A new strategy for determining fault zones in distance relays

A new strategy (denoted P-SS) for estimating the correct fault zone in distance relays is introduced. The main difference between the P-SS and conventional setting strategies is that the P-SS does not depend on fixed boundaries for backup zones. It depends on exchanging information between local relays in the same station in addition to a command from the remote end relay. With the proposed strategy, zone-1 covers the entire length of the protected line, zone-2 covers the entire length of any next line irrespective of its length, and zone-3 covers the entire length of any line next to zone-2. The governing rules for the proposed strategy are presented. The strategy is examined against a wide range of setting problems of a real part of a high-voltage network with real relay settings. The results confirm that the P-SS achieves the required accurate, sensitive, and selective relay operation.