Search

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.

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.

This study was to analyze the recovery characteristics for the superconducting element in the transformer-type superconducting fault current limiter (SFCL) consisted of iron core, elements in primary and secondary windings. The superconducting element was connected to the secondary windings of a transformer-type SFCL in series. In order to increase the power capacity of the SFCL, the number of the superconducting elements should be increased and the recovery time of each superconducting element should be also shortened. When the number of superconducting elements in secondary winding was increased, the recovery time of the superconducting elements according to the voltage increase in the transformer-type SFCL grew longer because of unbalanced quenching of the superconducting elements. However, as for the transformer-type SFCL that has neutral lines connected between the secondary winding and the superconducting elements, the recovery time grew shorter due to the enhancement of quenching behavior. The transformer-type SFCL with the neutral lines was more profitable for the capacity increase of the SFCL.

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.

In order to increase the capacity of the superconducting fault current limiter (SFCL), serial and parallel connections of the superconducting units are necessary. The resistive-type SFCL with serial and parallel connections has the unbalance of power burden because of the difference of critical current between the superconducting units. The transformer-type SFCL using a neutral line consists of a primary coil and several secondary coils with the superconducting units. Because the neutral line is connected with the secondary coils in the SFCL, it induces the simultaneous quench from compulsive current distribution in the superconducting units. The simultaneous quench enables the power burden between the superconducting units to be distributed equally. The neutral line also induces the equal voltage distribution between the superconducting units due to the equal turn's ratio of the secondary coil. In conclusion, the increase of the capacity in the transformer-type SFCL could be achieved easily through the application of the neutral line between the secondary coils and the superconducting units.

We investigated the operational characteristics of the hybrid-type superconducting fault current limiter (SFCL) according to the number of secondary windings. The SFCL consists of a transformer, which has a primary winding and several secondary windings with serially connected YBa2Cu3O7 films. In order to increase the capacity of the SFCL, the serial connection between each current limiting unit is necessary. Resistive-type SFCL has a difficulty in quenching simultaneously between the units due to slight differences of their critical current densities. The hybrid-type SFCL could achieve the simultaneous quenching through the electrical isolation and the mutual flux linkage among the units. We confirmed that the capacity of the SFCL could be increased effectively through the simultaneous quenching among the units. In addition, the power burden of the system could be reduced by adjusting the number of secondary windings. We will investigate the method to increase the capacity through serial and parallel connections among current limiting units

A superconducting fault current limiter (SFCL) has been proposed as an efficient method to protect a power grid from fault current. For applying a SFCL to the power grid, the various ways to increase the capacity of a SFCL should be researched in advance. Thus, the study on SFCL using a transformer has been performed. In this paper, we analyzed operational behaviors of integrated three-phase flux-coupling type SFCL under transient states in the power grid. When single and double line-to-ground fault occurred, all superconducting elements of sound and fault phase were quenched unlike segregated type SFCL. The fault current was limited by mutual supplementing in the all phases. As a result, the limited rate of fault current was small, even though the applied voltage was increased. It means this type SFCL limited the fault current efficiently by sharing of magnetic flux.

The power demand is rapidly increasing in Korea, especially in the urban areas that include the metropolitan area. In addition, the transmission system in Korea is a network structure that ensures the high reliability and stability of power supply. Accordingly, the fault current rapidly increases in the case of a power system fault, due to the decrease in the line impedance. The superconducting fault current limiter (SFCL) was devised to address these existing problems [1]-[4]. This paper analyses the sizes of fault currents limited by flux- coupling type SFCL using the symmetrical coordinate method in the case of unbalanced faults such as a single and double line-to- ground faults in the power system. An unbalanced current of three- phase was indicated by three balanced symmetrical components using the symmetrical coordinate method comparing the component sizes. This study examines the operating characteristics of the SFCL that are required by the system, considering the expected coordination with the protective devices in the actual system.

We propose a new structure of superconducting fault current limiters (SFCLs) coupled with a conventional transformer. The proposed SFCL systems have structures that the primary winding and the secondary winding of a transformer are connected with normal power grids and the tertiary winding of a transformer is connected with superconductors. These structures have advantages of both a transformer type SFCL and a resistive type SFCL. Therefore our SFCL can easily control the current limiting ratio by variation of the turn number of a transformer and minimize quantity of superconductors. Also it can be invisible in normal power grids and not bulky structure unlike a transformer type SFCL or a flux-lock type SFCL. Experimental results are reported in terms of current limiting properties, fault voltages and quench characteristics of superconductors in this system.