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Fig.1 shows a tipical current trace for Kapton with a negative point. The symbols ON, OFF and Bin this figure correspond to the onset of voltage applicatin, the start of voltage reduction and the time of the actual breakdown current onset, respectively. The first large current pulse which occurs just after voltage onset is the combination of injection current and displacement current. The prebreakdown...
This paper reports some of the results obtained from extensive tests on the variation of the breakdown voltage with gap length for polydimethylsiloxane (viscosity S0 cST) under highly nonuniform fields. Tests were carried out on degassed silicone oil, oxygen-saturated oil & on degassed & oxygen-saturated oil containing varying concentrations (0.05 to 1 molar) of methylnaphthalene (MN)&...
The effect of an electric field on the expansion and collapse of ionized bubbles in insulating fluids has been studied. The bubbles are generated by an electrical discharge in an auxilliary gap, recessed into one of a pair of parallel electrodes of a liquid-filled cell; the bubbles are recorded by a flash-illuminated shadowgraph camera. A field of 150 kV/cm has a small effect on the bubble expansion,...
The electrical conduction of cyclohexane was studied between metal electrodes electrochemically coated with thin films of alumina or polyphenyleneoxide. The weak injection observed at short times after a dc voltage was applied is similar with electrodes either coated or not. We conclude that the injected ions are created in the liquid. After long times of voltage application, a large increase of the...
Breakdown of dielectrics has been a serious challenge to physicists and engineers. Until the beginning of this century, very poor explanations were offered. An insulator was often portrayed as a vessel containing the electricity and exploding under the strain of electric pressure.
The thermalization distances defined and measured as above are smaller, for the same assumed distribution function, than those determined with other injection processes: X8- or γ619-ray ionization, VUV photoionization2, ionization of a dissolved molecule (i.e. TMPD10–11). However they are in the same order from one liquid to another.
Values of thermalization ranges bGp were estimated from measured free ion yields using the extended Onsager model in ethene, propene, cyclopropane, propane, n-butane and i-butane at 0.15 ≲ d/dc < 3 (dc = critical fluid density). At d/dc < 0.3 the density normalized range bGpd was (5.5 ± 0.2) 10−6 kg/m2 for the present alkanes and methane and ethane. The double bond in ethene, and the double...
The field enhancement of free-ion yield in liquid Argon and the concomitant reduction of radiation-induced luminescence implies an escape probability from recombination ∼ 0.35 at very low external fields. This, when interpreted using Onsager's equation, gives an electron thermalization length ∼ 200 nm which is larger than the inter-positive ion separation on the track (∼ 120 nm) obtained form the...
A long term stability of the signal was realized: the decreasing in the pulse height was less than 10% over one year. The peak position of the pulse height spectra due to 976 keV electrons is plotted versus electric field in fig.1, after charge calibration. Gf'(E), the ion yield measured by this method, can be related with the free ion yield, Gf(E), by equation where F(E, π) is the reduction due to...
The electron pulse shape produced by the passage of an ionizing particle through a liquid filled ionization chamber is analyzed theoretically. Parallel plate chambers are considered. The results are compared with experimental data.
The mechanisms of field emission and field ionisation are indeed operative but with very drastic conditions i.e., highly purified liquid and very sharp tips.
We describe the various processes by which positive ions at the interface of a metal oxide with a dielectric liquid can be neutralised, and their significance in relation to the initiation of breakdown.
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