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This paper proposed the structure that applied superconductors to the neutral line of a transformer and applied the normal conductors to the third line. The superconductor applied to the neutral line of a transformer limited the peak value of initial fault current, while the normal conductor finally limited the fault current. In order to secure the operating reliability of transformer type Superconducting Fault Current Limiter (SFCL) of previously proposed structure, we analyzed the operating characteristics according to the fault types. We tested a line-to-ground fault and a line-to-line fault. As a result of the experiment, all the faults showed that the superconductor stably limited the peak-value of initial fault current. Also, the normal conductor finally limited the fault current. Based on this research results, We thought that if the structure of inserting superconductor into the neutral line is applied to the real system, it could improve the reliability and stability of the power system.

These days, SFCLs are being developed in order to limit fault current. However, the superconducting elements that limit the fault current have such problems as capacity increase and require auxiliary devices including cooling device. If devices that comprise the current power network can withstand fault current for at least one cycle, it is possible to limit the fault current with current limiting elements by bypassing it on the fault line. In this study, the fault current limiter was configured with current transformer, vacuum interrupter, and current limiting element. Through the experience, it was confirmed that the fault current was limited within one cycle. The superconducting element, as a current limiting element, limited the fault current by 80 % within one cycle from fault occurrence, and the passive element limited it more than 95 %. Also, through the comparison between resistance curve and power consumption curve, it was confirmed that the current limiting element using a passive element was more stable than the superconducting element that required capacity increase and other auxiliary devices. It was considered that the FCL proposed in this study could limit fault current stably within one cycle from fault occurrence by using the existing power technologies such as fault current detection and solenoid valve operating circuit.

Various protective equipment have been used to enhance the supply reliability and transient stability of a power system. A superconducting fault current limiter (SFCL) is electric power equipment that reduces the fault current in a power system. In the power system in Korea, an SFCL that can consistently restrict fault currents for 1.5 s or longer without support from a stable current limiting operation, a reclosing operation, and a circuit breaker was required. In this study, we suggested methods of improving the performance of a transformer-type SFCL. The superconductor in the secondary winding of a transformer-type SFCL was connected to a vacuum interrupter in series. As a result, the current limiting performance was enhanced, and the burden of the superconductor was decreased significantly. The superconductor restricted only the initial fault currents, and thereafter, the limiting operation was conducted by reactor of the transformer, which significantly improved the duration time of the current limiting operation. These outcomes satisfy the SFCL conditions required by the power system, so practical applications may be possible.

This paper proposed an high-speed superconducting fault current limiter (H-SFCL). The proposed H-SFCL functioned the initial fault current could be covered by the SFCL and the continued fault current after the one-cycle from fault occurrence could be controlled current-limiting-element of the normal conduction. To investigate the operation characteristics of the H-SFCL, a simulation power system was constructed, and a single line-to-ground fault was occurred. As a result, the H-SFCL limited the fault current by more than about 70%, and it was confirmed that the electric power burden was reduced compared to the SFCL that consisted only of superconductors.

Many studies are being conducted to implement wireless charging, for example, for cellular phones or electronic tooth brushes, via wireless power transmission technique. However, the magnetic induction method had a very short transmission distance. To solve this problem, the team of Professor Marin Soljacic proposed a magnetic resonance system that use d two resonance coils with the same resonance frequency. It had an approximately 40% efficiency at a 2m distance. The system improvedthe low efficiency and short distance problems of the existing systems. So it could also widen the application range of wireless power transmission. Many studies on the subject are underway. In this paper, the superconductor coil was used to improve the efficiency of magnetic resonance wireless power transmission. The wireless power transmission system haresonance d a source coil, a load coil, and resonance coils (a transmitter and a receiver). The efficiency and distance depended on the characteristics of the transmitter and receiver coils that hathe same resonance frequency. Therefore, two resonance coils were fabricatedd by superconductors. The current density of the superconductor was higher than that of the normal conductor coil. Accordingly, it had a high quality-factor and improved efficiency

