Abstract: ABSTRACT: Taking an event of abnormal action of a small current grounding line selection device as an example, the analysis process of the abnormal action of the protection caused by the single-phase grounding fault of the 10kV line in the substation is described. And analyze the cause of the event according to the abnormal phenomenon, draw conclusions and propose solutions, so that the operation and maintenance personnel can accurately and skillfully judge and solve the abnormal operation of the device, improve the accuracy of line selection for single-phase grounding faults, and ensure power supply. reliability.