The resonant earthed neutral is the dominant neutral point treatment for the medium voltage level in many Central European countries, MELZER [1]. Because of the growing percentage of cable and increased use of power electronics in distribution networks both the fundamental and the harmonic components of the residual earth fault current IRES rise. This can lead to a violation of the upper limits of the residual earth fault current IRES according to DIN VDE 0845-6-2 [2] as well as the permitted touch voltage UTp according to EN 50522 [3]. Thus it is very convenient to be able to determine the residual earth fault current in case of a single phase earth fault by using the voltages measured in the faultless network. The presented model enables the calculation of residual earth fault
current without the realization of complex and costly field tests. The calculation uses the voltages measured at the busbar and the current network configuration. Fault location and fault impedance can be varied as pleased.