GB818071A - Improvements in or relating to feed-back speed regulating systems for electric motors - Google Patents

Abstract

818,071. Automatic speed control. IGRANIC ELECTRIC CO. Ltd. Dec. 23, 1955 [Jan. 19, 1955], No. 36917/55. Class 38 (4). [Also in Group XXXVII] In a Ward-Leonard system the motor speed is regulated by a voltage which is the difference between a reference voltage representing a base speed and a second voltage representing the difference between the actual and desired speeds, the regulating voltage being used to control the generator or motor field current depending on its polarity and amplitude. In the embodiment described, the generator 16 has an armature 14 connected in series with the armature 12 of the motor 10. The field windings 20, 18 respectively are supplied from full-wave rectifiers 38, 32 respectively fed from the A.C. line L1, L2 through the power windings 24b, 24c and 22b, 22c of magnetic amplifiers 24, 22 and oppositelypoled pairs of rectifiers 34, 36 and 28, 30 respectively. The amplifiers 24, 22 have biasing windings 24a, 22a, respectively, fed from a full-wave rectifier 47 and control windings 24d, 22d, respectively. The D.C. control current in lines 52, 54, depending upon its polarity, flows through rectifier 48 and winding 22d to decrease the motor field current and increase motor speed or through rectifier 50 and winding 24d to decrease the generator field current and hence decrease the motor speed. The voltage responsible for the control current is the difference between a fixed reference voltage produced across resistance 56 by a current derived from a rectifier 60 fed by transformer 62 and the voltage produced across resistance 46 by the current from a rectifier 44 supplied from the output windings 26b, 26c of a third magnetic amplifier 26. The control winding 26d of the latter carries current depending upon the difference between a speed reference voltage, derived from rectifier 47 through a setting potentiometer 66, and a voltage representing the actual motor speed, from a tacho-generator 64. The biasing winding 26a of amplifier 26 is also supplied from rectifier 47. A negative feedback loop supplies a control winding 26e with a current representing the rate of change of armature current from a transformer 70 and another loop feeds a control winding 26f with a current representing the rate of change of motor speed and derived from the resistance 46 through a capacitance 72. In a modification, the motor speeds at which rectifiers 48, 50 start conducting are different, the windings 22d, 24d being returned to different tappings on the load resistors of rectifier 60, Fig. 4 (not shown).