Synchrophasor Assisted Vulnerability Assessment of Zone 3 Distance Relays during Power System Stressed Condition

Analyses of the recent blackout worldwide demonstrates the contribution of zone 3 of distance relays in expanding the cascading outages in 75% of major wide area disturbances. Vulnerability assessment can be used as a useful approach for preventing of cascading outages by early detection of the critical relays which may be incorrectly operated in power system stressed conditions such as load encroachment events. In this study, in order to identify the critical relays whose maloperation can cause the cascading outages, a novel vulnerability index is introduced based on the relay margin and its sensitivity to power flow. Based on the relay operation margin sensitivity to flowing power of the protected line, a control method to increase the relay margin of the critical relay is also proposed. A novel supervisory index based on synchrophasor measurements is proposed to monitor the vulnerable distance relay to prevent its contribution in expanding the cascading outages. The efficiency and capability of the proposed approach is evaluated on IEEE-39 Bus test system and the obtained results confirm the effectiveness of the proposed method.