Patent GB-521541-A (GB)
Title: Improvements in or relating to electric protective arrangements
IPC: H02H7/22
Filed: 1938-09-20
Abstract: 521,541. Protective cut-out systems. REYROLLE & CO., Ltd., A., LEYBURN, H. and YOUNG, A. F. B. Sept. 20, 1938, No. 27392. [Class 38 (v)] Feeders or other circuits A .. D are connected over breakers A<1> &c. and selectors A <2> &c. to either busbars E, E' provided with a coupler F'. Current transformer groups A<3> &c. or a core-balance transformer, each arranged to yield a residual current; corresponding to the earth leakage in the associated circuit are connected through auxiliary switches A<4> &c. (operated by the selectors) to buswire G<1> or G<2>connected to current coils H', J' of discriminating relays H, J, respectively. The return buswire G includes an alarm relay G<4> and check relay G<3> responsive to internal faults on the system. The couplerconnection includes a transformer F<2>-connected to the coil K' of a further discriminating relay K, the "voltage" coils of H, J, K being energized by total earth leakage on the section or by the system voltage or current of circuits A &c. The armatures H', J' of H, J engage trip H', J<4> or lock-out contacts H<5> J<5> according as the fault is internal or not, but armature K' of'relay K engages either the trip contact K' and lock-out contact K', or trip contact K<5> and lock-out contact K<6>. Control relays L, M energized by the trip contacts H<4> &c. energize trip relays L<2>, M= <2> which have contacts L', M<3> for the trip coils A<6> &c. of all the feeder-breakers and contacts L', M<4> for the coupler trip coil F<3>, the trip coils A<6> &c. to be energized being determined by the position of contacts A<5> &c. operated by the selectors A<2>. The trip-producing circuits include contacts G<7>, G<8> of a relay controlled by the check relay G' which prevents undesired tripping due to failure of the protective system itself or to an external fault. On internal fault, with F<1> open, relays G<3> and H or J close their trip contacts to produce tripping. With F<1> closed and a fault on, say, E', relays H, J both close their trip contacts and relay K closes its contacts K<5>, K<6>. Closure of the latter causes the effect of closure J<4> to be nullified and hence L remains inoperative, but H<4>, K<5> produce energization of relay M which trips out the coupler F<1> and the feeders A, B connected to E<1>. The contacts H<5>, J<5> also prevent a .healthy busbar being tripped out when feeding a faulty busbar over feeders which are connected at their remote ends, the coupler being also open, and the relays L, M or G' operate with a time-lag to afford the lock-out contacts time to open. To ensure operation of the opposed-voltage protective system of a feeder itself (for example, A) when a fault occurs between the transformer-group A and the breaker A', opening of A<1> causes the pilot wire A' to be shorted at A', so bringing out the remote breaker A<10>. Similarly, for a fault between the opened coupler F' and transformers F<2>, operation of relay K would, due to the fault direction, be such as to close lock-out contacts K<6> and prevent tripping of the feeders connected to busibars E, so F<1> is arranged, when open, to make at F<5> an alternative circuit for L<2> over contacts K', which circuit is given a time-lag at contacts F<5> so as to be ineffective when F' opens due to a fault on the other side, for example, in E<1>. Preferably the circuits grouped according to the invention are those between which an interchange of fault current cannot take place, but transformer-groups in incoming feeders to either busbar-section may be paralleled with groups beyond the coupler, that is, in the other busbar-section, Fig. 2 (not shown). In a modification, Fig. 3 (not shown), discriminating relays of the centre-zero type are replaced by two-directional relays each comprising a pair of elements respectively responsive to opposite current-directions. One element of each relay operates a trip-relay contact whereas the other opens a lock-out contact in the circuit of the trip-relay contact, suitable time-lags being provided in the trip relay itself. The " voltage" windings of the two-directional relays are in the circuit of buswire G and check relay G<3> and the shorting of the feeder pilots A' is effected through contacts on selectors A' &c. by further contacts on the trip relays themselves. The check relay G' may be energized by independent transformer groups in the feeders, Fig. 4 (not shown), by a frame-to-earth Leakage connection, Fig. 6 (not shown), or in series with the "voltage" windings of relays H, J, Fig. 1, in a neutral-to-earth connection of the system, Fig. 7 (not shown). In Fig. 5, a pair of check relays G<9>, G<11> for the busbars E, E' respectively, are energized over buswires X, X' and contacts of the selectors A<2> &c. from trip contacts A" &c. of discriminating relays A<19> &c. in the feeders. These relays have current coils energized from transformer-groups A<12> &c. and voltage coils energized from transformers E<6> E' in the neutral-to-earth connection. The lock-out contacts A<18> &c. are connected to either of two buswires X<2>, X' connected to lock-out relays T, T<2> having contacts in the check-relay circuits. Thus, if a trip contact such as A<17> closes, the check relay associated with the busbar to which is connected the feeder corresponding to the trip contact, is energized unless the discriminating relay of another feeder on the same busbar operates first. The discriminating relays H, J connected over the buswires G<1>, G<2> to transformer-groups A<3> &c., have trip contacts H<4>, J<4> in series with the check-relay contacts for energizing the trip relays L', M<2> and lock-out contacts M', J<5> in series with lock-out relays T<4>, T' which open the trip-relay circuits at T', T'. The Specification also states that all the circuit-breakers associated with a protected section may be opened or only those of circuits in which fault current will flow to an internal fault, examples of circuits in which fault-current cannot flow being radial feeders, such circuits being provided with single-winding non-directional relays. Specification 453,525 is referred to.