JP3933253B2 - Oxide superconducting wire and cable for AC - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oxide superconducting wire, and more particularly to an oxide superconducting wire for alternating current having a large critical current and reduced alternating current loss, a method for manufacturing the same, and an oxide superconducting wire cable for alternating current.
[0002]
[Prior art]
In oxide superconducting wires with a large number of superconducting filaments embedded in a metal matrix, AC loss can be reduced by reducing the diameter of each superconducting filament and increasing the specific resistance of the metal matrix. It is known to reduce the pitch of the twist applied to each superconducting filament.
[0003]
Here, the relationship between the magnitude of the twist pitch and the AC loss will be described.
FIG. 10 is a diagram for explaining 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, the shielding current flows in a loop shape, preventing the magnetic flux from entering the inside. The purpose of increasing the number of cores is to facilitate the penetration of magnetic flux into the interior and improve the stability by allowing the shield current to flow back through the individual superconducting filaments. Immediately after that, as indicated by an arrow in FIG. 10A, a shielding current can flow through the portion of the metal matrix 2 between the superconducting filaments 1 and 1. This shielding current will eventually be attenuated by the resistance of the metal matrix 2. However, if the wire becomes long, the inductance of the shielding current loop increases, and it takes time to attenuate the shielding current. This state is called electromagnetic coupling. When in this coupled state, it behaves like an integrated superconductor and the effect of multi-core is lost.
[0005]
In order to reduce this electromagnetic coupling, it is effective to twist the superconducting filament 1. When the twist is applied, as shown in FIG. 10 (b), the shield current is circulated in a region of ½ of the twist pitch, the shield current loop inductance is reduced, and the decay of the shield current is accelerated. . And if the decay rate becomes shorter than the fluctuation period of the magnetic field, the above-mentioned coupled state is prevented. Critical length L at which the decay of the shield current is shorter than the fluctuation period of the magnetic field_c Is the specific resistance ρ of the metal matrix 2 and the diameter d of the superconducting filament 1_f , Critical current density J_c , Determined by the change rate dH / dt of the external magnetic field, and is expressed by the following equation.
[0006]
L_c = 2 {(2ρ · d_f ・ J_c ) / (Μ_o DH / dt)}^1/2
That is, this critical length L_c By twisting the superconducting filament 1 at a pitch of 2 times or less of this, it is possible to prevent the coupling current from flowing and reduce the AC loss.
[0007]
[Problems to be solved by the invention]
However, in the oxide superconducting wire, the critical length L_c There is a problem that it is very difficult to twist the superconducting filament 1 with a pitch of 2 times or less. For example, the specific resistance is 2.5 × 10 which is a general oxide superconducting wire.^-9Oxide superconducting multi-core tape wire with Ω · m silver as metal matrix 2 (tape thickness 0.25mm, tape width 3mm, superconducting filament thickness 15μm, critical current density J_c = 10^Four A / cm² ), Change rate μ_o When an alternating magnetic field of dH / dt = 1.2 T / sec is applied in a direction perpendicular to the longitudinal direction of the wire and parallel to the wide surface of the wire, the critical length L_c Is 5 mm, and the twist pitch needs to be 10 mm or less, which is twice that of the twist pitch. Moreover, in an actual high-current AC cable or an AC coil generating a high magnetic field, the critical length L_c Becomes even smaller.
[0008]
However, such a critical length L can be reduced to a practical size oxide superconducting wire._c It is extremely difficult to twist with a pitch of 2 times or less. Therefore, in the conventional oxide superconducting wire, L_c When twist processing cannot be performed at a pitch of 2 times or less, the AC loss increases due to the electromagnetic coupling of the superconducting filament 1, and therefore it was considered that the effect of reducing the AC loss due to the twist cannot be expected.
[0009]
On the other hand, there is an AC oxide superconducting cable in which a plurality of AC oxide superconducting wires are wound around a central member over a plurality of layers. In such an oxide superconducting cable for alternating current, when the impedance (sum of resistance and inductance) of each layer is different, a larger amount of alternating current flows in the layer with lower impedance, resulting in drift and an abnormal increase in alternating current loss. In order to align the impedance of each layer, there are various methods for adjusting and aligning only the inductance component of each layer, but no practical method for aligning the resistance component of each layer has been known so far.
