• Progress in Superconductivity and Cryogenics
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• v.19 no.1
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• pp.13-16
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• 2017

Water issue, especially water pollution, is a serious issue of 21st century. Being an significant technique for securing water resources, superconducting magnetic separation wastewater system was indispensable. A large bore conduction-cooled magnet was custom-tailored for wastewater treatment. The superconducting magnet has been designed, fabricated and tested. The superconducting magnet was composed of NbTi solenoid coils with an effective horizontal warm bore of 400 mm and a maximum central field of 2.56T. The superconducting magnet system was cooled by a two-stage 1.5W 4K GM cryocooler. The NbTi solenoid coils were wound around an aluminum former that is thermally connected to the second stage cold head of the cryocooler through a conductive copper link. The temperature distribution along the conductive link was measured during the cool-down process as well as at steady state. The magnet was cooled down to 4.8K in approximately 65 hours. The test of the magnetic field and quench analysis has been performed to verify the safe operation for the magnet system. Experimental results show that the superconducting magnet reached the designed magnetic performance.

• Progress in Superconductivity and Cryogenics
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• v.22 no.2
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• pp.7-11
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• 2020

When rivers and lakes are contaminated with numerous contaminants, usually the contaminants are finally deposited on the sediments of the waterbody. Many clean up technologies have been developed for the contaminated sediments. Among several technologies dredging is one of the best methods because dredging removes all the contaminated sediments from the water and the contaminated sediments can be completely treated with physical and chemical methods. However the most worried phenomenon is suspension of fine particles during the dredging process. The suspended particle can release contaminants into water and resulted in spread of the contaminants and the increase of risk due to the resuspension of the precipitated contaminants such as heavy metals and toxic organic compounds. Therefore the success of the dredging process depends on the prevention of resuspension of fine particles. Advanced dredging processes employ pumping the sediment with water onto a ship and release the turbid water pumped with sediment into waterbody after collection of sediment solids. Before release of the turbid water into lake or river, just a few minutes allowed to precipitate the suspended particle due to the limited area on a dredging ship. However the fine particle cannot be removed by the gravitational settling over a few minutes. Environmental technology such as coagulation and precipitation could be applied for the settling of fine particles. However, the process needs coagulants and big settling tanks. For the quick settling of the fine particles suspended during dredging process magnetic separation has been tested in current study. Magnetic force increased the settling velocity and the increased settling process can reduce the volume of settling tank usually located in a ship for dredging. The magnetic assisted settling also decreased the heavy metal release through the turbid water by precipitating highly contaminated particles with magnetic force.

• Progress in Superconductivity and Cryogenics
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• v.14 no.4
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• pp.24-27
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• 2012

The measurement of the coefficient of thermal expansion (CTE) of polypropylene laminated paper (PPLP) as electric insulating material is important for its practical superconducting device application. The thermal strain induced to HTS tapes and its insulating material during cooling from room temperature might largely affect the critical current ($I_c$) of HTS tapes. In this study, the thermal contraction of PPLP material was measured during cooling from 300 K to 77 K using double extensometers. Initially, the CTE of a brass tape was measured and it was compared with a reference data. It was found that the measured thermal expansion data of the brass material approaches that of the reference one. Based on the results, it was then confirmed that the measurement technique could be applied to thin and flexible samples. Therefore, the same measurement procedure was applied to PPLP material using double extensometers. As a result, the linear CTE of the PPLP at 77 K has been measured to be ${\sim}15.3{\times}10^{-6}/K$. Also, it was found that the thermal contraction characteristics of PPLP was dominated by polypropylene on the cross direction (higher thermal contraction) while it was dominated by Kraft paper on the machine direction (lower thermal contraction). Overall, this measurement procedure could be adopted for the determination of CTE of flexible materials such as PPLP.

