Effect of Site Grading and Earthwork on Substation Grounding Safety

The strata that is in close vicinity with the ground grid conductors, and other ground network components has an impact on its safety performance. Its resistivity will affect ground grid parameters such as contact resistance, current distribution, and current leakage. It will also affect the overall ground grid resistance. When not accounted for in the grounding study, site earthwork and grading can increase the error of the calculated touch and step potentials during a power system fault. In addition, based on concepts covered in IEEE 80, the surfacing rock could increase the magnitude of the calculated touch and step potentials. The effect is based on how the surface rock resistivity value compares to the resistivity of the gravel of the grading pad, and fill. This paper presents ways to estimate the impact of common earthwork techniques on ground grid safety performance. It gives recommendations for improving planning, and identifying issues.