Surface flashover that occurs along the gas-solid surface of the basin-type insulators is one of the essential failures of GIS/GIL

which significantly threatens the safe operation of ultra-high voltage transmission systems. To enhance the DC surface flashover characteristics of basin-type insulators

epoxy composites are treated by ultraviolet irradiation in a vacuum

and various techniques

such as surface potential measurement and quantum chemical simulation

are adopted to obtain the distance of molecular chain

density

thermal stability

energy level band

trap parameters

surface charge distribution

and DC surface flashover voltage; moreover

the influence of ultraviolet irradiation on DC surface flashover is clarified. The results show that the DC surface flashover voltage of the 12-hour ultraviolet irradiated epoxy composites shows a 17% increment compared to the untreated sample. After surface hetero-charging for 6 h with a +20 kV voltage

the DC flashover voltage increases by 24%. The DC surface flashover is decreased by less than 2% six months after treatment

which exhibits long-term stability. The analysis of trap level and charge transport characteristics indicates that high-energy photons accelerate molecular chain crosslink after ultraviolet irradiation in a vacuum. The crosslinking structure facilitates the LUMO level of epoxy composites to decrease

thus large amounts of deep traps are introduced

which improves the energy level and density of epoxy composites. The increase of deep trap level causes charge to accumulate near the electrode

which impedes carrier injection from electrodes

therefore

the electric field above the solid surface is reduced

and the DC surface flashover voltage is increased. Based on the relationship among ultraviolet irradiation in a vacuum

charge transport

and surface flashover

ultraviolet irradiation in a vacuum can be an essential strategy in improving DC surface insulation of GIS in the future.