WO2016202686A1 - A method of manufacturing a cable for a winding of an electromagnetic induction device - Google Patents

Abstract

The present disclosure relates to a method of manufacturing a cable for a winding of an electromagnetic induction device. The method comprises a) providing a layer of magnetic material onto a conductor.

Description

A METHOD OF MANUFACTURING A CABLE FOR A WINDING OF AN ELECTROMAGNETIC INDUCTION DEVICE

TECHNICAL FIELD

The present disclosure generally relates to electric power systems and in particular to a method of manufacturing a cable for windings of an

electromagnetic induction device.

BACKGROUND

Electromagnetic induction devices, such as transformers and reactors, are used in power systems for voltage level control. Hereto, a transformer is an electromagnetic induction device used to step up and step down voltage in electric power systems in order to generate, transmit and utilize electrical power in a cost effective manner. In a more generic sense a transformer has two main parts, a magnetic circuit, the core, made of e.g. laminated iron and an electrical circuit, windings, usually made of aluminium or copper wire.

Larger transformers used in electrical power networks are generally designed with high efficiency and with a set of stringent operational criteria e.g.

dielectric, thermal, mechanical and acoustic criteria. Due to continuously increasing power handling capacity, i.e. power and voltage rating, of transformers, transformer design faces more and more constraints.

Modern practice of design of transformers involves inter alia the balance of use of materials in core and windings, and losses. Due to the large amount of power handled by a large power transformer and due to long service life, typically 40 years, any improvement in reduction of losses would be appreciable, if it can be justified by the cost.

Power Loss in transformers due to load currents is a large part of the total losses. The load loss (LL) consists of perceivably three different types of losses based on their origin, i) the PR losses due to inherent resistance of winding conductors, also called DC loss, ii) the eddy current loss (ECL) in the windings due to the time-varying magnetic field created by the load current in all winding conductors, the leakage field and iii) the stray losses, i.e. ECL in other structural parts of the transformer due to the leakage field.

Present solutions for reducing eddy current losses include multi-strand continuously transposed cables (CTC). These cables require stronger copper in order to be able to handle short circuits in high voltage applications.

Moreover, the manufacturing of CTC cables having a plurality of sufficiently thin and transposed strands is a very expensive process and requires gluing and insulation of the strands by means of epoxy. The material cost of high voltage inductive devices hence increase tremendously.

EP2695174 discloses a cable with lower eddy current losses. In particular EP2695174 discloses a cable that comprises a conductor, and a layer comprising a magnetic material having a relative permeability in the range 100 to 5000. The layer at least partly surrounds the conductor, and has a thickness that is in the range 200 to 800 μιτι.

SUMMARY

An object of the present disclosure is to provide a method of producing a cable having a conductor that is provided with a layer of magnetic material.

Hence, according to a first aspect of the present disclosure there is provided a method of manufacturing a cable for a winding of an electromagnetic induction device, wherein the method comprises: a) providing a layer of magnetic material onto a conductor.

By providing a suitably chosen thin layer of magnetic material with reasonably high relative permeability compared to the material of which the conductor is made onto the conductor, the leakage flux will redistribute and part of it will be confined to the layer and thereby substantially reduce the eddy loss in the conductor. Thus, the operation of an electromagnetic induction device comprising the present cable may be made more efficient performance-wise. In particular, with optimised magnetic material parameters for a particular application, it is envisaged that the loss reduction may be of the order 5-10 %.

Moreover, due to the magnetic material, more magnetic energy can be stored in the cable and thus the winding, whereby the ability of large

electromagnetic induction devices to withstand the occurring force due to short circuit current is improved. In other words the impedance of an electromagnetic induction device arranged with the cable presented herein can be controlled by means of the magnetic material. To this end, the cable according to the present disclosure may be particularly advantageous for high voltage applications where high currents are present, thus resulting in high losses. It is to be noted, however, that the cable could also be used for medium voltage applications and even low voltage applications.

