Rapid Pilot Protection for LCC-HVDC Transmission Lines Utilizing Specific Frequency Measured Impedance Characteristics

To address the issues of slow operation speed, high synchronization requirements, and susceptibility to the influence of distributed capacitance in existing pilot protection for LCC-HVDC transmission lines, a novel pilot protection method utilizing the measured impedance characteristics is proposed. Measured impedance is utilized to characterize the frequency-domain differences under various fault conditions. Under forward fault conditions, the measured impedance exhibits purely capacitive or purely inductive characteristics within a specific frequency band. Under reverse fault conditions, the measured impedance corresponds to the transmission line wave impedance, with the line-mode wave impedance stabilizing within a specific frequency band, where the imaginary part much smaller than the real part. Leveraging the characteristics, a pilot protection scheme is proposed. Simulation analysis shows that the protection method can fast and correctly identify faults, withstand fault impedances of up to 900 Ω, is unaffected by distributed capacitance, and has low synchronization requirements on both sides. The method is capable of being applied as a rapid backup protection for long-distance LCC-HVDC transmission lines.