JP5939606B2 - Superconducting current limiting element - Google Patents

Description

  The present invention relates to a superconducting current limiting element, and is particularly useful when applied to a case where a superconducting thin film is formed on a substrate to limit a short-circuit current flowing in an electric circuit.

  A superconductor can flow a large current with zero electric resistance in a superconducting state, but an electric resistance is generated when a current larger than a predetermined current value (critical current) flows. Further, when the current is increased, the temperature of the superconductor rises due to the generated heat and becomes a normal conducting state, resulting in a larger electric resistance. A superconducting current limiting element has been proposed that takes advantage of such characteristics of the superconductor to generate zero resistance during normal operation and to generate a large resistance in the event of a short circuit in the power system, thereby suppressing an increase in the accident current. In this superconducting current limiting element, the superconducting thin film formed on the substrate can transition from the superconducting state to the normal conducting state at the time of short circuit, and instantaneously suppress a large current flowing at the time of the short circuit.

  By the way, in this type of superconducting current limiting element, when the energizing current of the superconducting thin film suddenly increases in the initial stage of current limiting immediately after the accident, the portion with a relatively small critical current density in the thin film suddenly increases. Transition (quenching). If the heat generated in the part where the normal conducting transition has occurred is much larger than the heat removed by diffusion, the temperature rises locally and the thin film burns out.

  In order to prevent such hot spot phenomenon, a normal conducting metal such as gold or silver is vapor-deposited on the superconducting thin film and used as a shunt layer (protective layer for preventing burnout) during the normal conducting transition. It is a general solution. However, if such a metal shunt layer is added, the electric resistance of the superconducting line is greatly reduced, and heat generation at the time of current limiting is increased, so the shared electric field must be lowered. As a result, in order to achieve the required current limiting capacity, the element length increases and a large amount of expensive superconducting thin film must be used, which is a major obstacle to practical use.

  For the purpose of solving such a problem, a superconducting film formed on at least one side surface of the insulating substrate, and a first resistance portion and a second resistance portion are alternately arranged in the energizing direction on one side surface of the superconducting film. In addition, a superconducting current limiting element that has a normal conducting resistance film formed in a stripe shape and that forms a stripe shape in a direction perpendicular to the energizing direction has been proposed (see Patent Document 1).

  In addition, as another superconducting thin film current limiting element, a superconducting film with a shunt protection layer in which an alloy layer having a room temperature resistivity higher than the room temperature resistivity of a pure metal is formed on a superconducting thin film formed on an insulator substrate. A shunt resistor made of a wire made of a pure metal or an alloy connected in parallel with a thin film and a superconducting thin film with a shunt protection layer, and an impedance more than 20 times the shunt resistance connected in parallel with a superconducting thin film with a shunt protection layer There has also been proposed a capacitor consisting of a capacitor having Thus, by arranging the superconducting thin film with the shunt protection layer, the shunt resistor and the capacitor in liquid nitrogen, the current capacity can be increased while maintaining the excellent current limiting characteristics, and the area of the superconducting thin film can be reduced. (See Patent Document 2).

JP 2010-278349 A JP 2008-283106 A

  However, since the superconducting current limiting element disclosed in Patent Document 1 is formed in stripes by alternately arranging the first resistance portions and the second resistance portions in the energizing direction, the structure is complicated accordingly. Further, Patent Document 2 has a problem that the structure becomes complicated as the number of parts increases because a superconducting thin film with a shunt protection layer, a shunt resistor, a capacitor, and the like are provided.

  In view of the above problems, the present invention eliminates the influence of variations in relative critical current density characteristics in a superconducting film, obtains good predetermined current limiting characteristics, and has a superconducting limit with a simplified structure as much as possible. An object is to provide a flow element.

A first aspect of the present invention that achieves the above object is a superconducting current limiting element in which a superconducting film is formed on a substrate, and a superconducting part having a constricted portion that becomes a weakened portion of a superconducting state that is most easily quenched. A superconducting current limiting element having a film and a heat sink abutted on the constriction so as to cover only the constriction.

  According to a second aspect of the present invention, in the superconducting current limiting element according to the first aspect, the constriction is in the flow direction so as to be axisymmetric with respect to a center line in a direction orthogonal to the current flow direction. The superconducting current limiting element has a shape in which the width of the electric circuit continuously decreases along the line.

