Numerical Calculation And Optimization Of 3D Electric Field For High Voltage SF₆ Current Transformer

In order to ensure the insulation performance of the SF6 current transformer,the uniformity degree and the distribution of electric field strength must be precisely controlled. And the numerical computation of electric field is a key method to perform the insulation analysis of high voltage SF6 current transformer.The structure of high voltage SF6 current transformer is a typical "T" type structure.And its primary conductor and secondary winding composes a coaxial cylinder of"T" type structure and the secondary coil with low voltage composes the other part of"T" type structure.In order to improve the electric field distribution of the whole structure,the shielding cover and rings are mounted near the terminal part of the primary coil.The shielding cover and secondary down-lead pipe approximately form a coaxial column electric field.The complex 3D electric filed is formed due to the above two coaxial cylindrical electric field,and the secondary winding and down-lead shield pipe are orthogonally intersected hereinto.The field of current transformer is a complexity structure.In order to perform the insulation analysis and structure design,220kV SF6 current transformer is adopted as the research object,and the FEM is adopted to establish the 3D electric field mathematical model including multiple media,such as,SF₆ gas,insulation porcelain and air. Combination of domain division analysis and self-adapt mesh technology are adopted to simulate and compute to 3D electric field.Moreover,the distribution of 3D electric field is obtained,and the location of maximum electric field strength and insulation weakness area is found.In order to improve the whole electric field evenness degree of SF₆ current transformer,and avoid the corona discharge breakdown phenomenon,two methods of adding shielding ring near the flange and primary conductor are adopted to analyze and optimize the electric field.The electric field distribution of every part surface of current transformer and the whole electric field distribution are contrastingly analyzed.The effect of improved electric field is researched,and the electric field distribution under different optimization condition is compared.And the optimal position and structure dimension of shielding ring is designed.Furthermore,the numerical foundation of current transformer insulation structure design is established.