王銀順

(1. 新能源電力系統(tǒng)國家重點(diǎn)實(shí)驗(yàn)室， 華北電力大學(xué)， 北京 102206； 2. 高壓與電磁兼容北京市重點(diǎn)實(shí)驗(yàn)室， 華北電力大學(xué)， 北京 102206)

基于第二代高溫超導(dǎo)帶材的高載流超導(dǎo)導(dǎo)體研究進(jìn)展

王銀順1,2

(1. 新能源電力系統(tǒng)國家重點(diǎn)實(shí)驗(yàn)室， 華北電力大學(xué)， 北京 102206； 2. 高壓與電磁兼容北京市重點(diǎn)實(shí)驗(yàn)室， 華北電力大學(xué)， 北京 102206)

由于其高臨界電流密度以及優(yōu)越的機(jī)械性能和電磁特性，第二代高溫超導(dǎo)帶材(也叫涂層導(dǎo)體)在高溫低場的電力傳輸和低溫高場下的磁體應(yīng)用具有廣闊的應(yīng)用前景。在電力傳輸?shù)牡蛨鰬?yīng)用中，高溫超導(dǎo)導(dǎo)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(yīng)用方面，為了避免由于過高電感在磁體失超和快速關(guān)斷過程中的感應(yīng)高壓問題，大載流容量、高電流密度高溫超導(dǎo)導(dǎo)體在運(yùn)行于4.2K及以下溫度的大型高場超導(dǎo)磁體方面具有很好的應(yīng)用前景。近年來，基于第二代高溫超導(dǎo)帶材，國際上相繼提出了幾種高載流容量的高溫超導(dǎo)導(dǎo)體，本文介紹幾種高溫超導(dǎo)導(dǎo)體的結(jié)構(gòu)及研發(fā)現(xiàn)狀和進(jìn)展，并對其結(jié)構(gòu)、性能和工藝進(jìn)行簡單的比較和評述。

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

1 引言

在過去二十幾年中，實(shí)用高溫超導(dǎo)材料的研究取得了很大進(jìn)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(dǎo)帶材BSCCO實(shí)現(xiàn)了工業(yè)化生產(chǎn)[1]。但是，由于第一代高溫超導(dǎo)帶材使用貴金屬Ag，且在高場下性能比第二代高溫超導(dǎo)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(dǎo)帶材(涂層導(dǎo)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(dǎo)帶材基板及織構(gòu)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(gòu)(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(xué)氣相沉積法(Chemical Vapor Deposition, CVD)[6],化學(xué)溶液沉積法(Chemical Solution Deposition, CSD)[7]， 金屬有機(jī)沉積法(Metal Organic Deposition, MOD)[8]， 金屬有機(jī)化學(xué)氣相沉積法(Metal Organic Chemical Vapor Deposition, MOCVD)[9]，循環(huán)沉積反應(yīng)共蒸發(fā)法(Reactive Co-Evaporation by Cyclic Deposition and Reaction, RCE-CDR)[10], 以及沉積反應(yīng)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(dǎo)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(shù)，超導(dǎo)帶材的臨界電流各向異性得到極大改善，同時(shí)其機(jī)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(jìn)的RCE-DR工藝，超導(dǎo)帶材的載流能力取得了很大提高，液氮自場下臨界電流達(dá)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(dá)到120m/h[18]。值得一提的是，與其他高溫超導(dǎo)體相比較，第二代高溫超導(dǎo)帶材的機(jī)械性能中沿c軸方向的臨界拉應(yīng)力較差。

盡管如此，單根超導(dǎo)帶材載流有限，多根并聯(lián)使用不可避免。常用低溫NbTi超導(dǎo)線制作電纜導(dǎo)體，容易實(shí)現(xiàn)扭絞和換位，目前商業(yè)化高溫超導(dǎo)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(dǎo)電纜導(dǎo)體過程中的扭絞和換位非常困難。為了解決這些技術(shù)難題，近幾年國際上提出了幾種基于第二代高溫超導(dǎo)帶材的超導(dǎo)導(dǎo)體結(jié)構(gòu)，每種電纜導(dǎo)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(dǎo)帶材的高載流電纜導(dǎo)體研發(fā)進(jìn)展情況，簡要分析比較各種超導(dǎo)電纜導(dǎo)體的技術(shù)特點(diǎn)，為高載流高溫超導(dǎo)導(dǎo)體在高溫低場和低溫高場的應(yīng)用提供有益參考。

