JP2013148440A - Critical current inspection device and critical current inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress burning of a superconductive wire material when a critical current is generated in spite of a simple structure.SOLUTION: A critical current inspection device 1 includes: a normal conductor 10 electrically connected in parallel to a superconductive wire material 2 and having a prescribed electrical resistance value Rn; and a current power supply 11 which is a constant current source having a variable current value and letting an inspection current I to flow into a parallel circuit 20 including the superconductive wire material 2 and the normal conductor 10. The critical current inspection device 1 varies a current value It of the inspection current I and inspects the critical current based on a current value that excludes a normal conductor shunt current value In which flows into the normal conductor 10 at the time of generating the critical current definition voltage Vt from the current value It of the inspection current I when the critical current definition voltage Vt that defines the critical current is generated in the superconductive wire material 2.

Description

  The present invention relates to a technique for inspecting a critical current of a superconducting wire.

In superconducting wires, critical current is one of the important characteristics that affect performance. The critical current refers to a limit current value that can be passed through the superconductor. Generally, a current value that generates a predetermined electric field (for example, 1 × 10 ⁻⁴ V / m) in the superconductor is defined as the critical current. .
The techniques for measuring this critical current include a direct energization method and an indirect measurement method. The direct energization method is a method in which an inspection current is directly applied to a superconducting wire to measure a critical current, and a DC four-terminal method is known as a representative method. In this DC four-terminal method, the current value of the inspection current passed through the superconducting wire is gradually increased, and the inspection current when a predetermined voltage corresponding to the predetermined electric field (hereinafter referred to as critical current definition voltage) is generated in the superconducting wire. The critical current is measured from the current value (see, for example, Patent Document 1).

  On the other hand, as an indirect measurement method, for example, a method is known in which the magnetization of a superconducting wire is measured with a Hall element and the critical current is obtained by converting the measured value of the magnetization measurement. However, since the conversion from the measured value to the critical current is used, the accuracy is lacking, and the current-carrying characteristics when a current is passed through the superconducting wire may not always match. For this reason, when a critical current characteristic is inspected as one of quality inspections of a superconducting wire, measurement by a direct energization method is often performed from the viewpoint of reliability.

  By the way, when a current in the vicinity of the critical current flows through the superconducting wire, the superconducting wire generates electric resistance and transitions to normal conduction, generating a large amount of heat due to a sudden increase in resistance, and the superconducting wire may burn out. As a countermeasure, in a superconducting wire, a first normal conducting metal layer called a protective layer made of a good conductor such as silver is provided immediately above the superconducting layer. Since this protective layer is usually relatively thin, in order to increase electrical stability and suppress burnout, a second normal conductive metal layer called a stable layer made of a good conductor such as copper is provided immediately above the protective layer. Is provided. As a result, even when the superconductivity of the superconducting layer becomes partially unstable and the resistance rises, the current flows through the stable layer having a lower electrical resistance than the superconducting layer with the increased resistance, so that the burning due to heat generation is not caused. Is prevented.

  However, when a critical current characteristic is inspected as part of quality inspection at a superconducting wire manufacturing site, the critical current cannot be measured unless a stable layer is provided on the superconducting wire. Therefore, the cost loss when a defect is recognized in the inspection of the critical current characteristic is increased by the amount required for the stable layer. In addition, when the formation of the stable layer is insufficient, there is a problem that the superconducting wire generates heat and burns out during the inspection of the critical current characteristics.

  Therefore, when an abnormal current is generated in the superconducting wire, that is, when there is a sudden decrease in critical current, disconnection, or generation of a current having a resistance higher than the resistance generated from the critical current definition voltage, the abnormal current is A technique for preventing burning of the superconducting wire by providing a shunt for bypassing separately from the superconducting wire is known (for example, Patent Document 2).

JP 2009-270916 A JP 2011-123046 A

However, there is a problem that it is very complicated and the configuration is complicated to control the abnormal current so as to go to the shunt when the abnormal current occurs.
The present invention has been made in view of the above-described circumstances, and provides a critical current inspection apparatus and a critical current inspection method capable of suppressing the burning of a superconducting wire when a critical current is generated while having a simple configuration. For the purpose.

  In order to achieve the above object, according to the present invention, a normal conductor having a predetermined electrical resistance value electrically connected in parallel to a superconducting wire, and a supercurrent conducting material and a parallel circuit including the normal conductor are caused to pass a test current. A constant current source of variable current value, and changing the current value of the inspection current, from the current value of the inspection current when a predetermined voltage defining the critical current flowing in the superconducting wire is generated in the superconducting wire, There is provided a critical current inspection apparatus that inspects the critical current based on a current value excluding a current value flowing through the normal conductor when the predetermined voltage is generated.

