WO2015139736A1

WO2015139736A1 - A method for manufacturing a high-power cable

Info

Publication number: WO2015139736A1
Application number: PCT/EP2014/055399
Authority: WO
Inventors: Marc Jeroense; Henrik Hillborg
Original assignee: Abb Technology Ltd
Priority date: 2014-03-18
Filing date: 2014-03-18
Publication date: 2015-09-24

Abstract

The present disclosure provides a method (30) for manufacturing a high power cable (20). The method (30) comprises providing (1a, 1b, 1c) a metal conductor core (1) with a carbon material, giving a carbon enhanced metal conductor (3), and preparing (10) the carbon enhanced metal conductor (3) with one or more layers, providing the high-power cable (20). A high-power cable (20) obtainable by the method (30) is also provided.

Description

A method for manufacturing a high-power cable Technical field

The technology disclosed herein relates generally to the field of high -voltage power cables, and in particular to methods for manufacturing of such power cables.

Background

Electrical power cables can be used for efficient transmission of large amounts of energy, but there is always a strive towards increasing the efficiency and the amounts of energy that can be transferred. The power P of the cable, i.e. current multiplied with voltage, is often given in mega watt (MW), and the power P can thus be increased either by increasing the voltage, current, or both.

An increased current can be obtained by increasing the conductor area, the conventional power cable having a copper or aluminum conductor. However, with increasing power transmission capacity this results in a heavy, stiff cable which is difficult to handle during transport and installation. Another alternative is to maintain the dimensions of the conductor and instead reduce the resistivity of the conductor. There are however no known processes for dramatically reducing the resistivity of these materials further. Advantages of copper are low resistivity and easy manufacturing due to the high ductility and tensile strength. The drawback is that the price of copper has a tendency to increase. Aluminum has a lower density, but higher resistivity, compared to copper.

There has lately been an increasing interest directed towards using carbon based materials and it has been envisaged to use it as conductor material in electrical wires, for example within the area of electronics. A carbon nanotube electrical wire is known, that is used as signal cable, i.e. at low voltages. Although functioning satisfactory at such low voltage application, it would have too high losses at higher currents, i.e. the conductivity at higher currents would be too poor.

Graphene, which is such a carbon based material, has a structure of a single molecular sheet of bonded carbon atoms which are packed in a sheet-like crystal lattice. Due to its unique two dimensional structures, graphene differs from most conventional three dimensional counterparts: it has high electron mobility at room temperature, high transparency in the spectra visible for the human eye, excellent thermal properties, high chemical stability, large surface area and it is mechanically strong. Recent application driven research evaluates graphene in various fields such as electronics, chemical sensors, electrode material and batteries. It has also been envisaged that graphene could be used as conductor material in electrical wires.

Summary

Owing to the properties of the graphene, it could be an interesting alternative to use graphene as conductor material in high-power cables. However, the graphene is difficult to handle properly, so as to maintain the desired high conductivity. For instance, the crystalline form of graphite consists of many graphene sheets stacked together, and when handling the graphene, issues such as contact resistance between the graphene sheets may lead to reduced conductivity.

As mentioned, there is a constant strive towards increasing the amount of power that a power cable can transfer, and thus to provide a power cable having corresponding characteristics. For the power cable to be cost-efficient, the process for

manufacturing the power cables also has to be cost-efficient.

An object of the present disclosure is to overcome or at least alleviate at least one of the above mentioned problems. It is a particular object of the present disclosure to provide a power cable manufacturing process providing a high-power cable having increased conductivity.

The object is according to a first aspect achieved by a method for manufacturing a high power cable. The method comprises providing a metal conductor core with a carbon material, giving a carbon enhanced metal conductor, and preparing the carbon enhanced metal conductor with one or more layers, providing the high-power cable.

The method for manufacturing provides different ways to provide a metal conductor core with a carbon material, wherein each such way can be incorporated into an existing manufacturing process by introducing new steps, e.g. a step of depositing carbon material, while keeping other existing steps and corresponding means such as extrusion steps and extruders, and cooling steps etc.

In an embodiment, the providing comprises depositing the carbon material onto the metal conductor core. In a variation of the above embodiment, the carbon material is deposited on the metal conductor core by a chemical vapor deposition or by electrostatic deposition.

In an embodiment, the providing comprises depositing the carbon material onto metal wires and twisting the deposited metal wires into carbon enhanced metal conductor.

In a variation of the above embodiment, the carbon material is deposited on the metal wires core by a chemical vapor deposition or by electrostatic deposition.

