GB583053A - Improvements connected with the speed control of electric motors supplied on the variable voltage system - Google Patents

Abstract

583,053. Control of D.C. motors. WHEELER, H. D., and MOSSAY, P. A. H. May 24, 1944, No. 10071. [Class 38 (iii)] A hoisting motor is supplied from a motorgenerator set, and the generator, or an exciter therefor, is provided with auxiliary windings the excitation of which opposes that of the main windings, and switching means under automatic control effect automatic selective excitation of said auxiliary windings accordingly as the current in the armature circuit of the controlled motor exceeds a pre-determined value in either direction. The armature of a constantly-excited motor 1 is supplied from a generator 3 which is driven by a motor 4. The generator field winding is fed from an exciter 8, a field, 11, of which opposes a main exciter winding 10 when the motor 1 takes power from the generator, and a winding 12 opposes the winding 10 when the hoisting motor regenerates when lowering. Short-circuiting means controlled by a polarized relay (not shown), are moved to place the winding 11 or 12 in circuit when the main motor armature current reaches a pre-determined value during hoisting or lowering respectively. In order to obtain substantially equal speeds under similar conditions of hoisting and lowering, the winding 12 is generally provided with more turns than the winding 11. At lower speeds the motor is run at constant speed irrespective of load, the abovementioned polarized relay is therefore overridden on low speed steps of the motor controller, and the windings 11 and 12 are placed in circuit and in mutual opposition.