JP5950951B2 - Superconducting fault current limiter and method for cooling superconducting element in superconducting fault current limiter - Google Patents

Description

  The present invention relates to a superconducting fault current limiter having a plurality of superconducting elements and a method for cooling the superconducting elements in the superconducting fault limiter.

The current limiter is a device to be introduced into a power system or the like. By introducing this current limiting device, it is possible to suppress an accident current such as a short-circuit accident and to reduce damage to connected devices.
The conventional current limiter is generally a normal conducting reactor type, but in recent years, a superconducting element is interposed in the current path to maintain the superconducting state when energized within the specified current range. A superconducting fault current limiter has been proposed in which, when an accident current exceeding the current occurs, a normal conduction state is established and the accident current is suppressed by its resistance.

Superconducting elements used in current limiters are cooled in a liquid refrigerant such as liquid helium or liquid nitrogen in order to maintain a cryogenic state. However, when an accident current occurs, the superconducting element is in a normal conducting state. As a result, the element temperature rises rapidly.
The fault current limiter is generally used in combination with the fault current circuit breaker. When the fault current occurs, the current limiter must reduce the fault current until the circuit breaker is activated (about 0.1 [s]). When the circuit breaker interrupts the fault current, unless the superconducting element is quickly cooled in the current limiter, the element life is significantly shortened, and the life as the current limiter is also shortened.
In particular, when a plurality of superconducting elements are provided, the superconducting element having the smallest critical current value tends to generate heat for the longest time, resulting in a shorter lifetime than the other superconducting elements, and as a result, The lifetime will be shortened significantly.
For this reason, in the superconducting fault current limiter, it is required to cool quickly when the superconducting element generates heat.

For example, Patent Document 1 discloses a refrigerant container that contains a semiconductor element as a heat generation source and a liquid refrigerant, a partition that separates the inside of the refrigerant container into a coolant supply side and an element arrangement region side, and the partition. A cooling structure is disclosed that includes a nozzle-like refrigerant outlet extending toward the semiconductor element and a turbulence forming member that disturbs the flow of the refrigerant in the vicinity of the outlet of the refrigerant outlet.
In this cooling structure, liquid refrigerant is ejected from the refrigerant outlet toward the semiconductor element by the supply pressure of the refrigerant, and at this time, the turbulence forming member disturbs the flow of the refrigerant, so that the core of the semiconductor element is uniformly distributed as much as possible. High efficiency of cooling is achieved by causing boiling.

Further, Patent Document 2 discloses a refrigerant container that contains a semiconductor element as a heat generation source and a liquid refrigerant, a cooling pipe provided between the inner wall and the outer wall of the refrigerant container, and a semiconductor from the inner wall of the refrigerant container. A cooling structure is disclosed that includes a plurality of protrusions that trap air bubbles extending toward the element side.
In this cooling structure, refrigerant bubbles generated by the temperature rise of the semiconductor element are collected on the inner wall side by the protrusions, and the bubbles are positively cooled to increase the cooling efficiency.

Japanese Patent Laid-Open No. 06-104358 JP-A-62-285449

However, since the cooling structure described in Patent Document 1 is based on the premise of cooling a semiconductor element whose temperature rise is relatively gradual, it is assumed only when nucleate boiling occurs on the surface of the element.
On the other hand, when an accident current occurs, the superconducting element is heated from the liquid nitrogen temperature (77K) to room temperature (300K). Therefore, the surface of the superconducting element is in a film boiling state. Even if the cooling structure of Patent Document 1 is applied to such a superconducting fault current limiter, the surface of the superconducting element is covered with the vaporized gas of the liquid refrigerant in the film boiling state, so that the liquid refrigerant from the refrigerant outlet is the superconducting element. It did not reach the surface and it was difficult to perform sufficient cooling.
In addition, the cooling structure described in Patent Document 1 requires a cooling container having a special structure such as providing a partition in the interior and forming a coolant outlet in the partition, which complicates the overall configuration and reduces the cost of the apparatus. There was a problem that an increase or the like occurred.

Also, in the case of the cooling structure described in Patent Document 2, since the cooling method is based on the premise of nucleate boiling of trapping bubbles, film boiling occurs as if the vaporized refrigerant stuck to the entire plane of the element. When this occurred, cooling could not be performed effectively.
Also, in the case of the cooling structure described in Patent Document 2, a cooling pipe having a special structure such as a cooling pipe provided between the inner wall and the outer wall and a protrusion on the inner wall is necessary, and the overall configuration is complicated. There has been a problem in that, for example, an increase in device cost is caused.

  An object of the present invention is to provide a superconducting fault current limiter that performs effective cooling when film boiling occurs on the surface of the superconducting element, and a method for cooling the superconducting element in the superconducting fault current limiter.

  The present invention relates to a superconducting fault current limiter including a superconducting element that is in a superconducting state when a current value is energized within a certain range and is in a normally conducting state when an accident current exceeding the range is energized. A refrigerant container that houses the superconducting element; and a cooling unit that cools the liquid refrigerant in the refrigerant container, wherein the superconducting element having the smallest critical current among the plurality of superconducting elements is replaced with another liquid superconducting element. It is arranged above any one of the superconducting elements.

