Method for manufacturing a submarine cable and a cable manufactured thus

Abstract

A method for manufacturing a cable (100) is disclosed, comprising: providing a cable core (110); providing a copper foil (300); providing a protective strip (130) on top of the cable core in a position substantially matching a soldering mold (550a), the protective strip having a radially inner surface and an outer surface and being made of copper, having a coating on at least the radially outer surface, the coating being made of a metal or metal alloy having a melting temperature between 90°C and 250°C; folding the copper foil around the cable core such that two longitudinal copper foil edges (310) contact each other; soldering the two contacting longitudinal copper foil edges using the soldering mold (550a), thereby obtaining a copper sheath having a solder joint (125); reducing the diameter of the copper sheath such that it is in direct contact with the cable core and the protective strip; heating the protective strip and the copper sheath at a temperature higher than the melting temperature of the coating of the protective strip such that the coating melts in the solder joint; extruding a polymer sheath (140) around the copper sheath. A cable is also disclosed.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for manufacturing an electrical cable, in particular, but not exclusively, a high voltage cable for underwater or underground deployment.

[0002] The present invention relates to an electrical cable manufactured by the above method. BACKGROUND

[0003] In the present invention, the expression "high voltage" (HV) denotes a voltage equal to or greater than 30 KV.

[0004] Generally, an electrical cable, in particular a HV cable, comprises at least one cable core, typically formed of an electrically conductive metallic conductor, covered by an insulation system. The insulation system is formed sequentially of an inner polymeric semiconductive layer, an intermediate polymeric insulating layer and an outer polymeric semiconductive layer. The insulation system is surrounded by one or more protective layers.

[0005] When the cable is to be installed in a wet or potentially wet environment, such as underwater or underground, the cable core should be protected against water vapor or water penetration, which can lead to electrical breakdown. Therefore, a submarine or underground cable typically comprises a metallic barrier surrounding each cable core of the cable (in this case, the cable core also comprises a buffer layer surrounding the outer polymeric semiconductive layer), in order to prevent water penetration during installation and operation of the cable.

[0006] The metallic barrier can be manufactured from aluminum, lead or copper. Copper is lighter than lead and less prone to corrosion than aluminum.

[0007] The metallic barrier can be manufactured by extrusion, in particular in the case of a lead barrier, or in the form of a longitudinally folded sheath having welded rims or overlapping and glued rims.

[0008] The longitudinally folded sheath with welded rims is more reliable in preventing water penetration under high voltage conditions (for example at underwater depths greater than, for example, 1000 m) than the longitudinally folded sheath with overlapping and glued rims.

[0009] Depending on the application of the cable, the metallic barrier can also have a straight or undulated longitudinal section (hereinafter also referred to as "straight metallic barrier" and "corrugated metallic barrier", respectively). The cable can be deployed as a static cable, which is placed on a surface (such as a seabed, etc.) between fixed points, or as a dynamic cable, which is suspended underwater and is therefore subject to sea movements (such as currents and / or waves). In the latter case, the corrugated metallic barrier provides greater flexibility to the cable with respect to the straight metallic barrier.

[0010] Furthermore, the metallic barrier can be covered by a protective sheath of a polymer (optionally semiconductive).

[0011] The manufacturing method of a cable with a copper barrier made of a longitudinally folded sheath with welded edges generally comprises the following steps: folding a copper foil around each cable core; welding the edges; and reducing the overall diameter of the resulting copper barrier, generally by drawing, so that its inner surface is in contact with the outer surface of the cable core.

[0012] After the drawing step, one or more polymeric sheaths can be extruded around the copper barrier. After the drawing step, the cable with the metal barrier is heated before entering the extruder, in order to ensure adhesion with the polymeric sheaths to be extruded.

[0013] GB 753 935 relates to a sheathed cable with an aluminium sheath and to a method for manufacturing it. The method for applying the aluminium sheath comprises providing the cable with a tightly fitting split metal tube, so that the opposite split edges of the tube are in contact with each other and so that the split edges are fused together by means of an electromagnetic field. The diameter of the tube is very close to the diameter of the cable. After the split edges have been fused, the sheathed cable passes through a sizing roller which slightly reduces the size of the sheath. In order to prevent any damage to the insulation due to the flying arcs of the welding and the excessive heat generated during the fusion of the opposite split edges, a protective strip is provided on the upper region of the cable. The strip can be made of any suitable material, such as aluminium foil, glass, asbestos, etc.

