IMPACT OF COMPRESSION RATIO ON SUBSTATION GROUNDING GRID RESISTANCE IN LAYERED SOIL

Abstract

This paper presents impact of grid compression ratio on substation grounding resistance. The minimization of substation grounding resistance is one of the very important criterions in design of substation grounding grid. The decrease in grid resistance reduces the ground potential rise and hence the transfer potential and to a certain extent the safety criterion touch voltage. The term compression ratio is related to unequally spaced grid. We have analyzed the grounding grid for various values of compression ratios for uniform soil model with and without vertical rods. Further the impact of compression ratio on grid resistance is analyzed for various values of soil resistivity reflection factors and top layer height in case of two layer soil model. The simulation has also been carried out for multilayer soil models using Autogrid-pro grounding software. The study results reveals that every ground grid has optimal compression ratio which makes the grid resistance minimum as compared to equally spaced grid for the same area, soil model and number of conductors. Use of ground rods, increases the compression ratio, makes the grid more uniform and decreases the grid resistance.