JP3872738B2

JP3872738B2 - High withstand voltage superconducting fault current limiter

Info

Publication number: JP3872738B2
Application number: JP2002259072A
Authority: JP
Inventors: 充森田; 芳生平野; 秀美林; 完一寺薗; 和夫船木; 一弘柁川
Original assignee: Kyushu Electric Power Co Inc; Nippon Steel Corp; Kyushu TLO Co Ltd
Current assignee: Kyushu Electric Power Co Inc; Nippon Steel Corp; Kyushu TLO Co Ltd
Priority date: 2002-09-04
Filing date: 2002-09-04
Publication date: 2007-01-24
Anticipated expiration: 2022-09-04
Also published as: JP2004104840A

Description

【０００１】
【発明の属する技術分野】
本発明は、超電導限流器に関するものである。
【０００２】
【従来の技術】
電力回路で短絡事故が発生すると、極めて大きな短絡電流が流れる。短絡電流は遮断器によって遮断されるが、数十msは短絡電流が流れてしまうため、大きな電磁力と多量のジュール熱が発生し、電力機器や電路が大きな機械的・熱的損傷を受ける。このような事故発生時の短絡電流を抑えて、遮断器の責務を軽減する事故時限流器(限流器)の開発が望まれている。また、このような限流器は、各種送配電系統の安定化に寄与する効果が極めて大きく、系統の複雑化が進む今日、限流器の早期実現が期待されている。
【０００３】
限流器には多くの方式のものが提案されているが、本発明者等も、ミアンダ形状を有する超電導バルク材料を用いた超電導−常伝導転移型で抵抗型の限流器を提案している。例えば、 Y系のバルク酸化物超電導材料をミアンダ形状に加工し、これに限流動作時のバイパス回路としてNiCrの板を接続すると同時に、短絡電流が流れた瞬間に超電導材料に磁場を印加するための小型マグネットを取付け限流器を提案し、性能評価を行っている (第61回1999年度秋期低温工学・超電導学会講演概要集P181及び第62回2000年度春期低温工学・超電導学会講演概要集P233)。
【０００４】
また、特開平2000-32654号公報には、REBa₂Cu₃O_7-x(ここでREはY、Pr、Nd、Sm、Eu、Gd、Dy、Ho、Er、Tm、Yb、Luから選ばれる１種類以上の元素を示す) 相中にRE₂BaCuO₅が微細分散した酸化物超電導体を用いた超電導-常伝導転移型限流素子の c軸方向に、短絡電流検出時に外部磁場を印加し、クエンチを助長することで、均等にかつ高速の限流動作が得られる限流器も提案している。
【０００５】
また、特開平 10-136563号公報には、高比抵抗材料をコーティングした限流素子が記載されており、 M. Moritaらの文献(IEEE TRANSACTION ON APPLIED SUPER CONDUCTIVITY, Vol9, No.2, June 1999)には、超電導材料の片面に、0.5mm厚さのNiCr製バイパスが貼り付けられた限流素子が記載されている。さらに、ドイツ公開特許19957981号公報、ドイツ公開特許19957982号公報、ドイツ公開特許19958727号公報には、超電導体の片面にバイパス回路となる導電性材料を有し、その間に超電導体と導電性材料を貼り付ける層が存在する限流素子について記載されている。また、特開平11-195332号公報には、超電導体の両面に比抵抗が10〜100μΩcmの金属バイパスが貼り付けられた超電導素子が記載されており、さらに、特開2002-76455号公報には、限流動作時においても超電導材料に引っ張り応力がかからないよう設計された限流素子について記載されている。
【０００６】
【発明が解決しようとする課題】
超電導限流器は、短絡電流通電時に、限流素子が超電導状態から常伝導状態に転移することによって限流させることが基本的な動作原理である。したがって、限流動作途中では、超電導体内に大きな電流が流れ、かつ、系統電圧に近い大きな電圧を担うことになり、大きな電力が消費されることになる。より高特性の超電導材料ほど臨界電流密度が高く、したがって、限流動作時には大きな熱衝撃が超電導体に加わることになる。この熱衝撃は、限流素子そのものにダメージを与え、ひいては素子を焼損に至らしめる。このダメージにより、本来、繰り返し使用を前提に導入される限流器の機能が果たさなくなる。
【０００７】
超電導素子が焼損する問題は、特に、酸化物系の超電導材料を用いた限流器では、「ホットスポット」問題と呼ばれ、限流動作時の大きな熱衝撃が直接の原因と考えられているのが一般的である。
本発明は、このような課題を解決し、限流動作に伴う熱衝撃対し、高い耐久性を有する限流器を提供するものである。
【０００８】
【課題を解決するための手段】
（１）単結晶状のREBa₂Cu₃O_7-x(ここで、REは、Y、La、Pr、Nd、Sm、Eu、Gd、Dy、Ho、Er、Tm、Yb又はLuから選ばれる1種類以上の元素を示す)相中にRE₂BaCuO₅ 相が分散してなる超電導バルク材料を超電導限流素子に用いた抵抗型超電導限流器であって、前記超電導限流素子にバイパス回路を構成する金属材料が貼り付けられた構造を有し、該金属材料の77Kにおける比抵抗が100μΩcm超であり、かつ、前記超電導バルク材料の結晶学的方位の c軸と前記超電導限流素子の通電方向とのなす角度が 60°〜120°の範囲にあることを特徴とする高耐電圧限流器。
（２）前記超電導体の常伝導状態における比抵抗が、前記金属材料の比抵抗よりも小さいことを特徴とする(１)記載の限流器。
（３）前記バイパス回路を構成する金属材料の77Kにおける比抵抗が400μΩcm以下であることを特徴とする（１）又は（２）に記載の限流器。
【０００９】
（４）矩形断面を有する板状、棒状、ミアンダ状又はコイル状の前記超電導限流素子に、前記バイパス回路を構成する矩形断面を有する金属材料が少なくとも上下又は左右から貼り付けられていることを特徴とする（１）〜（３）のいずれかに記載の限流器。
（５）前記超電導限流素子の周囲に少なくとも樹脂又はガラス繊維強化プラスチックが配置されている（１）〜（４）のいずれかに記載の限流器。
（６） Fe、Zn、Ni、Co、Cr、Mgの少なくとも一種類が0.05〜2質量%以下添加された超電導バルク材料を用いた（１）〜（５）のいずれかに記載の限流器。
（７）前記バイパス回路を構成する金属材料が、Ni合金、Cr合金又はTi合金の何れかであることを特徴とする（１）〜（６）のいずれかに記載の限流器。
【００１０】
（８）限流動作時において、前記超電導限流素子の少なくとも一部が可動な構造であることを特徴とする（１）〜（７）のいずれかに記載の限流器。
（９）前記超電導限流素子の可動方向が通電方向であり、可動方向に対しガイドする構造を有することを特徴とする（８）記載の限流器。
（１０）前記超電導材料と部分的にのみ接触し、全面で接触しない外付けのバイパス抵抗を有することを特徴とする（１）〜（９）のいずれかに記載の限流器。
（１１） 7.5V/cm 以上の耐電圧を有することを特徴とする（１）〜（１０）のいずれかに記載の限流器。
【００１１】
【発明の実施の形態】
特開2002-76455号公報に記載されているように、限流動作時に超電導体にクラックが入らず、高い耐電圧を示す限流素子を得るには、酸化物超電導体は、引張応力に対する強度が小さいため、超電導体に引張応力がかからないようにすることが重要である。
【００１２】
そのためには、超電導体とバイパスとなる金属材料の比抵抗の大小関係が重要になる。超電導体の常伝導状態での比抵抗ρs、金属材料の比抵抗ρmとした時、ρs≫ρmの場合、バイパス金属には大きな電流密度の電流が流れる。したがって、バイパス金属がより加熱され、より膨張するため、超電導体には引張応力が作用する。一方、ρs≪ρmの場合、超電導体に大きな電流密度の電流が流れる。したがって、超電導体がより加熱され、より膨張するため、超電導体には圧縮応力が作用する。
【００１３】
単結晶状のREBa₂Cu₃O_7-x(ここで、REは、Y、La、Pr、Nd、Sm、Eu、Gd、Dy、Ho、Er、Tm、Yb及びLuから選ばれる1種類以上の元素を示す)相中にRE₂BaCuO₅相が分散してなる超電導バルク材料(以後、RE系バルク超電導体という)の臨界電流密度は、77K、自己磁界中において、5〜10×10⁴A/cm²と極めて高く、電力系統における定格電流である1〜2kAの通電容量を3mm²程度の断面積で得られるため、限流素子が小型化でき、限流素子用超電導材料として極めて優れている。
【００１４】
一方、RE系バルク超電導体のc軸方向における引張強度及びa-b面方向の引張強度は、単結晶状材料故に、10MPa程度及び35MPa程度と極めて弱く、特に a-b面間にクラックが極めて発生しやすい。そのため、通電方向は a-b面と平行であること、すなわち、c軸と垂直 (90°)であることが望ましく、潜在的なミクロなクラック間隔を考慮すると、少なくともc軸と60°〜120°の範囲である必要がある。また、圧縮強度は、a-b面方向において 350MPa程度で、金属材料との比較においては、かなり低い値である。そのため、上記のようにρsとρmがかけ離れた場合、超電導体は、限流動作時すなわちクエンチ時に損傷を受けやすくなり、限流素子の単位長さ当たりの耐電圧が得られなくなる。そのため、高い耐電圧を有する限流器を作製するには、超電導材料の常伝導状態での比抵抗とバイパス金属の比抵抗を極力合わせることが重要となる。特に、RE系バルク超電導体は、 a-b面間にクラックが入り易く、素子の劣化が起こり易い。超電導特性に優れたRE系バルク超電導体を機械的強度の弱さに配慮して限流器として使用するには、バイパス金属との熱膨張挙動及び比抵抗のマッチングが重要になる。
【００１５】
また、前述のように長手方向の熱膨張を金属バイパスで補強すると同時に、長手方向及び長手方向と垂直方向の樹脂等による補強が有効である。このとき、樹脂中にフィラーを混ぜ、強度及び熱膨張率を適宜調整することが望ましい。さらに、ミアンダ状バルク超電導材料のように、ある平面内に表面を有する場合、金属バイパスを有する限流素子にガラス繊維強化プラスチック(GFRP)を貼り付けることは、補強の観点から望ましい。
【００１６】
RE系バルク超電導体の100K近傍の比抵抗は、通電方向であるa-b面方向で130〜170μΩcmであり、また、数万A/cm²程度の臨界電流密度を保ち得る鉄等を0.05〜2質量%程度添加したRE系バルク超電導体は、180〜400μΩcmとなり、比抵抗が増加する。また、Agを10〜30質量%添加したAg粒子を含むRE系バルク超電導体は、100〜150μΩ cmと比抵抗は僅かに低下する傾向にある。このように、RE系バルク超電導体の比抵抗は、概ね100〜400μΩcmの範囲にある。
