Phase-to-Phase Distance Relay Based on the Measured Impedance Trajectory

The measured impedance trajectory changing with fault resistance during multi-phase faults and the reasons that fault resistance may cause unwanted impedance relay operations in two-source systems were analyzed in this paper. To improve the impedance relay adaptive ability and reliability during three phase fault, a combined phase-to-phase impedance relay based on the measured impedance trajectory was presented. The relay is composed of three criteria respectively called the reactance line based on the measured impedance trajectory, the sending end and the receiving end directional lines, whose transient and steady state operating characteristics have been analyzed for forward and reverse faults. The simulation test was made by RTDS on a 340 km long 750 kV line in a two-source system. Theoretical analysis and dynamic simulation test results show that the adaptive relay can respond to three phase faults and phase-to-phase faults, and has satisfactory performances.