AD-750 699

ELECTRICAL BREAKDOWN OF DIELECTRICS WITHA DIPOLE STRUCTURE

N. A. Prikhodl'o

Foreign Technology DivisionWright-Patterson Air Force Base, Ohio

20 July 1972

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ELECTRICAL BREAKDOWN OF DIELECTRICS .'"TH A

DIPOLE STRUCTURE

by

N. Prikhod'ko

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ELECTRICAL BREAKDOWN OF DIELECTRICS WITH A DIPOLE STRUCTURE

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1" ABSTRACT -

On the basis of data obtained in the breakdown of water andF vcerine, as a function of the variation of the temperature, anddIso from data concerning breakdown voltages for ice, Seignette';nlt, and nolar linuids, it follows that with the variation of thedielectric constant of the matter its breakdown voltage also chanFes."The -variation of the Lreakdown voltage of a dielectric may be ex-A)lalned bv the variation of the Internal field. It is demonstratedthat in sharply heterogeneous fields liquids havinr large dinolemoments have a considerablv decreased electric strenrth in comnarisonwith nonpolar linuid. During breakdown in pulsed voltage dielectricswlth a dipole structure show a temnerature dependence of thebreakdown voltage. In conclusion, the author expresses hts 1-rati-tude to Professor Doctor A. A. Vorob'vev for suggestinF the subhectand sunervisinr the work.

!) j -

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I Dielectric BreakdownIDielectric Constant"Dielectric Strcnr~th-~it er

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FTD-HC-2L-l176-72

ELECTRICAL BREAKDOWN OF DIELECTRICS WITH ADIPOLE STRUCTURE

By: N. Prikhod'ko

English pages: 9

Source: Tomsk. Universitet. oibirskiv Fiziko-Tekhnicheskiv Institut. Trudy, (High-Voltage Laboratory), No. 2, Vol. 6,1945, pp. 1114-119.

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THIS TRANSLATION IS A RENDITION OF THE ORIGINAL FOREIGN TEXT WITHOUT ANY ANALYTICAL OREDITORIAL COMMENT. STATEMENTS OR THEORIES. PREPARED BY:.ADVOCATED OR IMPLIED ARE THOSE OF THE SOURCEAND 00 NOT NECESSARILY REFLECT THE POSITION TRANSLATION DIVISIONOR OPINION OF THE FOREIGN TECHNOLOGY DI- FOREIGN TECHNOLOGY DIVISIONVISION. WP-AFS. OHIO.

FTD-HC-.2 .u.-72 Date 20 .ju 19.._

ELECTRICAL BREAKDOWN OF DIELECTRICS WITH ADIPOLE STRUCTURE

[Article by N. A. Prikhod'ko; Tornsk, Trudy Sibirskogo fiziko-tekhniches-kogo instituta, High-Voltage Laboratory, Russian, No 2, volume 6, 1942.,signed to press 15 October 1939, pp 114-119]

1. Introduction

Up to this time the question remains open as to what determine" thebeginning of the disruption of the electric str,_ength of solid and liquid

dielectrics, the effect of either the superimposed potential difference orthe achievement of a definite magnitude of the intensity of the internal fieldin the dielectric.

Having applied a voltage V to a capacitor filled with the liquid beingtested, we subject each particle of this liquid to the effect of an electricalfield. The intensity E of the electrical field, actually operating at the givenpoint on a particle within the liquid, as a consequence of the dielectricpolarization of the dielectric, will differ from the calculated magnitude F,as

vd

where d is the distance between the electrodes.

The difference will depend upon the polarization of a unit of volume Jand is expressed by the formula

4l•E'=F+-4. J.

.3

The magnitude of the polarization may be connected via the molecularpolarization capacity with the magnitude cf the dielectric constant of thematter by means of the Clausius-Mossoti formula and the well-known

FTD-IIC-2 3-1176-72

expression may thus be obtained for the magnitude of the internal field

L. E+__2 (1)3

This expression is arrived with reference to gases and vapors. How-ever, we may assume that this formula at least qualitatively describes thephenomena in dipole liquids also.,

From formula (1) it is apparent that. the internal field will be a factorof ( E + 2)/3 greater than the external field. Consequently, if in electricalbreakdown of the dielectrics the internal field plays a part, then the mago3.-tudes of breakdown voltages obtained in the experiment are obviouslyunderstated.

In this article certain experiments in the breakdown of dielectricswith different magnitudes of the dielectric constant are described, theresults of which are explained with a consideration of the internal fieldsin the dielectric. The measurements were conducted on pulsed voltage,

with a duration of 10-6 seconds.

In the brief effect of the voltage, as the measurements of Dittertdemonstrate, adequately pure electrical conditions are provided andthermal phenomena are reduced to a minimum.

2. Experiments with Water and Glycerine

To determine the dependence of the possible effect of the internal

fields on the magnitude of the breakdown voltage, experiments were con-ducted with water and glycerine. Water and glycerine, in a variation oftemperature, change their dielectric coefficients, and in this case,according to formula (1), the. magnitude of the internal field will alsochanCe.

