JPH0196907A - Permanent current switch - Google Patents

Abstract

PURPOSE:To make the development of winding disorder causing fine movement difficult very much, by providing switch elements where a superconducting wire is wound into a limited number of layers at each spool end assembling a plurality of the elements in a bundle so that respective axes are not overlapped and they become in parallel one another. CONSTITUTION:Seven pieces of switch elements like bars having each round cross section with respect to each axis are packed into a bundle and are connected in parallel. Seven pieces of the switch elements 1 have the same forms and dimensions. At the winding pad of superconducting wires 6, required lengths of the wires are wound by lessening the number of layers on one hand and by increasing rows of winding in the axis direction on the other hand. Round cross section which is vertical with respect to each axis of respective switch elements allows spools 4 or outside covers 5 to be processed in a lathe and facilitates manufacturing of the elements. Further, a limited number of the layers at the winding part of the superconducting wires makes the development of winding disorder difficult. Accordingly, the fine movement of superconducting wires due to winding disorder as well as transition from superconductivity to normal conductivity with the movement of the superconducting wires are overcome and a permanent current switch may exhibit a stable performance. Further, as the switch elements having the same forms are connected in parallel, only a limited number of the spare switch elements are required for replacing or repairing elements.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a persistent current switch used in connection with a superconducting coil of a magnetic levitation train, a magnetic resonance imaging tomography apparatus, or the like.

[Conventional technology]

Persistent current switches are connected to superconducting coils used in magnetic levitation trains, magnetic resonance imaging tomography devices, etc. to keep a constant current flowing over long periods of time. Persistent current switches in this field operate by switching a superconducting wire in a cryogen such as liquid helium between a normal conductive state (resistance state) and a superconducting state (non-resistance state) by controlling the temperature of the wire using a heater. A permanent current switch is used.

The basic structure of such a persistent current switch is that a superconducting wire and a heater wire are wound around a winding frame, and the winding frame is impregnated with a resin such as epoxy. For superconducting wires, in order to maximize the electrical resistance when open, an ultrafine multifilamentary wire whose base material is a metal with a high specific resistance, such as a CuNi alloy, is generally used. However, a base material with a high resistivity hardly contributes to the stabilization of a superconducting wire. Therefore, such a superconducting wire has a lower resistivity than a superconducting wire whose base material is a metal with a low resistivity such as copper or aluminum. It is unstable in that it tends to undergo normal conduction transition when energized. In particular, it is generally said that this instability increases as the cross-sectional area of the superconducting wire increases in order to pass a large current. Therefore, in a persistent current switch that uses a superconducting wire with a high specific resistance as a base material, if there is even a slight thermal disturbance while the current is flowing in a non-resistance state, a part of the superconducting wire will transition to normal conductivity. Furthermore, the accompanying heat generation causes the normal conduction transition to spread throughout the persistent current switch, causing the persistent current switch to unexpectedly switch to a resistive state, which is an undesirable characteristic.

One way to improve these characteristics is to use a switch element made by non-inductively winding superconducting wire around a disc-shaped winding frame.
A disk-stacked persistent current switch in which a plurality of such switches are stacked and connected in parallel so that the axes of the winding frames are coaxial has already been published in patents and the like (for example, Japanese Patent Laid-Open No. 7779/1983). FIG. 4 shows an example of such a persistent current switch in which the number of switch elements is five.

In addition, as shown in Figure 6, a coaxial multiple cylindrical persistent current switch element in which superconducting wires are non-inductively wound around multiple cylindrical winding frames with different diameters are stacked and connected in parallel so as to be coaxial. Switches are also protected by patents (for example, Japanese Patent Laid-Open No. 53
-99794). In principle, a type of persistent current switch in which these switching elements are connected in parallel has a current of ■ during normal use and a parallel number of switching elements of N.
In this case, if a superconducting wire with a critical current of 1/(N-1) or more is used, even if one of the switch elements transitions to normal conductivity, the remaining switch elements can maintain the current during normal use. Therefore, the current conduction characteristics of the persistent current switch are stable.

In addition, the superconducting coil equipped with a persistent current switch is
Since it is cooled to liquid helium temperature during operation and kept at room temperature when not in operation for periodic inspections, persistent current switches also repeatedly experience such temperature changes. Depending on the number of repeated temperature changes and the rate of change, the resin impregnated with the switch element may deteriorate, causing cracks, peeling, etc. As a result, the switch element and the elemental superconducting wire tend to move slightly, and the heat generated by the slight movement makes the switch element more likely to transition to normal conductivity. As a persistent current switch, there is no problem if the normal conduction transition of the switch elements occurs one by one, but if the normal conduction transition of the switch elements occurs frequently and two or more switch elements undergo the normal conduction transition at the same time, , since the persistent current switch as a whole also undergoes a normal conduction transition, current carrying performance becomes unstable. However, if some of the switch elements deteriorate due to deterioration of the impregnating agent, both the disk stacked persistent current switch and the coaxial multi-cylindrical persistent current switch will detect the deteriorated or defective switch element. Performance can be restored through replacement and repair. Furthermore, the same applies if a defective switch element is incorporated due to the yield during manufacturing.

