GB361016A - Improvements in or relating to control or protective apparatus for use with electric-circuit interrupters - Google Patents

Abstract

361,016. Protective cut-out systems and electrically released switches. SHEPHERD, G. R., 2, Norfolk Street, Strand, London.- (Westinghouse Electric & Manufacturing Co. ; East Pittsburg, U.S.A.) Sept. 1, 1930, No. 26026. [Class 38 (v).] In a protective arrangement including a circuitbreaker which is tripped or released when the voltage in the circuit falls below a limiting value in order to prevent the opening of the circuit in response to a temporary diminution of voltage the current in the releasing circuit is caused by electromagnetic inertia to persist for a predetermined time interval after the voltage of the circuit has fallen below this value so that the release of the circuit-breaker is correspondingly delayed. As shown, a voltage transformer 9 connected across the supply 2, 3 is arranged with voltages above the limiting value to energize a relay 12 which completes at contacts 13 a circuit for the holding coil 4 of the circuit-breaker 1 which is fed through a bank of dry plate rectifiers 11 and includes a choking coil 18. Additional current through the choking coil passes through a resistance 21 connected by contacts 15 of the relay 12. When the relay 12 is de-energized it is released and the supply for the retaining circuit is broken but the current in the coil 4 persists for a time owing to the discharge of the choking coil through an adjustable resistance 19 the circuit of which, in series with the coil 4, is completed at contacts 14 of the relay 12. To prevent the breaking of the circuit of the coil 4 while the relay 12 is changing over its contacts a further discharge path is provided through a rectifier 23 in series with a resistance 22 and the maintenance of current in the coil 4 is assisted by a condenser 24. To provide an instantaneous manual release of the circuit-breaker a press-button switch 31 may be arranged as shown so that on depression the holding coil 4 is shortcircuited by a resistance 32. A similar release may also be effected by an overload relay 35 fed from a series transformer 37. The coil 4 may be arranged, for emergency purposes, to be fed directly from the secondary of the transformer 9 by changing over the control switches 28, 29. In an alternative arrangement, Fig. 2 (not shown), the rectifying arrangements may be dispensed with, the D.C. circuit for the coil 4 being fed from an auxiliary battery.