Modelling and live measurements of step and touch voltages at LV customers in urban areas caused by MV faults

Abstract

Earth faults in the medium voltage (MV) grid cause touch and step voltages in the low voltage (LV) grid. Since MV and LV grid share their earthing system at the MV-LV transformer, one might question the safety with respect to LV customers in case of a phase-to-earth fault, occurring in the MV grid. Models and actual measurements in a operating grid are preformed to determine the current distribution and touch voltages. The results show that phase-to-earth faults in urban global earthed areas leads to low source voltages for touching. The models show the current distribution phenomena in a global earthed grid.