JP2002075078A - Superconducting cable and method for analyzing electric-current distribution in superconducting cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a superconducting cable which is compact and has a large capacity, and can lower the alternating-current loss of the conductor, and the method for analyzing electric-current distribution in a superconducting cable. SOLUTION: A superconducting cable which comprises a core material, a conducting layer of laminated structure made by winding spirally a plurality of tape-shaped superconducting multiconductor wires around the core material, an electrically insulating layer, and a magnetic shielding layer of laminated structure made by winding a plurality of tape-shaped superconducting multiconductor wires. The following architecture 1-3 is provided. 1 The winding pitch of at least one of the conductor layer and the magnetic shielding layer is different from that of the other layer. 2 The tape-shaped superconducting multiconductor wire has a structure in which superconducting filaments are imbedded in a matrix, and the filaments are spirally twisted. 3 The core material is fabricated by twisting together insulated strands.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting cable capable of reducing AC loss and a method of analyzing a current distribution of the cable.

[0002]

2. Description of the Related Art As a conductor structure used in a superconducting cable, a conductor (simple multilayer conductor) in which a tape-shaped superconducting multi-core wire is spirally wound at the same pitch on a core material to form a multilayer is known. In such a conductor, the current density is smaller in the inner superconducting layer, and the current density is larger in the outer superconducting layer. For example, Japanese Patent Application No. 2000-5107 (not disclosed) discloses a technique for changing the pitch of a tape-shaped superconducting multifilamentary wire to equalize the current of each layer.

[0003]

However, when a large current of about 10 kA is applied, it is difficult to achieve low loss only by adjusting the pitch. The AC loss of the pitch adjusting conductor is determined by the magnitude of the magnetic field applied to the tape-shaped superconducting multifilamentary wires of each layer during energization. Since the magnetic field increases as the energizing current increases, the loss of a large current conductor of the 10 kA class is larger than that of the 1 kA class conductor by one order of magnitude or more. As the loss increases, a refrigerator having a large cooling capacity is required, and the advantage of the superconducting cable in terms of loss is reduced.

Accordingly, a main object of the present invention is to provide a superconducting cable which is compact and has a large capacity (particularly 3 kA or more) and which can reduce the AC loss of a conductor, and a method for analyzing the current distribution of the superconducting cable. .

[0005]

The superconducting cable according to the present invention is characterized in that the constitution of the core material, the constitution of the tape-shaped superconducting multifilamentary wire and the manner of winding the multifilamentary wire are devised, and the thickness of the tape-shaped superconducting multifilamentary wire is improved. The above object is achieved by limiting.

That is, the cable according to the first aspect of the present invention provides a core material, a conductor layer having a laminated structure in which a plurality of tape-shaped superconducting multi-core wires are spirally wound around the core material, an electrical insulating layer, and an insulating layer. A superconducting cable comprising a laminated magnetic shielding layer formed by spirally winding a plurality of tape-shaped superconducting multi-core wires on a layer. And it is characterized by comprising the following configuration (1).

[0007] At least one of the conductor layer and the magnetic shielding layer has a different winding pitch from the other layers. The tape-shaped superconducting multifilamentary wire has a configuration in which a superconducting filament is embedded in a matrix, and this filament is twisted in a spiral shape. The core is formed by twisting insulated wires.

Further, it is preferable that a high resistance barrier layer is provided on the outer periphery of the superconducting filament.

Hereinafter, each of the above structures will be described. (Pitch Adjustment of Conductive Layer and Magnetic Shielding Layer) A specific method of adjusting the pitch of the conductive layer and the magnetic shielding layer is any as long as the pitch of the tape-shaped superconducting multifilamentary wire that can reduce the AC loss can be selected. Although it may be a simple method,
For example, it is preferable to use the method disclosed in Japanese Patent Application No. 2000-5106. According to this method, the current distribution and the AC loss of a superconducting cable having an arbitrary core material resistance, an arbitrary conductor size, an arbitrary spiral winding direction, and an arbitrary spiral winding pitch can be analyzed in detail, and the AC loss is minimized. The winding pitch of the tape-shaped superconducting multi-core wire can be determined. Details of this method will be described later.

(Use of Twisted Wire) With respect to a configuration in which a superconducting filament is embedded in a matrix, and this filament is formed in a spiral shape,
It is described in JP-A-7-105753.

In a superconducting wire having a helical filament, the induced current flowing between the matrix and the filament is divided at every twist pitch and flows as a small loop, so that the magnitude of the current is also limited. As a result, AC loss can be reduced.

Silver or a silver alloy is preferred as the matrix material. Ag-Au alloy, Ag-Mg alloy, Ag
-Sb alloy and Ag-Mn alloy are preferable. The superconductor constituting the filament is preferably an oxide superconductor of yttrium, bismuth or thallium.

[0013] Such a twisted wire is manufactured by a powder-in-tube method or the like. For example, it can be obtained by the following steps. The raw material powder of the superconductor or the powder of the superconductor is filled in the first pipe, and this is drawn to form a single-core superconducting wire. A plurality of single-core superconducting wires are prepared, inserted into the second pipe and drawn again to obtain a multi-core superconducting wire. The multifilamentary superconducting wire is twisted at a required pitch, further lightly drawn, and then rolled into a tape shape. Normally, after the first sintering of the tape wire, it is rolled once more, and the second sintering is performed to obtain a tape-shaped superconducting multi-core wire. As an example of the raw material powder of the superconductor, a precursor having a Bi-2212 phase as a main phase (a Bi-2223 phase is formed after final sintering) is given. A silver pipe or the like may be used for the first and second pipes.

