JP5649682B2 - Superconducting device - Google Patents

Description

  The present invention is a superconducting device having a superconducting element (including a superconducting coil; hereinafter the same) that is cooled to a cryogenic environment for supplying a current to the superconducting element from a power supply or power system on the room temperature side. The present invention relates to a superconducting device having a current lead.

  Since superconductivity has the feature of allowing a large current to flow with zero resistance, development for various applications such as industrial applications, medical applications, and power applications is underway. In a conventional typical superconducting device, a superconducting element is cooled by being immersed in a refrigerant such as liquid nitrogen or liquid helium (see, for example, Patent Document 1). There may also be a method of cooling by using heat conduction to the cooling stage of the refrigerator without using a refrigerant. The refrigerant container is disposed in a heat insulating container placed at room temperature via a heat insulating space such as a vacuum. Current leads are arranged to connect the superconducting element to a power source or power system placed on the room temperature side.

  In designing such a superconducting device, the current lead is an important component. The reason is both in terms of thermal design and insulation design. The importance in the former thermal design is that the current lead becomes a heat penetration source into the low temperature side, that is, the inside of the refrigerant container. Since the current lead connects the room temperature side and the low temperature side, a metal such as copper is usually used. Increasing the cross-sectional area of the current lead and reducing the electrical resistance to suppress ohmic heat generation (heat generation due to electric resistance) reduces ohmic heat generation, but increases heat penetration due to heat conduction from room temperature. On the contrary, when the cross-sectional area of the current lead is reduced, heat intrusion due to heat conduction from room temperature is reduced, but ohmic heat generation is increased. Therefore, there is an optimum value for the cross-sectional area of the current lead.

  Strictly speaking, the concept of optimizing (current value) x (length) / (cross-sectional area) for the rated current value, the length from the room temperature end to the low-temperature end of the current lead, and the cross-sectional area is well known. . When (current value) x (length) / (cross-sectional area) is optimized, the heat intrusion by the current lead from the room temperature end to the low temperature end is 0.045W per one current lead with a rated current value of 1A. Yes, this value is proportional to the rated current value.

JP 7-312309 A

  Now, current leads designed in this way are often used in superconducting equipment, but have the following problems.

  To sum up the issues taken up here, the room temperature end of the current lead tends to frost. Certainly, the current lead can be considered to be literally near room temperature by design, but the temperature drops in actual operation, condensing moisture in the atmosphere, and water droplets adhere to the surface of the current lead There are things to do. In particular, this phenomenon is likely to occur when the current flowing through the current lead is smaller than the rated current value. In general, the rated current value is assumed to be the maximum current value assumed, but in actual operation of the superconducting device, there are many situations in which a current smaller than the rated current value flows.

  In an extreme case, the superconducting coil is cooled and held in a cryogenic environment and is not energized. Even in this state, since the current lead connects the room temperature end and the low temperature end, there is heat input at the low temperature end due to heat conduction. This heat penetration is about 0.03 W per current lead with a rated current value of 1A. The difference between the rated energization and the energization with a current value less than the rating (the most extreme case is de-energization) is that in the former case the ohmic heating of the current lead is the heat source to the low temperature end, whereas in the latter case Is that heat conduction becomes a heat source from the room temperature end to the low temperature end (when heat is not applied, which is an extreme case, all heat input by heat conduction). The constant heat input from the room temperature end means that heat is input from the atmosphere at the room temperature end surface of the current lead. This state is expressed by the following equation (1).

_{Q = hA (T air - T} lead) (1)
Here, Q is the amount of heat input [W], and is about 0.03 W per wire with a current lead having a rated current value of 1 A when not energized. h represents the convective heat transfer coefficient [W / m ² · K] on the current lead surface. A is the heat transfer area [m ² ], T _air is the atmospheric temperature (room temperature) [K], and T _lead is the temperature [K] at the room temperature end of the current lead.

The phenomenon of water droplets or frost adhering to the surface of the current lead described above is considered to be caused by a decrease in the temperature at the room temperature end of the current lead indicated by T _lead when the heat transfer represented by the equation (1) is not sufficient.

  When water droplets or frost adheres to the surface of the current lead, the following problems occur.

