This paper analyzes the effect of different equivalent circuits of grounding equipment at the neutral on the protection of ground fault by injecting signal, and points out that the accuracy of protection scheme using admittance is reduced if the leakage reactance and exciting impedance of grounding transformer or extinguishing coil ignored. The accuracy of calculating transient resistance and the sensitivity of protection can be improved by considering these parameters. The experimental results verify the influence of parameters of grounding equipment.