HK1089868B - Super-conductive cable operation method and super-conductive cable system - Google Patents

Description

Superconducting cable operation method and superconducting cable system

Technical Field

The present invention relates to a method of operating a superconducting cable and a superconducting cable system, and more particularly, to a method of operating a superconducting cable that provides increased capacity without an additional cable.

Background

One transmission path using a common conductive cable is composed of a plurality of loops for accommodating a fault (for example, non-patent document 1). For example, a path may consist of three loops, in which case the maximum transmission capacity provided by all the loops may be 3E, while the maximum capacity of each cable loop is 1.5E, so that in the event that one loop is unavailable due to a fault, the remaining two loops can still provide 3E of transmission capacity.

Basically, when it is desired to increase the power demand of an area, the transmission of power commensurate with the increased demand can only be achieved by installing additional cables.

Non-patent document 1: IIZUKA, Kihachiro, "cable technology Handbook, New Edition, denkishoon co., ltd., 3/25 1989, first Edition, pages 14-17.

Disclosure of Invention

Problems to be solved by the invention

The conventional operation using a common conductive cable reveals the following problems:

(1) overdesign of the cable installation results in increased costs of cable installation.

Conventional techniques for ordinary conductive cables can achieve a transmission capacity of 3E during normal operation using three loops, the transmission capacity per loop being E. However, consideration of the transmission capacity at the time of failure requires that the design capacity per cable be 1.5E, which brings more effort in the design than the design for the normal capacity. This results in an increase in the cost of cable erection.

(2) Additional cables may not be easily installed

In some countries, newly installing a transmission line having a voltage of a predetermined value or higher may require the consent of residents living near the installation site. In such a case, even when it is desired to increase the power demand, additional cables cannot be easily installed, making it difficult to accommodate the increased demand, and engineering costs are naturally required if additional installation is allowed.

In view of the above problems, a primary object of the present invention is to provide a method of operating a superconducting cable, which can adjust transmission capacity in an inexpensive manner without overdesign of cable erection or additional cables.

It is another object of the present invention to provide a superconducting cable system suitable for implementing the above method.

In order to achieve the above object, the present invention employs a superconducting cable maintained at a constant temperature instead of a variable refrigerant temperature.

The method of operating a superconducting cable according to the present invention transmits power using a conductor cooled by a refrigerant, characterized in that the transmission capacity of the superconducting cable is changed by changing the temperature of the refrigerant.

In the conventional development of the superconducting cable, it is emphasized that a constant refrigerant temperature is maintained to stabilize the superconducting state of the conductor. However, the superconducting material has a property that the critical current increases as the temperature decreases, as shown in the graph of fig. 3. This graph shows that the ratio of the critical current Ic to Ic0 (Ic/Ic0) is inversely proportional to the temperature, Ic0 being the critical current at 77K, where the temperature of the Bi2223 superconducting material is varied. That is, for a particular refrigerant temperature (T) during normal operation_O) The refrigerant temperature can be reduced below T_OTo increase the transmission capacity of the superconducting cable, and conversely, the temperature of the refrigerant can be raised to T_OIn order to reduce the transmission capacity. Thus, by changing the refrigerant temperature, the transmission capacity of the superconducting cable can be changed.

This variable transmission capacity can be utilized in a number of different modes. One mode relates to a case of increasing the power demand, in which the refrigerant temperature can be lowered below the temperature of normal operation to increase the transmission capacity of the superconducting cable, thereby providing power transmission matching the increased power demand.

In some countries, new installation of a transmission line having a voltage of a predetermined value or more may require consent of residents living in the vicinity of the installation point, so that it may be less easy to install additional cables when it is desired to increase the power demand, and also requires a great deal of expense and time when installation of additional cables is allowed. The method of the present invention can utilize the existing superconducting cable for transmission without an additional cable, thereby increasing power capacity with little cost and in a short time.

In the case where the power demand is reduced, the transmission capacity of the superconducting cable can also be reduced by raising the refrigerant temperature. This can reduce the cost of cooling the superconducting cable and thus can reduce the cost required to run the superconducting cable.

Of course, it is also possible to combine the lowering and raising of the refrigerant temperature strategically, in which case the power demand of the load connected to the superconducting cable can be monitored, and the temperature of the refrigerant can be lowered/raised to increase/decrease the power capacity in accordance with the increase/decrease in the power demand.

