中文摘要：

超/特高压直流输电工程中共用接地极技术的应用日趋普遍,单极大地运行方式下直流接地极承载的入地电流大幅增加。考虑直流接地极散流时土壤中温度场和电场的相互影响,准确计算其接地参数及电流场分布是直流接地极优化设计及后续相关课题研究的基础。提出了基于薄壳理论的直流接地极电热动态耦合有限元数值计算方法。在土壤中恒定电场与温度场耦合的基础上,分别通过将土壤电参数和热参数：电阻率、比热容和热导率设置为上一时刻该单元土壤温度的函数,实现由时变的温度分布控制土壤参数,准确地模拟散流过程中土壤电场、热场相互影响、相互耦合的动态过程;同时在数值计算过程引入＂薄壳＂理论,将接地导体用具有一定虚拟厚度的二维面代替,采用三角形单元离散,解决了直流接地极截面尺寸与求解区域差异巨大而带来的计算量大、求解困难的问题。最后,将数值计算结果与文献试验测量结果对比,验证了文中算法的有效性。并基于文中算法分析了土壤参数温度特性对接地极性能的影响,认为考虑土壤参数温度时变特性时,在一定范围内,较高土壤电阻率地区直流接地系统的接地电阻随运行时间有较明显的增大现象。

英文摘要：

Common grounding electrode technology applied in UHVDC becomes more and more popular. Grounding current of DC electrode is increased significantly under monopole-ground operation mode. Considering interactions of thermal and electric fields in soil, accurate calculation of grounding parameters and electric field distribution are basis of DC grounding electrode optimizing design and further research. This paper proposes a DC grounding finite element method of electric-thermal coupling based on shell theory. Based on coupling of constant electric and thermal fields in soil, electric and thermal parameters of soil, including resistivity, specific heat and thermal conductivity are set as functions of soil temperature at previous time respectively, realizing time-varying temperature distribution control of soil parameters, simulating dynamic current flowing process of soil electric and thermal fields and their mutual influence and mutual coupling accurately. Introducing shell theory into numerical calculation, a two-dimensional surface with certain virtual thickness instead of grounding conductor is constructed, using triangle discrete method to solve problems of large calculation amount and solution difficulty caused by huge differences between DC grounding section size and solving region. Finally, compared with experimental results, numerical results shows that the proposed algorithm is effective and feasible. Based on analysis, considering soil temperature time-varying characteristics, grounding resistance of DC grounding system shows an obvious increasing trend with running time in high soil resistivity region.