HK1100720A - Superconductive cable line - Google Patents

Description

Superconducting cable line

Technical Field

The present invention relates to a power supply line including a superconducting cable. More particularly, the present invention relates to a superconducting cable line which reduces the amount of heat intrusion into the superconducting cable, thereby reducing the energy for cooling the coolant used in the cable, and which can increase the coefficient of performance (COP) of the cable as a whole.

Background

There is generally known a superconducting cable including a thermal insulation pipe that accommodates a cable core with a superconductor layer. Such a superconducting cable includes, for example, a single-core cable having a thermal insulation pipe accommodating one cable core or a three-core cable accommodating three cable cores in a bundle. Fig. 7 is a cross-sectional view of a three-core superconducting cable for three-phase alternating current. Fig. 8 is a cross-sectional view of each cable core 102. This superconducting cable 100 has a structure in which three cables 102 are accommodated in one heat insulating pipe 101. The heat insulating pipe 101 has a structure in which a heat insulating material (not shown) is provided between double pipes formed of an outer pipe 101a and an inner pipe 101b and discharging air between the pipes 101a, 101 b. Each cable core 102 includes, from a central portion thereof, a sizing tube 200, a superconductor layer 201, an electrical insulation layer 202, a superconducting shield layer 203, and a protective layer 204. The space 103 surrounded by the inner tube 101b and each cable core 102 serves as a passage for a coolant such as liquid nitrogen. The superconducting state of the superconductor layer 201 and the superconducting shield layer 203 of the cable core 102 is maintained by coolant cooling. An anti-corrosion layer 104 is provided on the outer periphery of the heat insulating tube 101.

The superconducting cable must be continuously cooled with a coolant such as liquid nitrogen in order to maintain the superconducting state of the superconductor layer and the superconducting shield layer. Therefore, a line using a superconducting cable generally includes a cooling system for a coolant. With such a system, circulation cooling is performed in which the coolant ejected from the cable is cooled, and the cooled coolant flows into the cable again.

By cooling the coolant to an appropriate temperature by the cooling system, the superconducting cable can maintain the superconducting state of the superconductor layer and the superconducting shield layer by sufficiently reducing the increase in the temperature of the coolant caused by the heat of the coolant generated by the passage of current or the heat invading from the outside such as the environment. However, when the coolant is liquid nitrogen, the energy required to cool the coolant to overcome this generated or intrusive heat becomes at least 10 times higher than the energy required to cool the cable by the coolant. Therefore, when a superconducting cable line including a cooling system for a coolant is considered as a whole, a coefficient of performance (COP) becomes 0.1 or less. Such low COP is one of the reasons for reducing the effect of application of superconducting devices such as superconducting cables. Therefore, each of japanese patent application publication No. JP2002-130851 (patent document 1) and japanese patent application publication No. JP10-092627 (patent document 2) proposes cooling of the coolant of the superconducting coil using the cold heat (cold heat) of the Liquefied Natural Gas (LNG).

On the other hand, with the development of fuel cell vehicles, it is planned to establish a hydrogen station in many places in japan to store compressed hydrogen gas or liquid hydrogen to be supplied to the fuel cell vehicles. The hydrogen station includes, for example, tanks for storing liquid hydrogen produced and transported at a factory or produced at the hydrogen station, and a cooling system for liquefying vaporized hydrogen to maintain it in a liquid state. Although the hydrogen gas can be maintained in a liquid state by being cooled to an appropriate temperature using a cooling system, since the liquid hydrogen has a low-temperature boiling point of about 20K, which is significantly different from the normal temperature of the environment, the heat intrusion from the outside becomes large. Therefore, a large amount of energy is required to cool the liquid hydrogen to reduce the temperature increase due to heat intrusion.

Patent document 1: japanese patent application laid-open No. JP2002-130851

Patent document 2: japanese patent application laid-open No. JP10-092627

Disclosure of Invention

Each of the above-mentioned patent documents 1 and 2 only discloses the use of cold heat of LNG for a coolant for cooling a superconducting coil, and does not consider reducing heat intrusion from the outside. On the other hand, in the liquid hydrogen station, it is also desired to reduce the energy for cooling hydrogen, as described above.

Therefore, a main object of the present invention is to provide a superconducting cable line capable of reducing heat intrusion into a superconducting cable and capable of reducing energy for cooling the superconducting cable and energy for cooling liquid hydrogen as a whole.

The present invention achieves the above object by providing a superconducting cable in a heat insulating pipe that transports liquid hydrogen and exchanging heat between the liquid hydrogen and a coolant of the cable. That is, the superconducting cable line of the present invention includes a heat-insulating tube for fluid for transporting liquid hydrogen and a superconducting cable placed inside the heat-insulating tube for fluid to cool a superconducting portion with a coolant having a temperature higher than that of the liquid hydrogen. Further comprising heat exchange means for cooling the liquid hydrogen and raising the temperature of the coolant of the superconducting cable cooled by the liquid hydrogen. The present invention will be described in more detail below.

The structure of the superconducting cable used in the present invention includes a superconducting portion formed of a superconducting material and a heat insulating pipe (hereinafter referred to as a heat insulating pipe for a cable) which accommodates the superconducting portion and is filled with a coolant for cooling the superconducting portion. The superconducting portion may include a superconductor layer for flowing a power supply current and an external superconductor layer for flowing a current having substantially the same current value as that of the superconductor layer in an opposite direction. The superconducting portion is typically formed in a cable core. Therefore, the superconducting cable can be constructed by enclosing the superconducting cable including the superconducting layer in a heat insulating pipe for the cable. A more specific structure of the cable core includes, from a central portion thereof, a sizing tube, a superconductor layer, an electrically insulating layer, an outer superconductor layer, and a protective layer. The thermal insulation tube for a cable may accommodate one cable core (single core (one core)) or a plurality of cable cores (a plurality of cores). More specifically, for example, when the line of the present invention is used for three-phase AC transmission, a three-core cable having a heat insulating tube for an electric cable for accommodating three cores may be used, and when the line of the present invention is used for single-phase AC transmission, a single-core cable having a heat insulating tube for an electric cable for accommodating one core may be used. For example, when the line of the present invention is used for DC transmission (unipolar transmission), a single core cable having a thermal insulation tube for a cable for accommodating one core may be used, and when the line of the present invention is used for DC transmission (bipolar transmission), a two-core cable or a three-core cable having a thermal insulation tube for a cable for accommodating two or three bundles of cores may be used. As described above, the superconducting cable line of the present invention can be used for DC transmission or AC transmission.

