JP4728601B2 - Cooling system for superconducting power equipment - Google Patents

Description

  The present invention relates to a cooling system for cooling a superconducting cable, a superconducting bus line, a SMES, a superconducting transformer, etc., which can be industrially utilized as a superconducting state by being cooled by a liquefied gas such as liquid nitrogen. The present invention relates to a cooling system for cooling a superconducting power device in which the device is operated in a high voltage state.

  As one of superconducting power devices, the prior art will be described with reference to FIG. 6 by taking a superconducting cable using a liquefied gas such as liquid nitrogen for cooling. As a cooling system for a superconducting cable, one described in Japanese Patent Application Laid-Open No. 08-148044 is known. As shown in FIG. 6, the conventional cooling system pressurizes the liquefied gas in the subcooled state (the liquefied gas is cooled below the saturation temperature of the liquefied gas) from the reservoir tank 101 by the pump 105, and the refrigerator 108 The circulation cycle of supplying the cable 111 after cooling by the heat exchanger 107 and returning it to the reservoir tank 101 again is repeated.

  In the case of cooling a superconducting cable, if the liquefied gas to be circulated is in a gas-liquid mixed state, the pressure loss increases and the required amount of liquefied gas cannot be circulated stably, and the large-capacity large-scale circulation It is necessary to prepare a pump. Furthermore, the superconducting cable uses a cryogenic electrical insulation system that maintains high electrical insulation performance by impregnating the liquefied gas into the insulator, so if gas or bubbles are mixed in the liquefied gas, There was a problem that the electrical insulation performance was significantly reduced.

Therefore, in the conventional cooling system, in order to always maintain the liquefied gas in the subcooled state and circulate without being vaporized, for example, when using liquid nitrogen as the liquefied gas, the inside of the reservoir tank 101 is Hydrogen (H ₂ ) or helium (He), which is a gas having a sufficiently lower triple point than the liquefied gas, is supplied from a cylinder 123 or the like to increase the boiling point of the liquefied gas, and the liquefied gas is circulated. Does not boil (that is, it does not become a gas-liquid mixed state).
Japanese Patent Laid-Open No. 08-148044

    When the pressure in the reservoir tank is sufficiently lower than the liquefied gas, for example, liquid nitrogen as the liquefied gas is pressurized with helium (He) gas as in the prior art, a very small amount is contained in the liquid nitrogen. It was found that the phenomenon that He gas melts into the gas. That is, helium (He) is widely known as an inert gas, and it was recognized that it does not dissolve in liquid nitrogen. However, in reality, it has been found that a very small amount of He gas dissolves in liquid nitrogen.

  The amount dissolved in the liquid nitrogen is very small, but when the liquefied gas in which the He gas is dissolved is circulated, for example, the part where the flow rate of the liquefied gas that the pipe expands becomes relatively slow, or, for example, a valve from the reservoir tank, etc. In the part where the pressure of the liquefied gas suddenly decreases, such as after being squeezed in, the dissolved He gas can no longer maintain the state of being dissolved in the liquefied gas, resulting in bubbles, which are mixed into the liquid nitrogen and gas-liquid It becomes a mixed state.

  Also, if there is a part where the superconducting cable or superconducting power equipment is located higher than the cooling system depending on the state of the installation layout, the generated air bubbles will collect and stay in the upper part of the equipment in that part. It was found that liquid nitrogen could not be circulated by filling the liquid nitrogen cooling pipe.

  It has been clarified by the inventors' experiment that the phenomenon described above is a phenomenon that occurs in a very long time of several months. If He gas is contained in liquid nitrogen and the gas-liquid mixed state or cooling pipe is filled as a gas phase in the pipe, the liquid nitrogen cannot be circulated smoothly. Furthermore, since the withstand voltage characteristic of He gas is very small compared to other liquefied gases, the insulation characteristic is lowered by the contained He gas even though liquid nitrogen originally has high insulation characteristics. This may cause poor insulation or dielectric breakdown of superconducting power equipment.

