Dynamic submarine power cable for deep-sea applications

Abstract

To provide a dynamic submarine power cable capable of extending the lifetime of the cable even if installed in a deep-sea environment.SOLUTION: A dynamic submarine power cable (1) for deep-sea applications includes: a conductor (5); an insulation system (7) arranged around the conductor (5), the insulation system including an inner semiconducting layer (7a) arranged around the conductor (5), an insulation layer (7b) arranged around the inner semiconducting layer (7a), and an outer semiconducting layer (7c) arranged around the insulation layer (7b); a bedding layer (9) arranged around the insulation system (7); and a longitudinally welded corrugated metallic water barrier (11) arranged around the bedding layer (9).SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Dynamic submarine power cables are suspended from floating structures, such as floating wind turbines, to the seabed. These cables are designed to have better fatigue properties than other submarine power cables in order to withstand the constant wave load cycles.

[0003] The dynamic submarine power cable may include a metallic water barrier, such as a longitudinally welded metallic sheath, which may be corrugated along the axial direction of the cable to improve the fatigue properties of the cable.

[0004] Because of the corrugations, there is a gap between the inner surface of the ridges of the corrugations and the cable layer beneath the metal water barrier, and there is typically also a gap between the inner surface of the valleys of the corrugations and the cable layer beneath.

[0005] Typical corrugated metal water barriers may not be able to withstand the ambient hydrostatic pressures in deep-sea installations, which can be hundreds of bars, without plastic deformation, which may result in poor fatigue properties for dynamic submarine power cables.

[0006] Designs exist that offer better protection against high hydrostatic pressures, such as the design disclosed in EP 3084779, which uses a dielectric liquid between the insulation system and the water barrier to counteract radial pressure, or the design disclosed in EP 2896053, which provides a specific configuration of corrugations. However, the solution in EP 3084779 relies on oil as the liquid, and the solution in EP 2896053 may not be able to withstand depths of several thousand meters. Summary of the Invention

[0007] The bedding layer located beneath the metallic water barrier must be soft / compressible enough to compensate for the expansion and compression of the insulation system during thermal cycling resulting from various loading conditions. However, such elasticity results in the bedding layer being unable to internally support the metallic water barrier to withstand the ambient hydrostatic pressure in a deep-sea environment.

[0008] In this specification, deep sea means depths of up to several thousand metres, such as up to 3000m, 4000m or 5000m deep, where the surrounding hydrostatic pressure is on the order of 100 bar.

[0009] In view of the above, it is an object of the present disclosure to provide a dynamic submarine power cable that overcomes or at least mitigates the problems of the prior art.

[0010] Thus, according to a first aspect of the present disclosure, there is provided a dynamic submarine power cable for deep water use, comprising: a conductor; an insulation system disposed around the conductor, the insulation system comprising an inner semiconducting layer disposed around the conductor, an insulating layer disposed around the inner semiconducting layer, and an outer semiconducting layer disposed around the insulating layer; a bed layer disposed around the insulation system; and a longitudinally welded corrugated metal water barrier disposed around the bed layer, wherein the bed layer fills the corrugations of the metal water barrier, the bed layer comprising a single layer having an initial stiffness at the start of compressive stress to provide structural support against external hydrostatic pressure on the corrugated metal water barrier and an increased elasticity compared to the initial stiffness when the compressive stress reaches a stress threshold to accommodate cyclic thermal expansion and contraction of the insulating layer; or the bed layer comprises an outer layer and an inner layer, the outer layer fills the corrugations and is stiffer than the inner layer to provide structural support against external hydrostatic pressure on the corrugated metal water barrier, and the inner layer provides elasticity to accommodate cyclic thermal expansion and contraction of the insulating layer.

[0011] The bedding layer provides structural support to the metallic water barrier due to its ability to expand and contract radially during thermal cycling to compensate for the cyclic thermal expansion / contraction of the insulation system, and in addition provides structural support against high external hydrostatic pressures, minimizing the risk of collapse of the corrugated metallic water barrier, thereby extending the life of the dynamic submarine power cable, even when it is installed in deep sea environments.

[0012] The dynamic submarine power cable may be an AC dynamic submarine power cable or a DC dynamic submarine power cable.

