• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.8
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• pp.747-753
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• 2005

We Investigated the current limiting characteristics of the flux-lock type superconducting fault current limiter(SFCL) by fault angles. The flux-lock type SFCL consists of the primary and the secondary copper coils wound in parallel through the iron core and YBCO thin film. In this paper, the current limiting characteristics of the flux-lock type SFCL by fault angles in case of the subtractive and the additive polarity windings were compared and analyzed. The flux-lock type SFCL limited fault current more quickly as the fault angles increased. On the other hand, the initial power burden of the superconducting element during the fault increased as the fault angles increased. In addition, we found that the resistance of the flux-lock type SFCL in case of the subtractive polarity winding was more increased than that of the additive polarity winding. The peak current of the fault current in case of the subtractive polarity winding was larger than that of the additive polarity winding.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.2
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• pp.198-201
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• 2008

We investigated the operating characteristics of the flux-lock type superconducting fault current limiter(SFCL) with the parallel connection between the primary and secondary windings which are connected with two superconducting units in series. The parallel connection for current level increase of the flux-lock type SFCL is necessary to apply the SFCL into the power system. The resistance generated in superconducting units was dependent upon the winding direction of the primary and the secondary coils, which can reduce the power burden. The resistance of the superconducting elements in the subtractive polarity winding is higher than that of the additive polarity winding. The fault current limiting effect of the subtractive polarity winding is better than that of the additive polarity winding. From this results, we confirmed that the power capacity of the flux-lock type SFCL could be increased by the parallel connection of the superconducting units.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.3
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• pp.269-275
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• 2005

A flux lock-type SFCL consists of two coils which are wound in parallel each other through an iron core, and a HTSC thin film connects in series with coil 2. The operation of the flux-lock type SFCL can be divided into the subtractive polarity winding and the additive polarity winding operations according to the winding directions between coil 1, coil 2. When a fault occurs, the fault current in the HTS thin film exceeds the critical current so that resistance is generated in the HTS film, and thereby the fault current is limited by an instant rise in the impedance of the flux-lock type SFCL. We investigated he variances of initial fault current limiting instant according to the ratio of inductance of coil 1 and coil 2 in the flux-lock type SFCL. It was confirmed from experiments that the initial fault current limiting instant in the subtractive polarity and additive polarity windings were faster as the ratio of coil 2' inductance for coil 1's inductance increased. The 1st peak of fault current in case of the subtractive polarity winding was higher as the ratio of coil 2's inductance for coil 1's inductance increased. On the other hand, in case of the additive polarity winding, the 1st peak of fault current was lower.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.61-64
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• 2004

In this paper, we investigated the variations of initial fault current limiting instant according to fault angles in the flux-lock type SFCL. The flux-lock type SFCL consists of the coil 1 and the coil 2 that are wound in parallel each other through an iron core. The operation of the flux-lock type SFCL can be divided into the subtractive polarity winding and the additive polarity winding operations according to the winding directions between the coil 1 and coil 2. The subtractive polarity winding operation could be analyzed with three modes. On the other hand, the additive polarity winding operation could be analyzed with five modes. The variations of initial fault current limiting instant in two winding directions were dependent on the fault angles. It was confirmed from experiment that the fault current limiting instant was getting faster and the magnitude of fault current at the initial fault time was getting higher for higher fault angle.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.9
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• pp.70-77
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• 2006

We have fabricated an integrated three-phase flux-lock type SFCL, which consists of an YBCO($YB_a2Cu_3O_7$) thin film and a flux-lock reactor wound around an iron core of each phase. In order to apply the SFCL in a real power system, fault analyses for the three-phase system are essential. The short-circuit currents were effectively limited by adjusting the numbers of winding of each secondary coil and their winding directions. The flux flow generated in the iron core cancelled out under the normal operation due to the parallel connection between primary and secondary windings. However, the flux-lock type SFCL with same iron core was operated just after the fault due to the flux generating in the iron core. To analyze the current limiting characteristics, the additive polarity winding was compared with the subtractive one in the flux lock reactor. Whenever a single line-to-ground fault occurred in any phase, the peak value of the line current of the fault phase in the additive polarity winding increased up to about 12.87 times during the first-half cycle. On the other hand, the peak value in the subtractive polarity winding increased up to about 34.07 times under the same conditions. This is because the current flow between the primary and the secondary windings changed to additive or subtractive status according to the winding direction. We confirmed that the current limiting behavior in the additive polarity winding was more effective for a single-line-to-ground fault

• Tribology and Lubricants
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• v.17 no.2
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• pp.146-152
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• 2001

