Breakdown of liquid dielectrics

A study was made of electrical breakdown of a liquid (hexachlorodiphenyl) the viscosity of which is very dependent on temperature. It is shown that in uniform fields breakdown results from formation and growth of a vapour bubble in the liquid. This was established by direct microscopic observations of the ‘breakdown event’ at room temperature and by measurements of times to breakdown as the viscosity was changed by five orders of magnitude between room temperature and 56.5 °C. When the time of voltage application is too short for the vapour bubble to grow to its critical size then the breakdown strength is higher than that obtained under direct voltages. Under 10/50 μs impulses the breakdown strength of hexachlorodiphenyl at room temperature was 5 MV/cm. It is suggested that vaporization was initiated by development of points of zero pressure in the liquid. Assuming that, in an electric field, development of points of zero pressure resulted from the presence of submicroscopic particle impurities in the liquid, a simple expression was derived for the onset of vaporization. It is shown that this expression gives good predictions for the known dependences of breakdown strength of n -hexane on both temperature and pressure and for the variation of breakdown strength of aliphatic hydrocarbons with molecular weight. It is further shown that the time required for a vapour bubble in n -hexane to grow to the size at which breakdown occurs is comparable with the experimentally measured formative time lag.

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Significantly Improved Electrical Breakdown Strength of Natural Ester Liquid Dielectrics by Doping Ultraviolet Absorbing Molecules

IEEE Access ◽

10.1109/access.2019.2919969 ◽

2019 ◽

Vol 7 ◽

pp. 73448-73454 ◽

Cited By ~ 5

Author(s):

Suning Liang ◽

Feipeng Wang ◽

Zhengyong Huang ◽

Weigen Chen ◽

Youyuan Wang ◽

...

Keyword(s):

Breakdown Strength ◽

Electrical Breakdown ◽

Electrical Breakdown Strength ◽

Liquid Dielectrics ◽

Natural Ester

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A statistical interpretation of the electrical breakdown of liquid dielectrics

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1962.0173 ◽

1962 ◽

Vol 269 (1337) ◽

pp. 233-248 ◽

Cited By ~ 46

Keyword(s):

Short Duration ◽

Electrical Breakdown ◽

Short Pulse ◽

Time Lag ◽

Step Function ◽

Time Lags ◽

Statistical Interpretation ◽

Breakdown Time ◽

Formative Time ◽

Statistical Time

Previous investigators, when measuring the electric strength of hydrocarbon liquids with short-duration rectangular pulses, have assumed that the statistical component of the breakdown time was insignificant com pared with the formative time. In the present investigation, however, the time to breakdown was measured directly by the use of step-function pulses, and clear evidence for a statistical time lag was found. The formative time was ~ 0.1 us, being less than that given by previous estimates. A statistical interpretation of short-pulse measurements is presented and this provides a consistent explanation of the results of other workers. Furthermore, by using an experimentally derived equation for the variation of the mean rate of breakdown f ( E ) with applied stress E , it has been shown that the form of the relationship between strength and pulse duration obtained by other workers agrees with that obtained by a statistical analysis. Experiments on air-saturated n -hexane with both short-duration and step-function pulses support the statistical ideas presented and indicate that electrode conditions are extremely important. It was found that strength and time to breakdown were affected by the number of breakdown measurements on a sample. Experiments with gas-free n -hexane and non-uniform fields have demonstrated the importance of air content when long duration pulses are used. It was found that, although the statistical time lag was insignificant, formative time lags as long as 10 ys occurred with a point cathode-sphere anode configuration.

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The impulse breakdown voltage and time-lag characteristics of long gaps in air I. The positive discharge

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1964.0003 ◽

1964 ◽

Vol 256 (1069) ◽

pp. 185-212 ◽

Cited By ~ 5

Keyword(s):

