Method for preparing superconducting tape suitable for cable laying, superconducting tape and superconducting cable

Abstract

The present invention provides a method for preparing a superconducting tape suitable for stranding cables, a superconducting tape, and a superconducting cable, comprising: step S1, polishing a base tape; step S2, cutting the polished base tape to provide it with a straight edge portion and a beveled edge portion; and step S3, sequentially coating the cut base tape with a buffer layer and a superconducting layer. The present invention, through polishing, resolves the problem of the current in the beveled edge portion being affected by material marks, while ensuring that the current in the beveled edge portion is consistent with that in the straight edge portion, effectively addressing the current loss problem of conventional Roebel cables. Furthermore, by cutting the base tape before coating, the problem of overall tape damage caused by the propagation of cutting cracks is resolved.

Description

[0001] This application is a divisional application of the following original application:

[0002] Filing date of original application: June 9, 2021

[0003] Original application number: 202110644972.4

[0004] Title of the invention originally applied for: Method for preparing superconducting tape suitable for stranded cables, superconducting tape and superconducting cable Technical Field

[0005] The present invention relates to the field of superconducting technology, and in particular to a method for preparing a superconducting tape suitable for twisted cables, a superconducting tape and a superconducting cable. Background Art

[0006] Second-generation superconducting tapes are typically produced using a multilayer coating process on a nickel-based alloy substrate, as the ReBCO core, which serves as the superconducting current carrier, is inherently hard and brittle. Therefore, they are also called coated conductors. Second-generation superconducting tapes typically consist of a base tape, a buffer layer (transition layer), a superconducting layer, and a protective layer. Superconducting tapes typically range in thickness from 50 to 300 microns and in width from 4 to 12 millimeters. Therefore, second-generation high-temperature superconducting tapes are ribbon-shaped structures with an extremely high aspect ratio. The current carrying capacity of a single high-temperature superconducting tape is limited. To achieve greater current carrying capacity in engineering applications, multiple superconducting tapes are often bundled together to form a bundled conductor, known as a superconducting cable. The Roebel cable structure, proposed by Ludwig Roebel in 1912, involves cutting a single high-temperature superconducting tape and then twisting and braiding multiple strips together in a transposed, twisted pattern. This twisting significantly reduces the AC losses in the tape and also reduces shielding currents in the magnet.

[0007] However, the manufacturing of Roebel cables is extremely complex. Since second-generation high-temperature superconducting tapes must be stamped or cut into specialized shapes, the entire process can damage the edges and corners of the tape. In actual production, it has been found that post-cutting of the tape, especially mechanical cutting, can cause cracks at the cuts. Especially for irregularly shaped Roebel tapes, the subsequent copper plating and twisting process requires the application of tension, which can further expand local cracks in the tape due to stress, thereby damaging the various layers of the superconducting tape structure.

[0008] More importantly, the critical current of the oblique edge of the strip is much smaller than that of the straight edge. This causes a significant loss of current in the Roebel cable after it is manufactured. The reasons are as follows: Figure 1 As shown in the figure, the base tape of the superconducting tape is made of Hastelloy alloy, and there are material marks on the surface along its length. Since conventional superconducting tapes are straight, the material marks in the length direction have limited impact on current transmission. However, in the Roebel cable, each superconducting tape needs to be cut into Figure 2 In the straight edge + bevel edge structure shown, when the current is transmitted from the straight edge to the bevel edge, it will be affected by the material traces, resulting in current loss. Summary of the Invention

[0009] In view of the defects in the prior art, the object of the present invention is to provide a method for preparing a superconducting tape suitable for stranding cables, a superconducting tape and a superconducting cable.

[0010] According to the present invention, a method for preparing a superconducting tape suitable for stranded cables comprises:

[0011] Step S1, polishing the base tape;

[0012] Step S2, cutting the polished base tape so that the base tape has a straight edge portion and a bevel edge portion;

[0013] Step S3, sequentially plating a buffer layer, a texture layer, a superconducting layer, a silver protective layer, and a copper protective layer on the cut base tape to obtain a superconducting tape; or comprising:

[0014] Step S1, polishing the base tape;

[0015] Step S2, sequentially plating a buffer layer, a texture layer, a superconducting layer and a silver protective layer on the base tape to obtain a superconducting tape;

[0016] Step S3, cutting the plated superconducting tape so that the superconducting tape has a straight edge portion and a bevel edge portion;

[0017] Step S4: plating a copper protective layer on the cut superconducting tape.

