Method of manufacturing wet or semi-wet design high-voltage submarine power cable

Abstract

To provide a method of manufacturing a wet or semi-wet high-voltage or extra-high-voltage submarine power cable which can manufacture an insulation layer without or with only a very small quantity of foreign particles.SOLUTION: A method of manufacturing a wet or semi-wet design high-voltage or extra-high-voltage submarine power cable includes: a) supplying polymer materials to an extruder from a material handling room, where the material handling room fulfills clean room class 8 according to ISO-14644-1: 2015 or is cleaner; and b) extruding an insulation system, including an insulation layer, around a conductor in the extruder using the polymer material, where the extruder fulfills the requirements of clean room class 8 according to ISO-14644-1: 2015 or is cleaner.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Submarine power cables have traditionally been designed with a dry design, which means that they have a circumferential metallic water barrier outside the insulation system that seals the insulation system.

[0003] The circumferential metallic water barrier that seals the insulation system is formed by extrusion or longitudinal welding of a metal sheath. Water barriers have traditionally been made of lead, but today many different lead-free metals have been proposed, including various copper alloys, aluminum, or stainless steel.

[0004] If water is allowed to come into contact with the insulation system, the relative humidity within the insulation system will increase. If the relative humidity exceeds a threshold, the insulation system may be subject to water treeing, which may result in partial discharge activity or breakdown of the insulation system. Summary of the Invention

[0005] The inventors of the present invention have realized that the presence of impurities in an insulating layer, in combination with the electric field in the insulating layer, can cause water treeing. The stronger the electric field in the presence of a wet insulating layer, the greater the risk of water treeing if the insulating system contains impurities. Therefore, if the insulating layer can be manufactured without foreign particles or with only very small amounts of foreign particles, water treeing can potentially be avoided in submarine cables of non-dry, i.e., wet or semi-wet, design, even for high or extra-high voltage applications. This would result in savings in size, weight, and material.

[0006] Ultra-clean polymer insulating materials are available on the market, such as Borealis' Borlink™ compound, but simply using such materials does not necessarily result in an insulating layer that is sufficiently free of foreign particles of the type that can cause water treeing, especially in high voltage applications such as above 72 kV or 100 kV.

[0007] In view of the above, it is an object of the present disclosure to provide a method for solving or at least alleviating the problems of the prior art.

[0008] Thus, according to a first aspect of the present disclosure, there is provided a method of manufacturing a high or extra-high voltage submarine power cable of wet or semi-wet design, the method comprising the steps of: a) feeding a polymeric material from a material handling room that meets clean room class 8 per ISO-14644-1:2015 or cleaner to an extruder; and b) using the polymeric material to extrude an insulation system, including an insulating layer, around a conductor in an extruder that meets the requirements of clean room class 8 per ISO-14644-1:2015 or cleaner.

[0009] High voltage (HV) or extra high voltage (EHV) submarine power cables manufactured according to this method have insulation systems, particularly insulation layers, that can withstand wet environments even at high and extra high voltage levels, thereby eliminating the need to use metallic water barriers to protect the insulation system against radial water intrusion.

[0010] The HV or EHV submarine power cable may be a dynamic submarine power cable or a fixed submarine power cable.

[0011] HV or EHV submarine power cables may be AC ​​or DC submarine power cables. While water treeing is theoretically primarily a problem in AC applications where the electric field across the insulation layer varies, water treeing can also be a problem in DC applications because the voltage in DC applications can contain harmonics of various frequencies and amplitudes.

[0012] The HV or EHV submarine power cable may not include water-swellable tapes, which may contain contaminants that can migrate into the insulation system. This may make the insulation layer susceptible to water treeing after manufacture of the HV or EHV submarine power cable as a result of contamination from the water-swellable tapes.

