GB743323A - Improvements in electric protective and/or fault locating systems for polyphase alternating current power-transmission networks - Google Patents

Abstract

743,323. Protective cut-out systems. GIBSON, A. B'., and CENTRAL ELECTRICITY AUTHORITY, [formerly BRITISH ELECTRICITY AUTHORITY]. Jan. 1, 1953 [Oct. 1, 1951], No. 22868/51. Class 38(5) A polyphase distance protective system has current transformers 1a, 2a, 3a supplying a static network indicated at 4 which provides single-phase quantities I 1 , I 2 and KI o , the quantities I 1 , I 2 and I 0 being posi- .tive, negative and zero phase sequence current components respectively and K being the ratio of the zero sequence impedance to the positive sequence impedance. Voltage transformers 1b, 2b, 3b supply a further static network indicated at 5 which provides single-phase quantities V 1 , V 2 and V 0 , these quantities being positive, negative and zero phase sequence voltage .components respectively. These current and voltage components are supplied through transformers 12 to rectifiers 6 ... 11, the rectifiers 6, 7, 8 being connected so as to energize the direct coil 13a of an impedance relay 13 with a direct current proportional to 1, + I 2 + KI 0 and the rectifiers 9, 10, 11 being connected so as to energize the voltage coil 13b with a direct current proportional to V 1 - V 2 - V 0 . The arrangement so far described is stated to give equal distance response under singlephase-to-earth, phase-to-phase and threephase fault conditions. To provide equal response under two-phase-to-earth fault conditions, a double-earth fault selector relay 18 has one winding energized by the rectified positive phase sequence current I, and a second winding energized by the retified negative phase sequence current I 2 . When I, exceeds I 2 , the relay 18 opens contacts 19, 20 so that the relay 13 responds to the functions (I, + I 2 ) and (V 1 - V 2 ) only. A directional relay 16 energized by the alternating components V 1' I, controls contacts 17 which short circuit the relay coil 13a except when the direction of flow of positive sequence power in the protected feeder 1, 2, 3 is away from the station bus-bars (not shown). In the example shown, the relay 13 is a first zone relay and closes contacts (not shown) to trip a circuit-breaker immediately on the occurrence of a fault within its zone. A further, second zone, relay 14 has contacts (not shown) which control a time-delay relay (Fig. 2, not shown). Other impedance relays in conjunction with time-delay relays may cover further zones. Alternatively,. a single impedance relay may be used to cover all the zones, the relay having its impedance setting varied by means of a time-delay mechanism. The location of a fault may be determined by observation of the number of zonal impedance relays which operate, or where the single relay is used by observation of the setting at which the relay operates.