KR101706468B1 - Apparatus and Method for Measuring Critical Current of the High Temperature Superconducting Wire - Google Patents

Abstract

The present invention relates to an apparatus and method for measuring critical current density of a high-temperature superconducting wire. The present invention discloses the apparatus for measuring critical current density of a high-temperature superconducting wire, the apparatus comprising: a magnet which applies a magnetic field to a high-temperature superconducting wire; a force measurement means which measures the magnitude of force applied to the magnet and generated when the magnet moves toward or away from the high-temperature superconducting wire; and a control unit which controls the magnet to move toward or away from the high-temperature superconducting wire, and which measures critical current density of the high-temperature superconducting wire based on the magnitude of force. Furthermore, the present invention also discloses the method for measuring critical current density of a high-temperature superconducting wire by using the apparatus. According to the present invention, a spatial distribution of critical currents in a length-wise direction of a high-temperature superconducting wire, presence of a defect, a location of the defect, and the type of the defect can be detected, and thus basic characteristics of the high-temperature superconducting wire can be evaluated, thus, a high-temperature superconducting wire can be inspected prior to production of equipment configured to utilize the high-temperature superconducting wire.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for evaluating a critical current of a high-temperature superconducting wire using a permanent magnet,

The present invention relates to an apparatus and a method for measuring a critical current density of a high-temperature superconducting wire, and more particularly, to an apparatus and a method for measuring a critical current density of a high-temperature superconducting wire using a magnitude of a repulsive force generated when a permanent magnet approaches a high- And more particularly,

The high-temperature superconducting wire becomes a superconducting state when the current flowing through the wire rod, the temperature and the magnetic field are smaller than the threshold value, and the electric resistance becomes zero, thereby transmitting a very large current without loss. Such high-temperature superconducting wires can be applied in various fields. In particular, in the case of superconducting motors using high-temperature superconducting wires as field coils, it is possible to increase the weight of the superconducting motors by increasing the efficiency of the devices, A lot of research is being done because the volume can be reduced to about half.

Generally, the 4-terminal method was used to measure the critical current and the critical current density of a high-temperature superconducting wire. The four-terminal method is a method of measuring the critical current of a wire by detecting the voltage applied to the high-temperature superconducting wire while directly passing current through both ends of the high-temperature superconducting wire. That is, in the superconducting state, since the resistance is zero, the detected voltage becomes zero, and since the superconducting state is not over the critical current, a resistance is generated and a voltage of zero or more is detected. Therefore, the value of the current flowing at the time when a voltage of zero or more is detected can be regarded as a threshold current.

However, this 4-terminal method has a disadvantage that the high-temperature superconducting wire is liable to be damaged by the soldering and the over-current which flows to make contact between the measuring device and the high-temperature superconducting wire, and it is only to check the average critical current for the long portion There is a disadvantage in that it is not possible to evaluate the critical current density of a specific defect position or a partial region in the section.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and an apparatus for measuring critical current density of a non-contact high-temperature superconducting wire. It is another object of the present invention to provide an apparatus and a method for simultaneously measuring a defect position and a critical current density for each section.

According to an aspect of the present invention, there is provided an apparatus for measuring a critical current density of a high-temperature superconducting wire, comprising: a magnetic body for applying a magnetic field to the high-temperature superconducting wire; And a control unit for controlling the approach or the departure of the magnetic body and for evaluating the critical current density of the HTS wires based on the measured magnitude of the force .

In addition, the apparatus for measuring the critical current density of a high-temperature superconducting wire includes a container filled with a refrigerant, a reel supplying and recovering the high-temperature superconducting wire into the container, And may further include rollers. And a parallel holding means for controlling the rollers to keep the rollers horizontally parallel to each other.

Here, the magnetic body may be any one of a permanent magnet, an electromagnet, and a superconducting magnet.

The control unit of the apparatus for measuring the critical current density of the high-temperature superconducting wire can change the position of the magnetic body from 10 mm to 0 mm from the high-temperature superconducting wire, and can measure the magnitude of the force previously measured using the high-temperature superconducting wire of which the critical current density is known The critical current density of the HTS wires can be evaluated by using the critical current density correlation table.

The apparatus for measuring critical current density of a high-temperature superconducting wire may further include a plurality of magnetic bodies and force detecting means for simultaneous evaluation of a critical current density for a long section of the high-temperature superconducting wire.

According to another aspect of the present invention, there is provided a method of measuring a critical current density of a high-temperature superconducting wire, the method comprising: (a) changing a position of a magnetic body to cause a change in magnetic flux in the high- b) measuring a magnitude of a force applied to the magnetic body in accordance with the position change, and c) evaluating a critical current density of the HTS wires based on the magnitude of the measured force .

