JP3032610B2 - Superconducting device current leads - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current lead for supplying a DC exciting current from an external power supply to a superconducting coil housed in a vacuum insulated container, and more particularly to a current lead using an oxide superconducting conductor for a low-temperature side lead. The present invention relates to a device for reducing invasion heat.

[0002]

2. Description of the Related Art Since a superconducting coil of a superconducting device is cooled by a cryogenic refrigerant such as liquid helium to maintain a superconducting state, it is immersed in liquid helium in a vacuum shielded container having a radiation shield using liquid nitrogen and a multilayer heat insulating layer. It is stored in the state where it was done. In addition, the current leads are self-cooled by the low-temperature helium gas, which vaporizes the liquid helium due to the heat entering the low-temperature side, preventing the heat entering from the normal temperature side and the Joule heat generated by the current leads from entering the cryogenic part. Configured to block. Conventionally, electric current conductors such as copper have been used as conductors for current leads.However, since copper is a good conductor at the same time as a good conductor, the heat that penetrates into the cryogenic part increases,
The vaporization loss of expensive liquid helium increases. Therefore,
The current lead uses an oxide-based superconductor, which is a high-temperature superconductor, on the low-temperature side of the current lead, reduces the Joule heat to zero, and uses the low thermal conductivity to greatly reduce the heat entering the cryogenic part. It has already been proposed by the applicant and the like (for example, Japanese Patent Application No. 2-84252).

FIG. 5 is a partially broken sectional view showing a simplified structure of a superconducting current lead of a superconducting device, and FIG. 6 is an enlarged sectional view showing a main part of FIG. In the figure, a superconducting coil 1 is housed in a vacuum insulated container 2 in a state of being immersed in liquid helium He, and is electrically connected to a low-temperature terminal 5A of a current lead 3 by a lead wire 6. The current lead 3 is a high-temperature side lead 4 made of a good conductor having a normal temperature terminal 4A on the top.
And a low-temperature side lead 5 having a low-temperature terminal 5A, and is cooled by the low-temperature helium gas GHe passing through the lead to the room-temperature terminal 4A side. As shown in FIG. 6, the low-temperature side lead is made of, for example, a round bar having high rigidity and low thermal conductivity such as stainless steel, manganese steel, or nichrome steel as a core material 7 and an oxide superconducting conductor 8 spirally formed on the outside thereof. And housed in an outer tube 9 made of a metal having a low thermal conductivity, forming a cooling passage with a low-temperature helium gas between the outer tube and the outer tube, and adjusting the temperature of the oxide-based superconducting conductor 8 to the temperature of liquid nitrogen (about 77 K). ) By cooling below
The oxide-based superconducting conductor is in a superconducting state and has no Joule heat when current flows. In addition, since the heat transmitted from the high-temperature side lead is blocked by the low-temperature side lead by the oxide-based superconducting conductor 8, which is a thermal insulator, the amount of heat penetrated into the low-temperature terminal 5A is small, and therefore the consumption of liquid helium is small. A current lead for the superconducting device is obtained.

[0004]

In a conventional current lead (not shown) using a good conductor, the cooling is performed by injecting heat into the low-temperature terminal while the rated current is applied to the current lead. Is vaporized, and the vaporized helium gas GHe flows through the helium gas passage in the current lead,
A self-cooling system that performs stable operation at an equilibrium temperature determined by the amount of heat entering and the amount of flowing gas has been adopted. However, when the operation method maintaining the self-cooling condition is applied to the current lead 3 using the oxide superconductor on the low temperature side as described above, the low-temperature side lead 5 prevents heat from entering the low-temperature terminal 5A, Since the amount of vaporized gas of liquid helium He decreases with the decrease in the heat of penetration, and the equilibrium temperature of the high-temperature lead 4 rises mainly with this, even when an expensive oxide-based superconductor is used for the low-temperature lead. Regardless, recent analysis results have revealed that the infiltration heat can be reduced only about 30 to 40% of that of a conventional current lead using a good conductor, and a current lead using an oxide-based superconducting conductor has become clear. There is a demand for the development of a cooling system that is suitable for the environment.

