Patent GB-284202-A (GB)
Title: Improvements in protective systems for electrical circuits
IPC: H02H7/26
Filed: 1927-09-12
Abstract: 284,202. Longbottom, C. M. Jan. 24, 1927, [Convention date]. Cut-out arrangrments.-Relates to discriminating protective systems for sectionalized circuits in which a relav at the. circuit-breaber locations controlling the faulty section is arranged to complete through pilot wires the circuit of locking relays of preceding circuit-breakers so that only the circuit-breaker nearest to the faulty circuit on the power side will be operated. As shown in Fig. 1, multiple contact or master relays 12 operated an overload in the line 10 through current transformers 11 complete energizing circuits from local batteries 13 to time lag relays 14 controlling the local circuit-breaker trip coils 16 and to lock-out relays 15 through pilot wires 17, these lock-out relays controlling normallyclosed contacts in the trip-coil circuits of the adjacent circuit-breakers on the power side. Thus when the time. lag relays 14 have closed their contacts only the one nearest the fault will be effective in closing its circuit-breaker tripping coil as the lock-out relays in the circuits of all the other energized time-lag relays will have been operated by the multi-contact relays at succeeding circuit-breaker locations. Consequently only the circuit-breaker adjacent to the faulty circuit on the power side will be tripped. In a modified arrangement the operation of any master relay completes the circuits of all the preceding lockout relays. Each pilot wire circuit contains a time fuse 18 so that the corresponding lock-out relay may be de-energized if the desired circuitbreaker fails to open. Modifications of the invention are described, for use with parallel feeders or for operating two or more circuitbreakers at a single location, a common time lag and lock-out relay being provided for all the circuit-breakers at each location although separate multi-coloured relays are provided in each individual conductor. Such relays may be provided with potential windings so as to be responsive to the direction of flow of power. For ring main systems two systems of the type described are provided operating in opposite directions from the source of power, each system being provided with suitably arranged power directional relays. In the further modification shown in Fig. 4 the lock-out relays are replaced by multi-contact selectors 15, their energizing coils 21 being fed by impulse transmitters 23 driven on energization of the relays 12 by motors 22 fed by current diverted from the transformers 11. The timelag relays 14 are also substituted by multi-contact selectors on the motor shaft and by suitable contacts of the selectors 14, 15 one of these selectors may when overrunning the other complete the correct circuit-breaker trip coil circuit. In a further modification, Fig. 5, the selector 14 and impulse transmitter 23 are stepped round by an electromagnet 24 energized from the local battery 13. the lockout relay 15 being fed through a transformer 25. In this case the selector 14 is merely connected to have a suitable time delay in engaging sets of contacts in the local tripping circuit.