HK1106060B - Superconducting cable line - Google Patents

Description

Superconducting cable line

Technical Field

The present invention relates to a wire for a power supply, including a superconducting cable. More particularly, the present invention relates to a superconducting cable line which effectively reduces the amount of heat intrusion into the superconducting cable and can increase the coefficient of performance (COP).

Background

A superconducting cable including a heat insulation pipe accommodating a cable core having a superconducting conductor layer is generally known. Such a superconducting cable includes, for example, a single core cable having a heat insulation pipe accommodating one cable core or a three-core cable having three cable cores bundled. Fig. 11 is a sectional view of a three-core superconducting cable for three-phase AC power transmission. Fig. 12 is a sectional view of each cable core 102. This superconducting cable 100 has a structure in which three-strand cable core wires 102 are accommodated in a heat insulation pipe 101. The heat insulation duct 101 has a structure in which a heat insulation material (not shown) is disposed between double pipes formed with an outer duct 101a and an inner duct 101b, and air between the ducts 101a, 101b is evacuated. Each cable core 102 includes, from a central portion thereof, a former 200, a superconducting layer 201, an electrically insulating layer 202, a superconducting shield layer 203, and a protective layer 204. The space 103 enclosed with the inner guide pipe 101b and each cable core 102 becomes a passage for a coolant such as liquid nitrogen. By cooling with the coolant, the superconducting state of superconducting layer 201 and superconducting shield layer 203 of cable core 102 is maintained. An anti-corrosion layer 104 is included on the outer periphery of the insulated conduit 101.

The superconducting cable must be continuously cooled with a coolant such as liquid nitrogen to maintain the superconducting conductor layer and the superconducting shield layer in a superconducting state. Therefore, the electric wire using the superconducting cable generally includes a cooling system for the coolant. With this system, circulation cooling is performed in which the coolant sprayed from the cable is cooled and allowed to flow into the cable again.

The superconducting cable can maintain the superconducting state of the superconducting conductor layer and the superconducting shield layer by sufficiently reducing the increase in the temperature of the coolant due to the passage of current and the heat generation from the outside such as the atmosphere as the coolant is cooled to an appropriate temperature by the cooling system. However, when the coolant is liquid nitrogen, the energy required for cooling the coolant to solve such heat generation or heat intrusion becomes at least 10 times higher than the energy handled by cooling the cable by the coolant. Therefore, when a superconducting cable including the cooling system for a coolant is considered as a whole, a coefficient of performance (COP) becomes about 0.1 or less. Such a low COP is one of the reasons why the application effect of the superconducting cable is reduced. On the other hand, each of japanese patent laid-open No. 2002-.

Patent document 1: japanese patent laid-open No. 2002-

Patent document 2: japanese patent laid-open publication No. 10-092627

Disclosure of Invention

Problems to be solved by the invention

Each of the above patent documents 1 and 2 only discloses cooling of the coolant of the superconducting coil by cold melting of LNG, and does not consider reducing the amount of heat intrusion from the outside.

Accordingly, a main object of the present invention is to provide a superconducting cable line that can reduce heat intrusion from the outside and increase the coefficient of performance.

Means for solving the problems

The present invention achieves the above object by arranging a superconducting cable in a heat insulation pipe for transporting a cryogenic fluid. That is, the superconducting cable line of the present invention includes a heat insulation pipe for a fluid (first heat insulation pipe) for transporting a fluid having a temperature lower than the ordinary temperature, and a superconducting cable housed in the heat insulation pipe for a fluid (first heat insulation pipe). The present invention will be described in more detail below.

The superconducting cable utilized in the present invention has a structure including a superconducting portion formed with a superconducting material and a heat-insulating conduit (hereinafter referred to as a heat-insulating conduit 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 superconducting conductor layer for passing a current for a power supply and an outer superconducting layer for passing a current having substantially the same value as the superconducting conductor layer in the opposite direction. The superconducting portion is typically formed in a cable core. Therefore, the superconducting cable can be constructed by accommodating a cable core including a superconducting layer in a heat insulation pipe for a cable. More specific structure of the cable core, from the central portion thereof, may include a bobbin, a superconducting conductor layer, an electrically insulating layer, an external superconducting layer, and a protective layer. The heat insulating pipe for a cable can accommodate one cable core (single core (one core)) or a plurality of cable cores (a plurality of cores). More specifically, when the electric wire of the present invention is used for three-phase AC transmission, for example, a three-core cable having a heat insulation pipe for a cable accommodating three strands of cores may be used, and when the electric wire of the present invention is used for single-phase AC transmission, a single-core cable having a heat insulation pipe for a cable accommodating one core may be used. When the electric wire of the present invention is used for DC transmission (monopolar transmission), for example, a single core cable having a heat insulating guide tube for a cable accommodating one core can be used, and when the electric wire of the present invention is used for DC transmission (bipolar transmission), a two core cable or a three core cable having a heat insulating guide tube for a cable accommodating two or three cores can be used. As described above, the superconducting cable wire of the present invention can be used for any one of DC power transmission and AC power transmission.

The superconducting conductor layer may be formed by, for example, spirally winding a strip wire including a plurality of filaments made of a Bi-based oxide superconducting material arranged in a matrix, more specifically, a Bi 2223-based superconducting material such as a silver sheath. The superconducting conductor layer may have a single-layer or multi-layer structure. When the superconducting conductor layer has a multilayer structure, an interlayer insulating layer may be provided therein. The interlayer insulating layer may be provided by winding an insulating paper such as kraft paper or a semi-synthetic insulating paper such as PPLP (trademark of Sumitomo Electric Industries, ltd.). The superconducting conductor layer is formed by winding a wire made of a superconducting material around a bobbin. The former may be a solid or hollow body formed with a metallic material such as copper or aluminium, and may have a structure such as a multi-strand copper wire. Copper wire with an insulating coating may be utilized. The bobbin serves as a shape retaining member for the superconducting conductor layer. A spacer (cushion) layer may be interposed between the bobbin and the superconducting conductor layer. The liner layer prevents direct contact of metal between the former and the superconducting wire to prevent damage to the superconducting wire. In particular, when the bobbin has a strand structure, the backing layer also has a function of smoothing the bobbin surface. Insulating paper or carbon paper may be suitably used as a specific material of the cushion layer.

The electrically insulating layer may be formed by winding a semi-synthetic insulating paper such as PPLP (trademark) or an insulating paper such as kraft paper on the superconducting conductor layer. A semiconductive layer may be formed with carbon paper or the like on at least one of the inner periphery and the outer periphery of the electrically insulating layer, that is, between the superconducting conductor layer and the electrically insulating layer and between the electrically insulating layer and an outer superconducting layer (described below). With the formation of the inner semiconductive layer, the former, or the outer semiconductive layer, the latter, adhesion between the superconducting conductor layer and the electric insulating layer or adhesion between the electric insulating layer and the outer superconducting layer is increased to suppress damage due to partial discharge or the like.

When the electric wire of the present invention is used for DC transmission, the electric insulation layer may be subjected to ρ grading for obtaining low resistivity on the inner peripheral side face and high resistivity on the outer peripheral side face of the electric insulation layer to smooth the DC electric field distribution in the diameter direction (thickness direction) thereof. As described above, "ρ grading" means that the resistivity changes in a gradual manner in the thickness direction of the electrically insulating layer, the DC electric field distribution in the entire thickness direction of the electrically insulating layer can be smoothed, and the thickness of the electrically insulating layer can be reduced. Although the number of layers having varying resistivity is not particularly limited, two or three layers are practical. In particular, when the thickness of each layer is equal, smoothing of the DC electric field distribution can be performed more efficiently.

