JPH1050153A - Oxide supreconductive wire for alternating current, and cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress reduction of the critical current and at the same time remarkably lessen the A.C loss by twisting superconductive filaments at a pitch which satisfies a specified expression. SOLUTION: Twisting of superconductive filaments is easily carried out by setting the superconductive filament pitches to be within a prescribed range and at the same time while the critical current decrease being suppressed, alternating current loss lessened. That is, superconductive filaments are twisted at a pitch Lp which satisfies a specified expression (in the expression ρ stands for specific resistance (Ω.m) of a metal matrix 2; df for the diameter (m) of a filament 1; db for the diameter (m) of superconductive filament group; Jc for critical current density (A/m<2> ) of the filament 1; Jcb for critical current density (A/m<2> ) of the superconductive filament group; μo for magnetic permeability (H/m) in vacuum; and dH/dt for altering speed (A/m/sec) of a magnetic field). Consequently, twisting can be carried out easily and while the critical current decrease being suppressed, alternating current loss can be lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconducting wire, and more particularly to an alternating current oxide superconducting wire having a large critical current and reduced alternating current loss, a method for producing the same, and an alternating current oxide superconducting wire cable. .

[0002]

2. Description of the Related Art In an oxide superconducting wire in which a number of superconducting filaments are embedded in a metal matrix, a method for reducing AC loss is to reduce the diameter of each superconducting filament and to increase the specific resistance of the metal matrix. Besides, it is known to reduce the pitch of the twist applied to each superconducting filament.

Here, the relationship between the magnitude of the twist pitch and the AC loss will be described. FIG. 10 is a diagram illustrating the coupling current. In FIG. 10, reference numeral 1 denotes a superconducting filament, and 2 denotes a metal matrix.

[0004] When a magnetic field is applied to the superconductor, a shielding current flows in a loop to prevent the magnetic flux from entering the inside. The purpose of multifilamentation is to make it easier for magnetic flux to penetrate into the interior, and to increase the stability by allowing the shielding current to circulate through individual superconducting filaments. Immediately after that, as shown by an arrow in FIG.
A shielding current may flow through the portion. This shielding current is
Although the attenuation will eventually occur due to the resistance of the metal matrix 2, if the wire is long, the inductance of the shielding current loop increases, and it takes time to attenuate the shielding current. This state is called electromagnetic coupling, and when in this coupled state, it behaves like an integrated superconductor, and the effect of multicore is lost.

In order to reduce the electromagnetic coupling, it is effective to twist the superconducting filament 1. When the twist is applied, as shown in FIG. 10B, the shielding current returns in a region of の of the twist pitch, and the inductance of the shielding current loop decreases.
The decay of the shielding current is hastened. If the decay rate becomes shorter than the fluctuation period of the magnetic field, the above-described coupling state is prevented. The critical length L _c at which the attenuation of the shielding current is shorter than the fluctuation period of the magnetic field depends on the specific resistance ρ of the metal matrix 2, the diameter d _f of the superconducting filament 1, the critical current density J _c , and the rate of change dH / dt of the external magnetic field. Determined and represented by the following equation:

[0006] _{L c = 2 {(2ρ ·} d f · J c) / (μ o
· DH / dt)} ^1/2 That is, by applying the twist in 2 times or less than the pitch of the critical length L _c to the superconducting filaments 1, thereby preventing the coupling current flows, to reduce the AC loss Can be.

[0007]

[SUMMARY OF THE INVENTION However, in the oxide superconducting wire, subjected to a twist in the superconducting filaments 1 at 2 times or less than the pitch of the critical length L _c, there is a problem that it is very difficult. For example, an oxide superconducting multi-core tape wire (a tape thickness of 0.25 mm and a tape width of 3 mm) using silver as a metal matrix 2 having a specific resistance of 2.5 × 10 ⁻⁹ Ω · m, which is a general oxide superconducting wire. , Superconducting filament thickness 15 μm, critical current density J _c = 10 ⁴ A
/ Cm ² ), change rate μ _o · dH / dt = 1.2 T /
When an alternating magnetic field of sec is applied in a direction perpendicular to the longitudinal direction of the wire and in a direction parallel to the wide surface of the wire, the critical length _Lc is 5 mm, and the twist pitch is twice that of 10 mm or less. There is a need to. Moreover, in an actual high-current AC cable, an AC coil that generates a high magnetic field, or the like, the severer magnetic field condition is satisfied, so that the critical length _Lc is further reduced.