2 RAAC導(dǎo)體/電纜

德國是進(jìn)行基于第二代高溫超導(dǎo)帶材進(jìn)行超導(dǎo)導(dǎo)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(dǎo)帶材組成的完全換位導(dǎo)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(dǎo)帶材沿著長度方向周期性地裁剪成“梯形”，可以采用氣動(dòng)沖切或激光切割方法進(jìn)行裁剪。然后進(jìn)行編織形成Roebel電纜導(dǎo)體[24,25]。

RACC導(dǎo)體/電纜最顯著的特點(diǎn)在于其與眾不同的結(jié)構(gòu)，這種結(jié)構(gòu)載流均勻、可以減小交流損耗，使得RACC導(dǎo)體/電纜具有低交流損耗和高載流能力的特點(diǎn)[19]。研究發(fā)現(xiàn)寬度較小的高溫超導(dǎo)導(dǎo)體和位置交換的超導(dǎo)結(jié)構(gòu)可以減少交流損耗，因?yàn)榇艌龅拇帕€可以進(jìn)入超導(dǎo)帶材的內(nèi)部間隙，但是在生產(chǎn)上細(xì)絲狀的高溫超導(dǎo)導(dǎo)體并不能實(shí)現(xiàn),并且簡單的切割不利于實(shí)際生產(chǎn)[20-22]。RACC超導(dǎo)/電纜結(jié)構(gòu)由特定形狀的涂層導(dǎo)體相互換位組裝而成[23]，其導(dǎo)體/電纜圖片如圖1所示，常用涂層導(dǎo)體經(jīng)過手工裁剪的“梯形”涂層導(dǎo)體實(shí)物如圖1(a)所示，手工編織加工完成后的RACC導(dǎo)體/電纜試樣如圖1(b)所示。通過氣動(dòng)沖壓切割和機(jī)械編織的RACC導(dǎo)體/電纜實(shí)物照片如圖2所示。

圖1 用涂層導(dǎo)體手工編織的RACC導(dǎo)體/電纜Fig.1 RACC / cable manually woven by using CC

圖2 機(jī)械編制的RACC導(dǎo)體/電纜試樣Fig.2 RACC/cable woven by machine

為了盡量減小帶材寬度，RACC導(dǎo)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(shí)現(xiàn)的，并有利于多根的換位組裝，可以構(gòu)成有更高電流容量的RACC導(dǎo)體/電纜[24，25]。RACC導(dǎo)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(dǎo)體進(jìn)行RACC的制作[26]。FZK手工制作的 6m長 RACC導(dǎo)體/電纜如圖3所示，該導(dǎo)體/電纜由17根超導(dǎo)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(dǎo)體/電纜實(shí)物Fig.3 Overview of RACC/cable

研究發(fā)現(xiàn)RACC導(dǎo)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(diǎn)，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(dǎo)體/電纜。為了避免超導(dǎo)帶材過度彎曲和塑形形變，RAAC導(dǎo)體的機(jī)械繞制非常復(fù)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(shí)現(xiàn)了由5mm寬的15根超導(dǎo)帶材繞制的7.5m長RACC導(dǎo)體/電纜[28-30]。對常規(guī)電纜生產(chǎn)線進(jìn)行部分改造，即可進(jìn)行RACC導(dǎo)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(dǎo)體/電纜的加工現(xiàn)場如圖4所示，可以實(shí)現(xiàn)實(shí)用長度RACC導(dǎo)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(xué)等單位采用激光切割技術(shù)切割超導(dǎo)帶材[30]，實(shí)現(xiàn)了商業(yè)化RACC導(dǎo)體/電纜生產(chǎn)，為歐洲委員會(huì)支持的EuCARD-2未來磁體計(jì)劃提供的34m 長的RACC導(dǎo)體/電纜實(shí)物[31-34]如圖5所示。

圖5 新西蘭惠靈頓大學(xué)提供的34m長的RACC導(dǎo)體/電纜Fig.5 RACC /cable Cable supplied by Victoria University of Wellington, New Zealand