In this paper, a flux offset-type fault current limiter was proposed as a new means of reducing fault currents. The flux offset-type fault current limiter is a device that is integrated into the fault current technology, to which the flux offset principle of a transformer is applied, and is combined with a transformer and a fast switch. To secure the operation reliability of a flux offset-type fault current limiter, a simulation system was constructed to analyze its operation characteristics by generating a single line-to-ground fault and a triple line-to-line fault. According to the test results, the system performed stably without any impedance, because the primary and secondary winding fluxes of the transformer offset each other at normal times. However, when a fault current event occurred, because the fast switch was activated to limit the fault current by opening the secondary windings of the transfer within an average of 9.5 ms, which is shorter than the operation time of the existing electric circuit breakers by 3–5 cycles, the system is likely to perform protective coordination with circuit breakers in the future. In addition, the application of this current limiter could keep the fault current limit ratio to about 96 %.

As the capacity of power facilities increases with the power demand, the fault current also increases in the case of a power system fault. Many studies are underway to limit the increasing fault current. They especially include superconducting fault current limiters (SFCLs). The existing SFCLs operate almost without loss because of their zero resistance characteristic in the normal condition, but limit the fault current by generating impedance in the event of a fault. However, this mechanism gives a significant burden on the SFCL. In this study, a high-speed interrupter and a normal conduction current-limiting unit were applied to the SFCL. In this structure, the current flows through the b-switch of a high-speed interrupter and the current-limiting element in the normal condition, but in the event of a fault, the current was bypassed to the current-limiting unit by the quench of superconducting units and interrupter switching operations. In this case, the magnitude of the fault current was covered by the SFCL, and after the switching operation, the current was limited by the normal conduction current-limiting unit. The results of this study showed that this structure reduced the power burden on the expensive superconducting element, and limited a high fault current that was initially generated from the fault.

At present, the demand for electric power increases, the electric power system is complicated. The size of the line-to-ground fault and the line-to-line fault occurred with complication of electric power system continue to increase, therefore several issues are raised. To address these issues effectively, the superconducting fault current limiter (SFCL) has been proposed, this study is ongoing. In this paper, we applied the SFCL in three-phase transformer and comparative analysis of the electric power burden to the SFCL. The superconductor is combined to the third winding of transformers in connection structure. In case of a third line-to-line fault, we did comparative analysis of the electric power burden to the SFCL based on the turn ratio of transformer third winding. In this case, we could confirm as the third turn ratio increased, electric power impressed to the superconducting element increased.

We analyzed operating characteristics to limit the peak value of initial fault current by inserting superconducting element into a neutral line. In order to detect the fault current, a current transformer (CT) was installed at the secondary winding and a SCR that changed current-flow by switching operation was installed. The fault current was reduced by inserting the superconducting element into a neutral line and was limited by connecting the normal conductivity element to the third winding. We confirmed that the peak value of initial fault current was reduced at lower level due to quench of the superconducting element connected to a neutral line, and the burden given to the superconducting element was significantly reduced as the normal conductivity element limited the fault current remarkably after switching operation.

The increased electricity demands influenced by the recent industrial development make the electric power distribution system more comprehensive, and the risks are high to cause failures to steady state electric line due to the extended range of fault at the time of fault occurrence. Also, the high performance and the high precision electric appliances that sensitive to switching surge and fault current expose vulnerability of reduced life span and increased fault occurrence ratio. Therefore, this thesis analyzed the fault limiting characteristics by the fault types by applying the superconducting fault current limiter to the neutral line of the transformer in order to reduce the fault currents that flow such high performance appliances. A current transformer (CT) that detects the fault current in the simulated power distribution system, a switching control system that is self-developed and a transformer are used in constructing a circuit. When a fault occurs, the initial fault current is restricted by the superconducting fault current limiter and simultaneously detours the fault current by operating the SCR contact of the switching control system through the detection by CT. This thesis analyzed the limiting characteristics of the superconducting fault current limiter that are applied to the neutral line of the transformer by the fault types.