SUMMARY OF THE INVENTION An object of the present invention is to significantly reduce the amount of heat entering by adjusting the amount of low-temperature helium gas flowing through a current lead using an oxide superconductor on the low-temperature side. is there.

[0006]

According to the present invention, there is provided, in accordance with the present invention, a method of passing an exciting current from an external power supply through a superconducting coil housed in a vacuum insulated container and immersed in liquid helium. The lead is composed of a series connection of a high-temperature side lead made of a good conductive metal and a low-temperature side lead made of an oxide-based superconducting conductor, and the low-temperature helium gas vaporized from the liquid helium flows into the current lead. When the low-temperature side lead is brought into a superconducting state, the amount of flowing helium gas into the current lead is determined by the self-cooling condition when the rated current is passed through the current lead. Control means for controlling the vaporized amount of liquid helium and the amount of flowing gas is provided to control the amount of flowing gas to exceed the amount of gas. While maintaining the thermal equilibrium condition in cooling, the control means includes a flow control valve, and the flow rate is controlled by controlling the opening of the flow control valve so that the desired flow gas flows. I do.

The amount of flowing gas corresponding to the difference between the desired flowing gas amount and the flowing gas amount determined by the self-cooling condition when the rated current is passed through the current lead is increased from the vacuum insulated container. To be generated by the heat of penetration.

Further, a control device for controlling the amount of vaporized liquid and the amount of flowing gas of the liquid helium detects the temperature of the high-temperature side lead and issues a control signal of the amount of vaporized gas and a control signal of the amount of flowing gas; A heating element that is immersed in helium and receives the control signal of the amount of vaporized gas to control the amount of vaporized gas;
A flow control valve disposed on the outlet side of the flowing gas to receive the control signal for the flowing gas amount and control the flowing gas amount, and if necessary, detect a potential drop of the current lead. It is assumed that a control device that issues a control signal for a vaporized gas amount and a control signal for a flowing gas amount is combined.

[0009]

In the configuration of the present invention, the amount of flowing gas of helium gas into the current lead is set to be larger than the flowing gas amount determined by the self-cooling condition when the constant current is passed through the current lead. The current lead is forcibly cooled by a large amount of helium gas, so that the current lead is forcibly cooled by a large amount of helium gas. Since the heat entering the low-temperature side lead decreases as the temperature decreases, if the amount of flowing gas is the same as the self-cooling condition of the conventional normal conduction type current lead, the penetration heat will be reduced to the normal conduction type current lead. The function of greatly reducing to about 1/6 of that is obtained.

[0010] Further, by using the heat of invasion of the vacuum insulated container as a heat source for vaporizing the liquid helium, it is possible to forcibly cool the current lead by using a low-temperature helium gas which has not been used conventionally. Further, the control means for controlling the amount of vaporized liquid and the amount of flowing gas of liquid helium can have a simple configuration that only controls the amount of flowing gas.