用10kA級RACC導(dǎo)體/電纜首次繞制完成了Feather-M0跑道型線圈，并進(jìn)行了實(shí)驗(yàn)，由RACC導(dǎo)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(shí)驗(yàn)完成后，進(jìn)行實(shí)際尺寸的Feather-M2跑道型線圈的繞制。

圖6 全尺寸RACC導(dǎo)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(xué)研發(fā)電纜研究所(the Russian Scientific Research and Development Cable Institute, SRDCI) 探討RACC導(dǎo)體/電纜在飛行器電力系統(tǒng)中的應(yīng)用可行性[28]。此外，RACC導(dǎo)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(yīng)用前景。

RAAC導(dǎo)體/電纜的優(yōu)點(diǎn)是實(shí)現(xiàn)了完全換位，電流均勻分布；缺點(diǎn)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(fèi)帶材、成本高、力學(xué)性能差、不緊湊，需要環(huán)氧浸澤固化。根據(jù)SRDCI研究，RACC導(dǎo)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(dǎo)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(dǎo)體/電纜的應(yīng)用值得商榷。在高場磁體應(yīng)用方面應(yīng)更具有優(yōu)勢。

3 CORC導(dǎo)體/電纜

CORC(Conductor On Round Core)導(dǎo)體/電纜是由美國國家標(biāo)準(zhǔn)技術(shù)研究所(National Institute of Standard Technology, NIST)與Colorado大學(xué)合作，提出的一種結(jié)構(gòu)緊湊柔性超導(dǎo)導(dǎo)體，這種導(dǎo)體具有低電感、低交流損耗和高臨界電流的特點(diǎn)[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(yīng)用。CORC導(dǎo)體/電纜由3部分構(gòu)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(dǎo)帶材螺旋纏繞在中心骨架上，最外側(cè)部分使用絕緣材料進(jìn)行包覆，與超導(dǎo)電纜導(dǎo)體類似。并研制出1m長、外徑6.5mm導(dǎo)體，進(jìn)行了液氮溫度實(shí)驗(yàn)和彎曲接卸性能試驗(yàn)。在76K溫度自場情況下，其臨界電流達(dá)到2796A，彎曲半徑為125mm。其試樣結(jié)構(gòu)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(dǎo)帶材，CORC導(dǎo)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(shí)物截面圖如圖7(c)所示，導(dǎo)體外徑為6.5mm。黑色區(qū)域?yàn)槔@制在骨架上的碳紙。現(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(dǎo)之間的間隙，實(shí)現(xiàn)了實(shí)用長度的加工工藝，加工的12m長CORC導(dǎo)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(dǎo)帶材繞制而成。

圖7 緊湊型高溫超導(dǎo)導(dǎo)體/電纜示意圖Fig.7 View of compact CORC/cable

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

圖9 12m CORC導(dǎo)體/電纜樣品Fig.9 CORC/cable specimen with 12m in length

CORC導(dǎo)體/電纜中心骨架直徑比超導(dǎo)電纜小很多，所以CORC導(dǎo)體/電纜具有較高的臨界電流密度。CORC導(dǎo)體/電纜的臨界電流密度也會(huì)隨著纏繞層數(shù)的增加而隨之增加。CORC導(dǎo)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(dǎo)帶材的臨界電流的衰減要比磁場垂直帶材的導(dǎo)體小的多。研究人員制作了不同層數(shù)的CORC導(dǎo)體/電纜，最大的臨界電流為6.8kA，其工程電流密度達(dá)到86.58A/mm2[38]。

在2013年，van der Laan D C利用CORC導(dǎo)體/電纜制作了適用于高場20T的高場磁體,該磁體結(jié)構(gòu)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(dá)到了114A/mm2[39]。

4 TSTC 導(dǎo)體/電纜

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

圖10 TSTC導(dǎo)體/電纜樣品Fig.10 TSTC/cable specimen

TSTC導(dǎo)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(dǎo)帶材堆疊以200mm扭矩扭絞的TSTC導(dǎo)體/電纜結(jié)構(gòu)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(dá)到1.5kA,在液氦溫度下可達(dá)10kA。由于TSTC導(dǎo)體/電纜將超導(dǎo)帶材平行堆疊，帶材能夠相互支撐，可以防止帶材受到的應(yīng)力過于集中，并且多根帶材扭絞可以減輕帶材側(cè)向彎曲程度，在彎曲半徑為140mm時(shí)，由24根帶材組成的TSTC導(dǎo)體/電纜臨界電流退化僅為6%，因此TSTC導(dǎo)體/電纜可用于制作超導(dǎo)線圈[43-45]。