Furthermore, due to the eddy current loss reduction provided by the magnetic material, the cable cross section can be made solid, or the cable can be manufactured with a fewer number of strands, with each strand having a thicker cross-sectional dimension. Further the need for stronger copper material, i.e. the Yield strength, is reduced. Strands with thicker dimension are less expensive to manufacture, thereby reducing the costs for

manufacturing the cable. According to one embodiment the conductor is a single strand.

According to one embodiment step a) involves providing the magnetic material onto the strand by means of a cladding process.

According to one embodiment step a) involves coating the strand with the magnetic material. According to one embodiment the coating is made by one of the group of electroplating, spraying and physical vapour deposition.

According to one embodiment the coating involves coating the strand with epoxy comprising the magnetic material. According to one embodiment step a) involves providing a tape comprising the magnetic material onto the strand.

According to one embodiment step a) involves winding a plurality of overlapping layers of the tape onto the strand. According to one embodiment step a) involves annealing the tape.

According to one embodiment the tape is an amorphous tape or a non-grain oriented crystalline steel tape.

One embodiment comprises repeating step a) for a plurality of strands, and b) forming a bundle of strands of the strands. According to one embodiment the conductor is formed by a bundle of strands.

According to one embodiment step a) involves winding a plurality of overlapping layers of tape comprising the magnetic material onto the bundle of strands. According to one embodiment step a) involves annealing the tape.

According to one embodiment the tape is an amorphous tape or a non-grain oriented crystalline steel tape.

According to one embodiment step a) involves coating the bundle of strands with the magnetic material. According to one embodiment the coating is made by one of the group of electroplating, spraying and physical vapour deposition.

According to one embodiment the coating involves coating the bundle of strands with epoxy comprising the magnetic material.

One embodiment comprises b') winding layers of paper around the bundle of strands. According to one embodiment the electromagnetic induction device is a transformer or a reactor.

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.

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. l is a flowchart of a method of manufacturing a cable for a winding of an electromagnetic induction device;

Fig. 2 schematically shows a number of examples of manufacturing the cable; and

Fig. 3a shows a perspective view of a cable produced according to one variation of the method presented herein; and

Fig. 3b shows a longitudinal section of the cable in Fig. 3a, especially of a tape comprising magnetic material, and paper insulation, wound around a conductor of the cable.

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.

This disclosure describes methods of manufacturing a cable for a winding of an electromagnetic induction device. Such an electromagnetic induction device may in particular be a medium voltage (MV) or high voltage (HV) electromagnetic induction device. The cable may hence be a medium voltage or a high voltage cable. Examples of electromagnetic induction devices are a transformer such as a power transformer, distribution transformer and current transformer, and a reactor. The production methods presented herein are directed to the manufacturing of a cable that has a layer of magnetic material provided on its conductor. This conductor may be comprised of a single strand or a plurality of strands forming a bundle of strands. In the former case, the single strand is provided with the layer of magnetic material. In the latter case, each strand of the bundle of strands has been provided with a respective layer of magnetic material and/or the entire bundle of strands forming the conductor have been provided with a layer of magnetic material. This layer of magnetic material may surround the entire conductor in the case of a single strand conductor, or it may only partly surround the conductor. The same applies for each strand in case the conductor includes a bundle of strands, i.e. the layer of magnetic material may surround each strand or the layer may only partly surround the bundle of strands. It is also envisaged a variation in which some strands are fully surrounded by the magnetic layer while others are only partly surrounded by the magnetic layer. Additional insulation, such as by means of a resin e.g. epoxy, enamel, and cellulose-based material such as paper may furthermore be provided around the single strand in the case of a single strand conductor, or around the bundle of strands in the case of a conductor comprising a bundle of strands.

The provision of the magnetic layer onto the single strand conductor, onto each strand if the conductor comprises a plurality of strands or onto the bundle of strands may be obtained in a multitude of ways. A number of examples will be described in the following with reference to Figs i-3b.

