Influence of Replacing Oil with Different Natural Esters on the Thermal Ageing Behavior of Mineral Oil-Paper Insulation

摘要

Natural ester has high flash point, ignition point and good electrical strength, which could improve the overload capacity of transformer and delay the ageing of insulation pressboard. In this paper, the accelerated thermal aging test of oil-paper samples which composed of 25# mineral oil, FR3 oil, PFAE oil, cellulose insulation pressboard and thermally upgraded paper (TUP) are conducted at 120°C. In the middle ageing period, aged mineral oil in 6/33 samples were replaced with new PFAE and FR3, while aged PFAE in 3/33 samples were replaced with FR3, and then the accelerated thermal ageing test continued. The research on changing laws of DP of thermally upgraded paper (TUP) impregnated in PFAE oil, FR3 oil and mineral oil has been performed. The measurement of the insulation paper breakdown direct current (DC) and alternating current (AC) breakdown voltage is carried out. Comparison on kinematic viscosity and AC breakdown voltage of insulating oils are performed. Result shows that FR3 would increase over 1 time the lifespan of TUP in mineral oil, while PFAE shows a similar performance to mineral oil and could not obviously decrease the ageing rate of insulation paper. The kinematic viscosity of insulating oils did not change much after oil replacement. The AC breakdown voltage of natural esters are higher than that of mineral oil and could keep good insulation properties. This research would be helpful for the status evaluation of natural ester replacement transformer in the future.