Submarine DC power cable

Abstract

To provide a submarine DC power cable that requires only a single set of buoyancy modules, bend stiffener / bellmouth, and I-tube in a case it is a dynamic submarine power cable.SOLUTION: A submarine DC power cable (1) includes: three stranded cores (3a, 3b, 3c), wherein a first core (3a) and a second core (3b) of the three stranded cores (3a, 3b, 3c) are DC power cores, each including a conductor (4), and an insulation system 5 arranged around the conductor (4), and wherein a third core (3c) of the three cores (3a, 3b, 3c) is a dummy element having the same outer diameter as the first core (3a) and the second core (3b), or the outer diameter of the third core (3c) deviates at most ±10% from the outer diameter of any of the first core (3a) and the second core (3b), and wherein the third core in cross-section has a structure that is circular symmetric and which differs from a cross-sectional structure of the first core (3a) and the second core (3b).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates generally to submarine power cables. [Background technology]

[0002] Dynamic power cables are typically used to supply energy to floating oil and gas platforms or as array cables in floating wind applications. The dynamic power cables may be run through I-tubes that extend from the offshore platform, suspending the dynamic power cables to the seabed. Additionally, the dynamic power cables typically include several devices, such as bending stiffeners or bellmouths located at the ends of the I-tubes, and buoyancy and / or ballast modules. Summary of the Invention

[0003] In some cases, it may be desirable to use dynamic submarine power cables to transport direct current. This typically requires the installation of at least two separate dynamic DC submarine power cables, one for each electrode. Therefore, at least two sets of bending stiffeners / bellmouths and buoyancy modules must be used. Furthermore, at least two I-tubes must be present. This makes installation more time-consuming than AC power cable installations and results in a more congested water column with several cables and their respective sets of buoyancy and / or ballast modules. Furthermore, fixed DC submarine power cables must be spliced ​​to each dynamic DC submarine power cable, and each fixed DC submarine power cable typically requires its own trench, excavated, for example, by a cable plow, making installation even more cumbersome compared to AC power cable installations. Furthermore, if fiber optic cables are required, a separate set of accessories and additional I-tubes at the platform are required.

[0004] In view of the above, it is an object of the present disclosure to provide a submarine DC power cable that overcomes or at least mitigates the problems of the prior art.

[0005] Thus, there is provided a submarine DC power cable comprising three stranded cores, a first core and a second core of which are DC power cores, each comprising a conductor and an insulation system disposed around the conductor, and a third core of which is a dummy element having the same outer diameter as the first and second cores, or alternatively, the outer diameter of the third core deviates from the outer diameter of either of the first and second cores by a maximum of ±10%, and the third core has circular symmetry in cross section and a structure different from the cross-sectional structures of the first and second cores.

[0006] Therefore, this submarine DC power cable is a stranded multi-core power cable that requires only one set of buoyancy modules, bending stiffeners / bellmouths, and I-tubes if it is a dynamic submarine power cable, and only one trench if it is a fixed submarine power cable. Furthermore, this submarine DC power cable is easier to install because it uses a single circularly symmetric structure.

[0007] The purpose of the third core or dummy element is to fill the space within the submarine DC power cable so that the three cores form a trefoil configuration. The third core is not an electrical core, i.e. it does not carry current when in operation.

[0008] According to one embodiment, the third core is a single extruded dummy element comprising a polymer material.

[0009] According to one embodiment, in every cross section of the third core, the dummy element is made of a polymer material, which simplifies the manufacturing of the third core compared to the manufacturing of the first and second cores.

[0010] In one embodiment, the third core is made of a polymer material and a load-bearing element embedded in the polymer material, which reduces the tensile load on the conductors of the two DC cores.

[0011] According to one embodiment, the load-bearing element is made of metal or synthetic fibers.

[0012] According to one embodiment, in the cross section of the third core, the load-bearing element is centrally arranged.

[0013] The load bearing element may be a load bearing wire or may be a tubular element with a polymer material disposed radially inward and radially outward.

[0014] According to one embodiment, the load-bearing element comprises steel, which may be, for example, mild steel or stainless steel.

[0015] According to one example, the load-bearing element includes lead, copper, or aluminum.

[0016] According to one embodiment, the polymer material is thermosetting. The polymer material may be, for example, a cross-linked polymer (XLPE).

[0017] According to one embodiment, the polymer material is thermoplastic. The polymer material may be, for example, polypropylene.

