Research On Nonlinear Conductivity Of Polyaniline-Carbon Nanotubes/Epoxy Resin Anti-Corona Material

The stator wire rod is the core component of the generator and plays an important role in the process of electrical energy conversion.Corona phenomenon often occurs at the end of the stator wire rod due to the concentration of electric field,which seriously damages the main insulation of the stator wire rod,thereby affecting the normal operation of the generator.In engineering,an anti-halo material with nonlinear conductivity characteristics is usually coated at the corresponding position of the main insulating surface of the end of the wire rod,and the special conductivity characteristics of this material are used to homogenize the electric field.At this stage,anti-halo materials can only have nonlinear conductivity characteristics at higher electric field intensities,that is,the threshold field strength is higher and cannot play a better electric field homogenization effect.However,the insulation properties of low-threshold field strength materials often decrease significantly,limiting their application in engineering.In view of the problem of electric field concentration at the end of the wire rod,from the point of view of reducing the threshold field strength of the anti-halo material while ensuring the insulation properties of the material,this research uses epoxy resin(EP)as the base material,with one-dimensional structure of carboxylated multi-walled carbon nanotubes(MWCNTs)and zero-dimensional structure of polyaniline(PANI)as the filler,MWCNTs/EP,PANI/EP and PANIMWCNTs/EP composite materials with different mass fractions were prepared to characterize the microstructure of the composite material and the distribution of the filler,and test the DC conductivity,AC breakdown performance and dielectric spectrum of the sample.The influence of packing mass fraction,dimension,electric field strength,and temperature on the nonlinear conductivity characteristics of each composite material and the conductivity mechanism before and after the threshold field strength are systematically studied when single-doped and two fillers are synergistically doped.Establish a model of the end of the stator wire rod of a 26 k V hydroelectric generator,and use COMSOL Multiphysics software to simulate the electric field distribution at the end of the wire rod.The research results show that MWCNTs/EP composite materials have excellent nonlinear conductivity characteristics.The conductivity mechanism after the threshold field strength of MWCNTs/EP composite materials with low mass fraction is the combination of tunnel effect and space charge limiting current theory,but the threshold field strength of MWCNTs/EP composite materials decreases while its breakdown field strength decreases significantly.The nonlinear conductivity characteristics of PANI/EP composite materials are poor,but the doping of PANI improves the breakdown field strength of the composite materials.By changing the mass fraction of PANI in the PANI-MWCNTs/EP composite material,the threshold field strength of the composite material can be increased and the nonlinear coefficient can be increased,which plays a role in regulating the threshold field strength and the nonlinear coefficient.The conductivity mechanism after the threshold field strength is still the combination of tunnel effect and SCLC effect,zero-dimensional PANI doping affects the distribution of MWCNTs in the composite material,making the conductive path not easy to form,and improving the breakdown field strength of the composite material,reducing the probability of failure of the composite material as an anti-halo paint.COMSOL simulation results show that the three-stage anti-halo structure with PANI-MWCNTs/EP composite material as the anti-halo material can effectively improve the electric field concentration at the end of the motor stator wire rod,and the feasibility of homogenizing the electric field at the end of the wire rod with the two-stage anti-halo structure is verified,indicating that the PANI-MWCNTs/EP composite material prepared in this research has good application prospects as an anti-halo material for wire rods.