JP3181345B2 - Superconducting current lead - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting current lead, and more particularly, to a ceramic superconducting current lead having durability against mechanical shocks and the like.

[0002]

2. Description of the Related Art In recent years, MR has been developed using superconducting magnets.
Superconducting devices such as I devices and magnetic levitation trains have been put to practical use. However, even in these practical devices, there is a problem that heat enters the cryogenic region through a current lead that supplies a current from a power source placed at room temperature to a superconducting magnet placed at cryogenic temperature. Has become. For example,
The refrigerating machine power required to reliquefy liquid helium evaporated with a heating value of 1 W reaches 500 to 1000 W.Therefore, a large amount of heat entering through the current lead leads to an increase in cost. In addition, there is a problem that the size of a refrigerating mechanism (such as a refrigerator) for reliquefaction becomes large, and the advantages of superconductivity such as low power consumption and small size and light weight cannot be fully utilized. Therefore, in a medical MRI apparatus that uses a superconducting magnet in the permanent current mode, the current lead is connected to the superconducting magnet only when the superconducting magnet is deenergized, and during normal operation, the current lead is pulled out of the liquid helium to reduce heat penetration. It has a configuration to aim for. However, in the case of power equipment such as transformers, generators, current limiters, etc., which are under research and development for superconductivity, current supply from the power supply is required constantly and current leads and magnets cannot be separated. The development of current leads with low heat penetration is a particularly important issue.

[0003]

The heat intrusion through the conventional metal current lead is caused by the Joule heat generated by the current lead itself and by the heat conduction from the high temperature end, that is, from outside the cryogenic region (cryostat). There are things. The former can reduce the amount of heat entering by reducing the resistivity of the current lead material, and the latter can reduce the amount of heat entering by reducing the thermal conductivity of the current lead material. However, in general metals, the resistivity and the thermal conductivity are inversely proportional, so it is not possible to reduce both at the same time. With a conventional copper lead (current lead), the heat penetration is about 1 W / kA. Is the lower limit. On the other hand, in the case of an oxide superconductor discovered in 1986, a so-called high-temperature superconductor, the thermal conductivity is not less than one order of magnitude lower than copper, and since it does not generate Joule heat when cooled below the critical temperature, It is attracting attention as a next-generation current lead material that replaces conventional copper leads. In other words, by utilizing the characteristic of low thermal conductivity, a current lead made of an oxide superconductor is used to connect a superconducting wire in a cryogenic region to a current lead terminal at room temperature, thereby forming a current lead terminal at room temperature. It is intended to supply a required current while preventing heat from entering a superconducting wire at an extremely low temperature.
In the usage mode of such a current lead made of an oxide superconductor, the smaller the diameter is, the more the heat penetration is reduced. Therefore, it is desired to use an oxide superconductor wire as thin as possible.

[0004] However, oxide superconductors are generally brittle and may be damaged by a slight mechanical impact. Particularly, in the case of an oxide superconductor wire having a reduced diameter, the above-described mechanical impact or thermal shock may occur. The possibility of damage due to impact is remarkable, hindering use as a current lead, but no effective means has yet been developed.

[0005] The present invention has been made in view of the above circumstances, and by reinforcing in a form having thermal insulation,
An object of the present invention is to provide an oxide superconducting current lead that can always exhibit a highly reliable current carrying function.

[0006]

A superconducting current lead according to the present invention has an oxide superconductor lead body for passing a current and a part of the oxide superconductor lead body for passing a current axially partially overlapped with each other. It consists of a plurality of reinforcements that are arranged integrally over the entire length in the form and separated from each other ,
The thermal expansion coefficient of these reinforcements is determined by the oxide superconductor lead body.
Is characterized by having a coefficient of thermal expansion substantially equal to that of the above.

That is, according to the present invention, the oxide superconductor lead body for current conduction is partially overlapped so as to cover almost the entire length in the axial direction, so that the two parts are in a state where a thermal utility can be taken. Separated (substantially discontinuous)
A super-hard reinforcing body (for example, a wire or a ribbon) is embedded or provided integrally on the peripheral surface to achieve the required thermal insulation, while maintaining the required mechanical insulation as an oxide superconductor lead for current flow. The main point is that it has been thermally strengthened. Here, as the super-hard reinforcing member, a material having a thermal expansion coefficient substantially equal to that of the oxide superconductor and high mechanical strength, such as Kovar wire (trade name), is desirable.