With increasing demand of power, the equipment of power system is enlarging and the absolute capacity is going up. As a result, when a fault occurs, the fault current is consistently increasing. Therefore, I suggested some solution for limiting the fault current more efficiently. This study shows the characteristics of superconducting limiting elements and normal conducting elements combined with a transformer. We performed a short-circuit test about the fault current by using SCR switching control system operated from a CT. When short circuit accidents happened in the secondary side of a transformer, fault currents flowed and a SCR switching control system was operated. It resulted in a decrease of the fault current in the limited elements of third winding connected in parallel. For this test, we used YBCO thin films and normal conducting elements as the limited elements. Within a cycle, a superconducting fault current limiter with YBCO thin films reduced more than 90% of fault current because the resistance of superconducting elements sustainedly grew. On the other hand, the limiter with normal conductors limited as much as a set value because its resistance characteristic was linear. Consequently, in case of the limiter with superconductor, limiting range of the circuit was wide but the range of protective detection was undefined. In contrast, as for the limiter with normal conductors, limiting range and protection duty were appropriate.

Coercion transformer is commonly used in the electrical grid which in three phase of distribution system. The accident of the electrical grid is divided into a single, a double, a third line-to-ground faults and a double, a third line-to-line faults. A single line-to-ground fault accounts for nearly 75[%] among them. In this research, when a Superconducting Fault Current Limiters (SFCL) was applied to the three phase power system, operation in a single line-to-ground fault and limiting characteristics of fault current according to turns ratio of third winding were analyzed. When a single line-to-ground fault happened, secondary winding’s circuit was open. Then third winding’s circuit with a SFCL was closed. So fault current was limited by diverted circuit. At this time, we could find out that size of the limited fault current could be changed according to third winding rate. We confirmed that limiting operation of the fault current was carried out within one-period. These results will be utilized in adjusting the size of the SFCL.

With the increasing power demands, size of the fault current in electrical grids is steadily increasing, and it exceeds the breaking capacity of circuit breakers. To effectively cope with these problems, a high-speed interrupter was suggested. The high-speed interrupter provides fault current with a bypass to a fault current limiter in case of accidents and consequently, fault current can be restricted. In this study, behavioral characteristics of high-speed interrupter were analyzed by accident types occurred in a distribution system. When accidents occurred, a and b contact of the high-speed interrupter were turned-off and then, turned-on. Accordingly, fault current flowed to the circuit connected to a current limiting element, and the fault current limiter restricted fault current to within a half-cycle. Nevertheless, the behavior of the high-speed interrupter was slowed down by a switching surge. As a result, fault current was confirmed to be restricted not to within the anticipated half-cycle, but to after a half-cycle. Moreover, the behavioral characteristics of the high-speed interrupter changed not only by accident types, but by behaviors of R, S, and T phases. This was due to the errors in stroke lengths of the high-speed interrupters, which resulted in a slight time discrepancy among three interrupters. In addition, the switching behaviors of the b and a contact were confirmed not to have coincided due to the switching surge; b contact behaved first and a contact followed. because of this, accuracy of stroke length and switching surges through the solenoid suction increases may be necessary to resolve.

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.

When the fault occurs in power system, the fault-current exceeds breaking capacity of the circuit breaker. So, reliablity of the power system is decreased sharply. Superconducting fault-current limiter (SFCL) is operated without impedance in normal state. The fault-current is limited by its impedance during the fault condition. However, the SFCL has several weak points such as huge size, high-price, liquid-nitrogen operation for the real power system. In this paper, We suggested the high-speed interrupter to limit the fault-current in case of the single line-to-ground fault. In addition, we compared the high-speed interrupter with the SFCL to ensure the operation reliability. The proposed interrupter detected the fault-current through the CT, and the power was supplied by operation of the SCR control system. In this experiment, the power of high-speed interrupter was applied after the 4.8[msec] from fault instant. The on-off operation of the interrupter was started after half-cycle from the fault. The fault-current was flowed into the impedance element by the switching operation of the high-speed interrupter. So, the fault current was limited within one cycle, and then it didnt exceed the capacity of a circuit breaker. We confirmed that there was slight difference between the SFCL with high-speed interrupter in terms of limiting-time of the fault-current and switching speed of the SCR. The high-speed interrupter was considered to be more efficient than the SFCL in size, cost or reliability.

The proposed dipole antenna consists of the elliptical shaped driver, a tapered ground and a CPW-fed to a CPS transition. The proposed antenna offers a decreased an electrical size, and improved input impedance match than a conventional dipole antenna. Measurement results show a good operating impedance bandwidth and a radiation pattern.

