JP2001266668A - Superconducting cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a superconducting cable, particularly a superconducting cable having a core material and a multi-layer superconductive conductor with a reduced alternating current loss through an accurate current distribution analysis. SOLUTION: This superconducting cable comprises a core material, a conductor layer with a supercondcuting wire wound spirally around the core material, an electrically insulated layer, and a magnetic shielding layer around which a superconducting wire is spirally wound. In the superconducting element wire the shortest pitch is disposed on the outermost layer of the conductive layer while the longest pitch is disposed on the outermost layer of the magnetic shielding layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a superconducting cable. In particular, the present invention relates to a superconducting cable in which an AC loss is reduced by analyzing a current distribution of a superconducting cable having a core material, a multilayer superconducting conductor, and a magnetic shielding layer.

[0002]

2. Description of the Related Art There is known a superconducting conductor structure in which a tape-shaped superconducting element wire is spirally wound around a core material at the same pitch to form a multilayer structure. In such a conductor, there is a problem of drift in that the current density is lower in the inner superconducting layer and higher in the outer superconducting layer. It is considered that the AC loss increases due to the drift, and a reduction in the AC loss is required.

The invention described in Japanese Patent Publication No. Sho 29-6685 is known as a basic technique for suppressing the drift and loss of a multilayer conductor. This is a technique of adjusting the spiral winding pitch of each layer to adjust the impedance of each layer. Others
Japanese Unexamined Patent Publication No. Hei 11-506261 discloses a structure of a superconducting cable having a magnetic shielding layer in which a superconducting element wire is wound.

[0004]

However, in the superconducting conductor, no specific policy has been established for how to adjust the winding pitch. This is because the current-voltage characteristics of the superconducting conductor are non-linear, and the effective resistance changes with the flowing current. Unless this is taken into consideration, the current distribution and AC loss of the superconducting conductor cannot be predicted. On the other hand, no specific method has been established for how to consider the effective resistance.

Further, a method of analyzing current distribution and AC loss in a superconducting conductor in consideration of a core material and a superconducting magnetic shielding layer has not been established. This is because it has not been established what kind of equivalent circuit the high-temperature superconductor should be modeled.

Furthermore, the AC loss characteristics of the superconducting conductor including the core material and the magnetic shielding layer have not been clarified experimentally.
Theoretically, no model has been reported that considers the resistance and impedance of the core material at the same time. One of the reasons is that numerical calculations become very complicated if these are taken into account.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide a superconducting cable in which the current distribution of a superconducting cable, particularly a superconducting cable having a core material and a multilayer superconducting conductor, is accurately analyzed to reduce the AC loss. .

[0008]

According to the present invention, the reason why the AC loss of the cable takes the minimum value is not when the current in each layer is made uniform, but when the current flowing through the strand in the conductor layer is made uniform. The above object is achieved by optimizing the winding pitch of each superconducting wire in the conductor layer and the magnetic shielding layer.

That is, the cable of the present invention comprises a core material, a conductor layer in which a superconducting element wire is spirally wound on the core material, an electrical insulating layer, and a magnetic shielding layer in which the superconducting element wire is spirally wound. It is a superconducting cable equipped. The current values of the wires in each conductor layer and each magnetic shielding layer are analyzed by the following process, and the pitch between each conductor layer and each magnetic shielding layer is set based on the analysis result. .

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, specifications of superconducting wire including critical current and size, direction and pitch of spiral winding of conductor layer, thickness and outer diameter of conductor layer, number of conductor layers The process of entering the specifications of the conductor layer, including, as well as the required parameters, including frequency and current carrying. 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, the absolute value of the analysis current analyzed by the above process is different from the value I _all / n obtained by dividing the set value of the conduction current I _all by the number n of the wires used for the conductor layer. 30
%, The pitch of each superconducting element including the magnetic shielding layer is preferably set. A more preferable range of the absolute value of the analysis current is ± 20%, more preferably ± 5%, with respect to I _all / n. However, when the number of strands in each layer is substantially the same, for example, when the number of conductor layers is small, the minimum value of AC loss can be realized by equalizing the current in each layer. And even if the critical current of each layer is different due to the influence of the magnetic field and the bending strain due to the spiral winding,
By defining the critical current of the strand for each layer, the analysis by the above process is possible.

