JP5317034B2 - Superconducting current limiting element with improved environmental resistance - Google Patents
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Description
本発明は、電路に流れる短絡電流等の過大な電流を限流する超電導限流器を作製するときに用いる超電導限流素子であって、耐環境性が向上された超電導限流素子に関する。 The present invention relates to a superconducting current limiting element used when producing a superconducting current limiting device that limits an excessive current such as a short circuit current flowing in an electric circuit, and relates to a superconducting current limiting element having improved environmental resistance.
例えば、電力系統等において短絡事故が発生すると、過大な短絡電流が系統に流れ、電気機器や配線等に機械的損傷や熱的損傷を与える危険性がある。限流素子は、このような短絡事故時に生じる短絡電流を抑制し、電気機器や配線等を損傷から保護するものである。
最近、限流素子に用いる超電導体膜として、臨界温度が高く、冷媒として安価な液体窒素が使用可能であり、常電導状態における抵抗率が大きい酸化物超電導体膜が検討されており、特に優れた臨界電流密度等が得られる酸化物超電導体膜を限流素子に応用することが検討されている。
酸化物超電導膜は超電導状態から常電導状態に転移（SN転移）して抵抗が発生することにより短絡事故電流を瞬時に抑制できる。そのSN転移時に発生する熱により限流素子が破損することを防ぐため、酸化物超電導体膜の常電導転移後の抵抗より低い抵抗を持つ金属を酸化物超電導体薄膜と並列に接続してSN転移後の電流を分流させることが広く行われている。例えば、本発明者の一人である山崎らが出願した超電導限流素子は、酸化物超電導体膜の性質を低下させず、かつ純金の室温抵抗率より2倍以上高い室温抵抗率を有する金銀合金を分流抵抗とするため、コンパクトでかつ優れた限流特性を有している（特許文献１）。
For example, when a short-circuit accident occurs in an electric power system or the like, an excessive short-circuit current flows through the system, and there is a risk of causing mechanical damage or thermal damage to electrical equipment or wiring. The current limiting element suppresses a short-circuit current generated at the time of such a short-circuit accident, and protects electrical equipment, wiring, and the like from damage.
Recently, as a superconductor film used in a current limiting element, an oxide superconductor film having a high critical temperature and being able to use inexpensive liquid nitrogen as a refrigerant and having a high resistivity in a normal conducting state has been studied, and particularly excellent. The application of an oxide superconductor film capable of obtaining a critical current density or the like to a current limiting element has been studied.
The oxide superconducting film can instantaneously suppress a short-circuit fault current by transitioning from the superconducting state to the normal conducting state (SN transition) and generating resistance. In order to prevent the current limiting element from being damaged by the heat generated during the SN transition, a metal having a resistance lower than that after the normal conducting transition of the oxide superconductor film is connected in parallel with the oxide superconductor thin film. It is widely practiced to shunt the current after the transition. For example, the superconducting current limiting element applied by Yamazaki et al., One of the present inventors, is a gold-silver alloy that does not deteriorate the properties of the oxide superconductor film and has a room temperature resistivity that is at least twice as high as that of pure gold. Therefore, it is compact and has excellent current limiting characteristics (Patent Document 1).
酸化物超電導体薄膜は空気中の水分や二酸化炭素と反応してその超電導特性が低下することが知られている。超電導限流素子を実装する際には通常の部屋の中において作業しなければならないため、空気中の湿気や二酸化炭素による劣化を防ぐ必要がある。また、液体窒素への出し入れに伴い超電導限流素子の表面は固体および液体の水で覆われてこれが超電導体薄膜と反応するため、耐環境保護膜を設けることが必要不可欠である。
従来の酸化物超電導体薄膜を用いた超電導限流器では分流抵抗として用いる金属薄膜を超電導薄膜の上に形成し、超電導薄膜に対する耐環境性保護膜の役目を兼ねさせていた（例えば特許文献２）。
It is known that an oxide superconductor thin film reacts with moisture or carbon dioxide in the air to deteriorate its superconducting properties. When mounting a superconducting current limiting element, it is necessary to work in a normal room, so it is necessary to prevent deterioration due to moisture and carbon dioxide in the air. In addition, since the surface of the superconducting current limiting element is covered with solid and liquid water as it enters and leaves liquid nitrogen and reacts with the superconductor thin film, it is essential to provide an environmental protection film.
In a conventional superconducting fault current limiter using an oxide superconducting thin film, a metal thin film used as a shunt resistance is formed on the superconducting thin film, and also serves as an environmental protection film for the superconducting thin film (for example, Patent Document 2). ).
金属薄膜を超電導薄膜に対する耐環境性保護膜とすることにより、当初は耐環境性が維持されるが、長期間その特性を維持できるとはいいがたい。そこで、各種合成樹脂塗膜を超電導薄膜に対する耐環境性保護膜とする技術報告がある（非特許文献１）。この技術により、やや長い期間その特性を維持できるものの、それら保護膜は耐環境性の点において満足できるほどではない。 Although the environmental resistance is initially maintained by using the metal thin film as an environmental protection film for the superconducting thin film, it cannot be said that the characteristics can be maintained for a long time. Therefore, there is a technical report that uses various synthetic resin coatings as an environment-resistant protective film for a superconducting thin film (Non-patent Document 1). Although this technique can maintain the characteristics for a relatively long period of time, these protective films are not satisfactory in terms of environmental resistance.
