LAUSR

Abstract Fast and reliable DC line protection is an essential challenge for the modular multilevel converter (MMC) based multi-terminal direct current (MTDC) grid. This paper proposed a novel single-ended protection scheme for DC lines in MMC-MTDC grids. Firstly, the values of the initial voltage traveling wave (IVTW) generated by internal and external faults are calculated by using the equivalent model of the MTDC grid, respectively. Then a criterion for identifying internal and external faults is constructed based on the amplitude ratio of the low-frequency component of the IVTW to its high-frequency component. The amplitude of the IVTW in both frequency bands is concisely expressed by the modulus maximums of stationary wavelet transform (SWT). Additionally, the criteria for discriminating the fault direction and the faulted pole are also proposed, which are both based on the integral values of the fault component currents on positive- and negative-pole lines. Lastly, simulation results verify the effectiveness of the proposed protection scheme.