Agent Based Supervision of Zone 3 Relays to Prevent Hidden Failure Based Tripping

In this paper, we propose a distributed agent based supervisory scheme to make Zone 3 relays robust to hidden failure induced tripping, facilitated by the communication network -- soon to become an integral parts of the smart grid. Possible elimination of Zone 3 relays (remote backup protection) has been studied in the recent past and these remote backup relays have been adjudged to be essential for power system protection [23]. Even though Zone 3 relays are often overly sensitive to remote line overloading, and are known to cause unwarranted trips during cascading failure scenarios, they are prescribed as acceptable means for remote backup. Therefore, providing robustness to Zone 3 relays to minimize the risk of erroneous trips, especially when hidden failures [10, 1] make them vulnerable to over reaction, is an important problem. In our scheme, a synchronous grid is populated with agents at each relay, and an agent hierarchy is maintained in master/slave relationship. The communication established between relay agents decreases the probability of erroneous Zone 3 trips thereby preventing them from aggravating cascading failure scenarios, and reducing the probability of cascading blackouts. Unlike other agent based relay proposals, ours is a nonintrusive approach.