JP4284253B2 - Cryogenic container - Google Patents

Description

  The present invention relates to a cryogenic container used when configuring a power device using a superconductor.

Until now, most of the power supply has been transported from large-scale power plants to consumption areas via ultra-high voltage transmission lines. However, it is expected that many distributed power sources will be installed in the vicinity of the power consumption area in the future and these power sources will be connected to the power system. The possible reason is that large-capacity power consumers such as factories are attracting great interest because the introduction of distributed power sources is effective in reducing energy costs and preventing instantaneous voltage drops on the consumer side. One of the reasons is that active use at the national level is required because cogeneration systems using natural gas are also effective for environmental problems such as CO ₂ and NO _x reduction. It is. On the other hand, the introduction of such distributed power sources is not without problems. One of them is an increase in accident current. In general, the introduction of such a distributed power source causes an increase in the fault current that flows in the event of a ground fault or a short-circuit accident that has occurred in the power system. Become. Therefore, some countermeasures must be taken as soon as possible.

  One of the countermeasures for preventing such an increase in fault current is the practical use of a current limiter. A current limiter is a device that passes current with little loss during normal energization and instantaneously generates impedance when a large current flows to suppress the current. There are few examples of full-scale use of such devices in current power systems, but their introduction is strongly desired. Many studies have been conducted on current limiters, including those using arc discharge, those using semiconductors, and those using superconductors. Among them, the type of current limiter that creates an inductance component by winding a superconductor into a coil shape and forms a device in combination with a semiconductor bridge, or a phenomenon that utilizes the phenomenon of superconducting transition of a superconductor due to a large current is used. Current limiters and the like are expected to be put to practical use because of their excellent features that the speed from the occurrence of an accident to the start of the current limiting operation is high and a compact design is possible.

  However, in the case of a current limiter using a superconductor, it is necessary to cool the superconductor in order to bring it into a superconducting state. For example, when a YBCO thin film is used as a superconductor, the superconducting thin film is generally used by immersion cooling in liquid nitrogen (boiling point of 1 atm: 77K). For this reason, in a current limiter using a superconductor, there is almost no loss generated by the superconductor itself, but a loss for cooling this occurs. The amount of energy consumed for this cooling largely depends on the cooling method, the temperature of the low temperature part, etc., but in the case of cooling at the temperature of liquid nitrogen, generally about 20 to 30 times the amount of heat removed is about 20-30 times. It is known to be necessary. Therefore, if the heat penetration into the low temperature region is too large, it is necessary to use a large cooling device, which reduces the efficiency as a power device, and the high speed and compactness inherent in current limiting devices using superconductors. It becomes impossible to make use of the advantages such as sex.

  For this reason, the low temperature vessel currently used for cooling the superconductor has been devised to reduce the heat penetration into the low temperature region, and the intrusion heat in the entire cooling vessel has been reduced. However, it is difficult to reduce the heat intrusion from the current lead, and in the low temperature container provided with the current lead having a large current capacity, the intrusion heat from the lead occupies a large part of the total intrusion heat. The reason is that the current lead is usually made of a good electrical conductor to pass current, while the good electrical conductor is generally a good thermal conductor. For this reason, it is not easy to reduce heat penetration from the current lead. For example, in order to reduce heat intrusion from the outside of the cryogenic vessel, it is only necessary to reduce the cross-sectional area of the current lead and increase the overall length (that is, heat intrusion can be reduced by reducing the temperature gradient in the current lead). ). However, this simultaneously increases the electrical resistance of the current lead, and thus increases Joule heat generated in the current lead when energized. This amount of heat is superimposed on the amount of heat entering from the outside, so that if the resistance of the current lead is too large, the heat entering the low temperature portion will eventually increase. Therefore, the current lead that is usually used is designed so as to determine the current carrying capacity and minimize the heat intrusion under the current carrying (so-called optimum design). Even in a current lead having such an optimal design, for example, between about room temperature and liquid nitrogen temperature, about 20 W / kA (20 W with a 1 kA class current lead) intrusions when no current is applied, and about 50 W / kg when energized. There is kA heat penetration. Therefore, for example, when considering a 600A class device that is a typical current capacity of a feeder wire of a power distribution system, the intrusion heat from the current lead is about 12 W / line when no current is applied, as in a three-phase AC device. If a single current lead is required, the intrusion heat from the current lead will be about 72 W in total. This means that about 2 kW of energy is required to remove this amount of heat even in a non-energized state.

