Pole-to-ground fault analysis in transmission line of DC grids based on VSC

The DC transmission lines have become one of the components with high fault probability as DC transmission technology based on VSC is often used for long distance transmission in which system most of faults are pole-to-ground fault. Therefore, with pole-to-ground fault of DC lines being a typical fault of DC grids transmission system, a detailed analysis of the fault characteristics is of great practical significance for fault detecting and protection design. According to the characteristics of the fault current circuit when the pole-to-ground fault occurs, the three stages of fault process were presented in detail. Firstly, the voltage of capacitor and fault current expressions of DC-side capacitor discharge stage were derived. Secondly, the state equation of grid-side current feeding stage was listed. Thirdly, the distribution of DC-side capacitor voltage in voltage recovery stage was analyzed. Moreover, for different grounding resistance, the fault characteristics of the system in each stage were analyzed, which was divided into under-damping and over-damping. Finally, the accuracy and effectiveness of the fault analysis was validated through a two-terminal DC transmission system which was established in Simulink.