【００１７】
ρs≒ρmでかつ ρs<ρmである場合、限流動作時に少なくとも超電導体に引張応力がかかる可能性はなく、より高い耐電圧が得られる。したがって、超電導体の比抵抗に合わせて、金属材料の比抵抗を100μΩcm超、400μΩcm以下とする必要がある。
【００１８】
超電導体と金属材料とが矩形断面を有する場合、超電導体と金属材料との密着性を高めることができ、限流動作開始時の超電導体からのバイパス金属への分流がより短時間で起き、超電導体の熱負荷が軽減できる。
【００１９】
より高い比抵抗(ρ)を有する超電導体を限流素子として使用することは、より高い抵抗を有する限流器が可能となるため、設計上望ましい。しかしながら、多量の添加物は、超電導特性、特に臨界電流密度(Jc)そのものを低下させるため、ρ・Jcが向上する添加量を選択する必要がある。一例として、Feでは、0.6質量%の添加で、ρは約2倍向上し、Jcは約 0.8倍に低下するため、ρ・Jcは約1.6倍向上することになる。Zn、Ni、Co、Cr、Mg等についても、0.05〜2質量%の添加量においてρ・Jcが1を越える領域がある。
【００２０】
RE系バルク超電導体及び添加物を含むRE系バルク超電導体の比抵抗と同レベルの比抵抗を有する金属材料としては、Ni合金及びCr合金であるニクロム、ハステロイ、インコネル等の合金やTi合金等があり、また、熱膨張の温度変化に関しても適度な圧縮応力が加わる挙動を示すため、バイパス回路を構成する金属材料として望ましい。特に、Ti合金は、熱膨張挙動がRE系バルク超電導体のそれと 10%以内で一致しているため、特に望ましい。ニクロム及びTi合金は、通常の半田ではこれら金属との接着性が不十分であるため、ニクロムの接合表面には、 Sn-Pb系半田を塩化亜鉛−塩化アンモニウム系のフラックスを用いてコーティングした後、また、Ti合金の接合表面には銀合金を成膜した後に、超電導体と接合することが望ましい。
【００２１】
超電導限流素子は、何らかの形で基板等に取り付けられる必要がある。取付枠等の基板又は電流導入電極に完全に固定されると、限流動作時に急激な熱膨張が起き、固定部から受ける圧縮応力により、RE系バルク超電導体及びバイパス回路を構成する金属材料が湾曲し、超電導体にクラックが発生しやすくなる。このような限流素子の損傷を防ぐには、限流動作時の熱膨張による応力を逃がすため、限流素子全体を固定するのではなく、ある一部を固定し、限流素子全体は、延び縮みできる構造を取る必要がある。限流動作時に膨張する方向は、通電方向であり、この方向に可動な構造である必要があるが、素子周囲の材料との関係から、曲げ応力が働く場合が発生しやすくなるため、通電方向に膨張できるよう、ガイドする構造を有することが望ましい。
【００２２】
限流器は、短絡電流が停止し限流動作終了後、素早く超電導状態に復帰する必要がある。バイパス金属が超電導体に貼り付けられた限流素子は、金属材料の断面積が大きくなると、限流動作時に発生した熱を素早く放出することができなくなる。そのため、超電導体が元の冷却温度に戻るために長時間を必要し、復帰時間が長くなってしまう。超電導体に貼り付けられたバイパス金属の断面積は、機械的強度が十分に得られる範囲であれば良く、分流の量を制御する場合、超電導体と熱的に接触しない外付けの抵抗を用いればよい。外付け抵抗は、比抵抗の温度変化が少ないニクロム合金等が望ましい。
【００２３】
【実施例】
（実施例１）
YBa₂Cu₃O_7-x中に Y₂BaCuO₅が微細分散したバルク材料(Y系QMG)を用い、図１に示す電流路断面積が0.8×2.2mm²、有効長さが約250mmで、表面に厚さ約5μmの Ag-Au合金の薄膜を有するミアンダ形状の限流素子１を作製した。この時、YBa₂Cu₃O_7-xのc軸は、板面の法線に対し平行であり、100Kにおける比抵抗は155μΩcm であった。
【００２４】
このような超電導体に、図１に示す電極部を除いて同形状の厚さ 0.6mmのミアンダ状Ti合金(Ti-6Al-4V)２、３を両面から半田により貼り付けた。Ti合金の100Kにおける比抵抗は、175μΩcmであり、Ti合金の接着面には、予めAg-Au合金を1μm成膜した。
【００２５】
図２に示すように折り返し部分間には、5mΩのNiCr製の外付けバイパス抵抗４を取り付けた。さらに、Ti合金を貼り付けたミアンダ状素子の隙間に、フィラーを添加した樹脂を埋め込むと同時に、0.3mm厚さのガラス繊維強化プラスチック(GFRP) 板５を、電極部分を除いて樹脂を用い、両面から貼り付けた。得られた限流素子は、電流端子部分をホルダー８に取り付けられた銅電極６に半田接続された。また、電極の反対側には、素子が限流動作時に延びることができるようにホルダーに固定せず、ガイド７を設け、通電方向に伸縮できるようにした。図２はこのようにしてホルダーに取り付けられた限流素子を示す。
【００２６】
上記限流素子を液体窒素中で冷却し、パルス幅 4.1msの半波の正弦波電流を通電した限流応答を測定した。その結果、限流素子が無い場合に、ピーク値で4.2kAが流れる条件において、図３に示すように、損傷することなく、ミアンダ状限流素子全体で210V(1cm当たり8.5V)の電圧を担いつつ、2.1kAに限流できることが分かった。
【００２７】
比較例として、Ti合金を貼り付けないこと以外は同一条件で限流素子を作製し、通電実験を行ったところ、ピーク値で2.8kA通電時に、最大 62.5V(1cm当たり2.5V)の電圧を記録した後、焼損に至った。この比較から金属バイパスの有効性が確かめられた。
【００２８】
（実施例２）
GdBa₂Cu₃O_7-x中にGd₂BaCuO₅及び銀粒子が微細分散したバルク材料(銀添加Gd系QMG)を用い、図４に示す電流路断面積が0.8×2.0mm²、有効長さが約330mmで、表面に厚さ約2μmの Ag-Au合金の薄膜を有するミアンダ形状の限流素子１１を作製した。この時、GdBa₂Cu₃O_7-xの c軸は板面の法線に対し平行であり、100Kにおける比抵抗は115μΩcmであった。
【００２９】
このような超電導体に、図４に示す電極部を除いて同形状の厚さ 0.7mmのミアンダ状 NiCr合金１２、１３を両面から半田により貼り付けた。NiCr合金の 100Kにおける比抵抗は 120μΩcmであり、NiCr合金の接着面には、約10μmのSn-Pb系半田の膜を塗布した。
【００３０】
以下、先に図２に示したのと同様に折り返し部分間には4mΩのNiCr製の外付けバイパス抵抗を取り付けた。さらに、NiCrを貼り付けたミアンダ状素子の隙間に、フィラーを添加した樹脂を埋め込むと同時に、1.0mm厚さの GFRP板を、電極部分を除いて樹脂を用い、貼り付けた。得られた限流素子は、電流端子部分をホルダーに取り付けられた電極に半田接続された。また、電極は側面中央部にあるため、素子が限流動作時に延びることができるように折り返し部分のある両側は、ガイドを設け、通電方向に伸縮できるようにした。
【００３１】
上記限流素子を液体窒素中で冷却し、パルス幅 4.1msの半波の正弦波電流を通電した限流応答を測定した。その結果、限流素子が無い場合に、ピーク値で4.2kAが流れる条件において、損傷することなく、ミアンダ状限流素子全体で247V(1cm当たり7.5V)の電圧を担いつつ、2.3kAに限流できることが分かった。
【００３２】
（実施例３）
Feを0.5質量%添加したYBa₂Cu₃O_7-x中にY₂BaCuO₅が微細分散したバルク材料(Fe添加Y系QMG)を用い、図１、図４に示したのと同様に電流路断面積が1.0×2.2mm²、有効長さが約250mmで、表面に厚さ約2μmのAg-Au合金の薄膜を有するミアンダ形状の限流素子を作製した。この時、YBa₂Cu₃O_7-xのc軸は板面の法線に対し平行であり、100Kにおける比抵抗は280μΩcmであった。
【００３３】
このような超電導体に、図１、図３に示したのと同様に電極部を除いて同形状の厚さ0.6mmのミアンダ状 Ti合金(Ti-15V-3Cr-3Sn-3Al)を両面から半田により貼り付けた。このTi合金の 100Kにおける比抵抗は、200μΩcmであり、Ti合金の接着面には、予めAg-Au合金を1μm成膜した。
【００３４】
以下、先に図２に示したのと同様に折り返し部分間には、7mΩのNiCr製の外付けバイパス抵抗を取り付けた。さらに、Ti合金を貼り付けたミアンダ状限流素子の隙間に、フィラーを添加した樹脂を埋め込むと同時に、0.3mm 厚さのガラス繊維強化プラスチック(GFRP)板を、電極部分を除いて樹脂を用い、貼り付けた。得られた限流素子は、電流端子部分をホルダーに取り付けられた電極に半田接続された。また、電極の反対側は、素子が限流動作時に延びることができるようにホルダーに固定せず、ガイドを設け通電方向に伸縮できるようにした。上記限流素子を液体窒素中で冷却し、パルス幅 4.1msの半波の正弦波電流を通電した限流応答を測定した。その結果、限流素子が無い場合に、ピーク値で 4.2kAが流れる条件において、損傷することなく、ミアンダ状源流素子全体で237V(1cm当たり9.5V)の電圧を担いつつ、1.9kAに限流できることが分かった。
【００３５】
【発明の効果】
以上で述べたように、本発明の限流器は、焼損することなく高い電圧に耐えることができ、限流動作に伴う熱衝撃に対し高い耐久性を有するため、その工業的効果は甚大である。
【図面の簡単な説明】
【図１】素子の側面端部に電極を有し、金属バイパスが両面から貼り付けられた限流素子の例を示す図
【図２】本発明の超電導限流器の例を示す図
【図３】限流素子の通電特性を示すグラフ
【図４】素子の側面中央部に電極を有し、金属バイパスが両面から貼り付けられた限流素子の例を示す図
【符号の説明】
１限流素子
２、３Ｔｉ合金（金属バイパス）
４外付けバイパス抵抗
５ガラス繊維強化プラスチック板
６銅電極
７ガイド
８ホルダー
１１限流素子
１２、１３ＮｉＣｒ合金（金属バイパス）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a superconducting fault current limiter.
[0002]
[Prior art]
