Impulse and power frequency electrical breakdown of silicone oil

Both dielectrically and thermally, silicone oils have outstanding performance capabilities for use in transformers [1,2]. Their dielectric strength has already been shown to vary with volume [1], water [1,3-5] and gas content [1]. Impulse tests indicate a polarity effect [1,6] and insensitivity to viscosity [1,6], contrary to AC tests [1]. The exact breakdown mechanisms are still unclear. This paper presents detailed results of a study on the influence of moisture and gap length, and on the formation of a solid bridge between the electrodes in AC experiments. Comments are made on the validity or significance of the ASTM D 3300 test.