地磁暴是一种周期性的自然灾害，变化的地磁场会诱发感应地电场，通过接地变压器中性点在输电线路与大地导体中形成地磁感应电流（geomagnetically induced current, GIC）回路，对超高压和特高压交流输电系统的安全稳定运行带来严重威胁。中国地形种类较多，结构比较复杂，地质地貌对感应地电场的影响非常大。针对GIC建模难、计算难的问题，提出了一种基于三维大地电导率模型的GIC有限元计算方法。首先，建立了考虑地质结构各向差异的三维大地电导率模型，并给出了多层地质条件下的电磁场透入深度计算模型。其次，建立了基于时变电磁场数学模型，结合电网拓扑结构，推导了电网GIC等效计算模型。最后，以新疆莎车—吐鲁番750 kV输电线路作为算例，在COMSOL Multiphysics有限元仿真软件中搭建了相应的物理模型，通过几何建模、边界条件设定、网格划分和迭代求解得到了电网感应地电场的三维分布，进而得到了流过750 kV变压器中性点的GIC。研究结果表明，三维模型得到的GIC整体水平高于二维模型，且三维模型考虑了输电线路与不同地形的几何夹角，能够给出更加详细的感应地电场分布，从而验证了所提方法的有效性，为科学规划超高压和特高压输走廊路提供了参考依据。

A geomagnetic storm is a periodic natural disaster in which the changing geomagnetic field can induce an induced geoelectric field. A geomagnetic induced current (GIC) loop is formed between the transmission line and the earth conductor through the neutral points of grounding transformers. GIC seriously threatens the safe and stable operation of extra-high and ultra-high voltage AC transmission systems. There are many types of terrain and complex structures in our country, which makes the influence of geological landforms on induced geoelectric fields very significant. A finite element calculation method for GIC was proposed based on a three-dimensional earth conductivity model to address the difficulties in modeling and calculating GIC. Firstly, a three-dimensional earth conductivity model was established considering the anisotropy of geological structures. Meanwhile, a calculation model for electromagnetic field penetration depth under multi-layer geological conditions was given. Secondly, a mathematical model based on time-varying electromagnetic fields was established. Combined with the topology of the power grid, an equivalent calculation model for the power grid GIC was derived. Finally, taking the Shache-Turpan 750 kV transmission line in Xinjiang area as an example, a corresponding physical model was built in COMSOL Multiphysics finite element simulation software. The three-dimensional distribution of the induced ground electric field in the power grid was obtained through geometric modeling, boundary condition setting, grid division, and iterative solution. Furthermore, the GIC flowing through the neutral point of the 750 kV transformer was obtained. The research results indicate that the overall level of GIC obtained by the 3D model is higher than that of the 2D model. Besides, the 3D model considers the geometric angle between the transmission line and different terrains, which can provide a more detailed distribution of induced geoelectric fields. The research results verify the effectiveness of the method proposed, which provides a reference basis for scientific planning of ultra-high and ultra-high voltage transmission corridors.