[0018] Preferably, the texture degree and roughness of the texture layer are less than preset values, so that the retention rate of the current passing through the superconducting tape is above 90%.

[0019] Preferably, in the buffer layer with a size of 50 μm×50 μm, the undulation does not exceed 200 nm, and the texture degree Δω of the texture layer is less than 3.2°.

[0020] Preferably, a corner at a connection between the straight side portion and the oblique side portion comprises an arc shape.

[0021] Preferably, the width of the oblique side portion is greater than the width of the straight side portion.

[0022] Preferably, the base tape is cut by laser cutting or punching cutting.

[0023] Preferably, the polishing is performed by mechanical polishing.

[0024] Preferably, the polishing is achieved by first performing mechanical polishing and then performing electrochemical polishing.

[0025] A superconducting tape provided by the present invention is prepared by using the above-mentioned method for preparing a superconducting tape suitable for stranded cables.

[0026] A superconducting cable provided by the present invention is obtained by twisting a plurality of the above-mentioned superconducting tapes.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention solves the problem of current loss in the beveled portion due to material marks through polishing, while also ensuring that the current in the beveled portion is consistent with that in the straight portion, effectively addressing the current loss problem of traditional Roebel cables. Furthermore, by cutting the base tape before coating, the problem of overall damage to the tape due to the propagation of cutting cracks is resolved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0030] Figure 1 This is an electron microscope image of the base tape of a conventional superconducting tape;

[0031] Figure 2 This is a schematic diagram of the local structure of the Roebel cable;

[0032] Figure 3 Schematic diagram of the local structure of the superconducting tape of the present invention;

[0033] Figure 4 Schematic diagram of the scanning test of the sample;

[0034] Figure 5 Schematic diagram of the relationship between polishing times and bevel current;

[0035] Figure 6 Schematic diagram of the structure of the superconducting cable of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0037] The present invention provides a method for preparing a superconducting tape suitable for stranded cables, comprising:

[0038] Step S1: Polishing the base tape to remove material marks on the base tape surface. Polishing can be performed mechanically or by first mechanical polishing and then electrochemical polishing. Polishing can be performed multiple times. In mechanical polishing, a rough polishing followed by a fine polishing can also be performed, with the rough polishing wheel rotating in the opposite direction of the base tape's forward movement, while the fine polishing wheel rotates in the same direction as the base tape's forward movement.

[0039] Step S2: Cut the polished base tape so that the base tape has a straight edge portion and a bevel edge portion. The cutting method includes laser cutting or punching cutting. Figure 3 As shown, the corner at the junction of the straight-side portion and the oblique-side portion comprises an arc. In this embodiment, the inner corner is arc-shaped; in other embodiments, the outer corner may also be arc-shaped. The arc-shaped transition at the corner allows for smoother current transfer from the straight-side portion to the oblique-side portion. In the present invention, the width a of the oblique-side portion is greater than the width b of the straight-side portion to prevent current loss when transferring from the mass-changing portion to the oblique-side portion.

[0040] Step S3: a buffer layer and a superconducting layer are plated on the cut base tape in sequence. In addition, a silver layer can be plated on the superconducting layer, and copper is plated for packaging. The process in this step is the same as the principle of conventional superconducting tapes, and will not be described in detail in this invention. Figure 4 As shown in the figure, a buffer layer of CeO2 was continuously plated on the base tape. The out-of-plane scanning test of CeO2 found that with the increase of the number of polishing, the texture degree Δω of the texture layer gradually decreased, indicating that the out-of-plane texture of the sample was gradually improved. When the sample was rotated 90° and scanned again, it was found that the Δω of the five groups of samples was small and the values were consistent, indicating that the out-of-plane texture was anisotropic in different planes. The reason for the increase in Δω was indeed due to the material traces of the base tape. The relationship between the number of polishing times and the bevel current is shown in Figure 2. Figure 5 As shown, the optimal number of polishing cycles is 1 to 5. Polishing ensures that the texture and roughness of the texture layer coated on the substrate are less than preset values, ensuring that the current retention rate through the superconducting tape exceeds 90%. In a buffer layer measuring 50 μm x 50 μm, the undulation does not exceed 200 nm, and the texture layer's texture Δω is less than 3.2°.

