JPH10106365A - Superconductor for permanent electric current switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable switching property by electrically communicating mutually neighboring superconductive strands. SOLUTION: This superconductor 10 is produced by stranding superconductive strands 12, 12,... on a normal conductive core wire 11 as a center. No insulating layer is formed on each strand 12, 12,... and on the whole body of the stranded conductor 10 and the mutually neighboring strands 12 are kept in electrically communicated state. At the time when electricity is applied to a magnetic permanent electric current switch using this superconductor 10 or an external magnetic field intensity is changed, even if electric resistance and inductance of connection parts of respective strands are not even, the electric current flowing in the whole conductor body is made even and dispersion from design values of switching properties is suppressed attributed to the electric continuity between mutually neighboring strands. Moreover, the conductor is directly cooled not through an insulating layer, the temperature rise of the conductor is suppressed and switching operation is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called "permanent current switch" to which the superconducting phenomenon is applied, and more particularly to a superconducting conductor used for a magnetic field type permanent current switch. The present invention relates to a superconducting conductor for a permanent current switch, which can be realized without heat loss, can perform high-speed switching and high-speed current flowing, and can be manufactured at a low cost with a simplified manufacturing process.

[0002]

2. Description of the Related Art A permanent current switch is an essential element for realizing a permanent current circuit in combination with a superconducting coil. Is being applied. This permanent current switch is formed of a conductor that can transition between a superconducting state and a normal conducting state in any direction by setting environmental conditions, and when the conductor is in the superconducting state, the electric resistance is changed. Since the current becomes zero, the current is conducted without attenuation and the switch is turned on, and when the conductor is changed to the normal conducting state, the electric resistance is increased and the switch is substantially turned off. ing.

For example, in a superconducting magnetic energy storage system whose operation is shown in FIGS. 4 to 6, a permanent current switch is used as follows. In this superconducting magnetic energy storage system, the superconducting coil 1 and the permanent current switch 2 are connected in parallel, and this parallel circuit is connected to the AC / DC converter 5 via the power lead 3 and the open / close switch 4.
The AC / DC converter 5 is further connected to an AC power system (not shown). Each of the superconducting coil 1 and the permanent current switch 2 is formed of a superconducting conductor that transitions to a superconducting state at a low temperature, and the entire parallel circuit is cooled by a coolant such as liquid helium.

Now, in order to store electric power using this superconducting energy storage device, first, as shown in FIG. 4, the on / off switch 4 is closed and the permanent current switch 2 is brought into a normal conducting state by switching the switch. In the off state, a DC current is supplied to the superconducting coil 1, and the electric power is stored in the superconducting coil 1 as electromagnetic energy.

Next, as shown in FIG. 4, the permanent current switch 2 is turned on by bringing the permanent current switch 2 into a superconducting state with the open / close switch 4 closed, and the external current is reduced by reducing the external current. The current flows into. When the DC current from the outside becomes zero, a current equivalent to the current flowing through the superconducting coil 1 flows through the permanent current switch 2, and a permanent current mode is set. In this state, the open / close switch 4 is opened as shown in FIG. Then, since the electric resistance of both the superconducting coil 1 and the permanent current switch 2 is zero, the current becomes a permanent current and continues to flow in this parallel circuit without being attenuated, and the energy stored in the superconducting coil 1 loses no loss. Will be stored at

In order to take out the stored energy, as shown in FIG. 6, the permanent current switch 2 is turned off by bringing the permanent current switch 2 into a normal conduction state after closing the open / close switch 4. Then, the energy stored in the parallel circuit can be taken out as power through the power lead wire 3.

In the permanent current switch 2 described above, switching is performed by a transition between a superconducting state and a normal conducting state. Therefore, it is important to perform this transition stably with good reproducibility and at high speed. Becomes By the way, it is known that this transition is caused by any one of the temperature, the magnetic field, the electric current, and the mutual condition change.
That is, each of these three conditions has a critical value, and the conductor enters a superconducting state or a normal conducting state at least one of the critical values.