Fig. l shows a general flowchart of a method of manufacturing a cable for a winding of an electromagnetic induction device. In a step a) a conductor is provided with a layer of magnetic material.

The cable may comprise a conductor made of a single strand or a bundle of strands. In case the conductor is formed by a single strand, this single strand is provided with the layer of magnetic material.

Step a) may involve providing the magnetic material onto the single strand by means of a cladding process. To this end the magnetic material may be pressed onto the strand by means of high pressure, e.g. by means of rolls, such that it adheres to the strand.

According to another variation, step a) may involve coating the strand with the magnetic material, or providing the magnetic material onto the strand in a film-formation process. The coating may for example be made by

electroplating, spraying, physical vapour deposition, painting or varnishing. According to one variation, a resin such as epoxy may comprise the magnetic material e.g. in the form of magnetic particles dispersed therein. The coating process may then involve coating the strand with the resin. Another alternative to cladding and coating is that of providing a tape comprising the magnetic material onto the strand. The tape may for example be provided in the axial direction onto the strand as strips parallel with the longitudinal direction of the strand. Alternatively, the tape may be wound in several overlapping layers onto the strand, as shown in the example in Figs 3a-b. Adhering means such as glue may be used to make the tape adhere to the strand. When the tape has been arranged on the strand, the tape may be annealed in an annealing process, if necessary, e.g. by heating the tape which is provided on the strand. The tape may for instance be an amorphous tape or a non-grain oriented crystalline steel tape. Annealing is advantageously made in case the tape is an amorphous tape; if crystalline material is used, annealing may not be necessary.

According to one variation a layer of magnetic material may first be provided onto the strand by means of the cladding process or by means of coating, wherein a tape comprising the magnetic material may be provided onto the strand which already has been provided with a layer of magnetic material. To this end, the strand may be provided with more than one layers of magnetic material, e.g. two layers of magnetic material.

In case the cable comprises a multi-strand conductor that is formed by a bundle of strands, each conductor, i.e. strand, may be subjected to step a). To this end, step a) may be repeated until all strands have been provided with a layer of magnetic material. In a step b) the strands may then be bundled to form a bundle of strands. The strands may for example be bundled in such a way that they form a CTC. As an alternative to the above-described variations, the conductor may be formed by a bundle of strands, and the layer of magnetic material may be provided after the bundle of strands has been created. Thus, step a) may involve winding a plurality of overlapping layers of tape comprising the magnetic material onto the bundle of strands. The tape may be annealed if necessary, i.e. depending on the type of tape used. Examples of suitable tape are amorphous tape or non-grain oriented crystalline steel tape. The same considerations apply as above, i.e. in case the tape is an amorphous tape, annealing may be necessary, while in case the tape is a crystalline material, annealing may not be necessary. As an alternative to taping the entire bundle of strands, step a) may involve coating the bundle of strands with the magnetic material or providing the magnetic material onto the bundle of strands in a film-formation process. The coating may for example be made by electroplating, spraying, physical vapour deposition, painting or varnishing. The coating may involve coating the bundle of strands with epoxy comprising the magnetic material in the form of magnetic particles dispersed in the epoxy.

In a step b') the conductor in the form of the bundle of strands may be provided with paper. This step may hence be performed for any of the variations presented hereabove, i.e. for a bundle of strands where each strand individually has been provided with a layer of magnetic material, and for a bundle of strands provided with the layer of magnetic material after the strands have been bundled. Moreover, step b') may also be performed for the production of cables having single-strand conductors, i.e. for cables for which the conductor is made up of only one strand. The paper is preferably wound around the bundle of strands or single strand.

When forming the bundle of strands in any of the examples disclosed herein, the strands may for example be bundled in such a way as to form a CTC.

