Study Of Substation Grounding Design Method On Non-uniform Soil Regions

With the rapid increase of the power system capability in recent years, ground fault current increase greatly. How to design standard substation grids in limited, non-uniform, high soil resistivity regions using suitable decreasing resistance method to keep the safe and reliable operation of the power system stuffs and devices is crucial. Researches indicate that multi-layer soil structure model can represent actual soil structure and mostly two-layer soil model is enough to describe the soil. The study of the dissertation includes two-layer soil structure parameters analysis, the random shape grounding resistance calculation and the hollow-center devices grounding resistance calculation in two-layer soil structure. The apparent resistivity curve is the basis of correct interpretation of the soil structure. After deriving the formula of the apparent resistivity based on electromagnetic fields theory, the soil structure has been obtained by nonlinear optimization method. And the method has been checked by simulation and field datum. Classical two-layer soil structure grounding resistance formulas are complicate and inconvenience because their limited apply range and some parameters are determined using tables and figures. Professor Salama and Chow have derived simple two-layer soil structure grounding resistance formula based on multi images and novel synthetic asymptote theory, but for some cases (especially for large scale grid) the formula would bring error can't neglect and only suitable to square grid. The dissertation has analyzed the error reason, derived advanced Salama-Chow formula, and extended it to calculate random shape grid resistance. The advanced formula has been checked by accurate computer method and field datum. The hollow-center grounding device is a efficient method for decreasing grounding grid resistance on the high soil resistivity regions. The dissertation has anglicized its decreasing principle and derived the simplified grounding resistance buried in two-layer structure soil. Based on the research mentioned above, a substation grounding system has been designed and completed successfully.