Power cable with layer having anisotropic thermal conductivity

Abstract

To provide a power cable that at least mitigates the risk of damaging underlying layers, such as an insulation system, by heat generated in conjunction with welding or soldering of lead-free materials when a metallic water barrier is to be jointed between two conductor sections in a cable joint region or in a region where the insulation system has been repaired.SOLUTION: In a power cable, a metallic radial water barrier (13) of a first cable section and / or a second cable section are lead-free, a metallic radial intermediate cable section water barrier (13') of an intermediate cable section (1c) is lead-free, and an intermediate cable section bedding layer (12') has an anisotropic thermal conductivity, with a higher thermal conductivity in a longitudinal axial direction of the power cable than in a radial direction of the power cable.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates generally to power cables. [Background technology]

[0002] Submarine power cables traditionally have had a lead sheath that acts as a radial water barrier to protect the insulation system.

[0003] There is a trend toward lead-free radial water barrier designs. For example, copper, various copper alloys, aluminum, and stainless steel water barriers have been proposed.

[0004] Typically, the water barrier is created by first wrapping a metal tape longitudinally around the insulation system and then welding both edges of the metal tape longitudinally of the cable.

[0005] There are challenges with using lead-free metallic materials in water barriers. When a metallic water barrier is to be joined between two conductor sections, such as in a cable joint region or in an area where the insulation system has been repaired, the heat generated with welding or soldering the lead-free material is much higher than with a lead water barrier, as higher welding or soldering temperatures are required. This can risk damaging underlying layers, such as the insulation system. Summary of the Invention

[0006] In view of the above, it is an object of the present disclosure to provide a power cable that solves or at least alleviates the problems of the prior art.

[0007] Thus, according to a first aspect of the present disclosure, a cable casing includes a first cable section and a second cable section, each of the first cable section and the second cable section comprising a conductor section, an insulation system disposed about the conductor section, the insulation system comprising an inner semiconducting layer, an insulating layer disposed about the inner semiconducting layer, and an outer semiconducting layer disposed about the insulating layer, and a metallic radial water barrier disposed about the outer semiconducting layer; and an intermediate cable section located between the first cable section and the second cable section, the intermediate cable section comprising an intermediate conductor section, an intermediate cable section insulation system disposed about the intermediate conductor section, the intermediate cable section insulation system extending between and joining the insulation system of the first cable section and the insulation system of the second cable section, and an intermediate cable section bedding layer disposed about the intermediate cable section insulation system. and an intermediate cable section comprising a metallic radial mid-cable section bedding layer and a metallic radial mid-cable section water barrier disposed about the intermediate cable section bedding layer, the metallic radial mid-cable section water barrier being thermally bonded to the metallic radial water barriers of the first cable section and to the metallic radial mid-cable section water barriers of the second cable section, wherein A) the metallic radial water barriers of the first cable section and / or the second cable section are lead-free and / or B) the metallic radial mid-cable section water barrier is lead-free, and the intermediate cable section bedding layer has an anisotropic thermal conductivity, having a higher thermal conductivity in a longitudinal axial direction of the power cable than in a radial direction of the power cable.

[0008] The anisotropic mid-cable section bedding layer thus reduces radial heat propagation to underlying layers, such as the mid-cable section insulation system, and thus reduces the risk of thermally damaging the underlying layers in the process of thermally bonding the metallic radial mid-cable section water barrier with the metallic radial water barriers of the first and second cable sections.

[0009] The metallic radial water barrier of at least one of the first cable section and the second cable section, or both, may be made from the same metallic material as the metallic radial intermediate cable section water barrier.

[0010] The insulation system of the first cable section may be an extruded insulation system, and therefore may be polymer-based, for example polyolefin-based.

[0011] The mid-cable section insulation system may be made from a tape wrapped around the intermediate conductor section and heated under pressure or by a molding process. Thus, the mid-cable section insulation system may be polymer-based, for example polyolefin-based.

[0012] According to one embodiment, the metallic radial water barrier of the first cable section and / or the second cable section comprises one of copper, a copper alloy, aluminum, or stainless steel.