For example, the superconductor layer may be formed by spirally winding a strip-shaped wire including a plurality of metal wires made of a superconducting material based on a Bi oxide, more specifically, a superconducting material based on Bi2223, the metal wires being disposed in a matrix such as a silver sheath. The superconductor layer may have a single-layer or multi-layer structure. When the superconductor layer has a multilayer structure, an interlayer insulating layer may be provided therein. The interlayer insulating layer may be formed by winding an insulating paper such as kraft paper or a semisynthetic insulating paper such as PPLP (trademark of Sumitomo Electric Industries, ltd.). The superconductor layer is formed by winding a wire made of a superconducting material around a sizing tube. The sizing tube may be a solid body or a hollow body formed of a metal material such as copper or aluminum, and has a structure such as a bundle of copper wires. Copper wires with an insulating coating may be used. The sizing pipe serves as a shape maintaining member of the superconductor layer. A shim layer may be interposed between the sizing tube and the superconductor layer. The cushion layer prevents direct contact of metal between the sizing tube and the superconducting wire, thereby preventing the superconducting wire from being damaged. In particular, when the sizing pipe has a twisted structure, the cushion layer also has a function of smoothing the surface of the sizing pipe. Insulating paper or carbon paper may be suitably used as the prescribed material of the cushion layer.

The electrically insulating layer may be formed by winding a semisynthetic insulating paper such as PPLP (trademark) or an insulating paper such as kraft paper around the superconductor layer. The semiconductor layer may be formed of carbon paper or the like on at least one of the inner periphery or the outer periphery of the electrically insulating layer, that is, between the superconductor layer and the electrically insulating layer and between the electrically insulating layer and an external superconducting layer (described below). By forming the inner semiconductor layer (as the former) or forming the outer semiconductor layer (as the latter), adhesion between the superconductor layer and the electrical insulating layer or between the electrical insulating layer and the outer superconducting layer is increased, thereby suppressing deterioration due to partial discharge or the like.

When the wiring of the present invention is used for DC transmission, the electrically insulating layer may be subjected to ρ grading to obtain low resistivity at the inner peripheral side and high resistivity at the outer peripheral side of the electrically insulating layer, thereby smoothing the DC electric field distribution in the diameter direction (thickness direction) thereof. As described above, "ρ grading" means that the resistivity in the thickness direction of the electrical insulation layer changes in a stepwise manner, which can smooth the DC electric field distribution in the entire thickness direction of the electrical insulation layer and can reduce the thickness of the electrical insulation layer. Although the number of layers having different resistivities is not particularly limited, two or three layers are actually employed. Particularly, when the thicknesses of the respective layers are equalized, the smoothness of the DC electric field distribution can be more effectively performed.

ρ grading may be performed using insulating materials whose resistivities (ρ) are different from each other. When an insulating paper such as kraft paper is used, the resistivity can be changed by changing the density of the kraft paper or adding dicyandiamide to the kraft paper, for example. When a composite paper formed of an insulating paper and a plastic film such as PPLP (trademark) is used, the resistivity can be changed by changing a ratio k, which is a ratio between the thickness tp of the plastic film and the thickness T of the entire composite paper, or by changing the density, material, additives, and the like of the insulating paper. The value of the ratio k is preferably, for example, in the range of 40 to 90%. In general, the resistivity ρ increases as the ratio k increases.

Further, when the electric insulating layer has a high ∈ layer which is provided in the vicinity of the superconducting conductor and has a higher dielectric constant than another portion, in addition to increasing the direct-current withstand voltage characteristic, the imp. The dielectric constant ε (20 ℃) is about 3.2 to 4.5 in a typical kraft paper, about 2.8 in a ratio of 40% composite paper, about 2.6 in a ratio of 60% composite paper, and about 2.4 in a ratio of 80% composite paper. The electrical insulating layer constructed of composite paper using kraft paper of high ratio k and high airtightness is particularly preferable because the direct current withstand voltage and the imp.

In addition to the above ρ grading, a cable also suitable for AC transmission is formed by constructing an electrically insulating layer whose dielectric constant ∈ increases toward the inner peripheral side and decreases toward the outer peripheral side. The "epsilon grading" is also performed over the entire area in the diameter direction of the electrically insulating layer. The superconducting cable subjected to the ρ grading has a good DC characteristic and is applicable as a DC transmission line. On the other hand, most current transmission lines are constructed for AC transmission. When a transmission system is converted from an AC system to a DC system, there may occur a case where AC transmission is instantaneously transmitted using a superconducting cable subjected to ρ grading before being converted to DC transmission. This may occur, for example, when a part of the cable of the transmission line is replaced with the superconducting cable subjected to ρ grading while the other part is still the cable for AC transmission, or when the cable for AC transmission of the transmission line is replaced with the superconducting cable subjected to ρ grading while the transmission device connected to the cable is still the device for AC. In this case, AC transmission is instantaneously performed using the superconducting cable subjected to ρ grading, and then, the system is finally converted into DC transmission. Therefore, the superconducting cable can preferably be designed not only to have a good DC characteristic but also to be considered to have an AC characteristic. When the AC characteristic is also considered, a superconducting cable having a good pulse characteristic such as surge can be constructed by constructing an electrical insulation layer whose dielectric constant ∈ increases toward the inner peripheral side and decreases toward the outer peripheral side. Then, when the above-described transient period is ended and DC transmission is performed, the superconducting cables subjected to ρ grading used during the transient period can be continuously used as DC cables. That is, the use of the superconducting cable that is epsilon-staged in addition to the ρ -staged can be applied to each of the DC transmission and the AC transmission, and also to the lines for the AC and DC transmission.

The above-mentioned PPLP (trademark) generally has a higher value of ρ and a lower value of ε as the ratio k increases. Therefore, when the electric insulating layer is configured with PPLP (trademark) whose ratio k increases toward the outer periphery side of the electric insulating layer, ρ may increase toward the outer periphery side, and ∈ may decrease toward the outer periphery side.

Kraft paper, on the other hand, generally has a higher p value and a higher e value as air tightness increases. Therefore, it is difficult to construct an electrical insulating layer in which ρ increases toward the outer peripheral side and ε decreases toward the outer peripheral side, using only kraft paper. Thus, kraft paper may be used in combination with the composite paper to form the electrically insulating layer. As one example, a kraft layer may be formed on an inner circumferential side of the electrical insulation layer and a PPLP layer may be formed on an outer side thereof such that a resistivity p value of the kraft layer is lower than a p value of the PPLP layer, and a dielectric constant e value of the kraft layer is higher than a dielectric constant e value of the PPLP.

The outer superconducting layer is provided on the outer periphery of the above-mentioned electrically insulating layer. The outer superconductor layer is formed of a superconducting material, such as the material used to form the superconductor layer. The same superconducting material as that used to form the superconductor layer may be used in the outer superconducting layer. When the superconducting cable line of the present invention is used for DC transmission, the outer superconducting layer can be used as a return conductor in unipolar transmission and as a neutral conductor layer in bipolar transmission, for example. In particular, when bipolar transmission is performed, the external superconducting layer may be used to flow an unbalanced current when an unbalance is generated between the positive electrode and the negative electrode. In addition, when one electrode is in an abnormal state and bipolar transmission becomes unipolar transmission, the outer superconducting layer may be used as a return wire for flowing a current equivalent to a transmission current flowing through the superconducting layer. When the superconducting cable line of the present invention is used for AC transmission, the outer superconducting layer may function as a shielding layer for flowing a shielding current formed by current induction flowing through the superconducting layer. A protective layer also for insulation is provided on the outer periphery of the outer superconducting layer.

