Improvements relating to electrical protective relays

摘要

1,029,274. Protective arrangements. ENGLISH ELECTRIC CO. Ltd. Feb. 18, 1963 [Feb. 20, 1962], No. 6516/62. Heading H2K. A system for protecting a power line comprises a pilot link and a protective relay having an operating coil and a restraining coil at each end of the link, one coil of each relay being connected in series with an impedance in a shunt circuit terminating the respective end of the link and the other coil being connected in series with link. The impedance of each shunt circuit is equal in magnitude and phase angle to the characteristic impedance of the pilot link at the frequency of the current therein. The system is stated to improve the abilities of the relays to discriminate between internal and external faults and, in the ease of a fault fed from one end only, to render the relay setting at that end independent of the length of the pilot link. The system may be of the circulating-current or balanced-voltage types.