JP2000030776A - Connecting structure for superconducting current lead part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connecting structure for a superconducting current lead part using a structure wherein a superconducting rod is prevented from being loaded with mechanical stress caused by thermal contraction in the current lead connecting part, and heightening safety against an outside impact. SOLUTION: An oxide superconducting rod 12 is set between a low- temperature side connect electrode part 11 and a high-temperature side connect electrode part 10, and good conductive terminal blocks 15 are connected to both ends of the superconducting rod 12. The one terminal block 15 is connected to the low-temperature side connect electrode part 11 through a flexible conductor 17, and the other terminal block 15 is connected to the high-temperature side connect electrode part 10 through a flexible conductor 16. And a covering member 18 made of an insulating material and covering the terminal blocks 15, the superconducting rod 12, and the flexible conductors 16, 17 is mounted to the connect electrode parts 10, 11 outside both the terminal blocks 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a connection structure for a superconducting current lead used in a current introduction section of a cryogenic device.

[0002]

2. Description of the Related Art In general, superconducting devices such as an AC superconducting coil and a superconducting transformer are used by being immersed in a cryogenic refrigerant such as liquid helium. It is connected to a current lead led from a power supply. Further, in a normal superconducting device, a structure in which a primary cooling system using liquid nitrogen is arranged on an outer peripheral portion of the superconducting device is adopted for the purpose of preventing evaporation of expensive liquid helium and performing primary cooling. By the way, it is considered that a superconducting wire is more preferable than a normal conducting wire. Therefore, use of a rod-shaped superconducting conductor as a superconducting current lead wire has been considered. In this case, it is necessary to provide metal terminals for connection at both ends of the superconducting conductor.

[0003] However, the superconducting equipment has a central part of 4.2K.
When used at very low temperatures, the superconducting conductor on the lead shrinks when cooled, but if the metal terminal connected to the superconducting conductor is fixed to the housing of the superconducting device, the superconducting conductor shrinks. Accordingly, there is a problem that a mechanical stress is applied to the superconducting conductor in the lead portion, and the superconducting conductor in the lead portion is broken. Also, as the superconductor for the lead portion, it is considered to use an oxide superconductor having a high critical temperature that can be cooled by liquid nitrogen, but since the oxide superconductor is a ceramic and extremely brittle, it is mechanically High stress loading must be avoided. Therefore, conventionally, in order to solve the above-mentioned problem, a connection structure in which a flexible wire is disposed between a rod-shaped oxide superconductor and a metal terminal has been considered.

FIG. 9 is a longitudinal sectional view showing an example of this type of superconducting conductor connection structure. In this example, the structure is of a low temperature side (for example, a cryogenic side cooled by liquid helium such as 4.2K). A superconducting rod 3 made of an oxide superconducting material is arranged between the connecting electrode 1 on the high-temperature side (for example, the high-temperature side cooled by liquid nitrogen such as 77K). Then, cylindrical electrode terminals 5 and 5 are fixed to both ends of the superconducting rod 3 by soldering, one electrode terminal 5 is integrated with the connection electrode 2 on the high temperature side, and the other electrode terminal 5 is a flexible conductor. 6 and the connection electrode 1 on the low temperature side
It is connected to the. Further, a cylindrical cover member 7 covering the superconducting rod 3, the electrode terminals 5, 5 and the flexible conductor 6 is arranged so as to connect the connection electrodes 1 and 2.

The flexible conductor 6 has a braided structure made of a fine conductive metal wire, and is connected to the connection electrode 1 and the electrode terminal 5 by joining means such as soldering. The flexible conductor 6 has flexibility. are doing.

In the superconducting conductor connection structure shown in FIG. 9, the connection electrode 2 is connected to an external power supply, and the connection electrode 1 is connected to a superconducting wire of a superconducting coil immersed in liquid helium. In such a superconducting conductor connection structure, since the flexible conductor 6 is interposed between the connection electrodes 1 and 2, when the superconducting rod 3 contracts with cooling from room temperature, the flexible wire 6 The superconducting rod 3 is configured so as to absorb the thermal contraction difference between the cover member 7 and the superconducting rod 3 and prevent the superconducting rod 3 from being loaded with mechanical strain.

[0007]

In the connection structure shown in FIG. 9, the connection electrode 2 on the high temperature side and the superconducting rod 3 are directly connected by soldering, and when an external impact is applied, the impact is directly applied. Since the superconducting rod 3 is loaded, there is a problem that the structure is not made strong against external impact.

