ABSTRACT
The insulation requirements of a power network rarely consist of a single material. The use of two or more insulating materials becomes necessary due to design considerations or due to practical difficulties of fabrication. These different materials may be in parallel with one another such as an air gap in parallel with solid insulation, or oil in parallel with pressboard. Similarly they may be in series with one another, such as laminates. Apart from these, filled or reinforced insulating materials may have microscopic volumes of another phase of different materials present in the bulk, e.g., in polyethylene or in a mixture of two granulated substances in epoxy resins or impregnated solids, etc. Therefore, all of these forms of insulation are composite in nature.
