Research On Nonlinear Dielectric Properties Of Epoxy/BaTiO₃ Composite Insulation

Nonlinear dielectric is a dielectric whose permittivity and conductivity change with electric field.Nonlinear insulating material has a field-dependent permittivity and/or conductivity can regulate the nonuniform electric field distribution,so it is called as smart insulating material.It has been widely used in the anti-corona structure of motor and cable accessory structure.Due to the complexity of nonlinear problems,the researches on dielectric characterization and measurement of nonlinear insulating materials are not perfect.In order to further improve the relevant theoretical research of nonlinear insulation,this paper carried out basic experimental exploration by using existing test technology,taking the laboratory-prepared BT/EP composite material as the research object,by changing the filler properties such as the particle size and filler loading of Ba Ti O₃,the influences of inorganic fillers on the nonlinear dielectric properties of the nonlinear composite insulation was explored from perspectives steady-state dielectric properties and dynamic dielectric properties,which provide the basic support for the subsequent nonlinear theoretical research.The results of DC conductivity test indicate that the conductivity of composite material gradually increases with the increase of the electric field strength.As the nano-filler loading increases,the conductivity of the composite material shows a non-linear increase in the degree controlled by the electric field.From the AC steady-state dielectric spectroscopy test,the dielectric constant of BT/EP composites with different filler loading and different particle sizes both decreases with increasing frequency.The dielectric constant of nano-composite material decreases first and then increases with the increase of filler loading.Since the Ba Ti O₃crystal phase structure is determined by its particle size,the dielectric constant of micron materials is greater than that of nano material at the same filler loading.The dielectric loss of the nano-composite material decreases first and then rises with the frequency increases,and the dielectric loss increases with the increase of filler loading.According to the results of current time-domain spectrum and the theoretical analysis of isothermal relaxation current,as the amount of Ba Ti O₃filler increases,the corresponding time of the relaxation peak advances,at higher field strengths.It shows that the increase of the filler loading makes the depth of the main trap inside the medium shallower,the density of deep traps decreases and the density of shallow traps increases.The results of thermally stimulated current spectroscopy showed that the trapping level of the main peak of the nano BT/EP composite material was basically unaffected by the polarization electric field,but the density of the corresponding trap level obviously increased with the electric field;As the nano-filler loading increases,the trap density exhibits a nonlinear change.In addition,the main peak trap density of micro-composites is much greater than nano-composites,but when the trap energy level is greater than 1e V,the trap density of micro-composites decreases rapidly,it shows that micron Ba Ti O₃not only brings a large number of interface cavity traps,but also changes the depth of the traps.In summary,by changing the filler loading of Ba Ti O₃,particle size and other factors can affect the conductivity,dielectric properties,trap parameters and other dielectric characteristics of the composite material.Furthermore,the control of space charge,electric field distribution and electrical conductivity in the composite can be achieved by it.