In the step (a), the position of the magnetic body may be changed from 10 mm to 0 mm from the HTS wire, and the step (c) may be performed by using a high- The critical current density of the high-Tc superconducting wire can be evaluated by using a correlation-size-to-critical-current density correlation table.

Since the presence of defects, the position of defects and the type of defects can be detected along with the spatial distribution of the critical current in the longitudinal direction of the high-temperature superconducting wire, the basic characteristics of the high-temperature superconducting wire can be evaluated. There is an effect that pre-inspection of wire rod is possible before manufacturing.

1 is a view showing a repulsive force generated in a high-temperature superconducting wire by a magnetic flux change applied by a magnetic body.
FIG. 2 is a view showing a configuration of an apparatus for measuring critical current density of a high-temperature superconducting wire according to an embodiment of the present invention. Referring to FIG.
3 is a diagram illustrating a configuration of an apparatus for measuring critical current density of a high-Tc superconducting wire according to another embodiment of the present invention.
4 is a view showing an apparatus for simultaneously measuring long sections of the HTS wires according to an embodiment of the present invention.
FIG. 5 is a flowchart illustrating a method of measuring a critical current density of a high-temperature superconducting wire according to an exemplary embodiment of the present invention.

In the following description, well-known functions or constructions are not described in detail to avoid unnecessarily obscuring the subject matter of the present invention.

Although the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, But should be understood to include all modifications, equivalents, and alternatives.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout.

When a magnetic material such as a permanent magnet is placed around the high-temperature superconducting wire, the magnetic flux density applied to the high-temperature superconducting wire changes. In the high-temperature superconducting wire, an induced voltage is generated in a direction that interferes with the change in the external magnetic flux. This is expressed by the following equation (1) as Maxwell's equation.

는 유기전압이고

는 자속의 변화량이다. here

Is an induced voltage

Is the variation of magnetic flux.

Current is generated in the superconducting wire by the induced voltage. The high-temperature superconducting wire has a limit of critical current density rather than being able to flow an infinite current because the resistance is zero. As a result, the current that can be flowed by the induced voltage is limited by the critical current density.

1 is a view showing a repulsive force generated in a high-temperature superconducting wire by a magnetic flux change applied by a magnetic body.

Referring to FIG. 1, when the position of the magnetic body 130 is changed, the magnetic flux applied to the high-temperature superconducting wire 140 is changed. Then, in order to cancel out the varying external magnetic flux density in the superconducting wire, the relational expression is as shown in Equation (2).

는 고온초전도 선재(140)에 가해지는 자속의 변화를 상쇄시키기 위하여 고온초전도 선재 내부에서 발생하는 자속밀도이고,

는 공기중의 투자율(상수),

는 고온초전도 선재의 임계전류밀도(상수),

는 고온초전도 선재 박막의 두께(상수),

는 고온초전도 선재 내에서 유기 전류가 분포되는 폭(변수)이다. 고온초전도 선재 내에서의 유기 전류는 박막을 중심으로 대칭구조를 가지며, 분포의 최대값은 박막의 폭(w)의 1/2을 가질 수 있다. here

Is a magnetic flux density generated in the high-temperature superconducting wire to cancel a change in magnetic flux applied to the high-temperature superconducting wire (140)

(Constant) in the air,

Is the critical current density (constant) of the high-temperature superconducting wire,

(Constant) of the high-temperature superconducting thin film,

Is a width (variable) in which the organic current is distributed in the high-temperature superconducting wire. The organic current in the high-temperature superconducting wire has a symmetrical structure centered on the thin film, and the maximum value of the distribution can have a half of the width (w) of the thin film.

)은 상기

로부터 다음 [수학식 3]을 이용하여 구할 수 있다.Then, the susceptibility of the high-temperature superconducting thin film

),

Can be obtained from the following equation (3).

는 자성체의 자성밀도,

은 고온초전도 선재 박막의 자화율,

는 공기중의 투자율,

는 자성체의 극부분의 면적을 의미한다.here

The magnetic density of the magnetic body,

The magnetic susceptibility of the high-temperature superconducting thin film,

The permeability in the air,

Means the area of the pole portion of the magnetic body.

)이 발생하고 그에 따라 자성체에 힘(

)이 가해지는 원리를 이용하여 본 발명에서 제안하는 고온초전도 선재의 임계전류밀도 측정장치를 이용하여 고온초전도 선재의 임계전류밀도를 측정할 수 있다.As described above, due to the change in the magnetic flux due to the change in the position of the magnetic material, the offset flux proportional to the current density in the high-temperature superconducting wire

) Is generated and the magnetic force (< RTI ID = 0.0 >

), It is possible to measure the critical current density of the high-temperature superconducting wire using the apparatus for measuring the critical current density of the high-temperature superconducting wire proposed in the present invention.

