JP3125474B2 - Current lead using oxide superconductor - 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 superconductor for a low-temperature side lead. Abnormal protection structure.

[0002]

2. Description of the Related Art A superconducting coil of a superconducting magnet device is cooled by a cryogenic refrigerant such as liquid helium to maintain a superconducting state. It is stored in a immersed state. Further, the current lead is cooled by a low-temperature helium gas obtained by evaporating liquid helium, and is configured to prevent intrusion heat from the normal temperature side and Joule heat generated by the current lead from entering the cryogenic portion. Conventionally, electric current conductors such as copper were used as conductors for current leads.
Copper is a good conductor at the same time as a good heat conductor, so the heat entering the cryogenic portion increases, and the vaporization loss of expensive liquid helium increases. Therefore, a current lead that uses an oxide superconductor, which is a high-temperature superconductor, on the low-temperature side of the current lead, reduces the Joule heat to zero, and at the same time, uses the low thermal conductivity to greatly reduce the heat that penetrates into the cryogenic part has been developed. Are known.

FIG. 2 is a sectional view schematically showing a conventional structure of a current lead of a superconducting magnet device. In the figure, a superconducting coil 10 has a liquid helium He inside a vacuum heat insulating container 11.
And is conductively connected to the low-temperature terminal 9A of the current lead 1 by the lead wire 10A. A pair of current leads 1 is a high temperature side lead 2 having a normal temperature terminal 2A on the top.
And a low-temperature side lead 5 having a low-temperature terminal fitting 9 are connected in series by an intermediate connection fitting 6, so that the low-temperature helium gas GHe is cooled by passing through the lead to the room-temperature terminal 2A side. The high-temperature side lead 2 is made of a highly conductive metal wire such as copper or a copper alloy, the lower end of which is conductively coupled to an intermediate connection fitting 6, as shown in a fragmentary cross section in FIG. It has a structure in which the bundles 3 are housed, and when a low-temperature helium gas GHe flows through a cooling passage formed in the gap, the heat generated from the normal temperature terminal 2A side and a current generated in the conductor 3 are generated. Discharge of heat is performed.

The low-temperature side lead 5 has a rod-shaped oxide superconductor 8 made of, for example, yttrium-based or bismuth-based, inside a cylindrical container 7 made of a low heat conductive metal or an insulating material. Conductively coupled to the intermediate connection fitting 6,
The lower end is housed in a state in which it is conductively coupled to the low-temperature terminal fitting 9,
By forming a cooling passage made of low-temperature helium gas GHe between the cylindrical container 7 and cooling the oxide superconductor 8 to a temperature lower than the liquid nitrogen temperature (about 77 K), the oxide superconductor is brought into a superconducting state. As a result, the Joule heat is reduced to zero, and the current lead 1 of the superconducting magnet device is obtained in which the heat entering the low-temperature terminal 9A is small and the consumption of liquid helium is small.

Further, a pair of current leads 1 is connected to a circuit breaker 13.
Is connected to an external power supply 13 via a power supply, and an exciting current is supplied to the superconducting coil 10 by closing the circuit breaker 13, so that the superconducting magnet device is configured to exhibit its function.

[0006]

In the current lead constructed as described above, the oxide superconductor 8 is a baked material, so that it is mechanically brittle and has high dimensional accuracy. A minute crack is generated during the assembling process of the lead 5, and this becomes a mechanical weak point, and the damage of the oxide superconductor 8 progresses, and finally, a problem occurs that the damaged portion generates heat and burns out. In addition, when the oxide superconductor absorbs moisture, it deteriorates and cannot maintain the superconducting state.
This causes a problem that heat is generated and heat entering the cryogenic portion increases. Further, the oxide superconductor has a specific resistance that is three to four orders of magnitude higher than that of copper in a normal conducting state, so that if heat generation is excessive, the oxide superconductor 8 will be burned out, making it impossible to conduct electricity. There is. Furthermore, when the supply of the low-temperature helium GHe becomes abnormal and the cooling of the oxide superconductor 8 becomes insufficient, a quench occurs in the oxide superconductor, and as a result, the oxide superconductor is burned. In some cases, power cannot be supplied.

In particular, if the heat generated due to the deterioration of the oxide superconductor progresses to the burning of the oxide superconductor,
Extensive disassembly and repair of disassembling the entire current lead and replacing it with a new oxide superconductor is necessary, which not only causes a great economic loss, but also causes the current lead itself to be unusable. An object of the present invention is to detect an abnormality of an oxide superconductor and its cause at an early stage, shut off a power supply, and prevent burning of the oxide superconductor.

