Research On Calculation Method Of Grounding Parameters Of Corroded Grounding Grid In Horizontally Layered Soil

The domestic grounding grids are mainly made of carbon steel,and have long been in the current field of horizontally layered soil with many layers,and random soil resistivity.At the same time,the carbon steel grounding grid in operation usually has different degrees of corrosion.The corrosion products,attached to the surface of grounding grids,affect the grounding performance of the grounding grid.The grounding parameters of grounding grid(grounding impedance,leakage current,ground surface potential,etc.)are the key indicators to evaluate the grounding performance of grounding grid.Therefore,it is very important to accurately calculate the grounding parameters of carbon steel grounding grid with different degrees of corrosion in current field of horizontally layered soil,which can effectively avoid power accidents caused by corroded grounding grid.Firstly,the soil where the grounding grid is located presents a complex horizontally layered structure,the soil space is regarded as the current field of the horizontally layered medium space,and the basic properties of the field are reflected by the Green's function.Thusly,solving the Green's function of horizontally layered soil current field is the basis of calculating the grounding parameters.However,the integral kernel function in the Green's function of the complex horizontally layered soil current field usually has serious oscillation characteristics,the existing Green's function calculation methods usually adopt the numerical calculation method of global sampling,which is difficult to accurately calculate the Green's function of complex horizontally layered soil.Secondly,the horizontally layered soil is the medium space where the grounding grid is located,obtaining the structur parameters of the horizontally layered soil is the basis for the calculation of grounding parameters.The parameters(soil thickness and soil resistivity)of complex horizontally layered soil are usually obtained by inversion calculation of apparent resistivity measurements at different arrangement distances.The present methods often use non-heuristic optimization algorithms and heuristic optimization algorithm to calculate the parameters of complex horizontally layered soil,lack of in-depth research on the mathematical model of horizontally layered soil,it is difficult to determine a reasonable initial value range of the iteration,and there are problems such as easy to fall into the local optimum.Thirdly,during the calculation process of the grounding parameters of the corroded grounding grid,an accurate calculation model of the corroded grounding grid that conforms to the actual project needs to be established.Existing calculation methods usually ignore the influence of corrosion products to varying degrees,and lack of consideration of the expansion characteristics of the corrosion products of the grounding grid,which make it is difficult to achieve accurate calculation of the grounding parameters of the grounding grid with different degrees of corrosion.To solve above problems,this paper first studies the segmented sampling calculation method of the Green's function of horizontally layered soil current field,which realize the accurate calculation of Green's function of complex horizontally layered soil.The PSO-DE(Particle Swarm Optimization-Differential Evolution)optimization algorithm for the parameters estimation of horizontally layered soil parameters is studied,which can accurately and effectively obtain the parameters of horizontally layered soil.Finally,the numerical calculation method of frequency domain response of grounding parameters of corroded grounding grid in horizontally layered soil field is studied,which achieve the accurate calculation of frequency domain response of grounding parameters of grounding grid with different corrosion degrees in current field of horizontally layered soil.The research results lay a solid theoretical foundation for the accurate evaluation of grounding performance of corroded grounding grid,and have important theoretical significance and significant engineering value.The main research work is as follows:(1)The calculation basis of the Green's function of the horizontally layered soil current field are studied.The analytical and numerical calculation methods of Green's function of current field in horizontally layered soil are analyzed.The problems of the global sampling complex image method during calculating the Green's function of horizontally layered soil are analyzed.Finally,a novel segemented sampling calculation method of Green's function of horizontally layered soil current field is proposed,which is verified by the cases study.(2)The inversion method of soil parameters in horizontally layered soil is studied.The theoretical basis of measuring apparent resistivity of horizontally layered soil based on Wenner's equidistant quadrupole method is analyzed,and the influence of layered soil parameters on apparent resistivity is studied.Lastly,a novel PSO-DE optimization algorithm for the soil stuctrure parameters estimation of horizontally layered soil is proposed.The results show that the PSO-DE optimization algorithm can realize the accurate calculation of soil parameters of the horizontally layered.(3)The frequency domain response calculation method of the grounding parameters of the corroded grounding grid in the horizontally layered soil current field is studied.The influence of corrosion behavior of grounding grid on grounding parameters is analyzed,and the refined calculation model of corrosion grounding grid is established.The potential matrix of frequency domain response of grounding parameters of grounding grid without corrosion products is analyzed,and the influence of boundary accumulated charge of corrosion products on grounding parameters of grounding grid is analyzed by boundary element method.Finally,the frequency domain response calculation method of grounding parameters of corroded grounding grid is proposed innovatively.The cases study shows that the proposed method can accurately calculate the grounding parameters of grounding grids with different corrosion degrees.(4)The research content of the thesis was tested and verified,and the corroded grounding grid of 8 transmission towers and 2 substations were chosen as the research objects.Firstly,the apparent resistivity of the soil near the research object is measured,and the PSO-DE algorithm is used to estimate the parameters of the corresponding horizontally layered soil.The corrosion products at different locations on the surface of the research object are collected and XRD experiments are conducted to build a refined corroded grounding grid calculation model.Then,the 3-electrode method is used to get the measurement values of the grounding impedance frequency response of the research objects,and the theoretical calculation valuse of the grounding impedance frequency response of the research objects is calculated by the proposed method.Finally,the experimental measurement values and theoretical calculation values of the grounding impedance at different frequencies of the research object are compared,which verifies the correctness of the refined calculation model of the corroded grounding grid and the calculation method of the grounding parameters frequency response of the corroded grounding grid in current field of horizontally layered soil.