Electrical Aging Effect on Breakdown and Charge Trap Characteristics of Polyimide Films With Different Thickness in LN 2

The Polyimide (PI) film, as an excellent insulating material, is broadly utilized in superconductivity power equipment, especially under low temperature. There is an enormous influence on the breakdown performance of polymers because of the presence of surface and space charge. In order to investigate the electrical aging impact on breakdown and trap characteristics of PI films with 0.1 mm and 0.125 mm thickness, the samples suffer from diverse degrees of electrical aging in liquid nitrogen (LN2). The insulation strength test has been carried out on the PI film samples under different electrical aging stages in LN2. The isothermal surface potential decay (ISPD) method is performed on the PI films to explore the behaviors of trapped charges, and the trap characteristics of the PI films are obtained. Those results indicate that the breakdown strength of the thinner PI film (0.1 mm) in LN2 is higher than that of the thicker one (0.125 mm), and the breakdown field strength reduces with the electrical aging time increasing. The ISPD measurement results indicate that the average decay rate of surface potential in the 0.125 mm PI is faster than the other thickness during the whole decay process.