AU1544499A - Power cable with water swellable agents and elongated metal elements outside cable insulation - Google Patents

Description

,w Our Ref: 717457 P/00/01i Regulation 3:2 -tj

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): Pirelli Cable Corporation 325 Columbia Turnpike Florham Park New Jersey 07932 UNITED STATES OF AMERICA DAVIES COLLISON CAVE Patent Trade Mark Attorneys Level 10, 10 Barrack Street SYDNEY NSW 2000 Address for Service: Invention Title: Power cable with water swellable agents and elongated metal elements outside cable insulation The following statement is a full description of this invention, including the best method of performing it known to me:-

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5020 P'.:WDOCs.AMDsPECD717457n.PI -599 1 -1- POWER CABLE WITH WATER SWELLABLE AGENTS AND ELONGATED METAL ELEMENTS OUTSIDE CABLE INSULATION This application is a continuation-in-part of copending application Serial No. 287,486 filed Dec. 20, 1988 and entitled "Power Cable with Metallic Shielding Tape and Water Swellable Powder" which is a continuation-in-part of copending application Serial No.

068,670, filed July 1, 1987 and entitled "Filling Compound for Multi-Wire Conductor of an Electrical Cable and Cables Including Such Compound" which is a division of application Serial No. 864,196, filed May 16, 1986, now U.S. Patent No. 4,703,132, the disclosures of which are incorporated herein by reference.

Background of the Invention High voltage electrical power cables having at least one elongated metal element, such as metal tape, straps or wires, disposed around the cable insulation, either extending parallel to the cable axis or helically wound around the insulation, are well known in the art. Generally, such cables include a central stranded conductor with a semi-conducting shield therearound which is covered by a layer of insulation. Insulation shielding, in the form of a semi-conducting layer, is around the insulation, and the elongated metal elements are disposed around the insulation shield. A protecting jacket is disposed around the metal elements.

It is also known in the art that when the insulation of such cables is exposed to S: moisture, such as when they are installed underground, "electrochemical trees" are formed in the insulation which shorten the life of the cable.

Furthermore, attempts have been made to prevent the formation of such "trees" by introducing a sealant between the strands of the conductor and between the insulation shield and the metallic shielding tape. See U.S. Pat. Nos. 3,943,271 and 4,130,450. However, it .has been found that the mere introduction of sealant into such spaces is not entirely satisfactory when the sealant is merely asphalt/rubber or a polyester compound which is not water swellable.

For example, voids may be formed in the sealant during the application thereof or may be formed when the cable is punctured accidentally. Furthermore, the components of such t iz~, r.NWPmOC.VA.%f\SPECU71V7 7 PTR p a cable, being made of different materials, have different coefficients of expansion, and the components are subjected to different or varying temperatures during manufacture, storage and/or operation of the cable which can cause the formation of voids.

In addition, the straps or wires are usually spaced from each other in the direction circumferentially of the insulation which can result in spaces between the straps or wires for the migration of moisture. When the tape is wound with the edge portions of the overlapping, there is a small space between the overlapping tape and the insulation shield adjacent to the edge of the underlying tape and there may be some spaces between the overlapping edge portions of the tape. If the tape is wound with slightly spaced edge portions, there are spaces between the edge portions for the migration of moisture. Even if it is intended that the tape, which is relatively thin, be wound with abutting edge portions, spaces between the edge portions do occur because of manufacturing difficulties and tolerances. Such spaces may not be completely filled by the sealant when it is applied, but even if they are, voids can develop at such spaces when the cable, or its components, is subjected to temperature changes.

Any such spaces or voids form locations for the ingress of moisture which can cause the formation of the deleterious "electrochemical trees" in the cable insulation, and the conventional sealants used in the cables, being unaffected physically by water, cannot eliminate such voids.

Brief Summary Of the Invention The invention relates to improvements in cables of the type having at least one elongated metal element disposed outwardly of the cable insulation.

