JP5552805B2 - Oxide superconducting wire connection method - Google Patents

Description

  The present invention relates to a method for connecting an oxide superconducting wire applied to a coil of a superconducting device such as a superconducting transformer, a superconducting reactor, a superconducting current limiter, a superconducting motive motor, and a superconducting generator.

  As a superconducting wire, recently, a high-temperature superconductor that maintains a superconducting state even at a temperature of 77 K, which is the evaporation temperature of liquid nitrogen, has been put into practical use. A high temperature superconducting wire that has been rolled and formed into a tape shape is generally used.

  By the way, the superconducting equipment mentioned above is a superconducting wire that connects the superconducting wires at the middle part of the coil conductor wound around the winding frame, or is drawn in the axial direction toward the superconducting wire and the electrode at the coil end. For example, it is necessary to connect the superconducting wires. As a connection method between such superconducting wires, a connection method by soldering has been generally employed.

  In this connection method by soldering, the end portions of the superconducting wire are overlapped to a length of, for example, 30 mm to 50 mm, and the overlapping surfaces are soldered in this state. In this case, since the entire surface of the bismuth-based high-temperature superconducting wire is covered with a sheath material such as silver or a silver alloy as a base material, the sheath materials are overlapped regardless of the direction of the wire. By soldering, superconducting wires can be connected relatively easily.

  On the other hand, yttrium-based high-temperature oxide superconductors have recently attracted attention as next-generation superconducting wires from the viewpoint of increasing current capacity and reducing manufacturing costs. This yttrium-based oxide superconductor is formed by depositing an intermediate layer of insulating material on one side of a highly rigid metal tape (base material) such as stainless steel or hastelloy, and then depositing an yttrium-based oxide superconductor on this intermediate layer. Then, a high temperature superconducting wire is manufactured by coating silver on the superconducting layer as a quench protection stabilizing material. In addition, a silver layer deposited on an yttrium-based oxide superconducting layer is used as a seed layer, and a metal tape such as copper, which is cheaper than silver as a stabilizing metal, is solder-bonded onto the silver layer (the metal tape is subjected to solder plating). In addition, a superconducting wire having a structure in which a stabilizing material is combined by laminating with a conductive adhesive by heating and superposing on a silver layer has also been developed (see, for example, Patent Document 1).

  A schematic structure of the yttrium-based oxide superconducting wire is shown in FIG. In FIG. 5, 1 is a tape-shaped metal substrate that becomes a highly rigid metal material such as stainless steel or Hastelloy, 2 is an intermediate layer of an insulator deposited on one side of the metal substrate 1, and 3 is deposited on the intermediate layer 2. The yttrium-based superconducting layer 4 is a silver layer deposited on the superconducting layer 3, 5 is a tape-shaped stabilizing metal laminated on the silver layer 4, and the silver layer 4 and the stabilizing metal 5 are combined. The stabilizing layer is formed.

  As described above, the yttrium-based oxide superconducting wire is different from the bismuth-based high-temperature superconducting wire in which the entire surface of the wire is covered with a sheath material of silver or a silver alloy, and one side of the wire is interposed through an intermediate layer. In order to connect the superconducting wires to each other, a connection method corresponding to the wire structure is required. In this regard, various proposals have conventionally been made as connecting methods of oxide superconducting wires, and as a representative example, after superposing the stabilizing metal of the connecting superconducting wires facing each other (Face-to-Face), A connection method for soldering the overlapping surfaces is known (see, for example, Patent Document 2).

  On the other hand, since the power system in recent years has become larger and more complex with increasing power demand, it is expected that the fault current flowing in the system will also increase when a short circuit accident occurs in the power system. Therefore, as a current-limiting means to suppress the fault current that flows in the event of a short circuit in the power system so as not to exceed the breaking capacity of the circuit breaker connected to the system, the S / N transition of the yttrium-based oxide superconductor has recently been introduced. The superconducting fault current limiter is designed to limit the fault current by using, and its product development is underway.

  As the operation principle of this superconducting fault current limiter is well known, the current flows through the superconducting material in normal times, and an excessive fault current flows due to a sudden short circuit accident of the power system, etc., and the superconducting material becomes normal conducting state. At the time of transition, the current is bypassed to the stabilizing metal to limit the overcurrent. In this superconducting fault current limiter, CuNi, CuZn, or stainless steel is used as the stabilizing metal 5 of the superconducting wire shown in FIG. 5 in order to increase the impedance when overcurrent is bypassed from the superconducting material to the stabilizing metal. A relatively high resistance metal material is used.

  Also, development of a superconducting transformer with a current limiting function in which the operating principle of the superconducting current limiting device is applied to a superconducting transformer is underway.

Special Table 2007-524198 (FIG. 1, P8-9) JP 2000-133067 A

  By the way, as to the yttrium-based oxide superconducting wire (see FIG. 5) applied to a coil conductor such as a superconducting current limiting device or a superconducting transformer with a current limiting function, a coil wound around a winding frame as described above. Conventionally, when superconducting wires are connected to each other between the superconducting wires drawn in the axial direction toward the electrode at the middle of the conductor or at the coil end, the stabilizing metal of the superconducting wire is overlapped and soldered. If the above connection method (Patent Document 2) is employed as it is, the following problems occur in the conductivity of the current flowing through the connecting portion.