[0008]

According to the present invention, there is provided a superconducting coil which is housed in a vacuum insulated container and maintained at a very low temperature, and a current which flows an exciting current from an external power supply to the superconducting coil. The lead is composed of a series connection of a high-temperature side lead made of a good conductive metal, a low-temperature side lead made of an oxide superconductor, and an intermediate connection metal fitting connecting the two, and cooled by a low-temperature refrigerant gas. And an abnormality protection means for instructing shutoff of the external power supply when a flow abnormality or a temperature abnormality of the low-temperature side lead is detected.

In addition, the abnormality protection means includes a potential difference detector for monitoring a flow abnormality of the oxide superconductor by an increase in the potential drop of the low-temperature side lead, and when the detected potential difference exceeds a predetermined level, the external power supply side A trip command shall be issued to the breaker. Further, the abnormality protection means includes a temperature detector for monitoring the temperature abnormality of the oxide superconductor by a rise in the temperature of the low-temperature side lead portion including the intermediate connection fitting, and when the detected temperature exceeds a predetermined level, the external power supply side A trip command shall be issued to the breaker.

[0010]

In the configuration of the present invention, as abnormality protection means for instructing the shutoff of an external power supply when a flow abnormality or a temperature abnormality of the low-temperature lead is detected, for example, the abnormality of the flow of the oxide superconductor is detected by the potential of the low-temperature lead. Includes a potential difference detector that monitors by increasing the drop, and an abnormal protection device that issues a trip command to the circuit breaker on the external power supply side when the detected potential difference exceeds a predetermined level.
When the Joule heat increases due to the moisture absorption deterioration of the oxide superconductor and the oxide superconductor is insufficiently cooled due to an abnormal supply of helium gas, the superconducting state of the oxide superconductor is locally broken. Since quenching occurs and the electrical resistance of the low-temperature side lead increases, the abnormality protection device as abnormality protection means detects an increase in resistance as an increase in the potential difference (potential drop) of the low-temperature side lead, and detects a circuit breaker on the external power supply side. Therefore, the function of detecting an abnormality of the oxide superconductor or its cause at an early stage to prevent the accident from spreading and preventing the oxide superconductor from burning can be obtained.

Further, the abnormality protection means includes a temperature detector for monitoring an abnormal temperature of the oxide superconductor by a rise in the temperature of the low-temperature side lead portion including the intermediate connection portion, and an external device when the detected temperature exceeds a predetermined level. If the breaker on the power supply side is configured to issue a trip command, the heat generation of the oxide superconductor and the abnormal supply of low-temperature helium gas will affect the cooling of the high-temperature side lead connected downstream of the low-temperature side lead. This causes an increase in heat intrusion from the high-temperature side lead and an increase in the temperature of the intermediate connection fitting.The temperature detector detects this and issues a trip signal to determine whether the oxide superconductor is abnormal or its cause. It is possible to obtain the function of detecting the detection at an early stage to prevent the accident from spreading and preventing the oxide superconductor from burning.

Further, if both are used in combination,
Since the protective action is performed by detecting the abnormality of the oxide superconductor or the cause of the abnormality from both the abnormal temperature rise and the potential difference rise, the abnormality of the oxide superconductor is detected earlier to prevent the spread of the accident, A higher protection function for preventing burning of the superconductor can be obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. FIG. 1 is a configuration diagram showing a main part of a current lead using an oxide superconductor 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 is omitted. I do. In the figure, a current lead 1 for passing an exciting current from an external power supply 12 to a superconducting coil 10 immersed in liquid helium He and kept at a cryogenic temperature includes a high-temperature side lead 2 made of a good conductive metal and an oxide superconducting. A low-temperature side lead 5 is connected in series with an intermediate connection fitting 6 and is cooled by low-temperature helium gas GHe, and heat generated by the high-temperature side lead 2 and heat entering from the normal temperature terminal 2A side. The superconducting magnet device has a small amount of heat entering the low-temperature terminal 9A and a small amount of liquid helium because the oxide superconductor is in a superconducting state and the Joule heat is reduced to zero. Is obtained.

On the other hand, the abnormality protection means 20 includes a potential difference detector 21 which is conductively connected to the intermediate connection fitting 6 and the low-temperature terminal fitting 9 and monitors a voltage drop generated at both ends of the low-temperature side lead 5 by a current flowing through the current lead. , Intermediate connection fitting 6
Temperature detector 23 for detecting the temperature of
And a determination circuit 24 which receives output signals of the two detectors 21 and 23, determines an abnormality thereof, and issues a trip signal 24S to the circuit breaker 13 when an abnormality is recognized.