Further, the control means for controlling the amount of vaporized helium gas and the amount of flowing gas includes a control device for detecting a temperature of the high-temperature side lead and generating a control signal of the amount of vaporized gas and a control signal of the amount of flowing gas; A heating element that is immersed in helium and controls the amount of vaporized gas by receiving a control signal of the amount of vaporized gas; and a heating element that is disposed at the outlet of the flowing gas and controls the amount of flowing gas by receiving the control signal of the amount of flowing gas. If it is configured with a flow rate control valve to control, a function to constantly supply the amount of flowing gas that is insufficient due to the amount of vaporized gas due to the heat entering the vacuum insulated container while monitoring the temperature change of the high-temperature side lead due to forced cooling can be obtained. Can be Further, even if the control device of the control means is configured to detect a potential drop of the current lead and generate a control signal of the amount of vaporized gas and a control signal of the amount of flowing gas, the electric resistance of the current lead due to forced cooling may be reduced. The function of stably supplying the shortage of the flowing gas amount while monitoring the decrease is obtained.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. FIG. 1 is a simplified cross-sectional view showing a current lead of a superconducting device according to an embodiment of the present invention. The same components as those in the prior art are denoted by the same reference numerals, and redundant description will be omitted. In the figure, the flowing gas amount Q of the low-temperature helium gas required for forced cooling of the current lead 3 is obtained by vaporizing the liquid helium He by receiving the penetration heat P of the current lead 3 and the penetration heat p of the vacuum heat insulating container 2. The current lead 3 flows into the helium gas passage (not shown) of the low-temperature side lead 5 from the low-temperature terminal 5A, forcibly cools the current lead 3, and is discharged to the outside from the flow control valve 14 provided near the normal temperature terminal 4A of the high-temperature side lead 4. Is done. Therefore, if the vaporized gas amount of the helium gas is equal to or more than the desired flowing gas amount Q,
The control means 11 for controlling the amount of vaporized helium gas and the amount of flowing gas (hereinafter abbreviated as control means) 11 includes a control circuit 13 which detects a temperature drop of the high-temperature side lead 4 due to, for example, forced cooling by the temperature sensor 12. The flow control valve 1 is controlled by the control signal 13A of the flowing gas amount generated based on the temperature difference.
A simple structure for controlling the opening degree of 4 may be used. Forcibly cooling the current leads by effectively utilizing the heat of penetration p of the vacuum insulated container, which has not been effectively used in the past, as a heat source for vaporizing liquid helium. it can.

FIG. 2 is a characteristic diagram of the amount of heat flowing into the current lead of the superconducting device of the present invention to explain the principle of reducing the amount of heat flowing into the current lead. Is plotted on the horizontal axis by a value obtained by converting the amount Q of gas flowing into the current lead into the amount of liquid helium. In the figure, a straight line 101 is a self-cooling curve of a current lead,
Reference numeral 02 denotes a forced cooling curve of the superconducting current lead 3 having a rated current of 1000 A using an oxide superconducting conductor on the low-temperature side lead side, and reference numeral 103 denotes a rated current 10 composed entirely of a good conductor.
00A is a forced cooling curve of a normal conduction type current lead, and points A and B on the self-cooling curve show characteristic values satisfying the self-cooling condition of both current leads, and are lower than points A and B of both forced cooling curves. Indicates a forced cooling area.

As is apparent from the figure, when the self-cooling condition is satisfied, the flowing gas amount of the normal conduction type current lead is about 1.7 (l / hr) and the penetrating heat amount is about 1.2 W (point A). On the other hand, in the superconducting current lead, the flowing gas amount is about 1 (l / h).
r), about 0.75 W (point B) of the penetrating heat becomes the equilibrium point in the self-cooling, and the reduction rate of the penetrating heat P due to the use of the expensive oxide superconductor is only 37.5%. On the other hand, the gas flowing through the superconducting current lead 3 is 1.7 (l / h).
r) When forced cooling is performed by flowing (the same amount as the self-cooling condition of the normal conduction type current lead), the thermal equilibrium condition becomes the point C, and the amount of invading heat is 1 / (1/4 of 1.2 W of the normal conduction type current lead).
The value is reduced to 0.2 W corresponding to 6. Therefore, in the embodiment apparatus shown in FIG. 1, the amount of the vaporized gas of the liquid helium due to the heat of penetration p of the vacuum heat insulating container 2 is A in FIG.
Approximately 0.7 (l / l) corresponding to the difference in the amount of flowing gas between points B and B
hr), forced cooling can be performed by effectively utilizing this, and the invading heat can be reduced to one of that of the normal conduction type current lead.
A superconducting current lead reduced to / 6 can be obtained. The flowing gas amount of the normal conduction type current lead is set to 0.7
(L / hr) is increased to 2.4 (l / hr), and forced cooling may be considered.
It is limited to about W, so that the effect of reducing the invasion heat when the superconducting current lead is forcibly cooled is far from being reduced, and the vaporization loss of liquid helium increases.

