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The fault current limiting characteristics are examined according to the fault angle in the integrated three-phase flux-lock type superconducting fault current limiter (SFCL) in the fault type such as the single-line-to-ground fault, the double-line-to-ground fault and the triple-line-to-ground fault. The results have confirmed that the SFCL has a same current limiting rate irrespective of a fault angle in the same fault type.

Shunt-assisted simultaneous quenches in series-connected resistive superconducting fault current limiter (SFCL )components are examined and discussed.

A flux-lock high temperature superconducting fault current limiter (HTSC-FCL) is described and discussed.

The resistance development in resistive superconducting fault current limiters (SFCL) based on YBCO thin films prior to quench completion is examined and discussed.

A hybrid type of superconducting fault current limiter (SFCL) is described and discussed. It consists of transformers and resistive superconducting switches.

Y-Ba-Cu-O films were studied following overpowering quenches to determine their quench properties.

Resistive superconducting fault current limiters were studied to determine the initial quench development process.

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. [ABSTRACT FROM PUBLISHER]

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 refid="ref1"/refid="ref2"/refid="ref3"/ refid="ref4"/. [ABSTRACT FROM PUBLISHER]

Quantity of consumed electricity is increasing due to increase of population and industrial development. Consequently, fault current is increased during occurrences of faults. For restricting these fault currents, in this paper, recovery characteristics per types of faults was analyzed by applying reclosing motion to 3-phase transformer type superconducting fault current limiter. Established reclosing cycle (CO-t-cycle-CO-t-cycle) is 5-10-7-20-5 cycle. (C: Close, O: Open) Electricity burden of SFCL is different according to types of faults. So, according to turn ratio, a test was carried out with regard to fault current limit per types of faults and recovery characteristics. In single line-to-ground fault and in double line-to-ground fault, it could be confirmed that it limits electric current because fault current of fault phase provides impacts on coiling wire of different sound phase. And it was also confirmed that fault current limit rate is lowered during double line-to-ground fault instead of single line-to-ground fault. When it is triple line-to-ground fault, it was confirmed that size of fault current limit of T-phase is lower than R-phase and S-phase. In addition, it could be confirmed that size of fault current limit is lower the more transformer secondary stream turn ratio is smaller. Also, it was also confirmed that time of recovery of superconducting element became shorter in open cycle the more turn ratio per types of faults is smaller. And power consumption affecting superconducting element was related to recovery time. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

We investigated the optimum design for magnetic flux distribution of a superconducting flywheel energy storage system (SFES) using the Maxwell 3D program. A rotor was composed of the laminated structure by permanent magnets and iron, and a stator consisted of bulk type superconductors. To simulate, we assumed that the bulk type superconductors has the behaviors of type I superconductor. We designed the rotor to adjust one or two iron into the center or trisection points of superconductors. The interval between the superconductor and the permanent magnet is 5 mm. We observed that a rotor with two iron pieces in the magnet stack placed to coincide with the middle of the bulks generated a more uniform magnetic field than one with a single iron piece located to coincide with the top of the bulks. [ABSTRACT FROM AUTHOR]

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 (12R) 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. [ABSTRACT FROM AUTHOR]

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 transformertype 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. [ABSTRACT FROM AUTHOR]

A transformer is expected to be an useful component of resistive type superconducting fault current limiter (SFCL) using high-TC superconducting (HTSC) element with constant critical current for easier adjustment of both the limiting impedance and the initial limiting current level. Therefore, the analysis for the fault current limiting characteristics of the resistive type SFCL using a transformer considering the resistance variance of HTSC element is needed because the resistance of HTSC element during a fault period is affected by the design condition of the transformer. In this paper, we investigated the limiting impedance and the initial limiting current level of the resistive type SFCL using a transformer as a function of the turn numbers' ratio between the primary winding and the secondary winding. The limiting impedance of SFCL was extracted by applying discrete Fourier transform (DFT) equation for the measured voltage and current data of SFCL. It was confirmed from the analysis that the transformer design with the lower turn numbers' ratio of the primary winding for the secondary winding was advantageous for the larger load current capacity of SFCL and that the transformer with the higher ratio design condition, on the other hand, was favorable for the larger fault current limiting capacity of SFCL. [ABSTRACT FROM AUTHOR]

