GB736240A - Improvements relating to electric motor control systems - Google Patents

Abstract

736,240. Control of A.C. motors. ENGLISH ELECTRIC CO., Ltd. Feb. 12, 1954 [Feb. 13, 1953], No. 4107/53. Class 38 (3). The stator of a three-phase induction motor 10 driving a winder is adapted to be supplied from source 11 through forward or reverse contactors F, R, the rotor resistance 12 of the motor being so controlled by contactors 13 that a predetermined rate of acceleration is obtained for a specified payload. The motor is dynamically braked by disconnecting the stator from the source 11 and connecting it, by means of contactor B, to direct-current sources 14, 15, the voltages of which are respectively constant and variable in accordance with rotor current. The change to braking operation is effected by relay 16 energized through cam-operated switches 18 or 19 according to the direction of the wind. The closure of contactor B also energizes a timing device 20 for operating the contactors 13 in sequence at predetermined time intervals. The payload is measured during the full-speed run of the winder by means of a torque motor 21 having its armature temporarily connected to current transformer 23 and its field winding connected to source 17 in parallel with brake solenoid 26. The torque motor drives discs 27, 28 in opposite directions and is normally held against rotation by brake 32 which is released by brake solenoid 26 against the effect of weight 33. The discs are freely mounted on a shaft 31 driven by the winder and are both biased to the position shown by means of a tension spring 35 adjusted so that its torque balances that of the motor 21 at zero payload. The switches 18, 19 are mounted on discs 27, 28, and are operated by cam 36 keyed to the shaft 31. If a reverse winding operation is instituted with the cams in the positions shown, the cam-face 37 first operates switch 19 but braking is not introduced, due to the opening of interlock F1. Temporary energization of the torque motor causes the switches 18, 19 to be moved circumferentially with respect to cam 36 by an amount dependent on the payload, so that the switch 18 is operated later in the wind with an increased payload and the winder is still brought to a safe speed by the time the landing-position is reached. On a forward wind, the switch 18 is rendered ineffective by the interlock contacts R1 and braking is initiated by switch 19 in a similar manner.