| Epoxy resin?EP?materials have been widely used in electricity,electronics industry,automobile industry,aerospace industry and other fields due to their excellent insulation performance,mechanical properties and easy processing and molding.Insulation failure caused by corona discharge threatens the safety of electrical system,which has always been a concern in the development of electrical technology.Corona discharge generally does not lead to insulation failure in the short term,but it will lead to insulation degradation due to long-term effect and eventually lead to insulation failure.Therefore,improving the corona resistance of insulating materials on the basis of keeping the original excellent performance as much as possible is an important research direction.In this paper,a composite filler system is designed to modify epoxy resin,and the use of ultrasonic dispersion and sand grinding dispersion method to prepare epoxy resin composites.The influence and mechanism of composite filler on the properties of epoxy resin are explored.In this paper,the element-organized silicon-boron?Si-B?composite oxide,which is synthesized using phenyltriethoxysilane monomer and tributyl borate monomer by hydrolysis-condensation method.And fumed silica?SiO2?of different types are used to dope EP.SiO2/EP,Si-B/EP,Si-B/SiO2/EP?mixed with single SiO2 particles?and M-type Si-B/SiO2/EP?doping 2 kinds of SiO2 particles?composite materials are synthesized,respectively.The dielectric properties,space charge properties,heat resistance and corona resistance of the prepared epoxy resin composites are tested and analyzed,the influence mechanism of different composite structures of filler on the above properties of EP composites is expounded.The influence mechanism on corona resistance is emphatically discussed.The thermal stability,breakdown strength,dielectric coefficient,dielectric loss and conductivity of SiO2/EP composites increase with the increase of the doping amount of nano-SiO2 particles;when the doping amount of nano-SiO2particles is 2 wt%,the breakdown field strength reaches the maximum value of24.66 k V/mm,which is 21.35%higher than that of pure EP material;corona resistance of SiO2/EP composites increases with the increase of doping amount of nano-SiO2 particles.At room temperature and the electric field intensity of 80k V/mm,when the doping amount of nano-SiO2 particles is 8 wt%,the corona resistance life of SiO2/EP can reach 42.7 h,which is 18.9 times of that of pure EP.However,the increase of dielectric constant and dielectric loss is relatively large,which is not conducive to the practical application of composite materials.Compared with SiO2/EP composites,the doping of Si-B composite oxides designed and synthesized in Si-B/EP composites can effectively reduce the dielectric constant and dielectric loss of EP composites.At the same time,with the increasing of the doping amount of Si-B composite oxides,the breakdown field strength and corona resistance life of Si-B/EP nano-composites increases first and then decreases.When the content of Si-B composite oxide is 6 wt%,the corona resistance life of Si-B/EP composite material reaches 17.6 h,which is8.38 times that of pure EP material.However,when the doping amount of Si-B composite oxide further increases,the breakdown strength is further reduced,resulting in the decrease of corona resistance life.In order to inhibit the increase of dielectric loss of EP composites and increase the corona resistance life of EP composites,this paper designs and synthesizes Si-B/SiO2/EP composites with composite filler system.Based on the doping amount of 6 wt%Si-B composite oxides,Si-B/SiO2/EP composites with the content of SiO2 filler and different particle sizes of SiO2 filler are prepared.Increasing 15 nm SiO2 filler content or fixing 15 wt%SiO2 content reducing the particle size of SiO2 filler will increase the dielectric constant and dielectric loss of Si-B/SiO2/EP composites.But,the increase is much smaller than that of SiO2/EP composite material.At 1 Hz,the loss of SiO2/EP composites with 8 wt%SiO2 content is 0.2815,however,the loss of Si-B/SiO2/EP composite material added with 9 wt%SiO2 content is only 0.0076;Si-B/SiO2/EP composite material containing 15 wt%6 nm SiO2 filler has the best space charge inhibition effect and the best thermal stability.However,the Si-B/SiO2/EP composite material with 15 wt%15 nm SiO2 filler has the longest corona resistance life of 8.99 h?90°C,power frequency,measured at 80 k V/mm field strength?,7.49 times that of Si-B/EP composite material with 6 wt%S-B composite oxide content.According to the analysis of the experimental results,it is proposed that compared with the inhibitory effect of the material on the space charge and the influence of the heat resistance of the material on the Corona life of the material,the degradation path of materials under corona is a more important factor.In order to prolong the degradation path of the material under the action of corona and further improve the corona resistance of EP composites,M-type doping Si-B/SiO2/EP composites?M-type doping,mixed fillers with two kinds of SiO2 with different particle sizes?are designed and synthesized.It is expected to extend the degradation path of materials under the action of corona by using small particle size particles dispersed among the large.The experimental results show that M-type doping can not only increase the corona resistance of Si-B/SiO2/EP composites,it can also increase the breakdown field strength of M-type Si-B/SiO2/EP composites.When the mass ratio of 6 nm SiO2 filler to 15 nm SiO2 filler is 1/6.89,the breakdown field strength of M-type Si-B/SiO2/EP composites is 28.01 k V/mm,the corona-resistant life has also reached the maximum value of 13.23 h.Compared with the breakdown field strength of Si-B/SiO2/EP composite material with 15 wt%15 nm SiO2 added,the breakdown field strength has been increased by 8.5%,corona resistance life has been increased by 47%. |
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