[0010]
Here, the case where the inductance of each layer is made uniform, the ratio of the energization current to the critical current of each wire is made equal, and the energization current density of each layer is made equal is considered. Since the outer layer has a stronger self-magnetic field and an AC loss (resistance component) due to magnetization increases, 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. This time, a large amount of current will flow through the wire disposed in the outer layer with relatively low impedance, and the drift phenomenon will continue. This causes an abnormal increase in AC loss of the entire cable.
[0011]
The present invention has been made under the circumstances as described above, and an object of the present invention is to provide an oxide superconducting wire for AC that suppresses a decrease in critical current and significantly reduces AC loss.
[0012]
Another object of the present invention is to provide a method for producing an oxide superconducting wire for alternating current that suppresses a decrease in critical current and significantly reduces alternating current loss.
Still another object of the present invention is to provide an oxide superconducting cable for AC that suppresses a decrease in critical current and significantly reduces AC loss.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventor has intensively studied, and as a result, by making the superconducting filament twist pitch within a predetermined range, it is possible to easily perform twisting while suppressing a decrease in critical current. It was found that AC loss can be reduced. The present invention is based on such knowledge.
[0014]
  That is, the present invention (Claim 1) is an oxide superconducting round wire rod for alternating current comprising a metal matrix and a plurality of superconducting filaments embedded in the metal matrix,By twisting after heat treatment,Twist pitch L satisfying the following formula for the superconducting filament_p Provided is an oxide superconducting wire for alternating current, characterized by being twisted in
[0015]
     2L_c1<L_p ≦ 2L_c2
     L_c1= 2 {(2ρ · d_f ・ J_c ) / (Μ₀ DH / dt)}^1/2
     L_c2= 2 {(2ρ · d_b ・ J_cb) / (Μ₀ DH / dt)}^1/2
    (Where ρ is the specific resistance of the metal matrix (Ω · m), d_f Is the diameter of the superconducting filament (m), d_b Is the diameter of superconducting filaments (m), J_c Is the critical current density of the superconducting filament (A / m²), J_cbIs the critical current density of superconducting filaments (A / m²), Μ₀ Is the vacuum permeability (H / m), dH / dt is the magnetic field change rate (A / m / sec))
  Moreover, the present invention (Claim 2) is an oxide superconducting tape wire for alternating current comprising a metal matrix and a plurality of superconducting filaments embedded in the metal matrix,By twisting after heat treatment,Twist pitch L satisfying the following formula for the superconducting filament_p Provided is an oxide superconducting wire for alternating current, characterized by being twisted in
[0016]
2L_c1<L_p ≦ 2L_c2
L_c1= 2 {(2ρ · d_ft・ J_c ) / (Μ_o DH / dt)}^1/2
L_c2= 2 {(2ρ · d_bt・ J_cb) / (Μ_o DH / dt)}^1/2
(Where ρ is the specific resistance of the metal matrix (Ω · m), d_ftIs the thickness of the superconducting filament (m), d_btIs the thickness of superconducting filaments (m), J_c Is the critical current density of the superconducting filament (A / m² ), J_cbIs the critical current density of superconducting filaments (A / m² ), Μ_o Is the vacuum permeability (H / m), dH / dt is the magnetic field change rate (A / m / sec))
Furthermore, the present invention (Claim 3) includes a step of arranging a plurality of rod-shaped bodies made of a compressed powder of an oxide superconductor or a precursor thereof in a matrix metal and performing a wire drawing process, A step of heat-treating the composite wire subjected to the wire processing, a step of twisting the composite wire subjected to the heat treatment, and drawing or rolling the composite wire subjected to the twist processing and heat treatment are repeated. A method for producing an oxide superconducting wire for alternating current (Claim 1 or 2). Here, a precursor means what can become an oxide superconductor by post-processing.
[0017]
Furthermore, according to the present invention (Claim 4), a plurality of AC superconducting wires for AC (Claim 1 or 2) are arranged over a plurality of layers around the central member. Cable, said L_p 2L to the outer layer_c12L_c2Provided is an oxide superconducting cable for alternating current, characterized in that it is set close to.
[0018]
The feature of the oxide superconducting wire for alternating current of the present invention is the twist pitch L of the superconducting filament._p To the expression 2L_c1<L_p ≦ 2L_c22L as much as possible with a pitch that does not decrease the critical current._c1It is desirable to set it close to.