[0013] A wet HV or EHV submarine power cable does not have a metallic circumferential water barrier that seals the insulation system. Here, a wet HV or EHV submarine power cable does not include a longitudinally welded, soldered, extruded, or longitudinally bonded metallic water barrier or wrapped water-blocking metallic tape. A semi-wet HV or EHV submarine power cable has a metallic circumferential water barrier that does not seal the insulation system. The metallic water barrier may be formed, for example, by longitudinal bonding of a metal tape bent around the insulation system or by wrapping a water-blocking metallic tape around the insulation system.

[0014] According to one embodiment, step a) comprises feeding the polymeric material from containers arranged in the material handling chamber into the extruder via an outlet opening of each container.

[0015] According to one embodiment, step a) comprises feeding the polymeric material through a withdrawal opening into a glove box, the glove box meeting cleanroom class 6 according to ISO-14644-1:2015 or even cleaner.

[0016] Therefore, handling of the polymeric material before it enters the extruder is also very clean, ensuring that contamination of the polymeric material from contact with ambient air can be kept to a minimum.

[0017] One embodiment involves connecting the access opening inside the glove box to a material supply system that is connected to an extruder.

[0018] According to one embodiment, the glove box contains filtered air at a positive pressure relative to the pressure in the material handling chamber, thus reducing the risk of foreign particles entering the glove box from the material handling chamber.

[0019] One embodiment includes, prior to step a), forming a conductor by stranding a plurality of wires, the stranding including applying a water-blocking compound around the wires to eliminate voids between the wires within the conductor, thus reducing longitudinal water ingress within the conductor, which can be particularly important in wet or semi-wet power cables that, by design, allow radial water ingress into conductors with voids, which can quickly vaporize in the event of a short circuit current.

[0020] According to one embodiment, the submarine power cable is rated for at least 72 kV.

[0021] According to one embodiment, the submarine power cable is rated for at least 132 kV.

[0022] According to one embodiment, the submarine power cable of wet design has no extruded or longitudinally welded or soldered metallic water barriers, and no adhesive metallic water barriers.

[0023] According to one embodiment, a submarine power cable of semi-wet design does not have an extruded or longitudinally welded or soldered metallic water barrier, but rather has a bonded metallic water barrier surrounding the insulation system.

[0024] According to a second aspect of the present disclosure, there is provided a high or extra-high voltage submarine power cable of wet or semi-wet design obtainable by the method of the first aspect.

[0025] In general, all terms used in the claims are to be interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. All references to elements, devices, components, means, etc. are to be interpreted non-exclusively as referring to at least one instance of that element, device, component, means, etc., unless otherwise specified.

[0026] 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]

[0027] [Figure 1] 1 shows a schematic cross section of an example of a wet or semi-wet HV or EHV submarine power cable. [Figure 2] 2 is a flow chart of a method for manufacturing a wet or semi-wet HV or EHV cable, such as the submarine power cable of FIG. 1; [Figure 3] 1 shows a schematic diagram of a clean room system for polymer materials. DETAILED DESCRIPTION OF THE INVENTION

[0028] 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.

[0029] FIG. 1 shows an example of a wet or semi-wet HV or EHV submarine power cable 1 .

[0030] The submarine power cable 1 comprises a conductor 3. The conductor 3 may be, for example, a Milliken-type stranded round conductor, a stranded compacted conductor, or a solid wire. The conductor may comprise, for example, copper or aluminum.

[0031] The submarine power cable 1 comprises an insulation system 5. The insulation system surrounds the conductor 3. The insulation system 5 comprises an inner semiconducting layer 7 disposed around the conductor 3, an insulating layer 9 disposed around the inner semiconducting layer 7, and an outer semiconducting layer 11 disposed around the insulating layer 9.

[0032] Insulation system 5 is an extruded insulation system including a polymer material. Inner semiconductor layer 7 and outer semiconductor layer 11 each include a base polymer mixed with a conductive component, such as carbon black. Inner semiconductor layer 7 and outer semiconductor layer 11 may be the same material or different materials. In one example, inner semiconductor layer 7 may include acetylene black as the conductive component. In one example, outer semiconductor layer 11 may include a carbon black other than acetylene black as the conductive component. Semiconductor layers including acetylene black have lower water absorption than other types of carbon black.

