| Epoxy resin has been widely used in the field of high voltage insulation because of its good electrical and mechanical properties.It is easy to accumulate surface charges at the gas-solid interface at high field strength,causing electric field distortion.Once partial discharge is initiated,the insulation performance of epoxy resin will be directly affected,and then flashover along the surface or even more serious accidents will occur.Threatening the safe and stable operation of power system.Therefore,the surface modification of epoxy resin materials by atmospheric pressure plasma was carried out in this paper.Compared with direct fluorination technology,the mechanism of improving the surface hold off voltage of epoxy resin by the factors such as charge dissipation,surface morphology and chemical composition before and after modification was explored.Firstly,the properties of the samples under three treatment conditions and untreated samples were compared and analyzed.The accumulated surface charges were respectively reduced to about 60.1%,23.3%,and 42.0% for DBD etching,DBD deposition direct fluorination compared to untreated samples.The surface roughness of the DBD deposition samples is the lowest.The surface morphology shows a uniform cone peak of hundreds of nanometers high,and the flashover voltage is increased by up to 15%.However,fluorinated samples were affected by exothermic reaction,and some of the surface areas were expanded.There were a few high peaks in the halfmicron level and the flashover voltage increased by less than 10%.In addition,the surface hold-off voltage of the untreated samples with different shapes is slightly different,and the flashover voltage is obviously increased after sanding.Secondly,the properties of DBD deposition and direct fluorinated samples stored for 5~100 days at different treatment time were compared and analyzed.The results showed that the charge dissipation curves of DBD deposition samples changed significantly after 25 days while the fluorinated samples did not change until 35 days after drying.The water contact angle indicated that the hydrophilicity of fluorinated samples was stronger.The study of the sub-atmospheric pressure DBD treatment shows that the treatment time of 0.5~10 minutes has little effect on the charge dissipation curve.However,the flashover voltage is low,although the charge dissipation of the newly processed sample is greatly accelerated.After storage for 2 days,the flashover voltage of the samples will be increased.Finally,a reasonable substrate temperature and oxygen content were set to improve the discharge effect and film properties.The proper increase of oxygen content can enlarge the discharge channel,stabilize the discharge process and increase the film area effectively.By chemical group analysis,the thickness of the film increases and the film grows along the surface during 0~3 minutes.By morphology observation,it is found that oxygen can provide more nucleation sites and accelerate film growth,but the number and direction of atomic clusters are difficult to control.The heating of substrate can effectively inhibit the phenomenon of atomic agglomeration,prevent the film from cracking and control the growth of thin films.Thus,more compact and dense thin films are formed.After several days of heat curing,the pressure resistance along the surface can be improved by up to 25%,which indicates that the effective forming of the thin film is very important. |
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