  Further, in the critical current inspection apparatus, the upper limit is a current value obtained by adding a current value of a critical current preliminarily assumed in the superconducting wire to a current value flowing in the normal conductor when the predetermined voltage is generated. The inspection current is changed, and a failure in critical current characteristics of the superconducting wire is determined based on whether or not the predetermined voltage is generated before reaching the upper limit current value.

  Further, the present invention provides the critical current inspection apparatus, wherein the current value of the critical current preliminarily assumed for the superconducting wire is added to the upper limit current value obtained by adding the current value flowing through the normal conductor when the predetermined voltage is generated. The predetermined electrical resistance value of the normal conductor is set so that a ratio of a current value flowing through the normal conductor when a predetermined voltage is generated is 5% or more.

  Further, the present invention provides the critical current inspection apparatus, wherein the current value of the critical current preliminarily assumed for the superconducting wire is added to the upper limit current value obtained by adding the current value flowing through the normal conductor when the predetermined voltage is generated. The predetermined electrical resistance value of the normal conductor is set so that a ratio of a current value flowing through the normal conductor when a predetermined voltage is generated is 10% or less.

  In the critical current inspection apparatus, when the voltage generated in the normal conductor reaches the predetermined voltage, the inspection current is stopped from flowing into the superconducting wire or flows into the superconducting wire. It is characterized by reducing the current.

  According to the present invention, in the critical current inspection apparatus, a normal conductor having a different resistance value is provided in a replaceable manner in accordance with a current value of a critical current assumed in advance in the superconducting wire.

  In order to achieve the above object, the present invention electrically connects a normal conductor having a predetermined electric resistance value to a superconducting wire in parallel, and configures a parallel circuit including the superconducting wire and the normal conductor, An inspection current is passed through the parallel circuit, the current value of the inspection current is varied, and the normal conductor is generated when the predetermined voltage is generated from the current value of the inspection current when a predetermined voltage defining a critical current is generated in the superconducting wire. The critical current inspection method is characterized in that the critical current is inspected on the basis of a current value excluding a current value flowing through the current.

According to the present invention, the superconducting wire and the parallel circuit including the normal conductor are configured to inspect the critical current characteristics by passing the inspection current to the parallel circuit. Therefore, a sudden increase in resistance occurs in the superconducting wire with the generation of the critical current. However, since a certain percentage of the inspection current is shunted to the normal conductor, it is possible to suppress burning of the superconducting wire while having a simple circuit configuration without providing a special circuit.
Further, since the resistance value of the normal conductor is fixed to a predetermined electric resistance value and known, the current value that flows through the normal conductor when a predetermined voltage that defines a critical current is generated in the superconducting wire is also uniquely determined. By removing the current value from the inspection current, the critical current of the superconducting wire can be obtained.

It is a figure showing typically the composition of the critical current inspection device concerning the embodiment of the present invention. It is a figure which shows typically the example of arrangement | positioning of the normal conductor in a cooling container. It is a flowchart of a critical current characteristic test | inspection.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram schematically showing a configuration of a critical current inspection apparatus 1 according to the present embodiment.
The critical current inspection apparatus 1 is an apparatus that inspects the critical current characteristics of the superconducting wire 2. In particular, the critical current inspection apparatus 1 of the present embodiment is used for quality control at the production site of the superconducting wire 2, and the current value of the critical current of the superconducting wire 2 is the critical current design value (hereinafter referred to as the critical current specification value). Used to check if it falls below. When there is a range in the critical current specification value, the lower limit value of a value that should be satisfied is set as the critical current specification value in terms of product quality.
The superconducting wire 2 to be inspected is formed in a long tape shape having a length ranging from several tens of meters to several kilometers. The superconducting wire 2 is wound around a feed reel 3 and is driven by a so-called reel-to-reel method in which the take-up reel 4 sequentially winds while being fed by the feed reel 3.

  The superconducting wire 2 is obtained by forming a thin film of a superconducting layer on the surface of a tape-like substrate. For this superconducting layer, for example, a high-temperature superconductor that becomes superconducting at a liquid nitrogen temperature (77 K) or higher is used. RE-based superconductors (RE: rare earth elements) are known for high-temperature superconductivity, and in this embodiment, yttrium-based oxide superconductors represented by the chemical formula YBa2Cu3O7-Y are used. The superconducting wire 2 is provided with a protective layer made of a good conductor such as silver (referred to as a first normal conducting metal layer) on the superconducting layer. Further, the superconducting wire 2 is made of a good conductor such as copper on the protective layer. A second normal conducting metal layer called a stable layer may be provided, and in this embodiment, in order to cool the superconducting wire 2 to a superconducting transition temperature, as shown in FIG. A cooling container 5 is disposed in the path, and the cooling container 5 is filled with liquid nitrogen 6. The superconducting wire 2 is liquid in the cooling container 5 by a plurality of rollers 7 appropriately disposed in the traveling path. It is guided to travel in the nitrogen 6. Thus, the superconducting wire 2 is passed through the liquid nitrogen 6 so that it is cooled to a superconducting transition temperature or less and becomes a superconducting state.

