The Effect of Fault Resistance on the Earth Fault Characteristics in Unearthed and Compensated Neutral Medium Voltage Networks

In unearthed neutral medium voltage network the maximum earth fault current, at zero fault resistance, is limited by the total earth capacitance however for compensated neutral network the maximum earth fault current is limited by the total leakage conductance and the compensation branch. The effect of the fault resistance on the earth fault characteristics, in both unearthed and compensated neutral networks, is investigated in this paper. The investigations include the effect of the fault resistance on the fault current, fault voltage, the transient recovery voltage (TRV) and the rate of rise of the transient recovery voltage (RRTRV). A realistic 20 kV medium voltage network model is used for the required investigations. The network model has been implemented using EMTP-ATP program. Based on the simulation results, it is found that the fault resistance has a significant effect on the earth fault characteristics which is found different in compensated from unearthed neutral networks.