Abstract: Through the analysis of the abnormal sampling of zero sequence current, it is reflected that the boundary switch of customer property right is not configured reasonably in function. Selecting the simple "synthetic zero sequence" protection as the main protection of grounding fault will increase the false alarm rate of protection. A large number of field examples show that the boundary switch with"independent zero sequence CT"configuration can accurately collect small zero sequence current (commonly known as capacitive current), which is conducive to the accurate setting calculation of zero sequence current protection, and can ensure that the correct action rate reaches 100%, and the setting calculation method of zero sequence current protection has certain guiding significance for the on-site rapid setting calculation of distribution network personnel.