WO2017021423A1

WO2017021423A1 - Continuously transposed conducting cable

Info

Publication number: WO2017021423A1
Application number: PCT/EP2016/068467
Authority: WO
Inventors: Glyn KIRBY; Jaakko Samuel MURTOMAKI; Jeroen VAN NUGTEREN
Original assignee: Cern European Organisation For Nuclear Research
Priority date: 2015-08-03
Filing date: 2016-08-02
Publication date: 2017-02-09

Abstract

A conducting cable comprises a series of continuously transposed tapes of electrically conductive material and restraining members braided with the tapes. The restraining members are arranged to restrain the tapes in a lateral direction to resist movement between the respective tapes and restrain the position of the respective tapes.

Description

CONTINUOUSLY TRANSPOSED CONDUCTING CABLE

The present invention relates to an electrically conducting cable of the type used for numerous applications that require the conduction of high currents with accurate positioning of each element within the cable, to be able to generate high-quality magnetic fields.

One type of relatively well known conducting cable of this type is a continuously transposed cable, also known as a Roebel cable. Such a cable has a number of flat tapes of conductive material that are wound such that they are geometrically aligned along their cross section. In some cases the material forming the tapes is structured to be superconducting at the operating temperatures of the cable.

With such cables it is important to control the geometric alignment of the strands along the cross section of the cable so that field quality is controlled correctly. This is so that no unwanted field effects are generated by the passage of current through the cable in operation.

Maintaining geometric alignment of the tapes can be difficult in many situations, particularly when the cable is being manipulated during coil winding, where instability can cause the cable to become locally disassembled. Disassembly can lead to permanent damage of the delicate tapes.

Accordingly, whilst such cables therefore have significant benefits in terms of providing, in principle, a high level of control of electromagnetic fields during their operation, there is a need to improve their robustness with respect to maintaining precise geometry during handling, coil winding, coil impregnation. The present invention seeks to provide such improvements. Therefore this invention seeks to maintain geometric stability which also helps protects the cable from permanent damage.

According to the present invention there is provided a conducting cable comprising a series of continuously transposed tapes of electrically conductive material and restraining members braided with the tapes and arranged to restrain the tapes in a lateral direction to resist movement between the respective tapes and restrain the position of the respective tapes. With the present invention, by providing means to restrain the lateral movement of individual tapes relative to the bundle of tapes in the cable it is possible to improve significantly the cable's resistance to the effects of lateral misplacement. This in turn improves the overall electromagnetic characteristics of the cable specifically the random variation of magnetic fields that are generated. Controlling the position of each tape within the cable will reduce the magnetic field errors that will eventually be generated in the magnet.

Assembly of this type of cable will often require automation. The design of a cable capable of being assembled using an automatic machine requires clearances between tapes. These clearances lead to miss placement of individual tapes. This invention will enable accurate positioning of the tapes when combined with the clearances needed for automatic assembly of such cable and also for short lengths of hand assembled cable. The tapes in the cable may be formed from superconducting material, such as YBCO.

The means for restraining lateral movement may be provided by a tape or braid or single-filament, which may be formed from Kapton (RTM), or glass fibre woven tape, or metallic strip such as copper, or similar material compatible with electrical and mechanical requirements, there are several configurations possible that position and hold the tapes that are woven into the layers of strands of the cable. The means for restraining lateral movement in such a configuration may also restrain any central core that is present in the cable.

Alternatively, a means for restraining lateral movement between tapes within the cable may comprise "bracelets", for example made from copper or other materials, the sets of bracelets that restrain groups of cable tapes by repeatedly encapsulating the stacks of tapes at each position where access is available transversely through the centre of the cable. The bracelets can also position and hold any central core that may be present if this element is incorporated in the cable. In either of these cases, a further central conducting wire may be positioned within the centre of the cable to improve yet further the mechanical resistance to mechanical stability of the cable, this wire can be utilised for :quench detection, stress and strain management, temperature measurement, and other diagnostic purposes.

Examples of the present invention will now be described with reference to the accompanying drawings, in which:

Figures 1 A and B are side schematic views of a first example cable according to the invention;

Figure 2 is a side schematic view of a second example cable according to the present invention; Figure 3 is a series of schematic representations of different possible restraining means arrangements according to the invention; and

Figure 4 is a series of detailed representations illustrating the different parameters which determine the dimensions and geometry of the cable according to the invention.

Referring to Figure 1A, a cable 1 according to the present invention is provided in which a series of tapes 2 of conductive material are transposed and interweaved in a manner that is well known and conventional to low loss cables for alternating current. The size and nature of the interweaving, as well as the material from which the tapes 2 are formed, can be selected dependent upon the application for which the cable 1 is going to be used. The tapes are generally long and narrow with a rectangular or square cross- section, although other cross-sectional shapes are possible.

In general terms, the objective is to provide a cable 1 that operates in a high current regime in the range of around circa 10KA to around circa 50KA, which can provide cable positioning with high accuracy, yet which has a sufficiently low value of AC loss for the application to which it is being applied. A number of techniques are well known for producing such interweaving of tapes 2, with one example, along with an apparatus for making such tapes, being disclosed in EP2073218.

By way of example, in the use of such cables, in superconducting magnets, the High magnetic fields generated require the accurate positioning of individual cables and the accurate positioning of individual tapes within the cable, such cable positioning being nominally within 50 μιη of design position. Tapes within the cable should maintain similar tolerances.