  That is, FIG. 6 and FIG. 7 respectively show the ends of the yttrium-based oxide superconducting wires A and B shown in FIG. 5 in the direction parallel to and perpendicular to the longitudinal direction, and the overlapping surfaces are soldered. It is the schematic diagram of the connection part by the joined connection method, (a) of each figure before connecting the superconducting wire A and B, (b) represents the superconducting conduction state of the connection part after a connection. In addition, in each figure, the same code | symbol is attached | subjected to the same member as FIG.

  6B and 7B, the current flowing from the superconducting wire B on the right side to the superconducting wire A on the left side through the connecting portion is represented by the superconducting layer 3. → Silver layer 4 → stabilized metal 5 → solder layer 6 → stabilized metal 5 → silver layer 4 → flows along the path of superconducting layer 3. Therefore, the current flowing through the connection portion of the superconducting wire passes through the stabilizing metal 4 and the silver layer 3 twice regardless of the state of superconductivity or normal conduction.

  In this case, as a superconducting wire used for a superconducting fault current limiter, etc., as described above, if the stabilizing metal 5 uses a relatively high resistance metal material such as CuNi, CuZn, or stainless steel, the connection of the superconducting wire The Joule heat generated in the part is large, and especially when an overcurrent flows, the heat generation becomes large. For this reason, in the connection method, the resistance loss of the superconducting wire connection portion increases, and in the worst case, there is a risk that the wire rod may be burned by Joule heat generation.

  The present invention has been made in view of the above points, and its object is to eliminate the above-mentioned problems and reduce the resistance loss of the connecting portion, and to skillfully suppress problems such as wire burnout due to excessive heat generation. It is another object of the present invention to provide an oxide superconducting wire connection method improved so as to improve reliability.

To achieve the above object, according to the inventions, CuNi and CuZn stabilization metal or the oxide method for connecting superconducting wire employing a metal material having a relatively high resistance such as stainless steel, firstly, its on the selective removal of the stabilizing metal in the connecting portion, thereby Mukaiawa another silver layer surface exposed to the connection portion.

Then, between the silver layer surface facing, gold or gold alloy, silver or a silver alloy, copper or a copper alloy, on which is interposed a highly conductive metal piece, such as aluminum or aluminum alloy, superconducting wire connecting portion superposition, to connect between the silver layer surface of the highly conductive metal piece and the superconducting wire in this state by soldering.

  According to the connection method of the present invention described above, the current flowing through the connection portion of the superconducting wire can be passed without passing through the stabilizing metal of the high resistance metal material, thereby causing local heat generation at the connection portion. A low loss and highly reliable connection can be achieved by suppressing.

Further, in the connection portion between the superconducting wire, by interposing a highly conductive metal piece after eliminating the high-resistance-stabilized metal and to be soldered between the highly conductive metal piece and silver layer this According to the connection method of the invention, the highly conductive metal piece becomes a buffer without increasing the connection resistance, and the heat capacity of the connection portion is increased. Thereby, even when an overcurrent flows through the superconducting wire transiently for a short time, an excessive temperature rise of the connecting portion is suppressed by the buffer effect of the highly conductive metal piece, and a highly reliable connection can be achieved.

It is the schematic diagram of the connection part which shows the reference example of this invention which connected oxide superconducting wires in parallel along the longitudinal direction, (a) is an exploded perspective view, (b) is the connection state represented with the current path. It is a side view. It is a schematic view of a connection part showing a different reference examples and Figure 1 connected in a direction orthogonal to oxides superconducting wire together, (a) shows the exploded perspective view, (b) is the side of the connection state representing together the current path FIG. Is a schematic view of a connection portion showing an embodiment in which a more oxide superconducting wire together and connected in parallel along the longitudinal direction of the inventions, (a) shows the exploded perspective view, (b) is connected, it expressed with the current path It is a side view of a state. Is a schematic view of a connection portion of an embodiment connected in a direction orthogonal more oxide superconducting wire together to this inventions, (a) shows the exploded perspective view, (b) is the side of the connection state representing together the current path FIG. It is a schematic structure diagram of an yttrium oxide superconducting wire. It is the conventional structural diagram of the connection part which connected the oxide superconducting wires in parallel along the longitudinal direction, (a) is a disassembled perspective view, (b) is a side view of the connection state represented with the current path. It is the conventional structural diagram of the connection part which connected the oxide superconducting wires in the orthogonal direction, (a) is a disassembled perspective view, (b) is a side view of the connection state represented with the current path.