When a short circuit accident occurs in the power circuit, a very large short circuit current flows. The short-circuit current is interrupted by the circuit breaker, but since the short-circuit current flows for several tens of milliseconds, a large electromagnetic force and a large amount of Joule heat are generated, and the power equipment and the electric circuit are seriously damaged mechanically and thermally. Development of an accident time limiter (current limiter) that reduces the short circuit current at the time of such an accident and reduces the duty of the circuit breaker is desired. In addition, such a current limiter has an extremely large effect that contributes to the stabilization of various power transmission / distribution systems, and the current realization of the current limiter is expected today as the system becomes more complex.
[0003]
Although many types of current limiters have been proposed, the present inventors have proposed a superconducting-normal conduction transition type resistance type current limiter using a superconducting bulk material having a meander shape. Yes. For example, to process a Y-based bulk oxide superconducting material into a meander shape, connect a NiCr plate as a bypass circuit during current limiting operation, and simultaneously apply a magnetic field to the superconducting material at the moment when a short-circuit current flows The current limiter was proposed by installing a small magnet and the performance was evaluated. (The 61st 1999 Fall Cryogenic Engineering and Superconductivity Society Presentation Summary P181 and 62nd 2000 Spring Cryogenic Engineering and Superconductivity Society Presentation Summary P233 ).
[0004]
JP 2000-32654 discloses REBa ₂ Cu ₃ O _7-x (where RE is selected from Y, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu) The external magnetic field is applied in the c-axis direction of the superconducting-normal conduction transition type current limiting device using an oxide superconductor in which RE ₂ BaCuO ₅ is finely dispersed in the phase. In addition, a current limiting device is also proposed which can obtain a uniform and high speed current limiting operation by promoting quenching.
[0005]
Japanese Patent Application Laid-Open No. 10-136563 describes a current limiting element coated with a high specific resistance material, which is described in M. Morita et al. (IEEE TRANSACTION ON APPLIED SUPER CONDUCTIVITY, Vol9, No.2, June 1999). ) Describes a current limiting element in which a 0.5 mm thick NiCr bypass is pasted on one side of a superconducting material. Furthermore, German published patent No. 19957981, German published patent No. 19957982 and German published patent No. 19958727 have a conductive material that becomes a bypass circuit on one side of the superconductor, and the superconductor and conductive material are placed between them. A current limiting element having a layer to be attached is described. Japanese Patent Laid-Open No. 11-195332 describes a superconducting element in which a metal bypass having a specific resistance of 10 to 100 μΩcm is attached to both surfaces of a superconductor, and further, Japanese Patent Laid-Open No. 2002-76455 discloses In addition, a current limiting element designed to prevent tensile stress from being applied to the superconducting material even during current limiting operation is described.
[0006]
[Problems to be solved by the invention]
The basic principle of operation of the superconducting current limiter is to limit the current by passing the current limiting element from the superconducting state to the normal conducting state during short-circuit current conduction. Therefore, in the middle of the current limiting operation, a large current flows in the superconductor, and a large voltage close to the system voltage is assumed, and a large amount of power is consumed. A superconducting material with higher characteristics has a higher critical current density, and therefore a large thermal shock is applied to the superconductor during current limiting operation. This thermal shock damages the current limiting element itself and eventually causes the element to burn out. Due to this damage, the function of the current limiter that is originally introduced on the premise of repeated use is not fulfilled.
[0007]
The problem that the superconducting element burns out is called the “hot spot” problem, especially in the current limiter using an oxide-based superconducting material, and is considered to be directly caused by a large thermal shock during current limiting operation. It is common.
The present invention provides a current limiter that solves such problems and has high durability against thermal shock associated with current limiting operation.
[0008]
[Means for Solving the Problems]
(1) Single-crystal REBa ₂ Cu ₃ O _7-x (where RE is selected from Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, or Lu) A superconducting current limiting device using a superconducting bulk material in which a RE ₂ BaCuO ₅ phase is dispersed in a phase (indicating one or more elements) in the superconducting current limiting device, and a bypass circuit in the superconducting current limiting device And a specific resistance at 77K of the metal material of more than 100 μΩcm, and the c-axis of the crystallographic orientation of the superconducting bulk material and the superconducting current limiting element A high withstand voltage current limiting device characterized in that the angle between the energizing direction is in the range of 60 ° to 120 °.
