JP6180735B2 - Cooling system and cooling method for superconducting device - Google Patents

Description

  The present invention relates to a technical field of a cooling system and a cooling method for a superconducting device in which a liquefied gas is circulated in a circulation loop in a subcooled state in order to cool a superconducting device such as a superconducting cable.

  There is a phenomenon called superconductivity in which the electrical resistance suddenly becomes zero when a material such as a specific metal, alloy, or compound is cooled to a very low temperature. Superconducting cables that apply superconducting technology to power transmission cables use superconducting wires as current-carrying conductors and can flow large currents with a small cross-sectional area. It has gained attention because of its advantages such as improved efficiency.

  The superconducting cable is cooled by circulating a liquefied gas such as liquid nitrogen in a circulation loop. Here, when the circulating liquefied gas is vaporized in the insulator constituting the superconducting cable, it becomes a starting point of dielectric breakdown. Therefore, in this type of cooling system, it is necessary to circulate the liquefied gas while maintaining the subcooled state. Generally, the minimum pressure of the liquefied gas circulating in the cooling system is about 0.2 MPaG or more, which is a pressure at which partial discharge does not occur in the withstand voltage test.

  The pressure control of the circulated liquefied gas is performed by a reservoir tank provided on the circulation loop. In Patent Document 1, a method of applying pressure by supplying high-pressure nitrogen gas from a gas cylinder provided outside the reservoir tank into the reservoir tank, or heating the vapor phase portion of the reservoir tank with a heating means such as a heater, A method is described in which a part of the liquefied gas stored in the reservoir tank is vaporized and pressurized.

JP 2006-12654 A

  Since superconducting cables have good power transmission efficiency, they may be installed over a wide range including areas that are difficult to access, such as remote locations. Therefore, the superconducting cable cooling device is required to be capable of stable operation in the long term with as little maintenance as possible.

  In Patent Document 1, since it is necessary to supply nitrogen gas from a gas cylinder provided outside the reservoir tank, when the remaining amount of nitrogen gas in the gas cylinder decreases, replenishment work of nitrogen gas or replacement work of the gas cylinder, etc. Maintenance work is required. Further, since the nitrogen gas supplied from the gas cylinder is liquefied in the reservoir tank, the total amount of liquefied gas (liquid nitrogen) in the cooling system increases. Therefore, it is necessary to discharge the excess liquefied gas, which is wasteful.

Moreover, in patent document 1, when the pressure of a reservoir tank becomes high, pressure reduction is implemented by releasing the nitrogen gas vaporized in the reservoir tank outside. However, when nitrogen gas is released to the outside in this way, the liquefied gas in the entire cooling system is reduced, so that maintenance work for replenishing the shortage from the outside is required.
Thus, in the cooling system of Patent Document 1, various maintenance operations are required to maintain the cooling performance.

Moreover, when heating and pressurizing with a heater, power consumption is required to operate the heater. Therefore, even if good power transmission efficiency is obtained with the superconducting cable to be cooled, the power transmission efficiency in the entire system is reduced by the amount of power consumed by the heater.
Further, when the pressure in the reservoir tank is controlled by turning on / off the heater, a large time lag occurs between the pressure change in the reservoir tank. Specifically, when the heater is stopped, it takes a certain amount of time for the temperature in the reservoir tank to drop. Therefore, it is difficult for the pressurizing method using the heater to accurately control the reservoir tank within an appropriate pressure range.

  An object of at least some embodiments of the present invention is to provide a cooling system and a cooling method for a superconducting device that consumes less power and can be stably operated over a long period of time.

  A cooling system for a superconducting device according to an embodiment of the present invention includes a reservoir tank that stores liquefied gas, a circulation pump that circulates the liquefied gas stored in the reservoir tank, and cooling that cools the circulated liquefied gas. A cooling system for a superconducting device comprising a circulation loop having a device and cooling the superconducting device by circulating the liquefied gas in a subcooled state, wherein the cooling system is introduced through a first bypass line branched from the circulation loop. The liquefied gas is vaporized by a heat exchanger provided on the first bypass line and supplied to the upper portion of the reservoir tank, and to the second bypass line branched from the circulation loop. The reservoir tank is introduced by introducing vaporized gas in the reservoir tank and condensing in the second bypass line. Depressurizing means for depressurizing, pressure detecting means for detecting the pressure in the reservoir tank, and control means for operating the first pressurizing means and the depressurizing means based on a detection value of the pressure detecting means. It is characterized by that.

In the above cooling system, when the pressure in the reservoir tank decreases, the pressure is increased by the first pressurizing unit, while when the pressure in the reservoir tank increases, the pressure is decreased by the depressurizing unit. Thereby, the pressure in the reservoir tank can be controlled within a predetermined range, and the liquefied gas flowing through the circulation loop can be maintained in the subcooled state.
Since the first pressurizing means performs pressurization by vaporizing a part of the liquefied gas flowing through the circulation loop and supplying it to the reservoir tank, it is not necessary to replenish the liquefied gas from the outside. Further, since the liquefied gas can be vaporized by exchanging heat with, for example, the outside air using a heat exchanger, the power consumption can be reduced.
Since the decompression means decompresses the vaporized gas by introducing a part of the vaporized gas in the reservoir tank into the second bypass line and condensing it, there is no need to replenish the liquefied gas from outside the system. At this time, the decompression means condenses the vaporized gas present in the reservoir tank by bringing it into contact with the liquefied gas present in the second bypass line. For this reason, the vaporized gas in the reservoir tank is not discharged outside the system.
Therefore, in the cooling system, the pressure in the reservoir tank can be maintained in an appropriate range while effectively using the liquefied gas flowing through the circulation loop. In this way, it is possible to provide a cooling system for a superconducting device that consumes less power and can be stably operated over a long period of time.

