CA1046754A - Dielectric system for an electrical apparatus - Google Patents

Abstract

Abstract of the Disclosure An electrical apparatus, such as a capacitor, having an improved dielectric system. The dielectric system includes a polymeric film impregnated with low molecular weight polybutene having an average number molecular weight in the range of 300 to 500. The dielctric system has improved dielectrical properties and the polybutene is biodegradable which minimizes the pollution of the atmosphere if the dielectric liquid is exposed to the atmosphere. Further extended service life can be achieved by the addition of a cyclohexyl amine to the liquid dielectric.

Description

lQ46754 Background of the Invention Liquid dielectric compositions are used in various types of electrical apparatus, such as capacitors, condensor bushings, transformers, cables and the like. In the construction of capacitors, such as power factor correction capacitors, capacitor packs are formed of alternate layers of metal foil and a dielectric material which is impregnated with the liquid dielectric It is tesirable that the liquid dielectric have a high dielectric con-stant, maintain a low dissipation factor and be compatible with other materials in the capacitor structure Furthermore, the liquid dielectric must be capable of withstanding elevated and fluctuat-ing temperature, pressure and voltage stress conditions over the entire operational life of the capacitor.
In the past, various types of liquid dielectrics have been used in capacitors such as polychlorinated diphenyl, castor oil, mineral oil, silicone oil, and the like. Of the commonly used liquid dielectrics, polychlorinated diphenyl, such as tri--chlorodiphenyl, has been the most widely used in capacitor applications~
While the polychlorinated diphenyls produced an effect-ive electrical dielectric system for a capacitor, their usage ~as provided certain ecological problems in that the polychlorinated diphenyls are virtually non-biodegradable with the result that if leakage or rupture occurs in the capacitor casing, or if the capacitor is discarded as obsolete, the polychlorinated diphenyl w~11 remain as a pollutant in the environment and will not degrade to any appreciable extent even over extended pexiods of time.
Because of the ecological problems there has been increased actlvity in an attempt to develop a replacement for the polychlorinated diphenyls as a capacitor impregnant. Any sub-1~46754stitute impregnant should be biodegradable and have dielectric properties and performance characteristics comparable to those of the polychlorinated diphenyl.
While higher molecular weight polybutene, having a molecular weight of over 800 has had some limited use in the past as a liquid dielectric in electrical cables, polybutene has not been used in high stress electrical capacitors for use in power factor correction applications for several reasons. First, the relative dielectric constant of polybutene is about 2.10 to 2.25 compared to about 5.9 for trich?orodiphenyl. In a capacitor using all paper, or a combination of paper and polyolein film, as the solid dielectric material, a substantial amount of capacitance i~ lost due to the lower relative dielectric constant of the polybutene.
Secondly, polybutene tends to generate gas under con-ditions of aging at temperatures above room temperature and the development of gas tends to shorten the life of the capacitor by giving rise to corona discharges. It is also believed that the polybutene depolymerizes under high electrical stress, which can give rise to corona discharges and early dielectric failure.
However, higher molecular weight polybutene has found use in th~
past in the manufacture of cables, due to the fact that with cables it is desirable to have low capacitance, and the stresses on the 8ystem are considerably lower.
Summary of the Invention , The invention relates to an electrical apparatus, such as a capacitor, having a dielectric system with improved dielectric p~operties. The dielectric system is formed of a polymeric film, 6uch as polypropylene or polyethylene, which is impregnated with low molecular polybutene having an average number molecular weight o~ 300 to 500 10 46 7 ~ 4 With the use of the low molecular wei~ht polybutene, the rate of impregnation of the polymeric film is increased over conventional systems, with the result that the processing time for fabrication of the capacitor is ~ubstantially reduced.
As a further advantage, the dielectric system utilizing the polymeric film and the polybutene results in extremely low dielectric losses. For example, the losses are about one-fourth of the losses of a paper-film capacitor impregnated with tri-chlorodiphenyl.
As the polybutene is generally biodegradable it will decompose into harmless compounds when exposed to the atmosphere through leakage or rupture of the capacitor casing and there are no determined adverse effects on the environment.
The invention also offers a lower cost product in that the cost of polybutene is substantially less than that of the polychlorinated diphenyls presently used in the art.
Further improvement in the stability of the dielectric 8ystem can be achieved by the addition of 0.1% to 10% by weight of a cyclohexyl amine, such as dicyclohexylamine, to the poly-butene. The cyclohexylamine acts as a neutralizing agent or scavenger, serving to neutralize decomposition products that ar-e released fro~ or generated by, the liquid dielectric or other materials in the capacitor during its operation, thereby provid-ing a substantially longer service life, A further increase in the rate of impregnation can be achieved by the addition of trichlorobenzene to the liquid diel-ectric composition in an amount up to 20% by weight of the com-position. The trichlorobenzene acts to lower the viscosity of the liquid dielectric, as well as its pour point, and thereby further improve the impregnation characteristics.

