In this paper, the effect of field strength on the corona-resistant lifespan of a composite film and the effect of doping on the dielectric properties of the composite film were studied. The method for predicting corona-resistant lifespan under working electric field strength is discussed. Scanning electron microscopy (SEM) was used to characterize the morphology and the structure of the composite film near the breakdown point after corona formation. Fourier transform infrared spectroscopy (FT-IR) was used to characterize the imidiated film, and a conductivity current test was used to calculate the electrical aging threshold of the film. The results showed that the introduction of nano-SiO2 particles could greatly improve the corona-resistant lifespan of the material. At 155 °C, when the applied external electric field strength was extrapolated to 20 kV/mm, the corona-resistant lifespan of the PI/nano-SiO2 three-layer composite film with 10 wt% nano-particle doping was 7472.61 h.
Keywords: corona resistance; dielectric properties; electrical aging threshold; nano-SiO2 particles; polyimide.