JP5005582B2 - Superconducting current lead manufacturing method - Google Patents

Description

The present invention relates to a superconducting current that supplies power from a power source at room temperature to a superconducting device cooled to a cryogenic temperature in a superconducting device such as a superconducting energy storage device, a superconducting current limiter, a superconducting cable, a superconducting generator, and a superconducting transformer. a method of manufacturing a lead. In particular, the present invention relates to a method of manufacturing a superconducting current lead (hereinafter also simply referred to as a current lead ) using a high-temperature superconducting wire as a part of the conductor.

  Superconducting devices such as superconducting energy storage devices, superconducting current limiters, superconducting cables, superconducting generators, and superconducting transformers have features such as small size and high efficiency compared to conventional ordinary conducting devices, and are expected to be put to practical use. It is growing.

  The current lead has a role of supplying electric power from a power source at room temperature to a superconducting device at a cryogenic temperature, and is indispensable for the superconducting device. Current leads are often used with a length of 0.5m to 1.5m due to dimensional constraints due to the positional relationship with superconducting devices and surrounding equipment. The power supply side in the longitudinal direction is at room temperature, and the cryogenic temperature side is generally 4.2K to 80K, depending on the operating environment of the superconducting device and the current lead cooling method. Therefore, the current lead has a temperature distribution in the longitudinal direction, and heat penetrates from the room temperature end to the low temperature end of the current lead.

  As a material for the current lead, a highly conductive material such as copper is used. However, since the electrical conductivity is large and the thermal conductivity is large, the amount of heat penetration into the low temperature end of the current lead is large. If the amount of heat penetration of the current lead is large, the heat load at cryogenic temperatures increases, reducing the operating efficiency, and the penetration heat is transmitted to the connection between the current lead and the superconducting device. There is a risk of adverse effects such as a decrease in critical current. As a countermeasure for reducing the amount of heat penetration at the low temperature end of the current lead, one using a high temperature superconducting wire made of an oxide superconducting material in the current path on the low temperature side of the current lead has been developed (see Patent Documents 1 to 3).

  The high-temperature superconducting wire has a current density nearly 100 times that of copper, and since the conductor is an oxide (a kind of ceramic), it has a low thermal conductivity and is effective in suppressing the amount of heat penetration. The cooling method for the high-temperature superconducting current lead is roughly divided into a gas cooling method and a conduction cooling method. In the case of the gas cooling method, a refrigerant pipe is provided so as to wrap the conductor of the current lead (or inside the conductor), and the conductor is cooled by flowing a refrigerant gas such as helium gas through the pipe. On the other hand, in the case of the conduction cooling method, freezing is carried out in the cryogenic vessel with respect to the current lead connecting the superconducting device provided in the cryogenic vessel insulated from the surroundings by a vacuum shield or the like and the power supply provided outside. The conductor of the lead and the refrigerant pipe are brought into thermal contact, and the conductor of the current lead is cooled by the refrigerator or the refrigerant gas.

  By the way, as for the said patent documents 1-3, all are on the outer peripheral surface of the hollow cylindrical support member which consists of an electrically insulating material (for example, FRP) and a low heat conductive metal material (for example, stainless steel, a titanium alloy etc.). Discloses a current lead of a gas cooling system in which a plurality of oxide superconducting members are arranged and a cooling gas is passed through the hollow portion of the support member. And patent document 1 discloses the structure which adhere | attaches the said cylindrical support member and several oxide superconducting member with an epoxy-type adhesive agent. Moreover, as described in paragraph [0025] of the specification, Patent Document 2 brings a plurality of oxide superconducting members and a cylindrical support member into close contact by binding or diffusion bonding from the outer periphery side of the support member. The configuration is disclosed.

  As described in paragraphs [0005] to [0007] of the specification, Patent Document 3 describes the problem of the configuration as in Patent Documents 1 and 2 described above, that is, “the surface of the support member as viewed microscopically”. When the contact between the contact surface and the surface of the unit conductor (oxide superconducting member) is incomplete and the heat transfer resistance between the contact surfaces is large, the superconducting transition (quenching) of the superconductor occurs in the unit conductor. The support member does not sufficiently contribute as a heat capacity body that absorbs the heat of the unit conductor. For this reason, only the unit conductor abnormally rises in temperature, and in the worst case, the unit conductor may be burned out. In view of the problem, “the oxide superconducting member and the cylindrical support member are joined together by soldering, in order to improve solderability, in advance to stainless steel, gold, silver, copper, tin, zinc, etc. Vapor deposition or sputtering On which was formed, discloses a method "subjecting the solder.

