Investigation On The Preparation And Electrical Insulation Properties Of High Thermally Conductive And Corona Resistant Polyimide-based Micro-nano Composites

With the development of variable frequency control technology, inverter-fed motors are widely used in railway traction. Polyimide films used as insulation materials of inverter-fed motors are prone to breakdown after being subjected to the corona and thermal aging effects. Thus it is urgent to modify the traditional insulating materials or to develop new high-performance insulation materials to meet the demand for high performance and reliability. In recent years, polymer based nano-composite has become a hot spot in the field of electrical insulation. In this paper, PI/BN micro-nano composite films were designed and prepared. The structure characteristics, dielectric properties and thermal conductivity of the composite films with different filler contents and different filler types were studied to provide some experimental and theoretical basis for the development of new micro-nano composite dielectrics.PI/BN-mn and PI/BN-n films with different filler contents were prepared via in-situ polymerization. The cross section morphology and structure of PI films were studied by polarizing optical microscopy and scanning electron microscopy. The BN nanoparticle fillers show good dispersion in the polyimide matrix and good compatibility with polymer, while BN micron and nano particle fillers show obvious agglomeration.The breakdown strength of polyimide films firstly increases and then decreases with the increase in filler contents. The breakdown strength of PI composite films with micro-nano fillers and nano fillers reaches the maximum,219.6 kV/mm and 230.6 kV/mm respectively, when the filler content is 1wt%. The dielectric constant and dielectric loss of the composites with micro-nano fillers are higher than that of pure PI films and they increase with the increase of the filler content. The I-t results show that the conduction current of the composite is higher than that of the pure PI film at low temperature and lower than that of the pure PI film at high temperature. The resistivity of the composites with micro-nano fillers is lower than that of the pure PI film and gradually decreases with the increase of the filler content. When the filler content is 20%, the resistivity of the composites decrease to 4.1×1016Ω·m and 4.9×1016Ω·m.Results of corona aging test showed that with the increase of the filler content, the corona resistant ability of the composites was gradually increased. When the content of the micron and nano fillers and nano fillers is 20%, the corona aging life of the composite film is 116.7 times and 110 times that of the pure PI film.The thermal conductivity increases with the increase of the filler content. When the filler content is 20%, the thermal conductivity is 3.8 and 3.5 times of that of pure PI films. The Cheng-Vachon model and the experimental data are found to have a high degree of fit by comparing with several heat conduction models.