Insulation Failure Mechanism of Polyimide Under High-Frequency Electrical Stress: A Synergistic Analysis of Aging Experiments and Molecular Dynamics Simulations

Abstract

Polyimide (PI), an insulating material extensively employed in high-frequency power transformers, encounters accelerated insulation deterioration under high-frequency electrical stress. This study elucidates the insulation failure process of PI under high-frequency electrical stress by employing a combined approach of aging experiments and reactive force field molecular dynamics (ReaxFF MDs) simulation, with scanning electron microscopy (SEM) analysis and Fourier transform infrared spectroscopy (FTIR) used. The investigation reveals that the primary causes of PI insulation failure are partial discharge (PD) erosion and electrothermal aging. PD progressively erodes the PI surface, with the erosion intensity initially intensifying before diminishing over the material’s lifespan. The synergistic impact of electrothermal stress instigates the fracture of various chemical bonds within PI molecules. These include the C-H and C-N bonds in the imide ring and C-C bonds connecting the imide structure to the benzene ring, leading to the generation of gaseous byproducts like CO and H2 O. Concurrently, the rupture of the C-O–C bond between the benzene ring and the disintegration of the imine ring result in the main chain’s fragmentation. This process leads to the continual degradation and recombination of molecular chains with varying polymerization degrees and a small hydrocarbon product C2 H2 is produced. The influence of electrical stress on PI’s molecular configuration manifests in the alteration of the electric dipole moment and the elongation of polar bonds, notably the C-N bond in the imine ring, which rapidly fractures under electric heating stress.