Dielectric breakdown strength of silicone gel under various environmental conditions

Silicone gel belongs to the group of RTV-2 silicone rubbers, which are room-temperature-vulcanizable materials consisting of two components. The material combines the advantages of the electrical and chemical properties of silicones with the unique mechanical properties of gels. The attempt to use silicone gel as insulation material in long-term stable and reliable medium voltage applications, e.g. as insulation material for power cable joints, requires a comprehensive and consolidated knowledge of the dielectric breakdown strength. A test program has been performed testing model insulations consisting of silicone gel under various stress conditions. The influence of the processing of the material, the influence of humidity and temperature on the dielectric breakdown strength of silicone gel is investigated. Also, the findings on the interdependency between the dielectric breakdown strength and the electrically stressed material volume (scaling effect) are reported. A further section of this paper describes the ageing performance of silicone gel under homogeneous and strong inhomogeneous electrical field stress. Finally, the dielectric breakdown strengths of a silicone gel/silicone gel interface model on the one hand and a silicone gel/polypropylene interface model on the other hand are analysed.