SE2251121A1 - Armoured power cable - Google Patents

Abstract

ARMOURED POWER CABLEA power cable comprises a first conductor, a first insulation system provided around the first conductor and an armour (9) surrounding the first insulation system, the armour (9) comprising at least one armour layer (15) comprising metallic armour wires (17) and polymeric spacer elements (19), wherein the armour wires (17) have circular cross-section and the spacer elements (19) have a cross-section with a different shape and an area that is at least twice the area of the circular cross-section of the armour wires (17).

Description

The present disclosure generally relates to armoured power cables.

BACKGROUND Power cables, such as submarine power cables, may often have an armour comprising a plurality of armour wires. The armour wires normally extend helically around the single core or multi-core of the power cable. The armour provides mechanical protection against lateral impacts during installation and operation of the cable. The armour also provides tensional force for the cable laying. The armour is typically made of a metal, such as steel.

There are some disadvantages with metal armouring. A submarine cable is typically laid out on the seabed using a cable laying vessel. If only metal such as steel is used the cable will become very heavy, which makes it difficult to lay out the cable, especially if the cable is a high voltage cable.

This has typically been addressed through combining the metallic armour wires with polymeric spacer wires.

However, there may be a restriction on the armour circumference, which restriction may be caused by in armour wire limitation.

There is therefore a need for allowing the armour circumference to be increased.

SUMMARY In view of the above, a general object of the present disclosure is to provide an armoured power cable, where the circumference of the armour can be made large.

For this reason, there is provided a power cable comprising: a conductor, a first insulation system provided around the conductor and an armour 1O surrounding the first insulation system, the armour comprising at least one armour layer comprising metallic armour wires and polymeric spacer elements, wherein the armour wires have circular or rectangular cross-section and the spacer elements have a cross-section with a different shape and an area that is at least twice the area of the circular cross-section of the armour wires.

The circumference of the armour can thereby be increased for a certain limited amount of armour wire, which allows larger cables to be laid on the seabed. Moreover, this circumference increase is also achieved with a limited weight increase of the armour, which makes it easy to lay the cable out on the seabed. This also allows more cable to be loaded in the cable laying vessel.

The power cable may be a submarine power cable. It may also be a direct current power cable. The power cable may additionally be a torsion-balanced cable.

The power cable may be a medium voltage or high voltage submarine power cable.

Each spacer element may be flat and may additionally have a central part with a rectangular cross-section.

A long side of the rectangular cross-section may be at least twice as long as the diameter of the armour wires. A first long side of the rectangular cross- section of the spacer element may face radially inwards towards the centre of the power cable and a second long side of the rectangular cross-section of the spacer element may face radially outwards from the centre of the power cable.

A short side of the rectangular cross-section may face a corresponding armour wire. The height of the short side of the rectangular cross-section may be smaller than, equal to or larger than the diameter of the armour wire, where a height that is equal to or larger than the diameter may be preferred. 1O Each spacer element may additionally comprise a first and a second peripheral part, where the cross-section of each peripheral part may have a concave shape.

Each peripheral part may be joined to the corresponding central part at a short side of the rectangular cross-section therof. Each peripheral part may additionally be adapted to the shape of a neighbouring armour wire.

The armour wires may be placed alternatingly with the spacer elements in the armour layer.

The armour may additionally comprise more than one armour layer, such as two or more armour layers.

The polymer of the polymeric spacer element may be polyaramid or polyethylene, while the metal of the armour wire may be steel, such as mild steel or stainless steel.

The armour wires and spacer elements may be arranged helically along an axial direction of the power cable. The cable may also comprise an armour protection layer around the armour.

The cable may additionally comprise a first water barrier arranged between the first insulation layer and the armour, which first water barrier may comprise a metallic sheath such as a lead sheath and/ or a polymer sheath such as a polyethylene sheath.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to a/ an /the element, apparatus, component, means, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, etc., unless explicitly stated otherwise. 1O BRIEF DESCRIPTION OF THE DRAWINGS The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a cross-section of an example of a power cable; Fig. 2 shows a first example of an armour of the power cable comprising a layer of armour wires and spacer elements; and Fig. 3 shows a second example of the armour layer with armour wires and spacer elements.

DETAILED DESCRIPTION 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.

Fig. 1 shows a cross-sectional view of an example of a power cable 1, which cable may be a submarine power cable. The power cable 1 is a single core power cable. It is also a direct current (DC) power cable for instance for use in the medium voltage or high-voltage range. The cable may additionally be a torsion-balanced cable. The power cable 1 comprises a first conductor 3.

The submarine power cable 1 comprises a first insulation system 5 arranged around the first conductor 3.