The number of filaments is determined according to the final filament thickness and the size of the tape-shaped superconducting multifilamentary wire. Usually, it is about 7 to 127 cores.

In general, a short twist pitch of the filament is more effective in reducing loss. The lower limit of the current twist pitch is about 10 mm. However, even if an attempt is made to obtain an extremely short twisted wire, the filament is liable to be broken, and the long pitch is easier to process.
Therefore, it is practical to set the twist pitch to 5 times or more the wire diameter of the multi-core superconducting wire.

The final drawn diameter of the multi-core superconducting wire is set according to the thickness and the twist pitch of the tape wire. The final wire drawing diameter is generally about φ0.5 mm to φ3 mm.

When the tape-shaped superconducting multi-core wire is used, the final thickness is 0.1 to 0.4 mm and the aspect ratio (width / thickness) is 10 to 2
About 0 is preferable.

(High resistance barrier layer) The high resistance barrier layer is formed so as to cover the outer periphery of the filament. The presence of the high-resistance barrier layer can prevent the metal constituting the matrix of the tape-shaped superconducting multi-core wire from diffusing into the superconductor and lowering the critical current density, and also substantially increase the resistance of the matrix to reduce AC loss. Reduction can be achieved. The material of the high resistance barrier layer is selected as a main criterion such that it does not react with the superconductor and does not impair the workability of the wire during drawing and rolling. More specifically, Ca-C
uO-based oxides, Bi2201 phase, Sr-VO-based oxides, etc. are optimal.

A tape-shaped superconducting multi-core wire having a high resistance barrier layer can be obtained, for example, by the following steps. The raw material powder of the superconductor or the powder of the superconductor is filled in the first pipe, and this is drawn to form a single-core superconducting wire. Insert the single-core superconducting wire into the second pipe and connect the first silver pipe and the second
The material for the high resistance barrier layer is filled between the pipe and the pipe. The second pipe is drawn into a single core wire with a barrier layer.
A plurality of single-core wires with a barrier layer are prepared, inserted into a third pipe, and further subjected to wire drawing to form a multi-core superconducting wire. The multifilamentary superconducting wire is twisted at a required pitch, further lightly drawn, and then rolled to obtain a tape-shaped superconducting multifilamentary wire. A silver pipe or the like may be used for the first, second, and third pipes.

(Core material of twisted structure) Conventionally, a pipe material is generally used as the core material. However, by using a core material of a stranded wire structure, AC loss can be reduced and temperature rise due to overcurrent can be suppressed. Solve the two problems at the same time.

In a pitch-adjustable conductor in which the winding pitch of each layer of the superconducting layer is different, a magnetic field is generated in the conductor axis direction. When a metal pipe is used as a core material, a large eddy current loss occurs due to the axial magnetic field.

In order to suppress the eddy current loss, it is considered that increasing the resistance of the material is effective in reducing the loss, and it is considered that the material should not be made of metal. However, in order to suppress the rise in cable temperature when an overcurrent flows in the superconducting cable, it is necessary that the core material share the overcurrent, and for that purpose, the resistance of the core material must be as low as possible. There is. From that viewpoint, the material constituting the core material is preferably a metal.

In view of the structure, when metal is assumed as the core material, it is effective to divide the cross section of the core material to reduce the path of the eddy current. Specifically, the core material may be formed by twisting the insulated wires.

It is also preferable to smooth the surface of the core material. By this smoothing, mechanical deterioration due to bending of the cable or the like can be suppressed. A simple stranded conductor has poor surface smoothness, and when superconducting wires are directly assembled on this,
It was found that buckling of the superconducting wire frequently occurred when the cable conductor was bent. As a countermeasure against this problem, buckling of the superconducting wire due to conductor bending can be suppressed by smoothing the core material surface. The degree of smoothing may be such that unevenness due to twisted grooves of the metal wire can be reduced.

Means for smoothing the irregularities on the surface of the core material include a method of forming the surface of the core wire itself into a cylindrical surface and a method of separately providing a layer for smoothing the surface of the core material.

As the former, after twisting a metal wire having a circular cross section, the twisted wire is passed through a die to compress the core wire into a cylindrical surface, or after twisting a circular metal wire. Polishing the surface of the stranded wire to form the surface of the core wire into a cylindrical surface.

The following specific examples are given as the latter.

A tape material is wound around the twisted metal wire, or an extruded coating is formed. In that case, it is preferable to use an insulating tape material or an extruded covering material. This is because the eddy current loss of the tape material and the extrusion coating material itself can be avoided. Further, if the tape material is made of metal, the superconducting wire may buckle at the tape edge.

Of the metal wires in the core, the diameter of the wire used for the outermost layer is made smaller than the diameter of the wire on the inner layer side. In particular, by reversing the twisting direction of the outermost wire and the wire immediately below it, or by changing the twist pitch of both wires significantly, the wire of the outermost layer does not fall into the twist groove of the wire immediately below, and the surface of the core material Smoothing can be effectively realized.

