JP2009110668A - Superconductive wire and superconductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a superconductive wire and a superconductor with an AC loss reduced without degrading superconductivity characteristics, and with mechanical characteristics improved. <P>SOLUTION: The superconductive wire has 8 or more thin-film superconductive wire rods spirally wound around core wires with an outer diameter of 1.3 to 5 mm so as not to be overlapped. In the superconductor, the plurality of superconductive wires are wound around the core wires in a spiral shape so as not to overlap with each other. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a superconducting wire and a superconducting conductor, and more particularly to a superconducting wire and a superconducting conductor with reduced AC loss and improved mechanical properties.

As wire rods for high-temperature superconducting cables, Y-based wires such as YBCO (YBa ₂ Cu ₃ O _7-d ) and thin-film superconducting wires represented by Bi-based wires such as BSCCO (BiSr ₂ Ca ₂ Cu ₃ O ₁₀ ) are known. It has been. Each wire has a tape-like shape as shown in FIG. That is, (a) shows a tape-like BSCCO wire, and has a structure in which a BSCCO filament 41 is filled in a sheath 42 made of a silver alloy. Its thickness is about 0.2 mm. (B) shows a tape-shaped YBCO wire, on which a YBCO layer 53 having a thickness of about 1 μm is formed on a base 51 via an intermediate layer 52, and a silver layer 54 having a thickness of about 10 μm is coated thereon. It has a structure.

  Among these tape-shaped wires, the BSCCO wire has a problem that the critical current density rapidly decreases when an external magnetic field is applied. On the other hand, YBCO wire is strong against an external magnetic field and can maintain a high current density even in a strong magnetic field, and thus is expected to be applied to AC power equipment such as a superconducting cable.

  The Y-based wire has a structure in which a YBCO thin film is vapor-deposited on a metal substrate. Since the Y-based wire is a thin film, it has a high current density. Very small compared to. On the other hand, the AC loss perpendicular to the surface of the thin film is larger than that of the Bi-based wire.

  FIG. 16 shows various wire types of Bi-based wire and Y-based wire. FIG. 5 shows AC loss when energized under an AC external magnetic field of these wire types (see, for example, Non-Patent Document 1). The AC loss in FIG. 5 is the result when the external magnetic field is 50 mT, the peak of the energizing current is It = 90 A, and the critical current of each wire is 150 A. The horizontal axis is the direction of the magnetic field, 0 degrees is parallel to the plane and 90 degrees is perpendicular to the plane. From FIG. 5, the AC loss of the YBCO strip is small when the magnetic field is parallel to the superconducting surface. However, at 15 degrees, the AC loss is larger than that of the YBCO stack (YBCO stack), BSCCO tape, and BSCCO wire. I understand that. Also, the YBCO stack has no advantage compared to BSCCO.

  Therefore, as shown in FIG. 17, when a Y-based wire is made of a superconducting cylinder, even if a magnetic field is applied from the outside, the magnetic field is entirely parallel to the surface, and thus an ideal shape (this shape is a monoblock type). Called). However, it is very difficult to manufacture such an ideal Y-based superconducting wire, and even if it is possible, it is expected that the mechanical characteristics are very poor. Since this shape has no escape against bending, it is difficult to apply when considering the actual power equipment application.

Therefore, as a method of approaching the monoblock shape, a wire having a finite width is made finer as shown in FIG. 18 (a), and this fine wire is converted into a polygon, for example, a quadrangle as shown in FIG. 18 (b). Has been proposed, and is effective in reducing AC loss. However, the superconducting characteristics are deteriorated with the thinning, and the optimization considering these has not been performed so far.
Stravrey, Supercond. Sci. Technol. 18 (2005) 1300-1312

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a superconducting wire and a superconducting conductor in which AC loss is reduced without deteriorating superconducting characteristics and mechanical characteristics are improved.

  In order to solve the above problems, the first aspect of the present invention is to wrap around 8 or more thin film superconducting wires in a spiral shape around a core wire having an outer diameter of 1.3 to 5 mm so as not to overlap each other. A superconducting wire is provided.