Further, the present invention provides the superconducting element of a superconducting fault current limiter comprising a superconducting element that is in a superconducting state when energized within a certain range of current value and is in a normally conducting state when energizing an accident current exceeding the range. In the cooling method, in the liquid refrigerant in the refrigerant container, the superconducting element having the smallest critical current among the plurality of superconducting elements is disposed above any other superconducting element, and the superconducting element having the smallest critical current is arranged. The superconducting element having the minimum critical current is cooled by bubbles generated from the superconducting element disposed on the lower side of the element.
In the method of cooling a superconducting element in the superconducting current limiting device, the superconducting element having the minimum critical current may be cooled when the liquid refrigerant on the surface of the superconducting element having the minimum critical current is in a film boiling state.

  Also, in the invention of the method of cooling a superconducting current limiter or a superconducting element in the superconducting current limiter, the liquid refrigerant is arranged such that the smaller the supercurrent among the plurality of superconducting elements, the higher is the upper side. It is also good.

  Further, in the invention of a superconducting current limiter or a method of cooling a superconducting element in a superconducting current limiter, the plurality of superconducting elements are arranged in a plane along the vertical direction, and two superconducting elements are arranged adjacent to each other in the vertical direction. Any of the combinations may be arranged so that the upper side has a smaller critical current than the lower side.

  Further, in the invention of a superconducting current limiter or a method of cooling a superconducting element in a superconducting current limiter, a plurality of sets of the plurality of superconducting elements arranged in a plane along the vertical direction are arranged to arrange the entire superconducting element. It is good also as what arranges in three dimensions.

  Further, in the invention of the superconducting current limiter or a method of cooling a superconducting element in the superconducting current limiter, an element cover that surrounds the plurality of superconducting elements that is open at the top and bottom may be disposed in the refrigerant container. .

According to the present invention, in a liquid refrigerant in a refrigerant container, a superconducting element having a minimum critical current among a plurality of superconducting elements is arranged above any other superconducting element. Then, each superconducting element in which a rapid temperature rise is caused by the occurrence of an accident current is in a film boiling state. As a result, the vaporized gas of the liquid refrigerant generated from the surface of each superconducting element is released upward, and the superconducting element having the minimum critical current disposed above the other superconducting elements is exposed to the rising vaporized gas.
Since the superconducting element in the film boiling state is generated in a state in which the vaporized gas is stuck on the surface of the superconducting element, the cooling efficiency is reduced. When the superconducting element in such a state is exposed to vaporized gas bubbles rising from below and a liquid flow caused by the bubbles, the vaporization gas generated on the surface of the element is promoted to come into contact with the liquid refrigerant, so that the critical current The cooling efficiency of the superconducting element with the smallest is improved.
For this reason, it is possible to extend the life of the superconducting element having the shortest critical current and the shortest life, and it is possible to realize the long life of the entire superconducting fault current limiter.
In addition, since the cooling efficiency is improved by the arrangement of superconducting elements, there is no need for special structures or special structures for cooling, and it is possible to simplify the overall structure of the superconducting fault current limiter and reduce costs. It is.

  In addition, in the liquid refrigerant, when a plurality of superconducting elements having a smaller critical current are arranged on the upper side, even when a plurality of superconducting elements having a small critical current are included, all of these are superposed on other superconducting elements. Since the gas can be cooled by the vaporized gas from the gas, the life of the superconducting fault current limiter can be further increased.

In addition, in the case where any combination of two superconducting elements arranged vertically adjacent to each other in a plurality of superconducting elements arranged in a plane is arranged such that the upper side has a smaller critical current than the lower side. Since each superconducting element is distributed so that the critical current becomes smaller as the one located above the plurality of superconducting elements arranged in a plane, the effective life extension of the superconducting fault current limiter is realized. Is possible.
In addition, when a plurality of superconducting elements arranged in a plane are arranged in a plurality and the whole superconducting elements are arranged three-dimensionally, the flow of vaporized gas generated from the plurality of superconducting elements arranged below is combined. It is possible to bring the superconducting element having a small critical current to a longer life by providing the upper superconducting element, and it is possible to further extend the life of the superconducting fault current limiter.

  In addition, when a plurality of superconducting elements are arranged so as to be surrounded by the element cover, the flow of vaporized gas generated from the superconducting elements arranged below can be guided to the upper superconducting elements without diffusing. By extending the life of a superconducting element having a small current, it is possible to further extend the life of the superconducting fault current limiter.

