• Progress in Superconductivity and Cryogenics
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• v.9 no.2
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• pp.7-10
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• 2007

Persistent mode HTS pancake coil has been fabricated using a coated conductor by a "wind-and-flip" method. A coated conductor with the length of 1.2 meters was divided at the center along the length. The sliced coated conductor was wound on a pair of bobbins with a diameter of around 4 cm and two pancake coils connected superconductively without a resistive joint were prepared. By flipping one of the pancake coils, the magnetic field generated by each coil is to be aligned to the same direction and generate meaningful magnetic field while the magnetic fields of two spit coils are canceled without flipping. Permanent current was induced by flowing current to the coil immersed in liquid nitrogen pool using a power supply. A magnetic field of 48.8 Gauss was generated when 20 A of current was flowing in the pancake coils. The "Wind and flip" method can be applied for the fabrication of a long solenoid magnet by winding a sliced coated conductor on a cylindrical bobbin. It is also introduced that the construction of multiple sets of pancake (or solenoid) coils is possible by a "wind-and-flip" method using a wide coated conductor.

• Progress in Superconductivity and Cryogenics
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• v.15 no.4
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• pp.44-47
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• 2013

We had proposed a winding method so called "Wind-and-Flip", which enables a persistent current operation of an HTS pancake coil without any electrical joint. In order to improve the magnetic field drift characteristics, a prototype HTS coil with the technique was fabricated, and tested under various temperatures. Because the coil doesn't have any electric terminals for current leads, an HTS background magnet was used to induce the persistent current in the coil by field cooling process. A conduction cooling system with a GM cryocooler was prepared to keep the operating temperatures of the prototype coil much below the 77 K. We investigated the magnetic field drift characteristics under the various operating temperatures by measuring the center magnetic field with a cryogenic Hall sensor. The persistent current mode operation at 20 ~ 50K showed a strong possibility of the winding technique for the application such as MRI or NMR.

• Progress in Superconductivity and Cryogenics
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• v.12 no.4
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• pp.8-12
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• 2010

The properties of the conductor.mechanical, thermal, and electrical-are the key information in the design and optimization of superconducting coils. Particularly, in devices using second generation (2G) high temperature superconductors (HTS), whose base materials (for example, the substrate or stabilizer) and dimensions are adjustable, a design process for conductor optimization is one of the most important factors to enhance the electrical and thermal performance of the superconducting system while reducing the cost of the conductor. Recently, we developed a numerical program that can be used for 2G HTS conductor optimization. Focusing on the five major properties, viz. the electrical resistivity, heat capacity, thermal conductivity, Z-value, and enthalpy, the program includes an electronic database of the major base materials and calculates the equivalent properties of the 2G HTS conductors using the dimensions of the base materials as the input values. In this study, the developed program is introduced and its validity is verified by comparing the experimental and simulated results obtained with several 2G HTS conductors.

• Progress in Superconductivity and Cryogenics
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• v.9 no.2
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• pp.27-30
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• 2007

The electrical insulation design and withstanding test of mini-model coils for 600 kJ class conduction cooled high temperature superconducting magnetic energy storage (HTS SMES) have been studied in this paper. The high voltage is generated to both ends of magnet of HTS SMES by quench or energy discharge. Therefore, the insulation design of the high voltage needs for commercialization, stability, reliability and so on. In this study, we analyzed the insulation composition of a HTS SMES, and investigated about the insulation characteristics of the materials such as Kapton, AIN and vacuum in cryogenic temperature. Base on these results, the insulation design for 600 kJ conduction cooled HTS SMES was performed. The mini-model was manufactured by the insulation design, and the insulation test was carried out using the mini-model.

