Submarine power cable system with moisture buffer zone

Abstract

To provide a submarine power cable system that prevents or at least restricts longitudinal water ingress along the conductor of the static power cable section.SOLUTION: A submarine power cable system comprises: a wet design power cable section (1a) including: a first conductor section, a first insulation system section arranged around the first conductor section, and a screen layer formed by one or more of helically laid elongated metal elements arranged around the first insulation system section; a static power cable section (1b), which is a moisture buffer zone, including a second conductor section connected to the first conductor section; and a second insulation system section connected to the first insulation system section by means of a flexible joint (1c).SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Dynamic power cables are typically used to power floating oil and gas platforms or as array or export cables in floating wind applications. One failure mode of dynamic cables is fatigue-related, which can occur within the radial water barrier of the core in dry systems. Therefore, it is desirable to design dynamic power cables without a radial water barrier, i.e., with a wet insulation system, in applications involving significant fatigue loads. The second end of the dynamic power cable is often spliced ​​to a static power cable, preferably of a dry design, i.e., one that includes a sealed radial water barrier. Static cables are dry for two reasons: first, static power cables can be repaired with conventional rigid seam joints, including prefabricated core joints; and second, the consequences of unexpected failure modes of the wet insulation system are limited to the dynamic power cable, which is typically on the order of 1% of the total length of the submarine cable system. The wet interface between the joint and the cable is what makes prefabricated joints unsuitable for wet applications. This is also addressed, for example, in CIGRE TB 722, which states that the physical contact surface between the insulation system of the joint and the cable is not suitable for operation in wet conditions. Summary of the Invention

[0003] In view of the above, it is an object of the present disclosure to provide a submarine power cable system that solves or at least alleviates the problems of the prior art.

[0004] Thus, there is provided a submarine power cable system comprising: a wet-design power cable section including a first conductor section, a first insulation system section disposed around the first conductor section, and a screen layer formed by one or more elongated metal elements laid in a spiral around the first insulation system section; and a static power cable section that is a moisture buffer zone, the static power cable section including a second conductor section connected to the first conductor section and the second insulation system section connected to the first insulation system section by a flexible joint, the static power cable section further including a metallic radial waterproof jacket disposed around the second insulation system section, the metallic radial waterproof jacket being electrically connected to the screen layer, wherein from the flexible joint to a distal end of the static power cable section, the submarine power cable system has an axial length in the range of 1 to 1000 m, and the distal end is configured to be connected to or is connected to a submarine electrical component.

[0005] The static power cable section acts as a moisture buffer zone, so that the wet-design power cable section can be connected in a simple manner to a submarine electrical component, such as a dry submarine power cable section or a submarine electrical module, via the static power cable section, i.e., the moisture buffer zone.

[0006] For example, a submarine power cable system formed by a wet-design power cable section and a static power cable section may be a single-length repair cable. The repair cable is a replacement cable length. The repair cable is much shorter than the installed submarine power cable system and is typically stored near the location of the submarine power cable system and is intended to replace a portion as needed, such as in the case of localized mechanical damage to the original submarine power cable system. In one example, in a non-installed state, when stored, a submarine power cable system according to the present disclosure may be comprised of a wet-design power cable section and a static power cable section.

[0007] As an example, an existing, pre-installed cable system may include a wet-design dynamic submarine power cable section joined by a flexible joint with a dry export cable. According to this example, the dynamic power cable section suffers from a fault or damage requiring repair. While the flexible joint may not be moisture-sensitive, the repair requires the use of a moisture-sensitive rigid sea joint. The repair may include replacing the entire wet-design dynamic submarine power cable section and a portion of the dry export cable with a submarine power cable system according to the present disclosure. The distal end of the static power cable section of the single-length repair cable may then be joined to the existing dry export cable by a rigid sea joint, with the static power cable section acting as a moisture buffer zone between the wet-design dynamic submarine power cable section and the dry export cable.

[0008] The static power cable section is a dry static power cable section.

[0009] The first insulation system section can be based on, for example, XLPE or ethylene propylene rubber (EPR).

[0010] The second insulation system section can be based on, for example, XLPE or EPR.

