An appropriate parameter of the grounding resistance at the neutral point can effectively suppress the load-side voltage sag caused by the single phase earth fault, and accordingly is favorable for the development of power quality. However the grounding resistance changes the zero sequence impedance of the system and will cause it fairly different from the directly grounded system in the value and distribution of the zero sequence current and voltage and in their phase difference. Through analyzing characteristics of the zero sequence current and voltage, this paper proposes a setting calculation of zero sequence current protection in 110 kV systems grounded via resistances at neutral points. And the operating condition of the zero sequence directional element is modified. For an enhanced 110 kV system, correctness of the proposed setting calculation is proved through field experiments and trial operation.