A Novel Fault Impedance Calculation Method for Distance Protection Against Fault Resistance

Performance of distance protection based on the traditional fault-line impedance calculation method is adversely affected by fault resistance, which may cause distance protection to operate incorrectly, threatening the safe operation of power system. To improve immunity to the fault resistance, this paper presents a novel fault-line-impedance calculation method. The fault-line impedance, supplementary impedance, and measured impedance are rotated simultaneously in the complex plane until the supplementary impedance coincides with the positive direction of the real axis. Following the geometrical relationship between the rotated fault-line impedance and the rotated measured impedance in the complex plane, the fault distance and fault-line impedance are solved. The proposed method is immune to the fault resistance and insensitive to power angle and fault location variations. Furthermore, the proposed method can work well under various types of faults, e.g., AG, BC, BCG, and ABC. The simulation results show that the proposed method can calculate the actual fault distance accurately and identify in-zone and out-of-zone faults correctly.