Research On Nonlinear Conductivity Of Inorganic Filler/Epoxy Resin Composite

With the continual enlargement scale of modern power grids,and a large number of large power grids with ultrahigh voltage are gradually put into operation,high voltage direct current（HVDC）power transmission plays an increasingly important role in the field of power transmission.However,the structure of high voltage electrical equipment have the extremely non-uniform electric field,such as casing and insulator,the electric field at the edge of the intermediate flange is very concentrated.It easily causes dielectric breakdown,which can causes insulation failure.Meanwhile,the temperature distribution in the electrical equipment decreases along the radial direction,and there is a large temperature difference on the insulator,which in turn generates conductivity gradient.The local electric field distribution will be concentrated,forcing the insulation strength to decrease.In order to improve the insulation performance of electrical equipment,semiconductor fillers were doped into epoxy resin（EP）.In order to solve the problem of local electric field concentration,the nonlinear conductivity of epoxy resin composite was improved.However,obtaining excellent nonlinear conductivity characteristics is often at the expense of the breakdown field strength.Therefore,by changing the composition,structure and surface modification of the filler,the EP composite has excellent nonlinear electrical conductivity characteristics while still having excellent breakdown performance.In this paper,hexagonal boron nitride（h-BN）and silicon carbide particles（Si Cp）were used as inorganic fillers to prepare h-BN/Si Cp/EP composites by adjusting the doping ratio of h-BN and Si Cp.Then,silicon dioxide（Si O₂）was deposited on the surface of Si Cp to obtain Si Cp@Si O₂nano-filler with core@shell structure,and Si Cp@Si O₂/EP composites with different Si O₂shell thicknesses were prepared by adjusting the doping ratio of Si O₂and Si Cp.Finally,the silane coupling reagent was used to surface modify Si Cw.And the Si Cw/EP composites were prepared by adjusting the types and amounts of coupling reagents.The phase structures of inorganic fillers and composites were analyzed using X-ray diffractometer（XRD）and Fourier infrared spectroscopy（FTIR）,and the tissue structure was analyzed using scanning electron microscope（SEM）and transmission electron microscope（TEM）.The electrical conductivity and breakdown performance of composites were further explored through conductivity and breakdown tests.The results show that the epoxy resin composites with Si C increases with the increase of the doping concentration of Si C,and the nonlinear coefficient of conductivity and conductivity of the composites increases gradually,and the threshold field strength and the breakdown field strength decrease gradually.The breakdown field strength of the h-BN/EP composites increases first and then decreases with the increase of the filler concentration.The 3wt.%h-BN/Si Cp/EP composites containing more h-BN has no obvious nonlinear conductivity characteristics.With the increase of temperature,the conductivity of Si Cp@Si O₂/EP composites increases gradually,and the nonlinear coefficient of conductivity,threshold field strength and breakdown field strength decrease gradually.Compared with Si Cw/EP,Si Cw/EP（1%KH550）composites have better electrical conductivity and breakdown performance.