JP2008113535A - Power transmission system and operation method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power transmission system with smaller loss, which transmits power from a generator via a power transmission network, and to provide an operation method for the system. <P>SOLUTION: In the power transmission system, output of the generator 300 is transmitted to the power transmission network (overhead transmission line) 800 via a transformer 400. In the system, a superconducting cable 100 is used as a power transmission path between the generator 300 and the transformer 400. This superconducting cable 100 is a single multi-core cables where a plurality of cores exist or a plurality of single multi-core cables, where there are a plurality of cores or a plurality of bars of single-core cables. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power transmission system and an operation method thereof. In particular, the present invention relates to a power transmission system using a superconducting cable in a power transmission path from a generator to a transformer.

  As an example of a power transmission system from a power plant to a power grid, there is a system that transmits power from a generator of a hydroelectric power plant. A schematic configuration of this system is shown in FIG. Hydroelectric power plants are often installed in mountainous areas, and the generator 300 is installed in a predetermined space formed by excavating the mountain G. The generator 300 generates electricity by rotating the turbine with the water flow W. The output of the generator 300 is transmitted to the transformer 400 via the normal conducting cable 150. Since the output voltage of the generator 300 is about 20 kV, this voltage is boosted to a predetermined voltage (for example, 275 to 500 kV) by the transformer 400. The boosted electricity passes through the power cable 610 via the underground terminal 500 and is drawn to the terminal 710 at the switching station 700 on the ground. Then, power is transmitted from the terminal 710 to a power transmission network such as the overhead power transmission line 800.

  Meanwhile, superconducting cables are being developed. This superconducting cable is expected to be used as a power transmission system with extremely small loss during power transmission (for example, Patent Document 1).

JP-A-2005-93383

  However, the power transmission system using the normal conducting cable has the following problems.

(1) The loss associated with power transmission is very large.
The power generation voltage of the generator is about 20 kV, and the current when power is transmitted at that voltage is very large, for example, about 10 kA. Therefore, a large-capacity normal conductive cable is required in the power transmission path from the generator to the transformer. Specifically, a cable or a bus bar composed of a conductor having a large cross section is used as a transmission line with one or more lines per phase. Since this cable has an extremely large amount of heat generation, it needs to be cooled. For example, a pipe is disposed at the center of the cable, and cooling water is circulated through the pipe by the cooling system 160 (FIG. 5) to forcibly cool the conductor. That is, in the system of FIG. 5, a part of the generated electric power is not only converted into heat energy due to the heat generated by the normal conducting cable but also lost, and further energy is required to cool the generated heat. It is a power transmission system with low energy efficiency.

(2) The degree of freedom in selecting the installation route of the transmission path and the installation location of the transformer is small.
As described above, the normal conducting cable between the generator and the transformer has a very large calorific value. Therefore, it is not desirable to arrange the cables of each phase close to each other because the temperature rise of each cable is further increased. As a result, the cables of each phase are often laid at positions spaced apart to some extent, and the degree of freedom in selecting the cable laying route is small. In addition, this cable is required to be as short as possible because the longer the cable, the greater the loss, and the more difficult it is to secure a power transmission route. Therefore, it is practically difficult to install the transformer at a position far away from the generator. In particular, a pumped storage power plant often excavates in the mountains and installs a generator in a predetermined space in the ground. If a transformer is to be installed in the vicinity of the generator, it must be installed in the underground excavation space. Absent. As a result, the degree of freedom in selecting the installation location of the transformer is small. Furthermore, in order to form a space in the ground and install a transformer in the space, a series of construction work is complicated and the construction cost is increased.

  On the other hand, although superconducting cables are expected to be used as a transmission path with extremely low loss, it is clearly clear where the superconducting cables can be used to achieve more efficient transmission systems. It has not been. In particular, when considering replacing the existing normal transmission path with a superconducting cable, it is impractical to replace the entire length of the transmission path at once, so partial replacement will be considered. . In that case, no clear proposal has been made as to which part of the transmission line the normal conducting cable should be replaced with a superconducting cable.

