基于改进电测法的Bi-2223/Ag高温超导带的交流损耗研究

研究了B i-2223/Ag高温超导带材的交流传输损耗与频率及运行电流的关系。采用锁相放大器激励,内参考方式,首先对纯阻性相位进行定标的改良电测法,对带材的交流传输损耗进行测量。实验在温度77K,频率45-200Hz的范围内进行。实验结果显示:当运行电流幅值小于临界电流时,传输损耗与电流的关系式(P-In)中,指数n介于2-3之间,说明这时的损耗除来源于磁滞损耗外,涡流损耗的作用也不可忽略。鉴于电测法测得的交流损耗与Norris模型的理论计算值差别较大,分析了这种差别产生的原因,并与另一种B i系高温超导带的交流损耗情况进行了对比;此外还对实验误差的大小进行了理论估测。     

ITER电流引线高温超导叠制作工艺及性能测试

ITER高温超导电流引线载流能力最大要达到68 kA,一根电流引线共需要1000多根银金基Bi-2223高温超导带并联.这些高温超导带分成90叠,每叠由12层带组成.银金基Bi-2223带价格是普通银基Bi系带的4～5倍,而目前欧洲超导公司提供的超导叠的报价几乎是其带价格加倍,所以开发超导叠的制作工艺是非常有价值的.本文详细的介绍了超导叠的真空钎焊制作工艺,并进行了77 K下超导带的接头电阻测试和77 K自场下的临界电流测试,以及模拟在实际运行温度65～5 K条件下高温超导叠的载流能力测试和接头电阻的测试.测试结果证明了此工艺的可行性.     

Indirect measurement of AC current distributions in HTS tapes by a pickup coil method

It is necessary to develop HTS conductors with a large current capacity and low AC loss characteristics for practical use of HTS power devices. For large capacity power applications, HTS tapes such as Bi-2223 tapes and YBCO coated conductors are assembled. So, it is important to evaluate the characteristics of current distributions in such assembled HTS tapes. However, an adequate measurement method has not been established. In this study, we have tried the development of an indirect measurement method to evaluate the current distributions in stacked HTS tapes. In this method, the current distributions are indirectly found from the results of the field distributions measured by a pickup coil located around the surface of the sample tapes. To confirm the accuracy and the sensitivity of this method, current distributions in a test conductor made of copper tapes are measured. Numerical and measured current distributions are compared. Using this method, the current distributions in stacked Bi-2223 tapes are measured at room temperature and 77 K. On the basis of the obtained results, the characteristics of the AC current distributions in the HTS tapes are discussed.     

AC-induced DC voltage in HTS coil

The interplay between AC and DC currents in a High-T_c Superconducting (HTS) coil, made of multifilamentary silver-sheathed Bi-2223 tape, was investigated. We observed that the application of a small sinusoidal current in the frequency range of 50–500 Hz into the coil, while it is already carrying a DC current in the range of 16–22.5 A, caused an increase in the coil DC voltage. The DC voltage increment due to the AC signal is found to increase linearly with frequency and quadratically with amplitude. The DC voltage increment increases as the coil current grows towards its critical value of 22.2 A. This result may be important in some power applications such as fault current limiters (FCL) and superconducting magnet energy storage (SMES) based on HTS coils.     

Bi-2223/Ag高温超导带临界电流各向异性的实验测量及分析

本文介绍了Bi-2223/Ag高温超导带临界电流各向异性的实验测量方法及原理,指出了在不同磁场方向(与超导带面夹角)下,Bi-2223/Ag带临界电流随直流背景磁场的变化规律以及实验应注意的问题.Bi-2223/Ag带材的各向异性决定了其临界电流对垂直于带材表面的磁场非常敏感,这是该带材在高温超导磁体等强电应用方面的不利因素.     

Evaluation of critical current based on a new transition concept

The critical current of high-temperature superconductor (HTS) tapes depends on temperature, magnetic field, and flux angle against the tape. Analyzing the performance of an HTS coil relies on the critical current equation, which has these dependencies. To date, the critical current equation has been obtained by fitting the measured data. However, this fitting method requires the time-consuming and laborious work of measuring the tapes. In this study, based on a new transition concept in applying a magnetic field, we show how to obtain the critical current equation, while keeping the temperature constant. From the wave function of the Cooper pair which distributes along a magnetic flux quantum, a wave function at the transition state is obtained; this yields the wave functions with perpendicular and parallel magnetic components against the tape. Combining these wave functions yields the conclusive critical current density equation. To confirm the accuracy of this equation, used Bi-2223/Ag tapes, it was compared with the measured critical current under various magnetic fields and flux angles; it was found that they agree well. The parameters of this equation can be obtained by measuring the perpendicular/parallel critical magnetic field component. This equation does not require fitting the measured data, therefore, it can be employed with any Bi-2223/Ag tape.     