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.157-162
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• 2015

Large scale superconducting magnetic energy storage (SMES) system requires very high magnetic energy density in its superconducting coils to enhance the energy capacity and efficiency of the system. The recent high temperature superconducting (HTS) conductors, so called 2G conductors, show very good performance under very high magnetic field so that they seem to be perfect materials for the large scale SMES coils. A general shape of the coil system with the 2G HTS conductor has been a tor oid, because the magnetic field applied perpendicularly to the surface of the 2G HTS conductor could be minimized in this shape of coil. However, a toroid coil requires a 3-dimensional computation to acquire the characteristics of its critical current density - magnetic field relations which needs very complicated numerical calculation, very high computer specification, and long calculation time. In this paper, we suggested an analytic and statistical calculation method to acquire the maximum magnetic flux density applied perpendicularly to the surface of the 2G HTS conductor and the stored energy in the toroid coil system. Although the result with this method includes some errors but we could reduce these errors within 5 percent to get a reasonable estimation of the important parameters for design process of the HTS toroid coil system. As a result, the calculation time by the suggested method could be reduced to 0.1 percent of that by the 3-dimensional numerical calculation.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2001.02a
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• pp.57-60
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• 2001

In this paper, a design scheme of SMES coil with HTS wire(BSCCO 2223) for least stray field and conductor consumption is presented. Three types of coils (solenoid, multiple solenoid, and modular toroid) have been considered. Shape and size of the coil was decided by line element method with evolution strategy and confirmed with Finite Element Method. Modular toroid displayed least stray field with given conductor length. The goal of the study is to establish designing technology of a HTS coil for SMES which works in relatively high magnetic field.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.22-23
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• 2015

As wireless power transfer (WPT) technology using strongly coupled electromagnetic resonators is a recently explored technique to realize the large power delivery and storage without any cable or wire, this technique is required for diffusion of electric vehicles (EVs) since it makes possible a convenient charging system. Typically, since the normal conducting coils are used as a transmitting coil in the CPT system, there is limited to deliver the large power promptly in the contactless EV charging system. From this reason, we proposed the combination CPT technology with HTS transmitting antenna, In this study, we examined the improvement of transmission efficiency and properties for HTS and copper antennas, respectively, at 30 cm distance. Thus, we obtained improved transfer efficiency with HTS antenna over 10% compared with copper antenna

• Progress in Superconductivity and Cryogenics
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• v.17 no.1
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• pp.48-52
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• 2015

The electrical insulation design for a superconducting coil system is important for developing high voltage superconducting apparatuses. Also, the degraded characteristics of superconducting tapes due to an electrical breakdown should be considered for superconducting coils design. In this study, the degradation characteristics of 2G high temperature superconducting (HTS) tapes were studied with respect to electrical breakdown tests. The degradation tests of 2G HTS tapes were performed with various stabilizer materials. The degradation characteristics of 2G HTS tapes such as critical current(Ic) and index number were observed by performing electrical breakdown tests. It was found that the characteristics such as Ic and index number can be degraded by an electrical breakdown. Moreover, it was concluded that the degradation characteristics of 2G HTS tapes were affected by a stabilizer material and applied breakdown voltage. The cross sectional view of 2G HTS tapes was observed by using a scanning electron microscope (SEM). As results, it is found that the degradation characteristics of 2G HTS tapes are concerned with hardness and electrical resistivity of stabilizer layers.

• Progress in Superconductivity and Cryogenics
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• v.14 no.1
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• pp.30-33
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• 2012

A double pancake winding method is widely used to make the superconducting magnet, using high temperature superconductor (HTS) tape. In the double pancake winding method, the joints with contact resistances between double pancake coils are inevitably needed. The electrical joule heating on the contacts causes refrigerant loss during operation. And a space outside the winding, for splices and mechanical support, is more than that for its layer-wound equivalent. In this paper, a double pancake winding method in order to reduce the number of the joints was proposed. Both of the double pancake coils using the conventional winding method and the proposed winding method have been fabricated and tested to make the solution technically feasible in the double pancake winding method. Especially, critical-current tests of the fabricated double pancake coils were conducted in order to show the same performance and confirm contact resistances between double pancake coils.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1252-1254
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• 2005

High Tc superconducting(HTS) model coil was prepared. Current-voltage(I-V) characteristic curves of model coil, sub-coils and joints were investigated at 77K and other some temperatures. Cooling system for characteristics measurement was made by using G-M cryocooler. At 77K, quench current(Iq) of model coil was 43.9A and the lowest Iq of sub-coils was 38.8A. At 55K, sub coil SP #06 was 106A. So, 100A was chosen as the operating current at 55K with margin. Joule heat of model coil was 0.65W at 100A, operating current and 58K. Joint resistances between sub-coils were about $70n{\Omega}$ at 77K and about $30n{\Omega}$ at 55K.