Moisture migration in oil-impregnated film insulation under thermal ageing

Moisture produced in thermal degradation of insulating materials in transformer causes damage to the insulation system. To study the moisture diffusion and balance process in transformer insulation system and evaluate alternative insulation materials, three types of samples, including Kraft insulation paper, PC and PET film, were impregnated in oil and thermally aged under 90, 110 and 130°C respectively. By analysing the moisture variation in oil and solid insulation, it was found that the moisture diffusion, balance and hydrolytic degradation process of oil-paper insulation are different from those of other two types of samples. During the thermal ageing process, the moisture produced by polymer is much more than that by oil, and most of which is absorbed by sample surface. The ageing temperature has considerable influence on the moisture migration in polymers.

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