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.     

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。     

传输交流的Bi2223/Ag高温超导带在不同取向交流外场下的交流损耗

在高温超导的电力应用中，如超导电机、变压器等，多数情况下，高温超导带材在通以交流传输电流的同时还处于交变磁场中。此时，超导体的交流损耗不仅依赖于磁场的大小，还与磁场相对于超导带面的取向有关。本文在77K及工频50Hz情况下，实验研究了单根多芯Bi2223/Ag高温超导带及两带并联时的交流损耗随着外磁场与带面夹角的变化情况；以及交流磁场对临界电流的影响情况；并对单根带及两带并联的实验结果进行了比较与分析。     

On some consequences of an external magnetic field applied to HTS coils

A computational model which enables to evaluate the distribution of the critical currents, electric fields and the voltage in the winding of a solenoidal high temperature superconducting (HTS) magnets subjected to an external magnetic field parallel with the magnet axis, was developed. The model comes out from the well-known power law between the electric field and the transport current of the HTS tape short sample. It allows to predict the voltage–current V(I) characteristics of both the pancake coils and the complete magnet. The model was applied to the magnet system consisting of 22 pancake coils made of multifilamentary Bi(2223)/Ag tape at 20 K, which is subjected to an external uniform magnetic field parallel with the coil axis. A rather unexpected behavior of the magnet at different operating conditions (operating current and external magnetic field strength) is predicted, analyzed and reported together with a theoretical explanation. On one hand, the external uniform magnetic field parallel with the coil axis increases the resulting magnetic field strength, however, on the other hand it simultaneously decreases the angle between the resulting magnetic field and the tape surface. Thus, the effect of higher magnetic loading caused by the presence of an external magnetic field strength which is acting on individual turns located close to the coil’s flanges is compensated by more favorable orientation of the tape with respect to the resulting magnetic field. As a result, increase in the critical currents of these turns is expected. Further, the results indicate, that in case of the high field HTS insert coils the anisotropy in the I_c(B) characteristic does not play a substantial role. As a consequence, the technology of the production of the tapes for high field insert HTS coils should concentrate rather on the tapes having the current carrying capacity as high as possible, than on the attempt how to decrease the anisotropy in the I_c(B) by changing the architecture of the filaments in the tape.     

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。     

Experiment of enhancing critical current and reducing ac loss in pancake coil comprised of Ni-coated Bi-2223/Ag tape

An approach of realizing high performance HTS coil comprised of ferromagnetic material-coated BSCCO tape is proposed. The concept of influencing critical current and ac loss is based on the magnetic shielding effect resulting in redirection of self-field flux-lines. In the previous article, ac performance of Ni-coated tape was demonstrated where the Ni-coating was introduced at the edge-regime of the finished tape in order to redirect the perpendicular component of self-field lines. In order to investigate the shielding effect on ac performance in HTS coil, a two-turn pancake coil comprised of Ni-coated Bi-2223/Ag tape is demonstrated in the present article. About 6.4% of critical current was enhanced and 30% of transport current ac loss was reduced by means of 40 μm thick and 0.3 mm long (from the edge toward center of the tape) Ni-coating. This result suggests that additional ferromagnetic loss could be compensated well by the shielding effect of the partial Ni-coating. The degree of enhancement in critical current as well as ferromagnetic impact on ac losses depend on the volume and geometry of ferromagnetic coating introduced. Therefore, it is very important to control the parameter of ferromagnetic coating of the tape in order to balance the critical current and ac loss for optimum coil performance.     

Decrease of magnetic AC loss in twisted-filament Bi-2223 tapes

In AC power-engineering applications, a large part of the AC loss in the superconductor is due to magnetization by the external field. This magnetic AC loss has been well described for the low-T_c conductors. In Bi-2223 tapes the picture is different due to strong anisotropy, granularity and flux creep. Magnetic AC loss in various twisted and non-twisted Bi-2223 tapes has been measured at power frequencies by a pickup method. The results are compared to theoretical models of magnetization loss. When the field is parallel to the tape plane, the filaments in twisted tapes can be decoupled and the AC loss is decreased even when the matrix is pure silver. The extra effect of higher-resistance matrix materials is studied. In perpendicular field it is more difficult to decouple the filaments, due to the particular tape geometry. Contrary to a wire, there are essential differences between the AC loss mechanisms in a long twisted tape and those in a short piece of non-twisted tape. Finally, the dynamic resistance caused by the AC magnetic field is examined.     