超電導限流素子に対する従来の環境保護膜はピンホールの存在などにより、液体窒素への出し入れとそれに伴う水の付着や高温・高湿度における加速試験において超電導限流素子の特性が劣化しやすいとの不都合さがある。またSN転移時に発生する熱による局所的温度上昇に伴い結露した水との反応により酸化物超電導薄膜が破損しやすいとの問題点も指摘されている。これらの点が改善される技術の提供が必要であり、例えば、耐低温性および耐熱衝撃性に優れた特性を有する耐環境性保護膜の開発が求められている。
そこで、本発明の課題は、優れた特性を有する耐環境性保護膜を提供することであり、液体窒素への出し入れとそれに伴う水の付着や高温・高湿度における加速試験において、特性が劣化しにくい超電導限流素子の提供を目的とする。
The conventional environmental protection film for superconducting current limiting devices has a tendency to deteriorate the characteristics of superconducting current limiting devices due to the presence of pinholes, etc., and the accompanying water adhesion and accelerated tests at high temperatures and high humidity. There is inconvenience. In addition, it has been pointed out that the oxide superconducting thin film is easily damaged by the reaction with condensed water due to the local temperature rise caused by the heat generated during SN transition. It is necessary to provide a technique for improving these points. For example, development of an environment-resistant protective film having characteristics excellent in low temperature resistance and thermal shock resistance is required.
Therefore, an object of the present invention is to provide an environmentally-resistant protective film having excellent characteristics, and the characteristics deteriorate in the accelerated test at high temperature and high humidity with and without liquid nitrogen. The object is to provide a superconducting current limiting element that is difficult to conduct.
本発明者らは、上記課題を解決するために鋭意研究した結果、酸化物超電薄導膜表面に特定の天然樹脂保護膜または天然樹脂誘導体の保護膜を形成させると、意外にも上記課題が解決できるとの知見を得た。その知見を基にしてさらに研究を進め、遂に本発明を完成させた。 As a result of diligent research to solve the above problems, the present inventors have unexpectedly found that when a specific natural resin protective film or a protective film of a natural resin derivative is formed on the surface of the oxide superconducting thin film, The knowledge that can be solved. Based on this knowledge, further research was conducted and the present invention was finally completed.
以下、本発明を説明する。
本発明でいう超電導限流素子は特に限定されないのであるが、とくに酸化物系超電導体の限流素子が好ましい。その限流素子の中では、酸化物系超電導薄膜から作製される限流素子が好ましい。
酸化物系超電導薄膜としては、より具体的には、Ｙ1 Ｂａ2 Ｃａ3 Ｏ7等のイットリウム系超電導薄膜、Ｂｉ2 Ｓｒ2 Ｃａ1 Ｃｕ2 Ｏ10等のビスマス系酸化物超電導体薄膜が好ましい。例えば、Ｙ1 Ｂａ2 Ｃａ3 Ｏ7等のイットリウム系超電導薄膜は、単結晶基板上に金属有機化合物の溶液を基板に塗布して熱処理する塗布熱分解法（MOD）や気相からの蒸着法などによりエピタキシャル成長させることによって、結晶性がよく、高い臨界電流密度を有する超電導薄膜を得ることができる。このような薄膜を限流作用部として用い、高い臨界電流（Ｉｃ）を流すことができれば、Ｉｃより大きな電流が流れたとき高い抵抗を発生させ、効果的な限流を行なうことができる。なお、本発明では、超電導膜は超電導薄膜と同義であるとする。
The present invention will be described below.
The superconducting current limiting element referred to in the present invention is not particularly limited, but an oxide-based superconductor current limiting element is particularly preferable. Among the current limiting elements, a current limiting element manufactured from an oxide-based superconducting thin film is preferable.
More specifically, the oxide-based superconducting thin film is preferably an yttrium-based superconducting thin film such as Y 1 Ba 2 Ca 3 O 7 or a bismuth-based oxide superconducting thin film such as Bi 2 Sr 2 Ca 1 Cu 2 O 10. . For example, yttrium-based superconducting thin films such as Y 1 Ba 2 Ca 3 O 7 are coated pyrolysis (MOD) or vapor deposition from the vapor phase where a metal organic compound solution is applied to a single crystal substrate and heat-treated. By performing epitaxial growth by, for example, a superconducting thin film having good crystallinity and a high critical current density can be obtained. If such a thin film can be used as the current limiting action part and a high critical current (Ic) can flow, a high resistance can be generated when a current larger than Ic flows, and effective current limiting can be performed. In the present invention, the superconducting film is synonymous with the superconducting thin film.
これら超電導限流素子における超電導限流薄膜を保護膜で保護するのであるが、本発明の一つの大きな特徴がこの保護膜にある。
本発明で採用する保護膜は天然樹脂を含有する膜である。天然樹脂を含有する膜を超電導限流膜の保護膜とすることにより、優れた効果をもたらすことができる。
天然樹脂としては、バルサム樹脂、ダマール樹脂等の植物性樹脂、シェラック樹脂等の動物性樹脂、コバール樹脂等の化石樹脂等が挙げられるが、その中でもシェラック樹脂等の動物性樹脂が好ましく、さらにはシェラック樹脂が好ましい。本発明では、前記天然樹脂の誘導体も採用可能である。 前記シェラック樹脂はインド、タイ、中国南部等で栽培されている特定の灌木の枝に生育するラックカイガラ虫の分泌物を精製して得られた天然樹脂であり、その主成分はアリュリチン酸、シェロール酸、ヤラール酸及びラクショール酸などからなる一種のポリエステルである。シェラック樹脂分子中にカルボキシル基、ヒドロキシル基を多く有している。精製セラック（赤印品）或は漂白セラック（白印品）及び３０％濃度のエタノール溶液としての市販品を購入すれば容易に入手可能である。
The superconducting current limiting thin film in these superconducting current limiting elements is protected by a protective film, and one major feature of the present invention is this protective film.
The protective film employed in the present invention is a film containing a natural resin. By using a film containing natural resin as a protective film for the superconducting current limiting film, an excellent effect can be obtained.
