王銀順

(1. 新能源電力系統(tǒng)國家重點實驗室， 華北電力大學， 北京 102206； 2. 高壓與電磁兼容北京市重點實驗室， 華北電力大學， 北京 102206)

基于第二代高溫超導帶材的高載流超導導體研究進展

王銀順1,2

(1. 新能源電力系統(tǒng)國家重點實驗室， 華北電力大學， 北京 102206； 2. 高壓與電磁兼容北京市重點實驗室， 華北電力大學， 北京 102206)

由于其高臨界電流密度以及優(yōu)越的機械性能和電磁特性，第二代高溫超導帶材(也叫涂層導體)在高溫低場的電力傳輸和低溫高場下的磁體應用具有廣闊的應用前景。在電力傳輸?shù)牡蛨鰬弥?，高溫超導導體在低電壓大容量場合需要幾千安培甚至上萬安培的傳輸電流。在大型高場磁體應用方面，為了避免由于過高電感在磁體失超和快速關斷過程中的感應高壓問題，大載流容量、高電流密度高溫超導導體在運行于4.2K及以下溫度的大型高場超導磁體方面具有很好的應用前景。近年來，基于第二代高溫超導帶材，國際上相繼提出了幾種高載流容量的高溫超導導體，本文介紹幾種高溫超導導體的結構及研發(fā)現(xiàn)狀和進展，并對其結構、性能和工藝進行簡單的比較和評述。

第二代高溫超導帶材； 電纜； 涂層導體； 導體； 股線； 管內(nèi)電纜導體； 盧瑟福電纜

1 引言

在過去二十幾年中，實用高溫超導材料的研究取得了很大進展。采用相對簡單的粉末管裝法(Powder-in-Tube, PIT) 以Bi2223為代表的第一代高溫超導帶材BSCCO實現(xiàn)了工業(yè)化生產(chǎn)[1]。但是，由于第一代高溫超導帶材使用貴金屬Ag，且在高場下性能比第二代高溫超導帶材REBCO差，近年來國際上BSCCO帶材的生產(chǎn)逐漸停止。以REBCO為代表的第二代高溫超導帶材(涂層導體)經(jīng)過十幾年的發(fā)展，制備工藝逐漸成熟。目前，第二代高溫超導帶材基板及織構化隔離層的制備工藝有離子束輔助沉積(Ion Beam-Assisted Deposition, IBAD)[2]，軋制輔助雙軸織構(Rolling-Assisted Biaxially Textured Substrate，RABiTS)[3]和傾斜基板沉積法 (Inclined Substrate Deposition，ISD)[4]。在基板上采用脈沖激光沉積法(Pulsed Laser Deposition, PLD)[5]、化學氣相沉積法(Chemical Vapor Deposition, CVD)[6],化學溶液沉積法(Chemical Solution Deposition, CSD)[7]， 金屬有機沉積法(Metal Organic Deposition, MOD)[8]， 金屬有機化學氣相沉積法(Metal Organic Chemical Vapor Deposition, MOCVD)[9]，循環(huán)沉積反應共蒸發(fā)法(Reactive Co-Evaporation by Cyclic Deposition and Reaction, RCE-CDR)[10], 以及沉積反應共蒸發(fā)法(Reactive Co-Evaporation by Deposition and Reaction，RCE-DR)[11，12]。國內(nèi)外許多公司具有生產(chǎn)單根百米量級超導帶材長度的能力[13-16]。 尤其是日本古河電氣公司的子公司Superpower公司通過在ReBCO薄膜中摻雜Gd和Zr技術，超導帶材的臨界電流各向異性得到極大改善，同時其機械特性和高場載流能力得到顯著提高[17]。此外，韓國SuNAM公司采用改進的RCE-DR工藝，超導帶材的載流能力取得了很大提高，液氮自場下臨界電流達到794 A/cm，在650m長度上獲得極高的臨界電流均勻性，其生產(chǎn)速度達到120m/h[18]。值得一提的是，與其他高溫超導體相比較，第二代高溫超導帶材的機械性能中沿c軸方向的臨界拉應力較差。