The critical current inspection device 1 inspects the critical current characteristic by passing an inspection current through the superconducting wire 2 in the superconducting state in the cooling vessel 5 and monitoring the voltage generated in the superconducting wire 2. Specifically, as shown in FIG. 1, the critical current inspection apparatus 1 includes a normal conductor 10, a current power source 11, a pair of current electrodes 12 and 13, a pair of voltage electrodes 14 and 15, and a first A voltmeter 16 and a second voltmeter 17 and a control device 18 are provided.
The normal conductor 10 is formed of a normal conductive material (for example, a metal having a relatively high conductivity such as copper or a copper alloy is preferable) and has a known predetermined electric resistance value. The parallel circuit 20 is constituted by the normal conductor 10 and the superconducting wire 2 which are always electrically connected in parallel. The normal conductor 10 is disposed in the liquid nitrogen 6 of the cooling vessel 5 and the temperature is kept constant, so that the fluctuation of the electric resistance value accompanying the temperature change is suppressed.
The current power supply 11 is a constant current source that outputs a constant current regardless of load fluctuations on the output side and has a variable output current value. The current power supply 11 is connected in parallel to the parallel circuit 20 and is connected to the parallel circuit 20 as a test current. I flow. The current power source 11 is configured so that the current value It of the inspection current I can be increased sequentially from zero to a preset upper limit current value Imax at a preset sweep speed. The upper limit current value Imax will be described later.

The pair of current electrodes 12 and 13 and the pair of voltage electrodes 14 and 15 measure the current-voltage characteristics of the superconducting wire 2 by the direct current four-terminal method, and each of them is the liquid nitrogen 6 of the cooling vessel 5. Is placed inside.
More specifically, each of the current electrodes 12 and 13 is arranged at a predetermined distance in the longitudinal direction of the superconducting wire 2, and the current power source 11 is connected to the current electrodes 12 and 13. The current electrodes 12 and 13 include upper current electrodes 12A and 13A and lower current electrodes 12B and 13B, respectively, and the superconducting wire 2 is sandwiched between the upper current electrodes 12A and 13A and the lower current electrodes 12B and 13B. It is configured as a so-called clamp-type electrode that allows the inspection current of the current power source 11 to flow through the superconducting wire 2. The normal conductor 10 is connected to the pair of current electrodes 12 and 13 so as to form the parallel circuit 20 with the superconducting wire 2. Therefore, a current obtained by dividing the inspection current I flows through the superconducting wire 2 and the normal conductor 10 according to the reciprocal ratio of the respective resistance values.

  The voltage electrodes 14, 15 are arranged in the longitudinal direction of the superconducting wire 2 inside the spaced apart current electrodes 12, 13 in order to measure the voltage generated in the superconducting wire 2 due to energization between the current electrodes 12, 13. The first voltmeter 16 is connected to the voltage electrodes 14 and 15 at a predetermined distance. The voltage electrodes 14 and 15 include upper voltage electrodes 14A and 15A and lower voltage electrodes 14B and 15B, respectively, and a so-called clamp that sandwiches the superconducting wire 2 between the upper voltage electrodes 14A and 15A and the lower voltage electrodes 14B and 15B. It is configured as a formula electrode. The first voltmeter 16 detects a potential difference generated between the voltage electrodes 14 and 15 as a voltage V1, and monitors the voltage V1 during the inspection so that a critical current defining voltage Vt defining a critical current is obtained. Whether or not the superconducting wire 2 has occurred is detected.

The second voltmeter 17 is for monitoring the voltage V <b> 2 generated in the normal conductor 10 by energization of the current power source 11. As described above, since the normal conductor 10 forms the parallel circuit 20 with the superconducting wire 2, it is possible to detect whether or not the critical current defining voltage Vt has occurred in the superconducting wire 2 based on the voltage V2. Specifically, the second voltage when the critical current defining voltage Vt is generated in the superconducting wire 2 based on the separation distance of the voltage electrodes 14 and 15 and the electric resistance value Rn of the normal conductor 10 between the separation distances. The voltage V2 detected by the total 17 can be obtained in advance as the critical current defining voltage equivalent voltage Vr. At this time, when the second voltmeter 17 measures the potential difference between the pair of current electrodes 12 and 13 connected to the normal conductor 10 as the voltage V2, the critical current defining voltage equivalent voltage Vr is the critical current. It matches the definition voltage Vt.
During the inspection, the voltage V2 of the second voltmeter 17 is monitored to detect whether the critical current definition voltage equivalent voltage Vr has been reached, for example, in the superconducting wire 2 at a location other than between the voltage electrodes 14 and 15. Even in a situation where the critical current defining voltage Vt is not detected by the first voltmeter 16 due to reasons such as current generation, it is possible to quickly detect that the critical current defining voltage Vt is generated in the superconducting wire 2.