[0013] The melting temperatures of copper and stainless steel are approximately 1100°C and 1400°C, respectively, which is well above the melting temperatures of insulation systems, for example, typical polymer-based extrusion materials begin to melt at temperatures above 125°C.

[0014] According to one embodiment, the metallic radial intermediate cable section water barrier comprises one of copper, copper alloy, aluminum, or stainless steel.

[0015] One embodiment includes a mid-cable section polymer layer disposed about a metallic radial mid-cable section water barrier.

[0016] One embodiment includes a bedding layer disposed around the insulation systems of the first and second cable sections beneath a metallic radial water barrier, with an intermediate cable section bedding layer disposed axially between and in direct contact with the bedding layer of the first cable section and the bedding layer of the second cable section.

[0017] According to one embodiment, the bedding layers of the first and second cable sections comprise a swelling tape, which may be disposed above the insulation system and below the metallic radial water barrier.

[0018] One embodiment includes a water swellable material disposed between the mid-cable section insulation system and the mid-cable section bedding layer. Such water swellable materials often have a melting point of approximately 250° C., which is well below the temperature required to thermally bond two metallic materials, at least one of which is lead-free.

[0019] According to one example, the intermediate cable section bedding layer is a tape or is formed from a tape.

[0020] According to one embodiment, the intermediate cable section bedding layer may comprise two layers, the radially outer layer of which has anisotropic thermal conductivity and the inner layer of which comprises a water-swellable material. The outer layer and the inner layer may for example be laminated.

[0021] According to one embodiment, the metallic radial intermediate cable section water barrier is thermally joined to the metallic radial water barriers of the first cable section and to the metallic radial water barriers of the second cable section by welding or soldering.

[0022] The metallic radial mid-cable section water barrier is thermally bonded to the metallic radial water barriers of the first cable section and to the metallic radial water barriers of the second cable section along the entire circumference of the power cable.

[0023] According to one embodiment, the intermediate cable section bedding layer comprises pyrolytic graphite.

[0024] The intermediate cable section bedding layer may comprise, for example, SIGRAFLEX® flexible graphite tape or foil.

[0025] According to one embodiment, the power cable is a submarine power cable.

[0026] The power cable may be a medium voltage or a high voltage submarine power cable. High voltage means a nominal voltage of the power cable of 30 kV or more.

[0027] The metallic radial water barrier may be smooth or corrugated. If the metallic radial water barrier is smooth, the metallic radial mid-cable section water barrier may be closer to the underlying layer and therefore the heat generated during thermal bonding may potentially affect the underlying layer more than if the thermal bonding is performed at the crest of the corrugated metallic radial water barrier.

[0028] The metallic radial intermediate cable section water barrier may be smooth or corrugated.

[0029] According to a second aspect of the present disclosure, there is provided a method of making a bond between a metallic radial water barrier of a first cable section and a metallic radial water barrier of a second cable section of a power cable of the first aspect, the method comprising: a) making a mid-cable section insulation system that connects with the insulation systems of the first cable section and the second cable section; b) providing a mid-cable section bedding layer around the mid-cable section insulation system; c) providing a metallic radial mid-cable section water barrier around the mid-cable section bedding layer; and d) thermally bonding the metallic radial mid-cable section water barrier to the metallic radial water barriers of the first cable section and the second cable section.

[0030] In general, all terms used in the claims should be interpreted according to their customary meaning in the art, unless expressly defined otherwise herein. All references to "a / an / the element, device, component, means, etc., should be openly interpreted as referring to at least one instance of that element, device, component, means, etc., unless expressly stated otherwise.

[0031] Specific embodiments of the inventive concept will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 is a schematic diagram illustrating a side view of a portion of an example power cable. [Diagram 2] FIG. 2 is a schematic cross-sectional view of an example of a power cable taken along the cross section AA in FIG. [Diagram 3] FIG. 2 shows a schematic cross-sectional side view of a portion of the power cable in FIG. 1, including an intermediate cable section up to the polymer layer for reasons of simplicity. [Figure 4]1 illustrates a method of making a joint between a metallic radial water barrier of a first cable section and a metallic radial water barrier of a second cable section. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The inventive concepts will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. However, the inventive concepts may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein, but rather, these embodiments are provided as examples so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concepts to those skilled in the art. Like numbers refer to like elements throughout the description.

