LAUSR

The fast and selective protection using fast dc circuit breaker to break the fault current and isolate faulty lines satisfies the requirement of fault clearance in HVDC grids. However, traditional derivative-based traveling wave protection suffers from low-sensitivity problem when high-impedance faults occur. Based on the analysis of the fault initial traveling wave, it is concluded that the distortion degree of the fault initial traveling wave is related to the location of the fault, and the amplitude of the fault initial traveling wave is related to the fault impedance. Then a Levenberg–Marquart (LM) optimal approximation method is proposed to extract the fault distance information from zero-sequence fault current initial traveling wave. The optimal approximation parameters respectively reflecting the fault distance and fault impedance can be obtained. A non-unit traveling wave protection scheme is proposed based on the parameters. A ±400 kV modular multilevel converter (MMC) HVDC grid test system is built in PSCAD/EMTDC to verify the proposed method. The simulation results show that the parameters can directly correspond to the fault distance and fault impedance, and the proposed method can fast and reliably identify dc line faults. Finally, the sensitivity of the proposed method is studied by comparing with three different methods.