GB740256A - Improvements in or relating to control systems for electric motors - Google Patents

Abstract

740,256. Automatic speed-control systems. GENERAL ELECTRIC CO., Ltd., and MAER, C. A. April 14, 1954 [April 16, 1953], No. 10470/53. Class 38 (4). [Also in Group XXXVII] A speed-setting lever 40 is guided for forward or reverse operation of a winder motor 10 by movement in paths 201, 202, which have a gate 203 between them. Each path extends from a full-speed position of the lever, through a zero-speed position, to a position providing dynamic braking at the end next to the gate 203. The current-supply to the motor is arranged to be disconnected when the lever is in a central position in the transverse gate. The motor 10 is of the induction type and has its stator windings supplied with three-phase current for driving in the forward or reverse directions, and with direct current for dynamic braking, the magnitude of this direct-current excitation, as well as the value of a hydraulicallyregulated liquid rotor resistance 13, being controlled as described in Specifications 738,310 and 740,257 so as to maintain the actual speed of the motor equal to the desired speed set by a potentiometer 47, the output voltage of which is compared with that derived from a tachometer generator 33 coupled to the motor. The lever 40 pivots about axis 41 and has a toothed sector 42 engaging rack 43 on which is mounted a slider 44. This slider co-operates with the potentiometer 47 which has tappings connected to studs symmetrically arranged on either side of a central position, and which is connected across a direct-current supply obtained from rectifier 48. When the lever 40 is moved away from the central " off " position in the middle of the gate 203, a slider 45 engages contacts 52 or 54 for energizing the reverse or forward contactor coils 53 or 55. A slider 46 engages contacts 56 or 57 for reversing the field-connections of the tachometer generator. Connections from the armature of the tachometer generator are made to the slider 44 and to an intermediate tapping 73 in the potentiometer 47 so that the voltage between the slider and tapping provides an indication of the desired speed of the motor. When the actual speed of the motor is greater than the desired speed a polarized relay 72 is arranged to energize the operating winding 69 of the dynamic braking contactor.