JP6117126B2 - 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.
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 cooling device including a refrigerant container that contains a semiconductor element as a heat generation source and a liquid refrigerant, and cooling fins provided on the outer periphery of the refrigerant container.
In this cooling device, a semiconductor element is installed on the inner bottom portion of the refrigerant container, and a flow path directed directly upward from the semiconductor element and a flow path in which the refrigerant returns to the bottom are formed and are heated by the semiconductor element. When the liquid refrigerant rises in the central flow path and descends from the outer flow path, the liquid refrigerant is cooled by the cooling fins, thereby improving the cooling efficiency by circulation.

  Patent Document 2 discloses a refrigerant container that accommodates a superconducting device as a cooling target and a liquid refrigerant, a partition plate that surrounds the superconducting device inside the refrigerant container, and an inner region and an outer region of the partition plate. By providing a heat exchanger that individually cools and by cooling so that the inner region of the partition plate is cooler than the outer region, the liquid refrigerant is circulated so as to descend inside the partition plate and rise outside The cooling efficiency is improved.

Japanese Patent Laid-Open No. 04-023457 JP-A-63-299181

However, since the cooling device described in Patent Document 1 is a semiconductor element to be cooled, only cooling to room temperature is assumed, and cooling of the liquid refrigerant is a cooling fin provided outside the refrigerant container. It is entrusted to.
On the other hand, in the superconducting fault current limiter, it is necessary to cool the superconducting element to an extremely low temperature state, and when an accident current occurs, the superconducting element generates a severe film boiling state in the liquid refrigerant. In terms of efficiency, it has been difficult to cope with cooling of superconducting elements.

  Moreover, although the cooling apparatus described in Patent Document 2 assumes cooling of superconducting equipment, it has not been able to cope with a severe film boiling state of superconducting elements. That is, this conventional cooling device performs circulation that descends in the inner region of the partition plate where the superconducting equipment is arranged and rises in the outer region, so that when the superconducting element boils, a reverse flow occurs due to the rise of bubbles, It was difficult to perform efficient cooling.

  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 means that cools the liquid refrigerant in the refrigerant container, and in the liquid refrigerant, at least two of the plurality of superconducting elements are arranged one above the other, An element cover having an open top and bottom surrounding at least two superconducting elements arranged side by side in the upper and lower sides in the refrigerant container is provided.
Further, in the invention of a superconducting current limiter or a method of cooling a superconducting element in a superconducting current limiter, the element from the center of the superconducting element in the longitudinal direction in plan view of the two superconducting elements arranged side by side When the distance to the inner surface of the cover is R, and the distance between the centers of the two superconducting elements is L in the vertical vertical direction of the two superconducting elements arranged above and below, the following equation (1) is satisfied. The two superconducting elements are arranged as described above.
tan ⁻¹ (L / R) ≦ 70 ° (1)
(However, R ≦ α, α: the distance from the center of the superconducting element in the horizontal direction of bubbles generated when the critical current is exceeded)

Further, the present invention provides the superconducting current limiting device including a plurality of superconducting elements that are in a superconducting state when energized within a certain range and are in a normally conducting state when an accident current exceeding the range is energized. In the method for cooling an element, at least two of the plurality of superconducting elements are vertically arranged inside a cylindrical or frame-shaped element cover provided in the liquid refrigerant in a refrigerant container and opened vertically. It is arranged side by side, and bubbles generated from a superconducting element located on the lower side of the plurality of superconducting elements are guided to a superconducting element located on the upper side of the plurality of superconducting elements.
Further, in the invention of a superconducting current limiter or a method of cooling a superconducting element in a superconducting current limiter, the element from the center of the superconducting element in the longitudinal direction in plan view of the two superconducting elements arranged side by side When the distance to the inner surface of the cover is R, and the distance between the centers of the two superconducting elements is L in the vertical vertical direction of the two superconducting elements arranged above and below, the following equation (1) is satisfied. The two superconducting elements are arranged as described above.
tan ⁻¹ (L / R) ≦ 70 ° (1)
(However, R ≦ α, α: the distance from the center of the superconducting element in the horizontal direction of bubbles generated when the critical current is exceeded)
In the method of cooling a superconducting element in the superconducting current limiting device, the superconducting element may be cooled when the liquid refrigerant on the surface of the superconducting element located above the superconducting element is in a film boiling state. .

