Zone-2 setting of distance relays using user defined time-inverse over current relay charactieristics

Abstract

Distance relays are set in coordination with the over current relays for protection of sub-transmission lines. Depending upon the location of faults on the transmission lines, faults are cleared by the distance relays from their zone-1 or zone-2 operations. If the distance relays fails due to any relay failure reasons, then over current relays operates as backup relays to clear the same fault after some time delay. These time delays are known as coordination time margins. The coordination time margins with respect to backup over current relays are at minimum at starting of zone-1 and zone-2 of distance relays and increases in forward direction of zones of distance relays. In this research article, the zone -2 of distance relays are optimised in such a manner that desired coordination time margin remains valid for all the fault location in zone-1 and zone-2 of distance relays. Integration of decentralised distributed energy resources may cause the change in the fault levels which may lead to violation of coordination time interval among the distance and over current relays. In order to handle this problem, the non-standard time inverse over current relays are proposed for better zone-2 selection of distance relays. The proposed user defined non-standard time inverse over current relay have flexible relay characteristics to maintain the desired coordination time margin among the over current and distance relays for all possible fault locations on zone-1 and zone-2 of distance relays. The coordination of proposed user defined time-inverse over current relay and distance relays results in fast operation of backup over current relays and maintains the coordination among the distance and over current relays during any variable infeed from distributed energy sources.