[Problem that the invention seeks to solve]

In the disk-stacked persistent current switch shown in Figure 4, the cross-section of the disk-shaped switch element is as shown in Figure 5, the winding frame width is narrow, and the number of layers, that is, the superconducting wire in the radial direction, is narrow. If the winding frame width is narrow, there is a problem in that the workability of the winding becomes poor.Also, if the superconducting wire overlaps in the radial direction in a few layers, there is almost no problem, but if the superconducting wire overlaps in the radial direction in several layers, When layered, the superconducting wire is prone to winding irregularities that cause micro-tremors at the N transition point.As micro-tremors in 8i conductive wires generate heat and cause a normal conductive transition, there is winding irregularity in the switch element and the normal conductive transition occurs for a short time. If this occurs frequently, there is a problem in that the current carrying performance of the persistent current switch as a whole tends to become unstable.

On the other hand, the coaxial multiplex cylindrical persistent current switch shown in Fig. 6 does not have the above problem because the number of superconducting see-disk layers in the cylindrical switch element can be reduced. As for the spare switch elements, it is necessary to prepare many spare switch elements.In other words, in the case of disk-stacked persistent current switches, switch elements of the same shape are connected in parallel, so it is necessary to prepare many spare switch elements for replacement and repair. If there is only one spare switch element, it can be replaced and repaired even if any switch element becomes malfunctioning. However, with coaxial multiple cylindrical persistent current switches, there is no compatibility between switch elements of different diameters, so the number of parallel switches and It is necessary to prepare the same number of spare switch elements for replacement and repair. Therefore, although the coaxial multiple cylindrical persistent current switch uses expensive superconducting wire for the switch elements, there is a problem in that many spare switch elements must be prepared for replacement and repair.

[Means for solving problems]

In order to solve the above problems, the present invention provides a persistent current switch having a configuration in which a plurality of switch elements are connected in parallel.
This paper proposes a method in which a switching element is made by winding superconducting wire in a small number of layers around a winding frame, and a method is proposed in which a plurality of these elements are bundled and assembled so that their axes do not overlap and are parallel to each other.

[Effect]

Since the number of layers in the superconducting wire winding portion of the switch element is small, winding irregularities that cause micro-movements of the superconducting wire that cause normal conduction transition are extremely unlikely to occur. Furthermore, since the shapes and dimensions of the switch elements connected in parallel can be made the same, the number of spare switch elements prepared for replacement and repair using expensive superconducting wires can be reduced.

〔Example〕

Embodiments of the present invention will be specifically described based on the drawings.

FIG. 1 shows one embodiment of the invention. This is a persistent current switch in which seven rod-shaped switch elements with a circular cross section perpendicular to the axis are bundled and connected in parallel. The seven switch elements 1 have the same shape and dimensions, and their cross-sectional shape is as shown in FIG. In the winding portion of the superconducting i4 wire 6, the number of layers is reduced while the arrangement in the axial direction is increased to wind up a required length of superconducting wire. If the cross section perpendicular to the axis of the switch element is circular, then
Manufacturing is easy because the winding frame 4 and outer cover 5 can be lathe-processed.

Further, in this embodiment, the winding frame is elongated in the axial direction, and the switch element is shaped like a rod. By forming the switch element in such a shape, the persistent current switch can be made compact even when a large number of switch elements are bundled.

FIG. 3 is another embodiment of the invention. This is a persistent current switch in which four switch elements each having a rectangular cross section perpendicular to the axis are connected in parallel. If the cross section perpendicular to the axis is square in this way, there will be no gaps between the switch elements when assembled into a persistent current switch, resulting in a compact persistent current switch. In addition to this example, the cross section perpendicular to the axis is triangular;
The same applies to polygons such as hexagons.

〔Effect of the invention〕

Since the persistent current switch according to the present invention has the structure explained in the above embodiment, the number of layers in the superconducting wire winding portion is small and winding disorder is less likely to occur. , the accompanying normal conduction transition is eliminated,
Persistent current switch can exhibit stable performance. Also,
Since switch elements of the same shape are connected in parallel, the number of spare switch elements required for replacement and repair is reduced, thus avoiding the uneconomical effects of preparing a large number of switch elements that use expensive superconducting wires. be able to.

[Brief explanation of the drawing]

FIG. 1 shows one embodiment of a persistent current switch according to the present invention. FIG. 2 is a sectional view of a switch element constituting the persistent current switch of FIG. 1. FIG. 3 is another embodiment of the invention. FIG. 4 shows an example of a conventional persistent current switch, and FIG. 5 is a sectional view of the switch element. 6th
The figure also shows another example of a conventional persistent current switch. Note that the heater wires are omitted in all of these figures. l--switch element, 2... current lead, 3
-・-Binder, 4...-Reeling frame, 5-Outer cover,
6...Superconducting wire 7-...Spacer, 8-...
Fixing bolts Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (3)

[Claims] (1) In a persistent current switch with a configuration in which multiple switch elements are connected in parallel to open and close the transition between the normal conductive state and the superconducting state of the superconducting wire, the superconducting wire is wound around the winding frame with a small number of layers. A persistent current switch characterized by using objects as switch elements and assembling multiple pieces in a bundle so that their axes do not overlap and are parallel to each other. (2) The persistent current switch according to claim 1, wherein the winding frame is elongated in the axial direction, and the switch element is rod-shaped. (3) A persistent current switch according to claims 1 and 2, characterized in that a cross section perpendicular to the axis of the switch element is circular. (4) Perpendicular to the axis of the switch element. Persistent current switch according to claims 1 and 2, characterized in that the cross-sectional shape is polygonal.