JP6374305B2 - Superconducting cable system - Google Patents

Description

  The present invention relates to a superconducting cable system including a superconducting cable in which a superconducting conductor is housed in a heat insulating tube, and a cooling system that supplies a liquid refrigerant into the heat insulating tube and forms a refrigerant flow path together with the heat insulating tube. In particular, the present invention relates to a superconducting cable system that can suppress an increase in pressure and can avoid damage to a superconducting cable and a refrigerant channel when an abnormality occurs when the refrigerant pressure in the refrigerant channel increases.

  A superconducting cable is expected as a power cable constituting a transmission line because it can transmit large-capacity power with low loss compared to existing normal conducting cables (eg, OF cables and CV cables). In recent years, a superconducting cable system is constructed by laying a superconducting cable, and a demonstration test for actually transmitting power has been performed.

  The superconducting cable has a superconducting conductor part with a superconducting conductor layer on the outer periphery of the former, and the superconducting conductor part (superconducting conductor layer) is accommodated in a heat insulating pipe and liquid refrigerant (eg, liquid nitrogen) is circulated in the heat insulating pipe. A structure for cooling is typical.

  In general, a former is formed of a stranded wire conductor obtained by twisting together a plurality of copper strands with insulating coating. The superconducting conductor layer is formed by spirally winding a plurality of superconducting wires around the outer periphery of the former.

  The superconducting cable system is operated by connecting a cooling system to the superconducting cable and supplying and circulating a liquid refrigerant for cooling the superconducting conductor layer from the cooling system into the heat insulating pipe. The cooling system includes a refrigerator that cools the liquid refrigerant, a pump that pumps the liquid refrigerant, a reservoir tank that stores the liquid refrigerant, and the like, and constitutes a refrigerant flow path through which the liquid refrigerant flows together with the heat insulation pipe of the superconducting cable. In general, the superconducting cable system is cooled by a direct cooling system in which the liquid refrigerant cooled by the refrigerator is directly sent into the heat insulation pipe, and the liquid refrigerant is circulated by a pump.

  Also, when constructing a superconducting cable system, an intermediate connection part that connects the superconducting cables in the middle of the transmission line, or a termination that connects the superconducting cable and other power equipment (eg, normal conducting cable) at the end of the transmission line A connection unit is provided (hereinafter, the intermediate connection unit and the terminal connection unit may be simply referred to as a connection unit). These connection parts usually include a connection box that accommodates the end of the superconducting conductor part (see, for example, Patent Document 1). The junction box may constitute a part of the refrigerant flow path in the same manner as the heat insulating tube, and the junction box is also filled with the liquid refrigerant.

  By the way, in a superconducting cable system, when an accident such as a short circuit occurs in a nearby overhead line, an overcurrent flows in the former or the superconducting conductor layer, and the former or the superconducting conductor layer generates heat and the temperature of the superconducting conductor may rise. is there. At that time, the temperature of the liquid refrigerant existing between the copper wires constituting the former and between the superconducting wires constituting the superconducting conductor layer rises, and the refrigerant pressure in the refrigerant flow path rises due to the volume expansion of the liquid refrigerant accompanying the temperature rise. By doing so, there is a possibility that a member (for example, a heat insulating tube, a junction box, and a cooling system) constituting the superconducting cable or the refrigerant flow path may be damaged.

  For example, in Patent Document 1, a pressure adjustment unit capable of adjusting the pressure by deforming following the pressure change in the connection box is arranged in the connection box constituting the connection unit, thereby increasing the pressure in the event of an accident. Discloses a technique for preventing destruction of a superconducting cable and a junction box.

JP 2005-253203 A

  In a superconducting cable system, it is desired to develop a configuration that can suppress a pressure increase in an abnormal state in which the refrigerant pressure in the refrigerant flow path increases in a simple and safe manner.

  The technique described in Patent Document 1 arranges a pressure adjusting member capable of adjusting the pressure in the connection box in the connection box. As described above, the junction box may constitute a part of the refrigerant flow path. When the pressure adjustment member is disposed in the junction box, the pressure adjustment member hinders the flow of the liquid refrigerant, and the refrigerant flow path. Can cause pressure loss in Moreover, in the structure which arrange | positions a pressure adjustment member in a connection box, a connection box may enlarge or it may become complicated. If the connection box is enlarged, the connection box may not be installed at a predetermined position.

  Accordingly, one of the objects of the present invention is to provide a superconducting cable system that can suppress an increase in pressure and can avoid damage to the superconducting cable and the refrigerant channel when the refrigerant pressure in the refrigerant channel increases.