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

圖11 帶護(hù)套TSTC導(dǎo)體/電纜試樣Fig.11 TSTC /cable specimen with metal sheath

5 簡單堆疊導(dǎo)體(SSC)

100kA 級簡單堆疊導(dǎo)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(dǎo)導(dǎo)體。為了建造螺旋形核聚變演示反應(yīng)堆，超導(dǎo)線圈導(dǎo)體要在高達(dá)13T的磁場下載流能力達(dá)到100kA，研究人員采用在銅和不銹鋼套中把超導(dǎo)帶材并排堆疊的方法來構(gòu)造大電流導(dǎo)體，其結(jié)構(gòu)如圖12所示。圖12中為2排6層的結(jié)構(gòu)，實(shí)際結(jié)構(gòu)為3排18層，一共有54根超導(dǎo)帶材構(gòu)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(dǎo)簡單堆疊導(dǎo)體結(jié)構(gòu)Fig.12 Structure of 100-kA class HTS SSC

通過實(shí)驗(yàn)表明，該導(dǎo)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(dá)到118kA，在20K溫度和5.3T外場下臨界電流達(dá)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(dǎo)圓截面結(jié)構(gòu)導(dǎo)體，其結(jié)構(gòu)中心部分類似TSTC導(dǎo)體的布局結(jié)構(gòu)，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(jìn)行鍍錫焊接后扭絞制作成圓截面股線(Round Strand, RS)[51-53]。結(jié)構(gòu)示意和實(shí)物圖片如圖13所示。

圖13 圓截面股線結(jié)構(gòu)圖和實(shí)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(jié)構(gòu)：“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(jié)構(gòu)示意和實(shí)物Fig.14 Schematic view and photo of soldering profile

機(jī)械性能實(shí)驗(yàn)表明，“Plus”型加工導(dǎo)體的機(jī)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(yù)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(dǎo)體/電纜

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

圖15 HTS-CroCo導(dǎo)體/電纜結(jié)構(gòu)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(dǎo)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(jìn)行扭轉(zhuǎn)。采用HTS-CroCo導(dǎo)體/電纜結(jié)構(gòu)，則可以依據(jù)形狀配合的方式連續(xù)的扭轉(zhuǎn)超導(dǎo)線芯，制作超導(dǎo)線芯的速度可以達(dá)到3m/min, 適宜長距離導(dǎo)體的制作。此外，通過結(jié)構(gòu)優(yōu)化，這種結(jié)構(gòu)的導(dǎo)體工程電流密度可達(dá)700A/mm2，近期目標(biāo)是在2017年該導(dǎo)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(dǎo)體/電纜短樣機(jī)械加工1.1m實(shí)驗(yàn)完成，加工工藝基本成熟，可以進(jìn)行實(shí)用長度的加工。

對于HTS-CroCo導(dǎo)體/電纜之間的連接、端部連接等技術(shù)進(jìn)行了系統(tǒng)實(shí)驗(yàn)研究[60]，同時(shí)對不同骨架材料的溝槽加工等技術(shù)進(jìn)行理論和實(shí)驗(yàn)研究[61]，為HTS-CroCo導(dǎo)體/電纜和由其制成的CICC導(dǎo)體和Rutherford電纜實(shí)用化儲(chǔ)備關(guān)鍵技術(shù)。

8 準(zhǔn)各向同性導(dǎo)體(QI-S)