Examples of natural resins include plant resins such as balsam resins and damar resins, animal resins such as shellac resins, and fossil resins such as kovar resins. Among them, animal resins such as shellac resins are preferred, and Shellac resin is preferred. In the present invention, a derivative of the natural resin can also be used. The shellac resin is a natural resin obtained by refining the secretions of the shellworm, which grows on the branches of specific shrubs cultivated in India, Thailand, southern China, etc., and its main components are alylitic acid, sherol It is a kind of polyester composed of acid, yalaric acid, lactolic acid and the like. The shellac resin molecule has many carboxyl groups and hydroxyl groups. Purified shellac (red-marked product) or bleached shellac (white-marked product) and a commercially available product as a 30% strength ethanol solution are readily available.
本発明において前記天然樹脂と撥水性材料とから得られる物質や複合体を超電導限流薄膜の保護膜としてもよい。例えば、天然樹脂の変性物や、天然樹脂と撥水性材料との積層物が好ましく、とくに動物性樹脂と撥水性材料との積層物が好ましく、さらには、シェラック樹脂と撥水性材料との積層物が好ましい。
ここで、撥水性材料としては、テトラフルオロエチレン、フッ化ビニリデン等の重合体あるいは共重合体等のフッ素樹脂、ピセイン、シリコーン樹脂 が挙げられる。
In the present invention, a substance or a composite obtained from the natural resin and the water repellent material may be used as a protective film for the superconducting current limiting thin film. For example, a modified product of a natural resin or a laminate of a natural resin and a water repellent material is preferable, a laminate of an animal resin and a water repellent material is particularly preferable, and a laminate of a shellac resin and a water repellent material is further preferable. Is preferred.
Here, examples of the water repellent material include fluororesins such as polymers or copolymers such as tetrafluoroethylene and vinylidene fluoride, picein, and silicone resins.
本発明では炭素材料から調製される膜を超電導限流薄膜の保護膜としてもよい。前記炭素材料として、ダイアモンドライクカーボンあるいはナノダイヤモンドを例示することができるが、これに限定されない。ダイアモンドライクカーボンは、ダイヤモンドと結晶構造が類似した炭素薄膜材料を意味する。
上記保護のための炭素系薄膜は、アモルファス構造あるいは微結晶構造を持つ。アモルファス構造を有する炭素系薄膜としては、炭素がｓｐ２およびｓｐ３によって結合されたものであって、ｓｐ２およびｓｐ３の比は問わない。典型的な膜としては水素を含むが、含まなくてもかまわない。また、窒素、珪素などの第三の元素を含んでいてもかまわない。
微結晶の炭素系薄膜としては、ほとんどの炭素がｓｐ３によって結合されたものであって、ナノオーダーの結晶粒によって構成されるものである。
炭素系薄膜の作製のための炭素源としては、炭素のみ、または酸素、水素を有している炭化物、例えば、ベンゼン、アセチレン、メタン、メタノール、エタノール、フラーレン等を用いることができる。
炭素系薄膜の形成法としては、たとえば基板試料を、ホルダーに固定し、真空チャンバー内にて、トルエンあるいはメタンを原料ガスとして、熱電子励起CVD法により、１３０℃に加熱した基板にDCバイアスを印加することにより行うことができる。
In the present invention, a film prepared from a carbon material may be used as a protective film for the superconducting current limiting thin film. Examples of the carbon material include diamond-like carbon and nanodiamond, but are not limited thereto. Diamond-like carbon means a carbon thin film material having a crystal structure similar to that of diamond.
The carbon-based thin film for protection has an amorphous structure or a microcrystalline structure. As the carbon-based thin film having an amorphous structure, carbon is bonded by sp2 and sp3, and the ratio of sp2 and sp3 is not limited. A typical membrane contains hydrogen, but it does not have to be. Further, it may contain a third element such as nitrogen or silicon.
As a microcrystalline carbon-based thin film, most carbon is bonded by sp3, and is constituted by nano-order crystal grains.
As a carbon source for producing the carbon-based thin film, only carbon or a carbide having oxygen and hydrogen, for example, benzene, acetylene, methane, methanol, ethanol, fullerene, and the like can be used.
As a method for forming a carbon-based thin film, for example, a substrate sample is fixed to a holder, and a DC bias is applied to a substrate heated to 130 ° C. by thermionic excitation CVD method using toluene or methane as a source gas in a vacuum chamber. This can be done by applying.
本発明では、所期の目的を達成することができる限り、上記以外物質を適宜用いることができる。 In the present invention, substances other than those described above can be appropriately used as long as the intended purpose can be achieved.
本発明での常電導転移時の分流層は、例えば、超電導状態から常電導状態に転移（SN転移）した後に、過電流を分流させることができる層であれば特に限定されない。好ましい分流層は金と銀との合金からなる層であるが、その他の金属が共存してもよい。
本発明が規定する保護膜を有する超電導限流素子は、耐低温性および耐熱衝撃性に優れた超電導限流素子である。例えば下記耐久試験（以後、加速試験ともいう）のように、試料を高温・高湿下の下に長時間放置しても、臨界電流密度（Jc）の低下が２０％以内であれば、実用的だといえる。さらに、１０％以内であればより実用的だといえる。とくに、保護膜が、超電導薄膜および常電導転移時の分流層の表面および側面まで被覆している超電導限流素子は耐低温性および耐熱衝撃性に優れている。ここで臨界電流密度（Jc）の測定は、例えばドイツ国テーバ（THEVA）社製クライオスキャン（Cryoscan）を用いて測定できる。その原理は次の通りである。試料をホルダーにセットし、その上にカプトン膜を載せる。その上から直径5mmのコイルを押しつけ交流を流すと磁界が発生する。この磁界が超電導膜に入り込むのを遮蔽するために超電導薄膜中に誘導電流が生じる。コイルに流す電流を増加すると超電導薄膜中の誘導電流が増加する。この誘導電流が臨界電流をこえたところで磁界が超電導薄膜を貫通し第3高調波電圧が発生するのでこれをピックアップコイルで検出する。この第3高調波電圧が発生するときのコイル電流から超電導薄膜の臨界電流密度を求めることができる。
（加速試験）
試料を温度６０℃、相対湿度１００％に保持した装置内に2時間放置する。
The shunt layer at the time of normal conduction transition in the present invention is not particularly limited as long as it is a layer that can shunt overcurrent after transition from the superconducting state to the normal conducting state (SN transition), for example. A preferred shunt layer is a layer made of an alloy of gold and silver, but other metals may coexist.
