HVDC Grounding Soil Modeling And The Influence On Electrical Performance

DC transmission grounding pole is the return path of the DC working current when the HVDC transmission system is in the operation of monopole circuit mode.The adverse effects of DC currents flowing into the earth through the earth electrode for a long time can adversely affect the operation of the electrical facilities near the poles.The existing design method of earth electrode usually regards the heterogeneous soil as homogeneous soil,and establishes uniform layered soil model to determine the location of grounding pole through the soil resistivity data of a few measuring points.Because the soil model cannot accurately assess the impact of grounding on the surrounding power system,there are a number of substations which have been completed need DC bias magnetic treatment in practical projects.Using the magneto telluric method for soil resistivity survey can get much deep soil measurement points,and the measured data can be more realistic response to the earth electrode pole location geological situation.But the existing ground-related simulation software can only use the horizontal layered soil model to analyze the impact of grounding on the surrounding electrical environment,and the survey data of magneto telluric method cannot be directly dealt.Therefore,it is necessary to study the method of establishing horizontally stratified soil model with the magneto telluric survey data,and to establish a horizontal layered soil model with more accurate measurement data which can be processed by the existing simulation software,so as to provide the basis for further study on the influence of earth electrode to surrounding electrical environment.In this paper,the effects to be evaluated for ground electrode problems and the influence of complex geologic conditions on the ground electrode are studied firstly,as well as the importance of the research on the soil-based modeling of the ground electrode is clarified.Then the forward and inversion methods of the magneto telluric method are analyzed.The earth electrode poles of Xiluodu ~ West Zhejiang ± 800 kV HVDC transmission project in Wuyi County is investigated with magneto telluric method,and the measured data is processed with the method of magneto telluric inversion,so as to obtain the three-dimensional inversion model of magnetotellurics.Based on the inversion data,a modeling method based on potential fitting method is proposed.By analyzing the parameters and calculating methods of ground current field,the soil surface potential is selected as the fitting index.The potential distribution of three-dimensional inversion model is solved by finite element method,and the surface potential of horizontal layered soil model is obtained by using Green function recursive method,so as to establish the objective function of horizontal layered soil resistivity model.By using genetic algorithm to optimize the objective function,the horizontal layered soil model is completed.Finally,the main performance parameters related to the electrical environment around the earth electrode are studied.The data of the actual engineering survey is modeled by the modeling method proposed in this paper,and the DC bias calculation of the transformer is carried out by using the soil resistivity model.By comparing the results of this method with the DC bias of actual substation transformer,the reliability of the soil resistivity modeling method is validated,and at the same time,the influence of soil resistivity modeling of earth electrode on the electrical performance of pole periphery is analyzed.