Accurate Evaluation of Dynamic Impedance Characteristics in Distance Protection Relays

Almost all modern distance protection relays are designed and manufactured with dynamic impedance characteristics. Dynamic characteristics help to detect faults in which the impedance point of the fault will be situated with some distance from the actual location of the fault due to different uncertainties in the power system. In this article, a ZIV distance protection relay, model ZLF, which provides a dynamic quadrilateral impedance characteristic, is precisely set, and new formulations and methods are proposed in order to stabilize the dynamic characteristic into a static one during test sessions, so that all the sides of the quad characteristic can be accurately evaluated. The results of practical tests and simulations using this relay show that by using the proposed formulations and methods, it is possible to test and examine all sides of the impedance characteristic without any failures, and to obtain a satisfactory performance from the protective relay.