For measurement of the dielectric constants in water and glycerinein ',n impact voltage, at a value of the voltage close to breakdown value,a device was assembled according to a scheme which Kobeko and Kurchatovused (reference 2) in measuring the dielectric constant of Seignette saltin pulses.

The measuring capacitor, mounted in quartz, is submerged into thebath filled with the liquid being tested. The heating is performed by anelectric furnace sub iterged into the bath, containing the liquid being tested;

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!TP-H1C-2 3-.1176-72

the temperi L'1i, was measured by a me~c'cay thermometer. The results ofthe measurt, ents are presented in Figure 1.

r

40.

40 W X -g - -' -r AaO1 x/V/p 2

Figure 1.

Ica(1) e.

lin0 - - .. - * .- l - -..-

_V~ _4V _/ a Vr V4 VJ VW4

$00----

Figure 2. l1Rre.akdown voltage, kilovolts per centimeter.

From Figure I it is apparent that the dielectric constant of water(curve I) drops insignificantly with an increase in temperature.,

In glycerine (curve II) in the temperature interval of 35 to 40 degreesCentigrade, the dielectric con.itant has a maximum,

For this same temperature range, for the same substances, break-down voltages in a homogeneous field were measured, as well as in a fieldclose to homogeneous and in a heterogeneous field. The curves of thedependence of breakdown voltages for water are shown in Figure 2. Curve Iis for distilled water, and curv( II is for distilled water that was boiled fora long time.

FTD-HC-23-1176-72 3

In comparing these results with a fluctuation of the dielectric constant,and considering the assumptions expressed in Section 1, we should expectan i.ncrease in the breakdown voltage as the temperature rises for water.It is true that according to formula (1) this increase should not exceed fiveto ten percent, but since the errors of the experiment reached the samemagnitude, with ruch small variations of the magnitude of the internal fieldwe cannot speak of its effect in the given case.

4 --

IV - - - .

M- MX4M M NX it ?*#

Figure 3. (1) kilovolts.

In Figure 3 the dependence of the breakdown voltage in pulses ispresented for glycerine, taken in the interval from -25 degrees Centigradeto +120 degrees Centigrade. We will trace the fluctuation of this curve

in the section of temperatures from minus 25 degrees Centigrade to +18degrees Centigrade. At first we observe a growth of the breakdown voltagewith an increase in temperatur-, and then it remains at a constant value;in the temperature range of 25 to 50 degrees Centigrade there is a maximum,and then z'. gradual increase of the breakdown voltage occurs, reaching anincrease of 40 percent over the initial value at the end of the curve. Incomparing the curve of breakdown voltages in Figure 3 with the curve ofthe fluctuation of the dielectric constant in Figure 1, taken in a temperaturerange of 14 to 113 degrees Centigrade at the same voltages, we see thatin places where the curve of the breakdown voltages as a maximum value,the curve for the dielectric constant, on the contrary, has a maximum inthe interval of 25 to 50 degrees Centigrade, i.Le. , with an increase in thedielectric constant t!e breakdown voltage falls.

For a heterogeneous field approximately the same curves are obtained,only the end of the curve (at a high temperature) moves somewhat higher.

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3, Experiments with Ice and with Seignette Salt

(a) Breakdowt.. of ice. Out of the solids, two were investigated: iceand Seignette salt. Pure river ice was cut by means of a heated wire intopieces with din-ensions of 2 x 2 x 1 centimeter. Breakdown was performedboth in a homogeheous and in a heterogene,-L's field in pulsed voltage.

The expeliment was conducted in the following manner: the pieces of

ice were placed on a massive copper electrode. and then the upper elec-trode was forced into the specimen by pressure by means of a screw. Theinstrument was filled with dry cold oil and cooled in the open air to thetemperature of the latter, where breakdown was also performed. Thebreakdown voltages were fixed at four temperatures: -31, -22, -17, and-10 degrees. For the frequency on which the experiment was performedthe ice, according to the measurements of Errer (reference 3), does notchange its dielectric constant in a variation of temperature, therefore wecould not expect any great dependence of the breakdown voltage upon thechange in temperature.

The high breakdown values obtained for ice in breakdown duringpulses direct attention to themselves, Thus, in the breakdown of ice duringpulses n a homogeneous field the ice turned out to be stronger than manysolid dielectrics. The interval near zero degrees Centigrade, i.e. , theinterval of the transmission from a solid state to a liquid state, is ofinterest. The breakdown strength o the ice in melting changes suddenly,and the strength decreases approximately to a third of its former value(Figure 2). If we consider that the dielectric constant of the ice at thisfrequency is only approximately a tenth as much as in water, then such ajump in breakdown voltages may be explained by working from formula (1).

(b) Breakdown of Seignette salt. The breakdown vc!tage of Seignettesalt is of interest because its dielectric constant is not the same withrespect to different crystallographic directions.

