不同排布和通流下高温超导电缆交流损耗研究

运用实验的方法,系统研究了在堆叠与并列两种排布方式下YBCO和Bi2223两种高温超导电缆关于电流方向的交流损耗特性,并进行了分析比较。研究表明,在堆叠的情况下,反向电流的交流损耗大于同向电流的交流损耗,两者保持一定的比列;并列的情况下,同向电流的交流损耗大于反向电流的交流损耗,且随着电流的增大,两者的差异在逐渐减小。在堆叠的情况下,YBCO同向电流的交流损耗和反向电流交流损耗的差异远大于Bi2223。     

Bi系高温超导带材交流传输损耗的研究和分析

本文研究了Bi-2223高温超导带材的交流传输损耗和频率及运行电流的关系, 调查了热循环过程对交流传输损耗的影响. 实验中, 使用了Lock-in 放大器, 利用四引线法来测量带材交流传输损耗. 实验在温度为77K频率从45Hz到135Hz下进行. 在调查损耗和频率及运行电流的关系时, 发现在运行电流幅值小于临界电流时, 每周传输损耗和频率无关, 说明这时的损耗主要来源于磁滞损耗, 实验结果和Norris椭圆模型的计算结果很接近. 在研究交流传输损耗和热循环的关系时, 发现随着冷热循环次数的增加, 交流损耗也在增加. 这种损耗的增加来源于冷热循环过程中产生的应力, 这种应力的释放减弱了晶粒间的Josephson连接, 使临界电流下降, 从而造成了交流传输损耗的增加.     

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.     

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。     

10 kV紧凑型三相同轴高温超导电缆交流损耗研究

根据10 kV紧凑型三相同轴高温超导电缆参数,在COMSOL Multiphysics有限元软件中建立电缆的二维仿真模型,基于H方程求解了电缆在额定工况稳态运行时以及不同传输电流下的磁场分布和交流损耗;在此基础上,分析了绕制半径、相间距离以及相间相对角度对交流损耗的影响.仿真结果表明,各相超导层绕制半径越小,相间距离越小,各相产生的交流损耗越小;三相的交流损耗有随着超导层结构周期性变化的特点,且当相间相对角度为0°时,各相产生的交流损耗最大.     

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。     

45 kVA单相高温超导变压器交流损耗特性研究

本文研究以多芯不锈钢加强Bi2223/Ag带材绕制的45 kVA单相高温超导变压器的交流损耗特性.变压器绕组置于具有室温孔径的环形玻璃钢杜瓦内,铁芯穿过杜瓦室温孔径以保证铁芯与绕组分离并工作于室温环境.在77 K和工频下,基于Bean模型和绕组中的磁场分布计算了绕组的交流损耗,计算结果与传统电测法和热测法测量的变压器交流损耗结果一致;表明在77K绕组中交流损耗以磁滞损耗为主,涡流损耗和耦合损耗可以忽略不计.     

高温超导YBCO线圈交流损耗的频率特性

YBCO线圈的交流损耗直接关系到YBCO设备的运行成本及稳定性。实现对YBCO线圈交流损耗的快速、准确测量,对于开展YBCO涂层导体的应用研究具有重要的意义。文中采用电测量法,在77K、零场和不同频率条件下,对YBCO线圈通以不同运行电流时产生的交流传输损耗进行测量。构建了YBCO线圈交流损耗的数值计算模型,对YBCO线圈交流损耗进行理论研究,最后将实验数据与理论计算结果进行比较,两者结果基本一致。可以发现,YBCO线圈在频率低于75Hz时,交流传输损耗随频率的增大而减小,当频率从75Hz增加到195Hz时,交流传输损耗随频率的增大而增加。     

一种铁基超导带材交流损耗的测量

近年来铁基超导材料的发现掀起了又一轮新型超导材料研究的热潮,各种配方的铁基超导材料不断被制备出来,转变温度也不断提高,中国科学家在该领域取得了十分突出的成果,制备出了多种铁基超导材料,但对其交流损耗特性研究鲜有报道,而实际应用中交流损耗的特性又十分重要,因此搭建了一套采用探测线圈法的交流损耗测量平台,测试了一种中国科学院电工研究所采用PIT工艺制作的单芯铁基超导带材的交流损耗。该文介绍了采用探测线圈法测量超导材料交流损耗的一种测量平台的搭建与标定,以及采用标定过的测量平台在液氦温度下测量的一种采用PIT工艺制作的单芯铁基超导带材的交流损耗;并与计算得到的铁基带材超导芯的磁滞损耗和包套的涡流损耗进行了比较分析,得出了其交流损耗与背景磁场频率成正比,其涡流损耗可以忽略的结论。     

依靠传导冷却装置测试MgB_2电线的交流损耗特性

该实验使用传导冷却装置研究了以铁和铜作为隔离材料的MgB_2的交流损耗特性。通过传导冷却装置将MgB_2电线的工作环境冷却到4K,并采用交流脉冲技术测量并评估了它们在几百毫秒范围内的交流损耗特性。测试结果表明Fe/MgB_2的交流损耗主要产生在铁制隔离材料周围。它的交流损耗是Cu/MgB_2的十倍。在实验中通过使用传导冷却装置记录了交流损耗的测试结果,并且就交流损耗对频率,温度的依赖性也进行了实验,最后对结果进行讨论,并且对该技术进行评估。     

AC losses in multifilamentary HTS-composite tapes based on BiPbSrCaCuO

Some results of AC loss measurements are presented for 19, 61, 127-filamentary Bi-2223/Ag tapes prepared by the ‘powder-in-tube' method. All measurements have been made at T=77 K under sinusoidal transport current with frequency in the range of 30–600 Hz and the current amplitude up to 30 A. The measurements have been carried out both in self field conditions and at the external magnetic field applied to the tape at the different angles. The dependencies of the AC losses on current amplitude and frequency have been obtained. It is found that for all tapes the current amplitude dependencies of the AC losses show good agreement with the Norris prediction for an elliptical or strip geometry. The AC loss dependencies on frequency were linear. The measurements of AC losses in external magnetic field show that the change of AC losses is only through the change of the critical current. So the transport AC losses in the tapes are the ‘saturation losses' that is they are different from classic hysteresis losses.     

