A new 275 class non-silicone micaceous insulation system

The temperature index of micaceous insulation is influenced by that of the bonding resin used therein, the thermal degradation processes being synonimous. Systems using epoxy novolac and cycloaliphatic offer rigid insulation and pose discharge problems.; Their temperature index has been improved by adopting better backing materials. However, epoxies become brittle during ageing at 210/230°C because of shrinkage in the resin matrix as a result of chain scission and crosslinking in oxidative degradation process, which involves evaporation of low molecular weight materials. Systems based on silicones are flexible but are prone to moisture influence in tropical conditions. The polybenzimidazole resin being true thermoplastic, because of the linear chain, eliminates the above deficiencies. Its usage has resulted in the development of new micaceous insulation. They are made rigid to flexible by varying catalyst proportion. They offer improved fatigue performance and higher peel strength at elevated temperatures due to hydrogen bonding. Resistance to´moisture and improved dissipation factor-temperature characteristics are the prime features. The isothermal and dynamic weight loss studies indicate higher activation energy of 134kJ/mole even at different stages of degradation and confirm excellent thermal stability. The system has been ascribed 275 class. Its usage would improve the specific capacity of machines.