FIG. 3 is a block diagram showing a different embodiment of the present invention. A control circuit 23 of a control means 21 monitors a temperature change of a high-temperature side lead 4 by a temperature sensor 12 to control a flowing gas amount control signal 13A. And the heating power supply 25 is configured to control the current of the heating element 24 disposed in the liquid helium based on the control signal 23B. If the desired heat flowing gas amount Q cannot be obtained due to the small amount of heat p penetrating into the vacuum insulated container, a control condition is set such that the heating element 24 replenishes the liquid helium by vaporizing the liquid helium.
The current lead 3 is forcibly cooled in the same manner as in the above-described embodiment, so that heat entering the current lead 3 can be reduced.

FIG. 4 is a block diagram showing another embodiment of the present invention. The control circuit 33 monitors the potential drop between the upper and lower portions of the current lead 3 by applying a current to the current lead 3 by using a voltage detector 32. The third embodiment differs from the above-described embodiment in that a flow gas control signal 33A is output to the flow control valve 14 and a vaporized gas control signal 33B is output to the heating power supply 25 in accordance with the potential difference with respect to the reference value. Since the amount of vaporized gas of liquid helium by the heating element 24 and the opening degree of the flow control valve 14 can be controlled by utilizing the temperature dependence of the electric resistance of the current lead, insufficient vaporization due to heat entering the vacuum insulated container 2 can be performed. The current lead 3 can be forcibly cooled by replenishing the amount of gas and the amount of flowing gas without excess and deficiency, and the heat that enters can be reduced as in the above-described embodiments.

[0017]

As described above, according to the present invention, the flowing gas amount of helium gas into the current lead exceeds the flowing gas amount determined by the self-cooling condition when the rated current is passed through the current lead. Control means for controlling the amount of vaporized liquid helium and the amount of flowing gas to be controlled to the flowing gas amount is provided. As a result, the current leads are forcibly cooled by a large amount of helium gas, and the heat penetrating into the low-temperature side leads using the oxide-based superconducting conductor is reduced as the temperature of the high-temperature side leads made of a good conductor decreases. Since the amount of flowing gas is the same as the self-cooling condition of the conventional normal conduction type current lead,
The heat of penetration is reduced to nearly 1/6 that of the normal current lead in the self-cooling condition. Therefore, the problem of the prior art that the intruding heat cannot be reduced despite the use of the expensive oxide-based superconducting conductor is eliminated, and a superconducting device having a superconducting current lead with little invading heat can be provided. .

Further, if the heat of vaporization of the liquid helium is used as the heat of vaporization of the liquid helium, the amount of flowing gas exceeding the self-cooling condition can be secured without requiring a special heat source. Therefore, there is obtained an advantage that the current lead is forcibly cooled by utilizing the helium gas which has not been conventionally used, and the invasion heat can be reduced. Also, the control means for controlling the amount of vaporized liquid and the amount of flowing gas of the liquid helium only needs to control the amount of flowing gas, and a superconducting current lead having high cooling performance can be provided economically and advantageously. .

Further, the control means for controlling the amount of vaporized helium gas and the amount of flowing gas includes a control device for detecting the temperature of the high-temperature side lead and generating a control signal of the amount of vaporized gas and a control signal of the amount of flowing gas; A heating element that is immersed in helium and controls the amount of vaporized gas by receiving a control signal of the amount of vaporized gas; and a heating element that is disposed at the outlet of the flowing gas and controls the amount of flowing gas by receiving the control signal of the amount of flowing gas. If it is configured with a controlled flow rate control valve, the amount of flowing gas that is insufficient due to the amount of vaporized gas due to the heat of penetration of the vacuum insulated container is supplied stably without excess or shortage while monitoring the temperature change of the high-temperature side lead due to forced cooling. Thus, there is obtained an advantage that unnecessary vaporization loss of liquid helium can be eliminated. Further, even if the control device of the control means is configured to detect a potential drop of the current lead and generate a control signal of the amount of vaporized gas and a control signal of the amount of flowing gas, the electric resistance of the current lead due to forced cooling may be reduced. The shortage of the flowing gas amount can be stably supplied while monitoring the decrease, and the advantage that unnecessary vaporization loss of liquid helium can be eliminated is obtained.