(2) The current limiter according to (1), wherein a specific resistance in a normal state of the superconductor is smaller than a specific resistance of the metal material.
(3) The current limiter according to (1) or (2), wherein a specific resistance at 77K of the metal material constituting the bypass circuit is 400 μΩcm or less.
[0009]
(4) A metal material having a rectangular cross section constituting the bypass circuit is affixed to at least the upper and lower sides or the left and right sides of the superconducting current limiting element having a rectangular cross section, a plate shape, a rod shape, a meander shape, or a coil shape. The current limiting device according to any one of (1) to (3).
(5) The current limiter according to any one of (1) to (4), wherein at least a resin or glass fiber reinforced plastic is disposed around the superconducting current limiting element.
(6) The current limiting device according to any one of (1) to (5), wherein a superconducting bulk material to which at least one of Fe, Zn, Ni, Co, Cr, and Mg is added is 0.05 to 2% by mass or less. .
(7) The current limiting device according to any one of (1) to (6), wherein the metal material constituting the bypass circuit is any one of a Ni alloy, a Cr alloy, and a Ti alloy.
[0010]
(8) The current limiting device according to any one of (1) to (7), wherein at least a part of the superconducting current limiting element has a movable structure during a current limiting operation.
(9) The current limiting device according to (8), characterized in that the moving direction of the superconducting current limiting element is an energizing direction and has a structure for guiding the moving direction.
(10) The current limiting device according to any one of (1) to (9), wherein the current limiting device has an external bypass resistance that contacts only partly with the superconducting material and does not contact with the entire surface.
(11) The current limiting device according to any one of (1) to (10), which has a withstand voltage of 7.5 V / cm or more.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
As described in JP-A-2002-76455, in order to obtain a current limiting element that does not crack in the superconductor during current limiting operation and exhibits a high withstand voltage, the oxide superconductor has a strength against tensile stress. Therefore, it is important to prevent tensile stress from being applied to the superconductor.
[0012]
For that purpose, the magnitude relationship between the specific resistance of the superconductor and the metal material to be bypassed becomes important. When the specific resistance ρs in the normal state of the superconductor and the specific resistance ρm of the metal material are used, when ρs >> ρm, a current having a large current density flows in the bypass metal. Therefore, tensile stress acts on the superconductor because the bypass metal is further heated and expands more. On the other hand, when ρs << ρm, a current having a large current density flows through the superconductor. Therefore, since the superconductor is further heated and expands more, compressive stress acts on the superconductor.
[0013]
Single-crystal REBa ₂ Cu ₃ O _7-x (where RE is one or more selected from Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu) The critical current density of the superconducting bulk material in which the RE ₂ BaCuO ₅ phase is dispersed in the phase (hereinafter referred to as the RE-based bulk superconductor) is 77 K, and 5-10 × 10 ⁴ in the self-magnetic field. a / cm ² and very high, since the obtained cross-sectional area of about 3 mm ² to current carrying capacity of 1~2kA the rated current in the power system, current-limiting device can be miniaturized, very excellent as a superconductive material for current-limiting device ing.
[0014]
