A new index for evaluating protection vulnerability

A cascading trip of distance relay due to overload caused by another line tripping has been observed in some blackouts. Preventing such an unwanted trip of a distance relay could contribute to blackout prevention. In this paper, a new index (PVI) for evaluating vulnerability from distance protection viewpoint is proposed which indicates the risk level of a distance relay that can lead to multiple line outages due to overload. Case studies on a real system show effectiveness of the proposed index. The proposed index can be utilized to make a decision on execution of preventive actions before a blackout develops.