• Progress in Superconductivity and Cryogenics
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• v.7 no.3
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• pp.34-38
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• 2005

Multi-stacked HTS tapes are needed to conduct large current in the power application. In this paper, magnetization losses of the multi-stacked YBCO coated conductor and the BSCCO tape have been measured and compared. Magnetization losses of single tape, 2-stacked, 3-stacked and 4-stacked HTS tapes have been presented in this paper. Multi-stacked tapes have been fabricated using face-to-face type stacking method. Measurements of magnetization loss were performed under various angle of external magnetic field to consider the anisotropic characteristics of HTS tapes. Test results show that loss density per unit volume decreased for both YBCO coated conductors and BSCCO tapes when the stacking number of tapes is increased. The magnetization losses of YBCO CC are larger than those of BSCCO tapes when the external magnetic field is increased.

• Progress in Superconductivity and Cryogenics
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• v.10 no.3
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• pp.43-46
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• 2008

Design of current lead for 21T superconducting magnets is presented. The current lead is composed of a normal metal element, conducting the current from room temperature to intermediate temperature, and an HTS element, conducting the current down to liquid helium temperature. The metal element is disengaged from the HTS element without breaking vacuum after excitation. The optimization of the lead is performed to minimize the thermal heat load when carrying operational current with some margin. In order to confirm the feasibility of our new design, the intermediate joint between a normal metal and HTS element is fabricated and the reliability is tested during engage and disengage performance. The effects of vacuum level and performance cycle on the electrical contact resistance are also investigated.

• Progress in Superconductivity and Cryogenics
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• v.12 no.2
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• pp.21-24
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• 2010

This paper deals with numerical analysis on a high-$T_c$ superconducting (HTS) electrodynamic suspension (EDS) simulator according to the variation of the ground conductor conditions. Because the levitation force of EDS system is formed by the magnetic reaction between moving magnets and fixed ground conductors, the distribution of the magnetic flux on a ground conductor plays an important role in the determining of the levitation force level. The possible way to analyze HTS EDS system was implemented with 3D finite element method (FEM) tool. A plate type ground conductor generated stronger levitation force than ring type ground conductor. Although the outer diameter of Ring3 (335 mm) was larger than that of Ring2 (235 mm), the levitation force by Ring2 was stronger than that by Ring3. Considering the results of this paper, it is recommended that the magnetic flux distribution according to the levitation height and magnet current should be taken into account in the design of the ground conductors.

• Progress in Superconductivity and Cryogenics
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• v.19 no.3
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• pp.49-53
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• 2017

The superconducting magnets have a large inductance as well as high operating current. Therefore, mega-joule scale energy can be stored in the magnet. The energy stored in the magnet is sufficient to damage the magnet when a quench occurs. Quench heater and dump resistor can be used to protect the magnet. However, using quench heater to create quench resistors through heat transfer can be slower than instantly switching resistors. Also, electrical short, overheating and breakdown can occur due to quench heater. Moreover, the number of dump resistor should be limited to avoid large terminal voltage. Therefore, in this paper, we propose a quench protection method for extracting the energy stored in a magnet by charging and discharging energy through a capacitor switching without increasing resistance. The simulation results show that the proposed system has a faster current decay within the allowable voltage level.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.4
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• pp.552-560
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• 1997

Analysis is performed to determine the optimal lengths or cross-sectional areas of refrigerator-cooled current leads that can be applied to the conduction-cooled superconducting systems. The binary current lead is composed of the series combination of a normal metal at the upper(warm) part and a high $T_c$ superconductor(HTS) at the lower(cold) part. The heat conduction toward the cold end of HTS part constitutes a major refrigeration load. In addition, the joint between the parts should be cooled by a refrigerator in order to reduce the load at the low end and maintain the HTS part in a superconducting state. The sum of the work inputs required for the two refrigeration loads needs to be minimized for an optimal operation. In this design, three simple models that depict the refrigeration performance as functions of cooling temperature are developed based on some of the existing refrigerators. By solving one-dimensional conduction equation that take into account the temperature-dependent properties of the materials, the refrigeration works are numerically calculated for various values of the joint temperature and the sizes of two parts. The results show that for given size of HTS, there exist the optimal values for the joint temperature and the size of the normal metal. It is also found that the refrigeration work decreases as the length of HTS increases and that the optimal size of normal metal is quite independent of the size of HTS. For a given length of HTS, there is an optimal cross-sectional area and it increases as the length increases. The dependence of the optimal sizes on the refrigerator models employed are presented for 1kA leads.

