GB360455A - Improvements in electric protective arrangements - Google Patents

Abstract

360,455. Protective cut-out systems. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, and LANE, F. J., 97, Harlesden Gardens, Harlesden, both*in London. July 29, 1930, No. 22830. [Class 38 (v).] Relates to a protective system for lines and apparatus in which a vibrating relay 5, 13 at each end of the section 1 is energized by a current transformer 2, 3 and the contacts of the two synchronous relays are interconnected through pilot wires 9, 11 and the tripping coils 10, 14 of the circuit-breakers so that when the vibrating relays fall out of synchronism on fault the circuit breakers are tripped. According to the invention, in order to adapt the system to a circuit fed from one end only, an auxiliary overload relay 18 is produced at each end energized from current transformers 4, 12 and serving normally to short-circuit at the contact 19, the operating windings of the vibrating relays, and at the contacts 20 the trip coils 10, 14 of the circuit breakers and also the contacts of the vibrating relays. In consequence, the vibrating relays do not come into action until a fault develops. In the event of default, with the supply as from one end only, the " far end " relay 18 may not be energized but in this case the contacts of the vibrating relay at this end remain short-circuited and the pilot wire circuit is intermittently closed by the " near-end " vibrating relay thereby causing tripping of the " near-end " circuit breaker. With through faults both relays 18 operate to leave the protection in charge of the two vibrating relays which will vibrate in step without result if the fault is outside the section. In a modification for a three-phase circuit, Fig. 3 (not shown), a pair of vibrating relays at each end is employed energized by current transformers connected to provide for earth faults as well as for faults between phases ; a single vibrating relay at each end is adequate to give full protection if connected up to current transformers which are interconnected as described in Specification 304,357, [Class 38 (v), Electric switches &c.]. In this case, the auxiliary overload relays are unnecessary as the vibrating relays are energized only on fault. The system may be extended to provide for the tripping out fault of the circuit breakers at both ends although the supply is from one end only, Fig. 6 (not shown).