Voltage pole-wave protection scheme for multi-terminal DC grid

With the rapid development of flexible DC transmission and multi-terminal high voltage direct current transmission (HVDC) (MTDC) grid, the protection schemes of flexible DC transmission lines are still the traditional methods, which do not achieve the properties of fast and selective operation in the DC grid. In this study, using Zhangbei MTDC grid as the research object, the fast protection of DC transmission lines of MTDC grid has been studied. First, the voltage response characteristics of fault line and non-fault line at the boundary of DC lines are analysed. On the basis of this, using wavelet transform to extract the characteristic value of voltage pole-wave, this study put forward a high-speed non-unit protection criterion to identify the internal and external faults. In addition, two auxiliary criteria are constructed to identify lightning disturbance and faulted pole, respectively. Finally, a simulation model of Zhangbei MTDC grid is constructed, and the effectiveness of the proposed protection scheme is verified by extensive simulation results