In one embodiment, the control means activates the first pressurizing means when the detection value of the pressure detection means is less than a preset first threshold value, and detects the detection value of the pressure detection means. When the pressure becomes equal to or higher than the second threshold value set higher than the first threshold value, the pressure reducing means is operated.
In the cooling system, the pressure in the reservoir tank is accurately controlled to be equal to or higher than the first threshold value and lower than the second threshold value by operating the first pressurizing unit and the depressurizing unit based on the detection value of the pressure detecting unit. can do.

In one embodiment, the control means introduces the vaporized gas in the reservoir tank into the second bypass line by switching a pressure control valve provided in the second bypass line to an open state. Activate the decompression means.
In the cooling system, the pressure in the reservoir tank can be reduced to an appropriate range by controlling the open / close state of the pressure control valve provided in the second bypass line by the control means. For example, by adopting PID control for opening / closing control of the pressure control valve by the control means, even when the pressure in the reservoir tank rises, the second threshold value can be satisfactorily controlled.

The cooling system for a superconducting device according to an embodiment further includes a second pressurizing unit that pressurizes the reservoir tank by heating the liquefied gas stored in the reservoir tank, and the control unit includes: When the detection value of the pressure detection means becomes less than the third threshold set lower than the first threshold, the second pressurization means is operated.
In the cooling system, when the pressure in the reservoir tank becomes less than the third threshold value, the second pressurizing unit is operated to assist the pressurization performance by the first pressurizing unit, The pressure in the reservoir tank can be maintained within an appropriate range.
Since the second pressurizing means needs to heat the liquefied gas, the power consumption is larger than that of the first pressurizing means. Therefore, the pressure in the reservoir tank is maintained within an appropriate range while suppressing the power consumption by operating the second pressurizing unit only when the pressurizing performance by the first pressurizing unit is insufficient. can do.
Further, even when the first pressurizing unit is stopped due to some reason, the reservoir tank can be pressurized by operating the second pressurizing unit as a backup. Thereby, even when a malfunction occurs in the cooling system, the pressure in the reservoir tank can be maintained in an appropriate range, and the reliability can be improved. When the first pressurizing unit is stopped and the pressurization is controlled only by the second pressurizing unit, the pressure in the reservoir tank is increased with reference to a third threshold value lower than the first threshold value. However, it is possible to effectively prevent the cooling system from causing a serious failure due to an extremely low pressure in the reservoir tank.

A cooling system for a superconducting device according to an embodiment is configured to pressurize the reservoir tank by supplying the same kind of gas as the liquefied gas to the reservoir tank through a pressure regulating valve from a gas cylinder storing high-pressure gas. Pressurizing means, and when the detected value of the pressure detecting means falls below a fourth threshold set lower than the third threshold, the control means controls the third pressurizing means. Operate.
In the cooling system, when the pressure in the reservoir tank becomes less than the fourth threshold value, the third pressurizing unit is activated to apply pressure by the first pressurizing unit and the second pressurizing unit. By further assisting the pressure performance, the pressure in the reservoir tank can be maintained in an appropriate range.
Since the third pressurizing means supplies the vaporized gas from the gas cylinder to the reservoir tank, when the remaining gas in the gas cylinder decreases, maintenance such as replenishment work or replacement work of the gas cylinder is required. For this reason, the third pressurizing unit is operated only when the pressurizing performance is still insufficient even by the first pressurizing unit and the second pressurizing unit, thereby suppressing the gas consumption of the gas cylinder and performing maintenance. The pressure in the reservoir tank can be maintained within an appropriate range while reducing the frequency.
In addition, even if the first pressurizing unit and the second pressurizing unit are stopped due to a failure for some reason, the reservoir tank is pressurized by operating the third pressurizing unit as a backup. Can do. Thereby, even when a malfunction occurs in the cooling system, the pressure in the reservoir tank can be maintained in an appropriate range, and a cooling system having better reliability can be realized. When the first pressurizing unit and the second pressurizing unit are stopped and the pressurization is controlled only by the third pressurizing unit, the pressure in the reservoir tank is lower than the third threshold value. Although the pressure is increased based on the threshold value, it is possible to effectively prevent the cooling system from causing a serious failure due to the extremely low pressure in the reservoir tank.

  In one embodiment, the first bypass line branches from the upstream side of the pump in the circulation loop.

  In one embodiment, the second bypass line branches off from the upstream side of the reservoir tank in the circulation loop.

In one embodiment, the superconducting device is a superconducting cable.
The above cooling system can be applied to a superconducting device that requires stable operation over a long period of time with a small maintenance burden, such as a superconducting cable used for long-distance power transmission.