The ρ grading may be performed using insulating materials having different resistivities (ρ) from each other. When using insulating paper such as kraft paper, the resistivity can be changed, for example, by changing the density of the kraft paper or adding dicyandiamide to the kraft paper. 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 the ratio k of the thickness tp of the plastic film to the thickness T of the entire composite paper (tp/T) × 100 or by changing the density, material, additives, and the like of the insulating paper. The value of the ratio k is preferably in the range of, for example, about 40 to 90%. In general, the resistivity ρ becomes higher as the ratio k increases.

Further, when the electric insulating layer has a high ∈ layer provided near the superconducting conductor layer and has a higher permittivity than other portions, in addition to an increase in DC withstand voltage performance, imp. In the common kraft paper, the permittivity (20 ℃) is about 3.2 to 4.5, in the composite paper having a ratio k of 40%, the permittivity is about 2.8, in the composite paper having a ratio of 60%, about 2.6, and in the composite paper having a ratio of 80%, about 2.4. The electrical insulating layer constituted with the composite paper using kraft paper having a high ratio k and a higher air tightness is particularly preferable because both the DC withstand voltage and the imp.

In addition to the ρ -classification as described above, a cable suitable for AC transmission is also formed by constructing the electrically insulating layer with a permittivity e increasing towards the inner peripheral side and a permittivity e decreasing towards the outer peripheral side. This "epsilon sorting" is also performed over the entire area in the diameter direction of the electrically insulating layer. Further, the superconducting cable subjected to the ρ grading as described above has good DC performance, and can be suitably used as a DC transmission line. On the other hand, most current transmission lines are constructed for AC transmission. When a power transmission system is changed from an AC system to a DC system, where there may occur a case where AC is instantaneously transmitted using a superconducting cable subjected to ρ grading before changing to DC power transmission. This may occur, for example, when part of the cables of the transmission line is replaced with the superconducting cable subjected to the ρ grading but the other part is still the cable for AC transmission, or when the cables for AC transmission of the transmission line are replaced with the superconducting cable subjected to the ρ grading but the transmission equipment connected to the cables is still the equipment for AC. In this case, AC power transmission is performed instantaneously with the superconducting cable subjected to ρ grading, and then the system is finally changed to DC power transmission. Therefore, the superconducting cable for DC and AC power transmission is preferably designed to have not only good DC performance but also AC performance in consideration. When the AC performance is also considered, a superconducting cable having good pulse characteristics such as surge can be constructed by constructing the electrically insulating layer to have a permittivity ∈ that increases toward the inner peripheral side and decreases toward the outer peripheral side. Then, when the transient period ends and DC power transmission is performed as described above, the superconducting cables subjected to the ρ grading used in the transient period can be continuously used as DC cables. That is, a wire using a superconducting cable subjected to the epsilon classification other than the ρ classification can be suitably used for DC transmission and AC transmission, and also can be suitably used as a wire for AC and DC transmission.

The above-mentioned PPLP (trademark) generally has a higher ρ value and an s value which decreases as the ratio k increases. Therefore, when the electrical insulating layer is configured using PPLP (trademark) having a ratio k that increases toward the outer peripheral side surface of the electrical insulating layer, ρ may increase toward the outer peripheral side surface, and at the same time, ∈ may be decreased toward the outer peripheral side surface.

Kraft paper, on the other hand, typically has a higher p value and an epsilon value that increases with increasing air tightness. Therefore, it is difficult to construct an electrical insulation layer having ρ increasing toward the outer peripheral side face and ε decreasing toward the outer peripheral side face with only kraft paper. Thus, the electrical insulation layer is suitably constructed using kraft paper in combination with composite paper. For example, a kraft layer may be formed on an inner peripheral side of the electrical insulation layer, and a PPLP layer may be formed on an outer portion thereof, such that the resistivity ρ in the kraft layer is lower than the PPLP layer and the permittivity ∈ in the kraft layer is higher than the PPLP layer.

The outer superconducting layer is provided on the outer periphery of the electrically insulating layer, as described above. The outer superconducting layer is formed of a superconducting material with respect to the superconducting conductor layer. A superconducting material similar to that used to form the superconducting conductor layer may be used in the outer superconducting layer. When the superconducting cable line of the present invention is used for DC power transmission, the outer superconducting layer may be used, for example, as a return line in unipolar power transmission or a neutral line in bipolar power transmission. Specifically, when bipolar power transmission is performed, when unbalance occurs between the positive electrode and the negative electrode, the external superconducting layer may be used to pass the unbalanced current. Further, when one electrode is in an abnormal state and bipolar power transmission is changed to monopolar power transmission, the external superconducting layer can be used as a return line for passing a current equivalent to a transmission current flowing through the superconducting conductor layer. When the superconducting cable line of the present invention is used for DC power transmission, the outer superconducting layer may be used as a shielding layer by a shielding current caused by a current flowing through the superconducting conductor layer. A protective layer may be provided at the outer periphery of the outer superconducting layer, which also serves as insulation.

The heat insulation pipe for a cable for accommodating the cable core having the above-described structure may have a double pipe structure formed with an outer pipe and an inner pipe, including a heat insulation material between the pipes, and perform vacuum pumping to obtain a prescribed degree of vacuum forming the vacuum insulation structure. The space inside the inner conduit is used as a coolant passage through which a coolant such as liquid nitrogen is circulated, the coolant being used to cool the cable core (in particular, the superconducting conductor layer and the outer superconducting layer). The insulated conduit for the cable as such is preferably a flexible corrugated conduit. In particular, the heat insulation pipe for the cable is preferably formed of a metal material such as stainless steel having high strength.

The present invention has a structure in which a superconducting cable having the heat insulation pipe for a cable as described above is accommodated in a heat insulation pipe for transporting a fluid having a temperature lower than the ordinary temperature (hereinafter referred to as a heat insulation pipe for a fluid). With this structure, the superconducting cable housed in the heat insulation pipe for fluid has an outer periphery, and since the fluid has a temperature lower than the ordinary temperature, in a low-temperature environment, has a temperature lower than the ordinary temperature. Further, the superconducting cable may include a double heat insulation structure in which a heat insulation structure of a heat insulation pipe for fluid and a heat insulation structure of the cable itself are formed. Therefore, the heat intrusion from the outside can be effectively reduced as compared with the conventional cable, and the energy for cooling the coolant filling the superconducting cable can be reduced.

A heat insulation pipe having heat insulation performance corresponding to the fluid transported therein may be used as a heat insulation pipe for containing the fluid of the superconducting cable. For example, a heat insulation pipe having a structure similar to that for a superconducting cable, that is, a structure having a double pipe structure formed of an outer pipe and an inner pipe, including a holding cooling material arranged between the pipes, may be utilized. In this case, the space inside the inner conduit becomes a transfer passage for the fluid. Further, the fluid has a temperature lower than normal temperature. As described above, in the heat insulation pipe for a cable in the superconducting cable, the coolant for cooling the superconducting portion is circulated. For example, liquid nitrogen cooled to 77K is used as the coolant. Therefore, when the superconducting cable is laid in the atmosphere, the temperature difference between the inside and the outside of the heat insulation pipe for the cable (temperature difference between the coolant and the atmosphere) becomes at least 200K, and thus the amount of heat intrusion into the cable tends to increase. Therefore, in the conventional cable, the energy for cooling the coolant should be increased, or the heat insulation performance of the heat insulation duct for the cable should be increased to reduce heat intrusion. In contrast, in a superconducting cable housed in a heat insulation pipe for transporting a cryogenic fluid such as a fluid lower than the ordinary temperature, the temperature difference between the inside and the outside of the heat insulation pipe for a cable, more specifically, the temperature difference between a coolant and the fluid, may be less than 200K. Therefore, the heat intrusion becomes smaller as compared with the cable laid in the atmosphere, and the energy for cooling the coolant can be reduced. That is, when a cooling system for the coolant is also considered, the superconducting cable line of the present invention can increase the coefficient of performance as compared with the conventional electric wire. In particular, when the electric wire of the present invention is used as an electric wire for DC power transmission, the reduction of heat intrusion is extremely effective for increasing the coefficient of performance, in which heat is hardly generated with the passage of current (conductor loss), since in this case, heat intrusion becomes a main cause of energy loss. Further, since the superconducting cable housed in the heat insulation pipe for fluid in the present invention can reduce heat intrusion as described above, the heat insulation structure of the heat insulation pipe for cable can be simplified, that is, the heat insulation level for heat intrusion can be made lower.