It is desirable that the core material has a structure in which an insulated metal wire is concentrically twisted. The buckling of the superconducting wire described above occurs due to unevenness on the surface of the core material. In the case of a core material having a structure in which metal wires are twisted, irregularities are always more or less seen on the surface. Among the twisted structures, the concentric twisted structure can most suppress unevenness.

The superconducting cable according to the second aspect of the present invention comprises:
A core material, a conductor layer having a laminated structure in which a plurality of tape-shaped superconducting multi-core wires are spirally wound on the core material, and an electrical insulating layer,
A superconducting cable comprising: a magnetic shielding layer having a laminated structure in which a plurality of tape-shaped superconducting multifilamentary wires are spirally wound on an insulating layer. The thickness of the tape-shaped superconducting multifilamentary wire is 0.15 mm or less.

In the conventional tape-shaped superconducting multifilamentary wire, the winding pitch has been optimized by using a wire having a thickness of 0.2 mm or more from the surface of Jc. Estimation was made from the viewpoint of reducing the AC loss, and it was found that the AC loss could be reduced as the thickness of the tape-shaped superconducting multi-core wire was reduced. Therefore, the number of filaments is reduced without changing the filament size, thereby reducing the thickness of the filament bundle. By using this wire, a superconducting cable with a small AC loss can be obtained without changing Jc. A more preferable thickness of the tape-shaped superconducting multi-core wire is 0.1 mm or less. The thickness is preferably thinner from the viewpoint of reducing AC loss, but is preferably 0.01 mm or more from the viewpoint of mechanical strength and ease of handling.

Of course, the configuration of the first invention and the configuration of the second invention may be combined.

Next, an optimum method for determining the pitch of the tape-shaped superconducting multi-core wire of the superconducting cable according to the present invention is to spirally wind a core material and a plurality of tape-shaped superconducting multi-core wires around the core material. A conductive layer having a laminated structure,
A method for analyzing the current distribution of a superconducting cable comprising a magnetic shielding layer having a laminated structure in which a plurality of tape-shaped superconducting multi-core wires are spirally wound around the outer periphery of an insulating layer, comprising the following processes: Features.

A process of modeling the core material, the conductor layer and the magnetic shielding layer into a circuit composed of at least an inductive reactance. Specifications of core material including core size and specific resistance, critical current and size, specifications of tape-shaped superconducting multi-core wire including twist pitch of filament embedded in tape-shaped superconducting multi-core wire, conductor layer and magnetic shielding layer Spiral winding direction and pitch, thickness and outer diameter of conductor layer and magnetic shield layer, specifications of conductor layer and magnetic shield layer including number of conductor layers and magnetic shield layer, and necessary parameters including frequency and current flow The process of entering. The process of calculating inductance and effective resistance in a circuit using input parameters. A process of creating a circuit equation based on the model and calculating a current distribution of each layer.

Here, it is preferable that each layer of the tape-shaped superconducting multi-core wire in the conductor layer and the magnetic shielding layer be electrically insulated in order to correspond to “modeling” described later. When considering the impedance adjustment of each layer of the superconductor, modeling is easier with an interlayer insulated conductor completely excluding the effects of transfer resistance between layers than a conductor without interlayer insulation. This structure is also effective in reducing eddy current loss in the conductor.

As a modeling process, the core material, the conductor layer, and the magnetic shielding layer may be modeled as a circuit composed only of inductive reactance, but may be modeled as a circuit composed of resistance and inductive reactance. Is preferred. Conventionally, it has been considered that analyzing the current distribution in consideration of the resistance is extremely complicated and difficult. By using the "method of modeling" in the present invention and the "method of calculating inductive reactance and effective resistance in a modeled circuit" described later, it is possible to analyze an accurate current distribution in consideration of resistance, Further, the AC loss characteristics can be analyzed based on the analysis results.

The process of modeling will be described more specifically. First, the core material and the conductor layer are regarded as a lumped constant circuit in which inductive reactance and resistance are arranged in series. Also, the magnetic shielding layer is regarded as a closed circuit loop connected via a connection resistance of the terminal. It is preferable that a circuit formed by the conductor layer and the power supply attached thereto is regarded as a primary circuit, and a circuit formed by the magnetic shield layer and the connection resistance of the terminal portion is regarded as a secondary circuit as a secondary circuit.

In order to obtain the current distribution based on the modeled equivalent circuit, it is necessary to set necessary parameters for the modeled equivalent circuit in order to calculate the inductance and the effective resistance. The parameters are tape-shaped superconducting multi-core wire specifications (width, thickness, Ic), core material specifications (specific resistance, outer diameter, thickness), conductor layer / magnetic shielding layer specifications (winding direction of each layer) , Pitch, outer diameter of each layer, thickness of each layer, Ic retention rate in each layer), and energization conditions (energization current, frequency). When the Ic of each layer is different, the critical current and size of the tape-shaped superconducting multifilamentary wire may be set for each layer.

In the analysis method of the present invention, a tape-shaped superconducting multifilamentary wire obtained by twisting a filament is used.
In that case, a twist pitch is set for each layer as a parameter setting. The twisted tape-shaped superconducting multi-core wire is a wire in which a filament of an oxide superconductor is embedded in a matrix, and has a configuration in which the filament is spirally twisted along the longitudinal direction of the wire ( For example, see JP-A-7-105753. A specific circuit equation using the twist pitch of the filament as a parameter will be described later in detail.