[0011] The first conductor section may be round, compressed, or stranded, such as in segments, in which case the wet-design power cable section may include a water blocking compound disposed between the strands from which the first conductor section is formed and filling the voids between the strands.

[0012] The second conductor section may be round, compressed, or stranded, such as in segments. In this case, the static power cable section may include a water blocking compound disposed between the strands from which the second conductor section is formed and filling the voids between the strands, thereby preventing or at least limiting the ingress of water longitudinally along the conductor of the static power cable section.

[0013] Flexible joints can be performed at a factory before any armor layers, if any, are applied to one or more power cores in a submarine power cable system, or in the field if any armor layers are already present. Flexible joints are also called factory joints in the former case and flexible field joints or flexible repair joints in the latter case. In a flexible joint, a first conductor section and a second conductor section are welded together to form a conductor joint, and a joint insulation system is rebuilt over the conductor joint. Typically, in the joining process, the end sections of the first insulation system and the second insulation system are positioned to 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 semiconductive layer is connected to a corresponding layer of each of the first and second insulation system sections, the insulating layer is connected to a corresponding layer of each of the first and second insulation system sections, and the outer semiconductive layer is connected to a corresponding layer of each of the first and second insulation system sections. The flexible joint may be a vulcanized flexible joint, in which case the joint insulation system is vulcanized.

[0014] In contrast to flexible joints, prefabricated or preformed joints include a prefabricated polymer sleeve that slides over the conductor joint. This typically makes the joint larger than a flexible joint. In this case, the conductor joint is often formed using a tubular connector that is clamped or screwed onto the two conductor sections being joined.

[0015] The static power cable section may include a water-swellable layer disposed about the second insulation system section and beneath the metallic radial waterproofing jacket.

[0016] According to one embodiment, the axial length is in the range of 1 to 500 m, or 1 to 400 mm, or 1 to 200 m, or 1 to 100 m, or 1 to 50 m, or 1 to 10 m, or 5 to 500 m, or 5 to 400 mm, or 5 to 200 m, or 5 to 100 m, or 5 to 50 m, or 5 to 10 m.

[0017] According to one embodiment, the wet-design power cable section is a dynamic submarine power cable section.

[0018] According to one embodiment, the wet design power cable section is a static power cable section.

[0019] According to one embodiment, the metallic radial waterproof coating is an extruded metallic coating or is longitudinally welded. The metallic radial waterproof coating may be, for example, a lead coating or may comprise copper, a copper alloy, stainless steel, aluminum, or an aluminum alloy.

[0020] One embodiment includes a subsea electrical component, with the distal end of the static power cable section being connected to the subsea electrical component.

[0021] The static power cable section may be directly connected to the subsea electrical component.

[0022] According to one embodiment, the static power cable section is a first static power cable section, the submarine power cable system includes a second static power cable section, the submarine electrical component is a rigid sea joint, and the first static power cable section is coupled to the second static power cable section by the rigid sea joint.

[0023] According to one embodiment, the second static power cable section includes a third conductor section connected to the second conductor section and a third insulation system section disposed around the third conductor section, and the second static power cable section further includes a water-swellable layer disposed around the third insulation system section and a metallic radial waterproof jacket disposed around the water-swellable layer.

[0024] The third conductor section may be round-stranded, compressed, or stranded, such as in segments. In this case, the second static power cable section may include a water-blocking compound disposed between the strands from which the second conductor section is formed, which prevents or at least limits the ingress of water longitudinally along the conductor of the second static power cable section.

[0025] According to one embodiment, the second static power cable section is longer than the first static power cable section.

[0026] According to one embodiment, the second static power cable section is one, two, three, or four orders of magnitude longer than the first static power cable section.

[0027] According to one embodiment, the subsea electrical component is a subsea transformer module, a subsea reactor module, a subsea motor module, a subsea pump module, a subsea switchgear module, or a subsea frequency converter module.

[0028] According to one example, the subsea electrical components may include subsea connectors that connect static power cable sections with subsea transformer modules, subsea reactor modules, subsea motor modules, subsea pump modules, subsea switchgear modules, or subsea frequency converter modules. The subsea connectors may be wet-mate or dry-mate subsea connectors.