[0014] US 3 575 748 discloses a method of manufacturing a cable having, in addition to a thin vapour barrier of metal (e.g. aluminium or copper), a lap joint made of a plastic tape. The tape is bent longitudinally into a tube and the lap joint surrounds the core. A second, narrower tape (bridge or reinforcing) is also advanced. The tape and the second tape can have the same construction. The tape is made of a metal foil laminate having a plastic coating on its upper and lower surfaces. The metal foil is preferably aluminium or copper. The bridge tape is located beneath the lap joint. The plastic coatings on the tapes are heated sufficiently to cause them to adhere together. SUMMARY

[0015] The problem faced by the Applicant is to provide a cable, in particular for submarine applications, which can withstand water penetration under high pressure conditions existing at high underwater depths, i.e. greater than 1000 m, in particular greater than 1500 m.

[0016] The Applicant then considered a cable in which each core is surrounded by a copper barrier (also called "copper sheath" in the following) in the form of a longitudinally folded copper foil with welded edges. The welding of the edges of the copper foil is carried out at a temperature higher than the melting temperature of copper (1080°C), for example at a temperature of about 1100°C.

[0017] The applicant has observed that the heat and vapor generated during the welding process can locally melt and / or damage the polymer layer of the cable core beneath the weld.

[0018] The applicant also observed that the weld may have some defects, such as those smaller than 0.5mm. 2 These defects, such as holes, cannot be reliably detected, and water under high pressure can penetrate through these defects and pass through the metal barrier.

[0019] The applicant is considering providing a strip on the cable prior to the welding step, located below the weld.

[0020] The applicant discovered that coating the copper strip with a metal or metal alloy having a melting temperature between 90°C and 250°C on at least its radially outer surface could overcome the aforementioned problems. During the welding process, the coated strip is spaced a certain distance from the copper barrier so that the strip is not heated sufficiently to melt. However, during the heating process prior to polymer shell extrusion, the coating of the strip melts and adheres to the weld seam of the metal barrier, thus repairing potential defects / holes (e.g., smaller than 0.5 mm) that are not easily detected. 2 (Defects / holes).

[0021] In this way, the applicant experiences the ability to ensure that the weld is resistant to water penetration even at high underwater depths (e.g., approximately 2000m).

[0022] The strips also serve as protective barriers for the polymer layers of the cable, resisting the heat and steam generated during the soldering process in manufacturing the copper barriers.

[0023] Therefore, according to a first aspect, the present invention relates to a method for manufacturing a cable, comprising:

[0024] - Provide a cable core, which includes an electrical conductor and has an outer diameter;

[0025] - Provide copper foil with a width such that, after the copper foil is folded to provide a copper sheath around each cable core, the inner diameter of the copper sheath is 5 to 15 mm larger than the outer diameter of the cable core.

[0026] - A protective strip is provided on each cable core in a position substantially matching the welding mold. The protective strip has a radial inner surface and an outer surface and is made of copper. It has a coating on at least the radial outer surface, which is made of a metal or metal alloy with a melting temperature between 90°C and 250°C.

[0027] - Fold the copper foil around the cable core so that the two longitudinal copper foil edges come into contact with each other;

[0028] -Use a welding mold to weld two contacting longitudinal copper foil edges to obtain a copper sheath with weld seams and a diameter, in the form of a tube;

[0029] -Reduce the diameter of the copper shielding to allow it to make direct contact with the cable core and protective strip;

[0030] - Heating the protective strip and copper barrier at a temperature higher than the melting temperature of the protective strip coating allows the coating to melt in the weld.

[0031] - Extruding polymer casing around the copper barrier.

[0032] In this embodiment, the diameter of the copper blocking portion is reduced by rolling.

[0033] The method of the present invention allows for the welding of the opposing longitudinal copper foil edges at a sufficient distance from the outer surface of the cable core and from the strip, in order to avoid the heat and steam generated during the welding process from potentially damaging the cable core and the strip.

[0034] In an embodiment, the method of the present invention includes extruding an adhesive layer around a copper barrier before extruding a polymer sheath.

[0035] In an embodiment of the method of the present invention, prior to the diameter reduction step, the inner diameter of the copper sheath obtained in the form of a tube is 8 to 10 mm larger than the outer diameter of the cable core.

[0036] According to another aspect, the present invention relates to a cable comprising:

[0037] - Cable core, which includes an electrical conductor and has an outer diameter;

[0038] - Copper sheath, which surrounds each cable core and is formed in the form of a tube with welded seams;

[0039] The cable includes a protective strip with radial inner and outer surfaces, made of copper, and has a coating on at least the radial outer surface, the coating being made of a metal or metal alloy with a melting temperature between 90°C and 250°C, the coating being melted in the weld of the copper sheath.