  The present invention has been made in view of the above circumstances, and one of its purposes is to provide a power transmission system with less loss and a method of operating the power transmission system in which power is transmitted from a generator through a power transmission network. It is in.

  Another object of the present invention is to provide a power transmission system capable of increasing the degree of freedom of the location where the transformer is installed and a method for operating the power transmission system in which power is transmitted from the generator via the transformer. .

  The power transmission system of the present invention is a power transmission system that transmits the output of a generator to a power transmission network via a transformer. In this system, a superconducting cable is used as a power transmission path between the generator and the transformer. The superconducting cable is a single-core multi-core cable having a plurality of cores, a multi-core cable having a plurality of cores, or a single-core cable having a plurality of cores.

  In the present invention, the loss in the transmission line can be greatly reduced by using the superconducting cable in the transmission line between the generator and the transformer, which has generated a large amount of heat, in the conventional system using the normal conduction cable. . Accordingly, it is possible to effectively reduce the loss of the entire power transmission system.

  Moreover, since the superconducting cable itself has substantially no loss due to heat generation, it can be used as a long power transmission path. Therefore, a transformer can be installed in a location away from the generator, and the degree of freedom in selecting the installation location of the transformer can be increased.

  Further, if the superconducting cable is a single-core multi-core cable having a plurality of cores, for example, by assigning one core per phase, it is possible to perform multi-phase power transmission with a single cable. On the other hand, if the superconducting cable is a multi-core cable having a plurality of cores or a single-core cable having a plurality of cores, for example, even if one cable is assigned per phase, the superconducting cable itself does not generate heat in the first place. The cables of each strip can be laid close to each other. Therefore, even when using superconducting cables of any configuration, when transmitting power in multiple phases, there is no need to lay out the transmission paths of each phase more than a certain distance, and the cable routing route can be selected freely. Can be increased.

  As one form of this invention system, it is suitable that a generator is a generator of a hydroelectric power station.

  Hydroelectric power station generators are very limited in terms of location, and are often installed in mountainous areas. If the power transmission path connected to the generator is a superconducting cable, the transformer can be installed at a location away from the generator, which is preferable as a specific application target of the system of the present invention. In particular, the generator used in the system of the present invention is suitable when it is a generator of a pumped storage power plant with great restrictions on location.

  As one form of the system of the present invention, it is desirable that a switching station is provided between the generator and the power transmission network, and the transformer is installed in the switching station.

  Normally, in a power transmission system, a switching station is provided between a generator and a power grid. This switch is often installed outdoors or indoors on the ground. If the power transmission path connected to the generator is a superconducting cable, the power transmission path can be made long. Therefore, the transformer can be installed at a position away from the generator, that is, at the switch station. As a result, it is not necessary to construct an installation space for the transformer in the ground, and it is not necessary to provide an installation space for the underground terminal, which is necessary in the conventional system.

  As another form of the system of the present invention, the superconducting cable is a multi-core multi-core cable having a plurality of cores or a multi-core single-core cable, a cooling mechanism for cooling the refrigerant of the superconducting cable, and a refrigerant. It is desirable that each circulation mechanism that circulates in the superconducting cable is provided for each cable of each strip.

  If a cooling mechanism and a circulation mechanism are provided for each cable of each strip, all cooling mechanisms and circulation mechanisms are operated to transmit power, or some cooling mechanisms and circulation mechanisms are operated to transmit power. Can widen the choice of power transmission patterns. For example, when a failure occurs in one of the three cables, the refrigerant is circulated through the remaining two cables using a total of three sets of cooling mechanisms and circulation mechanisms corresponding to each of the cables. Can do. In that case, since the three sets of cooling mechanisms and the circulation mechanism for cooling the three-wire cable are used for cooling the two-wire cable, sufficient cooling capacity of the refrigerant can be exhibited. Accordingly, the cooling temperature of the superconducting cable can be changed to change the power transmission capacity.