  As a countermeasure, it was considered to pressurize the reservoir tank with the same type of gas as the liquefied gas, but the liquid nitrogen stored in the reservoir tank is liquid nitrogen at a temperature below the boiling point, so the pressure is increased. When the used nitrogen gas comes into contact with liquid nitrogen having a boiling point or less in the reservoir tank, the nitrogen gas used for pressurization is cooled and liquefied. Therefore, the pressurized pressure decreases, and there is a problem that the pressure cannot be kept constant unless nitrogen gas is constantly supplied from the cylinder. As a result, a large amount of nitrogen gas is consumed, and a large amount of nitrogen gas is consumed. There was a problem that the heat load increased by bringing the liquefaction heat into the cooling system.

  Therefore, the object of the present invention is to dissolve a gas having a lower boiling point than the liquefied gas used for pressurization in the liquefied gas, and to cause liquefaction without causing instability factors of the liquefied gas circulation and troubles regarding insulation of the electrical equipment. An object is to provide a cooling system for superconducting power equipment capable of smoothly circulating gas in a subcooled state for a long period of time.

  The present inventor has intensively studied to solve the above-mentioned problems of the prior art. As a result, rather than using helium (He) gas, which was conventionally used as a pressurized gas, pressurizing the reservoir tank with the same type of gas as liquefied gas eliminates the dissolution of a small amount of He gas into liquid nitrogen. can do. As a result, in the part where the pressure of the liquefied gas suddenly decreases, the He gas becomes bubbles, mixed in the liquid nitrogen and becomes a gas-liquid mixed state, the circulation of the liquid nitrogen cannot be performed smoothly, and the insulation characteristics deteriorate. It turns out that the problem can be solved. Similarly, if the height difference due to the arrangement of superconducting power equipment exceeds a predetermined value, the generated bubbles will stay in the upper part of the equipment and fill the cooling loop, making it impossible to circulate liquid nitrogen. It turns out that you can.

  Furthermore, the liquid level of the reservoir tank that stores the liquefied gas in a pressurized state is positioned at least above the outlet of the return line of the circulating liquefied gas by at least the depth of the pressurized gas plus the liquid level movement correction amount. This solves the problem that the nitrogen gas used for pressurization is liquefied, the pressurized pressure decreases, and the pressure cannot be kept constant unless nitrogen gas is continuously supplied from the cylinder. It turns out that you can. Therefore, the problem that a large amount of nitrogen gas is consumed and a large amount of liquefied heat is brought into the cooling system at that time is increased.

  The present invention has been made on the basis of the above research results. The first aspect of the cooling system for a superconducting power apparatus according to the present invention is a reservoir tank for storing liquid gas, a circulation pump, and heat for cooling the liquid gas. A cooling system for a superconducting power device, comprising a exchanger and a circulation loop through which the liquefied gas circulates, wherein the liquefied gas is circulated in a subcooled state using a circulation pump to cool the superconducting power device. The apparatus further comprises pressurizing means for pressurizing with the same kind of gas as the liquefied gas, and the liquid level of the reservoir tank for storing the liquefied gas in a pressurized state is at least pressurized gas from the outlet of the return line of the circulating liquefied gas This is a cooling system for a superconducting power device characterized in that it is located at the upper portion by the depth of penetration of + the liquid level movement correction amount.

  In a second aspect of the cooling system for superconducting power equipment according to the present invention, the pressurizing means for pressurizing the reservoir tank with the same kind of gas as the liquefied gas is supplied from a gas cylinder storing the same kind of gas as the liquefied gas at a high pressure. A cooling system for a superconducting power device, characterized by comprising pressurizing at a predetermined pressure via a regulating valve.

  According to a third aspect of the cooling system for superconducting power equipment according to the present invention, the pressurizing means for pressurizing the reservoir tank with the same kind of gas as the liquefied gas is provided from an outlet of a circulation pump for sending the liquefied gas in the subcooled state from the reservoir tank. The superconducting power device is characterized in that the reservoir tank is pressurized using the discharge pressure of the circulation pump by a pipe that branches off from a part of the liquefied gas to be sent to the superconducting power device and returns to the reservoir tank. The cooling system.

  According to a fourth aspect of the cooling system for a superconducting power apparatus of the present invention, the pressurizing means for pressurizing the reservoir tank with the same kind of gas as the liquefied gas has an outlet of the circulation pump for sending the liquefied gas in the subcooled state from the reservoir tank. From a vaporizer for vaporizing the liquefied gas and a pressure regulating valve for adjusting the pressure provided in a pipe branched from a part of the liquefied gas to be sent to the superconducting power device and returning to the reservoir tank This is a cooling system for superconducting power equipment.

