METHOD OF BUILDING AN INSULATION SYSTEM OF A POWER CABLE

Abstract

A method of building an insulation system around an axial section of a conductor of a power cable, the method including: a) providing a power cable including a conductor and an insulation system arranged around the conductor, the insulation system including insulation system layers, including an inner semiconducting layer arranged around the conductor, an insulation layer arranged around the inner semiconducting layer, and an outer semiconducting layer arranged around the insulation layer, wherein the power cable includes an axial section between a first insulation system section and a second insulation system section of the insulation system which at least is without an outer semiconducting layer, b) winding a tape around the conductor along the axial section in a plurality of layers to form a plurality of layers of tape connecting with the first insulation system section and the second insulation system section, and c) heating the plurality of layers of tape to melt and fuse the plurality of layers of tape to form an insulation system layer between the first insulation system section and the second insulation system section, wherein the tape has a width defined by a distance between lateral edges, wherein the tape has a mid-section between its lateral edges, wherein in the mid-section the tape has a largest thickness, and wherein the thickness of the tape decreases from the mid-section towards both lateral edges.

Claims

1. A method of building an insulation system around an axial section of a conductor of a power cable, the method comprising: a) providing a power cable including a conductor and an insulation system arranged around the conductor, the insulation system comprising insulation system layers, including an inner semiconducting layer arranged around the conductor, an insulation layer arranged around the inner semiconducting layer, and an outer semiconducting layer arranged around the insulation layer, wherein the power cable includes an axial section between a first insulation system section and a second insulation system section of the insulation system which at least is without an outer semiconducting layer, b) winding a tape around the conductor along the axial section in a plurality of layers to form a plurality of layers of tape connecting with the first insulation system section and the second insulation system section, and c) heating the plurality of layers of tape to melt and fuse the plurality of layers of tape to form an insulation system layer between the first insulation system section and the second insulation system section, wherein the tape has a width defined by a distance between lateral edges, wherein the tape has a mid-section between its lateral edges, wherein in the mid-section the tape has a largest thickness, and wherein the thickness of the tape decreases from the mid-section towards both lateral edges.

2. The method as claimed in claim 1, wherein the thickness decreases smoothly towards both lateral edges.

3. The method as claimed in claim 1, wherein the thickness decreases symmetrically towards the lateral edges.

4. The method as claimed in claim 1, wherein in cross-section of the tape, the tape has a convex shape.

5. The method as claimed in claim 4, wherein the convex shape is biconvex or plano-convex.

6. The method as claimed in claim 1, wherein in step b) in each layer of the plurality of layers, adjacent turns are arranged with an overlap.

7. The method as claimed in claim 1, wherein in each layer of the plurality of layers, each turn of tape is arranged axially shifted along the axial direction of the conductor relative to all turns of the tape of any adjacent layer of tape.

8. The method as claimed in claim 7, wherein each turn is shifted axially at least with 20%, such as at least 30%, such as at least 40% of the width of the tape.

9. The method as claimed in claim 1, wherein in step c) the tape is heated under pressure higher than atmospheric pressure.

10. The method as claimed in claim 1, comprising prior to step b) providing an inner semiconducting layer around the conductor, wherein in step b) the winding of the tape is around the inner semiconducting layer.

11. The method as claimed in claim 1, wherein the insulation system layer is an insulation layer or an outer semiconducting layer.

12. The method as claimed in claim 1, wherein the tape comprises a polymeric material.

13. The method as claimed in claim 12, wherein the polymeric material includes one of polyethylene, polypropylene, ethylene propylene rubber, EPR, and ethylene propylene diene monomer rubber.

14. The method as claimed in claim 1, wherein the building of the insulation forms part of a cable-jointing operation or a repair operation of the insulation system of the power cable.

15. The method as claimed in claim 1, wherein the power cable is a high voltage power cable.

16. The method as claimed in claim 2, wherein the thickness decreases symmetrically towards the lateral edges.

17. The method as claimed in claim 2, wherein in cross-section of the tape, the tape has a convex shape.

18. The method as claimed in claim 2, wherein in step b) in each layer of the plurality of layers, adjacent turns are arranged with an overlap.

