The use of grading rings is an important measure to control the surface electric field of insulators and fittings and thus corona discharges, and realize noise reduction of UHVAC transmission lines. However, due to the coexistence of the tower and insulator strings with the grading rings, the high complexity of simulation models leads to low quality of meshes, long meshing and computation time, and high memory usage, which hinders from fast optimization design of grading rings. Therefore, it is of need to device a numerical modeling method to reduce the complexity. In this paper, a numerical modeling method is proposed. Infinite element method is coupled with finite element method to reduce the modeling errors and the size of the computation domain. The connecting fittings of insulator strings are omitted and plates are used to model the trusses in order to further reduce the complexity. Moreover, The tower can be reduced to 1/4 size of the full model with the help of symmetry and computation experience. A meshing method based on domain decomposition is brought forward to speed up the grid generation. The results show that this modelling method can hugely decrease the complexity of the model and meshing time.

UHVAC transmission line; corona discharges; electric field; grading rings; insulator strings