[0034] FIG. 1 shows an axial section of an example power cable 1 according to the present disclosure.

[0035] The power cable 1 may be a submarine power cable or alternatively an underground power cable.

[0036] The power cable 1 comprises a first cable section 1a and a second cable section 1b.

[0037] The power cable 1 has an intermediate cable section 1c located between the first cable section 1a and the second cable section 1b.

[0038] The first cable section 1 a, the intermediate cable section 1 c and the second cable section 1 b are axial cable sections of the power cable 1.

[0039] The first cable section 1a, the intermediate cable section 1c and the second cable section 1b are arranged successively along the longitudinal axis of the power cable 1 in a direction from the first cable section 1a towards the second cable section 1b. The first cable section 1a transitions into the intermediate cable section 1c, which transitions into the second cable section 1b.

[0040] The intermediate cable section 1c is immediately adjacent to the first cable section 1a and the second cable section 1b.

[0041] FIG. 2 shows a cross section of the power cable 1 along the line AA.

[0042] Although the illustrated power cable 1 shows a single core power cable, the power cable 1 may alternatively be a multi-core power cable.

[0043] The power cable 1 can be an AC power cable or a DC power cable.

[0044] The power cable 1 comprises a conductor 3 and an insulation system 5 arranged around the conductor 3. The configuration is the same for the first cable section 1a and the second cable section 1b.

[0045] The axial sections of the conductor 3 that extend along the first and second cable sections 1a, 1b are referred to herein as "conductor sections."

[0046] The insulation system 5 comprises an inner semiconducting layer 7 disposed about the conductor 3 , an insulating layer 9 disposed about the inner semiconducting layer 7 , and an outer semiconducting layer 11 disposed about the insulating layer 9 .

[0047] The insulation system 5 may be an extruded insulation system or a paper-based insulation system impregnated with an insulating fluid such as oil.

[0048] When the insulation system 5 is an extruded insulation system, the insulation system includes a polymeric material, such as polyethylene, cross-linked polyethylene, polypropylene, ethylene propylene rubber (EPR) or ethylene propylene diene monomer rubber (EPDM).

[0049] The power cable 1 may comprise a bedding layer 12. The bedding layer 12 is arranged around the insulating system 5. The bedding layer 12 may comprise a swellable tape. The swellable tape may be wrapped around the insulating system 5.

[0050] The power cable 1 comprises a metallic radial water barrier 13. The metallic radial water barrier 13 is a layer disposed around the insulation system 5. If a bedding layer 12 is present, the metallic radial water barrier 13 is disposed around the bedding layer 12.

[0051] The metallic radial water barrier 13 may be lead-free or may be made of lead. If lead-free, the metallic radial water barrier 13 may include, for example, copper, copper alloy, aluminum, or stainless steel. The metallic radial water barrier of the second cable section 1b may be of the same material as the metallic radial water barrier 13 of the first cable section 1a. Alternatively, the metallic radial water barrier of the second cable section 1b may be made of a different material than the metallic radial water barrier 13 of the first cable section 1a. Thus, for example, both metallic radial water barriers may be made of lead, or both may be lead-free, or one of them may be made of lead and the other may be made of, for example, copper, copper alloy, aluminum, or stainless steel.

[0052] The metallic radial water barrier 13, if lead-free, has a longitudinal weld seam. The longitudinal weld seam may be formed, for example, without the use of a filler material. Thus, the metallic radial water barrier 13 may be autogenously welded.

[0053] The power cable 1 comprises a polymer layer 15 disposed about a metallic radial water barrier 13. The polymer layer 15 may be extruded onto the metallic radial water barrier 13.

[0054] The polymer layer 15 may be bonded to the outer surface of the metallic radial water barrier 13 by an adhesive, such as a hot melt adhesive, according to one example.

