JPH04314311A - Superconductive current lead - Google Patents

Abstract

PURPOSE:To obtain high capacity ratio of a current lead which consists of a superconductor by inserting the superconductor with variable inductance in series between the terminal on the low-temperature side and the connection part of it. CONSTITUTION:Superconductor inductors 22c, 23c and 24c are inserted in series, whose inductances can be set at will, between the electrodes 22b, 23b and 24b of superconductors 22, 23 and 24 and the terminal of low temperature side 21b. In short, as for the superconductive current lead, when internal resistance and inductance of superconductors 22, 23 and 24 and an inter-metal bond resistance are thought to be zero, the equivalent circuit means a series circuit of junction resistance R22a, R23a and R24a between each superconductive bulk and the normal side electrodes 22a, 23a and 24a, junction resistances R22a, R23b, R24b of the electrodes 22b, 23b and 24b on the low temperature side and superconductive inductor reactances X22, X23 and X24.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting current lead that can optimize the splitting ratio of each superconductor.

0002

2. Description of the Related Art A conventional superconducting current lead is shown in FIG. In Figure 6, the room temperature region and liquid helium temperature (4.2K
) A liquid nitrogen (77K) temperature region is provided between the
For example, the 77K and 4.2K regions are connected by an oxide superconductor 11b which becomes superconducting at a temperature higher than the liquid nitrogen temperature. Since this superconductor 11b is an oxide, its thermal conductivity is low, and compared to a metal current lead, the amount of conductive heat intrusion in the 77K to 4.2K region can be significantly reduced. Furthermore, since it is a superconductor, there is no conductor resistance, so it has the advantage of not causing joule loss due to current flow, unlike conventional metal current leads. Therefore, by applying oxide high-temperature superconductors to current leads for superconducting equipment, especially those using liquid helium, it is possible to suppress the amount of heat intrusion into the 4.2K region, thereby making cooling auxiliary equipment such as refrigerators more compact and saving power. It is possible to aim for

There are two major problems when putting such oxide superconducting current leads into practical use. First, if a superconductor is covered with a metal sheath such as silver, the insulation properties of the lead will be impaired in that area, so this type of current lead must basically be made of a bulk oxide material. Second, when trying to obtain a large current lead of several kA class or higher, increase the diameter to reach the target critical current value (hereinafter referred to as IC value).
Rather than achieving this, it is easier and more advantageous to construct a plurality of relatively small diameter bulks in parallel from the viewpoint of technology, performance, and reliability. In other words, in order to obtain a bulk with a large diameter, large-scale equipment is required, and at the same time, the larger the diameter of the bulk, the more difficult it is to obtain a homogeneous superconductor throughout, so the critical current value per unit cross-sectional area (
It becomes technically difficult to maintain the critical current density JC (hereinafter referred to as critical current density JC). This means that in order to obtain a constant IC value,
This means that a current lead with a larger cross-sectional area is required, and due to the increased cross-sectional area, the thermal resistance between 77K and 4.2K decreases, and the insulation performance also decreases. Therefore, taking these circumstances into consideration, a practical configuration of a large-capacity superconducting current lead is as shown in FIG. 7, for example. That is, by using a plurality of oxide superconductors (in this example, three oxide superconductors 22, 23, and 24) with relatively small diameters as shown in FIG. 8, the normal temperature side (77K) terminal 21a and the low temperature side (4.2K)
The structure is such that the terminals 21b are connected.

0004

[Problems to be Solved by the Invention] The conventional technology and the desirable structure of a large-capacity current lead using the same have been explained above, but even in the case of a superconducting current lead with the structure shown in Fig. 7, the following Similar issues remain.

The first problem is the variation in junction resistance that occurs between both ends of the superconducting bulk and the terminals. As is well known, a common problem with bulk oxide superconductors is the difficulty of attaching electrodes. In other words, when electrically connecting a superconducting bulk and a terminal, as shown in FIG. A method is used in which the electrode portion and the terminals 21a, 21b are soldered or brazed. At this time,
Although the resistance value of the solder joint is negligibly small, the problem is the resistance generated between the electrode and the superconducting bulk. As an example, we evaluated the bulk-to-bulk and junction resistance values of several samples of electrodes in liquid nitrogen (77K) when a 10-mm length of silver was deposited on both end surfaces of a Bi-based superconducting bulk material with a diameter of 10 mm. 10-6 to 10-9
"Variation" was observed in the range of (Ω). The cause of this is
This is thought to be due to the quality of vapor deposition, and is classified as boundary resistance between the oxide superconductor and the vapor-deposited metal film. With the current technology, it is difficult to eliminate such "variations" in boundary resistance values at an extremely small level of the order of 10-9 (Ω). However, if the current lead shown in FIG. 7 is manufactured while allowing such variations in connection resistance values, the ratio of the currents flowing through each superconductor 22, 23, and 24 will be on the order of 102, which is substantially Current concentrates only on the superconductor with the lowest junction resistance value, and the effect of paralleling is lost.