[0019]
L_p Is 2L_c1In the following, it becomes very difficult to apply twist, and the critical current tends to decrease. On the other hand, 2L_c2If it exceeds, the effect of the present invention of reducing AC loss cannot be obtained.
[0020]
The kind of oxide superconductor that can be used in the oxide superconducting wire for AC of the present invention is not particularly limited, but preferable examples include superconductors having a high critical temperature such as bismuth, yttrium, and thallium. I can do it.
[0021]
Moreover, as a metal matrix which can be used for the oxide superconducting wire for alternating current of this invention, silver alloys, such as silver or Ag-Au, Ag-Cu, Ag-Mg, etc. can be mentioned.
[0022]
Furthermore, examples of the central member that can be used in the oxide superconducting cable for AC of the present invention include a flexible hollow member made of stainless steel or aluminum.
[0023]
In addition, in the oxide superconducting cable for alternating current of the present invention, in order to make the current density of each layer uniform, it is preferable to interpose an insulating material between each layer, and as such an insulating material, a polyimide film or the like is used. Can be mentioned.
[0024]
According to the oxide superconducting wire for alternating current of the present invention configured as described above, since the twist pitch of the superconducting filament of the oxide superconducting wire is within a predetermined range, the twist can be easily applied and the critical current can be applied. It is possible to reduce the AC loss while suppressing the decrease in.
[0025]
In addition, according to the method for manufacturing an oxide superconducting wire for alternating current of the present invention, since the heat treatment is performed before the twist processing, the critical current is reduced when the oxide superconducting wire is twisted at a small pitch. Can be suppressed.
[0026]
Furthermore, according to the oxide superconducting cable for alternating current of the present invention, since the oxide superconducting wire for alternating current is used in which the twist pitch is selected so that the AC loss of the wire of each layer becomes equal at the rated energization of the cable, It is possible to suppress the bias of the energized current and prevent an abnormal increase in AC loss.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described 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. 1 (a) shows a cross-sectional structure, and FIG. 1 (b) shows an oxide superconducting round wire. The twist state of one superconducting filament is shown.
[0028]
In FIG. 1, a superconducting filament 1 is made of an oxide superconductor, and an oxide superconductor is formed by embedding a plurality of them in a metal matrix 2 made of silver or the like. Each superconducting filament 1 embedded in the metal matrix 2 has a predetermined pitch L_p The twist is given. The critical length L of this oxide superconducting round wire_c Is given by:
[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 critical current can be increased as the matrix ratio (volume ratio of the metal matrix when the volume of the superconducting filament is 1) is decreased, and the filament diameter is decreased. It is known that AC loss is reduced. Therefore, if the filament diameter is reduced while the matrix ratio is reduced and the number of superconducting filaments is increased accordingly, the distance between the superconducting filaments is reduced. When wire drawing or heat treatment is applied to such a wire, the superconducting filaments are deformed, and the superconducting filaments are partially very close to each other or come into contact with each other. This creates a portion where the filaments are likely to be coupled electromagnetically in an external magnetic field and a portion where the filaments are not likely to be coupled, so that the diameter of the superconducting filament is substantially increased and the equivalent filament diameter d_eff Is the actual filament diameter d_f The equivalent critical current density J_ceffIs the filament J_c It corresponds to becoming smaller. As a result, the equivalent critical length L_ceffBecomes larger, as shown in the following formula
L_ceff= 2 {(2ρd_eff ・ J_ceff) / (Μ_o DH / dt)}^1/2
Equivalent filament diameter d_eff Is the actual filament diameter d of the superconducting filament 1_f And the diameter d of the superconducting filament group_b Between the values. J_ceffIs J_c And J_cbBetween the values. Therefore, the equivalent critical length L_ceffIs the next L_c1And L_c2Between the values.
[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 / dt)}^1/2
Where d_b Is the diameter of superconducting filaments (m), J_cbIs the critical current density of superconducting filaments (A / m² ).
[0031]
As shown in the above equation, L_c1And L_c2Is determined in consideration of the rate of change of the magnetic field in which the wire is used.
The diameter d of the superconducting filament 1_f May be actually measured, but is also given by the following equation.
