Dynamic Power Cable

Abstract

A method of manufacturing a dynamic power cable (1) includes providing a cable core (2) made of an electrical conductor (3) and an electrically insulating layer (4) arranged radially outside of the electrical conductor (3). A metallic sheet (7) is wrapped radially around the cable core (2) the metallic sheet (7) having a copper-nickel alloy. Opposing edges of the metallic sheet (7) are welded together to form a continuous water barrier layer (5) around the cable core (2). The welding (8) is performed by autogenous welding.

Claims

1. A method of manufacturing a dynamic power cable comprising the steps of: providing a cable core having an electrical conductor and an electrically insulating layer arranged radially outside of the electrical conductor, wrapping a metallic sheet radially around the cable core, the metallic sheet comprising a copper-nickel alloy, welding together opposing edges of the metallic sheet to form a continuous water barrier layer around the cable core, wherein the welding is performed by autogenous welding.

2. The method according to claim 1, wherein the welding is performed by autogenous laser beam welding.

3. The method according to claim 1, wherein the welding is performed by autogenous electric resistance welding.

4. The method according to claim 1, wherein the metallic sheet comprises a copper-nickel alloy comprising: between 10 wt % to 50 wt % nickel, and between 50 wt % to 90 wt % copper.

5. The method according to claim 1, wherein the metallic sheet comprises a copper-nickel alloy comprising: between 20 wt % to 30 wt % nickel, and between 70 wt % to 80 wt % copper.

6. The method according to claim 1, wherein the metallic sheet comprises a copper-nickel alloy comprising: between 22 wt % to 28 wt % nickel, and between 72 wt % to 78 wt % copper.

7. The method according to claim 1, wherein the metallic sheet comprises a copper-nickel alloy comprising: between 23 wt % to 27 wt % nickel, and between 73 wt % to 77 wt % copper.

8. The method according to claim 1, wherein the metallic sheet has a thickness between 0.1-2 mm.

9. The method according to claim 8, wherein the metallic sheet has a thickness between 0.3-1.5 mm.

10. The method according to claim 9, wherein the metallic sheet has a thickness between 0.4-0.7 mm.

11. The method according to claim 1, wherein the welded water barrier layer is subjected to a forming process, whereby the diameter of the water barrier layer is reduced so that the water barrier layer fits tightly on the cable core.

12. A dynamic power cable comprising: at least one cable core having an electrical conductor and an electrically insulating layer that are arranged radially outside of the electrical conductor, a water barrier layer that is arranged radially outside of the cable core, wherein the dynamic power cable is manufactured according to the method of any one of the preceding claims.

13. A method for forming a continuous water barrier layer around a cable core in a dynamic power cable, the metallic sheet comprising a copper-nickel, said method comprising the step of welding at least one seam of said metallic sheet with autogenous welding.

14. The method as claimed in claim 13, said method including welding by an autogenous laser beam.

15. The method as claimed in claim 13, said method including electric resistance welding of said metallic sheet.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0023] The invention will be described in detail with reference to the attached drawings wherein:

[0024] FIG. 1 schematically illustrates an aspect of the invention, where an example of a dynamic power cable cross section is shown.

[0025] FIG. 2 schematically illustrates an aspect of the invention, where an example of a dynamic power cable cross section comprising three cable cores is shown.

[0026] FIG. 3 schematically illustrates an aspect of the invention, where the welding step of the manufacturing method is shown.

[0027] FIG. 4 schematically illustrates an aspect of the invention, where the step of forming the welded water barrier layer is shown.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings.

[0029] FIG. 1 schematically illustrates an example of a cross section of dynamic power cable 1, where the cable 1 is shown with one cable core 2. This invention is however not limited to a one-core cable, and the cable 1 may comprise two or any higher number of cores 2, as is deemed suitable for the cable's 1 purposes. Accordingly, FIG. 2 illustrates an example of a dynamic power cable 1 cross section comprising three cable cores 2.

[0030] Each core 2 comprises an electrical conductor 3 arranged in the centre of the core 2, and an electrically insulating layer 4 arranged radially outside each conductor 3. Outside the first electrically insulating layer 4, though not illustrated in the figures, there may be arranged a layer of sealing material disposed between the electrically insulating layer 4 and a water barrier layer 5. This sealing material swells upon contact with water thereby working as an extra redundancy measure to prevent ingress of moisture in case of a crack or other failure in the water barrier layer 5.

[0031] It should be noted that the cable 1, and variations thereof, may comprise additional layers, or filling material 10 as exemplified in FIG. 2, arranged radially outside each conductor 3 or the at least one cable core 2, which will not described further herein. These layers and materials may be arranged inside, in-between or outside the already mentioned layers herein, and may comprise for example additional insulating, semiconducting, conducting, shielding and armouring layers as is well known in the art.

