| Epoxy resin has the advantages of excellent mechanical properties and high insulation strength.It is often used as the insulation support of DC high-voltage electrical equipment such as gas insulated transmission lines.However,under the condition of DC high voltage,a large amount of charge will accumulate on the interface between epoxy resin and gas,which will seriously distort the external electric field on the one hand,and provide favorable conditions for the formation of penetrating conductive channels between electrodes on the other hand,which is easy to cause surface flashover.The surface flashover of epoxy resin will lead to the insulation failure of relevant electrical equipment and seriously threaten the safe and stable operation of power system.Therefore,improving the surface flashover performance of epoxy resin has become a research hotspot in recent years.The research shows that the surface flashover performance of epoxy resin is closely related to the aggregation and dispersion characteristics of interface charge,and the aggregation and dispersion characteristics of interface charge can be regulated by the surface morphology,chemical composition,surface conductivity,trap energy level distribution and other parameters of epoxy resin.Therefore,the research route of improving the surface flashover performance by regulating the surface physical and chemical properties of epoxy resin is widely used.However,there are two deficiencies in the current research.One is to only study the change law of the surface characteristics of epoxy resin before and after modification,and there is little direct comparison between different modification methods,resulting in the limitation of the regulation means and range of the surface characteristics of epoxy resin;Second,only pay attention to the uniformity of the modification effect,and mostly ignore the characteristic that the epoxy resin is often in non-uniform working conditions,which makes it difficult for the surface characteristics of the epoxy resin to match the electric field distribution,so the improvement of its surface flashover performance is limited.Based on the project of National Natural Science Foundation of China,this dissertation puts forward the regulation method of epoxy resin surface characteristics based on plasma gradient modification,and uses this method to study the surface flashover promotion mechanism of epoxy resin under non-uniform electric field.The main contents are as follows:The epoxy resin preparation platform and surface characteristic test platform were built to realize the mass preparation of epoxy resin and the comprehensive characterization of surface physical and chemical properties and electrical properties.The plasma dielectric barrier discharge and atmospheric pressure plasma jet modification platforms were built to realize the plasma fluorination and plasma SiOx deposition modification of epoxy resin.The regulation range of various plasma modification methods on the surface characteristics of epoxy resin and the improvement effect on the surface flashover performance of epoxy resin were comprehensively compared.The relationship among plasma modification method,physical and chemical properties of epoxy resin surface and electrical properties of epoxy resin surface was established.The epoxy resin simulation models under extremely uneven electric field and slightly uneven electric field are built respectively.The field strength distribution characteristics of non-uniform electric field are studied by finite element method.It is found that the spatial distribution of surface conductivity can regulate the maximum field strength of non-uniform electric field.In order to reduce the maximum field strength,a step gradient distribution strategy of surface conductivity is proposed for extremely uneven electric field.For slightly uneven electric field,a discrete gradient distribution strategy of surface conductivity is proposed by using depth learning and optimization algorithm.Aiming at the extremely uneven electric field,a plasma step gradient modification scheme is formulated,which greatly improves the surface flashover performance of epoxy resin under the extremely uneven electric field.Combined with the experimental and simulation results,three factors to improve the surface flashover performance of epoxy resin under extremely uneven electric field are summarized:reducing the maximum field strength by constructing the surface conductivity of step gradient distribution,inhibiting the accumulation of charge at the three junction points by increasing the interface charge dissipation rate in the high field strength region,and inhibiting the rapid charge migration between electrodes by controlling the interface charge dissipation rate in the low field strength region.For the surface modification of epoxy resin,only when three factors are met at the same time can the surface flashover performance of epoxy resin under extremely uneven electric field be improved to the greatest extent.Aiming at the slightly uneven electric field,the plasma discrete gradient modification scheme is formulated,which greatly improves the surface flashover performance of epoxy resin under the slightly uneven electric field.It is found that the improvement mechanism of surface flashover performance of slightly uneven electric field has similarities and characteristics with very uneven electric field.Among them,uniformly increasing the surface conductivity of epoxy resin has little effect on the slightly uneven electric field.The influence weight of surface conductivity in different regions on the maximum field strength is different,and the influence weight of surface conductivity at the three junction points on the maximum field strength is the largest.Finally,the mechanism of improving the surface flashover performance of epoxy resin under non-uniform electric field is summarized.It is considered that the surface flashover performance under non-uniform electric field can be improved to the greatest extent only by meeting the optimal distribution of surface conductivity and interface charge dissipation rate in space at the same time.If the above conditions cannot be met,the improvement of surface modification technology on the surface flashover performance is very limited or even negative. |
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