Impact of advancements of numerical distance relays over setting and testing the ground faults characteristics

The paper describes different techniques in testing the characteristics of modern microprocessor impedance relays and their influence over developing a valid test plan. First, a brief description of historical development of distance relays is described. Then, the need for automated testing of the relays is explained. A practical application in testing phase-to-ground faults characteristics is presented. First the concept of loop impedance calculation is described. Challenges experienced and solutions provided for automatic testing of the impedance relays are shown. The paper emphasizes the importance of correct selection of the zero sequence compensation factors and shows the impact over relay operation. Finally the results are summarized and conclusions are drawn.