Study On Electrical Properties Of Polyimide Nanocomposite Films Under Different Temperature And Humidity

The operation environment of offshore wind turbine is very bad.The polyimide film used for winding electromagnetic wire insulation has been in extreme climate such as high temperature and humidity for a long time.The problems of charge accumulation and partial discharge are prominent,which make the aging and damage process of insulation more complex.In this paper,polyimide insulation was used as the research object,and inorganic nano-Al₂O₃ and nano-Si O₂ filling methods were used to prepare polyimide nanocomposite films.The dielectric constant and resistivity of the films were measured.The surface potential attenuation characteristics,trap distribution characteristics and breakdown characteristics of the films under different temperature and humidity conditions were studied.The micro cracking process of polyimide was carried out through Reax FF molecular dynamics simulation is expected to provide theoretical basis and experimental basis for improving the insulation reliability of offshore fan winding.The main research work and achievements are as follows:(1)Polyimide nanocomposite films with different kinds and mass fractions were prepared.It was found that when the mass fraction of nanoparticles increased,the dielectric constant of nanocomposite films first decreased and then increased,and the volume resistivity and surface resistivity decreased accordingly.The addition of nanoparticles made the initial surface potential first increased and then decreased,the temperature increased,and the initial surface potential almost unchanged The surface potential depends on the material itself,and the increase of temperature only accelerates the charge dissipation,and the calculation results of trap distribution explain the change rule of surface potential;when the mass fraction of nanoparticles increases,the breakdown field strength increases first and then decreases,and the corona resistance time increases gradually,both of which decrease with the increase of temperature.(2)Through the measurement of surface potential and the calculation of trap distribution of polyimide nanocomposite film under different humidity environment,it is found that when the relative air humidity increases,the initial surface potential decreases,the depth and density of deep trap decreases,the density of shallow trap decreases,and the depth increases slightly,which is considered to be caused by"hydrolysis"and"bridging";it is measured that the polyimide film is not under the same humidity,and with the increase of relative air humidity,water molecules will hydrolyze with polyimide macromolecular chains,and further degrade,forming active ion groups,and forming conductive channels,which will reduce the breakdown field strength and corona resistance time.(3)It was found that the C-N bond and C-O-C bond on the main chain of polyimide decreased the polymerization degree of Polyimide by reaction molecular dynamics simulation.According to the fracture probability,the C-N bond was determined to be the main fracture bond of polyimide.Starting from the product,the relationship between the molecular number and time of the product after polyimide cracking was obtained.CO2 and CN were selected as the main products The C-N bond breaking is the main reason for the polyimide molecules to produce CO₂ and CN.