 FIG. 2 is a view showing a configuration of an apparatus for measuring critical current density of a high-temperature superconducting wire according to an embodiment of the present invention. Referring to FIG.

2, an apparatus for measuring a critical current density of a high-temperature superconducting wire 140 includes a magnetic body 130 and a magnetic body 130 that cause a magnetic field change in the high-temperature superconducting wire 140, A force detecting means 120 for measuring a force applied to the magnetic body 130 when approaching or leaving the magnetic body 130 and a force detecting means 120 for controlling the movement of the magnetic body 130 and based on the force measured by the force detecting means 120 And a control unit 110 for evaluating the critical current density of the HTS wires 140. [

The magnetic body 130 may be a permanent magnet, an electromagnet, or a superconducting magnet. When the magnetic body 130 is moved toward or away from the high-temperature superconducting wire 140, the high-temperature superconducting wire 140 undergoes a change in magnetic flux and applies a force to the magnetic body 130 while generating a magnetic flux for canceling it. The magnitude of the force applied to the magnetic body 130 by the canceling magnetic flux of the high-temperature superconducting wire 140 can be measured by the force detecting means 120.

One example of the force detecting means 120 may be a load cell. The load cell is a sensor that detects the force, and when it applies a force, it converts it into an electric signal and outputs it. Here, the sensor capable of measuring the force can use various sensors such as a spring, a PVDF sensor, a compression element, and a displacement sensor.

The control unit 110 may change the position of the magnetic body 130 in order to cause a change in the magnetic flux to the high-temperature superconducting wire 140. At this time, the control unit 110 can change the position of the magnetic body 130 from 0 mm to 10 mm from the HTS wire 140. At this time, the magnitude of the force applied to the magnetic body 130 is detected by the force detection unit 120, Can be estimated. Since the force detecting means 120 converts the measured force into an electric signal and transmits it, the controller 110 converts the electric signal coming from the force detecting means 120 into the magnitude of the force, The critical current density of the high-temperature superconducting wire 140 can be evaluated using a correlation table of the critical current density.

Since the magnitude of the force to be measured can be changed by the gap between the magnetic body 130 and the HTS wire 140 and the surrounding environment, it is difficult to obtain an accurate value by the basic formula. Therefore, it is possible to evaluate the critical current density of the HTS wire 140 by using the relationship between the magnitude of the force and the critical current density of each measurement device.

The correlation table of the magnitude of the force verses the critical current density can be obtained in advance using the high-temperature superconducting wire whose critical current density is known. The high-temperature superconducting wire 140 having a known critical current density is measured using a measuring apparatus according to the present invention, and the magnitude of the force generated at this time is extracted. Then, the critical current density with respect to the magnitude of the specific force can be known. If the above equations are used, since the relationship between the magnitude of the force and the critical current density is a linear equation type relationship, A correlation table of current density can be obtained.

If the evaluated critical current density is lower than a specific value, the high-temperature superconducting wire 140 may be defective. That is, in the superconducting state of the high-temperature superconducting wire 140, a much larger amount of current can flow than that of ordinary copper or metal, and therefore, the critical current density must be high. Therefore, when the critical current density is lower than the specific value, it can be determined that the high-temperature superconducting wire 140 has a defect.

3 is a diagram illustrating a configuration of an apparatus for measuring critical current density of a high-Tc superconducting wire according to another embodiment of the present invention.

Referring to FIG. 3, in general, the HTS wire 140 must fall below a critical temperature to have a superconducting characteristic. The refrigerant 220 is provided in the container 210 capable of accommodating the refrigerant such as liquid nitrogen and the high temperature superconducting wire 140 is immersed in the refrigerant 220 to lower the temperature of the high temperature superconducting wire 140 to a critical temperature or lower After dropping, the magnitude of the critical current density can be measured. The high temperature superconducting wire 140 has a rolled shape so that the high temperature superconducting wire 140 is inserted into the reel 230 and the reels 230 and the high temperature superconducting wire 140 are guided in the horizontal direction The refrigerant can be supplied into the refrigerant 220 by using the roller 240 and recovered. In order to precisely measure the critical current density, the magnitude of the force must be accurately measured. This force is inversely proportional to the interval between the high-temperature superconducting wire 140 and the magnetic body 130. Therefore, in order to increase the accuracy of the measurement, it is necessary to maintain the balance of the roller 240 that guides the high-temperature superconducting wire 140 in the horizontal direction. Accordingly, the measuring apparatus may further include parallel holding means for controlling the roller 240 to maintain the horizontal parallelism.

However, since it is not efficient to measure the critical current density for a certain section of the high-temperature superconducting wire 140 by using one magnetic body 130 and the force detecting means 120, the long section of the high-temperature superconducting wire 140 A device for simultaneous measurement is presented.