[0013] The dynamic submarine power cable may be a single-core or a multi-core dynamic submarine power cable.

[0014] The dynamic submarine power cable may be a high voltage dynamic submarine power cable, for example rated at a nominal voltage of at least 72 kV.

[0015] The metallic water barrier may include, for example, copper or a copper alloy.

[0016] According to one embodiment, the bedding layer comprises a polymer foam.

[0017] According to one embodiment, the polymer foam comprises a polyether polyol, a polyolefin such as a thermoplastic polyolefin elastomer or an ethylene copolymer, or an ethylene propylene diene monomer rubber (EPDM), or a silicone rubber.

[0018] Examples of suitable ethylene copolymers are ethylene-vinyl acetate (EVA), ethylene butyl acrylate copolymer (EBA), and ethylene acrylic acid copolymer (EAA).

[0019] The polyether polyol may be a linear polyether polyol.

[0020] The polymer foam may consist of or include, for example, PLIXXOPOL® FC 4800C010.

[0021] According to one embodiment, the polymer foam has a modulus of elasticity that is equal to or less than the modulus of elasticity of the insulating layer.

[0022] According to one embodiment, the modulus of elasticity of the polymer foam is less than the modulus of elasticity of the insulating layer.

[0023] The elastic modulus referred to here is the elastic modulus in the initial state, that is, in the zero strain state.

[0024] The elastic modulus referred to here is the elastic modulus at a temperature within the operating temperature range of the dynamic submarine power cable, which may be 10 to 100°C or 20 to 90°C.

[0025] According to one embodiment, the modulus of elasticity of the polymer foam is 95% or less, 90% or less, 80% or less, 70% or less, or 60% or less than the modulus of elasticity of the insulating layer, so that the polymer foam can absorb some of the expansion of the insulating layer during thermal cycling.

[0026] The stress threshold may be in the range of 5 to 15 MPa.

[0027] According to one embodiment, the bed layer is a single layer exhibiting compressive stress-compressive strain characteristics with a stress plateau at a stress plateau level in the range of 10-20 MPa.

[0028] According to one embodiment, the stress plateau extends from the stress threshold to a point within a range of 0.3 to 0.5 compressive strain.

[0029] According to one embodiment, the bed layer exhibits a stress increase at a rate greater than that at the stress plateau after reaching a point where the compressive strain is in the range of 0.3 to 0.5.

[0030] According to one embodiment, the inner layer is formed by a polymer foam.

[0031] According to one embodiment, the bed layer has a recovery rate of at least 60% upon unloading. Thus, the recovery rate of the bed layer is at least 60% when compression is removed.

[0032] According to a second aspect of the present disclosure, there is provided a method of manufacturing a dynamic submarine power cable according to the first aspect, the method comprising the steps of: a) providing a conductor and an insulation system disposed around the conductor; b) providing a smooth metal sheath around the insulation system, the metal sheath being longitudinally welded to form a smooth metal water barrier; c) providing a bedding layer around the insulation system before step b) or between the insulation system and the smooth metal water barrier after step b); and d) corrugating the smooth metal water barrier to obtain a corrugated metal water barrier.

[0033] One embodiment includes activating the bed layer after step d).

[0034] Activation of the bed layer may result in radial expansion of the bed layer.

[0035] According to one embodiment, the bed layer is provided in a liquid state after step b), and activation comprises thermal activation of the bed layer in a liquid state to solidify and expand the bed layer.

[0036] 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.

[0037] 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]

[0038] [Figure 1] 1 shows a schematic cross section of an example dynamic submarine power cable. [Figure 2] 1 is a longitudinal cross-section along a portion of a dynamic submarine power cable with a line of symmetry along the longitudinal axis of the dynamic submarine power cable; [Figure 3] FIG. 1 is a compressive stress-compressive strain diagram for an exemplary bed layer. [Figure 4] 1 is a flowchart of a method for manufacturing a dynamic submarine power cable. DETAILED DESCRIPTION OF THE INVENTION

[0039] 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.

[0040] 1 shows an example of a dynamic submarine power cable 1. According to this example, the dynamic submarine power cable 1 comprises a plurality of stranded or twisted cores 3a to 3c. Alternatively, the dynamic submarine power cable may be a single-core cable.

