Analysis of Soil Resistivity and its Impact on Grounding Systems Design

The purpose of designing suitable grounding system is to ensure reliable power supply, safety of equipment and people working in electrical power operation and to limit voltage elevation to a minimum. In this paper, a series of tests were conducted to compare apparent soil resistivity of two different locations and how it is affected by depth of the soil and moisture content. The Wenner method was used to measure resistivity in both locations. The results obtained show how the soil resistivity varies with depth and spacing, which informs the design of earthing protection schemes for worst case scenarios. It was observed that the soil resistivity varies based on the type of soil and moisture content. The wet soil had lower resistivity than the dry soil. The proposed design shows that the number of earth electrodes required varies from 4 to 11 for wet to dry soil conditions respectively in Site-1, and 18 to 35 earth electrodes for wet to dry soil conditions respectively in Site-2. Thus, the number of electrodes required is higher for dry soil condition, because the soil resistivity is high.