  A superconducting cable system according to one aspect of the present invention provides a superconducting cable having a superconducting conductor layer having a superconducting conductor layer on the outer periphery of a former, and a liquid refrigerant for cooling the superconducting conductor layer in the heat insulating pipe. And a cooling system that constitutes a refrigerant flow path together with the heat insulating pipe. The superconducting cable system is provided in the refrigerant flow path, is interposed between the refrigerant flow path and the pressure adjustment tank, the pressure adjustment tank into which liquid refrigerant from the refrigerant flow path flows, and the refrigerant flow path And a relief valve that opens and closes according to the refrigerant pressure. In the superconducting cable system, normally, the relief valve is closed, the pressure adjustment tank is separated from the refrigerant flow path, and a gas phase is secured in the pressure adjustment tank. Further, when the refrigerant pressure in the refrigerant flow path exceeds a predetermined pressure, the relief valve is opened, liquid refrigerant is released from the refrigerant flow path into the pressure adjustment tank, and the refrigerant pressure in the refrigerant flow path is reduced. Lower.

  The superconducting cable system can suppress an increase in pressure when the refrigerant pressure in the refrigerant channel rises, and can avoid damage to the superconducting cable and the refrigerant channel.

It is a schematic cross section which shows an example of a structure of a superconducting cable. It is a schematic block diagram which shows an example of a structure of the superconducting cable system which concerns on Embodiment 1. FIG. It is a schematic diagram which shows an example of a structure of the pressure adjustment tank with which the superconducting cable system which concerns on Embodiment 1 is equipped.

[Description of Embodiment of the Present Invention]
The inventors of the present invention have studied a technique for suppressing the pressure increase in the superconducting cable system when the refrigerant pressure in the refrigerant flow path increases. As a method for suppressing the pressure increase in the refrigerant flow path, for example, it is conceivable to reduce the pressure increase by the gas phase by providing a gas phase in a part of the refrigerant flow path. Specifically, a gas phase is formed in the junction box of the superconducting cable. However, since a liquid refrigerant is pumped into the refrigerant flow path, it is difficult to form a gas phase in the junction box. In order to secure a gas phase in the junction box, a separate apparatus for supplying pressurized gas refrigerant (eg, nitrogen gas) vaporized in the junction box is necessary, which may complicate the configuration. . Furthermore, even if the gas refrigerant is supplied, the gas refrigerant may be cooled and liquefied by the liquid refrigerant in the junction box, and it is difficult to maintain a gas phase in the junction box. On the other hand, when the gas phase in the junction box increases, the superconducting conductor layer is not immersed in the liquid refrigerant, and there is a concern about a decrease in electrical insulation. Therefore, in the superconducting cable system, it is preferable to circulate (circulate) the refrigerant flow path in a state in which the liquid refrigerant is filled without forming a gas phase in the connection box serving as the refrigerant flow path.

  Also, in a superconducting cable system, in order to ensure safety, a safety valve is usually attached to a junction box or a reservoir tank that constitutes a refrigerant flow path, and by any chance the refrigerant pressure in the junction box or the reservoir tank is reduced. When the danger zone (allowable pressure) is exceeded, the safety valve is automatically opened to reduce the pressure. However, since the safety valve operates at a high pressure, when the safety valve is opened, the liquid refrigerant may be ejected together with the gas evaporated from the liquid refrigerant.

  Based on the above knowledge, the present inventors considered that the pressure increase of the refrigerant flow path is suppressed by providing the refrigerant flow path with a pressure adjusting tank into which the liquid refrigerant from the refrigerant flow path flows. First, embodiments of the present invention will be listed and described.

  (1) A superconducting cable system according to one aspect of the present invention includes a superconducting cable in which a superconducting conductor portion having a superconducting conductor layer on the outer periphery of a former is housed in a heat insulating tube, and a liquid refrigerant that cools the superconducting conductor layer in the heat insulating tube. And a cooling system that configures a refrigerant flow path together with the heat insulating pipe. The superconducting cable system is provided in a refrigerant flow path, and is interposed between a pressure adjustment tank into which liquid refrigerant flows from the refrigerant flow path, and the refrigerant flow path and the pressure adjustment tank, according to the refrigerant pressure in the refrigerant flow path. And a relief valve that opens and closes. In the superconducting cable system, the relief valve is normally closed, the pressure adjustment tank is separated from the refrigerant flow path, and a gas phase is secured in the pressure adjustment tank. In addition, when the refrigerant pressure in the refrigerant flow path exceeds a predetermined pressure, the relief valve is opened, and the liquid refrigerant is released from the refrigerant flow path into the pressure adjustment tank to lower the refrigerant pressure in the refrigerant flow path.

