Pressure and temperature dependence of the dielectric properties of polyethyleneused in submarine telecommunication cablesBui Ai, P. Destruel, M. Farzaneh, and Hoang The Giam Citation: Journal of Applied Physics 52, 525 (1981); doi: 10.1063/1.328450 View online: http://dx.doi.org/10.1063/1.328450 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/52/1?ver=pdfcov Published by the AIP Publishing Articles you may be interested in On the temperature and pressure dependences of cavities in the dielectric continuum picture J. Chem. Phys. 123, 014504 (2005); 10.1063/1.1948375 Pressure and temperature dependence of the dielectric breakdown of polyethylene used in submarine powercables J. Appl. Phys. 57, 4805 (1985); 10.1063/1.335346 Pressure dependence of thermal conductivity in polyethylene J. Appl. Phys. 46, 4506 (1975); 10.1063/1.321384 Temperature and Pressure Dependence of Dielectric Constant of Cadmium Fluoride J. Appl. Phys. 40, 3115 (1969); 10.1063/1.1658150 The Frequency and Temperature Dependence of the Dynamic Mechanical Properties of a High DensityPolyethylene Trans. Soc. Rheol. 5, 261 (1961); 10.1122/1.548899

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Pressure and temperature dependence of the dielectric properties of polyethylene used in submarine telecommunication cables

Sui Ai, P. Destruel, M. Farzaneh, and Hoang The Giam Laboratoire de Genie Electrique associe au Centre National de la Recherche Scientifique, Universite Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex, France

(Received 25 March 1970; accepted for publication 12 August 1980)

In this work the dielectric losses oflow-density polyethylene used in submarine telecom­munication cables have been measured as a function of pressure (1-1150 bars), temperature (4-32 .C), and frequency (0.3-12 MHz). These results point out that the dissipation factor tan {j and permittivity E of the insulators increase on the sea bottom; for example, for a cable laying at the depth of 5000 m and temperature of 4 ·C, these variations are about.:l tan{j = 35 X 10- 6 (F = 12 MHz), .:lE = 5 X 10- 2

•

PACS numbers: 77.40+ 8S.S0.Fs.

The transatlantic telecommunication cables are laid on the sea bottom at a depth of several thousand meters. To resist the effect of high pressure, submarine telecommunica­tion cables adopt a polyethylene-filled structure. On the sea bottom, external conditions affecting the cables change sharply from those of normal temperature and pressure, so the isolator characteristics must be studied at nearly the same conditions. Numerous investigations l

-4 have been car­ried out on polyethylene to determine its losses with frequen­cy and temperature, but no measurement has been made with the same parameters under pressure. Although some measurements have been made of linear attenuation on im­mersed cables,1 their dielectric losses have never been mea­sured under conditions as are present in their real applications.

Let us recall the experimental apparatus for evaluating the dielectric losses oflow-Ioss materials.5 1t is composed of a high-pressure bomb in which is placed a sample-holder General Radio type 1690A. The pressure in the bomb is ob­tained by means of a two-stage diaphragm compressor. The maximum gas pressure is 1500 bars and the temperature of the sample can be obtained in the range - 20 to + 50 ·C, with a stability ofless than 0.1 ·C, by the circulation of a fluid around the electrodes.

The method of measurement is based on the Q-meter method.6-9 The measurement system is completely automa­tized and governed by a microcomputer [Commodor type

10t?tano .. °c 210 ---

! bars

1---0950

V V L/

),.--0 .... 1--0520

oV I-I-h~ 1-0300

--1--1- o~ 1-0

l---1-'- 1--°, 1-0- ~

~- ~ t::--1-0

t:::= r:::~

170

130

90

50 F

D.3 10 20 MHZ

FIG. I. Variations of tan 8 as functions of frequency and pressure obtained with low·density polyethylene at 4 ·C.

2001 (Ref. 10)] which computes the dissipation factor tan {j and the permittivity E as a function offrequency F, tempera­ture T, and pressure P from the following formulas. 5

tan (j = ____ C~o~ __ _ C2( P,T) + .:lCg ( P,T)

( 1 1 ) d2

X ~ - Q; do(P, T)+d2 -dl '

E = dol P,T) E (P T) do(P,T)+d

2-d l A , ,

where

.:lCg( P, T) = Cg2( P, T) - Cg1( P, T).

Here Cg t ( P,T) and Cg2( P,T) are the edge capacitances with and without the sample, respectively; Co is the total resonat­ing capacitance; C2( P,T) is the cell capacitance for the sepa­ration d2; QI and Q2 are the quality factors ofthe resonant circuit with and without the sample, respectively; d 1 and d2

are the separations of the electrodes with and without the sample, respectively; dol P,T) is the thickness of the sample; and E A ( P, T) is the permittivity of the gaseous nitrogen.

The experiments were made on the low-density poly­ethylene used in submarine telecommunication cables at temperatures of 4 and 21 ·C, under pressures of 1-1150 bars, in the frequency range 0.3-12 MHz. The variations of tan (j and E as functions of pressure, temperature, and frequency are presented in Figs. 1,2, and 3. We have represented these

106 .tanb 2' °c 200

bars 01150

1 ..... °950

VL/ 1/0750 160

Vo~ V V ,20

~ ~o-V V 0300

f- f--o~ ~

j..-o

I- ...... 1-0 I- 1

° 5- §~

120

80

40 F

0.3 10 20 MHZ

FIG. 2. Variations of tan 8 as functions offrequency and pressure obtained with low-density polyethylene at 21 .c.

