GB191027312A - Improvements in Methods of Clearing Faults from High Tension Alternating Current Distributing Systems. - Google Patents

Abstract

27,312. Taylor, A. M. Nov. 24. [Cognate Applications, 29,511/10 and 1766/11.] Protective arrangements.-Relates to the automatic disconnexion of sections or consumers' sub-stations on ring-main distributing- systems in the event of faults to earth, or between phases. Automatic circuit-breakers are arranged at the sides of each consumers' or substation as shown at a1, a2, &c., Fig. 1, and the arrangement according to the invention comprises means for automatically earthing the neutral point of the generator at the central station, together with pairs of relays at the consumers' stations adapted to open the circuitbreakers at both sides of any given station if the fault arises in the station, and at the adjacent sides of two different stations if the fault takes place between them. The action of the controlling-relays is made to depend upon the magnitude of the potential drop due to the fault, in order to prevent the circuit breakers of more distant stations from being opened. Fig. 2 shows the arrangement on a three-phase distributing - system for one consuming station provided with automatic circuit-breakers c1, C2, and wattmeter relays EB, EC of which the current coils are connected in series with each other in a circuit comprising the secondaries of six series transformers, three situated at one side of the station and three at the other, and all six in direct series connexion. The potential coils of the relays are connected in the manner shown with the secondaries of a potential transformer PT, which becomes active only if one of the phases leaks, the action being proportionate to the amount of drop of potential due to the leak. Differential relays may be employed instead of wattmeter relays. Under normal conditions of energy flow, both relays stand open. If a fault to earth arises outside the consuming station,'as at E, automatic means for earthing the generator through a resistance or reactance come into action first, and the potential coils of the wattmeter relays are energized. The fault current also disturbs the normal balance of the series transformers, and energizes the current coils of the relays in such a way that the contact of the relay on the near side of the station is urged to close its contacts, and the contact of the relay on the remote side is urged away from them. Thus the circuitbreaker c, is opened and the circuit-breaker c2 is unaffected. A similar action takes place at the station on the other side of the fault. In order to deal with a fault in the interior of the station, which affects neither of the wattmeter relays, the circuit of the series transformers is provided with a cross-connexion through a relay RT adapted to open both circuit-breakers. The cross-connexion is unaffected by fault current flowing to a fault outside the station, but takes current in the event of an inside fault. In order to deal with a fault between phases, one of the series transformer secondaries at each end of the station is shunted by a reactance or resistance in series with a fuse, the arrangement of wattmeter relays and relay in the crossconnexion being otherwise as above described. Overload relays, ammeters, or other measuring- instruments may be connected up to the seriestransformers. According to the Provisional Specification, use may be made of a doubleacting polarized or reverse-current relay in place of the pair of wattmeter relays; means may be provided for cutting-out one of a number of parallel feeders; and a relay arrangement comprising potential transformers, and series transformers with additional secondaries may be employed.