  Further, in the invention of a superconducting current limiter or a method of cooling a superconducting element in a superconducting current limiter, the superconducting located on the lower side of at least two superconducting elements arranged side by side surrounded by the element cover It is good also as what arrange | positions so that the lower end part of an element may become an upper side rather than the lower end part of the said element cover.

  The element cover may also surround superconducting elements other than the two superconducting elements arranged side by side. If there are a plurality of sets of two superconducting elements arranged side by side, each element cover individually. It may be provided.

In the present invention, in the liquid refrigerant in the refrigerant container, one of the two superconducting elements is arranged on the upper side of the other inside the element cover. Film boiling occurs. Thereby, the vaporized gas of the liquid refrigerant generated from the plane of the lower superconducting element is released upward, and the upper superconducting element is exposed to the vaporized gas rising along the element cover.
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, peeling of the vaporized gas generated on the element surface is promoted and comes into contact with the liquid refrigerant. The cooling efficiency of the superconducting element is improved.
In this way, the superconducting element located above any other superconducting element can be efficiently cooled by the element cover and its life can be extended, so that the life of the superconducting fault current limiter is also extended. It becomes possible.
In addition, because the cooling efficiency is improved by the arrangement of the element cover and the superconducting element relative to the element cover, there is no need for a special structure or special structure for cooling, and the entire structure of the superconducting fault current limiter is simplified and the cost is reduced. It is possible to plan.

  In addition, when the lower end of the superconducting element located in the lower side of the element cover is disposed above the lower end of the element cover, the vaporized gas bubbles from the lower superconducting element are removed from the outer side of the element cover. Therefore, the upper superconducting element can be guided to the upper superconducting element without leaking to the upper superconducting element, so that further efficient cooling of the upper superconducting element and a longer life can be realized.

For the two superconducting elements in the element cover, the relative relationship between the distance R from the center in the longitudinal direction to the inner surface of the element cover and the center-to-center distance L in the vertical vertical direction of the two superconducting elements is When defined in the numerical range of 1), the element cover can reduce the diffusion of the refrigerant gas and effectively cool the upper superconducting element.

It is sectional drawing along the vertical plane of the superconducting fault current limiter concerning a first embodiment. It is explanatory drawing which shows the principle of cooling based on arrangement | positioning of a superconducting element. It is sectional drawing along the centerline in an element cover. It is a top view of an element cover. It is a diagram which shows the relationship between the presence or absence of the bubble from the downward direction, and the temperature change at the time of cooling. It is a figure which shows the result of having compared the return time until a superconducting element returns to a refrigerant | coolant temperature from a heating state with the case where it does not provide with the case where an element cover is provided. It is a table | surface which shows the list | wrist of the return time from the heating state of a superconducting element at the time of changing the crossing angle based on arrangement | positioning of the upper and lower superconducting elements with respect to an element cover into several angles. It is the diagram which computed the correspondence of element distance and mutual inductance based on simulation. It is a figure which shows the comparison result of the return time from the heating state of a superconducting element by the case where an intersection angle is 45 degrees and 80 degrees and an element cover is not provided. 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 sectional drawing which shows the example which has arrange | positioned the superconducting element unit of FIG. 10 in the element cover. It is a top view which shows the example which has arrange | positioned the superconducting element unit of FIG. 10 in the element cover. It is a top view which shows the example which made the planar view shape of the element cover rectangular. It is explanatory drawing which shows the case where an element cover is provided for every group with respect to the superconducting element which consists of several groups.

[Outline of Embodiment]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In this embodiment, a superconducting fault current limiter 10 and a superconducting current limiter that are provided in the middle of a power supply path for a protection target device to which power is supplied from the outside and reduce an accident current generated on the power supply side. A method of cooling the superconducting elements 71 and 72 in the vessel 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. The lid 30 capable of closing the upper opening of the refrigerant container 20, the refrigerator 40 as a cooling means for cooling the liquid nitrogen 60 in the inner container 21, and two superconducting elements 71 in the liquid nitrogen 60 of the refrigerant container 20, And an element cover 93 surrounding 72.
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 (not shown) and the like, and intake and exhaust of nitrogen gas, which is a refrigerant gas, is performed inside the refrigerator.

