Power Cable With Mechanical Support Layer

Abstract

A power cable including: a conductor, an insulation system including an inner semiconducting layer arranged around the conductor, an insulation layer arranged around the inner semiconducting layer, and an outer semiconducting layer arranged around the insulation layer, an elastic mechanical support layer arranged around the outer semiconducting layer, a metallic water blocking layer having a longitudinal weld seam, the metallic water blocking layer being arranged around the mechanical support layer, wherein the mechanical support layer is permanently thermally expanded radially as a result of a heat treatment process, thereby mechanically supporting the metallic water blocking layer.

Claims

1. A power cable comprising: a conductor, an insulation system including an inner semiconducting layer arranged around the conductor, an insulation layer arranged around the inner semiconducting layer, and an outer semiconducting layer arranged around the insulation layer, an elastic mechanical support layer arranged around the outer semiconducting layer, and a metallic water blocking layer having a longitudinal weld seam, the metallic water blocking layer being arranged around the mechanical support layer, wherein the mechanical support layer is permanently thermally expanded radially as a result of a heat treatment process, thereby mechanically supporting the metallic water blocking layer.

2. The power cable as claimed in claim 1, wherein the mechanical support layer is permanently thermally expanded radially with a factor of at least 2.

3. The power cable as claimed in claim 1, wherein the mechanical support layer comprises polymer foam.

4. The power cable as claimed in claim 3, wherein the polymer foam comprises thermally expandable microspheres, TEM, embedded in a polymer matrix.

5. The power cable as claimed in claim 4, wherein the polymer matrix includes polyethylene, polyurethane, polyvinylchloride, ethylene-vinyl acetate, polydimethylsiloxane, or epoxy.

6. The power cable as claimed in any of claim 1, wherein the mechanical support layer comprises an intumescent material.

7. The power cable as claimed in claim 6, wherein the intumescent material comprises an acid source, a carbonization agent, and a blowing agent.

8. The power cable as claimed in claim 1, wherein the mechanical support layer is an extruded layer, is in the form of tape wrapped around the insulation system, or is a coating on an inner surface of the metallic water blocking layer.

9. The power cable as claimed in claim 1, wherein the metallic water blocking layer includes copper, aluminium, or stainless steel.

10. The power cable as claimed in claim 1, wherein the mechanical support layer is semiconducting, and wherein the mechanical support layer electrically connects the metallic water blocking layer with the outer semiconducting layer.

11. The power cable as claimed in claim 1, wherein the power cable is a submarine power cable.

12. A method of manufacturing a power cable, comprising: a) providing a conductor, b) providing an insulation system including an inner semiconducting layer arranged around the conductor, an insulation layer arranged around the inner semiconducting layer, and an outer semiconducting layer arranged around the insulation layer, c) providing an elastic semiconductive mechanical support layer around the outer semiconducting layer, d) welding opposing edges of a metallic sheet arranged radially outside of the mechanical support layer longitudinally to form a metallic water blocking layer, and e) heating the mechanical support layer to thermally expand the mechanical support layer permanently, thereby mechanically supporting the metallic water blocking layer.

13. The method as claimed in claim 12, wherein step c) comprises extruding the mechanical support layer radially outside of the outer semiconducting layer using an unexpanded polymer material.

14. The method as claimed in claim 13, comprising before step d), providing a protective tape that is thermally stable at the welding temperature axially along an outer surface of the mechanical support layer, the protective tape being radially aligned with the opposing edges of the metallic sheet before step d).

15. The method as claimed in claim 12, wherein in step c) the mechanical support layer is applied around the outer semiconducting layer as a tape comprising unexpanded polymer material or as a coating, including unexpanded polymer material, on the metallic sheet, wherein step e) is performed after step d).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

[0061] FIG. 1 schematically shows a cross section of an example of a power cable; and

[0062] FIGS. 2a-2d schematically shows cross sections of various steps of manufacturing a power cable; and

[0063] FIG. 3 is a flowchart of a method of manufacturing a power cable such as the power cable in FIG. 1.

