Influence Of Alumina Size On The Insulation Property Of Polyimide Composite Film Under Condition Square Impulses

Inverter-fed motor is one of the nine critical technologies of electrical motor unit?EMU?in China,its stability and reliability have importance meanings for ensuring the safe operation of EMU.The inverter-fed motor usually adopts pulse width modulation?PWM?driving technology,thus the turn-to-turn insulation should bear high-frequency and sharp-pulse electrical stress,and combined with other environmental stress like high temperature,humidity and mechanical vibration,breakdown happens easily.Polyimide is widely used as the turn-to-turn insulation material in inverter-fed motor for its excellent electrical,mechanical and high temperature resistance properties.Now nano particle modification is an important method to improve the insulation property of polymer and is also a research focus.But reports about the effect of alumina size on the insulation property of PI composite films are few.Therefore,study on the effect of alumina size on the insulation property of PI composite films is meaningful.In this paper,PI/Al₂O₃ composite films doped with different size of alumina were prepared,and their structure characteristics were analyzed.At the same time,the electrical properties of composite films under bipolar continuous impulse voltage were tested,and the influence mechanism of alumina size on the corona resistance of composite films was also investigated,main work is shown as follows:?1?PI/Al₂O₃ composite films with controlled thickness and well light transmittance were prepared by in situ method,the dispersion of alumina particles was characterized by scanning electron microscope?SEM?.The thermal stabilization and mechanical properties of composite films were also checked by thermal gravity analysis?TGA?and material test machine respectively,and the interfacial region between alumina and polyimide matrix was proven to be amorphous structure.?2?A rod-plate electrode system was made according to standard of ASTM 2275 01 and experiments of the partial discharge inception voltage?PDIV?,breakdown stress and corona resistance of composite films were conducted,the influence of temperature and water absorption on electrical properties of composite films were investigated simultaneously,results show that high-energy discharge plays a critical role in eroding films based on analysis of discharge amplitude and number.?3?The influence of corona aging to the physical and chemical structure of PI/Al₂O₃ composite films was explored by SEM and Fourier transform infrared spectroscopy?FTIR?respectively,and the surface conductivity as aging time was also measured.In addition,the trap energy level as aging was analyzed according to the data of thermal stimulated depolarization current?TSDC?,and the physical,chemical and electrical block effect of alumina with different sizes were discussed.Above research results showed the law and mechanism of the influence of alumina size on polyimide films electrical properties,which has great scientific meaning on instructing the design of nano modification on polyimide film and improve its insulating properties.