GB806735A - Motor control systems - Google Patents

Abstract

806,735. Automatic speed control. SQUARE D CO. Oct. 20, 1955 [Nov. 2, 1954], No. 29965/55. Class 38 (4). The control circuit of a speed-controlled motor in a Ward-Leonard system comprises a pair of signal receiving circuits, one controlling the generator energization and the other feeding a dummy load, to which proportions of the speed controlling signal are fed, the proportions being varied with variation of signal from a value corresponding to a predetermined speed and producing thereby an amplification of the signal output to the energization circuit. The speed of motor 10 is maintained constant at a speed predetermined by a potentiometer 38, by the control of the field 70 of a generator 20 of an A.C. driven motor-generator set 30, a deviation producing through tachometer generator 50 a signal on the grid of valve 25 which is amplified and applied to the D.C. winding 19 of a phasechanging saturable reactor 15 to produce on the grids of thyratrons 1, 2 a voltage having a phase with respect to the anode voltage which is such as to produce through winding 70 the current necessary to effect correction. The output of the tachometer generator is compared with a reference voltage from potentiometer 38 in a potential-divider across the rectified output from bridge 60. The rates of acceleration and deceleration are determined by the charge or discharge of condenser 37 through potentiometers 28 and 32 in the anode circuits of double diode 39. Power is connected through supply switches 14 and transformer 40, and start relay 8 is energized by relay 7 after an appropriate time delay to connect power to the thyratrons 1, 2. Relay 62 controlling dynamic braking through contacts 64, operates in response to the operation of start button 56 and in turn operates main start relay 66 to connect the output of generator 20 to the armature of motor 10. When relay 66 is released by stop-button 58 the generator output is regulated by the difference between the generator output and the falling motor back E.M.F., over contact 69, so that the motor circuit can be safely reclosed before the motor has stopped. Specification 806,736 is referred to.