Research On Insulation Properties Of Multilayer Polyimide Composite Dielectric Based On Gradient Structure Design

Polyimide（PI）with its good electrical insulation and excellent thermal stability is often used in the insulation field of high voltage electrical equipment such as winding insulation of UHV reactors and insulation materials of variable frequency motors and plays an important role in the safe and stable operation of electrical equipment and even the entire power system.However,with the rapid development of Chinese UHV transmission projects and the construction needs of new power systems,electrical equipment and power electronic devices are developing towards high power miniaturization and thin shape traditional PI film has been difficult to meet the special needs of modern electrical equipment so it is urgent to develop PI composite dielectric with excellent insulation performance.In order to obtain excellent insulation properties of PI composite dielectric,this paper mainly focuses on two aspects of doping modification and structural regulation of fillers.High insulation boron nitride nanosheet（BNNSs）was selected as the inorganic filling phase and the optimal doping ratio of the composite dielectric was explored by adjusting the content of the filling phase which was recorded as PI-BNNSs.The results show that the dielectric constant of the composite dielectric with3%volume fraction reaches 4.1,the loss angle tangent value is 0.006 and the breakdown strength is 406.92 k V/mm at 1 k Hz,which is 14.6%higher than that of the original PI dielectric.On the basis of the above experiments the sandwich structure composite dielectric was constructed based on this content which hindered the development of breakdown path through the interlayer barrier effect and achieved a slight increase in breakdown strength.In order to improve the insulation performance of the composite dielectric,the multi-layer positive and negative gradient structure composite dielectric was designed based on the content of the optimal single-layer dielectric.The experimental results show that the positive and negative gradient control can significantly improve the insulation performance of PI composite dielectric and the highest breakdown strength is 430.62 k V/mm.Based on this,BNNSs is coated with Si O₂ and PI-BNNSs@Si O₂ positive and negative gradient structure composite dielectric is prepared which reduces the degree of electric field distortion.The homogenizing electric field increases the breakdown strength of the composite dielectric to 442.43 k V/mm while the current density is kept low.In this experiment,by means of the dual control of insulation filling phase and structure PI dielectric has excellent insulation properties which provides a new idea for the development of new insulating PI dielectric materials in the future.