拉伸应变对YBCO涂层导体传输特性的影响

本文通过实验研究了拉伸应变对YBCO涂层导体的临界电流(Ic)、n值和交流损耗的影响(零场,77K),实验结果表明,随着拉伸应变的增大,YBCO涂层导体Ic的变化分为三个阶段,开始缓慢上升,然后缓慢下降,最后快速下降,Ic的上升表明带材中存在残余压缩应变,Ic的衰减是由于应变导致弱连接区域的钉扎势与晶界间临界电流密度同时减小引起的;而n值随应变增加基本上没有变化,说明沿导体长度方向的Ic分布没有变化.由于临界电流密度沿样品宽度方向分布不均匀,实验所得的交流损耗结果与采用Norris模型计算所得的结果不一致,同时,当应变超过不可逆应变、电流接近Ic时,交流损耗快速增加.     

金属芯尺寸对CORC缆REBCO带材临界性能影响

为推动CORC缆应用于CICC导体及高场磁体,研究金属芯尺寸对CORC缆上的ReBCO带材临界性能影响具有一定的重要性。手工绕制了多根单层CORC缆样品,研究了在77 K和自场条件下,芯部尺寸对上海超导生产的YBCO带材的临界电流的影响。随着缆芯尺寸减小,YBCO带材的临界电流产生衰退现象。当缆芯尺寸低于4.3 mm时,临界电流明显下降。当缆芯尺寸为4 mm时,临界电流为127 A,n值为32.5,临界性能衰退了21%。     

Ba-122铁基超导带材扭转下临界性能研究

为推动铁基超导带材实用化发展,本文研制出一种在铁基超导带材纯扭转测试装置,分析了7芯Ba_1-xK_xFe₂As₂(Ba-122)带材在扭转应变下临界性能变化。带材临界电流在扭转应变下会出现衰退行为,并且随扭转应变增大而减小。四对电压信号测量结果一致,表明扭转变形均匀。以95%的初始临界电流为临界扭转标准,带材临界扭转角为120°,相应的临界剪切应变为0.86%和临界扭转螺距为240 mm。扭转应力会损伤超导芯,导致带材临界载流性能降低。     

多芯Bi2223／Ag带材30K温区的临界电流密度和交流损耗

本文研究了３０Ｋ温区和工频下８１芯Ｂｉ２２２３／Ａｇ带材的临界电流特性和没背场下的交流损耗，临界电流是用ＳＱＵＩＤ磁化法和标准四引法测量；交流损耗理在样品通以正弦电流情况下采用电测法进行测量，结果发现交流损耗随背场的增加而增大，同时与频率的关系是非线性的，并且偏离基于Ｂｅａｎ模型所预言的结果；表明３０Ｋ温区多芯带材Ａｇ基中的涡流损耗的芯间的耦合损耗不可忽略。     

不同结构超导限流器线圈交流损耗实验研究

超导限流线圈交流损耗实验研究对于超导限流器具有重要现实意义.本文采用Bi-2223带材制作出单根螺旋线圈、两根带材串联螺旋线圈和两根带材并联螺旋线圈三种不同结构限流线圈样品,实验研究其交流损耗特性,并与Norris公式计算结果相比较,通过实验验证限流线圈在结构和电流模式不同时对交流损耗的影响.     

铝、碳共掺提高MgB_2临界电流密度

本文研究了在MgBq超导体中Al,C及两种元素共同掺杂时对样品的超导转变温度,不可逆场和临界电流的影响.研究发现,少量的铝掺杂可以提高MgB2超导材料在低场下的临界电流密度,但由于对Tc的抑制而降低其在高场下的载流能力,而碳掺杂则可以有效提高MgB2超导材料的上临界场和不可逆场,从而达到改善其在高场下的载流能力的目的.研究发现,在0-7T外磁场范围内,1%铝和1%碳共同掺杂的样品表现出最佳的载流性能.钉扎力曲线的分析也应证了这一结果.     

Bi（2223）／Ag复合带材的研制

采用粉末套管法制备了单芯,7芯,49芯和343芯Bi_(1.8)Pb_(0.4)Sr_2Ca_(2.2)Cu_3,O_x/Ag 复合带材,并研究了热处理条件,加工方式和弯曲应变对带材超导性能和组织结构的影响.研究表明,带材 J_c 对烧结温度十分敏感,在845℃附近作200h 烧结热处理,其 J_c 都有最大值.采用反复压制和烧结的工艺,可有效地改善带材的 J_c,其中49芯带材 J_c(77K,0T)=1.5×10~4A/Cm~2和 J_c(77K,1T)=1.20×10~3A/cm~2.在弯曲应变状态下,带材的 J_c 与其芯数密切相关,随着芯数增加,带材抗应变性能改善,其中343芯带材,当弯曲应变为～1%时,J_c 仍达无弯曲应变时的～70%,为单芯带材的5倍多.     

