Dielectric performance of silicone oil-paper composite insulation system under thermal aging

Silicone oil is a promising alternative insulating liquid especially for the sites where fireproofing and environment protection must be considered. In this paper, the chemical and dielectric performance of silicone oil-paper composite insulation system under thermal aging is discussed. Two kinds of oil-paper systems are tested: mineral oil and silicone oil (Shin-Etsu Chemical KF-96-20 Lower viscosity fluid). In this study, mineral oil is used as the comparison sample. The accelerated aging process is at 140 ^oC in nitrogen. Aging samples with the aging duration of 250 hours, 500 hours and 750 hours and 1000 hours are tested. Experimental results indicate that the silicone oil has much lower acidity content and dielectric loss compared to the mineral oil. New mineral has a little higher AC breakdown voltage compared to silicone oil. For both silicone oil and mineral oil, with the increase of impurities such as water and solid particles during the aging process, the AC breakdown voltage decreases slightly. Acidic materials generated during aging process have little influence on the AC breakdown voltage. Different from the mineral oil whose impulse breakdown voltage decreases significantly with the increase of aging time, however, the silicone oil´s negative impulse breakdown voltage of different aging time almost keeps the same.