In an embodiment, the providing comprises carbon treating twisted metal wires.

In a variation of the above embodiment, the carbon treating comprises applying a carbon material to interfacial volumes between the twisted metal wires and/or wrapping a tape filled with carbon around the twisted metal wires.

In an embodiment, the providing comprises carbon treating individual metal wires.

In a variation of the above embodiment, the carbon treating comprises applying a carbon material to the individual metal wires and/or wrapping a tape filled with carbon around the individual metal wires.

In an embodiment, the providing comprises wrapping a tape filled with carbon around a metal conductor core comprising twisted metal wires.

In a variation of the above embodiment, the method comprises preparing the tape in a percolation process using carbon and a matrix.

In an embodiment, the preparing the carbon enhanced metal conductor comprises cooling the carbon enhanced metal conductor, and extruding the carbon enhanced metal conductor, with an electrically conducting or semi-conducting polymer.

In a variation of the above embodiment, the method comprises repeating the cooling and extruding thus providing a high-power cable comprising one or more of an electrically insulating layer, an outer conductive shield, an outer jacket, a layer of metal armoring.

In an embodiment, the preparing the carbon enhanced metal conductor with one or more layers comprises one or more layer of: an inner conductive shield, an electrically insulating layer, an outer conductive shield, an outer jacket, a layer of metal armoring.

In an embodiment, the carbon material comprises graphene.

The object is according to a second aspect achieved by a high -power cable obtainable by any of the embodiments of the method as above.

The object is according to a third aspect achieved by a high -power cable for power ratings over 80 kV, comprising a carbon enhanced metal conductor, and one or more layers of an inner electrically conducting or semiconducting layer, an electrically insulating layer, an outer electrically semi-conducting or conducting layer, a metal armoring layer, and an outer jacket.

Further features and advantages of the present teachings will become clear upon reading the following description and the accompanying drawings.

Brief description of the drawings

Figures 1, 2 and 3 illustrate different embodiments of providing carbon material on a metal conductor core.

Figure 4 illustrates a manufacturing process of a high-power cable.

Figure 5 illustrates a high-power cable resulting from the manufacturing process of figures 1-4.

Figure 6 is a flow chart illustrating a method according to the present disclosure. Detailed description

In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding. In other instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description with unnecessary detail. Same reference numerals refer to same or similar elements throughout the description.

The present disclosure provides, in an aspect, a manufacturing process for manufacturing high power cables, wherein a carbon material, such as graphene, is used for giving the resulting high power cable an increased conductivity compared to known high-power cables. This step of providing the metal conductor core with a carbon material is, in various embodiments, incorporated into an existing

manufacturing process, thereby enabling a cost-efficient solution for manufacturing the high power cable. The metal conductor core may be a conventionally used conductor, e.g. comprising a number of metal wires stranded together. The, metal may for example be copper (Cu) or aluminium (Al) or some other metal having fairly high conductivity, while having a reasonable cost.

Figure 1 illustrates a first embodiment of providing la a metal conductor core 1 with a carbon material. In particular, in this embodiment, a layer of carbon material is provided on a metal conductor core 1. The metal conductor core 1 may comprise a number of metal wires (also denoted strands) that have been twisted ("stranded") into a single metal conductor core 1 (a single, stranded metal conductor core 1). The metal conductor core 1 is provided to a process step of taping 2.

In this process step of taping 2, the metal conductor core 1 is wrapped with a tape which is filled with a carbon material, e.g. graphene or carbon nanotubes.

The amount of e.g. graphene in the tape should be high enough for forming a percolated network. That is, a step (schematically illustrated at reference numeral 4) of preparing a tape may comprise dispersing e.g. graphene platelets in a polymer matrix, such as of thermoplastic or rubber, thereby forming the percolated network. The polymer is then shaped into desired dimensions, i.e. width, thickness and length. The carbon structures (i.e. graphene platelets in this example) are subsequently oriented upon uniaxial or biaxial stretching. Such stretching may be included as a final step during preparing of the tape.

The step 4 of preparing the tape may comprise using a matrix of a polymer, or a matrix of paper, but the matrix should withstand elevated temperatures (e.g. higher than 120 degree Celsius) during many years without significant degradation, e.g. in view of relaxation of tape or embrittlement (loss of ductility). The resulting output from the taping step 2 is a carbon enhanced metal conductor 3.

