【作者】 徐华；

【导师】 文习山；

【作者基本信息】 武汉大学 ， 高电压与绝缘技术， 2004， 硕士

【摘要】 接地网是变电站安全运行的重要保证,其接地性能一直受到设计和生产运行部门的重视。变电站接地网不仅为变电站内的各种电气设备提供一个公共的参考地,而且在电力系统发生故障时,将故障电流迅速排泄入地,控制接地网的最大电位升高,保证人身和设备安全。所以,合格的接地网在电力系统安全运行中具有十分重要的作用。随着电力系统容量不断增大,故障时流入地网的电流将随之增大,特别是三峡电站建成后,其值可达34kA,而为使接地网的电位升高不超过某一允许值,接地网的面积可能很大,地网最大对角线长度可达上千米。大型变电站接地网面积大,接地网不再是等电位的。等间距的大型变电站接地网的地表电位梯度大,散流不均匀,有必要在不等电位模型下研究不等间距的大型变电站接地网。 本文所做的主要工作如下: 1.详细介绍了基于复镜像法的恒定电场中多层土壤的格林函数及其对土壤参数偏导数的快速算法,并在此基础上建立了土壤电阻率测量数据的多层水平分层土壤电阻率的快速建模方法。为分析工频电流下接地网的性能奠定了理论基础。 2.基于矩量法和场路结合的思想,将电路中的节点电压法用于接地网工频参数计算中,该方法不仅考虑了接地导体的内自阻抗和自感,而且考虑了导体间的互感,导体的位移电流。用该方法可以计算接地网的工频电流下的任何参数,如工频接地阻抗、接触电压和跨步电压、网内电位差等。节点电压法是当前分析接地网最简单、计算中矩阵的阶数最小的方法之一。 3.为了降低接地网的接地阻抗,工程上有采用铜材代替钢材接地网和引外接地网的措施。本文详细比较了大型铜材和钢材接地网在工频电流下的接地性能,对工程应用有一定的参考价值。引外接地网是根据经验在离主接地网1～2km的范围内,一般采用钢材将此辅助接地网与主接地网相连。本文为引外接地的工程应用提供了一定的依据。 4.为了使地表面的电位均匀分布,进一步降低接触电压和跨步电压,更好地保障人身和设备的安全,本文提出了接地网的优化设计方法。在一些学者等电位模型的基础上,根据大型接地网不再等电位这一实际情况,在不等电位模型下,分析了均匀土壤下土壤电阻率和接地网面积对接地网最优布置的影响规律;分析了双层更多还原

【Abstract】 The grounding system is one of important components of a substation, to which much attention is always paid. The substation grounding grid can provide a reference ground for various electric devices within the substation. During a fault of an electric power system, the failure current drains quickly to the ground. The maximum ground potential rise can be controlled to ensure adequate safety for people and to protect the installation. Therefore, an effective grounding grid is very important for the safe operation of the electric power system. Along with the development of electric power system capacity, the value of failure current flowing into ground has been increased greatly. Particularly, after the construction of the three gorge power plant, 34kA can be reached. In order to control ground potential rise, the area of the grid may be very large and maximum diagonal of the grid can be above a kilometer. Because the area of large substation is big, it is inequipotential. The gradient of earth surface potential above the large equidistant substation is big, and the leakage current of theirs conductors are not uniform. It is very essential that the grounding grids of large substation using variable spacing be researched.The main achievements are as follows:1. A fast approach to Green function in multi-layer earth and its partial differentials to the earth parameters is introduced in detail by using the complex image method. An efficient method for estimating earth structure from Wenner’s four-probe test data is presented. Both of them provide theoretical foundation for analyzing performance of grounding grids in power current.2. Based on method of moment and field-circuit coupling theory, nodal method of analysis in circuit theory is applied to the power parameters calculation of grounding grids. The inner self-resistance and self-inductance of conductors, mutual inductance between conductors, and displacement current of conductors are taken into account. The methods are able to compute any parameter of grounding grids in power current, such as power ground impedance, touch and step voltage, potential differences within grounding grids and so on. Among current methods analyzing grounding grids in power current, the nodal method of analysis is the easiest and least exponent number of matrix in calculation.3. In order to reduce ground resistance of grounding grids, in project, measures are generally replacing steel material grounding grids by copper and subsidiary groundinggrids. The paper compares in detail the ground performance of large copper and steel material grounding grids in power current, which has some reference for the practical engineering. According to experience, the distance between subsidiary grid and the main grounding grids is 1-2 km, both grounding grids are generally connected with buried conductors. The paper gives some scientific foundation for practical engineering. 4. To equalize the potential and decrease touch voltage and step voltage on the earth surface, an optimum design of grounding grids is proposed in this paper. Based on equipotential models of some scholars, according to a practicable fact which large substation grounding grids are not equipotential any longer, in inequipotential model, the paper analyzes the influence of the soil resistivity and the grounding grid area on the optimum arrangement in the uniform soil; the paper analyzes the reflective coefficient of double-layer soil, the top-layer soil thickness and the grounding grid area on the optimum arrangement. The paper establishes the object function by the minimum difference between the maximum and the minimum touch voltage, in orderto obtain the optimum compression ratio, the paper uses the numerical method------thevariable metric method to analyze the obtained many data. The paper obtains the formula to calculate the optimum compression ratio of the optimum arrangement in the uniform and double-layer soil, which presents some reference to design the large substation grounding grids.更多还原