Some of the production steps described above will further be illustrated with reference to Fig. 2 which shows a number of schematic flow schemes for example-manufacturing processes 1-4 for manufacturing a cable 3 for a winding of an electromagnetic induction device. The figures show cross sections of the conductor/cable.

The process 1 flow scheme shows the manufacturing of a cable 3 which comprises a conductor 1 made of a single strand that is provided with a layer of magnetic material 2. The solid conductor 1 without the layer of magnetic material is shows in a state A. In a state B the conductor 1 is shown provided with the layer of magnetic material 2. In a state C, the conductor 1 already provided with the layer of magnetic material 2 has been coated with a resin layer 6 e.g. epoxy. Finally, in a state D, layers of paper 8 have been wound around the epoxy-coated conductor 1 thus forming the cable 3.

In process 4 in Fig. 2, states A and B are the same as in process 1. Each strand 7 is provided with a layer of magnetic material 2 in state B. Next, a plurality of strands 7 provided with a layer of magnetic material according to states A and B, are arranged as a bundle of strands 9 in a state C This bundle of strands 9 may then be coated with a resin 6 such as epoxy. Alternatively, each strand 7 may be individually coated with the resin 6 wherein the bundle of strands 9 is formed after the resin-coating. Furthermore, an electrical insulator such as enamel may be provided as electrical insulation in between the strands of the bundle of strands 9.

When the bundle of strands 9 has been obtained, the bundle of strands 9 may be provided with one or more layers of paper 8 thus forming the cable 3 shown in state D'. The paper may be provided for example by winding the paper around the bundle of strands 9. In process 2 in Fig. 2 states A and B are interchanged with states A' and B', respectively. In state A' a wire 5 that is to be shaped into a conductor 1 is provided. The wire 5 may be subjected to a shaping process such as a drawing process or an extrusion process, in which the wire 5 additionally is provided with the layer of magnetic material 2 thus forming the conductor 1 in state B'. In the case of a drawing process, a sheet comprising the magnetic material may be provided around the wire 5, wherein the wire 5 provided with the sheet of magnetic material is drawn through a die to form the conductor 1. After states A' and B' the process continues to process 1 and states C and D described hereabove. It should be noted that according to one variation the conductor may be shaped from a wire by means of an extrusion process or a drawing process, wherein the layer of magnetic material is provided onto the conductor after the extrusion process or the drawing process, according to any example disclosed herein of how the layer of magnetic material is provided onto the conductor.

In process 3 in Fig. 2 the process commences with states A' and B' and continues to states C and D' described hereabove.

State B in process 1 and 4 may for example be obtained according to the alternatives described herein, i.e. by means of cladding, coating or by providing a tape comprising the magnetic material onto the conductor/strand.

In each of the processes 1-4 described above, the dashed line 10 in Fig. 2 may be seen as a separator of step a) from additional steps to obtain the cable 3. In particular, states A, B, A', B' correspond to step a) of the method of manufacturing the cable 3.

Fig. 3 shows an example of a cable 3 comprising a conductor 1 provided with a plurality of overlapping layers of magnetic material. The conductor 1 may comprise one or more strands. The conductor 1 is provided with a plurality of layers of magnetic material in the form of tape wound around the conductor 1. The tape is arranged in an overlapping manner. A plurality of overlapping layers of paper 8 is wound around the conductor 1 and around the magnetic material. The overlaps of the paper 8 are illustrated by means of the dashed lines 11. Fig- 3b shows a section along the axial direction 13 of the conductor 1 in Fig. 3a. According to this example there is a plurality of overlapping layers of magnetic material 2 in the form of tapes wound around the conductor 1. There is furthermore a plurality of overlapping layers of paper 8 wound around the magnetic material 2. According to the present example there are three layers of tape and three layers of paper 8 wound around the conductor 1. There could however also be fewer or more layers than three. According to the example, there is a displacement between the edges 15 of any pair of adjacent layers of tape. There is also a displacement between the edges 17 of any pair of adjacent layers of paper 8. The edges 15 of every other layer of tape are aligned or essentially aligned. Similarly, the edges 17 of every other layer of paper 8 are aligned or essentially aligned.