On the other hand, the tensile strength in the c-axis direction and the tensile strength in the ab plane direction of the RE-based bulk superconductor are extremely weak, about 10 MPa and 35 MPa, because of the single crystal material, and cracks are particularly likely to occur between the ab planes. Therefore, it is desirable that the energization direction is parallel to the ab plane, that is, perpendicular to the c axis (90 °), and considering the potential micro crack spacing, at least 60 ° to 120 ° with respect to the c axis. Must be in range. In addition, the compressive strength is about 350 MPa in the ab plane direction, which is a considerably low value in comparison with metal materials. Therefore, when ρs and ρm are separated from each other as described above, the superconductor is likely to be damaged during the current limiting operation, that is, during quenching, and the withstand voltage per unit length of the current limiting element cannot be obtained. Therefore, in order to produce a current limiter having a high withstand voltage, it is important to match the specific resistance of the superconducting material in the normal state and the specific resistance of the bypass metal as much as possible. In particular, RE-based bulk superconductors are prone to cracks between the ab surfaces, and the elements are likely to deteriorate. In order to use a RE bulk superconductor with excellent superconducting properties as a current limiter considering the weak mechanical strength, matching of thermal expansion behavior and specific resistance with the bypass metal is important.
[0015]
Further, as described above, the thermal expansion in the longitudinal direction is reinforced with the metal bypass, and at the same time, the reinforcement with the resin in the longitudinal direction and the direction perpendicular to the longitudinal direction is effective. At this time, it is desirable to mix a filler in the resin and appropriately adjust the strength and the coefficient of thermal expansion. Further, when the surface is in a certain plane like the meander-like bulk superconducting material, it is desirable to attach glass fiber reinforced plastic (GFRP) to the current limiting element having the metal bypass from the viewpoint of reinforcement.
[0016]
The specific resistance in the vicinity of 100K of the RE bulk superconductor is 130 to 170 μΩcm in the ab plane direction which is the energization direction, and 0.05 to ² mass of iron etc. that can maintain a critical current density of about tens of thousands A / cm ² The RE bulk superconductor with about% added becomes 180 to 400 μΩcm, and the specific resistance increases. In addition, the RE bulk superconductor containing Ag particles to which 10 to 30% by mass of Ag is added has a specific resistance of 100 to 150 μΩcm, which tends to decrease slightly. Thus, the specific resistance of the RE bulk superconductor is generally in the range of 100 to 400 μΩcm.
[0017]
When ρs≈ρm and ρs <ρm, there is no possibility that tensile stress is applied to at least the superconductor during the current limiting operation, and a higher withstand voltage can be obtained. Therefore, the specific resistance of the metal material needs to be more than 100 μΩcm and less than 400 μΩcm in accordance with the specific resistance of the superconductor.
[0018]
When the superconductor and the metal material have a rectangular cross section, the adhesion between the superconductor and the metal material can be improved, and a shunt from the superconductor to the bypass metal at the start of the current limiting operation occurs in a shorter time, The thermal load on the superconductor can be reduced.
[0019]
The use of a superconductor having a higher specific resistance (ρ) as a current limiting element is desirable in design because a current limiter having a higher resistance is possible. However, since a large amount of additive lowers the superconducting properties, particularly the critical current density (Jc) itself, it is necessary to select an additive amount that improves ρ · Jc. As an example, when Fe is added in an amount of 0.6% by mass, ρ is improved about twice and Jc is reduced about 0.8 times, so that ρ · Jc is improved about 1.6 times. For Zn, Ni, Co, Cr, Mg, etc., there is a region where ρ · Jc exceeds 1 at an addition amount of 0.05 to 2 mass%.
[0020]
Ni-based and Cr-alloyed alloys such as Nichrome, Hastelloy, Inconel, Ti alloys, etc. as the metal material having the same level of resistivity as RE-based bulk superconductors and RE-based bulk superconductors containing additives In addition, since it exhibits a behavior in which an appropriate compressive stress is applied with respect to a temperature change of thermal expansion, it is desirable as a metal material constituting the bypass circuit. In particular, Ti alloys are particularly desirable because their thermal expansion behavior is consistent with that of RE bulk superconductors within 10%. Nichrome and Ti alloy have insufficient adhesion to these metals with ordinary solder, so the surface of Nichrome is coated with Sn-Pb solder using zinc chloride-ammonium chloride flux. Further, it is desirable to form a silver alloy film on the bonding surface of the Ti alloy and then bond it to the superconductor.
[0021]