As can be seen from Figure 1 , in the cable 1 of the present invention mechanical restraining components 3 are provided at intervals, which may be regular, along the axial direction of the cable 1 and span the cable in a lateral direction to provide mechanical constraint in that lateral direction.

In the example of Figure 1 these mechanical restraining components 3 are in the form of an polyimide film, such as Kapton (RTM) which are continuous and woven between the strands, but could also be from other suitable materials, conducting or non-conductive. Copper could be used to provide additional thermal stability to the cable. Kapton (RTM) and copper are particularly suitable for applications in high-energy physics as they keep the cable radiation-proof. As shown in Figure 1 B an alternative bands of electrically conductive material, for example copper, may be placed around groups of tape 2 and then connected to one another to provide the lateral mechanical constraint. The introduction of these restraining components 3, whilst not increasing to any significant degree the complexity of manufacture of the cable 1 , provide a significant amount of restraint to mechanical movement between respective tapes 2 or groups of tape within the cable 1. This restraint reduces lateral movement of the cable 1 that may otherwise cause misplacement of tapes within the cable which then lead to field errors.

Figure 2 shows a second example of the present invention which has a construction for the tapes 2 and their interweaving which is generally the same as that of the example of Figure 1 , but which has the addition of a further core conducting component 4 running generally through the centre of groups of the interleaved tapes 2. This conducting component 4 may be formed from the same material as the tapes 2, or may be formed from a different material. Again, mechanical restraining components 3 are provided at intervals along the cable 1 to provide mechanical constraint in a lateral direction. Those components may again be formed from Kapton (RTM) or other suitable material, and interweaved with the tapes within the cable, or, are bands 3 of a conductive metal, such as copper. In this example, the central conducting component 4 can be employed to provide additional mechanical constraint to improve yet further the control of variance in tape position due to bending. Figure 3 provides a series of cross-sectional and perspective views of the example cables to further explain the nature of the winding of the restraining members 3. Figures 3A and 3B show cross-sectional and perspective views of a cable according to the invention, with a first possible configuration for restraining members 3. Here two groups 5 of wound tapes 2 are formed with an anti- clockwise winding, each having a respective continuous restraining member 3 that is wound in a clockwise direction. Each restraining member 3 may on either a regular or irregular intermittent basis cross over to the other of the two groups 5. A central core 4 is shown in figure 3A but is optional as shown in figure 3B. Figures 3C and 3D show further configurations, in cross-sectional view, similar to that of figures 3A and 3B, but in which the restraining members 3 are wound such that they pass around the central core 4. In figure 3C the restraining members 3 each restrain one of the groups 5 and also restrain the core 4 by passing around it on alternating passes through the gap 6 around the core 4. In figure 3D there is a similar configuration but the restraining members 3 pass around the core 4 on each pass through the gap 6.

Figure 4 detailed representations illustrating the different parameters which determine the dimensions and geometry of the cable according to the invention.

In accordance with Figure 4A, the width of the cable is determined by the width of the tape (Wr) and the width of the central channel (Wc). In an exemplary embodiment, Wr is about 5.5 mm, and Wc is about 1 mm. The cross-over angles a and β need not be identical. They are preferably rounded angles, in order to avoid cutting into an optional glassfiber sock into which the cable can be inserted. The illustrated geometry is only exemplary, and the strands of the cable can take any shape, as long as each tape forms a topological connected space. Figure 4B provides a detailed cross-sectional view of the cable and Figure 4C a detailed side view of said cable. The thickness of the cable is determined by the number of tapes which it comprises. The present cable requires an even number of tapes. In the illustrated exemplary embodiment, the number of tapes is 14.

The cable can also be provided with diagnostic components on the top or bottom surfaces formed by the consecutive weaving of tapes, or on the means for restraining lateral movement mentioned above. Such diagnostic components may include temperature detection or quench protection components. As will be appreciated from the above, what has been provided in the present invention is an improved cable 1 that maintains all the characteristics of known cables with interleaved tapes according to the principles of a Roebel cable, yet which provides improved robustness and therefore improved operating characteristics in terms of precision of positioning cables and precision of the individual tapes within the cable. Losses and electromagnetic characteristics that would otherwise be caused by mechanical or temperature related effects on the cable 1. This has particular benefits in super conducting technologies, with the strands formed from YBCO and where the cables are employed in cryogenic applications, such as in high efficiency electrical grids, super conducting magnetic energy storage, or in medical MRI/NMR applications.

Claims

1. A conducting cable comprising a series of continuously transposed tapes of electrically conductive material and restraining members braided with the tapes and arranged to restrain the tapes in a lateral direction to resist movement between the respective tapes and restrain the position of the respective tapes.

2. A cable according to claim 1 wherein the restraining members are formed from Kapton (RTM).

3. A cable according to claim 1 wherein the restraining members are formed from a metal, preferably copper.

4. A cable according to claim 1 or claim 2, in which the restraining members are wound in with the tapes.

5. A cable according to any of claims 1 to 3, wherein the restraining members are positioned around the outside of the transposed tapes.

6. A cable according to any preceding claim wherein the restraining members a formed from continuous tape wound alond the axial direction of the cable.

7. A cable according to any preceding claim further comprising a central core of conducting material positioned within the transposed tapes.

8. A cable according to claim 7, wherein the restraining members are further wound around the central core.

9. A cable according to any preceding claim wherein the strands are transposed to form a Roebel tapes.

10. A cable according to any preceding claim wherein the tapes are formed from YBCO.