Patent GB-521543-A (GB)
Title: Improvements in or relating to electric protective arrangements
IPC: H02H7/22
Filed: 1938-09-20
Abstract: 521,543. Protective cut-out systems. REYROLLE & CO., Ltd., A., and LEYBURN, H. Sept. 20, 1938, No. 27394. Addition to 453,525. [Class 38 (v)] The invention of the parent Specification is modified in that the master relay is energized in accordance with the fault-current flow in at least one earth connection from a neutral point of the system. Fig. 1 (not shown) illustrates the application of the invention to the system shown in Fig. 1, of Specification 521,542, with the difference that the master relay is in series with the " voltage windings of the feeder-relays across the neutral-to-earth connection, instead of in the frame-to-earth leakage connection. In Fig. 2, feeders or other circuits A .. D are adapted to be connected over breakers A &c. and selector A<2> &c. to either busbars E, E<1> which are coupled by a breaker F<1>. Each feeder has an opposed-voltage protective system A<8> &c. which is shorted at A<9> by the opening of breaker A' in the conditions set out in Specification 521,541. Protective relays may be associated with groups of circuits as described in the latter Specification, but in the Fig. each circuit has its own relay A" &c. the current coil A<11> &c. of which are energized from current transformer A<12> &c. energized in turn by corebalance or parallel-connected transformers A<11> &c. which also operate overload gear. The "voltage" coils A<15> &c. may be volts-energized, but as shown are energized in series with a master relay G<3> from current transformers E<2>, E' so as to be responsive to the total earth-leakage current of the system the circuit including also the " voltage coil of a relay K, the current coil of which is energized by transformer F<2> in. the busbar coupling..The relayarmatures A<16> &c. co-operate, according to the direction of fault-current flow, with trip contacts A<17> &c. or lock-out contacts A<18> &c. which are respectively connected over selectoroperated contacts A<20>, A<19> to buswires X, X<1> or X<2>, X<3> so as to be connected to the buswire, appropriate to the busbar to which is connected the feeder of the particular relay. Relay K has trip contacts K<4>, K<5> and lock out contacts K‹, K', and the buswire X and contact K<5> are connected to a relay M whereas buswire X' and contact K<4> are connected to a relay L, the contacts M', L' of which are adapted to energize the trip relays M<2>, L<2>. Buswires X<2>, X<3> are connected to the lower ends of M, L and to lockout contacts K', K<6> respectively. The trip relays each have trip contacts M', L' for all the breakers A<1> &c. and contacts M<4>, L<4> for the breaker F', the former contacts being connected to the trip coils A<6> &c. over the selector-operated changeover switches A<5>, so that only the breakers of the feeders connected to the faulty busbars are opened. The trip-operating and trip circuits contain the contacts G<5>, G<8> respectively of the master relay G<3>, operation of which is therefore necessary in order to effect tripping. With an external fault, the systems A<8> &c. operate before relay G<3>, so that tripping is prevented. With F' open and a fault on, say, busbar E<1>, contacts G', G<8> and A<17>, B<17> of the feeders A, B feeding the fault, close, whereas A<18>, B<18> remain open. Relays M, M<2> produce energization of trip coils A<6>, B<6>. If, with F<1> closed, a fault occurs on E, all contacts A" &c. are closed. but with the faultcurrent direction obtaining, contact K' will close and apply a potential to M which is equal and opposite to that applied by closure of A", B", thus ensuring that only the relay L operates and trips out C<1>, D<1> and F'. If fault current from healthy busbars reaches the faulty busbar over the connected remote ends of the feeders when F' is open, the relay of one of the " outgoing " feeders at least will operate its lock-out contact and prevent disconnection of the healthy busbar. If, with F<1> open, a fault occurs between it and the transformer F<2>, the fault-current direction from busbar E would be such that K would close K<6> and prevent energization of relay L, and accordingly the busbar E would not be disconnected. Contacts F<5> on breaker F', however, make over contact K' of relay K an alternative circuit to L<2>, the contacts F<5> being time-delayed so as not to produce operation when F<1> legitimately opens to isolate faulty busbar E<1>, the delay allowing time for the relay K to restore and reopen contact K<6>. Transformers or generators as well as feeders, may constitute the circuits A &c. and when the latter are such that current can only flow one way in them, their relays may omit the " voltage coils.