The superconducting current limiting element having a protective film defined by the present invention is a superconducting current limiting element excellent in low temperature resistance and thermal shock resistance. For example, if the critical current density (Jc) decreases within 20% even if the sample is left under a high temperature and high humidity for a long time as in the following durability test (hereinafter also referred to as an acceleration test), it is practical. It can be said that. Furthermore, it can be said that it is more practical if it is within 10%. In particular, the superconducting current limiting element in which the protective film covers the superconducting thin film and the surface and side surfaces of the shunt layer at the normal conducting transition is excellent in low temperature resistance and thermal shock resistance. Here, the critical current density (Jc) can be measured using, for example, a Cryoscan manufactured by THEVA, Germany. The principle is as follows. Set the sample in the holder and place the Kapton membrane on it. When a 5mm diameter coil is pressed from above and an alternating current is applied, a magnetic field is generated. An induced current is generated in the superconducting thin film to shield the magnetic field from entering the superconducting film. Increasing the current flowing through the coil increases the induced current in the superconducting thin film. When this induced current exceeds the critical current, the magnetic field penetrates the superconducting thin film and a third harmonic voltage is generated, which is detected by the pickup coil. The critical current density of the superconducting thin film can be obtained from the coil current when the third harmonic voltage is generated.
(Accelerated test)
The sample is left in an apparatus maintained at a temperature of 60 ° C. and a relative humidity of 100% for 2 hours.
以下、本発明の超電導限流素子の作製法について説明する。
まず、基板を準備する。基板としては様々な材料を用いることができるが、熱伝導率の高い絶縁基板が好ましい。絶縁基板としては単結晶のサファイア基板を使用する場合が多い。
Hereinafter, a method for producing the superconducting current limiting element of the present invention will be described.
First, a substrate is prepared. Although various materials can be used as the substrate, an insulating substrate with high thermal conductivity is preferable. As the insulating substrate, a single crystal sapphire substrate is often used.
この基板上に超電導薄膜を形成させるのであるが、超電導膜と基板との反応を抑制するためおよび格子マッチングのために、超電導薄膜を形成させる前に基板上にバッファー層を形成させておくことが有利である。
前記基板上に超電導薄膜を形成させる手段は特に限定されないが、例えば特開２００７−７０２１６号公報あるいは特開２００７−３０２５０７号公報に記載される金属有機化合物の溶液を基板に塗布して熱処理する塗布熱分解法（MOD）や基板上に気相からエピタキシャル成長させることによって、超電導薄膜を形成させることができる。
A superconducting thin film is formed on this substrate. In order to suppress the reaction between the superconducting film and the substrate and for lattice matching, a buffer layer may be formed on the substrate before forming the superconducting thin film. It is advantageous.
The means for forming the superconducting thin film on the substrate is not particularly limited. For example, coating is performed by applying a metal organic compound solution described in JP-A-2007-70216 or JP-A-2007-302507 to the substrate and performing heat treatment. A superconducting thin film can be formed by thermal decomposition (MOD) or epitaxial growth from a vapor phase on a substrate.
次に、超電導薄膜面に常電導転移時の分流層を形成させる。この形成手段も特に限定されないが、例えば金と銀との合金のターゲットを用いて、スパッタリングし、金と銀との合金層を蒸着させることができる。この合金層は純金あるいは純銀の室温抵抗率より２倍以上高い室温抵抗率を示す合金層であることが好ましい。 Next, a shunt layer at the time of normal conduction transition is formed on the superconducting thin film surface. The forming means is not particularly limited, but, for example, an alloy layer of gold and silver can be deposited by sputtering using a target of an alloy of gold and silver. This alloy layer is preferably an alloy layer having a room temperature resistivity that is at least twice as high as that of pure gold or pure silver.
前記合金層の表面に本発明が規定する保護膜を形成させる。例えば、セラック樹脂等の天然樹脂の溶液を調製し、前記合金層の表面に塗膜を形成させる方法により保護膜を形成することができるが、その他の方法を用いてもよい。また、予め合金層表面を処理した後に保護層を形成してもよい。溶液を調製する手段は特に限定されないのであって、用いる溶媒は、天然樹脂等を溶解し、揮発性であって、塗膜を形成でき、塗膜から揮発した後に膜を保持できる溶媒から最適な溶媒を選べばよい。好ましい溶媒としては、炭素数が１〜８の脂肪族アルコール、芳香族化合物等が挙げられるが、これらに限定されない。好ましい脂肪族アルコールとしては、メタノール、エタノール、ｎ−プロパノール、ｉ―プロパノール、n−ブタノール、ｎ−アミルアルコール、ｎ−ヘキシルアルコール等が挙げられ、好ましい芳香族化合物としてはトルエン、キシレン等が挙げられる。
保護膜を形成させる方法は、スピンコート法、スプレー法、刷毛塗り法、スパッタリング法、蒸着法、気相成長法等が挙げられるが、これらの方法に限定されない。そのなかでも、スピンコート法、スプレー法、刷毛塗り法によることが好ましい。具体的には、スピンコート法では、シェラック樹脂等の天然樹脂を揮発性溶媒に溶かし、前記合金層表面に滴下し、合金層を回転させ、遠心力で滴下された溶液を均一に広げ、次いで乾燥して保護膜を形成させる。保護膜を形成させるときの条件は、用いる天然樹脂や溶媒等により変更されるので一概に規定できないのであって、最適な条件を適宜採用すればよい。
炭素からなる材料の保護膜の形成方法は、気相成長法によることが好ましい。アモルファス状炭素系薄膜を形成する場合、基板試料を、ホルダーに固定し、真空チャンバー内にて、トルエンあるいはメタンを原料ガスとして、熱電子励起CVD法により、１３０℃に加熱した基板にDCバイアスを印加することにより行うことができる。
A protective film defined by the present invention is formed on the surface of the alloy layer. For example, a protective film can be formed by preparing a solution of a natural resin such as shellac resin and forming a coating film on the surface of the alloy layer, but other methods may be used. Moreover, you may form a protective layer, after processing the alloy layer surface previously. The means for preparing the solution is not particularly limited, and the solvent to be used is optimal from a solvent that dissolves natural resin and the like, is volatile, can form a coating film, and can retain the film after volatilizing from the coating film. A solvent can be selected. Preferred solvents include, but are not limited to, aliphatic alcohols having 1 to 8 carbon atoms, aromatic compounds and the like. Preferred aliphatic alcohols include methanol, ethanol, n-propanol, i-propanol, n-butanol, n-amyl alcohol, n-hexyl alcohol and the like, and preferred aromatic compounds include toluene, xylene and the like. .