Conventionally, as a switching method of a permanent current switch, a thermal method of changing a temperature is most generally used. In the thermal method, a superconducting wire, which is a switch conductor, and a heater wire for temperature control are wound together in a coil shape, and are usually impregnated with epoxy resin to form a heat insulating structure. The winding conductor used for this purpose is mainly Nb
A superconducting wire made of -Ti alloy is used, and its critical temperature is about 9K. Therefore, the superconducting wire transitions between the superconducting state and the normal conducting state at about 9K.

When the permanent current switch is operated, if the heater wire is energized and the superconducting wire is heated to about 9K or more, the switch is turned off, the heater wire is turned off, and the superconducting wire is turned off for about 9K by the surrounding helium. The switch is turned on if cooled below. Therefore, switching can be performed by repeatedly lowering / raising the temperature of the superconducting wire across about 9K.

However, this thermal type device has a problem that it takes several seconds to several tens of seconds for the switching response of a switch for a large current, particularly because the temperature control system has a heat capacity or takes a long time to conduct heat. There is. In addition, in this structure, a heat insulation structure with poor heat dissipation must be used to raise the temperature of the superconducting wire, so when it is turned off, sudden local heat is generated in the superconducting wire, and the superconducting wire is melted. There was also a fear that it would be lost.

On the other hand, when a magnetic field type permanent current switch is applied with an external magnetic field to a superconducting wire in a low temperature range,
It utilizes the property of transition between the superconducting state and the normal conducting state at the critical magnetic field strength. Therefore, this magnetic field type permanent current switch is composed of a superconducting winding for switching and an electromagnet for generating a control magnetic field. As the switching wire, a superconducting material having a moderate critical magnetic field strength that facilitates magnetic field control is used, and for example, a Cu-Nb alloy having a critical magnetic field strength of about 1 T (tesla) or less is generally used. .

Since the magnetic field type permanent current switch does not need to raise the temperature of the wire in principle, a winding structure with good heat dissipation can be provided, and the wire and the winding are effectively cooled. The temperature rise due to the heat generated by the AC loss of the superconducting winding generated when the external magnetic field intensity is fluctuated at a high speed is relatively small, and has an advantage that stable and high-speed switching is possible as compared with the thermal type. Furthermore, in the magnetic field type permanent current switch, in order to suppress the induced voltage generated by the fluctuation of the external magnetic field strength, non-inductive winding for reducing the self-inductance is generally performed. The line structure also has the advantage of reducing the induced voltage generated between adjacent conductors.

[0013]

The superconducting conductor used in the conventional magnetic field type permanent current switch has a current carrying capacity of, for example, about tens to hundreds of amperes of a 0.3 mm.phi. In general, a plurality of strands are twisted into a stranded wire to increase the current capacity. In this case, for electrical insulation between the strands and the entire stranded conductor,
It is common practice to apply an insulating layer such as polyvinyl formal to each individual wire. However, this causes the following problems. Since the electrical resistance and inductance at the connection of individual stranded insulated wires vary, the superconducting current can be evenly distributed to each wire when applying current to the conductor or changing the external magnetic field strength. Therefore, the current does not become the sum of the number of wires, the switching characteristics of the permanent current switch deviate from the design values, and the operation becomes unstable. Because the insulating layer acts as a heat insulator, the temperature inside the conductor rises due to external magnetic field fluctuations and AC loss of the conductor due to current flow, even though it is cooled from the outside. Becomes unstable. Since the wire is provided with the insulating layer, the cooling rate of the refrigerant is reduced, and the cooling rate is rate-determining, so that sufficient high-speed switching cannot be performed. A process for insulating individual strands is required, which complicates the process and requires cost for an insulating material and the like.

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and an object of the present invention is to provide a superconducting conductor used for a magnetic field type permanent current switch, which has no variation in switching characteristics and stable operation. Another object of the present invention is to provide a superconducting conductor which has a small heat loss and can be manufactured at a low cost with a simplified manufacturing process.

