Thermal degradation characteristics of insulating paper and oils

In a search for mineral oil substitutes, the authors focus on silicone and ester oils. These insulating oils are fire-resistant and environmentally friendly. In previous studies, the authors investigated streaming electrification and dielectric breakdown phenomena in these fresh oils and found that their performance was similar to or better than that of mineral oil. In the present study, the authors focus on the thermal degradation of insulating oils. Thermal degradation tests in the presence of a solid insulator and copper for carried out 1000 hours. Changes in color and dielectric breakdown characteristics were investigated during thermal degradation of the insulating oils. The authors also investigated the mechanical strength of the solid insulator. The characteristics of aged oils were compared with those of fresh oil.