In the preferred embodiment of the invention, in addition to treating the conductor 25 with a water swellable material as described in said U.S. Pat. No. 4,703,132, a water swellable material, by itself or as part of the filling compound described in the last-mentioned said patent, is included in the spaces outside the insulation shield where voids can form.

Thus, the water swellable material can be between the insulation shield and the elongated metal elements or the turns of a tape, between the elongated metal elements and/or between the elongated metal elements or turns of a tape and the cable jacket, and preferably, is in all r r r ~r r ~r rrr r~ r r r rr r d.

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i: i ~w~mc~s~-nmr rr P- WPRKTASvD'SPEC1L7174S7.PIR 31b9 -3such places. In this way, the voids are filled by the water swellable material which absorbs moisture and swells preventing further migration of the moisture.

Brief Description of the Drawings The objects and advantages of the invention will be apparent from the following detailed description of the presently preferred embodiments thereof, which description should be considered in conjunction with the accompanying drawings in which: Fig. 1 is a cut-away, perspective view of a cable of the invention including metal tape wound helically around the semi-conducting insulation shield; Fig. 2 is a fragmentary cross-sectional view of a modified embodiment of the cable shown in Fig. 1; Fig. 3 is a fragmentary cross-sectional view of a water swellable tape forming part of the embodiment shown in Fig. 2; Figs. 4 and 5 are fragmentary cross-sectional views of further modified embodiments of the cable shown in Fig. 1; Figs. 6-8 are similar to Figs. 1, 2, 4 and 5 but the helically wound metal tape is replaced by wire serving in the cable; and i" Figs. 9-12 are similar to Figs. 1, 2, 4 and 5 but the helically wound metal tape is replaced by metal straps.

:e Detailed Description of the Invention Although the principles of the invention are applicable to high voltage power cables of a different type, the invention will be described in connection with a known cable structure which normally comprises, as a minimum: S 25 A central conductor of stranded wires of a good conductivity metal such as copper, aluminum, copper alloys or aluminum alloys; A conductor shield around the conductor which usually is a layer of .:semi-conductive plastic which has been extruded over the conductor; S* A layer of polymeric insulation around the conductor shield and which has been extruded over the conductor shield; iT-- WOcSA.MB' TECTV7174i.R- 5-2J -4- An insulation shield around the insulation and which usually is a semi-conductive plastic extruded over, or coated on, the layer of insulation; A metallic shield around the insulation shield and which usually is an elongated element, or elongated elements, in the form of copper or aluminum tape, straps or wires wrapped helically around the insulation shield; and A jacket around the metallic shield and which usually is a polymeric material extruded over the metallic shield.

The cable may have a fewer or greater number of layers and, for example, it may have protective layers outside the jacket, such as helical wire serving, corrugated armor, etc.

which is used in the art depending upon the conditions under which the cable is used. Also, the jacket may be of a material other than a polymeric material, and in cases where the water-swellable material is included in a semi-conductive filler which engages the conductor or the outer surface of the insulation, the conductor shield and the insulation shield, respectively, may be omitted.

respectIn U.S. Pat. Nobe. 4,703,132 referred to hereinbefore, high voltage power cables having the interstices of the stranded conductor filled with a filling compound containing water swellable particles for preventing the migration of water along the conductor and for preventing contact of moisture with the cable insulation and a preferred filling compound are S.:I described. Whenever a filling compound is referred to in this application, the preferred filling compound is the filling compound described in said Patent, but other filling compounds containing a water swellable material can be used. Said Patent also describes water swellable particles, and in the cable of the invention, the preferred water swellable particles are those described in said Patent although other water swellable particles can be used.

