• 한국초전도ㆍ저온공학회논문지
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• 제5권2호
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• pp.30-35
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• 2003

The inductive superconducting fault current limiter (SFCLJ limits the fault current with its dc reactor. To fabricate the optimal dc reactor for inductive SFCL, several design and manufacturing technologies are necessary. In this paper, the manufacturing technology for dc reactor and cryogenic cooling method are described in detail. GM-cryocooler was used enlarge the critical current of dc reactor by cooling down the temperature of dc reactor about 20 K. Moreover, the results of short circuit test were described. Finally, the thermal characteristics of conduction-cooled system were discussed and then, sub-cooled nitrogen system was proposed to enhance the thermal stability of dc reactor.

• 한국초전도ㆍ저온공학회논문지
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• 제6권1호
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• pp.38-42
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• 2004

The cryogenic system for 6.6 kV/200 A inductive superconducting fault current limiter (SFCL) was developed at Yonsei university in 2003. The sub-cooled nitrogen cryogenic system could be applied to not only SFCL but also many other applied high-Tc superconducting (HTS) devices like superconducting motor, superconducting generator and superconducting magnetic energy storage (SMES). Generally, the cooling capacity of GM-cryocooler depends on the load temperature. Therefore it is necessary to perform the cooling capacity test at no load condition to calculate the exact cooling power and heat load of cryogenic system. In this research, the cooling capacity test of GM-cryocooler was executed and the heat load of developed cryogenic system was calculated. The long run operation test results of sub-cooled nitrogen cryogenic system were successful in pressure and temperature condition. Moreover, the design and fabrication method of cryogenic system were introduced and the test results were described.

• 한국초전도ㆍ저온공학회논문지
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• 제5권2호
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• pp.58-65
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• 2003

The high temperature superconductivity(HTS) cable must be cooled below the nitrogen liquefaction temperature to applicate the cable in power generation and transmi-ssion system under the superconducting state. To obtain superconducting state. a reliable cryocooler system is required. Structural and thermal design have been performed to design cryocooler system operated with reverse Brayton cycle using gas neon as refrigerant. This cryocooler system consists of compressor. recuperator. coldbox. control valves and has 1 kW cooling capacity. Heat loss calculation was conducted for the given cryocooler system by considering the conduction and radiation through the multi-layer insulation(MLI) and high vacuum. The results can be summarized as: conduction heat loss is 7 W in valves and access port and radiation heat loss is 18 W through the surface of cryocooler. The full design specifications were discussed and the results were applied to construct in house HTS cable cooling system.

• 한국초전도ㆍ저온공학회논문지
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• 제12권2호
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• pp.25-28
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• 2010

A cooldown time is one of the major factors in many cryocooler applications, especially for the design of conduction-cooled superconducting apparatus. The estimation of cooldown seeks the elapsed time to cool thermal object by a cryocooler during initial cooldown process. This procedure includes the dimension of cold mass, heat transfer analysis for cryogenic load and available refrigerating capacity of a cryocooler. This method is applied to the specific cooling system for a 3 Tesla superconducting magnet cooled by a two-stage GM cryocooler. The result is compared with that of experiment, showing that the results of proposed method have a good agreement with experiments during initial cooling of superconducting magnet.

• Progress in Superconductivity
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• 제10권1호
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• pp.50-54
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• 2008

A conduction-cooled superconducting magnet system is developed for material separation. The superconducting magnet for material separation has to be designed to have a strong magnetic field in a control volume. Since the magnetic field gradient is larger at the end rather than at the center of the magnet, we developed a design method to optimize the superconducting magnet for material separation. The safety of the superconducting magnet is evaluated, taking into account the electro-magnetic field, heat and structure. The superconducting coil is successfully wound by the wet-winding method. The superconducting coil is installed in a cryostat maintaining high vacuum, and cooled down to approximately 4 K by a two-stage GM cryocooler. The performance of the conduction-cooled superconducting magnet system is discussed with respect to the supplied current, cooling medium and cooling power of a cryocooler.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2001년도 학술대회 논문집
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• pp.155-158
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• 2001

