JPH0864330A - Superconducting wire connection method - Google Patents

Abstract

(57) [Summary] [Object] To provide a superconducting wire connecting method capable of equalizing the current flowing through each superconducting wire when a plurality of superconducting wires are connected in parallel with a normal conducting metal. [Structure] A method of connecting two superconducting wires 1a and 1b in parallel with a normal conducting metal 2, wherein the superconducting wires 3a and 3b are connected in series between the normal conducting metal 2 and the respective superconducting wires 1a and 1b. It is characterized by connecting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for connecting superconducting wires, and more particularly to a superconducting wire for a current lead, a superconducting cable, etc., in which superconducting wires need to be connected in parallel in order to pass a large current. Connection method.

[0002]

2. Description of the Related Art Generally, when a plurality of superconducting wires are connected in parallel to a normal conducting metal terminal such as copper, the superconducting wires are soldered directly to the metal terminals.

[0003]

When the superconducting wire is connected as described above, the resistance of the superconducting wire itself is 0.
The resistance of the parallel wires is dominated by the contact resistance of each connection and the resistance of the solder. However, the contact resistance and the solder resistance depend on the soldering conditions (contact area, solder thickness, etc.), and it is very difficult to make the resistances of all the connection portions the same. Although the connection resistance itself is small, the current flowing through each superconducting wire is shunted by the inverse ratio of these resistances. Therefore, the smaller the resistance of the connection portion, the greater the error of the connection resistance, which affects the shunt value. Hereinafter, detailed description will be given with reference to the drawings.

FIG. 12 is a diagram showing a state in which two superconducting wires are connected in parallel to a normal conducting metal by a conventional method for simplification.

Referring to FIG. 12, two superconducting wires 1a,
1b is directly soldered to the normal conducting metals 2a and 2b. R ₁ , R ₃ , R ₄ and R ₆ are the sum of contact resistance and solder resistance, respectively, and R ₂ and R ₅ are superconductor resistances.

As described above, since the resistance of the superconductor itself is 0, R ₂ = R ₅ = 0. An equivalent circuit at this time is shown in FIG.

In FIG. 13, superconducting wires 1a and 1b are provided.
The electric currents i ₁ and i ₂ flowing through can be expressed by the following equations, respectively.

I ₁ = {(R ₄ + R ₆ ) / (R ₁ + R ₃ + R ₄ + R ₆ )} I (1) i ₂ = {(R ₁ + R ₃ ) / (R ₁ + R ₃ + R ₄ + R ₆ )} I (2) where R ₁ , R ₃ , which is the sum of contact resistance and solder resistance,
R ₄ and R ₆ can be small enough,
Variation occurs depending on the soldering conditions.

For example, R ₁ = R ₃ = R ₄ = 1 μΩ, R
Assuming ₆ = 2 μΩ, i ₁ = (3/4) I, i ₂ =
(1/2) I, and i ₁ is 1.5 times i ₂ .

As described above, when a plurality of superconducting wires are connected in parallel to the normal conducting metal by the conventional method, there is a problem that the current flowing through each superconducting wire becomes uneven in magnitude. . Further, as a result, there is a problem that the magnetic field distribution is different from that when the current is shunted uniformly.

An object of the present invention is to solve the above problems and to connect a plurality of superconducting wires in parallel with a normal conducting metal.
An object of the present invention is to provide a method of connecting superconducting wires, which can make the current flowing through each superconducting wire uniform.

[0012]

A method of connecting a superconducting wire according to the invention of claim 1 is a method of connecting a plurality of superconducting wires in parallel with a normal conducting metal. In addition, the normal conducting wire is connected in series.

A superconducting wire connecting method according to a second aspect of the present invention is a method of connecting a plurality of superconducting wires in parallel with a normal conducting metal, wherein the normal conducting metal is branched into the same number of branches as the plurality of superconducting wires. It is characterized in that each branched branch is connected to each superconducting wire.