It is sectional drawing along the vertical plane of the superconducting fault current limiter concerning a first embodiment. It is a diagram which shows the correspondence of the heating time at the time of heating a general superconducting element continuously at 100 degreeC, and the contact resistance value with an electrode. It is a graph which shows the characteristic at the time of performing a current-limiting operation | movement by arrange | positioning a superconducting element with a large critical current and a superconducting element with a small critical current each independently. It is the table | surface which compared the life by the frequency limiting operation frequency about Example 1 and Comparative Example 1. FIG. It is explanatory drawing which shows the principle of cooling based on arrangement | positioning of the superconducting element of Example 1. FIG. It is explanatory drawing which shows arrangement | positioning of the superconducting element in the superconducting fault current limiter which concerns on 2nd embodiment. 10 is a chart showing changes in the lifetime of each superconducting element in Example 2. 10 is a chart showing changes in the lifetime of each superconducting element in Comparative Example 2. It is explanatory drawing which shows the inclination limit of the arrangement | sequence of a superconducting element about arrangement | positioning of the superconducting element in the superconducting fault current limiter which concerns on 2nd embodiment. It is explanatory drawing which shows the other example regarding the direction at the time of installation of a superconducting element. It is explanatory drawing which shows the other example of arrangement | positioning of a superconducting element. It is explanatory drawing which shows the further another example of arrangement | positioning of a superconducting element. It is explanatory drawing which shows the further another example of arrangement | positioning of a superconducting element. It is explanatory drawing which shows the further another example of arrangement | positioning of a superconducting element. It is a top view which shows the example of a superconducting element unit. It is a top view which shows the other example of a superconducting element unit. It is explanatory drawing which shows the case where an element cover is provided around the superconducting element.

[First embodiment]
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.
In this first embodiment, a superconducting fault current limiter 10 for reducing an accident current generated on the power supply side, provided in the middle of the power supply path, for the protection target device to which power is supplied from the outside, and the concerned A method for cooling the superconducting elements 71 and 72 in the superconducting fault current limiter 10 will be described. FIG. 1 is a cross-sectional view of the superconducting fault current limiter 10 along a vertical plane.

The superconducting fault current limiter 10 includes an inner container 21 and an outer container 22 that are thermally insulated from vacuum, and a refrigerant container 20 that houses liquid nitrogen 60 that is a liquid refrigerant and two superconducting elements 71 and 72 described later. A lid 30 capable of closing the upper opening of the refrigerant container 20 and a refrigerator 40 as a cooling means for cooling the liquid nitrogen 60 in the inner container 21 are provided.
The superconducting fault current limiter 10 maintains the superconducting state when the two superconducting elements 71 and 72 are energized in a range that does not exceed the critical current of either of the superconducting elements 71 and 72. When an excessive accident current exceeding the critical current is energized, it becomes a normal conducting state and generates an electrical resistance, thereby preventing an excessive current from being supplied to the device to be protected.
Hereinafter, each part of the superconducting fault current limiter 10 will be described.

[Refrigerant container]
The refrigerant container 20 is composed of an inner container 21 and an outer container 22, and is a bottomed container having a double wall structure in which the two are vacuum-insulated.
The inner container 21 has a cylindrical shape along the vertical direction, and the lower end portion is closed to form a bottom portion, and the upper end portion is opened.
The outer container 22 has a cylindrical shape along the vertical direction like the inner container 21, and has a lower end closed to form a bottom, and an upper end opened. The outer container 22 is formed to be slightly larger than the inner container 21, and stores the inner container 21 inside. Furthermore, the upper ends of the inner container 21 and the outer container 22 are joined together so that the outer peripheral surface and bottom bottom surface of the inner container 21 and the inner peripheral surface and bottom upper surface of the outer container 22 form a gap space. It has become. In addition, the space between the inner container 21 and the outer container 22 is evacuated and thermally insulated.
Further, in the gap space between the inner container 21 and the outer container 22, there is a super insulation material 23 formed by laminating a polyester film on which aluminum is vapor-deposited over the entire area of the cylindrical portion and the bottom portion. The radiant heat is cut off.

[Lid]
The joint between the inner container 21 and the outer container 22 (the upper end surface of the refrigerant container 20) is smoothed horizontally, and a disc-shaped lid 30 is placed on the ring-shaped smooth surface (upper end surface). Has been.
The lid 30 is attached in a state where it can be detached from the refrigerant container 20 so that the inside of the refrigerant container 20 can be accessed by maintenance and inspection. For example, the lid 30 is fixed to the refrigerant container 20 by a well-known method such as a fitting structure based on an uneven shape between the lid 30 and the refrigerant container 20 or bolting.
Since the lid 30 supports the refrigerator 40 in a suspended manner, the lid 30 is preferably formed of a material having a certain degree of strength. Specifically, FRP (Fiber Reinforced Plastics), stainless steel, or the like can be used as the material of the lid 30.
Further, the lid 30 may have a double wall surface structure in which the hollow interior is thermally insulated by vacuum, like the refrigerant container 20, and the heat insulation may be enhanced.