The thermal insulation tube of the cable for accommodating the cable core having the above structure may have a double-layer tube structure formed of an inner tube and an outer tube, with a thermal insulation material interposed therebetween, and be evacuated to obtain a prescribed degree of vacuum required for forming a vacuum insulation structure. The space inside the inner pipe serves as a coolant passage filled with a coolant such as liquid nitrogen for cooling the cable core (particularly, the superconductor layer and the outer superconducting layer). Likewise, the thermal insulation tube for the cable is preferably a flexible corrugated tube. In particular, the thermal insulation tube for the cable is preferably formed of a metal material such as high-strength stainless steel.

The temperature of the coolant filled in the thermally insulating tube for the cable (which is used in the present invention) is higher than the temperature of the liquid hydrogen transported inside the thermally insulating tube for the fluid. For example, liquid nitrogen is used as the coolant. Since the temperature of the liquid hydrogen is lower than that of the coolant of the superconducting cable, the coolant of the superconducting cable contained in the thermal insulation pipe for the fluid can be cooled with the liquid hydrogen. Therefore, in the line of the present invention, without providing a separate cooling system for the coolant for cooling the coolant of the superconducting cable, it is possible to set a temperature capable of maintaining the superconducting state of the superconducting portion.

In the line of the present invention, a superconducting cable with a heat insulating pipe for a cable for transporting liquid hydrogen is housed in the heat insulating pipe for a fluid. With this structure, the superconducting cable housed in the heat insulating pipe for fluid has an environment around the cable at a temperature lower than normal temperature, more specifically, a low-temperature environment of about 20K (which is the temperature of liquid hydrogen), and thus the temperature difference between the inside and the outside of the heat insulating pipe for cable is reduced to less than 200K as compared with the case of being placed in the environment. In particular, when liquid nitrogen is used as a cable coolant, the temperature difference between the inside and the outside of the thermal insulation tube for the cable becomes about 50K. In addition, the superconducting cable housed in the thermal insulation pipe for fluid has a double-layer thermal insulation structure formed of a thermal insulation structure for liquid hydrogen and a thermal insulation structure for the cable itself. Therefore, since the line of the present invention has a small temperature difference between the inside and the outside of the heat insulating pipe for the cable and the superconducting cable has the double-layer heat insulating structure as described above, heat intrusion into the cable portion from the outside can be effectively reduced as compared with the superconducting cable line placed in the environment.

The heat insulating pipe having heat insulating properties corresponding to the liquid hydrogen transported therein can be used as a heat insulating pipe for a fluid for housing the superconducting cable. As one example, a thermal insulation pipe having a structure similar to that of the superconducting cable, that is, a double-pipe structure formed of an outer pipe and an inner pipe, which includes a thermal insulation material between the pipes and is evacuated, may be used. In this case, the space inside the inner tube becomes a transport passage for the liquid hydrogen.

For example, in forming a heat-insulating pipe for fluid by welding a metal plate made of stainless steel, or the like, a superconducting cable may be installed in the heat-insulating pipe for fluid by disposing the cable on the metal plate, bending the metal plate to cover the cable, and welding edges of the metal plate. When a metal pipe made of stainless steel, or the like is used as a heat insulating pipe for fluid, a cable can be incorporated in the heat insulating pipe for fluid by inserting a superconducting cable into the pipe. In this case, a sliding wire (sliding wire) may be spirally wound around the cable, thereby improving insertion characteristics of the superconducting cable. In particular, when the thermal insulation tube for an electric cable is a corrugated tube having a protrusion and a recess, the insertion characteristic can be improved by winding the slide wire with a pitch larger than the pitch (long pitch) between the protrusion and the recess of the corrugated tube, thereby preventing the slide wire from entering the recess portion of the corrugated tube, and thereby placing the slide wire over the protrusion and the recess of the corrugated tube, to prevent the outer periphery of the corrugated tube from being in direct contact with the thermal insulation tube for a fluid, that is, to obtain a point contact between the slide wire wound around the corrugated tube and the thermal insulation tube for a fluid. Further, a tension member or the like may be connected to the superconducting cable so that it can be pulled into the thermal insulation pipe for the fluid.

The superconducting cable housed in the heat insulating pipe for fluid may be disposed in contact with or not in contact with liquid hydrogen transported inside the heat insulating pipe for fluid. In the former case, the superconducting cable may be immersed in liquid hydrogen. In this case, since the entire periphery of the superconducting cable is in contact with the cryogenic liquid hydrogen, heat intrusion into the cable from the outside can be effectively reduced, and the cable coolant can be sufficiently cooled with the liquid hydrogen.

On the other hand, when the superconducting cable is immersed in liquid hydrogen, problems such as liquid hydrogen explosion may occur, for example, in the case where the superconducting cable is short-circuited to generate a spark. Therefore, the area inside the thermal insulation pipe for the fluid can be divided into a transport area for the liquid hydrogen and an area for disposing the superconducting cable therein. As the transport region, for example, a transport pipe for liquid hydrogen may be detachably provided inside the thermal insulation pipe for fluid, and the superconducting cable may be provided longitudinally along the transport pipe. In this case, when the heat exchanger partition having high thermal conductivity is disposed in the space inside the thermal insulation pipe for the fluid not occupied by the transport pipe and the superconducting cable, the heat of the liquid hydrogen can be efficiently conducted to the cable through the heat exchanger partition, and thus the cable can be efficiently cooled. Such heat exchanger baffles may be formed, for example, of a material having a high thermal conductivity, such as aluminum. More specifically, the heat exchanger separator may be formed by winding an aluminum foil.

In the present invention, a superconducting cable using a coolant having a temperature higher than that of liquid hydrogen can be used, and since the cable is housed in a heat insulating pipe for fluid, which is used for transporting liquid hydrogen, the coolant can be cooled using liquid hydrogen. However, the coolant of the superconducting cable may be excessively cooled by the liquid hydrogen, and the coolant solidification may occur. Therefore, it is necessary to raise the temperature of the coolant for excessive cooling of the superconducting cable housed in the thermal insulation pipe for the fluid to a range capable of maintaining the superconducting state. On the other hand, liquid hydrogen needs to be cooled to maintain a liquid state (liquefaction). The invention therefore comprises heat exchange means for exchanging heat between the liquid hydrogen and the liquid nitrogen in order to cool the liquid hydrogen and raise the temperature of the coolant, both cooled excessively by the liquid hydrogen.