The number of conductor layers and magnetic shielding layers may be one or multiple. It is preferable that the layers of the superconducting element wires in the conductor layer and the magnetic shielding layer are electrically insulated from each other 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 modeling process 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.

To obtain a current distribution based on a modeled equivalent circuit, it is necessary to set necessary parameters for the modeled equivalent circuit in order to calculate inductance and effective resistance.

The parameters include wire material specifications (width, thickness, Ic), core material specifications (specific resistance, outer diameter, thickness), conductor layer
Specifications of the magnetic shielding layer (winding direction and pitch of each layer, outer diameter of each layer, thickness of each layer, Ic retention rate in each layer), and energizing conditions (current and frequency).

In calculating the effective resistance, it is preferable that the resistance in the lumped constant circuit is treated as being changed by a 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. Is a source of 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 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 of the superconducting wire is
_{eff is set} to R _eff = W _layer / I ² using the AC loss amount W _layer and the conduction current I of each _layer, and R _eff may be regarded as the resistance in the lumped constant circuit. And this loss amount W _layer
Is preferably calculated based on the alternating current-loss characteristic of the superconducting element wire. For example, the AC loss amount W _layer may be obtained from the Norris equation. Then, the equation for calculating the AC loss W _layer when I> Ic is represented by the AC loss W when I <Ic.
_What is necessary is just to make it continuous with the formula which _{calculates |} requires a _layer .

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. If the current distribution of each layer is obtained, the current flowing per strand can be easily estimated from the current of each layer.

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.

As a specific structure of the superconducting cable which has been found based on the above process and in which the AC loss is reduced, a core material, a conductor layer in which a superconducting element wire is spirally wound on the core material, an electric insulating material, A superconducting cable comprising a layer and a magnetic shielding layer in which a superconducting element wire is spirally wound, wherein the shortest pitch in the superconducting element wire is arranged on the outermost layer of the conductor layer, and the longest pitch is determined by magnetic force. It may be arranged on the outermost layer of the shielding layer.

Furthermore, it is preferable that the shortest pitch of the superconducting wires in the conductor layer satisfies the following expression. By satisfying this condition, deterioration of the superconducting wire due to bending strain can be suppressed, and a superconducting cable having a large critical current and a small AC loss can be configured.

[0029]

(Equation 2)

It is also desirable that the longest pitch of the superconducting wires in the magnetic shielding layer satisfies the following expression. By satisfying this condition, deterioration of the superconducting element wire due to tension can be suppressed, and a superconducting cable having a large critical current and a small AC loss can be configured. Breaking load of superconducting wire> frictional force (kg / m) x length of superconducting wire for half pitch (m) + winding tension (kg)

Further, the circumferential magnetic field component and the axial magnetic field component of each layer are analyzed by the above process,
Among the analyzed magnetic field components, the magnetic shielding is such that the circumferential magnetic field component has only one maximum value from the inner layer to the outer layer, and the axial magnetic field component has a monotonically decreasing distribution from the inner layer to the outer layer. It is preferable to set the pitch of the superconducting wires including the layer. With this configuration, even when the variation of Iall / n is not within 5%, it is possible to obtain a conductor in which the AC loss is set to a small pitch.

[0032]

Embodiments of the present invention will be described below. <Test Example 1> Before describing the structure of the superconducting cable of the present invention, a method for accurately analyzing the AC loss of the superconducting cable will be described. The cable of the present invention is configured based on the analysis result of this analysis method.