  The superconducting wire configured as described above can be provided with a protective layer made of a good conductor or a high-resistance metal around it.

  The thin film superconducting wire may have a width of 0.48 to 1.8 mm. In addition, the gap between adjacent thin film superconducting wires can be ½ or less of the width of the thin film superconducting wire.

  As the thin film superconducting wire, an RE wire can be used. The RE system is indicated by RE-Ba-Cu-O, and the RE is selected from La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, and Y. The thin film superconducting wire may be obtained by equally dividing a wire formed by IBAD or PLD with a laser or slitter.

  The second aspect of the present invention provides a stranded superconducting wire characterized in that a plurality of the above superconducting wires are twisted at a pitch of 100 mm or less.

  According to a third aspect of the present invention, there is provided a superconducting conductor formed by winding a plurality of stranded superconducting wires according to the second aspect in a spiral shape around a core wire so as not to overlap. .

  According to a fourth aspect of the present invention, there is provided a superconducting conductor characterized in that a plurality of superconducting wires according to the first aspect are wound around a core wire in a spiral shape so as not to overlap.

  According to a fifth aspect of the present invention, there is provided a superconducting conductor characterized in that a plurality of superconducting conductors according to the fourth aspect are wound around a core wire in a spiral shape so as not to overlap.

  According to the present invention, a superconducting wire and a superconducting conductor with reduced AC loss and improved mechanical properties without degrading superconducting properties are provided.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is a perspective view showing a superconducting wire according to an embodiment of the present invention. In FIG. 1, a superconducting wire 1 is spirally arranged around a core wire 2 having an outer diameter of 1.3 to 5 mm so that eight or more (eight in the figure) thin film superconducting wires 3 do not overlap each other. It is characterized by becoming. At this time, adjacent thin film superconducting wires are arranged in parallel with a gap.

  The material of the core 2 can be properly used in consideration of the mechanical characteristics of the superconducting wire. If electrical characteristics are mainly used, copper or copper alloy having good electrical conductivity can be used. If mechanical characteristics are important, stainless steel or copper alloy can be used.

  The outer diameter of the core wire 2 needs to be 1.3 to 5 mm. In order to make it possible to dispose eight or more thin-film superconducting wires 3 so as not to overlap with each other in terms of mechanical strength and around the core 2, the outer diameter of the core 2 is 1.3 mm. When it is necessary to perform the secondary processing of winding and twisting the wire, if the diameter is too large, the secondary processing becomes difficult.

As the thin-film superconducting wire, there are Y-based wires such as YBCO (YBa ₂ Cu ₃ O _7-d ) and Bi-based wires such as BSCO (BiSr ₂ Ca ₂ Cu ₃ O ₁₀ ). In the present invention, YBCO A Y-based wire such as (YBa ₂ Cu ₃ O _7-d ) can be preferably used.

  The thin-film superconducting wire is a superconducting wire having a predetermined width, for example, a Y-based wire having a width of 10 mm formed by IBAD (Ion Beam Assist Deposition), which is equally divided by a laser, a slitter or the like. The width of the divided thin line is preferably about 0.48 to 1.8 mm, for example, 0.48 mm.

  Regarding the width of the thin wire, the present inventors have examined the width of the thin wire and the critical current ratio (the divided critical current Ic and the divided current) for a Y-based wire having a width of 10 mm manufactured by IBAD or PLD (Ion Beam Deposition). Experiments on the relationship with the previous critical current Ico) were performed, and the results shown in FIG. 2 were obtained. That is, from the graph shown in FIG. 2, the critical current decreases due to the division, but even when the division is 20 and the width is 0.48 mm (the remaining 0.02 mm is lost during laser processing), the critical current ratio is 0. 97, confirming that there was no significant deterioration.

  The width of the thin wire is considered to depend greatly on the material of the Y-based wire and the manufacturing method, and will be explained from the relationship of the crystal grain size (crystal grain size). According to Goyal et al. Paper (Goyal, Physica C 426-431 (2005) 1083-1090), if there is not enough wire width for the grain size, if one of the grain sizes becomes defective, the critical current The possibility of decline increases.

