Comparing measured impedance by distance relay in presence of resistive and inductive Fault Current Limiters

Distance relays are widely used as main and back-up protection for transmission lines. Their operation is based on impedance measurement at the relaying point, which can be affected by several factors, including pre-fault line loading and short circuit levels at the line ends. Continues demand for electricity energy leads to increase in short circuit levels along the power systems, which itself causes new problems. One of the proposed solutions for this problem is the utilization of Fault Current Limiter (FCL), which imposes further changes on the measured impedance at the relaying point, in spite of its benefits from the power system operation point of view. This paper studies the effects of superconductor series FCL, both resistive and inductive types, on the measured impedance at the relaying point. In addition to FCL impedance and peak current, its installation point affects the measured impedance. The ideal tripping characteristic would be presented and compared for both resistive and inductive FCLs.