• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.451-454
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• 2011

The traditional BCS superconductors $AOs_2O_6$ (A=K, Rb, and Cs) were investigated to find the relationship between their structures and superconducting transition temperatures. The $T_c$ decreases with increasing the unit cell parameter of $AOs_2O_6$. This is in contrast to the case of conventional BCS superconductivity in a single bond model, where $T_c$ may increase with increasing the the unit cell parameter since the DOS at Fermi level increases as the unit cell parameter increases. Instead, the $T_c$ of a $\beta$-pyrochlore oxide is proportional to the lattice softness of the compound.

• Journal of information and communication convergence engineering
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• v.5 no.4
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• pp.362-368
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• 2007

A single-phase uninterruptible power supply system equipped with a superconducting magnet energy storage unit is proposed to achieve a simple circuit configuration and higher system reliability. It reduces a number of switching devices by applying a common-arm scheme. Removing some switches or substituting passive elements for active switches can increase the sophistication and reduces degree of freedom in control strategy. However, high-performance DSP controller can execute the complicated control task with no additional cost. Operational principles to normal, stored-energy, and bypass mode are discussed in detail. The validity of the proposed system is verified by experimental results.

• Proceedings of the KIEE Conference
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• 2006.04b
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• pp.393-395
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• 2006

We investigated the operational characteristics of the hybrid-type superconducting fault current limiter (SFCL) according to the serial and parallel connections of secondary circuits. The hybrid-type SFCL consists of a transformer, which has a primary winding and several secondary windings with $YBa_2Cu_3O_7$ films connected in series and parallel. In order to increase the capacity of the SFCL, the serial connection between each current limiting unit is necessary. The hybrid-type SFCL with the serial connection in secondary circuits could show superior characteristics than those of the parallel connections in the current limiting and quench time. The resistances generated in the superconducting units were also lowered at the parallel connections. We confirmed that the parallel connection reduced the power burden of each superconducting unit under the same conditions because of the simultaneous quenching between superconducting units.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.10a
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• pp.249-251
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• 2008

We investigated a flux-coupling type superconducting fault current(SFCL) limiter. The SFCL consisted of the primary and secondary coils, which were wound in series each other through an iron core. Superconducting unit was connected with secondary coil in parallel. The flux generated from a coil in normal operation is cancelled out by its structure and the zero resistance of the superconducting unit. In this paper. In order to compare the current limiting effects of the SFCL by applied voltage. When a lied voltage was increased, quench time was shortened Fast quench time is important component under the same fault condition because power burden of the SFCL is reduced by that of the superconducting units. The current limiting behavior of flux-coupling type SFCL was dependent upon the applied voltage.

• Progress in Superconductivity and Cryogenics
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• v.15 no.4
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• pp.26-29
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• 2013

Smart fault current controller (SFCC) proposed in our previous work consists of a power converter, a high temperature superconducting (HTS) DC reactor, thyristors, and a control unit [1]. SFCC can limit and control the current by adjusting firing angles of thyristors when a fault occurs. SFCC has complex structure because the HTS DC reactor generates the loss under AC. To use the DC reactor under AC, rectifier that consists of four thyristors is needed and it increases internal resistance of SFCC. For this reason, authors propose a hybrid type superconducting fault current limiter (SFCL). The hybrid type SFCL proposed in this paper consists of a non-inductive superconducting coil and two thyristors. To verify the feasibility of the proposed hybrid type SFCL, simulations about the interaction of the superconducting coil and thyristors are conducted when fault current flows in the superconducting coil. Authors expect that the hybrid type SFCL can control the magnitude of the fault current by adjusting the firing angles of thyristors after the superconducting coil limits the fault current at first peak.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.2210-2211
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• 2008

