Instantaneous overcurrent relays for distance relaying

Instantaneous isolation of faults on transmission and distribution lines is ever a problem of the relay engineer. The use of instantaneous overcurrent relays as applied to the system of the Oklahoma Gas and Electric Company is discussed in this paper. Relays of this type were applied in conjunction with already installed overcurrent time delay relays, giving a form of distance relay protection. Operating results have proved the scheme to be highly satisfactory. Economies realized in the better coordination between relays and fuses by using instantaneous relays also are discussed briefly.