GB772596A - Improvements in or relating to control means for induction motors - Google Patents

Abstract

772,596. Control of A.C. motors. IGRANIC ELECTRIC CO., Ltd., and TAYLOR, J. R. Sept. 2, 1954 [Sept. 2, 1953]. No. 24264/53. Class 38(3) An induction motor M has the A.C. winding W1, W2, W3 of a three-phase saturable reactor connected between respective secondary resistors R1, R2, R3, and star-point P. The D.C. winding W4 of the reactor is energized in accordance with the output of a device D wherein a reference voltage derived from supplylines L2, L3, is compared with a control voltage obtained from two of the secondary terminals of the motor. When the motor is rotated by means of its load, the slip, and the control voltage both increase until the reference voltage is exceeded whereupon the reactor becomes saturated to increase the motor torque. In this manner, the torque is arranged to reach a value sufficient to ensure that the slip does not become excessive, the reference voltage being adjustable to vary the slip at which the control voltage becomes effective to energize the winding W4: In one form of the device D, the' reference voltage is supplied to rectifier T having resistor R4 across its output terminals, the source of control voltage being connected to an opposing rectifier T1 and the winding W4 to leads P2, P3. The rectifier Tl prevents energization of the winding W4 if the reference voltage exceeds the control voltage, but permits it if the control voltage is the greater. In a modification, Fig. 2 (not shown), the saturable reactor is of the single phase type and has the ends of its A.C. winding connected through respective secondary resistors to two of the secondary terminals of the motor, the third terminal being disconnected from the circuit. A magnetic or other amplifier may be connected in cascade with the winding W4.