In other words, mechanical weak points such as cracks in the oxide superconductor are enlarged, Joule heat is increased due to moisture absorption deterioration of the oxide superconductor, and insufficient cooling of the oxide superconductor is caused by abnormal supply of helium gas. When such an abnormality occurs, a quench occurs in which the superconducting state of the oxide superconductor is locally broken due to this, and the electric resistance of the low-temperature side lead increases. At this time, the increase in the electric resistance is caused by the abnormality protection means 2.
0 is detected by the potential difference detector 21 as a change in the voltage drop of the low-temperature side lead 5, and this detected value is used as a reference value (for example, 1).
When the voltage exceeds 00 μV, the determination unit 24 issues a trip command 24S to the circuit breaker 13 so that the external power supply 12
The supply of the exciting current from is interrupted. Therefore, it is possible to detect an abnormality of the oxide superconductor or its cause at an early stage, prevent the accident from spreading, and prevent burning of the oxide superconductor.

Further, if the abnormality protection means 20 is configured to include a temperature detector 23 for monitoring a temperature abnormality of the oxide superconductor by a rise in the temperature of the low-temperature side lead 5 including the intermediate connection fitting 6, the oxide superconductor is provided. And the abnormal supply of low-temperature helium gas affects the cooling of the high-temperature side lead 2 connected to the downstream side of the cooling gas of the low-temperature side lead 5, resulting in an increase in heat intrusion from the high-temperature side lead. Since the temperature of the connection fitting rises, this is detected by the temperature detector 23, and the judgment circuit 24 compares it with a reference value (for example, 80K) to generate a trip signal 24S. The function of detecting the cause at an early stage to prevent the accident from spreading and preventing the oxide superconductor from burning can be obtained.

Further, if the potential difference detector 21 and the temperature detector 23 are used in combination as the abnormality protection means 20, the abnormality of the oxide superconductor or the cause thereof can be grasped from both the abnormal temperature rise and the abnormal potential difference rise. Since the judging unit 24 performs the protection operation, there is obtained an advantage that the abnormality of the oxide superconductor can be detected earlier and the accident can be prevented from spreading and the oxide superconductor can be prevented from burning.

[0018]

As described above, the present invention includes a potential difference detector for monitoring the abnormal flow of the oxide superconductor by increasing the potential drop of the low-temperature lead, and an intermediate fitting for detecting the abnormal temperature of the oxide superconductor. It includes a temperature detector that monitors the temperature rise of the low-temperature side lead, or both, and is provided with an abnormal protection means that outputs a trip command to the circuit breaker when an abnormal voltage drop or abnormal temperature rise is detected. As a result, mechanical weak points such as cracks in the oxide superconductor are enlarged, Joule heat is increased due to moisture absorption deterioration of the oxide superconductor, and insufficient cooling of the oxide superconductor is caused by abnormal supply of helium gas. It is possible to detect an abnormality or its cause at an early stage to prevent the spread of accidents and prevent burning of the oxide superconductor. It is possible to provide a current lead having abnormal protection means capable of avoiding disassembly and repair and a great economic loss associated therewith, and maintaining the supply of the exciting current to the superconducting coil coil safely and stably.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a main part of a current lead using an oxide superconductor according to an embodiment of the present invention.

FIG. 2 is a simplified cross-sectional view showing a conventional structure of a current lead of a superconducting magnet device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Current lead 2 High temperature side lead 3 Bundle of good conductive metal wires 4 Cylindrical container 5 Low temperature side lead 6 Intermediate fitting 7 Cylindrical container 8 Oxide superconductor 9 Low temperature terminal fitting 10 Superconducting coil 11 Vacuum insulation container 12 External power supply 13 Circuit Breaker 20 Abnormality Protection Means 21 Potential Difference Detector 22 Temperature Sensor 23 Temperature Detector 24 Judgment Circuit He Liquid Helium GHe Low Temperature Helium Gas

Claims (3)

(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 kept at a cryogenic temperature comprises a high-temperature side lead made of a good conductive metal and an oxide superconductor. A low-temperature side lead, and an intermediate connection fitting for connecting both of them, which are connected in series and cooled by a low-temperature refrigerant gas. What is claimed is: 1. A current lead using an oxide superconductor, comprising: an abnormal protection means for instructing a shutoff of a power supply. 2. The abnormality protection means includes a potential difference detector for monitoring a conduction abnormality of the oxide superconductor by an increase in a potential drop of a low-temperature side lead, and when the detected potential difference exceeds a predetermined level, the external power supply side detects an abnormality. The current lead using the oxide superconductor according to claim 1, wherein a trip command is issued to the circuit breaker. 3. The abnormality protection means includes a temperature detector for monitoring an abnormal temperature of the oxide superconductor by an increase in the temperature of a low-temperature side lead portion including an intermediate metal fitting, and an external device when the detected temperature exceeds a predetermined level. 2. The current lead using an oxide superconductor according to claim 1, wherein a trip command is issued to a circuit breaker on a power supply side.