JPS61127106A - Superconductive electromagnet device - Google Patents

Abstract

PURPOSE:To prevent loss of the permanent-current mode and burning of a thermal permanent-current switch as well as to provide stable return even in transition of the switch to the normal conductive state by disposing in parallel with the thermal permanent-current switch an auxiliary circuit including mechanically operated electric contacts. CONSTITUTION:When the resistance of a superconductive wire 4a is R1 and the resistance of an auxiliary circuit including electric contacts 5a, 5b is R2, the current of the permanent-current mode usually all flows in the circuit of a thermal permanent-current switch 4. If disturbance such as temporary injection of a hot gas occurs, the switch changes to the normal conducting state in spite of no energization of the heater 4b, the auxiliary circuit is connected in parallel with the superconductive wire 4a, and the current of the thermal permanent- current switch 4 is increased by R2/(R1+R2) times. It is easy to cause R2<<R1, and thus the heat of the switch 4 can be cooled and maintained below the limit enabling return to the superconductive state. When the switch 4 returns to the superconductive state, the current of the permanent-current mode flows through the switch 4, causing no burning.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a persistent current switch for a superconducting electromagnet device, such as a superconducting electromagnet device for magnetic levitation, which is operated in a persistent current mode separated from an excitation power source.

[Prior art and its problems]

This type of persistent current switch conventionally opens and closes by mechanically touching and opening electrical contacts, or it uses a heater attached to a superconducting wire at extremely low temperatures to heat it, as shown in Figure 3.

BACKGROUND ART A thermal persistent current switch that opens and closes by causing a superconducting wire to transition between a normal conducting state and a superconducting state by cooling is generally known. Now, referring to FIG. 3, the superconducting coil 2 housed in the cryogenic container 1 is connected to an excitation power source (not shown) via current leads 3a and 3b. A thermal persistent current switch 4 connected in parallel to the superconducting coil 2 is composed of a superconducting wire 4a and a heater 4b provided close to the superconducting wire 4a for heating the superconducting wire 4a. Since the resistance value of the superconducting wire 4a in the closed state is zero, this thermal persistent current switch 4 is preferably used in superconducting devices that require a particularly small attenuation rate of persistent current. In this case, the open state is achieved by bringing the superconducting wire 4a into a normal conducting state, so even in the open state, the superconducting wire 4a remains in a short-circuited state with a low resistance value. In order to make the resistance value in this open state a resistance value that does not hinder the operation of the superconducting electromagnet device, 1. A composite material using a low-resistance metal such as copper as a stabilizing material for the superconducting wire used in normal superconducting coils. Unlike superconducting wires, superconducting wires made only of superconductors are generally used. Therefore, since thermal persistent current switches do not have low-resistance metals such as copper stabilizing materials, they have poor stability in the current-carrying state, and are susceptible to transition to a normally conducting state due to small thermal or mechanical disturbances. There is a problem in that when the switch is in an open state, the υ persistent current mode is lost and the switch burns out.

[Purpose of the invention]

In view of the above-mentioned problems, this invention prevents loss of the persistent current mode or burnout of the switch even if the thermal persistent current switch transitions to a normal conduction state, and stably obtains a persistent current mode with a low attenuation rate. The purpose of the present invention is to provide a superconducting electromagnet device that can perform the following steps.

[Key points of the invention]

In this invention, an auxiliary circuit equipped with a contact mechanism that can be mechanically opened/closed is provided in parallel with the thermal persistent current switch to share a part of the persistent current closed loop.In the persistent current mode, the thermal persistent current switch is It is used by turning it into a closed state and closing the electrical contacts of the auxiliary circuit. In this way, even if the thermal persistent current switch is opened due to some disturbance when the superconducting coil is operated with persistent current, the electrical contacts of the newly installed auxiliary circuit are closed, so the persistent current A closed loop is formed to prevent switch burnout without loss of persistent current mode, and to easily return to normal persistent current mode operation.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention, in which cryogenic container I
An auxiliary circuit including electrical contacts 5a and 5b for mechanical opening/closing operation is provided in parallel to the built-in superconducting coil 2 and the thermal persistent current switch 4 forming a closed circuit for persistent current operation. It is.

