Impact of thermal and electrical aging on breakdown strength of oil-impregnated paper

In this paper the impact of thermal and electrical aging on AC and impulse breakdown strength of oil-impregnated paper was investigated. Sheets of paper were thermally aged at 140 °C for 30 days. A comparison between AC and impulse breakdown strength of unaged paper layers, 10, 20 and 30 days thermally aged paper was performed. In order to investigate the effect of electrical aging, first the paper layers were exposed to partial discharges for 6 hours at accelerated electric stress. The partial discharge was created inside paper samples by introducing a disc shaped cavity on the center of the paper samples. The effect of partial discharges was then investigated on the impulse breakdown strength of oil-impregnated paper. The study shows that thermal aging has very small effect on AC breakdown strength. However, impulse breakdown strength of oil-impregnated paper may reduce up to 40% due to exposure to PD.