Preferably, the length of each branched branch of the normal-conducting metal is such that the resistance value of the branch portion is sufficiently larger than the resistance value of the connecting portion with the superconducting wire. It should be a feature.

[0015]

According to the invention of claim 1, when a plurality of superconducting wires are connected in parallel to the normal conducting metal, the superconducting wires are connected in series between the normal conducting metal and each superconducting wire.

According to the second aspect of the invention, each branch of the branched normal conductive metal and each superconducting wire are connected.

Therefore, the resistance of each parallel portion is the sum of the resistance of the connecting portion and the resistance of the normal conducting wire or the branch of the branched normal conducting metal. Here, the resistance of the connecting portion is sufficiently smaller than the resistance of the normal conducting wire or the branch of the branched normal conducting metal. As a result, the resistance value of each parallel wire is easily made uniform by making the resistance value of the normal conducting wire or the branch of the branched normal conducting metal uniform.

[0018]

FIG. 1 is a diagram showing an example of a state in which two superconducting wires are connected in parallel with a normal conducting metal according to the present invention.

Referring to FIG. 1, when two superconducting wires are connected in parallel with a normal conducting metal, the normal conducting metal 2 and each superconducting wire 1 are connected.
Normal conducting wires 3a and 3b are connected in series between a and 1b by soldering.

FIG. 2 is a diagram showing another example of a state in which two superconducting wires are connected in parallel to a normal conducting metal according to the present invention.

Referring to FIG. 2, the normal-conducting metal 2 is branched into two branches 4a and 4b, and the branched branches 4a and 4b are connected to the superconducting wires 1a and 1b by soldering.

An equivalent circuit of the connected state of the superconducting wire shown in FIG. 1 or 2 is shown in FIG. In FIG. 3, R ₁ and R ₄ represent connection resistance (contact resistance + solder resistance), and R
₂ and R ₅ represent normal conducting resistance (normal conducting resistance or normal conducting wire resistance of a branched branch), and R ₃ and R ₆ represent superconductor resistance.

At this time, the currents i ₁ and i ₂ flowing through the superconducting wires 1a and 1b can be expressed by the following equations, respectively.

I ₁ = {(R ₁ + R ₂ + R ₃ ) / (R ₁ + R ₂ + R ₃ + R ₄ + R ₅ + R ₆ )} I (3) i ₂ = {(R ₄ + R ₅ + R ₆ ) / ( R ₁ + R ₂ + R ₃ + R ₄ + R ₅ + R ₆ )} I (4) Here, the resistance of the superconductor itself is zero. Further, the connection resistances R ₁ and R ₄ (contact resistance + solder resistance) are sufficiently small in resistance value as compared with the normal conducting resistances R ₂ and R ₅ because the thickness of the solder with respect to the contact area is small. .

Therefore, R ₃ = R ₆ = 0, R ₁ <<
R ₂ , R ₄ << R ₅ , and the above equations (3) and (4) are
The following expressions (5) and (6) are obtained.

I ₁ ≈ {R ₅ / (R ₂ + R ₅ )} I (5) i ₂ ≈ {R ₂ / (R ₂ + R ₅ )} I (6) where R ₂ and R ₅ Since the value depends on the length of the superconducting wires 3a and 3b or the length of the branched branches 4a and 4b, R ₂ = R ₅ can be relatively easily set. As a result, it becomes possible to set i ₁ = i ₂ .

In particular, by increasing the respective lengths, it is possible to reduce the value of | R ₂ −R ₅ | for the respective resistance values R ₂ and R ₅ , and it is further preferable that i ₁ = i _2. It will be easy.

As shown in FIG. 2, the Joule loss due to branching of the normal-conducting metal is the same as that without branching. Hereinafter, description will be given with reference to the drawings.

FIG. 4 is a diagram for explaining the Joule loss of the normal conducting metal when it is not branched.