[0055] Power cable 1 may comprise an armour layer comprising a plurality of armour elements 17 helically disposed around polymer layer 15 in one or more layers.

[0056] The power cable 1 has an outer layer 19, which may be an outer sheath constructed from a polymeric material, or an outer serving constructed from a plurality of helically wound polymeric elements.

[0057] The power cable 1 may comprise additional layers not disclosed herein, for example an anti-corrosion layer outside the armour layer, for example made from bitumen.

[0058] 3 is a longitudinal cross-section of the power cable 1 showing the intermediate cable section 1c. The layers of the power cable are shown only up to the polymer layer 15 / intermediate cable section polymer layer 15' of the intermediate cable section 1c. The axis B is the axis of symmetry of the power cable 1.

[0059] The intermediate cable section 1c comprises an intermediate conductor section 3' which forms part of the conductor 3 of the power cable 1.

[0060] The intermediate cable section 1c comprises an intermediate cable section insulation system 5' disposed about the intermediate conductor section 3'.

[0061] The intermediate cable section insulation system 5' comprises an inner semiconducting layer 7' disposed about the intermediate conductor section 3', an insulating layer 9' disposed about the inner semiconducting layer 7', and an outer semiconducting layer 11' disposed about the insulating layer 9'.

[0062] The mid-cable section insulation system 5' is a restored insulation system.

[0063] The intermediate conductor section 3' may include a conductor joint, in which case the intermediate cable section insulation system 5' is restored across the conductor joint and connects with the insulation systems 5 of the first and second cable sections 1a and 1b. Alternatively, the intermediate conductor section 3' may be without a conductor joint, for example if the intermediate insulation system 5' is restored due to damage to the originally existing insulation system.

[0064] The intermediate cable section 1c comprises an intermediate cable section bedding layer 12'. The intermediate cable section bedding layer 12' is arranged around the intermediate cable section insulation system 5'. The intermediate cable section bedding layer 12' has anisotropic thermal conductivity, with a higher thermal conductivity in the longitudinal axial direction of the power cable 1 than in the radial direction of the power cable 1. Thus, the intermediate cable section bedding layer 12' conducts heat in the axial direction of the power cable 1, but generally not in the radial direction.

[0065] The mid-cable section bedding layer 12' may be, for example, a tape, or the mid-cable section bedding layer 12' may be extruded onto the mid-cable section insulation system 5'.

[0066] According to one example, the intermediate cable section bedding layer 12' may comprise two layers that may be laminated together. One of these layers may be a radially outer layer having anisotropic thermal conductivity properties. The other layer may be an inner layer that includes a water-swellable material.

[0067] The power cable 1 may, according to one example, include a water-swellable material disposed between the intermediate cable section insulation system 5' and the intermediate cable section bedding layer 12', in which case the water-swellable material is a separate layer from the intermediate cable section bedding layer 12', i.e., the two layers are applied separately.

[0068] The intermediate cable section bedding layer 12', when present along the first cable section 1 and the second cable section 1b, may be in direct contact with the bedding layers 12 of the first cable section 1a and the second cable section 1b.

[0069] The intermediate cable section 1c has a metallic radial intermediate cable section water barrier 13'. The metallic radial intermediate cable section water barrier 13' is disposed around the intermediate cable section bedding layer 12'.

[0070] The metallic radial intermediate cable section water barrier 13' may be made of lead. In this case, the metallic radial water barrier 13 of at least one of the first cable section 1a and the second cable section 1b is lead-free. The metallic radial intermediate cable section water barrier 13' may alternatively be lead-free. In this case, the metallic radial intermediate cable section water barrier 13' may include, for example, copper, a copper alloy, aluminum, or stainless steel.

[0071] The metallic radial intermediate cable section water barrier 13' is thermally bonded to the metallic radial water barriers 13 of the first cable section 1a and the second cable section 1b. The thermal bonding is by welding or soldering.