  On the other hand, the place where the current limiter is supposed to be installed is a bus connection point between substations, a connection point between an on-site power supply system using cogeneration and a distribution line system, or the like. A characteristic of these interconnection points is that the magnitude of the current value passing therethrough is not constant but varies greatly with time or day. For example, in the former case, in the normal operation mode, there is almost no amount of current passing through the current limiter, and a relatively large current passes only when fluctuations occur in the power supply / demand balance between the substations. In the latter case, the amount of current passing through the interconnection point differs greatly between day and night.

  When considering the application of a superconducting fault current limiter to a location with such characteristics, if the current lead is designed with a small current value, current can flow without any problem when the passing current value is small, and heat penetration can be reduced. . However, when a large current needs to flow, large Joule heat is generated. For this reason, the design is such that a large current value can be passed even though the intrusion heat at the time of energizing a small current is increased (that is, a current lead having a large invasion heat at the time of non-energization is used). As can be seen from this, if the current lead can be changed in accordance with the amount of current passing, the intrusion heat can be made smaller than the present one, but the cross-sectional area cannot be changed with a normal current lead.

In view of this, for example, a proposal has been made to reduce the intrusion heat from the current lead when no current is applied by a structure in which an opening portion is provided in the current lead and the opening portion region is vacuum insulated. (See Patent Documents 1 and 2)
Japanese Patent Laid-Open No. 9-223621 JP 2001-148520 A

  In the current leads proposed in Patent Documents 1 and 2, when a current is not passed, a part of the current lead can be opened to cut off the heat that enters due to conduction in the current lead. Heat intrusion caused by gas convection can be reduced by vacuum-insulating the pole portion. However, the intrusion heat due to radiation cannot be reduced simply by providing a contact portion that can be opened in the vacuum region. The intrusion heat at the portion opened in the vacuum can be estimated as follows (refer to Experimental Physics Course 15 “Low Temperature”, Kyoritsu Shuppan Co., Ltd.).

First, the magnitude of the intrusion heat that passes between two objects in the vacuum insulation space can be calculated by using Stefan-Boltzmann's radiation law: heat intrusion = 5.67 × 10 ⁻¹² × εA (T ₂ ⁴ − T ₁ ⁴⁾ ··· ₍₁₎
Given in. Here, A represents the area (cm ² ) of the solid surface facing each other in the vacuum heat insulating layer. Further, ε is a coefficient determined by the material of the electrode, but this coefficient is about 1 when the inner surface of the vacuum heat insulating region is made of a material such as glass. Therefore, if 300 K is substituted for T ₂ and 77 K of the liquid nitrogen temperature is substituted for T ₁ , the value of equation (1) is the heat penetration to 0.046 × A (2)
It turns out that it becomes. Here, if the cross-sectional area of the opening portion in the vacuum heat insulating layer is about 200 cm ² with reference to the vacuum region of the circuit breaker, the heat penetration per current lead can be estimated to be about 9 W. This value cannot be said to be remarkably improved as compared with the optimally designed heat penetration 12W when the 600A class current lead is not energized as described above. In this way, the intrusion heat and the significant reduction when no current is passed cannot be reduced simply by providing the opening portion in the vacuum heat insulating region.

  An object of the present invention is to provide a cryogenic container capable of reducing heat penetration into a low temperature region and reducing power required for cooling.

