Patent GB-481939-A (GB)
Title: Improvements relating to control systems for electrical winding equipments for mine hoists and the like
IPC: H02P3/22
Filed: 1936-09-16
Abstract: 481,939. Control of A.C. and D.C. motors. SMITH, G. D., LOYNES, E., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Sept. 16, 1936, No. 25262. [Class 38 (iii)] Dynamo-electric braking.-The generator of a Ward-Leonard system for a winding motor is driven by an alternating-current motor IM, Fig. 1, which, under conditions of emergency in which it is disconnected from the supply, has its stator or rotor winding supplied with direct-current, and its other winding connected to resistance LS used for starting, so that the motor acts as a generator and produces a braking effect on the winder, means being provided whereby, after starting the alternating- current motor, the winder motor cannot be started until the starting resistance LS for the alternating-current motor has been adjusted to a value which provides a suitable loading during braking. The liquid starter LS is in the secondary circuit of the motor IM, and an " off " interlock switch LS1 is provided between the starter and the circuit-breaker OCB. When the motor IM has been run up to speed its slip rings are short-circuited by a contactor RC energized by closing the upper contacts of a switch RS. Before the field of the generator supplying the winder motor can be energized and the winding motor started, a switch LS2 must be closed by returning the starter LS to a position such that the necessary resistance for braking is inserted in the secondary of the motor IM. If the supply to the motor IM fails and the main switch OCB opens, back contacts OCB2, and OCB3, effect energization of a contactor SEC to connect the primary circuit of the motor IM to an exciter BEX, and de-energize the contactor RC to render the predetermined starter resistance LS effective. Thus the motor IM acts as a generator and produces a braking effect on the winder. The field of the exciter BEX may be varied to control the braking in accordance with the speed of the motor IM by means of resistances controlled by switches FC1, FC2, actuated by coils FCC energized by a generator TG driven by the motor IM. The coils FCC may also control a contact FCO which de-energizes the contactor SEC when the speed of the motor IM reaches a low value. The application of the invention to an alternating-current driving motor started by secondary resistance and running normally as a synchronous motor is described with reference to Fig. 2, not shown. In this arrangement a resistance additional to the starting resistance may be provided for braking. In the arrangement shown in Fig. 4, the alternating-current driving motor SIM is started up by moving a switch SW to its starting position to energize a-coil of a contactor LSC which connects the starter LS. The switch SW is then moved to its other position to energize a contactor REC and connect the exciter SIMEX to the rotor circuit of the motor SIM. The contactor LSC is also de-energized. The starter LS is then moved to a position giving the requisite braking resistance to close the switch LS2 and the generator field may be energized to start the winding motor. If the supply fails and the main switch OCB opens, the interlock contact OCB2 opens, and de-energizes the contactor REC and disconnects the exciter SIMEX. Contacts REC1 also close to re-energize the contactor LSC and reconnect the starter. An auxiliary switch LSC1 also closes to connect a braking exciter BEX to the stator of the motor SIM. Specifications 197,753, 202,389, 204,805, [all in Class 78 (ii)], and 481,938 are referred to.