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The South Korean power grid has a network structure for the flexible operation of the system. The continuously increasing power demand necessitated the increase of power facilities, which decreased the impedance in the power system. As a result, the size of the fault current in the event of a system fault increased. As this increased fault current size is threatening the breaking capacity of the circuit breaker, the main protective device, a solution to this problem is needed. The superconducting fault current limiter (SFCL) has been designed to address this problem. SFCL supports the stable operation of the circuit breaker through its excellent fault-current-limiting operation [1] , [2] , [3] , [4] , [5] . In this paper, the quench and fault current limiting characteristics of the flux-coupling-type SFCL with one three-phase transformer were compared with those of the same SFCL type but with three single-phase transformers. In the case of the three-phase transformers, both the superconducting elements of the fault and sound phases were quenched, whereas in the case of the single-phase transformer, only that of the fault phase was quenched. For the fault current limiting rate, both cases showed similar rates for the single line-to-ground fault, but for the three-wire earth fault, the fault current limiting rate of the single-phase transformer was over 90% whereas that of the three-phase transformer was about 60%. It appears that when the three-phase transformer was used, the limiting rate decreased because the fluxes by the fault current of each phase were linked in one core. When the power loads of the superconducting elements were compared by fault type, the initial (half-cycle) load was great when the single-phase transformer was applied, whereas for the three-phase transformer, its power load was slightly lower at the initial stage but became greater after the half fault cycle.

The breaking capacity of circuit breakers currently reaches the saturation point in electric power systems when a fault occurs. This is because the fault current increases due to continuous increases in electric power demand and facilities. It is not efficient to change existing circuit breakers, however, because of some problems that will increase the replacement cost and cause technical difficulties. To solve such problems, a study on the superconducting fault current limiter (SFCL) is being actively conducted. In this paper, a three-phase flux-coupling-type SFCL was composed, and its recovery characteristic according to the change in the number of turns of its secondary coils and its reclosing operation were analyzed. The increase in the number of turns of the SFCL’s secondary coils enhances its limiting efficiency by increasing its total impedance. The recovery time was delayed, however, when the number of turns of the secondary coils increased, because the superconducting element was connected in parallel to the secondary coils, which increased the voltage and current of the superconducting element. In other words, the delay in the recovery time was due to the increase in the power burden between the superconducting elements. Thus, two superconducting elements that were connected in series were used to distribute the power burden to each other, and the recovery characteristics of the SFCL with and without a neutral line were experimented on.

We reported the fabrication and analysis of the reactor for matrix-type superconducting fault current limiters (SFCLs). Reactors take a role of inducting magnetic field to superconductors in reactors and bypassing partial fault currents to themselves. Superconductors used in this work were YBCO thin films deposited on 5.08 cm diameter Al 2 O 3 substrates. Also, reactors with a diameter of 90 mm and a length of 230 mm were fabricated. Then, we constructed the matrix-type SFCLs with a reactor which consists of a trigger part and current limiting parts. Experimental results are reported in terms of the characteristics of fault current in superconductors and reactors, and distribution of the fault power between them.

In a transformer-type superconducting fault current limiter (SFCL) with a neutral line, which is connected between the superconducting elements and secondary windings, we verified that the SFCL has excellent characteristics that induce the perfect simultaneous quench of the superconducting elements in the previous study. The application of the SFCL to the power networks requires its coordination with the reclosing operation duty, which protects a circuit. In this study, the fault current limiting and recovery characteristics of superconducting elements in the three-phase transformer-type SFCL with the neutral line were analyzed. The limiting rate of the fault current in the transformer-type SFCL could increased by an iron core, which allows quenching of the superconducting elements in a sound phase as well as in a faulted phase. In addition, the simultaneous quench led to uniform burdens on superconducting elements, all of which recovered their superconducting state within an opening cycle of a circuit breaker. Thus, the transformer-type SFCL with the neutral line could reliably conduct the fault current limiting and recovery operations of superconducting elements according to the reclosing operation duty and fault types.