[0029] According to one embodiment, the submarine electrical component is a submarine T-joint and the submarine power cable system includes two additional static power cable sections each connected to a submarine T-joint.

[0030] According to one embodiment, each of the two additional static power cable sections includes a respective insulation system section and a respective metallic radial waterproof jacket disposed around the insulation system section.

[0031] According to one embodiment, the wet-design power cable section does not include any helically laid elongated metallic elements radially outward from the first conductor section other than those forming the screen layer and, if present, those of the sheath, and does not include any metallic radial waterproof covering. Thus, the helically laid elongated elements radially outward from the first conductor section are only those of the screen layer, and, if the wet-design power cable includes an sheath having one or more sheath layers, also include the helically laid elongated elements of the sheath.

[0032] According to one embodiment, the submarine power cable system is a polyphase AC power cable system.

[0033] 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, apparatus, components, means, steps, etc." should be interpreted broadly as referring to at least one instance of an element, apparatus, component, means, step, etc., unless otherwise specified.

[0034] Specific embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0035] [Figure 1] FIG. 1 is a diagram illustrating a schematic of a submarine power cable system including a wet-design power cable section and a static power cable section. [Figure 2] FIG. 1 is a schematic diagram illustrating a cross section of an example wet-design power cable section. [Figure 3] 1A and 1B are schematic cross-sectional views of an example static power cable section; [Figure 4] FIG. 1 illustrates a schematic diagram of an example of a submarine power cable system including submarine electrical components in the form of rigid sea joints. [Figure 5] 1 is a schematic diagram of an example of a submarine power cable system including a submarine electrical component in the form of a submarine electrical module; [Figure 6] FIG. 1 illustrates a schematic diagram of an example of a submarine power cable system including a submarine electrical component in the form of a T-joint. [Figure 7] FIG. 1 illustrates a schematic diagram of an example of a submarine power cable system including a submarine electrical component in the form of a T-joint. DETAILED DESCRIPTION OF THE INVENTION

[0036] The concepts of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. However, these aspects may be embodied in many different forms and should not be construed as limiting. Rather, these embodiments are provided as examples so that this disclosure will be thorough and complete, and will fully convey the scope of all aspects of the present invention to those skilled in the art. Like numerals refer to like elements throughout the description.

[0037] FIG. 1 shows a schematic side view of an example of a submarine power cable system 1.

[0038] The submarine power cable system 1 includes a wet-design power cable section 1a and a static power cable section 1b. The submarine power cable system 1 also includes a flexible joint 1c that directly connects the wet-design power cable section 1a to the static power cable section 1b.

[0039] The wet-design power cable section 1a may be a wet-design dynamic power cable section or a wet-design static power cable section.

[0040] 2, a cross-section of a wet design power cable section 1a is shown. The cross-section may be at any point along the length of the wet design power cable section 1a.

[0041] According to this example, the wet-design power cable section 1a is a multi-core submarine power cable section. For example, the wet-design power cable section 1a may be a polyphase AC submarine power cable section, such as a three-phase AC submarine power cable section.

[0042] According to one example, the wet-design power cable section 1a can include three stranded cores 2a, 2b, and 2c. The cores 2a-2c are twisted together. Alternatively, the wet-design power cable section can include a single core.

[0043] Each core 2a-2c includes a respective first conductor section 3, which extends along the length of the wet-design power cable section 1a.

[0044] Each of the cores 2a-2c includes a respective first insulation system section 5. The first insulation system section 5 is disposed around the first conductor section 3. The first insulation system section 5 includes an inner semiconducting layer 7 disposed around the first conductor section 3, an insulating layer 9 disposed around the inner semiconducting layer 7, and an outer semiconducting layer 11 disposed around the insulating layer 9. The first insulation system section 5 may be polymer-based. The first insulation system section 5 may be extruded. The first insulation system section 5 may be, for example, XLPE- or EPR-based. Thus, each of the layers 7, 9, and 11 may include, for example, XLPE or EPR as the base polymer.

[0045] Each core 2a-2c includes a screen layer 13 formed by one or more spirally laid elongated metal elements 15 arranged around the first insulation system section 5. The one or more elongated metal elements 15 may be, for example, multiple wires or tapes. The elongated metal elements may comprise, for example, copper or aluminum. The screen layer 13 is designed to carry charge or fault currents in the event of an electrical fault.

