| Electric field distortion often occurs at the exit slot of the stator bar in large generators,which can result in localized electric field concentration on the surface of the main insulation at the end.This phenomenon can cause breakdown or corona discharge,leading to insulation failure and a reduction in the motor’s working life.A segmented insulation structure is an effective solution,achieved by applying anticorona materials with different resistance values at corresponding locations of the stator bar.This approach enables adaptive matching of material conductivity characteristics and distortion electric strength,reducing or eliminating the electron accumulation phenomenon on the surface of the bar ends.One such material is an epoxy resin(EP)based composite with nonlinear electrical conductivity properties.Micron filler doping in epoxy resin can enhance the nonlinear coefficient,but it can also significantly reduce the breakdown strength and increase the dielectric loss.Hence,micron filler-modified epoxy resin no longer meets current application requirements.To effectively improve the nonlinear coefficient and conductivity of composite materials,reduce the threshold field strength,and ensure good breakdown and dielectric properties,this study used epoxy resin as the matrix and incorporated micron silicon carbide(Si C),two-dimensional lamellar montmorillonite(MMT),onedimensional tetra-needle zinc oxide(T-Zn Ow),and zero-dimensional granular zinc oxide(Zn O)as inorganic fillers.We prepared Si C/EP micro-composites,MMT/Si C/EP,T-Zn Ow/MMT/Si C/EP,and Zn O/MMT/Si C/EP micro-nano composites.The effect of organic modification of MMT was verified using X-ray diffraction and infrared spectroscopy experiments.The dispersion state and mutual contact of the inorganic fillers in the matrix were characterized by scanning electron microscopy and energy spectroscopy.Nonlinear conductivity,AC breakdown strength,relative permittivity,and loss factor of the composites were tested using corresponding experimental platforms.We found that micron Si C has some advantages in modifying the nonlinear conductivity properties of epoxy resin.However,the high content of micron Si C can significantly reduce the breakdown strength and increase the dielectric loss while improving the nonlinear coefficient of the composite.Adding two-dimensional MMT to the Si C/EP micron composite system has a positive effect on the nonlinear coefficient improvement.The lamellar structure of two-dimensional MMT plays a limiting role on the matrix molecular chain and forms an interfacial region inside the composite system,increasing the nonlinear coefficient and improving the breakdown and dielectric properties,while decreasing the conductivity and increasing the threshold field strength.Continued doping of one-dimensional T-Zn Ow or zerodimensional Zn O in the MMT/Si C/EP composite system can compensate for the negative impact of two-dimensional MMT on the electrical properties of the composite system by constructing interfacial conductive pathways.The enhancement of electrical properties of the composites by doping with one-dimensional T-Zn Ow is better than that by doping with zero-dimensional Zn O.One-dimensional T-Zn Ow can more effectively increase the interfacial channels inside the system,constitute a good carrier circuit,form a conductive network,and effectively reduce the threshold field strength of the composite.This approach improves the conductivity and nonlinear coefficient of the composite,ensuring that it has superior nonlinear conductivity characteristics without deteriorating breakdown and dielectric properties. |
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