With the trend of miniaturization

the 40.5 kV switchgear is faced with size restrictions

and composite insulation which installs SMC insulation partition is general used. However

electrical fault between the switchboard bus bar and insulation partition is more common

thus researching the reasons for discharge fault is very necessary.In this paper

a KYN61-40.5 switchgear is first carried on power frequency withstand voltage test

which aims to verifying the possibility of discharge between the switch cabinet bus bar and the insulation partition. Secondly

accelerated thermal aging

hot and humid aging test of insulation baffle insulation partitions are carried on

and properties test of insulating materials such as SEM test

AC breakdown field strength

resistance to tracking index and hydrophobic detection are used to study the change rule of physical-chemical characteristic and reasons for insulation discharge. The experiments results show that the failure of the insulation cabinet of the switchgear is not caused by the decrease of the breakdown strength of the insulation partition. However

in the hot and humid environment

the protective film on the surface of the SMC insulation partition in the switchgear is decomposed and the contact angle is reduced

leading to conversion from hydrophobic to hydrophilic. When the external voltage is about 70 k V

discharge will occurs;and as epoxy insulation baffle still maintain good hydrophobic after aging

the switchgear insulation partition should better use epoxy material

and should not use unsaturated polyester glass fiber（SMC）material;in order to guarantee the physical-chemical properties of insulation partition

switchgear operating temperature should not exceed 80℃

and humidity should be controlled below 75%.