Comparison of the insulation characteristics of environmentally-friendly oils

We have investigated the performance of silicone oil as an insulation medium with the aim of developing environmentally-friendly, flame-retardant electric power equipment. In this paper, the insulation characteristics of silicone oil and ester oil, which is the alternative insulating oil candidate, have been investigated and compared. The insulation characteristics examined in this paper are the streaming electrification characteristics including electrification phenomena generated when an insulating oil streams, dielectric breakdown characteristics with increasing temperature and the surface breakdown characteristic when the insulator is placed between electrodes. The range of temperature investigated was 30 to 130 °C. Both kraft and aramid paper were used for the insulator. In the comparison between silicone and ester oil, it was found that the insulation performance of the ester oil was better than that of the silicone oil. We have considered possible mechanisms for these results.