盡管如此，單根超導帶材載流有限，多根并聯(lián)使用不可避免。常用低溫NbTi超導線制作電纜導體，容易實現(xiàn)扭絞和換位，目前商業(yè)化高溫超導帶材厚度在0.1mm左右，寬度在2～12mm范圍，常規(guī)制作多根并聯(lián)超導電纜導體過程中的扭絞和換位非常困難。為了解決這些技術難題，近幾年國際上提出了幾種基于第二代高溫超導帶材的超導導體結構，每種電纜導體在交流損耗、加工工藝、工程電流密度等方面各有利弊。本文介紹幾種基于第二代高溫超導帶材的高載流電纜導體研發(fā)進展情況，簡要分析比較各種超導電纜導體的技術特點，為高載流高溫超導導體在高溫低場和低溫高場的應用提供有益參考。

2 RAAC導體/電纜

德國是進行基于第二代高溫超導帶材進行超導導體/電纜研發(fā)的最早國家，為了均流和減小交流損耗[19-21]，2006年德國卡爾斯魯厄研究中心(Forschungszentrum Karlsruhe, FZK) 的 Goldacker W教授提出了由第二代高溫超導帶材組成的完全換位導體的方法[22,23]，通常簡稱RACC(Roebel Assembled Coated Conductor)。將一定寬度的第二代高溫超導帶材沿著長度方向周期性地裁剪成“梯形”，可以采用氣動沖切或激光切割方法進行裁剪。然后進行編織形成Roebel電纜導體[24,25]。

RACC導體/電纜最顯著的特點在于其與眾不同的結構，這種結構載流均勻、可以減小交流損耗，使得RACC導體/電纜具有低交流損耗和高載流能力的特點[19]。研究發(fā)現(xiàn)寬度較小的高溫超導導體和位置交換的超導結構可以減少交流損耗，因為磁場的磁力線可以進入超導帶材的內(nèi)部間隙，但是在生產(chǎn)上細絲狀的高溫超導導體并不能實現(xiàn),并且簡單的切割不利于實際生產(chǎn)[20-22]。RACC超導/電纜結構由特定形狀的涂層導體相互換位組裝而成[23]，其導體/電纜圖片如圖1所示，常用涂層導體經(jīng)過手工裁剪的“梯形”涂層導體實物如圖1(a)所示，手工編織加工完成后的RACC導體/電纜試樣如圖1(b)所示。通過氣動沖壓切割和機械編織的RACC導體/電纜實物照片如圖2所示。

圖1 用涂層導體手工編織的RACC導體/電纜Fig.1 RACC / cable manually woven by using CC

圖2 機械編制的RACC導體/電纜試樣Fig.2 RACC/cable woven by machine

為了盡量減小帶材寬度，RACC導體/電纜中帶材之間的換位是利用正反梯形相互交替的方法來實現(xiàn)的，并有利于多根的換位組裝，可以構成有更高電流容量的RACC導體/電纜[24，25]。RACC導體/電纜加工工藝日漸成熟，Goldacker W, Frank A等人采用45根更薄的涂層導體進行RACC的制作[26]。FZK手工制作的 6m長 RACC導體/電纜如圖3所示，該導體/電纜由17根超導帶材組成，帶材寬度為5.5mm，換位長度為226mm, 77K自場下臨界電流為2.05kA[27]。

圖3 RACC 導體/電纜實物Fig.3 Overview of RACC/cable

研究發(fā)現(xiàn)RACC導體/電纜具有臨界電流密度高、在交變磁場和交流載流下均流的特點，而且在垂直場下的交流損耗也顯著降低[24]。目前，F(xiàn)ZK通過手工只能制作5m長RACC導體/電纜。為了避免超導帶材過度彎曲和塑形形變，RAAC導體的機械繞制非常復雜。通過與新西蘭工業(yè)研究有限公司(Industrial Research Ltd，IRL) 合作， 2009年首次實現(xiàn)了由5mm寬的15根超導帶材繞制的7.5m長RACC導體/電纜[28-30]。對常規(guī)電纜生產(chǎn)線進行部分改造，即可進行RACC導體/電纜的加工。在稍加改造的常規(guī)電纜生產(chǎn)線上加工RACC導體/電纜的加工現(xiàn)場如圖4所示，可以實現(xiàn)實用長度RACC導體/電纜的生產(chǎn)和加工。

