Method of manufacturing three-core power cable

Abstract

To provide a three-core power cable for reducing the risk of damage, thereby solving the problem in which, in a cross-section at a 90-degree angle in relation to the longitudinal axis of a three-core power cable, the cross-sectional shapes of cylindrical cores are approximately elliptical and may risk damaging the power cable by large radial forces applied to the power cable, e.g., during cable laying from an offshore vessel or during cable installation on the ground.SOLUTION: A method of manufacturing a power cable 13 including three cores 3a-3c and three filler profiles 5a'-5c' arranged in a stranded configuration includes: defining a stranding pitch P of the cores; determining a shape of at least one of the cores; determining a cross-sectional shape of the filler profiles in a transverse section of a filler profile; manufacturing each of the cores with the nominal outer diameter; obtaining the filler profiles; and stranding the cores and the filler profiles with the stranding pitch P in an assembly machine.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure generally relates to a three-core power cable with a filler profile. [Background technology]

[0002] A power cable can include several cores, each of which has a circular cross section. For example, a power cable can include three cores twisted together to form a trefoil configuration in cross section. Filler elements can be twisted with the cores to give the power cable a circular or essentially circular cross section and provide radial stability.

[0003] The packing element may be of the type having an arcuate outer surface and two curved inner surfaces, as disclosed, for example, in EP 3097446. The inner arcuate surfaces form part of a circle that coincides with the diameter of the core. Summary of the Invention

[0004] While the inner arcuate surface should theoretically mate well with the outer surface of the core, this is not always the case. The inventors recognized that the level of matching depends on the strand pitch / helix angle of the core in its stranded state. In particular, in the cross-section of a three-core power cable, i.e., a cross-section at a 90-degree angle relative to the longitudinal axis of the power cable, the cylindrical core is not actually circular due to the helix angle. Instead, the cross-sectional shape is approximately elliptical. Therefore, the arcuate outer surface of the filler element may not necessarily perfectly match the outer surface of the core. Therefore, the pressure provided by the filler element to the core may not be uniform, which could damage the power cable, especially when large radial forces are applied to the power cable, such as during cable laying from an offshore vessel or cable installation on land. This may be particularly true for higher nominal voltages, such as 100 kV or higher, which require larger and therefore heavier power cables, and / or for deep-sea installations.

[0005] In view of the above, it is an object of the present disclosure to provide a method for manufacturing a power cable that solves or at least alleviates the problems of the prior art.

[0006] Thus, according to a first aspect of the present disclosure, there is provided a method for manufacturing a power cable comprising three cores and three filler profiles arranged in a stranded configuration, the method comprising: A) during a design stage of the power cable, A0) defining nominal outer diameters of the cores and defining a lay pitch P of the cores, A1) determining a shape of at least one of the cores in a cross-section of the power cable, and A2) determining a cross-sectional shape of the filler profile in the cross-section of the filler profile based on the shape determined in step A1); and B) during a manufacturing stage of the power cable, B1) manufacturing each core having the nominal outer diameter, B2) obtaining a filler profile having the cross-sectional shape obtained in step A2), and B3) stranding the cores and filler profiles with the lay pitch P in an assembly machine.

[0007] Thus, the power cable manufactured according to this method has a coordinated fit between the filler profile and the core, so that the pressure exerted by the filler profile on the core is more evenly distributed, reducing the risk of the core being damaged by the filler profile during cable installation.

[0008] Furthermore, the outer dimensions of the manufactured power cable can be known in advance, i.e., before the power cable is manufactured. Furthermore, for a better fit, the outer diameter of the power cable 13 can be smaller, which means that longer cross sections of the power cable can be stored on the cable-laying vessel and that material can be saved because the outer cable layers of the filler profile require less material. The power cable can therefore be lighter because the smaller outer diameter requires less armor, if any.

[0009] One embodiment includes, prior to step A2), estimating three-core outer dimensions of the assembly including the stranded cores based on the shape obtained in step A1), wherein in step A2), the cross-sectional shape is further based on the three-core outer dimensions.

