Abstract: 10 kV line zero sequence protection is a kind of protection in case of asymmetric grounding fault. When the line has asymmetric grounding fault, the zero sequence CT senses the fault zero sequence current, and then the switch acts and trips. If the arc suppression coil of the grounding transformer is put into operation, the inductive current generated will compensate the capacitive current at the fault point, resulting in the reduction of the zero sequence current at the line fault point and the failure to reach the protection setting value. The zero sequence current flowing through the grounding transformer will cause the zero sequence protection action of the grounding transformer to skip the level. Therefore, when the line zero sequence protection is put into operation, the arc suppression coil shall be withdrawn to ensure that the line with fault point can directly feel the fault current and trip at the outlet.