Another mode of utilizing variable transmission capacity involves the case where one of the superconducting cable loops fails so that transmission cannot be performed on the failed loop, in which case the transmission capacity of the remaining good loop(s) can be increased above before the failure. More specifically, when one of the plurality of superconducting cable circuits fails, the refrigerant temperature of the good circuit(s) that did not fail may be reduced below the temperature before the failure occurs, thereby increasing the transmission capacity of the good circuit(s). The good circuit(s) transmit power after the fault occurs that is greater than the respective capacity transmitted by the good circuit(s) prior to the fault occurring.

For example, assuming that there are three superconducting cable loops and the transmission capacity of each loop is E, transmission of a capacity of 3E is generally possible. When one of the superconducting cable circuits fails and becomes unusable, operation at a constant refrigerant temperature should only enable transmission at a capacity of 2E. In view of this, the refrigerant temperatures of the remaining two good circuits can be lowered to increase the transmission capacity of the good circuits to a level before the failure or higher (2E or higher), thereby achieving a larger power (current) capacity.

For the above mentioned modes, variable refrigerant temperature can be provided in several ways.

One approach involves first cooling the refrigerant using a chiller with a high cooling capacity. For example, if the refrigerant is liquid nitrogen and the refrigerant's normal operating temperature T_OSlightly below its boiling point, the refrigerator need only have a maintenance T_OThe required capacity. When the power demand increases or the fault circuit requires an increase in the transmission capacity of the superconducting cable, it is necessary to cool the refrigerant to not more than T_OThe temperature of (2). To achieve this, the refrigerator can be cooled substantially below the freezing point of the refrigerant. When the refrigerant is cooled below freezing, it freezes and cannot be circulated. Thus, the refrigerator need only have the ability to cool substantially to the freezing point of the refrigerant.

In addition, the refrigerant may be replaceable, in which case the refrigerant having a higher freezing point may be replaced with another refrigerant having a lower freezing point, and a refrigerator having the capability of cooling to substantially the same or lower freezing point than the refrigerant having a higher freezing point may be used. For example, when the transfer capacity is to be increased during an operation using liquid nitrogen as a refrigerant having a higher freezing point, the refrigerant may be replaced with liquid air (i.e., a refrigerant having a lower freezing point), and the temperature of the refrigerant may be lowered below the temperature at the time of the operation with liquid nitrogen. This approach enables the refrigerant temperature to be adjusted over a wide range, so that the transfer capacity can be more widely varied.

Such a refrigerant replacement, which may take several days, is more suitable for increasing the transmission capacity of the superconducting cable, for example, in advance to meet the expected future increase in power demand, and is less suitable for coping with a failure of one of the circuits by increasing the transmission capacity of a good circuit.

Furthermore, when one of the circuits fails, the refrigerant for the good circuit(s) can also be cooled using the refrigerator used by the failed circuit. More specifically, when there are a plurality of superconducting cable circuits, each having its own refrigerator for cooling the refrigerant, and one of the circuits fails, both the refrigerator for the failed circuit and the refrigerator for the good circuit(s) can be used to cool the refrigerant used by the good circuit(s) to a temperature lower than that before the failure. This approach presupposes that the refrigerator for the failed circuit is still available, while the superconducting cable in the circuit is not available due to the failure. For example, when one of the three superconducting cable circuits becomes unavailable, the cryocoolers for all circuits, i.e., the three cryocoolers, may be used to cool the refrigerant for the remaining two good circuits, thereby achieving more efficient refrigerant cooling.

In any of the above cases, the cryogen may be any fluid capable of being cooled to the temperature required to maintain the conductor in a superconducting state. In particular, materials having a large difference between the boiling point and the freezing point are preferable because they enable the transmission capacity of the superconducting cable to be changed in a wide range by changing the temperature of the refrigerant while keeping the refrigerant in a liquid state. The difference between the boiling point and the freezing point is desirably 5 ℃ or more, more preferably 10 ℃ or more. In general, liquid nitrogen, liquid air, liquid hydrogen, liquid neon, liquid helium, or liquid oxygen may be used. In particular, liquid air has a boiling point of about 79K and a freezing point of 55K, and shows a large difference between the boiling point and the freezing point, and has a freezing point lower than that of liquid nitrogen (boiling point of about 77K, freezing point of about 63K), and thus is a preferred refrigerant for increasing the transmission capacity of the superconducting cable. It should be noted that any boiling and freezing points identified herein are values measured at atmospheric pressure.

