基于薄壳理论的高压直流接地极电热动态耦合有限元分析

发布时间：2018-03-21 19:54

本文选题：土壤温度特性　切入点：直流接地极　出处：《郑州大学》2017年硕士论文　论文类型：学位论文

【摘要】：在我国高压直流输电工程飞速发展的同时,土地资源的短缺以及直流接地极极址选择的较高要求等因素,使共用接地极技术应用广泛,所以直流接地极工作环境日益复杂与严峻。单极大地运行方式下的散流过程中温升会导致接地极周围土壤局部硬化、甚至接地极烧毁等问题,或者产生埋地金属设施的腐蚀和变压器直流偏磁等影响。故对直流接地极的散流机理及温升过程进行精确模拟及分析,并研究地下暗河、岩石层等特殊块状土壤结构下接地极的接地性能,以及实际分层土壤结构下接地极极址附近埋地金属管道防护距离等相关课题,是超特高压直流输电接地极优化设计及解决由大电流入地导致的严重温升及直流腐蚀和偏磁等问题的理论基础。传统三维有限元数值算法计算接地问题时存在一个突出性难题:接地导体截面尺寸与其自身长度、散流土壤区域尺寸相差106数量级,导致计算过程中经常出现计算量激增甚至剖分失败等现象。针对此问题,本文引入薄壳理论进行处理;另外,在计算过程中引入土壤电、热参数温度特性曲线,精确模拟由土壤温升而导致的土壤参数变化现象;然后利用本文算法并基于COMSOL Multiphysics仿真软件建立了直流接地极电热动态耦合有限元模型;分析了不同表层土壤电阻率下土壤参数温度特性对直流接地极温升过程的影响,结果表明:考虑土壤参数温度特性时,直流接地系统的接地电阻随运行时间变化而变化;分析了高、低块状异阻区对直流接地极电场分布和接地电阻的影响。研究表明:异阻区水平位置和垂直深度对直流接地极接地参数有较明显的影响。故在实际直流接地极设计中,应考虑土壤电阻率异常较低或较高的区域对接地设计的影响;最后,基于本文数值算法对任何土壤结构的广泛适用性,系统地对简单两层水平分层土壤下的埋地金属管道防护距离进行分析。结果表明:土壤电阻率对埋地金属管道最小防护距离的影响与其所在的土壤层厚度密切相关,其所在土壤层厚度越大,对金属管道最小防护距离的影响越大;第一层土壤厚度d1对最小防护距离的影响程度主要取决于ρ1、ρ2之间的差距;相同的ρ1/ρ2比值下,最小防护距离随d1的变化趋势,在一定可允许误差范围内近似认为一致。
[Abstract]:With the rapid development of HVDC transmission projects in China, the shortage of land resources and the high requirements for the selection of DC electrode sites make the common earth pole technology widely used. Therefore, the working environment of DC earth pole is becoming more and more complex and severe. The temperature rise in the process of dispersion under unipolar operation mode will lead to the local hardening of the soil around the electrode, and even the burning of the earth pole, etc. Or the corrosion of buried metal facilities and the DC bias of transformer. Therefore, the mechanism of DC earth electrode dispersion and the temperature rise process are accurately simulated and analyzed, and the underground river is studied. Related issues such as earthing performance of the earth pole under special massive soil structure such as rock strata, and protection distance of buried metal pipeline near the electrode site under the actual stratified soil structure, and so on. It is the theoretical basis for the optimal design of the earth pole of UHV HVDC transmission and the solution to the serious temperature rise, DC corrosion and magnetic bias caused by the large current entering the ground. The size of the cross-section of the grounding conductor and its own length, The regional size of dispersed soil varies by 106 orders of magnitude, which often leads to the phenomenon of rapid increase of calculation amount and even failure of subdivision. In view of this problem, the thin shell theory is introduced to deal with this problem, and in addition, soil electricity is introduced into the calculation process. The temperature characteristic curve of thermal parameters is used to accurately simulate the variation of soil parameters caused by soil temperature rise, and then the dynamic coupled finite element model of DC earth electrode is established by using the algorithm in this paper and based on COMSOL Multiphysics simulation software. The effect of soil temperature characteristics on the temperature rise process of DC earthing pole under different surface soil resistivity is analyzed. The results show that the grounding resistance of DC grounding system changes with the running time when considering the temperature characteristics of soil parameters. Analysis of the high, The effect of low block hetero-resistance on the electric field distribution and grounding resistance of DC earth pole is studied. The results show that the horizontal position and vertical depth of the hetero-resistance zone have obvious influence on the grounding parameters of DC earth pole, so in the actual design of DC earth pole, The influence of regions with low or high soil resistivity anomalies on grounding design should be considered. Finally, based on the extensive applicability of the numerical algorithm in this paper to any soil structure, The protective distance of buried metal pipeline under simple two layers of horizontal stratified soil is analyzed systematically. The results show that the influence of soil resistivity on the minimum protective distance of buried metal pipeline is closely related to the thickness of the soil layer in which it is located. The greater the thickness of the soil layer is, the greater the influence on the minimum protective distance of the metal pipeline is, and the influence of the first layer soil thickness D1 on the minimum protective distance is mainly determined by the difference between 蟻 1 and 蟻 2, and under the same 蟻 1 / 蟻 2 ratio, The trend of minimum protective distance with D1 is approximately consistent within a certain allowable error range.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM862;TM721.1

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