A cryogenic container according to an aspect of the present invention includes a container part that holds a superconductor in a cooled state, a vacuum heat insulating part that is attached to the container part and has an internal space partitioned by a heat insulating material, and the vacuum heat insulating part. A low-temperature side current lead and a room- temperature side current lead connected to the superconductor, and disposed between the low-temperature side current lead and the room-temperature-side current lead. A conductor that is disposed and electrically disconnected from both the low temperature side current lead and the room temperature side current lead at the time of opening; and one or more radiation shields disposed inside the vacuum heat insulating portion. It is characterized by that.

  According to the low temperature container of the present invention, when no current is applied, the intrusion heat due to conduction or gas convection is reduced by opening the low temperature side current lead and the room temperature side current lead in the internal space of the vacuum heat insulating portion, and the radiation shield Heat intrusion due to radiation can also be reduced.

(Example 1)
FIG. 1 shows a schematic cross-sectional view of a cryogenic container. The container portion includes a container body 1 and a lid body 2. Two vacuum heat insulating portions 10 and 10 are attached to the lid 2. The container body 1 contains a low-temperature liquid 3 (for example, liquid nitrogen), and the superconductor 4 is immersed in the low-temperature liquid 3. The superconductor 4 is connected to the low-temperature current lead inserted in the vacuum heat insulating portions 10 and 10. In this embodiment, a pair of vacuum heat insulating portions 10 and 10 are provided and two current leads are used, and the power device is a so-called single phase device.

  2 and 3 show the inside of the vacuum heat insulating portion 10 in the first embodiment. FIG. 2 shows the time of joining, and FIG. 3 shows the time of opening. The vacuum heat insulating part 10 is made of a cylindrical heat insulating material, and a low temperature side current lead 11 and a room temperature side current lead 12 are inserted into the internal space thereof. A driving device 13 that drives the room-temperature-side current lead 12 up and down is provided above the vacuum heat insulating unit 10. Note that the low temperature side current lead 11 may be driven. The drive device 13 joins the low temperature side current lead 11 and the room temperature side current lead 12 as shown in FIG. 2, or opens the low temperature side current lead 11 and the room temperature side current lead 12 as shown in FIG. be able to. These parts are made by applying a commercially available vacuum circuit breaker.

  In the internal space of the vacuum heat insulating portion 10, a radiation shield 14 is fixed between the peripheral surfaces of the low temperature side current lead 11 and the room temperature side current lead 12 and the inner wall of the vacuum heat insulating portion 10. As shown in the plan view of FIG. 4, the radiation shield 14 has a ring shape with a hole in the center. The low temperature side current lead 11 or the room temperature side current lead 12 passes through the hole of the radiation shield 14. In this way, the radiation shield 14 is disposed so as to separate the room temperature side and the low temperature side as much as possible so as to suppress heat penetration due to radiation from the room temperature side to the low temperature side. The number of radiation shields 14 is not particularly limited, an appropriate number is provided, and the arrangement position is not limited.

  In this embodiment, the portion other than the contact point between the low temperature side current lead 11 and the room temperature side current lead 12 is optimally designed with a current carrying capacity of 600A.

  Using the cryogenic container of Example 1 and a cryogenic container (conventional example) provided with a current lead optimally designed at 600 A, an experiment was conducted to examine the magnitude of the intrusion heat. In this experiment, the cryogenic vessel was filled with liquid nitrogen, and continuous energization at 600 A and 50 Hz was performed for the first hour. Subsequently, the current was interrupted, and the current interrupted state was maintained for 5 hours. At this time, in the low temperature container of Example 1, the low temperature side current lead 11 and the room temperature side current lead 12 were opened. During this time, the evaporation amount (liter) of liquid nitrogen was measured. FIG. 5 shows the time change of the liquid nitrogen evaporation amount.

As can be seen from FIG. 5, about 1.7 liters of liquid nitrogen has evaporated in the first hour in either cryogenic vessel. If heat penetration from the current lead is estimated based on this value and the latent heat of vaporization of liquid nitrogen (about 160 J / cm ³ ), it can be seen that there is about 75 W of heat penetration in either low-temperature vessel when 600 A is energized. Estimating the heat penetration from the current lead based on this value and the heat penetration into the cryostat without the current lead (about 10 W), the value of about 50 W / 1 kA, which is the optimum design value of the current lead in either cryogenic vessel. It can be seen that almost has been achieved.