However, the oxide superconducting wire of practical size, in 2 times or less the pitch of such a short critical length L _c, it is extremely difficult to apply a twist. Therefore, in the conventional oxide superconducting wire, if not be twisted twice or less the pitch of L _c, since AC loss by electromagnetic coupling of the superconducting filaments 1 increases, AC loss reduction effect by twisting can not be expected Was considered.

On the other hand, there is an alternating current oxide superconducting cable in which a plurality of alternating current oxide superconducting wires are wound around a central member over a plurality of layers. In such an AC oxide superconducting cable for AC, when the impedance (sum of resistance and inductance) of each layer is different, the AC current flows more in a layer with a smaller impedance, so that a drift occurs, which causes an abnormal increase in AC loss. There are various methods for adjusting and adjusting only the inductance component of each layer in order to equalize the impedance of each layer, but a practical method for equalizing the resistance component of each layer has not been known so far.

Here, consider the case where the inductance of each layer is made uniform, whereby the ratio of the conduction current to the critical current of each wire is made equal, and the conduction current density of each layer is made equal. Since the outer layer has a stronger self-magnetic field and a larger AC loss (resistance component) due to magnetization, the impedance increases even if the inductance components are equal. Therefore, a large amount of current flows through the wire disposed in the inner layer having a relatively low impedance, and the AC loss in the inner layer increases. Then, a large amount of current will flow through the wire disposed in the outer layer where the impedance becomes relatively small, and the drift phenomenon will continue.
This will cause an abnormal increase in the AC loss of the entire cable.

The present invention has been made under the above circumstances, and has as its object to provide an oxide superconducting wire for AC in which a decrease in critical current is suppressed and an AC loss is greatly reduced.

Another object of the present invention is to provide a method for manufacturing an oxide superconducting wire for AC in which a reduction in critical current is suppressed and an AC loss is significantly reduced.
Yet another object of the present invention is to provide an oxide superconducting cable for AC in which a decrease in critical current is suppressed and an AC loss is significantly reduced.

[0013]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies and as a result, the twist can be easily performed by setting the superconducting filament twist pitch within a predetermined range. At the same time, they have found that it is possible to reduce the AC loss while suppressing the decrease in the critical current. The present invention is based on such findings.

That is, the present invention (claim 1) provides an AC oxide superconducting round wire comprising a metal matrix and a plurality of superconducting filaments embedded in the metal matrix. provides AC oxide superconducting wire, characterized in that subjected to twist twist pitch L _p satisfying the following equation.

[0015] _{2L c1 <L p ≦ 2L c2} L c1 = 2 {(2ρ · d f · J c) / (μ o · dH / d
_{^{t)} 1/2 L c2 = 2}} {(2ρ · d b · J cb) / (μ o · dH / d
t)｝ ^1/2 (where ρ is the specific resistance of the metal matrix (Ω · m), d _f
The diameter of the superconductive filaments (m), diameter d _b superconducting filament group (m), J _c is the critical current density of the superconducting filaments ^{(A / m 2), J} cb superconducting filament group of the critical current density (A / m ² ) and μ _o are the magnetic permeability of vacuum (H /
m) and dH / dt are the changing speed of the magnetic field (A / m / se).
c)) The present invention (Claim 2) provides an AC oxide superconducting tape wire comprising a metal matrix and a plurality of superconducting filaments embedded in the metal matrix, wherein the superconducting filament is provides AC oxide superconducting wire, characterized in that subjected to twist twist pitch L _p satisfying the following equation.