In this study, a new concept is proposed on a combination device with functions of a commercial transformer and a superconducting fault current limiter (SFCL). This device serves as a transformer by stepping the voltage up or down in normal condition. When a transient phenomenon occurs in the power system, it serves as an SFCL to limit the fault current. The device quickly detects the line current using a current transformer (CT), and is based on the high-speed, silicon-controlled rectifier (SCR) interrupter operation. This is done by identifying the fault using an SCR switching control system. The test results showed that the fault current was limited by the impedance of the superconducting element a half cycle after a fault occurred. An SCR that initially had a normally open contact was turned on within a half cycle. However, an SCR with a normally close contact was turned off after a half cycle because the current dropped below the holding current after a half cycle. The voltage of the superconducting element was low in the step-down turn ratio condition of the transformer. This was because the secondary and tertiary windings were connected in series due to the SCR-1 turn-off condition, and the sum of voltages on each winding appeared on the superconducting element. By combining the existing power device technology and an SFCL technology, it is expected that the existing problems of an SFCL can be addressed to construct a smart power system.

The research of superconducting fault current limiter (SFCL) for reduction of the fault current is actively underway in the worldwide. In this paper, we analyzed the characteristics of a SFCL using the transformer and superconducting elements combined mutually in accordance with the fault types. The structure of this SFCL was composed of the secondary and third windings of a transformer connected to the load and the superconducting element, respectively. The provided electric power flew into the load connected to the secondary winding of the transformer in normal state. On the other hand, when the fault occurred in power system, the fault current was limited by closing the line of third winding of the transformer. At this time, the effect of the fault was minimized by opening the fault line in secondary winding of a transformer in power system. The sensing of the fault state was performed by the current transformer(CT) and then turn-on and turn-off switching behavior of the secondary line in the transformer was performed by the silicon-controlled rectifier(SCR). As a result, the proposed SFCL limited the fault current within one-cycle efficiently. Also, the degradation of the superconducting element in the normal state was avoided.

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.

We report the increase of the current limiting capacity of SFCLs by using the basic 1 × 3 matrix module with 3 superconducting elements. To do this, we fabricated the basic superconducting module with the 1 × 3 matrix structure which consists of a trigger part and current limiting parts. Firstly, we analysed the current limiting characteristics of the basic superconducting module with the 1 × 3 matrix structure. Secondly, we investigated characteristics about the increase of the current limiting capacity of 2 × 3 matrix-type SFCLs and 3 × 3 matrix-type SFCLs which were connected in parallel with 2 or 3 basic 1 × 3 modules. From this procedure, we approved that the easy increase of the current limiting capacity of SFCLs could be realized throughout the simply parallel connection of basic 1 × 3 modules without complex wiring. We used YBCO superconducting thin films and constructed matrix-type SFCLs by using 9 superconductors and 3 reactors. Experimental results were reported in terms of the increase characteristics of the limiting capacity for fault currents and fault voltages.

Most of the transmission system has a network structure to improve the reliability and stability of a power system. Fault current is continuously expected to increase by the increase of the power demand. If fault current exceeds the cutoff capacity of a circuit breaker, the circuit breaker is broken and the damage by fault current is expanded throughout the power system. Superconducting fault current limiter (SFCL) was designed to solve this problem in a power system. In this paper, we investigated the current limiting characteristics and power burden of superconducting elements of a flux-coupling type SFCL in three-phase power system. A Flux-coupling type SFCL is one of the resistive type SFCLs. The flux-coupling type SFCL was made by using a transformer. Reactors connected in each phase shared an iron core. When the superconducting elements were quenched in fault phase, the fault current flowed into the primary and secondary coils simultaneously. Thus, the current flowed into primary and secondary coils of sound phase by the magnetic coupling flux. Meanwhile, when the current of sound phase exceeded the critical current of the SFCL, superconducting elements connected in the sound phase were quenched. The value of the fault current tended to decrease as the first reactor's ratio increased. Furthermore, the power burden of the superconducting element was reduced. The reduced power burden of the superconducting elements shortens the recovery time of the superconducting element, which is advantageous for cooperation with a reclosing system when the SFCL is applied to the system. As a result, we confirmed that the flux-coupling type SFCL operated effectively in the three-phase power system.