Here, a core material, a conductor layer in which superconducting wires are wound in multiple layers around the core material, an insulating layer formed in the outer periphery of the conductor layers, and a superconducting wire wound in multiple layers around the insulating layer. AC loss is determined for a three-phase superconducting cable having a magnetic shielding layer. The procedure for finding the AC loss is to model the superconducting cable into an equivalent circuit, derive the inductance and the effective resistance, create a circuit equation corresponding to the model,
The current distribution is calculated. Then, the magnetic field distribution is obtained from the current distribution, and the AC loss is calculated.

(Modeling) Focusing on one phase of the three-phase cable, a superconducting cable including a core material, a conductor layer (core), a magnetic shielding layer (shield), and a terminal and an equivalent circuit as shown in FIG. Was considered. 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.

Further, the magnetic shielding layer has a superconducting element wire connected at an end thereof with a connection resistance r _j to form a loop as shown in FIG. In the figure, i ₀ , i ₁ ...
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 ... the effective resistance of each layer, r _j is the inductance and resistance of the terminal , V _c , and V ₁ are 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 (conductor layer and magnetic shielding layer), the circumferential component is calculated by taking into account the mutual inductance between the layers.
It was defined as 1 and the axial component was defined as Equation 2.

[0037]

(Equation 3)

[0038]

(Equation 4) 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 .

[0040]

(Equation 5)

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

[0042]

(Equation 6)

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

[0044]

(Equation 7)

Here, n is the value of n 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.

[0048]

(Equation 8)

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. 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.

The current distribution should be obtained by solving the circuit equation of the equation (6). However, since it is necessary to incorporate the effect that the resistance component in the circuit changes with the current, the answer cannot be found analytically. 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 superconducting wires are spirally wound. As shown in FIG. It can be considered separately for the 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.

[0054]

(Equation 9)

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

[0056]

(Equation 10)

(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 each layer can be expressed by using the formula (Formula 9 and Formula 10) of the magnetization loss of the superconducting flat plate based on the Bean model.

[0059]

[Equation 11]

[0060]

(Equation 12)

Here, Equation 9 indicates that the magnetic field penetrates the entire flat plate.
If not, Equation 10 indicates that the magnetic field has penetrated the entire plate.
The magnetic field penetrates evenly from both sides of the plate.
It is assumed that F is frequency (Hz), Hm is outside
Partial magnetic field peak value (A / m), J _cIs the critical current density of the superconductor
Degree (A / m^Two) And t are the thickness (m) of the flat plate.

Using equations (9) and (10), the first
As in the case of the superconducting flat plate, the magnetization loss Wn of the _n- layer is different depending on whether the magnetic field does not penetrate the entire layer, or when the magnetic field penetrates the entire layer. It becomes 12.

[0063]

(Equation 13)

[0064]

[Equation 14]

Here, _Hopn is the magnitude of the magnetic field (external magnetic field for the n-layer part) created in the n-layer part by the current flowing in the layers other than the n-layer,
_opn is the magnitude of (the self-magnetic field for the n layer portion) magnetic field generated current flowing through the n-layer, using the circumferential magnetic field component H _cn the axial field component H _{a n} of n layer described in the previous section, _Hopn is given by Equation 13
It is represented by

[0066]

(Equation 15)

[0067] Further, using a current i _n flowing through the n-layer, I _opn
Is represented by Expression 14.

[0068]

(Equation 16)

Each of these units is A / m. R _n is the radius of the n-layer, and J _e is the overall J _c , t of the n-layer.
_an is the magnetic field penetration depth of the n-layer part viewed from the outside, and t _bn is the magnetic field penetration depth of the n-layer part viewed from the inside. Further, the unit of W _n is W
The unit of / m, _Hopn and _Iopn is A / m.

The eddy current loss W _{f, e} of the core material was calculated by the following equation (15).

[0071]

[Equation 17]

Equation 15 is, for example, “Case Studies in S
uperconducting Magnets "(PLENUM PUBLISHING C
o.) on page 41, where ρ is the specific resistance of the core material (＠ 77
K) and _Rf are the outer radius of the core, d is the thickness of the core, and _Hao is the axial magnetic field of the core.

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 provide an analyzer.