The heat exchange device may have such a structure that it includes, for example, a passage for circulating a heat exchange medium, an expansion valve for expanding the heat exchange medium, a compressor for compressing the heat exchange medium, and a thermally insulating housing for accommodating the passage, the expansion valve, and the compressor. A delivery pipe for liquid hydrogen is provided on a part of the passage which passes through the expansion valve to cool the liquid hydrogen with the expanded heat exchange medium, and a delivery pipe for the coolant for the cable is provided on a part of the passage which passes through the compressor to raise the temperature of the coolant for the superconducting cable with the compressed heat exchange medium. The supply line for liquid hydrogen may be provided, for example, to form a circulation path in which liquid hydrogen injected from inside the thermal insulation tube for fluid flows into the thermal insulation tube for fluid again. Alternatively, a tank storing liquid hydrogen may be connected to a thermally insulated pipe for fluid, and a delivery line may be provided to form a circulation path in which liquid hydrogen ejected from the tank flows into the tank again. Then, a part of such a delivery line for liquid hydrogen may be provided in contact with a part of the passage of the heat exchange medium passing through the expansion valve, or in the vicinity of the part. The transport pipe for the coolant may be provided as a circulation path in which the coolant sprayed from the thermal insulation tube for the cable flows into the thermal insulation tube for the cable again. A part of such a feed line for the coolant can then be arranged in contact with a part of the passage of the heat exchange medium through the compressor or in the vicinity of this part. In the heat exchanging device, the temperature of the coolant is raised to a temperature range in which the superconducting state of the superconducting portion can be maintained. The present invention can satisfy both the requirement of raising the temperature of the coolant of the superconducting cable and the requirement of cooling the liquid hydrogen, since it includes the heat exchanging means for cooling the liquid hydrogen and simultaneously heating the coolant of the cable.

It is to be noted that, in the present invention, since the heat intrusion into the superconducting cable housed in the heat insulating pipe for fluid can be reduced as described above, the heat insulating structure of the heat insulating pipe for cable can be simplified, that is, the level of the heat insulating performance of the heat intrusion into the cable from the outside can be reduced. When the heat insulating pipe for a cable has a double-layer pipe structure formed of an outer pipe and an inner pipe, the heat insulating property can be changed by, for example, changing the degree of vacuum between the outer pipe and the inner pipe, changing the number of windings of the heat insulating material provided between the outer pipe and the inner pipe, or changing the material of the heat insulating material, which is provided between the pipes and evacuated.

In addition, in the superconducting cable line of the present invention, the entire length in the longitudinal direction of the superconducting cable forming the line may be housed in the heat insulating pipe for fluid, or only a part of the cable may be housed in the heat insulating pipe for fluid. In view of reducing the heat of invasion, it is preferable to enclose the entire length of the superconducting cable in a heat insulating pipe for fluid.

Such a superconducting cable line of the present invention may be constructed, for example, by enclosing the superconducting cable in a pipe having a thermal insulation structure for connecting a hydrogen plant for producing liquid hydrogen to a hydrogen station for storing liquid hydrogen, or enclosing the superconducting cable in a thermal insulation pipe for transporting liquid hydrogen at the hydrogen station, and providing a heat exchange means in the vicinity of the hydrogen station. The circuit of the present invention can be used to supply power to various power devices used in hydrogen stations, or to absorb necessary power from pipes to supply power to various places.

As described above, the superconducting cable line of the present invention can be used for DC transmission or AC transmission. For example, in the case of three-phase AC transmission, the cable may be formed as a three-core superconducting cable in which the superconductor layer of each core is used for each phase transmission and the outer superconductor layer of each core is used as a shield layer. In the case of single-phase AC transmission, the cable may be formed as a single-core superconducting cable in which a superconductor layer contained in a core may be used for phase transmission and an outer superconducting layer may be used as a shielding layer. When performing unipolar DC transmission, the cable may be formed as a single-core superconducting cable, in which the superconductor layer of the core may be used as a "go" wire (go conductor) and the outer superconducting layer may be used as a return conductor. When bipolar DC transmission is performed, the cable may be formed as a two-core superconducting cable in which the superconductor layer of one core may be used for positive transmission, the superconductor layer of the other core may be used for negative transmission, and the outer superconductor layer of each core may be used as a neutral wire.

In addition, the superconducting cable of the present invention can also be used as a line for DC and AC transmission by using a superconducting cable including a cable core of an electrical insulation layer subjected to ρ grading and ∈ grading as described above. In this case, not only the superconducting cable but also a terminal structure formed in an end portion of the line for connecting the superconducting cable with a conducting portion on the normal temperature side (a normal conducting cable, a lead portion connected to the normal conducting cable) is preferably configured to be suitable for DC and AC transmission. A representative structure of the terminal structure includes a cable core end extending from an end of the superconducting cable, a drawn conductor part connected to a conduction part on the normal temperature side, a connection part electrically connected to the cable core end by the drawn conductor part, and a terminal box for accommodating the cable core end, the end of the drawn conductor part on the side connected to the cable core, and the connection part. The terminating terminal block typically includes a coolant pool for cooling the cable core end or the end of the extraction conductor portion and a vacuum insulation pool disposed on the outer periphery of the coolant pool. In such a terminal structure, the cross-sectional area of the conductor of the extraction conductor portion is variable as needed because the amount of current flowing through the extraction conductor portion differs in AC transmission and DC transmission. Therefore, a suitable structure of the terminal structure for AC and DC transmission has a conductor cross-sectional area of the extraction conductor portion that can be changed according to the load. Such a terminal structure may have, for example, a structure in which the extraction conductor portion is divided into a low-temperature-side conductor portion connected to the end of the cable core and an ordinary-temperature-side conductor portion provided on the side of the conducting portion on the ordinary-temperature side, wherein the low-temperature-side conductor portion and the ordinary-temperature-side conductor portion are detachable from each other. Further, a plurality of such extraction conductor portions are detachably included to allow the cross-sectional area of the conductor of the entire extraction conductor portion to be changed in accordance with the number of joints between the low-temperature-side conductor portion and the normal-temperature-side conductor portion. The cross-sectional areas of the conductors of the respective extraction conductor portions may be the same as or different from each other. The superconducting cable line of the present invention including such a terminal structure can be easily changed from DC transmission to AC transmission, or from AC transmission to DC transmission, by performing attachment and detachment of the extraction conductor part. In addition, since the cross-sectional area of the conductor of the drawn-out conductor portion can be changed as described above, the cross-sectional area of the conductor can also be appropriately changed when the amount of power supplied is changed during AC transmission or DC transmission.