1~46754 01 In addition, anti-oxidants, such as butylated 02 hydroxy toluene, or di-tert-butyl-p-cresol can be 03 incorporated in the liquid dielectric composition in an 04 amount up to 15% by weight and serve to improve the corona 05 extinction characteristics of the dielectric system.
06 More generally, the invention is an electrical 07 apparatus comprising a pair of electrical conducting 08 elements situated in spaced relation with respect to each 09 other and being adapted to provide an electrical potential therebetween. A dielectric system is interposed between the 11 elements, the dielectric system comprising a layer of 12 polymeric material and a liquid dielectric impregnated into 13 the polymeric material. The liquid dielectric is comprised 14 of polybutene having an average number molecular weight in the range of 300 and 500 and containing from 0.01% to 10% by 16 weight of a cyclohexylamine.
17 In another embodiment, the inventive electrical 18 capacitor is comprised of a sealed casing, with a capacitor 19 pack in the casing having a pair of electrically conductive strips and layers of a polymeric dielectric material wound 21 alternately with the conductive strips to form the capacitor 22 pack and a liquid dielectric impregnated into the polymeric 23 layers. The liquid dielectric is comprised of polybutene 24 having an average number molecular weight in the range of 300 to 500 and containing from 0.01% to 10% by weight of 26 cyclohexylamine.
27 In a further embodiment, the capacitor of the 28 last-noted embodiment utilizes layers of polypropylene as 29 the polymeric dielectric material. However, rather than the liquid dielectric utilizing cyclohexylamine, 31 dicyclohexylamine is used. The polypropylene layers contain 32 at least 1.0% by weight of the polybutene.

