• 한국초전도ㆍ저온공학회논문지
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• 제1권2호
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• pp.37-42
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• 1999

The stability of high-temperature superconducting current leads for cryogenic devices are investigated. By assuming full transition from superconducting state to normal state at a transition temperature, the HTS current at a transition temperature, the HTS current lead shows bifurcation phenomenon. There is a bifurcation shape-factor, HTS leads have three steady state. Below the bifurcation shape-factor, the superconducting current lead is unconditionally stable, because there exists only one steady-factor HTS current lead is conditionally stable depending on the shape and intensity of disturbance.

• 한국초전도ㆍ저온공학회논문지
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• 제10권3호
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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.

• 한국초전도ㆍ저온공학회논문지
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• 제16권2호
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• pp.54-58
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• 2014

High-temperature superconducting (HTS) rotating machines always require an electric current of from several hundreds to several thousand amperes to be led from outside into cold region of the field coil. Heat losses through the current leads then assume tremendous importance. Consequently, it is necessary to acquire optimal design for the leads which would achieve minimum heat loss during operation of machines for a given electrical current. In this paper, conduction cooled current lead type of 10 MW-Class HTS rotating machine will be chosen, a conceptual design will be discussed and performed relied on the least heat lost estimation between conventional metal lead and partially HTS lead. In addition, steady-state thermal characteristic of each one also is considered and illustrated.

• KIEE International Transactions on Power Engineering
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• 제3A권2호
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• pp.100-108
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• 2003

This paper presents the design and performance results of a pair of 6-kA high-temperature superconducting (HTS)-copper current leads, in which, over a short length at the warm end (e.g.,77K) of each HTS section, comprised of paralleled Bi-2223/Ag-Au tapes, is operated in the current-sharing mode. Because of their reliance on vapor cooling, the leads are applicable only to liquid helium cooled superconducting magnets such as those used in high-energy Physics accelerators and fusion machines. The experimental measurements have demonstrated that key performance data of the new 6-kA HTS-Copper leads agree reasonably well with those expected from design.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.131-136
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• 2001

In this paper, a high-temperature superconductor(HTS) current lead operating in current sharing mode is described. The minimum heat dissipation and the optimum safety factor(cross-sectional area) is obtained analytically for partial current sharing HTS leads. It is assumed that the current lead is in conduction cooled state, and the sheath material is the alloy of silver and gold. The reduced cross-sectional area results partial current sharing state, and consequently reduces conduction heat transfer, but the Joule heat generation is increased. The optimized HTS current lead is different from the conventional copper leads. In the copper leads, the minimum heat dissipation is obtained for the zero gradient of temperature at warm end. However, the temperature gradient at warm end is not zero when the HTS lead operates at minimum dissipation state.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 추계학술대회 논문집
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• pp.226-229
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• 2003

Following the successful development of practical high temperature superconducting (HTS) wires, there has been renewed activity in the development of superconducting power equipments. HTS equipments must be operated in the coolant, such as liquid nitrogen (L$N_2$) or cooled by cooler, such as GM-cryocooler to maintain the temperature below critical temperature. In this paper, dielectric strength of some insulating materials, such as epoxy, teflon, and glass fiber reinforced plastic (GFRP) in L$N_2$was measured. Surface breakdown voltage of GFRP which is basic property in design of HTS solenoid coil was measured. Epoxy is a goof insulating material but it is fragile at cryogenic temperature. The multi-layer insulating method of current lead is suggested to compensate this fragile property. It consists of teflon tape layer and epoxy layer fixed with texture. Based on these measurements, the 6.6㎸ class HTS magnet for DC reactor type high-T$_{c}$ superconducting fault current limiter (SFCL) was successfully fabricated and tested.d.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.36-39
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• 2003

HTS (High Temperature Superconducting) cable termination current lead has been designed based on simplified boundary conditions such as fixed temperature at both end and sdiabatic/convection in the side wall. However, in the real situation the current lead is enclosed with insulators and exposed to insulation oil and L$N_2$. Therefore it is necessary to consider them for the proper current lead design. In this paper, several important design parameters were chosen and their effect on the temperature distribution and heat loads on the current lead has been investigated. It was found that current lead has to be 2 stage to reach the minimum temperature requirement of insulation oil and insulator is required to reduce the cooling capacity of cryogenic system.

• 한국초전도ㆍ저온공학회논문지
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• 제16권4호
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• pp.62-65
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• 2014

To minimize most heat loss of current lead for high-temperature superconducting (HTS) rotating machine, the choice of conductor properties and lead geometry - such as length, cross section, and cooling surface area - are one of the various significant factors must be selected. Therefore, an optimal lead for large scale of HTS rotating machine has presented before. Not let up with these trends, this paper continues to improve of diminishing heat loss for HTS part according to different model. It also determines the simplification conditions for an evaluation of the main flux flow loss and eddy current loss transient characteristics during charging and discharging period.

• KIEE International Transactions on Power Engineering
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• 제3A권4호
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• pp.222-230
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• 2003

This paper presents reference designs for vapor-cooled HTS/Copper leads rated at 25 kA and 40 kA and that satisfy a protection criterion. Each HTS section is cooled by the effluent helium vapor boiling from a 4.2-K bath. Each HTS section is based on a design concept in which a short portion of its warm end (77.3 K) operates in the current-sharing mode; such operation results in a considerable saving for HTS materials required in the HTS section. Two designs of "fully superconducting" vapor-cooled HTS sections, one rated at 25 kA and the other at 40 kA are also presented as comparison bases for the new HTS sections. Each warm end of HTS sections is coupled to an optimal vapor-cooled copper lead rated at the same current as that for the HTS section. The extra coolant required at 77.3 K at the coupling station, an optimal length of the copper section will be shorter than that optimized for helium-vapor cooling between 4.2 K and room temperature.mperature.

• 설비공학논문집
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• 제9권4호
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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.