  The control device 18 centrally controls each part to execute a critical current characteristic inspection. Specifically, the control device 18 controls the current value It of the inspection current I output from the current power supply 11, the voltage V <b> 1 detected by the first voltmeter 16, and the voltage V <b> 2 detected by the second voltmeter 17. Through the monitoring, it is determined whether or not the current value of the critical current of the superconducting wire 2 falls below the critical current specification value, and if it falls below, a failure determination is output.

In this inspection, if neither generation of the critical current definition voltage Vt or the critical current definition voltage equivalent voltage Vr is detected before the current of the critical current specification value flows in the superconducting wire 2, the current of the critical current is detected. The value is not less than the critical current specification value, indicating that the critical current characteristic is not defective. In other words, the quality of the critical current characteristic of the superconducting wire 2 is sufficiently inspected by conducting the inspection with the current value at which the current of the critical current specification value flows in the superconducting wire 2 as the upper limit of the inspection current I (the above-described upper limit current value Imax). it can.
The upper limit current value Imax is determined by the following equation (1), where Is is the critical current specification value of the superconducting wire 2 and In is the normal conductor shunt current value that is shunted to the normal conductor 10.

  Upper limit current value Imax = critical current specification value Is + normal conductor shunt current value In (1)

  The normal conductor shunt current value In is obtained in advance by the following equation (2) based on the critical current defining voltage equivalent voltage Vr and the electric resistance value Rn.

  Normal conductor shunt current value In = critical current definition voltage equivalent voltage Vr / electric resistance value Rn (2)

  The upper limit current value Imax obtained in advance by these equations (1) and (2) is preset in the control device 18 as the upper limit value of the inspection current I. At the time of inspection, the control device 18 controls the current power source 11 to inspect the inspection current I. Are increased sequentially from zero to the upper limit current value Imax.

In the process of sequentially increasing the inspection current I, when the critical current of the superconducting wire 2 is lower than the critical current specification value Is (that is, when the critical current characteristic is poor), the inspection current I reaches the upper limit current value Imax. The occurrence of the critical current defining voltage Vt in the superconducting wire 2 and / or the occurrence of the critical current defining voltage equivalent voltage Vr in the normal conductor 10 is detected at the previous current value, and this current value is the superconducting wire to be inspected. The current value Ic of the critical current of 2 is indicated.
When the critical current is generated, a critical current defining voltage equivalent voltage Vr is generated in the normal conductor 10, so that the current of the normal conductor shunt current value In obtained by the above equation (2) among the inspection current I is always normal. The current is diverted to the conductor 10. Therefore, the current value Ic of the critical current is obtained by the following equation (3) using the current value It of the inspection current I and the normal conductor shunt current value In.

Current value Ic of critical current = current value It of inspection current I−normal conductor shunt current value In (3)

  As is clear from this equation (3), the ratio of the normal conductor shunt current value In to the inspection current I increases as the current value Ic of the critical current decreases. Therefore, since the ratio of the current flowing through the superconducting wire 2 when a critical current is generated is small, the heat generation of the superconducting wire 2 can be suppressed, and the possibility of occurrence of burning can be remarkably reduced.

However, as shown in the above equation (2), the normal conductor shunt current value In when the critical current is generated is inversely proportional to the electric resistance value Rn of the normal conductor 10. Therefore, the larger the electric resistance value Rn, the smaller the normal conductor shunt current value In, so that the ratio of the test current I being shunted to the normal conductor 10 when a critical current is generated is small, and the normal conductor 10 It will not be different from the state where I is not shunted. In such a case, when resistance is generated in the superconducting wire 2 and heat is generated, the shunt current to the normal conductor 10 is small, and therefore the superconducting wire 2 can be burned unless the inspection current I is interrupted or reduced instantaneously. Increases nature.
On the contrary, as the electric resistance value Rn is decreased, the normal conductor shunt current value In flowing in the normal conductor 10 when the critical current is generated can be increased. However, as apparent from the above formula (1), the upper limit current value Since Imax also increases, a current value larger than the critical current specification value Is is allowed to flow for a long time during inspection, which is not efficient.

