ELECTRICAL CABLES

Abstract

Electrical cables are disclosed, comprising a layer of a two dimensional material. In some embodiments, the cable is a subsea cable. In other embodiments, the cable may be an overhead power cable or a cable for forming electrical windings in a motor, generator or transformer. In some embodiments, the cable comprises a conductive core for carrying an electric current, and the layer of two dimensional material is disposed on the conductive core. In some embodiments, the subsea cable is a subsea power cable, umbilical cable or telecommunications cable. In some embodiments, the two dimensional material is configured to be superconducting or near-superconducting.

Claims

1. A method of forming an electrical cable comprising a layer of a two dimensional material, the method comprising: forming a layer of two dimensional material; and subsequently incorporating the layer of two dimensional material into an electrical cable.

2. The method of claim 1, wherein the cable comprises a conductive core.

3-4. (canceled)

5. The method of claim 2, wherein incorporating the layer of two dimensional material into an electrical cable comprises disposing the layer of the two dimensional material on a surface of the conductive core.

6. The method of claim 2, wherein the electrical cable comprises a sheath which surrounds the conductive core, and incorporating the layer of two dimensional material into an electrical cable comprises disposing the layer of the two dimensional material is on a surface of the sheath.

7. The method of claim 2, wherein the electrical cable comprises an electrical shield or screen surrounding the conductive core and configured to protect the conductive core from electrical interference, and incorporating the layer of two dimensional material into an electrical cable comprises disposing the layer of the two dimensional material on a surface of the electrical shield.

8. The method of claim 2, wherein the electrical cable comprises a layer of wires configured to prevent any defects from occurring in the structure, and wherein the layer of two dimensional material is incorporated into each of the wires.

9. The method of claim 1, wherein the electrical cable comprises a communications cable, comprising a plurality of fibre optic cores.

10. The method of claim 9, wherein the plurality of fibre optic cores are disposed within a tube, and incorporating the layer of two dimensional material into an electrical cable comprises disposing the layer of the two dimensional material on a surface of the tube.

11. The method of claim 9, wherein the communications cable comprises a layer of metallic wires, and wherein the layer of two dimensional material is incorporated into each of the metallic wires.

12. The method of claim 9, wherein the communications cable comprises a conducting layer and incorporating the layer of two dimensional material into an electrical cable comprises disposing the layer of the two dimensional material on a surface of the conducting layer.

13. The method of claim 9, wherein the communications cable comprises a layer of further wires configured to prevent any defects from occurring in the structure, and wherein the layer of two dimensional material is incorporated into each of the wires.

14. The method of claim 1, wherein the two dimensional material is selected from the group consisting of graphene; stanene; boron nitride; niobium diselenide; tantalum (IV) sulphide; and magnesium diboride.

15. The method of claim 1, wherein the two dimensional material is configured to be superconducting or near-superconducting.

16. The method of claim 1, wherein the layer of two dimensional material is formed on a non-conducting substrate before incorporating the layer of two dimensional material into the electrical cable.

17. The method of claim 1, wherein the layer of two dimensional material is incorporated into the electrical cable using a continuous wrapping or continuous taping process.

18. The method of claim 17, wherein the substrate comprises a thread or monofilament, and wherein the layer of two dimensional material is incorporated into the electrical cable using a cable manufacturing process for incorporating wires into cables.

19. An electrical cable formed using the method according to claim 1.

20. The electrical cable according to claim 19, wherein the electrical cable comprises one of: a subsea power cable; an overhead power cable; an electrical winding in a motor; an electrical winding in a generator: or an electrical winding in a transformer.

Description

[0054] All features described herein (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined with any of the above aspects in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0055] FIG. 1 is a schematic diagram of an electrical cable comprising a layer of two-dimensional material;

[0056] FIG. 2 is a schematic diagram of a direct current (DC) subsea power cable;

[0057] FIG. 3 is a cross-sectional view of an alternating current (AC) subsea power cable;

[0058] FIG. 4 is a subsea telecommunication cable; and

[0059] FIG. 5 is a schematic diagram of apparatus for use as an electric motor or generator.