The recloser that is used in distribution systems is a relay system that behaves sequentially to protect power systems from transient and continuous faults. This reclosing operation of the recloser can improve the reliability and stability of the power supply. For cooperation with this recloser, the superconducting fault current limiter (SFCL) must properly perform the reclosing operation. This paper analyzed the reclosing operation characteristics of the three-phase flux-coupling type SFCL in the event of a ground fault. The fault current limiting characteristics according to the changing number of turns of the primary and secondary coils were examined. As the number of turns of the first coil increased, the first maximum fault current decreased. Furthermore, the voltage of the quenched superconducting element also decreased. This means that the power burden of the superconducting element decreases based on the increasing number of turns of the primary coil. The fault current limiting characteristic of the SFCL according to the reclosing time limited the fault current within a 0.5 cycles (8 ms), which is shorter than the closing time of the recloser. In other words, the superconducting element returned to the superconducting state before the second fault and normally performed the fault current limiting operation. If the SFCL did not recover before the recloser reclosing time, the normal current that was flowing in the transmission line after the recovery of the SFCL from the fault would have been limited and would have caused losses. Therefore, the fast recovery time of a SFCL is critical to its cooperation with the protection system.

The amount of consumed power is increasing with industrial development and rapidly increasing population. In accidents due to increased power consumption, the fault current sharply increases. Superconducting fault current limiters (SFCL) are studied widely to limit such fault currents. In this study, the characteristics of a transformer-type SFCL are analyzed depending on reclosing in changing the number of secondary winding turns. For experiment conditions, the turn ratio of the primary and secondary windings of a transformer-type SFCL was set to 4:2 and 4:4. The voltage was incremented by 80 V from 120 V for the experiment. The circuit breaker was operated with two open times of CO-0.17 s – CO-0.17 s – CO seconds (C; closed, O; open), respectively. Comparing the result for the experiment conditions with the case of the turn ratios of the primary and secondary windings at 4:4 and 4:2, the fault current was limited effectively in 4:2 than in 4:4 for the fault current limit ratios. With respect to the result of recovery characteristics, it was examined that the superconducting unit recovered faster when the turn ratio of the primary and secondary windings was 4:2 than 4:4. Comparing the amount of consumed power related to the recovery characteristics of the superconducting element, it was examined that the recovery time was faster in less power consumption for the superconducting unit. As such, since a transformer-type SFCL depending on reclosing in changing the number of turns of the secondary winding controls the turn ratio of the secondary winding to control fault current limiting and recovery characteristics, it can normally operate.

When the fault occurred in the power system, the superconducting fault current limiter (SFCL) rapidly limited the fault current to protect the power devices with preventing power failure. Therefore, the application of the matrix-type SFCL in the power system could improve of its reliability and stability. To apply the SFCL into the real power system, many superconducting elements should be connected in series and parallel. If any superconducting element of the matrix-type SFCL breaks down, it cannot basically limit the fault current. In this paper, we analyzed operation stability of the matrix-type SFCL which was divided into trigger and current-limiting parts as follows: Case 1. Break-down of a superconducting element in the trigger part. Case 2. Break-down of a superconducting element in the current-limiting part. Case 3. Break-down of two superconducting elements in the current-limiting part. When any superconducting element was broken down, we confirmed that all fault current flowed into other normal superconducting element connected in parallel and its power burden was largely increased. At that time, the matrix-type SFCL was operated well to limit the fault, but the fault current was decreased a little bit because the resistance generated in the superconducting element was abruptly increased. If the excessive current of the superconducting element exceeds its capacity, it could cause the break-down of the other superconducting element, shunt resistors, or shunt reactors, and then the break-down could be extended to the whole matrix-type SFCL. Through these results, we found that the number of superconducting elements connected in series and parallel should be designed with enough margins against the break-down of superconducting elements and optimal conditions for shunt resistors and reactors should be determined.

In this paper we analyzed recovery characteristics of matrix-type SFCLs (MFCL) with 2 × 3 matrixes when triple lines-to-ground fault occurred. MFCLs used in this work consist of 18 superconductors, six reactors for induction of magnetic field and several parallel impedances for bypassing fault currents. Also we analyzed recovery characteristics of resistive-type SFCLs of which 18 superconductors are connected in series and parallel, without reactors and parallel impedances, for the purpose of comparison, under the same experimental conditions of MFCLs. Experimental results were reported in terms of recovery characteristics for individual superconductors in an R phase, dependency of faults cycles and applied fault voltages in each phase. We confirmed that recovery characteristics of MFCLs were more excellent than those of resistive-type SFCLs.