~ - 4 -1~46754 01 Other objects and advantages will appear in the 02 course of the following description.
03 Description of the Drawings 04 The drawings illustrate the best mode presently 05 contemplated of carrying out the invention.
06 In the drawings:
07 Fig. 1 is a perspective view of a typical 08 capacitor incorporating the dielectric composition of the 09 invention; and Fig. 2 is a perspective view of a capacitor pack.
11 Description of the Preferred Embodiment 12 Fig. 1 illustrates a typical capacitor comprising 13 an outer casing 1 composed of side walls 2, a bottom wall 3 14 and a cover 4. In service the casing is hermetically sealed and is provided with a small seal hole 5 through which the 16 dielectric liquid is introduced into the casing during 17 fabrication. In addition, a vacuum line can be connected to 18 the hole 5 for vacuum drying of the capacitor during 19 fabrication. A pair of terminals 6 project through the cover and are insulated from the cover.
21 A series of capacitor packs 7 are disposed within 22 the casing and each capacitor pack, as illustrated in Fig.
23 2, includes wound layers of metal foil 8, separated by 24 dielectric layer 9. Electrodes 10 are connected to the foil layers 8 and the electrodes of the various packs are 26 connected together in series for final connection to the 27 terminals 6.
28 Foil layers 8 may be formed of any desired 29 electrically - 4a -~;~3~l conductive material, generally a metallic materiaL such as aluminum, copper, and the like. The layers 8 may be in the form of 1at sheets, or the layers can be provided with a series of surface deformations formed by indentations on one side of the foil and corresponding elevations on theother side, as disclosed in United States patent 3,746,953.
The dielectric layers 9 are formed of sheets of poly-meric film, such as polypropylene, polyethylene, polyester, or ,.,~.
polycarbonate. In addition the dielectric layers may take the form of thin polymeric strips, such as polypropylene, having a layer of fine polymeric fibers adhering to one or both surfaces of the strip, as disclosed in United States patent 3,772,578. The term "all film" as used in the description means that the' dielectric layers 9 are formed of all polymeric materials including sheet ~S and fibrous types, although it is possible that other components of the capacitor can be formed of paper or non-polymeric materials, which would also be impregnated with electric dielectric composi-tions, According to the invention, the dielectric layers 9 are impregnated with a liquid dielectric composi'tion which consists of low molecular weight polybutene having an average number molecular weight in'the range of 300 to 500. The poIybutene hav-~ng a molecular weight in this range has a viscosity at 100F in D the range of ioo to 9ooo ssu, and has a viscosity at 210F in the range of 3~ to 150 ssu.
In the past, higher molecular weight polybutene having an average number of molecular weight of about 800 to 1400'has been used in the production of cables. However, the polybutene has not been successully applied to the production of capacitors.
Xn high stress, power factor capacitors, it is desirable to have a reasonably matched system with the dielectric constants of both the solid and liquid dielectrics being similar Paper has a tielectric constant of about 6.7, whlle in the case of high molecular weight polybutene, the dielectric constant is about 2.1, and thus no balanced dielectric system can be obtained with paper and polybutene. Utilizing high molecular weight polybutene with 8 paper dielectric results in poor performance at high stresses due to the fact that the polybutene depolymerizes, resulting in a lowering of the viscosity of the liquid and the eventual formation of gas pockets. The gas pockets ionize under stress and produce corona discharges and dielectric failure. Because of this, the h~gh molecular weight polybutene has been used in combination with all-paper or paper-film systems only in cables which are normally subjected to low stresses The higher molecular weight polybutene, as has been used ln the past with all-paper or paper-film systems in cables, has : not been employed in an all-film system in a capacitor due to the fact that adequate impregnation of the film could not be achieved.
~owever, in accordance with the invention, it has been found that when using a lower molecular weight polybutene, having an average number molecular weight in the range of 300 to 500, - catisfactory impregnation of an all-film solid dielectric can be - achieved and the resulting dielectric system has substantially improved dielectric properties over all-film systems impregnated with conventional liquid dielectrics, such as polychlorinated diphenyl.
The polymeric film is impregnated by the polybutene by -means of diffusion. When the polybutene contacts the film, poly-butene moleculcs enter the film. ~nce in the film, the liquid molecules migrate from regions o~ high concentrations to regions o low concentration until equilibrium is achieved. It has been i046754 recognized that at least 4% or more hy weight of the liquid dielectric must penetrate the fLlm to provide adequate impregna-tion. Using the low molecular weight polybutene in combination with polypropylene film at a temperature o~ 110C, it has been found that 18% by weight of the polybutene impregnated the film by d~ffusion. The low molecular weight polybutene will more readily impregnate an all-film system than conventional impreg-nants. This increase in the rate of impregnation is related to the surface energy of the polybutene and is also dependent at least in part on the relatively low viscosity of the polybutene.
An increase in the rate of impregnation can result in a substan-tial time saving in the processing or fabrication of the capacitor.
The combination of the low molecular weight polybutene with the polymeric film provides corona starting voltage (CSV) comparable ~ that of a system utilizing trichlorodiphenyl and polymeric film. However,the polybutene-polymeric film system has substantially lower dielectric losses than an all-film system i~pregnated with a trichlorodiphenyl.
. The polybutene is substantially fully biodegradable mean-ing that if it should be exposed to the environment because of leakage or rupture of the casing, or through discard of obsolete capacitors, the polybutene will decompose into a harmless compound and there will be no significant adverse environmental effect.
Thus, no pollution of the environment has been found to exist through use of the polybutene as the liquid dielectric.
The capacitor, as illustrated in the drawings, can be fabricated by standard procedures, in w~ich the casing containing the capacitor pack is initially vacuum dried to remove air and moisture and the liquid dielectric composi~ion is separ~tely dried.
The liquid dielctric is then introduced into the capacitor and 1~46754 permitted to ~oak under vacuum for an extended period in order to completely impregnate the dielectric layers 9 with the liquid tleiectric composition. Following this period of soaking,-the unit iQ sealed.
S During operat~on of the electrical apparatus or capacitor, the dielectric system may decompose if subjected for Iong periods to low stress, to elevated temperatures, or to the ~ction of reactive chemical agents. The decomposition products deteriorously effect the dielectric system and can lead to prema- 10 ture breakdown and failure of the capacitor. In the past, neutrslizing agents or scavengers have been used to neutralize the decomposition products, thereby improving the dielectric properties and service life of the capacitor. The scavengers have taken the form of epoxide compounds, such as 1,2,-epoxy-3-phenoxypropane; bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate;
l-epoxyethyl-3,4-epoxycyclohexane; 3,4-epoxycyclohexylmethyl-3,4,-epoxycyclohexanecarboxylate; 3,4-epoxy-6-methylcyclohexylmethyl-3,4,-epoxy-6-methylcyclohexanecarboxylate; and 3,4-epoxy-6- .
methylcyclohexane oxylate; and mixtures thereof.
In accordance with the invention, the dielectric liquid can include from 0.1% to lOZo by weight of a cyclohexylamine which acts to prevent the decomposition of the dielctric or acts as a scavenger which reacts with decomposition producte to insure greater reliability. The addition of the cyclohexylamine not only produces greater reliability in a capacitor impregnated with polybutene, but results in lower dielectric losses and a higher stress capability.
The preferred cyclohexylamine is dicyclohexylE~ine which is recognized to have the ollowing formula:

1~46754 ~ H2 CH ~ H ~ 2 ~ CH2 CH2 ~ / CH - N - H ~ ~ H2 From the above formula it can be seen that dicyclohexyl-S amine has a symmetrical structure which i9 particularly desirablein that a non-symmetrical structure will create greater electrical losses in the system.
Other cyclohexylamines which can be used are:
N-ethylcyclohexylamine; N-isopropylcyclohexylamine; N-(2-hydroxy-ethyl) cyclohexylamine; N-(2-cyanoethyl~ cyclohexylamine;
N-(3-aminopropyl) cyclohexylamine; N-cyclohexyl-'~- alanine;

2-cyclohexylamino-1-phenylethanol; N,N-dimethylcyclohexylamine;
N-phenylcyclohexylamine; N-cyclohexylpiperidine; N-methyleyclohexyl-amine; N-methyldicyclohexylamine; polyethoxylated cyclohexylamines, a ~ omocn-E-2, E-5, E-10, E-15, E-20, and X-25; N-cyclohexyl-morpholine; and N,N' dicyclohexylthiourea, hereinafter referred to in the specification and claims as "Group A'.' The liquid dielectric liquid can also include from about . 0.3% by weight to 20% by weight of trichlorobenzene which acts to lower the viscosity of the dielectric liquid and also lower the pour point. By lowering the viscosity and pour point, the ~mpregnation of the solid dielectric material is improved.
It is preferred to employ 1,2,4-trichlorobenzene which i8 liquid at low temperatures, but the other two isomers of ~5 trichlorobenzene, which are solid at room temperature, can also be used as the additive, if desired.
In the operation of a capacitor it is important that the dielectric system not be subjected to long periods of corona discharges. Corona discharges are very deterious to the dielectric system and can result in premature breakdown and 1~467S4 ailure~ of the capacitor~ Whlle a capac~tor is designed so as not to operate with the presence of corona discharges, switching surges and the like very often raise the stress on the dielectric into the corona region. When the switching surge has terminated, it S i8 necessary that the corona discharges also ext~nguish.
~ To improve the corona discharge characteristics, the dielectric liquid can contain from 0.05% to 15% by weight and preferably from 0.10 to 5% by weight of an antioxidant, such as butylated hydroxytoluene or di-tert-butyl-p-cresol. These materials act to raise the coronaextinction voltage and thereby ~'decrease the time that the dielectric system is'in corona.
The follo~ing examples illustrate the invention:
EXAMPLE
A series of small sample capacitors were constructed of two sheets of 0.005 inch polypropylen~ film ~etween sheets of aluminum foil~ One group of samples was impregnated with poly-butene having an average number molecular weight of 330, as the liquid dielectric, while a second group of identical samples D was impregnated with trichlorodiphenyl containing 0 5 ~/O by weight of an epoxide additive, bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate.
The following table lists the representative data of the two system;after impregnation,and after operation at 1000 hours at 1200 volts and after 1000 hours of operation at 1500 volts.
. TABLE

. . After After 1000 Hrs. After 1000 Hrs .Im~rePnation at 1200 Volts at 1500 Volts CSV in D F CSV in D.F c~r~ D.F.
Volts in % Volts in % Volts in %
_, . . .
rrlchlorO-Diphenyl Plus an 2,370 .270 2,270 .077 2~320 .060 Epoxide Additive . .. ... ._ _ Polybutene 2,280 021 2,110 .005 2,370 010 -10- , .