圖4 IRL電纜公司RACC加工生產(chǎn)線[29]Fig.4 Production line o IRL-General Cable for assembling RACC

新西蘭惠靈頓維多利亞大學等單位采用激光切割技術切割超導帶材[30]，實現(xiàn)了商業(yè)化RACC導體/電纜生產(chǎn)，為歐洲委員會支持的EuCARD-2未來磁體計劃提供的34m 長的RACC導體/電纜實物[31-34]如圖5所示。

圖5 新西蘭惠靈頓大學提供的34m長的RACC導體/電纜Fig.5 RACC /cable Cable supplied by Victoria University of Wellington, New Zealand

用10kA級RACC導體/電纜首次繞制完成了Feather-M0跑道型線圈，并進行了實驗，由RACC導體/電纜繞制的Feather-M2跑道型線圈三維效果圖如圖6所示，該線圈在Feather-M0實驗完成后，進行實際尺寸的Feather-M2跑道型線圈的繞制。

圖6 全尺寸RACC導體/電纜繞制的三維模型線圈Fig.6 Rendered image of the full three-dimensional Feather-M2 coil model by RACC/cable

考慮到大型空中飛行器電力系統(tǒng)電壓低(<1.0kV)、功率和重量不斷提高的情況，2016年俄羅斯科學研發(fā)電纜研究所(the Russian Scientific Research and Development Cable Institute, SRDCI) 探討RACC導體/電纜在飛行器電力系統(tǒng)中的應用可行性[28]。此外，RACC導體/電纜在大型軍用艦船、互聯(lián)網(wǎng)數(shù)據(jù)中心等低壓高電流、大容量輸電場合也具有潛在應用前景。

RAAC導體/電纜的優(yōu)點是實現(xiàn)了完全換位，電流均勻分布；缺點是垂直帶面磁場高，對臨界電流影響大。臨界電流衰減大，浪費帶材、成本高、力學性能差、不緊湊，需要環(huán)氧浸澤固化。根據(jù)SRDCI研究，RACC導體/電纜的損耗高于單相冷絕緣電纜和三軸電纜，由于磁場臨界電流衰減和由于切割帶材臨界電流衰減比單相冷絕緣電纜和三軸電纜分別高1倍和10倍，超導帶材用量也比單相冷絕緣電纜和三軸電纜分別多2倍和1倍[28]，因此作為輸電系統(tǒng)，RACC導體/電纜的應用值得商榷。在高場磁體應用方面應更具有優(yōu)勢。

3 CORC導體/電纜

CORC(Conductor On Round Core)導體/電纜是由美國國家標準技術研究所(National Institute of Standard Technology, NIST)與Colorado大學合作，提出的一種結構緊湊柔性超導導體，這種導體具有低電感、低交流損耗和高臨界電流的特點[35-37]，擬用于電力直流輸電、空軍及海軍電力傳輸和低溫高場應用。CORC導體/電纜由3部分構成，中心骨架使用的是截面較小的銅棒或銅絞線，中間部分是將高溫超導帶材螺旋纏繞在中心骨架上，最外側部分使用絕緣材料進行包覆，與超導電纜導體類似。并研制出1m長、外徑6.5mm導體，進行了液氮溫度實驗和彎曲接卸性能試驗。在76K溫度自場情況下，其臨界電流達到2796A，彎曲半徑為125mm。其試樣結構截面圖如圖7所示，骨架為直徑5.5mm的銅絞線，繞制8層超導帶材，CORC導體/電纜主視圖如圖7(a)所示；5倍放大截面圖如圖7(b)所示，中心為銅絞線；實物截面圖如圖7(c)所示，導體外徑為6.5mm。黑色區(qū)域為繞制在骨架上的碳紙?，F(xiàn)場加工照片如圖8所示，可以精確控制繞制張力、角度和超導之間的間隙，實現(xiàn)了實用長度的加工工藝，加工的12m長CORC導體/電纜長樣如圖9所示，骨架直徑為5mm，由38根4mm寬、0.1mm厚的古河電氣子公司-SuperPower公司生產(chǎn)的超導帶材繞制而成。