[0072] The intermediate cable section 1c may include an intermediate cable section polymer layer 15' disposed about the metallic radial intermediate cable section water barrier 13'. For example, the intermediate cable section polymer layer 15' may be formed by heat shrink tubing, by tape, or the intermediate cable section polymer layer 15' may be extruded. The intermediate cable section polymer layer 15' directly contacts the polymer layers 15 of the first cable section 1a and of the second cable section 1b.

[0073] According to one example, the bedding layer 12 of one or both of the first and second cable sections 1a and 1b may also have anisotropic thermal conductivity, with a higher thermal conductivity in the longitudinal axial direction of the power cable 1 than in the radial direction of the power cable 1. In this case, the bedding layer(s) 12 and the intermediate cable section bedding layer 12' therefore have anisotropic thermal conductivity. The bedding layers 12, 12' therefore have anisotropic thermal conductivity along all three cable sections 1a, 1b, 1c. The bedding layers 12, 12' may according to one example have anisotropic thermal conductivity along the entire length of the power cable 1.

[0074] If the power cable 1 is a multi-core power cable, each core may have the structure described above.

[0075] A method of making the joint between the metallic radial water barrier 13 of the first cable section 1a and the metallic radial water barrier 13 of the second cable section 1b will now be described with reference to FIG.

[0076] Splicing can be the process of making a conductor joint between the first and second cable sections 1a and 1b, or the process of repairing a damaged section of the power cable 1.

[0077] If a conductor joint is to be made, the ends of the first cable section 1a and the second cable section 1b are prepared by exposing end portions of the respective conductor sections. The conductor sections are then joined to form the conductor joint. Furthermore, the insulation system is mechanically processed, for example by removing a portion of the outer semiconductive layer and making an insulation layer taper.

[0078] When a cable repair is to be performed, the insulation system is mechanically treated in the same manner as described above.

[0079] In step a) an intermediate cable section insulation system 5' is produced, which connects the insulation systems 5 of the first cable section 1a and of the second cable section 1b. This can be done, for example, by winding a tape and heating the tape under pressure or by moulding.

[0080] In step b), the intermediate cable section bedding layer 12' is provided around the intermediate cable section insulation system 5'. The intermediate cable section bedding layer 12' may for example be formed by a tape wound around the intermediate cable section bedding layer 12'.

[0081] In step c) a metallic radial intermediate cable section water barrier 13' is provided around the intermediate cable section bedding layer 12'. The metallic radial intermediate cable section water barrier 13' can for example be made from a tube which is slid over the intermediate cable section 1c after the intermediate cable section bedding layer 12' has been formed in step b).

[0082] In step d) the metallic radial intermediate cable section water barrier 13' is thermally bonded to the metallic radial water barriers 13 of the first and second cable sections. The thermal bonding is along the entire circumference of the metallic radial intermediate cable section water barrier 13' and the metallic radial water barrier 13. The thermal bonding can be done by welding or soldering, such as soft soldering.

[0083] The intermediate cable section polymer layer 15' may be disposed around the metallic radial intermediate cable section water barrier 13'. According to one example, the intermediate cable section polymer layer 15' is glued onto the metallic radial intermediate cable section water barrier 13'. The glue may be a hot melt adhesive, which is heated to adhere the intermediate cable section polymer layer 15' to the metallic radial intermediate cable section water barrier 13'.

[0084] The inventive concept has been described above primarily with reference to a few examples. However, as will be readily appreciated by those skilled in the art, other embodiments than those disclosed above are equally possible within the scope of the inventive concept as defined by the appended claims.

