JPH07263760A - Superconductor permanent current switch and method of operating superconductor persistent current switch - Google Patents

Abstract

PURPOSE:To provide a persistent current switch that provides enough current, keeps the same current after on/off control and provides far faster switching speed than that by a temperature control method and a method of operating the persistent current switch. CONSTITUTION:The persistent current switch comprises a superconductor coil 21, a superconductive wire for a persistent current switch 19 connected in parallel with the superconductor coil 21, a power source that is connected with the superconductor coil 21 and the wire for the persistent current switch 19 and supplies current flowing through the superconductor coil 21, a superconductor magnet 26 that is provided near the wire for the persistent current switch 19, applies or decreases a magnetic field to the wire for the persistent current switch 19 and brings the wire for the persistent current switch 19 from a superconductive state to a conductive state or from the conductive state to the superconductive state, and an auxiliary power source 20 connected to the wire for the persistent current switch 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting permanent current switch device used in a superconducting-related device and a method of operating the superconducting permanent current switch.

[0002]

2. Description of the Related Art A superconducting persistent current switch is an essential element for realizing a persistent current circuit in combination with a superconducting magnet.
It is used in nuclear fusion systems, magnetic levitation trains, superconducting magnets for physics and chemistry experiments, etc. By the way, in a device that operates a superconducting magnet in a persistent current state in a superconducting energy storage system, etc., a superconducting coil and a persistent current switch are connected in parallel, and this parallel circuit is connected to a desired power source via a power lead. The configuration has become common.

3 to 5 show an example of a superconducting energy storage device having such a structure. In these drawings, reference numeral 1 denotes a superconducting coil, the superconducting coil 1 and a permanent current switch 2 are connected in parallel, and an AC / DC converter 5 is connected to this circuit via a power lead 3 and an opening / closing switch 4 to perform AC / DC conversion. An AC power supply system (not shown) is connected to the device 5. The superconducting coil 1 and the persistent current switch 2 are both formed of a superconductor which is transformed into a superconducting state at an extremely low temperature and are cooled by a refrigerant such as liquid helium. 3 to 5, the device for cooling the superconducting coil 1 and the persistent current switch 2 with liquid helium and its circuit are omitted.

In order to store electric power by using the superconducting energy storage device shown in FIGS. 3 to 5, the permanent current switch 2 is opened as shown in FIG.
And store electric power as magnetic energy. next,
As shown in FIG. 4, when the permanent current switch 2 is closed to short-circuit both ends of the superconducting coil 1 and the open / close switch 4 is opened, the superconducting coil 1 is cooled to a cryogenic temperature and its electric resistance is zero. The current continues to flow in the superconducting coil 1 without being attenuated, and the energy stored in the superconducting coil 1 at that time is stored without loss. Next, in order to take out the stored electric power, the magnetic energy stored in the superconducting coil 1 can be taken out as electric power by opening the permanent current switch 2 and closing the open / close switch 2 as shown in FIG. it can.

[0005]

Conventionally, a mechanical system, a temperature control system, a magnetic field control system and the like have been proposed as the principle of the device for performing the on / off control of the permanent current switch 2 as described above. Of these, the temperature control system is the one that is currently in practical use and is becoming the mainstream. In this temperature control system, the superconducting wire that constitutes the permanent current switch 2 is not induced along with the heater wire. In this state, the heater wire is used to make a permanent current switch 2 if necessary.
Switch the superconducting wire of No. 2 by heating it to a critical temperature or higher and causing normal conduction dislocation to turn it off, or turning off the heater to cool the superconducting wire of the persistent current switch 2 and turning it on. It is configured to realize.

However, in this temperature control type device,
There is a problem that it takes a long time for heat conduction, a problem that latent heat of a temperature control system affects, and the like, and there is a problem that it takes several seconds to several tens of seconds to switch the permanent current switch 2. Also, with this structure, in order to raise the temperature of the superconducting wire, there is no choice but to use an adiabatic structure with poor heat treatment.
When the switch is turned off, the superconducting wire for a persistent current switch may suddenly generate local heat, and the superconducting wire for a persistent current switch may be melted. Further, if the heater wire is broken, there is a problem that the superconducting persistent current switch in the on state cannot be turned off.

