New Method for Calculating Ground Resistance of Grounding Grids Buried in Horizon Two-Layer Soil

With the development of ultra high voltage AC and DC power system, fault current of power plants, substations and convertor station are great than before. Larger grounding grids are needed to meet the safety regulation. Grounding grids usually located in horizon multilayer or vertical multilayer soil structure which parameters such as thickness, resistivity of each layer can be estimated. This paper presents a new method for calculating ground resistance of grounding grid buried in horizon two-layer soil. It is consisting of three chapters. In the first part, simulations were done to obtain ground resistance of grounding grid in horizon two-layer soil and uniform soil. Then, results were preprocessed to two variables, one is the ratio of resistance of grid in horizon two-layer soil to uniform soil, the other is the ratio of soil resistivity about the top layer to the borrow layer. The relationship curve between the two ratios was plotted out. In the second part, an engineering estimation formula was simplified for calculating ground resistance in horizon two-layer soil. Results of the formula proposed are compared with results of simulation software and its error is acceptable. In the last part, examples of how to use this formula are illustrated.

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