[Superconducting element]
The two superconducting elements 71 and 72 are strip-shaped flat plates having a superconductor, 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 flat in the state in which the longitudinal direction is along the horizontal direction at a position lower than the liquid level 61 at the specified liquid level of the liquid nitrogen 60 in the refrigerant container 20. It is held by a frame (not shown) so as to be along the vertical direction.
These superconducting elements 71 and 72 have the same dimensions and the same structure, and one superconducting element 71 is disposed above the other superconducting element 72. In addition, as shown in FIG. 1, the two superconducting elements 71 and 72 are arranged on the same vertical plane along the vertical vertical direction, and are arranged so that the positions of both ends coincide with each other in plan view. Has been.

Although the superconducting elements 71 and 72 are cooled by the surrounding cryogenic liquid nitrogen, when a current that greatly exceeds a critical current such as an accident current flows to each superconducting element 71 and 72, these superconducting elements 71 and 72 72 transitions from the superconducting state to the normal conducting state, and suddenly generates heat as the electrical resistance increases. As a result, the superconducting elements 71 and 72 are extremely hot relative to the surrounding liquid nitrogen, and the liquid nitrogen exceeds the nucleate boiling state and becomes a film boiling state.
When the film boiling state occurs, the surfaces of the superconducting elements 71 and 72 are covered with nitrogen gas whose cooling efficiency is lower than that of liquid nitrogen, so that it takes time to cool the superconducting elements 71 and 72.

However, as shown in FIG. 2, when superconducting elements 71 and 72 are arranged side by side in the refrigerant container 20, a large amount of nitrogen gas is generated from the surface of the lower superconducting element 72 in a film boiling state. Ascending as bubbles, the upper superconducting element 71 is exposed to the rising amount of nitrogen gas bubbles and the upward liquid flow associated therewith.
At that time, the nitrogen gas in the film boiling state generated on the surface of the upper superconducting element 71 is peeled off by the bubbles and the liquid flow from below, and the surface of the upper superconducting element 71 is returned to the state in contact with the liquid nitrogen. Can be efficiently cooled.
Superconducting elements tend to have shorter lifetimes as the integrated value of time in a constant high-temperature state increases. Therefore, the faster the cooling from a high-temperature state during an accident current, the longer the element lifetime. It is possible to extend. Accordingly, by arranging the superconducting elements 71 and 72 vertically as described above, the life of at least one of the superconducting elements 71 is extended, and the overall life of the superconducting fault current limiter 10 is extended.
When the superconducting fault current limiter includes a plurality of superconducting elements, the superconducting element with the smallest critical current has the shortest life, and the life of the superconducting element with the shortest life becomes the life of the superconducting current limiter. Therefore, it is desirable that the superconducting element having the shortest lifetime be arranged on the upper side of any other superconducting element for efficient cooling.
For example, in the case of the superconducting current limiting device 10, it is desirable to select an upper superconducting element 71 having a critical current smaller than that of the lower superconducting element 72 and having a shorter life. Thereby, it becomes possible to extend the lifetime of the whole superconducting fault current limiter.

[Element cover]
3 is a cross-sectional view taken along the center line in the element cover 93, and FIG. 4 is a plan view. As shown in the figure, the element cover 93 is a circular body in plan view, and is a cylindrical body disposed inside the refrigerant container 20 with its center line C extending in the vertical vertical direction. The lower end is open.
Two superconducting elements 71 and 72 are arranged vertically inside the element cover 93.
As described above, the superconducting elements 71 and 72 are arranged such that one superconducting element 71 is disposed above the other superconducting element 72, so that nitrogen gas generated due to film boiling of the lower superconducting element 72 when an accident current occurs. The cooling efficiency of the upper superconducting element 71 is enhanced by utilizing the bubbles and the liquid flow caused thereby. In this way, when bubbles and liquid flow from the lower superconducting element 72 are used, if the bubbles diffuse to the surroundings, the ability of the upper superconducting element 71 to peel off nitrogen gas due to film boiling is reduced sufficiently. Therefore, it becomes impossible to improve the cooling efficiency.
Therefore, by surrounding each of the superconducting elements 71 and 72 with the element cover 93, it is possible to prevent the bubbles from diffusing from the lower superconducting element 72 and effectively guide the bubbles and the liquid flow to the upper superconducting element 71. It is possible.