[refrigerator]
The refrigerator 40 is a cold storage type so-called GM refrigerator, and has a cylinder source 41 that reciprocates a displacer container that holds a cold storage material up and down, and a motor that gives a vertical movement operation to the displacer container as a driving source. The drive part 42 in which the crank mechanism was stored, and the heat exchanger 44 as a heat exchange member provided in the low temperature transmission part 43 in which the cylinder part 41 becomes the lowest temperature are provided.
The refrigerator 40 is connected to a compressor or the like (not shown), and refrigerant gas is sucked into and exhausted from the inside thereof.

[Superconducting element]
The two superconducting elements 71 and 72 have the same dimensions and the same structure, are strip-shaped flat plates having superconductors, and are connected in series along the energization direction. Further, both end portions of the two superconducting elements 71 and 72 connected in series are individually connected to current leads 91 and 92 that are held through the lid 30 vertically. That is, an accident current is passed from one current lead 91 or 92 to the other current lead 92 or 91 via the two superconducting elements 71 and 72.
As a superconductor constituting each of the superconducting elements 71 and 72, an RE-based superconductor (RE: rare earth element) that becomes a superconducting state at a liquid nitrogen temperature or higher can be used. A typical example of the RE-based superconductor is an yttrium-based superconductor represented by the chemical formula YBa ₂ Cu ₃ O _7-y (hereinafter, Y-based superconductor). In the case of the RE-based superconductor, in addition to the strip-shaped flat plate, a tape-shaped superconducting wire in which an RE-based superconductor is formed on a tape-shaped metal substrate via an intermediate layer may be used. Further, it may be a tape-shaped superconducting wire in which a superconductor is formed in a metal matrix. As the superconductor, a bismuth-based superconductor, for example, the chemical formula Bi ₂ Sr ₂ CaCu ₂ O _{8 + δ} (Bi2212), Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + δ} (Bi2223) can be applied. In the chemical formula, δ represents an oxygen nonstoichiometric amount.

The two superconducting elements 71 and 72 are vertically positioned in the state in which the longitudinal direction is along the vertical direction at a position lower than the liquid level 61 of the liquid nitrogen 60 at the specified liquid level in the refrigerant container 20. It is held by a frame (not shown) so as to be along the vertical direction.
As the two superconducting elements 71 and 72, those having variations in the value of the critical current capable of maintaining the superconducting state are used. The superconducting element 71 having the smaller critical current is disposed above the superconducting element 72 having the larger critical current.
Specifically, one superconducting element 71 has a critical current value of 100 [A], and the other superconducting element 72 has a critical current value of 120 [A]. Note that this numerical value of the critical current is an example, and if the superconducting element 71 disposed on the upper side satisfies the condition that the critical current is smaller than that of the lower superconducting element 72, the critical current has other values. You may combine.

Here, the lifetime of the superconducting element will be described. FIG. 2 shows the correspondence between the heating time and the contact resistance value with the electrode when a general superconducting element is continuously heated at 100 ° C. (100 ° C.). The contact resistance value with the electrode in the superconducting element is a characteristic value that serves as an index of deterioration of the superconducting element, and FIG. 2 shows the percentage increase with respect to the initial resistance value of the superconducting element as a percentage. When the contact resistance value reaches 100%, the lifetime of the superconducting element is considered.
As shown in the figure, the superconducting element shows a tendency that the contact resistance increases as the heating time becomes longer.

Fig. 3 shows a case where a superconducting element having a large critical current and a superconducting element having a small critical current are individually arranged and energized with a current of 200 [A] at 0.1 [s]. "Current limiting operation"). In the case of a superconducting element (Ic = 120 [A]) with a large critical current Ic shown in the upper part of FIG. 3, the element temperature rises to 60 ° C. (60 degrees Celsius) by the above energization until it returns to the normal temperature. The duration of the current limit operation was 12 [s], and the durability of the current limiting operation until the end of the service life was approximately 2700 times.
On the other hand, in the case of a superconducting element having a small critical current Ic (Ic = 100 [A]) shown in the lower part of FIG. 3, the element temperature rises to 100 ° C. (100 degrees Celsius) by the above energization, and reaches a predetermined temperature. The time to return was 15 [s], and the service life of the current limiting operation until the end of the service life was approximately 700 times.
With a superconducting fault current limiter, if one of the superconducting elements reaches the end of its life, the life of the device will be increased. When arranged side by side, the lifetime of the superconducting fault current limiter is up to 700 current limiting operations.

On the other hand, in the superconducting fault current limiter 10 which is an embodiment of the invention, the superconducting element 71 (Ic = 100 [A]) having a small critical current in the liquid nitrogen of the refrigerant container 20 and the superconducting element 72 having a large critical current ( Ic = 120 [A]).
That is, the superconducting fault current limiter 10 according to the embodiment (referred to as Example 1) is a superconducting element 71 (Ic = 100 [A]) having a small critical current and a superconducting element 72 (Ic = 120 [A]) having a large critical current. It is arranged above.
Hereinafter, a comparison between Example 1 and the superconducting element (Ic = 120 [A]) having a large critical current in the liquid nitrogen of the refrigerant container is arranged above the superconducting element (Ic = 100 [A]) having a small critical current. The characteristics of Example 1 are compared with FIG.