[0046] According to one example, each core 2a-2c may include a bedding layer arranged between the first insulation system section 5 and the screen layer 13. The bedding layer may be semiconducting.

[0047] Additionally, each core 2 a - 2 c may include a polymer layer 17 disposed around the screen layer 13 .

[0048] Instead of, or in addition to, the bedding layers described above, each core may include an outer bedding layer disposed between the screen layer and the polymer layer 17 .

[0049] Cores 2a-2c do not include lead sheathing, longitudinally welded metal sheathing, or helically laid elongated metal elements other than those forming a screen layer in one example, and those of the stranded conductor sections if the first conductor sections are stranded, or, if wet-design power cable section 1a includes an armor with helically laid elongated elements, the armor. Thus, water that penetrates into cores 2a-2c through polymer layer 17 can diffuse into the corresponding first insulation system section 5.

[0050] Wet design power cable section 1 a can include one or more armor layers 19 disposed about cores 2 a-2 c. Additionally, wet design power cable section 1 a can include an outer coating or outer serving 20 disposed about armor layer 19, or about stranded cores 2 a-2 c if no armor layer is present.

[0051] FIG. 3 shows a cross-sectional view of the static power cable section 1b along any point thereof.

[0052] According to one example, the static power cable section 1b is a multi-core submarine power cable section. For example, the static power cable section 1b may be a polyphase AC submarine power cable section, such as a three-phase AC submarine power cable section.

[0053] The static power cable section 1b may include three stranded cores 21a, 21b, 21c, or, if the wet-design power cable section has a single core, the static power cable section may include a single core.

[0054] Each core 21a-21c includes a respective second conductor section 23 that extends along the length of the static power cable section 1b.

[0055] Each of the cores 21a-21c includes a respective second insulation system section 25. The second insulation system section 25 is disposed around the second conductor section 23. The second insulation system section 25 includes an inner semiconducting layer 27 disposed around the second conductor section 23, an insulating layer 29 disposed around the inner semiconducting layer 27, and an outer semiconducting layer 31 disposed around the insulating layer 29. The second insulation system section 25 may be polymer-based. The second insulation system section 25 may be extruded. The second insulation system section 25 may be, for example, XLPE, EPR, polypropylene, or ethylene propylene diene monomer-based, or any other suitable polymer. Thus, each of the layers 27, 29, and 31 may include, for example, XLPE, EPR, polypropylene, or ethylene propylene diene monomer as the base polymer.

[0056] Each core 21a-21c includes a water-swellable layer disposed around the second insulation system section 25. The water-swellable layer may be formed, for example, from a tape wrapped around the second insulation system section 25 or may be an extruded layer. The water-swellable layer may be semi-conductive. The water-swellable layer functions to prevent or reduce water infiltration along the static power cable section 1b in the longitudinal direction.

[0057] Each core 21a-21c further includes a metallic radial waterproof coating 33 disposed around the water-swellable layer. The metallic radial waterproof coating 33 may be, for example, an extruded metallic coating such as a lead coating, or may be longitudinally welded. If the metallic radial waterproof coating 33 is longitudinally welded, it may include, for example, copper, a copper alloy, stainless steel, aluminum, or an aluminum alloy.

[0058] The metallic radial waterproof coating 33 is electrically connected to the screen layer 13. The electrical connection may be direct or via a common ground point.

[0059] Each core 21 a - 21 c may include a polymer layer 35 disposed around a metallic radial waterproof coating 33 .

[0060] The cores 21a-21c are stranded together. The static power cable section 1b may include an armor layer 37 disposed around the cores 21a-21c. Additionally, the static power cable section 1b may include an outer coating or outer serving 39 disposed around the armor layer 37.

[0061] The first conductor section 3 of each of the cores 2a to 2c is joined to the second conductor section 23 of the cores 21a to 21c, respectively. The conductor joints thus formed may be made by welding.

