GB807903A - Improvements in or relating to electric motor control systems - Google Patents

Abstract

807,903. Control of A.C. motors; controllers. GENERAL ELECTRIC CO. Ltd. Sept. 20, 1957 [Sept. 21, 1956], No. 29007/56. Class 38 (3). [Also in Group XXXIX] The load on an electric motor is measured as a function of the current consumed by the motor, and compensation is provided for the varying current during periods of changing speed so that a true measure of the load is afforded. Current transformers 60, 61 are connected in the supply lines to a winder motor whereby the coils of a bi-phase wattmeter torque system 63 are energized to control a constant-speed regulating motor 64. If the load is above or below a datum value, either contacts 65 or 66 are closed by contact 67, and the motor 64 is rotated in one direction or the other. An induction regulator 84 is driven by the regulating motor to supply opposed coils 88, 89 of a polarized relay 90, so effecting a control upon the position of the contact 67. Thus rotation of the motor 64 continues until the torque produced by the relay 90 balances that of the system 63, whereupon the contact 67 takes up its mid-position and the motor 64 is quickly stopped by D.C. excitation. The contact arms of face-plate regulators 82, 83 are driven by motor 64, these regulators having studs connected to a pattern-of-speed potentiometer 91 for the winder motor having a cam-driven contact 92. A voltage signal for controlling the winder motor is developed across winding 93 in series with tachometer generator 94. To compensate for current-vari.ations during acceleration or deceleration periods of the winder motor, a relay coil 100 is connected in series with capacitor 101 across a D.C. tachometer generator 102 having its shaft coupled to that of the winder motor. The torque produced by the coil 100 balances the influence on the system 63 of the power involved in acceleration and deceleration, so that the position of contact 67 is unaffected by such changes of speed. A second additional coil on the relay 90 is effective during dynamic braking operation of the winder motor, or a dynamic braking current signal is applied to the winding 100. In another arrangement, the coil 100 is dispensed with and the coils 88, 89 are supplied with compensating signals by means of a magnetic amplifier 103 of the fourcore, push-pull type. The output windings a of the amplifier are centre-tapped and, when current is supplied to control windings c, voltage unbalance between the two halves of the output windings occurs, the amount of unbalance being proportional to the acceleration or deceleration of the winder motor. The windings b on the four cores provide bias excitation, and the windings d are fed with a dynamic braking signal. The excitation from the windings c and d assists the bias excitation on one side of the mid-point, and opposes it on the other. In a further modification, the windings b of cores 1 and 2 are connected in series with coil 88 across rectifier 86, and the windings b of cores 3 and 4 are connected in series with coil 89 across rectifier 87. This arrangement provides positive feedback to increase the amplification obtainable with a given set of cores, Fig. 2 (not shown).