Patent GB-492096-A (GB)
Title: Improvements in or relating to electric motor control systems
IPC: H02P7/06
Filed: 1937-03-09
Abstract: 492,096. Automatic control systems. GENERAL ELECTRIC CO., Ltd., COATES, H. J., and GIBSON, J. W. March 9, 1937, Nos. 6898 and 9449. [Class 38 (iv)] Speed.-In controlling the speed of a motor by means of a tachometer generator the E.M.F. of which is matched with a constant voltage, provision is made whereby when setting a new speed for the motor the value of the constant voltage source or the voltage of the tachometer machine is changed by a regulating device coupled with the main speed control regulator. The constant voltage source is derived through means such as a carbon-, tungsten-lamp bridge from the supply mains. The invention is described as applied in three different systems for maintaining related speeds of paper mill motors supplied from a variable source, one of which (Fig. 3) comprises photo-cell control of the speed of each mill motor. According to Fig. 1 mill motors 1 are manually controlled by a switch 17 which through a reversible motor 14 adjusts a potentiometer 12 determining the excitation of a booster 5 and the speed desired. The motors are maintained at constant and related speeds by means comprising a master frequency set 18 the speed of which is held by a rheostat 21 adjusted by a reversible motor 46 and relay 37 in accordance with balance between the voltages of a tachometer alternator 30 and a carbon and tungsten lamp-bridge 40. Ganged with the potentiometer 12 is a potentiometer 34 lying between the D.C. output of the alternator 30 and the relay 37 so that in all speed settings an appropriate voltage is provided to balance the constant voltage of the bridge 80. A modification is described wherein a tachometer alternator with rectifier is coupled to each mill motor and co-operates with the output of a master alternator and rectifier to control a relay and reversible motor adjusting a field rheostat of each mill motor ; a manual resistance in each motor field circuit is provided for " draw " adjustment. The rectified master alternator voltage is balanced against a lamp-bridge voltage for the control of the speed of the master alternator. In other respects this system is similar to that shown in Fig. 1. In the modification shown in Fig. 3 a reversible potentiometer 12 controls the booster 5 to give collective control of mill motors 1 and a magneto generator 65 and rectifier (not shown) feed a potentiometer 66 the voltage of which is balanced against that of a potentiometer 72. The last is supplied through a baretter 74 to give a constant voltage which is varied in accordance with speed settings of the mill motors by a coupling between potentiometers 12 and 72. The control of the speed of the motors 1 is effected by a reflecting galvanometer 76 and photo-cells 77, 78 with amplifiers and telephone-type stepper switches which control resistance (not shown) in the field circuits of the motors 1. " Draw adjustment is effected by a rheostat 82 in the motor field circuit, which is ganged with the potentiometer 66. Quick changes in voltage in the power supply are prevented from affecting the speed of motors by a resistance 81 and condenser 84 across the supply mains the former then developing a biassing voltage to cause motor field adjustment.