多芯Bi-2223/Ag带材交流损耗的特性研究

Bi-2223/Ag是一种很有前景的高温超导带材,交流损耗是高温超导在大规模电力应用方面的瓶颈,如何降低Bi-2223/Ag中的交流损耗是人们一直关注的问题。带材超导部分的横截面形状对交流损耗有很大的影响,前人曾通过双轴轧制等工艺制造矩形截面的带材,以降低其交流损耗;另有人在单芯带材中得到了环状结构,从中发现可降低交流损耗。本论文尝试利用抽换芯工艺制造多芯环状截面的Bi-2223/Ag高温超导带材,以期降低带材的交流损耗。论文中,通过解析方法计算了临界态模型下,临界电流密度在径向上分布不均匀的超导体的交流损耗特性,并得到结论:带材的外围临界电流密度越高,交流损耗性能越好。     

并绕铜带对高温超导绕组交流损耗影响实验研究

在许多超导电力设备的应用中,超导绕组的机械性能和电流过载能力是关乎设备运行安全性和可靠性的重要现实问题。利用铜线(或铜带)与高温超导带材平行绕制的方法是解决这一问题的可行方案之一。但这种方案有可能带来额外的交流损耗。为了研究这一问题,制作了两个尺寸相同的超导绕组,绕组内径70mm,外径90mm,高45mm,其中一个绕组由超导带与铜带并绕而成,另一个则由超导带材单独绕制而成。两个样品使用的超导带材均为一代Bi-2223/Ag高温超导带,宽4.6mm,厚0.22mm;铜加强带宽5mm,厚0.1mm。采用了卡路里法对比研究了两个样品的交流损耗。实验结果显示加入铜带没有明显增加超导绕组的交流损耗。因此,超导绕组中并绕铜带不失为一种有效提高超导绕组机械性能和过载能力的方法,在超导电力设备中有一定的应用价值。     

外场下机械振动对高温超导带材交流损耗的影响

高温超导带材在磁场中传输交变电流时,将受到电磁力的作用而产生机械振动,振动对带材的交流损耗将产生影响.本文讨论了振动情况下交流损耗的测量方法,在平行于带面的直流磁场下,测量了Bi-2223/Ag高温超导带材在不同振动情况下的交流损耗.结果显示:当传输电流频率偏离样品的共振频率时,振动对带材的交流损耗影响不大;只有当电流频率在共振频率附近时,样品产生剧烈振动,交流损耗才有明显的增加;另外,带材振动时的交流损耗随频率变化曲线的斜率比不振动时略有增加.     

Bi2223/Ag高温超导带的侧向弯曲率对载流能力的影响

Bi2 2 2 3银包套超导带材是研制高温超导磁体和高温超导强电应用的基础。文中就对高温超导磁体最大运行电流有重要影响的 Bi2 2 2 3银包套带材侧向弯曲形变进行了初步探讨 ,就不同的侧向弯曲率对超导带载流能力的影响进行了实验测试 ,并提出了提高 HTS磁体最大运行电流的方法。     

Reduction of AC losses applying novel resistive interfilamentary carbonate barriers in multifilamentary Bi(2223) tapes

Hysteresis losses and coupling losses, a main component of the AC losses in Bi(2223) tapes, can effectively be reduced by enhancing the resistivity of the matrix material between the filaments and applying a filament twist. Since through alloying the sheath, as using AgAu(8 wt.%), the resistivity can only be raised by a factor <10 (77 K), a new conductor configuration with a quite novel composite matrix having resistive SrCO₃ barriers inside the Ag matrix between the filaments was developed. These new barriers, a cheap and commercial material, withstand the tape annealing, do not react with the superconductor, sinter dense and have a good bonding to Ag. Applying two different preparation techniques for 19 filament prototype tapes, critical current densities up to 20.7 kA cm⁻² were achieved. We report on tape preparation, the effect on the phase texture and the superconducting properties of such barrier tapes.     

具有不同临界电流的Bi2223/Ag多芯超导带材的自场损耗和交流电流电压特性

对具有不同临界电流的Ｂｉ２２２３／Ａｇ多芯超导材的交流电流电压特性进行了测量和评价,当传输电流的有效值Ｉｎｎｓ小于临界电流Ｉｃ时,交流电压的大小与传输电流的频率成正比;但Ｉｎｎｓ接近临界电流时,不同频率所对应的交流电压的大小之间的差别减小了,所有的曲线都汇聚成一条曲线,传输电流的频率分别为４０Ｈｚ,６０Ｈｚ,８０Ｈｚ,２００Ｈｚ及３００Ｈｚ时,我们测量了交变传输电流在Ｂｉ２２２３／Ａｇ带材中产生的自场损耗。结果表明当传输电流的频率较低时,实验结果与基于Ｂｅａｎ模型的Ｎｏｒｒｉｓ方程预期的结果一致;另外,实验结果表明存在一个电流Ｉ′,它的值小于任何一个样品的临界电流,本实验中Ｉ′的值是１０安培,在传输相同大小的电流Ｉｎｎ且Ｉｎｎｓ〈Ｉ′时,Ｂｏｉ２２２３／Ａｇ带材的交流损耗与它的临界电流成正比;但当Ｉｎｎｓ〉Ｉ′     