  Next, a conventional configuration example employing the above-described conduction cooling method as a cooling method for the high-temperature superconducting current lead will be described.

  FIG. 5 shows an example of a schematic configuration of a superconducting device including a high-temperature superconducting current lead that employs a conduction cooling method. The superconducting device shown in FIG. 5 includes a superconducting device 21 cooled to a cryogenic temperature, a cryogenic container 22 that houses the superconducting device 21, a power source 24 at room temperature, and a current lead 23 that supplies power from the power source 24 to the superconducting device 21. It consists of.

  In the example of FIG. 5, a current lead for conducting cooling is shown by a cooling conductor 28 in which the high temperature side and the low temperature side of the high temperature superconducting conductor portion 27 are thermally connected to different refrigerators 25. The high temperature superconducting current lead includes a copper conductor portion 26 and a high temperature superconducting conductor portion 27. The copper conductor part 26 is provided on the room temperature side, and is made of a round bar or stranded copper. On the other hand, the high-temperature superconducting conductor portion 27 is provided on the low-temperature side, and is made of a high-temperature superconducting conductor, a support member, or the like. Details of the configuration example are shown in FIG.

  FIG. 4 is a cross-sectional view of the high-temperature superconducting conductor portion 27 along the line AA in FIG. The high-temperature superconducting conductor portion shown in FIG. 4 has a configuration in which, for example, a high-temperature superconducting conductor 2 made of a plurality of high-temperature superconducting wires 1 is fixed by a solder 5 in a groove 4 provided in a support member 3 made of stainless steel, for example. Is provided. As the high-temperature superconducting wire 1, a ceramic superconducting wire called bismuth or yttrium is used. Bismuth-based superconducting wire is manufactured by filling ceramic powder into a silver pipe as a base material and obtaining processes such as wire drawing, rolling, and sintering. Yttrium-based superconducting wires are mainly manufactured by forming an intermediate layer on a Hastelloy tape and forming a superconducting layer thereon, and for stabilization, the superconducting layer is coated with silver or a silver alloy. Is done.

  As the support member 3, a material having low thermal conductivity is suitable from the viewpoint of suppressing the heat penetration amount of the current lead as much as possible during normal operation. On the other hand, the support member 3 must be provided with a current bypass function in the event of an abnormality such as a supply stop of the refrigerant that cools the current lead, an abnormal stop of the refrigerator, or a deterioration or disconnection of the superconducting wire. A function as a conductor is required. Therefore, the support member 3 can also serve as a protective conductor and is preferably made of a material having a relatively low thermal conductivity, such as stainless steel or titanium alloy, which is a low thermal conductive metal material. The support member 3 and the high-temperature superconducting conductor 2 are configured to be electrically in parallel.

  The high temperature superconducting conductor 2 and the supporting member 3 are connected by placing the silver or silver alloy surface of the high temperature superconducting conductor on the supporting member and pouring solder melted by heating to 150 ° C. to 200 ° C. In this case, since stainless steel has poor solderability, a thin film such as silver or copper having good solderability is formed on the stainless steel by vapor deposition or sputtering in advance, as in the method disclosed in Patent Document 2 described above. Further, a groove 4 for fitting the high temperature superconducting conductor 2 is provided in the support member 3 so that the solder does not move during the operation so that the solder can be easily poured, and the solder is poured into the support member 3 for connection.

As an example of the connection method, the high-temperature superconducting conductor 2 and the solder 5 are inserted into the groove 4 of the support member 3 and a bar heater is brought into close contact with both ends of the current lead to heat the entire current lead to 150 ° C. to 200 ° C. . As a result, the solder 5 melts and spreads over the entire groove. At that time, it is necessary to spread the solder uniformly while holding the high-temperature superconducting conductor 2 so as not to float. Then turn off the heater power and wait for the entire current lead to cool. A copper jig may be used so that the heater can be in close contact with the support member. Soldering is performed not only in joining the support member 3 and the high-temperature superconducting conductor 2 but also in joining the conductor portions connected to both longitudinal ends of the high-temperature superconducting conductor portion 27.
JP-A-4-218215 Japanese Patent Laid-Open No. 10-188691 JP 2002-64014 A

  The conventional current lead having the soldering configuration as shown in FIG. 4 has the following problems.