Examples of the method for forming the protective film include spin coating, spraying, brush coating, sputtering, vapor deposition, and vapor deposition, but are not limited to these methods. Among these, the spin coating method, the spray method, and the brush coating method are preferable. Specifically, in the spin coating method, a natural resin such as shellac resin is dissolved in a volatile solvent, dropped onto the surface of the alloy layer, the alloy layer is rotated, and the solution dropped by centrifugal force is uniformly spread, Dry to form a protective film. The conditions for forming the protective film cannot be defined unconditionally because they are changed depending on the natural resin or solvent used, and the optimum conditions may be adopted as appropriate.
The method for forming the protective film made of carbon is preferably based on the vapor phase growth method. When forming an amorphous carbon-based thin film, a substrate sample is fixed to a holder, and a DC bias is applied to the substrate heated to 130 ° C. by thermionic excitation CVD method using toluene or methane as a source gas in a vacuum chamber. This can be done by applying.
以上説明したように、本発明の限流素子は、電力系統に用いられる限流素子として利用可能であり、通常運転時には抵抗がゼロであるため損失がなく短絡事故時には、超電導状態から常電導状態に転移（SN転移）して抵抗が発生することにより短絡事故電流を瞬時に抑制して、電力系統に過大な短絡電流を流さなくすることが可能となる。
本発明により、ピンホールやクラックがない耐環境保護膜が提供されるため、超電導限流素子が空気中の水分や二酸化炭素と反応してその超電導特性が低下することが抑制され、超電導限流素子の寿命が大幅に向上する。また、高温・高湿度における加速試験において超電導限流素子の特性が劣化しやすいとの不都合さが回避されるとともに、湿度や温度の高い環境下での作業が著しく容易になる。さらに、液体窒素への出し入れに伴い超電導限流素子の表面が固体および液体の水で覆われてもその超電導特性が低下することが抑制されるばかりでなく、SN転移時に発生する熱による局所的温度上昇に伴い結露した水との反応により酸化物超電導薄膜が破損することもなくなる。このように本発明により、長寿命でかつ耐低温性および耐熱衝撃性に優れた特性を有する超電導限流素子が提供されるため、省資源、省エネルギー、低コスト化が実現される。
As described above, the current limiting element of the present invention can be used as a current limiting element used in an electric power system, and since there is no resistance during normal operation and there is no loss, a superconducting state is changed from a superconducting state to a normal conducting state. It becomes possible to suppress the short-circuit fault current instantaneously by causing the resistance to occur (SN transition) and to prevent an excessive short-circuit current from flowing through the power system.
According to the present invention, since an environmental protection film free from pinholes and cracks is provided, it is suppressed that the superconducting current limiting element reacts with moisture or carbon dioxide in the air and its superconducting characteristics are deteriorated. The lifetime of the element is greatly improved. Further, inconvenience that the characteristics of the superconducting current limiting element are likely to be deteriorated in the accelerated test at high temperature and high humidity is avoided, and the operation in the environment with high humidity and temperature is remarkably facilitated. Furthermore, even if the surface of the superconducting current limiting element is covered with solid and liquid water as it enters and leaves the liquid nitrogen, not only the superconducting properties are suppressed, but also the local heat due to the heat generated during the SN transition. The oxide superconducting thin film is not damaged by the reaction with dewed water as the temperature rises. Thus, according to the present invention, a superconducting current limiting element having a long life and excellent characteristics in low temperature resistance and thermal shock resistance is provided, so that resource saving, energy saving, and cost reduction are realized.
以下に、本発明を実施例に基づいて詳細に説明する。本発明はこれらの実施例になんら限定されない。
（実施例１）
（保護膜形成用組成物の調製）
容器（１００ｍＬ）にシェラック樹脂（(株)フルウチ化学、レモンシェラック、品番L-1000）７ｇとｎ−アミルアルコール（(株)和光純薬工業 特級、品番０１３−０３６５６）６０ｇを加え、密封し、室温下３日間放置した後攪拌して、シェラック樹脂を含む保護膜形成用組成物を調製した。
（超電導薄膜の形成）
20mm角のCeO2中間層付きサファイア基板上に、モル比１：２：３のY、Ba、Cuのアセチルアセトナトの溶液を塗布し、まず、酸素分圧を１００ｐｐｍ に調整したアルゴンと酸素の混合ガス流中で加熱し、さらに雰囲気を純酸素に切り換えて熱処理する塗布熱分解法により膜厚１６０〜２３０ｎｍ、臨界電流密度２〜３ＭＡ／ｃｍ２のＹＢａ２Ｃｕ３Ｏ７薄膜を形成し、次いで、金に２３ｗｔ％の銀を混ぜた組成の合金のターゲットを用いて、膜厚約１００ｎｍで高抵抗率金銀合金層をスパッタ蒸着し、サファイア基板上に高抵抗率金銀合金層を有する超電導薄膜を形成した。
（保護膜の形成）
上記高抵抗率金銀合金層を有する超電導酸化物薄膜を形成したサファイア基板をスピンコート塗布機（協栄セミコンダクター(株) スピンナー 品番１Ｈ−ＩＩＩ）の回転台に載置し、上記保護膜形成用組成物を滴下し、回転台を低速回転させて、超電導酸化物薄膜全面に保護膜形成用組成物を行き渡らせ、次いで回転台を高速回転させて、保護膜形成用組成物を均一な厚みとし、６０℃で乾燥させた。この操作を繰り返し、超電導酸化物薄膜表面に膜厚５μｍの保護膜を形成させた。
Hereinafter, the present invention will be described in detail based on examples. The present invention is not limited to these examples.
