Influence Mechanism of High-Frequency Harmonics on Breakdown Characteristics of Epoxy Impregnated Paper Insulation under Multi-Parameter Conditions

The epoxy-impregnated paper (EPIP) insulation core layer used in dry-type bushings on the valve side of converters is subjected to prolonged exposure to high-frequency harmonics during operation. This exposure can lead to degradation of insulation properties and even breakdown, significantly increasing the risk of equipment failure. To elucidate the influence of high-frequency harmonics on the breakdown strength of EPIP, this study systematically conducted breakdown characteristic tests under various harmonic types, frequencies, and amplitudes. Results indicate that breakdown strength decreases more significantly with higher harmonic frequencies and amplitudes. Compared to sinusoidal harmonics, square-wave harmonics cause a more pronounced reduction in breakdown strength. Subsequently, this paper employed spherical plate electrodes to investigate the partial discharge patterns of epoxy impregnated paper. Findings revealed that under superimposed waveforms, partial discharges exhibited multi-peak discharges primarily concentrated at voltage rise/fall edges. Both discharge phase and discharge frequency increased with the superimposed sine wave amplitude, indicating that superimposing higher-frequency harmonics exacerbates partial discharge degradation.