  According to the superconducting cable system, the pressure adjustment tank is connected to the refrigerant flow path via the relief valve, so that an increase in pressure can be suppressed in the event of an abnormal increase in the refrigerant pressure in the refrigerant flow path. Damage to the flow path can be avoided. In the above superconducting cable system, since the relief valve is normally closed, the pressure adjustment tank is separated from the refrigerant flow path, and the liquid refrigerant is prevented from flowing into the pressure adjustment tank from the refrigerant flow path. Thus, a gas phase is secured in the pressure adjustment tank. On the other hand, when the refrigerant pressure in the refrigerant flow path exceeds a predetermined pressure due to an accident such as a short circuit, the relief valve opens and the liquid refrigerant is released from the refrigerant flow path into the pressure adjustment tank, thereby reducing the refrigerant pressure in the refrigerant flow path. Lower. Since the superconducting cable system stores the liquid refrigerant in the pressure adjustment tank, the safety is high as compared with the case where the liquid refrigerant is directly discharged to the outside.

  The pressure adjustment tank is normally isolated from the refrigerant flow path by the relief valve, and is unlikely to hinder the flow of the liquid refrigerant, and is unlikely to cause an increase in pressure loss in the refrigerant flow path at the normal time. Moreover, since the pressure adjustment tank can be provided at an arbitrary position in the refrigerant flow path, it is easy to secure an installation space.

  Further, in the superconducting cable system, when a safety valve is provided in the junction box or the like, the operating pressure of the relief valve is set lower than the operating pressure of the safety valve (for example, the allowable pressure of the members constituting the refrigerant flow path). . If it does so, before a safety valve operates, a relief valve will open, liquid refrigerant will be allowed to escape from a refrigerant channel into a pressure regulation tank, and a refrigerant channel can be decompressed. Therefore, the operation of the safety valve that releases the liquid refrigerant to the outside can be suppressed as an emergency evacuation measure, and the liquid refrigerant can be prevented from being ejected from the safety valve.

  (2) As one form of the superconducting cable system, the relief valve is a check valve that opens only in the direction toward the pressure adjusting tank.

  If the relief valve is a check valve, it is possible to prevent the liquid refrigerant in the pressure adjusting tank or the gas vaporized from the liquid refrigerant from flowing into the refrigerant flow path.

  (3) As one form of the superconducting cable system, the superconducting cable system is further connected to the refrigerant flow path, opens when the refrigerant pressure in the refrigerant flow path exceeds a predetermined pressure, and discharges the liquid refrigerant from the refrigerant flow path to the outside. Providing a release valve to be used. The relief valve operates at a pressure lower than the operating pressure of the release valve.

  By providing the release valve, even if the pressure reduction tank does not catch up with the increase in pressure in the refrigerant flow path, the release valve opens and the liquid refrigerant (the gas from which the liquid refrigerant is vaporized) is opened. The pressure of the refrigerant in the refrigerant channel can be reduced. In addition, since the operating pressure of the relief valve is lower than the operating pressure of the release valve, before the release valve is activated, the relief valve opens and the liquid refrigerant is released from the refrigerant flow path into the pressure adjustment tank, and the refrigerant flow path is decompressed. it can. Therefore, when the refrigerant pressure in the refrigerant channel rises, it is possible to suppress the increase in the pressure in the refrigerant channel by the pressure adjustment tank first, and the operation of the release valve that discharges the liquid refrigerant to the outside can be reduced.

  The discharge valve can function as a safety valve. The release valve may be a conventional safety valve or may be provided separately from the safety valve.

  (4) As one form of the superconducting cable system including the release valve, a heat exchanger that vaporizes the liquid refrigerant discharged from the release valve may be provided at an open end of the release valve.

  By providing the heat exchanger, the liquid refrigerant released from the release valve can be vaporized and released to the outside, so that the safety is higher than when the liquid refrigerant is directly discharged to the outside.

[Details of the embodiment of the present invention]
A specific example of a superconducting cable system according to an embodiment of the present invention will be described below with reference to the drawings. The same reference numerals in the figure indicate the same names. In addition, this invention is not limited to these illustrations, is shown by the claim, and is intended that all the changes within the meaning and range equivalent to the claim are included.

[Embodiment 1]
First, an example of a superconducting cable constituting the superconducting cable system will be described with reference to FIG.