  On the other hand, the operation method of the power transmission system of the present invention is an operation method of transmitting the output of the generator to the power transmission network via a transformer. In this operation method, a superconducting cable is used as a power transmission path between the generator and the transformer. The superconducting cable is a single multi-core cable having a plurality of cores, a multi-core cable having a plurality of cores, or a single-core cable having a plurality of cores. And the power transmission capacity is made variable by changing the cooling temperature of the superconducting cable.

  The superconducting conductor used for the superconducting cable can increase the critical current value as the cooling temperature is lowered. Therefore, by changing the refrigerant temperature in the temperature range where the refrigerant maintains a liquid state, the cooling temperature of the superconducting cable can be changed, and the transmission capacity can be increased or decreased accordingly. In particular, by lowering the refrigerant temperature, it is possible to transmit power with a higher capacity without adding a transmission path.

  According to the power transmission system of the present invention, it is possible to greatly reduce the loss in the transmission path from the generator to the transformer, which was large in loss in the conventional power transmission using the normal conductive cable, and to increase the degree of freedom of the installation location of the transformer. it can.

  According to the operation method of the power transmission system of the present invention, the power transmission capacity in the power transmission path from the generator to the transformer can be adjusted without adding a new power transmission path.

  Hereinafter, the components of the present invention will be described in more detail.

<Generator>
The generator is typically a generator installed in a power plant. There are hydropower (including pumped-storage power generation), thermal power, nuclear power, etc., but the power generation system boosts the output of the generator with a transformer and transmits it to the power grid. The transmission system up to is basically the same. Therefore, the present invention can be applied not only to a generator of a pumped storage power plant but also to a power transmission system from a power generator of another type of power plant.

<Transformer>
This transformer boosts the output of the generator to a predetermined voltage suitable for power transmission through the power grid. For example, the boosted voltage includes 275 kV and 500 kV.

  The installation location of the transformer is not particularly limited. If it can be installed at a position close to the generator, it can be installed at such a position using a short superconducting cable. On the contrary, if it is preferable to install at a position away from the generator in terms of the construction cost of the installation location, it may be installed at a position away from the generator using a long superconducting cable. In particular, it is preferable to install the transformer on the ground rather than in the ground in terms of transformer installation work and maintenance.

<Superconducting cable>
The superconducting cable constitutes a power transmission path that connects between the generator and the transformer. Typically, a cable having a structure in which a core is housed in a heat insulating tube is used. In this specification, “core” is the unit when counting the number of cores, and “strip” is the unit when counting the number of superconducting cables.

  The core usually includes a former, a superconducting conductor layer, an insulating layer, a superconducting shield layer (external conductor layer), and a protective layer in order from the center. For the former, a stranded wire made of a normal conductive material, a pipe material or the like is used. As the superconducting conductor layer, a superconducting wire wound in multiple layers can be used. As the superconducting wire, a superconducting filament in which a filament made of a superconductor is arranged in a stabilizing material or a superconductor thin film formed on a base tape can be used. In particular, as a superconductor, an oxide superconductor that is in a superconducting state at a liquid nitrogen temperature can be suitably used. The insulating layer can be formed by winding kraft paper, or can be formed by winding composite paper obtained by laminating a plastic film and insulating paper. In particular, PPLP (registered trademark) obtained by laminating polypropylene film and kraft paper can be suitably used for the insulating layer. A cloth tape or the like can be used for the protective layer.

  On the other hand, the heat insulating tube is a double tube having an inner tube and an outer tube, and a vacuum heat insulating tube having a vacuum between the two tubes can be suitably used. Usually, a heat insulating material such as super insulation is arranged between the two. A plastic anticorrosion layer is often formed on the outer tube.

