GB212608A - Improvements in protective apparatus for alternating electric current distribution systems and apparatus - Google Patents

Abstract

212,608. British Thomson-Houston Co., Ltd., and Fitzgerald, A. S. Nov. 16, 1922. Cut-out arrangements for alternating-current circuits, machines or apparatus of the kind in which the protection is dependent on the relative direction of power in the circuit &c. to be protected, employ a single relav per phase actuated by a fault on its own phase whether the fault is an earth fault or an interphase fault. Means are provided consisting in the employment and special connection of biassing transformers as described in Specification 193,434 or in the use of reverse power relays with additional windings whereby the current necessary to operate the relay is much greater in the case of a line or inter-phase fault than in the case of an earth fault. In the arrangement shown in Fig. 1 applied to a single three-phase feeder, the secondary windings of current transformers 4 in the feeder are adapted to energize the operating windings 34, 6 of biassing transformers, one for each phase, which have two restraining windings 5, 33 inductively related to one another and a single secondary winding 7. The secondary 22 of a potential biassing transformer which has a restraining winding 20 and an operating winding 21 energized from the potential transformer 24. In this way the current in each phase is associated with the potential difference due to which it flows in the phase conductor, and, con. sequently by including the relays 9 in the combined secondary circuits, the circuit-breaker is operated in accordance with the direction of power in the phase conductor. For interphase faults the protection is obtained by reason of the largely increased current in the operating windings when the relation between the voltage and current is appropriate. In the event of an earth fault, the leakage current energizes the additional restraining and operating windings 33, 34. The restraining winding 33 is wound so as to tend to neutralize the effect of 5 and the operating winding 34 to increase the effect of 6. Accordingly, with leakage currents the sensitiveness of the biassing transformers is increased. In a modification, adaptable to parallel feeders an additional simple transformer with the primary in series with the operating winding 6 and the secondary in series with the secondaries 7, 22 is employed to deal with interphase faults. In the adaptation to parallel feeders, auxiliary switches are arranged to dissociate the protective gear of a faulty feeder after it has been cut out and, instead of the secondary of the additional transformer being connected directly to windings 7, 22 and 9, an additional biassing transformer is introduced in the connection. The winding 5 may be excited by transformation instead of by connecting it directly in the operating circuit. The transformer for this purpose may have a magnetic circuit of limited cross-section so that its output is definitely restricted. Specifications 188,001, 205,866, and 210.294 also are referred to.