Novel transient current-based protection scheme for DC line faults in UHVDC system

DC line faults are a major threat for Ultra High Voltage Direct-Current (UHVDC) transmission systems. This paper proposes a non-unit protection scheme based on transient current. The difference in transient current magnitudes can be used to differentiate the faults on the protected DC line from the inverter-side-external faults. The magnitudes of transient currents on both sides of the boundary unit are used to distinguish DC line faults from the rectifier-side-external faults. Using these characteristics, the proposed protection is constructed. Since the measured transient currents are local, there is no need for fast telecommunication link and the relay can detect DC line faults within a few milliseconds. Theory analysis and simulation results have demonstrated the correctness and validity of the proposed method.