In Comparative Example 1, the life of the superconducting element with a large critical current disposed at the upper side is 3100 times of current limiting operation, and the life is extended by about 400 times compared with the case of single element placement, but it is disposed below. Since the life of the superconducting element having a small critical current remains at 700 times of the current limiting operation, the device life of the superconducting current limiter is 700 times the same as before.
On the other hand, in Example 1, the life of the superconducting element 72 with a large critical current disposed below is 2700 times of current limiting operation, which is not different from the case of single element arrangement, but is disposed above. The life of the superconducting element 71 having a small critical current is 800 times the current limiting operation, and the life is extended about 100 times compared to the case of a single element arrangement. The operation is 800 times, extending the life.

The superconducting element is cooled by the surrounding cryogenic liquid nitrogen, but when a current that greatly exceeds the critical current such as an accident current flows to the superconducting element, the superconducting element transitions from the superconducting state to the normal conducting state, It generates heat rapidly due to the increase in electrical resistance. As a result, the superconducting element becomes very high in temperature with respect to the liquid nitrogen, and the liquid nitrogen exceeds the nucleate boiling state and becomes a film boiling state.
When the film boiling state occurs, the surface of the superconducting element is covered with nitrogen gas whose cooling efficiency is lower than that of liquid nitrogen, so that it takes time to cool the superconducting element.
However, when superconducting elements 71 and 72 are arranged side by side, film boiling occurs in each superconducting element 71 and 72 at the time of occurrence of an accident current as shown in FIG. Nitrogen gas rises as bubbles and passes around the upper superconducting element 71. At this time, the surface of the upper superconducting element 71 is brought back into contact with the liquid nitrogen in order to promote the separation of the nitrogen gas in the film boiling state generated on the surface of the upper superconducting element 71 by the bubbles and the liquid flow caused by the rising of the bubbles. It is possible to suppress a decrease in cooling efficiency. As a result, the upper superconducting element 71 is cooled more quickly than a case where it is arranged in a single unit or arranged side by side with other superconducting elements, thereby extending the life. .
Therefore, the superconducting fault current limiter 10 also realizes a longer life of the superconducting fault current limiter 10 itself as the life of the superconducting element 71 having a smaller critical current that determines the life of the entire apparatus is increased.

[Second Embodiment]
A second embodiment of the present invention will be described in detail with reference to the drawings. The superconducting fault current limiter according to the second embodiment differs from the superconducting fault current limiter 10 according to the first embodiment described above in the number of superconducting elements and their arrangement, and other configurations (refrigerants) Since the container 20, the lid 30, the liquid nitrogen 60, the refrigerator 40, the current leads 91, 92, etc.) are the same, the superconducting element will be mainly described here.

In the superconducting fault current limiter according to the second embodiment, nine superconducting elements 81 to 89 are used as shown in FIG.
Each of the superconducting elements 81 to 89 is a strip-shaped flat plate made of a superconducting material, and is held in a state where each flat plate surface is arranged along the same vertical plane in a state where each longitudinal direction is along the vertical direction. Is done.
Further, each of the superconducting elements 81 to 89 includes a first element group composed of three superconducting elements 81, 82 and 83 and a second composed of three superconducting elements 84, 85 and 86 which are electrically connected in parallel by wiring. And a third element group consisting of three superconducting elements 87, 88 and 89 are electrically connected in series, with three elements arranged in the energizing direction. The wiring at one end is connected to the current lead 91 and the wiring at the other end is connected to the current lead 92 (the current leads 91 and 92 are not shown in FIG. 6).

  In addition, as a spatial arrangement of the superconducting elements 81 to 89, the superconducting elements 81 to 89 are arranged along a row direction and a column direction, and are arranged in a planar shape. That is, three superconducting elements 81, 82, and 83 (element positions A, B, and C in FIG. 6) constituting the first element group and three superconducting elements 84, 85, and 86 (second element group). The element positions D, E, F) in FIG. 6 and the three superconducting elements 87, 88, 89 (element positions G, H, I in FIG. 6) constituting the third element group are all along the horizontal direction. The superconducting elements 81, 84, 87 at the left end of each element group, the superconducting elements 82, 85, 88 at the center of each element group, and the superconducting elements 83, 86, 89 at the right end of each element group are vertically up and down, respectively. They are arranged along the direction.

And each superconducting element 81-89 uses the thing in which the numerical value of the critical current varies as shown in FIG. These superconducting elements 81 to 89 are arranged so that the critical current of the upper superconducting element is smaller than the critical current of the lower superconducting element with respect to all combinations of two superconducting elements arranged adjacent to each other in the vertical direction. .
Specifically, the superconducting elements 81, 82, 83 in the upper row have a critical current value of 90, 95, 100 [A], respectively, and the superconducting elements 84, 85, 86 in the middle row each have a critical current value. 105, 110, and 115 [A], and the superconducting elements 87, 88, and 89 in the lower row have critical current values of 115, 120, and 120 [A], respectively.
Also, the superconducting elements 81 (Ic = 90 [A]) having the smallest critical current among the superconducting elements 81 to 89 are arranged at the top of the whole, and the superconducting elements 88 and 89 (Ic having the largest critical current). = 120 [A]) is located in the lowest order in the whole.