Therefore, in the present embodiment, the normal conductor shunt current value In is inspected in order to increase the ratio at which the inspection current I is diverted to the normal conductor 10 when a critical current is generated and to reduce the possibility of the superconducting wire 2 being burned out. The electric resistance value Rn of the normal conductor 10 is set so as to be at least 5% or more of the upper limit current value Imax of the current I.
Further, the electrical resistance value Rn of the normal conductor 10 is set so that the normal conductor shunt current value In is the upper limit current value of the inspection current I so that the upper limit current value Imax does not become much larger than the critical current specification value Is. A resistance value that is at least 10% or less of Imax is set.
Thus, by appropriately setting the electrical resistance value Rn of the normal conductor 10 according to the critical current specification value Is of the superconducting wire 2, it is possible to reduce the possibility of the superconducting wire 2 being burned when the critical current is generated. Thus, the inspection can be performed without wastefully flowing a large inspection current I.

Since the critical current specification value Is of the superconducting wire 2, that is, the upper limit current value Imax of the inspection current I varies depending on the type of the superconducting wire 2 to be manufactured and the like, in the critical current inspection device 1 of this embodiment, the superconducting wire 2 For each critical current specification value Is, a normal conductor 10 having an electric resistance value Rn of 5% or more and 10% or less of the upper limit current value Imax of the inspection current I is prepared in advance, depending on the superconducting wire 2 to be inspected. It is configured to be exchangeable. In this configuration, in order to allow the normal conductor 10 to be exchanged without interfering with the superconducting wire 2 traveling in the cooling container 5, as shown in FIG. It is arranged at a position where it does not overlap the superconducting wire 2 when viewed in plan.
In addition, by arranging the normal conductor 10 in the cooling vessel 5 above the superconducting wire 2, the normal conductor 10 can also be arranged on the superconducting wire 2 in a plan view. Further, when the electric resistance value Rn that fluctuates with the temperature change falls within 5% and 10% or less of the upper limit current value Imax of the inspection current I, the normal conductor 10 is disposed outside the cooling container 5. Also good.

When the critical current characteristic of the superconducting wire 2 is inspected using the critical current inspection device 1, the superconducting wire 2 to be inspected is wound around the feed reel 3 and filled with liquid nitrogen 6 as shown in FIG. The cooling container 5 is set so that it can be connected. Then, the feed reel 3 and the take-up reel 4 are run on a reel-to-reel and stopped until the section to be inspected of the superconducting wire 2 is positioned between the pair of voltage electrodes 14 and 15. Then, an inspection current I is supplied to the superconducting wire 2 from the current power source 11 to inspect the critical current characteristics in the section to be inspected. Thereafter, until the critical current characteristic is inspected over the entire length of the superconducting wire 2, the next section is run so as to be positioned between the pair of voltage electrodes 14 and 15, and the critical current characteristic is inspected for this section. This process is repeated. Control of the travel of the superconducting wire 2 may be performed by the control device 18 or may be performed by a separately provided device.
The critical current characteristic inspection for the section to be inspected will be described with reference to FIG.

FIG. 3 is a flowchart of the critical current characteristic inspection.
When the section to be inspected is arranged between the pair of voltage electrodes 14 and 15, the control device 18 controls the current power source 11 to change the inspection current I from zero at a predetermined sweep speed as shown in FIG. The superconducting wire 2 is energized while being increased (step S1).
During energization, the control device 18 monitors the voltage V1 of the first voltmeter 16 and the voltage V2 of the second voltmeter 17, and generates a critical current defining voltage Vt for the section to be inspected, or a normal conductor. It is determined whether or not the generation of the critical current defining voltage equivalent voltage Vr to 10 has been detected (step S2).

When neither the critical current definition voltage Vt nor the critical current definition voltage equivalent voltage Vr is generated (step S2: No), the control device 18 determines whether or not the inspection current I has reached the upper limit current value Imax. (Step S3). When the inspection current I has not reached the upper limit current value Imax (step S3: No), the control device 18 returns the processing step to step S2 so as to continue monitoring the voltage V1 and the voltage V2.
On the other hand, when the inspection current I reaches the upper limit current value Imax (step S3: Yes), in the section to be inspected, the control device 18 indicates that the critical current is larger than the critical current specification value Is. Immediately stop the output of the inspection current I from the current power source 11 to stop the flow of the inspection current I into the superconducting wire 2 (step S4), and output “no defect” (step S5). Then, the processing step is returned to step S1 in order to inspect the critical current characteristic for the next section to be inspected.

  On the other hand, when it is detected as a result of the determination in step S2 that the critical current defining voltage Vt or the critical current defining voltage equivalent voltage Vr is detected (step S2: Yes), it means that the critical current has occurred in the section to be inspected. Therefore, the control device 18 immediately stops the output of the inspection current I from the current power supply 11 to stop the flow of the inspection current I into the superconducting wire 2 (step S6), and increases the resistance value in the superconducting wire 2. Prevent accompanying burnout. As described above, when the critical current is generated, the current having the normal conductor shunt current value In of the inspection current I flows through the normal conductor 10, so that the possibility of burning in the superconducting wire 2 is reduced.