The width of the thin line with a low possibility of reduction is 100 times the grain size.

  The grain size varies depending on the material of the Y-based wire and the manufacturing method, and is 0.1 to several μm in the IBAD-PLD method. If the grain size is several μm, several hundred μm, which is 100 times that, is an appropriate wire width, and the thin wire width of 0.48 mm by 20 divisions is considered to be a value close to the lower limit of the thin wire width that does not deteriorate so much. I can do it.

  The number of thin film superconducting wires 3 arranged around the core wire 2 is 8 or more, and if it is less than 8, the effect of reducing AC loss is insufficient.

  Eight or more thin film superconducting wires 3 are arranged along the periphery of the core wire 2 so as not to overlap each other, and are wound around a spiral. A protective material 4 is formed thereon. Furthermore, the protective material 4 may be coated.

  Protective material 4 is copper as a good conductor, or high resistance metal alloy such as stainless steel or hastelloy, and coating is a material that maintains its performance in liquid nitrogen such as enamel, formal, polyimide resin or Teflon (registered trademark) Can be used separately.

  Thus, by covering the superconducting wire with the protective material 4, a structure that is extremely resistant to changes in the external environment such as immersion in liquid nitrogen and contact with chemicals can be obtained.

  The smaller the gap between the thinned wires, the better. However, when winding around a spiral, a certain amount of gap is necessary. As a guide, it is desirable that the gap be ½ or less of the wire width.

  FIG. 3 is a graph showing the relationship between the number of wires wound around the core and the AC loss. From FIG. 3, it can be confirmed that the AC loss is drastically reduced up to seven, but when it is eight or more, the decrease also shows a slightly saturated tendency. Therefore, it is necessary to wind eight or more thin wires around the core wire. When the number of thinned wires is too large, the width of the thin wires becomes too small and the critical current decreases, so the preferred number of wires is 10 to 30. More preferably, it is 18-24.

  Compare AC loss of Y-based superconducting wire configured as described above with Bi wire (tape), Bi wire (wire), Y-based wire (tape), Y-stack (with Y-based wires stacked) If they do, they show low AC loss. In particular, it exhibits low characteristics in both current loss and magnetization loss in the AC loss, so it is useful for both high current / low magnetic field cables and high magnetic field magnets.

  The present inventors conducted a test showing this as follows.

  That is, first, a Y-based wire having a width of 10 mm produced by the IBAD method was divided into 20 by a laser. The width of the wire at this time is 0.48 mm.

  Ten Y-based wires thus obtained were wound around a core material having a diameter of 1.6 mmφ in a spiral to obtain a Y-based wire 1 having a cross-sectional shape shown in FIG. The spiral pitch was 300 mm, and the gap (gap) between the wires was 0.023 mm.

  Next, 18 Y-type wire rods having a width of 0.48 mm were similarly wound around a core material having a diameter of 2.9 mmφ in a spiral shape to obtain a Y-type wire 2 having a cross-sectional shape shown in FIG. It was. The spiral pitch was 300 mm, and the gap (gap) between the wires was 0.026 mm.

  When the relationship between the magnetic field angle and the AC loss was determined for these Y-based wires 1 and 2, the results shown in FIG. 5 were obtained. FIG. 5 also shows the relationship between the magnetic field angle and AC loss of the conventional BSCCO tape, BSCCO wire, YBCO stack, and YBCO strip shown in FIG.

  From the results shown in FIG. 5, it can be seen that the Y-system wire 1 has smaller AC loss at all magnetic field angles than the BSCCO tape, BSCCO wire, and YBCO stack. It can also be seen that the Y-system wire 2 has an AC loss that is 1/10 that of the BSCCO tape, BSCCO wire, YBCO stack, YBCO strip, and Y-system wire 1.