[0033] The polymer material used as the base for the inner and outer semiconducting layers 7, 11 may be, for example, polyethylene, cross-linked polyethylene, polypropylene, ethylene propylene diene monomer (EPDM) rubber, or ethylene propylene rubber (EPR).

[0034] The insulating layer 9 may comprise, for example, polyethylene, such as cross-linked polyethylene (XLPE), polypropylene, EPDM rubber, or EPR.

[0035] The submarine power cable 1 may include a polymer layer 13 disposed around the outer semiconducting layer 11. The polymer layer 13 may be bonded to the outer surface of the outer semiconducting layer 11 by an adhesive, such as a hot melt adhesive. According to one example, the polymer layer 13 may be applied directly onto the outer semiconducting layer 11 without any adhesive therebetween. The polymer layer 13 may be extruded onto the outer semiconducting layer 11. According to one example, the polymer layer 13 may be the outermost layer of the submarine power cable 1.

[0036] In one example, the submarine power cable 1 may include a screen layer (not shown) formed by helically arranged metal wires, such as copper wires, which may in this case be disposed between the outer semiconducting layer 11 and the polymer layer 13.

[0037] The submarine power cable 1 may include one or more armor layers 15. The armor layers 15 are disposed around the polymer layer 13. Each armor layer 15 may include a plurality of armor wires arranged in a spiral. The armor wires may be made of, for example, a metal or a synthetic material such as a polymer-based material, or some of the armor wires may be made of a metal and some of the armor wires may be made of a synthetic material.

[0038] Submarine power cable 1 may include an outer sheath or outer serving 17. Outer sheath or outer serving 17 is disposed around armor layer 15. Outer sheath or outer serving 17 is the outermost layer of submarine power cable 1, according to some examples.

[0039] A method for manufacturing a wet or semi-wet HV or EHV submarine power cable such as submarine power cable 1 will now be described with reference to Figures 2 and 3. It should be noted that although the example of Figure 1 discloses a single core submarine power cable, the method may also be used to manufacture an HV or EHV submarine power cable having multiple power cores, each of which may have a wet or semi-wet design, and thus this submarine power cable having several power cores may also be a submarine power cable of wet or semi-wet design.

[0040] In step a), a polymeric material, such as polymeric material 21, is fed to extruder 19 from material handling chamber 23. The polymeric material fed from material handling chamber 23 includes a semiconductive polymeric material and an electrically insulating polymeric material.

[0041] The polymeric material fed to the extruder 19 is typically in the form of pellets or granules.

[0042] The material handling room 23 meets the clean room class 8 standard according to ISO-14644-1:2015 or is even cleaner.

[0043] According to one example, step a) includes providing polymeric material from containers 25a-25c disposed within the material handling chamber. One or more of the containers 25a-25c contain polymeric material in the form of a semiconductive polymeric material. One or more of the containers 25a-25c contain polymeric material in the form of an electrically insulating polymeric material.

[0044] Each of the vessels 25a-25c has a discharge opening 27. The feeding in step a) may involve feeding the polymer material from the vessels 25a-25c through the discharge openings 27 into the extruder.

[0045] In one example, step a) includes feeding the polymer material through the access opening 27 into a glove box 29. The glove box 29 may be located within the material handling room 23. The glove box 29 meets clean room class 6 standards according to ISO-14644-1:2015 or is even cleaner.

[0046] In one example, the withdrawal openings 27 of the vessels 25a-25c are connected inside a glove box 29 to a material supply system 31 that is connected to the extruder 19. The withdrawal openings 27 may be connected such that several vessels 25a-25c containing different types of polymeric materials are connected to the material supply system 31 at the same time, or the withdrawal openings 27 may be connected such that after vessel 25a is emptied and then disconnected, the next vessel 25b, 25c is connected, emptied, and then disconnected.