Thus, the temperature of the fluid should be lower than normal temperature, and a lower temperature is particularly preferable because the amount of heat intrusion into the cable can be reduced. The fluid utilized may be the same as or different from the coolant of the superconducting cable. That is, the fluid may have a temperature substantially equal to, higher than, or lower than the temperature of the coolant of the superconducting cable. When the fluid has a temperature similar to that of the coolant of the superconducting cable, the temperature difference between the inside and the outside of the heat insulation pipe for the cable can be further reduced.

When the fluid has a temperature lower than that of the coolant of the superconducting cable, since substantially no heat intrudes from the fluid into the cable, the temperature of the coolant does not substantially increase with the intrusion of the heat, and on the contrary, the coolant inside the heat insulation pipe for the cable is cooled. Therefore, in the superconducting cable housed in the heat insulation pipe for fluid transporting the fluid, the level of cooling performance of the cooling system for the coolant in the cable can be made low, and the energy for cooling the coolant can be significantly reduced. When the fluid has a temperature higher than that of the coolant of the superconducting cable, although the temperature of the coolant may rise as heat intrudes from the fluid into the cable, the heat intrusion is extremely small as compared with the case of laying in the atmosphere, and therefore the degree of temperature rise is also extremely low. Therefore, the level of cooling performance of the cooling system for the coolant used in the superconducting cable can also be made lower in this case as compared with the case of arranging in atmospheric pressure. Specific examples of fluids include liquid helium (about 4K), liquid hydrogen (about 20K), liquid oxygen (about 90K), liquid nitrogen (about 77K), and liquefied natural gas (about 113K).

When the heat insulation pipe for fluid is formed by welding a metal plate made of stainless steel, or the like, the superconducting cable may be accommodated in the heat insulation pipe for fluid by arranging the cable on the plate, bending the plate to cover the cable, and welding the edge of the plate. When a metal pipe made of stainless steel, or the like is used as the heat insulation pipe for fluid, the cable can be accommodated in the heat insulation pipe for fluid by inserting the superconducting cable into the pipe. In this case, a slip-proof (ski) wire may be helically wound around the cable to improve the insertion performance of the superconducting cable. Specifically, when the heat insulation pipe for a cable is a corrugated (corrugated) pipe having protrusions and depressions, the insertion performance is improved by winding a non-slip thread having a pitch (long pitch) greater than that of the protrusions and depressions of the corrugated pipe to prevent the non-slip thread from entering the depressed portion of the corrugated pipe to position the non-slip thread on the protrusions and depressions, preventing the outer periphery of the corrugated pipe from directly contacting the heat insulation pipe for a fluid, that is, achieving point contact between the non-slip thread wound around the corrugated pipe and the heat insulation pipe for a fluid. Further, a tension member or the like may be connected to the superconducting cable to draw out the heat insulation pipe for fluid.

The superconducting cable housed in the heat insulation pipe for fluid may be arranged to contact the fluid transported within the heat insulation pipe for fluid or not to contact the fluid. In the former case, the superconducting cable may be immersed in the fluid. In this case, since the entire periphery of the superconducting cable contacts the cryogenic fluid, the amount of heat invading into the cable from the outside can be effectively reduced.

On the other hand, when the superconducting cable is immersed in the fluid, in case the superconducting cable is short-circuited, a problem such as explosion, for example, generation of a spark, may be generated depending on the fluid. Therefore, the area within the heat insulation pipe for the fluid can be divided into a transmission area for the fluid and an area for arranging the superconducting cable therein. As the transport region for the fluid, for example, a transport pipe for the fluid may be separately arranged inside the heat insulation pipe for the fluid, and the superconducting cable may be longitudinally arranged along the transport pipe. In this case, when a heat exchanger spacer having high thermal conductivity is disposed in a space inside the heat insulation pipe for fluid not occupied by the transmission pipe and the superconducting cable, that is, in a space surrounded by the inner periphery of the heat insulation pipe for fluid, the outer periphery of the transmission pipe, and the outer periphery of the cable, heat from the fluid can be efficiently transferred to the cable through the heat exchanger spacer, and thus the cable can be cooled with the fluid particularly when the fluid has a temperature lower than that of the cable coolant. The heat exchanger spacer may thus be formed of, for example, a material having a high thermal conductivity, such as aluminum. More specifically, the heat exchanger spacer may be formed by winding an aluminum foil.

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 accommodated in the heat insulation pipe for fluid, or only a part of the cable may be accommodated in the heat insulation pipe for fluid. For example, the wire may have only a part of the superconducting cable accommodated in the heat insulation pipe for fluid, and the other part of the superconducting cable may be laid in the atmosphere. In addition, the electric wire may have a low temperature zone portion in which an outer periphery of the cable is in a low temperature environment having a temperature of at most a coolant temperature, and a high temperature zone portion in an environment having a temperature higher than the coolant temperature. In particular, when the fluid has a temperature lower than that of the coolant, a portion of the superconducting cable housed in the heat insulation pipe for the fluid may be excessively cooled. With excessive cooling, solidification of part of the coolant may occur, which may inhibit circulation of the coolant of the cable. Therefore, it is desirable to increase the temperature of the portion of the superconducting cable cooled with the fluid in a temperature range in which the superconducting state can be maintained, to suppress the excessive cooling of the superconducting cable with the fluid, to prevent the portion of the coolant of the cable having the lowest temperature from reaching the solidification temperature, and to suppress the circulation of the coolant. Therefore, it is proposed to provide regions having different temperatures outside the superconducting cable in the longitudinal direction of the superconducting cable line to maintain the thermal balance of the entire wire. More specifically, it is proposed to provide a low temperature zone portion and a high temperature zone portion in the superconducting cable line to increase the coolant temperature of the superconducting cable excessively cooled in the low temperature zone portion in the high temperature zone portion or to cool the coolant of the superconducting cable having a temperature raised in the high temperature zone portion in the low temperature zone portion.

The insulated conduit for fluids includes a first insulated conduit and a second insulated conduit. The low temperature zone portion may be constituted by accommodating a superconducting cable in the heat insulation pipe for fluid (first heat insulation pipe) that transports a fluid having a temperature lower than that of a coolant that fills the heat insulation pipe for cable. The high-temperature zone portion may be constituted by laying a superconducting cable in the atmosphere, or by accommodating the cable in another heat insulation conduit for a fluid (second heat insulation conduit) that transports a fluid having a temperature higher than that of a coolant that fills the heat insulation conduit of the cable. For example, when liquid nitrogen is used as the coolant of the superconducting cable, liquid hydrogen or liquid helium may be used as the fluid (first fluid) for the low temperature region portion, and liquefied natural gas or liquid oxygen may be used as the fluid (second fluid) for the high temperature region portion.

