Research On Electrical Impedance Tomography System And Method Of Grounding Grids

The grounding grid in substation is an important guarantee to maintain safe operation of electric system and ensure the safety of staff and ground electrical equipment. But grounding grid is buried in the ground, if welding is not standardized or is corrode by soil, which will result in corrosion or fracture of grounding grid and leading wires, this will endanger the grounding equipment and personnel safety. In order to solve practical engineering issues which include the loss of grounding grid drawings and the lack of visualization fault location in the current method, the electrical impedance tomography system and method of grounding grid are researched in this paper and the method provides a new idea for the fault diagnosis of grounding grid. The main work in this paper is as follows:(1) The requirements for the grounding grid electrical impedance tomography system, composition and design ideas are analyzed in detail. In order to solve the current problems, such as: less measuring data, the unknown grounding grid topology and the difficulty of grounding grid test, electrical impedance tomography system for the grounding grid is designed into three parts: hardware measurement platform, experiment network platform, software calculation method, which can implement the automated measurement of voltage and current, the experiment of grounding grid, electrical impedance tomography for grounding grid, respectively.(2) An experiment platform of grounding grid electrical impedance tomography is built. The platform includes measurement platform and experiment network platform. Where, the measurement platform includes a current source module, a control module, a data communication module, a data acquisition module, a channel switch module and other auxiliary module. For experiment network platform, in order to meet different experiment cases, 1 ? resistance network and grounding grid analog network of 7×3 grid are constructed, and they will simulate grounding grids of different structures and grounding grids of similar resistance and the same material, respectively. Then the weld point resistance of resistance network is tested when branch resistance of analog network is calculated.(3) The electrical impedance tomography method is proposed for grounding grid. By the analysis of electrical impedance tomography method, the equations of EIT forward problem and inverse problem are established; then based on the analysis of regularization methods, Newton iterative method with Tikhonov regularization is used for the solution of inverse problem; the initial value selection and the calculation method of Jacobi matrix are studied; by the comparison of grounding grid electrical impedance tomography and medical science electrical impedance tomography, the imaging area and measuring leading wires selection are researched. Thus partitioned imaging thought and topology detection method based on graph theory are proposed, and then the optimal size of imaging area and the effect of leading wires number on the imaging results are obtained. Hence grounding gird electrical impedance tomography is realized in the end. The results show that: the small imaging area is more conducive for judgment of the fault location; the number of measurement leading wires affects the imaging results, and more leading wires for data measurement are beneficial to improving imaging quality.(4) The software simulation and modeling experiments are carried on. Firstly, the electrical impedance tomography of single area and grounding grid are researched by simulating calculation. And then the resistance network and analog network are used for the experiments which are based on the voltage measurement principle of grounding grid. The results show that the fault can be located accurately by imaging method.