A transformer-type superconducting fault current limiter (SFCL) can control fault current by adjusting a turn’s ratio of the primary and secondary windings. In addition, by inserting a neutral line into the secondary winding, the power burden of the superconducting elements can be evenly distributed. We compared the operating and transient characteristics of the three-phase resistive and transformer-type SFCLs in the balanced and unbalanced faults that occur in power systems. In transformer-type SFCLs, where the primary and secondary windings of each phase were connected to one iron core, flux was induced to each winding of the normal phases by the fault current of the fault phase, thus causing simultaneous quench between superconducting elements. In the three-phase power systems, however, when faults occurred in more than two phases, the flux from fault current of the fault phase affected the other normal phase, thus decreasing the reduction ratio of fault current. We confirmed, however, that the fault current was reduced by 70% relative to cases without SFCLs. The results of the analysis of the transient characteristics of the three-phase transformer-type SFCL through the symmetrical component calculus showed that in the case of triple line-to-ground fault, a difference between positive and negative phase currents was large enough to cause an increase in the phase angle ( δ ) between the generator creating the power and the motor acting as a load. Thus, we expect that the transient stability deteriorates.

A three-phase matrix-type superconducting fault current limiter (SFCL) with the 1 × 3 structure comprised of a trigger part and a current-limiting part was designed and manufactured. The trigger part, which is comprised of a superconductor and an reactor connected in parallel, improves the critical property of the superconductor by applying the external magnetic field to the superconductor, and the current-limiting part limits the fault current. In case of a single line-to-ground fault in the three-phase resistor-type SFCL, only two out of three superconductors were quenched, with large difference between them in resistance and power consumption. The three-phase matrix-type SFCL reduced the difference in the voltages generated from the quenched superconductors because the critical property was improved by applying the external magnetic field to the superconductors. In addition, the results showed that the power consumption was almost uniformly distributed in the superconductors.

Application of the superconducting fault current limiter (SFCL) to the power system requires connection of superconducting elements in parallel and series. The uneven critical property of the superconducting element, however, causes unbalanced quenching. This brings the increase in power burden to a specific superconducting element. To solve this problem, a transformer-type SFCL with neutral lines was studied. In this paper, the fault current-limiting characteristics and consumption power of the superconducting element were analyzed. As a method to increase the power capacity of the transformer-type SFCL, the number of secondary circuits of the transformer was also increased. As a result, we found that the voltage and current of the superconducting elements were efficiently controlled by turn ratios of the transformer. This structure resulted in minimized consumption power. The transformer-type SFCL with neutral lines induced the simultaneous quenching between superconducting elements. This enabled us to increase the number of secondary circuits. Therefore, it induced the increase in its power capacity in the transformer-type SFCL.

In this paper we described the improved design for the matrix fault current limiters (MFCL). To do this, we used thin film-type superconducting elements. therefore it means that we can make the MFCL with minimized size and high switching speed because of the high current density and the high indexing value of superconducting thin film. Also we could minimize the bulky shunt coil using the connection of a series resistance with a shunt coil. Also we could effectively block up a leakage current in shunt coils under no-fault condition and simply control total impedances of a current-limiting part using this method. After we designed an appropriated 1 × 2 basic MFCL module with an applied voltage of 160 V, we enlarged it to a 2 × 2 MFCL module and a 3 × 2 MFCL module where applied voltages were 320 V and 480 V, respectively. Experimental results for our MFCL were reported in terms of various fault currents, variation of series resistance and so on. We think that these methods will be useful in the optimum design of an m × n MFCL.

The quench characteristics of high- T C superconducting (HTSC) elements in the integrated three-phase flux-lock type superconducting fault current limiter (SFCL), which consisted of HTSC elements and a three-phase flux-lock reactor wound on one iron core with the same turn’s ratio between coil 1 and coil 2 in each single phase, were investigated. In a normal condition, the magnetic flux generated in the iron core is zero because the magnetic flux generated between two coils of each single phase is canceled out. However, unlike other three-phase SFCL with three isolated iron cores, the integrated three-phase flux-lock type SFCL showed the different fault current limiting characteristics for the three-phase faults such as the single line-to-ground fault, the double line-to-ground fault, the line-to-line fault and the triple line-to-ground fault. In addition, the power burden of HTSC elements comprising the integrated three-phase flux-lock type SFCL can be decreased. In this paper, we investigated the quench characteristics of HTSC elements in the integrated three-phase flux-lock type SFCL according to three-phase ground fault types. Through the experiments for the fault current limiting characteristics of this type SFCL according to three-phase ground fault types, the quench characteristics of HTSC elements were analyzed and compared with those of three-phase resistive type SFCL.