In this paper, we investigated the quenching characteristics of a superconducting fault current limiter (SFCL) with connection of $2{\times}3$ matrixes. This SFCL consists of the trigger part to apply magnetic field and the current-limiting part to limit the fault current. When the fault occurs, the magnetic field generated in the reactor connected in parallel was applied to the two superconducting units of the current-limiting part to reduce of inhomogeneous critical current behavior between the superconducting units. The quenching behavior of a superconducting unit in the trigger part was affected by the increase of turn numbers. This is because of the difference of current distribution between the inductance of the reactors and the resistance generated in the superconducting units in trigger part. We confirmed that the voltage differences between two superconducting units of the current-limiting part were decreased. This is because of the improvement of inhomogeneous critical current behavior between the superconducting units according to the increase of external magnetic field.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.4
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• pp.880-884
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• 2011

The matrix-type superconducting fault current limiter (MSFCL) consists of the trigger and current-limiting parts. The trigger part with reactors connected in parallel improves the quenching characteristics by applying the external magnetic field into the superconducting units. The current-limiting part with superconducting units connected in parallel and shunt reactors connected in series limit the fault current when the fault occurs. We developed the integrated reactor with the trigger and the current-limiting parts to apply high external magnetic field into the superconducting units. This was composed of a superconducting unit for the trigger part and two superconducting units for the current-limiting parts. We confirmed that the external magnetic field generated in the MSFCL with an integrated reactor was larger than that of the MSFCL with the separated reactors. So the differences of voltages generated between superconducting units were decreased in the difference according to the increment of the applied voltage. The whole magnitude of the SFCL was reduced because the volume of an integrated reactor could be reduced by one-third than that of the separated reactors. We confirmed that the critical behavior between the superconducting units in the MSFCL with an integrated reactor was more improved than that of the MSFCL with the separated reactors.

• Progress in Superconductivity and Cryogenics
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• v.14 no.4
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• pp.36-40
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• 2012

This paper presents an experimental and numerical study on current limiting characteristics of a fault current controller (FCC). The FCC consists of an AC/DC power converter, a superconducting coil, and a control unit. Even though some previous researches proved that the FCC could adjust the fault current level, the current limiting characteristics by the superconducting coil should be investigated for design of the coil. In this paper, four kinds of model coils were tested; 1) air core, 2) iron core without any bias, 3) reversely magnetized core (RMC) using permanent magnets, and 4) RMC using an electromagnet. Based on a comparative study, it is confirmed that a RMC by an electromagnet (EM) could increase the effective inductance of the coil. In this paper, a numerical code to simulate the HTS coil with RMC was developed. This code can be applied to design the HTS coil with active reversely magnetized bias coil.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.8
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• pp.102-106
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• 2007

To apply the flux-lock type superconducting fault current limiter(SFCL) into power system, its current and voltage ratings are required to increase. Especially, in case of series connection of SFCLs, the countermeasure for simultaneous quenches must be considered. The structure, which each flux-lock type SFCL unit was wound in series on the same iron core, can induce the simultaneous quench of superconducting elements. Through the fault current limiting experiment for the suggested structure, it was confirmed that the even voltage burden among the superconducting elements comprising SFCLs could be made.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.11
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• pp.1752-1757
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• 2012

With the development in industry, power demand has increased rapidly. As consumption of power has increased, Demand for new power line and electric capacity has risen. However, in the event of fault, problems occur in extending the range of fault coverage and increasing fault current. In these reasons, protection devise is recognized as the prevention of an accident and fault current. This paper dealt with minimizing fault propagation and limiting fault current by adjusting fault current limiter (FCL) with fast interrupter. At this point, we compared and analyzed characteristics between non-inductive resistance and fault current which is limited by superconducting units. In normal state of the power system, power was supplied to the load, but when fault occurred, the interrupter was operated as CT which detected the over-current. Its operation made the limitation of fault current through a FCL. We concluded that the limiter using superconducting units was more efficient with the increase of power voltage. Superconducting fault current limiter with the fast interrupter prevented the spread of a fault, and improved reliability of power system.