【作者】 李涛；

【导师】 曹晓斌；

【作者基本信息】 西南交通大学 ， 电气工程（专业学位）， 2022， 硕士

【摘要】 随着我国电网向着高电压、高智能、高可靠性的方向发展,设备的电磁敏感性变强,电磁干扰源的频率越来越高,接地网上通过的电流和电流的频率成分也呈现多样化趋势,对变电站接地系统的性能带来了极大的挑战,迫切需要从多频率的角度去考虑土壤的电气特性。离子电迁移是决定土壤电气特性的主要因素,同时孔隙是土壤中水、离子及空气迁移的主要通道。因此有必要研究土壤孔隙中离子电迁移引起的相关电参数的频谱特性。我国接地网面临的地质结构也越来越复杂,高土壤电阻率、冻土、盐碱土等特殊地质条件给它的设计、运行和维护提出挑战,这使得对复杂土壤结构中离子电迁移的研究也变得极为重要。本文主要围绕以下几方面展开:利用土壤孔隙的毛细管凝聚效应,以及土壤孔隙表面、石英玻璃表面和硅胶表面与电解质溶液接触时都会形成同性质的双电层,建立了土壤毛细管等效模型。同时设计了实验电路与实验方案,研究了孔隙孔径、溶液浓度及离子类型对电参数频谱特性的影响。在COMSOL软件中,利用电流模块添加电场,一般形式的偏微分方程模块计算流体中的压力变化,稀物质传递模块模拟离子浓度在电场影响下的迁移规律,建立了不同曲率半径和不同迂曲度的土壤孔隙模型,并进行了相关研究。通过实验发现了离子数量的变化和孔隙壁面积与孔隙体积比值的变化是影响电流和阻抗角频谱特性的两个主要因素。验证了离子在水溶液中是以水合的形式进行电迁移的,离子可稳定吸附的水分子数与电荷密度正相关,并从物理学角度验证了水合离子的带电荷量、大小及相对质量是影响其在水溶液中电迁移的主要因素。实验结果中还发现在交流电场下所有的孔隙电流都偏容性,并通过计算离子的迁移速率证实了容性电流的存在。将容性电流分解出来后发现在低频段和高频段会产生较大的容性电流,进而得知离子在孔隙中迁移会产生容性效应,从而造成容性电流存在。利用提出的等效电路模型和电容的频谱特性,并结合离子的水合迁移形式分析了该容性效应的形成机制,认为土壤孔隙的低频容性效应主要由电极附近形成的双电层产生;高频容性效应主要由离子迁移过程中正负离子团不重合形成的电容产生。通过研究土壤结构对离子电迁移影响,发现土壤孔隙曲率半径的改变会造成孔隙中各处电场强度和内部孔隙水压强的不均匀,进而影响离子的电迁移;在孔隙内电场强度和水压强不变时,单纯土壤孔隙结构的变化也会影响离子的电迁移。本文从离子电迁移的角度去研究土壤的电气特性,所得的研究成果可用于分析土壤的电离过程和土壤中接地装置的暂态性能,这对土壤频变特性检测方法的优化、输电线路接地装置的设计以及电力系统的安全运行具有极为重要的意义。更多还原

【Abstract】 With the development of power grid towards high voltage,high intelligence and high reliability,the electromagnetic sensitivity of the equipment becomes stronger,and the frequency of the electromagnetic interference source becomes higher,and the current passing through the grounding grid and the frequency component of the current show a diversified trend.These problems have brought great challenges to the performance of substation grounding system.It is urgent to consider the electrical characteristics of soil from the perspective of multi frequency.Ions electromigration are the main factor determining the electrical characteristics of soil,and pores are main channels for the migration of water,ions and air in soil.Therefore,it is necessary to study the spectral characteristics of relevant electrical parameters caused by the electromigration of soil characteristic ions in pores.The geological structure of grounding grids in China is becoming more and more complex.The special geological conditions such as high soil resistivity,frozen soil and saline-alkali soil pose challenges to its design,operation and maintenance,this makes it important to study the ions electromigration in complex soil structure.This paper focuses on the following aspects:Based on the capillary condensation effect of soil pores and the formation of the same electric double layer on the surface of soil pores,quartz glass and silica gel when they come into contact with electrolyte solution,the equivalent models of soil pores are established.The experimental circuit and experimental scheme are also designed,and the effects of pore diameter,solution concentration and ion type on the spectrum of electrical parameters are studied.In the COMSOL software,the current module is used to add an electric field,the general form of the partial differential equation module is used to calculate the pressure change in the fluid,and the dilute matter transfer module is used to simulate the changes of ion concentration under the influence of the electric field,soil pore models with different radius of curvature and different tortuosity are established,and carried out relevant research.It is found that the changes of the number of ions and the ratio of pore wall area to pore volume are the two main factors affecting the characteristics of the current and impedance angular spectra.It is verified that ions are electromigrated in the form of hydration in aqueous solution,and the number of water molecules that ions can stably adsorb is positively related to the charge density.It is proved that the charge amount,size and relative mass of hydrated ions are the main factors affecting their electromigration in aqueous solution.The experimental results show that all pore currents are capacitive under AC electric field,and the existence of capacitive current is confirmed by calculating the migration rate of ions.After decomposing the currents,it is found that the capacitive currents are generated in the low frequency band and high frequency band,and then it is known that the ions migration in the pores can produce capacitive effect,resulting in the existence of capacitive current.Based on the proposed equivalent circuit model and the spectral characteristics of the capacitance,the formation mechanism of the capacitive effect is analyzed in combination with the hydrate migration form of ions.The low frequency capacitance effect of soil pores is mainly caused by the electric double layer formed near the electrode,while he high frequency capacitance effect of soil pores is mainly caused by the noncoincidence of positive and negative ion groups during ions electromigration.By studying the influence of curvature radius,it is found that the change of soil pore curvature radius can cause the non-uniformity of electric field intensity and internal pore water pressure in the pores,and then affect the ions electromigration.By studying the effect of tortuosity on ion electromigration,it is found that the change of soil pores structure can also affect ions electromigration.In this paper,the electrical properties of soil are studied from the point of view of ions electromigration.The results can be used to analyze the ionization process of soil and the transient performance of grounding device in soil.It is of great significance to the optimization of soil frequency characteristic testing method,the design of transmission line grounding device and the safe operation of power system.更多还原