19. The method as claimed in claim 2, wherein in each layer of the plurality of layers, each turn of tape is arranged axially shifted along the axial direction of the conductor relative to all turns of the tape of any adjacent layer of tape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

[0030] FIG. 1 schematically shows a longitudinal section of a power cable with a joint;

[0031] FIG. 2 is a flowchart of a method of building an insulation system around an axial section of a conductor of a power cable;

[0032] FIG. 3a schematically shows an example of a tape; and

[0033] FIGS. 3b-3c show cross-sections of examples of tapes.

DETAILED DESCRIPTION

[0034] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

[0035] FIG. 1 schematically shows an example of a longitudinal section of a power cable 1 provided with a factory joint 3.

[0036] The power cable 1 comprises a first section 1a and a second section 1b joined by means of the factory joint 3.

[0037] The first section 1a includes a first conductor section 5a, an inner semiconducting layer 7a, also called conductor screen, arranged around the first conductor section 5a, an insulation layer 9a arranged around the inner semiconducting layer 7a, and an outer semiconducting layer 11a, also called insulation screen. The inner semiconducting layer 7a, the insulation layer 9a, and the outer semiconducting layer 11a arranged around the first conductor section 5a form a first insulation system section of the power cable 1.

[0038] The first insulation system section is an extruded insulation system. Each of the inner semiconducting layer 7a, the insulation layer 9a, and the outer semiconducting layer 11a may comprise a polymeric material, such as polyethylene, polypropylene, ethylene propylene rubber, EPR, or ethylene propylene diene monomer rubber (EPDM).

[0039] Similarly, the second section 1b comprises a second conductor section 5b, an inner semiconducting layer 7b arranged around the second conductor section 5b, an insulation layer 9b arranged around the inner semiconducting layer 7b, and an outer semiconducting layer 11b. The inner semiconducting layer 7b, the insulation layer 9b, and the outer semiconducting layer 11b arranged around the second conductor section 5b form a second insulation system section of the power cable 1.

[0040] The second insulation system section of the second section 1b is an extruded insulation system. Each of the inner semiconducting layer 7b, the insulation layer 9b, and the outer semiconducting layer 11b may comprise a polymeric material, such as polyethylene, polypropylene, ethylene propylene rubber, EPR, or ethylene propylene diene monomer rubber (EPDM).

[0041] The first and second conductor sections 5a and 5b are according to the example joined. The conductor sections 5a and 5b are thus connected via a conductor joint 13 and form a single conductor 5. The conductor sections 5a and 5b may for example be joined thermally such as by welding.

[0042] The first insulation system section and the second insulation system section are joined and form an insulation system of the power cable 1.

[0043] The first insulation systems section and the second insulation system section are joined using tapes to form an inner semiconducting layer 15 which connects the inner semiconducting layer 7a and 7b of the first insulation system section and the second insulation system section, respectively, to form an insulation layer 17 which connects the insulation layer 9a and 9b of the first insulation system section and the second insulation system section, respectively, and to form an outer semiconducting layer 19 which connects the outer semiconducting layer 11a and 11b of the first insulation system section and the second insulation system section, respectively.

[0044] A method of building an insulation system around exposed first and second conductor sections 5a and 5b to form a power cable such as power cable 1 will now be described with reference to FIGS. 2 to 3c.

[0045] The building of the insulation system may form part of a cable-jointing operation of the power cable 1 or a repair operation of the insulation system of the power cable 1.

[0046] In case the method concerns a cable-jointing operation, the first section 1a and the second section 1b are initially not joined. In this case, the first conductor section 5a and the second conductor section 5b are initially not connected. Prior to joining the first conductor section 5a and the second conductor section 5b, an end portion of the first conductor section 5a and the second conductor section 5b is exposed. Further, the respective inner semiconducting layer 7a, 7b, insulation layer 9a, 9b, and outer semiconducting layer 11a, 11 b are exposed sequentially for each of the first section 1a and the second section 1b. Moreover, each insulation layer 9a, 9b may be pencilled, i.e., formed as a cone, arranged tapering towards each other, as shown in FIG. 1.

[0047] The first conductor section 5a and the second conductor section 5b are joined to form the conductor joint 13.