AC losses dependence on a CuNi layer location in NbTi CICC

In the frame of the ITER fusion program, large Cable In Conduit Cables (CICC) made with NbTi superconductors are foreseen for the poloidal field system. These coils are pulsed and so subjected to fast variations in magnetic field. Superconductors have then to be designed in order to reduce AC losses to an acceptable level. A solution could be to insert a copper nickel resistive barrier in the copper stabilizer surrounding the filamentary area of the composite. The purpose of this barrier is to reduce interstrand coupling currents. In order to predict the effect of this barrier on AC losses, a modeling of a 36 strands CICC has been realized. According to this code, the ability of the resistive barrier to reduce coupling currents is dependent on its location. For this study, three CICC with three barrier locations, from the inner to the outer diameter of the copper crown stabilizer, have been produced. AC losses have been measured and compared to our numerical model.     

AC loss of low temperature superconducting AC wire caused by longitudinal and azimuthal AC magnetic field components

We investigated the AC loss characteristics of a low temperature NbTi AC wire by measuring the AC transport current losses in the external AC magnetic field whose components are the longitudinal and transverse ones. The measurement results showed that the AC losses were significantly dependent on the directions and magnitudes of the external longitudinal field component. The AC losses caused by the longitudinal and azimuthal field components were estimated by our previously derived model. The theoretical results well explained the dependence of the AC losses on the longitudinal field components. It was also shown that the AC losses can be substantially reduced by the proper choice of the twisting way.     

Self-field AC losses of textured Bi2Sr2CaCu2O8+δ thin rods

Self-field AC losses of polycrystalline Bi-2212 thin rods textured by a Laser Floating Zone (LFZ) melting technique have been measured at 77 K. With the optimal processing parameters, these rods, of 1.6–2 mm diameter and 10 cm length, have a transport critical current density of 3 kA/cm² in the self-field which decreases to about 1.5 kA/cm² in fields of 0.02 T applied perpendicular to the rod axis. The self-field AC losses have been measured in DC magnetic fields up to 0.03 T. The measurements in zero field show that for a large current range the losses are dominated by hysteresis losses as described by the Critical State Model for a cylinder. For the measurements in DC fields the losses show an increasingly resistive-like dependence with current, while the hysteretic component expected from the CSM becomes less important. Measurements at different frequencies also indicated that the loss per cycle in fields is strongly frequency dependent.     

大型超导电缆交流损耗的计算

给出了超导电缆交流损耗的表达式。使用这些表达式 ,并基于 HT- 7U极向场线圈系统在等离子体建立时的电流波形 ,计算了 AC损耗在 PF导体上的能量沉积。最后讨论了电缆参数对AC损耗的影响     

Electrical AC loss measurements of Bi-2223 tapes, performed under the Brite EuRam Research programme SACPA

A series of electrical AC loss measurements on Bi-2223 tapes have been performed under the Brite Euram project SACPA. This included, for the first time, a round-robin of independent self-field AC loss measurements between four laboratories. The very close agreement of data demonstrates the validity of the electrical technique and lays the basis for a measurement standard. Other preliminary measurements in SACPA showing the variation of losses with frequency, temperature and applied DC field are also reported.     

AC losses in multifilamentary Bi(2223) tapes with an interfilamentary resistive carbonate barrier

For the most common AC application frequencies, the main component of the AC losses in multifilamentary Bi(2223) tapes are caused by hysteresis- and coupling losses. These losses can be reduced enhancing the matrix resistivity and applying a twist to the filaments. We report on the AC loss properties of 37-filament tapes with AgAu (8 wt.%) matrix, and novel 19-filament tapes with SrCO₃ barriers between the filaments. We performed transport AC loss and magnetic AC loss measurements in parallel and perpendicular magnetic fields. Both kinds of tapes were also prepared with filament twists below a twist pitch of 20 mm. The influence of the different tape modifications on the AC loss behaviour is presented and compared with theoretical models to understand the effect of the resistive matrix. In the case of magnetic AC loss measurements, reduced AC losses due to decoupled filaments were observed for the twisted tapes with a resistive matrix in low parallel fields.     

The similarities in loss creation in LTS and HTS cables

The coupling current losses represent an essential contribution to AC losses in most practical superconducting conductors. The origin of this loss type is well known, being caused by induced currents in different loops consisting of superconducting and non-superconducting parts. However, the ‘current pattern' in different conductor types (strands, flat or round cables, more complicated cable structures, CICC) varies appreciably. These differences are mainly due to geometrical effects (size and shape of filaments and/or strands, their spatial distribution, conductor aspect ratio, demagnetization effects). Although the general knowledge about AC losses in low temperature cable structures is by far not complete (mainly at higher frequencies, in inhomogeneous fields and for inhomogeneous cable structure), an attempt is made to summarize those results which can be adopted to high T_c conductors and some remarks are made about new features of AC losses in these conductor types.