[0010] According to one embodiment of the cross section, each filler profile has a curved outer boundary and two curved inner boundaries, the curved outer boundary forming the outer boundary of the filler profile and connecting two curved inner boundaries, each adapted to abut the outer surface of the respective core.

[0011] According to one embodiment, the determining in step A2) comprises determining the curvature of each of the two curved inner boundaries to match the shape of the core.

[0012] According to one embodiment, in step A2), determining the cross-sectional shape of the filler profile in the cross-section of the filler profile comprises scaling at least one of the curvatures by a cosine of the core twist angle of the core, wherein the scaling of at least one of the curvatures is by multiplication with the cosine of the core twist angle of the core.

[0013] According to one embodiment, the shape of the core is elliptical, and step A1 comprises determining the major and minor axes of the ellipse.

[0014] One embodiment includes, before step A2), determining an average diameter based on an average of the major diameter and the minor diameter, and in step A2), the cross-sectional shape is determined based on the average diameter.

[0015] According to one embodiment, in step A2), determining the cross-sectional shape of the filler profile in the cross-section of the filler profile comprises scaling the radius, which is half the average diameter, by the cosine of the core twist angle of the core, where the scaling of the radius is by multiplication with the cosine of the core twist angle of the core.

[0016] According to one embodiment, step B2) comprises extruding a filler profile.

[0017] According to one embodiment, the power cable is a submarine power cable.

[0018] According to one embodiment, the submarine power cable is one of a static or a dynamic submarine power cable.

[0019] The power cable may have a rating of at least 100 kV, such as at least 150 kV.

[0020] According to a second aspect of the present disclosure, there is provided a power cable obtainable by the method of the first aspect.

[0021] 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 "a / an / the element, apparatus, component, means," etc. should be interpreted open-endedly as referring to at least one instance of the element, apparatus, component, means, etc., unless otherwise specified.

[0022] 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]

[0023] [Figure 1] 1 shows a schematic longitudinal cross section of a three-core power cable. [Figure 2] FIG. 2 is a perspective view of the cable of FIG. 1 showing cross section AA. [Figure 3] 2 shows a schematic cross-section of the prior art power cable of FIG. 1 along line AA. [Figure 4]1 is a flowchart of a method for manufacturing a power cable with three cores and three filler profiles. [Figure 5] Filler profile is shown. [Figure 6] 5 shows a schematic cross section of a three-core power cable manufactured according to the method of FIG. 4. DETAILED DESCRIPTION OF THE INVENTION

[0024] 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 reference numerals refer to like elements throughout the description.

[0025] The present disclosure relates to a method for manufacturing a power cable with three cores and three filler profiles.

[0026] The power cable may be an AC power cable. Typically, all three cores are power cores. Alternatively, the power cable may be a DC power cable.

[0027] 1 shows a schematic axial cross section of a power cable 1 with three cores 3a-3c and three filler profiles. For illustrative purposes, only three cores 3a-3c are shown inside the power cable 1.

[0028] Two or all three cores 3a-3c may include a central conductor and an insulating system disposed around the central conductor. The insulating system may include an inner semiconductor layer disposed around the central conductor, an insulating layer disposed around the inner semiconductor layer, and an outer semiconductor layer disposed around the insulating layer.

[0029] The cores 3a-3c are arranged in a stranded configuration, and thus the three cores 3a-3c are twisted during assembly of the power cable 1.

[0030] The cores 3a to 3c are twisted at a core twist angle α with respect to the central longitudinal axis B of the power cable 1. Therefore, the core twist angle α is the helix angle at which the cores 3a to 3c are placed.

[0031] FIG. 2 also shows filler profiles 5a, 5c that are spirally wound or twisted together with the three cores 3a-3c.

[0032] The appearance of the cross section of the power cable 1 depends on the core twist angle α. The cross section is perpendicular to the central longitudinal axis B and divides the power cable 1 into two axial lengths. The larger the core twist angle α, i.e., the shorter the core twist pitch, the more distorted the appearance of the cores 3a-3c in the cross section. Instead of the circular cross-sectional shape of the roughly cylindrical cores 3a-3c, the cores 3a-3c appear roughly elliptical or distorted elliptical in the cross section of the power cable 1.

