Method of manufacturing power cable joint

Abstract

To provide a method of manufacturing a power cable with a high dielectric strength and a joint of the power cable.SOLUTION: In a joint 3 of a power cable 1, each of two cable sections 1a and 1b to be jointed has a joint insulation system 13 including conductors 5a and 5b having a conductor end, an inner semiconducting layer 7, an insulation layer 9 arranged radially outside the inner semiconducting layer 7, and an outer semiconducting layer 11. A method of manufacturing the joint insulation system obtains a tapering insulation layer section that tapers toward the conductor end. After the conductors are electrically connected to each other by means of a conductor joint 5c, the joint insulation system is connected to the inner semiconducting layer 7 of each of the cable sections 1a and 1b, the tapering insulation layer section of each of the cable sections 1a and 1b, and the outer semiconducting layer 11 of each of the cable sections 1a and 1b.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates generally to power cable joints. [Background technology]

[0002] A power cable may be composed of several power cable lengths or sections joined by cable joints, which include conductor joints and joints in the insulation systems of the power cable lengths, the insulation system of the power cable comprising an inner semiconductive layer, an insulating layer outside the inner semiconductive layer, and an outer semiconductive layer outside the insulating layer.

[0003] A conventional flexible joint is prepared by preparing two power cable ends with exposed conductor ends, exposed conductor screen, and a frustoconical section of insulation. The joint's insulation system is then constructed in stages, typically by wrapping tape layers and fusing / crosslinking them under heat and pressure. First, the inner semiconductive layer is restored, then the insulation layer, and finally the outer semiconductive layer.

[0004] During operation, a strong electric field exists between the inner semiconductive layer, which has a potential equal to the operating voltage of the power cable, and the grounded outer semiconductive layer. Due to the aforementioned frustoconical shape of the insulation systems at each end of the power cable, the interface between the joint insulation systems of the two joined power cable lengths is inclined with respect to the longitudinal axis of the power cable and with respect to the radial direction of the power cable, which is also the primary direction of the electric field. As a result, at a given position along the longitudinal axis of the cable joint, the electric field between the inner semiconductive layer and the outer semiconductive layer always passes through only one radial point along the interface between the insulating material of the joint of the power cable lengths and the insulating layer, thereby increasing the dielectric strength of the power cable compared to a power cable with an interface that is not inclined in the radial direction parallel to the electric field. Summary of the Invention

[0005] Failure of a flexible or factory joint often initiates either at or near the triple point of the cable insulation, the joint insulation, and the outer or inner semiconducting layer, because any material transition / material interface between two sections of similar or the same material creates a vulnerability to the electric field. The two interfacing surfaces have the lowest dielectric strength when they run parallel to the electric field and are strongest when oriented at 90° to the field.

[0006] Furthermore, the electric field has a maximum near the inner semiconducting layer in the case of an AC power cable, or near the outer semiconducting layer in the case of a DC power cable under steady-state conditions, and in the case of joints having a frustoconical portion of the insulation system as described above, the electric field crosses the interface between the power cable insulation layer and the joint insulation layer at an angle far from 90°, i.e., at an angle that is not the strongest direction with respect to the insulation interface.

[0007] In view of the above, it is an object of the present disclosure to provide a method for manufacturing a power cable joint that solves or at least alleviates the problems of the prior art.

[0008] Thus, according to a first aspect of the present disclosure, there is provided a method for manufacturing a power cable joint, comprising: a) providing two cable sections to be joined, each cable section comprising a conductor having a conductor end and an insulation system including an inner semi-conductive layer disposed around the conductor, an insulating layer disposed radially outward of the inner semi-conductive layer, and an outer semi-conductive layer disposed radially outward of the insulating layer; and b) mechanically processing the insulation system of each cable section by gradually increasing a radius of the insulation layer in an axial direction away from the conductor end of the cable section to obtain a tapered insulation layer section tapering towards the conductor end, the processing comprising: a) processing the tapered insulation layer section such that an outer surface of the radially innermost portion of the tapered insulation layer section, which interfaces with the inner semi-conductive layer, acquires a first inclination relative to the longitudinal axis of the cable section, and an outer surface of the intermediate portion of the tapered insulation layer section acquires a second inclination greater than the first inclination, such that the outer surface of the radially innermost portion smoothly transitions into the outer surface of the intermediate portion; and b) manufacturing a joint insulation system after the conductors of the two cable sections are electrically connected to each other by a conductor joint, the joint insulation system connecting the inner semi-conductive layer of each cable section, the tapered insulation layer section of each cable section, and the outer semi-conductive layer of each cable section.