A cooling method for a superconducting device according to an embodiment of the present invention includes a reservoir tank that stores liquefied gas, a circulation pump that circulates the liquefied gas stored in the reservoir tank, and cooling that cools the circulated liquefied gas. A cooling method for a superconducting device comprising a circulation loop having a device and cooling the superconducting device by circulating the liquefied gas in a subcooled state, the step of detecting the pressure in the reservoir tank, and the detected pressure When it becomes less than a preset first threshold, the liquefied gas introduced through the first bypass line branched from the circulation loop is supplied to the second bypass line provided on the first bypass line. Vaporizing with a heat exchanger and supplying to the upper part of the reservoir tank;
When the detected pressure is higher than the first threshold and equal to or higher than a preset second threshold, the vaporized gas in the reservoir tank is introduced into the second bypass line branched from the circulation loop, And a step of depressurizing the reservoir tank by condensing inside the second bypass line.
The superconducting device cooling method according to an embodiment heats the liquefied gas stored in the reservoir tank when the detected pressure becomes lower than a third threshold set lower than the first threshold. Thus, the method further includes the step of pressurizing the reservoir tank.
In the cooling method for a superconducting device according to an embodiment, the pressurization speed is adjusted by providing a flow rate adjustment valve for the gas obtained by heating the liquefied gas.
The cooling method for a superconducting device according to an embodiment stores a gas of the same type as the liquefied gas at a high pressure when the detected pressure is lower than a fourth threshold set lower than the third threshold. The method further includes the step of pressurizing the reservoir tank by supplying the reservoir tank from the gas cylinder via the pressure regulating valve.

  The cooling method for the superconducting device can be implemented by the above-described cooling system for the superconducting device (including the various aspects described above).

In the above cooling system, when the pressure in the reservoir tank decreases, the pressure is increased by the first pressurizing unit, while when the pressure in the reservoir tank increases, the pressure is decreased by the depressurizing unit. Thereby, the pressure in the reservoir tank can be controlled within a predetermined range, and the liquefied gas flowing through the circulation loop can be maintained in the subcooled state.
Since the first pressurizing means performs pressurization by vaporizing a part of the liquefied gas flowing through the circulation loop and supplying it to the reservoir tank, it is not necessary to replenish the liquefied gas from the outside. Further, since the liquefied gas can be vaporized by exchanging heat with, for example, the outside air using a heat exchanger, the power consumption can be reduced.
Since the decompression means decompresses the vaporized gas by introducing a part of the vaporized gas in the reservoir tank into the second bypass line and condensing it, there is no need to replenish the liquefied gas from outside the system. At this time, the decompression means condenses the vaporized gas present in the reservoir tank by bringing it into contact with the liquefied gas present in the second bypass line. For this reason, the vaporized gas in the reservoir tank is not discharged outside the system.
Therefore, in the cooling system, the pressure in the reservoir tank can be maintained in an appropriate range while effectively using the liquefied gas flowing through the circulation loop. In this way, it is possible to provide a cooling system for a superconducting device that consumes less power and can be stably operated over a long period of time.

It is a conceptual diagram which shows the whole structure of a cooling system. It is sectional drawing which shows typically the internal structure of the pressure control valve in a 1st pressurization means. It is a flowchart which shows the control content of a cooling system. It is a figure which shows notionally the pressure range which each pressurization means and pressure reduction means operate | move. It is a flowchart which shows the detail of operation | movement control of a pressure reduction means. It is an example of the map which prescribes | regulates the relationship between deviation (PP ^* 2) and the operation amount MV of a pressure control valve. It is a graph which shows an example of the relationship between the operation amount MV by a control part, and the opening degree of a pressure control valve. An example of the pressure change of the reservoir tank when the pressure reducing means is operated will be shown. It is a flowchart which shows the detail of the control content in a 2nd pressurizing means.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, and are merely illustrative examples. Only.

  FIG. 1 is a conceptual diagram showing the overall configuration of the cooling system 100. The cooling system 100 has a superconducting cable 110 as an object to be cooled, and a circulation loop 130 is provided through which liquid nitrogen, which is a liquefied gas for cooling the superconducting cable 110, circulates.

  Liquid nitrogen is stored in the reservoir tank 120 and connected to the circulation pump 140 via a line 131 communicating with the reservoir tank 120. Circulation pump 140 pumps liquid nitrogen to cooler 150 via line 132. The liquid nitrogen cooled by the cooler 150 is supplied to the superconducting cable 110 via the line 133, and the superconducting cable 110 is cooled. The liquid nitrogen after cooling the superconducting cable 110 is returned to the reservoir tank 120 via the line 134. As described above, the lines 131 to 134 form a circulation loop 130, and the liquid nitrogen inside is circulated through the circulation loop 130 by the circulation pump 140.

  The reservoir tank 120 includes a storage tank 121 in which liquid nitrogen is stored, and an exterior part 122 provided outside the storage tank 121. The space between the storage tank 121 and the exterior part 122 is decompressed by a vacuum pump (not shown) and is thermally insulated by vacuum. The storage tank 121 has a gas phase portion 123 on the liquid nitrogen surface, and the gas phase portion 123 is filled with nitrogen gas obtained by vaporizing liquid nitrogen.