One aspect of a superconducting cable system using the method of the present invention is characterized in that: a superconducting cable; a cooling mechanism that cools a refrigerant used by the superconducting cable; a circulating transport mechanism that circularly transports the refrigerant cooled by the cooling mechanism to the superconducting cable; and a refrigerant temperature control mechanism that adjusts the temperature of the refrigerant according to the power demand of the load connected to the superconducting cable.

The cooling mechanism may be a refrigerator that cools the refrigerant. Generally, the circulating delivery mechanism may be a pump. The refrigerant temperature control mechanism may have a load current detection means and a temperature control means that controls the temperature in the cooling mechanism according to the load current detected by the detection means.

Another aspect of a superconducting electrical cable system using the method of the present invention is characterized in that: a plurality of superconducting cables; a cooling mechanism that cools the refrigerant used by the respective superconducting cables; a circulating transport mechanism that circularly transports the refrigerant cooled by the cooling mechanism to the superconducting cable; and a refrigerant passage switching mechanism that blocks supply of the refrigerant to the unusable superconducting cables and causes supply of the refrigerant to the remaining good superconducting cables when one of the superconducting cables becomes unusable.

The refrigerant passage switching mechanism may include a pipe that provides communication of the refrigerant passage between the superconducting cable of the refrigerant outflow end of the cooling mechanism and the superconducting cable of the refrigerant inflow end of the circulating conveying mechanism, and a valve provided on or along the pipe to block supply of the refrigerant to the unusable superconducting cable.

As described above, the method of operating a superconducting cable of the present invention can achieve the adjustment of the cable transmission capacity in an inexpensive manner and does not require overdesign of cable erection or additional cables.

Further, the superconducting cable system of the present invention is adapted to realize the above-described method.

Drawings

FIG. 1 is a schematic view of a superconducting electrical cable system of the present invention;

fig. 2 is a cross-sectional view of a superconducting cable used in the line of fig. 1;

FIG. 3 is a graph showing the inverse ratio of critical current to temperature of a superconductor;

fig. 4 shows the load current detection means and the temperature control means.

Description of the reference numerals

10 framework, 20 conducting layer, 30 electric insulating layer, 40 magnetic shielding layer, 50 protective layer, 60 heat insulation pipe, 61 inner corrugated pipe, 62 outer corrugated pipe, 70 anticorrosive layer, 110, 120, 130 superconducting cable, 211-

Detailed Description

Embodiments of the present invention are described below. Before describing the method of operating a superconducting cable of the present invention, a superconducting cable line in which the method of the present invention can be applied will be described first.

[ superconducting cable line ]

A schematic view of a superconducting cable line of the present invention is given in fig. 1. Referring to fig. 1, the line includes three superconducting cable circuits 110, 120, and 130 and a cooling system circulating a refrigerant to be supplied to the superconducting cable circuits 110, 120, and 130. Although not shown in fig. 1, the superconducting cables 110, 120, and 130 have one terminal connected to a power source and the other terminal connected to a load.

(superconducting Cable)

Fig. 2 shows a cross-sectional view of a three-core integrated superconducting cable used in a loop in the line of fig. 1. Referring to fig. 2, the cable is made up of three cores contained within an insulated tube. A cable loop is made up of three phases, each phase corresponding to a core. Each core includes (from the center to the outside) a former 10, a conductive layer 20, an electrically insulating layer 30, a magnetic shield layer 40, and a protective layer 50, wherein the conductive layer 20 and the magnetic shield layer 40 are made of superconducting wires.

< framework (former) >

The frame 10 may be a solid frame made of twisted metal wires, or may be a hollow frame, and a metal pipe may be used as the hollow frame. An example of a solid skeleton is a plurality of copper wires twisted together. The framework of twisted construction enables a reduction in alternating current losses and a minimization of temperature increase due to overloading. If a hollow frame is used, the interior thereof can be used as a passage for the refrigerant.