The present invention has been made in view of the above circumstances, and employs a structure in which a mechanical stress caused by thermal contraction at a current lead connection portion is not applied to a superconducting rod, and furthermore, an external shock is applied. It is another object of the present invention to provide a connection structure for a superconducting current lead portion which is also improved in safety.

[0009]

According to the first aspect of the present invention,
A superconducting rod made of an oxide superconducting material between a low-temperature side metal connection electrode and a high-temperature side metal connection electrode in a connection structure of a superconducting current lead used for a current introduction part of a cryogenic device. Are arranged, and a terminal block of good conductivity is connected to both ends of the superconducting rod,
The one terminal block is connected to a low-temperature side connection electrode portion via a flexible conductor formed by knitting a highly conductive thin metal wire, and the other terminal block is connected to a high-temperature side connection electrode portion. The terminal block is connected to the high-temperature side connection electrode section and the low-temperature side connection electrode section outside the both terminal blocks while being connected via a flexible conductor formed by knitting a highly conductive thin metal wire. A cover member made of an insulating material that covers the superconducting block and the flexible conductor is provided.

The invention according to claim 2 is characterized in that a cushioning material made of an elastic body is interposed between the cover member and each terminal block. The invention according to claim 3 is characterized in that the flexible conductor has a short structure whose length is smaller than its diameter.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a connection structure for a superconducting lead according to the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing one embodiment of a connection structure of a superconducting current lead portion according to the present invention. The structure of this example is connected to an external power supply (not shown) and is connected to a high-temperature side connection electrode portion 10 cooled by liquid nitrogen used in a primary cooling system of a superconducting device, and cooled by liquid helium. Low-temperature-side connection electrode portion 11 connected to a superconducting device such as a superconducting coil, and connection electrode portions 10 and 11
And a superconducting rod 12 made of an oxide superconducting material provided therebetween.

At both ends of the superconducting rod 12, terminal blocks 15, 15 made of highly conductive metal are attached, and a first flexible conductor is provided between the high-temperature side connection electrode section 10 and the terminal block 15. The second flexible conductor 17 is provided between the low-temperature side connection electrode portion 11 and the terminal block 15. Further, a cover member 18 made of fiber-reinforced plastic is arranged outside the terminal blocks 15 and 15 to cover them.

As shown in FIGS. 2 and 3, the connection electrode portion 10 on the high-temperature side includes a rectangular block-shaped base portion 20 and a cylindrical connection portion 21 protruding from one surface of the base portion 20. And the flexible conductor 1
A round concave portion 22 for soldering 6 is formed, and a plurality of fixing portions 23 such as screw holes are formed on the peripheral surface of the connecting portion 21 at intervals of 90 degrees around the circumference. As shown in FIG. 4, the low-temperature-side connection electrode portion 11 includes a columnar base portion 25 and a columnar connection portion 26 formed by extending the base portion 25. Are formed with three fixing holes 27 formed diametrically therethrough, and a round concave portion 28 for soldering the flexible conductor 17 is formed in the center of the distal end surface of the connecting portion 26. Along with
A plurality of fixing portions 29 such as screw holes are formed on the peripheral surface of the connecting portion 21 at intervals of 90 degrees around the circumference.

As shown in FIGS. 5 and 6, the cover member 18 is formed by combining a half-tubular cover body 30 into a single cylindrical body. Through holes 32 for bolting to fixing portions 23 of 10
Are formed, and the connection electrode portion 11 described above is provided on the other end side.
Are formed in the fixing portion 29 of the superconducting rod 12, and a plurality of through holes 34 for inserting a resistance measuring device or the like of the superconducting rod 12 are formed in a central portion thereof. The cover body 39 is made of fiber reinforced plastic such as epoxy resin filled with glass fiber.

As shown in FIGS. 7 and 8, the terminal block 15 is formed by forming a truncated cone-shaped tip portion 41 on the tip end surface side of a columnar base portion 40. A round recess 4 for joining to the above-mentioned flexible conductor is provided on the end face.
2, and a notch-shaped slit 43 is formed over the distal end portion 41 and the upper portion of the base portion 40. The slit 43 is provided for the superconducting rod 12 described above.
Are inserted and fixed by soldering, and the end of the superconducting rod 12 is formed in a size that can be inserted.