Environmentally adapted synthetic base oils of polyalkylene glycols (PAGs) and polyol esters (POEs) show a high polarity because of their functional groups containing oxygen atom. The lubricating performance of these polar base oils was investigated by using a four-ball tribometer under boundary lubrication condition. Four polyalkylene glycols and five polyol ester base oils were used as sample base oils of high polarity. A mineral oil (MO) and alkylnaphthalene (AN) were used as low polarity base oils. Tricrecylphosphate (TCP) was added to all the base oils, in the range of 10 mmol/L-2000 mmol/L, as an antiwear additive. All the TCP-for-mutated base oils showed optimum concentration characteristics for minimizing wear. The order of optimum concentration of all the base oils was in a good accordance with the order of relative stability of TCP in base oils. The interaction model on solvation between additive and different polar base oils can expect the stability order of TCP. Thus, the model on solvation can explain well the order of optimum concentration of all the base oils, by using the effect of polarity (dielectric constant, $\varepsilon$) and molecular size (molecular weight, MW) of them on stability of TCP in polar base oils. Finally, a good correlation of the optimum concentration for all the base oils was obtained when it was arranged as a function of C∝(M $W_{Base Oil}$/M $W_{TCP}$)$^{-2}$.71/.($\varepsilon$$_{Base Oil}$)$^{3.38}$ by these two parameters.s..

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.9
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• pp.812-815
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• 2007

To apply the superconducting fault current limiter(SFCL) into a power system, the analysis for its recovery characteristics as well as the consideration for its cooperation with other protecting machine such as a circuit breaker is required. The recovery characteristics of the flux-lock type SFCL like its current limiting characteristics are dependent on the winding direction of two coils. In this paper, the experiments of the current limiting and the recovery characteristics of the flux-lock type SFCL with YBCO thin film were performed. From the analysis on the experimental results due to the winding direction of two coils, the limited fault current in case of the additive polarity winding was observed to be lower than that for the case of the subtractive polarity winding. In addition, the recovery time was found to be faster in case of the additive polarity winding compared to the subtractive polarity winding.

• Progress in Superconductivity and Cryogenics
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• v.19 no.2
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• pp.44-47
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• 2017

In this paper, the current limiting characteristics of the transformer type superconducting fault current limiter (SFCL) with the two coupled secondary windings due to its winding direction were analyzed. To analyze the dependence of transient fault current limiting characteristics on the winding direction of the additional secondary winding, the fault current limiting tests of the SFCL with an additional secondary winding, wound as subtractive polarity winding and additive polarity winding, were carried out. The time interval of quench occurrence between two superconducting elements comprising the transformer type SFCL with the additional secondary winding was confirmed to be affected by the winding direction of the additional secondary winding. In case of the subtractive polarity winding of the additional secondary winding, the time interval of the quench occurrence in two superconducting elements was shorter than the case of the additive polarity winding.

• Proceedings of the KIEE Conference
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• 2004.11d
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• pp.93-96
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• 2004

In this paper, we analyzed the current limiting characteristics according to increase of source voltage in the flux-lock type high-Tc superconducting fault current limiter (SFCL). The flux-lock type SFCL consisted of two coils, which were wound in parallel each other through an iron core, and high-Tc superconducting (HTSC) element connected with coil 2 in series. The flux-lock type SFCL has the characteristics better in comparison with the resistive type SFCL because the fault current in the flux-lock type SFCL can be divided into two coils by the inductance ratio of coil 1 and coil 2. The fault current limiting operation of the flux-lock type SFCL can be different due to winding direction of the two coils. The winding method where the decrease of linkage flux between two coils in the accident happens is called the subtractive polarity winding and the winding method in case of the increase of linkage flux is called the additive polarity winding. The fault current limiting experiments according to the source voltage were performed for these two winding methods. Through the comparison and the analysis of the experimental data, we confirmed that the quench time was shorter, irrespective of the winding direction as the source voltage increased and that the fault current and the HTSC's resistance increased as the amplitude of the source voltage increased. The additive polarity winding made the fast quench time and the lower resistance of HTSC element in comparison with the subtractive polarity winding. The fault current of the subtractive polarity winding was larger than that of the additive polarity winding. In conclusion, we found that the additive polarity winding reduced the burden of SFCL because the quench time was shorter and the fault current was smaller than those of the subtractive polarity winding.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.467-470
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• 2006

Superconducting fault current(SFCLs) are expected to improve not only reliability but also stability of real power systems. The analysis on the single line-to-ground fault current of the integrated three phase flux-lock type SFCL, which consists of three flux-lock reactor wound on an iron core in each single phase and three YBCO thin films, was investigated in current limiting operating characteristics. We compared additive polarity winding with the subtractive one in the flux lock reactor. Its turns ratio each phase between the primary and the secondary coils is 63:42. When a single line-to-ground fault occurred in any phase, the peak value of line current in the fault phase of the additive polarity winding increased up to 31.44[A] during first-half cycle. On the other hand, the peak value in the subtractive polarity winding increased up to 81.77[A] under the same conditions. This is because the current flow between the primary and the secondary windings becomes to be additive or subtractive in each winding direction. We confirmed that the current limiting behavior in the additive polarity winding was more effective for a single-line-to ground fault.