4 is a view showing an apparatus for simultaneously measuring long sections of the HTS wires according to an embodiment of the present invention.

Referring to FIG. 4, an apparatus for simultaneously measuring a long section of the HTS wire 140 includes a plurality of magnetic bodies 130 for measuring a portion of a long section of the HTS wire 140, (120). A separate control unit 110 may be provided for each of the magnetic bodies 130 and the force detecting means 120 and one magnetic body 130 and / The force detecting means 120 may be controlled. The control unit 110 can access or disconnect all the connected magnetic bodies 130 with the HTS wires 140. The control unit 110 receives an electric signal indicating the magnitude of the force measured by the force detection unit 120, The current critical density of the measurement portion can be estimated.

FIG. 5 is a flowchart illustrating a method of measuring a critical current density of a high-temperature superconducting wire according to an exemplary embodiment of the present invention.

Referring to FIG. 5, the controller 110 of the measurement apparatus can change the position of the magnetic body 130 to cause a change in magnetic flux to the high-temperature superconducting wire (S510). In one embodiment, the position of the magnetic body 130 may be changed from a position 10 mm away from the HTS wire 140 to a position 0 mm away, and then to a position 10 mm away from the HTS wire 140. The force detecting means 120 may measure the magnitude of the force due to the position change (S520). The control unit 110 may evaluate the critical current density of the HTS wire 140 based on the magnitude of the measured force (S530). At this time, the critical current density can be evaluated by using a correlation table of the magnitude versus the critical current density obtained in advance. In particular, when the critical current density is lower than a predetermined value, it is judged that there is a defect in the measurement position of the high-temperature superconducting wire 140 can do.

The present invention proposes a measuring device for measuring a critical current density, which is one of the most important characteristics of a high-temperature superconducting wire, without damaging the high-temperature superconducting wire. In order to mass-produce high-temperature superconducting wire, It is a necessary device.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. Only. The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

Claims (10)

A magnetic body for causing a change in magnetic flux to the high-temperature superconducting wire by the position change;
A force detecting means for measuring a magnitude of a force applied to the magnetic body by a change in magnetic flux generated when the magnetic body approaches or leaves the high-temperature superconducting wire; And
A control unit for controlling the approach or departure of the magnetic body and for evaluating the critical current density of the HTS wires based on the magnitude of the measured force;
Wherein the critical current density of the high-temperature superconducting wire is measured. The method according to claim 1,
A container filled with refrigerant;
A reel supplying and recovering the high-temperature superconducting wire to the inside of the vessel; And
A roller for horizontally guiding the high-temperature superconducting wire at both inner sides of the vessel;
Wherein the critical current density measuring device further comprises: 3. The method of claim 2,
Parallel holding means for controlling the roller so as to maintain parallelism in the horizontal direction;
Wherein the critical current density of the high-Tc superconducting wire is at least one of the following: 4. The method according to any one of claims 1 to 3,
Wherein the magnetic body is one of a permanent magnet, an electromagnet, and a superconducting magnet,
An apparatus for measuring critical current density of high temperature superconducting wire. 4. The method according to any one of claims 1 to 3,
Wherein the control unit changes the position of the magnetic body from 10 mm to 0 mm from the HTS wire,
An apparatus for measuring critical current density of high temperature superconducting wire. 6. The method of claim 5,
Wherein the controller evaluates the critical current density of the HTS wires using a correlation table of force magnitudes versus critical current density measured in advance using the HTS wire with a known critical current density,
An apparatus for measuring critical current density of high temperature superconducting wire. The method according to claim 2 or 3,
And a plurality of magnetic bodies and force detection means for simultaneous evaluation of a critical current density for a long section of the high-temperature superconducting wire,
An apparatus for measuring critical current density of high temperature superconducting wire. (a) changing the position of the magnetic body to cause a change in magnetic flux in the high-temperature superconducting wire;
(b) measuring magnitude of a force applied to the magnetic body by a change in magnetic flux according to the position change; And
(c) evaluating the critical current density of the HTS wires based on the magnitude of the measured force;
Wherein the critical current density of the high-Tc superconducting wire is measured. 9. The method of claim 8, wherein step (a)
The position of the magnetic body is changed from 10 mm to 0 mm from the high-temperature superconducting wire,
A Method for Measuring Critical Current Density of High Temperature Superconducting Wire. The method as claimed in claim 8 or 9, wherein the step (c)
Wherein the critical current density of the high-temperature superconducting wire is evaluated by using a correlation magnitude vs. a critical current density correlation table measured in advance using a high-temperature superconducting wire having a known critical current density,
A Method for Measuring Critical Current Density of High Temperature Superconducting Wire.

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