Example 1
(Preparation of protective film forming composition)
To a container (100 mL), add 7 g of shellac resin (Furuuchi Chemical Co., Ltd., lemon shellac, product number L-1000) and 60 g of n-amyl alcohol (special grade, Wako Pure Chemical Industries, Ltd. product number 013-03656), and seal. The mixture was allowed to stand at room temperature for 3 days and then stirred to prepare a protective film-forming composition containing shellac resin.
(Formation of superconducting thin film)
On a 20mm square CeO2 intermediate sapphire substrate, a 1: 2: 3 molar solution of Y, Ba, Cu acetylacetonate was applied. First, a mixture of argon and oxygen with an oxygen partial pressure adjusted to 100 ppm. A YBa 2 Cu 3 O 7 thin film having a film thickness of 160 to 230 nm and a critical current density of 2 to 3 MA / cm 2 is formed by a coating pyrolysis method in which heating is performed in a gas flow and the atmosphere is switched to pure oxygen for heat treatment. A superconducting thin film having a high resistivity gold-silver alloy layer deposited on a sapphire substrate by sputtering deposition of a high-resistivity gold-silver alloy layer with a film thickness of about 100 nm using an alloy target having a composition in which 23 wt% silver is mixed with gold. Formed.
(Formation of protective film)
The sapphire substrate on which the superconducting oxide thin film having the high resistivity gold-silver alloy layer is formed is placed on a turntable of a spin coat coating machine (Kyoei Semiconductor Co., Ltd., Spinner No. 1H-III), and the protective film forming composition is formed. The product is dropped, the rotating table is rotated at a low speed, the protective film forming composition is spread over the entire surface of the superconducting oxide thin film, and then the rotating table is rotated at a high speed to make the protective film forming composition have a uniform thickness, Dry at 60 ° C. This operation was repeated to form a protective film having a thickness of 5 μm on the surface of the superconducting oxide thin film.
（耐環境保護膜の試験）
上記耐環境保護膜付き超電導薄膜について以下の各種試験を行った。
密着性試験
上記耐環境保護膜面にスコッチテープ（(株)住友スリーエム
品番８１０−１−１８Ｄ）を貼り付け、室温で６０分間放置後、前記スコッチテープをはがした際に保護膜が剥離しないことを確認する試験
耐水性試験
上記耐環境保護膜付き超電導薄膜を常温の水に１時間浸漬した後、取り出し、外見上異常がないことを目視で確認する試験
繰り返し耐液体窒素性試験
上記耐環境保護膜付き超電導薄膜の液体窒素への浸漬と常温への取り出し・結露を3回繰り返し、誘導法による臨界電流密度（Jc）の低下がないことを確認する試験
なお、誘導法による臨界電流密度（Jc）の測定はドイツ国テーバ（THEVA）社製クライオスキャン（Cryoscan）を使用し、液体窒素中で非特許文献２のp.3487-3490に記載されている方法で行った。
加速試験
加速試験は、試料を温度６０℃、相対湿度１００％に保持した装置内（エスペック(株) 小型環境試験器 SH-221）に2時間放置した後、当該試料を取り出し、上記と同様に操作して臨界電流密度（Jc）を測定した。
（試験結果）
上記試験結果を表２に記載した。
(Test of environmental protection film)
The following various tests were conducted on the superconducting thin film with the environmental protection film.
Adhesion test A scotch tape (Sumitomo 3M product number 810-1-18D) is applied to the surface of the environmental protection film, and after leaving at room temperature for 60 minutes, the protective film does not peel off when the scotch tape is peeled off. Water resistance test to confirm that the above superconducting thin film with environmental protection film is immersed in water at room temperature for 1 hour, and then taken out. Test to confirm that there is no abnormality in appearance. Repeated liquid nitrogen resistance test. A test to confirm that the superconducting thin film with protective film is immersed in liquid nitrogen, taken out to room temperature, and dew condensation three times to confirm that there is no decrease in the critical current density (Jc) by the induction method. The measurement of Jc) was performed by using a cryoscan manufactured by THEVA in Germany, in a liquid nitrogen, by a method described in Non-Patent Document 2, p.3487-3490.
Accelerated test
In the accelerated test , the sample is left for 2 hours in an apparatus (ESPEC Co., Ltd., small environmental tester SH-221) maintained at a temperature of 60 ° C. and a relative humidity of 100%, and then the sample is taken out and operated in the same manner as above. The critical current density (Jc) was measured.
(Test results)
The test results are shown in Table 2.