In the above embodiment, the conductor core 1 is assumed to comprise a number of metal wires ("strands") that have been twisted together into a single metal conductor core. In a variation of this embodiment, the process step of taping 2 is performed on each individual strand before twisting the strands together. That is, each individual strand is wrapped with such tape, and then twisted together, and possibly also compressed, into the single metal conductor core. In such embodiment, the above mentioned tape preparation step of stretching may then be performed during a winding step when winding the tape around the strands.

Figure 2 illustrates a second embodiment of providing lb a metal conductor core with a carbon material. A number of metal wires ("strands") 5 are provided to a twisting step 6, wherein the metal wires are twisted together into one metal conductor. This may be a step of an existing manufacturing process. The twisted metal wires 1' (also denoted stranded metal wires) are input to a carbon treatment step 7. In this carbon treatment step 7, a carbon material is applied to the interfacial volumes between the stranded metal wires 1'. The carbon material may for example comprise graphene, and a graphene powder may be applied to the surfaces of the strands in the form of a paste or coating, i.e. high or low loadings of graphene sheets dispersed in a suitable carrier liquid. An example of such suitable carrier liquid comprises water-based suspension of graphene sheets, which is beneficial also from an environmental point of view. In other embodiments, a carbon material in the form of a powder may be used, e.g. graphene powder, i.e. the carbon powder is applied to the stranded metal wires 1'. Next, the carbon treated stranded metal wires may be input to an optional compression step 8, wherein they are compressed into a single carbon enhanced metal conductor 3.

In a variation of the above embodiment, the individual metal wires are instead input to the carbon treatment step 7, i.e. each metal wire is coated with carbon before being twisted together. Such embodiment maximizes the cross-sectional area of highly conductive carbon, whereby a further increased conductance of the resulting conductor core is achieved. When twisting the individual strands together a high pressure should preferably be applied, in order to minimize contact resistance between the individual graphene platelets or carbon nanotubes (or other carbon- based material that might be used).

The above two embodiments may be combined. For example, the carbon filled tape as described in relation to figure 1 could be wrapped around each individual strand in the carbon treatment step 7. This taping could be performed as the single carbon treatment, or it could be combined with, in particular preceded by, application of a carbon powder to the interfacial volumes between the stranded metal wires. A carbon enhanced metal conductor 3 thus results also from such embodiments.

Figure 3 illustrates a further embodiment of providing ic a metal conductor core with a carbon material. In this embodiment, the metal conductor core 1, which may comprise a number of metal wires that have been twisted together into a single metal conductor core 1, is provided with a carbon material in a deposition step 9. In a variation, each individual strand may be provided with a carbon material in this deposition step 9 and then be twisted into a single metal conductor core 1, which have been carbon-enhanced.

In the deposition step 9, the carbon material may for example comprise graphene, and the graphene may be deposited by chemical vapour deposition (CVD) onto the metal conductor core 1. The metal conductor core or metal wires ("strands") may be treated multiple times with such CVD in order to maximize the thickness of the graphene layer. However, care must be taken so that the ductility/flexibility of the layer is high enough so as to endure subsequent stranding step (if CVD is performed on individual strands) without delamination and/or cracking. This deposition step 9 may be incorporated as a new step into an existing production line for manufacturing high power cables.

In another embodiment, the carbon material may be deposited by an electrostatic deposition method, wherein e.g. graphene is absorbed on a charged surface. This deposition method is again applicable both for the metal conductor core and the individual metal wires. Such deposition method does not require a high temperature.

Alternative deposition methods comprise passing the metal conductor core through a solution containing carbon nanotubes and/or graphene sheets which then adhere to the conductor surfaces. It is desirable to align the sheets/fibers along the conductor surfaces, which may be achieved by applying an electric or magnetic field during the deposition step. Further, multiple layers can be created by repeatedly passing the metal conductors through the solution, including intermediate steps of washing and drying. The number of such metal wires may be in the range of hundreds to thousands, obtaining a total cross section of the deposited carbon of higher than 600 mm². A cross section of such size would provide a conductor able to withstand 80 kV or more.

Figure 4 illustrates a remaining part 10 of the manufacturing process for

manufacturing a high-power cable. The carbon enhanced metal conductor 3 is now to be prepared 10 so as to provide it with a number of layers, resulting in a high -power cable. The carbon enhanced metal conductor 3 may first be cooled 11, e.g. in a water bath or by a gas flow and then dried if needed.

