• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.775-777
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• 2000

Superconducting racetrack coils are used in areas of generators, motors, wiggler magnets and so on. Especially now a days many advanced nations including U.S., Japan are developing high temperature superconducting(HTS) wire which has better performance than low temperature superconducting(LTS) wire. Most of HTS wires such as Bi-2223 are manufactured with PIT(Power In Tube Method) process, so the shape of the wire looks like tape different from LTS wire of round shape as normal conductors. Generally HTS racetrack coils are composed of a few partial double-pancake colis and then the double-pancakes are jointed each other according to their applications.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.147-149
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• 1995

The stabilization of the conductor in superconducting power cable is very important from the view point of protection. In this study, critical thicknesses of superconducting layer of $Nb_{3}Sn$ conductor and stabilizer Cu have been estimated under the adiabatic condition. The bending stress of $Nb_{3}Sn$/SUS composite superconducting tape on the curvature radius was also evaluated.

• Progress in Superconductivity and Cryogenics
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• v.24 no.1
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• pp.1-7
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• 2022

So far, large-scale scientific devices such as nuclear fusion tokamaks and high energy circular accelerators were constructed using high-current conductors made of metallic superconducting wires. Recently, as REBCO superconducting wires usable in high magnetic fields have been developed by several companies, researchesto apply high current cable type REBCO conductors to next-generation large superconducting magnets were also started. High critical currents of several kA or more in high magnetic fields have been successfully demonstrated on test samples of REBCO cable conductors by several research groups. In this review article, the main features and properties of the representative high current REBCO conductors such as CORC(Conductor On Round Core), TSTC(Twisted Stacked-Tape Cable) and RACC(Roebel-Assembled Coated Conductor), which are currently being developed at abroad are briefly introduced. Research activities of high-current density REBCO MHOS(Multi HTS layers on One Substrate) conductor at KERI, whose structure is different from other cable type REBCO conductors are also shortly introduced.

• Progress in Superconductivity and Cryogenics
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• v.11 no.4
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• pp.25-28
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• 2009

In order to apply superconducting electric machineries such as a Superconducting Fault Current Limiter (SFCL) to the power grid, the single module should be connected in series to have reasonable size. Superconducting tapes in the module also should be stacked to satisfy requirements such as large operation current of the power grid. This is because a single superconducting tape has restricted applicable current capacity. Moreover especially in SFCL at the fault, there should be equal voltage distribution in series-connected SFCL modules. In this paper, we investigated the voltage distribution in fault current of series-connected YBCO coated conductors (CC). Depending on characteristics of the CC samples such as critical current, even voltage distribution could be achieved or not. In addition, the effect of stacked CC on the change of voltage distribution comparing to non-stack cases in series connection was confirmed by experiments. As the CC stacked, voltage difference could be reduced.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.585-588
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• 2003

Bi-2223 superconducting wires were fabricated by stacking, drawing process with different precursor powders and different heat-treatment histories. The precursor powders were 2 kinds of Pb content. And a part of the tapes were experienced pre-annealing process which caused tetragonal structure of Bi-2212 phase to orthorhombic structure of it was during drawing process. We confirmed the transformation of Bi-2212 phase from tetragonal structure to orthorhombic structure and reduction of second phases. AC magnetization analysis were performed in order to investigate the fraction of Bi-2223 phase in Bi-2223/Ag HTS tape. The cross sections of 55 filaments and 61 filaments were investigated after rolled in order to understand deformation mechanism of superconducting cores. We could achieve best Ic of 70 A class at the Bi-2223/Ag tape using low Pb content of precursor powder and experienced pre-annealing process. AC magnetization analysis was useful to investigate the fraction of Bi-2223 phase in the Bi-2223/Ag tape.

• Progress in Superconductivity
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• v.14 no.1
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• pp.1-10
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• 2012

