The generation of gases in the dielectric breakdown of oil

It is shown that in a thoroughly degassed oil each impulse discharge generates a definite amount of gas. Under the conditions of the measurements this was about 3·6 × 10 −9 moles per discharge. A large fraction of the gas is hydrogen. Over a small range of temperatures the rate rises exponentially with the absolute temperature, the energy in the Boltzmann factor being about 8·1 kcal mol −1 , and roughly the same as that for the conductivity of the oil. As an explanation of the association of a definite yield of gas with each impulse breakdown, it is proposed that the breakdown avalanche can be generalized to include gas molecules as well as ions and electrons (stage I). After the avalanche has developed sufficiently a gas-phase channel forms and is propagated between electrodes by a space charge at its tip (stage II). When the interelectrode gap is bridged, conduction is entirely in the gas phase (stage III). Most of the breakdown current flows during stage III; most of the gas is produced during stage II. This three-stage model seems to be consistent with breakdown behaviour. Self-terminating alternating current breakdowns generate not more than several times as much gas as single impulse discharges.