As the superconducting rod 12, Y ₁ Ba ₂
Cu ₃ O _7-x is represented by the composition of Y-Ba-Cu-O based oxide superconductor, A-B-Cu-O system (where, A
Represents one or more elements of group IIIa of the periodic table such as La, Ce, Y, Sc, and Yb, and B represents one or more elements of group IIa of the periodic table such as Sr and Ba). , Tl ₂ Ba ₂
Tl-Ba-Ca represented by the composition formula of Ca ₂ Cu ₃ O _Z
Various oxide-based rod-shaped superconducting conductors such as -Cu-O-based oxide superconducting conductors are used.

The flexible conductors 16 and 17 are substantially cylindrical or rod-shaped having a mesh structure, and are deformable by external stress. It is formed by knitting. As the thin wire made of a highly conductive material here, a thin metal wire such as Ag or Cu is preferably used. If the diameter of the thin metal wire is too large, the flexible conductors 16 and 17 become hard, so that the superconducting rod 12 is not easily deformed when contracted, and the contraction stress cannot be sufficiently absorbed.

In order to increase the current capacity, it is preferable to increase the cross-sectional area of the flexible conductors 16 and 17 as much as possible. Also, the low-temperature side flexible conductor 17
In this case, the electric resistance can be sufficiently reduced by cooling the liquid helium to cryogenic temperature, so that problems such as connection resistance at the time of connection do not occur. Further, by forming the flexible conductor 17 itself sufficiently short as shown in FIG. 1 (for example, making the length of the flexible conductor 17 smaller than its diameter), the electric resistance of the flexible conductor 17 can be reduced as much as possible. . On the other hand, since the flexible conductor 16 on the high temperature side is cooled by liquid nitrogen, the resistance can be higher than that of cooling by liquid helium.
For example, the flexible conductor 16
By making the length shorter than the diameter (longitudinal width) of the flexible conductor 16, the resistance can be reduced, and the increase in resistance of the flexible conductor 16 can be minimized.

Next, in the structure of this embodiment, as shown in FIG. 1, the terminal block 15 with the tip 41 directed toward the center of the superconducting rod 12 is mounted so as to be located at both ends of the superconducting rod 12. ing. Each terminal block 15
Is a superconducting rod 1 formed in a slit 43 formed therein.
2 is fixed to the end side of the superconducting rod 12 by inserting solder into the slit 43. Also,
The end of the flexible conductor 16 is soldered to the recess 42 located outside the one terminal block 15, and the end of the flexible conductor 17 is soldered to the recess 42 located outside the other terminal block 15. The other end of the flexible conductor 16 is soldered to the recess 22 of the connection electrode 10 on the high temperature side, and the other end of the flexible conductor 17 is soldered to the recess 28 of the connection electrode 11 on the low temperature.

A cushioning member 45 made of an elastic material such as rubber is wound and fixed around the outer periphery of each terminal block 15.
The cover bodies 30, 30 are arranged in a cylindrical combination outside the cushioning material 45, and bolts that penetrate through the respective through holes 32 on one end side of the cover bodies 30 are screwed into the fixing portions 23 of the connection electrode unit 10. Then, the bolts are screwed into the fixing portions 29 of the connection electrode portions 11 through the through holes 33 on the other end side of the cover body 30, so that the connection electrode portions 10, 1
1 are connected. In the present embodiment, the cushioning material 45 may be, for example, a cylindrical material having a thickness of about 1 mm and a width of about 2 mm.

In the structure of the superconducting current lead portion of this embodiment, a flexible conductor 16 is interposed between one end of the superconducting rod 12 and the connection electrode portion 10, and is connected to the other end of the superconducting rod 12. Since the flexible conductor 17 is interposed between the superconducting rod 12 and the connecting electrode 11, when the whole is cooled, if there is a difference in the thermal expansion coefficient between the cover member 18 and the superconducting rod 12, the contraction of the superconducting rod 12 is prevented. Correspondingly, the flexible conductors 16 and 17 are deformed and can absorb the contraction stress caused by the difference in the coefficient of thermal expansion, so that no mechanical stress is applied to the superconducting rod 12 and the superconducting rod 1
2 can be prevented from being damaged or destroyed. Also,
When increasing the current capacity, the flexible conductors 16, 1
7 can be easily coped with by forming the cross-sectional area of the connection electrode portions 10 and 11 to be large, and by increasing the cross-sectional area of the connection electrode portions 10 and 11. Also, each current path is a highly conductive thin wire, so it is easy to deform.Moreover, since this highly conductive thin wire forms a mesh, the spring constant is hardly increased, and the contraction stress accompanying the increase in the cross-sectional area is reduced. The absorption capacity is not easily reduced. Further, since the lengths of the flexible conductors 16 and 17 are short with respect to the entire length of the superconducting current lead portion, the size of the superconducting current lead portion can be reduced even when the current capacity is increased.

