Logic-based supervised zone 3 decision using wide area information

Zone 3 of a distance relay is used to provide backup protection for adjacent transmission lines. Zone 3 is vulnerable to operate during stressed system condition which leads to cascade tripping of transmission lines. Zone 3 decision becomes more effective, if reliable fault pickup information of adjacent line relays is available. Today, substations are being operated remotely from a central location by integrating substation data for optimum utilization of assets. Such information is used in this work to avoid unnecessary tripping of zone 3. Relay and circuit breaker status signals of adjacent lines are processed with simple logical operators to supervise the zone 3 decision. WSCC nine-bus and 39-bus New England systems are tested for effectiveness of the proposed method and found correct.