  However, after the current is cut off, there is a large difference in the evaporation amount of liquid nitrogen between the conventional cryogenic container and the cryogenic container of Example 1. In the cryogenic container of the conventional example, about 4.3 liters of liquid nitrogen was evaporated in 5 hours, and heat penetration was about 28 W. On the other hand, in the low temperature container of Example 1, about 2.6 liters of liquid nitrogen was evaporated in 5 hours, and the intrusion heat was about 13 W. From these results, it was found that in the case of a cryogenic container applied to a place where there is no energization, the use of the cryogenic container of Example 1 can greatly reduce the heat intrusion from the current lead part to less than half. did.

  Next, using the low-temperature container of Example 1 and the low-temperature container (Comparative Example) having the same structure as Example 1 except that the radiation shield of the vacuum heat insulating portion was removed, the magnitude of intrusion heat was the same as above. An experiment was conducted to investigate. That is, after continuous energization at 600 A and 50 Hz for the first hour, the low temperature side current lead 11 and the room temperature side current lead 12 were opened in any of the low temperature containers, and the current interruption state was maintained for 5 hours. FIG. 6 shows the change over time in the amount of liquid nitrogen evaporation.

  From FIG. 6, it was found that in the low temperature container of the comparative example, the liquid nitrogen evaporated when no power was supplied for 5 hours was about 3.95 liters, and the intrusion heat was about 25 W. If the low temperature side current lead 11 and the room temperature side current lead 12 can be opened in the internal space of the vacuum heat insulating portion without providing a radiation shield as in this comparative example, the effect of blocking the intrusion heat is small. On the other hand, it was confirmed that the low temperature container of Example 1 can reduce the intrusion heat by about half compared with the low temperature container of the comparative example.

(Example 2)
7 and 8 show the inside of the vacuum heat insulating portion 10 according to the second embodiment. FIG. 7 shows the time of bonding, and FIG. 8 shows the time of opening. 7 and 8, a plate spring 15 is attached to the inner wall of the vacuum heat insulating portion 10, and a plate-like member 16 is fixed to the tip of the plate spring 15. The plate-like member 16 is connected to the low-temperature side current lead 11 and the room-temperature side current. It is arranged between the leads 12. The position (height) of the plate-like member 16 supported by the plate spring 15 is changed between joining and opening. This plate-like member 16 has a thickness of 5 mm, a central joint is formed of a conductor (in this example, oxygen-free copper), and the periphery thereof is an insulating material having low thermal conductivity (in this example, fiber-reinforced plastic FRP). Surrounded by As shown in FIG. 7, the low temperature side current lead 11, the central joint portion of the plate-like member 16, and the room temperature side current lead 12 are joined at the time of joining. As shown in FIG. 8, when the room temperature side current lead 12 is driven upward at the time of opening, the center joint portion of the plate-like member 16 is electrically disconnected from both the low temperature side current lead 11 and the room temperature side current lead 12. . That is, a total of two opening portions are formed between the low temperature side current lead 11 and the central joint portion of the plate-like member 16 and between the room temperature side current lead 12 and the central joint portion of the plate-like member 16.

  Using the low temperature container of Example 2 and the low temperature container of Example 1 above, an experiment was conducted to examine the magnitude of intrusion heat under the same conditions as described above. That is, after continuous energization at 600 A and 50 Hz for the first hour, the low temperature side current lead 11 and the room temperature side current lead 12 were opened in any of the low temperature containers, and the current interruption state was maintained for 5 hours. FIG. 9 shows the change over time in the evaporation amount of liquid nitrogen.

  From FIG. 9, it was found that in the low temperature container of Example 2, the liquid nitrogen evaporated at the time of no energization for 5 hours was about 2.2 liters, and the intrusion heat was about 9.5 W. As described above, the low temperature container of Example 2 was further less intruded by heat when no current was applied than the low temperature container of Example 1.