2L _c1 <L _p ≦ 2L _c2 L _c1 = 2 ｛(2ρ · d _ft · J _c ) / (μ _o · dH / d
t)｝ ^1/2 L _c2 = 2 ｛(2ρ · d _bt · J _cb ) / (μ _o · dH / d
t)｝ ^1/2 (where ρ is the specific resistance (Ω · m) of the metal matrix, d _ft
Thickness (m) of superconducting filaments, d _bt is the thickness of the superconducting filament group (m), J _c is the critical current density (A / m ²⁾ of the superconducting filaments, J _cb is the critical current density of the superconductor filament group ( A / m ² ), μ _o is the permeability of vacuum (H / m), dH / dt is the rate of change of the magnetic field (A / m / s)
ec)) Further, the present invention (Claim 3) further comprises a plurality of rod-shaped bodies made of a compressed powder of an oxide superconductor or a precursor thereof.
Arranging in a matrix metal and performing wire drawing,
A step of performing a heat treatment on the composite wire that has been subjected to the wire drawing, and a step of performing a twist processing on the composite wire that has been subjected to the heat treatment,
Providing a method for producing an oxide superconducting wire for alternating current (Claim 1 or 2), comprising a step of repeatedly performing wire drawing or rolling and heat treatment on the twisted composite wire. I do. Here, the precursor refers to a material that can become an oxide superconductor by post-treatment.

Furthermore, the present invention (Claim 4) provides an AC superconducting wire comprising a plurality of alternating current superconducting wires (Claim 1 or Claim 2) arranged over a plurality of layers around a central member. an oxide superconducting cable, provides the L _p and AC oxide superconducting cable, characterized in that toward the outer set closer to the 2L _c1, and was set close to the 2L _c2 toward the inner layer I do.

The feature of the oxide superconducting wire for AC of the present invention is that the twist pitch L _p of the superconducting filament is expressed by the following equation (2).
Although L _c1 <L _p ≦ 2L _c2 is satisfied,
2L as possible at a pitch that the critical current does not decrease
It is desirable to set it close to _c1 .

If L _p is 2L _c1 or less, it becomes extremely difficult to perform twisting, and the critical current tends to decrease. On the other hand, if it exceeds _2Lc2 , the effect of the present invention of reducing AC loss cannot be obtained.

The type of oxide superconductor that can be used for the AC oxide superconducting wire of the present invention is not particularly limited, but preferred examples thereof include bismuth-based, yttrium-based, and thallium-based superconductors having a high critical temperature. Can be mentioned.

The metal matrix that can be used in the alternating current oxide superconducting wire of the present invention is silver or Ag—
Silver alloys such as Au, Ag-Cu, and Ag-Mg can be used.

Further, as the center member usable in the oxide superconducting cable for AC of the present invention, a flexible hollow member made of stainless steel or aluminum can be used.

In the oxide superconducting cable for AC of the present invention, it is preferable that an insulating material is interposed between the layers in order to make the current density of each layer uniform. Films and the like can be mentioned.

According to the alternating current oxide superconducting wire of the present invention configured as described above, the twist pitch of the superconducting filament of the oxide superconducting wire is within a predetermined range, so that the twist can be easily applied. Further, it is possible to reduce the AC loss while suppressing the decrease in the critical current.

Further, according to the method for producing an oxide superconducting wire for AC of the present invention, since the heat treatment is performed before the twisting is performed, the criticality when a small pitch twist is applied to the oxide superconducting wire is performed. It is possible to suppress a decrease in current.

Further, according to the oxide superconducting cable for AC of the present invention, the oxide superconducting wire for alternating current whose twist pitch is selected so that the AC loss of the wire of each layer becomes equal during the rated energization of the cable is used. In addition, it is possible to suppress the current flowing in each layer from drifting, and to prevent an abnormal increase in AC loss.

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing an oxide superconducting round wire according to an embodiment of the present invention.
FIG. 1A shows a cross-sectional structure, and FIG. 1B shows a twisted state of one superconducting filament in the oxide superconducting round wire.

In FIG. 1, the superconducting filament 1 is
An oxide superconductor is formed by embedding a plurality of oxide superconductors in a metal matrix 2 made of silver or the like. Each superconducting filaments 1 are embedded in the metal matrix 2 is twisted is performed at a predetermined pitch L _p. Critical length L _c of the oxide superconducting round wire is given by the following equation.

