GB553511A - Improvements in and relating to electric motor control systems - Google Patents

Abstract

553,511. Master control of several A.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd. Dec. 12, 1941, No. 16036. Convention date, Dec. 17, 1940. [Class 38 (iii)] Motors 20, 21 used for winding and unwinding material that is being processed, e.g. passed through a dye vat, are controlled so as to obtain constant tension on the material. Both motors 20, 21, and also a motor 19 driving nip rollers between which the material passes, are 3-phase induction motors and all are reversible by means of a cam controller 22. The winding motor has associated with its wound rotor a star-connected reactance network, each phase comprising three parallel branches of resistance 26a, series resistance and. inductance 26b, and series condenser inductance and resistance 26. The reactance is adjusted so that the output of the motor is constant at all operating speeds and hence the tension of the strip. being wound remains constant. The unwinding motor is run as a generator of constant output either by exciting one phase of the stator with D.C. from a rectifier 33 and shorting the slip rings, or else exciting the stator with 3-phase A.C. to produce a field rotating contrary to the rotation of the rotor and connecting the slip rings 'to a network similar to the network 26 &c. The back tension on the material is thereby kept constant. Running is under control of buttons 35, 39. A delay drop out relay 37 with make before break contacts is normally energized over a rectifier 47. The controller 22 is set for desired direction and button 35 is depressed. Contactor 36 picks up, completes the star-point of network branches 26a, de-energises relay 37, locks itself up over stop button 39, energizes a relay 40, prepares the stator circuit of motor 19 through starting resistances 45 a, b, c and energizes contactor 44 which completes the starter circuit of the motor 19 and of motor 20 or 21 whichever is the winding motor. The latter motor starts with increased torque as part of the resistance-inductance branches of the network is shorted by contactor 38. After an interval, relay 37 drops and energizes contactor 38 which lifts, maintains contactor 44 independently of contactor 36, removes the short from the network, shorts the resistances 45 a, b, c and energizes the rectifier 33. All motors are now running normally. Opening of stop button 39 causes contactor 36 to drop out. This opens the star-point of the network resistances 26a so that the winding motor operates with reduced torque, re-energizes relay 37 which lifts immediately, de-energizes relay 40 which drops after a delay, opens the stator circuit of motor 19 which coasts to rest and'shorts a resistance 53 so that the unwinding motor exerts an increased drag. After a delay relay 40 drops out and de-energizes contactor 38 which drops and is immediately followed by contactor 44, whereupon the system is in its initial state ready for operation in the opposite direction upon reversal of the controller 22.