Next, the present inventors have a Y-based superconducting wire (a) having a width of 10 mm, a strip (b) obtained by dividing the Y-based superconducting wire (a) into 18 parts, and the Y-based wire 2 (above prepared) ( For c), a test was conducted to compare the conduction loss and the magnetization loss. In (b) and (c), the constituent materials are the same, but (c) is different in that it is wired. The result is shown in FIG.
From the results shown in FIG. 6, it can be seen that the critical current of superconductivity is reduced by 10% due to the thinning from (a) to (b). On the other hand, there was no decrease in critical current in the wiring from (b) to (c). In the graph of FIG. 6, in order to unify the difference between these critical currents, the horizontal axis is It / Ic (peak current It / critical current Ic), and the vertical axis AC loss is proportional to Ic ^ 2. Therefore, AC loss was divided by Ic ^ 2.

  FIG. 6 shows that the AC loss of (c) is the smallest. Compared with (a), the AC loss in (c) is reduced to 1/3 or less of (a). Moreover, since (a) and (b) are tape-shaped, there is a problem that they are vulnerable to twisting, bending and bending, and handling is bad, but (c) is wire-shaped, so handling is good.

  FIG. 7 is a graph showing the magnetization loss when a magnetic field perpendicular to the tape surface is applied. From the graph of FIG. 9, the Y-based wire 2 produced above has a lower magnetization loss than the 18 thin wires obtained by dividing the BSCCO tape, BSCCO wire, YBCO stack, YBCO strip, and YBCO into 18 pieces, and BSCCO with the lowest loss. Even if compared with a wire, it turns out that it is 1/10.

  Since the Y-based superconducting wire shown in FIG. 1 described above has a small diameter, various superconducting conductors as shown in FIGS. 8 to 13 can be produced by twisting or assembling a plurality of wires. Hereinafter, production examples thereof will be described.

  The example shown in FIG. 8 is a stranded superconducting wire 10 obtained by twisting three Y-based superconducting wires 1 shown in FIG. The example shown in FIG. 9 is a stranded superconducting wire 20 obtained by twisting two Y-based superconducting wires 1 shown in FIG. The example shown in FIG. 10 is a superconducting conductor 30 obtained by winding six Y-based superconducting wires 1 shown in FIG.

  As described above, the coupling loss caused by the parallel magnetic field in the longitudinal direction can be reduced by twisting or assembling a plurality of Y-based superconducting wires 1 shown in FIG.

  The example shown in FIG. 11 is a superconducting conductor obtained by winding six stranded superconducting wires 20 shown in FIG. 9 spirally around the core wire 22. The example shown in FIG. 12 is a superconducting conductor obtained by winding six stranded superconducting wires 10 shown in FIG. 8 spirally around the core wire 22. The example shown in FIG. 13 is a superconducting conductor obtained by spirally winding six superconducting conductors 30 shown in FIG. 10 around the core wire 22.

  As described above, by further assembling the stranded superconducting wires 10 and 20 and the superconducting conductor 30 shown in FIGS. 8, 9 and 10, a superconducting conductor having a large capacity and a small AC loss can be produced. The stranded superconducting wires 10 and 20 and the superconducting conductor 30 are all covered with a coating layer.

  Since the superconducting conductor manufactured in this way can easily form a gap between superconducting wires and has a high degree of freedom of movement, the mechanical strength against bending can be greatly increased.

  Usually, when producing a tape-shaped superconductor, as shown in FIG. 14A, a superconducting wire 32 is spirally wound around a core 31 as a former, and when the current capacity is small, As shown in 14 (b) and (14c), the superconducting wires 33 and 34 are further spirally wound to form a multilayer.

  In the case of a superconductor having a shape as shown in FIG. 14 (a), when the wire is bent, the wire is escaped only by the gap g between the superconducting wires. Furthermore, as shown in FIGS. 14B and 14C, in the case of a multilayer conductor, it is necessary to change the spiral pitch in order to equalize the current for each layer. When it is multi-layered, its spiral pitch changes greatly. When the spiral pitch is short, it is deteriorated during winding, and when the spiral pitch is long, deterioration is likely to occur when mechanical bending is performed. Therefore, a gap between superconducting wires is required to some extent.