In the electric wire of the present invention including the low temperature region portion and the high temperature region portion, the thermal balance can be maintained by using a plurality of heat insulation pipes for fluid for transporting fluids having various temperatures, or by combining a structure of accommodating a cable in the heat insulation pipe for fluid for transporting a fluid having a temperature lower than the coolant temperature of the superconducting cable and a structure of laying in the atmosphere. When the low temperature region portion and the high temperature region portion are alternately included in the longitudinal direction of the electric wire, the difference between the reduced temperature in the low temperature region portion and the increased temperature in the high temperature region portion can be reduced. In addition, by changing the heat insulation performance of the superconducting cable forming the wire, the heat balance of the entire wire can be maintained. That is, in the electric wire of the present invention, the heat insulation performance of the heat insulation pipe for a cable can be changed according to the temperature state of the region in which the superconducting cable is arranged. For example, the heat insulation performance of the heat insulation pipe for a cable of the superconducting cable arranged in the high temperature region portion may be made lower than the heat insulation performance of the heat insulation pipe for a cable of the cable arranged in the low temperature region portion. In a conventional superconducting cable line laid in the atmosphere, since the entire length of the cable and the temperature range outside the entire periphery are normal temperatures, the heat insulating performance along the entire length and the entire periphery should be set to a constant level, specifically, a high level, preventing heat from invading from the outside. However, in the electric wire of the present invention, since the amount of heat invading into the cable is reduced by including the portion of the superconducting cable accommodated in the heat insulation pipe for fluid, the heat insulation performance can be changed as appropriate depending on the environment in which the cable is laid. Therefore, when the electric wire includes, for example, a cable part accommodated in the heat insulation pipe for fluid for transporting a fluid having a higher coolant temperature than the superconducting cable and a cable part laid in the atmosphere, the level of the heat insulation performance of the cable part accommodated in the heat insulation pipe for fluid can be made lower than that of the cable part laid in the atmosphere. This is because the superconducting cable housed in the heat insulation pipe for fluid has a small heat intrusion from the outside, as described above. Therefore, in the present invention, the heat insulation performance of the superconducting cable forming the wire can be partially changed. When the heat insulation pipe for a cable has a double pipe structure formed of an outer pipe and an inner pipe, in which heat insulation material is disposed between the pipes and vacuuming is performed, the heat insulation performance may 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 insulation material disposed between the outer pipe and the inner pipe, or changing the material of the heat insulation material. With this heat balance maintained, the thermal energy handled by the coolant in the entire wire can be further reduced.

Further, when the superconducting cable line includes a structure for exchanging heat between the coolant of the superconducting cable and the fluid for cooling the coolant, that is, when the superconducting cable line has a structure additionally including a heat exchanging device for exchanging heat between the coolant of the cable and the fluid, the efficiency of heat exchange can be increased. The coolant of the superconducting cable is generally cooled with a cooling system that cools using a heat pump, and in the conventional superconducting cable line, water or normal temperature atmosphere is used as a condensation target of the heat pump. As a result, the temperature difference between the targets of the heat exchange becomes at least 200K. When the coolant is cooled to a temperature at which the superconducting state can be maintained, more heat energy is required because the temperature difference increases, and the COP becomes at most 0.1. In contrast, when a fluid having a temperature lower than the ordinary temperature is used as a target of heat exchange with the coolant, a temperature difference between the targets of heat exchange becomes small, as compared with a conventional electric wire using the ordinary temperature of the atmosphere or water, and thus extremely high heat exchange efficiency is obtained and COP may become at least 0.5. In particular, when a fluid having a temperature lower than the coolant temperature of the superconducting cable is used as a target of heat exchange with the coolant of the cable, more specifically, when the coolant is directly cooled with the fluid, a refrigerator for the coolant of the cable may not be required.

As described above, by using the fluid transported by the heat insulation pipe for fluid as a target of heat exchange with the coolant of the superconducting cable instead of the atmosphere or water at normal temperature, the exchange efficiency can be increased. In addition, the energy used to cool the coolant can be further reduced by taking advantage of the potential heat of vaporization of the fluid. When liquefied natural gas is used as the fluid, for example, the latent heat of vaporization (cold heat) of liquefied natural gas can be utilized. In a plant for liquefying natural gas (basic), the liquefied natural gas is vaporized to produce natural gas. Therefore, when heat is exchanged between the coolant of the superconducting cable and the liquefied natural gas, the coolant of the cable is cooled by receiving the latent heat of vaporization from the liquefied natural gas, and the liquefied natural gas is heated and evaporated by receiving the heat from the coolant of the cable. Thus, the needs of both objectives can be met without waste.

When the structure of heat exchange between the fluid and the coolant also provides a coolant for superconducting devices other than the superconducting cable using the cryogenic coolant, energy efficiency can be further increased, for example, a superconducting transformer, a Superconducting Magnet Energy Storage (SMES), or a superconducting current limiter.

When the superconducting cable of the present invention as described above is constructed in a position in which a heat insulation pipe for a fluid for transporting a fluid is arranged, the advantages of the superconducting cable can be fully used, for example, in a fluid plant that supplies power to various power supply apparatuses for transporting a fluid using the superconducting cable.

As described above, the superconducting cable wire of the present invention can be used for either DC power transmission or AC power transmission. When three-phase AC transmission is performed, for example, the cable may be formed as a three-core superconducting cable in which a superconducting conductor layer of each core is used for transmission of each phase, and an outer superconducting layer of each core is used as a shielding layer. When single-phase AC transmission is performed, the cable may be formed as a single-core superconducting cable in which a superconducting conductor layer included in a core is used for transmission of each phase, and an outer superconducting layer of each core is used as a shielding layer. When unipolar DC transmission is performed, the cable may be formed as a single-core superconducting cable in which the superconducting conductor layer included in the core is used as a outgoing line and the outer superconducting layer is returned. When bipolar DC transmission is performed, the cable may be formed as a two-core superconducting cable in which the superconducting conductor layer of one core is used for positive electrode transmission, the superconducting conductor layer of the other core is used for negative electrode transmission, and the outer superconducting layer of each core is used as a neutral conductor.

Further, the superconducting cable wire of the present invention can also be used as DC and AC power transmission by using a superconducting cable including a cable core having an electrical insulation layer subjected to the ρ grading and the ε grading as described above. In this case, not only the superconducting cable but also a terminal structure formed in an end portion of a wire for connecting the superconducting cable with the conductive portion on the normal temperature (a normal conductive cable, a lead wire connected to the normal conductive cable, or the like) side is preferably configured to be suitable for DC and AC power transmission. A representative structure of the terminal structure includes an end portion of a cable core extending from an end portion of the superconducting cable, a drawn conductor portion connected to the conductive portion on the ordinary temperature side, a connection portion electrically connecting the end portion of the core with the drawn conductor portion, and an end connection box accommodating the end portion of the core and the end portion of the drawn conductor portion connected to the side of the core, and the connection portion. The end connection box generally includes a coolant bath that cools the end of the wire core or the end of the extraction conductor portion, and a vacuum insulation bath disposed on the outer periphery of the coolant bath. In such a terminal structure, the cross-sectional area of the conductor of the extraction conductor portion can desirably be changed because the amount of current flowing through the extraction conductor portion can be different in AC power transmission and DC power transmission. Therefore, a suitable structure of the terminal structure for AC and DC power transmission has a cross-sectional area of the conductor of the extraction conductor portion that can be changed according to the load. Such a terminal structure may have a structure in which, for example, the extraction conductor portion is divided into a low-temperature-side conductor portion connected to an end of the wire core and an ordinary-temperature-side conductor portion arranged on a side surface of the conductive portion on the ordinary temperature side, the low-temperature-side conductor portion and the ordinary-temperature-side conductor portion being movable with each other. Further, such a plurality of movable extraction conductor portions are included to allow the cross-sectional area of the conductor of the entire extraction conductor portion to vary depending on the number of connections between the low-temperature-side conductor portion and the ordinary-temperature-side conductor portion. The cross-sectional area of the conductor of each extraction conductor portion may be the same as or different from each other. The superconducting cable line of the present invention including the terminal structure as such is configured by performing fixing or removal of the extraction conductor portion. It is possible to easily change from DC power transmission to AC power transmission, or from AC power transmission to DC power transmission. Further, since the cross-sectional area of the conductor of the extraction conductor portion can be changed as described above, when the amount of power supplied during AC power transmission or DC power transmission is changed, the cross-sectional area of the conductor can also be changed as appropriate.

