Time-lags of triggered breakdown in transformer oil subjected to power frequency stress

Previous work
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by the authors has shown that the breakdown time-lags for oil-filled trigatrons subjected to power frequency voltages can range from a small fraction of a cycle to several cycles of 60 Hz voltage. In general it was shown that long breakdown delays of one quarter to several cycles of power frequency voltage occurred with large amounts of available trigger energy (∼1 J) and low stresses across the main gap (−50 kV/cm rms), while short delays (<1 ms) resulted from the use of higher main-gap stresses and lower available trigger energies (tens of mJ). The present study has sought to examine in greater detail the time-to-breakdown characteristics in the submillisecond delay region and to discuss various breakdown mechanisms in terms of the dependence of the breakdown probability on time.