The arrangement of the superconducting elements 71 and 72 with respect to the element cover 93 will be described below.
In the following description, the center g of each superconducting element 71, 72 is intermediate in the longitudinal direction of each superconducting element 71, 72 in the plan view and intermediate in the short direction in plan view, and is vertically up and down. The intermediate point located in the middle of the direction is also referred to. The center g coincides with the center of gravity when each of the superconducting elements 71 and 72 is a rectangular flat plate (cuboid shape) and has a uniform density as a whole.
The superconducting elements 71 and 72 are arranged such that the centers g and g are on the center line C of the element cover 93.

  Furthermore, the distance between the centers, which is the distance between the centers g and g of the two superconducting elements 71 and 72 in the vertical direction, is L, and the superconducting elements 71 and 72 from the center g of each of the superconducting elements 71 and 72 to the inner surface of the element cover 93. The distance along the longitudinal direction of the superconducting element 71 is 72, the length of the superconducting elements 71 and 72 in the longitudinal direction in plan view is W, and the center g of one superconducting element 71 is extended along the longitudinal direction of the superconducting element 71. The intersection point where the straight line intersects the inner surface of the element cover 93 is r1, the intersection point where the straight line extending from the center g of the other superconducting element 72 along the longitudinal direction of the superconducting element 72 intersects the inner surface of the element cover 93 is r2, and the other When the crossing angle between the straight line connecting the center g of the superconducting element 72 and the intersection point r1 and the straight line connecting the center g of the other superconducting element 72 and the intersection point r2 is θ, the relationship of the following equation (1) holds: To make each Conductive elements 71, 72 are arranged.

tan ⁻¹ (L / R) ≦ 70 ° (1)

Since tan ⁻¹ (L / R) = θ, (1) is synonymous with θ ≦ 70 °.
Further, since it is desirable that air bubbles can pass between both end portions in the longitudinal direction of the superconducting elements 71 and 72 and the inner surface of the element cover 93, R> W so as not to completely block each other. / 2.
Further, in the superconducting elements 71 and 72, the arrival distance α (see FIG. 2) from the center g in the horizontal direction of bubbles generated when the critical current is exceeded is generally within a certain range, and the distance R is within a range of α or less. Is desirable (R ≦ α).
Further, the lower superconducting element 72 is arranged such that the lower end thereof is above the lower end of the element cover 93. Thus, bubbles generated during film boiling can be effectively guided upward without leaking outside the element cover 93.

[Improvement of cooling efficiency using bubbles by film boiling]
Here, the improvement of the cooling efficiency using the bubble by film | membrane boiling is demonstrated. The solid line in FIG. 5 shows the time and temperature change required to cool the single superconducting element 71 in the room temperature (303 [K]) state to the refrigerant temperature (77 [K]) by putting it in the liquid nitrogen in the refrigerant container 20. ing. Further, a dotted line in FIG. 5 shows that a single superconducting element 71 in a room temperature (303 [K]) state and a metal frame body in a room temperature state serving as a generation source of bubbles due to film boiling are disposed in the refrigerant container 20, It shows the time and temperature change required for cooling to the temperature (77 [K]). The frame was disposed obliquely downward at an angle of 70 ° with respect to a vertical line extending vertically downward from the center g of the superconducting element 71.
In either case, the superconducting element 72 and the element cover 93 are removed from the refrigerant container 20.