In calculating the effective resistance, it is preferable to treat the resistance in the lumped constant circuit as changing according to the current flowing through the conductor layer. One of the features of the high-temperature superconducting conductor is that the dislocation from the superconducting state to the normal conducting state is moderate. Taking DC conduction characteristics as an example,
The current-voltage curve of a high-temperature superconducting conductor looks like V to In ( ^{n to} 10), and a step-like (discontinuous) finite voltage is generated at I = Ic like an ideal superconductor. is not.

Such a high-temperature superconducting cable having a non-linear current-voltage characteristic can be treated as having a current-independent resistance such as a normal conductor, or can be used as an ideal tape-shaped superconducting multi-core wire. Treating the resistance as zero in, causes an error between the model and the actual cable.

Therefore, by considering the resistance that changes with the current, the AC loss of the superconducting cable can be handled more strictly.

Further, one of the most important characteristics of the high-temperature superconducting cable is that when a current exceeding the critical current (Ic) is applied, the quench phenomenon unlike the conventional metal-based superconducting wire does not occur, and the high-temperature superconducting cable is stable. It is possible to conduct electricity exceeding Ic. Further, comparing the AC loss of the pitch adjusting conductor and the AC loss of the pitch non-adjusting conductor having the same capacity, it can be theoretically predicted that the most difference between the two occurs near the conductor Ic.

As described above, for the analysis of the high-temperature superconducting cable, it is also important to predict the AC loss characteristics above the conductor Ic and near the conductor Ic. These effects can be incorporated into the model for the first time by considering that the resistance in the lumped constant circuit at the time of modeling changes with the current.

More specifically, the effective resistance R _eff of the tape-shaped superconducting multifilamentary wire is _calculated by calculating the AC loss W _{layer of} each _layer and the energizing current.
Using I, R _eff = W _layer / I ² and R _eff may be regarded as the resistance in the lumped constant circuit. It is preferable to calculate the loss W _layer based on the AC current-loss characteristics of the tape-shaped superconducting multi-core wire. For example, the AC loss amount W _layer may be obtained from the Norris equation. And I>
The formula for the AC loss W _layer in Ic may be so as to be continuous with the equation for the AC loss W _layer in I <Ic.

Subsequently, a circuit equation corresponding to the model is created, and the current distribution of each layer is calculated. At that time, in the process of inputting parameters, an appropriate initial value is given as a current value of each layer, and a current distribution of each layer is calculated based on the initial value. Next, the process from the parameter input process to the current distribution calculation process is repeated using the current value obtained by the calculation. This repetition may be performed until the difference between the current values of the respective layers before and after the calculation converges to a desired range.

The predetermined range for converging the operation result is 10% or less, more preferably 5% or less, and further preferably 1% or less. If the difference between the current values of each layer before and after the calculation exceeds 10%, the accuracy of the analysis result decreases. Further, if the difference between the current values before and after the calculation can be converged to a difference of about 1%, even if the calculation is further repeated, it takes a long time, and does not substantially contribute to the improvement of the accuracy of the analysis result.

It is preferable to provide a process for obtaining a magnetic field distribution from the calculated current distribution and further calculating an AC loss amount.

[0050]

Embodiments of the present invention will be described below. (Example 1) The outer diameter of the conductor layer is 24 mm, the capacity of the conductor is 8.4 kAp
Of superconducting cable was designed. This cable conductor includes a core material, a conductor layer, an insulating layer, and a magnetic shielding layer in this order from the center.

As the core material, in order to suppress the eddy current loss due to the magnetic field in the conductor axial direction, a material obtained by concentrically twisting an insulated copper wire was used. The copper wires used were 1 mm in diameter and 250 in number.

The conductor layer is formed in a laminated structure by spirally winding a tape-shaped superconducting multi-core wire on a core material at a predetermined pitch. It is effective to arrange a thin insulating layer (interlayer insulation) between each layer of the tape-shaped superconducting multi-core wire in terms of reducing eddy current loss. It is even better if each strand is provided with an insulating coating such as enamel or UV coating.

The tape-shaped superconducting multi-core wire used is as follows.
I got it. First Bi_TwoO_Three, PbO, SrCO _Three, CaCO_ThreeAnd CuO
By using, Bi: Pb: Sr: Ca: Cu = 1.81: 0.40: 1.98: 2.
It was blended so as to have a composition ratio of 21: 3.03. This powder
12 hours at 750 ° C and 8 hours at 800 ° C in air
8 hours at 760 ° C under 133.3Pa (1 Torr) pressure atmosphere
Heat treatment was performed. Grinding is performed after each of these heat treatments. This
The powder obtained through heat treatment and pulverization of
To a submicron powder. This powder
Is heat treated at 800 ° C for 2 hours, and then silver with an outer diameter of 12 mm and
Filled in pipe.

Next, this silver pipe was drawn to a diameter of 1 mm to obtain a single-core superconducting wire. A single-core superconducting wire with an outer diameter of 12 mm
Thirty-seven pieces were inserted into a silver pipe having an inner diameter of 9 mm, and this was drawn to a diameter of 1 mm to obtain a multi-core superconducting wire. This multifilamentary superconducting wire was rolled and heat-treated at 850 ° C. for 50 hours to obtain a tape-shaped superconducting multifilamentary wire having a predetermined thickness. In this example, two types of tape-shaped superconducting multi-core wires having a thickness of 0.24 mm (comparative example) and 0.15 mm (example) were used. No twist pitch is applied to the tape-shaped superconducting multi-core wires of any thickness.

