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In this paper, the superconducting fault current limiter (SFCL) using magnetic coupling of two coils with mechanical switch, which the extra driving coil to drive it unlike the previous hybrid SFCL was not required, was suggested. The operational principle of the suggested SFCL using magnetic coupling of two coils with the mechanical switch is basically the same as one without mechanical switch, except that the mechanical switch is driven by the electromagnetic repulsion force generated by the magnetic flux between two coils comprising the SFCL. With the operation of the mechanical switch, the fault current flowing through the SFCL using magnetic coupling of two coils can be commutated from the magnetically coupled two coils into the coil operated as the current limiting reactor (CLR) immediately after the fault occurs, which is contributed to the fault current limiting operation of this SFCL. To verify the operation of the suggested SFCL, the mechanical switch with electromagnetic contact comprised of the fixed and the moving parts, which were located just above open iron core wound by two parallel connected coils, was designed and fabricated. With the fabricated mechanical switch, the short-circuit tests of the SFCL with the suggested mechanical switch were carried out. Through the analysis on the results of the short-circuit tests, the current limiting characteristics of the suggested SFCL with the mechanical switch could be confirmed to be improved effectively with the reduction of the power burden of the high-TC superconducting (HTSC) element comprising the SFCL. [ABSTRACT FROM PUBLISHER]

The introduction of various dispersed generation (DG) in a power distribution system has caused the short-circuit current to increase, which can make the operation of the protective device deviate from its original set value. Especially, the increase of a short-circuit current in a power distribution system due to the increase of the DG is expected to be required for the related power utilities such as the circuit breaker to be replaced with a larger one. Among the countermeasures to solve the short-circuit problem in a power distribution system considering the increase of the DG, the superconducting fault current limiter (SFCL) has been noticed as one of the promising devices. [ABSTRACT FROM PUBLISHER]

The increase of various dispersed generations (DGs) such as wind power and solar cell in a power distribution system has been reported to increase the short-circuit current. In addition, the introduction of the DG in a power distribution system is expected to affect the operation of the protective device as well. The superconducting fault current limiter (SFCL), which has been continuously studied for the reduction of the circuit breaker's power burden, recently starts to be noticed as effective method to solve the fault current problem due to the introduction of the DG. Since the fault current limiting operation of the SFCL and the operations of the protective devices such as the over-current relay or the recloser are affected by the application location of the DG, the study on the protection cooperation of the protective devices with the SFCL considering the application location of the DG in a power distribution system is firstly required. [ABSTRACT FROM PUBLISHER]

In this paper, the application method of superconducting fault current limiter (SFCL) for the protection coordination of the protective devices in a power distribution system was analyzed. The SFCL has been announced as better solution among many methods to limit a fault current effectively, which has continuously increased due to more complex network of a power system. However, the application of the SFCL in a power system affects the operation of the protection devices and the protection coordination, which requires the study on the protection coordination of the protective devices considering the application of the SFCL in a power distribution system. [ABSTRACT FROM PUBLISHER]

We investigated the current limiting characteristics of a flux-lock type superconducting fault current limiter (SFCL) using an E-I core. Unlike the flux-lock type SFCL using a two-legged common coil (C-C) core, two parallel connected coils and a high-Tc superconducting (HTSC) element were placed on the left leg of a three-legged E-I core and an air gap was introduced into the central leg. Through the analyses for the fault current limiting experiments, the two parallel magnetic flux paths was confirmed to be contributed to the prevention of the magnetic saturation of the iron core and the improvement of the current limiting characteristics of the flux-lock type SFCL. [ABSTRACT FROM AUTHOR]