We analysed the protective cooperation between a reclosing system and a flux-coupling type superconducting fault current limiter (SFCL). In order to compare the recovery behavior, the SFCLs without or with a neutral line between secondary coil and superconducting elements were prepared. Most of power grid has a reclosing system, which controls the circuit breaker by the sequential procedure, to cope with various faults. Generally, fast recovery of the SFCL was very important for stable operation between the reclosing system and the SFCL. The reclosing cycles (CO-t-CO-t-CO) for the experiments was set to 5-10-7-20-5. Recovery time in a flux coupling type SFCL without a neutral line was lengthened due to unequal quench between superconducting elements and it caused decrease of the maximum applied voltage. In the meantime, recovery time in the SFCL with a neutral line was shortened due to simultaneous quench between the elements. So, applied voltage of the power system could be higher within same reclosing system. As turn's ratio between secondary coil and superconducting elements was increased, recovery time was longer due to increase of their power. We confirmed that a flux-coupling type SFCL with a neutral line was more profitable for good cooperation between superconducting elements and a reclosing system.

The requirements for the application of the superconducting fault current limiter (SFCL) to the power system include larger SFCL capacity, linkage with the protection system in the power system and reliable operation in the reclosing system. Among the requirements, securing the reliability of the reclosing operation is the most important factor to apply an SFCL to the power system. In the cases of line-to-ground faults, which frequently occur in the power system, the reclosing system removes the fault cause by separating the fault section. The power can be supplied again later by reclosing the breaker. The separating operation is conducted again if the fault cause has not been removed. After the separating operation of the breaker, the superconducting element that has limited the fault current must recover to the superconducting state within the breaker opening duration. In this study, the recovery characteristic of the transformer-type SFCL in the case of reclosing operation was analyzed. It was proved that the power burden must be uniformly distributed by the simultaneous quench of superconducting elements, for the superconducting elements to completely recover within the breaking time of the circuit breaker. It was also found that all superconducting elements recovered to the superconducting state within the breaker opening time. Thus, it was found that the transformer-type SFCL with neutral lines coordinates well with the reclosing procedure in the power system, due to the quick recovery of superconducting elements.

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.

In this work, we report the recovery characteristics of matrix-type superconducting fault current limiters (MFCL). To do this, we constructed three-phase MFCLs with 1 × 3 structures by using 9 superconducting elements. Also we constructed resistive-type SFCL without a reactor for inducing magnetic field for the purpose of comparison. Superconductors used in this work were YBCO thin film deposited on 2 inch diameter sapphire substrates. It was etched in meander line in order to achieve sufficient resistance when a fault occurs. Resistive-type SFCLs used the same superconductors of MFCLs and all experiments for both SFCLs were performed under the same experimental condition. We confirmed that recovery characteristics of MFCL were shorter and more balanced than those of resistive-type SFCLs under diverse experimental conditions.

We investigated the recovery characteristics of a three-phase matrix-type superconducting fault current limiter (SFCL) with 1 × 3 matrix array. Recovery characteristics of superconducting units indicate that quenched superconducting units are returned from their normal state to their superconducting state. The recovery and rapidly quenching characteristics of the superconducting units are very important for the application of the SFCL in the power system. Through analysis of the recovery time, we confirmed that the recovery time of superconducting units in current-limiting part became shorter by increasing turn's number of the shunt coils in the trigger part to generate the magnetic field. From these results, we found that the power burden of the superconducting units was almost equalized because the difference between their critical currents was extremely reduced by magnetic field of shunt coils. Finally, the more the power burden or the absorption energy density of the superconducting units was equalized, the shorter the recovery time of its superconducting units was.