<Superconducting cable>
The superconducting cable 1 includes a superconducting conductor portion 10 having a superconducting conductor layer 102 and a heat insulating tube 20 that houses the superconducting conductor portion 10. The superconducting cable 1 shown in FIG. 1 is a three-core collective type in which three superconducting conductor portions 10 are twisted and stored together in a heat insulating tube 20. The superconducting cable 1 circulates a liquid refrigerant (eg, liquid nitrogen) in the heat insulating tube 20 to cool the superconducting conductor portion 10 (superconducting conductor layer 102) with this liquid refrigerant to be in a superconducting state. Used for power transmission. Hereinafter, the configuration of the superconducting cable 1 will be described in more detail.

(Superconducting conductor)
The superconducting conductor portion 10 has a superconducting conductor layer 102 on the outer periphery of the former 101. In this example, the superconducting conductor portion 10 (hereinafter sometimes referred to as “cable core”) has a former 101, a superconducting conductor layer 102, an electrical insulating layer 103, a shield layer 104, and a protective layer 105 concentrically in order from the center. Is arranged.

(Former)
The former 101 is made of a normal conducting material such as copper or aluminum. In the superconducting cable 1 (cable core 10), an overcurrent caused by an accident such as a short circuit can be shunted to the former 101. In this example, the former 101 is formed of a stranded wire conductor obtained by twisting a plurality of copper strands coated with an insulating coating such as enamel.

(Superconducting conductor layer)
The superconducting conductor layer 102 is formed by winding a plurality of superconducting wires around the former 101 spirally in a single layer or multiple layers. As the superconducting wire, for example, a known tape-shaped wire such as a Bi-based silver sheathed wire or an RE123-based thin film wire can be used.

(Electrical insulation layer)
The electrical insulating layer 103 is for ensuring electrical insulation between the superconducting conductor layer 102 and a member (the shield layer 104 in this example) disposed outside thereof. The electrical insulating layer 103 is formed by winding a semi-synthetic insulating paper represented by PPLP (registered trademark; Polypropylene Laminated Paper), for example, in a spiral manner around the outer periphery of the superconducting conductor layer 102.

(Shield layer)
The shield layer 104 is formed by winding a conductive wire around the outside of the superconducting conductor layer 102, specifically, the outer periphery of the electrical insulating layer 103. For the conductive wire, for example, a normal conductive wire such as copper or aluminum or a superconductive wire can be used. The shield layer 104 is formed, for example, by winding a wire or tape made of a normal conducting material such as copper or aluminum, or a superconducting wire spirally wound in a single layer or multiple layers, or a braided wire made of a normal conducting material. It can be formed by winding.

(Protective layer)
The protective layer 105 is disposed on the outermost periphery of the cable core 10, and ensures electrical insulation between a member (in this example, the shield layer 104) disposed on the inner side of the cable core 10 and the heat insulating tube 20, and is disposed on the inner side. This is for mechanically protecting the formed member. The protective layer 105 is formed by spirally winding an insulating paper such as PPLP or kraft paper around the outer periphery of the shield layer 104.

(Insulated pipe)
The heat insulating tube 20 is a double tube having an inner tube 21 and an outer tube 22, and a space between the inner tube 21 and the outer tube 22 is evacuated, and a vacuum heat insulating layer is formed in this space. In the vacuum heat insulating layer, a heat insulating material (not shown) such as a super insulation (trade name) is disposed in order to enhance heat insulating properties. In this example, the inner tube 21 and the outer tube 22 are stainless steel corrugated tubes. A liquid refrigerant circulates in the heat insulation pipe 20 (a space between the cable core 10 and the heat insulation pipe 20 (inner pipe 21)). An anticorrosion layer 25 is formed of vinyl, polyethylene or the like on the outer periphery of the heat insulating tube 20 (outer tube 22).

<Superconducting cable system>
With reference to FIG. 2, the outline | summary of the superconducting cable system which concerns on Embodiment 1 is demonstrated. The superconducting cable system S of Embodiment 1 includes the superconducting cable 1 and the cooling system 40 described above with reference to FIG. The superconducting cable system S includes a pressure adjustment tank 50 into which the liquid refrigerant L flows from the refrigerant flow path, and a relief valve 51 interposed between the refrigerant flow path and the pressure adjustment tank 50. One. In FIG. 2, only one cable core is illustrated among the three cable cores 10 in the superconducting cable 1, and illustration of the other cable cores is omitted. Hereinafter, the configuration of the superconducting cable system S will be described in more detail.

