This paper is aimed at improving the anti-aging properties of power transformers via using mineral oil/natural ester mixtures (mixed insulating oil). Accelerated thermal aging of two kinds of oil-paper insulation at 110°C were conducted in order to compare the aging characteristics of Kraft paper immersed in mixed insulating oil and mineral oil. The extent of paper degradation after aging was determined using the paper degree of polymerization (DP). The dissipation factor of aged oils and papers in two kinds of oil-paper insulation, and the structure of papers immersed in mixed insulating oil and mineral oil were also investigated. Paper immersed in mixed insulating oil degrades at a slower rate than in mineral oil. Compared with mineral oil/paper insulation, the transesterification of cellulose impregnated with mixed insulating oil can restrain the aging of paper. After aging 782 days, the dissipation factor of mixed insulating oil is nearly all smaller than mineral oil from 10-1Hz to 106Hz, and the dissipation factor of paper aged in mixed insulating oil is smaller than paper aged in mineral oil from 10-1Hz to 103Hz.
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