Breakdown characteristics and mechanism of epoxy resin impregnated paper under high frequency harmonics with low temperature

High-frequency harmonics (>10 kHz) generated by high-voltage semiconductor devices, combined with extremely cold environments, pose a serious threat to the insulation reliability of power equipment for clean energy utilization. This paper investigates the breakdown characteristics of epoxy resin-impregnated paper (EPIP) used in dry type busing under low-temperature and high-frequency harmonic conditions, with focus on the influence of dielectric loss and the orientation of crepe paper within the EPIP on breakdown strength. Additionally, the breakdown mechanism is investigated in relation to space charge behaviour. The results indicate that breakdown strength decreases significantly under high-frequency harmonic voltages. For example, the breakdown strengths of Sample A and Sample B are 122.48 and 106.77 kV mm⁻¹ at power frequency, 64.32 and 57.76 kV mm⁻¹ at 10 kHz, and 51.98 and 46.85 kV mm⁻¹ at 25 kHz at ambient temperature of 253 K, respectively. The relationship between breakdown strength and voltage frequency follows the inverse power law. It is also found that the proportion of high-frequency voltage components nonlinearly affects the breakdown strength of EPIP under power frequency superimposed with high-frequency harmonics voltage. Moreover, breakdown strength decreases exponentially with temperature in the low-temperature range. Compared with the thermal decomposition temperature of EPIP, the temperature rise caused by dielectric loss under high-frequency voltage is insufficient to directly induce thermal breakdown. Therefore, this paper proposes that the breakdown of EPIP under high-frequency voltage is primarily attributed to space charge injection and recombination, which are thermally assisted by dielectric loss. It is demonstrated that charge recombination is significantly intensified under high-frequency conditions. Furthermore, the shallower trap depth in Sample B facilitates deeper charge injection, resulting in lower breakdown strength. These findings provide both theoretical and experimental support for improving the insulation performance of power equipment under high-voltage and high-frequency operating conditions.