[0029] _{L c = 2 {(2ρ ·} d f · J c) / (μ o
DH / dt)｝ ^1/2 On the other hand, in such a superconducting wire, the matrix ratio (the volume of the superconducting filament is 1
It is known that the smaller the volume ratio of the metal matrix, the larger the critical current, and the smaller the filament diameter, the smaller the AC loss. Therefore, when the filament diameter is reduced while the matrix ratio is reduced, and the number of superconducting filaments is increased accordingly, the interval between the superconducting filaments is reduced. When such a wire is subjected to wire drawing or heat treatment, the superconducting filaments are deformed, and the superconducting filaments partially approach each other or come into contact with each other.
This creates a electromagnetically portion filament otherwise the easy part bound in an external magnetic field, the diameter of the superconducting filaments is substantially greater than the equivalent filament diameter d _eff the actual filament diameter d _f And the equivalent critical current density J _ceff becomes the filament J
_This is equivalent to being smaller than _c . As a result, the equivalent critical length L _ceff increases, and becomes as shown in the following equation: L _ceff = 2 ｛(2ρd _eff · J _ceff ) / (μ _o · d
H / dt)} ^1/2 equivalent filament diameter d _eff is a value between the diameter d _b of the actual filament diameter d _f and the superconducting filament group of the superconducting filaments 1. J _ceff is a value between J _c and J _cb . Therefore, the equivalent critical length L
_ceff is a value between the following L _c1 and L _c2 .

[0030] _{L c1 = 2 {(2ρ ·} d f · J c) / (μ o
^{· DH / dt)} 1/2 L} c2 = 2 {(2ρ · d b · J cb) / (μ o · dH / d
t)} ^1/2 However, the diameter of d _b superconducting filament group (m), J _cb
Is the critical current density (A / m ² ) of the superconducting filament group.

As shown in the above equation, L _c1 and L _c2 are
It is determined in consideration of the change speed of the magnetic field in which the wire is used. Incidentally, the diameter d _f of the superconducting filaments 1,
Although it may be measured, it is also given by the following equation.

D _f = d / {(1 + λ) N} ^1/2 (where d is the outer diameter (m) of the wire, λ is the matrix ratio, N
Indicates the number of superconducting filaments 1. ) The critical current density J _c is given by the following equation.

The _{J c = I c (1 +} λ) / (πd 2/4) ( in the formula, I _c is the critical current of the wire (A).) And also the critical current density J _cb of the superconducting filament group
Is given by the following equation:

[0034] _{J cb = I c / (πd} b 2/4) FIG. 2 is a diagram showing the oxide superconducting tape wire according to another embodiment of the present invention. In such oxide superconducting tape, the twisted pitch L _p is applied to the superconducting filaments 1. In this case, instead of the diameter d _f of the superconducting filaments 1, using the thickness d _ft of the superconducting filaments 1 which faces the magnetic field applied to the wire. Further, instead of the diameter of the superconducting filament group d _b, using the thickness d _bt superconducting filament group facing the magnetic field applied to the wire.

Then, the thickness d of the superconducting filament
_{Since ft} varies in each superconducting filament 1 in the wire because the tape wire is formed by rolling or drawing a round wire, an average value is obtained using an equation.

In the present invention, the thickness of the wire superconducting filament and the group of superconducting filaments is defined as a plane including the direction of the twist pitch (the direction of the critical length, the direction of the length of the wire) and the direction of the fluctuating magnetic field applied during use. Means a dimension measured in a direction orthogonal to the direction (see FIGS. 1, 2, 7 to 9).

The thickness d _ft of the superconducting filament 1 is given by the following equation. d _ft = t / {(1 + λ) N} ^1/2 (where t is the thickness (m) of the wire). The critical current density J _c is given by the following equation.

J _c = I _c (1 + λ) / tw (where w is the width (m) of the wire) Further, the critical current density J _cb of the superconducting filament group is given by the following equation.

J _cb = I _c / d _bt d _bw (where d _bt and d _bw are the thickness and width of the superconducting filament group, respectively) The diameter and thickness of the superconducting filament group are as follows: Can be obtained as follows.

(1) Measure the cross section of the wire rod. The distance between one of the superconducting filaments and the outside of the superconducting filament at a position to be rotated by 180 ° is defined as the diameter and thickness of the group (see FIGS. 1A and 2A).

As the thickness of the superconducting filament group, a value actually measured at the thickest part in a cross section orthogonal to the length direction of the wire is used. The reason for this is that the thick portion has the largest amount of magnetic flux intersecting, and the AC loss of the wire has the greatest effect on this portion.