FIG. 4 shows the flow of calculation using this code. The calculation procedure is as shown in each of the following steps.
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.

Basic parameter setting: Parameters include wire material specifications (width, thickness, Ic), core material specifications (specific resistance, outer diameter, thickness), conductor specifications (winding direction of each layer, outer layer of each layer) Diameter, thickness of each layer, Ic retention rate in each layer), and energization conditions (energization current, frequency). Pitch input of each layer Calculation of inductance and effective resistance of each layer Creation of simultaneous equations and calculation of current value of each layer Calculation of magnetic field distribution and conductor AC loss in the calculated current distribution

<Test Example 2> A pitch-adjusting conductor with a magnetic shielding layer was designed and trial-produced using the above-described analyzer, and the AC loss measurement result was compared with the loss obtained in this simulation.
The specifications of the conductor are shown below. The pitch between the conductor layer and the shielding layer was set such that the current in each superconducting layer became substantially uniform.

Core material: Copper Outer diameter: φ19.2mm Wall thickness: 0.9mm Specific resistance (＠ 77K): 3 × 10 ^-9 Ωm Conductive layer Element wire: Bi2223-based Ag-Mn alloy coated high-temperature superconducting tape wire (thick Number of layers: 4 layers (with interlayer insulation) Winding direction: S / S / S / S Winding pitch: 1st layer 360mm / 2nd layer 200mm / 3rd layer 110mm / 4th layer 70mm Insulating layer Material: Paper Thickness: 7mm Magnetic shielding layer Element wire: Bi2223-based Ag-Mn alloy coated high-temperature superconducting tape wire (thickness 0.24mm) Number of layers: 2 Winding direction: S / S Winding pitch: 1st 180mm / 2nd 360mm

As a result of the direct current test, the conductor Ic was 2000 A (1 μm).
V / m definition). The experimental value and the calculated value were compared for the AC loss of the conductor layer. FIG. 5 shows the results. The experiment simulated the shielding effect of the magnetic shielding layer, connected the conductor layer and the magnetic shielding layer in series, applied an alternating current, and measured the voltage of the conductor layer. The frequency was 50 Hz, the temperature was 77 K, and the measurement was performed by an AC four-terminal method using soldered voltage terminals. At this time, the AC loss of the conductor layer can be estimated from the measured resistive voltage (voltage in phase with the flowing current). As shown in FIG. 5, it was confirmed that the experimental value and the calculated value agreed very well.

The dashed line in FIG. 5 is the theoretical value of the AC loss of the conductor obtained from the mono-block model (a model applicable to the case where the current flows in a non-uniform manner), but the experimental value deviates greatly from the dashed line. Furthermore, it was confirmed that drift was actually suppressed in the conductor in which the pitch at which the current of each layer was made uniform by the analysis code was actually set.

With respect to this conductor, the current of each layer obtained by the simulation code is divided by the number of wires of each layer to obtain a wire.
The current flowing per line was estimated. Then, as compared with the case where the current flowing through the strand was completely uniform (I _all / n), the variation Δ reached a maximum of 20% (when 2000 A was energized).

In order to suppress the variation Δ, the pitch of the innermost layer (the first layer) was changed to 340 mm for calculation, and the variation Δ was suppressed to a maximum of 15%, and the loss was 2,000 A. Sometimes the result was about 3% reduction.

From the above results, it can be seen that in the superconducting element wires, the shortest pitch may be arranged on the outermost layer of the conductor layer, and the longest pitch may be arranged on the outermost layer of the magnetic shielding layer.

The pitch of the conductor of Test Example 2 was reexamined on the assumption that the AC loss could be further reduced by reducing this variation. As a result, it was found that when the pitch of the conductor layer was set to 420 mm / 270 mm / 140 mm / 80 mm from the inner layer and the pitch of the magnetic shielding layer was set to 260 mm / 560 mm from the inner layer (minimal condition), the variation Δ was minimized. .