圖7 緊湊型高溫超導導體/電纜示意圖Fig.7 View of compact CORC/cable

圖8 CORC導體/電纜加工現(xiàn)場照片F(xiàn)ig.8 Photo of processing CORC/cable

圖9 12m CORC導體/電纜樣品Fig.9 CORC/cable specimen with 12m in length

CORC導體/電纜中心骨架直徑比超導電纜小很多，所以CORC導體/電纜具有較高的臨界電流密度。CORC導體/電纜的臨界電流密度也會隨著纏繞層數(shù)的增加而隨之增加。CORC導體/電纜的帶材纏繞的方式為螺旋纏繞，所以其磁場平行于帶材表面，因此超導帶材的臨界電流的衰減要比磁場垂直帶材的導體小的多。研究人員制作了不同層數(shù)的CORC導體/電纜，最大的臨界電流為6.8kA，其工程電流密度達到86.58A/mm2[38]。

在2013年，van der Laan D C利用CORC導體/電纜制作了適用于高場20T的高場磁體,該磁體結構在4.2K、19T的測量條件下臨界電流為5.021kA， 并且電流密度非常高，達到了114A/mm2[39]。

4 TSTC 導體/電纜

TSTC(Twisted Stacked-Tapes Cable)導體/電纜是由麻省理工學院(MIT)Takayasu T等人提出的一種新型超導導體，由超導帶材直接堆疊在一起，形成矩形截面超導導體，然后扭絞形成平行排列的高溫超導導體[40-42]，其試樣如圖10所示。

圖10 TSTC導體/電纜樣品Fig.10 TSTC/cable specimen

TSTC導體有著極高的臨界電流密度和良好的彎曲特性，由32根4.0mm寬，0.098mm厚的高溫超導帶材堆疊以200mm扭矩扭絞的TSTC導體/電纜結構股線，端部以Bi2223銀包套帶材與REBCO帶材交替堆疊焊接處理，液氮溫度下，接觸電阻小于10nΩ。臨界電流達到1.5kA,在液氦溫度下可達10kA。由于TSTC導體/電纜將超導帶材平行堆疊，帶材能夠相互支撐，可以防止帶材受到的應力過于集中，并且多根帶材扭絞可以減輕帶材側向彎曲程度，在彎曲半徑為140mm時，由24根帶材組成的TSTC導體/電纜臨界電流退化僅為6%，因此TSTC導體/電纜可用于制作超導線圈[43-45]。

為了對超導帶材進行保護，將超導堆疊導體嵌入有螺旋溝槽的金屬芯導體，外加金屬護套的方式構成一種靈活的超導導體，該導體有良好的機械特性，可應用于大型超導磁體線圈[46-49]。單螺旋溝槽單股和三螺旋溝槽三股TSTC導體/電纜試樣圖片如圖11所示。為了實現(xiàn)更大電流的超導導體，可由單股TSTC導體/電纜并聯(lián)并扭轉可制成更高載流導體。

圖11 帶護套TSTC導體/電纜試樣Fig.11 TSTC /cable specimen with metal sheath

5 簡單堆疊導體(SSC)

100kA 級簡單堆疊導體(Simply-stacked HTS Conductors, SSC)是由日本國立核聚變研究所(the National Institute for Fusion Science, NIFS)提出的一種簡單堆疊超導導體。為了建造螺旋形核聚變演示反應堆，超導線圈導體要在高達13T的磁場下載流能力達到100kA，研究人員采用在銅和不銹鋼套中把超導帶材并排堆疊的方法來構造大電流導體，其結構如圖12所示。圖12中為2排6層的結構，實際結構為3排18層，一共有54根超導帶材構成(帶材寬度10mm，厚度0.22mm)，77K下臨界電流約600A[50]。

圖12 100kA級高溫超導簡單堆疊導體結構Fig.12 Structure of 100-kA class HTS SSC

通過實驗表明，該導體具有很高的載流能力，在4.2K溫度和0.45T磁場下的臨界電流達到118kA，在20K溫度和5.3T外場下臨界電流達到100kA[50]。

6 扭絞圓股線(RS)