`1~46~754 From the above Table lt can be seen that the corona starting voltages (CSV) for both sets of samples were comparable both after impregnation and after operation at both 1200 volts and 1500 volts for 1000 hours, However, the dielectric losses for the samples impregnated with polybutene were considerably lower than the dielectric losses for ~he samples impregnated with the trichlorodiphenyl. This data clearly Lndicates that the samples utilizing polybutene do not deteriorate when under electrical stress, as was recognized in the past when high molecùlar weight 0 polybutene was utilized with paper in a capacitor construction.
EXAMPLE 2.
A series of tests were conducted to show the advantage of incorporating dicyclohexyl amine as a scavenger with the poly-butene. In this test a series of small capacitor samples were constructed having a dielectric layer of two sheets of 0,005 inch high density bi-axially oriented polypropylene film impregnated with polybutene. A second series of identical samples were pre-pared except that the dielectric liquid contained 0.2% by weight of dicyclohexylamine. After 1000 hours of operation at 1800 volts two of the six.samples containing only polybutene as the liquid dielectric had failed and a third had a sever increaee in dissipa-tion factor. Of the six samples containing the dicyclohexylamine in combination with the polybutene, none of the six samples had failed during the test period and none of the samples showed any deterioration in loss characteristics or corona starting voltages, ~hereby indicating an increase in stability achieved through the use of the dicyclohexylamine, XAMPLE 3, A series o small capacitor samples were constructed of two sheets of 0.0005 polypropylene film between aluminum foil. A

~ "

~046754 group of th~ samples was impregnatcd with trichlorodiphenyl containing ~,5/~ by weight of an epoxide scavenger, bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate, while a second group of samples was impregnated with polybutene ha~ing an average number molecular weight of 330, and a third group of samples was impregnated wi~'n polybutene containing 15% by weight of trichlorobenzene andO.075%
by weight of an epoxide scavenger, bis(3,4-epoxy-6-methyl~yclo-hexylmethyl) adipate. Each group of samples was tested at -45C, OCC, 30C and 90C, and the result of the tests are shown in the following table:
~E II
-4~C 0C 30C 1 90C
CSV D.F. CSV D.F ~~ CSV D.F. I
Description in Volts in % in Volts ,in % in Volts in~O in Yolts ~in %
.
Trichloro-Diphenyl plus an Epoxide 1,7001,15 2,4000.19 2,300 0.04 2,7000.07 Additive Polybutene 1,800.024 1,900.008 2,400 .012 ~,200.025 Polybutene plus 15% Over Over . trichloro- 2,500.0593 2,700.0082 2,700 .0045 2,700.0187 benzene . _ , As noted from the results shown in ~able II, the CSV o the samples impregnated with trichlorodiphenyl and polybutene are comparable throughout the entire operating range, although the polybutene samples had considerably lower dielectric losses.
The addition of the trichlorobenzene to the polybutene produced a higher CSV over the entire operating range. The ' ~ dielectric losses are comparable to those of the samples impreg-nated with the polybutene alone, but are considerably lower than the samples impregnated with the trichlorodiphenyl.
The above tes~ da~a indicates ~hat the capacitor samples ~0 impregnated with polybutene have a CSV similar to that of a system ' .

- ' ' '' ' '~ 'I

104675~
utilizing chlorinated diphenyl but have substantially lower dielectric losses over the entire operating range, which is of particular importance when the dielectric liquid is to be used in a capacitor.
S Furthermore, the liquid dielectric of the invention is biodegradable so that if it i8 exposed to the atmosphere it will decompose over a period of time, thereby preventing any permanent pollu~ion of t e env ronme~

.

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Claims (16)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electrical apparatus, comprising a pair of electrical conducting elements situated in spaced relation with respect to each other and being adapted to provide an electrical potential therebetween, and a dielectric system interposed between said elements, said dielectric system comprising a layer of polymeric material and a liquid dielectric impregnated into said polymeric material, said liquid dielectric comprising polybutene having an average number molecular weight in the range of 300 and 500 and containing from 0.01% to 10% by weight of a cyclohexylamine.