The insulating layer is formed by arranging PPLP (composite tape obtained by laminating kraft paper on a polypropylene film), kraft paper, polyethylene, rubber or the like on the conductor layer. Here, PPLP was used.

The magnetic shielding layer is formed by spirally winding the above-mentioned tape-shaped superconducting multi-core wire on an insulating layer to form a laminated structure. It is preferable that the tape-shaped superconducting multifilamentary wire is subjected to interlayer insulation or strand insulation as in the case of the conductor layer.

The above-described superconducting conductor is equivalent to one phase (one core) of the cable. In practice, three cores are twisted and used in an insulated tube. The heat insulating tube has a structure in which a heat insulating material such as super insulation is arranged in a double aluminum corrugated pipe and vacuum is evacuated. The outer diameter of the heat insulating pipe is preferably set to 130 mm or less in order to cope with the pipe laying. In the cable conductor having the above structure, the calculation of the optimum winding pitch for equalizing the current in the conductor layer and the magnetic shielding layer can be performed, for example, by a simulation code disclosed in Japanese Patent Application No. 2000-5107.

Table 1 shows the pitch and conductor parameters obtained based on the above simulation code. Table 1
In the above, “conductor layer pitch” and “shielding layer pitch” respectively describe values from the inner layer side to the outer peripheral side in order.

[0059]

[Table 1]

Regarding the above conductor structure, Japanese Patent Application No. 2000-5107
As a result of calculating the AC loss by the method disclosed in the above, even if the same conductor size, the same conductor Ic, than the case of using a wire of normal thickness (using a thickness of 0.2 to 0.3 mm) It was confirmed that the smaller the strand size, the smaller the AC loss.

Based on the calculation results, a reduced model conductor having a capacity of 1/4 was manufactured. The used wire size and conductor structure are the same as in Table 1. Conductor Ic is 2500A, 2100Ap
When the conductor (77K, 50Hz) is reciprocated between the conductor and the magnetic shielding layer, the loss of the conductor is 1W / m when the wire thickness is 0.24mm and 0.5W / m when the wire thickness is 0.15mm. It was experimentally confirmed that the smaller the thickness, the smaller the thickness. Similarly, a trial calculation was also performed for a wire thickness of 0.10 mm, and it was found that the loss was even smaller.

(Example 2) As in Example 1, it was confirmed that the AC loss was reduced by reducing the thickness of the tape-shaped superconducting multifilamentary wire. However, when 8.4 kAp is applied, the total loss is 12 W / m even when a thin wire is used. For practical use, the total loss is
It is said that 1W / m level is required. The AC loss of the pitch adjusting conductor is the sum of the strand-level magnetization loss, and the strand-level magnetization loss reduction is effective for reducing the conductor loss. Therefore, a trial calculation of AC loss was performed using a tape-shaped superconducting multi-core wire in which a superconducting filament was twisted.

The calculation method at this time will be described below. The procedure to find the AC loss is to model the superconducting cable into an equivalent circuit, derive the inductance and the effective resistance,
A circuit equation corresponding to the model is created, and the current distribution is calculated. After setting the pitch for equalizing the current distribution of each layer of the conductor layer and the shielding layer, the twist pitch of the filament was set under that condition, the magnetic field distribution was obtained from the current distribution, and the AC loss was calculated. .

(Modeling) A superconducting cable including a core material, a conductor layer (core), a magnetic shielding layer (shield), and a terminal was regarded as an equivalent circuit as shown in FIG. That is, the core material and the conductor layer are regarded as a lumped constant circuit in which inductive reactance and resistance are arranged in series. It is assumed that _Iall is supplied from an external power supply to the conductor layers, and insulation is provided between the conductor layers.

[0065] The magnetic shielding layer is connected tape-like superconducting multifilamentary wire is in connection resistance r _j at the end, and as forming a loop as shown in Figure 1. I _0, i ₁ ... the current flowing through the respective layers in FIG, L _co, L _c1 ... is the inductance due to the circumferential direction magnetic field of each layer, L _ao, L _al ... an inductance due to the axial magnetic field of the respective layers, r _0, r ₁ ... is the effective resistance of each layer, r _j is the inductance and resistance of the terminal, and V _c and V ₁ are the voltages on the conductor layer side and the magnetic shielding layer side, respectively. The suffix 0 represents the core material, and the conductor layer or the magnetic shielding layer is represented as 1, 2, 3,... From the inner layer. This model considers four conductor layers and two magnetic shielding layers.

(Derivation of Inductance) Regarding the inductance of each superconducting layer, the circumferential component is defined as Formula 1 and the axial component is defined as Formula 2 in consideration of the mutual inductance between the layers.

[0067]

(Equation 1)

[0068]

(Equation 2) Here, a _n in the expression is the radius P _n of the n-th layer and the pitch of the n-th layer. k is 1 when the n layer is Z-twisted, and 2 when the S layer is S-twisted.

(Derivation of Resistance Component) The resistance component of each layer is derived from the theoretical AC loss value W _norris (Norris' equation) of the strands constituting the conductor layer. At this time, the effective resistance r _wire per one _wire is defined as Expression 3 using the current I _wire flowing through the _wire .