- npod& no ou

u P (3)0.- ___ o

.~ ~~. VA EA A

.25 -

20~

- --A --

R J ~1/0 /S X0 25 30 3M .0 6 0 5 0 e

Figure 4. (1) breakdown along axis b; (2) breakdown along axis c;(3) breakdown along axis a; (4) Upr [Unp U pr = Ubreakdown]kv (kilovolts), maximum,

We performed the investigations with specimens cut along th .reecrystallographic axes: a, b, and c. Along axis a Seignette salt has a quitehigh value of the dielectric constant, and along axes b and c the value isconsiderably less. The result of the measurement is shown in Figure 4.The lower curve was taken for specimens polished along axis a. The break-down values along axes b and c were obtained at coinciding values and withrespect to strength lie at a point approximately twice as high. The fact ofthe very low breakdown voltages along axis a makes it possible to expressthe assumption here also that a decrease in breakdown voltage along thisaxis, in comparison with other directions, is associated with the variationof the dielectric constant, since all the other breakdown conditions were.entirely the same.

4. Dependence of the Breakdow'n Voltage ofLiquid Dielectrics Upon the Magnitude of the Dipole MomenOa

For completeness of the picture of the dependence of breakdownstrength upon the magnitude of the internal field, investigations were madeof the electric strength oi a number of liquids, the dipole moments of whichwere different. The basic investigations were performed with the followingliquids: benzene, xylene, transformer oil, toluene, aniline, ethyl alcohol,and water. All the liquids (with the exception of oil) were thoroughly puri-fied by double distillation. Breakdown was performed in a heterogeneous

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field (needles against the plane) in pulses with different duration and differ-ent polarity. The curves of breakdown voltages as a function of the distancebetween the electrodes are shown in Figure 5. In Figure 5 curves aregiven for xylene (I), benzene (II), transformer ol1 (III), toluene (IV), aniline(V), ethyl alcohol (VI) and water (VII), brokcn down at pulses with a durationof 6. 2 x 10-4 seconds. In Figure 6 the same curves are shown, but thebreakdown occurred with a different polarity of the electrodes, namely:the negative electrode was sharp and the positive electrode flat. FromFigure 6 it is apparent that the strength of benzere and xylene is almostthe sanre, and curves of breakdown voltages lie above all the othe rs forthese. Following them, in order, are: transformer oil, toluene, andaniline. Alcohol and water occupy the lowest positions with respect tostrength. Having arranged the liquids in a series according to the magni-tude of the dipole moment, and also according to breakdown srength, weobtain Table 1.

I I

-(2)0,4• o 4 6 4,5 td 1 .,.,

rigure 5. (1) breakdown voltage, kilovolts, maximum; (2) rr, llinwtcrs.

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rPTD-tC-2 3-1276-72

'rv,.-c (1.) i- -40 - - - -....-

Fiur . 1)klools maimm (2 iliees

40 3

S~(2 Y02O . . ...... 0 25 of #a1

Table I

lu .po6.tn~oe manpotwe...

Bentec Ao .c, 22.5'2o, .

1. KcTIo.'t ........... . 0 2 4 322. BCet13o., . . . . . .. • 0 25 3-13. Tpai1C4)opwaTopHoe mqcso. . - 22.5 2G, 5,1. Tonyox . . . .. .. .. ... 0,32.10-15 20 25,5

5. Anunuat.. .............. 1,6 . 10 -" 17,5 236. Cntip*.. , . . .. . .. 1,64.10-'* 17,5 227. Boa .... . ............ 1,.S4. 10- 17 21

Key: (a) substance; (b) dipole moment; (c) breakdown voltage per milli-meter, in kilovolts; (d) sharp electrode positive; (e) sharp electrodenegative; (1) xylene; (2) benzene; (3) transformer oil; (4) toluene;(5) aniline; (6) alcohol; (7) water.

Val'ter and Inge (reference 4) obtainea approximately the sameseries with respect to strength in purely electrical breakdown for verypure liquids in conditions of a homogeneous field.

FTi)-HC-2 3-1176-72

5. Conclusions

1. On the ba,., of data obtained in the breakdown of water andglycerine, as a function of the variation of the temperature, and also fromdata concerning breakdown voltages for ice, Seignette salt, and polarliquids, it follows that with the variation of the dielectric constant of thematter its breakdown voltage also changes. The variation of the breakdownvoltage of a dielectric may be explained by the variation of the internalfield.

2. It is demonstrated that in sharply heterogeneous fields liquidshaving large dipole moments have a considerably decreased electricstrezigth irn comparison with nonpolar liquid.

3. During breakdown in pulsed voltage dielectrics with a dipolestructure show a temperature dependence of the breakdown voltage.

In conclusion, the author expresses his gratitude to Professor Doctor A.A. Vorob'yev for suggestinr tle subject and supervising the work.

BIBLIOGRAPHY

1. Dittert, Dissertation, Dresden, 1930.

2. Kobeko and Kurchatov, Zhurnal Russ. Fiz.-Khim. Obshch. (Journal of theRussian Physics and Chemistry Society), 62, 251, 193T.

3. Errera, Zhurnal Tekh. Fiz. (Journal of Fnýineerinv Physics), 3, 16, 1933.

b. Va)'ter and Inge, Zhurnal Tekh. Fiz., 4, 1669, 193L.

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