The first bypass line 161 branches a part of the liquid nitrogen flowing through the circulation loop 130 from the line 132 and supplies it to the heat exchanger 162. The heat exchanger 162 vaporizes the supplied liquid nitrogen, for example, by exchanging heat with the outside air, and generates nitrogen gas. In the first bypass line 161, a pressure control valve 163 is provided on the downstream side of the heat exchanger 162, and the tip communicates with the gas phase portion 123 of the reservoir tank 120. The pressure control valve 163 opens when the pressure (reservoir tank internal pressure) downstream of the pressure control valve 163 in the first bypass line 161 falls below a predetermined value (pressure target value P ^* 1 described later) This valve has a pressure adjustment mechanism that closes when the pressure is exceeded. Further, an adjustment valve 167 is provided on the upstream side of the heat exchanger 162, and a mechanism capable of changing the pressurization speed of the reservoir tank 120 by adjusting the liquefied gas supply amount is provided.

Here, FIG. 2 is a sectional view schematically showing the internal configuration of the pressure control valve 163. The pressure control valve 163 includes a valve body 164, a spring 165, and a diaphragm 166, and is disposed in the middle of the first bypass line 161. Since the downstream side of the first bypass line 161 communicates with the reservoir tank 120, the pressure is substantially equal to the gas phase portion 123 in the reservoir tank 120. Therefore, when the pressure in the reservoir tank 120 becomes lower than a predetermined value (a first threshold value P ^* 1, which will be described later), the force applied to the diaphragm 166 is reduced, and the valve body 164 is pushed downward in the figure by the spring 165. The pressure control valve 163 is opened. Then, nitrogen gas flows from the upstream side to the downstream side of the first bypass line 161 and is pressurized to a predetermined value P ^* 1 by being supplied into the reservoir tank 120.
When the pressure in the reservoir tank 120 is increased to a predetermined value (a pressure target value P ^* 1 described later), the valve body is pushed up together with the spring 165 by the diaphragm 166, and the pressure control valve 163 is closed. Become. Then, the supply of nitrogen gas from the upstream side to the downstream side of the first bypass line 161, that is, the pressurizing operation is stopped.
As described above, the nitrogen gas generated by the heat exchanger 162 is supplied to the reservoir tank 120 according to the opening degree of the pressure control valve 163 so that the reservoir tank 120 can be pressurized. Thus, the first bypass line 161, the heat exchanger 162, and the pressure control valve 163 constitute the first pressurizing means 160.

Returning again to FIG. 1, the second bypass line 171 communicates the line 134 with the gas phase portion 123 of the reservoir tank 120, and a pressure control valve 172 is provided on the way. The pressure control valve 172 is an electromagnetic valve whose opening degree can be controlled by the control means 220 described later. When the pressure control valve 172 is in the open state, the nitrogen gas staying in the gas phase portion 123 of the reservoir tank 120 is introduced into the second bypass line 171.
The nitrogen gas introduced into the second bypass line 171 is condensed by contacting the liquid nitrogen existing in the second bypass line 171 and the reservoir tank 120 is depressurized. As described above, the second bypass line 171 and the pressure control valve 172 constitute the pressure reducing means 170.

  The gas phase portion 123 of the reservoir tank 120 is provided with a radiation plate 181 provided substantially parallel to the liquid nitrogen liquid level stored in the storage tank 121, and a heater 182 for heating the radiation plate 181. ing. The radiating plate 181 is heated by the heater 182 to supply radiant heat to liquid nitrogen and vaporize the liquid nitrogen to generate nitrogen gas. Thereby, the reservoir tank 120 can be pressurized. Thus, the radiation plate 181 and the heater 182 constitute the second pressurizing means 180.

The cooling system 100 has a gas cylinder 191 filled with high-pressure nitrogen gas. The nitrogen gas in the gas cylinder 191 is supplied to the reservoir tank 120 through the supply line 193 through the pressure control valve 192. Thus, the reservoir tank 120 can be pressurized by supplying high-pressure nitrogen gas to the gas phase portion 123. As described above, the gas cylinder 191, the pressure control valve 192, and the supply line 193 constitute the third pressurizing unit 190.
The pressure control valve 192 is a pressure adjustment valve that opens when the pressure (reservoir tank pressure) downstream of the pressure control valve 192 in the supply line 193 falls below a predetermined value (pressure target value P ^* 4 described later). is there. The specific configuration of the pressure control valve 192 is the same as the pressure control valve 163 in the first pressurizing means described above.

  The pressure in the gas phase portion 123 of the reservoir tank 120 is detected by the pressure sensor 200. The temperature of the radiation plate 181 is detected by the temperature sensor 210.

  The control unit 220 is a control unit for controlling the cooling system 100, acquires detection values from the pressure sensor 200 and the temperature sensor 210, and according to the values, the opening degree of the pressure control valve 172 and the heater 182. Are controlled to operate or stop the decompression means 170 and the second pressurization means 180, respectively. In the example of FIG. 1, the control unit 220 includes a first pressurizing unit 160 and a third pressurizing unit 190 that use pressure control valves that operate based on downstream pressure (internal pressure of the reservoir tank 120). By transmitting and receiving a control signal to an ON / OFF changeover switch (not shown) provided for each, the operating state of these pressurizing means can be controlled.

FIG. 3 is a flowchart showing the control contents of the cooling system 100.
First, the control unit 220 acquires the detection value P from the pressure sensor 200 and also acquires the pressure target value P ^* 1 from storage means such as a memory (not shown) (step S101). Here, the pressure target value P ^* 1 is a first threshold value used when the pressure in the reservoir tank 120 is controlled by the first pressurizing means 160.