  Such a superconducting cable is cooled by the refrigerant and the superconducting state of the conductor layer and the shield layer is maintained. As the refrigerant, liquid helium or liquid nitrogen can be used, but liquid nitrogen having a higher boiling point can be preferably used. This liquid nitrogen is not flammable even if it is gasified due to leakage of refrigerant, etc., and is suitable for use in power plants.

  As the refrigerant flow path, a space formed between the heat insulating pipe and the core, a refrigerant pipe accommodated in the heat insulating pipe together with the core, a refrigerant pipe arranged outside the heat insulating pipe, and the like can be used. When a pipe-shaped former is used, the interior of the former can also be used as a refrigerant flow path.

  When a superconducting cable having such a core and a heat insulating tube is used in the system of the present invention, the following combinations of the number of cores and the number of cables are preferable.

(1) A multi-core cable in which a plurality of cores are housed in a heat insulation pipe Since this cable is housed in a heat insulation pipe having a plurality of cores in common, the heat insulation structure can be shared by the cores. Typically, a cable housed in a heat insulating tube in a state where three cores are twisted together is mentioned. Because the core has a twisted structure, if a predetermined slack is provided in advance in the twist, the core contraction is absorbed during cooling of the superconducting cable, and excessive tension acts on each core. it can. With such a multi-core cable, three-phase power transmission can be performed with a single cable by assigning the output of each phase to one core. Of course, it is also possible to transmit three-phase power by using three multi-core cables and assigning one phase to each. In that case, since each cable is a superconducting cable, it does not inherently generate heat due to power transmission, and the cores of each cable are separated by a heat insulating tube. However, the cables in each strip do not have a thermal effect on each other and can be laid close together.

(2) Single-core cable with a single core housed in a heat insulation tube This cable has only one core in the heat insulation tube, so it is necessary to use multiple lines to transmit power in multiple phases . However, the single-core cable has no problem even if a plurality of cables are laid close to each other so that the cables of each cable do not affect each other thermally.

<Power grid>
The power transmission network is a power transmission path for transmitting the boosted output by the transformer. In general, an aerial transmission line installed on a steel tower or a power cable installed in a tunnel in the ground is used for the transmission network. The output transmitted through the power transmission network is further supplied to consumers via a substation and a distribution network.

<Cooling mechanism and circulation mechanism>
The cooling mechanism cools the refrigerant for cooling the conductor (shield layer) of the superconducting cable. Usually, a refrigerator is used for the cooling mechanism.

  The circulation mechanism circulates the cooled refrigerant through the refrigerant flow path of the superconducting cable. Usually, a pump is used for the circulation mechanism.

  When there are multiple superconducting cables, it is preferable to provide cooling mechanisms and circulation mechanisms corresponding to the number of superconducting cables. And it is desirable for the refrigerant | coolant flow path of each stripe | line to be mutually communicable via switching mechanisms, such as a valve | bulb.

  If the power transmission path between the generator and transformer is composed of multiple lines in consideration of the accident, the supply of refrigerant to the accident cable is cut off, and the refrigerant is supplied only to the remaining healthy cable. The refrigerant flow path is switched. At that time, if all the cooling mechanisms and the circulation mechanism are used, the refrigerant supplied to the sound cable can be cooled by using a high cooling capacity.

  In particular, if the refrigerant temperature is changed in the temperature range where the refrigerant (boiling point: about 77k, melting point: about 63k at atmospheric pressure in the case of liquid nitrogen) maintains the liquid, the critical current of the superconductor changes. That is, if the refrigerant temperature is lowered, the critical current becomes higher, and if the refrigerant temperature is raised, the critical current becomes lower. For this reason, even if a failure occurs in some cables, it can be expected that by adjusting the refrigerant temperature, power can be transmitted with the same capacity as when all the cables are healthy even with the remaining healthy cables alone. However, even if the set temperature of the cooling means is changed, a certain amount of time is required until the refrigerant actually reaches the set temperature, so the steady operation temperature of the refrigerant is lower than its boiling point and higher than its melting point. It is preferable to set with a margin.

