Surface charge accumulated on polymer insulating materials is considered as one of the main factors leading to insulator flashover

which affects the stable operation of power systems. By pre-depositing charge with different distribution characteristics on the insulator surface

we analyzed the dominant factors of surface charge’s influence on flashover under AC voltage through experiments and simulations. The experiments are performed under two different conditions: in the early stage of charges decay and after some time of the decay. The results suggest that the dominant factor changes with the process of charges decay. In the early stage of charges decay

the charges de-trapped from shallow traps is the main factor leading to the flashover

which enables the flashover voltage to drop by about 34%. After the charge decays for some time

the distortion of electric field caused by charges in deep traps plays a dominant role. However

this effect is uncertain

which may result in a maximum drop in flashover voltage of about 30%. It has also been shown that charges on the insulator surface always leads to the decrease of AC flashover voltage regardless of the polarity and the distribution characteristic of the charge

which is different from DC voltage.