【作者】 李景丽；

【导师】 孙才新；

【作者基本信息】 重庆大学 ， 电气工程， 2011， 博士

【摘要】 发、变电站及输电线路的接地装置是维护电力系统安全可靠运行的重要基础设备。随着电力系统的发展,故障、操作和雷电等暂态故障电流对接地系统的影响也越来越大,接地系统面临新的安全问题。高频故障电流作用下接地导体呈现的电感效应以及高幅值冲击电流作用下接地体周围土壤中的火花放电现象是影响接地性能的重要因素,考虑接地装置散流过程中各种因素的影响,对发变电站接地网在故障电流作用下的频域性能和输电线路杆塔接地极在雷电流作用下的动态冲击特性进行准确的数值计算和试验研究,是目前电力系统迫切需要解决的实际难题。本文在深入分析国内外对发、变电站接地网频域性能及输电线路杆塔接地装置冲击特性的试验研究和数值计算研究的基础上,首先针对入地故障电流频率较低的常规变电站接地网,阐述了故障散流过程引起的地中电位分布的数值计算原理,建立了考虑土壤中位移电流的计算地中电位分布的标量有限元模型。利用基于弱形式的有限元方程对接地导体和土壤分界面处介质参数突变的问题进行处理;引入空间几何变换方法,解决了接地系统无穷散流空间和有限计算资源之间的矛盾。通过与文献试验数据对比验证了该模型的正确性。然后针对入地故障电流频率较高的气体绝缘变电站,基于电磁场麦克斯韦全波方程,建立了考虑场域中位移电流和感应电流的接地装置高频特性矢量有限元模型。利用基于弱形式的矢量有限元方程处理接地导体与土壤分界面处介质突变的问题;详细推导了空间几何变换方法在矢量有限元分析模型中的应用,解决了无穷散流空间和有限计算资源之间的矛盾;在接地导体与土壤的分界面上使用阻抗边界条件考虑高频故障电流作用下接地导体中的集肤效应,它不仅考虑了接地导体在散流故障电流过程中的作用,同时解决了考虑接地导体集肤效应带来的计算量剧增的问题。采用此模型对简单水平、垂直接地极和接地网建立数值分析模型,与CDEGS计算结果对比验证了该方法的有效性。以接地装置高频特性的矢量有限元分析模型为基础,建立了单根水平、单根垂直接地极和水平接地网的数值计算模型,计算得到高频故障电流作用下于单根水平、单根垂直接地极和接地网时,散流过程产生的地中电流场、电位场、沿接地导体漏电流分布规律以及接地导体上电位分布规律与注入电流频率之间的关系特性。在重庆大学冲击接地模拟实验室对八种典型接地装置结构的冲击散流规律进行模拟试验研究,得出了各种接地装置结构在冲击电流作用下漏电流沿接地导体的分布规律,系统地分析了接地装置结构、冲击电流幅值、土壤电阻率等因素对冲击散流规律的影响。在深入分析冲击散流物理过程中土壤电离现象的基础上,建立了考虑土壤动态电离现象的接地装置冲击特性有限元分析模型。采用空间有限元格式与时域有限差分格式相结合的方法计算接地体冲击散流产生的动态电位分布;在分析大量接地装置冲击特性试验数据及本文冲击散流规律模拟试验结果的基础上,提出采用四分区结构的土壤模型来模拟土壤电离现象的不同程度;将离散土壤单元的电阻率设置为对应时刻该单元电场强度的函数,由时变的空间电场控制土壤电阻率,不需要事先假定土壤火花区域的形状,能够准确地模拟冲击散流过程中土壤参数的分布时变性。并且以此动态有限元模型为基础,对冲击模拟试验中使用的接地装置建立仿真模型,结合试验结果分析了冲击散流规律以及火花放电现象对电力设备和人身安全的影响。根据冲击散流规律的模拟试验及数值分析结果,提出高土壤电阻率地区输电线路杆塔采用针刺式接地装置的降阻措施,并应用本文提出的接地装置冲击特性有限元分析方法对星型针刺接地极降低冲击接地电阻的原理进行数值分析,结果表明,通过添加针刺引导冲击电流在接地导体各段平衡散流,可使土壤颗粒间局部空间电场强度畸变加强,促进了火花效应的产生;在实验室进行的冲击接地电阻测量试验结果进一步验证了针刺接地极降低冲击接地电阻的降阻效果。以上研究成果为实际接地装置的特性研究和接地工程设计提供理论依据和试验数据,具有重要的指导意义。更多还原

【Abstract】 The grounding device in the power plant and substation are basic equipment that protect power lines and power apparatus from severe ground faults and lightning currents. The performance of grounding grid affects the safe of power apparatus and staff, and the impulse characteristics of grounding device directly affects the lightning protection performance of power transmission lines. The accurate analysis of the lightning transient performances and the frequency characteristics of grounding devices is the fundament of lightning protection of power system and optimization of the grounding electrode.Based on the quasi-static maxwell equation, a finite-element model which takes the displacement current in to account is presented to calculate the response of grounding devices under the fault current with lower frequency in this paper. In this work, open boundaries of earth environment are processed by introducing a spatial transformation; the ill conditioning of the matrix to be solved because of the marked rise in conductivity between ground and copper are resolved by the weak form of finite element method.Based on the full wave maxwell equation, a finite-element model which takes the displacement current and the induced current in to account is presented to calculate the response of grounding devices under the fault current with higher frequency in this paper. In this work, open boundaries of earth environment are processed by introducing a spatial transformation too, and the application process of spatial transformation in the vector finite element method is deduced in this work. In order to take the skin effect in the grounding electrode in to account in the vector finite element method, the exact impedance boundary condition is derived out by using the general boundary condition in electromagnetic theory, applying Maxwell equations and considering propagation properties of plane wave. And the exact impedance boundary is used in the interface of grounding conductor and the soil, so the function of grounding electrode on the dispersal of fault current in added in the finite element method, the domain of conductor is not participate in the calculation of finite element modeling at the same time. So the introduction of impedance boundary condition dercrease the amount of calculation. And the frequency characteristic of simple horizontal and vertical grounding rod under fault current with higher frequency is analyzed by the vector finite element modeling.Based on the study of grounding performance, this paper makes simulation experimental investigations on the impulse current dispersal regularity of grounding electrodes with various structures, and analyzes the effect of grounding electrode structure, amplitude and soil resistivity on the impulse current dispersal regularity of grounding electrodes.This paper presents a numerical method, combined the finite element method in the spatial domain with the finite difference time domain, to calculate the transient impulse response of grounding systems considering the ionization phenomenon. In this numerical method, space-time variable soil resistivity is used to simulate the soil ionization phenomenon where soil resistivity is controlled according to its relationship with the local instantaneous value of the electric field and no a priori hypothesis on the geometrical shape of the ionized region around the electrodes is necessary. The proposed numerical scheme is validated by comparing computed results with experimental results and simulation results in literature. Based on the measurement and simulation results, the impulse response regularity of grounding electrodes is discussed and the effect of ionization on human and installations safety is reported.According to the impulse current dispersing experimental results, the tower grounding reduction measures for power transmission line in regions with high soil resistivity are proposed. By using the finite element analysis method, the impulse resistance reduction principle of the star-shaped grounding electrode is analyzed. the simulation results show that the impulse leakage currents on different parts of conductor are balanced by adding spicules, and as a result, it can strengthen local electric field intensity in the space between soil particles and promote the ionization breakdown. Impulse grounding resistance measurement test results in the laboratory further verify the effect on reducing impulse grounding resistance of grounding device with spicules.更多还原