  In the soldering process, it is necessary to pour the solder into the groove to the extent that the high-temperature superconductor is buried so that the high-temperature superconductor is not detached from the support member. Is not constant, and electrical and thermal conduction characteristics vary among current leads connected in parallel. In particular, when the amount of solder is too large, the amount of heat intrusion from that portion increases, which may cause an unexpectedly large heat load and cause a problem in the cooling system.

  Also, it is necessary to spread the solder evenly while pressing down so that the high-temperature superconducting conductor does not float as much as possible in the longitudinal direction of the current lead (for example, length 0.5m to 1m). There is also a problem that workability is poor and manufacturing takes time.

  Furthermore, it takes a long time to heat the current lead, pour the solder, and then cool it down, and it takes several hours if the size of the current lead is large. Moreover, when using stainless steel as a support member as described above, and forming a thin film such as silver or copper with good solderability on stainless steel in advance by vapor deposition or sputtering, the process also requires work and time, Overall, soldering has a problem of poor workability and increased manufacturing costs.

  As described above, since it is not preferable to solder the high-temperature superconducting conductor and the support member, it is desirable to adopt a different joining method, but in an actual superconducting current lead, as described in detail later, The high-temperature superconducting conductor needs to include at least two electrodes joined by solder, and the above-described problem needs to be solved in consideration of this point as a method of manufacturing a superconducting current lead.

The present invention has been made in view of the above points, and an object of the present invention is to suppress an increase in the amount of heat penetration into the low temperature end of the current lead, to obtain stable characteristics with little variation, and thereby improving the workability, it is to provide a superconducting current lead manufacturing method having the connection structure of the high-temperature superconductor and the support member.

In order to solve the above-described problems, the present invention supplies power from a power source installed in a room temperature environment to a superconducting device installed in a cryogenic container, and at least a part of the low temperature side is superconducting oxide. comprising a high temperature superconducting conductor portion using a high-temperature superconducting wire made of a material, prior Symbol HTS conductor portion includes a support member in comparison with the copper comprising a small low thermal conductivity metal material thermal conductivity, on the support member The support member and the high-temperature superconductor are bonded by a conductive resin material , and the high-temperature superconductor is joined by solder. A method for manufacturing a superconducting current lead having at least two electrodes includes the following steps (invention of claim 1).
(A) The process of apply | coating the said conductive resin material between the said high temperature superconducting conductor and the said supporting member, heat-hardening, and adhere | attaching.
(B) The process of cooling the adhesion part between the said high-temperature superconducting conductor and the said supporting member to temperature lower than the heat-hardening temperature of the said conductive resin material.
(C) A step of joining the high-temperature superconducting conductor and the electrode with solder during the cooling.

Further, in the method of manufacturing a superconducting current lead according to claim 1, the support member is made of a plate-like member, and the high-temperature superconducting conductor is a plurality provided in the longitudinal direction of one main surface of the plate-like support member. The support member and the high-temperature superconducting conductor are disposed in each groove, and are bonded to each other by a conductive resin material on the bottom surface of the groove (invention of claim 2).

Further, in the method of manufacturing a superconducting current lead according to claim 1 or 2, wherein the conductive resin material shall be the conductive resin paste made by mixing a silver particle as a conductive filler in an epoxy resin (according Item 3).

According to the invention, it becomes possible to easily apply the conductive resin material between the high-temperature superconducting conductor and the support member, particularly in the case of an epoxy resin, after application at room temperature, put it in an electric furnace or the like at 100 ° C. or less. Therefore, the workability can be improved and the working time can be shortened .

Further, since the paste-like conductive resin material can be extended thinly, an increase in the amount of heat penetration can be suppressed, and the characteristics can be stabilized. Details will be described later.