[0033] FIG. 3 shows, in an exaggerated manner for the sake of explanation, the cores 3a to 3c, which have a substantially elliptical shape, in a cross section taken along the line AA in FIG. 1 in the case of the power cable 1 of the prior art.

[0034] 3 also shows three filler profiles 5a to 5c. The filler profiles 5a to 5c are twisted together with the cores 3a to 3c. Therefore, the filler profiles 5a to 5c are also laid at the same helix angle as the core twist angle α of the cores 3a to 3c.

[0035] In a cross-section of the power cable 1, each filler profile 5a-5c has a curved outer boundary 7 and two curved inner boundaries 9, 11. The curved outer boundary 7 forms the outer boundary of the filler profile 5a-5c and connects the two curved inner boundaries 9, 11. Each curved inner boundary 9, 11 is adapted to abut the outer surface of a respective core 3a-3c.

[0036] In the cross-section of the power cable 1, the three cores 3a-3c have a generally elliptical shape with a major axis M and a minor axis m. This is due to the spiral layout of the three cores 3a-3c. The major axis M is the dimension of each core 3a-3c along its major axis, and the minor axis m is the dimension of each core 3a-3c along its minor axis. The minor axis m is the same as the nominal outer diameter of each core 3a-3c. For illustrative purposes, the circular shapes of the cores 3a-3c as they would appear in a cross-section of the cores 3a-3c are shown in dashed lines. These circular cores 3a-3c have the nominal outer diameter of the cores 3a-3c. Although not clearly shown in FIG. 3, it can be seen that there are portions of the curved inner boundaries 9, 11 of the generally elliptical cores 3a-3c that do not contact the outer boundary / surface.

[0037] Now, with reference to Figures 4 to 6, a method for manufacturing a power cable 13 having three cores 3a to 3c and three filler profiles 5a' to 5c' shown in Figure 6 will be described, in which the adjusted design of the filler profiles 5a' to 5c' results in a better fit between the cores 3a to 3c and the filler profiles 5a' to 5c'.

[0038] The method is divided into two stages: stage A) of designing the power cable 13, and stage B) of manufacturing the power cable 13 according to the design obtained in stage A).

[0039] The design stage includes steps A0) to A2) described below.

[0040] In step A0), the nominal outer diameters of the cores 3a to 3c are defined. The nominal outer diameters are the outer diameters of the cores 3a to 3c before the twisting process of the cores 3a to 3c.

[0041] The nominal outer diameter can be defined based on, for example, the required rating of the power cable 13 being manufactured, the conductor design and material, the water barrier design, if any, and the selection of polymer material, as will be apparent to one skilled in the art.

[0042] In step A0, the twist pitch P of the cores 3a to 3c is also defined. The core twist pitch P and the nominal outer diameter determine the core twist angle α.

[0043] In step A1), the shape of at least one of the cores 3a-3c in a cross section of the power cable 13 is determined. The shape is thus the cross-sectional shape of the cores 3a-3c. The shape is approximately elliptical or approximately elliptical, since it corresponds to a cross section along the tube that represents the cores 3a-3c at an angle that is not perpendicular to the longitudinal axis of the tube. The angle is the core twist angle α.

[0044] Typically, all of the cores 3a to 3c have the same twist pitch P, and therefore have the same approximately elliptical shape in the cross section of the power cable 13. Therefore, in step A1), it may be sufficient to determine the shape of only one of the cores 3a to 3c.

[0045] According to one example, step A1) may include determining the minor axis m and major axis M of the substantially elliptical cores 3a-3c.

[0046] According to one example, step A1) may include using a calculation tool to calculate the major diameter M and minor diameter m of the cores 3a to 3c using the twist pitch P and nominal outer diameter of the cores 3a to 3c as input to obtain the major diameter M and minor diameter m.