[0032]
d_f = D / {(1 + λ) N}^1/2
(Where d is the outer diameter (m) of the wire, λ is the matrix ratio, and N is the number of superconducting filaments 1)
Also, the critical current density J_c Is given by:
[0033]
J_c = I_c (1 + λ) / (πd² / 4)
(Wherein I_c Is the critical current (A) of the wire. )
And also the critical current density J of the superconducting filament group_cbIs given by:
[0034]
J_cb= I_c / (Πd_b ² / 4)
FIG. 2 is a diagram showing an oxide superconducting tape wire according to another embodiment of the present invention. Even in such an oxide superconducting tape wire, the pitch L is formed on the superconducting filament 1._p The twist is given. In this case, the diameter d of the superconducting filament 1_f Instead of the thickness d of the superconducting filament 1 facing the magnetic field applied to the wire._ftIs used. Superconducting filament group d_b The thickness d of the superconducting filament group facing the magnetic field applied to the wire instead of the diameter of_btIs used.
[0035]
And the thickness d of the superconducting filament_ftSince the tape wire is formed by rolling or drawing a round wire, the superconducting filaments 1 in the wire vary, so an average value is obtained using an equation.
[0036]
In the present invention, the thicknesses of the wire superconducting filament and the superconducting filament group are orthogonal to the plane including the twist pitch direction (critical length direction, wire length direction) and the direction of the varying magnetic field applied during use. This refers to the dimension measured in the direction (see Figures 1, 2, 7-9).
[0037]
Superconducting filament 1 thickness d_ftIs given by:
d_ft= T / {(1 + λ) N}^1/2
(In the formula, t is the thickness (m) of the wire.)
Also, the critical current density J_c Is given by:
[0038]
J_c = I_c (1 + λ) / tw
(In the formula, w is the width (m) of the wire.)
Furthermore, the critical current density J of the superconducting filament group_cbIs given by:
[0039]
J_cb= I_c / D_btd_bw
(Where d_bt, D_bwAre the thickness and width of the superconducting filament group, respectively. )
The diameter and thickness of the superconducting filament group can be obtained as follows.
[0040]
(1) A cross section of the wire is taken and measured.
The distance between one superconducting filament and the outside of the superconducting filament at the position to be rotated by 180 ° is defined as the diameter and thickness of the group (see FIGS. 1A and 2A).
[0041]
As the thickness of the superconducting filament group, a value measured at the thickest portion in the cross section orthogonal to the length direction of the wire is used. The reason is that the thick part has the most magnetic flux intermingled, and the influence of this part is the greatest on the magnitude of the AC loss of the wire.
[0042]
(2) Calculate by calculation.
Here, a round wire will be described as an example.
The outer diameter of the tube used lastly when manufacturing the oxide superconducting wire for alternating current (D₀ ), The outer diameter D of the assembly of wire rods stored in the_i This is calculated by multiplying the value obtained by dividing the outer diameter d of the final wire rod. d_b = D × D_i / D₀
In addition, the outer diameter D of the aggregate of stored wires_i Instead of, it is also possible to estimate using the inner diameter (diameter) of the last used tube.
[0043]
【Example】
Example 1
(Bi + Pb): Sr: Ca: Cu = 2: 2: 2: 3 oxide superconductor compressed mixed powder prepared in a composition having a 10 mm outer diameter and formed into a rod shape having an inner diameter of 10.5 mm and an outer diameter of 15 mm. Was inserted into a silver tube to obtain a composite. This composite was processed into a hexagonal wire having an opposite side dimension of 2.0 mm by a wire drawing machine. The 19 hexagonal wires were inserted into a silver tube having an inner diameter of 11 mm and an outer diameter of 15 mm, and the wire was drawn to a wire diameter of 1.5 mm.
[0044]
Next, after heat treatment at 300 ° C. for 1 hour, twist processing was performed at a pitch of 3 mm to 90 mm. Thereafter, rolling or wire drawing and heat treatment were repeated to process into a tape wire having a thickness of 0.24 mm and a width of 3.3 mm and a round wire having an outer diameter of 1 mm. The filament thickness of the tape wire at this time 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.
[0045]
Example 2
A plurality of oxide superconducting tape wires 3 produced by the procedure shown in Example 1 were wound around the central member over a plurality of layers to produce an oxide superconducting cable for alternating current. That is, as shown in FIG. 3, an oxide superconducting tape 3 is wound around a central member 4 having an outer diameter of 30 mmφ, and an insulating material 5 having a thickness of 0.35 mm is interposed between the layers, and five layers are spirally wound. An oxide superconducting cable having a diameter of 35.2 mmφ was produced.