[0041] According to this example, each of the cores 3a-3c comprises a conductor 5, an insulation system 7 disposed around the conductor 5, a bed layer 9 disposed around the insulation system 7, a corrugated metal water barrier 11 disposed around the bed layer 9, and a polymer sheath 13 disposed around the corrugated metal water barrier 11. Alternatively, one of the cores may be a dummy core.

[0042] The insulating system 7 comprises an inner semiconductor layer 7a, an insulating layer 7b arranged around the inner semiconductor layer 7a, and an outer semiconductor layer 7c arranged around the insulating layer 7b.

[0043] The insulation system 7 may be an extruded insulation system.

[0044] The insulating layer 7b may comprise a thermosetting or thermoplastic polymer, a polyolefin such as polyethylene, e.g., cross-linked polyethylene (XLPE), polypropylene, both homopolymers and copolymers, or an elastomer such as ethylene propylene diene monomer (EPDM) rubber or ethylene propylene (EPR) rubber.

[0045] The corrugated metal water barrier 11 is corrugated in the axial direction of the dynamic submarine power cable 1 .

[0046] The corrugated metal water barrier 11 is longitudinally welded. The corrugated metal water barrier 11 may comprise or consist of, for example, copper or a copper alloy such as a copper-nickel alloy.

[0047] The bedding layer 9, disposed between the outer surface of the outer semiconductor layer 7c and the inner surface of the corrugated metal water barrier 11, fills the corrugations, i.e., the spaces between the ridges and valleys of the corrugations. The bedding layer 9 preferably completely fills the corrugations.

[0048] According to one example, the bed layer 9 has a single layer that has an initial stiffness at the onset of compressive stress to provide structural support against external hydrostatic pressure acting on the metal water barrier 11. The single layer of the bed layer 9 becomes more elastic compared to the initial stiffness when the compressive stress reaches a stress threshold to accommodate cyclic thermal expansion and contraction of the insulating layer 7b. The single layer can fill the corrugations of the corrugated metal water barrier 11. Furthermore, the single layer is disposed radially inward of the corrugated metal water barrier 11 to support the corrugated metal water barrier 11.

[0049] The single layer may be formed from a nonlinear elastic material, ie, a material that has a nonlinear elasticity that changes with stress-strain conditions.

[0050] A single layer may exhibit asymmetric elastic behavior, such that the stress-strain response may be different under tension than under compression.

[0051] According to one example, the bed layer 9 consists of a single layer.

[0052] According to one example, the bed layer 9 may include an outer layer and an inner layer disposed radially inward of the outer layer. The outer layer is stiffer than the inner layer. Therefore, the inner layer is more elastic than the outer layer. The outer layer fills the corrugations of the corrugated metal water barrier 11, and the inner layer supports the corrugated metal water barrier 11.

[0053] The bed layer 9 may have a recovery rate of at least 60%, or at least 70%, upon unloading. A recovery rate of 60% means that the bed layer 9 fully recovers to its original radial thickness when released from a state in which it has been compressed to 40% of its relaxed thickness.

[0054] The polymer sheath 13 may be extruded onto the corrugated metal water barrier 11 .

[0055] The dynamic submarine power cable 1 may comprise filler profiles in a helical arrangement twisted together with the cores 3a-3c.

[0056] The dynamic submarine power cable 1 may comprise an armour 15 comprising one or more layers of armour elements 17. The armour 15 is common to all cores 3a-3c and is arranged around the cores 3a-3c.

[0057] Additionally, the dynamic submarine power cable 1 may comprise an outer sheath or outer serving 19 disposed around the cores 3a-3c and the armor 15 (if present).

[0058] 2 shows an example of a multi-layered bed layer 9. The bed layer 9 comprises an outer layer 9a that fills the corrugations of the corrugated metal water barrier 11, and an inner layer 9b that is disposed radially inward of the outer layer 9a.

[0059] The outer layer 9a may comprise, for example, a non-foamed thermoplastic polyolefin. The outer layer 9a may be extruded.

[0060] The outer layer 9a may comprise polyethylene, such as, for example, medium density polyethylene (MDPE) or high density polyethylene (HDPE).

[0061] The inner layer 9b may, for example, comprise a polymer foam, which may comprise a polyether polyol, or a polyolefin such as an ethylene copolymer, for example EVA, EBA, EAA, or EPDM, or a silicone rubber.