When exciting the superconducting coil 2 in such a configuration, the electrical contacts 5a and 5b are opened by a drive mechanism (not shown), and a predetermined current is passed through the heater 4b to turn on the thermal persistent current switch 4. After the superconducting wire 4a is in an open state (the resistance value of the superconducting wire 4a at that time is R1Ω), a predetermined current is caused to flow through the superconducting coil 2 from a power source (not shown) through the current leads 3a and 3b. When entering the persistent current mode after obtaining a predetermined excitation state, first the open electrical contacts 5a and 5b are closed by a drive mechanism (not shown), and the current of the heater 4b is cut off to switch to the thermal mode. The persistent current switch 4 is closed. At this time, electrical contact 5
Since a and 5b have contact resistance, the auxiliary circuit has a minute resistance value of 2Ω. On the other hand, since the main circuit of the thermal persistent current switch 4 is composed of the superconducting wire 4a, the resistance value is zero in the closed state. Therefore, normally all current in the persistent current mode flows through the circuit of the thermal persistent current switch 4 and not through the auxiliary circuit. In this operating state,
For example, if a disturbance occurs such as temporary injection of warm gas with a temperature higher than IOK, the thermal persistent current switch 4 becomes normally conductive even though the heater 4b of the thermal persistent current switch 4 is not heated. The superconducting wire 4alC produces a resistance value R1Ω, but since the auxiliary circuit is connected in parallel, the current flowing through the thermal persistent current switch 4 is R2/(R1
+R2) times. At this time, it is easy to make R2 sufficiently smaller than R, and the thermal persistent current switch 4
By cooling with a refrigerant, the amount of heat generated can be kept below the limit at which the superconducting state can be restored again. When the thermal persistent current switch 4 returns to the superconducting state, the persistent current mode current flows through the thermal persistent current switch again, and a low attenuation state is obtained. It goes without saying that the auxiliary circuit also plays a protective role in this configuration.

FIG. 2 shows a different embodiment of this invention.

In the above-mentioned FIG. 1, the auxiliary circuit was arranged in the cryogenic region, whereas the electrical contacts 5a and 5b were arranged in the cryogenic container 1.
It is installed in a room temperature space outside of the In this configuration, the auxiliary circuit connected in parallel with the thermal persistent current switch 4 includes electrical contacts 5a and 5b and a pair of current leads 3a.

3b and the leads connecting them, even if the electrical contacts 3a and 3b are closed, the lead resistance ratio is 3Ω, which is a larger value than R2 in Fig. 1, but generally R3 is Since it is sufficiently small compared to
The same effect as shown in the figure can be obtained. In the case of Figure 1]
The advantage is that since the electrical contacts are in the room temperature range, the contact opening/closing operation becomes easy.

By installing an auxiliary circuit containing mechanically operated electrical contacts in the superconducting coil, when operating the superconducting coil in persistent current mode,
Even if an accident occurs in which a thermal persistent current switch transitions to a normal conduction state due to some kind of disturbance, loss of persistent current mode and burnout of the switch can be prevented, and it is possible to return to normal persistent current mode operation. There is.

[Brief explanation of drawings]

Fig. 1 is a basic configuration diagram of a superconducting electromagnet device which is an embodiment of the present invention, Fig. 2 is a basic configuration diagram of a superconducting electromagnet device which is a different embodiment of this invention, and Fig. 3 is a basic configuration diagram of a superconducting electromagnet device of a conventional structure. FIG. 2: superconducting coil, 4: persistent current switch, 4a: superconducting wire, 4b: heap-p-15a, 5b: [gas-liquid point. q or R. Yamaguchi Tori/ Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1) A persistent current switch that obtains opening/closing operations by installing a heater close to the superconducting wire and placing it in an extremely low temperature region to heat and cool the superconducting wire to make the superconducting state transition between the superconducting state and the normal conducting state. A superconducting electromagnet device connected in parallel to a coil and operated in persistent current mode; characterized in that a circuit including an electrical contact that is mechanically opened and closed is connected in parallel with the persistent current switch.