[Brief description of the drawings]

FIG. 1 is a simplified sectional view showing a current lead of a superconducting device according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram of infiltration heat versus flowing gas amount for explaining the principle of reducing intrusion heat in the current lead of the superconducting device of the present invention.

FIG. 3 is a block diagram showing a different embodiment of the present invention.

FIG. 4 is a block diagram showing another embodiment of the present invention.

FIG. 5 is a partially broken cross-sectional view showing a simplified structure of a superconducting current lead of a superconducting device.

FIG. 6 is an enlarged sectional view showing a main part of FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Superconducting coil 2 Vacuum heat insulation container 3 Current lead 4 High temperature side lead 5 Low temperature side lead (using oxide superconducting conductor) 7 Core material 8 Oxide superconducting conductor 11 Control means of vaporized gas amount and flowing gas amount 12 Temperature sensor 13 Control circuit 14 Flow control valve 13A Flowing gas amount control signal 21 Control means of vaporized gas amount and flowing gas amount 23 Control circuit 23B Vaporized gas amount control signal 24 Heating element 25 Heating power supply 31 Volume of vaporized gas and flowing gas amount Control means 32 Voltage detector

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeo Kumagai 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. No. 1 Inside Fuji Electric Co., Ltd. (72) Yasuzou Tanaka 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Naoki Uno 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Masanao Mimura 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Hitoshi Shimizu 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric (56) References JP-A-55-16487 (JP, A) JP-A-2-256206 (JP, A) JP-A-63-133507 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 39/00 H01L 39/04 H01F 6/00 H01F 6/06 H01B 12/00-12/16

Claims (4)

(57) [Claims] A current lead for passing an exciting current from an external power supply to a superconducting coil housed in a vacuum insulated container and immersed in liquid helium includes a high-temperature-side lead made of a highly conductive metal, and an oxide-based superconductor. A low-temperature side lead made of a conductor, which is connected in series, and the low-temperature side lead is brought into a superconducting state by flowing a low-temperature helium gas in which the liquid helium is vaporized into the current lead; Liquid helium vaporization for controlling the amount of flowing helium gas into the inside to a desired amount of flowing gas exceeding the amount of flowing gas determined by self-cooling conditions when the rated current is passed through the current lead. Means for controlling the flow rate and the amount of flowing gas, while maintaining the thermal equilibrium conditions in the forced cooling at the desired flowing gas amount, the control means Comprising a quantity regulating valve, the current lead of a superconducting device, wherein the desired flowing gas amount by controlling the opening degree of the flow rate control valve is adjusted so that flows. 2. A flow-through gas amount corresponding to a difference between a desired flow-through gas amount and a flow-through gas amount determined by a self-cooling condition when a rated current is passed through a current lead, from the vacuum insulated container. 2. The current lead for a superconducting device according to claim 1, wherein the current lead is formed so as to be generated by invasion heat. 3. A control device for controlling the amount of vaporized liquid and the amount of flowing gas of liquid helium to generate a control signal of the amount of vaporized gas and a control signal of the amount of flowing gas by detecting the temperature of the high-temperature side lead; A heating element that is immersed in helium and controls the amount of vaporized gas by receiving the control signal of the amount of vaporized gas; and a heating element that is disposed on the outlet side of the flowing gas and controls the amount of flowing gas by receiving the control signal of the amount of flowing gas. 2. The current lead for a superconducting device according to claim 1, comprising a flow control valve to be controlled. 4. The superconducting device according to claim 3, wherein the control device detects a potential drop of the current lead and generates a control signal of a vaporized gas amount and a control signal of a flowing gas amount. Lead.