[0047] According to another example, the major diameter M and the minor diameter m can be determined manually by measuring the cores 3a-3c in a cross section of a three-dimensional model of the power cable 13 in which the cores 3a-3c are stranded with a strand pitch P and the cores 3a-3c have the nominal outer diameter defined in step A0. The three-dimensional model may be, for example, a CAD model.

[0048] In step A2), the cross-sectional shapes of the filler profiles 5a'-5c' are determined based on the shapes determined in step A1. The cross-sectional shapes are determined in transverse cross-sections of the filler profiles 5a'-5c', i.e., in cross-sections perpendicular to the longitudinal axes of the filler profiles 5a'-5c'.

[0049] The determination in step A2) involves determining the curvature of each of the two curved inner boundaries so that it matches the shape of the cores 3a-3c in the cross section of the power cable 13. This matching can be done, for example, by drawing the two curved inner boundaries of the filler profile so that they perfectly follow the shape of the two cores 3a-3c that the filler profile in question faces.

[0050] In another example, before step A2), the average diameter can be determined based on the average of the major diameter M and the minor diameter m, i.e., average diameter = (major diameter M + minor diameter m) / 2. Then, in step A2), the cross-sectional shape is determined based on the average diameter. For example, the radius r of the curved inner boundaries 9, 11 shown in Figure 5 may be set to half the average diameter, i.e., average diameter / 2, in step A2). The radius r is determined for the filler profile in the cross-section of the power cable 13.

[0051] One example includes, prior to step A2), estimating at least one three-core outer dimension of the assembly including the stranded cores 3a-3c based on the shape obtained in step A1). The at least one three-core outer dimension may be the three-core diameter of the assembly. The three-core dimension may be determined as the diameter of a circle defined by the boundaries of the three cores 3a-3c in the trefoil configuration. In both cases, in step A2), the cross-sectional shape is further based on the at least one three-core outer dimension. Here, the radius R of the curved outer boundary 7 of the filler profile 5a'-5c' may be determined based on the three-core outer dimension of the assembly.

[0052] Once the curvature or radius r of each of the two curved inner boundaries is determined in the cross-section of the power cable 1, the curvature or radius r of one or more of the two curved inner boundaries is determined in the cross-section of the filler profile, since the filler profile is produced by linear extrusion.

[0053] The curvature or radius of each of the two curved inner boundaries in the cross-section of the filler profile can be determined by scaling the curvatures, or according to one example, by scaling the respective curvatures if they are different, or by the radius r by the cosine of the core lay angle α. For example, the radius of each of the two curved inner boundaries in the cross-section of the filler profile can be determined by r*cos(α), where α is the core lay angle and r is the radius of the curved inner boundary in the cross-section of the power cable 13, as described above.

[0054] Based on the design obtained in stage A), stage B) of manufacturing the power cable 13 comprises steps B1) to B3) described below. The power cable 13 may be a submarine power cable, i.e. a static or dynamic submarine power cable.

[0055] In step B1), the cores 3a to 3c are manufactured to their nominal outer diameters.

[0056] Step B1) may include providing a conductor and constructing an insulation system around the conductor. The insulation system may be a paper-based wound insulation system or a polymer-based extruded insulation system. The insulation system includes an inner semiconducting layer disposed around the conductor, an insulating layer disposed around the inner semiconducting layer, and an outer semiconducting layer disposed around the insulating layer.

[0057] Step B1) can include providing a bedding layer around the insulation system. According to one example, step B1) can include providing a metallic water barrier, such as a lead sheath, or a longitudinally welded metallic water barrier comprising copper, aluminum, or stainless steel, around the insulation system and, if present, around the bedding layer. Step B1) can also include extruding a polymer layer around the insulation system, for example, around the metallic water barrier, if present.

[0058] In step B2), which may be performed before, simultaneously with, or after step B1), filler profiles 5a'-5c' are obtained with the cross-sectional shape obtained in step A2) of the design phase. Step B2) may involve producing the filler profiles 5a'-5c' by extrusion at the manufacturing site of the cores 3a-3c, or may involve obtaining the filler profiles 5a'-5c' from an external supplier who has produced the filler profiles 5a'-5c' according to the specifications, including the cross-sectional shape obtained in step A2).

