GB286369A - Improvements in or relating to load-discriminating arrangements for electric circuit-breakers in three-wire systems - Google Patents

Abstract

286,369. Reyrolle & Co., Ltd., A.. and Willoughby, R. Dec. 4, 1926. Protective arrangements. - In a three-wire system comprising two outer conductors and a neutral, the circuit-breakers between the supply and the load cannot be reclosed when there exists an excessive balanced load across the outers or an excessive (unbalanced) load on the neutral, both excess conditions being provided for together. In the arrangement shown in Fig. 1, the mid-point of a battery G is connected to the neutral A through the coil D of a relay D<1> with its contacts in the circuit of the closing coil H of the circuit-breaker C<1>, C<2> energized from the outers. The ends of the divided battery are connected through assisting coils F<1>, F<2> and' through back contacts H<1>, H<2> of the circuit breaker (opened when the circuit-breaker closes) to the respective outers on the load side of the circuit-breaker. The coil D carries a current proportional to unbalanced load on the neutral and the coils F<1>, F<2> a current proportional to the balanced load on the outers. When either of these test currents is excessive one or other of the relays opens its contacts and the electromagnetic closure of the circuit-breaker is prevented or the circuit-breakers are locked open. As the auxiliary source a tapped resistance across the outers may be used or, in the case of an A.C. supply, a transformer with its primary across the outers and with a divided secondary. Where the load to be tested before connection is made may already be supplied from another source the arrangement shown in Fig. 5 is used. The circuit-breaker contacts in the outers are bridged by equal high resistances P<1>, P<2> the midpoints (or other corresponding points) of which are connected through the coil of a voltage relay 0 and a resistance O<1> in series, the mid-point ohmically of the two being connected through the relay N to the neutral. The relay N prevents closure of the circuit-breaker with an unbalanced load and the relay 0 with a balanced overload.