DETAILED DESCRIPTION

[0064] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

[0065] FIG. 1 schematically shows a cross section of an example of a power cable 1.

[0066] The power cable 1 comprises a power core 3a.

[0067] The power core 3a comprises a conductor 5. The conductor 5 may for example be solid, stranded, or of Milliken type. The conductor 5 is made of metal. The conductor 5 may for example comprise copper or aluminium.

[0068] The power core 3a comprises an insulation system 7.

[0069] The insulation system 7 comprises an inner semiconducting layer 9 arranged around the conductor 5. The inner semiconducting layer 9 may for example comprise crosslinked polyethylene (XLPE), polypropylene (PP), thermoplastic elastomer (TPE) which is based on PP random copolymer, ethylene propylene diene monomer (EPDM) rubber, or ethylene propylene rubber (EPR), mixed with a semiconductive component such as carbon black to form a semiconducting polymer, or a semiconducting paper. The semiconducting polymer may be extruded.

[0070] The insulation system 7 comprises an insulation layer 11. The insulation layer 11 is arranged around the inner semiconducting layer 9. The insulation layer 11 may be in direct contact with the inner semiconducting layer 9. The insulation layer 11 may for example comprise XLPE, PP, thermoplastic elastomer (TPE) which is based on PP random copolymer, EPDM rubber, or EPR, or paper. The insulation layer 11 may be extruded.

[0071] The insulation system 7 comprises an outer semiconducting layer 13 arranged around the insulation layer 11. The outer semiconducting layer 13 may be in direct contact with the insulation layer 11. The outer semiconducting layer 13 may for example comprise XLPE, PP, thermoplastic elastomer (TPE) which is based on PP random copolymer, EPDM rubber, or EPR, mixed with a semiconductive component such as carbon black to form a semiconducting polymer, or a semiconducting paper. The semiconducting polymer may be extruded.

[0072] The insulation system 7 may be a triple extruded insulation system.

[0073] The power core 3 comprises an elastic mechanical support layer 15 arranged radially outside of the outer semiconducting layer 13.

[0074] According to one example, the mechanical support layer 15 may be semiconducting.

[0075] The power core 3a comprises a metallic water blocking layer 17. The metallic water blocking layer 17 is arranged concentrically with and around the mechanical support layer 17.

[0076] The mechanical support layer 17 is arranged between the outer semiconducting layer 13 and the metallic water blocking layer 17.

[0077] The mechanical support layer 17 may have been thermally expanded by a factor of at least 2 due to a heat treatment process during the manufacturing of the power cable 1.

[0078] The mechanical support layer 17 mechanically supports the metallic water blocking layer 17.

[0079] The mechanical support layer 17 may comprise a polymer foam.

[0080] The polymer foam may for example comprise TEM embedded in a polymer matrix.

[0081] The polymer matrix may for example comprise polyethylene, polyurethane, polyvinylchloride, ethylene-vinyl acetate, polydimethylsiloxane, or epoxy.

[0082] According to one example the mechanical support layer 15 comprises an intumescent material. The intumescent material may comprise an acid source, a carbonization agent, and a blowing agent.

[0083] The mechanical support layer 15 may for example be an extruded layer, or it may be in the form of tape wrapped around the insulation system 7, or in the form of a coating on an inner surface of the metallic water blocking layer 17.

[0084] The metallic water blocking layer 17 may comprise a metal sheath. The metal may for example be aluminium, an aluminium alloy, copper, a copper alloy, or stainless steel.

[0085] The power core 3a comprises a polymer layer 19 arranged concentrically with and around the metallic water blocking layer 17. The polymer layer 19 may for example comprise XLPE, PP, EPDM or EPR.

[0086] The polymer layer 19 may be semiconducting.

[0087] According to one example, the polymer layer 19 may be bonded to the metallic water blocking layer 17 by means of glue. The glue is semiconducting if the polymer layer 19 is semiconducting.

[0088] The polymer layer 19 may be a polymer jacket.

[0089] The polymer layer 19 may be in direct contact with the outer surface of the metallic water blocking layer 17.