Attention has been paid to magnetic field control type persistent current switches. This magnetic field control system utilizes the phenomenon that the superconducting wire that constitutes the permanent current switch 2 shifts to the normal conduction state when it is placed in a magnetic field exceeding the critical magnetic field.
An external magnetic field can be applied by a separately provided superconducting magnet for control magnetic field. And
According to this magnetic field control method, applying a desired external magnetic field to the superconducting wire and removing the external magnetic field,
Since it is possible to instantaneously switch the current by controlling the energization of the superconducting magnet for the control magnetic field, this magnetic field control method enables high-speed response of the on / off control of the permanent current switch 2 by the high-speed sweep of the external magnetic field. In addition, since the control superconducting magnet can be arranged outside the superconducting wire for a permanent current switch, the superconducting wire has a feature that it can adopt a structure with good heat removal.

Then, when the on / off control of the actual magnetic field control type permanent current switch 2 was examined, it was found that there was a problem described below. First,
For the on-state permanent current switch 2 in the energized state,
Although it is possible to easily turn off the external magnetic field by applying an external magnetic field higher than the critical magnetic field, even if the permanent current switch 2 in the off state is returned to the on state by lowering the external magnetic field below the switch magnetic field, There is a problem that the current value recovers only about a few percent of the current value flowing in the permanent current switch 2 in the ON state.

This phenomenon will be described in detail with reference to FIGS. 6 and 7. When a current of 300 A is passed through the superconducting wire for a persistent current switch in the on state as shown in FIG. 6, the wire for a persistent current switch is shown. On the other hand, when an external magnetic field is applied by a superconducting magnet, a normal conducting dislocation occurs at a specific external magnetic field value determined by the energizing current, the energizing current sharply decreases, and the state is turned off. In addition,
The magnetic field at which switching (off) starts at this time is called a switch magnetic field (off magnetic field). However, the current value in this case does not instantly become zero but shows a value of about several A, and gradually decreases as the external magnetic field increases to almost zero. Further, after that, even when the external magnetic field is lowered in the off state as shown in FIG. 7 to return it to the off magnetic field of the superconducting wire for a persistent current switch or less, the current value is not recovered, and about several% of the initial on state,
That is, there is a problem that the current returns to only a few amps.

This is because when the superconducting wire for a persistent current switch is in the normal conducting state in the off state, the superconducting wire itself has a finite predetermined resistance value (usually a fraction of 1 Ω to a few 1).
It is considered that this is because Joule heat generation due to a minute current occurs because it has a value of about 0Ω), and this Joule heat hinders the cooling of the superconducting wire and prevents the superconducting state from returning to a complete superconducting state. Therefore, if the persistent current switch 2 in which this phenomenon occurs is used, the conducting current must be about several percent of the critical current of the superconducting wire for a persistent current switch, which is not practical.

The present invention has been made in view of the above circumstances, and as a permanent current switch of the type in which on / off control is performed by a magnetic field, the energizing current can be made sufficiently high and the same current value can be obtained after the on / off control. At the same time, it is an object of the present invention to provide a permanent current switch device capable of performing on / off control far faster than a temperature control system and a method of operating a permanent current switch.

[0012]

In order to solve the above-mentioned problems, the present invention provides a superconducting coil, a wire for a permanent current switch comprising a superconducting wire connected in parallel to the superconducting coil, and the superconducting coil. And a power supply connected to the wire for the persistent current switch to supply a current to the superconducting coil, and installed in the vicinity of the wire for the persistent current switch to apply a magnetic field to the wire for the persistent current switch to make the wire for the persistent current switch from the superconducting state. It is provided with a superconducting magnet for shifting to a normal conducting state and a standby power source connected to the wire for permanent current switch.

In order to solve the above-mentioned problems, the second aspect of the present invention uses the standby power source according to the first aspect as a wire for a persistent current switch when the wire for a persistent current switch is changed from a normal conducting state to a superconducting state. The current is made to flow in the direction to cancel the returning current.

In order to solve the above-mentioned problems, the invention of claim 3 relates to a superconducting persistent current switch according to whether or not an external magnetic field is applied to a superconducting persistent current switch wire which is connected to a superconducting coil and cooled with a refrigerant. In a method for operating a superconducting persistent current switch that switches between an on state and an off state, a superconducting persistent current switch is moved to a normal conducting state by applying an external magnetic field to the superconducting persistent current switch while the superconducting coil is energized. Then, the external magnetic field added to the wire for superconducting persistent current switch is made smaller than the switch magnetic field, and in this state, the canceling current is applied for a predetermined time in the direction opposite to the backward current flowing through the superconducting persistent current switch. The superconducting persistent current switch is turned on by turning off the current and then canceling the canceling current. That.

According to a fourth aspect of the present invention, in order to solve the above-mentioned problems, the canceling current according to the third aspect is set to the same current value as the recurrent current, and the current flowing through the wire for a permanent current switch is set to zero. The current switch is turned on.

