A Pilot Protection for HVDC Transmission Lines Based on Current Correlation

A new DC line protection is presented on the basis of current correlation of DC filter and DC line. Characteristic analysis on DC filter shows that it behaves like an inductor at high frequency. Based on this characteristic, fault analysis demonstrates for DC line faults, at high frequency, currents of DC filter and DC line are negatively correlated, their correlation coefficient is theoretically -1 for either end of line. Under external faults, near faulty end, the currents of DC filter and DC line are positively correlated, their correlation coefficient is theoretically 1, whereas at the distance faulty end, they are negatively correlated, their correlation coefficient is -1. Thus, current correlations are used to detect faults. Simulations demonstrate that the proposed protection can identify DC line faults accurately. Meanwhile, it has no requirement for two-terminal data synchronization and has low communication requirement. Besides, it is sensitive to high-impedance faults.