[0062] The inner layer 9b preferably has a stiffness lower than that of the insulating layer 7b (and generally the insulating system 7). The inner layer 9b may have a modulus of elasticity equal to or less than that of the insulating layer 7b. The modulus of elasticity of the inner layer 9b may be 95% or less, 90% or less, 80% or less, 70% or less, 60% or less, or 50% or less of the modulus of elasticity of the insulating layer 7b.

[0063] For example, if the insulating layer 7b is XLPE, the modulus of elasticity of the inner layer 9b may be 70 MPa or less.

[0064] 3 illustrates the compressive stress-strain characteristics of another example of the bed layer 9. In particular, the illustrated compressive stress-strain characteristics are those of a single layer of the bed layer 9, which provides structural support against collapse of the corrugated metal water barrier 1 due to ambient hydrostatic pressure, while also accommodating the expansion-contraction cycle of the insulating layer 7b.

[0065] The bed layer 9 has an initial stiffness at the onset of compressive stress to provide structural support against external hydrostatic pressure acting on the metallic water barrier 11. In this example, the initial elastic compression is linear and is indicated by the first region R1 in Figure 3. The single layer of the bed layer 9 increases in elasticity relative to its initial stiffness when the compressive stress reaches a threshold stress to accommodate the cyclic thermal expansion and contraction of the insulating layer 7b. In the example shown in Figure 3, this increase in elasticity is achieved at a threshold stress of approximately 10 MPa. The bed layer 9 then reaches a stress plateau, indicated by the second region R2 in Figure 3, whose level is in the range of approximately 10 to 20 MPa. The stress plateau corresponds to the collapse of the bed layer 9. Here, the compressive strain increases much faster than the level of the compressive stress, i.e., the bed layer 9 becomes more elastic than during the initial compressive stress. The level of the stress plateau depends on the design of the corrugated metallic water barrier 11 and the maximum depth to which the dynamic submarine power cable 1 will be installed. According to this example, a stress plateau is reached at a compressive strain, or stress threshold, of approximately 0.05. The stress plateau extends from this stress threshold to a compressive strain of approximately 0.4. In the third region R3, this example bed layer 9 exhibits a higher rate of stress increase after the compressive strain reaches 0.4 than at the stress plateau. Thus, at these higher compressive strain levels, elasticity decreases.

[0066] The single layer of the bed layer 9 may have an elastic modulus equal to or less than that of the insulating layer 7b. The elastic modulus of the bed layer 9 may be 95% or less, 90% or less, 80% or less, 70% or less, 60% or less, or 50% or less of that of the insulating layer 7b.

[0067] For example, when the insulating layer 7b is made of XLPE, the elastic modulus of a single layer of the bed layer 9 may be 70 MPa or less.

[0068] FIG. 4 is a flowchart of a method for manufacturing the dynamic submarine power cable 1.

[0069] In step a), a conductor 5 and an insulating system 7 arranged around the conductor 5 are provided. The insulating system 7 may be extruded around the conductor 5. Alternatively, the insulating system 7 may be made of paper wrapped around the conductor 5.

[0070] In step b), a smooth metal sheath is provided around the insulation system 7. Furthermore, step b) includes longitudinally welding the metal sheath to form a smooth metallic water barrier around the insulation system 7.

[0071] In step c), a bedding layer 9 is provided or formed around the insulating system 7. Step c) may be performed before or after step b).

[0072] If step c) is performed after step c), the bed layer material can be injected or poured in liquid form into the gap between the insulating system 7 and the smooth metallic water barrier.

[0073] In step d) the smooth metal water barrier is corrugated to obtain the corrugated metal water barrier 11. The smooth metal water barrier is corrugated in a corrugating machine.

[0074] The bed layer 9 may, according to one example, be activated after step d). The activation may involve heat activation of the bed layer in a liquid state to solidify and expand the bed layer 9 to fill the corrugations of the corrugated metal water barrier 11. In this case, the bed layer 9 is activated after corrugating the metal water barrier 11 to facilitate the corrugation process.

