Efficient use of low resistivity material for grounding resistance reduction in high soil resistivity areas

Power system is generally protected from lightning strokes by surge arresters which are provided with a low earth resistance connection to enable the large currents encountered to be effectively discharged to the general mass of earth. This offers some resistance to the flow of current which depends on electrode arrangements as well as the surrounding soil resistivity. In Saudi Arabia, the soil resistivity varies in a large range because the geodetic terrain varies from sea shore to the arid desert and dry mountains. Therefore, getting an acceptable low value of grounding resistance is very important in those areas where the soil resistivity is very high. This can be achieved by efficient use of low resistivity material (LRM). When the LRM is used in too high volume, it does not reduce the grounding resistance in a corresponding manner and thus may not be economical and effective. This paper studies the effect of different design parameters of the earthing pit on the grounding resistance and finally a general approach for finding the optimized pit design is suggested that can effectively reduce the grounding resistance to an acceptable lower value. The suggested method can be readily used by engineers to obtain a good earthing pit configuration for efficient grounding of the power system components in high resistivity soils.