  Termination connection portions 3A and 3B are provided at both ends of the superconducting cable 1, respectively. The terminal connection portions 3A and 3B include connection boxes 30A and 30B that house the ends of the cable core 10. The heat insulating pipe 20 is connected to the connection boxes 30A, 30B, and the spaces in the connection boxes 30A, 30B communicate with the heat insulating pipe 20 and are filled with the liquid refrigerant L. Here, the description of the specific configuration of the termination connection unit is omitted, but the configuration of the termination connection unit is, for example, a known configuration described in JP-A-2005-32698, JP-A-2006-196628, or the like. Available.

(Cooling system)
The cooling system 40 supplies the liquid refrigerant L that cools the cable core 10 into the heat insulating tube 20 of the superconducting cable 1. The cooling system 40 includes a refrigerator 41 that cools the liquid refrigerant L, a circulation pump 42 that pumps the liquid refrigerant L, and a reservoir tank 43 that stores the liquid refrigerant L. In the superconducting cable system S shown in FIG. 2, the cooling system 40 is connected to the superconducting cable 1 to circulate the liquid refrigerant L (in FIG. 2, white arrows indicate the flow direction of the liquid refrigerant L). The cooling system 40 is connected to the terminal connection part 3A (connection box 30A) of the superconducting cable 1 via the refrigerant pipe 34A, and is connected to the terminal connection part 3B (connection box 30B) via the refrigerant pipe 34B. The spaces in the connection boxes 30A and 30B and the refrigerant pipes 34A and 34B communicate with each other, and the liquid refrigerant L flows through the refrigerant pipes 34A and 34B. In the superconducting cable system S, the liquid refrigerant L is pumped by the circulation pump 42 and cooled by the refrigerator 41, and then supplied from the cooling system 40 to the junction box 30A via the refrigerant pipe 34A. Circulate inside. The liquid refrigerant L flowing through the heat insulating pipe 20 is discharged from the connection box 30B, returned to the cooling system 40 through the refrigerant pipe 34B, and sent again to the refrigerator 41 through the reservoir tank 43. That is, the heat insulation pipe 20, the junction boxes 30A and 30B, the refrigerant pipes 34A and 34B, and the cooling system 40 constitute a refrigerant flow path, and the liquid refrigerant L circulates through the refrigerant flow path.

(Pressure adjustment tank)
The pressure adjusting tank 50 is provided in the refrigerant channel, and the liquid refrigerant L from the refrigerant channel flows in. A relief valve 51 that opens and closes according to the refrigerant pressure in the refrigerant channel is interposed between the refrigerant channel and the pressure adjusting tank 50. Normally, the relief valve 51 is closed, the pressure adjustment tank 50 is separated from the refrigerant flow path, and a gas phase is secured in the pressure adjustment tank 50. Therefore, at normal times, the liquid refrigerant L is prevented from flowing into the pressure adjusting tank 50 from the refrigerant flow path. On the other hand, when an abnormality such as a short circuit causes the refrigerant pressure in the refrigerant flow path to exceed a predetermined pressure, the relief valve 51 automatically opens and the liquid refrigerant L flows into the pressure adjustment tank 50 from the refrigerant flow path. It becomes possible. Therefore, when an abnormality occurs, the liquid refrigerant L can be released from the refrigerant flow path to the pressure adjustment tank 50 by opening the relief valve 51.

  The installation location of the pressure adjustment tank 50 is not particularly limited. For example, the pressure adjusting tank 50 is provided in the refrigerant flow paths, such as the refrigerant pipes 34A and 34B, the terminal connection portions 3A and 3B (connection boxes 30A and 30B), the reservoir tank 43, and the heat insulating pipe 20. A preferable installation location of the pressure adjusting tank 50 is the junction boxes 30A and 30B or the refrigerant pipes 34A and 34B in the vicinity of the junction boxes 30A and 30B, and more preferably, the downstream side (the end connection portion 3B side) as viewed from the heat insulating pipe 20. ) Or the refrigerant pipe 34B in the vicinity of the connection box 30B. In this example, the pressure adjustment tank 50 is provided in the refrigerant pipe 34B near the junction box 30B.

  Here, the reason why it is preferable to provide the pressure adjusting tank 50 at the terminal connection part (connection box) or in the vicinity thereof will be described. First, it is assumed that the superconducting cable 1 is installed in a pipeline or a cave, and providing the pressure adjusting tank 50 in the heat insulating pipe 20 may make it difficult to secure an installation space. Furthermore, when the pressure adjusting tank 50 is provided in the heat insulating pipe 20, it is considered that the heat insulating performance is lowered and the heat intrusion is increased. Since the cable core 10 is housed in the heat insulation pipe 20 and the cable core 10 needs to be cooled and held at a low temperature by the liquid refrigerant L, an increase in heat penetration in the heat insulation pipe 20 is not preferable. It is preferable to provide the connection boxes 30A and 30B and the refrigerant pipes 34A and 34B. As described above, since the installation of the pressure adjustment tank 50 can cause heat intrusion, it is preferable to provide the pressure adjustment tank 50 on the downstream side as viewed from the heat insulating pipe 20.