  According to a third aspect of the present invention, there is provided the superconducting current limiting element according to the second aspect, wherein an edge of the narrowed portion is formed to be continuous with a curve. .

  According to a fourth aspect of the present invention, in the superconducting current limiting element according to any one of the first to third aspects, a gap is formed between the superconducting film and the heat sink after a predetermined time after the occurrence of quenching. The superconducting current limiting element has a moving mechanism for moving the heat sink in a direction away from the superconducting film.

  According to the present invention, since the stenosis part becomes a fragile part of the superconducting state that is more easily quenched from the superconducting state to the normal conducting state, the quench starts from the stenosis part, but at this time, Joule heat due to the current concentrated on the stenosis part Is well absorbed by the heat sink. As a result, the constricted portion is not burned out, and the quench region can be expanded to the other in the meantime, and a large current can be shared and flowed in the entire superconducting film in the normal conducting state. As a result, it is possible to eliminate the influence of variations in relative critical current density characteristics in the superconducting film by forming a constriction in the superconducting film and adding a heat sink, and to achieve good predetermined current limiting characteristics. Can be obtained. In addition, since the heat sink is not limited to the entire superconducting film, but is configured to contact the constricted portion in a limited manner, even if the constricted portion is covered with the surface of the heat sink, the cooling heat of the liquid nitrogen is Of these, regions other than the constricted portion covered with the heat sink are in good contact with the liquid nitrogen, so that heat is transferred well. As a result, the recovery to the superconducting state is also realized well.

  Furthermore, since the constriction is pressed by the heat sink from the surface side, expansion due to Joule heat accompanying current flowing in the normal conducting state can be suppressed. As a result, deformation of the constricted portion can be prevented well.

1 is a perspective view conceptually showing a superconducting current limiting element according to a first embodiment of the present invention. It is a perspective view which shows notionally the superconducting current limiting element which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows notionally the superconducting current limiting element which concerns on the 3rd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view conceptually showing the superconducting current limiting element according to the first embodiment of the present invention. As shown in the figure, the superconducting current limiting element according to this embodiment includes a superconducting film 2 formed on the substrate 1 so that a part thereof becomes the constricted portion 2A, and the constricted portion 2A so as to cover the constricted portion 2A. And a heat sink 3 abutted on. Here, the board | substrate 1 can be suitably comprised with insulators, such as a sapphire board | substrate (alumina single crystal board | substrate), for example. Further, the superconducting film 2 is preferably formed by forming a thin film of a high-temperature superconducting oxide such as YBa ₂ Cu ₃ O ₇ (YBCO) on the substrate 1 through an intermediate layer that forms an oxide if necessary. Can be configured. The surface of the superconducting film 2 is usually covered with a protective film (not shown) formed of a thin film such as gold or silver to prevent deterioration due to moisture in the air before installation in a liquid nitrogen environment, and quenching. The current of time is shunted.

  Moreover, the heat sink 3 can be suitably comprised with the block of ceramics, such as a sapphire which has comparatively big thermal conductivity, for example. Further, the heat sink 3 can be made of metal if insulation from others is ensured. In particular, if it is made of a metal such as copper having a large thermal conductivity, Joule heat caused by the current flowing when the superconducting film 2 is quenched can be satisfactorily absorbed.

  In the narrowed portion 2A in this embodiment, the width of the electric circuit continuously decreases along the flow direction so as to be symmetric with respect to the center line in the direction orthogonal to the current flow direction (left and right direction in the figure; the same applies hereinafter). At the same time, the edges are curved. The entire superconducting current limiting element is accommodated in a container filled with liquid nitrogen.

  According to the present embodiment as described above, the superconducting state breakdown is most easily quenched from the superconducting state to the normal conducting state, even if the critical current density characteristic varies relative to the superconducting film 2. Since it becomes a fragile part, when a large current flows due to an accident or the like, the constricted part 2A is first quenched. As a result, large Joule heat is generated due to the concentration of a large current in the constricted portion 2A. However, the generated Joule heat is absorbed by the heat sink 3. As a result, it is possible to prevent the constricted portion 2A from being burned out by Joule heat.

  On the other hand, the region other than the constricted portion 2A of the superconducting film 2 is also quenched in the meantime. As a result, a large current at the time of an accident is shared by the entire superconducting film 2 and flows.