[0047] Glove box 29 may contain filtered air at a positive pressure relative to the pressure within material handling chamber 23 .

[0048] In step b), the insulating system 5 is extruded around the conductor 3 using polymer material supplied from a material handling room 23. The extruder 19 meets the requirements of a cleanroom class 8 according to ISO-14644-1:2015 or is even cleaner.

[0049] Extruder 19 may be configured to co-extrude inner semiconducting layer 7, insulating layer 9, and outer semiconducting layer 11 to form insulation system 5 by tri-extrusion.

[0050] In one example, the conductor 3 is formed prior to step a) by twisting a plurality of wires together, which twisting includes applying a water-blocking compound around the wires to eliminate voids between the wires within the conductor 3.

[0051] After step b), additional layers may be formed around the outer semiconductor layer 11 at various locations in the assembly line, such as a screen layer, a polymer layer 13, one or more armor layers 15, and / or an outer sheath / outer serving 17.

[0052] If the submarine power cable being manufactured has a wet design, no metallic water barrier is applied around the insulation system 5. Therefore, the submarine power cable does not have a metallic water barrier.

[0053] If the submarine power cable being manufactured has a semi-wet design, the metal tape can be bent around the insulation system 5 and the opposing edges joined longitudinally to form a non-sealed metallic water barrier. Alternatively, the metal tape can be wrapped around the insulation system 5 to form a non-sealed wrapped metallic water barrier.

[0054] A wet or semi-wet submarine power cable so produced may be rated for at least 72 kV, such as 132 kV.

[0055] 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 method for manufacturing a high or extra-high voltage submarine power cable (1) of wet or semi-wet design, comprising the steps of: a) feeding a polymeric material to an extruder (19) from a material handling room (23) that meets or exceeds the clean room class 8 standard according to ISO-14644-1:2015; b) using said polymer material, extruding an insulating system (5) including an insulating layer (9) around a conductor (3) in said extruder (19) that meets the requirements of clean room class 8 according to ISO-14644-1:2015 or is even cleaner; A method comprising:

2. 2. The method of claim 1, wherein step a) comprises feeding the polymeric material from containers (25a-25c) disposed within the material handling chamber (23) to the extruder (19) through an outlet opening (27) in each container (25a-25c).

3. 3. The method of claim 2, wherein step a) comprises feeding the polymeric material through the withdrawal opening into a glove box, the glove box meeting clean room class 6 according to ISO-14644-1:2015 or being even cleaner.

4. 4. The method of claim 3, further comprising connecting, inside the glove box (29), the outlet opening (27) to a material supply system (31) connected to the extruder (19).

5. 5. The method of claim 4, wherein the glove box (29) contains filtered air at a positive pressure relative to the pressure in the material handling room (23).

6. 6. The method of claim 1, further comprising, prior to step a), forming the conductor (3) by twisting a plurality of wires together, the twisting comprising applying a water-blocking compound around the wires to eliminate voids between the wires within the conductor (3).

7. 7. The method according to any one of claims 1 to 6, wherein the submarine power cable (1) is rated for at least 72 kV.

8. 8. The method according to any one of claims 1 to 7, wherein the submarine power cable (1) is rated for at least 132 kV.

9. 9. The method according to any one of claims 1 to 8, wherein the submarine power cable (1) of wet design has no extruded or longitudinally welded or soldered metallic water barrier, and no adhesive metallic water barrier.

10. 10. The method according to any one of claims 1 to 9, wherein the submarine power cable (1) of semi-wet design does not have an extruded or longitudinally welded or soldered metallic water barrier, but comprises a bonded metallic water barrier surrounding the insulation system (5).

11. A submarine power cable (1) of wet or semi-wet design of high or extra-high voltage obtainable according to any one of claims 1 to 10.

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