[0060] FIG. 1 illustrates an electrical cable according to an embodiment of the present invention. The cable comprises a conductive core 1 and a layer of two-dimensional material 2, for example a layer of graphene. The layer of two-dimensional material 2 can provide various benefits to the electrical cable, such as increased electrical conductivity, corrosion resistance and tensile strength. The electrical cable may be configured to operate at any voltage. In some embodiments, the electrical cable can be configured to operate at low voltage (LV), medium voltage (MV), high voltage (HV), extremely high voltage (EHV), or supertension voltages. In some embodiments, the electrical cable may comprise a distribution cable or domestic cable. Examples of specific embodiments of the invention will now be described in detail.

EXAMPLE 1: SUBSEA POWER CABLE

[0061] FIG. 3 shows a dry alternating current (AC) subsea power cable 60. The subsea power cable 60 comprises three core elements 62, each of which comprises an inner copper core 12 with a layer of a 2D material 16 disposed thereon. Immediately adjacent to the layer of the 2D material 16 there is disposed an inner semiconducting layer 20, which would typically comprise a carbon-loaded polyethylene or ethylene copolymer (such as ethylene vinyl acetate (EVA) and ethylene butyl acrylate (EBA)), or blends thereof. Adjacent the inner semiconducting layer 20, there is disposed an insulating layer 22 which may comprise cross-linked polyethylene, ethylene propylene rubber (EPR) or paper. The semiconducting layer 20 provides a degree of insulation for the insulating layer 22 from the conductive core 12 and the insulating layer 22 provides an insulating electrical barrier between the core 12 and the rest of the cable 18.

[0062] Adjacent the insulating layer 22, there is disposed an outer semiconducting layer, or insulation screen, 24, as with the inner semiconducting layer 20, this would typically comprise a carbon-loaded polyethylene or ethylene copolymer (such as ethylene vinyl acetate (EVA) and ethylene butyl acrylate (EBA)), or blends thereof. The purpose of the outer semiconducting layer 24 is to control the electrical stress levels within the cable and maintain a defined electric field within the insulating layer 22 and at value below that which would cause electrical breakdown of the insulating layer 22. It also allows safe discharge of any charge build-up within the insulation layer 22 when the cable 18 is switched off.

[0063] Adjacent to the outer semiconducting layer 24 of each core element 62 there is disposed a water blocking tape layer 26. If the cable 18 were to be damaged creating a defect therein the water blocking tape layer 26 is intended to swell upon contact with water which penetrates the cable 18, thereby preventing any water penetrating to the outer semiconducting layer 24, insulating layer 22, inner semiconducting layer 20, layer of the 2D material 16 and conductive core 12. While the water blocking layer 26 in the illustrated embodiment comprises a water blocking tape it will be appreciated that it could instead comprise a powder or gel type compound. Additionally, while not illustrated in FIG. 3, in some embodiments of the invention a water blocking layer can be included within the conductors to restrict water progress up the conductor strands. For example, a water blocking layer could be provided adjacent to the copper core 12 to restrict water progress up the core element 62.

[0064] Adjacent the water blocking tape layer 26, there is disposed an inner sheath 28 which would typically comprise lead, a lead alloy, aluminium, an aluminium alloy, copper or a copper alloy. The inner sheath 28 is provided to try and prevent any defects penetrating to the water blocking tape layer 26. The inner sheath 28 can act as an armouring layer to protect the internal components of the cable from mechanical damage. The inner sheath 28 may have been formed due to a solid extrusion or continuously welded for a Dry cable. Alternatively, the inner sheath 28 may have been formed from a flat extrusion of foil or tape where the extrusion was then wrapped around the water blocking tape layer 26 and bonded for a Semi dry cable. An additional layer of the 2D material 30 is disposed on the external surface of the inner sheath 28.

[0065] The additional layer of the 2D material 30 protects the inner sheath 28 from corrosion and significantly increases the tensile strength of the inner sheath 28. Accordingly, the cable 60 is stronger and could be used at greater depths. Alternatively, a thinner inner sheath 28 could be used to achieve the same strength resulting in a cable 60 which is cheaper to produce and has a reduced the mass per unit length.

[0066] In the illustrated embodiment the additional layer of the 2D material 30 is disposed on the outer surface of the inner sheath 28. However, it will be appreciated that a layer of the 2D material could be disposed on the inner surface of the inner sheath 28. This could be in addition to or instead of the layer of the 2D material 30 disposed on the outer surface of the inner sheath 28. The layer of the 2D material disposed on the inner surface of the inner sheath 28 would increase the tensile strength of the inner sheath 28 but would not protect the inner sheath 28 from corrosion.