  The first is the problem of current lead insulation degradation. In general, the current lead charging section is connected to the room temperature of the container at ground potential via some kind of insulator. It is necessary to secure the necessary distance by making the insulator surface creeping. However, when water droplets adhere to the surface of the current lead and the water droplets also drop on the insulation creepage surface, the insulation strength decreases. This is because the dielectric strength decreases in a wet state than in a dry state.

  The second is the problem of current lead material corrosion. The energization part of the current lead is made of a metal such as copper. If a state where water droplets or frost adheres to the surface of the current lead continues for a long time, problems such as rusting of the lead material occur.

  Third, there is a problem of corrosion of materials other than current leads. When water droplets on the surface of the current lead drop on the surface of the container of the superconducting device, the problem arises that the metal material becomes rusted as described above. Furthermore, if the amount of the flooring material is metal when dripping from the surface of the container and water droplets turn around the floor or the like, the same problem occurs.

  As described above, water droplets or frost adhering to the surface of the current lead is a problem that remarkably lacks the long-term reliability of the superconducting device.

  The present invention has been made in view of the above problems, and it is an object of the present invention to prevent water droplets or frost from adhering to the surface of the current lead of the superconducting device and to improve the long-term reliability of the superconducting device. .

  In order to achieve the above object, a superconducting device according to the present invention includes a superconducting element cooled to a cryogenic environment, a cryocontainer that accommodates the superconducting element, and an inside of the cryocontainer attached to the cryocontainer. A refrigerator for cooling, a current lead for supplying a current supplied from outside the cryocontainer to the superconducting element, electrically connected to the superconducting element through the wall of the cryocontainer, An insulating terminal disposed between the wall of the cryogenic vessel and the current lead and electrically insulating between the wall of the cryogenic vessel and the current lead; and the outside of the cryogenic vessel of the current leads And an electrically insulated heater disposed around the room temperature end of the current lead that is a part.

  According to the present invention, water droplets or frost is prevented from adhering to the surface of the current lead of the superconducting device, and the long-term reliability of the superconducting device can be improved.

1 is a schematic sectional elevation view of a first embodiment of a superconducting device according to the present invention. The typical elevation sectional view of a 2nd embodiment of the superconducting device concerning the present invention. The typical elevation sectional view of a 3rd embodiment of the superconducting device concerning the present invention. The typical elevation sectional view of the 4th embodiment of the superconducting device concerning the present invention. The typical elevation sectional view of the 5th embodiment of the superconducting device concerning the present invention. The typical elevation sectional view of the 6th embodiment of the superconducting device concerning the present invention. The typical elevation sectional view of the 7th embodiment of the superconducting device concerning the present invention. The typical elevation sectional view of the 8th embodiment of the superconducting device concerning the present invention. The IX-IX line arrow expanded plane sectional view of FIG. The typical elevation sectional view of the 9th embodiment of the superconducting device concerning the present invention.

  Hereinafter, various embodiments of a superconducting device according to the present invention will be described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

[First Embodiment]
FIG. 1 is a schematic vertical sectional view of a first embodiment of a superconducting device according to the present invention. The cryogenic container 40 includes a heat insulating container 12 and a refrigerant container 14 inside thereof. A vacuum 13 is formed between the heat insulating container 12 and the refrigerant container 14, and a refrigerant 15 such as liquid helium is accommodated in the refrigerant container 14.

  The cooling stage 17 is disposed so as to be immersed in the refrigerant 15, and the cooling unit 41 of the refrigerator 16 that cools the cooling stage 17 is attached to the cryogenic container 40. The refrigerator 16 includes a compressor 21 disposed outside the cryogenic container 40 and pipes 23 a and 23 b that connect the cooling unit 41 and the compressor 21. The refrigerator 16 further includes an air cooling radiator 22 for discharging heat generated in the compressor 21 to the atmosphere. The air cooling radiator 22 preferably has a cooling fan (not shown), but may be air cooling by natural convection.

