Optimization design of grading ring and electrical field analysis of 800 kV UHVDC Wall wall bushing

This paper has analyzed the reason for the flashover of a typical 800 kV converting transformer bushing. The finite element method is applied to calculate the electric field and potential distribution along HV bushing as well as optimize the design of grading rings for the 800 kV UHVDC bushing. The three-dimensional (3D) model of 800kV bushing with valve hall configuration is established using ANSYS software. According to the calculation of electric field and potential distribution along the bushing without any grading ring, the joint of flange and shed and sheath has higher field intensity, and the electric field is rather unevenly distributed. Afterwards, this paper presents a method of adding a grading ring to the flange side in order to reduce the field intensity around the surface of shed & sheath. This method also optimizes the location and the configuration parameters of the grading ring, with an aim to limit the maximal electric field intensity around the metal fitting and the grading ring and obtain the optimal design of grading ring. Finally, it is verified by the 3D model that the maximal field intensity around the surface of flange, shed and sheath, and the grading ring is controlled within acceptable range, and the optimized design can be applied to the ±800 kV UHVDC power station project to reduce the occurrence probability of flashover of UHVDC bushing.