  Here, regarding the example of FIG. 6 (referred to as Example 2) arranged in the order of the superconducting elements 81 to 89 at the element positions A to I, FIG. 7 shows changes in the lifetimes of the superconducting elements 81 to 89. Moreover, the change of the lifetime of each superconducting element 89-81 is shown in FIG. 8 about the comparative example 2 arrange | positioned in order of the superconducting element 89-81 in element position AI. In each of the superconducting elements 81 to 89 of Comparative Example 2, the critical current of the upper superconducting element is larger than the critical current of the lower superconducting element for all combinations of the two superconducting elements arranged adjacent to each other in the vertical direction. Will be arranged as follows.

In both Example 2 and Comparative Example 2, the superconducting elements in the lower row are not exposed to the nitrogen gas bubbles from the other superconducting elements, and thus have the same lifetime as that of the single arrangement.
In both Example 2 and Comparative Example 2, the superconducting elements arranged in the middle and upper stages are exposed to nitrogen gas bubbles from the other superconducting elements below, so that the lifetime is longer than in the case of single arrangement. Figured.
However, in the case of the comparative example 2, the superconducting element 81 having the smallest critical current and the second and third smallest superconducting elements 82 and 83 are arranged in the lower stage, so that it is not possible to extend their life. Also, the life of the superconducting fault current limiter cannot be extended.
On the other hand, in the case of Example 2, all the superconducting elements 81 to 86 whose lifetime tends to be shortened can all be extended, so that a longer effective lifetime can be realized for the superconducting fault current limiter. Is possible.

  In the superconducting fault current limiter according to the second embodiment, the case where nine superconducting elements are arranged in a plane is illustrated, but two superconducting elements that can be arranged in a plane and are adjacent to each other vertically. As long as the critical current of the upper superconducting element can be arranged to be smaller than the critical current of the lower superconducting element, the number of the combinations can be arbitrarily changed.

  Moreover, in the superconducting fault current limiter which is said 2nd embodiment, although the case where the element group which consists of several superconducting elements connected in parallel about the wiring is illustrated in series, the connection method is restricted to this. It is not a thing. For example, an element group composed of a plurality of superconducting elements connected in series may be bundled in parallel connection.

Further, as shown in FIG. 9, the arrangement direction of superconducting elements adjacent in the vertical direction may be arranged slightly inclined with respect to the vertical vertical direction.
That is, when the intersection of the horizontal center line and the vertical vertical center line of the flat surface of the superconducting element is defined as the center g of the superconducting element, two superconducting elements adjacent in the vertical direction (for example, 83 and 86) If the inclination angle θ with respect to the vertical vertical direction of the line segment connecting the centers g and g is within the range of 70 ° (degrees) or less (0 ° ≦ θ ≦ 70 °), it is generated from the superconducting element 86 below. Nitrogen gas bubbles can be exposed to the upper superconducting element 83.
At this time, when the distance between the centers of the two superconducting elements 83 and 86 in the vertical direction is L, and the horizontal deviation of the center of each element is δ, θ = tan ⁻¹ (δ / L) Can be arranged so that the following formula (1) or (2) is satisfied for all combinations of two superconducting elements adjacent to.

0 ° ≦ tan ⁻¹ (δ / L) ≦ 70 °… (1)
0 ≦ δ ≦ L ・ tan70 °… (2)
However, δ ≦ α.
α: Horizontal distance of bubbles generated from the superconducting element when the critical current is exceeded

It is good also as the arrangement | positioning which inclines each superconducting element 81-89 to the vertical up-down direction in said range.
In FIG. 9, only the inclination to the right side is shown, but the inclination to the left side can be inclined within the same numerical range.

Alternatively, all the superconducting elements may be arranged three-dimensionally by preparing a plurality of sets of a plurality of superconducting elements arranged in a plane and arranging them in parallel with each other. For example, two or more sets of nine superconducting elements 81 to 89 shown in FIG. 6 are prepared, and these are arranged in parallel and in a direction that intersects the plane with the same height, for example, in a horizontal direction. An arrangement can also be realized.
As a result, the flow of vaporized gas generated from a plurality of superconducting elements arranged below can be brought to the upper superconducting element in a composite manner, extending the life of the superconducting element having a small critical current and the length of the superconducting fault current limiter. It is possible to achieve a long life.

[Others]
The above-described superconducting elements 71, 72, 81-89 can be changed in posture and orientation.
For example, although the case where the longitudinal directions of the superconducting elements 71 and 72 are arranged along the vertical vertical direction has been illustrated, as shown in FIG. 10, these longitudinal directions may be arranged along the horizontal direction. . The same applies to superconducting elements 81-89.
Moreover, when arrange | positioning so that the longitudinal direction of each superconducting element 71 and 72 may follow a horizontal direction, you may arrange | position in the direction in which those flat surfaces become horizontal.

