Study of the time to breakdown in transformer oil under impulse conditions

The time to breakdown in dielectric fluids has been studied extensively, and it has been shown that the time elapsed between the start of the pulse and breakdown decreases with increasing voltage. Basically, two regimes can be distinguished, depending on whether breakdown occurs on the rise of the pulse or on its tail. The first regime occurs at much higher voltages than the latter one and it usually occurs at small electrode separations. In the first regime the time to breakdown decreases more or less regularly with increasing crest voltages while in the second one the time to breakdown shows interesting statistical fluctuations. The significance of these fluctuations is discussed. An attempt is made to show that these temporal fluctuations at more or less constant crest voltage are a reflection of the electron emission characteristics of the cathode.