[0018] One embodiment includes an outermost layer disposed around three stranded cores, a filler profile disposed between the outermost layer and the three stranded cores, and an optical fiber cable disposed in one of the filler profiles.

[0019] Alternatively, the fiber optic cable may be disposed in an armor layer that may be provided on a submarine DC power cable.

[0020] According to one embodiment, the submarine DC power cable is an HVDC power cable, where HVDC means a DC voltage of 50 kV or higher.

[0021] According to one embodiment, the third core has an outer diameter that deviates by at most ±5% from the outer diameter of either of the first and second cores.

[0022] The submarine DC power cable may be a dynamic submarine power cable.

[0023] According to a second aspect, there is provided a power cable system comprising a first submarine DC power cable according to the first aspect and a second submarine DC power cable according to the first aspect, the second submarine DC power cable being connected to the first submarine DC power cable by a joint joining corresponding poles of the first and second cores, and the first submarine DC power cable being a dynamic power cable and the second submarine DC power cable being a fixed power cable.

[0024] According to one embodiment, the joint is a flexible joint or a factory joint.

[0025] In the case of flexible joints and factory joints, the two conductors being joined are welded together, thus forming a conductor joint, and a joint insulation system is rebuilt over the conductor joint. Typically, in the joining process, the ends of the insulation systems of the two cable lengths being joined are positioned so that they taper toward the conductor joint, and the joint insulation system is rebuilt by applying tape or injection molding to form an inner semiconducting layer around the conductor joint, an insulating layer around the inner semiconducting layer, and an outer semiconducting layer around the insulating layer. The inner semiconducting layer is connected to the inner semiconducting layer of the insulation system of the two cable lengths being joined. Furthermore, the insulating layer is connected to the insulating layer of the two cable lengths being joined. Furthermore, the outer semiconducting layer is connected to the outer semiconducting layer of the two cable lengths being joined. The flexible joint or factory joint may be a vulcanized flexible joint or factory joint, in which case the joint insulation system is vulcanized.

[0026] In general, all terms used in the claims should be interpreted according to their ordinary meaning in the art unless otherwise expressly defined herein. All references to "elements, devices, components, means," and the like should be interpreted non-exclusively as referring to at least one instance of the element, device, component, means, etc., unless otherwise specified.

[0027] Specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0028] [Figure 1] 1 shows a schematic cross section of an example submarine DC power cable. [Figure 2] 2 shows a schematic cross section of another example of a submarine DC power cable. [Figure 3] 1 shows a schematic diagram of a submarine power cable system. DETAILED DESCRIPTION OF THE INVENTION

[0029] 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 limited to the embodiments set forth herein; 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 specification.

[0030] FIG. 1 is a cross-sectional view of an example of a submarine DC power cable 1.

[0031] The submarine DC power cable 1 comprises three cores 3a to 3c arranged in a twisted wire configuration.

[0032] The first and second cores 3a, 3b of the three cores are DC power cores. The DC power cores are configured to carry a load current. The third core 3c of the three cores is a dummy element different from the first and second cores 3a, 3b. Like the first and second cores 3a, 3b, the third core 3c has a circular cross section. The third core 3c has the same outer diameter as the first and second cores 3a, 3b. Alternatively, the third core 3c may have an outer diameter that deviates from the outer diameter of either of the first and second cores 3a, 3b by up to ±10%, for example, up to ±5%.

[0033] The third core 3c has a circularly symmetric structure in the cross section of the third core. Therefore, the cross-sectional layout or structure of the third core 3c can be rotated to any angle and mapped onto itself. That is, the cross-sectional layout or structure is completely rotationally symmetric. The cross-sectional layout or structure is the visual pattern that the third core 3c exhibits in the cross section, such as the visual configuration of several concentric layers, if any.

[0034] The third core 3c functions as a tubular stranded element together with the first core 3a and the second core 3b, making the submarine DC power cable 1 a three-core stranded submarine DC power cable with a circular cross section. The third core 3c is not connected to power when the submarine DC power cable 1 is installed.

[0035] According to one example, the third core 3c includes a polymer material. In the example shown in Figure 1, the third core 3c is made of a polymer material. The third core 3c may be solid. The third core 3c may be composed of a single solid tubular polymer element. The third core 3c may be formed from a single extrusion.

[0036] The polymeric material may be, for example, a thermosetting polymer such as XLPE, or alternatively, the polymeric material may be a thermoplastic resin such as polypropylene.