[0009] Therefore, when the electric field tends to be strongest, it will be perpendicular to the interface between the joint insulation layer of the joint insulation system and the insulation layer of each cable section, which is close to the optimum direction for electrical interface strength. This will result in a high dielectric strength for the joint.

[0010] The first slope may be a minimum slope along an outer surface of the radially innermost portion. The first slope may be different from 0 degrees relative to a longitudinal axis of the power cable.

[0011] The intermediate portion of the tapered insulation layer section may be frustoconical, and thus the outer surface of the intermediate portion may have a second slope along the entire length of the intermediate portion.

[0012] The power cable may be a submarine power cable or an underground cable.

[0013] The power cable may be a high voltage, extra high voltage or extra high voltage power cable, where high voltage means herein a nominal voltage of at least 72 kV, such as at least 145 kV, for example at least 220 kV.

[0014] The power cable may be an AC power cable or a DC power cable.

[0015] According to one embodiment, the processing is performed such that the outer surface of the radially outermost portion of the tapered insulating layer section that joins with the outer semiconducting layer acquires a third slope that is smaller than the second slope, and the outer surface of the intermediate portion smoothly transitions into the outer surface of the radially outermost portion.

[0016] Therefore, when the electric field tends to be strongest, it will be perpendicular to the interface between the joint insulation layer of the joint insulation system and the insulation layer of each cable section, which is close to the optimum direction for electrical interface strength. This will result in a high dielectric strength for the joint.

[0017] The third slope may be a minimum slope along an outer surface of the radially outermost portion. The third slope may be different from 0 degrees relative to a longitudinal axis of the power cable.

[0018] According to one embodiment, the first and third tilts are substantially the same, for example, the angles of the first and third tilts may differ by at most 3°, such as at most 2°, for example at most 1°.

[0019] According to one embodiment, the outer surface of the radially outermost portion is convex.

[0020] According to one embodiment, the second slope has a slope angle in the range of 8 to 20 degrees. By processing the intermediate portion to have a slope angle in this range, an optimal trade-off can be obtained between not requiring an extremely long joint and having an interface with the insulating layer of the joint insulation system that provides sufficient dielectric strength along the intermediate portion due to a slope angle relatively close to 0 degrees, i.e., close to 90 degrees relative to the electric field.

[0021] According to one embodiment, the outer surface of the radially innermost portion is concave.

[0022] According to one embodiment, before step c), the tapered insulation layer section of each cable section has a generally S-shape or S-shape in a side view of the power cable.

[0023] According to one embodiment, the insulation system of each cable section is an extruded insulation system.

[0024] According to a second aspect of the present disclosure, there is provided a power cable comprising: two spliced ​​cable sections, each of the cable sections comprising a conductor and an insulation system including an inner semi-conductive layer disposed around the conductor, an insulating layer disposed radially outward of the inner semi-conductive layer, and an outer semi-conductive layer disposed radially outward of the insulating layer; the conductors of the two cable sections are electrically connected to each other by a conductor joint; the insulation system of each cable section has a radius that gradually increases in an axial direction away from the conductor joint, forming a tapered insulation layer section that tapers toward the conductor joint and joins with the inner semi-conductive layer; an outer surface of a radially innermost portion of the tapered insulation layer section has a first inclination with respect to a longitudinal axis of the power cable; and an outer surface of an intermediate portion of the tapered insulation layer section has a second inclination that is greater than the first inclination; and the outer surface of the radially innermost portion smoothly transitions into an outer surface of the intermediate portion, as well as into a joint insulation system that connects to the inner semi-conductive layer of each cable section, the tapered insulation layer section of each cable section, and the outer semi-conductive layer of each cable section.