[0046]
In this oxide superconducting cable, 29, 30, 31, 32, and 33 oxide superconducting tapes 3 are arranged in order from the first innermost layer to the fifth outermost layer, for a total of 155 tapes. Line 3 was used. When the critical current of the cable is estimated by the number of times of the critical current of the tape wire, it becomes 2325A. The rated AC energization current (50 Hz) of this cable was set to a peak value of 1000 A, and the magnetic field calculation at the time of rated energization was performed when the energization current of each strand was the same (when the energization current density of each layer was the same). From the obtained average magnetic field change rate applied to the oxide superconducting tape 3 of each layer, L for each tape is obtained._c1And L_c2Asked.
[0047]
By adjusting the electromagnetic coupling state of the superconducting filaments of the tape wires of each layer, the twist pitch of each layer of tape is 44 mm in order from the first innermost layer to the fifth outermost layer so that their AC losses are equal. It was set to 23 mm, 16 mm, 12 mm, and 9 mm. These twist pitches are 2L for the outer layer._c12L for the inner layer_c2It is set to be close to.
[0048]
Conventional example
(Bi + Pb): Sr: Ca: Cu = 2: 2: 2: 3 oxide superconductor compressed mixed powder prepared in a composition having a 10 mm outer diameter and formed into a rod shape, 10.5 mm inner diameter, outer diameter It was inserted into a 15 mm silver tube to obtain a composite. This composite was processed into a hexagonal wire having an opposite side dimension of 2.0 mm by a wire drawing machine. Nineteen 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.
[0049]
Thereafter, rolling or wire drawing and heat treatment were repeated to process into a tape wire having a thickness of 0.24 mm and a width of 3.3 mm and 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.
[0050]
Comparative example
(Bi + Pb): Sr: Ca: Cu = 2: 2: 2: 3 oxide superconductor compressed mixed powder prepared in a composition having a 10 mm outer diameter and formed into a rod shape, 10.5 mm inner diameter, outer diameter It was inserted into a 15 mm silver tube to obtain a composite. This composite was processed into a hexagonal wire having an opposite side dimension of 2.0 mm by a wire drawing machine. Nineteen 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, twist processing was performed at a pitch of 3 mm to 90 mm without heat treatment.
[0051]
Thereafter, rolling or wire drawing and heat treatment were repeated to process into a tape wire having a thickness of 0.24 mm and a width of 3.3 mm and a round wire having an outer diameter of 1 mm. The filament thickness of the tape wire at this time 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.
[0052]
The AC loss of the produced wire was measured using a magnetization method. The measurement condition is that the magnetic field amplitude is fixed at 30 mT and the frequency is changed by changing the frequency._o -DH / dt was changed. The sample was a bundle of 75 wires having a length of 40 mm, the wires were insulated, and the ends of the sample were polished so that there was no contact between the superconducting filaments. The varying magnetic field was applied perpendicular to the longitudinal direction of the wire, and applied in parallel to the wide surface of the tape wire. On the other hand, the critical current (self magnetic field, 77K) was measured by the four-terminal method. The critical current was defined as a current value when a voltage of 1 μV / cm was generated between the voltage taps.
[0053]
FIG. 4 shows the twist pitch dependence of the AC loss of the tape wire of the example normalized by the AC loss of the conventional example. In FIG. 4, the dotted line A is μ_o ・ 2L at dH / dt = 1T / s_c1, Dotted line B is μ_o ・ 2L at dH / dt = 1T / s_c2, Solid line C is μ_o ・ 2L at dH / dt = 0.1 T / s_c1, Solid line D is μ_o ・ 2L at dH / dt = 0.1 T / s_c2Respectively.
[0054]
2L_c12L_c2Was determined based on the calculation results of each parameter of the tape wire as follows.
J_c = 15 × {1 / (0.24 × 3.3 × 10^-6)} × (1 + 3.5)
= 85.2 × 10⁶ [A / m² ]
d_f = 26 × 10^-6[M]
λ_b = (15² -10.5² ) / 10² = 1.148
J_cb= 15 × {1 / (0.24 × 3.3 × 10^-6)} × (1 + 1.148)
= 40.7 × 10⁶ [A / m² ]
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^-Fivem = 26 μm
Λ_b Indicates the area of the matrix portion when the area of the filament group is 1.