Effects of the invention

According to the superconducting cable of the present invention having the above-described structure, substantial effects of effectively reducing the amount of heat intrusion into the cable and increasing the coefficient of performance can be obtained. Specifically, in the superconducting cable line of the present invention including the low temperature region portion and the high temperature region portion, the heat balance of the entire line can be maintained, and the energy of the coolant for cooling the cable can be reduced.

When a superconducting cable including a cable core having an electrical insulation layer subjected to ρ grading is utilized in the wire of the present invention, the wire can have good DC withstand voltage performance and can be suitable for DC transmission. Further, when a superconducting cable including a cable core having an electrical insulation layer subjected to ρ grading and providing a high ∈ value in a portion close to a superconducting conductor layer is utilized in the electric wire of the present invention, the imp. In particular, the electrical wire of the present invention can also have good AC electrical properties when the electrically insulating layer is formed to have an epsilon value that increases towards the inner peripheral side and decreases towards the outer peripheral side. Therefore, the superconducting cable line of the present invention can be suitably used for each of DC power transmission and AC power transmission. Further, when a superconducting cable including a cable core having an electric insulation layer subjected to ρ grading and ∈ grading is used as the electric wire of the present invention and a terminal structure formed in an end portion of the electric wire has a structure in which a conductor of a lead-out conductor portion arranged between the superconducting cable and a conductive portion on an ordinary temperature side has a variable cross-sectional area, the electric wire of the present invention can be suitably utilized in a transient period of the electric wire of the present invention in which a power transmission system is changed from an AC system to a DC system.

Drawings

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

Fig. 2 is a schematic sectional view of a structure of a part in the vicinity of the superconducting cable in the superconducting cable line of the present invention.

Fig. 3 is a schematic front view of a superconducting cable structure of the present invention.

Fig. 4 is a schematic sectional view of a superconducting cable line of the present invention including a transport pipe for a fluid, a superconducting cable, and a heat exchanger spacer in the heat insulation pipe for a fluid.

Fig. 5 is a schematic view of a superconducting cable structure of the present invention, including a low temperature zone portion and a high temperature zone portion.

Fig. 6 is a schematic view of a superconducting cable structure of the present invention in which the superconducting cable is accommodated in each of two heat insulation pipes for fluids, the heat insulation pipes being used to transmit different fluids.

Fig. 7 is a schematic view of an example structure of a superconducting cable of the present invention including a cooling system for cooling a coolant of the superconducting cable, the cooling system including a heat exchanging device for exchanging heat between the coolant and a fluid.

Fig. 8 is a schematic view of the structure of the superconducting cable line of the present invention, including a heat exchanging device for directly cooling the coolant of the superconducting cable with a fluid.

Fig. 9 is a schematic view of a terminal structure configuration formed in an end portion of a superconducting cable line of the present invention using a three-core type superconducting cable in the case of an AC power transmission line.

Fig. 10 is a schematic view of the configuration of a terminal structure formed in an end portion of a superconducting cable line of the present invention using a three-core type superconducting cable in the case of a DC power transmission line.

Fig. 11 is a sectional view of a three-core type superconducting cable for three-phase AC power transmission.

Fig. 12 is a sectional view of each cable core 102.

Description of the reference symbols

1: fluid, 2M, 2N: insulated conduit for fluid, 2 a: external conduit, 2 b: inner pipe, 3: delivery catheter, 4: heat exchanger spacer, 5: temperature adjusting device, 10: superconducting cable, 10 a: line, 11: heat insulation pipe for electric cable, 11 a: outer catheter, 11 b: inner conduit, 12: cable core, 13: space, 14: superconducting conductor layer, 15. external superconducting layer, 20, 30: heat exchange device, 21, 31: passage, 22: expansion valve, 23: compressor, 24, 32: insulation box, 25. pipeline, 40: extraction conductor portion, 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: lead, 44: ground line, 50: end connection box, 51, 52: coolant bath, 53: vacuum insulated bathroom, 53 a: extensible portion, 60: bushing (bushing), 61: extraction conductor portion, 62: hollow porcelain (porcelain), 63: epoxy resin unit, 70: and a short-circuited portion. 100: superconducting cable for three-phase AC transmission. 101: insulated conduit, 101 a: external catheter, 101 b: inner catheter, 102: cable core, 103: space, 104: anti-corrosion layer, 200: bobbin, 201: superconducting conductor 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 a superconducting cable structure of the present invention. Fig. 2 is a schematic sectional view of a part of the structure in the vicinity of the superconducting cable in the superconducting cable line of the present invention. Fig. 3 is a schematic front view of a superconducting cable structure of the present invention. Like characters in the drawings denote like parts. The superconducting cable line of the present invention includes a heat insulation pipe 2 for a fluid, the heat insulation pipe 2 being used for transporting a fluid 1 having a temperature lower than an ordinary temperature, and a superconducting cable 10 accommodated in the heat insulation pipe 2 for a fluid.

The superconducting cable 10 utilized in this example has a structure in which three cable cores 12 are stranded and housed in a heat insulation pipe 11 for a cable, the structure being substantially similar to that of the superconducting cable shown in fig. 11. Each cable core 12 includes, from its central portion, a bobbin, a superconducting conductor layer, an electrically insulating layer, an outer superconducting layer, and a protective layer. Each of the superconducting conductor layer and the outer superconducting layer is formed with a Bi 2223-based superconducting tape wire (Ag — Mn sheathed wire). The superconducting conductor layer and the outer superconducting layer are formed by spirally winding a superconducting tape wire on an outer periphery of the bobbin and on an outer periphery of the electric insulating layer, respectively. Stranded copper wire is used as the bobbin. A liner layer is formed between the bobbin and the superconducting conductor layer with an insulating paper. The Electric insulation layer is constituted by winding semisynthetic insulating paper (PPLP: trademark of Sumitomo Electric Industries, Ltd.) around the outer periphery of the superconducting conductor layer. An inner semiconductive layer and an outer semiconductive layer may be provided on the inner peripheral side and the outer peripheral side (below the outer superconducting layer) of the electrically insulating layer, respectively. The protective layer is provided by winding kraft paper on the outer periphery of the outer superconducting layer. Such three cable cores 12 are prepared, loosely twisted into a strand (strand) to have a margin for thermal shrinkage, and accommodated in the heat-insulating guide tube 11. In this example, SUS corrugated pipes are used to form the heat insulating pipe 11, in which a heat insulating material (not shown) having a multi-layer structure is disposed between double pipes formed with the outer pipe 11a and the inner pipe 11b, and air between the outer pipe 11a and the inner pipe 11b is evacuated to obtain a prescribed degree of vacuum, forming a vacuum multi-layer insulation structure. The space 13 surrounded by the inner periphery of the inner conduit 11b and the outer peripheries of the three cable cores 12 becomes a passage of the coolant. A coolant for cooling the superconducting conductor layer and the outer superconducting layer is circulated in the passage using a pump or the like. In this example, liquid nitrogen (about 77K) was used as the coolant.

The superconducting cable 10 having the above-described structure is accommodated in the heat insulation pipe 2 for fluid. The insulated conduit 2 for fluid in this example has a configuration of a double conduit structure formed by an outer conduit 2a and an inner conduit 2b, with a cooling material (not shown) arranged between the conduits 2a, 2b being maintained. The space surrounded by the inner periphery of the inner pipe 2b and the outer periphery of the superconducting cable 10 becomes the transmission passage 1 for the fluid. Each of the pipes 2a, 2b is a welded pipe made of steel, and the cable 10 is housed in the inner pipe 2b by arranging 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 arranged in the inner pipe 2b while being immersed in the fluid. In this example, liquefied natural gas (about 111K) was used as the fluid.