[0025] According to one embodiment, the outer surface of the radially outermost portion of the tapered insulating layer section that connects with the outer semiconductive layer has a third slope that is less than the second slope, and the outer surface of the intermediate portion smoothly transitions into the outer surface of the radially outermost portion.

[0026] According to one embodiment, the first slope and the third slope are substantially the same.

[0027] According to one embodiment, the outer surface of the radially outermost portion is convex.

[0028] According to one embodiment, the second tilt has a tilt angle in the range of 8 to 20 degrees.

[0029] According to one embodiment, the outer surface of the radially innermost portion is concave.

[0030] According to one embodiment, in the longitudinal sections of the power cable, the tapered insulation layer section of each cable section has a generally S-shaped or S-shaped configuration.

[0031] 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.

[0032] 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]

[0033] [Figure 1] 1 shows a schematic longitudinal cross section of an example power cable. [Figure 2]1 is a flowchart of a method for manufacturing a power cable joint. DETAILED DESCRIPTION OF THE INVENTION

[0034] 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.

[0035] FIG. 1 shows a schematic longitudinal cross section of a portion of an example power cable 1 according to the present disclosure.

[0036] The power cable 1 comprises two cable sections 1a and 1b and a joint 3. The two cable sections 1a and 1b are joined by the joint 3.

[0037] The joint 3 may be a flexible field joint or a factory joint.

[0038] Each cable section 1a, 1b comprises a conductor 5a, 5b, which are electrically connected to each other by a conductor joint 5c.

[0039] The conductors 5a, 5b may comprise aluminum, an aluminum alloy, or copper or a copper alloy. Both conductors 5a, 5b may be made of the same metal material or different materials. For example, one of the conductors 5a, 5b may comprise copper and the other may comprise aluminum.

[0040] The conductors 5a, 5b may have the same outer dimensions or different outer dimensions.

[0041] In one example, the conductor joint 5c may comprise an adapter piece, for example if the two conductors 5a, 5b are of different materials and / or different dimensions.

[0042] Each of the conductors 5a, 5b may be one of a solid conductor, a round stranded conductor, a compacted conductor, or a segmented / Milliken conductor.

[0043] Each cable section 1a, 1b comprises an insulation system comprising an inner semiconductive layer 7 disposed around the conductors 5a, 5b, an insulating layer 9 disposed around the inner semiconductive layer 7, and an outer semiconductive layer 11 disposed around the insulating layer 9.

[0044] The insulation system may be an extruded insulation system.

[0045] The insulating layer 9 may comprise a thermosetting or thermoplastic polymer, for example a polyolefin such as polyethylene, e.g., cross-linked polyethylene (XLPE), polypropylene, or an elastomer such as ethylene propylene diene monomer (EPDM) rubber or ethylene propylene (EPR) rubber.

[0046] The power cable 1 comprises a joint insulation system 13 connecting the insulation systems of the two cable sections 1a and 1b. The joint insulation system 13 comprises an inner semi-conductive layer 15 that is directly connected to or fused with the inner semi-conductive layer 7 of each of the two cable sections 1a, 1b. The joint insulation system 13 comprises an insulation layer 17 that is directly connected to or fused with the insulation layer 9 of each of the two cable sections 1a, 1b. Furthermore, the joint insulation system 13 comprises an outer semi-conductive layer 19 that is directly connected to or fused with the outer semi-conductive layer 11 of each of the two cable sections 1a, 1b. The joint insulation system 13 may be heat-sealed to the insulation systems of the two cable sections 1a, 1b.

[0047] The insulation system of each cable section 1a, 1b has a radius that gradually increases in the axial direction away from the conductor joint 5c, forming a tapered insulation layer section that tapers towards the conductor joint 5c.