FIG. 6 shows that the minimum value of 4
The relationship between the pitch and the maximum variation Δ when only the pitch of the layer is changed, and the relationship between the pitch and the AC loss (normalized by the minimum value of the AC loss) are shown. As shown in this graph, the current of the wire is not completely uniform, but if the maximum value Δ of the deviation of the wire current from the ideal value is within 5%, it is possible to select the minimum value of the loss. I understand.

<Test Example 3> It was confirmed that the calculated value and the measured value of the conductor AC loss designed using the analyzer in Test Example 2 were in good agreement. However, this conductor has a minimum pitch of 70
mm, the Ic of the wire is reduced by the bending strain during the spiral winding, the Ic retention of the fourth conductive layer is reduced, and the Ic of the conductor is lower than an ideal value.

Strain ε _a applied to tape wire during spiral winding
Can be expressed by Equation 16 where t is the thickness of the tape wire, P is the spiral winding pitch, and D is the outer diameter of the core material. Therefore, the shortest pitch of the superconducting wires may be set so that ε _c (critical bending strain of the superconducting wires)> ε _a . The critical bending strain ε _c may be a strain in a bending state in which a decrease in Ic of the superconducting wire becomes remarkable. For example, with respect to Ic of the superconducting wire without added bend, reduction ratio of Ic is the critical bending strain epsilon _c strain when is 2% or more.

[0087]

(Equation 18)

FIG. 7 is a graph showing the relationship between the pitch and the distortion using the equation (16). Here, the thickness of the tape wire and the size of the core material were 0.24, respectively, as in Test Example 2.
mm and φ19.2 mm.

From the experiments so far, it has been found that the decrease in Ic of the superconducting wire due to the spiral winding can be prevented by setting the range of 0.3% or less in the formula (16). It turned out that it is necessary to set the pitch to 100 mm or more in the conductor of the specifications. In this example, the critical bending strain of the superconducting wire is set to 0.3%, but it goes without saying that this value may be determined according to the characteristics of the superconducting wire.

Further, it has been found that when the longest pitch in the conductor exceeds 600 mm, disconnection frequently occurs due to pulling caused by drum winding. This longest pitch can be obtained as follows. That is, the tension applied to the superconducting wire at the time of bending the cable determined by Expression 17 may be set so as to be less than the breaking load of the superconducting wire.

Friction force (kg / m) × length of superconducting wire for half a pitch (m) + winding tension (kg) Equation 17

The breaking load of a normal superconducting element wire is about 10 kg,
The friction force is about 30 kg / m by actual measurement, and the winding tension is about 1 kg. Therefore, when these values are substituted into Expression 17, the winding pitch is determined to be 600 mm. Of course, since the breaking load, frictional force, and winding tension of the superconducting wire differ depending on the characteristics of the superconducting wire, a value according to the characteristics may be used.

From the above, using the cord of Test Example 1, a condition that the minimum pitch was 100 mm or more and the maximum pitch was 600 mm or less was added to design and prototype a pitch-adjusting conductor with a magnetic shielding layer. The loss obtained in this simulation was compared. The specifications of the conductor are shown below. This time,
As a core material, FRP (FiberRe
inforced Plastics) pipes were used. The pitch between the conductor and the shielding layer was set such that the current in each superconducting layer became uniform.

Core material: FRP pipe Outer diameter: φ19.2 mm Wall thickness: 0.9 mm Conductive layer Element wire: Bi2223-based Ag-Mn alloy coated high-temperature superconducting tape wire (thickness 0.24 mm) Number of layers: 4 layers (interlayer insulation) Available) Winding direction: S / S / Z / Z Winding pitch: 1st layer 140mm / 2nd layer 320mm / 3rd layer 420mm / 4th layer 120mm Insulation layer Material: Paper Thickness: 7mm Magnetic shielding layer Element wire: Bi2223 Ag-Mn alloy coated high-temperature superconducting tape wire (thickness
0.24mm) Number of layers: 2 layers Winding direction: S / S Winding pitch: 350mm for the first layer / 520mm for the second layer

As a result of the DC current test, Ic of the conductor layer was 2100 A
(1μV / m definition) and the wire I without distortion
It was consistent with Ic (2100A) of the conductor estimated from c.