  A superconducting element 11 such as a superconducting coil is disposed so as to be immersed in the refrigerant 15, and current leads 18 a and 18 b for supplying a current to the superconducting element 11 penetrate the walls of the refrigerant container 14 and the heat insulating container 12 at a low temperature. The current leads on the outside of the container 40 extend to the room temperature ends 118a and 118b. An insulating terminal 19 is disposed at a portion where the current leads 18a and 18b pass through the wall of the heat insulating container 12, and the electric insulation between the current leads 18a and 18b and the heat insulating container 12 is maintained and the airtightness of the heat insulating container 12 is maintained. It has a structure to do.

  In this embodiment, the air cooling radiator 22 is disposed in the vicinity of the current lead room temperature ends 118a and 118b, and the air heated by the air cooling radiator 22 is configured to heat the current lead room temperature ends 118a and 118b. When the air cooling radiator 22 has a fan (not shown), the current lead room temperature ends 118a and 118b may be positioned on the downstream side of the air cooling radiator 22 in consideration of the air flow by the fan.

  According to this embodiment, since the air temperature around the current lead room temperature ends 118a and 118b is higher than the atmospheric temperature, frost formation on the surface of the current lead room temperature ends 118a and 118b can be prevented or suppressed.

[Second Embodiment]
FIG. 2 is a schematic vertical sectional view of a second embodiment of the superconducting device according to the present invention. The second embodiment differs from the first embodiment in that fins 43 are attached to the surfaces of the current lead room temperature ends 118a and 118b. The fins 43 have a large surface area, and may have various shapes such as a large number of plate shapes and a large number of wire-like protrusions. In the case of a plate shape, it is preferable to extend along the air flow. In the example of FIG. 2, the air flow is substantially horizontal, so the fin 43 is preferably a plate shape extending in the horizontal direction. The shape of the plate-shaped fin 43 is, for example, a disk shape centering on the axis of the current lead room temperature end 118a, 118b. When the current lead room temperature ends 118a and 118b are close to each other, a non-axisymmetric shape may be used to avoid interference between the fins 43.

  According to this embodiment, since the surface area of the current lead room temperature ends 118a and 118b is increased as compared with the first embodiment, heat input from the air to the current lead room temperature ends 118a and 118b further increases, and the current lead room temperature ends 118a. , 118b can be raised, and the effect of preventing or suppressing frost formation on the surface of the current lead room temperature ends 118a, 118b can be further enhanced.

[Third Embodiment]
FIG. 3 is a schematic vertical sectional view of a third embodiment of the superconducting device according to the present invention. In the third embodiment, the superconducting element 11 and the cooling stage 17 are thermally connected directly by the heat transfer plate 26 without using the refrigerant container 14 and the refrigerant 15 in the first embodiment (FIG. 1). is there. Even in such an example, as in the first embodiment, the air-cooling radiator 22 is disposed in the vicinity of the current lead room temperature ends 118a and 118b, and the air heated by the air-cooling radiator 22 is the current lead room temperature end. 118a, 118b can be configured to be heated.

  As a result, as in the first embodiment, the air temperature around the current lead room temperature ends 118a and 118b increases, so that frost formation on the surface of the current lead room temperature ends 118a and 118b can be prevented or suppressed.

[Fourth Embodiment]
FIG. 4 is a schematic vertical sectional view of a fourth embodiment of the superconducting device according to the present invention. In the fourth embodiment, the entirety including the cryogenic container 40, the refrigerator 16, the current leads 18 a and 18 b and the insulating terminal 19 is accommodated in the storage container 24. The storage container 24 is provided with an air inlet / outlet port 25. In this embodiment, the position of the compressor 21 and the air cooling radiator 22 may be anywhere within the storage container 24, and in the example of FIG. 4, the compressor 21 and the air cooling radiator 22 are arranged on the floor in parallel with the low temperature container 40. Other configurations are the same as those of the first embodiment.

  According to this embodiment, the environmental temperature in the storage container 24 becomes higher than the atmospheric temperature due to the operation of the compressor 21, thereby preventing or suppressing frost formation on the surfaces of the current lead room temperature ends 118 a and 118 b. be able to.