[0070]

(Equation 3)

Here, the wire loss W _norris is expressed as z = I _wire /
Assuming Ic, when z <1 (less than the critical current value), Equation 4 is obtained from Norris' equation.

[0072]

(Equation 4)

Then, when z> 1, the flux throw loss is as shown in Expression 5.

[0074]

(Equation 5)

Here, n is the n value near Ic when the voltage is proportional to the current n raised to the nth power.
1 is set to be continuous with Equation 4. Equation 4
5 agrees well with the experimental results.

For the joint resistance, the terminal resistance value (3 × 10 ⁻⁶ Ω / cable length) determined in the test was adopted.

(Circuit Equation) In this model, the circuit equation is as follows.

[0078]

(Equation 6)

In the above equation, the pitch of each layer as an initial condition,
L _c, L _a, be given the _{r 1, I all, i 0} ~i 6, V c, by 9-way simultaneous equations relating V _s, it is possible to obtain a current distribution of each layer by computation.

(Calculation of current distribution) In the calculation, first, an initial current distribution (current value of each layer) is appropriately given to the entire energized current (I _all ), and the resistance value of each superconducting layer at that time is determined by the aforementioned resistance value. Determined according to the component derivation process. Then, since all the numerical values except i _i , V _c , and V _s in the circuit equation of Expression 6 become known values, it is possible to obtain i _{o to} i ₆ , V _c , and V _s by solving Expression 6. . After the resistance value of each superconducting layer is obtained again based on this current value, i _{o to} i ₆ are obtained from Expression 6. This work,
The process is repeated until the difference between the calculation results before and after the calculation becomes equal to or smaller than a certain value. In this case, when the difference between the calculation results before and after becomes 1% or less, the calculation is considered to be completed.

Although the current distribution should be obtained by solving the circuit equation of Equation 6, the answer cannot be found analytically because the effect that the resistance component in the circuit changes due to the current needs to be taken into account. By adopting the technique of "repeating until the difference between the calculation results before and after the calculation becomes equal to or less than a certain value", the current distribution of the superconducting cable under an arbitrary winding pitch condition can be estimated by calculation for the first time. Since the current distribution is obtained at the time of passing through the above process, the AC loss is obtained by the following process based on the result.

(Calculation of Magnetic Field) In this model, the conductor layer has a structure in which a plurality of tape-shaped superconducting multifilamentary wires are spirally wound. As shown in FIG. And the conductor axial magnetic field component.

At this time, the circumferential magnetic field component H applied to the n-th layer
_cn (unit: A / m) is represented by Expression 7.

[0084]

(Equation 7)

The axial magnetic field component H added to the n-th layer
_an (the unit is A / m) is represented by Expression 8.

[0086]

(Equation 8)

(Calculation of AC Loss) The AC loss of the conductor was calculated by modeling the conductor into n adjacent infinite planes as shown in FIG. Such modeling is, for example, "H.IS
HII (ISS'97 Proceedings) "etc., and it is a simple model to represent the magnetic field distribution of a cylindrical conductor.

The magnetization loss of the conductor is the sum of the magnetization losses of the respective layers. The magnetization loss of a conductor using a twisted strand is calculated by calculating the magnetization loss per filament in each layer and the coupling loss per strand, and based on this, the AC loss of the conductor is calculated.

The magnetization loss W _f per filament (unit: W / m ³ ) is given by a formula (Formula 9,
10).

[0090]

(Equation 9)

[0091]

(Equation 10)

Here, Equation 9 is for the case where the magnetic field does not penetrate the entire filament, and Equation 18 is for the case where the magnetic field has penetrated the entire filament. f is the frequency (Hz), J _c is the superconducting filament critical current density (A / m ^2), Hm is the peak value of the external magnetic field (A / m), t is the thickness of the filament (m).

[0093] The H _opn's a size n layer of the circumferential magnetic field component H _cn the axial field component H _an, (external magnetic field for the n layer portion) field current flowing through the non-n layer is made in the n layer portion When used, _Hopn is represented by Equation 11.

[0094]

[Equation 11]

Here, the magnetic field I generated by the current flowing through the n-layer
_opn (the self-magnetic field for the n-layer) was set to be sufficiently smaller than that of _Hopn . Based on this value, the magnetization loss W _fn per unit length of the n-th layer was obtained by Expression 12.

[0096]

(Equation 12)

[0097] x _n is the number of filaments in strand, y _n is the number of the strands of the n-th layer, the S _f is the cross-sectional area of one filament.

The coupling loss W _c (W /
m ³ ) is represented by Expression 13.

[0099]

(Equation 13)

Here, λ is the occupancy of the superconductor in the superconducting wire, σ _i is the equivalent conductivity in the superconducting flux, and l _p is the twist pitch of the wire.

Based on this value, the coupling loss W _cn per unit length of the n-th layer was obtained by Expression 14.

[0102]

[Equation 14]

However, when ωγ> 1, it is assumed that the effect of reducing the AC loss due to the twist is small, and the overall Jc = Jc of the wire, the thickness of the filament = the thickness of the tape-shaped superconducting multi-core wire, the number of filaments = 1, The loss _Wfn and _Wcn are calculated when the coupling loss is zero.

If the frequency is 50 Hz, the magnetic permeability is 4π × 10 ⁻⁷ , and the specific resistance is 77K of pure silver, the twist pitch is 1
At 2 mm or less, ωγ <1.

