Critical Current Of Tape Research Articles

Impact of shock waves on the conductive properties and structure of MgB2 tapes

This article presents data on shock waves effect on the structure and the critical current of superconducting MgB 2 tapes. To generate shock waves, a plasma focus installation (PF) was used. The conductive characteristics of the superconducting tapes dependence on the intensity of the impact and the number of shock pulses were studied. A distinct pattern of change in critical currents in transversal and longitudinal magnetic fields in the range of 2–9 T is studied at a temperature of 4.2 K. The microstructure of the superconducting tape and chemical composition of its layer are studied in the original state and after the shock wave effect. Changes were found in a microstructure of layers of MgB 2 (granulation, subdivision of grains and consolidation), which arose due to the shock-wave impact (SWI), are found. The possibility of increasing the critical current of tapes on 50–80 A in a transversal magnetic field of 2–3 T by means of SWI has been established. In a parallel magnetic field, the impact of the shock effect was essential in magnetic fields lower than 4 T.

Mechanical Behaviours in Bi2223/Ag/Ag Alloy Composite Tape with Different Volume Fractions

Bi2Cr2Ca2Cu3O x (Bi2223) composite tapes consisting of Bi2223 filaments, metal Ag and Ag alloy are usually exposed to a high magnetic field. The mechanical behaviour of composites is determined by the distribution and content of Bi2223 filaments in a magnetic field. Several Bi2223 composite tapes have different volume fractions of Bi2223 filaments, and the volume fraction is of fundamental importance in the determination of mechanical behaviour. In this paper, we present mechanical response to understand the effect of volume fraction of Bi2223 filaments. The critical current density is determined with consideration of the self field effect firstly. Then, the results of effective elastic moduli and mechanical stresses are presented based on the micromechanics approach. The mechanical response depends not only on the material properties but also on the Lorentz force. It is concluded from the computational results that the reduction of volume fraction of filaments can increase the mechanical stability, while the critical current density is decreased. Thus, it is necessary to consider both the mechanical limitation and requirement of the critical current of tape.

Winding Design and Electromagnetic Analysis for a 1250-kVA HTS Transformer

Because high-temperature superconducting (HTS) coils possess low-resistivity, large-current-carrying, and state transition characteristics, the design of HTS transformers is much different from that of conventional ones. The general design of 10.5-kV/1250-kVA HTS transformer is given first. In the electromagnetic design of the 1250-kVA HTS transformer windings via field-circuit coupling simulation, the influence of leakage magnetic field on the critical current of tapes and the circulating current of parallel branches was considered. Moreover, the transient stability of transformer windings combined with superconducting fault current limiter in the HTS power substation is discussed. Based on electromagnetic analysis, the primary and the secondary windings are constructed, and a special transposed method for double pancakes wound with four parallel tapes is proposed. Finally, the current-carrying ability of the primary and the secondary windings is tested in 77 K. Their critical currents are higher than 200 and 3200 A, respectively, which is enough in rated operating condition.

The Study of Mechanical Properties of HTS Tapes for Power Cables Use

Power cables are considered as the most advanced HTS applications. During cables' production numbers of HTS tapes are twisted around a circular former in several layers. The twisting leads to mechanical stresses for the tapes that may affect their superconducting properties. In this work we performed experiments to reproduce the influence of twisting on superconducting properties of HTS tapes. The HTS tapes were wound with different twist pitch around a former with the certain diameter and critical currents of tapes have been measured. We found the minimal twist pitch when the critical currents start decay after twisting. We tested several types of HTS tapes to compare their certified parameters with the measured ones. The details of the experimental method used are discussed and data about mechanical properties of different HTS tapes are presented.