[0037] Each of the first core 3 a and the second core 3 b comprises a respective conductor 4 and a respective insulation system 5 arranged around the conductor 4 .

[0038] The insulating system 5 comprises an inner semiconducting layer 7 disposed around the conductor 4, an insulating layer 9 disposed around the inner semiconducting layer 7, and an outer semiconducting layer 11 disposed around the insulating layer 9. The insulating system 5 may be polymer-based or paper-based. The first insulating system 5 may be extruded.

[0039] Each of the first core 3a and the second core 3b may include a bedding layer 13 disposed around the insulation system 5. The bedding layer 13 may, for example, comprise a water-swellable material.

[0040] Each of the first core 3 a and the second core 3 b may include a metallic waterproof sheath 15. The metallic waterproof sheath 15 may be, for example, a lead sheath, or may include copper, stainless steel, or aluminum. Depending on the metallic material, the metallic waterproof sheath 15 may be extruded or longitudinally welded.

[0041] Each of the first core 3 a and the second core 3 b may comprise a polymer layer 17 disposed around a metallic waterproof sheath 15 .

[0042] As previously mentioned, the three cores 3a-3c are arranged in a stranded configuration. The submarine DC power cable 1 may include a tape wrapped around the three stranded cores 3a-3c. The tape holds the three stranded cores 3a-3c together during manufacture before additional surrounding layers are applied around the stranded cores 3a-3c.

[0043] The submarine DC power cable 1 may comprise an armor 19 comprising one or more armor layers. If present, the armor 19 is disposed around the three cores 3a-3c.

[0044] The submarine DC power cable may include an outermost layer 23, which may be an outer sheath or an outer serving. The outermost layer 23 is disposed around the armor 19, if present.

[0045] The submarine power cable 1 may include three filler profiles 21. Each filler profile 21 is disposed between an adjacent pair of cores 3a-3c inside the tape, armor 19, and outermost layer 23. The submarine power cable 1 may include an optical fiber cable 25 disposed in one of the filler profiles 21.

[0046] Figure 2 shows another example of a submarine DC power cable 1'. The submarine DC power cable 1' is identical to the submarine DC power cable 1 described with reference to Figure 1, except for the third core 3c'. According to the example of Figure 3, the third core 3c' consists of a polymer material and a load-bearing element 6 embedded in the polymer material. The load-bearing element 6 may be made of a metal, such as steel, for example mild steel or stainless steel, or lead, aluminum, an aluminum alloy, copper, or a copper alloy, or may be made of a synthetic fiber, such as an aramid fiber.

[0047] According to one example, the load-bearing element 6 may be a load-bearing wire. In one example, the load-bearing wire may be a wire rope, i.e., may include a plurality of strands, which may form stranded subunits, and the stranded subunits may be arranged in a twisted fashion.

[0048] The load-bearing element 6 is not connected to any power source or load when the submarine DC power cable 1' is installed. If the load-bearing element 6 is made of metal, the load-bearing element 6 may be connected to earth to avoid stray voltages.

[0049] The purpose of the load-bearing element 6 is to bear tensile loads on the submarine DC power cable 1' and to provide additional weight to the submarine DC power cable 1'. The load-bearing element 6 may be disposed centrally in the third core 3c'. Therefore, in the cross section of the third core 3c', the load-bearing element 6 may be disposed at the center of the third core 3c'. Figure 3 shows an example of a submarine power cable system 27. The submarine power cable system 27 includes a first submarine DC power cable 29 and a second submarine DC power cable 31 connected to the first submarine DC power cable 29 by a joint 33.

[0050] The first submarine DC power cable 29 is a submarine DC power cable 1, 1' in the form of a dynamic power cable.

[0051] The second submarine DC power cable 31 is a submarine DC power cable 1, 1' in the form of a fixed power cable.

[0052] The joint 33 may be a flexible joint or a factory joint, but may also be a rigid subsea joint.

[0053] A first subsea DC power cable 29 is suspended from a floating structure 32, such as an oil and gas platform or a floating wind turbine, to the seabed 34. The first subsea DC power cable 29 may include a bending stiffener or bellmouth 36 that limits movement of the cable as the first subsea DC power cable 29 leaves the floating structure 32. Additionally, one or more buoyancy and / or ballast modules 38 may be disposed around a portion of the first subsea DC power cable 29.

[0054] The second submarine DC power cable 31 may be placed in a trench in the seabed 34. Because the second submarine DC power cable 31 is a three-core DC power cable, only one trench is required for its installation.