Said U.S. Pat. No. 4,703,132 and said application Serial No. 287,486 are directed to cable areas of particular concern with respect to the affecting of the cable insulation. A demand has arisen for a high voltage cable which is "fully sealed" cable, i.e. a cable which has all otherwise empty spaces within the cable jacket filled with a water swellable material, either alone, in a filling compound or as part of a tape. The present invention is directed the prevention of water contact with the cable insulationby way of other portions of the cable and to a fully sealed cable.

|T "i It is knownin the art that if the diameter of the insulation varies, due to the presence Sof layers of material outwardly of the insulation or otherwise, the dielectric, or voltage breakdown, strength of the insulation is lowered, paticularly where the diameter of the insulation is smaller. Standards have been proposed for the maximum permissible indentation of the insulation.

i When there is metallic shielding outside the insulation, indentations in the cable Sinsulation can be caused when the jacket is extruded tightly over the metallic shielding to prevent water ingress. MYLAR tape has been applied over the metallic shielding, intermediate such shielding and the jacket, in an attempt to reduce such indentation of the insulation. The prevent invention is also directed to minimizing such indentations of the insulation which is accomplished by the use of water swellable material intermediate the jacket and the insulation. In this way, the jacket need not tightly enclose the layers therewithin to prevent water ingress. Instead, the jacket can be applied so that the significant indentations in the insulation are not caused, and water ingress is prevented by the water swellable material. Thus, the jacket can be applied over the metallic shield, e.g. tape, straps or wires, in a known manner which will prevent significant compression of the insulation.

Figs. 1, 2, 4 and 5 illustrate embodiments of the cable of the invention in which the 1: insulation is encircled by a helically wound metal tape, such as a copper or aluminum tape.

In Fig. 1, a cable 1 comprises a conductor 2 of stranded wires of copper or aluminum or S 20 alloys thereof. Preferably, a layer 3 of semi-conductive filling compound containing water S:..swellable particles encircles the conductor 2 and fills any spaces between the wires of the conductor 2, but alternatively, the conductor 2 may merely have the particles themselves filling such spaces and on the surface of the wires of the conductor 2. As a further, but less preferable alternative, the layer 3 and the particles may be omitted.

25 The preferred electrical cable conductor filling compound comprises a polymer which S.can be readily pumped at elevated temperatures about 100 0 C. Normally, this means that the polymer will be a low molecular weight polymer such as low molecular weight polyisobutylene rubber and a low molecular weight copolymer of isobutylene-isoprene rubber and can be a mixture of ethylene propylene rubber compounded with a substantial amount of carbon black as described in said U.S. Pat. Nos. 4,095.039 and 4,145,567 or other suitable Li

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Wp, ocSAMDSPE ,71"'i 57PIr -5219 -6mineral fillers. Other polymers having such characteristics will be apparent to those skilled in the art. A polymer which has been found to be particularly suitable is low molecular weight LM polyisobutylene sold by Exxon Chemical Americas, P.O. Box 3272, Houston.

Tex. under the trade mark VISTANEX.

The preferred base polymer of the filling compound of the invention does not have any significant Shore A hardness. A test of determining whether or not the base polymer has acceptable properties is the Penetrometer Test incorporated in ASTM D5 Penetration of SBituminous Materials. The 100 grams needle penetration value at 25"C. should be in the range from 110 to 180 tenths of a millimetre.

The material which swells or expands in the presence of water should be a powder having the following properties: The powder has to be substantially insoluble in water.

the ph of the water dispersion of the powder obtainable by dispersing 1 gr. of powder in 200 cm 3 of bi-distilled water should be in the range from 6.5 to The weight loss of the powder after heating at 105C. should be lower than 7%; The powder wetting time (corresponding to the time lapse between the moment the powder is put in contact with water and the moment at which the expansion and swelling begins) should be in the range of less than 1 to 10 seconds whether the water is tap water, industrial use water, or sea water; 20 The powder water absorbing capability expressed in cm 3 of water absorbed by 1 gr.