Superconducting fault current limiters (SFCLs) using magnetic coupling of two coils can be divided into the insulated type SFCL and the non-insulated type SFCL depending on whether the two coils are insulated through one iron core or not. Among such SFCLs, the transformer type SFCL belongs to the insulated type SFCL because of its insulated two coils. On the other hand, the flux-lock type SFCL, its two coils electrically connected in parallel or series, can be classified into the non-insulated type SFCL. Basically, the structural component and the operational principle of these SFCLs rely upon the magnetic coupling of two coils, and might therefore be considered to be the same. However, there are important differences in the current limiting and the recovery characteristics of these SFCLs depending on design conditions such as the winding direction and the inductance ratio between two coils. In this paper, the current limiting and the recovery characteristics of SFCLs using magnetic coupling of two coils were investigated through the fault-current limiting and the recovery experiments. Through the analyses of the experimental results, the current limiting and the recovery characteristics of the SFCLs were confirmed to be affected by the SFCL's operational current. [ABSTRACT FROM AUTHOR]

We suggested that the neutral line is a more effective location for a superconducting fault current limiter (SFCL) in a three-phase power system. To confirm it, we analyzed the quench and recovery characteristics of SFCL applied into the neutral line in cases of non-symmetrical ground faults, such as single line-to-ground and double line-to-ground faults. Through a comparative analysis based on the experimental results for two SFCLs applied either to the neutral line or to the three-phase power line, it was confirmed that the SFCL applied into the neutral line of the power system was more advantageous from the viewpoint of both the practical use of the SFCL and the SFCL's coordination with other related protective devices in the power system. [ABSTRACT FROM AUTHOR]

This paper proposes a voltage-controlled voltage source inverter (VCVSI) using a coated conductor (CC) as a decoupling inductor. Up to the present, the topologies to protect the power system from a short circuit effectively and to improve power quality simultaneously have been rarely developed. In the proposed topology, a decoupling inductor, which is essential component for a VCVSI operation, was designed with a YBCO CC and was integrated into a VCVSI. However, to determine the optimal CC specification, it is necessary to consider design parameters such as fault current, active power flow from the system and reactive power required by the decoupling inductor. With the optimal CC specification, the proposed system can perform the fault current limiting operation for a short circuit. In addition, in the normal time, it can compensate for the reactive power that a non-linear load requires, as well as perform load voltage stabilization. Specifications for a test model are discussed and the fault current limiting and power conditioning operations are presented. By using computer simulations, we validate the analyses and discuss its multi-operation. [ABSTRACT FROM AUTHOR]

Abstract: For the fabrication as piezoelectric transformer, we investigate the structural and piezoelectric properties of 0.96PbZr x Ti1−x O3-0.04Pb(Mn,W,Sb,Nb)O3 (PZT-PMWSN) ceramics as a function of Zr/Ti and sintering temperatures. PZT-PMWSN ceramics show the highest piezoelectric properties at the morphotropic phase boundary. The composition sintered at 1100°C with Zr/Ti ratio of 52/48 shows highest values of electromechanical coupling factor k p of 0.56 and mechanical quality factor Q m of 2344. Also we fabricate the step-down piezoelectric transformers with optimized PZT-PMWSN composites and measure the characteristics as input/output electrode ratio. The step-down ratio 1/5 was obtained by disk-type piezoelectric transformers. [Copyright &y& Elsevier]

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]

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]

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]

We analyzed the fault current limiting characteristics of a flux-lock type high-Tc superconducting fault current limiter (HTSC-FCL) using series resonance between capacitor for series resonance and magnetic field coil which was installed in coil 3. The capacitor for the series resonance in the flux-lock type HTSC-FCL was inserted in series with the magnetic field coil to apply enough magnetic field into HTSC element, which resulted in higher resistance of HTSC element.However, the impedance of the flux-lock type HTSC-FCL has started to decrease since the current of coil 3 exceeded one of coil 2 after a fault accident. The decrease in the impedance of the FCL causes the line current to increase and, if continues, the capacitor for the series resonance to be destructed. To avoid this operation, the flux-lock type HTSC-FCL requires an additional device such as fault current interrupter or control circuit for magnetic field.This paper investigated the parameter range where the operation as mentioned above for the designed flux-lock type HTSC-FCL using series resonance occurred from the experimental results. In the design of the flux-lock type HTSC-FCL, the some methods to avoid the continuous increase of the line current were suggested and confirmed by the experiments that the suggested methods were available to prevent the continuous increase of the line current after a fault happened. [Copyright &y& Elsevier]

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]