  Therefore, the superconducting film 2 is not burned by a large current at the time of an accident, etc., and the increase in the large current is suppressed well, and after the large current ceases, it is cooled to liquid nitrogen and returned to the original superconducting state. . Here, the heat sink 3 is not limited to the entire superconducting film 2 but is configured to be brought into contact with the constricted portion 2A in a limited manner. Therefore, even if the constricted portion 2A is covered with the lower surface of the heat sink 3, the cooling of liquid nitrogen is performed. Heat is transferred well when the region other than the constricted portion 2A covered with the heat sink 3 in the superconducting film 2 is in contact with liquid nitrogen, and the entire portion including the constricted portion 2A is cooled. As a result, recovery to the superconducting state can be realized quickly and reliably.

  In the first embodiment, the edge of the narrowed portion 2A is formed as a curve as described above, but it is not necessary to be limited to this curve. As shown in FIG. 2 as the second embodiment, the width of the electric circuit continuously decreases gradually along the flow direction so as to be line-symmetric with respect to the center line in the direction orthogonal to the current flow direction. If so, the edge of the narrowed portion 12A may be a straight line. Also in this embodiment, the heat sink 13 is in contact with the narrowed portion 12A so as to cover only the narrowed portion 12A.

  Furthermore, in the present invention, it is sufficient that a narrow constriction part, that is, a fragile part in a superconducting state that is easy to quench, be formed in a part of the superconducting film as compared with other parts, and the shape of the constriction part is special. There is no limitation. For example, it may be a shape like the superconducting current limiting element according to the third embodiment shown in FIG. As shown in the figure, in the superconducting current limiting element according to this embodiment, a constricted portion 22A is formed by hollowing out the central portion of the superconducting film 22 into a rectangle, and a heat sink 23 is placed on the upper surface of the constricted portion 22A. .

  However, when the outer edge shape of the constricted portions 12A and 22A is a straight line as in the second and third embodiments, a corner portion where the straight lines intersect with each other is formed. As a result of concentration, there is a risk of becoming a vulnerable part to quenching. Considering this point, it is most desirable that the curved shape is the same as that of the first embodiment shown in FIG.

  In short, quenching always starts from the constriction, and the heat dissipation absorbs the Joule heat generated by the heat sink to prevent burnout of the constriction, while the quench region extends to the superconducting film other than the constriction. Just do it.

  Further, due to the presence of the heat sinks 3, 13, and 23, the heat of liquid nitrogen is absorbed by the heat sinks 3, 13, and 23, and in particular, the constriction in contact with the heat sinks 3, 13, and 23 in the superconducting films 2, 12, and 22. There is a possibility that the timing at which the parts 2A, 12A, and 22A are restored to the superconducting state is delayed. In order to prevent this and quickly restore the predetermined superconducting state, a gap is formed between the superconducting films 2, 12, 22 and the heat sinks 3, 13, 23 after a predetermined time after the occurrence of quenching. It is effective to provide a moving mechanism that moves the heat sinks 3, 13, and 23 in a direction away from the superconducting film (upward in FIGS. 1 to 3). In this case, after recovering to the superconducting state, the heat sinks 3, 13, and 23 are moved in the opposite directions and are again brought into contact with the narrowed portions 2A, 12A, and 22A.

  INDUSTRIAL APPLICABILITY The present invention can be effectively used in an industrial field where an electric power system is operated and maintained, and an industrial field where an electrical device used in the industrial field is manufactured and sold.

1 Substrate 2, 12, 22 Superconducting film 2A, 12A, 22A Narrowed portion 3, 13, 23 Heat sink

Claims (4)

A superconducting current limiting element in which a superconducting film is formed on a substrate,
A superconducting film having a constricted portion, which is a weakened portion of superconducting state destruction that is most easily quenched ,
A superconducting current limiting element, comprising: a heat sink abutted on the narrow portion so as to cover only the narrow portion. In the superconducting current limiting element according to claim 1,
The constriction portion has a shape in which the width of the electric circuit is continuously reduced along the flow direction so as to be symmetrical with respect to a center line in a direction orthogonal to the flow direction of current. Current limiting element. In the superconducting current limiting element according to claim 2,
The superconducting current limiting element is characterized in that the edge of the narrowed portion is formed to be continuous with a curve. In the superconducting current limiting element according to any one of claims 1 to 3,
A superconducting current limiting element having a moving mechanism for moving the heat sink in a direction away from the superconducting film so that a gap is formed between the superconducting film and the heat sink after a predetermined time after the occurrence of a quench.

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