  This is because the radiation between the opposing surfaces of the low temperature side current lead 11 and the room temperature side current lead 12 cannot be reduced in the first embodiment, whereas this radiation can be reduced in the second embodiment. Actually, when the temperature was measured by attaching a thermocouple to each electrode portion in the low temperature container of Example 2, the surface temperature of the plate-like member 16 was an intermediate temperature between the low temperature side current lead 11 and the room temperature side current lead 12. Was showing. As described above, in order to reduce the heat intrusion due to radiant heat, it is important that the temperature of the plate-like member 16 provided between the low temperature portion and the room temperature portion is almost determined by radiation as in the second embodiment. In such a structure, radiant heat can be reduced to 1 / the number of the plate-like members 16 provided between the low temperature part and the room temperature part. (See Experimental Physics Course 15 “Low Temperature”, Kyoritsu Publishing Co., Ltd. P81).

Example 3
10 and 11 show the inside of the vacuum heat insulating portion 10 in the third embodiment. FIG. 10 shows the time of bonding, and FIG. 11 shows the time of opening. In the third embodiment, in addition to the fixed shielding shield 14, a shielding shield 17 that can be moved by a moving mechanism (not shown) is provided inside the vacuum heat insulating portion 10. As shown in FIG. 11, the movable shield shield 17 is inserted between the low temperature side current lead 11 and the room temperature side current lead 12 at the time of opening.

  As a result of conducting an experiment for examining the magnitude of the intrusion heat under the same conditions as described above for the low temperature container of Example 3, it was found that the intrusion heat could be lowered to about 3 W. The value of the intrusion heat is simply that of the low temperature container of the comparative example (see the description of Example 1) in which the low temperature side current lead 11 and the room temperature side current lead 12 can be opened in the internal space of the vacuum heat insulating portion. It means that it can be reduced to about 1/8.

(Example 4)
12 and 13 show the inside of the vacuum heat insulating portion 10 in the fourth embodiment. FIG. 12 shows the time of bonding, and FIG. 13 shows the time of opening. In the fourth embodiment, not only the low temperature side current lead 11 but also the room temperature side current lead 12 is fixed, and they are separated from each other. In addition to the fixed shield shield 14, a shield shield 19 that can be moved in the horizontal direction by the moving mechanism 18 is provided inside the vacuum heat insulating portion 10. A joining member 20 is attached to the shielding shield 19. As shown in FIG. 12, in the state where the shielding shield 19 is inserted between the low temperature side current lead 11 and the room temperature side current lead 12 at the time of bonding, a bonding member is attached to the side surfaces of the low temperature side current lead 11 and the room temperature side current lead 12. 20 are joined. As shown in FIG. 13, the bonding member 20 is separated from the side surfaces of the low temperature side current lead 11 and the room temperature side current lead 12 at the time of opening, but the shielding shield 19 is interposed between the low temperature side current lead 11 and the room temperature side current lead 12. Keep inserted.

  As a result of an experiment for examining the magnitude of the intrusion heat under the same conditions as described above for the low temperature container of Example 4, the intrusion heat was estimated to be about 5 W. This value is slightly larger than that of Example 3, but is sufficiently smaller than that of the comparative cryogenic container. In addition, since the mechanism of the cryogenic container of Example 4 is simple, high reliability is expected.

(Example 5)
14 and 15 show the inside of the vacuum heat insulating portion 10 in the fifth embodiment. FIG. 14 shows the time of joining, and FIG. 15 shows the time of opening. The cryogenic containers of the embodiments so far are applied to locations where the power supply form takes two cases of normal energization and non-energization. However, such a cryogenic container cannot be applied to a place where the energization current is not reduced to zero. In contrast, the cryogenic container of the fifth embodiment can be applied to such a place. The low temperature container of the fifth embodiment includes a bypass current lead 21 that constantly connects the low temperature side current lead 11 and the room temperature side current lead 12 to pass a small current in addition to the low temperature container of the second embodiment. More specifically, the low-temperature side current lead 11 and the room temperature-side current lead 12 are optimized at 550 A, whereas the bypass current lead 21 connected in parallel is designed with a normal current value of 50 A.