Space Charge ◽

Wave Front ◽

Breakdown Voltage ◽

Breakdown Strength ◽

Electrical Breakdown ◽

Time Lag ◽

Short Wave ◽

Time Lags ◽

Long Time ◽

Statistical Time

The electrical breakdown of rod/rod, rod/sphere and rod/plane gaps in the atmosphere has been examined oscillographically and photographically. Positive polarity impulse potentials of crest value up to 1 MV, of wave-front variable between 0.06 and 2.0 μs and of wave tail 2 ms were used. It has been found that the lack of a sharply defined breakdown potential was due to the existence of long time lags quite distinct from the shorter times to breakdown observed with the conventional short wave-tail impulse. A ‘ dead-time ’ of low probability of breakdown on the wave tail separated the two classes of breakdown. The breakdown voltage of a rod/rod gap has been found to be dependent upon the wave front of the impulse. An accompanying photographic examination of the initial corona phase of breakdown also revealed a variation with the impulse voltage wave front. It is shown that these results were consistent with the electric field distortion arising from space charge. The corona phase of breakdown was responsible for this space charge. The statistical behaviour of long gap breakdown was due to random variations in the corona phase. The effect of the statistical time lag in the production of initiatory electrons upon the corona phase is discussed. A rotating-mirror camera of f/1.0 aperture and a technique for controlled suppression of the breakdown enabled the growth of the discharge with time to be studied in some detail. It was shown that the positive leader either preceded or was coincident with the negative leader, depending upon the gap arrangement. It is concluded that the establishment of the leader at the high-tension electrode is the criterion for breakdown. The role of the earthed cathode in aiding this leader development was dependent upon its size and geometry. For cathodes of small dimensions the occurrence of a negative corona phase increased the anode electric gradient; for large cathodes the surface charge induced by the anode corona discharge became important. The variation of breakdown strength with gap geometry is accountable in these terms.

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Secondary Ionization Mechanisms in an E × B Discharge in Hydrogen

Australian Journal of Physics ◽

10.1071/ph730761 ◽

1973 ◽

Vol 26 (6) ◽

pp. 761

Author(s):

J Fletcher ◽

TI Walsh

Keyword(s):

Experimental Data ◽

Theoretical Model ◽

Electrical Breakdown ◽

Time Lag ◽

Ionization Mechanisms ◽

Formative Time ◽

Townsend Discharge

A study of the secondary ionization mechanisms operative in an Ex B Townsend discharge in hydrogen has been made by investigating the formative time lag to electrical breakdown in such discharges. Comparison of the experimental data with predictions from a theoretical model enables the secondary mechanisms to be distinguished and their separate contributions to be estimated. The results so obtained are compared with those derived from the equivalent pressure concept.

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Electrical breakdown strength enhancement in aluminum scandium nitride through a compositionally modulated periodic multilayer structure

Journal of Applied Physics ◽

10.1063/5.0064041 ◽

2021 ◽

Vol 130 (14) ◽

pp. 144101

Author(s):

Jeffrey X. Zheng ◽

Dixiong Wang ◽

Pariasadat Musavigharavi ◽

Merrilyn Mercy Adzo Fiagbenu ◽

Deep Jariwala ◽

...

Keyword(s):

Multilayer Structure ◽

Breakdown Strength ◽

Electrical Breakdown ◽

Scandium Nitride ◽

Strength Enhancement ◽

Electrical Breakdown Strength

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A modified bioassay for heat-stable Escherichia coli enterotoxin

Canadian Journal of Microbiology ◽

10.1139/m77-049 ◽

1977 ◽

Vol 23 (3) ◽

pp. 331-336 ◽

Cited By ~ 8

Author(s):

S. Stavric ◽

D. Jeffrey

Keyword(s):

Escherichia Coli ◽

Body Weight ◽

Incubation Time ◽

Evans Blue ◽

Room Temperature ◽

Blue Dye ◽

Evans Blue Dye ◽

Heat Stable ◽

Stomach Distention ◽

Time Required

Infant mice were injected orally with preparations containing Escherichia coli heat-stable enterotoxin (ST) and Evans blue dye, and incubated at 22 °C. With enterotoxin-positive samples, the stomach was distended and contained essentially all of the dye. With enterotoxin-negative samples, the stomach remained normal in size and the dye passed freely into the intestines. The time required to obtain the maximum ratio of gut weight to body weight varied from 30 to 90 min and was dependent upon the concentration of enterotoxin. Heat-labile enterotoxin (LT) had no effect during this period.Based on these findings, the mouse incubation time was reduced from 4 h to 90 min, and the heating of test samples was retained only for confirmation of ST. The location of the dye and stomach distention served as an indicator of positive responses to ST. Incubation of the mice at room temperature (22 °C) was found satisfactory.

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