Further, regarding the AC loss of the conductor layer, an experimental value and a calculated value were compared. The experiment simulated the shielding effect of the magnetic shielding layer, connected the conductor layer and the magnetic shielding layer in series, applied an alternating current, and measured the voltage of the conductor layer. The frequency was 50 Hz, the temperature was 77 K, and the measurement was performed by an AC four-terminal method using soldered voltage terminals. At this time, the AC loss of the conductor layer can be estimated from the measured resistive voltage (voltage in phase with the flowing current).

As a result of the experiment, the conductor AC loss when 1 kArms was applied was
0.5 W / m, which is the loss value (0.
47W / m).

Therefore, in the superconducting element wire, the shortest pitch is arranged on the outermost layer of the conductor layer, the longest pitch is arranged on the outermost layer of the magnetic shielding layer, and the shortest pitch is 0.3% or less. A superconducting cable having excellent mechanical characteristics and not causing a decrease in critical current can be constructed by setting the winding pitch to be as follows and setting the longest pitch to such an extent that the wire is not disconnected by the tension accompanying the drum winding (less than 0.6 m).

Further, also for the conductor of Test Example 3, the relationship between the pitch and the maximum variation Δ when only the pitch of the fourth layer in the conductor layer was changed from the manufacturing conditions, and the pitch and the AC loss (minimum AC loss) (Normalized by the value). The relationship is shown in the graph of FIG. As shown in this graph, the current of the wire is not completely uniform, but if the maximum value Δ of the deviation of the wire current from the ideal value is within 5%, it is possible to select the minimum value of the loss. I understand.

<Test Example 4> In the conventional theory, it was considered that the conductor AC loss could be minimized when the current distribution in each layer was completely uniform. However, using the above analyzer,
When we checked the relationship between the variation of the current distribution in each layer and the amount of AC loss in the entire conductor, we found that even if the current in each layer was somewhat uneven, the loss was minimized if the current values of the superconducting wires were uniform. In other words, it has been found that the same level of AC loss as when the current in each layer is uniformed can be realized.

By utilizing this result, if the pitch condition for completely equalizing the current of each layer does not match the mechanical properties of the wire rod, the design is changed to a realistic pitch in terms of mechanical properties. Although a slight current imbalance occurs between the layers, the AC loss can be made substantially the same as when the current distribution in each layer is made uniform.

A specific analysis is made of a conductive layer having a conductive core material (copper) and four superconducting layers formed by spirally winding a plurality of superconducting wires on the core material; For a three-phase superconducting cable (for one phase) composed of a superconducting magnetic shielding layer composed of two layers of superconducting wires, only the pitch is slightly changed to change the current distribution of each layer and the current value of each superconducting wire. I went with subtle changes.

As a result, if the current value (absolute value) of the superconducting element wire based on the analysis result is within ± 5% of a value I _all / n obtained by dividing the set value current I _all by the number n of element wires, If the loss takes a minimum value, the change in the AC loss is 10% or less as compared with the case where the current is completely uniform in each layer. However, it was found that when the fluctuation of the absolute value of the current of the superconducting wire became larger, the loss increased sharply as compared with the case where the current was completely uniform in each layer. Therefore, even if a slight current imbalance occurs between the layers, it is necessary to obtain the current of the superconducting element wire based on the analysis result so that the AC loss is equivalent to the case where the current distribution is completely uniform between the layers. If the pitch of each superconducting element wire including the magnetic shielding layer is set so that the value falls within a range of ± 5% with respect to a value I _all / n obtained by dividing the energizing current as a set value by the number n of elements. good.

