Non-Unit Transient Protection for LCC-HVDC Transmission Lines Based on Correlation of Current Derivatives

The reliability and sensitivity of HVDC transmission line's protection for HVDC system are in need of further improvement. So a new non-unit transient protection based on correlation of current derivatives (CDs) is proposed in this paper. According to the impedance frequency characteristics of converter and DC filter, the correlation characteristics between line current derivative (LCD) and DC filter current derivative (DFCD) are analyzed during fault transients. Simulation results show that the proposed protection scheme can correctly identify internal and external faults and is of high reliability and sensitivity.