking position of the switch 7, the driving contacts are opened and contacts h-o, y-p and x-q are closed, .thereby connecting a bridge-connected rectifier 9 across both the star point G of the exciter winding and a tapping H adjacent thereto on the section F-G of the winding. Simultaneously, the rectifier output terminals P, Q are connected across the section R, T of the motor stator 8. The tapped portion HG of the winding FG of the frequency-changer forms the secondary winding of a step-down auto-transformer. In a modification, Fig. 3 (not shown), similar tappings are taken from each of the starconnected stator windings of the frequencychanger and the control switch is adapted to connect them to a three-phase metal rectifier when set to the braking position.