< conductive layer >

A suitable conductive layer 20 is a tape wire having a plurality of oxidized high temperature superconducting filaments coated with a silver sheath. Bi2223 strip was used here. The tape wire is wound around the former in multiple layers to form a superconducting layer 20. The superconducting layers 20 have different superconducting wire winding pitches for their respective layers. Furthermore, the winding direction may be changed for each or every one of its layers so that a uniform current flows uniformly in the layers.

< interlayer insulating layer (not shown) >

Interlayer insulating layers are provided between the innermost superconducting layer in the conductive layer 20 and the former 10, between the layers forming the conductive layer 20, and between the layers forming the magnetic shield layer 40. The interlayer insulating layer is formed by kraft paper winding each layer of the conductive layer 20 or each layer of the magnetic shield layer 40. The interlayer insulating layer makes the conductive layer 20 and the magnetic shield layer 40 electrically independent from each other.

< electrically insulating layer >

An electrically insulating layer 30 is disposed around the electrically conductive layer 20. The insulating layer 30 may be formed by laminating, for example, kraft paper with, for example, polypropylene (pplp (r), produced by Sumitomo electric industries, ltd., or the like) resin film wound around the conductive layer 20.

< magnetic shield layer >

The ac superconducting cable includes a magnetic shield layer 40 disposed outside the insulation layer 30 for shielding a magnetic field. The magnetic shield layer 40 is formed by winding a superconducting wire similar to that used for the conductive layer around the outside of the insulating layer 30. A current of substantially equal magnitude but opposite direction to the current in the conductive layer 20 is induced in the magnetic shield layer 40 to cancel the externally generated magnetic field.

< protective layer >

Further, a protective layer 50 is provided on the magnetic shield layer 40. The protective layer 50 serves to mechanically protect the magnetic shield layer 40 and the structure therein, and is formed by winding kraft paper or color tape on the magnetic shield layer 40.

< Heat-insulating pipe >

The thermal insulation piping 60 is of a double piping structure having an inner bellows 61 and an outer bellows 62. Generally, a space is established between the inner and outer bellows 61 and 62, and a vacuum is applied to the space. A superior (trademark) is provided in the space where the vacuum is applied to reflect radiant heat. The space defined by the inner corrugated tube 61 and the core may be used as a refrigerant passage. For example, the refrigerant passage for the return may be formed by a space inside the hollow frame and a space inside the inner bellows. Further, a corrosion prevention layer 70 of, for example, polyvinyl chloride is provided on the outer bellows 70.

(Cooling System)

Referring to fig. 1, the cooling system includes: a refrigerator 211 213 for cooling the refrigerant; a pump 221 and 223 for circulating the refrigerant; a refrigerant piping system connecting the refrigerator or the pump with the superconducting cables 110, 120 and 130; and a plurality of valves 231, 233, 241, 243, 251, 252, 261, 263 arranged on the refrigerant piping system.

In this cooling system, the refrigerant cooled by the refrigerator 211-. The number of refrigerators 211-213 and pumps 221-223 used here corresponds to the number of circuits. Specifically, three refrigerators 211-213 and three pumps 221-223 are used, each connected in series with the associated pump by a conduit. The pipe extending from the refrigerator at the refrigerant outflow end is connected to one end of the superconducting cables 110, 120 and 130 via the valve 231 and 233, wherein the pipes between the refrigerator 221 and the valve 231, between the refrigerator 212 and the valve 232, and between the refrigerator 213 and the valve 233 are communicated with each other to provide a connected refrigerator passage between the circuits, and the valves 251 and 252 are provided on the connecting pipe. The other end of each superconducting cable 110, 120 and 130 is connected to a refrigerant outflow piping system that is joined together by a valve 261 and 263 and leads to a pump at one end of the cable. The merging line leading to the pumps is divided into three branches which are connected via valves 261 and 263 to the respective pumps 221 and 223. In this way, a connected refrigerant passage may be provided at the refrigerant outflow end of the refrigerator 211-213 and the refrigerant inflow end of the pump 221-223, thereby sending the refrigerant cooled by any one of the refrigerator 211-213 to any one of the superconducting cable circuits 110-130.

In this example, the refrigerant is liquid air (boiling point: about 79K, freezing point: 55K), and each of the refrigerators 211-213 can cool to the freezing point of the liquid air.

