Study On Electrical Character Of Grounding Grids In Non-Uniform Soil Regions

The substation grounding system is important to the reliable operation of power system and the safety guarantee of person and equipment. Only uniform soil model is considered to calculate the grounding resistance of the grounding grid in DL/T621-1997 and IEEE Std 80-1986. In practice, the soil structure is complex in many regions, a big error would occur if only the uniform soil model considered. At present, most researchers think that the multi-layer soil structure can be simplified as an equivalent two-layer soil structure to analyze the electrical character. But the influence of various parameters on the electrical character of the grounding grid is not clear, so the influence of different parameters on the electrical character of the grounding grid in the multilayer soil is studied. The simplification method for the multilayer soil structure is proposed. This method is helpful to the design of the grounding system in the multilayer soil.The influence of soil resistivity, soil thickness and the reflective coefficient on the grounding resistance of the grounding grid in various structures is analyzed. The influence of grounding area, soil resistivity and the reflective coefficient on the equivalent soil resistivity is also analyzed. The key parameters that influence the equivalent soil resistivity are found, and the system model of BP ANN to calculate the equivalent soil resistivity is discussed. The method of designing the grounding system in the complex soil structure is introduced, and the design principles of grounding grid in Ge-La segment are proposed. The selection of grounding grid material and the measurement of grounding resistance are discussed. To select copper or steel as the grounding grid material depends on outlay, corrosion and other factors, and the corrosion-proof measures need to be taken according to the environment. The soil structure around the substation should be studied before measuring the grounding resistance of the grounding grid, with the proper arrangement of current and voltage probes as well as proper measurement method, the accurate result can be obtained.