New adaptive scheme for calculating zone-3 setting of distance relay

The undesirable operation of zone 3 is perhaps 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 distance relay is considered to be necessary. This paper is focused on the development of a new scheme for calculating zone-3 reach setting of distance relays. The proposed technique utilizes impedance seen by distance relays to calculate zone-3 reach of the relays when faults are modeled on the zone-2 reach of distance relays of the transmission lines emanated from remote bus for the maximum and minimum generation outputs of the power system. The proposed technique is also improved to be used in an adaptive protection system. The proposed technique and its adaptive version are applied to the IEEE 30-bus system under different operating conditions to reveal its robust performance. System simulation studies show that the proposed scheme is able to increase the reach of zone-3 relays considerably without causing coordination problems. Therefore, the two main requirements of the protection system, security (without causing coordination) and simultaneity, are satisfied.