Experimental study of oil-paper insulation under combined thermal stress and corona discharge

This paper investigates the aging properties of oil-paper insulation under thermocorona discharge. The oil-paper insulation samples were heated and kept at 140°C, and a corona discharge was generated with a needle-plate at a frequency of 15 times/day, with each discharge lasting 5 minutes. The aging properties of oil-paper insulation were investigated by measuring the degree of polymerization (DP) of insulation paper samples along with the furfural content and acid value of the transformer oil samples. The results show that corona discharge at 140°C in oil rapidly decreased the insulation paper DP and increased the furfural content and acid value of the oil compared with thermal aging and corona discharge aging at 20°C. The DP of the insulation paper was reduced to 392.12, the furfural content in oil rose to 33.75 mg/L, and the acid value grew to 4.41 mgKOH/g after 15 days under the combined thermal stress and corona discharge. Both electric and thermal stress accelerated the aging of oil-paper insulation. This research has practical significance for understanding the process of insulation failure caused by the accelerated aging of oil-paper insulation.