The change of microstructure of epoxy mica insulation in multi-stress aging

The epoxy mica insulation system has been in service as the main insulation of large generator since 1960s. The real stator bars of an 18 kV/300 MW generator are used for accelerated multi-stress aging experiments to investigate their changes of microstructure of epoxy mica insulation. The stator insulation of a large generator is a composition system composed of epoxy resin, mica and glassfiber. A study on interface of the composite is significant for overall comprehension of its properties. A scanning electronic microscope is used to observe the pattern of interface during the aging process, and it is brought up that change in interface is the main reason of aging. The variation of components in insulation is also analyzed by the technique of infrared spectrum and X-ray energy spectrum. The results of experiment show that the epoxy resin causes hydrolytic reaction, the mica undergoes structural change.