S. of powder should be in the range from 10 to 800 cen/gr. or greater. In particular, the Spowder capability in relation to industrial water should be in the range from 200 to 800 cm 3 /gr. or greater, while its capability for the absorption of sea water should be in the S range from 10 to 150 cm 3 gr. or greater; and S 25 The particle size of the powder should be less than 200 microns and preferably, at S: least 50% of the particles of such powder should have sizes less than 150 microns.

Examples of materials which may be used for the swellable powders are polyacrylates -"and polyacrylamides, by themselves or copolymerized with natural polymers such as amides and cellulose and the esthers of, methyl cellulose and cellulose ethers, such as carboxymethyl cellulose- A material which has been found to be especially suitable in the Type 1-550 *y *V P: HTDOCSAM.'SPECl'77457.PIR 5aS9 -7sodium polyacrylate formerly sold by the Grain Processing Corporation, Muscatine, Iowa and now sold by Absorbent Technologies Corporation, Muscatine, Iowa.

The weight of the powder to the weight of the resin (PHR) may vary over a fairly wide range, but preferably, the powder is present from an effective amount to the amount necessary to provide the desired results which can be determined empirically. Normally, the powder will be present in an amount of at least 0.5 PHR to not more than 50 PHR and preferably, is present in an amount in the range from 0.5 PHR to 20 PHR.

In the preferred embodiments of the invention, the filler material that fills all spaces of the stranded conductor, as illustrated herein, is a compound of low molecular weight polyisobutylene rubber or a low molecular weight copolymer of isobutylene-isoprene rubber.

To either of these isobutylene rubber materials 15 to 150 parts by weight of electrical conductive carbon black or graphite material or non-conductive mineral filler such as silica, talc, titanium dioxide, clay, is added for each 100 parts of the isobutylene rubber material.

The addition of the carbon makes the filler material semi-conductive. The addition of the carbon or non-conductive mineral fillers serves an important function in that it prevents flow of the isobutylene rubber material at temperatures up to 200°C. Thus the filler material can withstand temperatures encountered during heavy loads on the power transmission lines without softening and having its viscosity become so low that it will flow out of the cable at cable ends or flow lengthwise where the cable is on a substantial slope.

Some material can be added, if necessary, as a processing aid; for example, a 1 hydrocarbon oil, such as used in rubber compounding, or a chlorinated paraffin or isobutylene liquid plasticizer can be used to bring the isobutylene rubber compound to a pumping consistency without utilizing excessive heat. It is preferable, however, to use as little processing aid as possible or none at all when it is not necessary for obtaining a pumping consistency.

The disadvantages of the processing aids are that they may migrate into the insulation shield and cause swelling and a consequent reduction in the conductivity of the shield.

The amount of electical conductive carbon black or graphite material or mineral filler which is mixed with the isobutylene rubber material is from 15 to 150 parts by weight of the 7 30 filler to 100 parts of the isobutylene rubber compound; and the preferred range is from 15 to p xc AMD SPECT71T7457- -8parts. The 100 grams needle penetration of the preferred compound at 25 0 C. should be in the range of 50 to 100 tenths of a millimetre.

When particles of water sweliable powder are applied as a thin layer over one, several or all layers of the filling compound applied over the concentric layers of wires, the thickness of the particles of water swellable powder preferably is on the order of several tens to several hundreds of microns.

The layer 3 is encircled by a conventional, semi-conductive layer 4 of a plastic material extruded over the layer 3, the layer 4 forming a conductor stress control layer. The layer 4 is encircled by a layer 5 of polymeric insulating material extruded over the conductor stress control layer 4. A semi-conductive layer 6 of plastic material encircles the insulation layer 5 and can be extruded over the layer 5 or applied thereto as a coating. The layer 6 is an insulation stress control layer.

Preferably, a layer 7 of the filling compound with water swellable particles previously described, and preferably, semi-conductive, is extruded over the insulation stress control layer 6- However, sufficient sealing without the layer 7 can be obtained, and the layer 7 can be omitted. A metal shield, in the form of acopper or aluminum tape 8, is helically wound around the layer 7. Water swellable particles of the type previously described, and preferably, the sodium acrylate particles having a particle size of less than 200 microns, are applied to the outer surface of the tape 8 to form a layer 9 which encircles the tape 8. However, if the layer 7 is included and sufficient sealing without the layer 9 can be obtained, the layer 9 can be omitted.