• 한국초전도학회:학술대회논문집
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• 2009.07a
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• pp.121-121
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• 2009

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.367-368
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• 2009

BSCCO HTS(High Temperature Superconductor) could be applied to superconducting cable, magnet and motor, using its hight critical properties. Especially, superconducting cable has a hight possibility of practical use due to the possibility of low voltage and high capacity transmission caused by its lower power loss than copper cable. In this paper, the transport characteristics of BSCCO superconducting cable, according to the change of BSCCO superconducting cable's accident point at phase $0^{\circ}$ and $45^{\circ}C$, were analyzed and compared each other. Consequently, when the accident was occur the resistance of the HTS was higher at the point phase $0^{\circ}$ than $45^{\circ}$ which means it will cause much higher load on the HTS.

• Progress in Superconductivity and Cryogenics
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• v.22 no.3
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• pp.1-6
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• 2020

This paper presents the analysis results on the electrical output performance characteristics of a 746 W high temperature superconducting generator (HTSG). The HTS field winding is charged by non-contact excitation method, i.e., contactless superconducting field exciter (CSFE) which is originated by rotary flux pump based on permanent magnet. In this paper, the preliminary current charging test was carried out using a 70 A CSFE to evaluate the performance of field exciter and analyze its non-contact excitation characteristics for the full-scale HTS field winding of the 746 W HTSG. First, the various contactless current-charging tests were conducted using assembly with HTS field winding and CSFE. Then, in order to estimate the output power performance characteristics of the 746 W HTSG, finite element analysis was conducted based on field excitation information which is experimentally measured under various operating conditions. Finally, the electrical output characteristics in no-load and load models were simulated by two-dimensional transient solver in ANSYS electromagnetics 19.0 release.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.835-837
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• 1998

Current lead plays the part of connector between ambient temperature and liquid helium superconducting magnet. Having zero resistance characteristic, it is expected that HTS has very low thermal conductivity and generate no joule heat when fabricated to current lead. In particular, among the HTS meterials, HTS tape has high Jc and Ag-sheath of tape plays the part of stabilizer, but it has too poor mechanical strength to be applied and when fabricated as long length tape, it has tendency to decline Jc seriously. In this study, we fabricated Bi-2223 multifilamentary tapes and then made current lead with stacking type using them. Through this work, we conclude that the defect of HTS long length tape is decreased by addition the number of stacking tape and that current lead is able to operate more stably by minimizing the gap of tapes.

• Progress in Superconductivity and Cryogenics
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• v.17 no.1
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• pp.14-16
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• 2015

Due to the considerable development of the technology of second generation high-temperature superconductors and a significant improvement in their mechanical and transport properties in the last few years it is possible to use HTS tapes in the magnetic levitation systems. The advantages of tapes on a metal substrate as compared with bulk YBCO material primarily in the strength, and the possibility of optimizing the convenience of manufacturing elements of levitation systems. In the present report presents the results of the magnetic levitation force measurements between the stack of HTS tapes containing $n=2{\div}200$ of tapes $12mm{\times}12mm$ and NdFeB permanent magnet in the FC and ZFC regimes. It was found a non- linear dependence of the levitation force from the height of the array of stack in both modes: linear growth at small thickness gives way to flattening and constant at large number of tapes in the stack. Established that the levitation force of stacks comparable to that of bulk samples. The numerical calculations using finite element method showed that without the screening of the applied field the levitation force of the bulk superconductor and the layered superconductor stack with a critical current of tapes increased by the filling factor is exactly the same, and taking into account the screening force slightly different.