Analysis of influence of imperfect contact between grounding electrodes and surrounding soil on electrical properties of grounding loops

The measurements of the grounding resistance of grounding loops installed in soils characterised by the structure that prevents a good contact between the grounding electrodes and the surrounding soil (e.g. karst and sandy terrains) showed that it is considerably influenced by the effective contact surface. Therefore, in such cases the grounding resistance cannot be predicted using the standard engineering methods based on the Laplace solution of the problem, where the perfect contact was assumed. The aim of this research was the estimation of the influence of imperfect contact on the loop grounding resistance and potential distribution in the soil during the earth fault. The research is performed applying the finite-element method on a real grounding loop buried in a two-layer soil. Imperfect contact is modelled by air gaps placed between the grounding loop electrodes and the surrounding soil. The analysis of the influence of size, number and position of such air gaps on the loop grounding resistance and potential distribution in the soil showed the dominant effect of the grounding loop surface covered with air gaps.