[0062] The purpose of static power cable section 1b is to act as a moisture buffer zone between the wet-design power cable 1a and the submarine electrical components, which may be dry, connected directly to the far end 1d of static power cable section 1b, i.e., to protect the submarine electrical components from longitudinal water ingress that may enter the submarine power cable system 1 radially through the wet-design power cable section 1a.

[0063] The axial length of the static power cable system 1 from the flexible joint 1c to the distal end 1d of the static power cable section 1b is in the range of 1 to 1000 m to protect the submarine electrical components from moisture, e.g., to keep the moisture level in the submarine electrical components below a predetermined value, such as below 70% relative humidity, due to longitudinal water ingress from the wet-design power cable section 1a into the static power cable section 1b in the electrical insulation layer within the submarine electrical components throughout the predefined expected operating life of the static power cable section. The predefined expected operating life may be 30 or 40 years.

[0064] Next, a modified example including the submarine power cable system 1 will be described with reference to FIGS.

[0065] In the example of FIG. 4, the wet-design power cable section 1 a is a dynamic submarine power cable suspended from a floating structure 44 to the seabed 43 .

[0066] In the example of Figure 4, the submarine power cable system 1 includes a second static power cable section 41 and a submarine electrical component 45 in the form of a rigid sea joint that connects the static power cable section 1b with the second static power cable section 41 on the seabed 43. The second static power cable section 41 is a dry static power cable section.

[0067] The second static power cable section 41 is longer than the first static power cable section 1b. The second static power cable section 41 is one, two, three, or four orders of magnitude longer than the first static power cable section 1b.

[0068] The rigid sea joint has a non-watertight outer casing. The rigid sea joint includes three watertight inner casings, each configured to accommodate an electrical joint between a pair of cores of the static power cable section 1b and the second static power cable section 41. The static power cable section 1b and the second static submarine power cable section 41 must be dry for the electrical joint, and each may include a pre-formed or pre-fabricated joint sleeve as a joint insulation system on the respective conductor joint. The second static power cable section further includes a respective water-swellable layer disposed around each insulation system section of its core.

[0069] The wet-design power cable section 1a and the static power cable section 1b can be used as repair cables to connect with a second static submarine power cable 41 located on the seabed 43. Therefore, the wet-design power cable section 1a can be easily joined with the second static power cable section 41 by a rigid sea joint due to the moisture buffer zone provided by the static power cable section 1b.

[0070] In the example of FIG. 5, the wet-design power cable section 1 a is a dynamic submarine power cable suspended from a floating structure 44 to the seabed 43 .

[0071] In the example of FIG. 5 , the submarine power cable system 1 includes a second static power cable section 41 and a submarine electrical component 45′ that connects the static power cable section 1b to the second static power cable section 41 on the seabed 43. The second static power cable section 41 is a dry-type static power cable section. In this example, the submarine electrical component 45′ is a submarine electrical module such as a submarine transformer, a submarine reactor, a submarine motor, a submarine pump, a submarine switchgear, or a submarine frequency converter. The electrical connection between the static power cable section 1b and the second static power cable section 41 may need to be dry, and the interior of the submarine electrical component 45′, which may be filled with a dielectric liquid, may need to have a dry-type connection interface, such as a dry-mate submarine connector, for connecting the wet-type design cable section 1a to the dry-type static power cable section 1b.

[0072] In the example of Figures 6-7, the wet design power cable section 1a is a dynamic submarine power cable suspended from a floating wind turbine 47 of a floating wind farm 49 to the seabed 43. The floating wind farm 49 may include many floating wind turbines 47, each connected to a static submarine cable 51 on the seabed via a respective wet design power cable section 1a in the form of a dynamic submarine power cable and static power cable section 1b. This is shown in more detail in Figure 7, which is an enlarged view of circle A in Figure 6.

[0073] According to this example, the submarine power cable system 1 includes two additional static power cable sections 53a and 53b forming part of a static submarine cable 51, connected to each other and to the static power cable section 1b by a submarine electrical component 45", which in this example is a submarine T-joint or multi-cable joint. The additional static power cable sections 53a, 53b are dry static power cable sections. Each core therefore includes a respective metallic radial waterproofing covering, which may be extruded or longitudinally welded, to prevent radial water penetration into the insulation system sections of the additional static power cable sections 53a and 53b.

