Influence of proportion of vegetable insulating oil and mineral insulating oil on thermal aging of oil-paper insulation

Vegetable insulating oil shows good performance in electric, high anti-aging ability and environmental protection. Thus it is considered as a promising substitute for mineral insulating oil. In order to the wide spread application of vegetable oil in large power transformers, this paper presents accelerated aging experiments of oil-paper insulation involving insulating paper and the mixed oil. The mixed oil combined with different proportion of vegetable and mineral insulating oil. The experiments were performed at 130 °C to analyze the generation principle of aging products for different types of oil-paper insulation samples. Experimental results showed that the moisture content of insulating oil and paper increased with increasing of aging time and the different proportion of vegetable and mineral insulating oil during the aging process. Besides, acid value of insulation oil increased with aging time, and acid value was related to the different proportion of vegetable and mineral insulating oil. The degree of polymerization (DP) of the insulation paper decreased with the aging time. However, the DP declining rate decreased with increasing of different proportion of vegetable and mineral insulating oil.