(2) Calculate by calculation. Here, a round wire is described as an example. The outer diameter of the tube (D) used last in producing the oxide superconducting wire for AC
_0), is calculated by multiplying the value obtained by dividing the outer diameter D _i of the collection of wires which are housed therein, the outer diameter d of the final wire. _{d b = d × D i /} D 0 In place of the outer diameter D _i of the collection of paid was wires, can be estimated using the inner diameter (diameter) of the tube used in the end.

[0043]

【Example】

Example 1 A compressed mixed powder of an oxide superconductor prepared to have a composition of (Bi + Pb): Sr: Ca: Cu = 2: 2: 2: 3 was formed into a rod having an outer diameter of 10 mm, and an inner diameter of 10.5 mm. Outer diameter 15
The composite was obtained by inserting it into a silver tube of mm. This composite was processed into a hexagonal wire having an opposite dimension of 2.0 mm by a wire drawing machine.
19 hexagonal wires were inserted into a silver tube having an inner diameter of 11 mm and an outer diameter of 15 mm, and were drawn to a wire diameter of 1.5 mm.

Next, after a heat treatment at 300 ° C. × 1 hour, twist processing was performed at a pitch of 3 mm to 90 mm. Thereafter, rolling or drawing and heat treatment are repeated, and a tape wire having a thickness of 0.24 mm and a width of 3.3 mm and an outer diameter of 1 m
m round wire rod. At this time, the filament thickness of the tape wire was 26 μm, and the filament diameter of the round wire was 110 μm. The silver ratio was 3.5, and the final twist pitch was 7 mm to 200 mm.

Example 2 A plurality of oxide superconducting tape wires 3 produced by the procedure shown in Example 1 were wound around a central member over a plurality of layers to produce an oxide superconducting cable for AC. That is, as shown in FIG. 3, the oxide superconducting tape 3 is wound around a central member 4 having an outer diameter of 30 mmφ with a 0.35 mm-thick insulating material 5 interposed between the layers, and spirally wound into five layers. Diameter 35.
An oxide superconducting cable of 2 mmφ was manufactured.

In this oxide superconducting cable, 29, 30, 3 from the first innermost layer to the fifth outermost layer, in that order.
1, 32 and 33 oxide superconducting tapes 3 were arranged, and a total of 155 tape wires 3 were used. When the critical current of the cable is estimated by the number of times the critical current of the tape wire, it becomes 2325A. The rated alternating current (50 Hz) of the cable was set to a peak value of 1000 A, and the magnetic field calculation at the time of the rated current was performed when the current flowing through each strand was the same (when the current density of each layer was the same). L _c1 and L _c2 for each tape were determined from the average magnetic field change rate applied to the oxide superconducting tape 3 of each layer thus determined.

The electromagnetic coupling of the superconducting filaments of the tape wire of each layer is adjusted, and the twist pitch of the tape of each layer is adjusted to one of the innermost layers so that their AC losses are equal.
44mm, 23m in order from the layer to the outermost fifth layer
m, 16 mm, 12 mm, and 9 mm. These twist pitches are set so that the outer layer is closer to 2L _c1 and the inner layer is closer to 2L _c2 .

Conventional Example A compressed mixed powder of an oxide superconductor prepared to have a composition of (Bi + Pb): Sr: Ca: Cu = 2: 2: 2: 3 was formed into a rod shape having an outer diameter of 10 mm and an inner diameter of 10 mm. 0.5mm, outer diameter 1
It was inserted into a 5 mm silver tube to obtain a composite. This composite was processed into a hexagonal wire having an opposite dimension of 2.0 mm by a wire drawing machine. 19 hexagonal wires, 11 mm inside diameter, 15 m outside diameter
m, and the wire was drawn to a wire diameter of 1.5 mm.

Thereafter, rolling or drawing and heat treatment are repeated to form a tape wire having a thickness of 0.24 mm and a width of 3.3 mm;
It was processed into a round wire having an outer diameter of 1 mm. At this time, the filament thickness of the tape wire was 26 μm, the filament diameter of the round wire was 110 μm, and the silver ratio was 3.5.

