Comparative Study on Dielectric Performance of Thermal Aged Silicone Oil and Mineral Oil

The dielectric spectrums properties of silicone oil and mineral oil with different aging status were experimentally studied for comparison in this paper. Frequency domain spectroscopy as a non-destructive diagnosis method to evaluate the insulation status of oil-immersed paper insulation. Study the dielectric spectroscopy difference between thermal aged silicone oil and mineral oil can provide principles for evaluating the insulation status of silicone oil. Samples are conditioned to the same initial conditions through the heating at a temperature of 100 °C for 24 hours at first. Then silicone oil samples and mineral oil samples were thermal aged at 140°C in hermetical bottles with paper insulation sheets inside. Dielectric measurement was done after aging time of 0 hour, 500 hours and 1000 hours. The results show that the relative permittivity of the silicone oil is a little lager than that of mineral oil, which can improve the electric distribution inside the power apparatus with oil-impregnated paper insulation system. With the increasing of aging duration, the relative permittivity of silicone oil almost remains constant, while the mineral oil's relative permittivity shows low frequency dispersion phenomenon and becomes higher. The thermal stability of silicone oil is obviously better than that of mineral oil.