[0015]

An object of the present invention is to provide a superconducting wire composed of a plurality of superconducting wires twisted together without forming an electrical insulating layer on each of the superconducting wires. Can be solved by providing a superconducting conductor for a permanent current switch, which is made electrically conductive.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an embodiment of a superconducting conductor for a permanent current switch according to the present invention. FIG.
In the superconducting conductor 10 for a permanent current switch, a superconducting wire 12 having a diameter of 0.3 mm and a superconducting wire 12, 1
2,.. Consist of a stranded wire conductor (10). The insulating layer is not formed on each of the superconducting wires 12, 12,..., Nor on the entire stranded conductor 10, and the superconducting wires 12 adjacent to each other are in an electrically conductive state. The DC critical current of this stranded conductor 10 at 4.2 K and zero magnetic field strength was 570 A.

In the magnetic field type permanent current switch using the superconducting conductor as a wire, when the conductor is energized or when the external magnetic field strength is changed, the electric resistance and the inductance of the connection portions of the individual wires vary. However, since there is conduction between the superconducting wires adjacent to each other, the current flowing through the entire conductor is leveled, and the variation of the switching characteristics from the design value is reduced. In addition, since the superconducting conductor is directly cooled without passing through the insulating layer, fluctuations in the external magnetic field strength and temperature rise of the conductor due to the inflow of current are effectively suppressed, and switching operation due to thermal fluctuations in the critical magnetic field strength is prevented. Stability is reduced and high speed switching is possible.

The superconducting wire 12 used for the stranded conductor 10
Was manufactured as follows. A Cu-50% by weight Nb alloy is used as a superconducting material.
mm rod, outer diameter 30 mm, inner diameter 21 mm x length 20
It was combined with a 00 mm Cu-30 wt% Ni alloy pipe to form a single core wire. This single-core wire is drawn to a diameter of 2 mm, and 55 obtained single-core wires are bundled to form an outer diameter of 2 mm.
5mm, Cu-30 of inner diameter 20mm x length 2000mm
Weight percent Ni alloy pipe, and insert this pipe with a diameter of 0.
The superconducting element wire 12 was drawn until it became 3 mm. In addition, Cu used as a pipe material used when compounding this superconducting element wire 12 and as a core wire 11 of the stranded conductor 10 is used.
The -Ni alloy was used in this embodiment to prevent the apparent specific resistance from decreasing in the normal conductive region, whereby the electric resistance at the time of switch-off was kept high, and the current interrupting effect was improved. It became certain.

Next, an example of a permanent current switch incorporating the superconducting conductor 10 of the embodiment and a superconducting magnetic energy storage device incorporating the permanent current switch will be described with reference to FIG. This superconducting magnetic energy storage device 2
0, reference numeral 21 denotes a superconducting coil, reference numeral 22 denotes a magnetic field type permanent current switch connected in parallel to the superconducting coil 21, reference numeral 23 denotes a power lead connected to the superconducting coil 21 and the permanent current switch 22, and reference numeral 24 denotes power. Reference numeral 25 denotes an open / close switch incorporated in the lead 23 and an AC / DC converter connected to the power lead 23. The above-mentioned permanent current switch 22 is configured using the superconducting conductor 10 of the embodiment shown in FIG. Reference numeral 26 denotes the on / off of the magnetic field type permanent current switch 22.
Reference numeral 27 denotes a control superconducting electromagnet for controlling turning-off, and reference numeral 27 denotes an exciting current source for the control electromagnet 27. This control electromagnet 26 can generate a magnetic field of about 1T. Reference numeral 28 denotes a cryogenic region by a cooling vessel. By cooling this region to a cryogenic temperature with liquid helium, the superconducting coil 21, the permanent current switch 22, and the control electromagnet 26 can be brought into a superconducting state. ing.