Comparative Example (Bi + Pb): A compressed mixed powder of an oxide superconductor prepared to have a composition of Sr: Ca: Cu = 2: 2: 2: 3 was formed into a rod shape having an outer diameter of 10 mm and an inner diameter of 10 mm. 0.5mm, outer diameter 1
It was inserted into a 5 mm silver tube to obtain a composite. This composite was processed into a hexagonal wire having an opposite dimension of 2.0 mm by a wire drawing machine. 19 hexagonal wires, 11 mm inside diameter, 15 m outside diameter
m, and the wire was drawn to a wire diameter of 1.5 mm. Next, twist processing was performed at a pitch of 3 mm to 90 mm without heat treatment.

Thereafter, rolling or drawing and heat treatment are repeated to form a tape wire having a thickness of 0.24 mm and a width of 3.3 mm.
It was processed into a round wire having an outer diameter of 1 mm. At this time, the filament thickness of the tape wire was 26 μm, and the filament diameter of the round wire was 110 μm. The silver ratio was 3.5, and the final twist pitch was 7 mm to 200 mm.

The AC loss of the manufactured wire was measured by using a magnetization method. The measurement conditions were as follows: the magnetic field amplitude was fixed at 30 mT,
By changing the frequency, the magnetic field change rate μ _o · dH
/ Dt was changed. The sample was a bundle of 75 wires each having a length of 40 mm. The wires were insulated from each other, and the ends of the sample were polished so that the superconducting filaments did not contact each other. The fluctuating magnetic field was applied perpendicular to the longitudinal direction of the wire, and was applied parallel to the wide surface of the tape wire. On the other hand, the critical current (self-magnetic field, 77K) was measured by a four-terminal method. The critical current is 1 μV / c between the voltage taps.
The current value when a voltage of m was generated was defined.

FIG. 4 shows the twist pitch dependence of the AC loss of the tape wire of the embodiment, normalized by the AC loss of the conventional example. 4, dotted line A is μ _o · dH / dt = 1
2L _{c1 at} T / s, dotted line B indicates μ _o · dH / dt = 1
2L _{c2 at} T / s, solid line C indicates μ _o · dH / dt =
2L _{c1 at} 0.1 T / s, solid line D is μ _o · dH / d
2L _c2 at t = 0.1 T / s is shown.

Incidentally, 2L _c1 and 2L _c2 were obtained based on the calculation results of the following parameters of the tape wire. _{J c = 15 × {1 /} (0.24 × 3.3 × 10 -6)} × (1 + 3.5) = 85.2 × 10 6 [A / m 2] d f = 26 × 10 -6 [ m] λ _b = (15 ² −10 ² ) / 10 ² = 1.148 J _cb = 15 × {1 / (0.24 × 3.3 × 10 ⁻⁶ )} × (1 + 1.148) = 40.7 × 10 ⁶ [A / m ² ] ρ = 2.5 × 10 ^-9 (Ω · m) (Specific resistance of silver at 77K) d _f = t / {(1 + λ) N} ^1/2 = 0 .24 × 10 ⁻³ /{(1+3.5)×19} ^1/2 = 2.6 × 10 ⁻⁵ m = 26 μm where λ _b is the area of the matrix portion when the area of the filament group is 1. Is shown.

[0055] By substituting these parameters into the following equation can be obtained critical length L _{c. L c = 2 {(2ρ ·} d f · J c) / (μ o · dH / d
t)｝ ^1/2 (1) 2L _{c1 at} μ _o · dH / dt = 1 T / s is
In FIG. 4, it is indicated by a dotted line A.

(2) 2L _{c2 at} μ _o · dH / dt = 1 T / s is shown by a dotted line B in FIG. (3) 2L _{c1 at} μ _o · dH / dt = 0.1 T / s
Is indicated by a solid line C in FIG.

(4) 2L _{c2 at} μ _o · dH / dt = 0.1 T / s is shown by a solid line D in FIG. As is clear from FIG. 4, even when μ _o · dH / dt = 1 T / s, μ _o · d
Even when H / dt = 0.1 T / s, 2L _c1 <L _p <2L
_The AC loss decreases as the twist pitch decreases in the region of _c2 . Also, the magnetic field change rate μ _o · dH / d
As t increases, L _c1 and L _c2 shift to a smaller side, so that the electromagnetic coupling of the filament becomes remarkable,
It can be seen that the AC loss has increased. Thus, L _c1
Even if the twist pitch is larger than twice as large as _Lc2 ,
If the pitch is twice or less, an increase in AC loss due to electromagnetic coupling of the filaments can be suppressed.

