GB597155A - Improvements in or relating to electrical protective systems - Google Patents

Abstract

597,155. Protective cut - out systems. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. June 30, 1944, No. 12455. Convention date, Aug. 26, 1942. [Class 38(v)] In an electrical system, a plurality of circuits e.g. a supply circuit 3, a distribution feeder 5 and a tie circuit 7, are connected to a bus 1 through circuit-breakers 11 and disconnecting switches 13, 15. A differential relay 18 partially energised from each circuit by current transformers 25, affords protection of the portions of the system above the transformer 25 as viewed in Fig. 1, the remaining parts of the system being protected by over-current relays 27 energised by current transformers 29. In the event of a fault occurring at F, the balance of current entering and leaving the bus 1 is disturbed resulting in relay 18 closing its contact 19 to effect the tripping of all the circuit-breakers 11. Should a fault occur at G, this joint being outside the zone of protection afforded by relay 18 only results in the energisation of the relay 27 associated with line 5 consequently only tripping the circuit-breaker 11 in line 5. Fig. 4 illustrates a compact arrangement of the apparatus associated with each circuitbreaker 11 which may be that of Specification 563,641 wherein the current transformers 25, 29 are mounted in a single insulating housing 39, the current transformers 25 being mounted on the line side to afford " overlapping " protection over the portion of the system between the current transformers. In order that proper selective operation of the relays may obtain in the event of line 5 being subjected to an abnormally high voltage, the insulation of the housing 39 and supports 47, 49, 51 for the circuit-breaker 11 and switches 13, 15 is graded by the provision of spark gaps 53, 55; 57, 59; 61, 63 and 65, 67. The spark-gap 53, 55 nearest the line 5 is set to have the lowest break-down voltage so that the presence of an abnormal voltage on the line 5 results in the break-down thereof, the restriction of the break-down to this point thereby ensuring that only the relay 27 associated with the faulty line 5 is energised to trip the circuit-breaker 11 thereof, since the said point of break-down is outside the zone of protection of relay 18.