A statistical interpretation of the electrical breakdown of liquid dielectrics

1962 ◽  
Vol 269 (1337) ◽  
pp. 233-248 ◽  
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.

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

1964 ◽  
Vol 256 (1069) ◽  
pp. 185-212 ◽  
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.

Empirical and semiempirical models of the formative time delay in nitrogen

2008 ◽  
Vol 86 (7) ◽  
pp. 947-951
Author(s):  
V Lj Marković ◽  
S N Stamenković ◽  
S R Gocić
Keyword(s):  
Time Delay ◽  
Time Dependence ◽  
Voltage Drop ◽  
Electrical Breakdown ◽  
Breakdown Time ◽  
Formative Time ◽  
Delay Times ◽  
Statistical Time ◽  
Semiempirical Models ◽  
Good Agreement

The formative time dependence on working voltages tf(U) in nitrogen is determined: (1) from the Laue diagrams, by taking the values where the linear approximation of the electrical breakdown time delay (td) intersects the time axis, (2) from histograms, by taking the minimum values of the delay times for the formative time, and (3) from a difference tf = [Formula: see text] – [Formula: see text] ≈ [Formula: see text] – σ (td), where standard deviation σ,(td) is approximately equal to the mean of the statistical time delay [Formula: see text]. The breakdown time delay measurements are supported by oscilloscopic measurements of the voltage drop and the current rise time during inception of the discharge. Several simple models were applied to describe the experimental formative time dependence on working voltages tf,(U) and a good agreement with experimental data was found.PACS Nos.: 51.50.+v, 52.80.–s

scholarly journals Breakdown of liquid dielectrics

1966 ◽  
Vol 294 (1438) ◽  
pp. 393-404 ◽  
Keyword(s):  
Room Temperature ◽  
Breakdown Strength ◽  
Electrical Breakdown ◽  
Time Lag ◽  
Simple Expression ◽  
Vapour Bubble ◽  
Field Development ◽  
Formative Time ◽  
Liquid Dielectrics ◽  
Time Required

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.

scholarly journals Secondary Ionization Mechanisms in an E × B Discharge in Hydrogen

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.

Formative time lags in the electrical breakdown of gases

1953 ◽  
Vol 4 (6) ◽  
pp. 170-175 ◽  
Author(s):  
J Dutton ◽  
S C Haydon ◽  
F Llewellyn Jones
Keyword(s):  
Electrical Breakdown ◽  
Time Lags ◽  
Formative Time

scholarly journals In Vitro Model of Mycobacterial Growth Arrest Using Nitric Oxide with Limited Air

2008 ◽  
Vol 53 (1) ◽  
pp. 157-161 ◽  
Author(s):  
Syed Hussain ◽  
Muhammad Malik ◽  
Lanbo Shi ◽  
Maria Laura Gennaro ◽  
Karl Drlica
Keyword(s):  
Nitric Oxide ◽  
In Vitro Model ◽  
Transition Period ◽  
Time Lag ◽  
Growth Arrest ◽  
Ring Structure ◽  
Time Lags ◽  
Vitro Model ◽  
Mycobacterial Growth

ABSTRACT An in vitro model of mycobacterial growth arrest was developed using Mycobacterium bovis BCG. When an exponentially growing culture was transferred to an evacuated tube, growth continued; treatment with a source of nitric oxide (diethylenetriamine-nitric oxide adduct [DETA-NO] at 50 μM) halted growth immediately, and aeration restored growth. When the period of growth arrest exceeded 4 h, a time lag occurred before aeration could restore growth. The lag time was maximal (24 h) after 16 h of growth arrest. These time lags indicated that one transition period was required for cells to achieve full arrest of growth and another for them to recover fully from growth arrest. DETA-NO-induced growth arrest failed to protect from the lethal effects of anaerobic shock, which caused rapid lysis of both growing and growth-arrested cells. While growth arrest had little effect on the lethal action of rifampin, it eliminated isoniazid lethality. Growth arrest reduced but did not eliminate fluoroquinolone lethality. Two fluoroquinolones, moxifloxacin and gatifloxacin, were equally lethal to exponentially growing cells, but moxifloxacin was more active during growth arrest. This difference is attributed to the fluoroquinolone C-7 ring structure, the only difference between the compounds. Collectively these data characterize a new system for halting mycobacterial growth that may be useful for evaluating new antituberculosis agents.

IRREVERSIBLE INVESTMENT, OPERATING FLEXIBILITY, AND TIME LAGS

2010 ◽  
Vol 27 (02) ◽  
pp. 271-286 ◽  
Author(s):  
RYUTA TAKASHIMA ◽  
MAKOTO GOTO ◽  
MOTOH TSUJIMURA
Keyword(s):  
Time Lag ◽  
Peak Load ◽  
Price Volatility ◽  
Optimal Investment ◽  
Capacity Expansion ◽  
Fixed Cost ◽  
Time Lags ◽  
Investment Timing ◽  
Power Company ◽  
Optimal Investment Problem

We consider an optimal investment problem when a firm such as an electric power company has the operational flexibility to expand and contract capacity with fixed cost. This problem is formulated as an impulse control problem combined with optimal stopping. Consequently, we obtain optimal investment timing, optimal capacity expansion and contraction timing, and the investment value. We also show investment, capacity expansion and contraction rule are influenced by the price volatility and the initial capacity is also influenced by the ratio between base-load plant and peak-load plant. In addition, we investigate how time lag between investment and operation influences the investment rule.

scholarly journals Reconciling Lagrangian Diffusivity and Effective Diffusivity in Contour-Based Coordinates

2019 ◽  
Vol 49 (6) ◽  
pp. 1521-1539
Author(s):  
Yu-Kun Qian ◽  
Shiqiu Peng ◽  
Chang-Xia Liang
Keyword(s):  
Time Lag ◽  
Effective Diffusivity ◽  
Delta Function ◽  
Spreading Rate ◽  
Particle Dispersion ◽  
Small Scale ◽  
Time Lags ◽  
Conservative Tracer ◽  
Stirring Effect ◽  
Short Time

AbstractThe present study reconciles theoretical differences between the Lagrangian diffusivity and effective diffusivity in a transformed spatial coordinate based on the contours of a quasi-conservative tracer. In the transformed coordinate, any adiabatic stirring effect, such as shear-induced dispersion, is naturally isolated from diabatic cross-contour motions. Therefore, Lagrangian particle motions in the transformed coordinate obey a transformed zeroth-order stochastic (i.e., random walk) model with the diffusivity replaced by the effective diffusivity. Such a stochastic model becomes the theoretical foundation on which both diffusivities are exactly unified. In the absence of small-scale diffusion, particles do not disperse at all in the transformed contour coordinate. Besides, the corresponding Lagrangian autocorrelation becomes a delta function and is thus free from pronounced overshoot and negative lobe at short time lags that may be induced by either Rossby waves or mesoscale eddies; that is, particles decorrelate immediately and Lagrangian diffusivity is already asymptotic no matter how small the time lag is. The resulting instantaneous Lagrangian spreading rate is thus conceptually identical to the effective diffusivity that only measures the instantaneous irreversible mixing. In these regards, the present study provides a new look at particle dispersion in contour-based coordinates.

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