A survey of thermal decomposition of solid insulations and its relevance to breakdown mechanisms in partial vacuum

Several practical issues must be considered when solid electrical insulation is used in a low pressure environment. While the low pressure environment or partial vacuum (in this context, a region which is almost devoid of any gaseous media) can exhibit good electrical insulating properties, the materials contained within the partial vacuum will effect the insulation integrity over time. Degradation of the insulating properties of the partial vacuum may be due to outgassing of enclosed materials and/or adverse media contained in the natural vacuum (space) environment. This paper addresses the thermal degradation of some polymer materials typically used as electrical insulation in partial vacuum. Pyrolysis data for various polymers, from the literature, is discussed. The results of a survey of published pyrolysis data, which identifies the primary gaseous decomposition species for such materials, is presented. The importance of identifying these by-products as they relate to microscopic volume breakdowns and partial discharges is highlighted.