  A fifth aspect of the cooling system for superconducting power equipment according to the present invention further comprises auxiliary means for the pressurizing means, and the auxiliary means supplies and pressurizes a gas of the same type as the liquefied gas from a gas cylinder. A cooling system for a superconducting power device.

  The sixth aspect of the cooling system for superconducting power equipment according to the present invention further comprises auxiliary means for the pressurizing means, and the auxiliary means arranges a heating device in a gas phase portion of the reservoir tank, and A cooling system for superconducting power equipment, characterized in that the gas in the phase part is superheated and volume-expanded.

  According to the present invention, since the reservoir tank is pressurized with the same kind of gas as the liquefied gas, the liquid nitrogen can be smoothly circulated without introducing bubbles into the liquid nitrogen, and a cooling system for superconducting power equipment having excellent insulation characteristics can be provided. Can be provided. Further, according to the present invention, the liquid level of the reservoir tank that stores the liquefied gas in a pressurized state is at least the depth of the pressurized gas plus the liquid level movement correction amount from the outlet of the return line of the circulating liquefied gas. Since the gas used for pressurizing the reservoir tank is not liquefied, the superconducting power equipment cooling system in which the pressurized pressure does not decrease can be provided.

The cooling system for superconducting power equipment according to the present invention will be described in detail with reference to the drawings.
The cooling system for superconducting power equipment according to the present invention includes a reservoir tank for storing liquid gas, a circulation pump, a heat exchanger for cooling the liquid gas, and a circulation loop for circulating the liquefied gas. A cooling system for a superconducting power device that circulates in a subcooled state and cools the superconducting power device, further comprising pressurizing means for pressurizing the reservoir tank with the same kind of gas as the liquefied gas, and the liquefied gas in the pressurized state Superconducting power equipment characterized in that the liquid level of the reservoir tank to be stored is located at least above the outlet of the return line of the circulating liquefied gas by at least the depth of the pressurized gas plus the liquid level movement correction amount The cooling system.

The liquid level of the reservoir tank that stores the liquefied gas in a pressurized state is positioned at least above the outlet of the return line of the liquefied liquefied gas at least by the penetration depth of the pressurized gas + the liquid level movement correction amount. It is explained below that is necessary.
The relationship between the penetration depth of the pressurized gas and the pressure reduction rate was investigated by experiment. FIG. 5 is a diagram showing the relationship between the pressurized gas penetration depth [m] and the pressure reduction rate [%].

  In FIG. 5, the horizontal axis indicates the depth at which the pressurized gas dissolves from the liquid level of the reservoir tank (that is, the depth of penetration of the pressurized gas), and the vertical axis indicates the rate of decrease in the pressure in the reservoir tank due to liquefaction per hour. Each is shown. As experimental conditions, a container having a diameter of 1 m and a height of 1 m was used as the internal volume of the reservoir tank, and the pressure was set to 0.3 MPa. As a result, as is apparent from FIG. 5, when the penetration depth is up to 10 cm, the rate of pressure decrease is remarkably large, and when the penetration depth is up to about 20 cm, the gaseous nitrogen gas used for pressurization becomes liquid. Condensation and pressurization pressure decrease is still fast. On the other hand, it was found that if the penetration depth was kept at 20 cm or more, the pressure decrease could be kept at a small value of 1% or less. Actually, in addition to the penetration depth of the pressurized gas, the liquid level changes due to the influence of temperature, pressure, etc. of liquid nitrogen, so it is necessary to consider the liquid level movement correction amount.

  Therefore, the liquid level of the reservoir tank that stores the liquefied gas in a pressurized state is positioned at least above the outlet of the return line of the circulated liquefied gas by at least the depth of the pressurized gas plus the liquid level movement correction amount. It is necessary to be. Specifically, the penetration depth of pressurized gas (20 cm) + the liquid level movement correction amount (30 cm) is preferably 50 cm or more. As described above, the dependency of the reservoir tank on the container shape is small, and the required depth is almost the same even if the size changes. Therefore, in the system of the present application, a height that can ensure the required depth (preferably 50 cm or more) is required as the container height of the reservoir tank.

