Research on electrical properties of natural ester-paper insulation after accelerated thermal aging

As an environmental insulating medium, natural ester fluid has many advantages such as renewable, biodegradable, fireproof and heat resistance. In order to master the natural ester's insulation properties of long-term high temperature operation, the electrical properties of the natural ester — paper insulation under long-term thermal aging condition, especially the partial discharge characteristic test research is very necessary. In this paper, the natural ester — paper and mineral oil — paper composite insulation test sample were processed after the same treatment. Long-term thermal aging experiments were performed under the 110 Ό and 130 Ό to compare the power frequency breakdown voltage, volume resistivity and dielectric loss factor of two kinds of oil — paper composite insulation thermal aging process, and the partial discharge inception voltage with its apparent discharge, partial discharge extinction voltage with its apparent discharge of two kinds of oil were compared. Experimental results showed that the power frequency breakdown voltage(DBVE) of natural ester and mineral insulating oil decreases with aging, and the power frequency breakdown voltage of natural ester is larger than that of mineral oil under the same condition. The volume resistivity of the natural ester and its oil-impregnated pressboards is less than that of mineral oil and oil-impregnated pressboards. The dielectric loss factor of the natural ester is one order of magnitude larger than that of the mineral oil. The aging temperature has great influence on the dielectric loss of the natural ester, and the dielectric loss factor of the insulating pressboards in the natural ester is larger than that in the mineral oil. The partial discharge inception and extinction voltage of natural ester are slightly less than that of mineral insulating oil. The pressboard insulation partial discharge inception voltage is greater than the natural ester impregnated paper impregnated with mineral oil, but the partial discharge of pressboard impregnated natural ester out of the insulating board voltage was significantly less than that of mineral oil impregnated. The partial discharge inception voltage of insulating pressboards impregnated with natural ester is higher than that of insulating pressboards impregnated with mineral oil under 110 Ό and 3000h aging condition, but the partial discharge extinction voltage of insulating pressboards impregnated with natural ester is obviously smaller than that of insulating pressboards impregnated with mineral oil.