The loss W (W / m) of the entire conductor is expressed by Expression 15.

[0106]

(Equation 15)

In accordance with the above-described concept, a simulation code for analyzing the system by calculating the magnetic field distribution of the conductor and the amount of AC loss was prepared and incorporated into a computer to obtain an analysis device.

FIG. 4 shows the flow of calculation using this code.
Returning from the step of “current distribution calculation” to the step of “setting the pitch of each layer” indicates that the process is repeated until the difference between the calculation results before and after the calculation becomes equal to or smaller than a certain value. The reason for returning from the “AC loss calculation” step to the “Set twist pitch of each layer” is to perform AC loss calculation at a certain twist pitch and change the twist pitch until the loss becomes less than or equal to a predetermined value. This indicates that the calculation is repeated. This predetermined value is preferably set to about 1 W / m in total loss due to restrictions of the cooling system.

In the above code, the winding pitch of each layer and the twist pitch of the filament are input independently in different steps, but it is also possible to input the winding pitch and the twist pitch of the filament simultaneously. In that case, it is possible to adjust the impedance at the filament level of the strand.

Using the above analyzer, the relationship between the AC loss of the cable conductor and the twist pitch was examined. The cable conductor structure is the same as the cable described in the first embodiment except that the filament of the tape-shaped superconducting multi-core wire is twisted and the matrix is made of an Ag-Au alloy. The tape-shaped superconducting multi-core wire used in this example, after obtaining a multi-core superconducting wire, subjected to twist processing at a required pitch,
Further, the wire was lightly drawn and then rolled into a tape. In the obtained tape-shaped superconducting multifilamentary wire, as shown in FIG. 5, a filament of a superconductor is embedded in a matrix of an Ag-Au alloy, and the filament is formed in a spiral shape. Since the shorter the twist pitch of the filament is, the more effective it is to reduce the AC loss, 10 mm was selected as the shortest possible twist pitch. Table 2 shows the specifications of the tape-shaped superconducting multi-core wire. In Table 2, "base metal specific resistance" is the specific resistance of the Ag-Au alloy, and "jacket thickness" is the matrix (here, Ag
-Au alloy), the "filament volume fraction" is the volume fraction of the filament per unit volume of the tape-shaped superconducting multifilamentary wire, and "Ic / wire" is the tape-shaped superconducting multifilamentary wire 1
It shows the critical current value per book.

[0111]

[Table 2]

As a result of the calculation, the conductor AC loss was 0.7 W / m, and it was found that a practical level of AC loss could be realized even with a tape-shaped superconducting multi-core wire having a thickness of 0.24 mm. That is, even with a compact conductor having a cable conductor outer diameter of 40 mm or less including the shielding layer, the AC loss when a large current of 8.4 kAp is applied can be made 1 W / m or less.

(Embodiment 3) As in Embodiment 2, the electromagnetic coupling between the superconducting filaments is eliminated by using a twisted tape-shaped superconducting multifilamentary wire, and the specific resistance of the matrix is approximately equal to that of silver. It was found that using a 100 × 1 × 10 ⁻⁷ Ωm strand, a compact and large-capacity conductor with a loss of 1 W / m or less could be realized.

However, in practice, it is very difficult to increase the resistance of the matrix of a high-temperature superconductor which easily reacts with a metal other than silver immediately. Also, in the case of tape-shaped high-temperature superconducting wires in which the superconducting filament is made of ceramics, there is bridging in which the filaments are connected to each other to form a network-like current path due to workability problems. It is difficult. Therefore, the following conductor structure was studied as a conductor that overcomes these problems.

Core material-Stranded wire structure using insulated wires corresponding to eddy current loss in the axial direction. Tape-shaped superconducting multi-core wire for conductor layer and magnetic shielding layer-Uses a wire in which the filament in the strand is twisted. -Uses a wire with a high resistance barrier layer applied to the superconducting filament. -The pitch of each layer of the strand is adjusted so that the current of each strand becomes uniform.

The tape-shaped superconducting multifilamentary wire having a high resistance barrier layer is preferably produced by a powder-in-tube method. An example of this manufacturing method is as follows.

As in Example 1, Bi ₂ O ₃ , PbO, SrCO ₃ , C
aCO ₃ and CuO are mixed in a predetermined composition ratio, and heat treatment and pulverization are repeated on the powder to obtain a submicron powder. After heat treating this powder at 800 ° C for 2 hours, the outer diameter is 25mm and the inner diameter is 22mm.
mm of the first silver pipe and fill the first silver pipe with a diameter of 20 mm.
Wire drawing up to mm.

Next, a second silver pipe having an outer diameter of 23 mm and an inner diameter of 22 mm was prepared, and the first silver pipe filled with powder was inserted into the second silver pipe, and a high-resistance barrier layer was formed between the two pipes. Become Sr
-Fill with VO oxide. This second silver pipe has a diameter of 1.44
Draw to a single-core superconducting wire. 37 single-core superconducting wires were fitted into a third silver pipe having an outer diameter of 14 mm and an inner diameter of 13 mm, and were drawn to a diameter of 1.25 mm to form a multi-core superconducting wire. This multifilamentary superconducting wire is twisted at the required pitch, further lightly drawn, and then rolled.
Heat treatment was performed at 0 ° C. for 50 hours to obtain a tape-shaped superconducting multi-core wire having a thickness of 0.24 mm.

