基于薄壳理论的大型接地装置有限元模型

Finite Element Model of Large Grounding Device Based on Shell Theory

准确计算复杂土壤结构中大型地网的性能是优化地网结构、保障电力系统安全稳定运行的重要基础。为此提出基于薄壳理论的大型接地装置有限元模型,针对有限元方法在大型地网计算中网格剖分困难、计算量大的问题,将接地导体等效为具有一定虚拟厚度的金属薄壳;并提出二维有限元与三维有限元耦合的方法求解。建立某变电站地网模型,分析复杂土壤结构对大型地网接地性能的影响,结果表明：引入薄壳理论使得该方法在保证计算精度的基础上大大减小了计算内存和时间;复杂土壤结构中的高阻区对故障电流的阻碍作用会抬升地网电位升;高阻区的电流密度较小,地表电位分布起伏较大,较之均匀土壤高阻区接触电压、跨步电压高出数倍,地网设计中应加以关注。

The performance of large grounding grid in complex soil structure is foundation of optimization design of the grounding device and the safe and stable operation of power system. We proposed a finite element model of large grounding grid based on the shell theory. To deal with the problem of difficult subdivision and large computation induced by traditional finite element method in dealing with large grounding grid, we prepared a long sheet metal instead of the grounding conductor and using the three prism shell element to scatter it, and proposed a method of the couple of twodimensional finite element and three-dimensional finite element. Then we established a finite element model of a substation grounding grid in different soil structure, and analyzed the impact of complex soil structure on performance of large grounding grid briefly. The results show that the introduction of the thin shell method can induce the amount of calculation, while the accuracy has been improved. The high resistance area in complex soil structure can reject the fault current, which can increase the ground potential and grounding resistance. In high resistance area, the current density is less, the surface potential distribution fluctuates in a wide range, and the contact potential and step voltage in high resistance area may be several times higher than that in the homogeneous soil. So when we calculate the performance and design the large grounding grid, the impact of complex soil structure should be taken into consideration.