[0048] The outer surface of the radially innermost portion 9.1 of the tapered insulating layer section, which joins with the inner semiconductive layer 7 of the cable section 1a, 1b in question, has a first inclination relative to the longitudinal axis of the power cable 1.

[0049] At the interface with the inner semiconducting layer 7 where the radially innermost portion 9.1 terminates, the outer surface of the radially innermost portion 9.1 may have an inclination angle close to 0 with respect to the longitudinal axis of the power cable 1. The inclination angle may, for example, be less than 5°, such as less than 4°, for example less than 3°, such as less than 2°, for example less than 1°.

[0050] The outer surface of the intermediate portion 9.2 of the tapered insulation layer section of FIG. 1, defined to extend between vertical lines 21 and 23, has a second slope greater than the first slope. The outer surface of the entire intermediate portion 9.2 may have the same slope. The intermediate portion 9.2 may have a frustoconical shape. The second slope may have a slope angle α in the range of 8 to 20 degrees.

[0051] The innermost portion 9.1 extends from the axial point where the insulating layer 9 begins or ends at vertical line 24 in FIG. 1 to the point where the tapered insulating layer section becomes frustoconical, i.e., at vertical line 21, where the intermediate portion 9.2 begins.

[0052] The outer surface of the innermost portion 9.1 transitions smoothly to the outer surface of the intermediate portion 9.2, so there is no step or mathematical discontinuity where the outer surface of the innermost portion 9.1 transitions to the outer surface of the intermediate portion 9.2.

[0053] The outer surface of the innermost portion 9.1 may have different slopes at different positions in the direction toward the intermediate portion 9.1. The slope of the outer surface of the innermost portion 9.1 may increase as it approaches the intermediate portion 9.2. The outer surface of the innermost portion 9.1 may be concave. The outer surface of the innermost portion 9.1 may have an exponential shape or a curved shape with a radius in the range of 1 / 5 to 3 times the thickness of the insulating layer 9, for example, in the range of 3 / 10 to 2.5 times the thickness of the insulating layer 9, for example, in the range of 4 / 10 to 2 times the thickness of the insulating layer 9, for example, 0.5 to 1.5 times the thickness of the insulating layer 9.

[0054] The outer surface of the radially outermost portion 9.3 of the tapered insulating layer section, which extends between the vertical line 23 and the point where the insulating layer 9 first contacts the outer semiconducting layer 11 / 19 indicated by the vertical line 25 and thus joins with the outer semiconducting layer 11 / 19, has a third slope which is less than the second slope.

[0055] At the interface with the outer semiconductive layer 11 / 19 where the outer surface of the radially outermost portion 9.3 first contacts the outer semiconductive layer 11 / 19, the outer surface of the radially outermost portion 9.3 may have an inclination angle close to 0, for example less than 5°, for example less than 4°, for example less than 3°, for example less than 2°, for example less than 1°, relative to the longitudinal axis of the power cable 1.

[0056] The first slope and the third slope may be substantially the same. For example, the first slope and the third slope may differ by up to 3°, such as up to 2° or up to 1°.

[0057] The outer surface of the intermediate portion 9.2 smoothly transitions to the outer surface of the radially outermost portion 9.3, so there is no step or mathematical discontinuity as the outer surface of the intermediate portion 9.2 transitions to the outer surface of the radially outermost portion 9.3.

[0058] The outer surface of the outermost portion 9.3 may have different slopes at different positions toward the outer semiconductive layer 11 / 19. The slope of the outer surface of the outermost portion 9.1 may be smaller the closer it is to the outer semiconductive layer 11 / 19. The outer surface of the outermost portion 9.3 may be convex. The outer surface of the outermost portion 9.3 may have a curved shape with a radius ranging from 1 / 5 to 3 times the thickness of the insulating layer 9, for example, from 3 / 10 to 2.5 times the thickness of the insulating layer 9, for example, from 4 / 10 to 2 times the thickness of the insulating layer 9, for example, from 0.5 to 1.5 times the thickness of the insulating layer 9.