In the superconducting cable line according to the present invention having the above structure, the superconducting cable is installed in the thermal insulation pipe for transporting liquid hydrogen to reduce a temperature difference between the inside and the outside of the thermal insulation pipe for the cable, and the thermal insulation structure of the cable is formed as a double-layer thermal insulation structure including the thermal insulation pipe for the cable and the thermal insulation pipe for the fluid to effectively reduce heat intrusion into the cable. In addition, in the line of the present invention, the coolant of the superconducting cable may be cooled with liquid hydrogen transported in the thermal insulation pipe for the fluid. With reduced heat intrusion and cooling of the coolant with the fluid as described above, the circuit of the present invention may substantially reduce or substantially eliminate the energy required for cooling the coolant for the cable. In particular, a cooling system for cooling the coolant of the superconducting cable is not required, or even if a cooling system is provided, the level of cooling performance thereof can be made lower as compared with the conventional system.

Therefore, as described above, when the cooling of the coolant of the superconducting cable is also taken into consideration, the coefficient of performance of the superconducting cable of the present invention having the structure as described above is increased as compared with the conventional line, because the energy required for cooling the coolant can be sufficiently reduced by reducing the heat intrusion into the cable as described above. In particular, when the line of the present invention, in which heat is hardly generated by a current path (conductor loss), is used as a line for DC transmission, the reduction of heat intrusion is extremely effective for increasing the coefficient of performance, because the heat intrusion becomes a main cause of energy loss in this case.

In addition, in the line of the present invention, the energy for cooling the liquid hydrogen is also greatly reduced by using the coolant of the superconducting cable as a heat exchange target for cooling the liquid hydrogen. Therefore, the present invention can completely reduce the energy required for cooling the coolant of the superconducting cable and the energy required for cooling the liquid hydrogen, thereby sufficiently increasing the coefficient of performance.

Further, when a superconducting cable including a cable core having an electrical insulation layer subjected to ρ grading is used in the line of the present invention, the line can have a good DC withstand voltage characteristic and be suitable for DC transmission. In addition, in the line of the present invention, using a superconducting cable including a cable core having an electrical insulation layer which is p-graded and provided with a high value of ∈ at a portion close to the superconductor layer, in addition to the above-described increase in DC withstand voltage characteristics, imp. In particular, when the electrically insulating layer is formed so that the value of ∈ increases toward the inner periphery side and the value of ∈ decreases toward the outer periphery side, the wiring of the present invention can also have good AC electrical characteristics. Therefore, the superconducting cable of the present invention can be applied to various DC transmission and AC transmission. In addition, when a superconducting cable including a cable core having electric insulation layers subjected to ρ grading and ∈ grading is used as the line of the present invention and the terminal structure formed at the end of the line has a structure in which the cross-sectional area of the conductor of the extracted conductor section is variable, the line of the present invention can be applied to a transient period in which the transmission system is changed from an AC system to a DC system, wherein the extracted conductor section is provided between the superconducting cable and the conduction section on the normal temperature side.

Drawings

Fig. 1 is a schematic cross-sectional view of the structure of a superconducting cable line of the present invention;

fig. 2 is a schematic cross-sectional view of a part of a structure in the vicinity of a superconducting cable in the superconducting cable line of the present invention;

fig. 3 is a schematic view of a structure in which a superconducting cable line of the present invention is constructed;

fig. 4 is a schematic view of a structure of a superconducting cable line of the present invention including a delivery pipe for liquid hydrogen, a superconducting cable, and a heat exchanger bulkhead inside a thermal insulation pipe for fluid, which is a schematic cross-sectional view of a part of the structure in the vicinity of the cable;

fig. 5 is a schematic view of a configuration of a terminal structure formed in an end portion of a superconducting cable of the present invention with a superconducting cable of a three-core type in the case of an AC transmission line;

fig. 6 is a schematic view of a configuration of a terminal structure formed in an end portion of a superconducting cable of the present invention with a superconducting cable of a three-core type in the case of a DC transmission line;

fig. 7 is a cross-sectional view of a superconducting cable of a three-core type for three-phase AC transmission;

fig. 8 is a cross-sectional view of each cable core.

Description of the reference numerals

1: liquid hydrogen, 2: thermal insulation pipe for fluid, 2 a: outer tube, 2 b: inner tube, 3: delivery pipe, 4: heat exchanger separator, 10: superconducting cable, 11: thermal insulation tube for electric cable, 11 a: outer tube, 11 b: inner tube, 12: cable core, 13: space, 14: superconductor layer, 15: external superconducting layer, 16: conveying pipeline, 20: hydrogen station, 21: tank, 22: delivery line, 30: heat exchange device, 31: passage, 32: expansion valve, 33: compressor, 34: thermal insulation housing, 40: extraction conductor part, 41: low-temperature-side conductor portion, 41 a: low-temperature-side seal portion, 42: ordinary temperature-side conductor portion, 42 a: ambient temperature side seal portion, 43: guide portion, 44: ground line, 50: terminating terminal block, 51, 52: coolant pool, 53: vacuum insulation cell, 53 a: extendable portion, 60: insulating sleeve, 61: extraction conductor portion, 62: porcelain tube, 63: epoxy unit, 70: short-circuit portion, 100: superconducting cable for three-phase AC transmission, 101: thermal insulation tube, 101 a: outer tube, 101 b: inner tube, 102: cable core, 103: space, 104: anticorrosive coating, 200: sizing tube, 201: superconductor layer, 202: electrically insulating layer, 203: superconducting shielding layer, 204: and a protective layer.

Detailed Description

Embodiments of the present invention will now be described

Example 1

Fig. 1 is a schematic cross-sectional view of the structure of a superconducting cable line of the present invention. Fig. 2 is a schematic cross-sectional view of the structure of the vicinity of the superconducting cable in the superconducting cable of the present invention. Fig. 3 is a schematic view of a structure in which the conductive cable line of the present invention is constructed. Like characters in the drawings denote like parts. The superconducting cable of the present invention includes a thermal insulation tube 2 for fluid for transporting liquid hydrogen 1, a superconducting cable 10 housed in the thermal insulation tube 2 for fluid, and a heat exchanging device 30 for adjusting the temperature of the liquid hydrogen 1 and the temperature of a coolant of the cable.