  As described above, the operation of the superconducting cable requires energy for driving the refrigerator and the pump. This cooling is performed in order to maintain the superconductor in the superconducting state. In a conventional power transmission system that uses a normal conducting cable and circulates cooling water to cool a conductor, the temperature of the conductor changes greatly with the load, and therefore the control of the cooling temperature is complicated and difficult. On the other hand, in a power transmission system using a superconducting cable, the temperature change of the refrigerant during operation is less affected by the load, and the temperature change is very small, so that the cooling control of the refrigerant can be easily performed. In addition, power transmission systems using superconducting cables have very little loss due to heat generated by the cables, so even if energy for cooling the refrigerant is taken into account, energy efficiency is significantly higher than that of conventional power transmission systems using normal conductive cables. High power transmission system.

<Other configurations>
Another component that can be used in the system of the present invention is a circuit breaker. This circuit breaker interrupts power transmission in the event of an accident, for example, between a generator and a superconducting cable or between one terminal of the superconducting cable (terminal opposite to the transformer) and the power grid. Installed.

  Hereinafter, the power transmission system of the present invention will be described with reference to FIG.

  Here, a power transmission system from the generator 300 to the power transmission network (overhead transmission line) 800 in the pumped storage power plant will be described. In the pumped-storage power plant, the nighttime power from another power plant (not shown) is used to pump the water stored in the lower pond into the upper pond, and the pumped water is used to generate power during the daytime when there is a large demand for power. The system of the present invention includes a generator 300, a superconducting cable 100, a transformer 400, and a power transmission network 800 as main components.

  This power plant is constructed in a mountainous area, and the generator 300 is installed in a predetermined space in the ground provided by excavating the mountain G. The generator 300 generates electricity by rotating the turbine with a water flow W generated when the water in the upper pond is discharged into the lower pond. The output voltage of the generator 300 is about 20 kV. The generator 300 is also used for pumping water by rotating the turbine in the reverse direction to that during power generation.

  The output of the generator 300 is sent to the transformer 400 via the superconducting cable 100. The superconducting cable 100 here is a three-core cable. As shown in FIG. 2, this cable has a structure in which three cores 10 are stranded in a heat insulating tube 20.

  Each core 10 includes a former 11, a superconducting conductor layer 12, an insulating layer 13, a superconducting shield layer 14, and a protective layer 15 in order from the center. A copper stranded wire is used for the former 11. Superconducting conductor layer 12 and superconducting shield layer 14 are formed by winding a superconducting wire having a Bi2223 oxide superconducting phase in multiple layers. The insulating layer 13 is formed by winding PPLP. A cloth tape is used for the protective layer 15.

  The core 10 is twisted in advance with a predetermined slack in the twist so as to absorb the shrinkage during cooling.

  On the other hand, the heat insulating tube 20 includes a double tube of inner and outer tubes 21 and 22 made of a stainless corrugated tube, and a vacuum heat insulating layer formed between both the tubes 21 and 22. A super insulation (not shown) is disposed in the vacuum heat insulating layer. Further, a corrosion protection layer 23 made of polyvinyl chloride is formed on the outer tube 22.

  In the superconducting cable 100, liquid nitrogen serving as a refrigerant is circulated in a heat insulating pipe using a refrigerator and a pump (not shown). Specifically, a space formed between the heat insulating inner tube and the core is used as a refrigerant flow path.

  The electric power transmitted through the superconducting cable 100 is introduced into the transformer 400 and boosted to a predetermined voltage. Here, the voltage is boosted to 275 kV and transmitted (FIG. 1). The boosted power is supplied to the underground transmission line 600 via a terminal 500 that is connected to the transformer 400 and installed.

  For the underground transmission line 600, an OF cable, a CV cable, a bus bar, or the like is preferably used. The end of the underground power transmission line 600 opposite to the terminal 500 is exposed to the ground at the switchgear 700, and a terminal 710 is formed there.

