GB397499A - Improvements in or relating to electric motor control systems - Google Patents

Abstract

397,499. Master control of A.C. motors. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, COATES, H. J., c/o General Electric Co., Witton, Birmingham, and SAUNDERS, C. W., Magnet House, Kingsway, London. Feb. 23, 1932, No. 5443. [Class 38 (iii).] In a control system applicable to ship propulsion in which an A.C. motor is connected to its supply generator through reversing contactors 1, 2, and in which upon return of the main controller 3 to its " off " position, changes are effected in the motor or generator fields, each reversing contactor is prevented from opening while the induced currents in the main circuit are excessive. Bv movement of the controller 3 from its " off " to its 1st position, one or other of the self-maintaining reversing contactors 1, 2 is closed, depending on the position of a reversing switch 10, and the turbine driving the supply generator is run up to one-thirtieth full speed. By moving the controller to its 2nd position the turbine speed is increased to one-fifth full speed whilst the generator field is doublv excited, and in the 3rd position, attained subject to the motor reaching one-fifth full speed, the motor field is energized. The motor and generator field circuits are maintained over contact 5c, and if the motor pulls into synchronism further movement of the controller may be made to excite a booster to reduce the alternator field, and then to gradually increase the turbine governor setting from one-fifth to full speed. When the controller is moved to its " off " position the generator and motor fields are maintained down to the 1st position, and in the " off " position the energized reversing contactor is maintained over contacts 44 of a timedelayed relay. This relay is energized in the " off " position and after a time sufficient for the induced current to fall sufficiently, it opens its contacts to de-energize the closed reversing contactor. The arrangement may be modified bv providing an auxiliary relay effective to de-energize the closed reversing contactor when itself energized by contacts on the relay 44 closed after a time interval. The contactors 1, 2 are electrically interlocked to prevent simultaneous closure. In a modification, Fig. 2 (not shown), the reversing contactors are closed by momentary energization of a closing coil, maintained closed by a latch, and opened by energization of a tripping coil under the control of a timed relay. In a further modification, the relay 44 is held closed through contacts on an auxiliary relay energized by the main current, so that when the current in the main circuit falls sufficiently the relay 44 is de-energized, and after a certain time opens its contacts to effect opening of the closed reversing contactor. Specifications 352,615 and 354,899 are referred to.