[0055]
By substituting these parameters into the following equation, the critical length L_c Can be requested.
L_c = 2 {(2ρ · d_f ・ J_c ) / (Μ_o DH / dt)}^1/2
(1) μ_o ・ 2L at dH / dt = 1T / s_c1Is 0.0133
In FIG. 4, it is indicated by a dotted line A.
[0056]
(2) μ_o ・ 2L at dH / dt = 1T / s_c2Is 0.0228
In FIG. 4, this is indicated by a dotted line B.
(3) μ_o ・ 2L at dH / dt = 0.1 T / s_c1Is 0.042
In FIG. 4, this is indicated by a solid line C.
[0057]
(4) μ_o ・ 2L at dH / dt = 0.1 T / s_c2Is 0.072
In FIG. 4, it is indicated by a solid line D.
As is clear from FIG._o ・ When dH / dt = 1T / s, μ_o ・ 2L even when dH / dt = 0.1 T / s_c1<L_p <2L_c2In this region, the AC loss decreases as the twist pitch decreases. Magnetic field change rate μ_o ・ The larger dH / dt, the more L_c1, L_c2It can be seen that the electromagnetic coupling of the filament becomes remarkable and the AC loss is increased. Thus, L_c1Even if the twist pitch is larger than twice the_c2If the pitch is twice or less, the increase in AC loss due to electromagnetic coupling of the filaments can be suppressed.
[0058]
The above low-frequency effect of AC loss was also confirmed in the round wire.
Next, FIG. 5 shows the twist pitch dependence of the critical current in the example and the comparative example, normalized by the critical current when each twist is not applied. In addition, the critical current in the state where twist was not applied was 15A for the tape wire of the example, and 5A for the round wire of the example, and the critical currents of the tape wire and the round wire of the comparative example were almost the same.
[0059]
As is apparent from FIG. 5, in the tape wire of the example, the critical current hardly decreases even when the twist pitch is reduced, and is almost constant. On the other hand, in the tape wire of the comparative example, the critical current decreases as the twist pitch decreases in the region where the pitch is about 20 mm or less. Similarly, the critical current of the round wire rods in the examples hardly decreases even when the twist pitch is small. On the other hand, the round wire of the comparative example has a decrease in critical current when the pitch is about 15 mm or less. From this, it can be seen that moderate heat treatment before twisting improves twist workability and suppresses a decrease in critical current due to twisting of the wire.
[0060]
In addition, although it was set as 300 degreeC and 1 hour in the said Example as the temperature and time of the heat processing before twist processing, respectively, it is not necessarily limited to this, Heating temperature is 200 degreeC-400 degreeC, and heating time is 3 hours or less It is desirable to set the optimal temperature and time appropriately within the range.
[0061]
On the other hand, the AC loss at the time of rated energization (1000 A) of the oxide superconducting cable shown in Example 2 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 values of the conduction loss and the magnetization loss of the strand by the number of the strands used. This is considered to be because an abnormal increase in AC loss did not occur because the AC loss in each layer was made substantially equal, thereby suppressing the drift in each layer.
[0062]
Example 3
Various examples of cables in which a plurality of strands are wound around a central member over a plurality of layers via an insulating material are shown in FIGS. 6 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. 6 shows an example using a round wire, and FIGS. 7 to 9 show examples using a tape wire. In the figure, B represents an external magnetic field (the direction of a varying magnetic field), and i represents a current.
[0063]
FIG. 6 shows a cable in which a plurality of round rod wires are wound around a cylindrical central member over a plurality of layers. FIG. 7 shows a plurality of tape wires on a cylindrical central member, and the wide surface of the tape is a central member. FIG. 8 shows a cable wound around a plurality of layers so as to be in contact with each other. In FIG. FIG. 9 shows a cable in which a plurality of tape wires are arranged over a plurality of layers around a flat central member. 9C shows one tape wire disposed on the upper and lower surfaces of the center member, and FIG. 9D shows one tape wire disposed on the side of the center member.
[0064]
【The invention's effect】
As described above, according to the oxide superconducting wire for alternating current of the present invention, since the twist pitch of the superconducting filament of the oxide superconducting wire is within a predetermined range, the twist can be easily applied and the critical current can be reduced. The AC loss can be reduced while suppressing the decrease.