  In the switching station 700, switching between power transmission and interruption to the power transmission network is performed. Electric power is supplied from the terminal 710 through an overhead power transmission line 800 constituting a power transmission network.

  In such a system, by using the superconducting cable 100 in the transmission line between the generator 300 and the transformer 400, even if the voltage is relatively low, loss due to heat generation in this transmission line can be substantially ignored. Since the level can be reduced, an efficient power transmission system can be constructed.

  For example, comparing the loss generated in a conductor in a normal conducting cable and a superconducting cable having a 10 kA class transmission capacity, the value of the superconducting cable is three orders of magnitude smaller. In the superconducting cable, since the refrigerant is cooled to the temperature of liquid nitrogen, the energy consumed by the superconducting cable is two orders of magnitude smaller even if the energy required for operating the cooling system is considered as a loss due to the power transmission.

  In the conventional system shown in FIG. 5, when conducting three-phase power transmission, one or more normal conducting cables 150 per phase are required. In the system of the present invention, these are one three-core superconducting cable. Can be consolidated or reduced.

  In this example, it is assumed that the normal conducting cable 150 of the conventional system shown in FIG. 5 is replaced with a superconducting cable. In this case, the transformer is installed in the ground because it is a partial upgrade of the existing equipment, but the loss in the transmission line between the generator and the transformer will be dramatically improved. .

  In addition, as a modification of the present embodiment, the single three-core superconducting cable 100 is replaced with three single-core superconducting cables, or the three-core three-conductor superconducting cable is replaced. Power transmission may be performed by matching the phases.

  Next, an embodiment of the present invention in which a transformer is also installed on the ground will be described with reference to FIG. 3, the same reference numerals as those in FIG. 1 denote the same members.

  In the case of this example, it is assumed that a pumped storage power plant will be newly established. In this system, the point that the generator 300 is provided at a predetermined position in the ground is the same as that of the first embodiment. However, a part or all of the transformer 400 is exposed at the switching station 700 on the ground, and A terminal 710 is formed at the switchgear 700 to transmit power to the overhead power transmission line 800.

  Further, the generator 300 and the transformer 400 are connected by a superconducting cable 100 longer than that in the first embodiment. The configuration of the superconducting cable 100 is the same as that of the first embodiment.

  Since the resistance of the superconducting cable 100 is substantially negligible even if it becomes long, the increase in loss is small. Therefore, even with a low voltage output from the generator 300, long-distance power transmission can be performed with extremely low loss.

  Furthermore, since there is no need to install the transformer 400 in the ground, the construction for installing the transformer 400 or the construction for constructing the underground terminal 500 can be substantially omitted, which is extremely economical. A simple power transmission system.

  Next, an embodiment using three superconducting cables will be described with reference to FIG. Since the cable of each strip is the three-core cable shown in FIG. 2, description of the configuration is omitted. In FIG. 4, the generator and the transformer are omitted, and the superconducting cable and its circulation cooling system are shown. That is, in the power transmission system of this example, the superconducting cable 100 in FIG. 1 or FIG. 2 is replaced with three superconducting cables, and these superconducting cables are operated by the circulating cooling system of FIG.

  This circulation cooling system includes refrigerators 211 to 213 that cool the refrigerant, pumps 221 to 223 that circulate the refrigerant, superconducting cables 110 to 130, a refrigerant pipe that connects the refrigerator and the pump, and a plurality of valves provided in the refrigerant pipe 231 to 233, 241 to 243, 251 to 253, and 261 to 263.