As shown in FIG. 5, when the superconducting element 71 is disposed alone (solid line), the time required for cooling to the refrigerant temperature is approximately 13 [s], and the frame is disposed obliquely below the superconducting element 71. In this case (dotted line), the time required for cooling to the refrigerant temperature was approximately 11 [s].
This is because, when the frame is arranged, film boiling occurs on the surface of the frame that is high in temperature with respect to the liquid refrigerant, and a large number of bubbles due to nitrogen gas rise with a liquid flow. Then, the superconducting element 71 in a film boiling state is exposed to bubbles and a liquid flow from the frame, nitrogen gas having a low cooling efficiency is peeled off from the surface, and cooling with liquid nitrogen is performed to cool the superconducting element 71. It is for improving.
Thus, the superconducting element improves the cooling efficiency at the time of film boiling of the superconducting element due to the bubble and liquid flow of nitrogen gas generated therefrom by disposing the bubble generating source due to film boiling below.
Accordingly, by disposing one superconducting element 71 above the other superconducting element 72 as in the superconducting current limiter 10 shown in FIG. 1, when an accident current exceeding the critical current occurs, the lower superconducting element 72 Becomes a bubble generation source, and even when film boiling occurs in the upper superconducting element 71, cooling can be performed more rapidly.

[Cooling improvement effect by element cover]
The results of comparing the return times from when the superconducting elements 71 and 72 are energized and heated to when the element cover 93 is provided in the refrigerant container 20 until the temperature returns to the refrigerant temperature are shown in FIG. It is shown in FIG. In FIG. 6, the amount of heat generated when the superconducting elements 71 and 72 are heated by energization and the return time are compared. Further, in each of the superconducting elements 71 and 72 in the refrigerant container 20, the crossing angle θ is 30 ° in the arrangement shown in FIG.

In FIG. 6, “♦” indicates no element cover, and “□” indicates that an element cover is present. When the element cover 93 is provided compared to the case where the element cover 93 is not provided, the return time is shortened, and the difference in the return time increases as the amount of generated heat increases. For example, at a charging voltage of 1000 [V], the return time when the element cover 93 is not provided is 3.7 [sec], but when the element cover 93 is provided, the return time is 3.1 [sec], which is approximately 20% shorter. .
As a result, as the amount of generated heat increases, the amount of nitrogen gas bubbles generated from the lower superconducting element 72 increases. However, the element cover 93 effectively guides the bubbles to the upper superconducting element 71 to improve the cooling efficiency. You can see that it is increasing.

[Cooling improvement effect by arrangement of upper and lower superconducting elements to element cover]
Heating of the superconducting element 71 when the element cover is not provided and when the crossing angle θ in the arrangement of the upper and lower superconducting elements 71 and 72 with respect to the element cover 93 is 20, 25, 30, 45, 60, 70, 75, and 80 °, respectively. A list of return times from the state is shown in FIG. In the comparative test of FIG. 7, the intersection angle θ is changed by changing only the distance L between the centers of the two superconducting elements 71 and 72 while keeping the distance R from the center of the superconducting element to the element cover constant. Other arrangements are the same as in the example of FIG. In addition, a comparison was made when the amount of generated heat was 400 [J] for each of the superconducting elements 71 and 72.

As a result of the above comparison, there is no significant difference from the return time when the element cover 93 is not provided when the crossing angle θ is 75 ° or more, and the return time is remarkably shortened within the crossing angle θ ≦ 70 °. It was.
In other words, it is effective to set tan ⁻¹ (L / R) ≦ 70 °, and when it exceeds 70 °, the cooling efficiency decreases.

[Effect of inter-element distance and mutual inductance of superconducting elements]
Next, the influence of the distance between elements of the superconducting element and the mutual inductance will be described. FIG. 8 is a diagram in which the correspondence between the inter-element distance and the mutual inductance is calculated based on simulation, and the solid line indicates a state in which the flat surfaces of the superconducting elements 71 and 72 are vertically aligned (arrangement of FIG. 3). The dotted lines indicate the case where the flat surfaces of the superconducting elements 71 and 72 are both horizontal. Here, the inter-element distance indicates the distance from the upper end surface of the lower superconducting element 72 to the lower end surface of the upper superconducting element 71.
As shown in the figure, the mutual inductance is the size of the superconducting elements 71 and 72: 210 × 30 × 1 (horizontal width × vertical vertical width × width in the thickness direction in the state of FIG. 3, all units are [mm]. When the distance between the superconducting elements 71 and 72 is less than about 20 [mm], the result is abruptly increased. Therefore, the distance between the elements of the superconducting elements 71 and 72 is preferably 20 [mm] or more.