由上文可知，國際上基于涂層導(dǎo)體提出的主要6種超導(dǎo)導(dǎo)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(diǎn)。華北電力大學(xué)提出了臨界電流準(zhǔn)各向同性的高溫超導(dǎo)導(dǎo)體概念[62，63]。其概念結(jié)構(gòu)設(shè)計(jì)如圖17所示，分別為圓截面和方形截面高溫超導(dǎo)導(dǎo)體。導(dǎo)體由4股直接堆疊子股對稱排列而成，外面以金屬護(hù)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(dǎo)體短樣圖片如圖18所示，超導(dǎo)線采用由古河電氣子公司SuperPower公司生產(chǎn)的涂層導(dǎo)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(zhǔn)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(zhǔn)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(dǎo)體結(jié)構(gòu)和加工工藝分別進(jìn)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(jìn)行了理論分析和實(shí)驗(yàn)。依據(jù)不同電流下股線自場和超導(dǎo)帶材臨界電流隨磁場的變化特性，理論計(jì)算在77K溫度和自場臨界電流2.38kA，實(shí)驗(yàn)臨界電流值為2.28kA, 兩者接近。同時(shí)，在77K溫度下，理論分析和實(shí)驗(yàn)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(shí)驗(yàn)表明在0.5T以下，超導(dǎo)股線臨界電流各向異性小于5%，驗(yàn)證了該股線臨界電流的準(zhǔn)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(jìn)行了穩(wěn)定性、機(jī)械特性、交流損耗等理論研究和實(shí)驗(yàn)研究[67-72]，為股線的實(shí)際應(yīng)用奠定了初步基礎(chǔ)。

為實(shí)現(xiàn)實(shí)用長度股線的機(jī)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(dǎo)股線生產(chǎn)工藝進(jìn)行概念設(shè)計(jì)，其生產(chǎn)示意如圖20所示。采用成熟的激光焊接技術(shù)焊接金屬包套，使用不同結(jié)構(gòu)磨具可以實(shí)現(xiàn)方形和圓形截面金屬包套的焊接。

圖20 圓截面實(shí)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(shù)進(jìn)行的臨界電流準(zhǔn)各向的高溫超導(dǎo)股線的加工。在中天集團(tuán)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(dǎo)股線的加工，加工完成的導(dǎo)體如圖22所示。通過10m長度股線的成功加工，可以實(shí)現(xiàn)長度的高溫超導(dǎo)股線的加工[62,67]。

圖21 臨界電流準(zhǔn)各向同性超導(dǎo)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(zhǔn)各向同性股線Fig.22 Quasi-isotropic stand in 10m length fabricated by production line

9 CICC導(dǎo)體

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

9.1TSTC導(dǎo)體/電纜-CICC導(dǎo)體

基于TSTC導(dǎo)體/電纜，設(shè)計(jì)成CICC導(dǎo)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(dǎo)線，骨架中心有孔，用以低溫介質(zhì)流過，超導(dǎo)帶外放置銅線作為襯墊，外面鎧裝不銹鋼, 通過測試相關(guān)機(jī)械及電磁參數(shù)取得了優(yōu)化結(jié)構(gòu)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(dǎo)體能夠進(jìn)行實(shí)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(dǎo)體結(jié)構(gòu)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(dǎo)體/電纜的CICC導(dǎo)體結(jié)構(gòu)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(dǎo)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(dǎo)體/電纜提出另一種結(jié)構(gòu)CICC導(dǎo)體結(jié)構(gòu)概念，是9.1節(jié)CICC的進(jìn)一步推廣。相當(dāng)于將9.1節(jié)中的CICC導(dǎo)體作為子纜，進(jìn)一步組合成大電流容量的CICC導(dǎo)體，其典型截面結(jié)構(gòu)概念設(shè)計(jì)之一[49,76-80]如圖25所示。該CICC導(dǎo)體由6股子股線扭絞構(gòu)成，每個(gè)子股線由3組TSTC導(dǎo)體/電纜扭絞構(gòu)成，形成3×6結(jié)構(gòu)CICC導(dǎo)體，中心為冷卻通道。目前，此種CICC導(dǎo)體仍處于短樣設(shè)計(jì)、實(shí)驗(yàn)研發(fā)階段，未實(shí)現(xiàn)實(shí)用長度生產(chǎn)工藝。

圖25 3×6 CICC導(dǎo)體結(jié)構(gòu)設(shè)計(jì)Fig.25 Design of 3×6 CICC

9.2CORC導(dǎo)體/電纜-CICC導(dǎo)體

盡管CORC導(dǎo)體/電纜工程電流密度低于其他導(dǎo)體，但是其機(jī)械性能好，對于高場應(yīng)用的CICC導(dǎo)體具有很好的應(yīng)用前景。其CICC結(jié)構(gòu)如圖26所示，以鋁鎧裝、中空管為冷卻通道、由6根CORC導(dǎo)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(shù)基本完成，還未實(shí)現(xiàn)實(shí)用長度的成產(chǎn)。

