Diagnosis of severity degree for oil/pressboard insulation surface discharge

To research the diagnosis method based ultra high frequency (UHF) signal and dissolved gases analysis (DGA) in oil of severity degree for oil/pressboard insulation surface discharge, a surface discharge simulation and test equipment and measurement system have been set up in laboratory, which were consisted of surface discharge model, test tank, UHF sensor, gas-phase chromatographic instrument and partial discharge detector. Surface discharge growth from inception to breakdown has been simulated, test voltage was raised step by step, ultra high frequency signal and dissolved gases in oil have been measured in the growth. The results show that severity degree of surface discharge can be divided tree stages: inception stage, growth stage and critical stage according to statistics spectrum of the ultra high frequency signal; ultra high frequency signal and dissolved gases in oil both can indicate the oil/pressboard surface discharge severity degree, however, dissolved gases analysis method was not as sensitive as ultra high frequency method; C₂H₂/total hydrocarbon generated by oil/pressboard surface discharge was more than 10%; Surface discharge was in critical stage when C₂H₂/total hydrocarbon value more than 50% and raised rapidly.