| The grounding system of power station and transmission line is an important equipment to ensure the normal operation of power system and the safe of electrical equipment.At present,in a large number of studies,the soil around the grounding body is simplified to horizontal homogeneous soil structure,but but in most areas the topography is more complex,the soil stratification structure is obvious and the soil resistivity is larger,if the grounding resistance is designed and calculated according to the uniform horizontal soil,the calculation result will be quite different from the actual operation.The accurate analysis of earthing performance and dispersion mechanism of earth pole in complex soil structure is the basis of reasonable optimum design of grounding pole for substation and overhead transmission line.This paper is based on the detailed analysis of the research and numerical calculation methods of the soil structure around the grounding pole of the substation and overhead transmission lines in various countries,in view of the difficulty of dissection and the large amount of calculation in the analysis and calculation of large earthing body by finite element method,etc.In the process of establishing the model,the problems existing in the calculation of the ground performance of a large area can be solved on the basis of ensuring the accuracy of the calculation by selecting the 2-D surface simulated grounding conductor with a certain virtual thickness.The accuracy of the model is verified by comparing the actual measured data and the CDEGS calculation results.Vertical three-layer soil structure model,massive soil model,and a drop soil structure model are established based on the presented method.Based on the results of numerical calculation,the mechanism of dispersion of grounding body of hydropower station under complex soil structure is analyzed in detail,the effects of soil resistivity,river depth and grounding device buried depth on the dispersion mechanism and grounding resistance of the grounding device of hydropower station are analyzed quantitatively.The results show that river depth is the main factor affecting the grounding performance of grounding grid in hydropower stations,in the design process of the grounding device of hydropower station,a massive soil structure model of the actual river depth should be considered to simulate the soil structure around the ground.,in the design process of the grounding device of hydropower station,a massive soil structure model of the actual river depth should be considered to simulate the soil structure around the ground.In order to simulate the soil structure around the earthing device of pole tower as accurately as possible,based on the theory of finite element,a soil structure model considering river and mountain is established,the influence of the distance between the river water and the grounding conductor,the gradient of the mountain body and the area of the mountain top on the grounding resistance of the grounding body is analyzed.The results show that when the soil resistivity is high,the distance between the ground conductor and the river is less than 5m,and the mechanism of the grounding conductor and the impact grounding resistance are greatly influenced by the river,when the top area of the mountain is 20m×20m,slope to change within the range of 75~o to 15~o degrees,the grounding device installed on the top and side of mountain impact grounding resistance were increased by 79.6%and 25%,lightning protection design of transmission line in mountain area should be integrated into the slope of the mountain and mountain top area of effect of grounding device diffuser and impulse grounding resistance. |
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