[0059] In a longitudinal cross section of the power cable 1, the tapered insulation layer section of each cable section 1a, 1b may have a generally S-shape, an S-like shape, or an S-shape.

[0060] The tapered insulation section consists of a radially innermost portion 9.1, an intermediate portion 9.2, and a radially outermost portion 9.2.

[0061] FIG. 2 is a flow chart of a method for manufacturing a joint 3 of a power cable 1 .

[0062] In step a), two cable sections 1a and 1b to be joined are provided. Each of the conductors 5a and 5b has a conductor end, which is joined during the process of manufacturing the joint 3 to form a conductor joint 5c.

[0063] In step b), the insulation system of each of the two cable sections 1a and 1b is mechanically machined by gradually increasing the radius of the insulation layer 9 in the axial direction away from the conductor ends of the cable sections 1a, 1b to obtain tapered insulation layer sections that taper towards the conductor ends. The machining may be performed, for example, using a lathe tool. The machining may be performed by a robot or by a human.

[0064] The processing of step b) is performed so that the tapered insulating layer section obtains a radially innermost portion 9.1 and an intermediate portion 9.2. Optionally, the processing of step b) may be performed so that the tapered insulating layer section also obtains a radially outermost portion 9.3 structured as described above.

[0065] Step b) may be performed before manufacturing the conductor joint 5c or after manufacturing the conductor joint 5c.

[0066] In step c), the joint insulating system 13 is produced after the conductors 5a, 5b of the two cable sections 1a, 1b have been electrically connected to one another by means of a conductor joint 5c.

[0067] The joint insulation system 13 may be manufactured, for example, by first wrapping semiconductive tape around the conductor joint 5c and the exposed portions of each of the two conductor ends up to the inner semiconductive layer 7 of both cable sections 1a, 1b. The semiconductive tape may then be heat-treated and optionally cross-linked to form the inner semiconductive layer 15 of the joint insulation system 13. Next, insulating tape may be wrapped around the inner semiconductive layer 15. The insulating tape may then be heat-treated and optionally cross-linked to form the insulating layer 17 of the joint insulation system 13. Finally, semiconductive tape may be wrapped around the insulating layer 17. The semiconductive tape may then be heat-treated and optionally cross-linked to form the outer semiconductive layer 19 of the joint insulation system 13. Instead of using tape, the joint insulation system 13 may be formed by injection molding or 3D printing.

[0068] In one example of a power cable, the tapered insulation section consists only of a radially innermost portion 9.1 and an intermediate portion 9.2, which in this case extends to the outer semiconducting layer 11.

[0069] If the power cable 1 comprises multiple power cores, each power core may have a joint 3 as described herein.

[0070] 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. A method for manufacturing a joint (3) of a power cable (1), comprising the steps of: a) providing two cable sections (1a, 1b) to be joined, each cable section (1a, 1b) comprising a conductor (5a, 5b) having a conductor end, and an insulation system including an inner semiconductive layer (7) arranged around the conductor (5a, 5b), an insulating layer (9) arranged radially outward of the inner semiconductive layer (7), and an outer semiconductive layer (11) arranged radially outward of the insulating layer (9); b) mechanically processing the insulation system of each cable section (1a, 1b) by gradually increasing the radius of the insulation layer (9) in the axial direction away from the conductor ends of the cable sections (1a, 1b) in order to obtain tapered insulation layer sections tapering towards the conductor ends, processing the insulation system, wherein said processing is carried out so that an outer surface of the radially innermost portion (9.1) of the tapered insulation layer section, which is connected to the inner semiconducting layer (7), acquires a first inclination relative to the longitudinal axis of the cable section (1a, 1b), and an outer surface of the intermediate portion (9.2) of the tapered insulation layer section acquires a second inclination greater than the first inclination, and said outer surface of the radially innermost portion (9.1) smoothly transitions into the outer surface of the intermediate portion (9.2); c) manufacturing a joint insulation system (13) after the conductors of the two cable sections (1 a, 1 b) are electrically connected to each other by a conductor joint (5 c), the joint insulation system (13) connecting the inner semi-conductive layer (7) of each cable section (1 a, 1 b), the tapered insulation layer section of each cable section (1 a, 1 b), and the outer semi-conductive layer (11) of each cable section (1 a, 1 b).