  As described above, the present invention is a system that cools a superconducting power device with a liquefied gas. A gas having a lower boiling point than the liquefied gas used for pressurization is dissolved in the liquefied gas, and the instability factor of the liquefied gas circulation In addition, the present invention provides a cooling system that can circulate liquefied gas in a subcooled state for a long period of time without causing problems related to insulation of electrical equipment.

  The pressurizing means for pressurizing in the above-described state consists of pressurizing the reservoir tank to a predetermined pressure with the same kind of gas as the liquefied gas stored in the reservoir tank. In order to prevent the pressurized gas from being cooled and liquefied by the liquefied gas, the liquid level of the reservoir tank is at least 20 cm or higher, preferably 50 cm or higher, relative to the outlet of the return pipe of the circulation pump in the reservoir tank. is there.

  Further, as means for pressurization, in addition to means for pressurization with a high-pressure gas cylinder, there is means for pressurization by returning a circulation pump outlet pressure higher than the pressure of the reservoir tank to the reservoir tank. As a specific means of using the pressure at the circulation pump outlet, a part of the liquefied gas is divided from the pressure of the reservoir tank by branching the outlet pipe of the circulation pump that pumps the liquid from the reservoir tank and pressurizes it to send it to the superconducting power equipment. Means for gasifying the branched liquefied gas using a vaporizer and returning it to the reservoir tank via a pressure regulating valve that opens and closes according to the pressure for maintaining the pressure of the reservoir tank at a predetermined pressure. is there.

  In order to explain the operation of the present invention, a case where liquid nitrogen is used as the liquefied gas will be described. The boiling point of liquid nitrogen at atmospheric pressure (1.013 MPa) is 77K. When this liquid nitrogen is pressurized to 0.3 MPa, the boiling point of liquid nitrogen becomes 90K or higher. Therefore, when 77K liquid nitrogen is pressurized to 0.3 MPa, the liquid nitrogen enters a subcooled state in which no bubbles are generated. The liquid collecting part of the circulation pump is located at the bottom of the reservoir tank and is connected to the circulation pump by piping.

  On the other hand, the return pipe of the circulation is connected to the reservoir tank, but the position of the outlet of the pipe is lower than the liquid level. The liquefied gas delivered from the circulation pump cools the superconducting power device and returns to the reservoir tank. At that time, since the piping outlet is at a position lower than the liquid level, the returned liquefied gas does not touch the pressurized gas phase of the reservoir tank, moves to the liquid nitrogen inlet of the circulation pump, and circulates again. To do.

  In the present invention, the position of the liquid level is set higher than a predetermined height (20 cm) from the outlet of the pipe and the intake port of the circulation pump (that is, a predetermined liquefied gas layer is provided). The temperature of the liquid nitrogen above the subcooled cold liquid nitrogen in the mouth increases in order toward the liquid level, and the liquid nitrogen temperature at the liquid level is almost the same as the boiling point temperature of the liquefied gas of 0.3 MPa. It has become. Therefore, in the past, when the inside of the reservoir tank was pressurized with the same kind of gas, there was a problem that the gas was liquefied and the pressure decreased because the gas supply was not in time, but by placing this liquefied gas layer, It was found that almost no gas was liquefied.

  In the present invention, a method other than the method of pressurizing with a cylinder was also considered as a pressurizing method. The method of pressurizing with self pressure in the present invention will be described with reference to FIG. First, liquid nitrogen is pumped out from the inside of the reservoir in the atmospheric pressure state (point a) and is sent by a circulation pump. At the outlet of the circulation pump, liquid nitrogen flows at 50 L / min, and the liquid nitrogen is pressurized to 0.2 MPa against the inlet (point b). In utilizing the pressure at the outlet, the pressure of the reservoir tank is increased by vaporizing liquid nitrogen branched and pressurized from the outlet pipe into a gas by a vaporizer and returning it to the reservoir tank. (Arrow c).

  Accordingly, the outlet pressure of the circulation pump is also increased (arrow d), and the reservoir tank can be constantly pressurized. When the pressure in the reservoir tank exceeds the upper limit set pressure (P2) (point e), the valve attached to the piping is closed and the gas supply to the reservoir tank is stopped. Thereafter, inside the reservoir, the nitrogen gas in the gas phase is cooled with liquid nitrogen below the triple point of the nitrogen gas, and the nitrogen gas in the gas phase is liquefied to become liquid nitrogen. The pressure in the reservoir tank decreases by the amount of gas volume decreased due to liquefaction (arrow f). When the lower limit set pressure (P1) is reached (point g), the valve is opened, and nitrogen gas is again supplied into the reservoir tank by the pressure at the circulation pump outlet, and the pressure in the reservoir tank is increased.