[0067] Immediately adjacent the additional layer of the 2D material 30 there is disposed an outer sheath 32, which would typically comprise medium or high density polyethylene (MDPE or HDPE), polypropylene (PP) and/or poly(oxymethylene). The outer sheath 32 is provided to prevent the inner sheath 30 from being exposed to water and thereby further protects the inner sheath 30 from corrosion.

[0068] In addition to the three core elements 62 the subsea power cable 60 can comprise a number of optical fibre units 64. The core elements 62 and optical fibre units 64 are disposed in a filler package 66.

[0069] The filler package 66 comprising the core elements 62 and optical fibre units 64 is surrounded by a layer of binder tape 68. Adjacent the binder tape layer 68 is a layer of copper or brass tape 70. This layer is configured to protect the cable against boring marine organisms such the teredo, pholads and limnoria, and is often referred to as the anti-teredo layer 70. Adjacent to the anti-teredo layer 70 is disposed a bedding layer 34, and adjacent the bedding layer 34 there is disposed a layer of galvanised steel wires 36. As described above, each of the steel wires has a layer of graphene disposed on its surface. Since the outer layer of steel wires 36 in a subsea power cable are the main contributor of tensile strength to the cable, adding a layer of graphene or other two-dimensional material to the steel wires 36 as in the present embodiment can significantly increase the overall tensile strength of the cable. Finally, an external jacket layer 38 is provided which typically comprises a water permeable yarn cladding made of polypropylene. The external jacket layer 38 is provided to assist the bedding layer 34 in holding the layer of galvanised steel wires 36 in place.

[0070] While only a dry AC subsea power cable 60 is illustrated it will be appreciated that wet and semi-dry cables can also be used. A wet cable would be as described above but the cable elements 62 would not comprise a water blocking metallic tape layer 26, an inner sheath 28, an additional layer of the 2D material 30 or an outer sheath 32. Instead, the insulating layer 22 comprises a material configured to retard water tree growth therein.

[0071] Similarly, a semi-dry cable would be as described above but instead of comprising a water blocking layer 26, an inner sheath 28, an additional layer of the 2D material 30 or an outer sheath 32 each cable element 62 would comprise an overlapping tape or foil laminate layer adjacent to the outer semiconducting layer 24. The overlapping tape or foil laminate layer would be configured to provide an intermediate level of water blocking. A layer of 2D material could be provided on the overlapping tape or foil laminate layer to increase the tensile strength of this layer and protect it from corrosion.

[0072] FIG. 2 shows a direct current (DC) subsea power cable 18. The subsea power cable 18 comprises a single inner copper core 12 with a layer of a two dimensional material 16 disposed thereon. Similar to the AC subsea power cable 60, the DC subsea power cable comprises an inner semiconducting layer 20, an insulating layer 22 and an outer semiconducting layer 24.

[0073] Adjacent to the outer semiconducting layer 24 there is disposed an inner sheath 28, with an additional layer of the two dimensional material 30 is disposed on the external surface of the inner sheath 28. Immediately adjacent the additional layer of the two dimensional material 30 there is disposed an outer sheath 32. A fibre optic cable unit 64 is disposed between the additional layer of the two dimensional material 30 and the outer sheath 32.

[0074] Adjacent the outer sheath 32 there is disposed a bedding layer 72, and adjacent the bedding layer 72 there is disposed a first layer of copper wires 74 which are wound around the first bedding layer to form a helix. A layer of graphene is disposed on the surface of each of the copper wires. This increases the conductivity, tensile strength and corrosion resistance of the wires. Accordingly, less copper can be used than would be necessary in a prior art cable leading to a cost saving and reduced mass per unit length.

[0075] Adjacent the first layer of copper wires is a bedding layer 76 and a second layer of copper wires 78 which are wound around the bedding layer 76 in the opposite direction to the first layer of copper wires 74 to form a further helix. A layer of graphene is disposed on the surface of each of the copper wires as described above. The two layers of copper wires 74, 78 form an integrated return conductor and are configured to protect the core 12 from electrical interference. Alternatively, or additionally, a layer of copper foil could be used.

[0076] Adjacent to the second layer of copper wires 78 is a bedding layer 80 and then a further insulating layer 82 configured to electrically insulate the integrated return conductor.