2013年，Uglietti D等人提出一種高載流容量超導圓截面結構導體，其結構中心部分類似TSTC導體的布局結構，采用平行的REBCO帶材堆疊扭絞而成，然后使用2根擠有方形溝槽的半圓形截面銅棒將其夾緊，堆疊帶材和銅棒進行鍍錫焊接后扭絞制作成圓截面股線(Round Strand, RS)[51-53]。結構示意和實物圖片如圖13所示。

圖13 圓截面股線結構圖和實物圖片F(xiàn)ig.13 Sketch of the round strand

在77K液氮溫度下每根股線的臨界電流大約為1.15kA。圓截面扭絞股線焊接主要有2種結構：“S”型和“Plus”型，有兩種加工工藝：先扭絞后焊接(first-twisted-then-soldered, TS)，先焊接后扭絞(first-soldered-then-twisted, ST)，如圖14所示[54-56]。

圖14 金屬包套焊接結構示意和實物Fig.14 Schematic view and photo of soldering profile

機械性能實驗表明，“Plus”型加工導體的機械性能優(yōu)于“S”型工藝性能。退火處理可以大大提高彎曲性能，未退火的試樣彎曲半徑約為500mm。在經(jīng)過300℃溫度預退火處理1h后，彎曲半徑可以減小到240mm，彎曲半徑減小一半[54]。

7 HTS-CroCo導體/電纜

HTS-CroCo(HTS-Cross Conductor)導體/電纜是由FZK的Fietz W H等人新近提出的一種新型超導導體，這種結構的導體適用于長距離導體的制作，可以優(yōu)化工程電流密度并簡化導體之間的連接[57，58]。與TSTC導體/電纜和扭絞圓截面股線超導導體類似，由寬度為4mm的超導帶材對稱地堆疊在6mm導體兩側，然后以圓截面銅包套包裹堆疊導體，銅包套與導體之間的間隙以錫填充，中間超導導體可以扭絞。該HTS-CroCo導體/電纜試樣、截面示意圖和其2種截面結構的實物照片如圖15所示。為研究扭絞堆疊超導帶材加金屬護套擠壓(即旋鍛)的影響，采用機械方法對纏繞焊錫絲的試樣進行不同外徑下的擠壓、旋鍛處理實驗， HTS-CroCo導體/電纜試樣截面圖如圖16所示，HTS-CroCo導體/電纜超導芯纏繞Pb37Sn63焊錫絲并加外銅護套如圖16(a)所示；擠壓到直徑為8.9mm時截面如圖16(b)所示；擠壓到直徑為8.5mm時截面如圖16(c)所示。銅管外套內(nèi)外徑分別為8.5mm和9.5mm。外徑擠壓到8.9mm時超導帶開始變形，當擠壓外徑減小到8.5mm時，超導帶材嚴重變形。經(jīng)過試驗驗證，擠壓直徑9mm是安全的。

圖15 HTS-CroCo導體/電纜結構示意圖和試樣及其截面圖片F(xiàn)ig.15 Schematic view and specimen photo and cross sections of two types of HTS-CroCo/cable specimen

圖16 旋鍛對HTS-CroCo導體/電纜的影響Fig.16 Influence of jacketing with compaction by rotary swaging on HTS-CroCo cable

對于圓形截面的股線，很難以1種連續(xù)的方式進行扭轉。采用HTS-CroCo導體/電纜結構，則可以依據(jù)形狀配合的方式連續(xù)的扭轉超導線芯，制作超導線芯的速度可以達到3m/min, 適宜長距離導體的制作。此外，通過結構優(yōu)化，這種結構的導體工程電流密度可達700A/mm2，近期目標是在2017年該導體在77K溫度自場條件下工程電流密度大于650A/mm2[59]。目前，HTS-CroCo導體/電纜短樣機械加工1.1m實驗完成，加工工藝基本成熟，可以進行實用長度的加工。

對于HTS-CroCo導體/電纜之間的連接、端部連接等技術進行了系統(tǒng)實驗研究[60]，同時對不同骨架材料的溝槽加工等技術進行理論和實驗研究[61]，為HTS-CroCo導體/電纜和由其制成的CICC導體和Rutherford電纜實用化儲備關鍵技術。

