Study On The Electrical Properties Of Epoxy Mica Insulation For HV Motor Based On Nano-Dielectric

The dissertation is put forward for solving the problem that the electric field strengthen of epoxy/mica decreases and its life shortens because of the electrical stress and thermal stress during normal operation.The insulation of form-wound stator coil in current use is the epoxy mica insulation system which improves the properties of stator insulation.With the HV motor developing to the compact and powerful motor,the requirement for the properties of stator insulation grows.Not only should the reliability of the electrical and thermal properties of stator insulation be ensured,but both the thickness and the production costs of insulation should be diminished as well.Thus,it is significant to research the new type epoxy mica insulation for high efficient and powerful HV motor.Moreover,with the development of nano-technology,nano-composites based on the polymer matrix as the third insulation materials exhibit excellent insulating properties.Nanodielectric has being a major method on improving the properties of electrical insulation and provides a new idea for making the electrical and thermal properties of stator winding of HV motor better.However,the research of epoxy mica based on the nano-technology is still on the initial stage and has some problems,such as the indeterminacy of modified mechanism,the study on the properties after modified,and lack of application research for the original coil.Therefore,the study on the electrical properties of epoxy mica insulation for HV motor based on nano-dielectric,especially the understand of mechanism on the properties of nano epoxy mica,is meaningful forenhancing the reliability of HV motor insulation,and applying the nano-technology to HV motor.The dissertation with the stator coil of HV motor as the object of research focuses on the study of the electrical properties of nano silica epoxy resin and epoxy mica with different content,and the application of nano silica to the insulation of original stator coil.The research content is as follows:As the unique part which can be modified in the epoxy mica insulation system of HV motor,epoxy resin has an effect on the properties of epoxy resin.Therefore,the epoxy resin nanodielectric samples with different content were prepared.The dispersion of nano particles was measured.The physical and chemical properties of samples were analyzed the differential scanning calorimetry,dynamic thermo-mechanical analysis and Fourier transform infrared and so on.Experimental results show that with the increase of nano particles content,the distance between nano particles decreases,the specific surface area increases,and the glass temperature and active energy increases first and then decreases,because the interface area overlaps when the nano silica content is 2.5 wt%,and the movement of molecular chain is restrained by the interface area.The content of nano particles and temperature can influence the macroscopic electrical properties of epoxy resin matrix.The relative permittivity,dielectric loss factor,conductivity,modulus,space charge,electrical trees and breakdown electric field were measured and analyzed.Experimental results show that the properties of epoxy resin nanodielectric,such as relative permittivity,dielectric loss factor,the accumulation of space charge,is lower than that of pure epoxy resin.At high temperature,epoxy resin nanodielectric is of higher initial voltage of electrical trees,and enhances the breakdown strengthen.The properties of epoxy mica tape decide the quality of HV motor insulation.The epoxy adhesive nanodielectric and epoxy micananodielectric were prepared.The dielectric and breakdown properties of epoxy adhesive nanodielectric was measured.The breakdown properties of epoxy mica nanodielectric was also measured.Experimental results show that the filling nano silica with 0.5 wt% can decrease the relative permittivity and dielectric loss of epoxy adhesive nanodielectric,and enhances the breakdown electric field at the ambient and 155 °C.For the stator insulation system of HV motor,the properties and quality of original stator coil have to be measured before use.In order to verify the properties of epoxy mica nanodielectric,the 6 kV original stator coils with the 0.5 wt% nano silica was prepared.The dielectric loss,capacitance,insulation resistance,polarization index and partial discharge of coils were measured.The tip-up of dielectric loss,capacitance,and conductivity of nano silica coils is lower than that of pure epoxy mica coils.At the same voltage,the peak of partial discharge amplitude of nano silica coils is slightly higher than that of pure epoxy mica coils.In summary,when the filling content of nano silica particles is 0.5wt%,epoxy resin,adhesive and mica tape nanodielectrics will exhibit better electrical properties.The properties of original stator coils are also enhanced,but the effect of temperature on the results cannot be ignored.The results provide a support in theory and experiment for applying nanodielectric to the insulation of HV motor,and a method for improving the properties of stator coils.