Soil Resistivity, its Impact on Optimum Depth of Electrodes in Earthing System– Case Study University of Port Harcourt Residential Staff Quarters

Abstract

A well-designed earthing system plays a vital role in any Electrical Facility. Soil resistivity measurement is an important parameter when designing earthing system. However, it is a known fact that the resistance of an earth electrode which is a component of earthing system is heavily influenced by the resistivity of the soil in which it is driven to. A knowledge of the soil resistivity at the intended site, and how this varies with parameters such as moisture content, temperature and depth, provides a valuable insight into how the desired earth resistance value can be achieved and maintained over the life of the installation with the minimum cost and effort. One of the main objectives of earthing electrical systems is to establish a common reference potential for the power supply system, building structure, plant steelwork, electrical conduits, cable ladders and trays and the instrumentation system. To achieve this objective, a suitable low resistance connection to earth is desirable. In this research paper, soil resistivity was investigated in three different residential staff quarters of University of Port Harcourt Choba, Abuja and Delta Campuses during the wet and dry season of 2022 using the relevant IEEE standards and International best practices for determining Electrical substation and residential buildings earthing system designs. To determine the optimum depth of grounding electrodes that will have the acceptable values of earth resistance and resistivity for earthing system designs, the Wenner four pin method of measuring soil resistivity was employed. The findings of this research paper show the optimum depth the grounding electrodes will get to in order to obtain the best earth resistance and resistivity values that is suitable for substation and residential earthing system designs. The outcome of this study is also useful for purposes of estimating the number of grounding electrodes, ground resistance and potential gradients including step and touch voltages of substation grounding installations around the three locations of study in university of Port Harcourt residential staff quarters.