In the structure shown in FIG.
The side is cooled with liquid helium to a very low temperature (about 4.2K) and the connection electrode section 10 side is cooled with liquid nitrogen to a low temperature (about 77K) higher than the liquid helium temperature before use. Therefore, when the superconducting rod 12 is cooled from room temperature to each temperature, mechanical stress tends to act on the superconducting rod 12 due to a difference in thermal expansion coefficient between the cover member 18 and the superconducting rod 12. Since the flexible conductors 16 and 17 are disposed, no mechanical stress acts on the superconducting rod 12 due to the deformation thereof. Further, even if a shock or the like acts on the superconducting rod 12 in the radial direction from outside the cover member 18 or outside the connection electrode portions 10 and 11, the shock absorbing material 45 and the flexible conductors 16 and 17 absorb the shock. The superconducting rod 12 will not be damaged or destroyed. Here, the flexible conductor 1 is attached to both ends of the superconducting rod 12.
Since it is significant to dispose the flexible conductors 6 and 17 and the cushioning material 45, even if the flexible conductor 17 is arranged only on the low temperature side and the cushioning material 45 is further arranged as in the conventional structure, the flexible conductor is There is a high possibility that the superconducting rod 12 will be damaged near the high-temperature side terminal block where it is not provided.

[0023]

EXAMPLE (Example) A superconducting rod as shown in FIG.
Pure copper terminal blocks are soldered at both ends.
And a copper braided wire outside the terminal block.
Solder a flexible conductor shaped like a bar,
Solder the copper connection electrodes to the outside of them
did. In addition, fiber reinforced plastic
Cover them with the cover body and cover both ends.
Was fixed to the connection electrode part by bolting. The cover
Half the part where the position matches the terminal block on the inner side of the main unit
A cushioning material consisting of a cylindrical rubber sheet is placed, and the cover body
When the terminal block is combined with a cylindrical
Cover so that the outer peripheral part can be surrounded in a cylindrical shape
The main body was attached to a cylinder. As a superconducting rod here
Is Y with a diameter of 2.5 mm and a length of 160 mm₁Ba_TwoCu _ThreeO_7-x
(Y123) A superconducting conductor was used. Also flexible
As a conductor, a Cu mesh wire is shaped into a rod shape with an outer diameter of 20 mm.
Was used. Flexible conductor and connection electrode part are half
The depth of the recess to be padded is 3mm, high temperature side and low temperature
The total length of the connection electrodes on both sides is 68 mm and the terminal block
The overall length of the hole was 36 mm. Next, the connection electrode on the high temperature side
To the external power supply, and connect the low-
Connected to the superconducting wire wound on the conducting coil to
Produced.

Then, the superconducting current lead portion of the embodiment was tested for the AC current conduction characteristics. The above-described AC superconducting coil and a superconducting wire derived therefrom,
The superconducting lead portion of the example was accommodated in a sealed Dewar vessel, and filled with liquid helium until the superconducting wire and the low-temperature side connection electrode portion were immersed. An AC voltage of 100 V and a current of 30 A was applied to the system through the connection electrode. 2
During the operation period of time, a current of 95% of the design value flowed through the superconducting coil, and the superconducting coil operated normally. After the completion of the energization test, cooling with liquid helium was stopped and the whole was returned to normal temperature. Thereafter, a test in which cooling with liquid helium was performed again and energization was performed again and again was performed three times. Did not.

COMPARATIVE EXAMPLE For comparison, the flexible conductor between the high-temperature side connection electrode portion and the terminal block was omitted, the terminal block was directly attached to the high-temperature side connection electrode portion by soldering, and the periphery of the terminal block was further removed. Substantially the same superconductive current lead as in the example except that the buffer material was omitted.

