Patent GB-409669-A (GB)
Title: Improvements in or relating to electric protective arrangements for polyphase electric circuits
IPC: H02H7/26
Filed: 1932-11-01
Abstract: 409,669. Protective cut-out systems. REYROLLE & CO., Ltd., A., Hebburn-on- Tyne, and LEBEN, H., 212, Wingrove Road, Newcastle-on-Tyne. Nov. 1, 1932, No. 30746. [Class 38 (v).] In split-conductor systems employing a current transformer with opposed primaries at each end in each phase, in order to avoid the possibility of a fault close to the end of the section which is remote from the supply end producing in the transformer of the associated phase at the supply end insufficient unbalance, to trip the breaker at that end, current from a faulty phase is injected into another phase, preferably by a relay connecting the secondary of the transformer of the faulty phase to that of the other phase. The splits B<1>, B<2> of each phase are provided at each end with transformers C the secondaries C<3> of which are Y-connected, and supply the coils D<1> of protective relays D over normally-closed contacts E<1> of a relay E. The contacts D<2>, when closed, energize a transfer relay F having contacts F<1> which when closed, energize relay E, contacts F<3> which, when closed, are in series with those F<2> of the relay F of the next phase, and contacts F<4> which, when closed, are in series with one another. The trip coil A<2> of each breaker A is in parallel with the coil E and has a contact A<3> to disconnect the coil A<2> when the breaker has opened. With an earth fault near the end of one phase remote from the supply, relay D at that end of that phase closes D<2> and energizes F, which at F<1> makes the circuit of A<2> to trip the breaker, and of E which disconnects at E<1> the coil D<1>. Relay F also closes F<3> to connect the secondary C<3> of the faulty phase to that of the next phase over closed contacts F<2> of the relay F of that phase, so injecting current from the faulty phase into the loop formed by the splits of that phase, the resulting unbalance at the supply end tripping the breaker at that end. With a fault between two phases near one end, current is injected from one of them into the third phase, whereas with a 3-phase fault contacts F<4> all close to connect one phase with another. Relays E, F are provided with time-delay means for their return movements, and relays D because of their low settings are provided with restraining windings D<3> which are energized either from beyond the breaker contacts or, as shown, by a summation transformer G so as to be responsive to normal load current and unaffected by injected currents. In Fig. 2, the secondaries C<3> feed relay coils H<1> the Y-point of which is connected to that of the secondaries C<3> over normally-closed contacts A' of the breaker and a current-limiting resistance J. The breaker may have contacts (not shown) which, when the breaker opens, shortcircuit the coils H<1>. With an earth fault on one phase, the appropriate coil H<1> energizes at H<2> the trip coil A<2> and the breaker on opening removes at A<4> the Y-point connection and short-circuits the coils H<1> if such connections are provided. Current is thus injected from the faulty phase into the loops of both other phases and the supply-end is cut out. With a fault between two phases, the currents injected by them into the third phase would be equal and opposite if the transformers were equal, so the secondaries C<3> are given different turnratios, e.g. 2 : 3 : 4. An overload relay K is placed in series with the restraining coil H<3> in each phase.