JPH08287746A - Superconducting cable for ac - Google Patents

Abstract

PURPOSE: To provide a superconducting cable for AC which has little increase of an AC current loss in a heavy current area by making approximately uniform AC current flow in respective layers of tape-like superconducting wire material so that such a phenomenon as one part of the superconducting material having low inductance reaches a critical current value earlier so that the redistribution of current happens is not allowed to occur so as to be capable of suppressing the increase of the AC loss in the heavy current area. CONSTITUTION: In a superconducting cable for AC which is formed by winding a tape-like superconducting wire material 2 on a center member 1 into plural layers, a winding pitch of the tape-like superconducting wire material 2 is made to be as larger as it goes to outer layers so as to uniform the inductance of the respective layers of the tape-like superconducting wire material 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC superconducting cable.

[0002]

2. Description of the Related Art In recent years, high-temperature superconducting cables using Y-based, Bi-based, etc. oxide superconductors have been developed.
For the wires of a high-temperature superconducting cable, a tape-shaped superconducting wire is usually used in which a large number of oxide superconductors are embedded in a silver sheath to form a tape. To increase the flexibility of the superconducting cable, the tape-shaped superconducting wire is wrapped in multiple layers outside the elongated central member.

The winding pitch of the tape-shaped superconducting wire in this case is determined to be the minimum value based on the distortion characteristics of the tape-shaped superconducting wire. The winding pitch of each layer is selected in consideration of the performance of the winding machine, bending of the wire winding, etc., within a range not exceeding this minimum value.

[0004]

However, when the AC loss was measured by passing an AC current through the superconducting cable configured as described above, it was found that the measured value of the AC loss in the large current region was a calculated value (hysteresis loss). , Coupling loss). This indicates that an unexpected AC loss occurs when a large current is applied to the superconducting cable having the above structure.

In view of the above problems, an object of the present invention is to provide an AC superconducting cable in which the increase of AC loss is small in a large current region.

[0006]

DISCLOSURE OF THE INVENTION As a result of diligent consideration of the factors that increase the AC loss in the conventional cable construction, the present inventors have noted that the tape-shaped superconducting wire material of each layer has non-uniform inductance. As a result of further research based on this, the following phenomena were clarified. That is, when the inductance of the superconducting wire of each layer is nonuniform, the value of the current flowing through the superconducting wire of each layer becomes nonuniform. Therefore, when the energizing current is increased, the superconducting wire in the layer having the smallest inductance first reaches the critical current. As a result, the current is redistributed, and the current is shunted to the superconducting wire of the other layer through the sheath (normal conductor). This is a factor that generates Joule heat and increases the loss.

The present invention has been made on the basis of the above-described examination results, and its constitution is, in a superconducting cable for alternating current formed by winding a plurality of layers of a tape-shaped superconducting wire around a central member, a tape-shaped superconducting wire. It is characterized in that the winding pitch is increased toward the outer layer to reduce the difference in the inductance of the tape-shaped superconducting wire material of each layer.

[0008]

By doing so, since a substantially uniform alternating current flows through the tape-shaped superconducting wire rods of each layer, some superconducting wire rods with low inductance reach the critical current value first and the current is redistributed. Such a phenomenon can be suppressed, and an increase in AC loss in a large current region can be suppressed.

[0009]

Embodiments of the present invention will be described below. In the superconducting cable, the individual tape-shaped superconducting wire rods are spirally wound around the outer periphery of the central member or the outer periphery of the tape-shaped superconducting wire winding layer. The wound tape-shaped superconducting wire can be regarded as the same as the solenoid coil. Since the contact resistance between the sheaths of adjacent tape-shaped superconducting wires is considered to be sufficiently higher than that of the oxide superconductor inside, it may be considered that the oxide superconductors inside the wire are electrically independent. Therefore, if there are n layers of solenoid coils,
In order to equalize the inductance of each layer, the magnetic flux Φn inside the solenoid coil of each layer may be made uniform. If this is applied to a superconducting cable, the winding pitch Pn of each layer may be determined so that the internal magnetic flux Φn of the tape-shaped superconducting wire of each layer becomes uniform.

FIG. 1 shows an embodiment of the present invention. This superconducting cable has a tape-shaped superconducting wire 2 wound in six layers around the outer periphery of a central member 1 made of a corrugated pipe. The outer diameter of the central member 1 is 18 mm. The tape-shaped superconducting wire 2 is a Bi-based silver sheath multi-core wire having a silver ratio of 3, a thickness of 0.2 mm, a width of 3 mm, and a critical current value of 10 A. The total number of windings of the tape-shaped superconducting wire 2 is 114.

The winding pitch of each layer is initially 180 mm, 185 mm, 190 mm and 195 m from the innermost layer.
Magnetic field analysis was performed with m, 200 mm, and 205 mm.
Based on the result, the winding pitch is adjusted in the direction in which the inductance of each layer is made uniform, and finally the winding pitch is 180 mm, 183 mm, 189 in order from the innermost layer.
mm, 196 mm, 209 mm, 220 mm. This is called the cable of this embodiment.

On the other hand, for comparison, a cable having a winding pitch of each layer of 180 mm was prototyped. This is called a conventional cable. The AC loss of these cables was measured by a current-carrying method using a cancel coil. The measurement results are shown in FIG.

It can be seen from FIG. 2 that when the energizing current is increased, the AC loss of the conventional cable tends to increase sharply from several hundred amperes. This is because the inductance balance of each layer is insufficient, so the tape-shaped superconducting wire in the innermost layer, which has the smallest inductance, reaches the critical current density first, causing the phenomenon that the current is shunted to the outer layer via the silver sheath. This is because the AC loss increases due to Joule heat.

On the other hand, in the cable of the present embodiment in which the inductance of each layer is made uniform, a rapid increase in AC loss is not seen up to about 1100 A, and the loss is substantially equal to the sum of hysteresis loss and coupling loss (calculated value). .

[0015]

As described above, according to the present invention, it is possible to obtain an AC superconducting cable with a small increase in AC loss in a large current region.

[Brief description of drawings]

FIG. 1 is a perspective view showing an end portion of an AC superconducting cable according to an embodiment of the present invention in a step-peeled state.

FIG. 2 is a graph showing the measurement results of AC loss.

[Explanation of symbols]

 1: Central member 2: Tape-shaped superconducting wire

Claims (1)

[Claims] 1. In an AC superconducting cable in which a tape-shaped superconducting wire is wound around a central member in a plurality of layers, the winding pitch of the tape-shaped superconducting wire is increased toward the outer layer to reduce the inductance of the tape-shaped superconducting wire of each layer. A superconducting cable for alternating current characterized by reducing the difference.