Fault detection method for flexible DC grid based on current limiting reactance voltage variability

Fast and reliable identification of DC line faults is the key to the stable operation of flexible DC grids. Based on the boundary element characteristics of DC lines, a fault detection method for flexible DC grids based on current limiting reactance voltage variability is proposed. First, the equivalent model of DC grid when different faults occur is established, and the filtered voltage change rate is used as the protection startup criterion by taking advantage of the rapid change of fault voltage. Secondly, according to the characteristics of voltage change at both ends of the current limiting reactance of the DC line after the fault, the peak factor is used to extract the voltage change characteristics to constitute the internal and external faults criterion. Finally, the ratio of energy values of positive and negative current limiting reactance voltages on the DC line is calculated to constitute the fault pole selection criterion. Simulation results show that the proposed protection scheme can effectively identify internal and external faults and fault poles, and its principle is simple, with low communication requirements, strong resistance to transition resistance, strong anti-interference ability, and can better meet the requirements of DC grid for the protection of the rapidity and selectivity.