35kJ高温超导储能磁体的优化设计

介绍了35kJ高温超导储能磁体的设计步骤。为了减少常规寻优方法的计算量,将加权粒子群优化算法(WPSO)引入到高温超导储能磁体的优化设计中,给出了用B i-2223超导线材进行35kJ储能磁体设计的优化结果,分析了高温超导线材的各向异性对磁体临界电流的影响,并比较了两种不同的单螺线管磁体结构在不同优化目标的情况下,超导线材用量和杂散磁场的分布的变化。     

Bi-2223／Ag超导闭合线圈的制备及其电流衰减特性的研究

本文研究了使用Bi-2223／Ag超导带材制备超导闭合线圈的工艺及超导闭合线圈中电流衰减的特性．在闭合线圈焊接点的制作上，分别采用了超导焊接和普通焊锡焊接两种不同方法．通过测量闭合线圈中心点的磁场衰减过程，观察了这两种闭合线圈中电流衰减的特性．实验发现，使用超导焊接技术制备的闭合线圈，电流衰减与时间的自然对数成线性关系，在线圈局部受损伤的情况下，上述关系仍然成立；使用普通焊锡焊接方法制备的闭合线圈，电流衰减不存在上述关系，但也不是时间的e指数函数．     

A simple electromagnetic method of cyclic loss measurement for superconducting wires in a combined alternating transverse magnetic field and transport current

We measured cyclic losses in a superconducting wire, carrying alternating transport current, simultaneously exposed to an alternating transverse magnetic field. Samples of Bi-2223 Ag-sheathed tapes have configuration of a double-layer non-inductive coil, which itself is a pickup coil to measure the AC losses. Potential taps were attached to both terminals of the sample coil. The external field was applied along the axis of the sample coil. In this procedure, we can estimate an averaged Poynting's vector on a cylindrical surface between the two layers by means of signals from a pair of the potential taps and from pickup coils for the external magnetic field and the transport current. We can also measure a magnetization and an extended transport-current components of AC losses in addition to a total cyclic loss for a combined alternating external field and transport current. Obtained results are compared with numerical predictions of the critical state model taking into account the magnetic field dependence of critical current density.     

跑道型Bi系高温超导双饼线圈I～E特性计算与实验研究

本文使用Ansys有限元分析软件,建立三维跑道线圈模型,考虑超导线截面电流密度的非均匀分布特性,计算Bi系高温超导双饼线圈中各区域磁场分布、临界电流分布、电流密度分布和电场分布,从而计算线圈的I～E关系曲线,为超导线圈提供一个更为准确的检验标准,对照线圈的测试结果,用此程序计算的线圈I～E关系曲线与测试曲线吻合的较好.     

Bi-2223/AgAu 带材及应用进展

Bi-2223/AgAu 高温超导带材因为较低的热导率和较高的载流性能, 被认为是制备高温超导电流引线的最佳材料之一. 这篇文章简单介绍了高温超导电流引线的工作特点和不同包套 Bi-2223 带材的热导率, 在此基础上详细介绍了目前 Bi-2223/AgAu 带材和高温超导电流引线国内外研究进展, 最后展望了 Bi-2223 带材的发展趋势.     

电力系统动模实验用50kJ高温超导储能磁体的设计研究

介绍了 2 0 K下对电力系统动模实验用 5 0 k J高温超导储能磁体的设计步骤 ,给出了用 Bi- 2 2 2 3单根超导带进行5 0 k J磁体线圈的设计和优化结果 ,分析了高温超导体的各向异性对磁体临界电流的影响和磁体漏磁的分布 ,并讨论了用单根高温超导带组成的超导体和用多根高温超导带组成的超导体设计的储能磁体的特性参数对改善电力系统动态特性的能力的影响。     

舰船电力系统用1MJ高温超导环型储能磁体的设计研究

介绍了舰船电力系统用 1MJ环型高温超导储能磁体的设计优化步骤 ,进行了环型磁体线圈最大磁场的优化、环型磁体单元尺寸的优化和环型磁体单元数目的优化 ,并得出了合适的磁体线圈尺寸。磁体线圈上的最大磁感应强度为 3-4 T,单元数目较大的环型磁体适用于 1MJHTS- SMES