Research On Electrical Properties Of The Filled EPDM Composites

Rubber-based insulating materials have important applications in transmission systems such as submarine cables,cable jackets,and cable accessories.As an important part of DC transmission system,the continuous improvement of transmission voltage level also puts forward higher requirements for its electrical performance.Due to the conductivity difference of different materials in cable accessories,it is easy to cause uneven distribution of local electric field and serious distortion of interface electric field.The self-adaptive matching of conductivity and electric field strength of nonlinear conductive insulating materials is expected to improve the problem of uneven distribution of electric field in cable accessories.In this thesis,ethylene propylene diene monomer(EPDM)was used as the rubber matrix,and inorganic conductive fillers nano copper(cunps),carbon nanotubes(CNT)and organic conductive polymer polypyrrole(PPy)were selected as the functional fillers,which were co-doped with boron nitride to improve the electrical properties of EPDM.In this thesis,CuNPs/BN fillers,CNT/BN fillers,and PPy/BN fillers were prepared by liquid-phase chemical reduction method and liquid-phase blending method,respectively.The above three fillers were mixed into EPDM matrix and nonlinear conductive composites were prepared.Systematically characterize the morphology and size of the filler and the microstructure of the composites,test and analyze the DC conductivity and breakdown field strength of the composite under different electric fields and temperatures,and systematically study the influence law and mechanism of filler doping content,microstructure and filler type on the electrical properties of the composites.Using the finite element software COMSOL multiphysics,the DC steady-state electric field distribution in the middle joint of the cable and the electric field distribution at the root of the stress cone of the cable accessories under lightning impulse voltage are simulated and analyzed.The results show that doping CuNPs/BN filler can significantly improve the DC conductivity of EPDM,and with the increase of CuNPs doping content,the nonlinear conductivity of the composite becomes more and more significant,and higher nonlinear coefficient can be obtained under lower electric field intensity.At the same time,the breakdown field strength of the composites will gradually decrease,and the temperature rise will further reduce the breakdown field strength.However,compared with pure EPDM,the breakdown field strength of CuNPs/BN/EPDM composites has a weaker temperature dependence.Because carbon nanotubes(CNTs)have the advantages of high conductivity and high aspect ratio,CNTs are easier to form conductive networks in composites.Compared with CuNPs/BN/EPDM composites,CNT/BN/EPDM composites can obtain excellent nonlinear conductivity at relatively low doping content.For PPy/BN/EPDM composites,doping PPy organic filler can also endow EPDM with nonlinear electrical conductivity.Increasing the filler doping content and increasing the temperature will reduce the nonlinear conductivity threshold field strength of the composites.The simulation analysis shows that when the composites with nonlinear conductivity are used as the reinforced insulation,the DC steady-state electric field distribution in the cable accessory is more uniform,and the maximum electric field at the root of the stress cone under lightning impulse voltage is also lower than its breakdown field strength,which shows a good potential in the rubber insulation material for cable accessories.