The influence of insulation active power losses on the single line-to-ground fault in medium voltage electrical networks with resonant grounding

Power delivery at medium voltage level over an ever-expanding electrical grid is more prone to faults than at other higher voltage level. The most common fault type in these electrical networks is the single line-to-ground fault. It is therefore necessary to design protection schemes that ensure a fast and selective detection of such faults. A reliable operation of the protective relays depends on the accurate analytical computation of the single line-to-ground fault current. This paper tackles a key issue of long-term scenario planning, namely the influence of the medium voltage distribution network insulation state on the fault current and on the medium voltage busbars zero-sequence voltage based on which the protective relays make a discriminatory decision when such a fault occurs. The purpose of this paper is to emphasise that the setting of these relays must be reviewed periodically and updated according to the latest insulation strength parameters values.