Initial traveling wave waveform-based single-ended setting-less protection for VSC-MTDC grids

The main challenges associated with the existing protection schemes are that they are easily affected by the transition resistance and require threshold settings. To address such challenges, this paper proposes a single-ended setting-less protection scheme for VSC-MTDC grids which is based on waveform characteristics of initial traveling waves (ITWs). In this paper, first, the amplitude and transmission characteristics of the ITW are deduced, and then the characteristic that transition resistance only affects the amplitude of the ITW but does not affect its waveform is revealed. Subsequently, the difference between the ITWs in internal and external faults are investigated. Moreover, the time domain expressions of the ITW are obtained when faults occur on both sides of current-limiting reactor (CLR), respectively. Finally, an overall protection scheme is proposed which can distinguish between internal and external faults through comparing the similarity of ITW waveform. The salient feature of the proposed strategy is that it is not affected by the transition resistance, and has an adequate tolerance to the fault location, lightning disturbance, noise, etc. To verify the effectiveness and reliability of the proposed scheme, several simulations have been carried out on Zhangbei four-terminal VSC-HVDC grid using PSCAD/EMTDC software.