[0077] Adjacent the further insulating layer 82 is a bedding layer 84, which is adjacent to a layer of galvanised steel wires 36. As described above, each of the steel wires has a layer of graphene disposed on its surface. Since the outer layer of steel wires 36 in a subsea power cable are the main contributor of tensile strength to the cable, adding a layer of graphene or other two-dimensional material to the steel wires 36 as in the present embodiment can significantly increase the overall tensile strength of the cable. Finally, an external jacket layer 38 is provided.

[0078] In some embodiments of the present invention, a layer of 2D material in a subsea power cable may be configured to act as a superconductor in a certain temperature range. For example, a layer of graphene can be made superconducting or near-superconducting by coating with a layer of lithium or by doping the graphene layer with calcium atoms. By near-superconducting, it is meant that the 2D material exhibits an extremely low, but finite, electrical resistance. By using a superconducting or near-superconducting layer of 2D material, the copper core can be reduced in size or even omitted altogether, leading to a significant reduction in the physical size and mass per unit length of the subsea cable. Furthermore, the superconducting or near-superconducting 2D material can also avoid the voltage drop associated with conventional subsea cables. For example, the maximum length of an alternating current (AC) subsea power cable operating at 132 kilovolts (kV) is currently limited to roughly 80 kilometers (km), due to the voltage loss in the cable. By utilising a superconducting or near-superconducting layer of 2D material as described above, embodiments of the invention may enable a significant increase in AC system length, potentially to several thousands of km.

EXAMPLE 2: SUBSEA TELECOMMUNICATION CABLE

[0079] FIG. 4 shows a subsea telecommunication cable 86. The cable 86 comprises a plurality of fibre optic cores 88 disposed in a tube 90. The tube 90 can comprise a metallic or plastic tube.

[0080] Adjacent to the tube 90 is a first layer of high tensile wires 92 and then a second layer of high tensile wires 94. In both cases, the high tensile wires 92, 94 may comprise steel and are configured to physically protect the core. The high tensile wires 92, 94 each comprise a layer of graphene on their surface which increases the tensile strength of the wires meaning that less steel can be used when compared to prior art cables. In subsea telecommunication cables, the primary contributor to tensile strength is the high tensile wires 92, 94 that surround the inner cable package. The graphene layer included in the high tensile wires 92, 94 in the present embodiment therefore increases the overall tensile strength of the subsea telecommunication cable. In other embodiments, a 2D material other than graphene may be used.

[0081] Adjacent to the second layer of high tensile wires 94 is a conductor layer 96. In a long repeatered cable system a direct current of around 8 kV is applied to the conductor layer 96 to provide power for repeaters which are placed at intervals in the order of 80 km apart. The conductor layer 96 which comprises copper with a layer of graphene disposed thereon. The graphene advantageously increases the conductivity of the conductor layer 96. Adjacent the conductor layer 96 is an insulating layer 98.

[0082] Adjacent the insulating layer 98 is a bedding layer 100, which is adjacent to a layer of galvanised steel wires 102, there is then a further bedding layer 104 and layer of galvanised steel wires 106 followed by an external jacket layer 38. The steel wires in both layers 102, 106 comprise a layer of graphene disposed on their surfaces to increase their tensile strength and corrosion resistance.

[0083] As in the first example, in some embodiments of the present invention a layer of 2D material in a subsea telecommunication cable may be configured to act as a superconductor in a certain temperature range, thereby enabling a reduction in size and mass of the copper core and the cable as a whole.

EXAMPLE 3: SUBSEA UMBILICAL CABLES

[0084] Subsea umbilical cables are typically custom made with specific cores rated for specific requirements and bundled together in the umbilical package. They are typically laid up with sub-component power cables, fibre optic cables, hydraulic pipes, strength members, water blocking and armour layers as required.

[0085] It will be appreciated that the present invention could be applied to a subsea umbilical cable by providing a layer of a two dimensional material, such as graphene, on the conductor, strength members and/or armour layers.

[0086] As in the first and second example, in some embodiments of the present invention a layer of 2D material in a subsea umbilical cable may be configured to act as a superconductor in a certain temperature range, thereby enabling a reduction in size and mass of the conductor and the cable as a whole.