[0075] Whether step c) is performed before or after step b) depends on the material of the bed layer 9. A thick bed layer 9 may, according to one example, be applied by extrusion before step b). In this case, the bed layer 9 may be radially compressed by a metallic water barrier in step b) and therefore an activation step to fill the corrugations may not be required.

[0076] 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. A dynamic submarine power cable (1) for deep sea applications, comprising: A conductor (5), an insulating system (7) disposed around the conductor (5) and comprising an inner semiconductor layer (7a) disposed around the conductor (5), an insulating layer (7b) disposed around the inner semiconductor layer (7a), and an outer semiconductor layer (7c) disposed around the insulating layer (7b); a bed layer (9) arranged around said insulation system (7); a longitudinally welded corrugated metal water barrier (11) disposed around the bed layer (9); Equipped with The bed layer (9) fills the corrugations of the corrugated metal water barrier (11), the bed layer (9) comprises a single layer having an initial stiffness at the onset of compressive stress to provide structural support against external hydrostatic pressure applied to the metallic water barrier (11) and an increased elasticity compared to the initial stiffness when the compressive stress reaches a stress threshold to accommodate cyclic thermal expansion and contraction of the insulating layer (7); or The bed layer (9) comprises an outer layer (9a) and an inner layer (9b), the outer layer filling the corrugations and being stiffer than the inner layer (9b) to provide structural support against external hydrostatic pressures applied to the corrugated metal water barrier (11), and the inner layer (9b) providing elasticity to accommodate cyclic thermal expansion and contraction of the insulating layer (7). Dynamic submarine power cable (1).

2. 2. The dynamic submarine power cable (1) according to claim 1, wherein the bedding layer (9) comprises a polymer foam.

3. 3. The dynamic submarine power cable (1) according to claim 2, wherein the polymer foam comprises polyether polyol, polyolefin such as thermoplastic polyolefin elastomer or ethylene copolymer, or ethylene propylene diene monomer rubber (EPDM), or silicone rubber.

4. 4. Dynamic submarine power cable (1) according to claim 2 or 3, wherein the polymer foam has an elastic modulus equal to or less than the elastic modulus of the insulating layer (7).

5. 5. A dynamic submarine power cable (1) according to claim 4, wherein the modulus of elasticity of the polymer foam is less than the modulus of elasticity of the insulating layer (7).

6. 5. The dynamic submarine power cable (1) according to claim 4, wherein the modulus of elasticity of the polymer foam is 95% or less, 90% or less, 80% or less, 70% or less, or 60% or less of the modulus of elasticity of the insulating layer (7).

7. 7. The dynamic submarine power cable (1) according to any one of claims 1 to 6, wherein the bed layer (9) is a single layer exhibiting compressive stress-compressive strain characteristics with a stress plateau at a stress plateau level in the range of 10 to 20 MPa.

8. 8. The dynamic submarine power cable (1) according to claim 7, wherein the stress plateau extends from the stress threshold to a point within a range of 0.3 to 0.5 compressive strain.

9. 9. The dynamic submarine power cable (1) according to claim 8, wherein the bed layer (9) exhibits a stress increase at a rate higher than that at the stress plateau after the compressive strain reaches a point in the range of 0.3 to 0.

5.

10. 7. A dynamic submarine power cable (1) according to any one of claims 2 to 6, wherein the inner layer (9b) is formed by the polymer foam.

11. 11. The dynamic submarine power cable (1) according to any one of claims 1 to 10, wherein the bed layer (9) has a recovery rate of at least 60% upon unloading.

12. A method for manufacturing a dynamic submarine power cable (1) according to any one of claims 1 to 11, comprising the steps of: a) providing said conductor (5) and said insulating system (7) arranged around said conductor; b) providing a smooth metal sheath around the insulation system, the metal sheath being longitudinally welded to form a smooth metallic water barrier; c) providing a bedding layer (9) around the insulation system (7) before step b) or between the insulation system (7) and the smooth metallic water barrier after step b); d) corrugating the smooth metal water barrier to obtain the corrugated metal water barrier (11); A method comprising:

13. 13. The method according to claim 12, comprising activating the bed layer (9) after step d).

14. 13. The method according to claim 12, wherein the bed layer (9) is provided in a liquid state after step b), and activation comprises thermal activation of the bed layer (9) in a liquid state to solidify and expand the bed layer (9).

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