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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]

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]

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]

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]