We investigated the operational characteristics of the hybrid-type superconducting fault current limiter (SFCL) with the closed and the open cores, which induced the variation of the magnetic flux between the primary and the secondary windings. The experimental set-up of the hybrid-type SFCL with the closed and the open cores were prepared and the experimental analyses for the current limiting characteristics were performed. The peak value of the fault current in the hybrid-type SFCL with the open core was higher than that of the closed core at the first cycle after fault occurrence. However, in the case of the hybrid-type SFCL with the open core, the limiting current level after fault occurrence was decreased less than that of the hybrid-type SFCL with the closed core, because the magnetic leakage reluctance of the open core was higher than that of the closed core. The quench time ( T q ) and the arrival time ( T a ) for the peak voltage ( V SC ) in the hybrid-type SFCL with the closed core were faster than that of the hybrid-type SFCL with the open core due to the increase of the mutual flux. We verified that the consumption power in the hybrid-type SFCL with the open core was larger owing to the increase of leakage flux by the reduction of mutual inductance between primary and secondary windings.

In isolated cardiac sarcoplasmic reticulum (SR) vesicles, methyl methacrylate (2.5–100 mM) directly inhibited initial rates of Ca 2+ uptake as well as the maximal uptake. Inhibition of SR Ca 2+ uptake by methyl methacrylate was concentration-dependent, and the highest concentration of methyl methacrylate (100 mM) almost completely inhibited the SR Ca 2+ uptake. EC 50 of methyl methacrylate in percent inhibition of SR Ca 2+ uptake was 16.1, 31.9, and 53.4 mM at pCa 7.0, 6.6, and 6.0, respectively. At low Ca 2+ concentrations (0.1–1 μM), SR vesicles treated with 20 mM methyl methacrylate showed the decreased Ca 2+ uptake rates. However, further increase of Ca 2+ concentration to pCa 5.5 abolished the inhibitory effect of methyl methacrylate on SR Ca 2+ uptake, showing no difference between the control and the methyl methacrylate-treated SR vesicles. From these results we could conclude that methyl methacrylate exerts a direct inhibition of cardiac SR Ca 2+ uptake. This mechanism, at least in part, might contribute to the profound hypotension induced by methyl methacrylate. Supplementation of calcium ion appears to reduce the methyl methacrylate-induced cardiovascular disturbances efficiently.

Diabetic cardiomyopathy has been suggested to be caused by abnormal intracellular Ca2+ homeostasis in the myocardium, which is partly due to a defect in calcium transport by the cardiac sarcoplasmic reticulum (SR). In the present study, the underlying mechanism for this functional derangement was investigated with respect to SR Ca2+-ATPase and phospholamban (the inhibitor of SR Ca2+-ATPase). The maximal Ca2+ uptake and the affinity of Ca2+-ATPase for Ca2+ were decreased, and exogenous phosphorylation level of phospholamban was higher in streptozotocin-induced diabetic rat SR. Levels of both mRNA and protein of phospholamban were significantly increased in the diabetic hearts, whereas those of SR Ca2+-ATPase were significantly decreased. Consequently, the relative phospholamban/Ca2+-ATPase ratio was 1.88 in the diabetic hearts, and these changes were correlated with changes in the rates of SR Ca2+ uptake. However, phosphatase pretreatment of phospholamban for dephosphorylation of the sites phosphorylated in vivo did not change the levels of subsequent phospholamban phosphorylation in either control or diabetic rat hearts. The above data indicated that the increased phospholamban phosphorylation was not due to autonomic dysfunction but possibly due to increased phospholamban expression. These findings suggest that reduction of the SR Ca2+-ATPase level would contribute to decreased rates of SR Ca2+ uptake and that this function is further impaired by the enhanced inhibition by phospholamban due to its increased expression in the diabetic heart.