EXAMPLE 4: OVERHEAD POWER CABLES

[0087] Overhead power cables are well known in the art and can be constructed and laid up in a number of ways. Some common examples of overhead power cables comprise an all aluminium alloy conductor (AAAC), an aluminium conductor alloy reinforced (ACAR), an aluminium conductor steel reinforced (ACSR) or a gap type aluminium conductor steel reinforced (GTACSR).

[0088] It will be appreciated that the present invention could be applied to an overhead power cable by providing a layer of a two dimensional material, such as graphene, on the conductor, which will improve the electrical conductivity thereof. Accordingly, less material can be used to achieve the same level of conduction and the mass per unit length of the cable is reduced. The overhead cable will also benefit from increased tensile strength and improved corrosion resistance.

[0089] By utilising a layer of 2D material in an overhead power cable, embodiments of the present invention can allow electrical power to be distributed at higher currents than are possible with conventional overhead power cables, for a given power transmission, resulting in a corresponding reduction in voltage. By enabling a lower voltage to be used, the size of the towers or pylons used to carry the overhead power cables can be reduced, since the distance between adjacent cables can be reduced. Alternatively, such embodiments could allow existing towers to be operated at lower voltages but with much higher current and power carrying capacity.

EXAMPLE 5: ELECTRIC MOTORS AND GENERATORS

[0090] FIG. 5 shows apparatus for use as an electric motor or an electric generator, according to an embodiment of the present invention. The principles of operation of electric motors and generators are well understood, and a detailed description will not be provided here so as to avoid obscuring the present inventive concept. In brief, in the present embodiment the apparatus 110 comprises a rotor 112 comprising a plurality of arms, a stator 114 formed from a permanent magnetic material, and a plurality of electrical windings 116 around the arms of the rotor 112. When used as an electric motor, the rotor 112 can be driven to rotate by passing electrical current through the electrical windings 116, which may also be referred to as coils. When used as a generator, an electric current can be induced in the electrical windings 116 by using an external force to drive rotation of the rotor 112. In other embodiments, the rotor 112 may be formed of the permanent magnetic material, and the electrical windings 116 may be provided in the stator 114.

[0091] In embodiments of the present invention, the cable from which the electrical windings are formed in a motor or generator, such as the one shown in FIG. 5, can comprise an electrical cable which comprises a layer of 2D material, such as the one shown in FIG. 1. For example, the cable which forms the electrical windings may comprise a layer of graphene. The 2D material, for example graphene, can increase the electrical conductivity of the cable used to form the windings, and consequently the current-carrying capacity of the windings is increased. Accordingly, the mass of the conductive core, for example a copper core, can be reduced, thereby decreasing the mass of the apparatus and improving its efficiency.

[0092] It will also be appreciated that the above-described benefits can be obtained when a cable such as the one shown in FIG. 1 is used to form electrical windings in other types of apparatus, such as transformers.

EXAMPLE 6: MANUFACTURE

[0093] In all of the above examples, the layer of the 2D material can be grown directly onto the surface of the component on which it is to be used, or can be fabricated separately and subsequently attached or wrapped to the surface. For example, a layer of 2D material can be grown directly on the surface of a substrate using (vacuum) vapour deposition, centrifugal atomisation/deposition, or (electro) plating, or can be fabricated separately using a suitable method, for example mechanical exfoliation or sintering, and subsequently attached to the surface of the component by a continuous wrapping/taping process.

[0094] In some embodiments, the layer of 2D material may be formed on the surface of a non-conducting substrate, for example a polymer substrate. The substrate may comprise a thread, monofilament or sheet of material, thereby allowing the layer of 2D material formed on the surface of the substrate to be easily handled during the cable manufacturing process. For example, when a layer of 2D material is provided on the surface of a thread or monofilament, the layer of 2D material can be incorporated into the electrical cable using conventional cable manufacturing techniques, similar to the process by which the conducting cores or steel reinforcing wires are incorporated into a conventional cable.

CONCLUSION

[0095] In conclusion, a layer of a 2D material, such as graphene, deposited onto a material increases the electrical conductivity thereof dramatically. It also increases the tensile strength of the material and protects the material from corrosion.

[0096] Accordingly, electrical cables comprising a layer of a 2D material may be stronger, have a reduced mass per unit length and be cheaper to manufacture. These cables will also be more resistant to corrosion than prior art cables.