As a conventional technique, as a general pitch condition for making the current distribution uniform with a multi-layered superconducting cable having a magnetic shielding layer, there is a technique described in Japanese Patent Publication No. Hei 11-506261. The magnetic shielding layer is set so that the current value (absolute value) of the superconducting wire based on the analysis result is within ± 5% of the value I _all / n obtained by dividing the set value current I _all by the number n of wires. It has been found that when the pitch of each superconducting element wire is set, the current distribution can be made uniform even under the pitch condition that does not satisfy the conditional expression proposed in the above-mentioned publication.

<Test Example 5> The current equalization conditions in a conductor having a larger number of layers were investigated using a simulation code. Table 1 shows the specifications of the calculated superconducting element wires.

[0106]

[Table 1]

Using this superconducting wire, a superconducting conductor structure having a core material, a conductor layer, an insulating layer, and a magnetic shielding layer is manufactured in order from the inner periphery, and the pitch at which the current of each wire is made uniform is calculated. did. Table 2 shows the specifications of the superconducting conductor structure.

[0108]

[Table 2]

Under these conditions, no pitch condition was found in which the variation of Iall / n was within 5%. In such a case, the conditions under which the AC loss was reduced were investigated. As a result of the investigation, we found the conditions that minimize the AC loss. Table 3 shows the pitch conditions.

[0110]

[Table 3]

The loss in this case was estimated to be 2.8 W / m for the conductor layer and the shielding layer. Further, a graph of the magnetic field distribution of each layer was as shown in FIG. The graph shows the circumferential magnetic field component (Bc) and the axial magnetic field component (Bc).
a) shows the total magnetic field component (Ball). The characteristic of this magnetic field distribution is that "the circumferential magnetic field component has only one maximum value from the inner layer to the outer layer, and the axial magnetic field component has a monotonically decreasing distribution from the inner layer to the outer layer."

Next, if the pitch of the eighth conductor layer in Table 3 is changed by ± 10 mm to 150 mm (or 130 mm), the loss increases to 3.0 W / m (3.2 W / m). The magnetic field distribution at this time is shown in FIG. 10 (FIG. 11).

As shown in FIG. 10, under the pitch condition (150 mm) where the loss deviates from the minimum value, the circumferential magnetic field component (Bc)
There are two local maxima, and the axial magnetic field component (Ba) does not have a monotonically decreasing distribution. As shown in Fig. 11, under the pitch condition (130mm) where the loss deviates from the minimum value, the circumferential magnetic field component (Bc) has only one maximum value, but the axial magnetic field component (Ba) monotonically decreases. Not distributed.

By adjusting the pitch of each layer based on the shape of the magnetic field distribution as described above, even when the variation of Iall / n is not less than 5% (when the number of layers is large), the AC loss can be reduced to a small pitch. It is possible to provide a set conductor.

It should be noted that the superconducting cable of the present invention is not limited to the above-described specific example, and it is needless to say that various changes can be made without departing from the gist of the present invention.

[0116]

As described above, according to the superconducting cable of the present invention, the current distribution of the superconducting cable having any core resistance, any conductor size, any spiral winding direction, any spiral winding pitch, As a result of a detailed analysis of the loss, a structure with a small AC loss can be obtained. In particular,
By setting the shortest pitch of the superconducting wires from the viewpoint of bending strain and setting the longest pitch from the viewpoint of tensile strength, a superconducting cable having a high critical current and a small AC loss can be constructed.

[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 graph showing a relationship between current and AC loss.

FIG. 6: Pitch of fourth conductive layer and deviation from ideal value Δ
6 is a graph showing a relationship with the graph.

FIG. 7 is a graph showing the relationship between the pitch of superconducting wires and strain.

FIG. 8 is a diagram showing a pitch Δ of a fourth conductor layer and a deviation Δ from an ideal value.
6 is a graph showing a relationship with the graph.

FIG. 9 is a graph showing a magnetic field distribution of each layer in the superconducting conductor layer and the shielding layer.

[FIG. 10] The pitch of the superconducting element wires in the outermost layer of the conductor layer is 150 mm.
4 is a graph showing a magnetic field distribution of each layer in a superconducting conductor layer and a shielding layer, which are referred to as “superconducting conductor layer” and “shielding layer”.

