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Currently, HVDC is in the spotlight for long-distance transmission and power connection between countries. Among them, MMC-HVDC is a new conversion technology that can solve the problems of switching loss and harmonics. MMC consists of many submodules connected in series. And the one submodule is composed of IGBTs, Diode, and Capacitor. At the transient state, the charged capacitor is discharged and added to the fault current. It will generate tens of times the surge current during the delays all IGBTs turn-off. This causes semiconductor device destruction. To solve this problem, we applied SFCL with fast response characteristics to the MMC. The response speed of the resistive SFCL is faster than that of the MMC system protection device, which can effectively limit the capacitor discharge current before the protection device operates. In this paper, AC grid, MMC-HVDC, DC cable and SFCL were modeled using PSCAD/EMTDC. After that, we confirmed the capacitor discharge current, current limiting rate, and interruption characteristics through DC line short circuit failure simulation. As a result, SFCL effectively limits the capacitor discharge current and continuously lowers the level of the fault current. [ABSTRACT FROM AUTHOR]

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 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We report the increase of the current limiting capacity of SFCLs by using the basic 1 \times 3 matrix module with 3 superconducting elements. To do this, we fabricated the basic superconducting module with the 1 \times 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 \times 3 matrix structure. Secondly, we investigated characteristics about the increase of the current limiting capacity of 2 \times 3 matrix-type SFCLs and 3 \times 3 matrix-type SFCLs which were connected in parallel with 2 or 3 basic 1 \times 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 \times 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. [ABSTRACT FROM AUTHOR]