GB291155A - Improvements in or relating to protective gear for alternating-current distribution systems - Google Patents

Abstract

291,155. Bell, H. G., and Metropolitan- Vickers Electrical Co. Ltd. Feb. 25, 1927. Cut-out arrangements.-A sub-station, situated either in a ring-main or in a radial main,. has feeders 14, 18 connected through circuitbreakers 13, 17 to its bus-bars 10, which in turn supply local circuits through circuit breakers 21. Current transformers 22, 25 are connected in a series circuit through a wattmeter relay, whose potential coils 44, 45 are supplied from the feeders 14, and across this series circuit are connected relay coils 35, 39 and equivalent impedance 137 to a star point 38 which is connected through a relay coil 42 to the star point 29 of the current transformers Relay coils 35, 39 are thus sensitive to the total current supplied to the station, whether from either or both of the feeders and operate to close their contacts on the occurrence of an internal fault and so energize both tripping coils 48, 49. Relay coil 42 is sensitive to an earth fault and similarly energizes coils 48, 49 in the manner described in Specification 144,073. On the occurrence of an external fault, the wattmeter relay operates to close its movable contact 55 on to either contacts 54, 59 according to the direction of flow opening 7 through the station and then energizes either coil 48 or 49 so as to trip the circuit breaker on the side of the station adjacent the fault. A wattmeter having coils 37, 41, 46, 47 may be used to indicate the total load on the station. In a modification the wattmeter relay is duplicated and is arranged symmetrically with respect to the internal faults relays.