The cross section of the tape-shaped superconducting multi-core wire is shown in FIG.
As shown in the figure, a plurality of filaments 2
Are arranged, and the outer periphery of the filament 2 is covered with the high-resistance barrier layer 3.

Using the tape-shaped superconducting multi-core wire described above, a cable conductor having the same structure as in Example 1 was prototyped, and the AC loss was estimated. As a result, the conductor AC loss was 0.2 W / m. By using a tape-shaped superconducting multi-core wire with a high resistance barrier layer, even when a large current of 8.4 kAp is applied to a compact conductor with a conductor outer diameter of 40 mm or less including the shielding layer,
A conductor with an AC loss of 1 W / m or less can be realized.

When a high resistance barrier is arranged, the specific resistance of the effective base material increases. The equivalent electric conductivity σ _i in the superconducting flux in the above-mentioned Expression 13-C is expressed as Expression 16 when the electric conductivity of the base material is σ _O.

[0122]

(Equation 16)

On the other hand, when a high resistance barrier layer having a conductivity σ _m is provided, the equivalent conductivity σ _i in the superconducting flux can be approximated as in Expression 17.

[0124]

[Equation 17]

Therefore, if a high-resistance barrier material having a resistance about two orders of magnitude higher than silver is provided, the equivalent conductivity will be about two orders of magnitude higher, and the high-resistance barrier material such as Sr-V-0 described above will not be sufficiently used. Satisfies this condition (Multi-core wire and conductor Fumio Sumiyoshi, Kazuo Funaki, Sangyo Tosho). At this time, since there is a relationship of ωτ∝σ _i · l _p ² , the upper limit of the twist pitch at which the twist is effective increases by about one digit.

Heretofore, it has been considered that the effect of reducing the loss by the twist is not obtained only with the short pitch twist due to the restriction of the specific resistance of the base material. However, by arranging the high resistance barrier layer, even with a long pitch twist that can be easily processed, a twist condition effective for reducing the AC loss of the conductor can be realized.

[0127]

As described above, according to the superconducting cable of the present invention, the current in the conductor layer can be made uniform and the AC loss can be greatly reduced. In particular, if a wire having a high resistance barrier layer applied to a superconducting filament is used, further reduction in AC loss can be achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a method of modeling a superconducting cable into an equivalent circuit.

FIG. 2 is an explanatory diagram of a magnetic field component during energization in a superconducting cable.

FIG. 3 is an explanatory diagram of a method of modeling a cylindrical conductor into an infinite plane.

FIG. 4 is a flowchart of a procedure for evaluating an AC loss of a superconducting cable.

FIG. 5 is a schematic perspective view of a twist line.

FIG. 6 is a cross-sectional view of a tape-shaped superconducting multi-core wire having a high-resistance barrier layer.

[Explanation of symbols]

 1 Matrix 2 Filament 3 High resistance barrier layer

Claims (4)

[Claims] 1. A core material, a conductor layer having a laminated structure in which a plurality of tape-shaped superconducting multi-core wires are spirally wound around the outer periphery of the core material, an electrical insulating layer, and a plurality of tape-shaped superconducting wires disposed on the outer periphery of the insulating layer. A superconducting cable comprising: a magnetic shielding layer having a laminated structure formed by spirally winding a multifilamentary wire, wherein the superconducting cable has the following configuration. At least one of the conductor layer and the magnetic shielding layer has a different winding pitch from the other layers. The tape-shaped superconducting multifilamentary wire has a configuration in which a superconducting filament is embedded in a matrix, and this filament is twisted in a spiral shape. The core is formed by twisting insulated wires. 2. The superconducting cable according to claim 1, wherein a high resistance barrier layer is provided on the outer periphery of the superconducting filament. 3. A core material, a conductor layer having a laminated structure formed by spirally winding a plurality of tape-shaped superconducting multi-core wires on the core material,
A superconducting cable comprising an electric insulating layer and a magnetic shielding layer having a laminated structure in which a plurality of tape-shaped superconducting multi-core wires are spirally wound on the insulating layer, wherein the tape-shaped superconducting multi-core wire has a thickness of 0.15. A superconducting cable having a diameter of not more than mm. 4. A core material, a conductor layer having a laminated structure in which a plurality of tape-shaped superconducting multi-core wires are spirally wound around the outer periphery of the core material, an electric insulating layer, and a plurality of tape-shaped superconducting wires disposed on the outer periphery of the insulating layer. A method for analyzing the current distribution of a superconducting cable comprising a magnetic shielding layer having a multilayer structure formed by spirally winding a multi-core wire, comprising the following processes: . A process of modeling the core, the conductor layer and the magnetic shielding layer into a circuit composed of at least an inductive reactance. Specifications of core material including core size and specific resistance, critical current and size, specifications of tape-shaped superconducting multi-core wire including twist pitch of filament embedded in tape-shaped superconducting multi-core wire, conductor layer and magnetic shielding layer Spiral winding direction and pitch, thickness and outer diameter of conductor layer and magnetic shield layer, specifications of conductor layer and magnetic shield layer including number of conductor layers and magnetic shield layer, and necessary parameters including frequency and current flow The process of entering. The process of calculating inductance and effective resistance in a circuit using input parameters. A process of creating a circuit equation based on the model and calculating a current distribution of each layer.