  Since low-temperature nitrogen gas flows through the piping, the piping and valves may freeze, and as a vaporizer, liquid nitrogen is gasified to raise the temperature to room temperature in order to prevent it. As a vaporizer, there are a method in which a heater is wound around a pipe, a pipe is passed through water or the like, and fins are attached to the pipe to increase the temperature by heat exchange with outside air. In addition, as the valve functions, if gas continues to be sent through a pipe branched from the pump, the pressure in the reservoir tank will continue to rise and may exceed the design pressure of the reservoir tank. When the pressure exceeds a predetermined pressure, the gas is closed and pressurization by the gas is stopped. When the pressure is lower than the predetermined pressure, the gas is opened and the pressure is automatically maintained to maintain a constant pressure.

If the capacity of the reservoir tank is large, a large amount of nitrogen gas is required to pressurize to a predetermined pressure, so prepare a separate nitrogen cylinder and pressurize the reservoir tank to the predetermined pressure. You can also. It is also possible to use a method in which a heating device such as a heater is disposed in the gas phase portion inside the reservoir tank, and the gas in the reservoir tank is pressurized and expanded to pressurize it.
Hereinafter, the present invention will be described in more detail by way of examples.

Example 1
FIG. 2 is a diagram showing one embodiment of a cooling system for a superconducting power device according to the present invention. Liquid nitrogen is used as the liquefied gas. Liquid nitrogen is stored in the reservoir tank 1. The reservoir tank 1 has a double container structure, and between the double containers, a heat insulating material is constructed so as to surround the inner container 1b, and is maintained in a vacuum state in order to further reduce heat penetration. . Further, the reservoir tank is a sealed container, and can be formed by pressurizing the inside.

  At the bottom of the reservoir tank, there is a liquid inlet 3 connected to the circulation pump, from which it is connected to the inlet of the circulation pump 5 by a pipe 4 having a diameter of 3 cm. The circulation pump 5 is a vortex type rotary pump. Between the motor 5a for rotating the fin 5c and the fin, a long shaft 5b of about 50 cm is connected in order to suppress heat inflow due to conduction.

  Moreover, the fin itself is arrange | positioned in the vacuum vessel inside 5e, and suppresses the heat | fever penetration | invasion from the outside. The rotary pump of the present invention can flow a flow rate of 30 L / min as a flow rate of liquid nitrogen at a rotation speed of 50 Hz, and can obtain a discharge pressure of 0.2 MPa as a pressure difference between the inlet and the outlet. . From the pump outlet, a pipe 6 having a diameter of 3 cm is connected to a heat exchanger 7 of the freezer.

  The refrigerator 8 is composed of a GM refrigerator, a Stirling refrigerator, or the like, and a heat exchanger is connected to a low-temperature head for generating cold, and the circulating liquid nitrogen is cooled to a low temperature. In the present invention, a Stirling refrigerator having a refrigeration capacity of 1 kW is used, and 30 L / min of liquid nitrogen passes through a heat exchanger cooled by the refrigerator, so that what was 77 K at the inlet is 74 K. Can be cooled down to.

  The liquid nitrogen cooled by the refrigerator is water-tightly connected to the inlet 10 of the superconducting power equipment by a pipe 9 having a diameter of 3 cm. In the cooling system for cooling the superconducting cable 11 of this embodiment, the superconducting cable is cooled by circulating liquid nitrogen cooled by a refrigerator in the superconducting cable. The temperature of the liquid nitrogen that has cooled the superconducting cable is increased, but since the increased temperature is lower than the boiling point, a subcooled state in which no bubbles are generated is maintained in the liquid nitrogen. Therefore, even with a 500 m superconducting cable, the pressure loss is 0.1 MPa or less, which is sufficiently small and allows liquid nitrogen to flow stably.

