Study on microstructure and electrical properties of oil‐impregnated paper insulation after exposure to partial discharge

SUMMARY This paper studied microstructure and its relationship with electrical properties for oil‐impregnated paper insulation during partial discharge damage process. Material analysis apparatuses such as for atomic force microscopy and X‐ray diffraction instrument, combined with electrical analysis apparatuses such as high‐resistance meter, dielectric spectra meter, and cylinder–cylinder electrodes, were employed to investigate molecule chain structure, aggregation state structure, permittivity, dielectric loss factor, volume conductivity, and electrical strength of oil‐impregnated paper insulation during the damage process. Results reveal that crystal regions of insulation paper suffer more severe damage during partial discharge damage process compared with the amorphous regions. Crystallinity exhibits an increasing trend and crystal grain orientation is enhanced, whereas crystal grain size, crystal type, and two‐phase‐coexistent structure are retained. Increased crystallinity and enhanced crystal grain orientation result in permittivity, volume conductivity, and dielectric loss factor decreasing, but electrical strength increasing. Changes in the activity of molecules, ions, and electrons are the results of variations of crystallinity and orientation; these are the main reasons for the change in electrical properties.