Creepage discharge performance for high moisture pressboard

To research the creepage performance of high moisture pressboard, possible high moisture of pressboard in service power transformer has been analyzed, a creepage discharge simulation and test equipment and measurement system have been set up in laboratory, which were consisted of creepage discharge model, test tank, UHF sensor, gas-phase chromatographic instrument and partial discharge detector. Creepage discharge growth from inception to stop has been simulated by raised voltage step by step up to 50kV, ultra high frequency signal, apparent discharge magnitude and dissolved gases in oil have been measured in the growth. The results show that moisture of pressboard in part may reach 7% in service power transformer; creepage discharge inception voltage has a remarkable decrease under this high moisture; creepage discharge appeared at small oil gap firstly and bright spark can been observed; creepage discharge was intermittent and even stop at some time; lots of bubbles were generated in the creepage growth; C₂H₂ and H₂ generated by creepage discharge was very high.