JPS6025844B2 - Composite superconducting conductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite superconducting conductor used in superconducting power transmission cables, various superconducting magnets, and the like.

A composite superconducting conductor consists of a superconducting material and a normal conducting material. For example, a superconducting wire with a diameter of 54 m to 250 m is placed in a normal conducting material such as copper, aluminum, other metals, or alloys of these metals. They are embedded into round wires, flat wires, and hollow wires.

Figure 1 is a cross-sectional view showing an example of a conventional composite superconducting conductor.
A large number of superconducting wires 1 are embedded in a normal conductive material 2 such as copper or aluminum and finished as a rectangular wire.

An insulator 3 is placed on the farthest side of the rectangular cross section, and is wound on the long side surface with the insulator 3 interposed therebetween to form a coil. Since the wire exhibits superconductivity, it does not generate heat under a constant magnetic field and constant current, but it generates loss due to magnetization when the current changes over time. Furthermore, if the superconductivity is broken for some reason, a large amount of Joule heat will be generated. For this reason, a part of the composite superconducting conductor, for example, the short side 4 of the rectangular cross section, is directly acidified with liquid helium and cooled. The conditions for preventing the expansion of the normal conductivity region with Joule heat generation when superconductivity is broken are given by the following equation.

Mackerel<1. ．．・．． ．．・．． ．．・'1) Here, 0: Electrical specific resistance of the normal conductor, 1 is the current flowing, P
: Cooling perimeter, A: Cross-sectional area of superconducting material, q: Cooling heat flow east,
It is.

When the current value and cooling conditions are given, the cooling peripheral length P and the cross-sectional mirror A of the normal conductor must be increased in order to satisfy the equation {1'.

That is, a large amount of normal conductive material must be used, which is a major factor in increasing costs, such as increasing the size and weight of the device. As one countermeasure against this problem, a method is known in which, for example, a rectangular groove with a depth of one line and a pitch of one side is provided on the surface of the composite superconducting conductor on the pitch two side (Mochiko No. 45-22388).

Although this method is expected to have the effect of increasing the above-mentioned cooling peripheral length P by about twice, it cannot be said that it is completely satisfactory, and there are also problems with the method of forming the grooves. Like superconducting magnets,
When fitted into narrow cooling channels, such cooling surfaces necessarily provide a cooling amount proportional to the increase in surface area (P x q)
This does not necessarily mean that you will be able to get the best results, and it will be lower. The present invention has been made to solve the above-mentioned problems, and includes a plurality of closely spaced grooves having acute angles at the bottom and separated by these grooves in the skin zone of the cooling surface of a composite superconducting conductor. , a large number of protuberances each having an acutely tapered tip are provided to increase the amount of cooling. An embodiment of the present invention will be described below with reference to FIG.

FIG. 2 shows a case where a cooling surface is formed on the shorter side of the rectangular cross section of a composite superconducting conductor finished into a rectangular wire, and an insulator 3 is stretched on the outermost side.

In the skin band of the cooling surface of the normal conductive material 2 such as copper or aluminum surrounding a large number of superconducting wires 1, there are a large number of parallel grooves 5 that are close to each other and a large number of continuous grooves separated by the grooves 5. Parallel raised portions 6 are formed. The first grooves 5 are formed by cutting which deforms the epidermal zone so as to plow it up without cutting it, so that fine and deep grooves are brought close to each other. Thereby, the first groove 5 has an acute angle part at the bottom,
Also, a number of parallel ridges 6 separated by the first groove 5
The tip is tapered to an acute angle. The size of this first groove 5 is, for example, 0.2 ribs in the center, 0.8 in depth, and 0.4 pitch in pitch. Therefore, the size of the raised portion 6 is also medium 0.
．． 2 side, height 0.8 side. In such a configuration, the surface area is three times that of the unprocessed surface. FIG. 3 is an enlarged view of the skin zone of the cooling surface showing another embodiment of the composite superconducting conductor of the present invention.