（比較例１〜２）
（保護膜形成用組成物の調製）
表１記載の材料を用い、保護膜形成用組成物とした。
（耐環境保護膜の形成）
実施例１での保護膜形成用組成物の代わりに比較例１の保護膜形成用組成物を用い、それ以外は実施例１と同様に操作し、超電導薄膜限流素子の全面に耐環境保護膜を形成させた。
（耐環境保護膜の試験）
上記耐環境保護膜付き超電導薄膜について実施例１と同様に各種試験を行った。
（試験結果）
上記試験結果を表２に記載した。
（比較例３）
（保護膜形成用組成物の調製）
表１記載の材料を用い、保護膜形成用組成物とした。
（耐環境保護膜の形成）
上記保護膜形成用組成物を実施例１と同様なサファイア基板上の超電導薄膜にスプレー塗布し、乾燥させた。スプレー塗布と乾燥処理の操作を繰り返し、超電導酸化物薄膜表面に膜厚５μｍの保護膜を形成させた。
（耐環境保護膜の試験）
上記耐環境保護膜付き超電導薄膜について実施例１と同様に各種試験を行った。
（試験結果）
上記試験結果を表２に記載した。
(Comparative Examples 1-2)
(Preparation of protective film forming composition)
Using the materials shown in Table 1, a protective film forming composition was obtained.
(Formation of environmental protection film)
The protective film forming composition of Comparative Example 1 was used in place of the protective film forming composition of Example 1, and the other operations were performed in the same manner as in Example 1 to protect the entire surface of the superconducting thin film current limiting element. A film was formed.
(Test of environmental protection film)
Various tests were conducted on the superconducting thin film with the environmental protection film in the same manner as in Example 1.
(Test results)
The test results are shown in Table 2.
(Comparative Example 3)
(Preparation of protective film forming composition)
Using the materials shown in Table 1, a protective film forming composition was obtained.
(Formation of environmental protection film)
The said protective film formation composition was spray-coated on the superconducting thin film on the sapphire substrate similar to Example 1, and was dried. The operation of spray coating and drying treatment was repeated to form a protective film having a thickness of 5 μm on the surface of the superconducting oxide thin film.
(Test of environmental protection film)
Various tests were conducted on the superconducting thin film with the environmental protection film in the same manner as in Example 1.
(Test results)
The test results are shown in Table 2.
表１
表２
表中の測定不可は、臨界電流密度（Jc）が低下したので、数値を求めることができなかったことを意味する。また、比較例１〜３の超電導薄膜限流素子の加速試験を行っていない。加速試験は繰り返し耐液体窒素性試験よりも過酷な試験であるから、比較例１〜３の加速試験の結果は測定不可になることが明らかであることによる。
なお、臨界電流密度（Jc）の測定は上記と同様の操作・手順にて行った。
この試験結果から単層の環境保護膜材料としては実施例１の保護膜を構成する親水性のシェラックが優れていることがわかった。
Table 2
Inability to measure in the table means that the numerical value could not be obtained because the critical current density (Jc) decreased. Moreover, the acceleration test of the superconducting thin film current limiting element of Comparative Examples 1 to 3 was not performed. Because the accelerated test is a severer test than the repeated liquid nitrogen resistance test, it is clear that the results of the accelerated tests of Comparative Examples 1 to 3 are unmeasurable.
The critical current density (Jc) was measured by the same operation and procedure as described above.
From this test result, it was found that the hydrophilic shellac constituting the protective film of Example 1 was excellent as a single-layer environmental protective film material.
（実施例２）
（耐環境保護膜の形成）
実施例１で作製した超電導薄膜限流素子を、実施例１と同様に操作した後、さらに超電導薄膜限流素子の側面に、実施例１の保護膜形成用組成物を刷毛塗り法により塗布し、乾燥させる操作を数回繰り返して、超電導薄膜限流素子の表面および側面に耐環境保護膜を形成させた。
（耐環境保護膜の試験）
上記耐環境保護膜付き超電導膜について、上記加速試験を実施例１と同様な操作で行った。
その結果、実施例１での加速試験で認められた試料周辺部の劣化が、実施例２では抑制された。
(Example 2)
(Formation of environmental protection film)
After operating the superconducting thin film current limiting element produced in Example 1 in the same manner as in Example 1, the protective film forming composition of Example 1 was further applied to the side surface of the superconducting thin film current limiting element by a brush coating method. The drying operation was repeated several times to form an environmental protection film on the surface and side surfaces of the superconducting thin film current limiting element.
(Test of environmental protection film)
The acceleration test was performed in the same manner as in Example 1 for the superconducting film with the environmental protection film.
As a result, the deterioration of the periphery of the sample observed in the acceleration test in Example 1 was suppressed in Example 2.
（実施例３）
（超電導薄膜限流素子の作製）
実施例１で用いたサファイア基板上に、実施例１と同様に操作し、実施例１と同様の膜厚１６０〜２３０ｎｍのＹＢａ２Ｃｕ３Ｏ７薄膜および高抵抗率金銀合金層を形成した。その両端に厚さ１μｍの銀電極を形成して電流端子とし、電流リード線と接続するとともに、電流が流れる方向に沿って金銀合金層の数カ所に電圧端子を取り付け電圧リード線と接続し、超電導薄膜限流素子を作製した。
（超電導酸化物薄膜の形成）
実施例１と同様に操作し、超電導薄膜限流素子表面に膜厚５μｍの耐環境保護膜を形成した。
（耐環境保護膜の試験）
上記耐環境保護膜付き超電導薄膜について下記限流試験を行った。
限流試験
上記耐環境保護膜付き超電導膜限流素子の電流リード線を電流可変交流電源と接続し、電圧リード線を電圧計と接続した。耐環境保護膜付き超電導膜に、まず臨界電流以下の交流電流を流し、途中で５サイクルのみ臨界電流以上の電流を流した。臨界電流以上の電流が流れると超電導膜は常電導状態に転移し、電圧が発生する。この発生した電圧から超電導膜および金銀合金膜の抵抗値を計算し、抵抗率の温度依存性から超電導限流素子の温度上昇を推算することができる（非特許文献２のp.1843-1846）。
測定結果は次のとおりであった。
SN転移後の温度上昇の測定結果から、環境保護膜の形成による熱容量の増加により、温度上昇が１０−２０℃抑制された。すなわち環境保護膜は限流素子を熱的にも保護することが明らかとなった。
(Example 3)
(Production of superconducting thin film current limiting element)
On the sapphire substrate used in Example 1, the same operation as in Example 1 was performed to form a YBa 2 Cu 3 O 7 thin film and a high-resistivity gold-silver alloy layer having a film thickness of 160 to 230 nm as in Example 1. A silver electrode with a thickness of 1 μm is formed at both ends to form a current terminal, which is connected to the current lead wire. At the same time, voltage terminals are attached to several points of the gold-silver alloy layer along the direction of current flow and connected to the voltage lead wire. A thin film current limiting element was fabricated.