[FIG. 11] The pitch of the superconducting element wire of the outermost layer of the conductor layer is 130 mm.
4 is a graph showing a magnetic field distribution of each layer in a superconducting conductor layer and a shielding layer, which are referred to as “superconducting conductor layer” and “shielding layer”.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toru Okazaki 1-3-1, Shimaya, Konohana-ku, Osaka-shi Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor Takato Masuda 1-1-1, Shimaya, Konohana-ku, Osaka-shi No. 3 Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor Takeshi Kato 1-3-1, Shimaya, Konohana-ku, Osaka-shi Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor Hiroyasu Yumura Konohana, Osaka-shi 1-3-3, Shimaya-ku, Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor Yoshihisa Takahashi 4-1 Egasakicho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Tokyo Electric Power Company Electric Power Research Laboratory (72) Invention Person Kimiyoshi Matsuo 4-1 Egasaki-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside the Electric Power Research Laboratory, Tokyo Electric Power Company (72) Inventor Shoichi Honjo Yokohama-shi, Kanagawa Prefecture 4-1 Egasakicho, Mi-ku Tokyo Electric Power Co., Inc. Electric Power Research Laboratory (72) Inventor Tomio Mimura 4-1 Egasaki-cho, Tsurumi-ku, Yokohama, Kanagawa Prefecture Reference) 5G321 BA01 CA16 CA26 CA48

Claims (7)

[Claims] 1. A superconducting cable comprising a core material, a conductor layer in which a superconducting element wire is spirally wound on the core material, an electrical insulating layer, and a magnetic shielding layer in which the superconducting element wire is spirally wound. Then, the current value of the wires in each conductor layer and each magnetic shielding layer was analyzed by the following process, and the pitch between each conductor layer and each magnetic shielding layer was set based on the analysis result. Superconducting cable. 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, specifications of superconducting wire including critical current and size, direction and pitch of spiral winding of conductor layer, thickness and outer diameter of conductor layer, number of conductor layers The process of entering the specifications of the conductor layer, including, as well as the required parameters, including frequency and current carrying. 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. 2. The current value of the superconducting element wire in the conductor layer is analyzed by the above-described process, and the absolute value of the analysis current is determined by the number of element wires using the conduction current I _all which is a set value for the conductor layer. 2. The superconducting cable according to claim 1, wherein the pitch of each superconducting wire including the magnetic shielding layer is set so as to fall within a range of ± 30% with respect to a value I _all / n divided by n. 3. The absolute value of the analysis current is a value I _{all obtained} by dividing the set current I _all by the number n of wires used for the conductor layer.
The superconducting cable according to claim 2, wherein the pitch of each superconducting element wire including the magnetic shielding layer is set so as to fall within a range of ± 5% with respect to / n. 4. A superconducting cable comprising a core material, a conductor layer in which a superconducting element wire is spirally wound on the core material, an electrical insulating layer, and a magnetic shielding layer in which the superconducting element wire is spirally wound. A superconducting cable, wherein the shortest pitch of the superconducting wires is arranged on the outermost layer of the conductor layer, and the longest pitch is arranged on the outermost layer of the magnetic shielding layer. 5. The superconducting cable according to claim 4, wherein the shortest pitch of the superconducting wires in the conductor layer satisfies the following expression. (Equation 1) 6. The superconducting cable according to claim 4, wherein the longest pitch of the superconducting wires in the magnetic shielding layer satisfies the following expression. Breaking load of superconducting strand> frictional force (kg / m) x
Length of superconducting wire for half pitch (m) + winding tension (k
g) 7. A circumferential magnetic field component and an axial magnetic field component of each layer are analyzed by the above-mentioned process, and among the analyzed magnetic field components, a circumferential magnetic field component has one maximum value from the inner layer toward the outer layer. 2. The superconducting cable according to claim 1, wherein the pitch of the superconducting wires including the magnetic shielding layer is set such that the axial magnetic field component has a monotonically decreasing distribution from the inner layer to the outer layer.