The controller 220 determines the magnitude relationship between the detected value P and the pressure target value P ^* 1 based on the data acquired in step S201 (step S102). When the detected value P is equal to or lower than the pressure target value P ^* 1 (P <P ^* 1), the control unit 220 determines that the pressure in the reservoir tank 120 needs to be increased to approach the pressure target value P ^* 1. Then, operation control of various pressurizing means is performed.

The controller 220 first activates the first pressurizing means 160 (step S103). The first pressurizing unit 160 is configured to open and close the pressure control valve 163 based on the pressure difference between the upstream side and the downstream side of the pressure control valve 163 disposed in the first bypass line 161, thereby Is pressurized by supplying nitrogen gas to the reservoir tank 120 via the first bypass line 161 so that the pressure becomes the pressure target value P ^* 1.
In the case where an electromagnetic valve is used as the pressure control valve 163, the controller 220 may be configured to switch and control the open / closed state of the electromagnetic valve.
The first pressurizing means 160 performs pressurization by vaporizing a part of the liquid nitrogen flowing through the circulation loop 130 and supplying it to the reservoir tank, so there is no need to replenish liquid nitrogen or nitrogen gas from the outside. Maintenance burden is small. In the first pressurizing means 160, heat is exchanged between the liquid nitrogen and the outside air by the heat exchanger 162, and nitrogen gas can be generated without supplying energy from the outside, so that power consumption can be reduced. .

On the other hand, when the detected value P is equal to the pressure target value P ^* 1, the control unit 220 stops the first pressurizing unit 160 because it is not necessary to pressurize the reservoir tank 120 (step S104).

After operating the first pressurizing unit 160 in this way, the control unit 220 acquires the detection value P again and also acquires the pressure target value P ^* 3 from a storage unit such as a memory (not shown) (step S105). ). Here, the pressure target value P ^* 3 is a third threshold value used when the pressure in the reservoir tank 120 is controlled by the second pressurizing means 160, and is set smaller than the pressure target value P ^* 1 described above. Yes.

The controller 220 determines whether or not the detected value P is lower than the pressure target value P ^* 3 (step S106). When the detected value P is lower than the pressure target value P ^* 3 (step S106: YES), it is difficult to pressurize the pressure in the reservoir tank 120 to an appropriate range with only the pressurizing ability of the first pressurizing means 160. Judging, the 2nd pressurizing means 180 is operated (step S107). The second pressurizing means 180 heats the radiation plate 181 with the heater 182, thereby vaporizing the liquid nitrogen stored in the storage tank 121 by radiant heat and pressurizing the reservoir tank 120.

Unlike the first pressurizing unit 160 described above, the second pressurizing unit 180 consumes electric power for heating by the heater 182. Therefore, by operating the second pressurizing unit 180 only when the pressurizing performance by the first pressurizing unit 160 is insufficient, the pressure in the reservoir tank 120 is appropriately controlled while suppressing power consumption. Can be kept in range.
Further, even if the first pressurizing unit 160 is stopped due to some cause or the like, the reservoir tank 120 can be pressurized by operating the second pressurizing unit 180 as a backup. Thereby, even when a malfunction occurs in the cooling system 100, the pressure in the reservoir tank 120 can be maintained in an appropriate range, and the reliability can be improved. Incidentally, when the first pressurizing means 160 has pressure control only by the second pressurizing unit 180 is stopped, the pressure in the reservoir tank 120 is pressure target value P ^※ 1 lower pressure target value P ^※ Since the pressure is increased with reference to 3, the pressure in the reservoir tank 120 is not drastically reduced by setting P ^* 3 to an appropriate value, and the cooling system 100 is prevented from falling into a serious failure. Can do.

On the other hand, when the detected value P is equal to or greater than the pressure target value P ^* 3 (step S106: NO), the control unit 220 determines that the reservoir tank 120 can be pressurized only by the operation of the first pressurizing means 160. Then, the second pressurizing means 180 is stopped (step S108).

After operating the second pressurizing means 180 in this way, the control unit 220 obtains the detection value P again and obtains the pressure target value P ^* 4 from storage means such as a memory (not shown) (step S109). ). Here, the pressure target value P ^* 4 is a fourth threshold value used when the pressure in the reservoir tank 120 is controlled by the third pressurizing means 190, and is set smaller than the pressure target value P ^* 3. Yes.

The controller 220 determines whether or not the detected value P is lower than the pressure target value P ^* 4 (step S110). When the detected value P is lower than the pressure target value P ^* 4 (step S110: YES), the pressure in the reservoir tank 120 is set appropriately only by the pressurizing ability of the first pressurizing means 160 and the second pressurizing means 180. It is determined that it is difficult to pressurize the range, and the third pressurizing means 190 is activated (step S111). The third pressurizing means 190 is configured to open and close the pressure control valve 192 based on the pressure difference between the upstream side and the downstream side of the pressure control valve 192 disposed in the supply line 193, so that the pressure in the reservoir tank 120 is increased. Pressurization is performed by supplying nitrogen gas from the gas cylinder 191 to the reservoir tank 120 via the supply line 193 so that the pressure target value P ^* 4 is obtained.
When a solenoid valve is used as the pressure control valve 192, the controller 220 may be configured to switch and control the open / closed state of the solenoid valve.