  Then, the control device 18 outputs “failure detection” to indicate that the current value Ic of the critical current of the superconducting wire 2 is equal to or less than the critical current specification value Is (step S7). In order to check the critical current characteristic for the section, the processing step is returned to step S1. In step S7, the control device 18 determines the inspection current I when the occurrence of either the critical current definition voltage Vt or the critical current definition voltage equivalent voltage Vr is detected based on the above equation (3). The current value Ic of the critical current may be calculated and output from the current value It and the normal conductor shunt current value In flowing through the normal conductor 10 at that time. Moreover, you may complete | finish a critical current characteristic test | inspection with respect to the superconducting wire 2 at the time of detecting a defect.

Next, a specific example of the critical current inspection by the critical current inspection apparatus 1 will be described.
(Specific example 1)
As the superconducting wire 2, a YBCO tape wire having a critical current specification value Is of 250A was passed through the cooling vessel 5 by the reel-to-reel method and inspected. At this time, the distance between the current electrodes 12 and 13 was 1 m, and the distance between the voltage electrodes 14 and 15 was 0.8 m. The reference voltage of the critical current is 1 μV / cm = 1 × 10 ⁻⁴ V / m, and the critical current defining voltage Vt is 8 × 10 ⁻⁵ V. For the normal conductor 10, copper having a specific resistance of 2 × 10 ⁻⁹ Ωm at a cooling temperature (77 K) with liquid nitrogen 6, a round bar having a diameter of 25 mmφ, and a normal conductor 10 having a length of 1 m is used. It was. The distance between measurements for measuring the potential difference of the normal conductor 10 by the second voltmeter 17 was 0.8 m. Since the current value (normal conductor shunt current value In) of the current flowing through the normal conductor 10 when the voltage equivalent to the critical current definition voltage Vt is measured by the second voltmeter 17 is calculated as 20A. The upper limit current value Imax of the inspection current I is 270 A based on the above equation (1).

Then, when the superconducting wire 2 is inspected by the critical current inspection device 1, the critical current defining voltage Vt and the critical current defining voltage equivalent voltage before the inspection current I reaches the upper limit current value Imax in a section to be inspected. Any occurrence of Vr was detected (FIG. 3: Step 2: Yes), and the current value It of the inspection current I at that time was 264A.
Therefore, the current value Ic of the critical current of the superconducting wire 2 is calculated as 244A based on the above equation (3). The normal conductor shunt current value In was 8.2% of the critical current value Ic (7.4% of the upper limit current value Imax). When the current sweep speed of the current power source 11 is 5 A / s, after the critical current defining voltage Vt is generated, the voltage V1 of the superconducting wire 2 is twice the critical current defining voltage Vt (the possibility of burning) The time to reach a very high voltage) was about 5 s. That is, there was a time delay of 5 s until the risk of burning occurred, and the current could be cut off with a sufficient time delay.

(Specific example 2)
In Specific Example 2, the measurement was performed by changing only the diameter of the normal conductor 10 to 10 mmφ in Specific Example 1. In this normal conductor 10, since the normal conductor shunt current value In is calculated as 3A, the upper limit current value Imax of the inspection current I is set to 253A based on the above equation (1).
Then, when the superconducting wire 2 is inspected by the critical current inspection device 1, the critical current defining voltage Vt and the critical current defining voltage equivalent voltage before the inspection current I reaches the upper limit current value Imax in a section to be inspected. Any occurrence of Vr was detected (FIG. 3: Step 2: Yes), and the current value It of the inspection current I at that time was 248A.
Therefore, the current value Ic of the critical current of the superconducting wire 2 is calculated as 245A based on the above equation (3). The normal conductor shunt current value In was 1.2% of the critical current value Ic (1.1% of the upper limit current value Imax). When the current sweep speed of the current power source 11 is 5 A / s, after the critical current defining voltage Vt is generated, the voltage V1 of the superconducting wire 2 is twice the critical current defining voltage Vt (the possibility of burning) The time to reach a very high voltage) was about 1.5 s. In other words, there is only a grace period of 1.5 s until the danger of burning occurs, which is not much different from the case where the normal conductor 10 is not installed, and there was a danger of burning.

