GB720000A - Improvements in and relating to electric motor control systems - Google Patents

Abstract

720,000. Control of D.C. motors. GENERAL ELECTRIC CO. Dec. 22, 1952 [Dec. 28, 1951], No. 32444/52. Class 38(3) [Also in Group XXXV] A hoist is driven by a compound wound D.C. motor 2 having a series field winding 2b and a shunt field winding 2c. A generator 5 for supplying the motor with variable voltage is driven at constant speed by an induction motor 6 which also drives a machine 11 for exciting the generator field winding 5b. The shunt field winding 2c of the motor is supplied from the exciter and is poled so that its magnetization is added to that of the series field winding 2b during motoring operation in the hoisting direction. A rectifier 17 is connected in parallel with the winding 2b to prevent demagnetization of the hoist motor during regenerative braking in the hoisting direction or during motoring operation in the lowering direction, the rectifier acting as a by-pass for the series field winding so that its magnetization affords no substantial opposition to that due to the shunt field winding 2c. There will be a slight voltagedrop across the rectifier 17 when it passes current. A resistor 18 is therefore connected in series with the winding 2b to reduce the field current to a negligible value. The direction of rotation of the motor and the strength of the generator field winding 5b is controlled by a master switch 12 which regulates resistor 19 in series with exciter 11. In the " off " position of the controller the field winding 5b is connected across the armature of the generator.