(Formation of superconducting oxide thin film)
In the same manner as in Example 1, an environmental protection film having a thickness of 5 μm was formed on the surface of the superconducting thin film current limiting element.
(Test of environmental protection film)
The following current limiting test was conducted on the superconducting thin film with the environmental protection film.
Current-limiting test The current lead wire of the superconducting film current-limiting element with the above environmental protection film was connected to a current variable AC power source, and the voltage lead wire was connected to a voltmeter. First, an AC current having a critical current or less was passed through the superconducting film with an environmental protection film, and a current exceeding the critical current was passed only for 5 cycles. When a current exceeding the critical current flows, the superconducting film transitions to the normal conducting state, and a voltage is generated. The resistance value of the superconducting film and the gold-silver alloy film can be calculated from the generated voltage, and the temperature rise of the superconducting current limiting element can be estimated from the temperature dependence of the resistivity (p.1843-1846 of Non-Patent Document 2). .
The measurement results were as follows.
From the measurement result of the temperature rise after the SN transition, the temperature rise was suppressed by 10-20 ° C. due to the increase of the heat capacity due to the formation of the environmental protection film. That is, it became clear that the environmental protection film also protects the current limiting element thermally.
（実施例４）
（保護膜形成用組成物の調製）
実施例１と同様に操作し、シェラック樹脂を含む保護膜形成用組成物を調製した。
また、容器（１００ｍＬ）に表３の化合物を注ぎ、１０分間攪拌し、ピセインを含む保護膜形成用組成物を調製した。
（耐環境保護膜の形成）
実施例１で作製した超電導薄膜限流素子を、実施例１と同様に操作し、超電導酸化物薄膜表面に膜厚５μｍの耐環境保護膜を形成させた。次いで、前記耐環境保護膜を形成させた超電導薄膜限流素子をスピンコート塗布機の回転台に載置し、上記ピセインを含む保護膜形成用組成物を滴下し、回転台を低速回転させて、保護膜全面に上記保護膜形成用組成物を行き渡らせ、次いで回転台を高速回転させて、上記保護膜形成用組成物を均一な厚みとし、６０℃で乾燥させた。この操作を繰り返し、超電導酸化物薄膜表面に膜厚５μｍの耐環境保護膜を形成させた。
（耐環境保護膜の試験）
上記耐環境保護膜付き超電導薄膜について実施例１と同様に各種試験を行った。
（試験結果）
上記試験結果を表２に記載した。
Example 4
(Preparation of protective film forming composition)
In the same manner as in Example 1, a protective film-forming composition containing shellac resin was prepared.
Moreover, the compound of Table 3 was poured into the container (100 mL), and it stirred for 10 minutes, and prepared the composition for protective film formation containing picein.
(Formation of environmental protection film)
The superconducting thin film current limiting element produced in Example 1 was operated in the same manner as in Example 1 to form an environmental protection film having a thickness of 5 μm on the surface of the superconducting oxide thin film. Next, the superconducting thin film current limiting element on which the environmental protection film is formed is placed on a turntable of a spin coat applicator, the composition for forming a protective film containing the above picein is dropped, and the turntable is rotated at a low speed. Then, the protective film-forming composition was spread over the entire surface of the protective film, and then the turntable was rotated at a high speed to make the protective film-forming composition uniform thickness and dried at 60 ° C. This operation was repeated to form an environmental protection film having a thickness of 5 μm on the surface of the superconducting oxide thin film.
(Test of environmental protection film)
Various tests were conducted on the superconducting thin film with the environmental protection film in the same manner as in Example 1.
(Test results)
The test results are shown in Table 2.
（実施例５）
（保護膜形成用組成物の調製）
実施例１と同様に操作し、シェラック樹脂を含む保護膜形成用組成物を調製した。
また、表３の化合物を用い、それ以外は実施例４と同様に操作し、フッ素樹脂を含む保護膜形成用組成物を調製した。
（耐環境保護膜の形成）
ピセインを含む保護膜形成用組成物の代わりにフッ素樹脂を含む保護膜形成用組成物を用い、それ以外は実施例４と同様に操作し、超電導酸化物薄膜表面に膜厚５μｍの耐環境保護膜を形成させた。
（耐環境保護膜の試験）
上記耐環境保護膜付き超電導薄膜について実施例１と同様に各種試験を行った。
（試験結果）
上記試験結果を表４に記載した。
(Example 5)
(Preparation of protective film forming composition)
In the same manner as in Example 1, a protective film-forming composition containing shellac resin was prepared.
Further, a composition for forming a protective film containing a fluororesin was prepared in the same manner as in Example 4 except that the compounds shown in Table 3 were used.
(Formation of environmental protection film)
A protective film forming composition containing a fluororesin is used in place of the protective film forming composition containing picein, and the rest is operated in the same manner as in Example 4 to protect the surface of the superconducting oxide thin film with a film thickness of 5 μm. A film was formed.
(Test of environmental protection film)
Various tests were conducted on the superconducting thin film with the environmental protection film in the same manner as in Example 1.
(Test results)
The test results are shown in Table 4.
表３
表４
Claims (9)
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