Molecular dynamics and finite element analysis of partial discharge mechanisms in polyimide under high-frequency electric stress

High-frequency power transformers (HFPTs) are critical components of solid-state transformers (SSTs), enabling voltage conversion and electrical isolation in advanced power distribution systems. However, the insulation systems of HFPTs face significant challenges due to high-frequency electrical stress and partial discharges (PD). This study investigates the failure mechanisms of polyimide (PI) insulation under high-frequency electrothermal stress through a combination of experimental analysis and numerical simulations. A high-frequency partial discharge test platform was utilized to evaluate PD behavior in PI films under sinusoidal voltages at various frequencies. Experimental results revealed that increasing frequency reduced the insulation breakdown time and discharge counts while intensifying discharge amplitude and accelerating material degradation. Fourier Transform Infrared Spectroscopy (FTIR) confirmed the successful synthesis of PI films and demonstrated a reduction in key chemical bonds following degradation. ReaxFF molecular dynamics simulations provided insights into the degradation mechanisms, identifying CO as the most abundant degradation product, followed by HB, HBO, CN, and acetylene (CBHB). Finite element simulations, based on a one-dimensional non-equilibrium plasma model, elucidated the spatiotemporal evolution of electric fields, electron density, electron temperature, space charge, and PD currents. The results demonstrated a direct correlation between higher frequencies and intensified PD activity, including stronger electric fields and increased electron energy. This comprehensive study bridges experimental observations with simulation results, advancing the understanding of insulation failure mechanisms in HFPTs under high-frequency stress.