Thickness effect on breakdown and lifespan of multilayer polyimide films under repetitive pulsed voltage

Multilayer polymer films play a significant role in high-voltage equipment. For better multilayer film insulation design, this study focused on the thickness effect on both the breakdown field and lifespan of single-layer and multilayer polyimide films subjected to repetitive pulsed voltage. The findings reveal that in addition to the total sample thickness, the number of layers also affects the breakdown field and lifespan. A comparative analysis of the breakdown field–thickness relationship between the single-layer and multilayer polyimide films was conducted. The results demonstrate that the breakdown field of polyimide films follows a negative power-law relationship with thickness, characterized by an exponent of ∼0.25–0.4. The exponent for single-layer films is found to be 0.04–0.14 greater than that for multilayer films. An expression delineating the breakdown field of multilayer films as a function of the film thickness and number of layers was derived. Furthermore, the thickness effect on the lifespan of both single-layer and multilayer polyimide films was analyzed. The results indicate that the lifespan similarly follows a negative power-law relationship with film thickness, with an exponent ranging from 2.5 to 4.5. Expressions were derived for the lifespan of single-layer films based on the applied electric field strength and thickness, as well as for the lifespan of multilayer films in relation to the applied electric field strength, film thickness, and number of layers.