GB171904A - Improvements in and relating to electric motor control systems - Google Patents

Abstract

171,904. British Thomson - Houston Co., Ltd., (General Electric Co.). Nov. 29, 1920. Systems fcr continuous-current motors only.- The sequence of varying resistance in the armature circuit, as in the lowering operation of a hoist motor, provides for the temporary inclusion of an additional resistance by the action of an electromagnetic switch having two windings 13, 19. During lowering, which corresponds to the right-hand set of controller contacts, the winding 13 is energized when the controller reaches an intermediate position, and a short-circuit is opened around a resistance R<3>, which is thus included in the circuit of the motor-armature A. The winding 13 is de-energized by the further advance of the controller, but the contact 12 is held open by a winding 19 composed of two branches connected to contacts 17, 18 of a relay 15 subject to the counter electromotive force of the motor. Whether this is increasing or decreasing, the relay responds after a definite change, depending on the adjustment of the winding, and, in responding, momentarily breaks the circuit of the active branch of the winding 19. The contact 12 then closes again and the resistance R<3> is short-circuited. The arrangement shown is an improvement on that described in Specification 113,473, and comprises a field winding F, connected in series for hoisting and in shunt for lowering an electromagnetic brake B, which is applied when its coil is de-energized, a lock-out switch 10 controlling an initial resistance R', and a resistance R<2> adapted to be connected with the motor armature and field in a closed loop when the controller is in the off position.