The change of microstructure of large stator winding insulation in multi-stress aging

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