As needed, a refrigerant temperature control mechanism that adjusts the refrigerant temperature according to the power demand of the loads connected to the superconducting cables 110, 120, and 130 may be provided. Fig. 4 shows a load current detection means and a temperature control means constituting the refrigerant temperature control mechanism. Referring to fig. 4, a general conductive cable is connected to both ends of the ultra-electric cables 110, 120 and 130. Load current detecting members 271, 272 and 273 are provided on those general conductive cables near the load to measure the load current. The load current detecting means 271, 272 and 273 are connected to the corresponding temperature control means 281, 282 and 283. The temperature control means 281, 282, and 283 control the temperature of the refrigerant in their respective refrigerators 211, 212, and 213 according to the value of the load current measured by the respective load current detection means 271, 272, and 273.

Note that, in fig. 4, the double lines between the refrigeration machines 211, 212, and 213 and the respective superconducting cables 110, 120, and 130 indicate refrigerant paths. The single line between the load current detection members 271, 272, and 273 and the corresponding temperature control members 281, 282, and 283 represents the path of the detection signal, and the single line between the temperature control members 281, 282, and 283 and the corresponding refrigerators 211, 212, and 213 represents the path of the control signal.

[ operating method ]

< first embodiment >

A method of operating based on a change in power demand of a load connected to the superconducting cable will be described below.

In the circuit of fig. 1, during normal operation, the refrigerator temperature is slightly below, for example, 77K, and all circuits are operational. During such normal operation, the valves 251 and 252 provided on the associated piping for the circuit's refrigeration machine passages are closed, while the other valves 231-. When the power demand of the load increases, the temperature set for the refrigerator 211-213 is adjusted to lower the temperature of the refrigerant. For example, as is evident from the graph in FIG. 3, cooling to about 68K will result in a critical current that is 1.5 times the critical current under normal operation. Generally, power is transmitted at a constant voltage. The current capacity is increased by a factor of 1.5 and thus the transmission capacity is increased by a factor of 1.5. Furthermore, cooling to 60K or less will result in a critical current twice that of normal operation, resulting in a larger capacity for transmission.

In this way, the operating method reduces the refrigerant temperature so that approximately twice the transfer capacity in normal operation is achieved in a simple manner. In particular, the existing superconducting cable can be advantageously utilized to increase the power capacity of transmission without additional cables.

Further, when the power demand is reduced, the transmission capacity of the superconducting cable can be reduced by increasing the refrigerant temperature. Although this requires the superconducting wire to be able to maintain a superconducting state at an elevated refrigerant temperature, the cost of cooling the superconducting cable can be reduced, resulting in a reduction in the cost required to operate the superconducting cable.

Also, the load current Ip may be measured and the refrigerant temperature T may be repeatedly adjusted such that Ip is α × Ic (α is a margin, where α < 1), Ic is a critical current of the superconducting cable. This approach operates at the highest possible refrigerant temperature depending on the margin between the load current and the critical current in order to reduce the load on the refrigeration system. Of course, the refrigerant temperature is adjusted between the boiling point and the freezing point of liquid air.

< second embodiment >

Now, a description is given of a case where one loop fails to become unavailable and the remaining good loop transmits. Assume that one of the three superconducting cable loops 130 shown in fig. 1 fails to become unusable and transmission can only be performed by the remaining two loops. It is further assumed that the entire cooling system is good and usable, although the superconducting cable in the fault circuit 130 is not usable.

Initially, the switching state of each valve during normal operation before the occurrence of a failure is the same as in the first embodiment.

When the superconducting cable 130 becomes unavailable, the three refrigerators 211-. For this purpose, the refrigerant supply valve 233 and the refrigerant outflow valve 243 of the failed circuit are closed to isolate the failed circuit from the cooling system, while the valves 251 and 261 on the connected piping system are opened and all the pumps 221 and 223 are driven to circulate the refrigerant. In this way, the refrigerant sent to the two good circuits is cooled/circulated by means of the three refrigerators 211-213 and the three pumps 221-223.

In this way, a cooling system capable of supplying refrigerant to three circuits is used to supply refrigerant to two circuits, achieving efficient cooling of the refrigerant. As a result, the refrigerant temperature can be easily lowered below before the failure, thereby achieving an increase in the transmission capacity of the good circuit. For example, when the individual circuits are operating at a refrigerant temperature slightly below 77K before the failure, the refrigerant temperature of the good circuits after the failure may be about 68K to ensure that the transfer capacity of each circuit is about 1.5 times that before the failure, so that two good circuits can achieve transfer with a capacity matching that of the three circuits before the failure.