We analyzed the unsymmetrical fault characteristics of resistive superconducting-fault-current-limiters (SFCL) based on YBCO thin films with the unbalanced faults such as a single line-to-ground fault, a double line-to-ground fault, and a line-to- line fault in a three-phase system. The unsymmetrical rates of fault phases were 6.4, 9.2, 8.8 at the fault onset, but decreased by 1.4, 1.5,3.7 after 50 ms in the fault types, respectively. The positive sequence current I¹ was the highest in a double line-to-ground fault, immediately after the fault onset, but that of a line-to-line fault was the highest after 50 ms. This means the current limiting effect was the worst in a line-to-line fault, due to the unbalanced quench between the SFCL units. The negative sequence currents I² of a single and double line-to-ground faults were relatively low, except for the quench instant, because of the rapid interruption of fault currents by the SFCL. The zero sequence current I0 was similar to the behavior of the negative sequence current. Finally, the positive sequence resistance Z¹ was reduced remarkably immediately after the fault but gradually approached the balanced positive sequence resistance prior to the system fault, except during a line-to-line fault. The simultaneous quench between the SFCL units was important for low line-to-line fault currents. [ABSTRACT FROM AUTHOR]

The flux-lock type superconducting fault current limiter (SFCL) uses the magnetic coupling between two coils connected in parallel with each other. This SFCL has the merit that both the resistance of high-TC superconducting (HTSC) element and the limiting current capacity can be simultaneously increased through the application of magnetic field into HTSC element. However, unlike other types SFCLs, the different fault current limiting characteristics can appear according to the winding direction between the two coils. In this paper, the relation of the impedance of the flux-lock type SFCL with the resistance of HTSC element was derived from its equivalent circuit using the current and the voltage relationship between the two coils. The limiting impedances of the flux-lock type SFCL due to the winding direction through the discrete fourier transform (DFT) analysis for the voltage and the current data obtained from the fault current limiting experiments were extracted and analyzed from the point of view of the limited line current and the resistance of HTSC element. [ABSTRACT FROM AUTHOR]

The flux-lock type superconducting fault current limiter (SFCL) combined with a power compensator was proposed in this paper. This SFCL consists of a flux-lock reactor and a power compensator. The former, which has coil 1 and coil 2 wound in parallel through high-TC superconducting (HTSC) element, can perform the fault current limiting operation during a fault period. The latter is composed of a current-controlled inverter and an AC/DC converter between coil 3 and grid, which can be operated as the power compensator for nonlinear load during a normal operation. The specification for a test model was determined and its operational characteristics were analyzed through computer simulation using PSIM program. It was confirmed that the suggested flux-lock type SFCL, combined with the power compensator, could protect the system from over-current by a short circuit accident and compensate the reactive power due to a nonlinear load during a normal operation as well. [ABSTRACT FROM AUTHOR]

The authors investigate the operational characteristics of a flux-lock-type high-Tc superconducting (HTSC) fault cur- rent limiter (SFCL) with a tap changer which could adjust the number of turns of the third winding. In the case of conventional flux-lock-type SFCL, the phase adjusting capacitor is connected in series with magnetic field coil to adjust the magnetic field applied to the HTSC element in phase with the current flowing through the HTSC element during a fault time. However, the current flowing at the third winding, which is connected with magnetic field coil, affects the fault current limiting characteristics. To analyze the influence of current flowing at the third winding on the fault current limiting characteristics, the fault current limiting characteristics of the flux-lock type SFCL, whose inductance of coil 3 could be adjustable through a tap changer, are investigated through the experiments and the computer-aided simulations. The relation of line currents flowing into the flux-lock-type SFCL during a fault time and numbers of turns of a tap changer is drawn. [ABSTRACT FROM AUTHOR]