[0040] In an embodiment, the cable of the present invention comprises two or more cable cores, such as three cable cores.

[0041] In the cable embodiment of the present invention, the thickness of the copper sheath is in the range of 0.2 mm to 1.5 mm.

[0042] In the cable embodiment of the present invention, the width of the strip is in the range of 15 mm to 50 mm. This dimension is proportional to the diameter of the cable core. The width of the weld is safely within the width of the strip, thus ensuring that water cannot penetrate at the weld.

[0043] In the cable embodiment of the present invention, the thickness of the protective strip is in the range of 0.05 mm to 0.3 mm. Such a thickness is sufficient to provide suitable protection for the cable core against heating during welding, while substantially not altering the roundness of the finished cable.

[0044] In an embodiment, the cable of the present invention includes a polymer sheath surrounding the copper barrier. Optionally, the polymer sheath is semiconductor or includes a semiconductor layer.

[0045] In an embodiment, the cable of the present invention includes an adhesive layer disposed between a copper blocking portion and a polymer sheath.

[0046] For the purposes of this invention and the following claims, unless otherwise stated, all figures representing quantities, amounts, percentages, etc., shall in all circumstances be understood to be modified by the term "approximately". Furthermore, all ranges include any combination of the disclosed maximum and minimum points, and include any intermediate ranges therein, which may or may not be specifically listed herein.

[0047] Furthermore, the terms "a" and "an" are used to describe elements and components of the present invention. This is done merely for convenience and to give the general meaning of the invention. The description should be understood to include one or at least one, and the singular includes the plural, unless it is obvious that it means otherwise.

[0048] "Cable core" refers to the portion of a cable that includes a conductive metal conductor covered by an insulation system surrounded by a buffer layer. The insulation system is formed sequentially by an inner polymer semiconductor layer, an intermediate polymer insulation layer, and an outer layer. The buffer layer surrounds and directly contacts the outer polymer semiconductor layer of the polymer insulation system.

[0049] The buffer layer is made of a polymeric material, optionally a semiconductor. The buffer layer can be an extruded polymer layer or a strip spirally wound around an outer polymeric semiconductor layer. The compressive modulus of the buffer layer is lower than that of the outer polymeric semiconductor layer.

[0050] "Insulating layer" means a layer with an electrical conductivity of 10. -16 and 10 -14 Layers made from materials with a S / m ratio.

[0051] "Semiconductor layer" means a layer with an electrical conductivity of 10. -1 Layers made from materials with a strength between 10 S / m and 10 S / m.

[0052] "Compression modulus" means the ratio of mechanical stress to strain of an elastic material under compression (compression modulus = compressive force per unit area / volume change per unit volume), for example, according to ISO 604_1997-02. Attached Figure Description

[0053] Other features will become clear from the detailed description given below with reference to the accompanying drawings, in which:

[0054] - Figure 1 This is a schematic perspective cross-sectional view of a cable according to an embodiment of the present invention;

[0055] - Figure 2 This is a schematic diagram of an apparatus for manufacturing cables according to the present invention;

[0056] - Figure 3a , 3b And 3C are Figure 1 Three schematic perspective views of the cable in three consecutive steps of the manufacturing process. Detailed Implementation

[0057] refer to Figure 1 The figure schematically illustrates the cable 100 according to the present invention.

[0058] The cable 100 includes a cable core 110, which includes an electrical conductor 115 and a polymer insulation system 200 surrounding the electrical conductor 115. The polymer insulation system 200 is formed sequentially by an inner polymer semiconductor layer 210, an intermediate polymer insulation layer 220, and an outer polymer semiconductor layer 230.

[0059] A copper barrier 120, in the form of a tube with a weld 125, surrounds the cable core 110. The copper barrier 120 serves as a water barrier and an electrical shield.

[0060] The copper blocking section can be a straight metal blocking section or a corrugated metal blocking section, depending on the application of the cable (stationary or dynamic, as described above).

[0061] The copper used for the copper barrier can be copper with a conductivity of at least 85% IACS (International Standard for Annealed Copper), for example, at least 95% IACS. Suitable copper for the copper barrier should be high-purity copper with a copper content of more than 90% and a low oxygen content, for example, 50 ppm to 15 ppm or less.

[0062] The cable 100 includes a protective strip 130 disposed between the outer surface of the cable core 110 and the copper blocking portion 120, and fused to the copper blocking portion 120 at a weld 125. The protective strip 130 is made of copper coated with a metal or metal alloy, the metal or metal alloy having a melting temperature between 90°C and 250°C.