Hereinafter, Reference Examples showing an embodiment of the present invention in FIGS. 1 and 2, and will be described with reference to the embodiments shown in FIG. 3 and Figure 4. In the drawings of the reference example and the embodiment, the members corresponding to those in FIGS.
(Reference Example 1)

First, as a first reference example of the present invention, a structure of a connecting portion in which yttrium-based oxide superconducting wires are connected in parallel in the longitudinal direction, and a connecting method will be described with reference to FIGS. To do.

In this reference example , as a pretreatment step when connecting the superconducting wires A and B, the stabilizing metal 5 is selectively removed in accordance with the width W of the connecting portion of the superconducting wires A and B. In this processing step, when the stabilizing metal 5 is soldered to the silver layer 4, for example, after making a cut in the surface of the stabilizing metal 5 in accordance with the width W, the connecting portion of the superconducting wire is formed. The tape-shaped stabilizing metal 5 is partially peeled off from the end and cut while being heated to the solder melting temperature by a torch or the like. As a result, the silver layer 4 with the solder layer remaining is exposed at the connection portion.

  Next, as shown in (a), the superconducting wires A and B of the silver layer 4 are superposed face to face and soldered together. Depending on the situation, a solder sheet may be interposed between the joint surfaces of the superconducting wires A and B, or cream solder may be applied. As a result, the superconducting wires A and B are connected as shown in FIG.

Then, when the superconducting wires A and B are energized (steady state) after the connection, the current path follows the superconducting layer 3 → the silver layer 4 → the solder bonding layer 6 → the silver layer 4 → the superconducting layer 3 as indicated by the arrows in the figure. A current will flow through the connection along. Therefore, no current flows through the stabilizing metal 5 as in the conventional connection method shown in FIG. As a result, even if the stabilizing metal 5 is a relatively high resistance metal material such as CuNi, CuZn, or stainless steel as in the superconducting fault current limiter described above, an increase in resistance loss at the connecting portion, local Joule A highly reliable low resistance connection can be achieved by preventing the wire from burning due to heat generation.
(Reference Example 2)

FIGS. 2A and 2B are modifications of the first reference example, and the superconducting layers A and B are connected in directions orthogonal to each other. In this reference example 2 as well, in the same manner as in reference example 1, the stabilizing metal 5 of the superconducting wires A and B is selectively removed in accordance with the width W of the connecting portion, and then the space between the silver layers 4 stacked face to face is removed. The superconducting wires A and B are connected by soldering. Thereby, an effect equivalent to that of Reference Example 1 can be achieved.
Example 1

Then, as the actual施例of the present invention, FIG structure of the connecting portion of connecting the oxide superconducting lines of the Y-based in the same manner as in Reference Example 1 of Sakiki in parallel in the longitudinal direction, and the connection 3 (a ) And (b).

In this embodiment, the selective removal of the stabilizing metal 5 of the superconducting wires A and B in accordance with the width W of the connecting portion is the same as in Reference Example 1, but the silver layer 4 facing each other face to face. In between, a highly conductive metal piece 7 such as gold or gold alloy, silver or silver alloy, copper or copper alloy, aluminum or aluminum alloy is interposed, and the silver layer 4 of the superconducting wires A and B is electrically conductive. The metal pieces 7 are superposed on each other and soldered together.

  In this connection method, the highly conductive metal piece 7 is interposed in the current path between the superconducting wires A and B. This highly conductive metal piece 7 is a stabilizing metal (high resistance metal material) of the superconducting wire. ) Since the resistance is lower than that of 5, there is almost no increase in resistance loss at the connection portion.

Moreover, due to the interposition of the highly conductive metal piece 7, the metal piece 7 serves as a thermal buffer material and the heat capacity of the connecting portion increases. As a result, even when an overcurrent exceeding the critical current of the superconducting material (a fault current in the power system) flows transiently for a short time during energization, Joule heat generation at the connection is absorbed by the highly conductive metal piece 7, Due to the buffer effect, it is possible to prevent an excessive increase in temperature of the connecting portion and prevent burnout, thereby ensuring higher reliability.
(Example 2)

Figure 4 (a), (b) is a modification of the first embodiment, superconducting layer A and B are connected in a direction perpendicular to each other. Also in this Example 2 , after the selective removal of the stabilizing metal 5 of the superconducting wires A and B in accordance with the width W of the connecting portion as in Example 1 , good conductivity between the stacked silver layers 4 is achieved. The superconducting wires A and B are connected by soldering with the conductive metal piece 7 interposed therebetween. Thereby, an effect equivalent to Example 1 can be produced.

1: Metal substrate 2: Intermediate layer 3: Superconducting layer 4: Silver layer 5: Stabilized metal 6: Solder joint layer 7: Highly conductive metal piece A, B: Oxide superconducting wire

Claims (1)

  In a method for connecting an oxide superconducting wire that employs a metal material having a relatively high resistance as a stabilizing metal, the stabilizing metal at the connecting portion is selectively removed, and a good portion is provided between the silver layers exposed at the connecting portion. An oxide characterized in that, after interposing a conductive metal piece, superconducting wire connection portions are overlapped, and in this state, the good conductive metal piece and a silver layer of each superconducting wire are solder-joined. Superconducting wire connection method.

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