  In addition, since liquid nitrogen that does not generate bubbles penetrates into the electrical insulation layer of the superconducting cable, good electrical insulation can be maintained. The liquid nitrogen that has exited the outlet 12 of the superconducting cable returns to the reservoir tank 1 through the pipe 13 to form a circulation loop. The reservoir tank 1, the circulation pump 2, the heat exchanger 3 of the refrigerator, the superconducting cable 4, and the nitrogen piping connecting these devices all have a double container structure using vacuum insulation in order to reduce intrusion heat from the outside. It has become.

  The pipe 13 returned to the reservoir tank is a pipe 14 that reaches from the top to the bottom of the reservoir tank, and returns the liquid from the outlet 15 to the bottom of the reservoir tank to the reservoir tank. A liquid inlet 3 connected to the circulation pump is also located at the bottom of the reservoir tank. During the circulation, the nitrogen in the reservoir tank is stored so that the liquid level 2 is at least 20 cm higher than the position of the outlet 15.

  In the method of pressurizing the reservoir tank by the outlet pressure of the circulation pump of the present invention, a stainless steel pipe 16 having a diameter of 6 mm is branched and taken out from the pipe 6 at the pump outlet. The liquid nitrogen passing through the inside of the pipe 16 passes through the vaporizer 17 after leaving the vacuum container of the circulation pump, and all changes from liquid nitrogen to nitrogen gas at room temperature.

  As the vaporizer, in this embodiment, a 6 mm pipe made of copper wound in a 6 m coil shape is used inside the hot water container, and the liquid nitrogen inside is heated by being immersed in the hot water. . As a vaporizer, in addition to the present embodiment, for example, a method in which a heater is wound around the outside of the coil and the temperature is increased by heating the heater by energization, or a method in which fins are attached to the piping and heat is exchanged with the atmosphere. Any material that can convert the liquid nitrogen inside into a gas at room temperature may be used. The pipe 18 exiting the vaporizer 17 is provided with a valve 19 having a pressure control function for flowing a gas when the outlet pressure becomes a predetermined pressure or lower and stopping the gas when the outlet pressure becomes a predetermined pressure or higher. The pipe 20 exiting the valve 19 is attached to the upper part of the reservoir tank so that the reservoir tank can be pressurized.

  Since the pipes 18 and 20 after passing through the vaporizer 17 are at room temperature, there is no need for a heat insulation structure, but the pipe 16 from the circulation pump outlet to the vaporizer is surrounded by a heat insulating material such as urethane foam. However, the piping 16 does not form frost and is more suitable for aesthetic reasons. If the valve 19 is a valve that operates at a low temperature, the positions of the valve 19 and the vaporizer 17 can be reversed. However, the low temperature valve is more expensive than the normal temperature, and economically. It is not an appropriate arrangement. In this embodiment, the pressure extraction pipe 16 is taken out from the pump outlet pipe 6. However, the pressure of the reservoir tank can be determined from the pipe 9 at the outlet of the heat exchanger of the refrigerator or the inlet 10 of the superconducting device. If it is a high part, the object of the present invention can be achieved regardless of where it is taken out. In this sense, the pump outlet does not simply indicate the immediate vicinity of the pump outlet, but generically refers to everything downstream from the pump outlet.

Example 2
In the first embodiment, the case where the circulation pump is outside the reservoir tank has been described. However, the present invention can be implemented even when the circulation pump is inside the reservoir tank. FIG. 3 is a diagram showing a part of another aspect of the cooling system for a superconducting power device according to the present invention. That is, FIG. 3 shows an extraction diagram of the reservoir tank portion for explaining the present embodiment in the cooling system. Of the circulation pump 5, a fin portion 5c for sending the liquid is in the liquid in the reservoir tank, and the rotation of the motor 5a is transmitted by the long shaft 5b. Liquid nitrogen is pumped out of the reservoir tank, passes through the pipe 6, exits the reservoir tank, and is connected to a refrigerator that cools the liquid nitrogen.
In this case, the pressurizing piping is attached to the portion of the piping 6 coming out of the reservoir tank, and thereafter returns to the reservoir tank through the vaporizer 17 and the valve 19 as in the first embodiment.