Research on Effect of Ferromagnetic Material on the Critical Current of Bi-2223 Tape

In this paper we mainly focus on the effect of a ferromagnetic material on the critical current of Bi-2223 tape. The magnetic field distributions of tapes with several different layouts of a ferromagnetic material are investigated by calculation and the corresponding critical current is tested experimentally. The analysis indicates that the critical current of the tape can be improved effectively by laying the ferromagnetic material perpendicularly next to the tape edge. Furthermore, various other ferromagnetic parameters are also important for reducing the magnetic field induced by the current flowing through the tape.

Modelling method for critical current of YBCO tapes in cable use

Superconducting YBCO cables are suitable to transfer large amounts of energy due to their small space requirements and low losses. The large energy transfer capacity is achieved by connecting several coated conductor (CC) tapes in parallel. The critical currents of the tapes will be changed when they are placed from self-field to the magnetic field of the cable. In this paper, the change was determined from the cable geometry and intrinsic Jc(B)-dependence with fast and robust integral element method exploiting thin elements. The critical current distribution and the magnetic fields of 1kA cable were computed. The so-called gap effect causes the critical current of the individual tapes to rise from 86.5 to 88.8A when they are moved from the self-field to the cable field. The gap effect was studied as a function of width of the superconducting layers, cable radius and the number of the tapes. It was shown that the cable critical current can be given as a function of the tape number and the layer fill factor defined in this paper. In addition, the gap effect was studied as a function of zero field critical current density. The results suggest that up to 16% rise can be obtained with a cable of 25 tapes with critical current per tape width 500Acm−1.

Detecting and describing the inhomogeneity of critical current in practical long HTS tapes using contact-free method

The nondestructive and contact-free apparatus for measuring local critical current of long high temperature superconducting (HTS) tapes is presented. The local critical current of tape is acquired by using Hall probe array sensor to measure the remanent field after exposed to dc external magnetic field since the critical current is proportional to remanent field based on Bean critical state model. A detailed experiment on multifilamentary Bi2223/Ag tape is made to validate reproducibility, reliability, resolution, nondestructiveness and usefulness for manufacturer and user of tapes. The parameter COV (coefficient of critical current variation) is suggested for quantitatively describing the inhomogeneity and quality of practical long HTS tape based on Gaussian statistical analysis. The developed apparatus can detect HTS tape at velocity of 100 m/h with resolution smaller than 3 mm in liquid nitrogen.

Numerical calculation of critical current in Bi-2223 stacked tapes

As we stack HTS tapes, the critical current of stacked tapes is much less than the total summation of the critical current of each tape. This is mainly due to self magnetic field effects, and its behavior has been analyzed by load line or numerical methods with some assumptions. In this paper, we propose a simple numerical model to calculate the critical current of stacked tapes more exactly. To do this, we measured J/sub c/-B curves of a HTS tape for various values of external magnetic fields and the angles between the magnetic field and the tape surface. Using this experimental data, the current density distribution in the cross section of stacked tapes is calculated numerically and the results are compared to both experimental values and the ones from load line analysis method, calculated simply by assuming uniform current density across the tapes.

Mechanical tests on the surface-coated Bi-2212 superconducting tapes

The strain dependence of the critical current of surface-coated Bi-2212 tapes is reported. Two methods are used in the measurements. The effect of bend strain on the critical current is obtained by a stepped cone apparatus. Peak stress or strain dependence of the critical current and the effect of the number of strain cycles on the critical current is also studied on multiple samples by employing a new in situ stress/strain device. The results show that the number of strain cycles does not significantly affect the critical current. Rather, the critical current of the tape depends only on the level of peak strain.

Grain-boundary links and critical current of tapes

The nature of grain-boundary links in high-quality tapes is clarified. The investigations focus on the role that various types of links play in the restriction of the critical current. The multiple exponential function is found to be a good approximation for the magnetic-field dependence of critical current . The behaviour of at different temperatures gives clear evidence of the two-dimensional character of critical current. It is shown that at all temperatures higher than the Kosterlitz - Thouless transition temperature of isolated superconducting layers the critical current is totally defined by the Josephson interaction between the layers.