The above-described low-frequency effect of the AC loss was also confirmed in a round wire. Next, FIG. 5 shows the dependence of the critical current on the twist pitch in the example and the comparative example, normalized by the critical current when no twist is applied. In addition, the critical current in the state without twist is 15 A for the tape wire of the example, and 5 A for the round wire of the example.
The critical currents of the tape wire and the round wire of the comparative example were almost the same.

As is clear from FIG. 5, in the tape wire of the embodiment, even when the twist pitch becomes small, the critical current hardly decreases and is almost constant. In contrast, in the tape wire of the comparative example, the pitch was about 20
In the region of not more than mm, the critical current decreases as the twist pitch decreases. Similarly, the critical current of the round wire in the embodiment hardly decreases even when the twist pitch is small. On the contrary,
In the round wire of the comparative example, the critical current was reduced when the pitch was about 15 mm or less. From this, it is understood that the appropriate heat treatment before the twisting process improves the twisting processability and suppresses the decrease in the critical current due to the twist of the wire.

The temperature and the time of the heat treatment before the twisting are 300 ° C. and 1 hour, respectively, in the above embodiment, but are not necessarily limited thereto.
It is desirable to appropriately set the optimal temperature and time within a range of 00 ° C. to 400 ° C. and a heating time of 3 hours or less.

On the other hand, the AC loss of the oxide superconducting cable shown in Example 2 at rated current (1000 A) was measured by a four-terminal method using a lock-in amplifier. The measured value of the AC loss of the cable almost coincided with the value obtained by multiplying the calculated value of the conduction loss and the magnetization loss in the strand by the number of the used strands. It is considered that this is because the AC loss in each layer was substantially equal, and the drift in each layer was suppressed, so that an abnormal increase in AC loss did not occur.

Embodiment 3 FIGS. 6 to 9 show various examples of a cable in which a plurality of strands are wound around a central member over a plurality of layers via an insulating material. 6A to 9, (a) is a perspective view, (b) is a cross-sectional view, and (c) and (d) are perspective views showing one wire taken out. FIG. 6 shows an example using a round wire, and FIGS. 7 to 9 show examples using a tape wire. In the drawing, B indicates an external magnetic field (the direction of a fluctuating magnetic field), and i indicates a current.

FIG. 6 is a cable in which a plurality of round rods are wound over a plurality of layers around a cylindrical central member, and FIG.
A cable wound around a plurality of layers such that a plurality of tape wires are wound on a cylindrical center member, and a wide surface of the tape is in contact with the center member. FIG. 8 shows a plurality of tape wires wound on a cylindrical center member. FIG. 9 shows a cable in which a plurality of tape wires are arranged over a plurality of layers around a flat central member so that the narrow surface of the tape is in contact with the center member. Are respectively shown. 9C shows one tape wire disposed on the upper and lower surfaces of the central member, and FIG. 9D shows one tape wire disposed on the side of the central member.

[0064]

As described above, according to the oxide superconducting wire for AC of the present invention, the twist pitch of the superconducting filament of the oxide superconducting wire is within a predetermined range, so that the twist can be easily applied. At the same time, it is possible to reduce the AC loss while suppressing the decrease in the critical current.

Further, according to the method for producing an oxide superconducting wire for alternating current of the present invention, the critical current when a small pitch twist is applied to the oxide superconducting wire by performing the heat treatment before the twisting is performed. Can be suppressed.

Further, according to the oxide superconducting cable for AC of the present invention, the oxide superconducting wire for alternating current whose twist pitch is selected so that the AC loss of the wire of each layer becomes equal at the time of rated energization of the cable is used. In addition, it is possible to suppress the current flowing in each layer from drifting, and to prevent an abnormal increase in AC loss.

[Brief description of the drawings]

FIG. 1 is a view showing an oxide superconducting round wire according to an embodiment of the present invention.

FIG. 2 is a view showing an oxide superconducting tape wire according to another embodiment of the present invention.