• Progress in Superconductivity and Cryogenics
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• v.25 no.2
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• pp.5-9
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• 2023

The effect of La_0.7Sr_0.3MnO₃ (LSMO) addition on the superconducting property of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ ((Bi, Pb)-2223) polycrystalline samples was studied. LSMO (0.3 wt.% to 2.0 wt.%) added (Bi, Pb)-2223 samples were prepared by using a solid-state reaction method. The XRD analyses show that as the LSMO addition increases, the volume fraction of the Bi-2223 phase is gradually decreased. The critical temperature (T_c) exhibits a gradual decrease with a single transition as the LSMO amount increases up to 1.0 wt.%, but a further addition of LSMO induces an abrupt decrease of T_c with a dual transition. The analyses on the local structure of the CuO₂ plane from the X-ray absorption fine structure (EXAFS) measurements showed that for the samples with low concentration of LSMO up to 1.0 wt.%, the Cu-O bond length and the CuO₂ plane ordering do not degrade from the values of pure (Bi, Pb)-2223, while they get worsen with a further increase of LSMO addition. These results open up the possibility of LSMO as artificial pinning centers of the (Bi, Pb)-2223 system for power application.

• Progress in Superconductivity and Cryogenics
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• v.21 no.2
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• pp.31-35
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• 2019

Andong-dam was built up in 1967 and it is one of the biggest dams in Korea. Previous studies showed that the sediments are highly contaminated with heavy metals such as arsenic, cadmium, and lead. Many research projects are going on to find out the source of the contamination, to evaluate the toxicities to ecosystem, to estimate the volume of sediment to be treated and to find out a good remediation method. Reports show that the sediment is highly contaminated and the main contamination source is supposed to be abandoned mines and a zinc refinery located upper stream of the river. A magnetic separation has been tested as a treatment method for the dredged sediment. Lab scale test showed that the magnetically captured portion is about 10% in weight but the contamination of heavy metal is much higher than the contamination of the passed portion. This indicates that a magnetic separation could be applied for the purpose of reduction of sediment to be treated and for increasing the volume of low toxic sediments which can be dumped as general waste. A magnetic separation using a HGMS has been tested for the sediment with variable magnetic field and the results showed the higher magnetic field increase the captured portion but the concentrating effect of heavy metal was weakened. Further study is needed to establish a useful technology and optimization between decontamination and reduction of sediment volume.

• Progress in Superconductivity and Cryogenics
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• v.9 no.4
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• pp.32-36
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• 2007

We fabricated and tested a novel hybrid superconducting fault current limiter (SFCL) of three-phase $24kV_{rms}/630A_{rms}$ rating. In order to apply conventional resistive SFCLs into electric power systems, the urgent issues to be settled are as follows, such as initial installation price of SFCL, operation and maintenance cost due to ac loss of superconductor and the life of cryostat, and high voltage and high current problems. The ac loss and high cost of superconductor and cryostat system are main bottlenecks for real application. Furthermore in order to increase voltage and current ratings of SFCL, a lot of superconductor components should be connected in series and parallel which resulted in extreme high cost. In addition, the method to quench all components at the same instant needs very sophisticated skill and careful operation. Due to these problems, the practical applications of SFCL were pending. Therefore, in order to make practical SFCL, the price of SFCL should be lowered and should meet the demand of utilities. We designed novel hybrid SFCL which combines superconductor and conventional electric equipment including vacuum interrupter, power fuse and current limiting reactor. The main purpose of hybrid SFCL is to drastically reduce total usage of superconductor by adopting current commutation method by use of superconductor and high fast switch. Consequently, it was possible to get the satisfactory test results using this method, and further works for field tests are in the process.

• Progress in Superconductivity and Cryogenics
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• v.20 no.3
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• pp.21-27
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• 2018

It is difficult to fabricate and maintain moving parts of expander at cryogenic temperature. This paper describes numerical analysis and experimental investigation on a cryogenic reciprocating expander without moving piston. An intake valve which takes high-pressure gas, and an exhaust valve which discharges low-pressure gas, are connected to a tube. The inside pressure of the tube is pulsated for work production. This geometric configuration is similar to that of pulse tube refrigerator but without regenerator. An orifice valve and a reservoir are installed to control the phase of the mass flow and the pressure. At the warm end, a heat exchanger rejects the heat which is converted from the produced work of the expanded gas. For the numerical analysis, mass conservation, energy conservation, and local mass function for valves are used as the governing equations. Before performing cryogenic experiments, we carried out the expander test at room temperature and compared the performance results with the numerical results. For cryogenic experiments, the gas is pre-cooled by liquid nitrogen, and then it enters the pulse tube expander. The experiments are controlled by the opening of the orifice valve. Numerical analysis also found the expander conditions that optimize the expander performance by changing the intake pressure and valve timing as well as the opening of the orifice valve. This paper discusses the experimental data and the numerical analysis results to understand the fundamental behavior of such a newly developed non-mechanical expander and elucidate its potential feature for cryogenic application.