圖26 基于CORC導(dǎo)體/電纜的CICC短樣結(jié)構(gòu)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(dǎo)體/電纜應(yīng)用于CICC導(dǎo)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(jié)構(gòu)如圖27所示，并開始研發(fā)基于RACC導(dǎo)體/電纜的CICC導(dǎo)體研究。

圖27 Al6036合金和無氧銅骨架結(jié)構(gòu)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(dǎo)體除了CICC外，為了降低交流損耗，另一種可換位大載流導(dǎo)體是Rutherford 電纜，由多根導(dǎo)體繞制在扁平狀導(dǎo)體上，其結(jié)構(gòu)示意如圖28所示。原則上講，上述7種超導(dǎo)導(dǎo)體/電纜都可以用來制作Rutherford電纜[59], 即所謂的涂層導(dǎo)體Rutherford電纜 (Coated Conductor Rutherford Cable, CCRC)。下面簡單介紹目前已經(jīng)開始進(jìn)行研發(fā)的Rutherford 電纜的情況。

圖28 Rutherford 電纜結(jié)構(gòu)示意圖Fig.28 Schematic view of Rutherford cable

10.1RACC導(dǎo)體/電纜-Rutherford電纜

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

圖29 基于RACC導(dǎo)體/電纜導(dǎo)體的Rutherford 電纜試樣Fig.29 Rutherford cable specimen made from RACC/cable

10.2HTSCroCo導(dǎo)體/電纜-Rutherford電纜

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

圖30 11根HTS-CroCo導(dǎo)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(chǔ)上，將20根單根股線沿銅板繞制Rutherford電纜結(jié)構(gòu)，這種超導(dǎo)體結(jié)構(gòu)的實(shí)物如圖31所示，整個(gè)導(dǎo)體寬70mm厚19mm，長度2m， 在77K自場下，實(shí)驗(yàn)得到其臨界電流1.15kA, 其n值達(dá)到25，估算在4.2K溫度12T下，其工程電流密度達(dá)790A/mm2，大于同等條件下Nb3Sn的688A/mm[55,88-93]。

圖31 Rutherford 電纜實(shí)物圖Fig.31 Picture of prototype Rutherford cable

11 結(jié)論

國際上第二代高溫超導(dǎo)帶材工藝成熟，實(shí)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(dǎo)帶材的超導(dǎo)導(dǎo)體并進(jìn)行相關(guān)關(guān)鍵技術(shù)工藝研究，為其高溫低場電力應(yīng)用和低溫高場下的應(yīng)用奠定了堅(jiān)實(shí)基礎(chǔ)。同時(shí)， 7種超導(dǎo)導(dǎo)體中的4種即RACC 導(dǎo)體/電纜、CORC導(dǎo)體/電纜、CroCo導(dǎo)體/電纜和圓截面股線(RS)已經(jīng)研制成Rutherford 電纜短樣；TSTC導(dǎo)體/電纜也已研制成實(shí)用長度CICC導(dǎo)體，為高場大電流應(yīng)用做好技術(shù)了儲(chǔ)備。

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

表1 7種超導(dǎo)導(dǎo)體/股線的結(jié)構(gòu)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(dǎo)導(dǎo)體的研究進(jìn)展，國外提出的6種超導(dǎo)導(dǎo)體已經(jīng)進(jìn)行了溫度77K和4.2K下的研究和Rutherford電纜及CICC導(dǎo)體研究，而國內(nèi)只有1種準(zhǔn)各向同性股線(QI-S)研發(fā)，雖然實(shí)現(xiàn)了實(shí)用長度的生產(chǎn)工藝，但是只進(jìn)行了液氮溫度(77K)的實(shí)驗(yàn)研究，缺乏液氦溫度(4.2K)下的研究和基于準(zhǔn)各向同性股線的Rutherford電纜及CICC導(dǎo)體的實(shí)驗(yàn)研究。就目前看，這種差距趨勢還在逐步擴(kuò)大，希望引起國內(nèi)相關(guān)管理部門和研究部門的關(guān)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(xué)基金項(xiàng)目(51477053)

王銀順(1965-), 男, 河北籍, 教授, 博士, 研究方向?yàn)槌瑢?dǎo)電力技術(shù)。

10.12067/ATEEE1705027

1003-3076(2017)11-0021-15

TM26