In the superconducting cable line of the present invention including the above-described structure, since the superconducting cable is accommodated in the heat insulation pipe for fluid for transporting a fluid having a temperature lower than the ordinary temperature, it is possible to make the difference between the temperature inside the cable and the ambient temperature around the outer periphery of the cable less than 200K. Therefore, the electric wire of the present invention can reduce the intrusion of heat from an ordinary temperature environment such as the atmosphere, as compared with a superconducting cable line laid in the atmosphere. Specifically, since the electric wire of the present invention forms a double heat insulation structure using the heat insulation pipe for fluid together with the heat insulation pipe of the superconducting cable itself, it is possible to more effectively reduce the intrusion of heat into the cable from the outside or the like. Therefore, the superconducting cable line of the present invention can reduce the energy of the coolant for cooling the superconducting cable, and can sufficiently increase the coefficient of performance of the entire wire.

Example 2

Although in the above example 1, the superconducting cable is immersed in the fluid, the superconducting cable may be accommodated in the heat insulation pipe for the fluid without being immersed in the fluid. For example, a transfer channel for the fluid may be separately provided in the insulated conduit for the fluid. Fig. 4 is a schematic sectional view of a superconducting cable line of the present invention including a transport conduit for a fluid, a superconducting cable, and a heat exchanger spacer in the heat insulation conduit for a fluid. The superconducting cable line has a structure including a separate transport conduit 3 for fluid in an inner conduit 2b of an insulated conduit 2 for fluid. A heat exchanger spacer 4 having high thermal conductivity is arranged in a space surrounded by the inner pipe 2b, the outer periphery of the transmission pipe 3, and the outer periphery of the superconducting cable 10. With this structure, the superconducting cable 10 has a double heat insulation structure, and the heat insulation pipe 2 for the fluid and the heat insulation pipe 11 (see fig. 1, 2) of the cable 10 itself are formed as in example 1, and therefore, the intrusion of heat from the outside can be reduced. Furthermore, since heat from the fluid is transferred to the superconducting cable 10 through the heat exchanger spacer 4, the cable 10 can also be cooled with the fluid 1 particularly when the fluid is, for example, liquid hydrogen (about 20K) or liquid helium (about 4K) having a temperature lower than the coolant (liquid nitrogen) of the cable 10. Further, since the fluid 1 is physically separated from the superconducting cable 10 by the heat exchanger spacer 4 and the transfer pipe 3, when a short-circuit accident such as the cable 10 occurs and a spark is generated, a problem such as burning of the fluid 1 can be prevented. In this example, the heat exchanger spacer is formed by winding an aluminum foil.

Example 3

Although the superconducting cable of the entire wire is accommodated in the heat insulation pipe for fluid in the structure described in example 1, in the wire, a part of the cable may be accommodated in the heat insulation pipe for fluid and another part of the cable may be laid in the atmosphere. Fig. 5 is a schematic view of a superconducting cable structure of the present invention, which includes a low temperature region portion and a high temperature region portion. The superconducting cable includes a low temperature region portion in which a superconducting cable 10 is housed in a heat insulation pipe 2 for a fluid, and a high temperature region portion in which the cable 10 is laid in the atmosphere without being housed in the heat insulation pipe 2 for the fluid. Specifically, a fluid having a temperature lower than the coolant temperature of the superconducting cable 10, for example, liquid hydrogen is used as the fluid transported in the heat insulation pipe 2 for the fluid. With this structure, in a portion of the superconducting cable of the electric wire housed in the heat insulation pipe 2 for the fluid, that is, in the low temperature region portion, since the outer periphery of the cable is arranged in a low temperature environment having a temperature of at most the coolant, and since there is the heat insulation pipe 2 for the fluid in addition to the heat insulation pipe of the cable 10 itself, it is possible to reduce the amount of heat intrusion into the cable. On the other hand, since the outer periphery of the superconducting cable has a temperature lower than that of the coolant, the coolant can be excessively cooled and solidified, and therefore the circulation of the coolant can be suppressed. Therefore, as shown in fig. 5, a portion of the superconducting cable forming the electric wire is laid in the atmosphere without being accommodated in the heat insulation pipe for fluid 2 to heat the excessively cooled coolant with heat invading from the atmosphere, mitigating excessive cooling of the coolant. That is, the wire can maintain the thermal balance of the entire superconducting cable line. It should be noted that the superconducting cable inside the heat insulation pipe for fluid may be immersed in the fluid as shown in example 1, or the transmission passages for the fluid and the cable may be separately provided as shown in example 2. This similarly applies to the example described below.

Example 4

Although a fluid having a temperature lower than the coolant temperature of the superconducting cable 10 is used in the above example 3, a fluid having a temperature higher than the coolant temperature, for example, liquid oxygen or liquefied natural gas, may be utilized. In this case, the superconducting cable accommodated in the heat insulation pipe for fluid 2 and the superconducting cable laid in the atmosphere may have different heat insulation properties. The superconducting cable accommodated in this heat insulation pipe for fluid 2 has heat intruded from the atmosphere, which is smaller than that of the cable laid in the atmosphere. Therefore, the heat insulation performance of the superconducting cable housed in the heat insulation pipe for fluid 2 can be made lower than that of a cable laid in the atmosphere. In the superconducting cable line of the present invention, as described above, the heat insulating performance can be partially changed. The heat insulating performance of the superconducting cable can be changed by changing the degree of vacuum in the heat insulating pipe for the cable for accommodating the cable core, changing the amount of heat insulating material arranged in the heat insulating pipe, or changing the material of the heat insulating material.

Example 5

Although the structure described in example 3 is such that a part of the cable of the electric wire is accommodated in one heat insulation pipe for fluid, when there are a large number of heat insulation pipes for fluid for transporting various fluids, the superconducting cable may be accommodated in each of the heat insulation pipes for fluid. Fig. 6 is a schematic view of a superconducting cable structure of the present invention in which the superconducting cable is accommodated in each of two heat insulation pipes for fluids, the heat insulation pipes being used to transmit different fluids. The superconducting cable line includes a heat insulation pipe 2M for a fluid for transporting a fluid (for example, liquid hydrogen) having a temperature lower than a coolant (liquid nitrogen) of the superconducting cable 10, and a heat insulation pipe 2N for a fluid for transporting a fluid (for example, liquefied natural gas) having a temperature higher than the coolant, and the superconducting cable 10 is accommodated in each of the heat insulation pipes 2M, 2N. That is, in this structure, a part of the superconducting cable of the electric wire housed in the heat insulation pipe 2M for the fluid for transporting the low temperature fluid becomes a low temperature region portion, and a part of the cable housed in the heat insulation pipe for the fluid for transporting the high temperature fluid, which is lower than the normal temperature, becomes a high temperature region portion. With this structure, when the coolant of the superconducting cable in the low temperature region portion is excessively cooled, the temperature of the coolant is raised by the heat from the fluid in the high temperature region portion, and thus the heat balance of the entire wire can be maintained. As shown in fig. 6, in this example, a temperature adjusting device 5 for adjusting the temperature of the coolant of the superconducting cable 10 is included between the low-temperature region portion and the high-temperature region portion to perform fine adjustment of the temperature of the coolant. Since the temperature difference between the coolant of the superconducting cable 10 and the fluid (liquid hydrogen) in the low temperature region portion and the temperature difference between the coolant and the fluid (liquefied natural gas) in the high temperature region portion are relatively small in this example, the temperature adjusting device 5 having a low adjustment level (small span adjustable range for the temperature difference) can be utilized.

