Ionization Currents and the Breakdown of Insulation

Certain theories of the breakdown of gases are reviewed. Their limitations or correctness in the light of recent data on the breakdown of large gaps with surge voltages are considered. The work of various investigators on the time lag of breakdown also is discussed briefly. It is shown that comparisons are made difficult and that large discrepancies, particularly at the shorter time lags, may result from variations in the definitions of time lag and breakdown time. The existence of ionization or streamer currents of high magnitude previous to the final breakdown is established and a number of volt¿time and ampere¿time oscillograms of flashovers on various types of insulation is shown and discussed. The effect of these streamer currents in attenuating a traveling chopped wave is shown.