[0065]
In addition, according to the method for producing an oxide superconducting wire for alternating current of the present invention, the critical current can be reduced when a small pitch twist is applied to the oxide superconducting wire by performing heat treatment before twisting. It is possible to suppress.
[0066]
Furthermore, according to the oxide superconducting cable for alternating current of the present invention, since the oxide superconducting wire for alternating current is used in which the twist pitch is selected so that the AC loss of the wire of each layer becomes equal at the rated energization of the cable, It is possible to suppress the bias of the energized current and prevent an abnormal increase in AC loss.
[Brief description of the drawings]
FIG. 1 shows an oxide superconducting round wire according to an embodiment of the present invention.
FIG. 2 is a diagram 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 changes in AC loss with respect to twist pitch.
FIG. 5 is a characteristic diagram showing a change in critical current with respect to twist pitch.
FIG. 6 is a diagram showing an example of an oxide superconducting cable according to the present invention.
FIG. 7 is a diagram showing an example of an oxide superconducting cable according to the present invention.
FIG. 8 is a diagram showing an example of an oxide superconducting cable according to the present invention.
FIG. 9 is a diagram showing an example of an oxide superconducting cable according to the present invention.
FIG. 10 is a diagram for explaining a coupling current of an oxide superconducting wire.
[Explanation of symbols]
1 ... Superconducting filament
2 ... Metal matrix
3. Superconducting tape wire
4 ... Center member
5 ... Insulating material

Claims (4)

An oxide superconducting round wire for alternating current comprising a metal matrix and a plurality of superconducting filaments embedded in the metal matrix, and the following formula is applied to the superconducting filament by twisting after heat treatment: AC oxide superconducting wire, characterized in that subjected to twist twist pitch L _p satisfying.
2L _c1 <L _p ≦ 2L _c2
L _c1 = 2 {(2ρ · d _f · J _c ) / (μ ₀ · dH / dt)} ^1/2
L _c2 = 2 {(2ρ · d _b · J _cb ) / (μ ₀ · dH / dt)} ^1/2
(Wherein the specific resistance (Omega · m of ρ metal matrix), d _f is the diameter of the superconductive filaments (m), d _b is the diameter of the superconductor filament group (m), J _c is the superconducting filament critical current density ( A / m ² ), J _cb is the critical current density (A / m ² ) of the superconducting filament group, μ ₀ is the magnetic permeability (H / m) of vacuum, and dH / dt is the rate of change of the magnetic field (A / m / sec). )) An oxide superconducting tape wire for alternating current comprising a metal matrix and a plurality of superconducting filaments embedded in the metal matrix, and the following formula is applied to the superconducting filament by twisting after heat treatment: AC oxide superconducting wire, characterized in that subjected to twist twist pitch L _p satisfying.
2L _c1 <L _p ≦ 2L _c2
L _c1 = 2 {(2ρ · d _ft · J _c ) / (μ ₀ · dH / dt)} ^1/2
L _c2 = 2 {(2ρ · d _bt · J _cb ) / (μ ₀ · dH / dt)} ^1/2
(Wherein ρ is the specific resistance of the metal matrix (Ω · m), d _ft is the thickness of the superconducting filament (m), d _bt is the thickness of the superconducting filament group (m), and J _c is the critical current of the superconducting filament. Density (A / m ² ), J _cb is the critical current density (A / m ² ) of the superconducting filament group, μ ₀ is the magnetic permeability (H / m) of the vacuum, and dH / dt is the rate of change of the magnetic field (A / m) / Sec))  A step of arranging a plurality of rod-shaped bodies made of a compressed powder of an oxide superconductor or a precursor thereof in a matrix metal and performing wire drawing, and heat-treating the composite wire subjected to the wire drawing And a step of twisting the composite wire subjected to the heat treatment, and a step of repeating the wire drawing or rolling and heat treatment of the composite wire subjected to the twist processing. The manufacturing method of the oxide superconducting wire for alternating currents of Claim 1 or 2. An AC oxide superconducting cable in which a plurality of AC oxide superconducting wires according to claim 1 or 2 are arranged over a plurality of layers around a central member, wherein L _p is An alternating-current oxide superconducting cable characterized by being set closer to the 2L _{c1 as} it goes to the outer layer and set closer to the 2L _{c2 as} it goes to the inner layer.

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