In the processes of electrical performance test for a large number of basin insulators

it is found that the partial discharge test of the basic insulator with metal flange existed the phenomenon of instability under normal test conditions. This paper combines the three dimensional finite element simulation analysis with the verification test at the same time

it is confirmed that the main cause of this phenomenon is due to the lower air gap width

and the air gap has contributed to partial discharge. the same simulation results showed that

the width of the gap and the dielectric constant of epoxy resin casting materials have a greater impact on the electric field in air gap. The smaller the width of the air gap leads to the higher electric field in the gap

and the greater the dielectric constant leads to the higher the electric field in the gap. By changing the proportion of filler parts to adjust the dielectric constant and the air gap width of the epoxy resin casting material

the electric field in the air gap has been optimized. The qualified rate of the product has been improved.