[0048] Alternatively, if the method concerns a repair operation of the insulation system, the conductor 5 may not require jointing in the region where the insulation system is to be built around the conductor 5. Also in this case, the first conductor section 5a and the second conductor section 5b are exposed to enable rebuilding of the insulation system in the damaged region. Further, the respective insulation layer 9a, 9b, and outer semiconducting layer 11a, 11 b are exposed sequentially for each of the first section 1a and the second section 1b. Also in this case, the insulation layer 9a, 9b may be pencilled, i.e., formed as a cone, arranged tapering towards each other.

[0049] In both cases, at this point the first insulation system section and the second insulation system section are axially distanced from each other. In particular, the power cable 1 has an axial section between the first insulation system section and the second insulation system section which is at least without an outer semiconducting layer.

[0050] In a step a) of the method, the power cable 1 having an axial section between the first insulation system section and the second insulation system section, which is at least without the outer semiconducting layer, is provided.

[0051] Typically, the inner semiconducting layer 15 is provided around the exposed and joined conductor sections 5a, 5b prior to step a). The inner semiconducting layer 15 may alternatively be provided around the exposed, and in the region non-jointed, conductor 5 in examples that concern repair of the insulation system of the power cable 1.

[0052] The inner semiconducting layer 15 may for example be made by winding tape around the exposed first and second conductor sections 5a, 5b, and heating the tape to cure the tape.

[0053] In a step b) tape is wound around the conductor 5 along an axial section between the first insulation system section and the second insulation system section.

[0054] The tape is wound in a plurality of layers to form a plurality of layers of tape connecting with the first insulation system section and the second insulation system section of the power cable 1.

[0055] According to one example in step b) in each layer of the plurality of layers, adjacent turns are arranged with an overlap.

[0056] According to one example in each layer of the plurality of layers, each turn of tape is arranged axially shifted along the axial direction of the conductor 5 relative to all turns of the tape of any adjacent layer of tape. Each turn may for example be shifted axially at least with 20%, such as at least 30%, such as at least 40% of the width of the tape.

[0057] In a step c) the plurality of layers of tape are heated to melt and fuse the plurality of layers of tape to form an insulation system layer between the first insulation system section and the second insulation system section. Further, the thus obtained insulation system layer is also fused with the first insulation system section and the second insulation system section. In particular, the insulation system layer is fused with the corresponding insulation system layer of the first insulation system section and the second insulation system section.

[0058] The insulation system layer formed in step c) may be the insulation layer 17 or the outer semiconducting layer 19, connecting the first insulation system section and the second insulation system section.

[0059] In step c) the tape may be heated under pressure higher than atmospheric pressure. For example, the pressure may be at least 2 bar, such as at least 3 bar, or at least 4 bar.

[0060] FIG. 2 shows an example of the tape 21-1 used in step b). The tape 21-1 has a width w defined by the distance between its lateral edges 21a, 21b. The tape 21-1 has a mid-section 21c between the lateral edges 21a, 21b. In the mid-section 21c, the tape 21-1 has its largest thickness t. The thickness of the tape 21-1 decreases from the mid-section 21c in a direction towards the lateral edge 21a and in a direction towards the lateral edge 21b. The thickness of the tape 21 at the lateral edges 21a, 21b is thus smaller than the largest thickness tin the mid-section 21c.

[0061] The thickness of the tape 21 may preferably decrease smoothly towards both lateral edges 21a, 21b.

[0062] The thickness of the tape 21 may taper symmetrically towards the lateral edges 21a, 21b. With respect to a centre axis A through the mid-section 21c, the tapering is symmetric on both sides of the centre axis A.

[0063] The tape may in cross-section have a convex shape, as shown FIGS. 3b and 3c. According to the example in FIG. 3b, the tape 21-2 is plano-convex. In the example depicted in FIG. 3c, the tape 21-3 is biconvex.

[0064] The tape 21-1, 21-2, 21-3 comprises a polymeric material. The polymeric material may for example include one of polyethylene, polypropylene, ethylene propylene rubber, and ethylene propylene diene monomer rubber.

[0065] Tape with a geometric structure as shown in FIGS. 3a-3c may be used for the insulation layer or the outer semiconducting layer, or for both these layers. The material of the tape 21-1, 21-2, 21-3 would however differ for the two layers. It is made of an insulating material for the insulation layer and of a semiconducting material for the outer semiconducting layer.

[0066] The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.