  Further, the pressure increase in the refrigerant flow path is caused by an overcurrent flowing through the cable core 10 due to an accident such as a short circuit, whereby the temperature of the cable core 10 rises and the liquid refrigerant L existing around the cable core 10 expands in volume. Get up. That is, the pressure increase in the refrigerant flow path at the time of the accident basically occurs on the superconducting cable 1 (heat insulating pipe 20) side. When the pressure adjustment tank 50 is provided at a position far away from the superconducting cable 1, since the flow path distance from the starting point of the pressure increase to the pressure adjustment tank 50 becomes long, the pressure propagation to the relief valve 51 of the pressure adjustment tank 50 Takes time. Therefore, the responsiveness of the relief valve 51 to the pressure increase in the superconducting cable 1 may be reduced, and the pressure adjustment tank 50 may not function effectively, and the short-time pressure increase in the superconducting cable 1 is mitigated. Can be difficult. Therefore, it is considered that the pressure adjusting tank 50 is preferably provided in the vicinity of the superconducting cable 1, specifically, in the connection pipes 30A and 30B or the refrigerant pipes 34A and 34B in the vicinity of the connection boxes 30A and 30B. If the cooling system 40 is installed in the vicinity of the superconducting cable 1, the pressure adjusting tank 50 may be provided in the reservoir tank 43. The “near end connection part (connection box)” here refers to the pressure increase in the superconducting cable 1 except for the superconducting cable 1 (heat insulation pipe 20) side in the vicinity of the end connection part (connection box). For example, the flow path distance in the refrigerant flow path is within 30 m, preferably within 10 m from the end connection part (connection box).

(Relief valve)
The relief valve 51 is interposed between the refrigerant flow path and the pressure adjustment tank 50, and opens and closes according to the refrigerant pressure in the refrigerant flow path. In this example, the relief valve 51 is a check valve that opens only in the direction toward the pressure adjusting tank. By using the relief valve 51 as a check valve, it is possible to prevent the liquid refrigerant L in the pressure adjusting tank 50 or the gas vaporized from the liquid refrigerant L from flowing back into the refrigerant flow path. Moreover, what is necessary is just to set the operating pressure of the relief valve 51 suitably, for example, setting higher than the pumping pressure of the liquid refrigerant | coolant L by the circulation pump 42, and lower than the allowable pressure of the member which comprises a refrigerant flow path is mentioned.

(Exhaust valve)
The pressure adjusting tank 50 temporarily stores the liquid refrigerant L in the pressure adjusting tank 50 when the relief valve 51 is opened and the liquid refrigerant L flows in from the refrigerant flow path at the time of abnormality. An exhaust valve 52 is attached to the pressure adjustment tank 50 shown in FIG. 2, and the exhaust valve 52 exhausts the gas evaporated from the liquid refrigerant in the pressure adjustment tank 50. It is also possible to collect the liquid refrigerant L stored in the pressure adjusting tank 50 and return it to the refrigerant flow path for reuse after returning from the accident.

(Moving bulkhead)
With reference to FIG. 3, one configuration example of the pressure adjustment tank 50 will be described. The pressure adjustment tank 50 shown in FIG. 3 has a moving partition 55 in the pressure adjustment tank 50 that separates the gas phase 50G and the liquid phase 50L. The moving partition wall 55 moves up and down due to the buoyancy caused by the liquid refrigerant L that has escaped into the pressure adjusting tank 50 in the event of an abnormality, and the position changes according to the amount of the liquid refrigerant L. The gas whose liquid refrigerant is vaporized in the pressure adjustment tank 50 accumulates in the gas phase 50G through the gap between the pressure adjustment tank 50 and the moving partition wall 55. Thereby, it is easy to exhaust only the gas which the liquid refrigerant vaporized from the exhaust valve 52 (refer FIG. 2).

<Pressure rise suppression mechanism>
A mechanism for suppressing the pressure increase in the refrigerant flow path by the pressure adjusting tank 50 in the superconducting cable system S will be described.