In FIG. 3, a plurality of raised portions 6 separated by a plurality of first grooves 5 in FIG. A large number of valleys 7 are formed. To obtain such a surface, first, a large number of relatively shallow second grooves 8 having an interval of 4 mm are formed at a constant pitch by knurling, for example, on the surface of the normal conducting material 2 of the composite superconducting conductor. Next, cutting is performed to deform the normally conductive material 2 in a direction that intersects the second groove 8 in a plowing manner without cutting it, so that a first groove 8 which is deeper than the relatively shallow second groove 8 is formed. The grooves 5 of the grooves 5 are brought close to each other. As a result, the skin band of the cooling surface of the normal conductive material 2 has a large number of parallel first grooves 5 having an acute angle at the bottom and are separated by the first grooves 5. A raised part having small valleys 7 at V-shaped intervals, tapered at an acute angle, and having a depth from the tip shallower than the depth of the first groove 5 and an acutely inclined bottom part. 6 is formed. For example, the first
0.2 side of groove 5, depth 0.8 sail, pitch 0.4 sail,
In the case of the pitch 0.6 side of the valley 7 and the depth 0.4 ribs, the surface area reaches 3.5 tones of the unprocessed surface. The effects obtained in this manner will be explained with reference to FIG.

In Fig. 4, in order to express the cooling performance, the horizontal axis shows the temperature Tw of the conductor surface and the temperature Tb (
4.2 K), and the vertical axis is the heat flow east q (the value obtained by dividing the heat flow Q by the surface area A) transferred from the conductor surface to the liquid helium. Here, the projected area (ie, the surface area of the unprocessed surface) is taken as A. The size of the cooling channel is approximately 2.3 skins in gap, approximately 50 skins in length, and 10 skins in length.
It is a rib, and Tw is an average value in the length direction. curve a
curve b is the characteristic of the surface of conventional polished copper, and curve b is the characteristic of the surface of the example shown in FIG. As the heat flow east q increases, heat transfer begins by nucleate boiling, and a certain heat flux q
Transition to pus boiling at max. Here, if q is lowered, qm
In, it returns to nucleate boiling again. Since experiments cannot be performed between qmax and qmin, the values are estimated. If the temperature of a superconducting conductor rises for some reason and transitions to the film boiling region, once the cause disappears, it will return to the nucleate boiling region and restore the superconducting properties, so it is desirable that qmax and qmin be as high as possible, especially The influence of qmin is large.

qmax of curve b does not increase much compared to qmax of curve a. This shows that with a fine surface structure as shown in the example, an increase in qmax corresponding to an increase in surface area cannot necessarily be obtained in a narrow space. on the other hand,
The qmin of the curve b is more than four times as large as the curve qmin, and there is an increase in the heat flow east by more than an amount proportional to the increase in the surface area. It is thought that the fine surface structure shown in this example impedes the stability of film boiling. It is thought that the acute angles of the ridges have a particularly positive effect. As described above, according to the invention, a large number of grooves each having an acute bottom are provided in the epidermal zone of the cooling surface, and a large number of protrusions separated by the grooves and tapered at an acute angle can prevent pus boils. The critical heat flow east qmjn can be made extremely large, and the cooling amount P×q used in the stabilization design of the composite superconducting wire can be made large. Therefore, it is possible to reduce the cross-sectional area of the normal conductor, increase the effective flow density, and greatly contribute to reducing the cost of the entire system by downsizing the superconducting magnet, reducing the amount of superconducting wire used, and reducing the refrigeration capacity. There is an effect.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a conventional composite superconducting conductor, FIG. 2 is a diagram illustrating an embodiment of the composite superconducting conductor of the present invention, and FIG. 3 is another embodiment of the composite superconducting conductor of the present invention. FIG. 4 is a characteristic diagram comparing the conventional composite superconducting conductor and the embodiment shown in FIG. 3 of the present invention. 1...Superconducting wire, 2...Normal conductive material,
3... Insulator, 5... First groove, 6...
Ridge, 7... Valley. Chrysanthemum Figure 2 Figure 3 Tsutomu Figure 4

Claims (1)

[Claims] 1. A large number of continuous first grooves provided with small gaps in a part or all of the surface of a composite superconducting conductor made of a superconducting material and a normal conducting material, and the first grooves. a plurality of ridges separated by a tapered tip and having a plurality of valleys having a depth from the tip shallower than the first groove and extending in a direction intersecting the first groove; A composite superconducting conductor characterized by being provided with. 2. The composite superconducting conductor according to claim 1, wherein the first groove has an acute angle at the bottom, and the valley is V-shaped.