[Fifth Embodiment]
FIG. 5 is a schematic vertical sectional view of a fifth embodiment of the superconducting device according to the present invention. In the fifth embodiment, the current lead room temperature ends 118 a and 118 b and the insulated terminal 19 are covered with the box 27. The air heated by the air-cooling radiator 22 is introduced into the box 27 through the blow-in port 28 and then discharged through the discharge port 29. Other configurations are the same as those of the first embodiment.

  According to this embodiment, since the air heated by the air-cooling radiator 22 is reliably supplied to the periphery of the current lead room temperature ends 118a and 118b, the current lead room temperature end 118a is more reliably compared to the first embodiment. 118b, the air temperature around 118b can be increased. As a result, frost formation on the surface of the current lead room temperature ends 118a and 118b can be more reliably prevented or suppressed.

[Sixth Embodiment]
FIG. 6 is a schematic vertical sectional view of a sixth embodiment of the superconducting device according to the present invention. In the sixth embodiment, heaters 30a and 30b are arranged around the current lead room temperature ends 118a and 118b. The heaters 30a and 30b are, for example, electric heaters. The electric heater needs to be electrically insulated from the current lead room temperature ends 118a and 118b. For example, a sheathed heater coated with insulation can be used. In the example shown in FIG. 6, the heaters 30 a and 30 b are electric heaters and are connected to a heater power supply 50. The heater power supply 50 is controlled by a heater controller 51.

  According to this embodiment, the temperature of the current lead room temperature ends 118a and 118b can be increased by the heaters 30a and 30b. As a result, frost formation on the surface of the current lead room temperature ends 118a and 118b can be prevented or suppressed.

  In particular, in this configuration, the heater controller 51 can change the amount of heat generated by the heaters 30a and 30b in accordance with the increase and decrease of the energization current of the current leads 18a and 18b. That is, when the energization current is smaller than when the rated current value is energized, the amount of heat penetration may be reduced by the heat generated by the heaters 30a and 30b. Thereby, the power consumption by the heaters 30a and 30b and the amount of heat flowing into the cryogenic container 40 through the current leads 18a and 18b can be suppressed to the minimum necessary.

[Seventh Embodiment]
FIG. 7 is a schematic vertical sectional view of a seventh embodiment of the superconducting device according to the present invention. In the seventh embodiment, the surfaces of the current lead room temperature ends 118a and 118b are coated with insulators 31a and 31b. The insulators 31a and 31b are electrical insulating materials and materials having low thermal conductivity, and are, for example, epoxy resin, fiber reinforced plastic (FRP), or the like.

  According to this embodiment, since the surfaces of the current lead room temperature ends 118a and 118b are covered with the insulators 31a and 31b, frost formation can be avoided here. In addition, since the temperature gradient is generated inside the insulators 31a and 31b having low thermal conductivity, the surface temperature of the insulators 31a and 31b becomes relatively high, and frost formation on the surfaces of the insulators 31a and 31b and the insulating terminal 19 is prevented. Can be suppressed.

[Eighth Embodiment]
FIG. 8 is a schematic vertical sectional view of an eighth embodiment of the superconducting device according to the present invention. 9 is an enlarged cross-sectional view taken along line IX-IX in FIG.

  In the eighth embodiment, fins 53 are attached to the outside of the current lead room temperature ends 118a and 118b. The fins 53 have a large surface area, and can be various types such as a large number of plate shapes and a large number of wire-like protrusions. In the case of a plate shape, it is generally preferable to extend along the air flow. In this embodiment, since the fins 53 have a lower temperature than the surrounding air, natural convection of the air going downward occurs around the fins 53. Therefore, the fin 53 preferably has a shape extending radially in the vertical direction toward the outside of the current lead room temperature ends 118a and 118b. Usually, it is preferable that the plurality of fins 53 be arranged in an axially symmetrical manner at equal intervals in the circumferential direction. However, when the current lead room temperature ends 118a and 118b are close to each other, a non-axisymmetric arrangement may be employed in order to avoid interference between the fins 53.

  According to this embodiment, since the effective surface area of the current lead room temperature ends 118a and 118b is increased as compared with the case without the fins 53, the heat input from the air to the current lead room temperature ends 118a and 118b is increased. The temperature of the ends 118a and 118b can be increased. Thereby, frost formation on the surface of the current lead room temperature ends 118a and 118b can be prevented or suppressed.