The above-described superconducting magnetic energy storage device 20
As shown in FIG. 3, the permanent current switch 22 used for
It comprises a non-inductive coil formed by winding the superconducting conductor 10 of the embodiment in a length of 15 m on a bobbin 31 having a diameter of 50 mm and a length of 250 mm without induction. The coil turns the superconducting conductor 10 at its midpoint 32, and spirally superposes the superconducting conductors 10a and 10b extending from the midpoint 32 to the bobbin 31 in parallel, but maintaining a 0.4 mm interval so as not to make contact. It is obtained by winding. The spiral winding was performed by forming two spiral grooves on the bobbin 31 in advance for guiding the conductor. In the obtained coil, for example, when current flows from one terminal A to another terminal B, a current flows in an opposite direction to an adjacent conductor, and a non-inductive coil is realized as a whole.

The above-described superconducting magnetic energy storage device 2 using the superconducting conductor 10 of the embodiment for the permanent current switch 22.
0 can charge, store, and discharge power as in the superconducting magnetic 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, and the constant current source 27 is operated to energize the control electromagnet 26, so that the superconducting conductor 10 of the permanent current switch 22 has a voltage higher than its critical magnetic field. Apply a magnetic field. As a result, the superconducting conductor 10 transitions to a normal conducting state even at a very low temperature, so that the permanent current switch 22 is turned off, and a DC current is passed through the superconducting coil 21 so that electric power can be stored as magnetic energy.

Next, when the current supplied to the control electromagnet 26 is reduced to zero with the open / close switch 24 closed,
The magnetic field received by the superconducting conductor 10 of the permanent current switch 22 in the normal conduction state becomes zero, and the permanent current switch 22
Is in a superconducting state and is switched on. If the current from the outside is reduced in this state, the current flows into the permanent current switch 22. When the current from the outside becomes zero, a current equal to the current flowing through the superconducting coil 21 flows through the permanent current switch 22, and a permanent current mode is set. In this state, the open / close switch 24 is opened. Then, since the electric resistance of both the superconducting coil 21 and the permanent current switch 22 is zero, the current becomes a permanent current and continues to flow in this closed circuit without being attenuated, and the energy stored in the superconducting coil 21 is lost without loss. Stored in.

Next, in order to take out the stored energy, the control electromagnet 2 is closed after the open / close switch 24 is closed.
6 to apply a magnetic field to cause the permanent current switch 22 to transition to the normal conduction state. Thereby, the superconducting coil 21
Magnetic energy stored in the vehicle can be extracted as electric power.

The above series of operations was performed at an operating current of 300 A. When this permanent current switch 22 raises the magnetic field of the control electromagnet 26 from zero, the magnetic field strength becomes 0.2.
It turned off stably at 25T, and it was possible to cut off 95% of the current. Even if the external magnetic field fluctuation speed when the switch is turned off is increased to 1 T / sec, the off magnetic field is 0.25
T was maintained and stable. This indicates that stable high-speed cutoff is possible. When the magnetic field is increased to 1T, the electric resistance of the permanent current switch 22 becomes 10
Ω.

COMPARATIVE EXAMPLE The superconducting conductor of the permanent current switch has the same configuration as that of the embodiment, except that an insulating layer of polyvinyl formal resin is applied to each superconducting element wire and normal conducting core wire according to a conventional method. Then, a permanent current switch was manufactured using the obtained material, and a superconducting magnetic energy storage device was configured using the permanent current switch. The DC critical current of the comparative example conductor was the same as in the example,
It was 570 A at 4.2 K and zero magnetic field strength.

The superconducting magnetic energy storage device was operated at an operating current of 300 A in the same manner as in the embodiment, and the external magnetic field intensity was increased from zero at an external magnetic field fluctuation speed of 1 T / sec. Has quenched.
Therefore, the external magnetic field fluctuation speed is sequentially set to 0.9 T / sec, 0.
The off-field was measured at 8 T / sec. However, until the external magnetic field fluctuation speed is reduced to 0.1 T / sec, the magnetic field strength at which the switch is turned off is from 0 T to 0.25 T.
There was variation between T and reproducibility was not obtained. Only when the external magnetic field fluctuation speed reaches 0.1 T / sec, the conductor does not quench, and a stable off-field value with good reproducibility can be obtained with a magnetic field of 0.25 T.