(Specific example 3)
In the specific example 3, the measurement was performed by changing only the diameter of the normal conductor 10 to 50 mmφ in the specific example 1. In this normal conductor 10, since the normal conductor shunt current value In is calculated as 78A, the upper limit current value Imax of the inspection current I is set to 328A based on the above equation (1).
Then, when the inspection of the superconducting wire 2 is advanced by the critical current inspection device 1, the generation of the critical current definition voltage equivalent voltage Vr is detected in the section to be inspected, although the generation of the critical current definition voltage Vt is not detected ( FIG. 3: Step 2: Yes), the current value It of the inspection current I at that time was 323A.
Therefore, the current value Ic of the critical current of the superconducting wire 2 is calculated as 245A based on the above equation (3). The normal conductor shunt current value In was 32% of the critical current value Ic (24% of the upper limit current value Imax).
When the current sweep speed of the current power source 11 is 5 A / s, after the critical current defining voltage Vt is generated, the voltage V1 of the superconducting wire 2 is twice the critical current defining voltage Vt (the possibility of burning) The time to reach a very high voltage) was about 17 seconds. In other words, the current value It of the inspection current I is too large with respect to the current value Ic of the critical current, and unnecessary current is consumed unnecessarily. Further, for the purpose of avoiding burnout of 17 s until the risk of burnout occurs. The excess time caused a longer time delay, and the measurement time was wasted.

As shown in the specific example 1, the electric resistance value Rn of the normal conductor 10 is appropriately set, and the normal conductor shunt current value In is about 8.2% of the current value Ic of the critical current (the upper limit current value Imax is By setting it to about 7.4%, a sufficient grace time is obtained until the inspection current I is cut off and the occurrence of burnout is avoided, and the upper limit current value Imax is not increased unnecessarily.
On the other hand, as shown in the specific example 2, the electric resistance value Rn of the normal conductor 10 is increased so that the normal conductor shunt current value In is about 1.2% of the critical current value Ic (upper limit current). If the value is too small (about 1.1% of the value Imax), a sufficient grace time cannot be obtained before the occurrence of burning by avoiding the inspection current I.
Further, as shown in the specific example 3, the electrical resistance value Rn of the normal conductor 10 is reduced, and the normal conductor shunt current value In is about 32% of the critical current value Ic (24% of the upper limit current value Imax). If it is too large, a large amount of current is consumed unnecessarily, and an excessive amount of time is delayed, resulting in wasted measurement time.
That is, among these specific examples 1 to 3, it is shown that specific example 1 in which the normal conductor shunt current value In is at least within the range of 5% to 10% of the upper limit current value Imax is optimal. It was.

As described above, according to the present embodiment, the critical current characteristic is inspected by passing the inspection current I through the parallel circuit 20 including the superconducting wire 2 and the normal conductor 10. With this configuration, even if a sudden increase in resistance occurs in the superconducting wire 2 due to the generation of the critical current, a certain amount of the inspection current I is shunted to the normal conductor 10, and thus a special circuit is provided separately. Even though the circuit configuration is simple, burning of the superconducting wire 2 can be suppressed. In particular, even if only the first normal conductive metal layer called a protective layer having a thickness of about 1 to 20 μm made of a good noble metal conductor such as silver is provided on the superconductive layer of the superconductive wire 2, it suppresses burning. However, the current value Ic of the critical current of the superconducting wire 2 can be obtained.
In addition, since the electric resistance value Rn of the normal conductor 10 is fixed to a predetermined electric resistance value and known, the critical current defining voltage Vt that defines the critical current flows through the normal conductor 10 when it is generated in the superconducting wire 2. The current value (normal conductor shunt current value In) is also uniquely determined, and by removing the normal conductor shunt current value In from the current value It of the inspection current I, the current value Ic of the critical current of the superconducting wire 2 is obtained. be able to.

Further, according to the present embodiment, the upper limit current value Imax obtained by adding the normal conductor shunt current value In to the critical current specification value Is that is a current value of a critical current assumed in advance in the superconducting wire is used as an upper limit. The current I is varied, and a failure of the critical current characteristic of the superconducting wire 2 is determined based on whether or not the critical current defining voltage Vt is generated before reaching the upper limit current value Imax.
Thereby, since the critical current generation is limited only to the case where the critical current is lower than the critical current specification value Is and is defective, the possibility of burning due to the generation of the critical current can be reduced. In particular, in the case of a non-defective product whose critical current is higher than the critical current specification value Is, since the critical current does not occur, burnout is reliably suppressed, and the yield can be improved.

According to the present embodiment, since the electric resistance value Rn of the normal conductor 10 is set so that the ratio of the normal conductor shunt current value In to the upper limit current value Imax is 5% or more, the inspection current is generated when the critical current is generated. Sufficient grace time is obtained until the occurrence of burnout is avoided by blocking I, and the occurrence of burnout can be reliably prevented.
In particular, by setting the electric resistance value Rn of the normal conductor 10 so that the ratio of the normal conductor shunt current value In to the upper limit current value Imax is 10% or less, the upper limit current value Imax is reduced for the purpose of avoiding burnout. Therefore, it is not excessively large and current is not wasted.

Further, according to the present embodiment, when the voltage V2 generated in the normal conductor 10 reaches the critical current definition voltage equivalent voltage Vr corresponding to the critical current definition voltage Vt, the inspection current I flows into the superconducting wire 2. It was set as the structure which interrupts.
Thereby, even when the generation of the critical current defining voltage Vt is not detected due to the generation of the critical current outside the section where the voltage V1 of the superconducting wire 2 is measured, the generation of the critical current is detected and the superconducting wire is detected. It is possible to prevent the burnout by stopping the flow of the inspection current to 2.