The superconducting cable 10 used in this example has a structure in which three cable cores 12 are twisted and incorporated in a thermal insulation pipe 11 for a cable, and the structure thereof is substantially similar to that of the superconducting cable shown in fig. 7. Each cable core 12 includes, from the central portion, a sizing tube, a superconductor layer, an electrically insulating layer, an outer superconductor layer, and a protective layer. Both the superconductor layer and the external superconducting layer are formed of Bi 2223-based superconducting tape lines (Ag — Mn sheathed lines). The superconductor layer and the outer superconductor layer are formed by winding the superconducting tape line around the outer periphery of the sizing pipe and the outer periphery of the electrical insulation layer, respectively. A plurality of stranded copper wires may be used as sizing tubes. The cushion layer is formed between the sizing pipe and the superconductor layer using insulating paper. The Electric insulation layer is configured by winding semisynthetic insulation paper (trademark of PPLP: Sumitomo Electric Industries, ltd.) around the outer periphery of the superconductor layer. The protective layer is formed by winding kraft paper around the outer periphery of the outer superconducting layer. The inner semiconductor layer and the outer semiconductor layer may be provided on the inner periphery side and the outer periphery side (under the outer superconducting layer) of the electrically insulating layer, respectively. Such three cable cores 12 are prepared, loosely twisted to have a tolerance of thermal shrinkage, and housed in a thermal insulation tube 11 for a cable. In this example, an SUS corrugated pipe is used to form the heat insulating pipe 11 for a cable, in which a heat insulating material (not shown) having a multi-layer structure is disposed between double-layer pipes formed of an outer pipe 11a and an inner pipe 11b, and air between the outer pipe 11a and the inner pipe 11b is evacuated, thereby obtaining a prescribed degree of vacuum for forming a vacuum multi-layer insulating structure. The space 13 enclosed by the inner periphery of the inner tube 11b and the outer periphery of the three-core cable 12 becomes a passage of the coolant. A coolant for cooling the superconductor layer and the external superconductor layer is circulated in this passage by a pump or the like. In this example, liquid nitrogen (about 77K) is used as the coolant. The piping 16 is connected to the heat insulating pipe 11 for the cable of the superconducting cable 10 to perform circulation conveyance of the coolant, wherein, for example, the coolant is injected from the heat insulating pipe 11 to the side of the heat exchanging device 30, and the coolant flows into the heat insulating pipe 11 from the side of the heat exchanging device 30. A pump (not shown) is provided on a part of the pipe 16 to circulate the coolant.

The superconducting cable 10 having the above-described structure is housed in the thermal insulation tube 2 for fluid. In this example, the heat insulating pipe 2 for fluid has a double-layer pipe structure formed of an outer pipe 2a and an inner pipe 2b, in which a heat insulating material (not shown) is provided between the pipes 2a, 2b and air between the pipes is evacuated. The space surrounded by the inner periphery of the inner tube 2b and the outer periphery of the superconducting cable 10 becomes a delivery passage for the liquid hydrogen 1. Each of the pipes 2a, 2b is a welded pipe made of steel, and the cable 10 can be installed in the inner pipe 2b by providing the superconducting cable 10 on a steel plate for forming the inner pipe 2b and welding both edges of the steel plate. In this example, the superconducting cable 10 is disposed in the inner pipe 2b while being immersed in liquid hydrogen. In this example, the thermal insulation pipe 2 for the fluid constitutes a conduit for conveying liquid hydrogen from a hydrogen plant (not shown) to the respective hydrogen stations 20. Each hydrogen station 20 includes a tank 21 for storing liquid hydrogen and a heat exchange device 30 for heat exchange between the liquid hydrogen 1 and the coolant of the superconducting cable 10. The tank 21 is connected to the thermal insulation tube 2 for fluid and stores liquid hydrogen delivered through the thermal insulation tube 2 for fluid. In addition, a pipe 22 is connected to the tank 21 to perform circulation transportation of the liquid hydrogen, wherein, for example, the liquid hydrogen is injected from the tank 21 to the side of the heat exchange device 30, and then the liquid hydrogen flows from the heat exchange device 30 into the tank 21. A pump (not shown) is included in a portion of the line 22 to circulate the liquid hydrogen.

In this example, the heat exchange device 30 includes a passage 31 for circulating a heat exchange medium such as helium, an expansion valve 32 for expanding the heat exchange medium, a compressor 33 for compressing the expanded heat exchange medium, and a thermally insulating housing 34 provided with these elements. The line 22 is arranged such that a portion of the line 22 for circulating the liquid hydrogen is in contact with a portion of the passage 31 passing through the expansion valve 32 to cool the liquid hydrogen with the expanded heat exchange medium. With this structure, the liquid hydrogen is cooled in the vicinity of the portion of the pipe 22 that is in contact with the portion of the passage 31 that passes through the expansion valve 32. Thus, the liquid hydrogen ejected from the tank 21 flows through the line 22, is cooled by the heat exchange device 30, and returns to the tank 21. In addition, the piping 16 is provided such that a part of the piping 16 for circulating the coolant (liquid nitrogen) for transporting the cable 10, which is cooled with liquid hydrogen, is in contact with a part of the passage 31 passing through the compressor 33, so as to raise the temperature of the coolant of the cable 10 with the compressed heat exchange medium in a temperature range capable of maintaining the superconducting state. With this structure, the temperature of the coolant rises near the portion of the pipe 16 that contacts the portion of the passage 31 that passes through the compressor 33. Thus, the coolant sprayed from the thermal insulation tube 11 for the electric cable passes through the piping 16, raises its temperature with the heat exchanging device 30, and returns to the thermal insulation tube 11.

The superconducting cable housed in the heat-insulating pipe for fluid has an outer periphery covered with cryogenic liquid hydrogen, and has a double-layer heat-insulating structure formed with the heat-insulating pipe of the cable itself and the heat-insulating pipe for liquid hydrogen. With this configuration, the line of the present invention can sufficiently reduce the heat that enters the superconducting cable from the outside. In addition, since the outer periphery of the superconducting cable is covered with cryogenic liquid hydrogen, the heat of the liquid hydrogen is conducted to the cable and cools the coolant of the cable. Therefore, a cooling system for cooling the coolant of the superconducting cable is not necessary. As a result, by constructing the superconducting cable line of the present invention, the energy required for cooling the coolant of the superconducting cable is reduced, and the coefficient of performance can be increased.

Further, since the circuit of the present invention includes the heat exchanging means for heat exchange between the coolant of the superconducting cable and the liquid hydrogen to simultaneously perform heating of the coolant and cooling of the liquid hydrogen, a temperature difference between objects of heat exchange can be reduced and energy required for cooling the liquid hydrogen can be reduced by the heat exchanging means. In addition, with the heat exchange device included in the line of the present invention, heat associated with the cooling of liquid hydrogen can be used to raise the temperature of the coolant of the superconducting cable, which is excessively cooled due to being contained in the thermal insulation pipe for the fluid. Therefore, with the heat exchanging apparatus configured to perform heat exchange between the liquid hydrogen and the coolant of the superconducting cable, the line of the present invention can adjust the temperature of the liquid hydrogen to an appropriate temperature, and also can adjust the temperature of the cable coolant to an appropriate temperature. As a result, the energy required for cooling the coolant of the superconducting cable and the energy required for cooling the liquid hydrogen can be reduced by constructing the superconducting cable line of the present invention.

