GB227523A - Improvements in or relating to balanced electric protective arrangements for alternating current systems and relays therefor - Google Patents

Abstract

227,523. Reyrolle & Co., Ltd., A., and Leeson, B. H. Oct. 16, 1923. Cut-out arrangements; automatic circuitbreakers.-In balanced protective systems of the Merz-Price type, the relays or circuit-breakers are rendered immune from the effects of disturbances external to the protected section due, for example, to an arc fault between phases or to earth and resulting in high frequency currents, by tuning the relays or the pilot circuit containing them so that they will be responsible only to a predetermined range of current and frequency. As shown in Fig. 1, the relays at the two ends of the pilot wire system are themselves tuned by a condenser J and inductance H connected across them. Alternatively, the pilot wire system may be tuned by including in series with it a condenser and an inductance. The relay may be mechanically tuned. In Fig. 3, a reed K tuned to the required range of frequencies is set in motion by the current in the coil D, and, when its amplitude becomes sufficient, it strikes a spring latch L and releases the contactmember F<1> of the relay. Instead of a reed, a spring-controlled balance-wheel may be used. In the arrangement shown in Fig. 5, the tuned reed K, at a certain amplitude, completes the circuit of a holding magnet O<1> and the circuit of the relay is completed at G. Specification 200,876 is referred to.