Then, the superconducting current lead portion of the comparative example was tested for the alternating current conduction characteristics in the same manner as in the above-described embodiment. As a result, during the operation period of 2 hours, a current of 95% of the designed value flowed in the superconducting coil, and the superconducting coil operated normally. However, after completion of the energization test, the cooling with liquid helium was stopped and the whole was returned to room temperature. Thereafter, the test with cooling with liquid helium and energizing again was repeated three times, and the energizing current decreased by 3%. did. It is presumed that this is because the repetition of the temperature history from the extremely low temperature to the normal temperature causes some heat shrinkage stress to act on the superconducting rod, and the superconducting characteristics of the superconducting rod have deteriorated.

[0027]

As described above, in the connection structure of the superconducting current lead portion according to the present invention, flexible conductors are arranged on both ends of a superconducting rod made of an oxide superconducting material and connected to the connection electrode portion. Therefore, even if the thermal expansion coefficient of the superconducting rod and the connection electrode portion connected thereto are different, and the stress caused by thermal contraction acts on the superconducting rod at the time of cooling, the flexible conductor exerts a buffering action at both ends of the superconducting rod. As a result, there is an effect that mechanical stress caused by heat shrinkage during cooling is not applied to the superconducting rod. Therefore, even if the cooling is repeatedly performed between the room temperature and the extremely low tone, there is an effect that the superconducting rod is not adversely affected by the mechanical strain due to the thermal stress. Furthermore, since flexible conductors are arranged at both ends of the superconducting rod, even if an impact or force acts from the outside of the cover member in the radial direction of the superconducting rod, it is difficult for these to be transmitted to the superconducting rod. And a connection structure for a superconducting lead portion resistant to external force.

Also, since flexible conductors are arranged at both ends of the superconducting rod and a buffer material is interposed between the cover member and the terminal electrode, external impact acts on the cover member and the connection electrode. Also has a structure in which mechanical strain is hardly applied to the internal superconducting rod. Therefore, it is possible to provide a connection structure of the superconducting current lead portion which is particularly resistant to external impact.

Further, if the flexible conductor has a short structure, the increase in the resistance of the flexible conductor can be extremely reduced, and the increase in the overall length of the superconducting current lead can be suppressed. The size and weight can be reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of a superconducting current lead portion according to the present invention.

FIG. 2 is a plan view of a high-temperature side connection electrode portion used in the structure shown in FIG. 1;

FIG. 3 is a side view of the connection electrode unit shown in FIG. 2;

FIG. 4 is a plan view of a low-temperature side connection electrode portion used in the structure shown in FIG. 1;

FIG. 5 is a plan view of a cover member used in the structure shown in FIG. 1;

FIG. 6 is a side view of the cover member shown in FIG. 5;

FIG. 7 is a side view of a terminal block used in the structure shown in FIG. 1;

FIG. 8 is a front view of the terminal block shown in FIG. 7;

FIG. 9 is a longitudinal sectional view showing a structure of a superconducting current lead portion used by the present inventors.

[Explanation of symbols]

10, 11 ... connection electrode, 12 ... superconducting rod, 15 ...
.Terminal electrodes, 16, 17 ... flexible conductors, 18 ...
Cover member, 45 ... cushioning material.

Claims (3)

[Claims] In a connection structure of a superconducting current lead portion used for a current introduction portion of a cryogenic device, an oxide superconducting material is provided between a low-temperature side metal connection electrode portion and a high-temperature side metal connection electrode portion. A superconducting rod made of a material is disposed, and a terminal block having good conductivity is connected to both ends of the superconducting rod, and the one terminal block is connected to a low-temperature side connection electrode part by a highly conductive thin metal wire. The other terminal block is connected via a flexible conductor formed by knitting a highly conductive thin metal wire between the other terminal block and the connection electrode portion on the high-temperature side, while both terminals are connected to each other. A cover member made of an insulating material attached to the high-temperature side connection electrode section and the low-temperature side connection electrode section to cover the terminal block, the superconducting rod, and the flexible conductor is provided outside the block. A connection structure for a superconducting current lead portion, characterized in that: 2. The superconducting current lead connection structure according to claim 1, wherein a buffer material made of an elastic material is interposed between said cover member and each terminal block. 3. The connection structure for a superconducting current lead according to claim 1, wherein the flexible conductor has a short structure having a length smaller than a diameter thereof.