GB643772A - Improvements in or relating to electric motor control systems - Google Patents

Abstract

643,772. Automatic control systems for D.C. motors. GENERAL ELECTRIC CO., Ltd., and DALE, S. H. Feb. 11, 1948, No. 4045. [Class 38 (iv)] [Also in Group XXXVII] An automatic control system for a reversible D.C. motor supplied from gridcontrolled rectifiers or from a motor generator set includes a resistance capacity circuit, the time constant of which limits the rate of rise of starting current. The motor 1 is supplied by full-wave connected rectifiers 3, 4, the output of which is controlled by phase shift of the grid voltage by a phase-shifting network 17 including a saturable reactor. 20 controlled by a valve 21 which, at low values of load current, is controlled by a valve 23 in accordance with the resultant of the rectifier output voltage and an opposing reference voltage derived from a potentiometer 30 and a battery 31. When the load current exceeds a predetermined value, valve 21 is controlled by a valve 24 in accordance with the resultant of a voltage proportional to load current and a variable reference voltage. The load current is measured at 37 by means of saturable reactors controlling an A.C. supply in accordance with load current, or by means of current transformers in the rectifier anode circuits. The reference voltage, obtained from battery 43 and potentiometer 41 is applied to a condenser 38 through a resistor 49. Condenser 38 is short-circuited by series connected contacts 39, 40 on the forward and reverse motoring contactors 15, 16 when the contactors are not energized. Thus the reference voltage is zero and the rectifier output is zero. On energizing either contactor, contact 39 or 40 opens, and the reference voltage rises at a rate determined. by the time constant of resistor 49 and condenser 38. This is so arranged that the rise in load current is limited and transient overcurrents on starting or reversing are substantially reduced. Specification 643,771 is referred to.