  Normally, the relief valve 51 is closed, the pressure adjustment tank 50 is separated from the refrigerant flow path, and a gas phase is secured in the pressure adjustment tank 50. On the other hand, when the refrigerant pressure in the refrigerant flow path exceeds a predetermined pressure due to an accident such as a short circuit, the relief valve 51 is actuated and opened, causing the liquid refrigerant L to escape from the refrigerant flow path into the pressure adjustment tank 50 and the refrigerant flow. Reduce the refrigerant pressure in the passage. Therefore, the superconducting cable system S can suppress an increase in pressure when the refrigerant pressure in the refrigerant channel rises, and can avoid damage to the superconducting cable and the refrigerant channel. Further, the liquid refrigerant L that has escaped into the pressure adjustment tank 50 in the event of an abnormality is stored in the pressure adjustment tank 50, and the gas vaporized by the liquid refrigerant in the pressure adjustment tank 50 is exhausted. Higher safety than direct release to the outside.

(Release valve)
The superconducting cable system S shown in FIG. 2 further includes a discharge valve 60. The release valve 60 is connected to the refrigerant flow path, and opens when the refrigerant pressure in the refrigerant flow path exceeds a predetermined pressure, and discharges the liquid refrigerant L from the refrigerant flow path to the outside. The discharge valve 60 is normally closed, and automatically opens when the refrigerant pressure in the refrigerant channel exceeds a predetermined pressure.

The installation location of the release valve 60 is not particularly limited. For example, the release valve 60 may be attached to the refrigerant pipes 34A and 34B, the terminal connection portions 3A and 3B (connection boxes 30A and 30B), the reservoir tank 43, and the heat insulating pipe 20 that constitute the refrigerant flow path. For the same reason as the pressure adjustment tank 50, the release valve 60 is preferably installed in the connection boxes 30A and 30B or the refrigerant pipes 34A and 34B in the vicinity of the connection boxes 30A and 30B. It is more preferable to install in the connection box 30B located on the terminal connection part 3B side) or in the refrigerant pipe 34B in the vicinity of the connection box 30B. In this example, the discharge valve 60 is attached to the connection box 30B.

  The release valve 60 shown in this example functions as a safety valve. The operating pressure of the release valve 60 is set to be higher than the operating pressure of the above-described relief valve 51. For example, the operating pressure of the members constituting the refrigerant flow path can be set. That is, the relief valve 51 operates at a pressure lower than the operating pressure of the release valve 60. The release valve 60 is a check valve that opens only in a direction in which liquid refrigerant (including gas evaporated from the liquid refrigerant) is discharged from the refrigerant flow path.

  In the superconducting cable system S having the release valve 60, even if the pressure adjustment tank 50 does not catch up with the pressure increase in the refrigerant flow path, the discharge valve 60 opens and the liquid refrigerant flows from the refrigerant flow path. By releasing L to the outside, the refrigerant pressure in the refrigerant flow path can be reduced. In addition, since the operating pressure of the relief valve 51 is lower than the operating pressure of the release valve 60, the relief valve 51 is opened before the release valve 60 is activated, and the liquid refrigerant L is released from the refrigerant flow path into the pressure adjustment tank 50. The refrigerant flow path can be decompressed. Therefore, when the refrigerant pressure in the refrigerant flow path rises, the pressure adjustment tank 50 can first suppress the pressure rise in the refrigerant flow path, and the operation of the release valve 60 that discharges the liquid refrigerant L to the outside can be performed. Can be reduced.

(Heat exchanger)
The superconducting cable system S shown in FIG. 2 includes a heat exchanger 61 that vaporizes the liquid refrigerant L discharged from the discharge valve 60 at the open end of the discharge valve 60 described above. The “open end of the release valve” refers to the end of the release valve 60 opposite to the side connected to the refrigerant flow path. The gas obtained by vaporizing the liquid refrigerant in the heat exchanger 61 is released from the outlet of the heat exchanger 61. By providing the heat exchanger 61, the liquid refrigerant L discharged from the release valve 60 can be vaporized by the heat exchanger 61 and discharged to the outside from the outlet of the heat exchanger 61, so that the liquid refrigerant L is directly discharged to the outside. It is safer than the case.

(Silencer)
In the superconducting cable system S shown in FIG. 2, a silencer 62 is provided at the outlet of the heat exchanger 61 described above. When the liquid refrigerant L is vaporized in the heat exchanger 61, the volume of the liquid refrigerant L expands explosively, and high-pressure gas is released from the outlet of the heat exchanger 61. When the high-pressure gas is released at the outlet of the heat exchanger 61, a large explosion may occur at the outlet. Therefore, by attaching a silencer 62 to the outlet of the heat exchanger 61, explosion sound generated at the outlet of the heat exchanger 61 can be reduced. Various known configurations can be used for the configuration of the silencer 62. For example, a known configuration used for an automobile muffler can be employed.

