Maloperation of Zone-3 Distance Relay Prevention Using Distribution Entropy

Maloperation of third-zone distance relays is predominantly caused by power swings, load encroachment, and voltage instability events. Another possibility for third-zone distance relay maloperation is a delayed voltage recovery event. If the impedance trajectory enters the zone-3 reach of a distance relay owing to a delayed voltage recovery event, it can be identified using the severity index-based method. However, the same method requires a relay margin index to be calculated, which is possible only if the impedance trajectory lies outside the zone-3 reach following fault clearance. If the impedance trajectory lies inside the zone-3 reach, even after the fault clearance and event changes from a fault to a delayed voltage recovery event, then there is a chance of maloperation of the third zone distance relay. The proposed method using distribution entropy identifies fault occurrence and fault clearance events critically which is been used in the distance relays for IEEE 39 bus test system and the results are found to be satisfactory in terms of prevention of maloperation of third zone distance relay during non-fault events and operation during fault events. In addition, the security index of the distance relays with proposed algorithm is enhanced by 20% compared to their operation without algorithm while the dependability index remains same.