In order to solve the above-mentioned problems, the invention described in claim 5 eliminates Joule heat generation of the wire for superconducting permanent current switch by setting the current flowing in the wire for permanent current switch to zero due to the canceling current, thereby eliminating wire heating for superconducting permanent current switch. After the temperature of is reduced by the refrigerant, the canceling current is removed and the superconducting persistent current switch is turned on.

[0017]

[Operation] By applying an external magnetic field to the superconducting wire that exceeds the switch magnetic field of the superconducting wire for a permanent current switch by the superconducting magnet, the superconducting wire is transformed into the normal conducting state and the permanent current switch is turned off. it can. To switch from this OFF state to the ON state, the external magnetic field is made smaller than the switching magnetic field of the superconducting wire, and then the reverse current flowing in the superconducting wire in the normally conducting state in the OFF state is canceled by the standby power supply. Apply current. As a result, the Joule heat generation of the superconducting wire in the normal conducting state disappears or becomes extremely small, and the superconducting wire can be sufficiently cooled by the refrigerant to be transformed into the complete superconducting state. Will be able to. The reduction operation of the external magnetic field, the application of the canceling current and the complete cooling of the superconducting wire can be completed in a short time, and the total state can be switched from the off state to the on state in about 0.1 to 1 second. High-speed switching is possible compared to the temperature control method.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a superconducting energy storage device provided with a persistent current switch. In the device of this example, 21 is a superconducting coil, 22 is a persistent current switch connected in parallel to the superconducting coil 21, and 23 is a superconducting coil. 21 is a power lead connected to the permanent current switch 22, 24 is an open / close switch incorporated in the power lead 23, and 25 is an AC / DC converter connected to the power lead 23. Further, the permanent current switch 22 of this example is formed by processing the superconducting wire 19 into a non-inductive winding coil shape, and the superconducting wire 19 is connected to a standby power source 20. Further, in FIG. 1, reference numeral 26 is a control magnetic field superconducting magnet, and 27 is a constant current source connected to the control magnetic field superconducting magnet 26. Further, in FIG. 1, reference numeral 28 denotes an extremely low temperature region by a cooling container. By cooling this region to an extremely low temperature with liquid helium, the superconducting coil 21, the permanent current switch 22 and the control magnetic field superconducting magnet 26 are brought into a superconducting state. Is able to. The superconducting magnet 26 for control magnetic field is capable of generating a magnetic field of about 1 Tesla (T).

The device having the above-mentioned structure is capable of charging, storing and discharging electric power, like the conventional superconducting energy storage device described with reference to FIGS. First, in order to perform charging, the open / close switch 24 is closed to connect the circuit, the constant current source 27 is operated to energize the control magnetic field superconducting magnet 26, and the control magnetic field superconducting magnet 26 superconducts the permanent current switch 22. Wire 1
Apply an external magnetic field to 9. In this case, an external magnetic field higher than the critical magnetic field of the superconducting wire 19 is applied. As a result, the superconducting wire 19 is in the normal conducting state even at an extremely low temperature, so that the permanent current switch 22 is turned off and a direct current flows through the superconducting coil 21 so that electric power can be stored as magnetic energy. Become.

Next, when the external magnetic field to the permanent current switch 22 is released, the superconducting wire 1 of the permanent current switch 22 is released.
Since 9 is in a superconducting state, both ends of the superconducting coil 21 are short-circuited. As a result, since the superconducting coil 21 is cooled to a cryogenic temperature and its electric resistance is zero, the current continues to flow through the superconducting coil 21 without being attenuated, and the energy stored in the superconducting coil 21 at that time is It will be saved without loss. Further, the open / close switch 24 is opened to stop energization of the control magnetic field superconducting magnet 26.

Next, in order to take out this stored electric power,
The open / close switch 24 is closed to connect the circuit, and the superconducting magnet 26 for control magnetic field is energized to shift the superconducting wire 19 of the permanent current switch 22 to the normal conducting state.
Thereby, the magnetic energy stored in the superconducting coil 21 can be taken out as AC power. In this way, the on / off control of the permanent current switch 22 can be performed. If the on / off control of the permanent current switch 22 is performed by applying and releasing such an external magnetic field, the response is fast, so that a high-speed response can be easily accommodated.

By the way, when the ON / OFF control of the permanent current switch 22 is performed, it is simply performed by operating the superconducting magnet 26 with an external magnetic field higher than the critical magnetic field. As described above, the value of the energizing current that can flow through the superconducting wire 19 decreases during the period when the off state is switched to the on state. Therefore, in this example, the on / off control is performed by operating the superconducting switch 22 by implementing a special method described below.