The superconducting current limiting element needs to be attached to the substrate or the like in some form. When it is completely fixed to a substrate such as a mounting frame or a current introduction electrode, rapid thermal expansion occurs during current limiting operation, and the metal material that constitutes the RE bulk superconductor and bypass circuit is caused by the compressive stress received from the fixed part. It bends and cracks are likely to occur in the superconductor. In order to prevent such damage to the current limiting element, in order to release the stress due to thermal expansion during the current limiting operation, instead of fixing the entire current limiting element, a certain part is fixed, It is necessary to take a structure that can be expanded and contracted. The direction of expansion during the current limiting operation is the energization direction, and it is necessary to have a structure that can move in this direction. However, because the bending stress is likely to occur due to the relationship with the material surrounding the element, the energization direction It is desirable to have a guiding structure so that it can expand.
[0022]
The current limiter needs to quickly return to the superconducting state after the short-circuit current stops and the current limiting operation ends. The current limiting element in which the bypass metal is bonded to the superconductor cannot quickly release the heat generated during the current limiting operation when the cross-sectional area of the metal material increases. Therefore, a long time is required for the superconductor to return to the original cooling temperature, and the recovery time becomes long. The cross-sectional area of the bypass metal affixed to the superconductor only needs to be within a range where sufficient mechanical strength can be obtained.When controlling the amount of shunt, an external resistor that is not in thermal contact with the superconductor is used. That's fine. The external resistor is preferably a nichrome alloy or the like with a small specific resistance temperature change.
[0023]
【Example】
Example 1
Using a bulk material (Y-based QMG) in which Y ₂ BaCuO ₅ is finely dispersed in YBa ₂ Cu ₃ O _7-x , the current path cross-sectional area shown in Fig. 1 is 0.8 × 2.2mm ² and the effective length is about 250mm. Then, a meander-shaped current limiting element 1 having an Ag—Au alloy thin film with a thickness of about 5 μm on the surface was produced. At this time, the c-axis of YBa ₂ Cu ₃ O _7-x was parallel to the normal line of the plate surface, and the specific resistance at 100 K was 155 μΩcm 2.
[0024]
To such a superconductor, meandering Ti alloys (Ti-6Al-4V) 2 and 3 having a thickness of 0.6 mm except for the electrode portion shown in FIG. 1 were attached from both sides by soldering. The specific resistance of the Ti alloy at 100K was 175 μΩcm, and an Ag—Au alloy film was formed in advance on the Ti alloy adhesion surface by 1 μm.
[0025]
As shown in FIG. 2, a 5 mΩ NiCr external bypass resistor 4 was attached between the folded portions. Furthermore, a resin added with filler is embedded in the gap between the meandering elements to which the Ti alloy is attached, and at the same time, a glass fiber reinforced plastic (GFRP) plate 5 having a thickness of 0.3 mm is used except for the electrode portion. Pasted from both sides. The obtained current limiting element was solder-connected to the copper electrode 6 attached to the holder 8 at the current terminal portion. Also, on the opposite side of the electrode, a guide 7 is provided without being fixed to the holder so that the element can extend during the current limiting operation, so that the element can be expanded and contracted in the energizing direction. FIG. 2 shows the current limiting element thus attached to the holder.
[0026]
The current limiting element was measured by cooling the current limiting element in liquid nitrogen and applying a half-wave sine wave current with a pulse width of 4.1 ms. As a result, when there is no current limiting element, a voltage of 210 V (8.5 V per cm) is applied to the whole meandering current limiting element without damage as shown in FIG. It was found that the current can be limited to 2.1kA.
[0027]
As a comparative example, a current limiting element was manufactured under the same conditions except that no Ti alloy was attached, and a current application experiment was conducted.A maximum voltage of 62.5 V (2.5 V per 1 cm) was applied when a current of 2.8 kA was applied at the peak value. After recording, burnout occurred. This comparison confirmed the effectiveness of the metal bypass.
[0028]
(Example 2)
Using a bulk material (silver-added Gd-based QMG) in which Gd ₂ BaCuO ₅ and silver particles are finely dispersed in GdBa ₂ Cu ₃ O _7-x , the current path cross-sectional area shown in FIG. 4 is 0.8 × 2.0 mm ² , effective length A meander-shaped current limiting element 11 having a thickness of about 330 mm and an Ag—Au alloy thin film having a thickness of about 2 μm on the surface was produced. At this time, the c-axis of GdBa ₂ Cu ₃ O _7-x was parallel to the normal of the plate surface, and the specific resistance at 100 K was 115 μΩcm.