The symmetrical components of the three-phase resistive-type and three-phase matrix-type superconducting fault current limiters (SFCL) were analyzed in the single line-to-ground fault and the double line-to-ground fault using symmetrical component calculus. Positive sequence current was highest in the resistive-type SFCL with a single line-to-ground fault and in the 380 turns matrix-type SFCL with a double line-to-ground fault, and negative sequence current was lowest in the resistive-type SFCL with a single line-to-ground fault. These indicate that and are determined from the total impedance of the SFCL and the uniform quenching characteristics of the superconducting element. Zero sequence current rapidly appeared from the three-phase resistive-type SFCL, but approached zero after three cycles. The application of magnetic field in the three-phase matrix-type induced the simultaneous quench of the superconducting elements, but a large amount of the symmetrical component appeared after three cycles from the fault occurrence due to the shunt resistor and the shunt reactor.

We analysed the characteristics of the single, double and triple lines-to-ground fault of matrix type SFCLs (MFCL) with reactors for magnetic field. We compared characteristics of our MFCLs with those of resistive type SFCLs without reactors under the same experimental conditions. The magnitude of a limited fault current of MFCLs with a reactor according to fault voltages showed similar patterns directly after a fault. Also, the current limiting characteristics of MFCLs according to turn numbers of reactors showed similar patterns directly after a fault. However, the limitation of fault currents after 3 cycles showed a tendency to increase with increasing applying voltages. Our MFCLs had balanced patterns of limited currents between the R, S, and T phases. However unbalanced patterns of limited currents were observed in case of resistive-type SFCLs. It was because of unbalanced quenches between superconducting elements in resistive-type SFCLs and each phase. We reported the experimental results in terms of the properties of quenches, patterns of limited currents and limited voltages in the R, S and T phase systems.

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.

In this paper, we report the improved and integrated matrix-type superconducting fault current limiter (MFCL). The new MFCL proposed in this work has a structure that easily improves the quench characteristics of superconducting elements. This integrated MFCL is simply constructed by mounting a trigger element and superconducting elements in a single reactor, whereas older MFCL designs require several complex reactors for proper operation. Also this integrated type of structure provides a uniform and strong magnetic field with superconducting elements, compared with an old type MFCL. We designed and characterized the integrated MFCL with 1 times 3 superconducting modules and 2 times 3 superconducting modules. From experimental results, we confirmed that our integrated MFCL had advantages including a compact design, better quench characteristics and an easily adjustable increment of the capacity for fault current limiting.

The flux-coupling type superconducting fault current limiter (SFCL) is made by using the transformer. The flux-coupling type SFCL consists of the primary and the secondary coils connected in series, and the secondary coil has a superconducting unit connected in parallel. Before the fault occurrence in power system, the SFCL is operated without power loss (I2R) because of the zero impedance behavior of the superconducting unit. When the fault occurs and the short-circuit current exceeds the critical current in the superconducting unit, the superconducting unit is quenched, and the short-circuit current is limited. The flux-coupling type SFCL could be divided into the additive and the subtractive polarity windings according to winding direction. The short-circuit current of the flux-coupling type SFCL with the additive polarity winding was limited more effectively than that of the subtractive polarity winding. It was because the direction of current according to the winding direction of a secondary coil was reversed. In the case of the voltage generated in the superconducting unit, the voltage in additive polarity winding was generated more than in the subtractive polarity winding. Consequently, we found that the additive polarity winding could reduce the power burden of the superconducting unit in the comparison with the subtractive polarity winding.

In this paper, for the usefulness to the performance improvement of the photovoltaic (PV) array and inverter and their design, construction, and post-operation and management, which can become the key elements for the future PV system, the performance characteristics of the 50kW grid-connection PV system in Korea was evaluated and analyzed.

In this paper, for the field test of the first photovoltaic (PV) systems in Korea, the performance of a 3kW grid-connected PV systems for house, separately installed in the solar energy demonstration research complex, had been analyzed for the four years from January 2003 to December 2006.

Prior to performing handoffs for indoor services, a mobile station (MS) needs to scan for an accessible femtocell in hierarchical cellular networks. The longer scanning time denotes the higher power consumption for the femtocell and gives an extra burden to the MS as well. Using adaptive thresholds with a margin for received signal strength indicator (RSSI) of adjacent macrocells, we propose a new scanning scheme to minimize unnecessary scanning procedures for an accessible femtocell. Also, it is shown that the proposed scheme outperforms a conventional scheme through analysis and simulations. The proposed scheme can be a reasonable solution to lessen power usage and processing burdens in scanning procedures.