GB1276632A - Improvements in or relating to distance protective arrangement for electrical networks - Google Patents

Abstract

1276632 Protective arrangements SPRECHER & SCHUH AG 11 Nov 1970 [25 Nov 1969] 53691/76 Heading H2K In a network in which protection is provided by multi-zone distance relay arrangements, each being operative in first, second, third and "backup" zones with progressively increasing time delays, incorrect operation due to an increase in transmission load is prevented by switching means 22 ... 24 which normally "block" the third and "backup" stages of each relay arrangement, the switching means being operated to "unblock" these stages when a central computer 19 connected to various points of the network has calculated the existence of a fault within the reach of the relay arrangement. Each relay arrangement comprises current and voltage transformers 2, 1 connected to a replica impedance 5, 6 and a resistor 7 to provide an output to a directional relay element 16. An under impedance relay 4 is also connected to the transformers and when operated energizes relays 14, 18, 25; 26 which operate with the appropriate time delays to select in sequence the zone of operation for the arrangement. A relay 22 at contacts 23 complete the circuit for the third zone relay 25 only in response to a signal from the computer 19. This relay also closes contacts 24 in series with the contacts 27 of the relay 26 so that on expiration of time delay of the relay 26 a tripping circuit is directly completed by the contacts 24, 27, the back-up protection provided by the relays 4, 26 being non- directional.