2. 2. The method of claim 1, wherein the processing is performed such that an outer surface of the radially outermost portion (9.3) of the tapered insulating layer section, which connects with the outer semiconducting layer (11 / 19), acquires a third slope that is smaller than the second slope, and an outer surface of the intermediate portion (9.2) smoothly transitions into the outer surface of the radially outermost portion (9.3).

3. The method of claim 2 , wherein the first slope and the third slope are substantially the same.

4. 4. The method according to claim 2 or 3, wherein the outer surface of the radially outermost portion (9.3) is convex.

5. 5. The method according to claim 1, wherein the second tilt has a tilt angle (α) in the range of 8 to 20°.

6. 6. The method according to any one of claims 1 to 5, wherein the outer surface of the radially innermost portion (9.1) is concave.

7. 7. The method according to any one of claims 1 to 6, wherein before step c), the tapered insulation layer section of each cable section (1 a, 1 b) has a substantially S-shape or S-shape in a side view of the power cable (1).

8. 8. A method according to any one of claims 1 to 7, wherein the insulation system of each cable section (1a, 1b) is an extruded insulation system.

9. A power cable (1), two joined cable sections (1a, 1b), each cable section (1a, 1b) comprising a conductor (5a, 5b) and an insulation system including an inner semiconductive layer (7) arranged around the conductor (5a, 5b), an insulating layer (9) arranged radially outside the inner semiconductive layer (7), and an outer semiconductive layer (11) arranged radially outside the insulating layer (7), the conductors (5a, 5b) of the two cable sections (1a, 1b) are electrically connected to each other by a conductor joint (5c); the insulation system of each cable section (1 a, 1 b) forms a tapered insulation layer section having a radius that gradually increases in the axial direction away from the conductor joint (5 c) and that tapers towards the conductor joint (5 c); a cable section (1a, 1b) in which an outer surface of a radially innermost portion (9.1) of the tapered insulation layer section, which is connected to the inner semiconducting layer (7), has a first inclination relative to the longitudinal axis of the power cable (1), and an outer surface of an intermediate portion (9.2) of the tapered insulation layer section has a second inclination greater than the first inclination, and the outer surface of the radially innermost portion (9.1) smoothly transitions into the outer surface of the intermediate portion (9.2); a joint insulation system (13) that connects the inner semiconductive layer (7) of each cable section (1a, 1b), the tapered insulation layer section of each cable section (1a, 1b), and the outer semiconductive layer (11) of each cable section (1a, 1b).

10. 10. The power cable (1) according to claim 9, wherein an outer surface of the radially outermost portion (9.3) of the tapered insulating layer section that joins with the outer semiconducting layer (11, 19) has a third slope that is smaller than the second slope, and the outer surface of the intermediate portion (9.2) smoothly transitions into the outer surface of the radially outermost portion (9.3).

11. 11. The power cable (1) according to claim 10, wherein the first slope and the third slope are substantially the same.

12. 12. Power cable (1) according to claim 10 or 11, wherein the outer surface of the radially outermost portion (9.3) is convex.

13. 13. The power cable (1) according to any one of claims 9 to 12, wherein the second inclination has an inclination angle (α) in the range of 8 to 20°.

14. 14. The power cable (1) according to any one of claims 9 to 13, wherein the outer surface of the radially innermost portion (9.1) is concave.

15. 15. The power cable (1) according to any one of claims 9 to 14, wherein in the longitudinal sections of the power cable (1), the tapered insulation layer section of each cable section (1a, 1b) has a substantially S-shape or S-shape.

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