When switching the superconducting switch 22 from the off state to the on state, first, the external magnetic field applied to the superconducting wire 19 is made smaller than the above-mentioned off magnetic field. In this state, as shown in FIG. 7, a backward current of several% of the critical current flows through the superconducting wire 19. In this state, the superconducting wire 19 is supplied with a current in a direction opposite to the return current for a predetermined time, for example, about a few seconds for a few seconds, so that the voltage across the superconducting wire 19 becomes zero or almost zero, and the predetermined time elapses. Later, this reverse current is stopped. By the above operation, the superconducting wire 1
Since the Joule heat of 9 disappears or becomes extremely small, the temperature of the superconducting wire 19 is sufficiently lowered by cooling the refrigerant, whereby the superconducting wire 19 is switched and the current flowing in the on state before the off state is applied. The energizing current is restored in a short time to a current value equivalent to the current value.
As a result, the superconducting switch 22 can be switched at high speed so as to have a sufficient energizing current.

When the countercurrent of the superconducting wire 19 is eliminated or reduced by passing the canceling current as described above, the return current is completely eliminated so that the superconducting wire 19 is cooled quickly. However, if the cooling capacity of the refrigerant such as liquid helium is sufficiently large and the Joule heat generation is sufficiently lower than that, it is not necessary to completely set the return current to zero. That is, since it is sufficient that the superconducting wire 19 is cooled in a short time so that it can return to a superconducting state that can withstand a sufficiently high energizing current, it is also possible to reduce the return current to such an extent that the return is not affected. Can be achieved. Therefore, the canceling current applied to the superconducting wire 19 from the standby power source 20 may be smaller than the return current.

(Production Example 1) An in-situ alloy rod having a composition of Cu-50 wt% Nb and Nb filaments dispersedly arranged inside a Cu base was used, and Cu-30 wt% Ni was used for the in-situ alloy rod. The cupronickel tube having the composition of is covered and subjected to wire drawing, and 55 wires are drawn to form Cu-30wt.
% Ni was inserted into a cupronickel tube body and subjected to wire drawing to obtain a superconducting element wire rod having a diameter of 0.3 mm in which 55 Cu-Nb cores exist in a Cu-Ni alloy matrix. Prepare six superconducting wire rods and use one Cu-Ni
A superconducting wire for a permanent current switch was obtained by arranging the wire around the outer circumference of the alloy wire and forming a stranded wire.

20 m of this superconducting wire was prepared, and it was non-inductively wound and mounted in a control field superconducting magnet to form a permanent current switch, which was incorporated into the apparatus shown in FIG. 1 and the energizing current was 300 A. Then, when the superconducting magnet for control magnetic field was excited at the liquid helium temperature,
It turned off at 3T and was flowing into the superconducting wire 300
The current of A was cut off. After that, when the external magnetic field was lowered to 0.2 T in order to turn on the superconducting persistent current switch, a current of 10 A returned to the superconducting wire in this state. In this state, a voltage was applied to both ends of the superconducting wire for a permanent current switch from a standby power source, and a current in the reverse direction of the recurrent current was flowed for 0.27 seconds to completely eliminate the current flowing through the superconducting wire. After applying the voltage for 0.27 seconds, the voltage application from the standby power supply was stopped and the same state as in the previous ON state was set. Then, in 0.2 seconds, the current flowing through the superconducting wire returned to 300A and the ON state was reached. I was able to The above-mentioned progress state is shown in FIG. From the above, it has been clarified that the superconducting persistent current switch can be switched from the OFF state to the ON state in a fraction of 1 second to 1 second at a sufficiently high applied current.

[0027]

As described above, according to the present invention, in a switch device using a persistent current switch for a superconducting wire, an external magnetic field exceeding the critical magnetic field of the superconducting wire for a persistent current switch is applied to the superconducting wire by a superconducting magnet. By doing so, the superconducting wire is transformed into the normal conducting state, and the persistent current switch can be turned off to bring it into the off state. Since the switching to the off state can be performed instantly, the switching can be performed at a high speed as compared with the temperature control method.

Next, in order to switch from the OFF state to the ON state, the external magnetic field is made smaller than the switching magnetic field of the superconducting wire, and then the backward current flowing in the superconducting wire in the normal state in the OFF state is applied. Apply a canceling current from the standby power supply to cancel it. As a result, the Joule heat generation of the superconducting wire in the normal conducting state is eliminated or extremely reduced, and the superconducting wire is sufficiently cooled by the refrigerant and can easily be transformed into the complete superconducting state. You will be able to flush. Therefore, as a result, the current value from the off state to the on state, which has been partially recovered in the past, can be increased to a sufficiently practical level. The reduction operation of the external magnetic field, the application of the canceling current and the complete cooling of the superconducting wire can be completed in a short time, and the total state can be switched from the off state to the on state in about 0.1 to 1 second. Compared to the temperature control method, switching can be performed at extremely high speed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of a superconducting energy storage device including a persistent current switch according to the present invention.