(Other)
In the superconducting cable system S shown in FIG. 2, a safety valve (not shown) may be provided separately from the release valve 60. The safety valve may be provided in the connection boxes 30A and 30B and the reservoir tank 43. When a safety valve is provided, the operating pressure of the discharge valve 60 may be set lower than that of the safety valve. The operating pressure of the relief valve 51 _{P 1,} when the operating pressure of the discharge valve 60 to _{P 2,} the working pressure of the safety valve and _{P m,} the operating pressure of each _valve, be _{P 1 <P} 2 _{<P m} Can be mentioned.

  In the superconducting cable system S of the first embodiment described above, the case where the pressure adjustment tank 50 is provided in the refrigerant pipe 34B in the vicinity of the connection box 30B has been described as an example, but the pressure adjustment tank 50 is provided in the connection box 30B. It is also possible to provide the connection box 30A, the refrigerant pipe 34A in the vicinity thereof, and the reservoir tank 43. In the superconducting cable system S of the first embodiment, the installation location of the release valve 60 may be changed. The release valve 60 is provided in the refrigerant pipe 34B in the vicinity of the connection box 30B, or the refrigerant in the connection box 30A or in the vicinity thereof. It is also possible to provide the pipe 34 </ b> A and the reservoir tank 43. A plurality of pressure adjusting tanks 50 and a plurality of discharge valves 60 may be provided. Furthermore, when the superconducting cable system S includes an intermediate connecting portion (not shown) for connecting the superconducting cables, the pressure adjusting tank 50 and the discharge valve 60 can be provided in the intermediate connecting portion.

  In the first embodiment, the superconducting cable system using the three-core type superconducting cable has been described as an example. However, the configuration of the superconducting cable can be changed as appropriate. For example, the superconducting cable may be a single-core superconducting cable in which one superconducting conductor is housed in a heat insulating tube. The superconducting cable may perform AC power transmission or may perform DC power transmission. There are two types of superconducting cables: a low-temperature insulation method in which an electrical insulation layer is provided in a heat insulation tube, and a room temperature insulation method in which an electrical insulation layer is provided outside the heat insulation tube. Either method can be adopted.

  The superconducting cable system according to one embodiment of the present invention can be suitably used for a power transmission line.

S Superconducting cable system 1 Superconducting cable 10 Superconducting conductor (cable core)
DESCRIPTION OF SYMBOLS 101 Former 102 Superconducting conductor layer 103 Electrical insulation layer 104 Shield layer 105 Protective layer 20 Heat insulation pipe 21 Inner pipe 22 Outer pipe 25 Corrosion prevention layer 3A, 3B Termination connection part 30A, 30B Connection box 34A, 34B Refrigerant piping 40 Cooling system 41 Refrigerator 42 Circulating pump 43 Reservoir tank 50 Pressure adjustment tank 51 Relief valve 52 Exhaust valve 55 Moving partition wall 50L Liquid phase 50G Gas phase 60 Release valve 61 Heat exchanger 62 Silencer L Liquid refrigerant

Claims (3)

A superconducting cable having a superconducting conductor layer having a superconducting conductor layer on the outer periphery of the former is housed in a heat insulating tube, and a liquid refrigerant for cooling the superconducting conductor layer is supplied into the heat insulating tube, and a refrigerant flow path is formed together with the heat insulating tube. A superconducting cable system comprising a cooling system,
A pressure adjustment tank provided in the refrigerant flow path, into which the liquid refrigerant from the refrigerant flow path flows;
A relief valve interposed between the refrigerant flow path and the pressure adjustment tank, and opened and closed according to a refrigerant pressure in the refrigerant flow path ;
A discharge valve that is connected to the refrigerant flow path and opens when a refrigerant pressure in the refrigerant flow path exceeds a predetermined pressure, and discharges the liquid refrigerant from the refrigerant flow path to the outside ,
Normally, the relief valve is closed, the pressure adjustment tank is separated from the refrigerant flow path, and a gas phase is secured in the pressure adjustment tank,
When the refrigerant pressure in the refrigerant flow path exceeds a predetermined pressure, the relief valve is opened by operating at a pressure lower than the operating pressure of the discharge valve, and the liquid refrigerant is discharged from the refrigerant flow path into the pressure adjustment tank. And a superconducting cable system for reducing the refrigerant pressure in the refrigerant flow path.   The superconducting cable system according to claim 1, wherein the relief valve is a check valve that opens only in a direction toward the pressure adjusting tank. The superconducting cable system according to claim 1 or 2 , further comprising a heat exchanger that vaporizes the liquid refrigerant discharged from the discharge valve at an open end of the discharge valve.

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