8 準各向同性導體(QI-S)

由上文可知，國際上基于涂層導體提出的主要6種超導導體，外磁場下其任一截面上臨界電流仍然具有各向異性的缺點。華北電力大學提出了臨界電流準各向同性的高溫超導導體概念[62，63]。其概念結構設計如圖17所示，分別為圓截面和方形截面高溫超導導體。導體由4股直接堆疊子股對稱排列而成，外面以金屬護套包裹。金屬包套可以是銅、鋁或不銹鋼。3種不同金屬包套的圓形和方形截面的導體短樣圖片如圖18所示，超導線采用由古河電氣子公司SuperPower公司生產(chǎn)的涂層導體。股線由4股堆疊股線對稱組合排列，2股橫向排列，2股縱向排列，每股子股線由18根2mm×0.1mm堆疊組成，單根帶材在77K溫度和自場條件下臨界電流為48A。

圖17 圓形和方形截面臨界電流準各向同性股線示意圖Fig.17 Schematic view of quasi-isotropic critical current strand specimen with circular and square cross sections

圖18 準各向同性股線短樣照片F(xiàn)ig.18 Photos of quasi-isotropic stand specimen

對3種包套材料的導體結構和加工工藝分別進行了系統(tǒng)研究，制作不同包套材料的股線試樣。在液氮溫度下進行了理論分析和實驗。依據(jù)不同電流下股線自場和超導帶材臨界電流隨磁場的變化特性，理論計算在77K溫度和自場臨界電流2.38kA，實驗臨界電流值為2.28kA, 兩者接近。同時，在77K溫度下，理論分析和實驗測量了在外磁場0.1T和0.5T下股線臨界電流的各向異性，歸一化臨界電流隨外磁場角度的變化如圖19所示。實驗表明在0.5T以下，超導股線臨界電流各向異性小于5%，驗證了該股線臨界電流的準各向同性[64-66]。

圖19 歸一化臨界電流隨外磁場角度的變化Fig.19 Plot of normalized critical current against angle of external magnetic field

此外，對該股線也分別進行了穩(wěn)定性、機械特性、交流損耗等理論研究和實驗研究[67-72]，為股線的實際應用奠定了初步基礎。

為實現(xiàn)實用長度股線的機械加工工藝，依據(jù)現(xiàn)有電力光纜生產(chǎn)線生產(chǎn)工藝，對圓截面超導股線生產(chǎn)工藝進行概念設計，其生產(chǎn)示意如圖20所示。采用成熟的激光焊接技術焊接金屬包套，使用不同結構磨具可以實現(xiàn)方形和圓形截面金屬包套的焊接。

圖20 圓截面實用長度股線加工成產(chǎn)示意Fig.20 Schematic of fabricating methods for Q-IS with round cross section

在現(xiàn)有光纜生產(chǎn)線上，采用成熟的激光焊接光纖技術進行的臨界電流準各向的高溫超導股線的加工。在中天集團科技股份有限公司光纜生產(chǎn)線上，加工現(xiàn)場如圖21所示，完成了10m長度超導股線的加工，加工完成的導體如圖22所示。通過10m長度股線的成功加工，可以實現(xiàn)長度的高溫超導股線的加工[62,67]。

圖21 臨界電流準各向同性超導股線加工現(xiàn)場圖片F(xiàn)ig.21 Overview of field fabrication equipment for quasi-isotropic starnd

圖22 加工完成的10m長度臨界電流準各向同性股線Fig.22 Quasi-isotropic stand in 10m length fabricated by production line

9 CICC導體

以上7種超導導體，除了應用于高溫低場超導電力應用外，另一重要領域是低溫高場下的大型超導磁體應用，將導體制作成管內(nèi)電纜導體(Cable-In-Conduit Conductor, CICC)。