[0032] It should be noted that any percentage amount of a metal component in an alloy described herein is provided as a fraction of the weight of the metal per total weight of the alloy as a percentage, also known as mass fraction, percentage by mass, percentage by weight and abbreviated wt %.

[0033] The wt % of nickel in the copper is determined by how this wt % affects the fatigue resistance of the copper alloy, and especially how this affects the properties of the alloy which is important in the welding process. Table 1 displays some relevant properties of a conventional Electrolytic Tough Pitch Copper (ETP) and several different CuNi alloys which may be employed for the water barrier layer. The properties for the Copper ETP and the various alloys are shown in the columns according to the wt % of copper and nickel of the Copper ETP and the alloys. As can be seen, many of the desired properties with respect to welding increase as the wt % of nickel increases. Especially noteworthy is the fact that the laser welding speed is drastically increased. It should also be noted that the use of autogenous welding with a CuNi alloy also maintains a high level of weld quality which adds to the fatigue strength of the water barrier layer 5.

TABLE-US-00001 TABLE 1 Copper ETP CuNi alloys wt % Cu ~99.9% ~90% ~85% ~80% ~75% ~70% ~60% wt % Ni ~0% ~10% ~15% ~20% ~25% ~30% ~40% Thermal ~390 ~50 ~40 ~30 ~25 ~24 ~22 Conductivity at 20 C. [W/(m * K)] Reflectivity High Minor Minor Minor Minor Minor Minor Mean Linear ~17 ~16 ~15.9 ~15.8 ~15.6 ~15.4 ~14.7 thermal expansion between 20-300 C. [10.sup.6/K] Estimated laser 2 4 6 7 9 10 10 welding speed for a 0.5 mm sheathing [m/s]

[0034] It will be appreciated by the skilled person that, where a range of a percentage amount of a metal in an alloy is given, the amount of said metal in that alloy may vary within that range, provided that the total amount, i.e. total wt % of all metals in that alloy adds up to a total of 100 wt %. It will also be appreciated that some metals and alloys may inevitably have small quantities of impurities within them. Such impurities may include lead, manganese, iron, zinc, and other metals. These impurities may be present since they are typically too difficult and/or costly to remove when the metal or alloy is being produced. The amount of impurities are typically present in the range from 0.0001 wt %, to 1 wt %.

[0035] It should also be noted that minor amounts of iron, manganese, carbon and titanium may also be intentionally added as alloying elements. Any additional alloying elements may typically be present in the range from 0.01 wt % to 10 wt %. Table 2 provides some examples of different CuNi alloys, which may be used in the water barrier layer, with intentionally added alloying elements. Their specific compositions being given by in various standards.

TABLE-US-00002 TABLE 2 Alloy Standard Material - No. DIN/UNS CuNi8 2.0807 CuNi10 DIN 17471 2.0811 C70700 CuNi20 BS 2870 2.0822 C71000 CuNi30 ASTM B122 CuNi30Mn1FeTi 2.0882 CuNi10Fe1Mn EN 1652 2.0872 C70600 CuNi30Mn1Fe EN 1652 2.0882 C71500 CuNi30Fe2Mn2 DIN 17664 2.0883 CuNi44Mn1 DIN 17664 2.842 4401

[0036] FIG. 3 schematically illustrates part of the manufacturing process of a cable 1. The metallic sheet 7 is shown wrapped around the cable core 2, and the welding process 8 is represented by an arrow 8 on FIG. 3 where the welding together of the opposing edges of the sheet 7 takes place to form the continuous water barrier layer 5. It will therefore be apparent that the water barrier layer 5 in this example is made up of the metallic sheet 7, welded together along the opposing longitudinal edges of the metallic sheet 7 as it is wrapped around the cable core 2. It will be appreciated that the pre-weld metallic sheet 7 is illustrated to the left on FIG. 3, and that the post-weld water barrier layer 5 is on the right of FIG. 3.

[0037] Though the example in FIG. 3 shows a gap between the opposing longitudinal edges of the metallic sheet, this is merely for illustrative purposes and the edges may be abutting, overlapping or arranged in whichever suitable manner, which will be apparent to the person skilled in the art.

[0038] For the sake of clarity, it should be mentioned that in FIG. 3 and FIG. 4, the metallic sheet 7 is shown with a larger inner diameter than the outer diameter of the cable core 2. The gap between the metallic sheet 7 and the cable core 2 being exaggerated in FIG. 3 and FIG. 4 for illustrative purposes. In finished cable 1, as illustrated in FIG. 1 and FIG. 2, the water barrier layer 5 will fit tightly on the cable core 2 or the layer or layers arranged on the cable core 2.