6 illustrates the case where the superconducting elements 81 to 89 are arranged so that the longitudinal direction thereof is along the vertical vertical direction, but as shown in FIG. 11, the superconducting elements 81 to 89 are arranged so that the longitudinal directions thereof are along the horizontal direction. May be.
Moreover, when arrange | positioning so that the longitudinal direction of each superconducting element 81-89 may follow a horizontal direction, you may arrange | position in the direction in which those flat surfaces become horizontal.

  In FIG. 6, superconducting elements 81, 82, 83, superconducting elements 84, 85, 86 and superconducting elements 87, 88, 89 are connected in parallel, and these three sets of superconducting elements are connected in series. However, the connection method is also arbitrary. For example, as shown in FIG. 12, the superconducting elements 81 to 89 may be connected in series.

  12 illustrates the inductive type in which the directions of the currents flowing through the superconducting elements 81 to 89 are arranged in the same direction, but a non-inductive type may be used. For example, as shown in FIG. 13, the superconducting elements 81 to 89 are thin film elements using a thin film of a superconducting material, and the superconducting elements 81 to 89 are connected in series. Then, the three superconducting elements 81, 82, 83 are arranged horizontally, folded at the lower side thereof, and arranged in the opposite direction, and the three superconducting elements 84, 85, 86 are arranged horizontally, and further folded at the lower side thereof, the three are arranged in the opposite direction. Two superconducting elements 87, 88 and 89 may be arranged horizontally. In this case, the directions of the currents flowing through these three sets of superconducting elements are alternately reversed for each set, resulting in a non-inductive arrangement.

Further, the non-inductive arrangement is not limited to the case of FIG. For example, as shown in FIG. 14, superconducting elements 81, 82, and 83 are elements using superconducting wires (elements longer than the superconducting element of FIG. 13), and superconducting elements 81 to 83 are connected in series. . Then, the superconducting element 81 may be horizontally arranged, folded back at the lower side, the superconducting element 82 may be arranged horizontally in the opposite direction, and further folded at the lower side, and the superconducting element 83 may be arranged horizontally in the opposite direction. . In this case, the directions of currents flowing through these three superconducting elements are alternately reversed, resulting in a non-inductive arrangement.
As in the examples of FIGS. 13 and 14, the superconducting element and the superconducting wire are arranged in a meander-type non-inductive arrangement, so that the inductance of the element group is reduced as compared with the configuration of FIG. The voltage generated when the rated current is applied to the power supply 10 can be suppressed.

In addition, when the superconducting element is not a strip shape but a wire that can be easily deformed is transferred, an arbitrary shape may be formed by the superconducting element. For example, two or more superconducting element units 100 in which the superconducting elements 101 to 106 are installed in a spiral shape along the upper surface of the support plate 110 shown in FIG. It may be arranged. In addition, on the upper surface of the support plate 110, a portion 111 where the superconducting elements 101 to 106 are arranged in a coil shape is formed with a net-like or innumerable slits and small holes, and air bubbles can pass through the front and back.
In this case, at least one of the superconducting elements attached to the superconducting element unit 100 arranged at the top and bottom is one below the superconducting element unit 100 to which the superconducting element having the smallest critical current value is attached. It is desirable that the other superconducting element unit 100 is disposed, and it is more desirable that the superconducting element unit 100 to which the superconducting element having the smallest critical current value is attached is disposed on the uppermost side.
Thereby, the element life of the superconducting element having the smallest critical current can be extended, and the life of the entire apparatus can be extended.
The number of superconducting element units is arbitrary as long as it is two or more, and the number of superconducting elements provided in one superconducting element unit 100 is arbitrary as long as it is one or more.
Further, the shape of the superconducting element of the superconducting element unit 100 may be a non-inductive winding shape as shown in FIG. That is, by winding the wire-shaped superconducting element 101 folded in the central portion in a coil shape and energizing from one end portion to the other end portion, the adjacent wire-shaped superconducting elements are mutually connected with the folded portion in the central portion as a boundary. A current flows in the opposite direction. As a result, the inductance of the element group is reduced, and the generated voltage when the superconducting fault current limiter 10 is rated to be energized can be suppressed.
Further, even in the case of the non-inductive winding shape, a plurality of wire-like superconducting elements may be wound in a coil shape as shown in FIG.

Further, the values of the critical currents of the above-described superconducting elements 71, 72, 81 to 89 are just examples, and can be arbitrarily changed as long as the above-described element arrangement and the critical current are satisfied. .
In the above embodiment, a configuration in which a part of a plurality of superconducting elements is arranged on a horizontal plane is shown, but the number of superconducting elements arranged on the plane and the direction of arrangement are not limited to the above configuration. As shown in FIG. 9, it is preferable to arrange a superconducting element having a small critical current value at the arrival position of bubbles generated from other superconducting elements. The arrangement of the plurality of superconducting elements is preferably higher as the value of the critical current is smaller, but at least one or more other superconducting elements are arranged below the superconducting element having the smallest critical current. For example, the lifetime of the superconducting element having the smallest critical current can be extended, and the lifetime of the entire apparatus can be extended.

