| With the development of high-voltage transmission technology and the increasing demand for wide-area energy allocation,power systems have higher requirements for the safety and stability of equipment operation.Composite insulation components based on epoxy resin(EP)are facing enormous challenges in increasingly complex working conditions.However,epoxy composites can accumulate a large amount of electric charge on their surface under the action of high voltage electric fields.Long-term contact between external insulation and external environment also easily leads to aging of materials,which makes the surface of materials become the weakest part of insulation.And the relevant problems such as surface flashover discharge and dampness deterioration become the key factors threatening the safety of power system.This seriously restricts the popularization and application of epoxy composite materials.So how to further explain the mechanism of improving the surface insulation performance of epoxy composite materials,and develop reliable,efficient and environmentally friendly methods to improve the surface insulation performance,has become an urgent scientific and technical problem to be solved.The results show that both surface flashover discharge and surface water intrusion are closely related to the package-matrix interface properties of epoxy composites.A large number of charge traps introduced in the interface region are the key factors affecting the gas-solid interface charge convergence and dispersion behavior.The relatively loose molecular structure in the interfacial region also provides a good medium for water diffusion.Therefore,adjusting the filler-matrix interface is an important means to improve the surface insulation performance of epoxy composites.In recent years,plasma and nanotechnology have shown obvious advantages in the research of insulating materials modification,providing a new idea and means for enhancing the surface insulation properties of epoxy composites.In this paper,plasma was used to fluorinate nano-filler and doping fluorinated filler to modify epoxy resin.The influence mechanism of fluorinated fillers on the surface pressure resistance and hydrophobic properties of epoxy resin was studied.And the method of synergistic improvement of surface pressure resistance and hydrophobic performance of epoxy resin was proposed.The main contents are as follows:(1)Plasma fluorination modification platform was established,and fluorinated graft on the surface of nanofiller was realized.Plasma fluoridation modification of nanofillers with different morphologies and conductivity characteristics has been implemented relying on a plasma fluoridation processing platform based on Dielectric Barrier Discharge(DBD).The-CFx group was grafted onto the surface of nanofillers successfully,and the influence of plasma fluorination on the fabric parameters of different kinds of nanofillers was studied.Epoxy composite samples were synthesized with nano-filler before and after fluorination.and the surface electrical properties were tested.(2)The characteristics of nanofiller and the influence of plasma fluorination on the surface flashover characteristics of EP were studied.Firstly,the influence of nano-fillers with different morphology and conductance characteristics on the surface flashover voltage of EP composites before and after plasma fluorination was compared by experiments.It is found that the low dimension nanofiller and semiconductor nanofiller have obvious advantages in improving the surface flashover voltage of EP composites.Plasma fluorination can improve the modification effect of nanofiller on EP surface pressure resistance.Among them,doping of 2.5%barium titanate fluoride nanofibers can increase the DC surface flashovers voltage of epoxy composites by 27.51%compared with that of pure epoxy resin.The simulation and characterization results show that plasma fluorination can reduce the interaction energy of nanoparticles and significantly improve their dispersion in polymer matrix.Fluorinated groups introduce more deep trap energy levels to the interface region,which can effectively inhibit carrier migration behavior.Plasma fluorinated semiconductor nanofillers can fully leverage the synergistic effect between the intrinsic properties of the fillers and the nano interface,which provides a new modification method for improving the surface pressure resistance of epoxy composites.(3)The liquid diffusion behavior and property deterioration of EP composites in typical hygrothermal were revealed.Through the simulating hygrothermal aging experiments,it is found that the insulation properties of EP composites showed periodic variation rules.The conductivity and trap characteristics of samples in deionized water present a monotonous downward trend.Combined with simulation and microscopic characterization,the "segregation" effect of solute particles in salt spray and acid rain environment was revealed.NaCl tends to diffuse and accumulate at the interface,resulting in serious fiber peeling.In acid rain,oxidizing acid particles are easy to react with EP matrix,making them easier to be bound in EP layer,and the diffusion behavior is a layer by layer erosion process.The diffusion behavior of liquid particles and the reaction such as hydrolysis play a dominant role in different deterioration stages,which leads to the periodic variation rules of the macroscopic electrical properties of EP composites.At the same time,it is found that liquid particles are more easily diffused in the interfacial region,and the competition effect between solute particles and water molecules can inhibit the diffusion of water molecules to a certain extent.(4)A method for suppressing the internal water diffusion behavior of EP using plasma fluorinated nanofillers was proposed.The influence of nano-filler before and after plasma fluorination on the water diffusion behavior of epoxy composites was studied.It was found that the plasma fluorinated nano-filler can reduce the saturation moisture absorption of epoxy composites,restrain the decrease of surface deep trap energy level and density,and delay the downward trend of the material flashover voltage along the surface during the process of hydrothermal aging.The results of molecular dynamics(MD)simulation show that the fluorinated filler can reduce the mobility of water molecules inside the epoxy composite,and the fluorine atoms on the surface of the filler can play a role in binding water molecules through hydrogen bonding.The inhibition effect of the two-dimensional structure of boron nitride nanosheets(BNNS)on the water molecular diffusion behavior was revealed.And it is proposed that the modification idea of regulating the tangential distribution of nanosheets to inhibit the water diffusion in epoxy composites.(5)A method for simultaneous improvement of EP surface hydrophobic and pressure resistance based on synergistic fluorinated nanofiller was proposed.The nanofiller was treated by plasma and fluorine-containing coupling agent.It is found that the method can effectively graft long chain fluorine-containing groups onto the surface of the nanofiller,so that it has both high fluorine content and high reactivity at the end of the chain segment.The fluorinated nanofiller has surface enrichment effect,which can form a bionic structure similar to water strider floating on the surface of epoxy resin.At the same time,the surface of the material is endowed with high reactivity in the plasma treatment process,which can promote it to form stable bond cooperation with the epoxy matrix,so as to construct the high reliability of the nano self-assembly structure.The surface structure synchronously improves the surface voltage resistance and hydrophobic performance of epoxy composite material.The maximum flashover voltage along the surface increases by 37.58%,and the maximum water contact Angle increases to 154°,reaching the superhydrophobic state.The research expands the application of plasma and nanotechnology in the field of high voltage insulation material modification and provides a new idea for the performance control of epoxy composite materials.The research results provide modification strategies for solving the problems of surface flashover and hydrothermal aging of epoxy composite insulators.It is of great practical value to improve the surface insulation performance of domestic epoxy composite and promote the application of high voltage insulation equipment. |
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