[0063] Examples of metals suitable as coatings for copper protective strips used in this invention are selenium and tin, as well as alloys containing one or more of silver, antimony, tin, zinc, and lead.

[0064] Examples of metal alloys suitable as coatings for copper protective strips used in this invention include one or more of silver, antimony, tin, zinc, and lead, such as lead-antimony alloys, lead-tin alloys, tin-lead alloys (tin-antimony-copper alloys), bismuth-tin-lead alloys (bismuth-lead-tin alloys), and silver-lithium alloys.

[0065] In this embodiment, the protective strip is in direct contact with the outer surface of the cable core.

[0066] exist Figure 1 In the image, the thickness of the protective strip 120 is enlarged for clarity, but in reality, its thickness does not significantly alter the roundness of the cable cross-section.

[0067] The cable core 110 may include a buffer layer 135 that surrounds the polymer insulation system 200 and is in direct contact with the outer semiconductor layer 230.

[0068] The buffer layer, comprising or composed of polymeric materials, can be in the form of one or more strips wound helically or longitudinally around the polymeric insulation system, with or without overlap. Each of the strips can have a thickness of approximately 1.0 mm to approximately 2.0 mm. Optionally, the buffer layer can be moisture-wicking and / or semiconductor.

[0069] The buffer layer provides a filling effect between the polymer insulation system and the copper barrier. It also acts as a water barrier to prevent longitudinal water penetration and, as a mechanical shock absorber beneath the copper barrier, absorbs impact forces and prevents damage to the underlying layers (particularly the outer polymer semiconductor layer of the polymer insulation system).

[0070] The cable core 110 may include a polymer sheath 140 surrounding the copper barrier 120.

[0071] The adhesive layer 145 can be placed between the copper barrier 120 and the polymer sheath 140, as in Figure 1 In the illustrated embodiment, this is to ensure adhesion between the polymer housing 140 and the copper blocking portion 120.

[0072] Cable 100 can be manufactured by the methods described below.

[0073] For the sake of simplicity, this method will refer to Figure 2 The device 500 and reference shown Figures 3a-3c Let me introduce it.

[0074] The method includes the step of providing a cable core 110, which includes an electrical conductor 115 and a polymer insulation system 200 surrounding the electrical conductor 115. Optionally, the cable core 110 also includes a buffer layer 135 surrounding the insulation system 200. The method of manufacturing the cable core 110 is not described, as it is known in itself. The cable core 110 can be wound onto a drum 510 for storage and advanced in the forward direction X.

[0075] The method also includes the step of providing copper foil 300. The copper foil 300 can be wound around the second drum 520 for storage and advanced in the forward direction X under the cable core 110.

[0076] In this embodiment, the copper foil 300 is passed through a set of flattening rollers 500 to flatten the copper foil and apply appropriate tension to it. In the case of a corrugated metal blocking section, appropriate tension can be provided by a suitable conveyor belt.

[0077] In one embodiment, the centering unit aligns the copper foil 300 with the axis of the welding line.

[0078] In one embodiment, the cutting device scrapes the two longitudinal edges 310 of the copper foil 300 to remove copper oxide and other potential sources of defects (such as the presence of grease or edge deformation) and to adjust the final width of the copper foil 300. The cutting device can be made of two cylinders with blades at their ends.

[0079] According to the invention, the method includes the step of providing a protective strip 130 on the cable core 110. The protective strip 130 can be wound around a third drum 530 for storage and advanced in a forward direction X to meet the cable core 110 at the axis of the welding line. At this welding line, the longitudinal edge 310 is welded.

[0080] The copper foil 300 is folded around the cable core 110 so that the two longitudinal copper foil edges 310 face each other. The folding of the copper foil 300 can begin at the point on the production line where the protective strip 130 is placed on the cable core 110, but it ends at the point on the production line where the protective strip 130 has already contacted the cable core 110.

[0081] The folding step of the copper foil 300 is performed using a forming unit 540, which includes, for example, a continuous set of forming rollers or dies.

[0082] Then, the two facing longitudinal copper foil edges 310 are brought into contact with each other, pressure is optionally applied, and they are welded by a welding unit 550 having a welding mold 550a, thereby obtaining a copper blocking portion 120 in the form of a tube with a weld seam 125.

[0083] For example, the welding unit is a tungsten inert gas (TIG) welding unit. Welding can be performed by blowing a shielding gas (such as argon or helium or a mixture thereof) from the inside and outside of the copper tube to prevent oxidation of the weld seam 125.