An intermediate cooling is indispensible to reduce the refrigeration power at superconducting system that is cooled conductively by a cryocooler without liquid cryogens. The cooling load at the intermediate stage is caused by the mechanical supports, the radiation shield and the current lead. From the cooling load calculation, a thermodynamic analysis that take into account the temperature-dependent properties of the materials and the actual performance of the cryocooler is developed. For any given physical dimensions of the various components, it is shown that there exist a unique optimum for the intermediate temperature to minimize the overall refrigeration power. The results of this study can be usefully applied to the selection of the cryocooler as well as the design of the conduction-cooled cryostat.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2171-2174
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• 2008

The design of thermal radiation shield cooled by a cryocooler is presented. This study is motivated mainly by our recent development of prototype superconducting magnet system for the Cyclotron K120. The superconducting magnet system is composed of the magnet cryostat, transfer line and supply cryostat. In order to minimize thermal radiation load, the superconducting coil form in the magnet cryostat is enclosed by the thermal radiation shield which is thermally connected to the first-stage cold head of a two-stage cryocooler in the supply cryostat. Since the supply cryostat is located far from the magnet cryostat large temperature gradient along the thermal shield is unavoidable. In this paper, the thermal radiation shield is optimized to minimize temperature gradient with taking into account the cryogenic load, system structure and electrical load. The effect of heat source from thermal conduction through mechanical supports on the temperature distribution of thermal radiation shield is also discussed.

• 한국초전도ㆍ저온공학회논문지
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• 제15권4호
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• pp.59-62
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• 2013

The conductive link is used as a cooling medium between a cryocooler and magnet in a cryogen-free superconducting magnet system. The low temperature superconducting (LTS) magnet has one solenoidal configuration with a metal former which has a 52 mm room temperature bore. The superconducting coil is installed in the cryostat maintaining high vacuum and cooled by a two-stage cryocooler. In order to maintain the operating temperature of magnet at the designed level, the cold head temperature of the cryocooler must be lower so that heat can be removed from the superconducting coil. Also, temperature difference is occurred between the magnet and cryocooler and its magnitude is dependent upon the contact resistance at the interfacial surface between metals in the conductive link. In the paper, the performance of the LTS magnet is investigated with respect to the conductive link between the magnet former and the cold head of the cryocooler. The effects of the contact pressure and interfacial materials on the temperature distribution along the conductive link are also presented.

• 한국초전도ㆍ저온공학회논문지
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• 제7권3호
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• pp.43-46
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• 2005

A Protomodel Space Infrared Cryogenic System (PSICS) cooled by a stirling cryocooler was designed. The PSICS has an IR sensor inside a cold box which is cooled by a stilting cryocooler with refrigeration capacity of 500mw at 80K in a vacuum vessel. It is important to minimize heat load for reducing background thermal noise. In order to design the cryogenic system of low heat load and to reduce heat load, we did several numerical analyses and tested using boil-off calorimetry with liquid nitrogen to measure the heat leak of the system. In this paper, we present the results obtained by thermal analysis and heat load measurement for designing the PSICS.

• 한국초전도ㆍ저온공학회논문지
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• 제17권3호
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• pp.57-61
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• 2015

A Superconducting Fault Current Limiter is an electric power device which limits the fault current immediately in a power grid. The SFCL must be cooled to below the critical temperature of high temperature superconductor modules. In general, they are submerged in sub-cooled liquid nitrogen for their stable thermal characteristics. To cool and maintain the target temperature and pressure of the sub-cooled liquid nitrogen, the cryogenic cooling system should be designed well with a cryocooler and coolant circulation devices. The pressure of the cryostat for the SFCL should be pressurized to suppress the generation of nitrogen bubbles in quench mode of the SFCL. In this study, we tested the performance of the cooling system for the prototype 154 kV SFCL, which consist of a Stirling cryocooler, a subcooling cryostat, a pressure builder and a main cryostat for the SFCL module, to verify the design of the cooling system and the electric performance of the SFCL. The normal operation condition of the main cryostat is 71 K and 500 kPa. This paper presents tests results of the overall cooling system.