Since the third pressurizing means 190 supplies nitrogen gas from the gas cylinder 191 to the reservoir tank 120, maintenance such as replenishment work or replacement work of the gas cylinder 191 is required when the remaining gas in the gas cylinder 191 decreases. . Therefore, by operating the third pressurizing unit 190 only when the pressurizing performance is still insufficient even by the first pressurizing unit 160 and the second pressurizing unit 180, the gas consumption amount of the gas cylinder 191 is reduced. It is possible to maintain the pressure in the reservoir tank 120 within an appropriate range while suppressing the maintenance frequency.
Even if the first pressurizing unit 160 and the second pressurizing unit 180 are stopped due to some reason, the reservoir tank 120 is operated by operating the third pressurizing unit 190 as a backup. Can be pressurized. Thereby, even when a malfunction occurs in the cooling system 100, the pressure in the reservoir tank 120 can be maintained in an appropriate range, and the cooling system 100 having better reliability can be realized. When the first pressurizing unit 160 and the second pressurizing unit 180 are stopped and the pressurization is controlled only by the third pressurizing unit 190, the pressure in the reservoir tank 120 is the pressure target value P ^*. Although the pressure is increased with reference to the pressure target value P ^* 4 lower than 3, it is possible to effectively prevent the cooling system from causing a serious failure due to the extremely low pressure in the reservoir tank 120.

On the other hand, when the detected value P is equal to or greater than the pressure target value P ^* 4 (step S110: NO), the control unit 220 performs only the operation of the first pressurizing unit 160 and the second pressurizing unit 180, and the reservoir tank It is determined that the pressure in 120 can be increased to an appropriate range, and the third pressurizing means 190 is stopped (step S112).

When it is determined in step S102 that the detected value P is larger than the pressure target value P ^* 1 (P> P ^* 1), the control unit 220 makes the pressure in the reservoir tank 120 approach the pressure target value P ^* 1. Therefore, it is determined that the pressure needs to be reduced, and the operation of the pressure reducing means 170 is controlled.

The control unit 220 acquires the detection value P again and also acquires the pressure target value P ^* 2 from storage means such as a memory (not shown) (step S113). Here, the pressure target value P ^* 2 is a second threshold value used when the pressure in the reservoir tank 120 is controlled by the pressure reducing means 170.
The controller 220 determines whether or not the detected value P is higher than the pressure target value P ^* 2 (step S114). When the detected value P is higher than the pressure target value P ^* 2 (step S114: YES), the decompression means 170 is operated to decompress the reservoir tank 120 (step S115). The decompression means 170 introduces nitrogen gas existing in the gas phase portion 123 of the reservoir tank 120 into the second bypass line 171 by adjusting the opening degree of the pressure control valve 172, and the second bypass line 171 is condensed and depressurized by contact with liquid nitrogen present in 171.

  Since the decompression means 170 decompresses the nitrogen gas in the reservoir tank 120 by introducing it into the second bypass line 171, there is no need to replenish liquid nitrogen from the outside. At this time, the decompression means 170 circulates the liquid nitrogen generated by being introduced into the second bypass line 171 and condensing together with the liquid nitrogen flowing through the circulation loop 130, so that the nitrogen gas is discharged outside the system and is wasted. There is no need to make it.

On the other hand, when the detected value P is equal to or less than the pressure target value P ^* 2 (step S114: NO), the controller 220 stops the pressure reducing means 170 because it is not necessary to reduce the pressure of the reservoir tank 120 (step S116).

  Control of the cooling system 100 by the control part 220 demonstrated above is repeatedly performed at a fixed or indefinite timing. Thereby, the pressure of the liquid nitrogen which flows through the circulation loop 130 can be made into an appropriate range, and a subcooled state can be maintained.

FIG. 4 is a diagram conceptually showing a pressure range in which each pressurizing means and decompressing means operate.
As described with reference to FIG. 3, when the pressure in the reservoir tank 120 becomes lower than the first pressure target value P ^* 1, the first pressurizing means 160 operates. When the pressure in the reservoir tank 120 becomes lower than the third target pressure value P ^* 3, the second pressurizing means 180 is further activated. When the pressure in the reservoir tank 120 becomes lower than the fourth pressure target value P ^* 4, the third pressurizing means 190 further operates.
In this way, by operating the first pressurizing means 160, the second pressurizing means 180, and the third pressurizing means 190 in order as the pressure in the reservoir tank 120 deviates from the appropriate pressure range, It is controlled so that the operating period of the third pressurizing means 190, which requires the supply of nitrogen gas from the outside during the operation, is shortened. As a result, it is possible to realize the cooling system 100 that can be operated stably over a long period of time even if it is unattended. Further, nitrogen gas and power consumption can be suppressed.