[0090] The polymer layer 19 may be extruded onto the metallic water blocking layer 17.

[0091] The power cable 1 may comprise an armour layer 21 arranged radially outside of the polymer layer 19.

[0092] The armour layer 21 comprises a plurality of armour wires 23 arranged helically around the polymer layer 19. The armour layer 21 may comprise armour wires 23 made of metal such as galvanized carbon steel, austenitic stainless steel, copper, or aluminium, and/or armour wires 23 made of synthetic material such as aramid fibres in a jacket.

[0093] In case at least some of the armour wires 23 are made of metal, the armour layer 21 may be covered in bitumen.

[0094] FIGS. 2a-2d show exemplary production steps for manufacturing the power cable 1.

[0095] In the example in FIG. 2a, the mechanical support layer 15 is provided around the outer semiconducting layer 13.

[0096] The mechanical support layer 15 is in this example thermally unexpanded at this stage. The mechanical support layer 15 may comprise an unexpanded polymer material 16.

[0097] The mechanical support layer 15 may for example be in the form of tape that is wrapped around the insulation system 7.

[0098] Overlapping edges of the tape may be bonded to each other, for example by means of adhesive.

[0099] FIG. 2b illustrates when the metallic water blocking layer 17 has been formed around the mechanical support layer 15 which is still unexpanded.

[0100] The metallic water blocking layer 17 has been made by wrapping a metallic sheet around the unexpanded polymer material 16 at a radial distance from the unexpanded polymer material 16. Opposing edges of the metallic water blocking layer 17 have been welded longitudinally to form the weld seam 17a.

[0101] FIG. 2c shows when the structure obtained in FIG. 2b is subjected to heat treatment. This causes the unexpanded polymer material 16 to thermally expand permanently.

[0102] FIG. 2d shows when the heat treatment has been completed. The mechanical support layer 15 is in the example in direct contact with the inner surface of the metallic water blocking layer 17.

[0103] According to one variation, the metallic water blocking layer 17 may be subjected to a diameter reduction before or after the heat treatment to ensure that the mechanical support layer 15 is in direct contact with the inner surface of the metallic water blocking layer 17.

[0104] FIG. 3 is a flowchart of a method of manufacturing the power cable 1.

[0105] In a step a) the conductor 5 is provided.

[0106] In a step b) the insulation system 7 is provided around the conductor 5. The insulation system 7 may for example be provided around the conductor 5 in a triple extrusion process or in a tape winding process.

[0107] In a step c) the mechanical support layer 15 is provided around the outer semiconducting layer 13 of the insulation system 7.

[0108] The mechanical support layer 15 may be extruded onto the insulation system 7 in step c). The mechanical support layer 15 is in this case subjected to thermal expansion after the extrusion process, preferably after a step d) of welding described below. The mechanical support layer 15 may be extruded using an unexpanded polymer material fed to the extruder, which is thermally expanded after step d) of welding.

[0109] A protective tape that is thermally stable at the welding temperature may be provided axially along an outer surface of the mechanical support layer 15 before the opposing edges of the metallic sheet are welded longitudinally in case the mechanical support layer 15 has been extruded.

[0110] The protective tape is radially aligned with the opposing edges of the metallic sheet.

[0111] In a step d) the opposing edges of a metallic sheet are welded longitudinally to form the metallic water blocking layer 17.

[0112] In the case of a thermally expanded extruded mechanical support layer 15, the metallic sheet may be in physical contact or essentially be in physical contact with the mechanical support layer 15 during step d).

[0113] In a step e) the mechanical support layer 15 may be heated to thermally expand the mechanical support layer 15 permanently.

[0114] The thermal expansion may for example be with a factor of at least 2.

[0115] If the mechanical support layer 15 is formed of a tape, step c) may involve wrapping the tape longitudinally around the insulation system 7.

[0116] If the mechanical support layer 15 is formed as a coating on the metallic sheet, comprising unexpanded polymer material, step c) may involve wrapping the metallic sheet longitudinally around the insulation system 7 with the coating facing the insulation system 7.

[0117] The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.