[0055] The joint 33 connects the first core 3a of the first submarine DC power cable 29 to the first core 3a of the second submarine DC power cable 31, and connects the second core 3b of the first submarine DC power cable 29 to the second core 3b of the second submarine DC power cable 31. The cores 3a of the connected first submarine DC power cable 29 and second submarine DC power cable 31 have the same polarity. The cores 3b of the connected first submarine DC power cable 29 and second submarine DC power cable 31 have the same polarity.

[0056] The third core of the second submarine DC power cable 31 may, according to one example, be a dummy element having the same or essentially the same outer diameter as the first and second cores of the second submarine DC power cable 31.

[0057] The third core 3c of the first submarine DC power cable 29 is typically not joined to the third core of the second submarine DC power cable 31. Alternatively, the third core 3c of the first submarine DC power cable 29 may be joined to the third core 3c of the second submarine DC power cable 31. Thus, according to one example, two dummy elements may be joined to each other.

[0058] The inventive concept has been described above primarily with reference to a few examples. However, as will be readily apparent to those skilled in the art, other embodiments besides those disclosed above are equally possible within the scope of the inventive concept as defined by the appended claims.

Claims

1. Three stranded cores (3a, 3b, 3c) It is equipped with a first core (3a) and a second core (3b) of the three cores (3a, 3b, 3c) are DC power cores, each comprising a conductor (4) and an insulation system (5) disposed around said conductor (4); the third core (3c) of the three cores (3a, 3b, 3c) is a dummy element having the same outer diameter as the first and second cores (3a, 3b), or the outer diameter of the third core (3c) deviates from the outer diameter of either of the first and second cores (3a, 3b) by a maximum of ±10%; A submarine DC power cable (1, 1'), wherein the third core (3c) has a cross-sectional structure that is circularly symmetric and different from the cross-sectional structures of the first and second cores (3a, 3b).

2. 2. A submarine DC power cable (1, 1') according to claim 1, wherein the third core (3c) is a single extruded dummy element comprising a polymer material.

3. 3. A submarine DC power cable (1) according to claim 2, wherein in every cross section of said third core (3c), said dummy elements consist of said polymer material.

4. 3. A submarine DC power cable (1') according to claim 2, wherein the third core (3c) consists of the polymer material and a load-bearing element (6) embedded in the polymer material.

5. 5. The submarine DC power cable (1') according to claim 4, wherein the load-bearing elements (6) are made from metal or synthetic fibers.

6. 6. A submarine DC power cable (1') according to claim 4 or 5, wherein in the cross section of the third core (3c), the load-bearing element (6) is centrally arranged.

7. A submarine DC power cable (1') according to any one of claims 4 to 6, wherein the load-bearing elements (6) comprise steel.

8. A submarine DC power cable (1, 1') according to any one of claims 2 to 7, wherein the polymer material is thermosetting.

9. A submarine DC power cable (1, 1') according to any one of claims 2 to 7, wherein the polymer material is thermoplastic.

10. 10. The submarine DC power cable (1, 1') according to claim 1, comprising: an outermost layer (23) arranged around the three stranded cores (3 a, 3 b, 3 c); a filler profile (21) arranged between the outermost layer (23) and the three stranded cores (3 a, 3 b, 3 c); and an optical fiber cable (25) arranged in one of the filler profiles (21).

11. A submarine DC power cable (1, 1') according to any one of claims 1 to 10, which is an HVDC power cable.

12. 12. The submarine DC power cable (1, 1') according to any one of claims 1 to 11, wherein the third core (3c) has an outer diameter that deviates from the outer diameter of either of the first and second cores (3a, 3b) by a maximum of ±5%.

13. A submarine DC power cable (1, 1') according to any one of claims 1 to 12, which is a dynamic submarine power cable.

14. a first submarine DC power cable (29) according to any one of claims 1 to 12; A second submarine DC power cable (31) according to any one of claims 1 to 12; Equipped with the second submarine DC power cable (31) is connected to the first submarine DC power cable (29) by a joint (33) joining corresponding poles of the first and second cores (3a, 3b); A submarine power cable system (27), wherein the first submarine DC power cable (29) is a dynamic power cable and the second submarine DC power cable (31) is a fixed power cable.

15. 15. The submarine power cable system (27) of claim 14, wherein the joint (33) is a flexible joint or a factory joint.

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