[0039] The welding process 8 is preferably performed by autogenous welding, as this welding technique delivers high process continuity, weld quality and weld integrity. A water barrier layer 5 comprising CuNi alloy is especially advantageous as the added nickel improves laser welding properties by decreasing thermal conductivity to concentrate heat allowing for increased throughput and/or decreased power requirements of the welding equipment. A decrease in the thermal conductivity limits the heat affected zone which again limits detrimental geometrical distortion and change in microstructure and composition. Geometrical distortion, changes in microstructure and local changes in composition are detrimental for the fatigue properties of the water barrier layer 5. Increased wt % of nickel furthermore decreases thermal expansion to limit geometrical distortion. However, other considerations such as the thickness of the water barrier layer, the cost of nickel and the desired fatigue resistance of the water barrier layer are also considered.

[0040] In one aspect of the invention, the welding process 8 is performed by autogenous laser beam welding. An autogenous laser beam welding process additionally benefits from being used in conjunction with a CuNi alloy as the additional nickel decreases laser reflectivity to increase heat absorption and allocate for increased throughput and/or decreased laser power requirement.

[0041] In another aspect of the invention, the welding process 8 is performed by electric resistance welding, which also draws similar benefits from the properties of CuNi alloys as laser beam welding. Electric resistance welding is also preferably performed autogenously, and this method also benefits from CuNi alloys with low reflectivity, thermal conductivity and susceptibility to thermal expansion.

[0042] In other aspects of the invention, it is conceivable that several different kinds of autogenous welding techniques are used on one cable. Other autogenous welding techniques may comprise autogenous tungsten inert gas welding (TIG) or friction stir welding (FSW). Non-autogenous welding may also be performed on parts of a cable 1, where the filler material comprises minimum the same nickel content as the alloy in the metallic such as tungsten inert gas welding (TIG), metal inert gas welding (MIG) or manual metal arc welding (MMA). Other welding techniques known which the person skilled in the art will be familiar with may also be used. The thickness of the cable, the composition of the CuNi alloy will vary accordingly.

[0043] In a non-limiting example, the metallic sheet 7 may comprise a copper alloy, comprising 25 wt % nickel with 0.5 mm thickness being welded by autogenous laser beam welding to a water barrier layer. In this example, the invention provides an optimal balance between a relatively low amount of nickel, and a thin water barrier layer, thus saving material required for the cable whilst providing properties that are especially beneficial to the welding and forming process and maintaining high resistance to fatigue. It should be noted, however, that for certain cable applications, these parameters may vary, and there may therefore be other equally beneficial combinations of thickness, welding technique and composition of the alloy used in the water barrier layer 5 which will be apparent to the person skilled in the art based on the disclosure of the invention herein.

[0044] FIG. 4 schematically illustrates the forming process 9, which occurs after the metallic sheet 7 has been welded to form a continuous water barrier layer 5. As is illustrated in FIG. 4, the water barrier layer 5 may have a diameter which is larger than the outside diameter of the cable core 2. The forming process 9 is therefore performed to ensure that the water barrier layer 5 tightly fits the cable core 2, by applying pressure on the outside of the water barrier layer 5, illustrated by arrows 9 acting on the water barrier layer 5.

[0045] In one aspect of the invention, the forming process 9 comprises moving the water barrier layer 5 and the cable core 2, through at least one die in the longitudinal direction of the cable core 2.

[0046] In a further aspect of the invention, there may be a plurality of dies, with a decreasing cross sectional diameter which the water barrier layer 5 and the cable core 2 are moved through.

[0047] In another aspect of the invention, the forming process 9 comprises rolling the water barrier layer 5 and cable core 2 in a longitudinal direction of the cable core 2 across at least one roller wheel. In further aspects there may be a plurality of roller wheels, with varying shapes and sizes or applying an increasing amount of pressure which the water barrier layer 5 and the cable core 2 are rolled across. These aspects of the forming process 9 will be apparent to the person skilled in the art, and are therefore not illustrated in detail in the figures.

[0048] Once the forming process 9 is completed a polymer layer 6 may be extruded radially outside the water barrier layer 5. This process is not detailed further herein since this is a well-known process in the art will be apparent to the person skilled in the art. In other aspects of the invention, one cable core 2 may be put together with several other cable cores, as is illustrated in FIG. 2.

[0049] It should be understood that within the scope of the claims, yet further variations and combinations of CuNi alloys than those disclosed above can be designed for a certain welding technique and water barrier layer thickness, as will be obvious to the person skilled in the art based upon the disclosure of the invention herein.