SJ. The layer 9 of water swellable particles is encircled by a jacket 10, preferably, of S" extruded polymeric material.

The cable 1 described in connection with Fig. I can be used without further layers S. encircling the jacket 10, but under some conditions, it may be desirable to encircle the jacket 9 with one or more further layers, such as layers of bitumen andlor armoring in the form of helically wound steel wires or corrugated steel tape. These statemene also apply to the embodiments of the cables described hereinafter.

30 Also, in the embodiments of the cables described hereinafter, the conductor and layers *2 77-

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i' I coc, x[D SPE 71-14- 12.S of the cables up to and including the insulation stress control layer 6 can be the same as those described in connection with Fig. illusrated in Fig. by the The cable 11 illustrated in Fig. 2 differs from the cable i rm ed i i e f ill addition f a layer 12 of helically wound water swellable tapeite eite compound layer 7 and the metal tape 8. If desired, the layer 9 of waterswellable particles may be omitted in cable 11.

The waiter sweiable ae used for the layer 12 is a tape known in the art. One form o he tape is sold under the trade mark FIRET by Lantor BV in Veenedal, Holland and is illusated in enlarged cros-ec n ig. 3. The pe comprises a porous subtrate 3 of iluslrdr; sw ellable po w d er 14 is coated- 0 i n-woven plastic, e-ni bonded plastic fibers on which water eb 14.

The powder 14 is covered by a porous, non-woven plastic cover of water The cable 16 illustrated in Fig. 4 differs from the cable in that the layer 12 of water swellable tape is outside, rather than inside, the metal tape 8 and is intermediate the metal swellab a Ouide, r thi dsi, the layer 9 f water swellable particles can be tape 8 and the jacket 10. Again, if desired, the layer 9 of water swellable particles can be omitted. ,I 1 in that the positions of the

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!1 t The cable 17 illustrated in Fig. 5 differs trom mue I water swellable tape 12 and the water swellable particle layer 9 are interchanged, the tape 12 is radially outward, rather than radially inward, of the layer 9.

Figs. 6-8 illustrate cables of the invention similar to the ables desribed in onnection with the preceding figures except for the substitution of cpper wire serving for the metal tape 8. nd 19 which can be the same as iS

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Sanr In the cable 18 illustrated in Fig. 6, a rulig tV 2 but the filling compound for the layer 3, is in the intersties between the conductor wires 2 u can be omitted. The conductors 2 are encircled by a stress nt laer 4 hic in trn is 25 encircled by the insulation 5. The insulation 5 is encircled by the insulaion stress conrol layer 6. rentiallY spaced relation, -7I

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The wires 20 of the serving are helically wouna, m around the layer 5, are partially embedded in the extruded jacket 10 and are in contact with the layer 5. The wires 20 can be annealed copper wires.

The spaces between the wires 20 ar filled with water P WPDOC.AMDPECr L7T457.PIR-5.299 The cable 1 illustrated in Fig. 7 differs from the cable 18 illustrated in Fig. 6 in that the wires 20 are not embedded in the jacket 10, a layer 7 of the filling compound previously described and preferably, semi-conductive, is intermediate the insulation stress control layer 6 and the wires 20 and a layer of the water swellable tape 12 is intermediate the wires 20 and the jacket 10. If desired, the layer 7 can be omitted.

The cable 22 illustrated in Fig. 8 differs from the cable 21 illustrated in Fig. 7 in that the layer 9 of water swellable particles is replaced by the filling compound 7, preferably, semi-conductive and a separate layer 7 intermediate the wires 20 and the insulation stress control layer 6 is omitted. If desired, the layer of water swellable tape 12 can be omitted.