Claims

1. A first cable section (1a), A second cable section (1b), Each of the first cable section (1a) and the second cable section (1b) comprises: A conductor section; an insulation system (5) disposed around the conductor section, the insulation system (5) comprising an inner semiconducting layer (7), an insulating layer (9) disposed around the inner semiconducting layer (7), and an outer semiconducting layer (11) disposed around the insulating layer (9); a metallic radial water barrier (13) disposed around the outer semiconductor layer (11); A first cable section (1a) and a second cable section (1b) comprising: an intermediate cable section (1c) located between the first cable section (1a) and the second cable section (1b), the intermediate cable section (1c) comprising: an intermediate conductor section (3'); an intermediate cable section insulation system (5') disposed around said intermediate conductor section (3'), said intermediate cable section insulation system (5') extending between and joining said insulation system (5) of said first cable section (1a) and said insulation system (5) of said second cable section (1b), said intermediate cable section insulation system (5') comprising an inner semiconducting layer (7') disposed around said intermediate conductor section (3'), an insulating layer (9') disposed around said inner semiconducting layer (7'), and an outer semiconducting layer (11') disposed around said insulating layer (9'); an intermediate cable section bedding layer (12') disposed around said intermediate cable section insulation system (5'); and a metallic radial intermediate cable section water barrier (13') disposed around said intermediate cable section bedding layer (12'), said metallic radial intermediate cable section water barrier (13') being thermally bonded to the metallic radial water barriers (13) of said first cable section (1a) and of said second cable section (1b); an intermediate cable section (1c) comprising A) the metallic radial water barrier (13) of the first cable section (1a) and / or the second cable section (1b) is lead-free; and / or B) the metallic radial intermediate cable section water barrier (13′) is lead-free; An electric power cable (1), wherein the intermediate cable section bedding layer (12') has anisotropic thermal conductivity, with a higher thermal conductivity in a longitudinal axial direction of the electric power cable than in a radial direction of the electric power cable (1).

2. 2. The power cable (1) according to claim 1, wherein the metallic radial water barrier (13) of the first cable section (1a) and / or the second cable section (1b) comprises one of copper, a copper alloy, aluminum, or stainless steel.

3. The power cable (1) according to claim 1 or 2, wherein the metallic radial intermediate cable section water barrier (13') comprises one of copper, a copper alloy, aluminium or stainless steel.

4. 4. The power cable (1) according to any one of claims 1 to 3, comprising an intermediate cable section polymer layer (15') arranged around the metallic radial intermediate cable section water barrier (13').

5. 5. The power cable (1) according to claim 1, further comprising a bedding layer (12) arranged around the insulation systems (5) of the first cable section (1 a) and the second cable section (1 b) beneath the metallic radial water barrier (13), the intermediate cable section bedding layer (12') being arranged axially between and in direct contact with the bedding layer (12) of the first cable section (1 a) and the bedding layer (12) of the second cable section (1 b).

6. 6. The power cable (1) according to claim 5, wherein the bedding layers (12) of the first cable section (1a) and the second cable section (1b) comprise a swellable tape.

7. 7. The power cable (1) according to any one of claims 1 to 6, comprising a water-swellable material arranged between the intermediate cable section insulation system (5') and the intermediate cable section bedding layer (12').

8. 7. The power cable (1) according to claim 1, wherein the intermediate cable section bedding layer (12') comprises two layers, a radially outer layer of the two layers having the anisotropic thermal conductivity and an inner layer of the two layers comprising a water-swellable material.

9. 9. The power cable (1) according to any one of claims 1 to 8, wherein the metallic radial intermediate cable section water barrier (13') is thermally joined to the metallic radial water barriers (13) of the first cable section (1a) and of the second cable section (1b) by welding or soldering.

10. 10. The power cable (1) according to any one of the preceding claims, wherein the intermediate cable section bedding layer (12') comprises pyrolytic graphite.

11. The power cable (1) according to any one of the preceding claims, wherein the power cable (1) is a submarine power cable.

12. A method for making a joint between a metallic radial water barrier (13) of a first cable section (1a) and a metallic radial water barrier (13) of a second cable section (1b) of a power cable (1) according to any one of claims 1 to 11, comprising the steps of: a) making an intermediate cable section insulation system (5') which connects with the insulation systems (5) of said first cable section (1a) and of said second cable section (1b); b) providing an intermediate cable section bedding layer (12') around said intermediate cable section insulation system (5'); c) providing a metallic radial intermediate cable section water barrier (13') around said intermediate cable section bedding layer (12'); d) thermally bonding said metallic radial intermediate cable section water barrier (13') to said metallic radial water barriers (13) of said first cable section (1a) and to said second cable section (1b); A method comprising:

Images