Example 3
In the first embodiment, the pressurizing means for the reservoir tank is only by gas from the pump outlet. In this case, since the pipe is as thin as 6 mm and the pressure is only the discharge pressure of the pump, the gas supply is small and it takes a very long time to reach a predetermined pressure. Especially when the reservoir tank is large, it takes tens of hours. Therefore, as shown in FIG. 4, as auxiliary means, an external pipe 21 is attached to the reservoir tank, and gas is supplied from a high-pressure nitrogen cylinder 22 or nitrogen curdle. Further, since the liquefaction is accelerated when the gas phase portion inside the reservoir tank is cooled to a low temperature, the heater 23 may be arranged in the gas phase portion to suppress the liquefaction.

  According to the present invention, a gas having a boiling point lower than that of the liquefied gas used for pressurization is dissolved in the liquefied gas, and the liquefied gas is subcooled without causing instability of circulation of the liquefied gas and troubles relating to insulation of the electrical equipment. It is possible to provide a cooling system for superconducting power equipment that can circulate for a long time in a state, and has high industrial utility value.

FIG. 1 is a diagram illustrating a method of pressurizing a reservoir tank with a circulation pump outlet pressure according to the present invention. FIG. 2 is a configuration diagram of a cooling system for explaining the first embodiment of the present invention. FIG. 3 is a configuration diagram in the vicinity of the reservoir tank for explaining the second embodiment of the present invention. FIG. 4 is a configuration diagram in the vicinity of the reservoir tank for explaining the third embodiment of the present invention. FIG. 5 is a diagram showing the relationship between the pressurized gas penetration depth [m] and the pressure reduction rate [%]. FIG. 6 is a diagram for explaining a conventional superconducting cable cooling system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reservoir tank 1b Reservoir tank inner container 2 Reservoir tank inside Liquid nitrogen liquid level 3 Liquid inlet 4, 6, 9 Feed side liquid nitrogen circulation piping 5 Circulation pump 5a Circulation pump motor 5b Circulation pump long axis 5c Fin 5e Vacuum container 7 Freezing Machine heat exchanger 8 Refrigerator 10 Inlet of superconducting power equipment 11 Superconducting cable 12 Outlet of superconducting cable 13 Return-side liquid nitrogen circulation pipe 14 Nitrogen return pipe in reservoir tank 15 Nitrogen return pipe outlet 16, 18, 20 Pressurizing branch pipe 17 Vaporizer 19 Valve 21 External piping for pressurization 22 High-pressure nitrogen cylinder 23 Heater inside reservoir tank

Claims (4)

Reservoir tank for reserving a with liquefied gas having an outlet return line of the circulating liquefied gas, a circulating pump, a heat exchanger for cooling the liquefied gas, and comprises a circulation loop liquefied gas is circulated, circulated through the circulation loop A superconducting power equipment cooling system that cools a superconducting power equipment with a liquefied gas in a subcooled state ,
(A) pressurizing means for pressurizing the reservoir tank with the same kind of gas as the liquefied gas;
(B) the reservoir tank placed under pressure by the pressurizing means is a sealed container;
(C) a liquefaction suppression mechanism that suppresses liquefaction of the pressurized gas in the reservoir tank;
(D) The liquefaction suppression mechanism has the outlet located at least below the liquid level of the reservoir tank by the depth of the pressurized gas plus the liquid level movement correction amount, and the penetration depth is at least 20 cm. in a cooling system of the superconducting power apparatus. The pressurizing means for pressurizing the reservoir tank with the same kind of gas as the liquefied gas comprises means for pressurizing at a predetermined pressure via a pressure regulating valve from a gas cylinder storing the same kind of gas as the liquefied gas at a high pressure. The cooling system for superconducting power equipment according to 1. The pressurizing means for pressurizing the reservoir tank with the same kind of gas as the liquefied gas branches a part of the liquefied gas to be sent to the superconducting power device from the outlet of the circulation pump that sends the subcooled liquefied gas from the reservoir tank. The cooling system for a superconducting power device according to claim 1, comprising a pipe returning to the reservoir tank, a vaporizer for vaporizing the liquefied gas, and a pressure regulating valve for regulating pressure, provided in the pipe . The liquefaction suppression mechanism further includes a heating device disposed in a gas phase portion of the reservoir tank , and the heating device causes the gas in the gas phase portion of the reservoir tank to be heated and expanded by the heating device. Item 2. The cooling system for superconducting power equipment according to Item 1 .

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