The carbon enhanced metal conductor 3 may thus be cooled 11 if needed, and then extruded 12 with a layer of electrically conductive or semi-conducting polymer, e.g. a polymer filled with carbon black or graphene. Such electrically conductive or semiconducting layer smooth out the surface of the conductor, and thereby the electrical fields around the conductor can be more easily controlled. Examples of such conductive or semi-conducting polymer comprise cross linked polyethylene (PEX), polyethylene (PE), polypropylene (PP), PP-PE copolymers, polyethylene-co- butylacrylate, silicone rubber, ethylene propylene diene monomer (EPDM) and ethylene-propylene-rubber (EPR). The polymer matrix is filled with conductive fillers, such as carbon black, carbon nanotubes, graphene. The result is thus a carbon enhanced metal conductor 3 with an electrically conducting or semi-conducting layer.

This conductive or semi-conducting layer is comparable with an inner conductive shield ("inner semi-con") as used in conventional high-power cables. However, it is noted that owing to the small diameter of the coated strands this inner conductive shield may be omitted, and an insulation layer may be provided directly on the carbon enhanced metal conductor core 3.

It is noted that the carbon enhanced metal conductor 3 may be provided with e.g. two layers simultaneously, i.e. in a co-extrusion step. As a particular example, the carbon enhanced metal conductor 3 may be provided with an inner semi-con layer and an insulating layer in a co-extrusion process.

The above steps may then be repeated for each layer that is required in the particular high-power cable to be manufactured. For example, the carbon enhanced metal conductor 3 (having the "inner semi-con" layer, or not having such inner semi-con) may then be cooled (i.e. repeating step 11) and extruded (i.e. repeating step 12) with an electrically insulating layer, which may be accomplished by extruding 12 the carbon enhanced metal conductor 3 having the layer of semi-conducting or conduction layer, with an electrically insulating polymer material. Examples of such electrically insulating polymer material comprise cross-linked polyethylene (PEX), polyethylene (PE), polypropylene (PP), PP-PE copolymers, polyethylene-co- butylacrylate, silicone rubber, ethylene propylene diene monomer (EPDM) and ethylene-propylene-rubber (EPR). From this extrusion 12 then, a carbon enhanced metal conductor with an electrically conducting or semi-conducting layer and an electrically insulating layer results.

In still another repetition of the cooling 11 and extrusion (or co-extrusion), a second conducting or semi-conducting layer may be provided. Such second conducting or semi-conducting layer is comparable with an outer conductive shield ("outer semi- con") as used also in conventional high-power cables.

Still further layers may be provided in a corresponding way, i.e. by cooling, possibly drying and then extruding. The high-power cable may thus be provided with any required layers. For example, the high-power cable may be provided with one or more layer of: an inner conductive shield (as described), an electrically insulating layer (as described), an outer conductive shield (as described), a layer of metal armoring, and an outer jacket.

Figure 5 illustrates a high-power cable 20 resulting from the above described manufacturing process la, lb, IC, 10. The high-power cable 20 comprises the carbon enhanced metal conductor 3, provided in any of the ways as described in relation to figures 1, 2 and 3. Next, the high-power cable 20 may comprise an electrically conducting or semi-conducting layer 21 surrounding the carbon enhanced metal conductor 3. The illustrated high-power cable 20 further comprises an electrically insulating layer 22 which may have been extruded as described. The electrically insulating layer 22 surrounds the electrically conducting or semi-conducting layer 21 and thus also the carbon enhanced metal conductor 3. Next, the high-power cable 20 may comprise an electrically conducting or semi-conducting layer 23 surrounding the electrically insulating layer 22. Although not illustrated in the figure 5, the high- power cable 20 may comprise still further layers, as has been described earlier, e.g. metal armoring, outer jacket etc. The high-power cable 20 is suitable for various high current applications. Owing to the carbon enhancement, the resulting high-power cable 20 has a reduced electrical resistance, i.e. an increased conductivity, as compared to conventional high-power cables comprising pure metal conductor cores.

As has already been noted, the method for manufacturing may use at least parts of an existing factory line for manufacturing power cables, such as for example the cooling and extrusion steps whereby additional layers are provided.

The various embodiments and features as have been described may be combined in various ways. Figure 6 is a flow chart illustrating a method 30 according to the present disclosure. The method 30 for manufacturing a high power cable 20 comprises providing 31 a metal conductor core 1 with a carbon material, giving a carbon enhanced metal conductor 3. This providing may be accomplished in any of the described ways or combinations thereof. The providing may thus be accomplished e.g. by depositing a carbon material on individual metal wires 5 or on a stranded metal conductor core 1; or by carbon treating 7 twisted metal wires 1' or individual metal wires 5; or by applying a carbon material to the individual metal wires 5 and/or wrapping a tape filled with carbon around the individual metal wires 5; or by wrapping 2 a tape filled with carbon around a metal conductor core 1 comprising twisted metal wires 5.