On the other hand, when the pressure in the reservoir tank 120 becomes higher than the second pressure target value P ^* 2, the pressure reducing means 170 is activated. As described above, in the cooling system 100, when the pressure in the reservoir tank 120 is decreased, the pressure is increased by each pressurizing unit, and when the pressure in the reservoir tank 120 is increased, the pressure is decreased by the depressurizing unit 170. Thereby, the pressure in the reservoir tank 120 can be controlled within a predetermined range (P ^* 4 <P <P ^* 2), and the liquefied gas flowing through the circulation loop 130 can be maintained in the subcooled state. Note that P ^* 1, P ^* 3, and P ^* 4, which are pressurization control set values of the pressure of the reservoir tank 120, may be set in the range of, for example, 0.15 to 0.2 MPa.
Therefore, in the cooling system 100, the pressure in the reservoir tank 120 can be maintained in an appropriate range while effectively using the liquid nitrogen flowing through the circulation loop 130. Thus, it is possible to provide a cooling system 100 for a superconducting device that consumes less power, has high reliability, and can be operated stably over a long period of time.

FIG. 5 is a flowchart showing details of operation control of the decompression means 170.
The control unit 220 acquires the detection value P from the pressure sensor 200 and also acquires the pressure target value P ^* 2 from storage means such as a memory (not shown) (step S201). Then, to calculate the difference (P-P ^※ 2), based on a map prepared in advance, obtains the manipulated variable MV of the pressure control valve 172 corresponding to the deviation (P-P ^※ 2) (step S202).
FIG. 6 is an example of a map that defines the relationship between the deviation (P−P ^* 2) and the operation amount MV of the pressure control valve 172. The manipulated variable MV tends to increase proportionally as the deviation (PP ^* 2) increases, and is kept constant when the deviation (PP ^* 2) reaches a predetermined value.

The control unit 220 adjusts the opening degree by operating the pressure control valve 172 according to the obtained operation amount MV, so that the nitrogen gas introduced into the second bypass line 171 from the gas phase unit 123 of the reservoir tank 120. Is controlled (step S203). FIG. 7 is a graph showing an example of the relationship between the operation amount MV by the control unit 220 and the opening degree of the pressure control valve 172.
As described above, the decompression unit 170 depressurizes the reservoir tank 120 by adjusting the amount of nitrogen gas introduced from the reservoir tank 120 into the second bypass line 171 to condense the nitrogen gas in the gas phase portion 123. .

FIG. 8 shows an example of a pressure change in the reservoir tank 120 when the decompression means 170 is operated. In FIG. 8, the solid line indicates the pressure value in the reservoir tank 120, and the broken line indicates the opening degree of the pressure control valve 172.
As shown in FIG. 8, the controller 220 can maintain the pressure in the reservoir tank 120 at an appropriate value by increasing or decreasing the opening degree of the pressure control valve 172.

FIG. 9 is a flowchart showing details of control contents in the second pressurizing means 180.
First, the control unit 220 acquires the detection value P from the pressure sensor 200, acquires the detection value T from the temperature sensor 210, and obtains the pressure target value P ^* 3 and the temperature target value T ^* from storage means such as a memory (not shown). Obtain (step S301). Here, the pressure target value P ^* 3 is a target value used when the pressure in the reservoir tank 120 is controlled by the second pressurizing means 180. The temperature target value T ^* is a target value used when controlling the temperature of the radiation plate 181 required to achieve the pressure target value P ^* 3.

Based on the data acquired in step S301, the controller 220 determines whether or not the detected value P is higher than the pressure target value P ^* 3 (step S302). If the detected value P is higher than the target pressure value P ^※ 3 (step S302: YES), the control unit 220 subtracts the correction value T _beta temperature target value T ^※, decreasing the temperature set point T ^※ (Step S303) . On the other hand, if the detected value P is equal to or less than the target pressure value P ^※ 3 (step S302: NO), the control unit 220 further detection value P is determined whether pressure target value P ^※ 3 is smaller than (Step S304) . If the detected value P is pressure target value P ^※ 3 smaller (step S304: YES), the control unit 220 of the correction value T _alpha addition to the temperature target value T ^※, increasing the temperature target value T ^※ (step S305).

Subsequently, the control unit 220 determines whether or not the detected value T from the temperature sensor 210 is larger than the temperature target value T ^* based on the temperature target value T ^* changed based on the detected value P from the pressure sensor 200 in this way. Is determined (step S306). If the detected value T is higher than the target temperature T ^※ (step S306: YES), the control unit 220 subtracts the correction value I _beta to the current target value I ^※, it decreases the current target value I ^※ (step S307). On the other hand, when the detected value T is equal to or lower than the temperature target value T ^* (step S306: NO), the control unit 220 further determines whether or not the detected value T is smaller than the temperature target value T ^* (step S308). If the detected value T is pressure target value T ^※ smaller (step S308: YES), the control unit 220 a correction value I _alpha added to the current target value I ^※, increasing the current target value I ^※ (step S309).

The second pressurizing means 180 performs PID control so that the current value I of the drive current applied to the heater 182 becomes the current target value I ^* set in this way (step S310). Thereby, the pressure in the reservoir tank 120 is pressurized so as to become the pressure target value P ^* 3.

Thus, by setting the target of the current value (current target value I ^* ) for directly controlling the output of the heater 182 based on the deviation between the detected value P of the pressure sensor 200 and the pressure target value P ^* 3. By the ON / OFF control of the heater 182, the pressure in the reservoir tank 120 can be made to accurately follow the target value.

  As described above, in the cooling system 100 according to the present embodiment, the pressure in the reservoir tank 120 can be maintained in an appropriate range while effectively using the liquefied gas flowing through the circulation loop 130. Thus, it is possible to provide the cooling system 100 that consumes less power and can be stably operated over a long period of time.

