Adaptive Reach of the 3rd Zone of a Distance Relay With Synchronized Measurements

In this paper an adaptive reach of the 3rd zone of a distance relay supported by synchronized measurements is presented. The operation of the proposed algorithm focuses on reducing the impact of infeed current in cases when there is more than one adjacent line. It is assumed that the synchronized measurements of voltages and currents are taken at the location of the relay and at the end of each adjacent line. The algorithm detects internal events and identifies infeed currents to extend the reach of the 3rd zone appropriately and eliminate the problem of zone under-reach. The performance of the algorithm is tested using the IEEE 39-bus test system. This includes processing computer simulations directly as well as replaying instantaneous values with an Omicron test set and feeding three phasor measurement units for more realistic conditions. The results confirm that the proposed algorithm can effectively improve the reach of the 3rd zone to cover the full length of the adjacent lines under different infeed current conditions.