9.1TSTC導體/電纜-CICC導體

基于TSTC導體/電纜，設計成CICC導體，如圖23所示，將銅或鋁棒擠壓加工成螺旋形多溝槽骨架，溝槽中放置堆疊超導線，骨架中心有孔，用以低溫介質流過，超導帶外放置銅線作為襯墊，外面鎧裝不銹鋼, 通過測試相關機械及電磁參數(shù)取得了優(yōu)化結構的電纜及更高的載流能力[73-75]。經(jīng)過近3年的研發(fā)，CICC導體能夠進行實用長度生產(chǎn)。由TRATOS Cavi S.p.A公司連續(xù)加工的150m長度的CICC導體結構如圖24所示。中心為鋁制骨架，溝槽通過460℃熱擠壓成形。

圖23 基于TSTC導體/電纜的CICC導體結構Fig.23 CICC conceptual design of CICC based on TSTC cable

圖24 TRATOS Cavi S.p.A 連續(xù)加工150m長CICC導體Fig.24 Image of spool collecting 150m aluminum slotted core manufactured by using continuous facility at TRATOS Cavi S.p.A

美國MIT基于TSTC導體/電纜提出另一種結構CICC導體結構概念，是9.1節(jié)CICC的進一步推廣。相當于將9.1節(jié)中的CICC導體作為子纜，進一步組合成大電流容量的CICC導體，其典型截面結構概念設計之一[49,76-80]如圖25所示。該CICC導體由6股子股線扭絞構成，每個子股線由3組TSTC導體/電纜扭絞構成，形成3×6結構CICC導體，中心為冷卻通道。目前，此種CICC導體仍處于短樣設計、實驗研發(fā)階段，未實現(xiàn)實用長度生產(chǎn)工藝。

圖25 3×6 CICC導體結構設計Fig.25 Design of 3×6 CICC

9.2CORC導體/電纜-CICC導體

盡管CORC導體/電纜工程電流密度低于其他導體，但是其機械性能好，對于高場應用的CICC導體具有很好的應用前景。其CICC結構如圖26所示，以鋁鎧裝、中空管為冷卻通道、由6根CORC導體/電纜扭絞組成[81-84]。1.7m CICC試樣[85，86]如圖26(b)所示，對于其端部連接技術基本完成，還未實現(xiàn)實用長度的成產(chǎn)。

圖26 基于CORC導體/電纜的CICC短樣結構示意和試樣.Fig.26 Schematic view and picture of CICC specimen based on CORC cables

此外，為了將 RACC導體/電纜應用于CICC導體，F(xiàn)ZK已經(jīng)開展了鋁合金和無氧銅CICC骨架溝槽工藝研究[61]，其骨架結構如圖27所示，并開始研發(fā)基于RACC導體/電纜的CICC導體研究。

圖27 Al6036合金和無氧銅骨架結構Fig.27 Example of possible formers as proposed by using Al6063 alloy and OFHC Cu

10 Rutherford電纜

高場大電流容量導體除了CICC外，為了降低交流損耗，另一種可換位大載流導體是Rutherford 電纜，由多根導體繞制在扁平狀導體上，其結構示意如圖28所示。原則上講，上述7種超導導體/電纜都可以用來制作Rutherford電纜[59], 即所謂的涂層導體Rutherford電纜 (Coated Conductor Rutherford Cable, CCRC)。下面簡單介紹目前已經(jīng)開始進行研發(fā)的Rutherford 電纜的情況。

圖28 Rutherford 電纜結構示意圖Fig.28 Schematic view of Rutherford cable

10.1RACC導體/電纜-Rutherford電纜

2011年，F(xiàn)ZK開始進行基于RACC導體/電纜的Rutherford 電纜的研究，由RACC導體/電纜繞制的Rutherford 電纜試樣如圖29所示，目標是研發(fā)10kA Rutherford電纜[87]。

圖29 基于RACC導體/電纜導體的Rutherford 電纜試樣Fig.29 Rutherford cable specimen made from RACC/cable

10.2HTSCroCo導體/電纜-Rutherford電纜

基于HTS Croco導體/電纜設計Rutherford電纜的概念也是由FZK提出，用HTS CroCo導體/電纜繞制在扁平銅或鋁板上制成。HTS CroCo導體/電纜由厚度0.1mm和寬度4mm+6mm+4mm的第二代高溫超導帶材制成的，其截面示意如圖30所示。