According to any example given herein, the magnetic material may have a relative permeability in the range 2 to 100000. With relative permeability of the magnetic material is meant relative magnetic permeability μ_Γ of the magnetic material. Advantageously, the relative permeability of the magnetic material is in the range of 10 to 500. Alternatively, the relative permeability of the magnetic material is in the range 100-5000. Advantageously, the relative permeability of the magnetic material may be greater than 300, and preferably above 500. The layer may have a thickness which is at least 100 μιτι, preferably in the range 200 to 800 μιτι. The conductivity of the magnetic material is according to one example relatively low, the conductivity being of an order of 10000 or less Siemens per meter. According to one variation, the magnetic material has a Steinmetz coefficient having a value that is less than or equal to 20, preferably less than 10. Other variations of the magnetic material may exhibit a higher Steinmetz coefficient value than 20.

According to one variation, the magnetic material comprises an amorphous material. Alternatively, the magnetic material may comprise a crystalline material. The magnetic material may be ferromagnetic. According to one variation, the magnetic material has a saturation flux density of at least 0.5 tesla.

According to any embodiment presented herein, the conductor may for example comprise copper, aluminium, a combination of copper and aluminium, or any other conductive material suitable for conducting current with low losses, and which conductive material has a lower relative magnetic permeability than the relative magnetic permeability of the magnetic material.

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.

Claims

1. A method of manufacturing a cable (3) for a winding of an

electromagnetic induction device, wherein the method comprises: a) providing a layer of magnetic material (2) onto a conductor (1; 7).

2. The method as claimed in claim 1, wherein the conductor (1; 7) is a single strand.

3. The method as claimed in claim 2, wherein step a) involves providing the magnetic material (2) onto the strand by means of a cladding process.

4. The method as claimed in claim 2, wherein step a) involves coating the strand with the magnetic material (2).

5. The method as claimed in claim 4, wherein the coating is made by one of the group of electroplating, spraying and physical vapour deposition.

6. The method as claimed in claim 4, wherein the coating involves coating the strand with epoxy comprising the magnetic material.

7. The method as claimed in claim 2, wherein step a) involves providing a tape comprising the magnetic material (2) onto the strand.

8. The method as claimed in claim 7, wherein step a) involves winding a plurality of overlapping layers of the tape onto the strand.

9. The method as claimed in claim 7 or 8, wherein step a) further involves annealing the tape.

10. The method as claimed in any of claims 7-9, wherein the tape is an amorphous tape or a non-grain oriented crystalline steel tape.

11. The method as claimed in any of claims 2-10, comprising repeating step a) for a plurality of strands, and b) forming a bundle of strands (9) of the strands.

12. The method as claimed in claim 1, wherein the conductor (1) is formed by a bundle of strands (9).

13. The method as claimed in claim 12, wherein step a) involves winding a plurality of overlapping layers of tape comprising the magnetic material (2) onto the bundle of strands.

14. The method as claimed in claim 12 or 13, wherein step a) involves annealing the tape.

15. The method as claimed in claim 13 or 14, wherein the tape is an amorphous tape or a non-grain oriented crystalline steel tape.

16. The method as claimed in claim 12, wherein step a) involves coating the bundle of strands (9) with the magnetic material (2).

17. The method as claimed in claim 16, wherein the coating is made by one of the group of electroplating, spraying and physical vapour deposition.

18. The method as claimed in claim 17, wherein the coating involves coating the bundle of strands (9) with epoxy comprising the magnetic material.

19. The method as claimed in any of claims 11-18, comprising b') winding layers of paper (8) around the bundle of strands (9).

20. The method as claimed in any of the preceding claims, wherein the electromagnetic induction device is a transformer or a reactor.