With reference to FIG. 4, the heat generation P can be expressed by the following equation from the resistance R = ρ (L / S).

P = I ² R = I ² × ρ (L / S) (7) On the other hand, FIG. 5 is a diagram for explaining Joule loss of the normal conducting metal when branched.

With reference to FIG. 5, the heat generation P'can be expressed by the following equation. P ′ = (I / 2) ² × ρ {L / (S / 2)} + (I / 2) ² × ρ {L / (S / 2)} = (1/2) × I ² × ρ ( L / S) + (1/2) × I ² × ρ (L / S) = I ² × ρ (L / S) (8) Therefore, from the results of the above equations (7) and (8), P =
From P ', it can be seen that even when the normal-conducting metal is branched according to the present invention, heat generation does not increase.

The present invention will be described below with reference to more specific examples. First, two superconducting wires are soldered in parallel to a copper plate, and each superconducting wire has a total of 40A (20A / piece).
Think of shedding. The contact area between each superconducting wire and the copper plate by soldering is 50 mm ^2, and the thickness of the solder is 0.1 mm to 0.2 mm. In addition, 7 of each material
The resistivity at 7K is as follows.

Copper: 2.0 × 10 ^-9 Ωm Solder: 3.0 × 10 ^-8 Ωm Superconductor: 0 (A) When there is no branch in the copper plate (normal conductive terminal) (conventional example) FIG. It is a figure which shows the state which connected two superconducting wires to the copper plate which does not have.

Referring to FIG. 6, two superconducting wires 1a and 1b are attached to a copper plate 2 having a cross-sectional area of 40 mm ² and a length of 200 mm.
Connected by solder 5.

An equivalent circuit at this time is shown in FIG. Figure 7
Where R₁And R₈Indicates the resistance of the copper plate (Cu)
Then R₂, R_Four, R _FiveAnd R₇Indicates solder resistance
Then R₃And R₆Indicates the resistance of the superconducting wire (SC).

Here, for example, the thickness of the solder corresponding to the portions of R ₂ , R ₄ and R ₅ is 0.1 mm, the thickness of the solder corresponding to the portion of R ₇ is 0.2 mm, and R = ρ
Considering (L / S), the current I ₁ flowing in each superconducting wire,
I ₂ is as follows.

I ₁ = {(R ₅ + R ₆ + R ₇ ) / (R ₂ +
R ₃ + R ₄ + R ₅ + R ₆ + R ₇ )} × 40A = 24A I ₂ = {(R ₂ + R ₃ + R ₄ ) / (R ₂ + R ₃ + R ₄ +
R ₅ + R ₆ + R ₇ )} × 40A = 16A (B) When the copper plate (normal conductive terminal) has a branch (invention example) FIG. 8 shows a state in which two superconducting wires are connected to a branched copper plate. FIG. Note that the right half is omitted because it is symmetrical.

With reference to FIG. 8, a copper plate 2 having a cross-sectional area of 40 mm ² and a length of 200 mm is composed of two branches 4 having a length of 190 mm.
a, 4b, each branch 4a, 4b and each superconducting wire 1
a and 1b are connected by a solder 5, respectively.

An equivalent circuit at this time is shown in FIG. Figure 9
In, R ₁ , R ₅ , R ₆ and R ₁₀ represent the resistance of each branch of the branched copper plate (Cu), R ₂ , R ₄ , R ₇ and R ₉ represent the resistance of solder, and R ₃ And R ₈ represents the resistance of the superconducting wire (SC).

If the thickness of the solder corresponding to the portions of R ₂ , R ₄ and R ₇ is 0.1 mm and the thickness of the solder corresponding to the portion of R ₉ is 0.2 mm, then each superconducting wire will have The flowing currents I ₁ and I ₂ are as follows.