It should be noted that although the structure shown in this example is housed in the thermal insulation pipe for the fluid over the entire length in the longitudinal direction of the superconducting cable, only a part of the cable may be housed in the thermal insulation pipe for the fluid. In the line of the present invention, the effect of heat intrusion can be reduced, and when only a small part of the superconducting cable is contained in the heat insulating pipe for fluid, it becomes difficult to adjust the temperature of the coolant of the superconducting cable with the heat exchanging device. Therefore, in the line of the present invention, a sufficient portion of the superconducting cable is housed in the thermal insulation pipe for the fluid, thereby allowing the temperature of the coolant of the superconducting cable to be adjusted with the heat exchanging means.

Example 2

Although the superconducting cable was immersed in liquid hydrogen in example 1 described above, the superconducting cable may be installed in a thermal insulation pipe for a fluid without being immersed in liquid hydrogen. As an example, the transport channel for liquid hydrogen may be detachably arranged in a thermally insulated tube for fluid. Fig. 4 is a schematic view of the structure of a superconducting cable of the present invention including a transport pipe for liquid hydrogen and a heat exchanger bulkhead inside a thermal insulation pipe for fluid, which is a schematic cross-sectional view of the structure in the vicinity of the cable. The superconducting cable has a structure including a separate delivery pipe 3, the separate delivery pipe 3 being for delivering liquid hydrogen in an inner pipe 2b of a thermal insulation pipe 2 for a fluid. The heat exchanger partition 4 having high thermal conductivity is provided in a space surrounded by the inner periphery of the inner pipe 2b, the outer periphery of the delivery pipe 3, and the outer periphery of the superconducting cable 10. With this structure, the superconducting cable 10 has a double-layer thermal insulation structure formed of the thermal insulation pipe 2 for fluid and the thermal insulation pipe 11 (see fig. 1, 2) of the cable 10 itself as in example 1, and thereby the heat intrusion into the cable from the outside can be reduced. In addition, since the heat of the liquid hydrogen is conducted to the superconducting cable 10 via the heat exchanger partition 4, the cable 10 can also be cooled by the liquid hydrogen 1. Further, since the superconducting cable 10 is physically separated from the liquid hydrogen 1 by the delivery pipe 3, it is possible to prevent problems such as burning of the liquid hydrogen 1 when an accident such as short-circuiting of the cable 10 or generation of sparks occurs. In this example, the heat exchanger separator is formed by winding aluminum.

The superconducting cable of the present invention shown in each of the above-described examples 1 and 2 can be used for DC transmission or AC transmission. In the case of DC transmission, when a superconducting cable including a cable core having an electric insulation layer which is p-graded to have a low resistivity on the inner circumference side and a high resistivity on the outer circumference side is used, it is possible to smooth the DC electric field distribution in the thickness direction of the electric insulation layer and to increase the DC withstand voltage characteristic. The resistivity can be varied using PPLP (trademark) with various ratios k. The resistivity tends to increase as the ratio k increases. In addition, when the high ∈ layer is provided in the electric insulating layer in the vicinity of the superconductor layer, imp. The high epsilon layer can be formed, for example, with a low k ratio of PPLP (trademark). In this case, the high ∈ layer also becomes a low ρ layer. Further, the superconducting cable including the cable core having the electrical insulation layer in which ρ grading is performed and also formed such that the dielectric constant ∈ toward the inner periphery side increases and the dielectric constant ∈ toward the outer periphery side decreases also has a good AC characteristic. Therefore, the line of the present invention using such a cable can also be applied to AC transmission. As one example, the electrically insulating layer may be provided using PPLP (trade mark), where PPLP has various ratios k as indicated below, to have three different resistivities and dielectric constants. The following three layers may be provided in order from the inner periphery side (X and Y are constants).

Low ρ layer: the ratio k is 60%, the resistivity ρ (20 ℃) is X [ Ω · cm ], and the dielectric constant ∈ is Y

Intermediate ρ -layers: the ratio k is 70%, the resistivity ρ (20 ℃) is about 1.2X Ω · cm, and the dielectric constant ∈ is about 0.95Y

High ρ layer: the ratio k is 80%, the resistivity ρ (20 ℃) is about 1.4X Ω · cm, and the dielectric constant ∈ is about 0.9Y

In performing unipolar transmission with the line of the present invention using the superconducting cable subjected to ρ grading and ∈ grading, two of the three cable cores 12 (see fig. 2) may be used as auxiliary cores, the superconductor layer of one core may be used as a "go" line, and the outer superconducting layer of the core may be used as a return conductor. Alternatively, the superconductor layer of each core may be used as a "go" line and the outer superconductor layer of each core may be used as a return conductor to form a three-wire, single pole transmission line. On the other hand, when bipolar transmission is performed, one of the three cores may be used as an auxiliary core, the superconductor layer of one core may be used as a positive electrode line, the superconductor layer of the other core may be used as a negative electrode line, and the outer superconductor layer of the two cores may be used as a neutral conductor layer.

The line of the present invention using the superconducting cable subjected to the ρ grading and the ε grading and including the terminal structure as described above can easily perform DC transmission such as unipolar transmission or bipolar transmission after AC transmission, or AC transmission after DC transmission. Fig. 5 and 6 are schematic views each of the configuration of the terminal structure having the detachable extraction conductor part, which is formed at the end of the superconducting cable line of the present invention using the superconducting cable of the three-core type. Fig. 5 shows the case of an AC transmission line, and fig. 6 shows the case of a DC transmission line. Although only two cable cores 12 are shown in fig. 5 and 6, they are actually three cores.

The terminal structure includes an end portion of the cable core 12 extending from the end portion of the superconducting cable 10, extraction conductor portions 40, 61 connected to a conductive portion (not shown) on the normal temperature side, a connection portion electrically connecting the end portion of the cable core 12 with the extraction conductor portion 40 and the end portion of the cable core 12 with the extraction conductor portion 61, and a terminal junction box 50 mounting the end portion of the cable core 12, the end portions of the extraction conductor portions 40, 61 on the side connected to the cable core, and the connection portion. Terminating terminal box 50 includes a coolant pool 51 filled with a coolant for cooling superconductor layer 14, a coolant pool 52 for cooling outer superconductor layer 15, and a vacuum insulation pool 53 provided on the outer peripheries of coolant pools 51, 52, wherein superconductor layer 14 exposed by stepwise stripping of the ends of cable cores 12 is introduced into coolant pool 51, and outer superconductor layer 15 exposed by stepwise stripping is introduced into coolant pool 52. The extraction conductor part 61 is connected to the superconductor layer 14 via a joint (connection part) so as to allow power transmission and reception between the superconducting cable 10 and the normal temperature side conductive part, wherein the extraction conductor part 61 is embedded in the insulation sleeve 60 provided between the normal temperature side conductive part and the superconductor layer 14. One side (ordinary temperature side) of the insulating sleeve 60 attached to the ordinary temperature side conducting portion protrudes from the vacuum insulation bath 53, and is housed in a porcelain tube 62 protruding from the vacuum insulation bath 53.