Bi—2223带材在拉伸应力下的临界电流

研究了不锈钢加强的Bi-2223/Ag高温超导带材在不同的拉伸应力下临界电流的变化情况。采用改造后的拉伸设备,在温度77K下对超导带材施加拉伸应力的同时,利用四引线法测量带材的临界电流,得到了超导带材的应力—应变曲线以及临界电流—应变曲线。利用理论公式计算了应力对超导带材临界电流的影响,与实验结果进行对比,并对两者的差别进行了分析。     

Twist effect on hysteresis loss in Bi2223 multifilamentary wires exposed to an AC magnetic field

We fabricated Bi2223 multifilamentary sample wires with various twist pitches and investigated the electromagnetic properties experimentally. They showed monofilamentlike electromagnetic properties regardless of twisting due to the contacts among filaments and/or proximity effect. The observed AC losses in the non-twisted sample wire agreed roughly with the theoretical prediction for a homogeneous superconducting slab with the same thickness of the filamentary region on the basis of Irie–Yamafuji model. However the AC losses in the twisted wires deviated from the theoretical ones, especially for the amplitude around the theoretically predicted penetration field of the slab. We showed that the observed AC loss properties can be explained by both the twist effect for the macroscopic shielding current and the contribution of the local shielding current.     

Comparison of transport and magnetic AC losses in Bi-2223/Ag tapes — the role of superconducting core geometry

AC losses were measured by 4-probe transport method and by external magnetization method in three samples of Bi-2223/Ag tape: a multifilamentary tape with separated filaments, another multifilamentary tape with ‘bridges' between filaments, and a two-shell tape. The transport losses agreed with those calculated using I_c from DC experiment. Magnetization experiments gave indications about the various paths of induced currents. For the tape with well separated filaments the main part of screening current closes inside individual filaments. Additional screening of the whole filamentary zone involves the normal metal matrix, leading to frequency dependent losses. In the case of tape with ‘bridged' filaments, supercurrents interconnect the filaments into bundles whose screening (and loss) is frequency-independent. Matching the experimental data indicates that a typical bundle was composed of 8 filaments. Magnetic losses of the two-shell tape were explained by a model for magnetization of superconducting wire with elliptical cross-section.     

Frequency dependence of AC loss in Bi(2223)Ag-sheathed tapes

The AC self-field loss in Bi(2223)Ag-sheathed tapes with different number of filaments has been measured between 59 and 2500 Hz by means of a dual lock-in amplifier. Due to the wide frequency range of the measurements, we have been able to dissociate quantitatively the different self-field loss contributions: hysteretic, eddy current and resistive loss (near I_c). This is an important advantage compared to single frequency measurements where such loss dissociation is only qualitative. The hysteresis losses of the different tapes fall between Norris' predictions for elliptical and strip cross-section. The relative weight of eddy current loss is found to be inversely proportional to the current ratio—the higher the i, the less is their contribution. Frequency-independent resistive loss due to flux-creep is observed for high currents at low frequencies; this loss becomes quickly negligible with the increasing frequency.     

Reduced filament coupling in Bi(2223)/BaZrO3/Ag composite tapes

Multifilamentary Bi(2223)/Ag tapes often exhibit AC loss levels comparable to those measured in monofilamentary samples, which is partly due to the large coupling currents induced in the low resistive sheath material. Surrounding the individual filaments by electrically insulating barrier layers suppresses these currents and strongly reduces the coupling. We demonstrate this effect with various types of magnetic and self-field AC loss measurements on a series of Bi(2223)/BaZrO₃/Ag tapes. We also discuss the influence of barrier thickness, twist pitch length and filament arrangement on the measured losses in these composite conductors.     

Bi-2223带材制备的高温超导电流引线

为了降低沿电流引线的漏热,用于制备高温超导电流引线的B i-2223带材要求具有较低的热导率。文中介绍了低热导率银金合金B i-2223高温超导带材;给出了其热导率的测试结果;并采用该带材制造了高温超导电流引线样机。液氮条件下测试该段高温超导引线的临界电流为332A。     

Influence of tape-specific properties on local stress and strain in Bi-2223/Ag tapes

Superconductors are typically fragile, and their superconducting properties are reduced under strain. Moreover, superconductor wires operate under large mechanical loads in most applications. Thus, a careful mechanical analysis is essential when designing superconducting applications. So far, plenty of experimental and computational studies concerning stress and strain in, e.g. Bi-2223/Ag tapes have been carried out. However, Bi-2223 tapes contain several properties that vary between different tapes and are often unknown when designing a specific application. The largest uncertainties are related to the creep at high temperatures, stiffness and anisotropy of filaments and the yield strength of silver. In this paper, the influence of uncertainties on the local stress and strain in Bi-2223/Ag tapes is studied computationally to determine efficient strategies to reduce inaccuracy of the results. The results suggest that the filaments can be described as an isotropic material and the filament stiffness is the most important input parameter to estimate the total stiffness of the tape.