  According to the present invention, a superconducting device having a connection structure between a high-temperature superconducting conductor and a support member that suppresses an increase in the amount of heat penetration into the low temperature end of the current lead, stabilizes characteristics, and improves workability. A current lead and a method for manufacturing the current lead can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 3 is a cross-sectional view of the principal part showing a schematic configuration of the superconducting current lead showing the embodiment of the present invention, and is a cross-sectional view corresponding to FIG. The same members as those shown in FIG. 4 are denoted by the same reference numerals, and detailed description thereof is omitted. 3 is different from that shown in FIG. 4 in that the high-temperature superconducting conductor 2 and the support member 3 are connected by the conductive resin material 6.

  The required number of high-temperature superconducting conductors 2 is determined from the energization specifications and the characteristics of the superconducting wire 1. In the case of multiple pieces, they are arranged side by side or stacked in consideration of the empirical magnetic field. FIG. 3 shows an example in which three sets are arranged side by side as one set of high-temperature superconducting conductors 2 formed by stacking four sheets. As the high-temperature superconducting wire 1, for example, a Bi2223 series wire is used. In this case, the superconducting filament is surrounded by a silver alloy base material in the wire itself. In the case of stacking, a plurality of high-temperature superconducting wires are further wrapped with a silver alloy in advance, and in any case, the surface is a silver alloy.

  Since the support member 3 also needs a function as a protective conductor, in the unlikely event of stainless steel, a material that can commutate electricity from the high-temperature superconducting conductor and is strong is desirable. The shape may be a plate as shown in FIG. 3 or a circular tube as disclosed in Patent Document 3. In the case of a circular tube, a high-temperature superconducting conductor is arranged on the surface of the circular tube. In addition, it is more workable to provide the support member 3 with a groove 4 in which the high-temperature superconducting conductor 2 is accommodated so that the conductor does not move during connection work.

  The conductive resin material 6 is made by mixing particles (filler) such as silver having an average diameter of about 10 μm with an epoxy resin, and is in a paste form at room temperature. Curing and bonding are performed by heating the object to be bonded under certain conditions in an electric furnace or the like. As the conductive resin material 6, a commercially available product can be used. In addition to the above conductive paste, various types using resins and conductive fillers different from those described above are commercially available, and some have thermal conductivity and mechanical strength equivalent to solder. However, from the viewpoint of electrical characteristics, thermal characteristics, and workability, a combination of the above silver particles and an epoxy resin is preferable.

Next, a method for manufacturing the current lead will be described. A predetermined amount of the above-mentioned conductive resin material is applied to the bottom of the groove 4 of the support member 3, and extends uniformly in the longitudinal direction. In some cases, it is also applied to the high-temperature superconducting conductor 2 side. The high temperature superconducting conductor 2 is fitted into the groove 4 of the support member, and light pressure is applied so that the high temperature superconducting conductor 2 does not float. It is desirable to hold down with uniform pressure using a jig.

  Next, in order to cure the conductive resin material, it is heated in an electric furnace. Since the glass transition temperature of the epoxy resin is low and is around 50 ° C. to 60 ° C., the temperature may be higher than that, and the heating time can be shortened by increasing the temperature. For example, heating is performed for about 1 hour at 100 ° C and for about 3 hours at 80 ° C.

  According to the above embodiment, the workability of the connection between the high-temperature superconducting conductor of the superconducting current lead and the support member is improved, and by adjusting the coating amount of the conductive resin material, there is little variation and stable characteristics. A superconducting current lead that suppresses an increase in the amount of heat penetration of the current lead can be provided.

  Next, a configuration of a superconducting current lead including a high-temperature superconducting conductor having two electrodes joined by solder and a manufacturing method thereof will be described.

  FIG. 1 is a diagram schematically showing the configuration of a superconducting current lead having two electrodes, and FIG. 2 is a schematic diagram conceptually illustrating the procedure of the method for manufacturing the superconducting current lead of FIG. According to FIG. 1, the three high-temperature superconducting conductors 2 are each composed of a plurality of superconducting wires 1 as shown in FIG. 3 schematically showing the AA cross section in FIG. The high temperature superconductor 2 and the support member 3 are connected by a conductive resin not shown in FIG. 1, and the high temperature superconductor 2 and the electrode 11 are not shown. Connected with solder. Depending on the use conditions, the high-temperature superconducting conductor may be composed of a single superconducting wire.