圖30 11根HTS-CroCo導體/電纜鎧裝繞制的Rutherford電纜截面示意圖Fig.30 Cross section of Rutherford cable with 11 HTS CroCo cables and jacked

10.3扭絞圓截面股線(RS)-Rutherford電纜

2015年，Uglietti D等人在單根扭絞圓截面股線的基礎上，將20根單根股線沿銅板繞制Rutherford電纜結構，這種超導體結構的實物如圖31所示，整個導體寬70mm厚19mm，長度2m， 在77K自場下，實驗得到其臨界電流1.15kA, 其n值達到25，估算在4.2K溫度12T下，其工程電流密度達790A/mm2，大于同等條件下Nb3Sn的688A/mm[55,88-93]。

圖31 Rutherford 電纜實物圖Fig.31 Picture of prototype Rutherford cable

11 結論

國際上第二代高溫超導帶材工藝成熟，實現(xiàn)了商業(yè)化生產(chǎn)，但是由于單根帶材載流有限，國內(nèi)外提出了7種基于第二代高溫超導帶材的超導導體并進行相關關鍵技術工藝研究，為其高溫低場電力應用和低溫高場下的應用奠定了堅實基礎。同時， 7種超導導體中的4種即RACC 導體/電纜、CORC導體/電纜、CroCo導體/電纜和圓截面股線(RS)已經(jīng)研制成Rutherford 電纜短樣；TSTC導體/電纜也已研制成實用長度CICC導體，為高場大電流應用做好技術了儲備。

7種超導導體/電纜或股線的結構特征、臨界電流各向異性特性以及工藝方法總結見表1，其中除了RACC導體/電纜必須使用第二代高溫超導帶材外，其他6種導體/電纜或股線不排除使用第一代高溫超導帶材。盡管有些方法和工藝對于實用長度導體的加工還不完全成熟，需要進一步研究，但是它們對于未來高場和大載流應用場合具有潛在的應用價值。

表1 7種超導導體/股線的結構和臨界電流各向異性特性Tab.1 Geometrical structures and characteristics for seven types of superconducting conductors/strands

縱觀國內(nèi)外高溫超導導體的研究進展，國外提出的6種超導導體已經(jīng)進行了溫度77K和4.2K下的研究和Rutherford電纜及CICC導體研究，而國內(nèi)只有1種準各向同性股線(QI-S)研發(fā)，雖然實現(xiàn)了實用長度的生產(chǎn)工藝，但是只進行了液氮溫度(77K)的實驗研究，缺乏液氦溫度(4.2K)下的研究和基于準各向同性股線的Rutherford電纜及CICC導體的實驗研究。就目前看，這種差距趨勢還在逐步擴大，希望引起國內(nèi)相關管理部門和研究部門的關注。

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Recentstatusanddevelopmentofhighcurrentconductormadefrom2gHTStapes

WANG Yin-shun

(1. State Key Lab. of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China; 2. Beijing Key Lab. of HV and EMC, North China Electric Power University, Beijing 102206, China)

The second-generation high-temperature superconductors (HTS) tapes, so called REBCO coated conductor (CC), are attractive for power transmission at liquid nitrogen temperature and high-field application at low temperatures because of their high critical current density and the excellent mechanical performance as well as electro-magnetic characteristics. For the former application, high-current cables or conductors made from HTS tapes with capacity of tens kA up to more than 100kA are desirable. In the latter application, high-current HTS conductors are essential for larger high-field magnets operated at 4.2K or lower to avoid high inductances which would cause high-voltage breakdown in case of quench or fast shutdown. In recent years, several prototypes of HTS conductors, consisting of 2G HTS tapes, were successively proposed internationally. This paper presents an overview of such configurations as well as their progress and status, and briefly reviews their geometrical structure and performance as well as processing technology.

second high temperature superconducting(2G HTS) tape; cable; coated conductor(CC); conductor; strand; cable-in-conduit conductor(CICC); Rutherford cable

2017-05-08

國家自然科學基金項目(51477053)

王銀順(1965-), 男, 河北籍, 教授, 博士, 研究方向為超導電力技術。

10.12067/ATEEE1705027

1003-3076(2017)11-0021-15

TM26