Abstract: When the 35 kV line of a 35 kV Substation in Guangdong triped due to fault, the low-voltage zero sequence protection of the substation transformer acted. The breakers on both sides of the substation transformer tripped and the ATS was locked. The substation power system was lost. Through analysis, it was caused by improper installation position of zero sequence TA at low voltage side of the substation transformer. This paper presents an improved method for the installation position of the substation transformer low voltage zero sequence TA, which solves the problem of incorrect action of station transformer low voltage zero sequence protection.