Analysis of fault characteristic of HVDC transmission lines and its influence on current differential protection

As the main protection of AC system, the current differential protection performs well in rapidity and selectivity. However, for DC system, current differential protection can only be used as backup protection; in the meantime to avoid the influence of external fault and unbalanced current and ensure the selectivity of current differential protection, such protection often needs quite a delay. Starting from the characteristics of DC transmission lines, this paper mainly theoretically analyzes the characteristics of distributed capacitance and frequency variation of impedance parameters of DC transmission lines, and studies the influence of line characteristics on current differential protection of DC system. In addition, the DC transmission line solution model is compared and analyzed, and the factors causing poor performance of current differential protection are analyzed from the perspective of the solution model. Finally, the research of current differential protection is prospected.