The first insulation system 5 may comprise an inner semiconductive layer 5a. The inner semiconductive layer 5a is a conductor screen. The inner semiconductive layer 5a is arranged around the first conductor 3. 1O The first insulation system 5 may comprise an insulation layer 5b. The insulation layer 5b is arranged around the inner semiconductive layer 5a. The insulation layer 5b may for example comprise cross-linked polyethylene (XLPE), impregnated paper tapes, or polypropylene.

The first insulation system 5 may comprise an outer semiconductive layer 5c. The outer semiconductive layer 5c is an insulation screen. The outer semiconductive layer 5c is arranged around the insulation layer 5b.

The submarine power cable 1 may comprise a first water barrier 7. The first water barrier 7 may be arranged around the outer semiconductive layer 5c. The first water barrier 7 may for example comprise a metallic sheath. The metallic sheath may for example comprise lead. Alternatives to lead include copper, stainless steel and aluminium. The metallic sheath may for example be one or more metal sheets that is / are folded around the insulation system 5 and longitudinally welded along the length of the submarine power cable 1.

The first water barrier 7 may comprise a polymer sheath. The first water barrier 7 may comprise the polymer sheath instead of the metallic sheath. Alternatively, the water barrier 7 may comprise the metallic sheath and a polymer sheath arranged around the metallic sheath. The polymer sheath may comprise polyethylene. It may also be semiconductive. For this reason, the polymer sheath may comprise carbon black. The first water barrier 7 may comprise an adhesive arranged between the metallic sheath and the polymer sheath so that the polymer sheath adheres to the metallic sheath. The adhesive may be a semiconductive adhesive in case the polymer sheath comprises a semiconductive polymer material.

The first conductor, first insulating system and first water barrier may together form a core of the cable.

The power cable 1 also comprises an armour 9 comprising a number of individual armour wires and spacer elements forming one or more armour layers that surround the insulation system 5. If there is more than one armour layer 9, such as two, it is possible that one surrounds the other. 1O The armour 9 also surrounds the first water barrier 7, if present.

The power cable 1 may comprise an armour protection layer 11. The armour protection layer 11 is arranged to cover the armour 9. The armour protection layer 11 is arranged radially outside of the armour 9.

The power cable 1 may also comprise an outer layer 13. The outer layer 13 is arranged around the armour 9. The armour protection layer 11 is arranged between the outer layer 13 and the armour 9. The outer layer 13 forms the external surface of the submarine power cable 1. The outer layer 13 may for example comprise polymer yarn, such as polypropylene yarn, wound around the armour layer.

It should be realized that the cable could include more cores, such a three, that are all surrounded by the armour 9, the armour protection layer 11 and the outer layer 13.

Fig. 2 shows a first example of one way of realizing an armour layer 15 of the armour 9.

The armour layer 15 comprises metallic armour wires 17 and polymeric spacer elements 19. The polymer of the polymeric spacer element may be polyaramid or polyethylene, while the metal of the armour wire may be steel, such as mild steel or stainless steel.

In the present example, the armour wires 17 have circular cross-section and the spacer elements 19 have a cross-section with a different shape and an area that is at least twice the area of the circular cross-section of the armour wires 17. In the first example the spacer elements 19 are flat and each has a central part with a rectangular cross-section. In the example of fig. 2 the spacer elements 19 only comprise the central part. The rectangular cross- section has a first long side that faces radially inwards towards the centre of the cable 1. In the case of the single-core cable 1, the first long side faces the centre of the first conductor 3. The rectangular cross-section also has a second long side that faces radially away from the centre of the cable 1. The 1O rectangular cross-section also has a first and a second short side, which are both perpendicular to the first and second long sides and where the first short side interconnects first ends of the first and second long sides and the second short side interconnects second ends of the first and second long sides.

Furthermore, a long side of the rectangular cross-section has a length L that is at least twice as long as the diameter D of the armour wires 17. It may thus be more than twice as long. On the other hand, a height H of a short side of the rectangular cross-section may be smaller than, equal to or larger than the diameter D of the armour wires 17, where a height H that is equal to or larger than the diameter D may be preferred.

Furthermore, the armour wires 17 and the spacer elements 19 are alternatingly provided in the armour layer 15. Each armour wire 17 may thereby be separated from a neighbouring armour wire 17 by a spacer element 19. Thereby each short side of the rectangular cross-section of the spacer element 19 faces a corresponding armour wire 17. The armour wires 17 and the spacer elements 19 may furthermore be arranged helically along an axial direction of the power cable 1. They may thus be laid helically along the axial direction of the power cable 1.

Fig. 3 schematically shows a second example of how an armour layer 15 of the armour 9 may be realized.

