Study On Nonlinear Conductivity Characteristics Of Donor-doped Zinc Oxide/EPDM Based Composite

The weakest link in the HVDC transmission system is the cable accessories and the fundamental reason is the uneven electric field distribution in the cable accessories.At present,the use of material with non-linear conductivity as the reinforced insulation of the cable accessory can effectively alleviate the problem of electric field concentration at the root of the stress cone of the cable accessory.However,the conductance nonlinearity of composite media often comes at the expense of breakdown field strength.How to balance the conductance nonlinearity and breakdown field strength of rubber based composite media has become a research hotspot in the field of electrical materials.In this thesis,EPDM is selected as the matrix material,and zinc oxide doped with ferric ion donors is selected as the inorganic filler.Among them,the sol-gel method and co-precipitation method are used to prepare donor zinc oxide nanoparticles and donor zinc oxide nanosheets;then the prepared nanoparticles and nanosheets are melt blended with EPDM rubber,hot pressed,etc.Process,finally obtain the EPDM rubber based composite medium.Systematic study of the influence of donor doping content,inorganic filler filling content and filler shape on the microstructure and electrical properties of composite media.Through the establishment of a simulation model of the intermediate joint,COMSOL Multiphysics software was used to simulate the effect of EPDM rubber based composite media on the improvement of the spatial electric field distribution of the intermediate joint.The study found that with the increase of the iron ion donor doping content,the conductivity nonlinear coefficient of the composite medium showed an overall increasing trend;when the donor doping content was low,the breakdown field strength showed a changing trend of first increasing and then decreasing.With the increase of the filling content of inorganic fillers,the non-linear coefficient of the composite dielectric conductivity gradually increases,and the threshold field strength and breakdown field strength gradually decrease.With the increase of temperature,the non-linear coefficient of composite dielectric conductivity,threshold field strength and breakdown field strength gradually decrease.Composite media prepared by nano-sheet inorganic fillers generally have higher nonlinear coefficients,lower threshold field strength and breakdown field strength than composite media prepared by nano-particle inorganic fillers.The simulation results show that when EPDM is used as reinforced insulation,the electric field is concentrated at the root of the stress cone.When the composite medium is reinforced insulation,the field strength at the root of the stress cone gradually decreases with the increase of the mass fraction of the inorganic filler in the composite medium,and the electric field concentration position gradually moves to the main insulation direction.