  Further, according to the present embodiment, the normal conductors 10 having different electrical resistance values Rn are replaceably provided according to the critical current specification value Is, so that the critical currents of various superconducting wires 2 having different critical current specification values Is can be obtained. It can be suitably used for inspection.

The above-described embodiment is merely an example of one aspect of the present invention, and can be arbitrarily modified and applied without departing from the spirit of the present invention.
For example, in the above-described embodiment, the configuration is such that the flow of the inspection current I into the superconducting wire 2 is stopped when the occurrence of either the critical current definition voltage Vt or the critical current definition voltage equivalent voltage Vr is detected. However, the present invention is not limited to this, and the inflow of the inspection current I to the superconducting wire 2 is not completely stopped, but may be configured to be reduced from a critical current to a sufficiently low current value.
In the above-described embodiment, in order to stop the flow of the inspection current I into the superconducting wire 2, the current power supply 11 is controlled to stop the output of the inspection current I. However, the present invention is not limited to this. 11 and the superconducting wire 2 are provided with a switch circuit that cuts off the current path or an electric circuit that reduces the current, and the occurrence of either the critical current definition voltage Vt or the critical current definition voltage equivalent voltage Vr is detected. In some cases, the flow of the inspection current I from the current power source 11 to the superconducting wire 2 may be blocked or reduced.

DESCRIPTION OF SYMBOLS 1 Critical current inspection apparatus 2 Superconducting wire 10 Normal conductor 11 Current power supply (constant current source)
12, 13 Current electrodes 14, 15 Voltage electrodes 16 First voltmeter 17 Second voltmeter 18 Controller 20 Parallel circuit I Inspection current Ic Current value of critical current Imax Upper limit current value In Normal conductor shunt current value Is Critical current specification Value It Current value of inspection current Rn Electrical resistance value V1 Voltage of superconducting wire V2 Voltage of normal conductor Vr Critical current definition voltage equivalent voltage Vt Critical current definition voltage

Claims (7)

A normal conductor having a predetermined electrical resistance value electrically connected in parallel to the superconducting wire;
A constant current source having a variable current value for supplying an inspection current to a parallel circuit including the superconducting wire and the normal conductor; and
A current that flows through the normal conductor when the predetermined voltage is generated from a current value of the inspection current when a predetermined voltage that defines a critical current that flows through the superconducting wire is generated in the superconducting wire by changing a current value of the inspection current. A critical current inspection apparatus, wherein the critical current is inspected based on a current value excluding the value.   The inspection current is changed to an upper limit of a current value obtained by adding a current value flowing through the normal conductor when the predetermined voltage is generated to a current value of a critical current assumed in advance in the superconducting wire, and the upper limit current value is set. The critical current inspection device according to claim 1, wherein a defect in critical current characteristics of the superconducting wire is determined based on whether or not the predetermined voltage is generated until the end.   A current value that flows through the normal conductor when the predetermined voltage is generated with respect to an upper limit current value obtained by adding a current value that flows through the normal conductor when the predetermined voltage is generated to a current value of a critical current that is assumed in advance in the superconducting wire. The critical current inspection apparatus according to claim 1 or 2, wherein a predetermined electric resistance value of the normal conductor is set so that a ratio of the electric current is 5% or more.   A current value that flows through the normal conductor when the predetermined voltage is generated with respect to an upper limit current value obtained by adding a current value that flows through the normal conductor when the predetermined voltage is generated to a current value of a critical current that is assumed in advance in the superconducting wire. The critical current inspection device according to claim 1, wherein a predetermined electric resistance value of the normal conductor is set so that a ratio of the current conductor becomes 10% or less.   The current flowing into the superconducting wire is reduced or the flow of the inspection current into the superconducting wire is stopped or the current flowing into the superconducting wire is reduced when the voltage generated in the normal conductor reaches the predetermined voltage. 4. The critical current inspection device according to any one of 4 above.   6. The critical current according to claim 1, wherein a normal conductor having a different resistance value is replaceably provided in accordance with a current value of a critical current assumed in advance in the superconducting wire. Inspection device. A normal conductor having a predetermined electric resistance value is electrically connected in parallel to the superconducting wire, and a parallel circuit including the superconducting wire and the normal conductor is formed, and an inspection current is passed through the parallel circuit,
A current obtained by changing a current value of the inspection current and excluding a current value flowing through the normal conductor when the predetermined voltage is generated from a current value of the inspection current when a predetermined voltage defining a critical current is generated in the superconducting wire. A critical current inspection method characterized by inspecting the critical current based on a value.

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