  If the gap is sufficient, the deterioration is small even with 1 mR bending, but if it is 0.9 mR, 10% deterioration is observed. On the other hand, in the conductor shape shown in FIG. 12 and FIG. 13, the conductor shown in FIG. 12 that does not show deterioration even at 0.5 mR is taken as an example, and when the conductor is bent, the superconducting wire is directly strained. The conductor shown in FIG. 8 slides and absorbs the bending, and even when bent, the superconducting wire shown in FIG. 1 which is a further constituent material of the constituent conductor slides and absorbs the bending, thus exhibiting excellent bending characteristics. .

  Also, in terms of AC loss, the conductor shown in FIG. 12 was compared with the three-layer conductor shown in FIG. 14C. The magnitude of AC loss in the conductor shown in FIG. Very small, less than 10%.

The perspective view which shows the superconducting wire which concerns on one Embodiment of this invention. The characteristic view which shows the relationship between the width | variety of the divided | segmented thin wire | line, and a critical current ratio. The characteristic view which shows the relationship between the number which winds the thinned wire around a core wire, and alternating current loss. The figure which shows the Y type | system | group wires 1 and 2 obtained by winding 10 and 18 Y type | system | group wire rods around a core material spirally. The characteristic view which shows the relationship between the magnetic field angle about the Y-type wires 1 and 2, and an alternating current loss. The characteristic view which shows the loss of electricity supply about a Y type superconducting wire, a strip, and a Y type wire. The characteristic view which shows the magnetization loss when a perpendicular magnetic field is applied to a tape surface about Y type | system | group superconducting wire, a strip, and the Y type | system | group wire 2. FIG. The figure which shows the conductor obtained by twisting three Y-type superconducting wires shown in FIG. The figure which shows the conductor obtained by twisting two Y-type superconducting wires shown in FIG. The figure which shows the conductor obtained by winding 6 Y-type superconducting wires shown in FIG. 1 in the spiral shape around the core wire. The figure which shows the conductor obtained by winding the six conductors shown in FIG. 8 spirally around the core wire. The figure which shows the conductor obtained by winding six conductors shown in FIG. 9 spirally around the core wire. The figure which shows the conductor obtained by winding six conductors shown in FIG. 10 in the spiral shape around the core wire. The figure which shows the conductor formed by winding a superconducting wire spirally around the conventional core. The figure which shows the conventional tape-shaped BSCCO wire and tape-shaped YBCO wire. The figure which shows the format of the various wire materials of the conventional Bi type | system | group wire material and Y type | system | group wire. The figure which shows a superconducting cylinder. The figure which shows the wire rod thinned and the wire arrange | positioned in the quadrangle | tetragon in order to reduce alternating current loss.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Superconducting wire, 2, 12, 22 ... Core wire, 3 ... Thin film type | system | group superconducting wire, 10, 20 twisted-wire superconducting wire, 30 ... Superconducting conductor, 31 ... Core, 32, 33, 34 ... Superconducting wire.

Claims (10)

  A superconducting wire comprising eight or more thin film superconducting wires wound in a spiral shape around a core wire having an outer diameter of 1.3 to 5 mm so as not to overlap each other.   The superconducting wire according to claim 1, wherein a protective layer made of a good conductor or a high-resistance metal is provided around the periphery.   The superconducting wire according to claim 1 or 2, wherein a width of the thin film superconducting wire is 0.48 to 1.8 mm.   4. The superconducting wire according to claim 3, wherein a gap between adjacent thin film superconducting wires is ½ or less of a width of the thin film superconducting wire.   The superconducting wire according to claim 1, wherein the thin film superconducting wire is an RE wire.   The superconducting wire according to any one of claims 1 to 5, wherein the thin film superconducting wire is obtained by equally dividing a wire formed by IBAD or PLD with a laser or a slitter.   A stranded superconducting wire comprising a plurality of the superconducting wires according to any one of claims 1 to 6 twisted at a pitch of 100 mm or less.   A superconducting conductor formed by winding a plurality of stranded superconducting wires according to claim 7 in a spiral shape around a core wire so as not to overlap.   A superconducting conductor formed by winding a plurality of superconducting wires according to any one of claims 1 to 6 in a spiral shape around a core wire so as not to overlap.   A superconducting conductor formed by winding a plurality of superconducting conductors according to claim 9 in a spiral shape around a core wire so as not to overlap.

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