Patent GB-553073-A (GB)
Title: Improvements in or relating to protective systems for electricity distribution networks
IPC: H02H7/26
Filed: 1941-11-04
Abstract: 553,073. Protective cut-out systems. HABGOOD, E. V. C. Nov. 4, 1941, No. 14218 [Class 38 (v)] A discriminative protective system for sectionalized systems such as radial feeders or ring mains inter-connecting substations, has a quickacting, overlead-responsive relay at each breaker-location for rendering inoperative for a period the next breaker away from the fault, the lock-out means acting at the end of the period to remove the lock and allowing the next breaker to operate in case the breaker nearest the fault fails to open. When the desired breaker has operated it may make an additional trip circuit for the breaker beyond the fault so as to ensure isolation of the faulty section. In Fig. 1 substations 2 ... 4 containing breakers I, O with appropriate subscript, are interconnected by a ring main 1, the substation 3 including a "key " breaker K which always opens regardless of the fault-location, to divide the ring main into two radial feeders. Each breaker is controlled by a trip coil, as 5a for I<SP>2</SP> shunted by a time-fuse 7a, the circuit including a quick-acting relay 8a contralling contacts 80a, 81a in a lockout circuit of the preceding breaker in the ring, the contacts 80b, 81b of breaker O<SP>2</SP> being connected over reversing switch 11b and pilot wire 12b to the lock-out relay coil 13a of breaker I'. Thus on fault at F<SP>1</SP>, 5b trips O<SP>2</SP> when the time-limit of 7b expires, and 8b at once energizes 13a which closes contacts 15a to short-circuit the trip coil 5a and prevent it from opening I<SP>2</SP>. Similarly 8a prevents opening of the preceding breaker, by closing contacts 80a, 81a. If breaker O 2  fails to open, a time-relay 10b open the circuit of 13a at 101b, so allowing I<SP>2</SP> to open, thereby closing contacts 16a and making over contacts 80a, 81a, reversing switch 17a and pilot lead 18b to the shunt trip coil 19b of O<SP>2</SP>. This circuit can also be made by contacts 102a of time-relay 10a so as to trip the breaker beyond the fault if I<SP>2</SP> fails to trip and close contacts 16a, such tripping being required with a fault F<SP>2</SP> at the substation 2, when the " key " breaker , is required to be reclosed as soon as may be after tripping. This reclosing is, however, prevented by lock-out windings 21. 20 energized by contacts 16b of a breaker O<SP>2</SP> if and when it opens, over the pilot circuit 18f and reversing switch 17b, this arrangement also preventing K being reclosed if O<SP>2</SP> fails to trip a fault F'. When K, O' has isolated a fault F<SP>3</SP> in substation 3. an isolating switch S can be opened to allow K to be reclosed. Contactors 13a &c. have additional contacts 14a &c. in the circuit of relays 10a &c. to prevent their energization while the contactors are themselves energized. Any breaker can be converted into a "key " breaker by opening its reversing switches and moving all the other reversing switches to the position away from the " key breaker. Instead of shortcircuiting the trip coils by means of the contactors, the trip coils may have neutralizing coils which may either be energized by the relays 8a &c. Fig. 3. (not shown), or may be short circuited by contacts operated by the contactors. Fig. 4 (not shown), this latter arrangement also dispensing with the contacts 102a &c. In Fig. 5, the protective gear of a substation 2 is interlocked with the gear of the feeders supplying it. such that a fault at F<SP>2</SP> causes opening of breaker O but not of I. Thus relay 25b closes contacts 251b energizing the shunt trip coil 19b of breaker O and also the relay 24b, which opens the trip circuit of coil 19a at 241b, and as the contactor 13a is energized to shortcircuit the trip coil 5a, the breaker I remains closed. On fault at F' in the station, fed from the left, 13a is not energized, so I trips, whereas 13b is energized to render inoperative the coil 5b; the breaker O is. however tripped by its shunt coil 19b over contacts 80a, 81a. 241a and closed contacts 16a of the opened breaker I. The breaker may be replaced by fuses, in which case the relavs 8a &c. are energized bv the current transformers and the contactors place short-circuits about the fuses for a period. In yet another form. Fig. 2 (not shown), comprising substations in series in a ring main, the outgoing breakers only are tripped. depending on the direction of the power-flow, and a shunt trip coil for the outgoing breaker at the substation preceding the fault is energized when the outgoing breaker at the substation beyond the fault is tripped.