  In this circulation cooling system, the refrigerant cooled by the refrigerators 211 to 213 is sent by the pumps 221 to 223 and circulated through the superconducting cables 110 to 130 to cool the superconducting wire. Here, the number of refrigerators 211 to 213 and pumps 221 to 223 corresponding to the number of lines is used. That is, three refrigerators 211 to 213 and three pumps 221 to 223 are used, and the refrigerators and the pumps are connected in series by piping. A pipe drawn from the refrigerator to the refrigerant discharge side is connected to one end side of each of the superconducting cables 110 to 130 via valves 231 to 233. At that time, the piping between the refrigerator 211 and the valve 231, between the refrigerator 212 and the valve 232, and between the refrigerator 213 and the valve 233 are mutually connected to connect the refrigerant flow paths between the respective lines. The connecting piping is provided with valves 251, 252, and 253. On the other hand, a refrigerant discharge pipe is connected to the other end of each of the superconducting cables 110 to 130, and is converged to one after passing through valves 241 to 243 and led to the pump side on one end side of the cable. One pipe led to the pump side is branched into three and connected to each pump 221 to 223 via valves 261 to 263. In this way, by connecting the refrigerant flow path on the refrigerant discharge side in the refrigerators 211 to 213 and the refrigerant introduction side to the pumps 221 to 223, the refrigerant cooled by any of the refrigerators 211 to 213 can be connected to any line. To superconducting cables 110-130.

  In this example, liquid air (boiling point: about 79K, melting point: 55K at atmospheric pressure) is used as the refrigerant, and each of the refrigerators 211 to 213 has a capability of cooling to the melting point of liquid air.

  Here, an operation method corresponding to a change in power demand on the load side connected to the power transmission network will be described.

  In the track of FIG. 4, at the time of steady operation, for example, all the lines are operated with the refrigerant temperature set at a little less than 77K. During this steady operation, the valves 251, 252, and 253 provided in the connecting pipes of the refrigerant flow paths of the respective lines are closed, and the other valves 231 to 233, 241 to 243, and 261 to 263 are all opened, and the refrigerators 211 to 213 are opened. In each of these, the refrigerant of the superconducting cables 110 to 130 of each line is cooled. When the power demand increases on the load side, the set temperature of the refrigerators 211 to 213 is adjusted to lower the refrigerant temperature. For example, if it is cooled to about 68K, the critical current will be about 1.5 times. Normally, power transmission from the generator to the transformer is performed at a constant voltage, so if the current capacity is increased 1.5 times, the transmission capacity can be increased 1.5 times. Furthermore, if it is cooled to 60K or less, the critical current is approximately doubled, so that it is possible to transmit a larger amount of power.

  That is, according to this operation method, by reducing the refrigerant temperature, it is possible to easily realize a power transmission capacity that is about twice that in the steady operation. In particular, it is possible to increase the power capacity that can be transmitted by using an existing superconducting cable as it is without adding a cable, which is very effective.

  In addition, when the power demand decreases, it is possible to increase the refrigerant temperature and decrease the transmission capacity of the superconducting cable. In that case, it is necessary to use a superconducting wire that can maintain the superconducting state at the raised refrigerant temperature, but the cooling cost of the superconducting cable can be reduced, and the cost required for the operation of the superconducting cable can be reduced.

  Next, the case where power is transmitted through the remaining sound line when some lines are disconnected due to an accident will be described. It is assumed that, among the three lines shown in FIG. 4, one superconducting cable 130 is disconnected due to an accident and power can be transmitted using only the remaining two lines. In this case, it is assumed that the superconducting cable 130 of the disconnected line cannot be used, but the circulating cooling system is all sound and usable.

  First, the open / close state of each valve during steady operation before the accident is the same as the open / close state of the valve in the third embodiment.

  If the superconducting cable 130 is disconnected, the refrigerant is supplied to the two healthy lines (superconducting cables 110, 120) using the three refrigerators 211 to 213 and the three pumps 221 to 223, and the refrigerant is sufficiently cooled. Cool to a lower temperature. In that case, close the refrigerant supply side valve 233 and the refrigerant discharge side valve 243 of the accident line to separate the accident line from the circulation cooling system, open the valves 251 to 253 of the connecting piping, and drive all the pumps 221 to 223 Circulate the refrigerant. Thus, the refrigerant introduced into the two healthy lines is cooled and circulated using the three refrigerators 211 to 213 and the three pumps 221 to 223.