A comparison of the test results of the embodiment and the comparative example shows that the conventional permanent current switch using a stranded conductor having an insulating layer enables low-speed switching but unstable operation at high-speed switching. The off-field value was not stable, and there was a problem in practicality. On the other hand, in the case of using the stranded conductor of the embodiment in which the adjacent superconducting wires do not have an insulating layer and are connected to each other, even in high-speed switching, stable on / off with a constant off-field magnetic field strength is achieved. It can be seen that is possible.

Next, the energizable speeds of the permanent current switches using the stranded conductors of the embodiment and the comparative example were compared. The energization for each permanent current switch is
In each case, the current value was 300 A when the external magnetic field strength was zero. First, in the case of the permanent current switch using the stranded conductor of the comparative example, the conductor was quenched at an energizing speed of 10 kA / sec or more, and the ON state could not be maintained. At an energizing speed of up to 10 kA / sec, current could be supplied,
At this energizing speed, it takes 30 milliseconds or more to flow a current of 300 A, and there is a problem in practicality at the current flowing speed. On the other hand, in the case of the permanent current switch using the stranded conductor of the embodiment, the on state is always stably maintained even when the current is supplied at an energizing speed of 100 kA / sec, and high-speed energizing is possible. Was.

The superconducting conductor of the embodiment uses C as a superconducting material.
was used u-Nb alloy, superconducting materials that can be used in the superconductor of the present invention is not limited thereto, for example, Nb ₃ Sn, intermetallic compound superconducting material such as V ₃ Ga, NbTi etc. Alloy superconducting material, and C
A composite superconducting material in which a large number of superconducting filaments are dispersed and arranged in a metal base material having high electric resistance by adding Zn or Ni to u can also be used. Further, the normal conductive material is not limited to the Cu-Ni alloy used in the embodiment, but may be a Cu-Zn alloy, stainless steel, or the like.

[0030]

The superconducting conductor for a permanent current switch according to the present invention comprises a stranded wire in which a plurality of superconducting wires are twisted, and the superconducting wires adjacent to each other are formed without forming an electric insulating layer on each of the superconducting wires. Because they are electrically connected to each other, the magnetic field type permanent current switch using this as a wire reduces the drift between the strands and achieves stable switching with the off-field strength as designed with good reproducibility. It can be carried out. In addition, heat generated by the AC loss of the conductor when the external magnetic field fluctuates or the current flows can be effectively cooled without passing through the insulating layer, so the rise in the conductor temperature is suppressed, and high-speed switching and high-speed current Pouring becomes possible, and it can be advantageously used for a superconducting magnetic energy storage device or the like. Furthermore, the superconducting conductor for a permanent current switch according to the present invention has an advantage that the process is simplified and the cost is reduced because the insulating process is omitted when the stranded conductor is manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view perpendicular to an axis showing a superconducting conductor for a permanent current switch according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a superconducting magnetic energy storage device using the superconducting conductor of FIG.

FIG. 3 is a perspective view showing an example of a permanent current switch using the superconducting conductor of FIG. 1;

FIG. 4 is a circuit diagram showing an operation mode of an example of the superconducting magnetic energy storage device.

FIG. 5 is a circuit diagram showing another operation mode of the superconducting magnetic energy storage device shown in FIG.

FIG. 6 is a circuit diagram showing still another operation mode of the superconducting magnetic energy storage device shown in FIG.

[Explanation of symbols]

10 ... superconducting conductor for permanent current switch, 11 ... normal conducting core wire, 12 ... superconducting element wire.

Continuing on the front page (72) Inventor Satoshi Kono 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Co., Ltd. (72) Inventor Jin Honma 7-2-1, Nakayama, Aoba-ku, Aoba-ku, Sendai, Miyagi Tohoku Electric Power Stock Inside the company R & D center

Claims (1)

[Claims] 1. A superconducting element comprising a stranded conductor in which a plurality of superconducting elements are twisted, an electric insulating layer is not formed on each superconducting element, and superconducting elements adjacent to each other are electrically connected. A superconductor for permanent current switches.