[0008]

According to the present invention, as described above, the amount of heat entering the liquid helium (ultra-low temperature region) in which the superconducting magnet is immersed can be reduced by using the oxide superconductor for current conduction as the current lead body. Reduce. On the other hand, the current lead main bodies are separated from each other (substantially discontinuous) so as to be able to take a thermal utility so as to partially overlap almost the entire length in the axial direction, and A rigid reinforcing body is arranged and integrated to form a reinforced structure. In other words, the current leads are basically composed of oxide superconductors with low thermal conductivity, so that the amount of heat entering the cryogenic region is significantly reduced or reduced, and on the other hand, thermal insulation is impaired. Because it is reinforced while considering that there is no
Even when the diameter is reduced, it retains excellent mechanical shock resistance and thermal shock resistance, and can always function as an excellent and highly reliable superconducting current lead.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an example of the configuration of a superconducting current lead according to the present invention in a sectional view in the axial direction. Reference numeral 1 denotes, for example, an oxide superconductor lead for passing a current having a diameter of about 20 mm and a length of about 10 cm. The main bodies 2a, 2b, and 2c are inside the lead main body 1,
It is a super-hard reinforcement body integrally embedded in the axial direction, for example, a wire (wire) made of Kovar wire having a diameter of about 1.5 mm and a length of about 5 cm. However, the diameter and length of the current lead body 1 are variously changed according to the magnitude of the current to be passed and other design conditions, and there are a wide variety of modes. A diameter of about 1/10 to 1/20 of the diameter of 1 is preferable.
The super-hardened reinforcing members 2a, 2b, 2c are separated from each other as shown in the drawing and partially (partly) overlap with each other in the axial direction so as to extend over the entire length of the oxide superconductor lead body 1. And is integrally embedded. In other words, inside the oxide superconductor lead body 1, super hard wires 2 are provided at both ends.
a, 2b are disposed, and a super-hard wire 2c is disposed at a central portion so as to partially overlap with the super-hard wires 2a, 2b, so as to mechanically reinforce substantially the entire length. It has an integrally embedded configuration. Here, the super-hard reinforcement 2
a, 2b, and 2c, which are not embedded (separated or discontinuous) in a state where they are substantially in contact with each other (substantially or discontinuously), are embedded and mechanically reinforced substantially over their entire length. This is because, by being continuous, the insulating region (discontinuous region) 3 has thermal insulation and the oxide superconductor lead 4 maintains or maintains a required low thermal conductivity (rate).

As described above, the structured and reinforced oxide superconductor lead 4 sufficiently withstands bending, for example, as shown in cross section in FIG. Damage caused by mechanical or thermal shock is completely eliminated. In other words, the oxide superconductor lead 4 that connects the superconducting wire in the cryogenic region and the current lead terminal in normal temperature without breaking even if subjected to a mechanical shock or a thermal shock in a practical process, It is possible to always maintain and demonstrate highly reliable functions. In other words, the wire diameter can be set as thin as possible to the extent that the required current capacity as the superconductor lead 4 can be secured, so that heat intrusion from the outside into the cryogenic region can be reduced. It is possible to make full use of the advantages of superconductivity, such as increasing the size of refrigeration mechanisms (such as refrigerators), reducing power consumption, and reducing size and weight.

It is sufficient that the oxide superconductor lead 4 has a sectional area corresponding to a required current capacity.
The cross-sectional shape is not limited to a circle, but can be arbitrarily selected and set. However, in order to minimize the amount of heat entering the cryogenic region, it is disposed (arranged) in the oxide superconductor lead body 1.
The cross-sectional area of the super-hard reinforcements 2a, 2b, 2c, etc. is as small as possible (small diameter) as long as the required mechanical reinforcement effect can be obtained.
In addition, it is desirable that the oxide superconductor lead body 1 has thermal insulation and a coefficient of thermal expansion close to that of the oxide superconductor lead body 1. Also,
The super-hardened reinforcements 2a, 2b, 2c and the like may have a shape other than a linear shape (wire), for example, a flat plate such as a ribbon shape.

[0013]

As described above, according to the superconducting current lead according to the present invention, the oxide superconductor lead body for passing a current is disposed in the superconductor lead body along the axial direction. The reinforcing member protects the oxide superconductor lead body, which is weak in mechanical strength. In other words, the oxide superconductor lead body through which a current flows is reinforced with a mechanical external force in a direction perpendicular to the length direction, so that the possibility of breakage due to mechanical shock or thermal shock is also eliminated. In addition, since the intrusion of heat from the outside can be reduced, it can greatly contribute to lower power consumption of the cooling mechanism required for maintaining (holding) the cryogenic temperature.

[Brief description of the drawings]

FIG. 1 is a sectional view in the axial (length) direction showing a configuration example of a superconducting current lead according to the present invention.

FIG. 2 is a cross-sectional view in the axial (length) direction showing a state in which a superconducting current lead according to the present invention is bent.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Lead body made of oxide superconductor 2a, 2b, 2c ... Super-hard reinforcement body 3 ... Separation (discontinuous) area of super-hard reinforcement body 4 ... Lead made of oxide superconductor for passing current

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-161810 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01F 6/00 ZAA

Claims (1)

(57) [Claims] 1. An oxide superconductor lead body for supplying a current and an oxide superconductor lead body for supplying a current are formed so as to partially overlap each other in an axial direction over substantially the entire length and are separated from each other. It consists of a plurality of reinforcements that are arranged integrally ,
The thermal expansion coefficient of these reinforcements is determined by the oxide superconductor lead body.
A superconducting current lead having a coefficient of thermal expansion substantially equal to that of the superconducting current lead.