Prevention of Cascaded Events of Distance Relay Zone Three: Using Logic Control Circuits

Transmission lines are a vital part of the electrical system, as they provide the path to transfer power between generation and load. Factors like deregulated market environment, economics, right of way clearance, and environmental requirements have pushed utilities to operate transmission lines close to their operating limits. The effects of a major blackout have become more serious as a result of the wide area interconnections. Due to the lack of transmission enhancement during the last decades and the resulting low security margins, the risk of major outages for the power grid has also increased. The load encroachment is a problem particularly in zone 3 of distance relay caused by increasing load. This book presents a new method to prevent cascaded events of distance relays caused by zone 3 elements in case of heavy loaded transmission line or during load encroachment by using logic control circuits. Undesired operation of distance relay is a very critical situation; leading to more operation of other distance relays and cascaded to partial or total blackout in the end.