The method 30 further comprises preparing 32 the carbon enhanced metal conductor 3 with one or more layers, providing the high-power cable 20. Such preparing may comprise extruding additional layers such as electrically conducting or

semiconducting layers, electrically insulating layers etc. and intermediate steps such as cooling and drying.

In an aspect of the present disclosure, a high-power cable 20 is provided which is obtainable by the method according to any of the above described embodiments.

In an aspect of the present disclosure, a high-power cable 20 for power ratings over 80 kV is provided. The high-power cable 20 comprises a carbon enhanced metal conductor 3, and one or more layers of an inner electrically conducting or

semiconducting layer 21, an electrically insulating layer 22, an outer electrically semiconducting or conducting layer 23, a metal armoring layer, and an outer jacket.

The invention has mainly been described herein with reference to a few

embodiments. However, as is appreciated by a person skilled in the art, other embodiments than the particular ones disclosed herein are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

1. A method (30) for manufacturing a high power cable (20), the method (30) comprising:

- providing (la, lb, IC) a metal conductor core (1) with a carbon material, giving a carbon enhanced metal conductor (3),

- preparing (10) the carbon enhanced metal conductor (3) with one or more layers, providing the high-power cable (20).

2. The method (30) as claimed in claim 1, wherein the providing (ic) comprises depositing (9) the carbon material onto the metal conductor core (1).

3. The method (30) as claimed in claim 2, wherein the carbon material is deposited on the metal conductor core (1) by a chemical vapor deposition or by electrostatic deposition.

4. The method (30) as claimed in claim 1, wherein the providing (lb) comprises depositing the carbon material onto metal wires (5) and twisting the deposited metal wires (5) into carbon enhanced metal conductor (3).

5. The method (30) as claimed in claim 4, wherein the carbon material is deposited on the metal wires core (5) by a chemical vapor deposition or by electrostatic deposition.

6. The method (30) as claimed in claim 1, wherein the providing (lb) comprises carbon treating (7) twisted metal wires (ι'). . The method (30) as claimed in claim 6, wherein the carbon treating

(7) comprises applying a carbon material to interfacial volumes between the twisted metal wires (ι') and/or wrapping a tape filled with carbon around the twisted metal wires (ι').

8. The method (30) as claimed in claim 1, wherein the providing comprises carbon treating (7) individual metal wires (5).

9. The method (30) as claimed in claim 8, wherein the carbon treating (7) comprises applying a carbon material to the individual metal wires (5) and/or wrapping a tape filled with carbon around the individual metal wires (5).

10. The method (30) as claimed in claim 1, wherein the providing (la) comprises wrapping (2) a tape filled with carbon around a metal conductor core (1) comprising twisted metal wires (5).

11. The method (30) as claimed in claim 10, comprising preparing (4) the tape in a percolation process using carbon and a matrix.

12. The method (30) as claimed in any of the preceding claims, wherein the preparing (10) the carbon enhanced metal conductor (3) comprises:

- cooling (11) the carbon enhanced metal conductor (3), and

- extruding (12) the carbon enhanced metal conductor (3), with an electrically conducting or semi-conducting polymer.

13. The method (30) as claimed in claim 12, comprising repeating the cooling (11) and extruding (12) providing a high-power cable (20) comprising one or more of an electrically insulating layer, an outer conductive shield, an outer jacket, a layer of metal armoring.

14. The method (30) as claimed in any of the preceding claims, wherein the preparing (10) the carbon enhanced metal conductor (3) with one or more layers comprises one or more layer of: an inner conductive shield, an electrically insulating layer, an outer conductive shield, an outer jacket, a layer of metal armoring.

15. The method (30) as claimed in any of the preceding claims, wherein the carbon material comprises graphene.

16. A high-power cable (20) obtainable by the method as claimed in any of the preceding claims.

17. A high-power cable (20) for power ratings over 80 kV, comprising:

- a carbon enhanced metal conductor (3), and

- one or more layers of an inner electrically conducting or semiconducting layer (21), an electrically insulating layer (22), an outer electrically semi-conducting or conducting layer (23), a metal armoring layer, and an outer jacket.