Electerical Engineering, University of Zanjan
The undesired operation of zone 3 may be one of the most conspicuous protective relay features due to the incorrect zone 3 relay operations which have been conducive to the severity of blackouts. Therefore, determining the accurate zone 3 setting of the distance relay is deemed to be necessary. This paper 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 setting of the relays when faults are modeled on the reach of zone-2 of primary distance relays for the maximum and minimum generation outputs of the power system. The new technique is also improved to be used in an adaptive protection system. The technique and its adaptive version are applied to the IEEE 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 relays without causing mis-coordination problems. Therefore, the two main requirements of the protection system, namely security (without causing coordination) and simultaneity, would be satisfied.