GB820711A - Improvements in protective switch gear systems for polyphase electric power transmission and distributing networks - Google Patents

Abstract

820,711. Protective cut-out arrangements. ELECTRICITE DE FRANCE, SERVICE NATIONAL. Feb. 3, 1956 [Feb. 3, 1955], No. 3535/56. Class 38 (5). A polyphase protective system comprises a circuit-breaker connected between a bus-bar set and earth, the several phases of the circuitbreaker being individually controlled by respective fault-responsive means in the several phases of the protected circuit whereby a fault to earth in one or more phases or a fault between phases causes the contacts of the corresponding phase or phases of the circuit-breaker to operate, thereby short-circuiting the fault path and permitting disconnection of the faulty phase by an isolating switch. As shown in Fig. 4, a 3-phase bus-bar J supplies feeders L 1 , L 2 , L 3 through isolating switches SRS 1 &c., the circuit-breaker I being normally closed and connected to the bus-bar J through a normally open isolating switch SR, the other side of the breaker I being connected to earth through a bus-bar Jm and normally closed isolating switch ST. Normally open isolating switches SRD 1 &c. may connect the feeders L &c. to earth through the switch ST. Relays 1, 2, 3 controlled by potential transformers Tp and current transformers Ti 1 &c. operate the respective phases of the breaker I and isolating switches in response to abnormal conditions in the feeders. On occurrence of a transient earth fault the respective relay of the faulty phase of that feeder causes closure of the corresponding phase of switch SR, followed immediately by opening of the corresponding phase of breaker I, the switch SR consequently opening and breaker I closing. In the event of a permanent earth fault the following additional operations occur: switch SR closes, the respective switch SRD of the faulty feeder closes to earth that feeder through switch ST, the switch SRS of the faulty feeder opens, the breaker I opens, the switch SR opens, and breaker I closes, the feeder thus remaining earthed. For normal control operation a feeder L is switched in by closure of its respective switch SRS. To open a feeder L, switch ST is opened, SR is closed, the corresponding switch SRD is closed, and SRS can now be opened with zero volts across its terminals. The breaker I is opened, switch SRD is opened and switch SR opened. Breaker I and switch ST are then closed. Fig. 5 (not shown) shows a pair of 3-phase busbar stations supplying a pair of 3-phase feeders, either one of which may be connected to either station, the whole system being protected and controlled by a pair of circuit-breakers and a number of isolating switches as described with reference to Fig. 4.