[0084] The inner diameter of the copper barrier obtained after the welding step is larger than the outer diameter of the cable core 110 and corresponds to the protective strip 130 applied thereon, so that the welding occurs at a sufficiently large distance from the outer surface of the cable core 110 and from the strip 130 to avoid damage to the cable core 110 and the strip 130 by the heat and steam generated during the welding process.

[0085] The method then provides a step of reducing the diameter of the copper blocking portion 120 so that its inner surface is in direct contact with the outer surface of the cable core 110 and with the strip 130.

[0086] The diameter of the copper stop portion 120 is reduced by rolling. The rolling is performed by a rolling unit 560, which may include one or more rolling stages (the rolling stages are not described as they are known).

[0087] The method then includes the step of heating the protective strip 130 and the copper barrier 120 at a temperature higher than the melting temperature of the coating of the strip 130, so that the coating of the strip 130 can fuse with the weld 125.

[0088] Heating can be performed by sensor 590 or by a hot air blower, which heats the copper barrier 120 to at least 100°C.

[0089] In addition to allowing the protective strip coating to melt into the copper casing weld, the heating step also enhances the adhesion between the copper casing and the polymer casing 140. The adhesive layer 145 can be extruded onto the copper barrier 120 (via the second extruder 570b) to further improve this adhesion.

[0090] Following the heating step, the method includes the step of extruding a polymer sheath 140 around a copper barrier 120 via a first extruder 570a, the copper barrier 120 optionally being covered by an adhesive layer.

[0091] Then, the cable manufactured in this way passes through cooling tank 580.

Claims

1. A method for manufacturing a cable (100), the method comprising: - Provide a cable core (110), the cable core (110) including an electrical conductor (115) and having an outer diameter; - Provide copper foil (300) with a width such that after the copper foil (300) is folded to provide a copper sheath (120) around each cable core (110), the inner diameter of the copper sheath (120) is 5 mm to 15 mm larger than the outer diameter of the cable core. - A protective strip (130) is provided on the cable core (110) in a position that roughly matches the welding mold (550a). The protective strip (130) has a radial inner surface and a radial outer surface and is made of copper. It has a coating on at least the radial outer surface, the coating being made of a metal or metal alloy with a melting temperature between 90°C and 250°C. - Fold the copper foil (300) around the cable core (110) so that the two longitudinal copper foil edges (310) come into contact with each other; - Using a welding mold (550a), two longitudinal copper foil edges (310) in contact are welded to obtain a copper sheath (120) in the form of a tube with a weld seam (125) having a diameter; -Reduce the diameter of the copper sheath (120) so that the copper sheath is in direct contact with the cable core (110) and the protective strip (130); - Heat the protective strip (130) and the copper shell (120) at a temperature higher than the melting temperature of the coating of the protective strip (130) so that the coating melts in the weld (125); - Extruding polymer casing (140) around copper casing (120).

2. The method according to claim 1, wherein: Before the diameter reduction step, the inner diameter of the copper sheath (120) obtained in tube form is 8 mm to 10 mm larger than the outer diameter of the cable core (110).

3. The method according to claim 1, wherein: The diameter of the copper sheath (120) is reduced by rolling.

4. The method according to claim 1, further comprising: The step of extruding an adhesive layer (145) around a copper shell (120) prior to the step of extruding the polymer shell (140).

5. A cable (100), said cable comprising: - Cable core (110), the cable core (110) includes an electrical conductor (115) and has an outer diameter; - Copper sheath (120), which surrounds the cable core and is in the form of a tube with a weld (125); The cable (100) includes a protective strip (130) having a radial inner surface and a radial outer surface and being made of copper, having a coating on at least the radial outer surface, the coating being made of a metal or metal alloy with a melting temperature between 90°C and 250°C, the coating being melted in the weld (125) of the copper sheath (120).

6. The cable (100) according to claim 5, wherein: The thickness of the copper casing (120) ranges from 0.2 mm to 1.5 mm.

7. The cable (100) according to claim 5, wherein: The width of the protective strip (130) is in the range of 15mm to 50mm.

8. The cable (100) according to claim 5, wherein: The thickness of the protective strip (130) is in the range of 0.05 mm to 0.3 mm.

9. The cable (100) according to claim 5 further comprises: Polymer casing (140) surrounding copper casing (120).

10. The cable (100) according to claim 9, further comprising: An adhesive layer (145) is placed between the copper housing (120) and the polymer housing (140).

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