[0059] In step B3), the cores 3a-3c and the filler profiles 5a'-5c' are twisted together in an assembly machine with a twist pitch P. This results in an assembled power cable 13 having a cross-section as shown diagrammatically in FIG. 5. The filler profiles 5a'-5c' therefore fit better with the cores 3a-3c. Thus, the pressure exerted by the filler profiles 5a'-5c' on the cores 3a-3c is distributed more evenly, reducing the risk of the cores 3a-3c being damaged by the filler profiles 5a'-5c'.

[0060] The inventive concept has been described above primarily with reference to a few examples, however, as will be readily appreciated by 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. 1. A method for manufacturing a power cable (13) comprising three core (3a, 3b, 3c) and three filler (5a', 5b', 5c') profiles arranged in a twisted configuration, comprising: A) In the design stage of the power cable (13), A0) defining a nominal outer diameter of the core (3a, 3b, 3c) and defining a twist pitch P of the core (3a, 3b, 3c); A1) determining the shape of at least one of the cores (3a, 3b, 3c) in a cross section of the power cable (13); A2) determining a cross-sectional shape of the filler profile (5a', 5b', 5c') in a cross section of the filler profile (5a', 5b', 5c') based on the shape determined in step A1); B) In the manufacturing stage of the power cable (13), B1) manufacturing each of said cores (3a, 3b, 3c) having said nominal outer diameter; B2) obtaining the filler profile (5a', 5b', 5c') having the cross-sectional shape obtained in step A2); B3) twisting said core (3a, 3b, 3c) and said filler profiles (5a', 5b', 5c') with said twist pitch P in an assembly machine.

2. 2. The method of claim 1, further comprising, prior to step A2), estimating three-core outer dimensions of an assembly comprising the stranded cores (3 a, 3 b, 3 c) based on the shape obtained in step A1), wherein in step A2), the cross-sectional shape is further based on the three-core outer dimensions.

3. 3. The method according to claim 1 or 2, wherein in cross section, each filler profile (5a', 5b', 5c') has a curved outer boundary (7) and two curved inner boundaries (9, 11), said curved outer boundary (7) forming the outer boundary of said filler profile (5a', 5b', 5c') and connecting said two curved inner boundaries (9, 11), each adapted to abut the outer surface of a respective core (3a, 3b, 3c).

4. 4. The method of claim 3, wherein said determining in step A2) comprises determining the curvature of each of said two curved inner boundaries (9, 11) to match said shape of said core (3a, 3b, 3c).

5. 5. The method of claim 4, wherein in step A2), determining the cross-sectional shape of the filler profile (5a', 5b', 5c') in a cross-section of the filler profile (5a', 5b', 5c') comprises scaling at least one of the curvatures by the cosine of the core twist angle (α) of the core (3a, 3b, 3c).

6. 4. The method of claim 1, wherein the shape of the core is an ellipse, and step A1) comprises determining the major axis (M) and minor axis (m) of the ellipse.

7. The method of claim 6, further comprising, before step A2), determining an average diameter based on an average of the major diameter (M) and the minor diameter (m), and in step A2), determining the cross-sectional shape based on the average diameter.

8. 8. The method according to claim 7, wherein in step A2), determining the cross-sectional shape of the filler profile (5a', 5b', 5c') in a cross-section of the filler profile (5a', 5b', 5c') comprises scaling a radius (r), which is half the mean diameter, by the cosine of the core twist angle (α) of the core (3a, 3b, 3c).

9. 9. The method according to any one of the preceding claims, wherein step B2) comprises extruding said filler profile (5a', 5b', 5c').

10. 10. The method according to any one of claims 1 to 9, wherein the power cable (13) is a submarine power cable.

11. The method of claim 10 , wherein the submarine power cable is one of a static or a dynamic submarine power cable.

12. A power cable (13) obtainable by the method according to any one of claims 1 to 11.

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