Nonlinear Characteristics And Simulation Study Of SiC/SiO₂/EP Micro-nano Composite Materials

As an important part of the power system,the generator operation stability is affected by the insulation performance of the stator.The electric field distribution at the end of the stator bar is not uniform,which is prone to partial discharge.In the manufacturing process of the stator bar,the method of adding corona protection layer is usually used to homogenize the surface electric field.The corona protection layer is usually made of epoxy-based materials doped with SiC and graphite,it has nonlinear conductivity characteristics.Although nonlinear conductivity materials have been used in the field of engineering technology,their inherent defects limit their further development.In recent years,scholars in related fields have conducted research on composite nano-mediums,and it is proved that nano-doping can improve the overall performance of materials.With the development of nanomaterial science,its special properties provide a new direction for the modification of composite materials.In this dissertation,epoxy resin（EP）is used as the matrix,micron SiC and nanometer SiO₂ are used as inorganic fillers,and polyamide resin is used as the curing agent.16 crossover samples with different micro/nano doping concentrations are prepared by the blending method.Polarized light microscope（PLM）and scanning electron microscope（SEM）were used to observe the dispersion of SiC crystals and nano-SiO₂ in the composite medium.A high resistance meter was used to study the influence of different micro/nano doping concentrations on the conductivity of the composite material.Using broadband dielectric spectrometer and high-voltage Schering bridge to study the influence of temperature and frequency on the dielectric constant and loss of composite materials.Through AC breakdown test,the influence of micro/nano doping concentration on the breakdown field strength of composite materials is discussed.Finally,COMSOL was used to establish the EP/SiC,EP/SiO₂ interface electric field model to explore the distribution of the internal electric field and polarization intensity when the composite material was doped with micro-nano fillers.The experimental results show that the micron SiC particles appear irregular in the composite material,and the increase of the SiC doping concentration will reduce the dispersibility of nano-SiO₂.The electrical conductivity of the composite material increases with the increase of the SiC doping content,and the nano-SiO₂ doping the influence of concentration on the conductivity is related to the dispersibility of SiC particles.Low-concentration doping with SiO₂ will reduce the conductivity of the composite material,when the nano-doping concentration is 1wt%,the dielectric constant and loss of the composite material are both minimum.When the nano-doping content increases,the change of the dielectric parameter is related to the dispersibility of the nano-particles.When the SiO₂ doping content is the same,the breakdown field strength of the composite material decreases with the increase of the SiC content,and when the SiC doping content is the same,the breakdown field strength increases with the increase of SiO₂ content.When the applied electric field is the same,the electric field intensity at the interface of the micron particles is much greater than the average electric field of the medium,and the electric field is close to the critical electric field of the tunneling effect.The polarization intensity at the interface of the nanoparticles increases with the concentration of nano-SiO₂.It is related to the transport capacity of carriers.The more conducive the interface area is to the migration of carriers,the greater the polarization intensity at the interface.The interface polarization is one of the main reasons for the increase in the dielectric constant of the composite material.