The second problem is the variation in IC values of superconductors. This type of superconducting bulk has not yet been sufficiently theoretically elucidated, and even if it is formed into a certain shape and subjected to similar superconducting treatment, it is currently difficult to control the IC values to the same degree. In other words, even if the aforementioned junction resistance value becomes almost constant, if there is variation in the IC value of the superconducting bulk, the lowest I of the three superconductors 22, 23, 24
An unreasonable situation arises in that a current can actually only flow up to a current value three times the C value.

As described above, in conventional superconducting current leads in which multiple oxide superconductors are configured in parallel, variations in the junction resistance between the superconductors and the electrodes and in the IC value of the superconductors themselves make it difficult to configure them in parallel. However, it was not possible to efficiently increase capacity. SUMMARY OF THE INVENTION An object of the present invention is to provide a superconducting current lead that can increase the capacity of a current lead made of superconductors arranged in parallel. [Structure of the invention]

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention has a normal temperature side terminal and a low temperature side terminal, and between these terminals, one end is connected to the normal temperature side terminal and the other end is connected to the low temperature side terminal. In a superconducting current lead including a plurality of superconductors to which a superconductor is connected, a superconductor having a settable inductance is provided in series between a low-temperature side terminal connection part and a low-temperature side terminal.

[0009]

[Function] In such a configuration, even if the junction resistance value varies or the IC value of each superconductor differs, the inductance value of the superconductor provided in series between each low temperature side terminal connection part and the low temperature side terminal By adjusting , it becomes possible to increase the capacity by optimizing the shunting.

0010

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that description of parts similar to those in FIGS. 7 and 8 will be omitted. FIG. 1 is a configuration diagram of the superconducting current lead of the present invention,
FIG. 2 is a block diagram of each superconductor of the superconducting current lead of the present invention, and FIG. 3 is an equivalent circuit of the superconducting current lead of the present invention.

[0011] In the present invention, superconducting inductors 22c, 23c, 24c, whose inductances can be arbitrarily set, are provided in series between the electrodes 22b, 23b, 24b of the superconductors 22, 23, 24 and the low temperature side terminal 21b. It is characterized by Therefore, this superconducting current lead is connected to the superconductor 22.
, 23, 24 and the so-called intermetallic junction resistance between each electrode and terminal are assumed to be zero, and the equivalent circuit is as shown in FIG. , 24a junction resistance R22
a, R23a, R24a, and low temperature side electrodes 22b, 23b
, 24b portion junction resistance R22b, R23b, R24b,
and the reactance of the superconducting inductor X22, X23,
It is a series circuit of X24. The superconducting inductors 22c, 23c, and 24c are superconducting coils using metallic superconducting wires having arbitrary shapes and arbitrary inductance values, and are wound around metallic or highly thermally conductive ceramic coil bobbins 22d, 23d, and 24d, respectively. At the same time, one end of each superconductor electrode 22b, 23
b, 24b, and the other end is connected to the low temperature side terminal 21b by a method such as soldering. In addition, the superconducting inductors 22c, 23c, and 24c are wound at a predetermined pitch, and when setting the inductance value to a required value, it can be easily adjusted by short-circuiting the required number of turns with a superconducting wire. It has a structure like this.

FIG. 4 is an equivalent circuit showing an example of the finished characteristics of the present superconducting current lead. In this example, superconductor 2
2 and 23 electrode part boundary resistance R22a, R23a, R2
2b, R23b is 1 x 10-6 (Ω) per location,
The electrode portion boundary resistances R24a and R24b of the superconductor 24 are each 1×10-9 (Ω), and the I of the superconductors 22, 23, and 24 is
The C values are 1000A, 1000A and 1000A, respectively, to simplify the conditions.
Assume that they are 1000A and 1500A. In addition, superconducting inductors 22c and 23C, which are a feature of the present invention,
, 24c have an effective number of turns of 20 turns and an inductance of 0.5 (μH). Further, it is assumed that the inductances L22, L23, and L24 change in proportion to the square of the number N of coil turns. L22=L23=L24=k0 ・N2
(H) k0: Constant of proportionality = 0
．． 5 x 10-6/202 = 1.25 x 10-9

In this example, since the IC value of the superconductors 22 and 23 is 1/1.5 of the IC value of 24, the circuit impedances Z22 and Z23 of the superconductors 22 and 23 are equal to that of the superconductor 24. It is necessary to make it 1.5 times the circuit impedance Z24. By doing so, the quenching of each superconductor is synchronized and the current carrying capacity of the current lead is maximized.