When both the two superconducting elements 71 and 72 are in a state in which the flat plate surface is vertically aligned (in the direction and arrangement of FIG. 3), the distance L between the centers of the two superconducting elements 71 and 72 is as described above. Therefore, it is desirable that L ≧ 50 [mm] because the distance between the elements considering the mutual inductance (20 [mm]) + the vertical vertical width of the element (30 [mm]).
Further, when it is assumed that one end of the superconducting elements 71 and 72 is disposed close to the inner surface of the element cover 93, the distance R = 210/2 = 105 from the center g of each superconducting element 71 and 72 to the inner surface of the element cover 93. [mm].
When the numerical values of L and R are input to tan ⁻¹ (L / R) in the formula (1),
tan ⁻¹ (L / R) = tan ⁻¹ (50/105) = tan ⁻¹ (0.48) ≈25 °, and in order to avoid deterioration of mutual inductance, tan ⁻¹ (L / R) ≧ 25 It is desirable that the angle is θ (θ ≧ 25 °).
Thus, it is desirable to determine the lower limit value of θ (= tan ⁻¹ (L / R)) from a range in which deterioration of the mutual inductance between the superconducting elements 71 and 72 can be avoided. For example, as described above, the lower limit value of θ (= tan ⁻¹ (L / R)) may be determined from the inter-element distance at which the rate of change of the mutual inductance becomes significant, and the upper limit value of the mutual inductance value may be set. The lower limit value of θ (= tan ⁻¹ (L / R)) may be determined based on this.

[Cooling improvement effect due to the arrangement of upper and lower superconducting elements in the element cover when the amount of generated heat is different]
Further, when the crossing angle is 45 ° within the proper range, the crossing angle is 80 ° outside the proper range, and the case where the element cover 93 is not provided according to the comparison of FIG. FIG. 9 shows a comparison result of the recovery time when the heat quantity is changed in the range of 0 to 480 [J].
In FIG. 9, “♦” indicates no element cover, “□” indicates an intersection angle of 45 ° (with an element cover), and “Δ” (with a pattern in FIG. 9) indicates an intersection angle of 80 ° (with an element cover).
From this comparison, it can be seen that when the crossing angle is 45 °, the recovery time is significantly shortened as the amount of generated heat increases as compared to the case where the element cover 93 is not provided. It can be seen that even if the charging voltage changes, it does not differ greatly from the return time when the element cover 93 is not provided.

[Technical effects in the embodiment of the invention]
As described above, the superconducting fault current limiter 10 disposes one superconducting element 71 above the other superconducting element 72 in the liquid nitrogen 60 in the refrigerant container 20, thereby lowering the superconductivity below the occurrence of an accident current. It is possible to efficiently cool the upper superconducting element 71 in the film boiling state by utilizing the bubbles and the liquid flow of nitrogen gas generated from the element 72. The improvement of the cooling efficiency due to the vertical arrangement of the superconducting elements 71 and 72 is supported by the result of the improvement of the cooling efficiency when accompanied by the nitrogen gas generation source by the film boiling shown in FIG.

  Furthermore, the superconducting fault current limiter 10 includes an element cover 93 that surrounds the two superconducting elements 71 and 72, thereby cooling air by efficiently guiding bubbles generated from the lower superconducting element 72 to the upper superconducting element 71. Increases efficiency. The improvement of the cooling efficiency by the element cover 93 is supported by the result of the comparison test of the return time to the cooling temperature with and without the element cover 93 shown in FIG.

In addition, the arrangement of the two superconducting elements 71 and 72 in the element cover is determined by the distance R from the center g, g to the inner surface of the element cover 93 and the distance L between the centers of the two superconducting elements 71, 72. By satisfying ⁻¹ (L / R) ≦ 70 °, it is possible to improve the cooling efficiency of the upper superconducting element 71. The improvement in cooling efficiency due to such element arrangement is supported by the result of a comparative test in which the crossing angle θ based on L and R is changed according to FIGS. 7 and 9.

Further, as shown in FIG. 8 described above, by setting the distance between the superconducting elements 71 and 72 to 20 [mm] or more, it is possible to reduce the influence of the mutual inductance of each superconducting element 71 and 72. is there. In order to satisfy this condition, it is desirable that the crossing angle θ based on the arrangement of the superconducting elements 71 and 72 is in a range of 25 ° or more.
That is, by setting 25 ° ≦ tan ⁻¹ (L / R) ≦ 70 °, it is possible to improve the cooling efficiency while suppressing the influence of the mutual inductance of each superconducting element 71, 72.