• Progress in Superconductivity
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• v.13 no.2
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• pp.127-132
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• 2011

Many research groups have been manufacturing coated conductor by various processes such as PLD, MOD, and MOCVD, but the methods with production cost suitable for wide and massive application of coated conductor did not develop yet. Spray pyrolysis method adopting ultrasonic atomization was tried as one of the possible option. GdBCO precursor films have been deposited on IBAD substrate by spray pyrolysis method at low temperature and converted to GdBCO by post heat treatment. Ultrasonic atomization was used to generate fine droplets from precursor solution of Gd, Ba, and Cu nitrate dissolved in water. Primary GdBCO films were deposited at $500^{\circ}C$ and oxygen partial pressure of 1 torr. After that, the films were converted at various temperatures and low oxygen partial pressures. C-Axis oriented films were obtained IBAD substrates at conversion temperature of around $870^{\circ}C$ and oxygen partial pressures of 500 mtorr ~ 1 torr in a vacuum. Thick c-axis epitaxial film with the thickness of 0.4 ~ 0.5 ${\mu}m$ was obtained on IBAD substrate. C-axis epitaxial GdBCO films were successfully prepared by ex-situ methods using nitrate precursors on IBAD metal substrate. Converted GdBCO films have very dense microstructures with good grain connectivity. EDS composition analysis of the film showed a number of Cu-rich phase in surface. The precursor solution having high copper concent with the composition of Gd : Ba : Cu = 1 : 2 : 4 showed the better grain connectivity and electrical conductivity.

• Progress in Superconductivity and Cryogenics
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• v.8 no.1
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• pp.39-44
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• 2006

Before applying HTS power cable to the real utility. system analysis should be carried out by some simulation tools . Hereby the electrical power system analysis is very important for practical use of HTS devices. Nowadays PSCAD/EMTDC simulation tool is one of the most popular and useful analysis tool for the electrical power system analysis. Unfortunately the model component for HTS power cable is not provided in the PSCAD/EMTDC simulation tool In this paper. the EMTDC model component for HTS power cable has been developed considering critical current, critical temperature and recovery time constant that depend on the sorts of HTS wire. The numerical model of HTS Power cable in PSCAD/EMTDC was designed by using the real experimented data obtained from the real HTS 1G wire test. The utility application analysis of HTS power cable was also performed using the developed model component and the parameters of the real utility network in this study. The author's got good results. The developed model component for HTS power cable could be variously used when the power system includes HTS power cable, especially it will be readily analyzed by PSCAD/EMTDC in order to obtain the data for the level of fault current power flow, and power losses, and so on.

• Progress in Superconductivity and Cryogenics
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• v.9 no.1
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• pp.9-13
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• 2007

Coated conductor(CC) is recently in actively progress for the research and development, and its can be used various stabilizer lot the specific requirements for each application. Among various superconducting applications, coated conductor applied to superconducting fault current limiters(SFCLS) bypasses fault current to its stabilizer, where the surge is abruptly reduced ; thus, stainless steel, which has large resistivity can be a suitable stabilizer for SFCLS. Despite high n-value of the YBCO, CC stabilized with stainless steel did not effectively limit the first peak fault current. In the short circuit test results of AMSC's 344S, a half period delay was observed between the fault and the generation of resistance(60Hz). In this paper, we performed short-circuit experiments with stacked and unstacked CC and compared the test results to analyze effective fault current limiting characteristics. we compared time of the generated resistance as the fault current limiting characteristics and made the samples one is the stacked CC and the other is unstacked CC. These samples were used equal numbers of pieces of CC. In addition, comparison and analysis was made for the stacked structure by measuring fault current limiting characteristics with respect to thermal insulation by impregnating with epoxy resin.