Optimal design analysis of grounding grids for substations built in nonuniform soil

The optimal design of grounding system can ensure the safety of a substation. The influences of reflective coefficient of double-layer soil and the thickness of top-layer soil and the grounding grid area on the optimum arrangement of grounding system were analyzed by a numerical method. It states the optimum compression ratio (OCR) should be determined by the target function of touch voltage reaching the minimum value. The OCR decreases with the increase of reflective coefficient, when the soil resistivity of the bottom-layer soil is smaller than that of upper-layer soil, the arranged horizontal conductors are more uniform than that when the soil resistivity of the bottom-layer soil is higher than that of upper-layer soil. The formulae to calculate the OCR of double-layers soil structure are obtained from analysis results, which can provide reference for engineers to design the grounding systems of substations with high safety