[0029]
On such a superconductor, meander-shaped NiCr alloys 12 and 13 having a thickness of 0.7 mm except for the electrode portions shown in FIG. 4 were attached from both sides by soldering. The specific resistance of the NiCr alloy at 100K was 120 μΩcm, and a Sn—Pb solder film of about 10 μm was applied to the adhesion surface of the NiCr alloy.
[0030]
Thereafter, a 4 mΩ NiCr external bypass resistor was attached between the folded portions as shown in FIG. Further, a resin added with a filler was embedded in the gap between the meander-like elements pasted with NiCr, and at the same time, a 1.0 mm-thick GFRP plate was pasted using the resin except for the electrode portion. The obtained current limiting element was solder-connected to the electrode attached to the holder at the current terminal portion. In addition, since the electrode is in the center of the side surface, guides are provided on both sides of the folded portion so that the element can extend during the current limiting operation so that the electrode can be expanded and contracted in the energizing direction.
[0031]
The current limiting element was measured by cooling the current limiting element in liquid nitrogen and applying a half-wave sine wave current with a pulse width of 4.1 ms. As a result, when there is no current limiting element, under the condition that 4.2 kA flows at the peak value, the whole meandering current limiting element bears a voltage of 247 V (7.5 V per cm) and is limited to 2.3 kA. I understood that I can flow.
[0032]
(Example 3)
Using a bulk material (Fe-doped Y-based QMG) in which Y ₂ BaCuO ₅ is finely dispersed in YBa ₂ Cu ₃ O _7-x to which 0.5% by mass of Fe has been added, the current is the same as shown in FIGS. A meander-type current limiting element having a road cross-sectional area of 1.0 × 2.2 mm ² , an effective length of about 250 mm, and a thin film of an Ag—Au alloy with a thickness of about 2 μm was fabricated. At this time, the c-axis of YBa ₂ Cu ₃ O _7-x was parallel to the normal of the plate surface, and the specific resistance at 100 K was 280 μΩcm.
[0033]
To this superconductor, a meandering Ti alloy (Ti-15V-3Cr-3Sn-3Al) with a thickness of 0.6 mm is used from both sides, except for the electrodes, as shown in FIGS. Affixed with solder. The specific resistance of this Ti alloy at 100K was 200 μΩcm, and an Ag—Au alloy film was formed in advance to a thickness of 1 μm on the bonding surface of the Ti alloy.
[0034]
Thereafter, an external bypass resistor of 7 mΩ NiCr was attached between the folded portions as shown in FIG. In addition, a filler-added resin is embedded in the gap between the meander-type current limiting elements with a Ti alloy attached, and at the same time a 0.3 mm thick glass fiber reinforced plastic (GFRP) plate is used except for the electrodes. , Pasted. The obtained current limiting element was solder-connected to the electrode attached to the holder at the current terminal portion. The opposite side of the electrode is not fixed to the holder so that the element can extend during the current limiting operation, and a guide is provided so that the element can be expanded and contracted in the energizing direction. The current limiting element was measured by cooling the current limiting element in liquid nitrogen and applying a half-wave sine wave current with a pulse width of 4.1 ms. As a result, when there is no current limiting element, under the condition that 4.2 kA flows at the peak value, the entire meandering current source element bears a voltage of 237 V (9.5 V per cm) and is limited to 1.9 kA. I understood that I could do it.
[0035]
【The invention's effect】
As described above, the current limiter of the present invention can endure a high voltage without burning out, and has high durability against the thermal shock accompanying current limiting operation, so its industrial effect is enormous. is there.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a current limiting device having electrodes at side end portions of the device and metal bypasses attached from both sides. FIG. 2 is a diagram showing an example of a superconducting current limiting device according to the present invention. 3] Graph showing the current-carrying characteristics of the current-limiting element [Fig. 4] Diagram showing an example of a current-limiting element with an electrode in the center of the side of the element and metal bypass attached from both sides
1 Current limiting element 2, 3 Ti alloy (metal bypass)
4 External bypass resistance 5 Glass fiber reinforced plastic plate 6 Copper electrode 7 Guide 8 Holder 11 Current limiting element 12, 13 NiCr alloy (metal bypass)