Figs. 9-12 illustrate cables of the invention similar to the cables previously described except that the metal tape 8 and the wires 20 are replaced by metal straps 23, such as copper straps. Thus, the cables 24, 25, 26 and 27 in Figs. 9, 10, 11 and 12, respectively, are the same as the cables 1, 11, 16 and 17 except for the substitution of the metal straps 23 for the metal tape 8. As described in connection with cables 1, 11, 16 and 17, certain layers can, if desired, be omitted in the cables 24, 25, 26 and 27.

It will be observed that in the embodiments described and which include water swellable material between the insulation and the jacket, it is not essential that the jacket tightly enclose the layers therewithin or enter into the spaces between the wires or straps, i.e.

the interior size of the jacket can be essentially equal to the exterior size of the elongated 20 elements so that compression of the elongated elements, and hence, indentation of the layers therewithin including the insulation, is prevented. Accordingly, the indentation of the insulation is reduced as compared to cables in which the jacket tightly encloses the layers therewithin, and the dielectric properties of the cables of the invention are improved as compared to the prior art cables.

Although preferred embodiments of the present invention have been described and illustrated, it will be apparent to those skilled in the art that various modifications may be made without departing from the principles of the invention.

Claims (27)

1. An electrical power cable comprising a stranded conductor formed by a plurality of wires stranded together, a semi-conductive stress control layer around said conductor, a layer of insulation around said stress control layer, a semi-conductive insulation shield around said insulation, said insulation shield having an outer surface of substantially constant cross-sectional radius and a metal shield which is disposed around said insulation shield and which is one of a helically wound metal tape, a plurality of metal straps and a plurality of metal wires, said metal shield having surfaces extending longitudinally of said cable and being adjacent to each other, and particles of a water swellable material at least at the adjacent surfaces of said metal shield.

2. An electrical power cable as set forth in claim 1 wherein said particles of water swellable material are distributed around the circumference of the surface of said insulation shield.

3. An electrical power cable as set forth in claim 2 wherein said particles of a water S 15 swellable material are admixed with an extrudable polymeric material and conductive particles in an amount sufficient to make the mixture semi-conductive.

4. An electrical power cable as set forth in claim 3 wherein said mixture has a 100 gram needle penetration value between 50 and 100 tenths of a millimetre at 25 0 C. and said particles Sof water swellable material have a size not greater than 200 microns.

5. An electrical power cable as set forth in claim 3 further comprising a jacket around said metal shield and particles of water swellable material intermediate said metal shield and said jacket.

6. An electrical power cable as set forth in claim 1 further comprising a jacket around said metal shield and wherein said particles of water swellable material are intermediate said metal shield and said jacket.

7. An electrical power cable as set forth in claim 1 wherein all otherwise empty spaced within said stress control layer contain water swellable particles.

8. An electrical power cable as set forth in claim 7 wherein said particles of a water swellable material are admixed with an extrudable polymeric material and conductive particles A in an amount to make the mixture semi-conductive. VO.C m 1DsP-i t -12-

9. An electrical power cable as set forth in claim 8 wherein said mixture has a 100 gram needle penetration value between 50 and 100 tenths of a millimetre at 25oC and said particles of water swellable material have a size not greater than 200 microns. An electrical power cable as set forth in claim 1 further comprising a jacket around said metal shield and wherein al otherwise empty spaces within said jacket contain water swellable powders. sw. An electrical power cable as set forth in claim 10 further comprising a layer of a water swellable tape intermediate said insulation shield and said metal shield.

12. An electrical power cable as set forth in claim 10 further comprising a layer of a water swellable tape intermediate said metal shield and said jacket.

13. An electrical power cable a3 set forth in claim I further comprising a jacket around said metal shield, said jacket being of an interior size which prevents compression of said metal shield sufficient to cause significant indentation of said insulation by said metal shield and wherein said particles of water swellable material are contained in any otherwise empty spaces between said jacket and said semi-conductive insulation shield.