  For the low temperature container of the fifth embodiment, when the low temperature side current lead 11 and the room temperature side current lead 12 are opened and 50 A is energized through the bypass current lead 21, the intrusion heat per current lead is about 8 W. I knew it was possible. On the other hand, when a current lead optimally designed at 600 A is used as in the conventional cryogenic container, there is about 30 W of intrusion heat per current lead even when 50 A is energized. Thus, it can be seen that the low temperature container having the bypass current lead 21 as in the fifth embodiment can significantly reduce the intrusion heat from the current lead when a small current is applied, as compared with the conventional low temperature container.

1 is a schematic cross-sectional view of a cryogenic container according to an embodiment of the present invention. Sectional drawing which shows the state at the time of joining of the vacuum heat insulation part in the cryogenic container of Example 1. FIG. Sectional drawing which shows the state at the time of opening of the vacuum heat insulation part in the cryogenic container of Example 1. FIG. 2 is a plan view of a radiation shield used in Embodiment 1. FIG. The figure which shows the time change of liquid nitrogen evaporation about the low temperature container of Example 1, and the low temperature container of a prior art example. The figure which shows the time change of liquid nitrogen evaporation about the low temperature container of Example 1, and the low temperature container of a comparative example. Sectional drawing which shows the state at the time of joining of the vacuum heat insulation part in the cryogenic container of Example 2. FIG. Sectional drawing which shows the state at the time of the opening of the vacuum heat insulation part in the cryogenic container of Example 2. FIG. The figure which shows the time change of liquid nitrogen evaporation about the low temperature container of Example 2, and the low temperature container of Example 1. FIG. Sectional drawing which shows the state at the time of joining of the vacuum heat insulation part in the cryogenic container of Example 3. FIG. Sectional drawing which shows the state at the time of opening of the vacuum heat insulation part in the cryogenic container of Example 3. FIG. Sectional drawing which shows the state at the time of joining of the vacuum heat insulation part in the cryogenic container of Example 4. FIG. Sectional drawing which shows the state at the time of the opening of the vacuum heat insulation part in the cryogenic container of Example 4. FIG. Sectional drawing which shows the state at the time of joining of the vacuum heat insulation part in the cryogenic container of Example 5. FIG. Sectional drawing which shows the state at the time of opening of the vacuum heat insulation part in the cryogenic container of Example 5. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Container main body, 2 ... Cover body, 3 ... Low temperature liquid, 4 ... Superconductor, 10 ... Vacuum heat insulation part, 11 ... Low temperature side current lead, 12 ... Room temperature side current lead, 13 ... Drive apparatus, 14 ... Radiation shield, DESCRIPTION OF SYMBOLS 15 ... Leaf spring, 16 ... Plate-shaped member, 17 ... Radiation shield, 18 ... Moving mechanism, 19 ... Radiation shield, 20 ... Joining member, 21 ... Bypass current lead.

Claims (4)

A container for holding the superconductor in a cooled state;
A vacuum heat insulating part attached to the container part and having an internal space partitioned by a heat insulating material ;
A low temperature side current lead and a room temperature side current lead connected to the superconductor, arranged so as to be openable in the internal space of the vacuum heat insulating part,
A conductor disposed between and joined to the low temperature side current lead and the room temperature side current lead, and electrically disconnected from both the low temperature side current lead and the room temperature side current lead at the time of opening,
A cryogenic container comprising one or more radiation shields arranged inside the vacuum heat insulating portion.   The cryogenic container according to claim 1, further comprising a driving device that drives the low temperature side current lead or the room temperature side current lead to open the electrode.   The at least one of the radiation shields is movably held so as to be inserted between the low temperature side current lead and the room temperature side current lead at the time of opening. The cryogenic container described.   The low-temperature container according to claim 1, further comprising a bypass current lead that constantly connects the low-temperature side current lead and the room-temperature side current lead to pass a small current.

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