[0041] X-ray diffraction (XRD) is one of the most important methods in thin film structure analysis and is often used to analyze the cell parameters, epitaxial quality, epitaxial relationship, crystal orientation, etc. of thin films. XRD has two scanning modes: θ-2θ scanning and Scanning. During a conventional θ-2θ scan, the angle between the sample and the incident light is θ. Rotating the sample angle also synchronizes with the receiver, maintaining the angle between the receiver and the incident light at 2θ. This ultimately yields a θ-2θ spectrum of the film. Characteristic peaks in the spectrum reveal the growth of film grains along the c-axis. The smaller the full width at half maximum (FWHM) obtained by integrating the characteristic peaks along the χ direction, the more consistent the film's growth along the c-axis. The scanning is mainly to obtain the orientation of the film grains in the ab plane and the epitaxial relationship between the film and the substrate. CeO2 and ReBCO grains are epitaxial on the tetragonal lattice. During the test, the sample rotates around its own normal, so The scanned diffraction peaks have 90° rotational symmetry, and the ideal pattern has four narrow peaks separated by 90°. The smaller the full width at half maximum (FWHM) of the scan, the better the consistency of the ab-plane orientation of the film. The present invention uses a D8 discover X-ray diffractometer from Bruker.

[0042] In other embodiments of the present invention, the polishing step further includes cleaning the base tape to remove residual substances generated by the polishing.

[0043] like Figure 6 As shown, the present invention also provides a superconducting cable, which is obtained by twisting a plurality of superconducting tapes prepared by the above method.

[0044] In other embodiments, a method for preparing a superconducting tape suitable for stranded cables includes:

[0045] Step S1: polishing the base tape.

[0046] Step S2: a buffer layer, a texture layer, a superconducting layer and a silver protective layer are sequentially plated on the base tape to obtain a superconducting tape.

[0047] Step S3: cutting the plated superconducting tape so that the superconducting tape has a straight edge portion and a bevel edge portion.

[0048] Step S4: plating a copper protective layer on the cut superconducting tape.

[0049] In the description of this application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0050] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A method for preparing a superconducting tape suitable for stranding cables, characterized in that: include: Step S1, polishing the base tape; Step S2, cutting the polished base tape so that the base tape has a straight edge portion and a bevel edge portion; Step S3, sequentially plating a buffer layer, a texture layer, a superconducting layer, a silver protective layer, and a copper protective layer on the cut base tape to obtain a superconducting tape; or comprising: Step S1, polishing the base tape; Step S2, sequentially plating a buffer layer, a texture layer, a superconducting layer and a silver protective layer on the base tape to obtain a superconducting tape; Step S3, cutting the plated superconducting tape so that the superconducting tape has a straight edge portion and a bevel edge portion; Step S4, plating a copper protective layer on the cut superconducting tape; The polishing adopts mechanical polishing; The texture and roughness of the texture layer are less than preset values, so that the retention rate of the current passing through the superconducting tape is above 90%; At the scale of 50μm×50μm in the buffer layer, the roughness of the buffer layer does not exceed 200nm, and the texture degree Δω of the texture layer is less than 3.2°; The corner at the connection between the straight edge portion and the oblique edge portion comprises an arc shape; The width of the oblique side portion is greater than the width of the straight side portion.

2. The method for preparing a superconducting tape suitable for stranding cables according to claim 1, characterized in that: Methods for cutting the base tape include laser cutting or punching cutting.

3. The method for preparing a superconducting tape suitable for stranding cables according to claim 1, characterized in that: The polishing is achieved by first performing mechanical polishing and then performing electrochemical polishing.

4. A superconducting tape, characterized in that: The superconducting tape is prepared by the method for preparing a superconducting tape suitable for stranded cables according to any one of claims 1 to 3.

5. A superconducting cable, characterized in that: The superconducting tape is obtained by twisting a plurality of superconducting tapes as claimed in claim 4.

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