14. An electrical power cable comprising a stranded conductor formed by a plurality of wires stranded together, a semi-conductive stress control layer around said conductor, a layer of insulation around said stress control layer, and a semi-conductive insulation shield around said insulation, and a metal shield which is disposed around said insulation shield metawhich is one of a helically wound metal tape, a plurality of metal straps and a plurality of said metal shield having surfaces extending longitudinally of said cable and being adjacent to each other, a layer of water swellable tape intermediate said metal shield and said insulation shield, and Sparticles of a water swellable material admixed with an extrudable polymeric material and S conductive particles in an amount sufficient to make the mixture semi-conductive at least at the adjacent surfaces of said metal shield.

15. An electrical power cable as set forth in claim 14 further comprising a jacket around said metal shield and particles of water swellable material intermediate said jacket and said metal shield. S16. An electrical power cable as set forth in claim 14 further comprising ajacket around lable tape and particles of water swellable material said metal shield and a layer of water swellable tape and particles i P-lP'ro\CS\MtDZSPEC 7m7457.PIR 5.2 13 intermediate said jacket and said metal shield.

17. An electrical power cable comprising a stranded conductor formed by a plurality of wires stranded together, a semi-conductive stress control layer around said conductor, a layer of insulation around said stress control layer, a semi-conductive insulation shield around said insulation, and a metal shield which is disposed around said insulation shield and which is one of a helically wound metal tape, a plurality of straps and a plurality of metal wires, said metal shield having surfaces extending longitudinally of said cable and being adjacent to each other, a jacket around said metal shield, a layer of water swellable tape intermediate said metal shield and said jacket, and particles of a water swellable material at least at the adjacent surfaces of said metal shield.

18. An electrical power cable comprising a stranded conductor formed by a plurality of wires stranded together, a semi-conductive stress control layer around said conductor, a layer of insulation around said stress control layer, a semi-conductive insulation shield around said insulation, said shield having an outer surface of substantially constant cross-sectional radius, and a metal shield formed by a plurality of metal wires wound helically around said insulation shield in circumferentially spaced relation, a jacket around said plurality of wires and particles of water swellable material adjacent said wires.

19. An electrical power cable as set forth in claim 18 wherein said particles of water swellable material fill all otherwise empty spaces between said jacket and said insulation shield. An electrical power cable as set forth in claim 18 wherein said particles of water swellable material are admixed with an extrudable polymeric material and conductive particles in an amount sufficient to make the mixture semi-conductive and wherein the mixture is intermediate said metal shields and said insulation shield.

21. An electrical power cable as set forth in claim 20 wherein said mixture has a 100 gram needle penetration value between 50 and 100 tenths of a millimetre at 25 0 C. and said particles of water swellable material have a size not greater than 200 microns.

22. An electrical power cable comprising a stranded conductor formed by a plurality of wires stranded together, a semi-conductive stress control layer around said conductor, a layer of insulation around said stress control layer, a semi-conductive insulation shield around said 7 P-.WPDOCSIAM.D'SECT 17457-PIR 512M 14- insulation and a metal shield formed by a plurality of metal wires wound helically around said insulation shield in circumferentially spaced relation, a jacket around said plurality of wires, a layer of water swellable tape intermediate said jacket and said metal shields and particles of water swellable material adjacent said wires.

23. An electrical power cable comprising a stranded conductor formed by a plurality of wires stranded together, a semi- conductive stress control layer around said conductor, a layer of insulation around said stress control layer, a semi-conductive insulation shield around said insulation and a metal shield formed by a plurality of metal wires wound helically around said insulation shield in circumferentially spaced relation, a jacket of polymeric material around said plurality of wires, said wires being at least partly embedded in said jacket and particles of water swellable material adjacent said wires.