In the formula (1), for example, the current rating of the current leads 18a and 18b is 0.001 square meter per 1A, and a typical value of the natural convection heat transfer coefficient h is about 3 W / m ² . Assuming K, since the amount of heat penetration when current is not applied is 0.03 W per rated current value of 1 A, the surface area of the current leads at the room temperature ends 118 a and 118 b (including the surface area of the fin 53) is 0.001 square meter per 1 A rated current value. If secured above, the temperature difference between the atmosphere and the current lead room temperature ends 118a and 118b can be made 10K or less. As a result, a decrease in the surface temperature of the current lead room temperature ends 118a and 118b can be suppressed, and frost formation on the surface of the current lead room temperature ends 118a and 118b can be suppressed.

[Ninth Embodiment]
FIG. 10 is a schematic vertical sectional view of a ninth embodiment of the superconducting device according to the present invention. In the ninth embodiment, the insulation terminals 33a and 33b are disposed at the portions where the current leads 18a and 18b penetrate the wall of the heat insulating container 12, and the electric insulation between the current leads 18a and 18b and the heat insulating container 12 is performed. It has a structure that holds the airtightness of the heat insulating container 12 while holding it. The room temperature portions of the insulating terminals 33a and 33b, that is, the portions protruding from the upper surface of the heat insulating container 12 are entirely inclined in a conical shape.

  According to this embodiment, even if water droplets are attached to the surfaces of the current lead room temperature ends 118a and 118b, and the water droplets drip onto the insulating terminals 33a and 33b, they can be dropped toward the heat insulating container 12 due to the inclination. It is possible to suppress degradation of creeping insulation due to water adhering to the surfaces of the insulating terminals 33a and 33b.

[Other Embodiments]
Although various embodiments of the superconducting device according to the present invention have been described above, these are merely examples, and the present invention is not limited to these embodiments.

  In addition, the features of the above-described embodiments can be combined in various ways.

  For example, the fins 43 of the second embodiment (FIG. 2) can be applied to the third to fifth embodiments. The second and fourth to eighth embodiments are examples of the case where the refrigerant container 14 and the refrigerant 15 similar to those of the first embodiment are used, but the second and fourth to eighth embodiments are used. The characteristics of the embodiment can also be applied to the case where the heat transfer plate 26 similar to that of the third embodiment is used.

11 ... Superconducting element (superconducting coil)
DESCRIPTION OF SYMBOLS 12 ... Thermal insulation container 13 ... Vacuum 14 ... Refrigerant container 15 ... Refrigerant 16 ... Refrigerator 17 ... Cooling stage 18a, 18b ... Current lead 19 ... Insulation terminal 21 ... Compressor 22 ... Air-cooling radiator 23a, 23b ... Piping 24 ... Storage container 25 ... Air inlet / outlet 26 ... Heat transfer plate 27 ... Box 28 ... Gas inlet 29 ... Gas outlet 30a, 30b ... Heater 31a, 31b ... Insulator 33a, 33b ... Insulated terminal 40 ... Low temperature vessel 41 ... Cooling part 43 ... Fin 50 ... Heater power supply 51 ... Heater controller 53 ... Fin 118a, 118b ... Current lead room temperature end

Claims (2)

A superconducting element cooled to a cryogenic environment;
A cryogenic container that houses this superconducting element;
A refrigerator attached to the cryocontainer to cool the inside of the cryocontainer,
A current lead for passing through the wall of the cryocontainer and being electrically connected to the superconducting element and supplying a current supplied from outside the cryocontainer to the superconducting element;
An insulating terminal disposed so as to be interposed between the wall of the cryogenic vessel and the current lead, and electrically insulating between the wall of the cryogenic vessel and the current lead;
A heater that is disposed around a current lead room temperature end that is an outer portion of the cryogenic vessel of the current leads and is electrically insulated;
A superconducting device characterized by comprising: The heater is an electric heater,
Further comprising a control device for controlling the electric heater so that the amount of heat generated by the electric heater increases when the current supplied to the superconducting element is small;
The superconducting device according to claim 1.

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