FIG. 2 is a diagram showing a change in current value when the apparatus of the embodiment changes from an off state to an on state.

FIG. 3 is a configuration diagram showing a state in which an example of a superconducting energy storage device including a conventional persistent current switch is being charged.

FIG. 4 is a configuration diagram showing a state in which electric power is stored in an example of a superconducting energy storage device including a conventional persistent current switch.

FIG. 5 is a configuration diagram showing a state in which electric power is taken out from an example of a superconducting energy storage device including a conventional persistent current switch.

FIG. 6 is a diagram showing a change of a current value flowing in the superconducting wire with respect to the magnetic field when a magnetic field exceeding a critical magnetic field is applied to the superconducting wire for a persistent current switch to turn it off.

7 is a diagram showing a change in a magnetic field of a current value flowing in a superconducting wire for a persistent current switch when an external magnetic field is reduced from the off state shown in FIG.

[Explanation of symbols]

19 ... Permanent current switch wire, 20 ... Standby power supply, 21 ... Superconducting coil, 22 ... Permanent current switch, 23 ... Power lead,
24 ... open / close switch, 25 ... AC / DC converter,
26 ... Superconducting magnet for control magnetic field, 28 ... Cryogenic region, 27 ... Constant current source,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Saito 1-5-1 Kiba, Koto-ku, Tokyo Fujikura Ltd. (72) Inventor Satoru Kono 1-1-5 Kiba, Koto-ku, Tokyo Stockholders Company Fujikura (72) Inventor Hitoshi Honma 7-2-1 Nakayama, Aoba-ku, Sendai-shi, Miyagi Tohoku Electric Power Co., Inc. Electric Power Research Laboratory (72) Inventor Tatsuki ▲ 匡 ▼ 7-chome, Nakayama, Aoba-ku, Sendai-shi, Miyagi No. 1 Power Engineering Laboratory, Tohoku Electric Power Co., Inc. (72) Inventor, Kochichi, No. 8-12 Tsukigaoka, Morioka, Iwate Prefecture (72) Noriaki Matsukawa, No. 1, 31 Ueda, Morioka, Iwate Prefecture

Claims (5)

[Claims] 1. A superconducting coil, a wire for a permanent current switch comprising a superconducting wire connected in parallel to the superconducting coil, and a power supply connected to the superconducting coil and the wire for a persistent current switch to supply an energizing current to the superconducting coil. Installed in the vicinity of the wire for permanent current switch and applying a magnetic field to the wire for permanent current switch or reducing the magnetic field to shift the wire for permanent current switch from the superconducting state to the normal conducting state or from the normal conducting state to the superconducting state. A superconducting permanent current switch device comprising a superconducting magnet and a standby power source connected to the permanent current switch wire. 2. The standby power supply according to claim 1, wherein a current flows in a direction to cancel a current returning to the wire for a persistent current switch when the wire for a persistent current switch is changed from a normal conducting state to a superconducting state. A superconducting persistent current switch device characterized by being present. 3. A superconducting persistent current for switching a superconducting persistent current switch between an on state and an off state depending on whether or not an external magnetic field exceeding a critical magnetic field is applied to a superconducting permanent current switch wire connected to a superconducting coil and cooled with a refrigerant. In the operating method of the switch, the superconducting permanent current switch wire is transferred to the normal conducting state by applying an external magnetic field to the superconducting permanent current switch while the superconducting coil is energized, and the superconducting persistent current switch is turned off. The external magnetic field added to the wire for superconducting persistent current switch is made less than the switch magnetic field,
In this state, a canceling current is passed for a predetermined time in the opposite direction to the return current flowing through the superconducting persistent current switch, and then the canceling current is stopped to turn on the superconducting persistent current switch. how to drive. 4. The superconducting permanent current switch is turned on by setting the canceling current to the same current value as the return current and setting the current flowing through the wire for permanent current switch to zero. How to operate a superconducting persistent current switch. 5. The cancellation current is removed by eliminating the Joule heat generation of the wire for superconducting permanent current switch by making the current flowing through the wire for permanent current switch to zero by the canceling current, and lowering the temperature of the wire for superconducting persistent current switch with a refrigerant. , A method of operating a persistent current switch, characterized in that the superconducting persistent current switch is turned on.