Grounding Grid Electrical Impedance Tomography Based On Homotopy-Tikhonov Algorithm

Grounding grid is an important part of power plant and substation,which provides discharge channel for fault current.The grounding grid is buried underground all the year round.Problems such as soil corrosion and non-standard welding may lead to corrosion or fracture of the grounding grid,which may endanger the normal operation of the power system and the safety of workers.The convergence of electrical impedance tomography of grounding grid is difficult because of the huge difference in resistivity between conductor and soil.In order to enlarge the convergence range and improve the ill-posedness of the inverse problem of electrical impedance tomography for grounding grid,this paper proposed an electrical impedance tomography method for grounding grid based on the Homotopy-Tikhonov algorithm(HT-GN).Firstly,the corrosion mechanism of grounding grid and the principle of electrical impedance tomography were analyzed,and the mathematical model of electrical impedance tomography was studied on the basis of Maxwell’s equations.The equivalent variational principle and the finite element subdivision of the field in the forward problem of electrical impedance tomography were analyzed emphatically,and the inverse problem of electrical impedance tomography was briefly summarized.Based on the modified Newton-Raphson algorithm,the HT-GN algorithm which could expand the convergence range was proposed,and the iterative formula for solving the resistivity distribution was deduced.Secondly,with the help of COMSOL and MATLAB software,the voltage data acquisition model of the grounding grid for simulation was established,and the imaging model of EIT inverse problem of the grounding grid was established accordingly.Before EIT simulation imaging of the grounding grid,the optimal initial iteration value was obtained,and the optimal regularization parameter was obtained by L-curve method.Then,the HT-GN algorithm and Tikhonov algorithm were used to simulate the EIT imaging of the grounding grid,the subdivision unit map,color cloud map and three-dimensional topographic map of the two algorithms were compared,and the advantages of the two imaging were quantitatively compared by using the voltage relative error.At the same time,the HT-GN algorithm was used to analyze the reconstructed images with different initial iteration values,different regularization parameters and different corrosion degrees under the conditions of light corrosion,heavy corrosion and fracture.Finally,the light corrosion state of the grounding grid was simulated,and the imaging experiments of one and two corrosion of the grounding grid were carried out by using the EIT imaging system of the grounding grid.The simulation and experimental results show that the corrosion position of the grounding grid reconstructed image based on the HT-GN algorithm is clearer,and the voltage relative error after convergence is significantly smaller than that of the Tikhonov algorithm,and the convergence performance is better,which effectively improves the ill-posedness of the inverse problem of electrical impedance tomography of the grounding grid.The paper has 34 figures,4 tables,and 73 references.