  FIGS. 2A and 2B show the procedure of the method of manufacturing such a superconducting current lead. First, as shown to Fig.2 (a), the conductive resin material 6 is apply | coated between the high temperature superconducting conductor 2 and the supporting member 3, and it heat-hardens in this state. When kept at the curing temperature for a certain time, the high-temperature superconducting conductor 2 and the support member 3 are bonded together by a conductive resin. When the temperature is returned from this state to room temperature, stress is applied to the high-temperature superconducting conductor 2 due to the difference in thermal shrinkage rate. Therefore, it is important to match the heat shrinkage rates of the high-temperature superconducting conductor 2 and the support member 3 as much as possible, but it is very difficult to match them. On the other hand, since the electrode 11 and the high-temperature superconducting conductor 2 are not connected at this stage, they are irrelevant to the heat shrinkage during heat curing.

  FIG. 2B shows the next manufacturing procedure. Solder 12 is melted between the electrode 11 and the high-temperature superconducting conductor 2. At this time, the conductive resin material 6 is cured by cooling at least the cooling portion 13 in the vicinity of the electrode in the vicinity of the joint portion of the support member 3 and the high-temperature superconducting conductor 2 with the conductive resin. Can be held. For cooling, for example, by bringing a cooling body (not shown) cooled by a coolant such as water into contact with the cooling unit 13, the cooling unit 13 can be brought to a desired temperature or lower.

  As described above, the high-temperature superconducting conductor 2, the support member 3, and the electrode 11 can be connected by the conductive resin material 6 and the solder 11 having different melting points, and the superconducting current lead according to the present invention can be manufactured easily and safely. .

The typical block diagram which concerns on embodiment of a superconducting electric current lead provided with two electrodes of this invention. FIG. 2 is a schematic diagram conceptually illustrating a procedure of a method for manufacturing the superconducting current lead of FIG. 1. FIG. 3 is a cross-sectional view of a main part showing a schematic configuration of the superconducting current lead according to the embodiment of the present invention. The principal part sectional drawing which shows the structural example of the conventional superconducting electric current lead. The figure which shows an example of the typical structure of the superconducting apparatus provided with the high temperature superconducting current | flow lead which employ | adopted the conduction cooling system.

1: High-temperature superconducting wire, 2: High-temperature superconducting conductor, 3: Support member, 4: Groove, 6: Conductive resin material, 11: Electrode, 12: Solder, 13: Cooling unit, 21: Superconducting device, 22: Cryogenic temperature Container, 23: current lead, 24: power supply, 25: refrigerator, 26: copper conductor part, 27: high-temperature superconducting conductor part, 28: cooling conductor.

Claims (3)

High-temperature superconducting conductors that use high-temperature superconducting wires made of oxide superconducting material at least partially on the low-temperature side to supply power from a power source installed in a room-temperature environment to a superconducting device installed in a cryogenic container with a part,
The high-temperature superconducting conductor portion is composed of a supporting member made of a low thermal conductive metal material having a thermal conductivity smaller than that of copper, and a plurality of high-temperature superconducting conductors electrically distributed in parallel on the supporting member. The supporting member and the high-temperature superconducting conductor are bonded by a conductive resin material , and the high-temperature superconducting conductor is a method of manufacturing a superconducting current lead having at least two electrodes joined by soldering, as described below. A method of manufacturing a superconducting current lead comprising the steps of:
(A) The process of apply | coating the said conductive resin material between the said high temperature superconducting conductor and the said supporting member, heat-hardening, and adhere | attaching.
(B) The process of cooling the adhesion part between the said high-temperature superconducting conductor and the said supporting member to temperature lower than the heat-hardening temperature of the said conductive resin material.
(C) A step of joining the high-temperature superconducting conductor and the electrode with solder during the cooling. 2. The method of manufacturing a superconducting current lead according to claim 1, wherein the support member is made of a plate-like member, and the high-temperature superconducting conductor is in a plurality of grooves provided in a longitudinal direction of one main surface of the plate-like support member. A method of manufacturing a superconducting current lead, wherein the supporting member and the high-temperature superconducting conductor are bonded to each other by a conductive resin material on a bottom surface of the groove. The method of manufacturing a superconducting current lead according to claim 1 or 2, wherein the conductive resin material, characterized by a conductive resin paste made by mixing a silver particle in the epoxy resin as the conductive filler superconducting Current lead manufacturing method .

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