  INDUSTRIAL APPLICABILITY The present invention can be used for a cooling system and a cooling method for a superconducting device in which a liquefied gas is circulated in a circulation loop in a subcooled state in order to cool a superconducting device such as a superconducting cable.

DESCRIPTION OF SYMBOLS 100 Cooling system 110 Superconducting cable 120 Reservoir tank 121 Reservoir 122 Exterior part 123 Gas phase part 130 Circulation loop 131-134 Line 140 Circulation pump 150 Cooler 160 First pressurization means 161 Bypass line 162 Heat exchanger 163 Pressure control valve 170 Pressure reducing means 171 Bypass line 172 Pressure control valve 180 Second pressurizing means 181 Radiation plate 182 Heater 190 Third pressurizing means 191 Gas cylinder 192 Pressure control valve 193 Bypass line 200 Pressure sensor 210 Temperature sensor 220 Controller

Claims (14)

A reservoir tank for storing the liquefied gas; a circulation pump for circulating the liquefied gas stored in the reservoir tank; and a circulation loop having a cooling device for cooling the liquefied gas to be circulated. A superconducting device cooling system for cooling the superconducting device by circulating,
The liquefied gas introduced through the first bypass line branched from the circulation loop is vaporized by a heat exchanger provided on the first bypass line, and supplied to the upper portion of the reservoir tank. Pressurizing means;
Cooling of a superconducting device having functional means for depressurizing the reservoir tank by introducing vaporized gas in the reservoir tank into a second bypass line branched from the circulation loop and condensing in the second bypass line system.   A pressure detection means for detecting the pressure in the reservoir tank, and a control means for operating the first pressurization means and the pressure reduction means based on a detection value of the pressure detection means. The cooling system for a superconducting device according to claim 1.   The control means activates the first pressurizing means when a detection value of the pressure detection means is less than a preset first threshold value, and the detection value of the pressure detection means is the first detection value. The cooling system for a superconducting device according to claim 2, wherein the pressure reducing means is operated when the pressure becomes equal to or higher than a second threshold set higher than the threshold.   The control means switches the pressure control valve provided in the second bypass line to an open state, thereby introducing the vaporized gas in the reservoir tank into the second bypass line and operating the pressure reducing means. The cooling system for a superconducting device according to claim 2. A second pressurizing means for pressurizing the reservoir tank by heating the liquefied gas stored in the reservoir tank;
The control means operates the second pressurizing means when a detection value of the pressure detecting means becomes less than a third threshold set lower than the first threshold. Item 4. The superconducting device cooling system according to Item 3. A temperature detecting means for detecting the temperature in the reservoir tank;
The control means calculates a target temperature value based on a deviation between a detection value of the pressure detection means and a preset target pressure value, and the detection value of the temperature detection means becomes the calculated target temperature value. The superconducting device cooling system according to claim 5, wherein the second pressurizing unit is controlled as described above. A third pressurizing unit that pressurizes the reservoir tank by supplying the same type of gas as the liquefied gas from a gas cylinder storing the gas at a high pressure to the reservoir tank via a pressure regulating valve;
The control means activates the third pressurizing means when a detected pressure value of the pressure detecting means becomes less than a fourth threshold set lower than the third threshold. The cooling system for a superconducting device according to claim 5.   The cooling system for a superconducting device according to claim 1, wherein the first bypass line is branched from the upstream side of the pump in the circulation loop.   2. The cooling system for a superconducting device according to claim 1, wherein the second bypass line is branched from the upstream side of the reservoir tank in the circulation loop.   The superconducting device cooling system according to claim 1, wherein the superconducting device is a superconducting cable. A reservoir tank for storing the liquefied gas; a circulation pump for circulating the liquefied gas stored in the reservoir tank; and a circulation loop having a cooling device for cooling the liquefied gas to be circulated. A superconducting device cooling method for cooling a superconducting device by circulating,
Detecting the pressure in the reservoir tank;
When the detected pressure is less than a preset first threshold, the liquefied gas introduced through the first bypass line branched from the circulation loop is provided on the first bypass line. Vaporizing with a second heat exchanger and supplying it to the upper part of the reservoir tank;
When the detected pressure is higher than the first threshold and equal to or higher than a preset second threshold, the vaporized gas in the reservoir tank is introduced into the second bypass line branched from the circulation loop, And a step of reducing the pressure of the reservoir tank by condensing inside the second bypass line.   Pressurizing the reservoir tank by heating the liquefied gas stored in the reservoir tank when the detected pressure falls below a third threshold set lower than the first threshold; The method for cooling a superconducting device according to claim 11, further comprising: The flow rate of the liquefied gas guided to the second heat exchanger via the first bypass line is adjusted by an adjustment valve provided in the first bypass line on the upstream side of the second heat exchanger. The method of cooling a superconducting device according to claim 11, wherein the method is adjusted .   When the detected pressure falls below a fourth threshold set lower than a third threshold, a gas cylinder storing the same kind of gas as the liquefied gas at a high pressure is supplied to the reservoir tank via a pressure regulating valve. 13. The method of cooling a superconducting device according to claim 12, further comprising the step of pressurizing the reservoir tank by supplying the same.

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