| Epoxy resin are widely used in DC converter valves,saturable reactors,DC bushings and gas-insulated switches because of its excellent insulation and mechanical properties.Different from the AC insulation system,due to the high resistivity of the epoxy resin,a large amount of surface charge are accumulate on epoxy resin surface due to carrier injection under DC electric field,which may cause insulation failure of the power transmission system.In this paper,the influence of nanoparticles on the breakdown and flashover performance of epoxy resin was studied.The influence of nanoparticles and surface molecular modification on surface charge dynamics of epoxy resin was researched.The DC flashover characteristics of modified epoxy resin in air,SF6 and vacuum were obtained and the influence mechanism was analyzed.The main research work and achievements are as follows:（1）Epoxy/Al2O3 nanocomposites with nanoparticle mass fractions of 0,1,3 and5 wt%were prepared,their dielectric properties,charge dynamics,volume and surface resistivity,AC and DC breakdown strength and DC flashover strength were studied.The results showed that when the mass fraction of Al2O3 nanoparticles is 1 wt%,the surface charge decay rate of the composite is lowest and the surface resistivity,DC breakdown voltage is the highest,while the DC flashover voltage is the lowest.Interaction zone model of nano-dielectrics was used to analyze the experimental results.It is also found that the charge accumulation will cause the decrease of DC flashover of epoxy resin.（2）Surface molecular structure of epoxy/Al2O3 nanocomposite was modified by surface fluorination with different fluorination time.The influence of surface fluorination on the chemical structure,micromorphology was obtained,and the charge dynamic under DC electric filed was studied using needle-grid and plate.Influence of nanoparticle mass fraction and fluorination time on the charge dynamic and surface trap energy level of epoxy resin was measured.It was found that surface fluorination can significantly increase the surface potential decay rate of epoxy resin,while nanoparticle can reduce the rate of surface potential decay of epoxy resin.The DC breakdown voltage of epoxy/Al2O3nanocomposite was slightly increased after fluorination.（3）The effect of surface fluorination and nanocomposite on DC flashover performance of epoxy resin was studied.It was found that surface fluorination of epoxy resin can improve its DC flashover voltage in air and SF6,while the nanoparticle will lead to a slightly decrease of the DC flashover voltage;prove that suppression of charge accumulation can increase the DC flashover voltage of epoxy resin in air and SF6atmosphere.Considering the breakdown performance of surface fluorinated epoxy/Al2O3nanocomposite,the Combination of surface fluorination and nano-doping would provide epoxy resin excellent insulation properties.However,the vacuum DC flashover voltage of fluorinated samples decreased a lot,the lower trap energy level and higher secondary electron emission coefficient may cause lower flashover strength. |
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