Next, the setting values of the superconducting inductor will be explained. Based on the above-mentioned ratio of critical current values, the relationship between each circuit impedance Z22, Z23, and Z24 is expressed by the following equation. Z22=Z23=k1 ・Z24...(
1) Here, the required reactance of the superconducting inductor 24c is determined from equation (1). In equation (2), if the reactance to be inserted is minimized (X22=X23=0), the required inductance value L24 of the superconducting inductor 24c is
is ∴L24=X24/(2・π・f) =4.23×10−9(H) However, f=50Hz. Therefore, in this example, the required number of turns N24 of the superconducting inductor 24 is as follows.

In this embodiment, as described above, superconducting inductors L22, L23 are completely short-circuited, and only L24 is short-circuited with about 2 turns remaining, so that each superconductor 22, 23,
24 optimal diversions are performed.

FIG. 5 shows the current distribution and allowable current value of the conventional current lead and the current lead according to the present invention. In the prior art, when the superconductors 22, 23, and 24 are in a superconducting state, a maximum current of 1500 A flows through the superconductor 24. However, the other superconductors 22 and 23 each have 1.5A.
Only current flows. This current imbalance is due to the aforementioned variation in the electrode boundary resistance, and as a result, the total current as a current lead is 1503 A (conventional case 1).

Next, when the total current increases even slightly, the superconductivity of the superconductor 24 first disappears (hereinafter referred to as quench), and the superconductor 24 undergoes a phase transition to a high resistance material of several mΩ. As a result, the entire current is commutated to the other superconductors 22, 23 and divided almost equally. Since the superconductors 22 and 23 each have an IC value of 1000 A, the total current is 20
If it is within 00A, it can function as a current lead (conventional case 2). However, when the superconductor quenches, a large Joule loss occurs, causing various adverse effects, and therefore, in general, it is basic to follow the above-mentioned case 1.

On the other hand, the current leads are set so that the superconductors 22, 23, and 24 are quenched almost simultaneously by the action of the superconducting inductors 22c, 23c, and 24c. That is, superconductors 22, 23
, 24 are both in a superconducting state, when the current applied to the current leads is increased, the shunt current value of superconductors 22 and 23 reaches 1000A each, and the shunt current value of superconductor 24 reaches 1500A. The current leads maintain superconductivity. Therefore, in the proposed current lead, the total current value is 35
It can fulfill its function up to 00A (this invention).

The case where the IC values of the superconductors are different has been explained above, but even when the internal resistances of the superconductors 22, 23, and 24 are irregularly different, the superconducting inductor 22c can be adjusted based on the same concept. ,23c,2
4c may be set to predetermined values.

[0020]

[Effects of the Invention] As described above, the present invention provides a superconductor having a normal temperature side terminal and a low temperature side terminal, and between these terminals, one end is connected to the normal temperature side terminal and the other end is connected to the low temperature side terminal. In multiple superconducting current leads, a superconductor with a settable inductance is placed in series between the low-temperature side terminal connection part and the low-temperature side terminal, so the junction resistance value may vary and there may be problems between the normal temperature side and low temperature side terminals. Even if the IC values connected to the superconductors are different, it is possible to increase the capacity by adjusting the inductance value of the superconductors inserted in series and optimizing the shunting. Furthermore, even if the cross-sectional area is small, the I of each superconductor can be adjusted by adjusting the inductance value of the superconductor mentioned above.
Since the C value can be kept apparently constant, it can also be made compact.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a superconducting current lead of the present invention.

FIG. 2 is a configuration diagram of a superconductor of the superconducting current lead of the present invention.

FIG. 3 is an equivalent circuit of the superconducting current lead of the present invention.

FIG. 4 is an equivalent circuit showing an example of the superconducting current lead of the present invention.

FIG. 5 is a characteristic diagram of current carrying capacity of a superconducting current lead.

FIG. 6 is a configuration diagram of a superconducting device.

FIG. 7 is a configuration diagram of a conventional superconducting current lead.

FIG. 8 is a configuration diagram of a superconductor of a conventional superconducting current lead.

[Explanation of symbols]

21a...Normal temperature side terminal 21b...low temperature side terminal 22, 23, 24...superconductor

Claims (1)

[Claims] 1. A superconducting current lead having a normal temperature side terminal and a low temperature side terminal, and having a plurality of superconductors between these terminals, one end of which is connected to the normal temperature side terminal, and the other end of which is connected to the low temperature side terminal. A superconducting current lead according to claim 1, characterized in that a superconductor having a settable inductance is provided in series between the low temperature side terminal connection portion and the low temperature side terminal.