Example 6

The electric wire of the present invention can also utilize a fluid as a target of heat exchange in cooling the coolant of the superconducting cable. Fig. 7 is a schematic view of a superconducting cable structure of the present invention including a cooling system for cooling a coolant of the superconducting cable, which is an example of a heat exchanging apparatus included in the coolant for exchanging heat with a fluid. The superconducting cable line includes a heat exchange device 20 for cooling a coolant of the superconducting cable 10, using a fluid as a target of heat exchange. The heat exchange device 20 includes a passage 21 for circulating a heat exchange medium such as helium, an expansion valve 22 for expanding the heat-exchange medium, a compressor 23 for compressing the expanded heat-exchange medium, and an insulating box 24 for accommodating these elements. Then, a line 10a for transmitting the coolant of the cable 10 is disposed on a portion of the passage 21 passing through the expansion valve 22 to cool the coolant of the superconducting cable 10 by heat exchange of the expansion, and a line 25 for transmitting the fluid is disposed on a portion of the passage 21 passing through the compressor 23 to condense and heat the compressed heat exchange medium by the fluid.

With the above-described structure, the coolant of the superconducting cable 10 having a temperature increased due to conductor loss or the like associated with the passage of the current is cooled by the heat exchanging device 20 and returned to the cable 10. In this case, since the fluid having a temperature lower than the normal temperature is used as the condensation target of the heat exchange device 20, the energy of the coolant cooling the cable 10, more specifically, the energy such as for driving the expansion valve 22 and the compressor 23, can be sufficiently reduced as compared with the case where the normal atmospheric air or water is used as the target. Further, although in a fluid plant (plant), the fluid may be heated and evaporated with the heat exchange device 20, the fluid is evaporated and utilized as appropriate. Thus, the vaporized fluid may be cooled and liquefied with a cooling device such as a refrigerator additionally included as appropriate, or may be directly utilized in an evaporated state. With the heat exchange between the coolant and the fluid of the superconducting cable described above, the energy for cooling the coolant can be reduced, and the coefficient of performance of the wire can be further increased. In addition, since the wire can also cool the coolant of the superconducting cable using the latent heat of vaporization of the fluid, the energy for cooling the coolant can be further reduced. Further, since the wire can simultaneously evaporate the fluid with the cooling of the coolant of the superconducting cable, the energy associated with the vaporization of the fluid can also be reduced. Liquefied natural gas is suitable for use as such a fluid.

Example 7

When the fluid has a temperature lower than that of the coolant of the superconducting cable, the electric wire of the present invention may have a structure in which the coolant of the cable is directly cooled with the fluid. Fig. 8 is a schematic view of a superconducting cable structure of the present invention including a heat exchanging apparatus for directly cooling a coolant of the superconducting cable with a fluid. The superconducting cable line includes a heat exchange device 30 for cooling a coolant of the superconducting cable 10, using a fluid as a target of heat exchange. The heat exchange device 30 comprises an insulating box 32 housing a line 10a and a line 31, the line 10a conveying the coolant sprayed from the cable 10 and allowing the coolant to flow into the cable 10 again, and the line 31 conveying the fluid sprayed from the insulating duct for fluid 2. The transfer line 10a is arranged within the thermally insulated box 32 so that the transfer line 10a for the coolant contacts the transfer line 31 for the fluid. With this structure, the coolant of the superconducting cable can be efficiently cooled with the cryogenic fluid. It should be noted that a heat exchanger material may be disposed within the insulated box 32 to facilitate heat transfer of the cryogenic fluid to the transfer line 10a for the coolant. For example, an aluminum material may be used as the heat exchanger material.

The superconducting cable line of the present invention shown in each of examples 1 to 7 described above can be used for any one of DC power transmission and AC power transmission. In the case of DC power transmission, when a superconducting cable including a cable core having an electrical insulation layer subjected to ρ grading to have a low resistivity on an inner peripheral side and a high resistivity on an outer peripheral side is utilized, a DC electric field distribution in a thickness direction of the electrical insulation layer can be smoothed, and a DC withstand voltage performance can be increased. The resistivity can be varied using PPLP (trade mark) with various ratios k. The resistivity tends to increase as k increases. Further, when a high ∈ layer is provided in the electric insulation layer in the vicinity of the superconducting conductor layer, imp. The high-epsilon layer may be formed using, for example, PPLP (trademark) having a low ratio k. In this case, the high ∈ layer also becomes the low ρ layer. Further, the superconducting cable includes a cable core having an electrical insulation layer subjected to ρ grading and also formed to have a permittivity ∈ that increases toward the inner peripheral side face and decreases toward the outer peripheral side face, and also has good AC performance. Therefore, the electric wire of the present invention using such a cable can also be suitably used for AC power transmission. For example, the electrically insulating layers may be provided using PPLP (trademark) having various ratios k as shown below to have three different resistivities and permittivities. The following three layers may be continuously provided from the inner peripheral side (X and Y are constants).

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

A middle rho layer: the ratio k is 70%, the resistivity ρ (20 ℃) is about 1.2 × [ Ω · cm, and the permittivity ∈ is about 0.95Y

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

When unipolar power transmission is performed with the electric wire of the present invention, using the superconducting cable subjected to ρ grading and ∈ grading, two cores (see fig. 2) among the three cable cores 12 can be used as auxiliary cores, the superconducting conductor layer of one core can be used as outgoing line, and the outer superconducting layer of the core can be used as return line. In addition, the superconducting conductor layer of each core may be used as a outgoing line and the external superconducting layer of each core may be used as a return line to constitute a three-line unipolar transmission line. On the other hand, when bipolar transmission is performed, one core among the three cores may be used as an auxiliary core, the superconducting conductor layer of one core may be used as a positive electrode line, the superconducting conductor layer of the other core may be used as a negative electrode line, and the outer superconductors of the two cores may be used as a neutral line layer.

The electric wire of the present invention uses a superconducting cable subjected to ρ grading and ε grading and includes a terminal structure as described below, and can easily perform DC power transmission such as unipolar power transmission, or perform bipolar power transmission after AC power transmission, or perform AC power transmission after DC power transmission. Each of fig. 9 and 10 is a schematic view of the configuration of a terminal structure having a removable extraction conductor portion, which is formed in an end portion of a superconducting cable line of the present invention using a three-core type superconducting cable. Fig. 9 shows the case of an AC power line, and fig. 10 shows the case of a DC power line. Although only two cable cores 12 are shown in fig. 9 and 10, three cores are actually used.

The terminal structure includes an end portion of the cable core 12 extending from an end portion of the superconducting cable 10, extraction conductor portions 40, 61 connected to a conductive portion (not shown) on the ordinary temperature side to electrically connect the end portion of the core 12 with the extraction conductor portions 40, 61, and an end connection box 50 accommodating the end portion of the core 12, the end portions of the extraction conductor portions 40, 61 connected to the side surfaces of the core, and the connection portions. The end connection box 50 includes a coolant bath 51 filled with a coolant for cooling the superconducting conductor layer 14, in which the superconducting conductor layer 14 exposed by step stripping of the end of the core 12 is introduced, and a coolant bath 52 filled with a coolant for cooling the external superconducting layer 15, in which the external superconducting layer 15 exposed by step stripping is also introduced, and a vacuum insulation bath 53 arranged on the outer periphery of the coolant baths 51, 52. Extraction conductor portion 61 embedded in bushing 60 arranged between the conductive portion on the ordinary temperature side and superconducting conductor layer 14 is connected to superconducting conductor layer 14 by a joint (connection portion) to allow transmission and reception of electric power between superconducting cable 10 and the conductive portion on the ordinary temperature side. The side face (ordinary temperature side) of the bushing 60 connected to the conductive portion on the ordinary temperature side is projected from the vacuum insulation bath 53 and is housed in the hollow, and this porcelain 62 is provided to be projected from the vacuum insulation bath 53.

