Zone-3 Impadance Reach Setting of Distance Relays by Including In-feed CurrentEffects in an Adaptive Scheme

The undesired operation of zone-3 distance relay may be one of the most conspicuous protective relaydue to the incorrect operations of this relay that have been conducive to the severity of blackouts.Therefore, determining the accurate zone-3 setting of the distance relay is deemed to be necessary. Thispaper focuses on the development of a new technique for calculating zone-3 setting of distance relays.The proposed technique utilizes impedance seen by distance relays in order to compute zone-3 settingof the relays when faults are modeled on the reach of zone-2 of primary distance relays for themaximum and minimum generation outputs of the power system. The new technique is also improvedto be used in an adaptive protection system. The technique and its adaptive version are applied to theIEEE 30-bus test system under different operating circumstances to reveal its robust performance.System simulation studies show that the proposed scheme is able to increase the reach of zone-3 relayswithout causing mis-coordination problems. Therefore, the two main requirements of the protectionsystem, namely security (without causing coordination) and simultaneity, would be satisfied.