Just as in the first example, the armour layer 15 comprises metallic armour wires 17 with circular cross-section and polymeric spacer elements 19” with a cross-section of a different shape, where the area of the cross section of the spacer elements 19” is at least twice as large as the area of the cross-section of the armour wires 17. As in the first example, the armour wires 17 have circular cross-section and the spacer elements 19” have a central part 19a with a rectangular cross-section. However, in addition to this, the spacer elements 19” each comprise a first and a second peripheral part 19b, 19c, where the cross-section of each peripheral part 19b, 19c has a concave shape.

Furthermore, each peripheral part 19b, 19c is joined to a corresponding short 1O side of the central part 19a. The shape of each peripheral part 19b, 19c is also adapted to the shape of a neighbouring armour wire 17. It is more particularly adapted to the shape of half or less than half of the corresponding armour wire 17.

For cables, such as torsion-balanced cables, there may exist a need for more than one armour layer in order to enable the cable to be laid at a considerable depth.

However, if two layers are used, then both cages of an armouring machine spinning in different directions may be needed. This will limit the number of wires in each armour layer. This also means that the circumference of the armour is limited if there is a limited number of wires. Therefore, there is a size constraint of the underlying cable to cover a certain circumference. The size coverage is not good and the "unordered" laying creates a problem. This problem together with the fact that often the strength of all armouring wires is not used, but a limited number, has inspired the inventor to consider spacer elements. Plastic wires have previously been used as spacer elements. Aspects of the present disclosure are directed towards designing the spacer elements with a different shape then the armouring wires.

When a spacer element according to the above-described examples is used, then it is possible to have the spacer element cover twice the area of an armouring wire. This means that if there are 50% spacer elements and 50% armour wires, then the total possible circumference is 150 % of the known circumference using the same shape for spacer elements and armour wires. This means that it is possible to double armour a cable that is 150% in circumference compared to if the spacer elements and armour wires have the same cross-section.

The armour provides mechanical strength that supports the conductor when being laid out on the seabed. Through the use of polymer in the spacer elements, the weight of the cable is also reduced, which makes it easier to roll 1O it out on the seabed. This also allows more cable to be loaded in the cable laying vessel used for the roll-out. The invention can be varied in many ways.

For instance, in the examples given above the armour wires had a circular cross-section. It should be realized that as an alternative they may have a rectangular cross-section, in which case the spacer elements would have a different type of shape, such as one with a circular cross-section. It is also possible that there are holes in the interior of the spacer elements in order to further reduce their weight. However, such holes should not be allowed to influence the perimeter of the spacer elements.

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.

It is for instance possible to apply the teachings to an alternating current power cable and/ or a multi-core cable.

Claims (10)

1. A power cable (1) comprising: a first conductor (3), a first insulation system (5) provided around the first conductor (3), and an armour (9) surrounding the first insulation system, the armour comprising at least one armour layer (15) comprising metallic armour wires (17) and polymeric spacer elements (19; 19”), wherein the armour wires (17) have circular or rectangular cross-section and the spacer elements (19, 19”) have a cross-section with a different shape and an area that is at least twice the area of the circular cross-section of the armour wires (17).

2. The direct current submarine power cable (1) as claimed in claim 1, wherein each spacer element has a central part (19a) with a rectangular cross-section.

3. The power cable (1) as claimed in claim 1 or 2, wherein a long side of the rectangular cross-section has a length L that is at least twice as long as the diameter D of the armour wires (17).

4. The submarine power cable (1) as claimed in claim 2 or 3, wherein a short side of the rectangular cross-section faces a corresponding armour wire (17) -

5. The submarine power cable (1) as claimed in claim 4, wherein the height H of the short side of the rectangular cross-section is smaller than, equal to or larger than the diameter D of the armour wire (17), where a height H that is equal to or larger than the diameter D may be preferred.

6. The power cable (1) as claimed in claim 5, wherein the spacer elements (19”) comprise a first and a second peripheral part (19b, 19c), where the cross- section of each peripheral part (19b, 19c) has a concave shape. 1O

7. The power cable (1) as claimed in claim 6, wherein each peripheral part (19b, 19c) is joined to the corresponding central part (19a) at a short side of the rectangular cross-section thereof.

8. The power cable (1) as claimed in claim 6 or 7, wherein each peripheral part (19b, 19c) is adapted to the shape of a neighbouring armour wire (17)

9. The power cable (1) as claimed in any previous claim, wherein the armour wires (17) are placed alternatingly with the spacer elements (19; 19”) in the armour layer (15).

10. The power cable (1) as claimed in any of the previous claim, wherein the cable is a submarine direct current power cable.