2. The apparatus of claim 1, wherein the liquid dielectric contains from 0.3% to 20% by weight of trichlorobenzene.

3. The apparatus of claim 1, wherein the liquid dielectric contains from 0.05% to 15% by weight of a compound selected from the group consisting of butylated hydroxy toluene and ti-tert-butyl-p-cresol.

4. The apparatus of claim 1, wherein the cyclohexylamine is dicyclohexylamine.

5. The apparatus of claim 1, wherein the cyclohexylamine is selected from the group consisting of dicyclohexylamine; N-ethylcyclohexylamine; N-isopropylcyclohexylamine; N-(2-hydroxy-ethyl) cyclohexylamine; N-(2-cyanoethyl) cyclohexylamine;
N-(3-aminopropyl) cyclohexylamine; N-cyclohexyl-.beta.-alanine;
2-cyclohexylamino-1-phenylethanol; N,N-dimethylcyclohexylamine;
N-phenylcyclohexylamine; N-cyclohexylpiperidine; N-methylcyclo-hexylamine; N-methyldicyclohexylamine; polyethoxylated cyclohexylamines, abbomeen E-2, E-5, E-10, E-15, E-20 and E-25;
N-cyclohexyl morpholine; and N,N' dicyclohexylthiourea.

6. The apparatus of claim 1, wherein said polymeric material has impregnated therein at least 1.0% by weight of said polybutene.

7. The apparatus of claim 1, wherein said polymeric material is a polyolefin and the electrical connecting elements are metal foil.

8. The apparatus of claim 7, wherein the metal foil has surface deformations formed by indentations on one side of the foil and corresponding elevations on the other side of the foil.

9. The apparatus of claim 7, wherein the polyolefin layer comprises a film of polyolefin and a multiplicity of polyolefin fibers bonded to at least one surface of said film.

10. An electrical capacitor, comprising a sealed casing, a capacitor pack in the casing having a pair of electrically conductive strips and layers of a polymeric dielectric material wound alternately with the conductive strips to form the capacitor pack and a liquid dielectric impregnated into said polymeric layers, said liquid dielectric comprising polybutene having an average number molecular weight in the range of 300 to 500, and containing from 0.01% to 10% by weight of cyclohexylamine.

11. The capacitor of claim 10, wherein the liquid dielectric contains from 0.3% to 20% by weight of trichlorobenzene.

12. The capacitor of claim 10, wherein the liquid dielectric contains from 0.05% to 15% by weight of a compound selected from the group consisting of butylated hydroxy toluene and di-tert-butyl-p-cresol.

13. Th capacitor of claim 10, wherein the cyclohexylamine is dicyclohexylamine.

14. The capacitor of claim 10, wherein the cyclohexyl-amine is selected from the group consisting of dicyclohexyl-amine, N-ethylcyclohexylamine; N-isopropylcyclohexylamine; N-(2-hydroxyethyl) cyclohexylamine; N-(2-cyanoethyl) cyclohexyl-amine; N-(3-aminopropyl) cyclohexylamine; N-cyclohexyl-.beta.-alanine; 2-cyclohexylamino-1-phenylethanol; N,N-dimethylcyclo-hexylamine; N-phenylcyclohexylamine; N-cyclohexylpiperidine;
N-methylcyclohexylamine; N-methyldicyclohexylamine; poly-ethoxylated cyclohexylamines, abbomeen E-2, E-5, E-10, E-15, E-20, and E-25; N-cyclohexylmorpholine; and N,N' dicyclohexyl-thiourea.

15. An electrical capacitor, comprising a sealed casing, a capacitor pack in the casing and having a pair of electrically conductive strips and layers of polypropylene wound alternately with the conductive strips to form the capacitor pack, said polypropylene layers being impregnated with a liquid dielectric comprising polybutene having an average number molecular weight in the range of 300 to 500, and containing from 0.01% to 10% by weight of dicyclohexylamine, said polypropylene layers containing at least 1.0% by weight of said polybutene.

16. The capacitor of claim 15, wherein the conductive strips are metal foil having surface deformations formed by indentations on one side of the foil and corresponding elevations on the other side of the foil.