I₁= {(R₆+ R₇+ R₉+ R_Ten) / (R₁+ R₂+ R_Four+ R_Five+ R₆+ R ₇ + R₉+ R_Ten)} × 40 A (9) I₂= {(R₁+ R₂+ R_Four+ R_Five) / (R₁+ R₂+ R_Four+ R_Five+ R₆+ R ₇ + R₉+ R_Ten)} × 40 A (10) Here, from R = ρ (L / S), R₁= R_Five= R₆= R_Ten= 1.9 × 10^-Five(Ω) R₂= R_Four= R₇= 6 x 10^-8Since it is (Ω), it is substituted into the above equations (9) and (10) to obtain I₁= I₂≈20.0A.

As is apparent from the results of the conventional example (A) and the present invention example (B), it is understood that branching the metal terminals makes the shunt current uniform.

FIG. 10 is a perspective view showing an example of application of the present invention to a superconducting current flow lead. With reference to FIG. 10, the current-carrying terminal 2 made of a normal-conducting metal is branched into two branches 4a and 4b, and the branched branches are connected to the respective superconducting wires 1a and 1b. The longer the branched branches 4a and 4b are, the more uniform the resistance of each branch section becomes, and the more uniform the shunt current becomes.

FIG. 11 is a perspective view showing an application example of the present invention to a superconducting cable. With reference to FIG. 11, the current-carrying terminal 2 made of a normal-conductive metal arranged around the winding core 6 has a branch structure branched into branches 4a, 4b, 4c, ..., Each branch 4a, 4b, 4c, ... and each superconducting wire 1a, 1b, 1
are connected to each other.

[0046]

As described above, according to the present invention, when a plurality of superconducting wires are connected in parallel with a normal conducting metal,
By including the normal conducting metal in the parallel portion, the resistance value of each parallel wire can be made uniform, and as a result, the current flowing through each superconducting wire can be made uniform.

Therefore, the present invention can be applied to a superconducting current lead, a superconducting cable and the like.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a method for connecting superconducting wires according to the present invention.

FIG. 2 is a perspective view showing another example of a method for connecting superconducting wires according to the present invention.

FIG. 3 is a diagram showing an equivalent circuit in the state shown in FIG. 1 or FIG.

FIG. 4 is a diagram for explaining Joule loss of normal-conducting metal when not branched.

FIG. 5 is a diagram for explaining Joule loss of normal conducting metal when branched.

FIG. 6 is a diagram showing a state in which two superconducting wires are connected to a copper plate without branching.

FIG. 7 is a diagram showing an equivalent circuit in the state shown in FIG.

FIG. 8 is a view showing a state in which two superconducting wires are connected to a branched copper plate.

9 is a diagram showing an equivalent circuit in the state shown in FIG.

FIG. 10 is a perspective view showing an application example of the present invention to a superconducting current lead.

FIG. 11 is a perspective view showing an application example of the present invention to a superconducting cable.

FIG. 12 is a view showing a state in which two superconducting wires are connected in parallel to a normal conducting metal by a conventional method.

13 is a diagram showing an equivalent circuit in the state shown in FIG.

[Explanation of symbols]

 1a, 1b, ..., 1e superconducting wire 2 normal conducting metal 3a, 3b superconducting wire 4a, 4b, ..., 4e branched branch of normal conducting metal 5 solder .

Claims (3)

[Claims] 1. A method of connecting a plurality of superconducting wires in parallel with a normal conducting metal, wherein a normal conducting wire is connected in series between the normal conducting metal and each of the superconducting wires. , Superconducting wire connection method. 2. A method of connecting a plurality of superconducting wires in parallel with a normal conducting metal, wherein the normal conducting metal is branched into the same number of branches as the plurality of superconducting wires, and the branched branches and the respective superconducting wires. A method of connecting a superconducting wire, characterized by connecting a wire. 3. The length of each branched branch of the normal-conducting metal is such that the resistance value of the branch portion is sufficiently larger than the resistance value of the connection portion with the superconducting wire. The method for connecting a superconducting wire according to claim 2, wherein: