Accelerated Zone II Operation of Distance Relay Using Impedance Change Directions

Legacy distance protection introduces an intentional delay before the trip command for zone 2 internal faults. Instantaneous fault clearance in such faults can be achieved if distance relays are equipped with reliable communication. However, communication channel is not available or enabled in some lines. Besides some channels are prone to faults occurred on the line degrading their reliability. To overcome such drawbacks in instantaneous fault clearance, a local algorithm is proposed that uses the relay local signals to accelerate the trip for zone 2 internal faults. The change seen in the relay impedance resulted by remote circuit breaker operation (RCBO) is the decision criterion in this method. The related impedance change equations are analytically derived and formulated. It is shown that the proposed method outperforms the similar approaches and improves their shortcomings in light-and no-load conditions and zero resistance faults. While most of the methods in the literature are not sensitive enough to detect single-phase RCBO, which is common during single-phase transient faults, significant improvement is attained by the proposed method in this regard. Performance of the proposed method is investigated under various fault and system conditions. Simulation results disclose high reliability of the proposed algorithm during all these conditions.