This article describes a novel method for identifying the correct fault zone in distance relays . The major difference of this from the conventional strategies is that it does not depend on fixed boundaries for backup zones. Here, information is exchanged between local relays and also a a command from the remote end relay.

EXSITING DISTANCE SETTING STRATEGIES
A distance relay usually contains three staggered distance zones which is divided into zone-1(an underreaching fast tripping, nondelayed zone), zone-2(set to cover the protected line plus 50% of the shortest adjacent line), and zone-3(It provides backup protection for uncleared faults) and also a starting zone called as zone-4.

PROPOSED SETTING STRATEGY
The ways in which the relays are set inorder to achieve the goals of selectivity and security of the power transmission system constitutes the setting strategy. It consists of a set of rules for rules for the relaying system. First, a a self preestimated fault zone is calculated by the relay at each end of a transmission line. This is done based on the setting rules like any conventional relay and also its own readings. In the second step, each
relay updates its self preestimated fault zone based on this local information. The third stage involves the sending of a command to the corresponding relay at the other end of the TL. This is done via an available communication medium via a specific modulated frequency.

get the report pdf here:
http://goo.gl/yo49G