525 J. Appl. Phys. 52(1), January 1981 0021·8979/81/0525-02$01.10 @) 1981 American Institute of PhYSics 525

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£

2.351-----,--------.-------,

~ 2.30 I------::-'I"-----=-"-f------------i

2.25 L-___ '--..l ___ --'--______ --'----:-'-p 950 bar 520 300

FIG. 3. Variations of to vs pressure obtained with low-density polyethylene at 4 and 32 "c.

results in terms of the tan 0 pressure coefficient (lltan 0 ) ..1 tan 0 / ..1P in Tables I and II. The results show that the dielectric loss and the permittivity of polyethylene vary with pressure and temperature, and we can draw the following conclusions: (i) For a given frequency and temperature, the loss increases with pressure, for example, (lltan 0 ) (..1 tan 0/ ..1P = 2.65 X 10-4 bars -I for T = 4°C, F = 0.3 MHz, and 1.;;P.;;300 bars. (ii) For a given frequency and tempera­ture, the loss decreases with temperature, for example, (lltan 0)..1 tano /..1T = 6.78X 10-3 °C- I

, for P = 300bars, F = 0.3 MHz, and 4.;; T .;;21 0c. (iii) The permittivity E is in­dependent of frequency, increases with pressure, and de­creases with temperature, for example, (lIE}..1d..1P = 2.3 X 10-5 ]Jars-I, for 1.;;P.;;950 bars and T= 4°C. and (liE)

..1E/..1T= - 2.0X 10- 4 °C- I, for 4 °C.;;T.;;32 °c and P = 300 bars. The values of tan 0 are found with an accuracy of 5% and for permittivity with an accuracy of about 0.3%.

These results are in agreement with those of Matsuoka. 1

Assuming that polyethylene compression changes the mo­lecular relaxation in the way as thermal contraction might, he showed that there is an increase in loss tangent of about lOX 10-6 per 500 bars.

TABLE I. The tan {j pressure coefficient 1041 I!tan {j)A tan {j/ AP at 4 "C for low-density polyethylene.

F(MHz) 0.3 0.85 2.5 5 12

P (bar)

1-300 2.65 2.72 5.02 5.55 3.39

300-520 9.92 7.07 5.63 5.41 9.22

520-950 1.95 3.67 5.73 8.05 8.13

526 J. Appl. Phys., Vol. 52. No.1, January 1981

TABLE II. tan {j presure coefficient 1041 I!tan{j)A tant>/ AP at 21 "C for low­density polyethylene.

FIMHz) Plbar) 0.3 0.85 2.5 5 12

1-300 2.51 2.52 2.99 3.37 3.44 300-520 3.04 1.88 2.67 4.08 5.52 520-950 3.19 4.55 7.23 8.26 9.10

Concerning the permittivity of low-loss materials, our measurements show that it is practically independent of fre­quency. The Clausius-Mossotti formula for the static con­stant can therefore be applied to the permittivity ofpolyeth­ylene regardless offrequency. A large volume of data 11.12 for polyethylene complies with the equation E = 2.276 + 2.01 (p - 0.92(0), wherep is the density in glml. This equation illustrates that the permittivity of polyethylene depends on its density. The density increases with pressure and de­creases with temperature; thus the preceding expression is in good qualitative agreement with our experimental results.

Using our method, the study oflow-density polyethyl­ene with different concentrations of antioxidants can give some information leading to the improvement of this material.

The authors would like to acknowledge useful discus­sions with Y. Le Calvez and P. Viros (CNET Lannion) and the financial support of the Centre National d'Etudes des Telecommunications .

's. Matsuoka and L. D. Loan, presented at the First International Confer­ence on Plastics in Telecommunications, London, 1974Iunpublished).

2J. Farenc These de 3e Cycle, Universite Paul Sabatier, 1974Iunpublished). 'T. Barrie, Proc. IEEE 113,1849 (1966). 4A. Kakimoto, M. Ochi, and Matsushita, Rev. Sci. Instrum. 46, 1338 \1975).

'Bui Ai, D. Lebarbier, Hoang The Giam, J-c. Bapt, and M. Farzaneh, Rev. Sci. Instrum. 50, 5 \1979).

"L. Hartshorn and W. H. Ward, JIEE 79,597 (1936). 7J. T. Barrie, Proc. IEEE 112, 408 \1962). "W. Redish and K. A. Buckingham, Proc. IEEE 118, 225 \1971). 9 ASTIM D-150-70 standard testing for ac loss characteristics and dielec­tric constant of solid electrical insulating materials.

10M. Farzaneh and P. Destruel, Rev. Sci. Instrum. lin press). "V. L. Lanza and D. B. Herrman, J. Polym. Sci. 28, 622(1958). "D. W. Call, in Polyethylene, edited by A. Renfrew and P. Morgan (Inter­

science, London, 1960), Chap. 7, p. 147.

Communications 526

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