Of course, it is also possible that two refrigerators and two pumps circulate the refrigerant to be supplied to the two good circuits, in which case each refrigerator may have the capability of cooling the refrigerant for one circuit to a temperature of the capacity increasing operating state (about 68K). In this case, valves 233 and 243 at both ends of the fault circuit are closed to isolate the fault circuit from the cooling system. Further, the valve 263 at the refrigerant inflow end of the valve 223 is closed to isolate the refrigerator 213 and the pump 223 from the cooling system. The refrigeration machines 211, 212 and pumps 221, 222 are then used to deliver refrigerant for cooling/circulating the superconducting cables 110, 120.

It is to be understood that the above disclosed embodiments are illustrative and exemplary in all respects, and not restrictive. The scope of the present invention is set forth by the claims, rather than the description above, and is intended to cover all modifications within the spirit and scope equivalent to the spirit and scope of the claims.

Industrial applicability

The present invention provides a variable refrigerant temperature for varying the transmission capacity of a superconducting cable during operation. Thus, when an increase in power demand is desired, the increased demand can be satisfied without additional cables, or, when one of the plurality of loops fails and transmission can be performed only by the remaining loop, transmission can be performed with a transmission capacity equal to or close to the level before the failure. Thus, the present invention can be effectively utilized in an area to which electric power is to be supplied.

Claims (9)

1. A method of operating a superconducting cable that transmits electric power using a conductor cooled by a refrigerant, characterized in that transmission capacities of a plurality of superconducting cables (110, 120, 130) are changed by changing a temperature of the refrigerant,

a plurality of the superconducting cables constitute a circuit of the superconducting cables, each of the circuits has a refrigerator for cooling a refrigerant of the circuit, and when a failure occurs in one of the circuits, the refrigerator of the failed circuit and the refrigerator of the good circuit in which no failure occurs are used to supply the refrigerant to the good circuit.

2. The method of operating a superconducting cable according to claim 1, wherein when a power demand of a load connected to the superconducting cable (110, 120, 130) increases, the refrigerant temperature is decreased to increase a transmission capacity of the superconducting cable (110, 120, 130) to transmit power matching the power demand.

3. The method of operating a superconducting cable according to claim 1, wherein when a power demand of a load connected to the superconducting cable (110, 120, 130) is lowered, the temperature of the refrigerant is raised to lower a transmission capacity of the superconducting cable (110, 120, 130) to transmit power matching the power demand.

4. The method of operating a superconducting cable of claim 1,

when one of the circuits fails, the refrigerant temperature of the good circuit is lowered to a temperature lower than that before the failure to increase the transmission capacity of the good circuit.

5. The method of operating a superconducting cable of claim 4, wherein the temperature of the good loop is reduced to a temperature below the temperature before failure.

6. The method of operating a superconducting cable according to claim 1, wherein a refrigerator (211, 212, 213) having a capability of cooling to a freezing point of the refrigerant is used to change a temperature of the refrigerant between a boiling point and a freezing point of the refrigerant.

7. The method for operating a superconducting cable according to claim 1, wherein the high freezing point refrigerant is replaced with a low freezing point refrigerant having a freezing point lower than that of the high freezing point refrigerant, and a refrigerator (211, 212, 213) capable of cooling the high freezing point refrigerant to a freezing point or below is used, and the temperature of the low freezing point refrigerant is changed between the boiling point and the freezing point of such low freezing point refrigerant.

8. The method of operating a superconducting cable of claim 1, wherein the refrigerant is one of liquid nitrogen, liquid air, liquid hydrogen, liquid neon, liquid helium, and liquid oxygen.

9. A superconducting electrical cable system characterized by: comprises that

A plurality of superconducting cables (110, 120, 130);

cooling mechanisms that cool refrigerants used by the respective superconducting cables (110, 120, 130), the cooling mechanisms being respectively mounted to the plurality of superconducting cables;

a circulating transport mechanism that circulates the refrigerant cooled by the cooling mechanism to the superconducting cables (110, 120, 130); and

a refrigerant passage switching mechanism that, when one of the superconducting cables (110, 120, 130) becomes unavailable, blocks the supply of the refrigerant to the unavailable superconducting cable and causes the supply of the refrigerant to the remaining good superconducting cable.