• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.243-244
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• 2006

As an preliminary study for the quench protection of high temperature superconducting (HTS) cable using superconducting fault current limiter (SFCL), experimental research was carried out. The test circuit was composed of Bi-2223/Ag HTS tape and a SFCL made of YBCO thin films. In the normal state, the applied current of 56 A, which was critical current of HTS tape, could be flown through the circuit without resistive loss. Increasing the currents, the quench development of both materials was investigated from the voltage signal acquired from the resistance of the quenched superconductor. Up to around 10 times of the critical current was applied to the HTS tape and the current limiting characteristics of SFCL were investigated. In addition, for the finding out the optimal operating condition of SFCL such as the numbers of elements, a shunt resistor was applied to the SFCL and quench characteristics were analyzed as well.

• 소성∙가공
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• 제29권1호
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• pp.37-43
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• 2020

Increasing the critical current density of superconducting wire is one of the difficult challenges in the field of superconductivity. It is well known that the higher volume fraction of uniformly dispersed α-Ti is able to enhance the critical current density of superconducting material NbTi because α-Ti serves as a flux pinning center. The volume fraction of α-Ti highly depends on the grain size of NbTi because α-Ti precipitates at the grain boundaries or triple points. For this purpose, we investigated the effect of initial microstructures of NbTi obtained from hot rolling in various temperature conditions on the critical current density. In addition, subsequent heat treatment was assigned to precipitate α-Ti and groove rolling/cold drawing was adopted to produce a wire with a diameter of about 1.0 mm. It was observed that the band structure was formed after hot rolling at 500~600℃. It was also found that the volume fraction of α-Ti after hot rolling at 500~600℃ was higher and it led to the highest critical current density.

• Transactions on Electrical and Electronic Materials
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• 제6권5호
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• pp.193-197
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• 2005

We investigated fault current limiting characteristics of the flux-lock type superconducting fault current limiter (SFCL), which consisted of a primary winding and several secondary windings connected in series between $high-T_C$ superconducting (HTSC) thin films. Each YBCO thin film has a 2 mm wide and 42 cm long meander line with 14 stripes of different length. The power imbalance due to the slight difference of Ie between YBCO current limiting elements causes the significant power burden on YBCO element with lower $I_C$. We confirmed from our experiments that the mutual coupling between the primary winding and secondary windings of the flux-lock type SFCL reduced the power imbalance between YBCO current limiting elements compared with the resistive type SFCL connected in series.

• Transactions on Electrical and Electronic Materials
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• 제18권1호
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• pp.42-45
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• 2017

In this paper, a transformer type SFCL (superconducting fault current limiter) using an additional magnetically coupled circuit was suggested. Its transient fault current limiting characteristics, due to the winding direction of additional coupled circuit, were analyzed through fault current limiting tests. The suggested transformer type SFCL was composed of the primary winding, and one secondary winding wound on the same iron core together with an additional magnetically coupled circuit. That circuit consists of the other secondary winding together with the other SC (superconducting) element connected in parallel with its other secondary winding. As one of the effective design parameters to affect the transient fault current of the SFCL, the fault current limiting tests of the suggested SFCL were carried out considering the winding direction of its additional coupled circuit. It was confirmed that, through the analysis on the fault current tests of the SFCL, the quench sequence of two SC elements comprising the suggested SFCL could be adjusted by the winding direction of the additional coupled circuit.

• 한국초전도ㆍ저온공학회논문지
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• 제16권2호
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• pp.24-28
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• 2014

Magnesium diboride superconductor is still of considerable interest because of its appealing characteristics towards application mainly at around 20 K. Unlike Nb-based superconductors, $MgB_2$ can be operated by cryogen-free cooler which provides a cost effective alternative at low field of around 2-5 T. To explore this operating field region considerable efforts are necessary to marginally improve the superconducting properties of $MgB_2$. Under this situation, even the heat treatment environment during the synthesis is considered as an important factor. The addition of $H_2$ gas in small amount with Ar as a mixed gas during annealing has an adverse effect on the superconducting properties of $MgB_2$. It is although interesting to find that the presence of Mg vapor along with hydrogen during heat treatment results in the appreciable improvement in the flux pinning and the overall response of the critical current density for the ex-situ $MgB_2$ samples.