On the other hand, the external superconducting layer 15 is connected to the drawn conductor part 40 provided between the normal temperature side conducting part and the external superconducting layer 15 via a short-circuit part 70 (connection part) described below, thereby allowing transmission and reception of electric power between the superconducting cable 10 and the normal temperature side conducting part. The extraction conductor part 40 is formed with a low-temperature-side conductor part 41 connected to the short-circuit part 70 and an ordinary-temperature-side conductor part 42 provided on the ordinary temperature side, the ordinary-temperature-side conductor part 42 being detachable from the low-temperature-side conductor part 41. In this example, the ordinary temperature-side conductor part 42 is formed in a rod shape of a prescribed cross-sectional area, and the low temperature-side conductor part 41 is formed in a cylindrical shape, into which the rod-shaped ordinary temperature-side conductor part 42 can be fitted. When normal temperature-side conductor portion 42 is inserted into low temperature-side conductor portion 41, both conductor portions 41, 42 are electrically connected to each other, thereby allowing transmission and reception of electric power between the low temperature side and the normal temperature side. When normal temperature-side conductor portion 42 is detached from inside low temperature-side conductor portion 41, conduction between conductor portions 41 and 42 is cancelled. A plurality of such extraction conductor portions 40 are included in the terminal structure. The low-temperature-side conductor part 41 is fixed in the coolant pool 52, and one end thereof is electrically connected to the short-circuiting part 70 and the other end enters the vacuum insulation pool 53. A low temperature side sealing portion 41a made of FRP is provided on the outer periphery of the fixing portion of the low temperature side conductor portion 41, thereby avoiding leakage of the coolant, short-circuiting of the coolant pool 52 and the conductor portion 41, and the like. The ordinary temperature-side conductor portion 42 is fixed to the vacuum insulation bath, and one end thereof is disposed in the vacuum insulation bath 53 and the other end thereof is arranged to be exposed to the outside of the ordinary temperature. An ordinary temperature side seal portion 42a made of FRP is provided on the outer periphery of the fixing portion of the ordinary temperature side conductor portion 42, thereby allowing heat intrusion to be reduced and avoiding short-circuiting of the vacuum insulation tank 53 and the conductor portion 42 and the like. In addition, an extensible portion 53a formed of a bellows is provided on the vacuum insulation tank 53 in the vicinity of the fixing portion of the ordinary temperature-side conductor portion 42 to maintain the vacuum state of the vacuum insulation tank 53 during attachment and detachment of the drawn-out conductor portion 40. It should be noted that the external superconducting layer 15 of each of the three cores 12 is short-circuited in the short-circuited portion 70. Further, a guide portion 43 connected to an external device or the like or a ground line 44 is attached to the normal temperature side end portion of the normal temperature side conductor portion 42. The epoxy unit 63 is provided on the outer periphery of a part of the superconductor layer 14 and in the vicinity of the part between the coolant pools 51, 52.

When the superconducting cable of the present invention including the terminal structure having the structure as described above is used as a three-phase AC line, for example, the extraction conductor part 40 connected to the external superconducting layer 15 should have a cross-sectional area of a conductor necessary to obtain a voltage to ground. Therefore, as shown in fig. 5, when the low-temperature-side conductor part 41 and the normal-temperature-side conductor part 42 of the required extraction conductor part 40 are connected to each other, it is not necessary to separate the low-temperature-side conductor part 41 and the normal-temperature-side conductor part 42 of the extraction conductor part 40 from each other to obtain a required conductor cross-sectional area. In this example, a ground wire for grounding is connected to the end on the ordinary temperature side of the ordinary temperature-side conductor part 42 of the extraction conductor part 40 to be connected.

On the other hand, when it is necessary to convert the three-phase AC transmission shown in fig. 5 into DC transmission, a current equivalent to that for the superconductor layer 14 flows through the external superconductor layer 15. That is, the current flowing through the external superconducting layer 15 increases as compared with those in the case of AC transmission shown in fig. 5, and the current flowing through the extraction conductor portion 40 also increases. Therefore, as shown in fig. 6, the low temperature-side conductor part 41 and the normal temperature-side conductor part 42 of the extraction conductor part 40, which are separated from each other during AC transmission, are connected to each other, thereby ensuring a sufficient conductor cross-sectional area required for flowing a required amount of current. In this example, the guide portion 43 for grounding is connected to the normal temperature side end portion of the normal temperature side conductor portion 42 of the connected extraction conductor portion 40. Conversely, when it is desired to convert the DC transmission shown in fig. 6 into an AC transmission, one of the extraction conductor portions 40, which is conductive during the DC transmission, is separated, and is disconnected from conduction.

The superconducting cable line of the present invention is suitable for a line that performs transmission of electric power to each power supply device (powerapplication). The superconducting cable of the present invention can be constructed, for example, by enclosing the superconducting cable in a pipe for transporting liquid hydrogen and providing the heat exchanging device at a hydrogen station connected to the pipe. In this case, the line of the present invention can be used as a power supply line for a power supply device inside a hydrogen station or as a power supply line for any power supply device, which absorbs electric power as needed from a heat insulating pipe for fluid. In addition, since the cable line of the present invention can be constructed in the process of constructing a transfer passage for liquid hydrogen or a hydrogen station, the workability of laying can be increased.

Claims (7)

1. A superconducting cable line comprising:

a thermal insulation tube (2) for fluids for transporting liquid hydrogen (1);

a superconducting cable (10) which is housed in the thermal insulation tube (2) for fluid so as to cool a superconducting portion (12) with a coolant having a temperature higher than that of the liquid hydrogen (1); and

-heat exchange means (30) for cooling the liquid hydrogen (1) and raising the temperature of the coolant of the cable cooled with the liquid hydrogen (1).

2. Superconducting cable line according to claim 1, wherein the superconducting cable (10) is immersed in the liquid hydrogen (10).

3. The superconducting cable line of claim 1, wherein the area inside the thermal insulation tube for fluid (2) is divided into a delivery area for delivering the liquid hydrogen (1) and an area for disposing the superconducting cable (10) therein.

4. The superconducting cable line of claim 1, wherein the coolant of the superconducting cable (10) is liquid nitrogen.

5. The superconducting electrical cable line of claim 1,

the superconducting cable (10) includes a superconductor layer (14) and an electrically insulating layer provided on an outer periphery of the superconductor layer (14), and

the electric insulating layer is subjected to ρ grading to obtain a low resistivity on an inner peripheral side of the electric insulating layer and a high resistivity on an outer peripheral side thereof, thereby making a DC electric field distribution in a diameter direction thereof smooth.

6. Superconducting cable line according to claim 5, wherein the electrically insulating layer has a high epsilon layer which is provided in the vicinity of the superconductor layer (14) and has a higher dielectric constant than the other part.

7. The superconducting cable line of claim 5, wherein the electrically insulating layer is configured such that the dielectric constant increases toward the inner circumference side and decreases toward the outer circumference side.