GB538864A - Protective apparatus for electrical distribution networks - Google Patents

Abstract

538,864. Protective cut-out systems. MASCHINENFABRIK OERLIKON. Nov. 16, 1939. No. 30212. Convention date, Nov. 17, 1938. [Class 38 (v)] A network is protected by a system which combines .the advantages of instantaneous tripping and reconnecting, with the consequent minimum of disturbance by transient faults, and selective protection which localizes the effects of faults of a more permanent nature, by operating with a time-delay depending on the magnitude of the current or voltage or circuit-constants, such as impedance. On overload, a circuit-breaker is tripped instantaneously and at once reclosed, and if the fault persists, further selectively-retarded trippings and resettings occur, the first operation being so rapid that the selective relays do not have time to operate. A single relay may be employed for both actions but, as shown, separate relays g, g<1> are provided, the latter being instantaneous and responsive to current, voltage or impedance. When energized, g<1> makes the circuit of the trip coil c and of one coil of a slow-release relay r over the contact a which is closed and opened with the main switch (not shown). The latter opens and an auxiliary contact thereof d closes and energizes over contacts of relay r a second coil of that relay and a coil p which operates contacts z or the closing valve of a motor, magnet, or compressed-air cylinder b for closing the main switch. Coil p also makes, over auxiliary contacts p<2>, p', respectively, a holding circuit for itself and an energizing circuit for a coil q which opens at q<3>, q<2>, respectively, the original energizing circuits of c, p and makes a further holding circuit for itself at q'. Hence, when d reopens, due to reclosure of the main switch, q remains energized and p is deenergized; r is also de - enerigized but remains lifted until its time-lag expires. If, therefore, on reclosure, the fault persists, reclosure of contacts g' is ineffective to make the circuit of trip coil c, this circuit being however made by the retarded operation of the selective relay g. When the main switch again opens and d closes, the circuit of reclosing coil p cannot be made until r falls back and de-energizes q. Further retarded reclosings can be effected by operating contacts in parallel to those of relay r by means of an adjustable time relay in dependence on relay g, the subsequent trippings, if any, being subject also to relay g. A change-over control switch h comprises contacts 7, 8 in the trip circuit and a contact 2 which can be changed over so as to be depressed against either contact 1 or 3 for, respectively, manual closure and manual tripping not followed by automatic reclosure. Only switches connected to actual or potential sources of energy need be equipped with automatic resetting apparatus.. By placing a voltage or phase-measuring relay in the circuit of the reconnecting relays of all except one of the circuit-breakers, reconnection of those circuitbreakers may be made dependent on voltagephase conditions, while the one breaker recloses instantly.