Calculation of Electric Field Distribution Along Composite Insulator Strings and Design of Grading Ring of UHVDC Transmission Line

Having summarized the calculation methods of electric field and the actualities of the research on the calculation of electric field and design of grading rings at home and aboard, this paper combines the finite element method and charge simulation method nicely in order to calculate the electric field and potential distribution along composite insulators as well as design the grading rings for the 800kV UHVDC transmission lines according to the features of composite insulator and the domain decomposition method.The three-dimensional (3D) model of 800kV two polar DC transmission lines with tower configuration and the simplified two-dimensional (2D) model are established by using ANSYS 8.0 and ANSOFT software. The electric field and potential distribution along composite insulator without any grading ring is calculated, which is rather too uneven in the case of running under 800kV UHVDC transmission lines. The potential distribution along composite insulator of 800kV UHVDC transmission line and lower voltage class is contrasted for the further study on the relationship between the nonlinearity of the electric field and potential distribution along composite insulator and the length of the composite insulator. The result shows that the higher the voltage class is, the more uneven the electric field and potential distribution along composite insulator will be.A method to optimize the location and the configuration parameters of the grading ring is presented; the aim of the optimization is the limitation of the maximal electric field around the metal fitting and the grading ring, while the variables are the configuration parameters of the grading ring. If the result of the 3D model is lower than the set electric field intensity, the approving parameters of the grading ring is gained. Finally, the optimized parameters of the grading ring are verified in the 3D model, the result indicates that the maximal electric field around the sheath, metal fitting and the grading ring is controlled to be acceptable, and the optimized grading ring can meet the needs of the ±800kV UHVDC power transmission project.