24. An electrical power cable comprising a stranded conductor formed by a plurality of wires stranded together, a semi-conductive stress control layer around said conductor, a layer of insulation around said stress control layer, a semi-conductive insulation shield around said insulation and a metal shield formed of a plurality of metal wires wound helically around said insulation shield in circumferentially spaced relation, a jacket around said plurality of wires, a layer of water swellable tape intermediate said jacket and said metal shield, and particles of water swellable material adjacent said wires, said particles of water swellable material being admixed with an extrudable polymeric material and conductive particles in an amount S 20 sufficient to make the mixture semi-conductive and wherein the mixture is intermediate said wires and said insulation shield. S 25. An electrical power cable comprising a stranded conductor formed by a plurality of wires stranded together, a semi-conductive stress control layer around said conductor, a layer of insulation around said stress control layer, a semi- conductive insulation shield around said insulation, said shield having an outer surface of substantially constant cross-sectional radius, .I and a metal shield formed by a plurality of metal straps wound helically around said insulation shield in circumferentially spaced relation, said straps having their edges extending longitudinally of said cable and being adjacent to each other, a jacket around said plurality of straps, and particles of water swellable material adjacent said straps.

26. An electrical power cable as set forth in claim 25 wherein said particles of water r :1 p ,klVMcsrxU)ISPE4M717457.?IEL 5,109 swellable material fill all otherwise empty spaces between said jacket and said insulation shield.

27. An electrical power cable as se forth in claim 25 wherein said particles of water swellable material are admixed with an extrudable polymeric material and conductive particles in an amount sufficient to make the mixture semi-conductive and wherein the mixture is intermediate said metal shields and said insulation shield.

28. An electrical power cable as set forth in claim 27 wherein said mixture has a 100 gram needle penetratioh. value between 50 and 100 tenths of a millimetre at 25 0 C. and said particles of water swellable material have a size not greater than 200 microns.

29. An electrical power cable comprising a stranded conductor formed by a p!urality of wires stranded together, a semi-conductive stress control layer around said conductor, a layer of insulation around said stress control layer, a semi-cofnductive insulation shield around said insulation and a metal shield formed by a plurality of metal straps wound helically around said insulation shield in circumferentially spaced relation, said straps having their edges extending longitudinally of said cable and being adjacent to each other, a layer of water swellable tape intermediate said jacket and said straps, and particles of a water swellable material at least at the adjacent edges of said straps. An electrical power cable comprising a stranded conductor formed by a plurality of wires stranded together, a semi-conductive stress control layer around said conductor, a layer of insulation around said stress control layer, a semi-conductive insulation shield around said insulation and a metal shield formed by a plurality of metal straps wound helically around said insulation shield, said strap having their edges extending longitudinally of said cable and being adjacent to each other, a layer of water swellable tape intermediate said jacket and said metal shield, and particles of a water swellable material at least at the adjacent edges of said straps.

31. An electrical power cable comprising a stranded conductor formed by a plurality of wires stranded together, a semi-conductive stress control layer around said conductor, a layer of insulation around said stress control layer, a semi-conductive insulation shield around said insulation, said shield having an outer surface of substantially constant cross-sectional radius, a metal shield, disposed around said insulation shield and which is one of a helically wound X 1 Z I 6i 1 6 I i i ii- 8.. rHw~DOCS .DS P CIn"Pi'nLP-5p-99 -16- metal tape, a plurality of metal straps and a plurality of metal wires, said metal shield having surfaces extending longitudinally of said cable and being adjacent to each other, a jacket around said metal shield, a layer of tape intermediate said jacket and said insulation shield, and particles of a water swellable material filling any otherwise empty spaces within said ja32. An electrical power cable as set forth in claim 31 wherein said layer of tape is intermediate said insulation shield and said metal shield.

33. An electrical power cable as set forth in claim 31 wherein said layer of tape is intermediate said jacket and said metal shield. DATED this 5th day of February

1999. PIRELLI CABLE CORPORATION By Its Patent Attorneys DAVIES COLLISON CAVE w.as ea*