• 한국초전도ㆍ저온공학회논문지
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• 제21권3호
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• pp.32-37
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• 2019

In various types of large-scale electrical applications, the number of coil turns in such machines is usually large. Electromagnetic simulation of large-scale superconducting coils (tens to hundreds of turns) is indispensable in the design process of superconducting electrical equipment. However, due to the large scale of the coil and the large aspect ratio of super-conducting material layer in HTS coated conductor, it is usually difficult or even unable to perform 3-D transient electromagnetic simulation. This paper introduces an effective 3-D electromagnetic simulation method for large-scale HTS coated conductor coil based on T-A formulation. The simulation and experimental results show that the 3-D model based on the T-A formulation using homogeneous strategy is more accurate than the traditional 2-D models. The memory usage is not sensitive to the number of turns and this model will be even more superior as the number of turns becomes larger.

• 한국초전도ㆍ저온공학회논문지
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• 제11권3호
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• pp.10-14
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• 2009

Since a stabilizer of YBCO coated conductor (CC) plays a very important role of bypassing over-current and transferring heat generated in the moment of fault, it is one of big issues to determine the material of the stabilizer and its dimension for the high performance of the HTS power application system. Especially, in the case of a superconducting fault current limiter (SFCL), which requires it to react immediately to the occurrence of fault, characteristics of stabilizer are decisive in limiting fault current and recovering superconducting properties during and after quenching. In this paper, the quench / recovery characteristics of YBCO CCs with various thickness of stabilizer were analyzed. The quench/recovery test carried out at 20 $V_{rms}$, 5 cycles (60 Hz) and results showed that as the thickness of the stabilizer decreased, both the final approach temperature and the recovery time decreased.

• 한국초전도ㆍ저온공학회논문지
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• 제9권3호
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• pp.32-36
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• 2007

On the contrary of a conventional motor with very narrow air-gap. it is difficult to calculate the accurate magnetic field distribution and the performance of an air-cored superconducting motor by 2 dimensional analysis. which does not use high permeability material except outer machine shield. This paper aims to do analysis of magnetic field and force distribution from the 3 dimensional modelling of a 1MW class superconducting synchronous motor. Especially. the field coil composed of Bi-2223 high-temperature superconductor and the outer machine shield are modelled by finite element analysis software according to their structures and the self-inductance and Lorentz force are calculated based on the 3 dimensional magnetic field calculation. Moreover. the influence of an important parameter, synchronous reactance, has been analyzed on the machine performances such as voltage variation and output power.

• 한국초전도ㆍ저온공학회논문지
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• 제9권3호
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• pp.26-31
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• 2007

In recent years. YBCO coated conductor (CC) called as second generation HTS (high temperature superconducting) wire has been developed as a suitable material for resistive superconducting fault current limiter (SFCL). For designing the SFCL. the required length of superconducting wire is inverse proportional to the maximum temperature reached when a fault occurs. Since the required length strongly affects a manufacturing cost, it is the most important parameter to determine the maximum temperature reached. It is necessary to observe the repetitive over-current characteristics of HTS wire. This paper attempts to measure the variation of critical current of YBCO CC after repetitive over-current pulse. No degradation of the critical current of CC sample was observed by applying 100 times over-current pulse which makes temperature above 400 K after 100ms. This study can be useful in designing optimally resistive SFCL employing YBCO CC. The maximum permissible temperature can be set to 400K. so wire length could be reduced by 30% compared in case of 300K-criterion.

• 한국전기전자재료학회논문지
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• 제26권12호
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• pp.904-908
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• 2013

When an abnormal condition occurs due to a fault current at a consumer location where electricity is supplied through a high-capacity and high-$T_c$ superconducting(HTS) cable, the HTS cable would be damaged if there is no appropriate measure to protect it. Therefore, appropriate measures are needed to protect HTS cables. The fault-current-limiting HTS cable that was suggested in this study performs an ideal transport current function in normal operations and plays a role in limiting a fault current in abnormal operation (i.e., when a fault current is applied). It has a structure that facilitated its self-current-limiting ability through device change and reconfiguration in the existing HTS cable without extra switching equipment. To complete this structure, it is essential to investigate about the selection of the superconducting wire. Therefore, in this paper, HTS wire using two types of different stabilization layer is compared and examined the stability and current limiting properties under the existence of a fault current.