  According to this method, since the refrigerant is supplied to the two lines using the circulating cooling system capable of supplying the refrigerant to the three lines, the refrigerant can be efficiently cooled. As a result, the refrigerant temperature can be easily made lower than the temperature before the accident, and the transmission capacity of the sound line can be increased. For example, if the refrigerant temperature of each line is operated at less than 77K before the accident and the refrigerant temperature of the healthy line is about 68K after the accident, the transmission capacity can be secured about 1.5 times per line before the accident. The capacity equivalent to 3 lines before the accident can be transmitted with 2 healthy lines. Thereby, a highly reliable power transmission system can be constructed.

  Of course, each refrigerator has the capacity to cool one line of refrigerant to an increased capacity operating temperature (about 68K), and circulates and supplies refrigerant to two healthy lines with two refrigerators and two pumps. You may do it. In that case, the valves 233 and 243 at both ends of the accident line are closed to separate the accident line from the circulating cooling system, and the valve 263 located on the refrigerant introduction side of the pump 223 is also closed to connect the refrigerator 213 and the pump 223 to the circulating cooling system. Separate from. In this state, the refrigerant in the superconducting cables 110 and 120 is cooled and circulated using the refrigerators 211 and 212 and the pumps 221 and 222. At this time, the valve 251 may be opened to connect the two-line healthy line refrigerant pipes.

  In addition, each Example demonstrated above is only an illustration, and the range of this invention is not necessarily limited to these Examples. For example, the refrigerant of Example 3 may be replaced with liquid nitrogen.

  The system of the present invention is expected to be suitably used as a power transmission system from a generator to a transformer in a power plant.

1 is a schematic configuration diagram of a power transmission system of the present invention related to Example 1. FIG. It is sectional drawing of the superconducting cable used for this invention system. It is a schematic block diagram of this invention power transmission system which concerns on Example 2. FIG. It is a schematic block diagram of the superconducting cable track | line used for this invention power transmission system which concerns on Example 3. FIG. It is a schematic block diagram of the conventional power transmission system.

Explanation of symbols

100,110,120,130 Superconducting cable
10 Core 11 Former 12 Superconducting conductor layer 13 Insulating layer
14 Superconducting shield layer 15 Protective layer
20 Heat insulation pipe 21 Inner pipe 22 Outer pipe 23 Anticorrosion layer
150 Normal conducting cable 160 Cooling system
211 to 213 Refrigerator 221 to 223 Pump
231 to 233, 241 to 243, 251,252,253, 261 to 263 Valve
300 Generator 400 Transformer 500 Terminal 600 Underground transmission line
610 Electric power cable 700 Switching station 710 Terminal 800 Transmission network (overhead transmission line)
w Water current G Yamanaka

Claims (5)

A power transmission system for transmitting the output of a generator to a power grid via a transformer,
Using a superconducting cable as the transmission path between the generator and the transformer,
The superconducting cable is a single-core multi-core cable having a plurality of cores, a multi-core multi-core cable having a plurality of cores, or a multi-core single-core cable. 2. The power transmission system according to claim 1, wherein the generator is a generator of a hydroelectric power plant. There is a switching station between the generator and the grid,
The power transmission system according to claim 1, wherein the transformer is installed in a switching station. The superconducting cable is a multi-core multi-core cable having a plurality of cores or a multi-core single-core cable;
The power transmission system according to claim 1, wherein a cooling mechanism for cooling the refrigerant of the superconducting cable and a circulation mechanism for circulating the refrigerant through the superconducting cable are provided for each cable. A method of operating a power transmission system that transmits the output of a generator to a power grid via a transformer,
Using a superconducting cable as the transmission path between the generator and the transformer,
The superconducting cable is a single multi-core cable having a plurality of cores, a multi-core cable having a plurality of cores, or a single-core cable having a plurality of cores.
A method for operating a power transmission system, wherein the power transmission capacity is variable by changing the cooling temperature of the superconducting cable.

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