DocumentCode :
901668
Title :
Conduction and breakdown mechanismsin transformer oil
Author :
Butcher, Michael ; Neuber, Andreas A. ; Cevallos, Michael D. ; Dickens, James C. ; Krompholz, Hermann
Author_Institution :
Electr. Eng. Dept., Texas Tech Univ., Lubbock, TX, USA
Volume :
34
Issue :
2
fYear :
2006
fDate :
4/1/2006 12:00:00 AM
Firstpage :
467
Lastpage :
475
Abstract :
With a fast coaxial test setup using high speed electrical and optical diagnostics, prebreakdown current pulses and shadowgraphy images are measured for direct current (dc) breakdown in Univolt 61 transformer oil. Also, dc currents across the gap are measured using a high sensitivity electrometer. The conduction and breakdown mechanisms in transformer oil as function of applied hydrostatic pressures are quantified. Together, this information provides data on the development of current flow in the system. We have identified three stages in the conduction process prior to breakdown for highly nonuniform fields. Stage 1 is characterized by a resistive current at low fields. Increasing the applied electric field lowers the effective barrier at the metal/dielectric interface allowing a "tunneling" mechanism to begin, leading to the rapid rise in the injection current observed in stage 2. In stage 3, at high fields, the current reaches space charge saturation with an apparent mobility of 3·10-3 cm2/V·s prior to breakdown. The processes of final breakdown show a distinct polarity dependence. A strong pressure dependence of the breakdown voltage is recorded for negative needle/plane breakdown; a 50% reduction in breakdown voltage is observed when the hydrostatic pressure is lowered from atmospheric pressure to hundreds of mtorr. Positive needle discharges show a reduction of only about 10% in breakdown voltage for the reduced pressure case. Weak pressure dependence indicates the breakdown mechanism does not have a strong gaseous component. We will discuss possible links between conduction current and dc breakdown.
Keywords :
electric breakdown; plasma diagnostics; plasma pressure; plasma transport processes; space charge; transformer oil; Univolt 61 transformer oil; atmospheric pressure; coaxial test setup; conduction current; current flow; direct current breakdown; electrical diagnostics; high sensitivity electrometer; hydrostatic pressures; injection current; metal-dielectric interface; negative needle breakdown; optical diagnostics; plane breakdown; positive needle discharges; prebreakdown current pulses; resistive current; shadowgraphy images; space charge saturation; tunneling; Coaxial components; Current measurement; Electric breakdown; High speed optical techniques; Needles; Oil insulation; Optical saturation; Optical sensors; Pulse measurements; Testing; Bubble formation; conduction mechanisms; liquid breakdown; mobility; pressure effects; temperature effects;
fLanguage :
English
Journal_Title :
Plasma Science, IEEE Transactions on
Publisher :
ieee
ISSN :
0093-3813
Type :
jour
DOI :
10.1109/TPS.2006.872487
Filename :
1621332
Link To Document :
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