Pyrolysis of Stator Coil Insulation in Air and Hydrogen

The study of changing properties of generator stator coil insulation on long-time exposure at elevated temperature is an accepted part of insulation development. This aging, however, has usually been done in air, while the windings of modem turbine generators operate in hydrogen atmosphere. Samples of synthetic resin bonded insulation were pyrolyzed in air and hydrogen at 200°C and one atmosphere. The gaseous, liquid, and residual products were analyzed by chromatography and infrared spectroscopy. Heated in air, the gases contained C3, C4, and C5 straight chain hydrocarbons, but the products in hydrogen contained, in addition, cyclohexane. The liquid and residual products indicate the sample pyrolyzed in air degrades by depolymerization and oxidation, while the sample in hydrogen depolymerizes, followed by some degree of hydrogenation.