Epoxy resin

widely used in the high voltage insulation

is often utilized to make cone-type or pillar insulators in gas insulated switchgear（GIS）

which operate stable under common AC voltage. However

due to the operation of disconnecting switch operation in GIS

very fast transient over-voltage（VFTO）-induced flashover along the insulator surface seriously threatens the stability of GIS. It is necessary to study this phenomenon in depth. In this paper

the influence of Al

2

O

3

doping content on gas-solid interface characteristics of epoxy resin was investigated by various test methods

and the effect of Al

2

O

3

doping content on VFTO resistance of insulators was studied by simulation. The e

xperimental results show that

as the Al

2

O

3

doping content increases

the surface particle density

the percentage of Al atoms on the surface

the steady photon number of electroluminescence

surface conductivity

bulk conductivity

dielectric constant

tangent of loss angle and partial discharge of epoxy insulating materials will increase

whereas

the water contact angle and the AC flashover voltage will decrease. The experimental results and simulation results show that reducing the doping content of Al

2

O

3

is effective to improving the VFTO tolerance of epoxy resin insulators.