FIG. 3 is a view showing an oxide superconducting cable according to still another embodiment of the present invention.

FIG. 4 is a characteristic diagram showing a change in AC loss with respect to a twist pitch.

FIG. 5 is a characteristic diagram showing a change in a critical current with respect to a twist pitch.

FIG. 6 is a view showing an example of the oxide superconducting cable of the present invention.

FIG. 7 is a diagram showing an example of the oxide superconducting cable of the present invention.

FIG. 8 is a diagram showing an example of the oxide superconducting cable of the present invention.

FIG. 9 is a diagram showing an example of the oxide superconducting cable of the present invention.

FIG. 10 is a diagram illustrating a coupling current of an oxide superconducting wire.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Superconducting filament 2 ... Metal matrix 3 ... Superconducting tape wire 4 ... Central member 5 ... Insulating material

Continued on the front page (72) Inventor Masanao Mimura 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd. (72) Inventor Hideo Ishii 4-1 Egasakicho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Tokyo Electric Power Co., Inc. (72) Inventor Shoichi Honjo 4-1 Egasaki-cho, Tsurumi-ku, Yokohama, Kanagawa Prefecture Tokyo Electric Power Co., Inc. (72) Inventor Yoshihiro Iwata Tsurumi-ku, Yokohama, Kanagawa 4-1 Egasakicho Tokyo Electric Power Company

Claims (4)

[Claims] An alternating current oxide superconducting round wire comprising a metal matrix and a plurality of superconducting filaments embedded in the metal matrix, wherein the superconducting filament has a twist pitch L _p satisfying the following formula: An oxide superconducting wire for alternating current, characterized in that it has been twisted. _{2L c1 <L p ≦ 2L c2} L c1 = 2 {(2ρ · d f · J c) / (μ o · dH / d
_{^{t)} 1/2 L c2 = 2}} {(2ρ · d b · J cb) / (μ o · dH / d
t)｝ ^1/2 (where ρ is the specific resistance of the metal matrix (Ω · m), d _f
The diameter of the superconductive filaments (m), diameter d _b superconducting filament group (m), J _c is the critical current density of the superconducting filaments ^{(A / m 2), J} cb superconducting filament group of the critical current density (A / m ² ) and μ _o are the magnetic permeability of vacuum (H /
m) and dH / dt are the changing speed of the magnetic field (A / m / se).
c)) 2. An alternating current oxide superconducting tape wire comprising a metal matrix and a plurality of superconducting filaments embedded in the metal matrix, wherein the superconducting filament has a twist pitch L _p satisfying the following formula: An oxide superconducting wire for alternating current, characterized in that it has been twisted. 2L _c1 <L _p ≦ 2L _c2 L _c1 = 2 ｛(2ρ · d _ft · J _c ) / (μ _o · dH / d
t)｝ ^1/2 L _c2 = 2 ｛(2ρ · d _bt · J _cb ) / (μ _o · dH / d
t)｝ ^1/2 (where ρ is the specific resistance (Ω · m) of the metal matrix, d _ft
Thickness (m) of superconducting filaments, d _bt is the thickness of the superconducting filament group (m), J _c is the critical current density (A / m ²⁾ of the superconducting filaments, J _cb is the critical current density of the superconductor filament group ( A / m ² ), μ _o is the permeability of vacuum (H / m), dH / dt is the rate of change of the magnetic field (A / m / s)
ec)) 3. A step of arranging a plurality of rods made of a compressed powder of an oxide superconductor or a precursor thereof in a matrix metal and performing wire drawing; A step of performing a heat treatment on the wire, a step of performing a twist process on the composite wire that has been subjected to the heat treatment, and a step of repeatedly performing a wire drawing or rolling process and a heat treatment on the composite wire that has been subjected to the twist processing. 2. The method of claim 1, wherein
Or the method for producing an alternating current oxide superconducting wire according to 2. 4. The method according to claim 1, wherein a plurality of the members are provided around the center member.
Or AC oxide superconducting wire according to claim 2, a AC oxide superconducting cable formed by arranging for a plurality of layers, the L _p, set close to the 2L _c1 toward the outer layer, and 2. An oxide superconducting cable for alternating current, characterized in that it is set closer to _2Lc2 as it goes to the inner layer.