Assessment of fault potential and touch voltage in the low-voltage distribution line system of the residential community

Abstract

Considering the increasing risk of electric shock in old residential communities, this paper investigated fault potential and consequential human-body touch voltage in the low-voltage (LV) distribution network under typical line-fault conditions by numerical simulation with a circuit approach. Three protective grounding configurations of the LV distribution system were of concern, and the electric shock scenarios considering practical situations were introduced for assessment. It has been observed that the phase-to-ground fault potential of equipment increases when the fault location is closer to the faulty equipment itself and decreases when it moves further toward the circuit end. The equipment in a building is likely exposed to the dangerous phase-to-ground fault potential under the line fault. As for line-to-neutral short circuit and neutral-line-open fault, the fault potential distribution mainly depends on the specific grounding configurations. Bonding of non-exposed steelwork in the buried building foundation to the nearby grounded grid may not be recommended in the literature, but it could effectively mitigate the touch voltage in and around the building of concern in this paper. Note that this measure, together with the local equipotential bonding method inside a flat, can provide enhanced protection against electric shock even if the protective device fails to operate or is unavailable. Among three grounding configurations, the one with multiple grounding points of the neutral wires up to the entrance of a building leads to the least dangerous touch voltage cases.