Claims

Single crystalline REBa ₂ Cu ₃ O _7-x (where RE is one or more selected from Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb or Lu) A resistive superconducting fault current limiter using a superconducting bulk material in which a RE ₂ BaCuO ₅ phase is dispersed in the phase, and a bypass circuit is formed in the superconducting current limiting element A metal material pasted structure, the specific resistance of the metal material at 77K is more than 100 μΩcm, and the c-axis of the crystallographic orientation of the superconducting bulk material and the conduction direction of the superconducting current limiting element, A high withstand voltage superconducting fault current limiter, characterized in that the angle formed by is in the range of 60 ° to 120 °.

The current limiting device according to claim 1, wherein a specific resistance of the superconductor in a normal state is smaller than a specific resistance of the metal material.

3. The current limiting device according to claim 1, wherein a specific resistance at 77 K of the metal material constituting the bypass circuit is 400 μΩcm or less.

A metal material having a rectangular cross section constituting the bypass circuit is attached to the superconducting current limiting element having a rectangular cross section in a plate shape, a rod shape, a meander shape, or a coil shape, at least from above and below or from the left and right. The current limiting device according to claim 1.

The current limiting device according to any one of claims 1 to 4, wherein at least a resin or a glass fiber reinforced plastic is disposed around the superconducting current limiting element.

The current limiting device according to any one of claims 1 to 5, wherein a superconducting bulk material to which at least one of Fe, Zn, Ni, Co, Cr, and Mg is added in an amount of 0.05 to 2% by mass is used.

The current limiting device according to any one of claims 1 to 6, wherein the metal material constituting the bypass circuit is any one of a Ni alloy, a Cr alloy, and a Ti alloy.

The current limiting device according to any one of claims 1 to 7, wherein at least a part of the superconducting current limiting element has a movable structure during a current limiting operation.

9. The current limiting device according to claim 8, wherein the moving direction of the superconducting current limiting element is an energizing direction and has a structure for guiding the moving direction.

The current limiting device according to any one of claims 1 to 9, wherein the current limiting device has an external bypass resistance that contacts only partly with the superconducting material and does not contact with the entire surface.

The current limiting device according to claim 1, wherein the current limiting device has a withstand voltage of 7.5 V / cm 2 or more.