  Further, by arranging the lower end portion of the superconducting element 72 located below in the element cover 93 to be higher than the lower end portion of the element cover 93, nitrogen gas from the superconducting element 72 is generated when an accident current occurs. Can be guided toward the superconducting element 71 without leaking to the outside of the element cover 93, so that the superconducting element 71 can be further efficiently cooled.

Thus, by providing the element cover 93 in the refrigerant container 20 with the superconducting fault current limiter 10 and arranging the superconducting elements 71 and 72 so as to satisfy the various arrangement conditions described above with respect to the element cover 93, Since the superconducting element 71 can be efficiently cooled and its life can be extended, the life of the superconducting fault current limiter 10 can be extended.
Further, since the cooling efficiency is improved by the arrangement of the element cover 93 and the superconducting elements 71 and 72 corresponding thereto, there is no need to add a special structure or a special structure for cooling to the refrigerant container 20, and the superconducting current limiting device It is possible to simplify the configuration of the entire 10 and reduce the cost.

[Others]
The superconducting element is not limited to a strip shape but may be a wire shape that can be easily deformed. In that case, you may form arbitrary shapes with a superconducting element. For example, two or more superconducting element units 100 in which the superconducting elements 101 to 106 are coiled so as to vortex are prepared 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.
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.

Then, as shown in FIGS. 12 and 13, a plurality of the superconducting element units 100 are prepared and arranged side by side inside the element cover 93. In this case, it is desirable that each superconducting element unit 100 is in a horizontal state.
At least one of the superconducting elements attached to the superconducting element unit 100 arranged in the upper and lower sides is at least one below the superconducting element unit 100 to which the superconducting element having the smallest critical current value is attached. It is desirable that another 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 element cover 93 described above is not limited to a cylindrical shape, and may be an arbitrary plan view shape as long as it is a cylindrical body or a frame body in which upper and lower ends are opened. For example, as shown in FIG. 14, an element cover 93A made of a frame having a quadrangular shape in plan view may be used. Also, other polygons, ellipses, ellipses, etc. may be used. However, it is desirable to penetrate through the entire length with a uniform cross-sectional shape over the entire length in the vertical direction.
Even when the element cover 93 </ b> A is a rectangular frame as described above, it is desirable that the superconducting elements 71 and 72 are arranged so as to satisfy tan ⁻¹ (L / R) ≦ 70 ° in the longitudinal direction. Further, considering the influence of mutual inductance, it is more preferable that 25 ° ≦ tan ⁻¹ (L / R) ≦ 70 °.
Further, the superconducting elements 71 and 72 may be surrounded by a cover having 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. In addition, depending on the shape of the superconducting element, there may be a case where the longitudinal direction does not exist in the shape in plan view (for example, in the case of a circle in plan view). In that case, any direction is defined as the longitudinal direction. Assuming that the distance R from the center of the superconducting element to the inner surface of the element cover is defined in the assumed longitudinal direction, each superconducting element may be arranged so that the formula (1) is satisfied.

The superconducting elements 71 and 72 described above can be changed in posture and orientation.
For example, although the case where it arranged so that the longitudinal direction of each superconducting element 71 and 72 followed a horizontal direction was illustrated, you may arrange | position so that these longitudinal directions may follow a vertical up-down direction.
Moreover, although the case where it arrange | positioned so that the flat plate surface of each superconducting element 71 and 72 followed a perpendicular direction was illustrated, you may arrange | position so that a flat plate surface may become horizontal.
Furthermore, the number of superconducting elements is not limited to two, and more superconducting elements may be used. In that case, all the superconducting elements may be connected in series, or each superconducting element may be connected by combining series connection and parallel connection. When more superconducting elements are used, they may be arranged in multiple stages instead of in two upper and lower stages. In that case, it is desirable to arrange so that at least two superconducting elements adjacent in the vertical direction satisfy the formula (1), and arrange so that the formula (1) holds for all combinations of the superconducting elements adjacent in the vertical direction It is more desirable.

