Transient current curvature based protection for multi‐terminal flexible DC distribution systems

Abstract

In a flexible DC distribution system, the converters will be blocked within a few milliseconds for its self-protection during the DC line fault. Using such a short period of the fault transient, it is challenging to identify the correct faulted area. In this study, the characteristics of fault current waveform and sudden change are analysed in detail, and the curvature algorithm is used to extract the current waveform difference between the internal and external faults. Then this study proposes a new scheme for the multi-terminal DC distribution system. This protection is developed based on natural variation characteristics and curvature of DC current under fault transients. Compared with the di/dt protection to correctly identify internal high impedance fault. The proposed method could identify faults with different high resistances quickly, meet the speed and reliability requirement of the DC distribution system. Numerous tests are carried out in both simulation and hardware experiments. Testing results derived under various fault conditions have demonstrated that internal faults with different impedances can be correctly identified by employing the proposed protection scheme.