On the other hand, outer superconducting layer 15 is connected via short-circuit portion 70 (connection portion) as described below to extraction conductor portion 40 arranged between the conductive portion on the ordinary temperature side and outer superconducting layer 15 to allow transmission and reception of electric power between superconducting cable 10 and the conductive portion on the ordinary temperature side. Extraction conductor portion 40 is formed with low-temperature-side conductor portion 41 connected to short-circuit portion 70 and ordinary-temperature-side conductor portion 42 arranged on the ordinary temperature side, removable from low-temperature-side conductor portion 41. In this example, ordinary temperature-side conductor portion 42 is formed in a bar shape having a prescribed cross-sectional area, and low temperature-side conductor portion 41 is formed in a columnar shape, in which bar-shaped ordinary temperature-side conductor portion 42 can be fitted. When ordinary temperature-side conductor portion 42 is inserted into low temperature-side conductor portion 41, portions 41 and 42 are electrically connected to each other to allow transmission and reception of electric power between the low temperature side and the ordinary temperature side, and when ordinary temperature-side conductor portion 42 is removed from low temperature-side conductor portion 41, portions 41 and 42 start to conduct electricity. Such a plurality of extraction conductor portions 40 are included in the terminal structure. Low-temperature-side conductor portion 41 is fixed on coolant bath 52 and has one end electrically connected to short-circuit portion 70 and the other end arranged into vacuum insulation bath 53. A low temperature side seal portion 41a made of FRP is provided on the outer periphery of the fixing portion of low temperature side conductor portion 41 to avoid leakage of the coolant, short circuit of coolant bath 52 and conductor portion 41, and the like. The ordinary temperature-side conductor portion 42 is fixed on the vacuum insulation bath 53 and has one terminal arranged in the vacuum insulation bath 53 and the other end arranged outside exposed to 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 to allow reduction of heat intrusion and avoidance of short circuit of the vacuum insulation bath 53 and the conductor portion 42 and the like. Further, an extensible portion 53 formed with a bellows is provided on the vacuum insulation bath 53 in the vicinity of the fixed portion of the ordinary temperature-side conductor portion 42 to maintain the vacuum state of the vacuum insulation bath 53 during the fixing and removal of the extraction conductor portion 40. It should be noted that in the short-circuited portion 70, the external superconducting layer 15 of each of the three cores 12 is short-circuited. Further, a lead wire 43 or the like connected to an external device or a ground wire 44 is connected to an end portion on the ordinary temperature side of the ordinary temperature-side conductor portion 42. An epoxy resin unit 63 is disposed on the outer periphery of the part of superconducting conductor layer 14 disposed near the part between coolant baths 51, 52.

When a superconducting cable line including the terminal structure having the above-described structure is used as, for example, a three-phase AC line, the extraction conductor portion 40 connected to the external superconducting layer 15 should have a cross-sectional area of a conductor required to obtain a ground voltage. Therefore, as shown in fig. 9, although low-temperature-side conductor portion 41 and ordinary-temperature-side conductor portion 42 of extraction conductor portion 40 need to be connected to each other, low-temperature-side conductor portion 41 and ordinary-temperature-side conductor portion 42 of extraction conductor portion 40 need not be spaced apart from each other to obtain a desired cross-sectional area of the conductor. In this example, a ground wire 44 for grounding is connected to an end portion on the ordinary temperature side of the ordinary temperature-side conductor portion 42 of the extraction conductor portion 40.

On the other hand, when a change from three-phase AC transmission to DC transmission as shown in fig. 9 is requested, a current equivalent to that for superconducting conductor layer 14 flows through outer superconducting layer 15. That is, as compared with the case of AC transmission shown in fig. 9, the current flowing through the external superconducting layer 15 increases and the current flowing through the extraction conductor portion 40 also increases. Therefore, as shown in fig. 10, low-temperature-side conductor portion 41 and ordinary-temperature-side conductor portion 42 of extraction conductor portion 40 separated during AC power transmission are connected to each other to ensure a sufficient cross-sectional area of the conductor for passing a required amount of current. In this example, the lead wire 43 is connected to an end portion on the ordinary temperature side of the ordinary temperature-side conductor portion 42 of the extraction conductor portion 40, which is connected. In contrast, when a request is made to change from DC power transmission to AC power transmission as shown in fig. 10, one extraction conductor portion 40 that starts conducting during DC power transmission is separated and does not conduct.

Industrial applicability

The superconducting cable of the present invention is suitable for use as a wire for supplying electric power to various electric power equipment or consumers. When the wire is used as a wire for supplying electric power to electric power equipment in a fluid plant which transmits a fluid having a low temperature lower than the normal temperature, the advantages of the superconducting cable, such as supplying a large amount of electric power with a low resistance, can be sufficiently used. Furthermore, since the cable line can be constructed during the construction of the transmission passage for the fluid, workability for laying is increased.

Claims (8)

1. A superconducting cable line comprising:

-an insulated conduit (2, 2M, 2N) for a fluid for conveying the fluid (1) having a temperature lower than the normal temperature; and

a superconducting cable (10) housed in the heat insulation conduit (2, 2M, 2N) for the fluid,

wherein the superconducting cable includes a cable core and a coolant for cooling the cable core; each cable core includes, from a central portion thereof, a bobbin, a superconducting conductor layer, an electrically insulating layer, an outer superconducting layer, and a protective layer,

the positional relationship between the fluid and the superconducting cable includes: the superconducting cable is immersed in the fluid; or a region within the heat insulation pipe for fluid is divided into a transport zone for transporting the fluid and a region for arranging the superconducting cable therein; or the superconducting cable line has a low temperature zone portion in which an outer periphery of the superconducting cable is in a low temperature environment having a temperature of at most the coolant temperature, and a high temperature zone portion in which an outer periphery of the superconducting cable is in a high temperature environment having a temperature higher than the coolant temperature, and in which the superconducting cable is accommodated in the heat insulation pipe for the fluid.

2. A superconducting cable line according to claim 1, wherein

The fluid (1) is any one of liquid helium, liquid hydrogen, liquid oxygen, liquid nitrogen and liquefied natural gas.

3. A superconducting cable line according to claim 1, wherein

The fluid (1) is different from a fluid used for a coolant of the superconducting cable (10).

4. A superconducting cable line according to claim 1, wherein

The fluids include a first fluid and a second fluid different from the first fluid,

said insulated conduits (2, 2M, 2N) for fluids comprise a first insulated conduit (2M) for conveying said first fluid and a second insulated conduit (2N) for conveying said second fluid;

in the high-temperature zone portion, the superconducting cable (10) is housed in the second heat insulation pipe (2N); and

the coolant of the superconducting cable (10) is liquid nitrogen, the first fluid is liquid hydrogen, and the second fluid is liquefied natural gas.

5. A superconducting cable line according to claim 1, wherein

The superconducting cable line comprises heat exchanging means (20, 30) for exchanging heat between the coolant and the fluid (1).

6. A superconducting cable line according to claim 1, wherein

The electrically insulating layer is subjected to resistivity classification for obtaining a low resistivity on an inner peripheral side of the electrically insulating layer and a high resistivity on an outer peripheral side for smoothing a direct current electric field distribution in a diameter direction thereof.

7. The superconducting cable line according to claim 6, wherein

The electrically insulating layer has a high permittivity layer disposed adjacent to the superconducting conductor layer (14) and having a permittivity higher than that in other portions.

8. The superconducting cable line according to claim 6, wherein

The electrically insulating layer is configured to have a permittivity epsilon that increases towards the inner peripheral side and decreases towards the outer peripheral side.