We fabricated a closed coils by using resistive-joint method and the joint resistance of the coils were estimated by field decay technique in liquid nitrogen. We used the Runge-kutta method for the numerical analysis to calculate the decay properties. The closed coil was wound by $(Bi,Pb)_2Sr_2Ca_2Cu_3O_x$/Ag tape. Both ends the tape were overlapped and soldered to each other. The current was induced in a closed coils by external magnetic flux density. Its decay characteristic was observed by means of measuring the magnetic flux density generated by induced current at the center of the closed coil with hall sensor. The joint resistance was calculated as the ratio of the inductance of the loop to the time constants. The joint resistances were evaluated as a function of critical current of loop, contact length, sweep time, and external magnetic flux density in a contact length of 7 cm. It was observed that joint resistance was dependent on contact length of a closed coil, but independent of critical current, sweep time, and external magnetic flux density. The joint resistance was measured to be higher for a standard four-probe method, compared with that for the field decay technique. This implies that noise of measurement in a standard four-probe method is larger than that of field decay technique. It was estimated that joint resistance was $8.0{\times}10^{-9}{\Omega}$ to $11.4{\times}10^{-9}{\Omega}$ for coils of contact length for 7 cm. It was found that 40Pb/60Sn solder are unsuitable for persistent mode.

• Proceedings of the KIEE Conference
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• 1999.11b
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• pp.438-441
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• 1999

One of the most important aspect in developing High-Tc Superconducting Synchronous Motor is producing high-Tc superconducting tapes that withstand the amount of currents that is needed to run the motor with stability. The purpose of this paper is to find the magnetic field distribution inside the motor in order to find out if the high-Tc superconducting tapes operate stably in actual motor operation. With this goal, magnetic field distribution in a detailed model of the actual motor was analyzed through F.E.M. By analyzing the field distribution acquired through the computer simulation, it has been observed whether the high-Tc superconducting tape maintains its superconductivity in actual motor operation. Also, the effects of the flux damper on the motor's operational characteristics and the magnetic field distribution have been analyzed. As a result, it has been proved that the high-Tc superconducting tapes can withstand 600 A turns which is required by the previous simulation aimed at developing this motor. It has also seen that the flux damper reduces armature reactance during the motor operation and change of load, helping the stable motor operation.

• Progress in Superconductivity and Cryogenics
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• v.17 no.3
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• pp.47-50
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• 2015

The high temperature superconducting (HTS) magnet has been developed for the high magnetic field applications such as NMR, MRI and other industrial machinery. In designing process of these HTS magnets, the accurate estimation on the critical current (Ic) is essential to predict and secure the electromagnetic performance. The critical current of 2G HTS tape has anisotropic Ic degradation characteristics with the application of magnetic field - angular dependency of critical current. It is known that the perpendicular magnetic field to the face of HTS tape makes dominant degradation on the critical current for conventional 2G HTS tape. However, recently developed 2G HTS tape has more complex characteristics due to the artificial pinning center. Therefore, the method for Ic estimation reflecting such characteristics of 2G HTS tape needs to be devised. The method considering the angular dependency is introduced in this paper. And the result of newly devised method is compared with that of previous method.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.298-303
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• 2000

We evaluated the electric properties of Bi-2223 jointed tapes processed by both resistive- and supercondcuting-joint methods. For the resistive-joint, filler materials of wood metal, Pb/Sn, In, and silver paste were used, whereas, for the superconductive-joint, the lap joint method were used. In the resistive-joint tape, it was observed that the electrical properties such as current transport property, n-value, and contact resistance of the tape were significantly related to the resistivity of filler materials. On the other hand, in the superconducting-joint tape, the current transport property was dependent on the uniaxial pressure. Specifically, the current transport property varied 50 to 80% with uniaxial pressure, probably due to the irregular microstructure in the transition region.

• Progress in Superconductivity and Cryogenics
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• v.7 no.2
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• pp.11-15
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• 2005

The I$_{c}$ degradation behavior of Bi-2223 tapes bent at RT and 77K were investigated using the bending device invented by Goldacker. Test results on fixing the tape at RT and 17K showed no difference. At 17K and RT bending, the critical strain was 0.67 and 0.50$\%$, respectively, for the VAM-l tape. For the AMSC tape, it was 0.94 and 0.88$\%$, respectively. These results show that there is additional residual stress in the superconducting filaments to be bent at 17K which shifts the formation of cracks into smaller bending radii. This was proved by computational analysis based on the mixture rule of composites. For the VAM-l tape, the Ie degradation behavior using the Goldacker type device shifted to higher strain levels at about 0.5$\%$, as compared with the FRP sample holders which have a critical bending strain of about 0.24$\%$. Also, for the externally reinforced AMSC tape, Ie degradation using the Goldacker type device begins at a higher strain level, at 0.88$\%$ as compared with using FRP sample holders, at 0.74$\%$. The difference between both cases can be explained by the tensile' and thermal stresses that the tapes were subjected to during fixing (soldering) when the FRP sample holders were used.