In addition, as shown in FIG. 17, in the liquid nitrogen 60 of the refrigerant container 20, there is provided a cylindrical or frame-shaped element cover 93 that is open at the top and bottom and surrounds each superconducting element 71, 72, 81-89. Also good. Although FIG. 17 illustrates the case where the superconducting elements 71 and 72 are surrounded, the superconducting elements 81 to 89 may be surrounded by the element cover 93 as a whole.
The element cover 93 can suppress the diffusion of nitrogen gas bubbles generated in the lower superconducting element at the time of occurrence of an accident current and can be directed upward, and the upper superconducting element can be effectively directed to the bubbles and the liquid flow caused thereby. It is possible to perform more efficient cooling.
Note that the superconducting elements 71 and 72 may be surrounded by a shape other than a cylindrical shape or a frame shape as long as the upper and lower sides are opened to suppress the diffusion of nitrogen gas bubbles.

Moreover, although the case where the superconducting element was strip-shaped was illustrated, it is not restricted to this, For example, it is good also as rod shape, wire shape, sheet shape, and other arbitrary shapes.
Moreover, the superconductor which comprises each superconducting element is not limited to an illustration, You may use the superconducting element which consists of another superconducting material. However, in that case, it is desirable to appropriately select a refrigerator and a liquid refrigerant capable of maintaining the superconducting state by the newly selected superconducting material or cooling to a possible temperature.

10 Superconducting Current Limiter 20 Refrigerant Container 30 Lid 40 Refrigerator (Cooling Means)
60 Liquid nitrogen (liquid refrigerant)
71, 72, 81-89 Superconducting element

Claims (11)

In a superconducting fault current limiter including a superconducting element that is in a superconducting state when energized within a certain range of current value and is in a normally conducting state when energizing an accident current exceeding the range,
A refrigerant container containing a liquid refrigerant and a plurality of the superconducting elements;
Cooling means for cooling the liquid refrigerant in the refrigerant container,
A superconducting fault current limiter, wherein a superconducting element having a minimum critical current among the plurality of superconducting elements is disposed above any other superconducting element in the liquid refrigerant.   2. The superconducting fault current limiter according to claim 1, wherein the liquid refrigerant is arranged such that the smaller the critical current among the plurality of superconducting elements, the higher the upper one. Arranging the plurality of superconducting elements in a planar shape along the vertical direction,
2. The superconducting fault current limiter according to claim 1, wherein any combination of two superconducting elements arranged adjacent to each other in the upper and lower sides is arranged such that the upper side has a smaller critical current than the lower side. .   4. The superconducting fault current limiter according to claim 3, wherein a plurality of sets of the plurality of superconducting elements arranged in a plane along the vertical direction are arranged to arrange the whole superconducting elements in a three-dimensional manner.   5. The superconducting fault current limiter according to claim 1, wherein an element cover that surrounds the plurality of superconducting elements is provided in the refrigerant container. In the method of cooling the superconducting element of a superconducting fault current limiter comprising a superconducting element that is in a superconducting state when a current value is energized within a certain range and is in a normal conducting state when energizing an accident current exceeding the range,
In the liquid refrigerant in the refrigerant container, the superconducting element having the smallest critical current among the plurality of superconducting elements is arranged above any other superconducting element, and the superconducting element having the smallest critical current is disposed below the superconducting element. A cooling method for a superconducting element in a superconducting fault current limiter, wherein the superconducting element having the minimum critical current is cooled by bubbles generated from the arranged superconducting element.   The superconducting device in the superconducting fault current limiter according to claim 6, wherein when the liquid refrigerant on the surface of the superconducting element having the smallest critical current is in a film boiling state, the superconducting element having the smallest critical current is cooled. Method for cooling the element.   8. The cooling of a superconducting element in a superconducting fault current limiter according to claim 6 or 7, wherein the liquid refrigerant is arranged so that the smaller the critical current among the plurality of superconducting elements, the upper is the upper side. Method. Arranging the plurality of superconducting elements in a planar shape along the vertical direction,
The superconducting device according to claim 6 or 7, wherein any combination of two superconducting elements arranged adjacent to each other in the upper and lower sides is arranged such that the upper side has a smaller critical current than the lower side. Cooling method for superconducting element in current limiter.   10. The superconductivity in a superconducting fault current limiter according to claim 9, wherein a plurality of sets of the plurality of superconducting elements arranged in a plane along the vertical direction are arranged to arrange the entire superconducting elements in a three-dimensional manner. Method for cooling the element.   The superconducting fault current limiter according to any one of claims 6 to 10, wherein the plurality of superconducting elements are arranged inside an element cover provided in the refrigerant container and open at the top and bottom. Cooling method for superconducting element.

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