[0074] The inventive concept has been described above primarily with reference to a few examples, however, as will be readily understood 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 submarine power cable system (1), comprising: a wet-type design power cable section (1a) including a first conductor section (3), a first insulation system section (5) disposed around the first conductor section (3), and a screen layer (13) formed by one or more helically laid elongated metal elements disposed around the first insulation system section (5); a static power cable section (1b) that is a moisture buffer zone, the static power cable section (1b) including a second conductor section (23) connected to the first conductor section (3) and a second insulation system section (25) connected to the first insulation system section (5) by a flexible joint (1c), the static power cable section (1b) further including a metallic radial waterproof sheath (33) disposed around the second insulation system section (25), the metallic radial waterproof sheath (33) being electrically connected to the screen layer (13); The submarine power cable system (1) has an axial length in the range of 1 to 1000 m from the flexible joint (1 c) to the far end (1 d) of the static power cable section (1 b), and the far end (1 d) is configured to be connected to or is connected to a submarine electrical component (45; 45'; 45").

2. 2. A submarine power cable system (1) according to claim 1, wherein the axial length is in the range of 1 to 500 m, or 1 to 400 mm, or 1 to 200 m, or 1 to 100 m, or 1 to 50 m, or 1 to 10 m, or 5 to 500 m, or 5 to 400 mm, or 5 to 200 m, or 5 to 100 m, or 5 to 50 m, or 5 to 10 m.

3. 3. The submarine power cable system (1) according to claim 1 or 2, wherein the wet-design power cable section (1a) is a dynamic submarine power cable section.

4. 3. The submarine power cable system (1) according to claim 1 or 2, wherein the wet-design power cable section (1a) is a static power cable section.

5. 5. A submarine power cable system (1) according to any one of claims 1 to 4, wherein the metallic radial waterproof sheath (33) is an extruded metallic sheath or is longitudinally welded.

6. 6. A submarine power cable system (1) according to any one of claims 1 to 5, comprising a submarine electrical component (45; 45'; 45"), the distal end (1d) of the static power cable section (1b) being connected to the submarine electrical component (45; 45'; 45").

7. 7. The submarine power cable system (1) of claim 6, wherein the static power cable section (1 b) is a first static power cable section, the submarine power cable system (1) includes a second static power cable section (41), the submarine electrical component (45) is a rigid sea joint, and the first static power cable section (1 b) is joined to the second static power cable section (41) by the rigid sea joint.

8. 8. The submarine power cable system of claim 7, wherein the second static power cable section includes a third conductor section connected to the second conductor section and a third insulation system section disposed around the third conductor section, and the second static power cable section further includes a water-swellable layer disposed around the third insulation system section and a metallic radial waterproof jacket disposed around the water-swellable layer.

9. 9. The submarine power cable system (1) according to claim 8, wherein the second static power cable section (41) is longer than the first static power cable section (1b).

10. 10. The submarine power cable system (1) according to claim 9, wherein the second static power cable section (41) is one, two, three or four orders of magnitude longer than the first static power cable section (1b).

11. 7. The submarine power cable system (1) according to claim 6, wherein the submarine electrical component (45') is a submarine transformer module, a submarine reactor module, a submarine motor module, a submarine pump module, a submarine switchgear module, or a submarine frequency converter module.

12. 7. The submarine power cable system (1) of claim 6, wherein the submarine electrical component (45") is a submarine T-joint, and the submarine power cable system (1) includes two additional static power cable sections (53a, 53b) each connected to the submarine T-joint.

13. 13. The submarine power cable system (1) according to claim 12, wherein each of the two additional static power cable sections (53a, 53b) comprises a respective insulation system section and a respective metallic radial waterproof jacket disposed around the insulation system section.

14. 14. A submarine power cable system according to any one of claims 1 to 13, wherein the wet-design power cable section (1 a) does not include, radially outside the first conductor section (3), any elongated metal elements helically laid other than those forming the screen layer and, if present, the sheath, and does not include a metallic radial waterproof sheath.

15. A submarine power cable system (1) according to any one of claims 1 to 14, wherein the submarine power cable system (1a) is a polyphase AC power cable system.

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