  Further, as shown in FIG. 15, when the superconducting fault current limiter has a plurality of sets 73 and 74 composed of superconducting elements arranged above and below, element covers 93 and 93 are provided for each of the superconducting element sets 73 and 74, respectively. It may be prepared and placed individually inside. In addition, when a plurality of sets 73 and 74 composed of superconducting elements arranged above and below are provided, these may be arranged in one element cover.

  In addition, when two superconducting elements adjacent to each other in the upper and lower sides are used in which the value of the critical current that can maintain the superconducting state is varied, the one with the smaller critical current value has a longer life. Since it tends to be shorter, it is desirable to dispose the superconducting element having a small critical current value above the superconducting element having a larger critical current value. By increasing the cooling efficiency of the superconducting element having a shorter lifetime and extending the lifetime, it is possible to more effectively realize the longer lifetime of the superconducting fault current limiter.

Further, if both ends in the longitudinal direction of the superconducting element are equal to the inner surface of the element cover (a state where the center g is located on the center line C), the above-described equation (1) is the length of the superconducting element. It is desirable that the arrangement be established on both sides of the direction.
In addition, when both ends in the longitudinal direction of the superconducting element are not equal in distance to the inner surface of the element cover, the above-described formula (1) is expressed on the end side closer to the inner surface of any element cover. It is desirable that the arrangement is established.

10 Superconducting Current Limiter 20 Refrigerant Container 30 Lid 40 Refrigerator (Cooling Means)
60 Liquid nitrogen (liquid refrigerant)
71, 72 Superconducting elements 93, 93A Element cover

Claims (5)

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,
In the liquid refrigerant, at least two of the plurality of superconducting elements are arranged one above the other,
An upper and lower element cover surrounding at least two superconducting elements arranged above and below the refrigerant container;
Regarding the longitudinal direction of the two superconducting elements arranged side by side in the plan view, the distance from the center of the superconducting element to the inner surface of the element cover is R,
When the distance between the centers of the two superconducting elements is L in the vertical vertical direction of the two superconducting elements arranged side by side,
A superconducting fault current limiter, wherein the two superconducting elements are arranged so as to satisfy the following formula (1).
tan ⁻¹ (L / R) ≦ 70 ° (1)
(However, R ≦ α, α: the distance from the center of the superconducting element in the horizontal direction of bubbles generated when the critical current is exceeded)   Of the at least two superconducting elements arranged side by side above and below the element cover, the lower end part of the superconducting element located on the lower side is arranged above the lower end part of the element cover. The superconducting fault current limiter according to claim 1. In a method for cooling the superconducting element of a superconducting fault current limiter having a plurality of superconducting elements that are in a superconducting state when energized within a certain range and are in a normally conducting state when an energizing current exceeds the range. ,
At least two of the plurality of superconducting elements are arranged side by side inside the element cover that is provided in the liquid refrigerant in the refrigerant container and is open at the top and bottom, and the lower side of the plurality of superconducting elements Introducing bubbles generated from the superconducting element located in the superconducting element located on the upper side of the plurality of superconducting elements,
Regarding the longitudinal direction of the two superconducting elements arranged side by side in the plan view, the distance from the center of the superconducting element to the inner surface of the element cover is R,
When the distance between the centers of the two superconducting elements is L in the vertical vertical direction of the two superconducting elements arranged side by side,
A method of cooling a superconducting element in a superconducting fault current limiter, wherein the two superconducting elements are arranged so as to satisfy the following formula (1):
tan ⁻¹ (L / R) ≦ 70 ° (1)
(However, R ≦ α, α: the distance from the center of the superconducting element in the horizontal direction of bubbles generated when the critical current is exceeded)   4. The superconducting fault current limiter according to claim 3, wherein the superconducting element is cooled when the liquid refrigerant on the surface of the superconducting element located on the upper side of the plurality of superconducting elements is in a film boiling state. 5. Cooling method for superconducting element.   Of the at least two superconducting elements arranged side by side above the element cover, the lower end part of the superconducting element located on the lower side is arranged above the lower end part of the element cover. The cooling method of the superconducting element in the superconducting fault current limiter according to claim 3 or 4.

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