Silicone fluids, compounds, rubbers and resins are described in terms of their chemical structure and physical properties, alone or in combination with inorganic insulating materials.There follows a brief review of thermal endurance evaluation and the position of siliconeinsulation in British and other Standards. Applications are then discussed, with reference to conductors, cables, rotating machines, transformers and other electrical apparatus. Economic aspects are considered, and it is shown that, though silicones are more expensive than organic materials used for lower temperature insulation, frequently there are compensating improvements in performance, reliability or installation cost.The paper also notes desirable improvements in properties and processing requirements. It is considered that cost will probably restrict the use of silicone insulation at lower temperatures, but that the trend towards replacement of Class B insulation with silicones will continue. Novel and economical manufacturing techniques with silicone rubbers may offer particular advantages.
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