Pilot Protection for HVDC Transmission Lines Utilizing Phase Features of Measured Surge Impedance

Abstract

For the sake of improving reliability and speed of backup protection for HVDC transmission lines, a pilot protection method for HVDC lines is proposed based on phase features of measured surge impedances. Based on analysis of the phase features at line terminals for internal and external faults, it can be seen that within a certain frequency range, when an internal fault occurs, the measured surge impedance phases at the two line terminals are both nearly -90°. When an external fault occurs, the phases at the two line terminals are, respectively, about -90°and 0°. Since the phase differences between the measured surge impedances at the two line terminals are apparent under internal and external faults, the internal faults can be discriminated from the external ones with measured surge impedance phases. Because the phase features are only related to DC line boundary and line surge impedance but has nothing to do with fault distance, fault resistance and fault type, the proposed method can be easily set. A large amount of simulation results based on PSCAD/EMTDC indicate that the proposed protection method can discriminate internal faults from external ones fast and reliably under different fault distances, fault resistances and fault types with good sensitivity and quick action performance.