The large-scale grid integration of renewable energy power systems subjects the transformers in renewable energy stations to prolonged high-frequency electrical stress

thereby accelerating the degradation of oil-paper insulation. However

the aging mechanism under the coupled electro-thermal effects of high-frequency conditions remains unclear. To address this

a high-frequency electro-thermal aging platform was established in this study

and the degradation behaviors of macroscopic dielectric properties and microscopic chemical structure of oil-paper insulation under accelerated aging with 100 kHz high-frequency voltage and 50 Hz power-frequency voltage were compared. The results show that

after high-frequency aging

the dielectric loss across the entire frequency range in frequency domain dielectric spectroscopy increases

with a relaxation peak appearing near 104 Hz; the volume resistivity decreases by three orders of magnitude; the scale parameter of breakdown voltage decreases by 53.5% and the shape parameter also decreases; the space charge density near both positive and negative electrodes increases substantially

with a multi-peak distribution in the curve. Moreover

scanning electron microscopy reveals extensive fiber breakage and micron-scale pores. Molecular dynamics simulations and infrared spectroscopy jointly confirm that high frequency accelerates the breakage of C—C and C—O bonds in the cellulose main chain and the generation of polar products. This study reveals that the extremely high voltage change rate under high-frequency conditions intensifies polarization loss and space charge injection

forming a positive feedback loop with thermal stress

which leads to defect accumulation and structural loosening

thereby synergistically accelerating oil-paper insulation degradation from both macro and micro perspectives. The research results provide reference for the condition assessment and life prediction of oil-paper insulation in transformers at renewable energy stations under high-frequency operating conditions.