When GIL changes from single-phase operation to three-phase

the insulation structure of post insulator with sliding design will become more complex

and the difficulty in design will be significantly increased. In order to improve the operation reliability of 252 kV compact GIL

the electric field distribution characteristics of three-phase tri-post insulator were simulated and analyzed by using the finite element method. The design indexes of insulation structure were extracted and transformed into dimensionless index f. The variation law of f with typical structure parameters was discussed and the influence degree of typical structural parameters on design indexes was obtained by variation coefficient method. On this basis

this paper presented the optimization design sequence and the improvement scheme. In addition

the method of improving the capacitance distribution between electrodes to the surface field distribution of metal parts uniform was analyzed. The results show that the total and tangential field strength on insulator surface of the improved scheme are reduced by 6.9% and 11.1%

respectively. While on metal insert surface

the total filed strength is reduced by 30.1%. The usage of improved scheme ensures the design indexes to meet the requirements of the critical value

which has an important significance and reference for the design of three-phase tri-post insulator in 252 kV compact GIL.