Abstract: In order to greatly improve the fault prevention ability of distribution network and the rapid disposal ability of single-phase grounding fault of distribution line, the transformation of arc suppression coil parallel low resistance grounding is comprehensively promoted in the substation. After the low resistance is put into operation, the current generated by single-phase grounding fault is large, which has a certain impact on the setting value of main transformer low backup, 10 kV line and grounding transformer, and the setting principle has changed. Whether the original setting value of 10 kV system can meet the requirements must be checked to prevent overcurrent protection tripping caused by low resistance input. The 10 kV system adds zero sequence overcurrent protection tripping or alarm function to realize rapid fault isolation or location and line selection after single-phase grounding fault. This method is used to calculate and check the setting value of 10 kV system, which has good adaptability to the power grid, and there is no misoperation of relay protection in case of single-phase grounding fault. It completely solved the problem that dispatchers used to select lines by pulling wires, and the operation and maintenance unit dispatched a large number of human and material resources to patrol the lines blindly, and improved the fault prevention ability of distribution network.