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As the penetration of distributed energy resources (DER) has increased, research on direct current (DC) power transmission and distribution has been actively performed. The DC system has the advantage of high-power transmission efficiency. However, it has a very large and rapid increase in fault current in the DC system directly after a fault occurs. As one of the countermeasures, studies on the application of the superconducting fault current limiter (SFCL) into the DC system have been conducted to protect major facilities from DC fault current, which is expected to alleviate the power burden on the DC circuit breaker through its quench operation. Among the studied DC SFCLs, the trigger-type DC SFCL using a transformer, which can achieve the peak DC fault current-limiting operation, has been suggested. However, the DC fault current-limiting operation, in the case of the DC SFCL with a current-limiting reactor (CLR), was analyzed to not be effectively executed in the steady state since the transient state directly follows the fault occurrence. In this paper, the DC fault current-limiting operation of a twice-quench trigger type SFCL using a transformer considering magnetizing current and its CLR was analyzed. Through DC fault current-limiting experiments according to the inductance of its current-limiting reactor (CLR), the effective current-limiting design of twice-quench trigger type SFCL using a transformer was described. [ABSTRACT FROM AUTHOR]

Due to the demand for eco-friendly energy, distributed energy resources (DERs) using renewable energy have increased. The increase in DER has caused the power system to become more complex and caused problems in the protection system. Typical problems include an increase in fault current and a problem that causes malfunction of the overcurrent relay (OCR). If the fault current increases and exceeds the capacity of the existing protection devices, it may lead to a large blackout. The most effective way to limit the fault current is to install a superconducting current limiter (SFCL). The installation of SFCL and system penetration of DER both affect OCR operating characteristics. In this paper, a simulated power distribution system is constructed and OCR malfunctions caused by DER penetration and SFCL installation are analyzed. [ABSTRACT FROM AUTHOR]

As the energy demand increases due to the developing electric power industry, the fault current becomes higher during the fault time. A new approach is needed to reduce a fault current in a power distribution system, since the fault currents influence other protective devices' operation. To decrease the fault current, the superconducting fault current limiter (SFCL) has been suggested. The SFCL has no power loss with no effect on a power distribution system because the SFCL impedance only occurs during the fault time. However, the SFCL can reduce the fault current; it causes the trip time delay of the over current relay (OCR). Compensation methods for the balanced fault have been invented in previous studies, while research on unbalanced ground fault compensation are few. In this paper, the compensation method configured with impedance components of a power distribution system is introduced to eliminate the influence of the SFCL on the OCR. In addition, the components of the SFCL impedance are removed from the characteristic equation of the OCR. To verify the effect of the impedance compensation method, fault simulations are carried out in 3 types of ground faults using PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

As the importance of renewable energy increases, the capacity of dispersed generations (DGs) has increased worldwide. However, the connection of DGs in the power distribution system can cause the fault current to increase as well as malfunction of the overcurrent relay (OCR) due to the reverse directional fault current. As the countermeasure to limit the fault current in the power distribution system with DG, though the superconducting fault current limiter (SFCL) is reported to be more effective, the research on the protection algorithm of the protective relay considering the application of SFCL is preferentially required. In this paper, the correction method of the OCR using voltage components for application of SFCL in a power distribution system with DG was suggested. To verify the effectiveness of the suggested method, the fault simulation for the power distribution system with DG including the OCR and the SFCL was performed. By applying the proposed correction method in the OCR, the protection coordination of OCRs for the application of SFCL in power distribution system with DG was confirmed to be improved through the suppression of the malfunction of the OCR. [ABSTRACT FROM AUTHOR]

Recently, the development of the electric power industry has led to an increase in the fault current when a fault occurs. It is important to reduce the fault current, since fault currents exceeding the capacity of protective devices can result in large blackouts. In order to reduce the fault current, there is a method to separate the bus line of main substation. However, this method has the disadvantage of complicating the power system. Another method is to install a superconducting fault current limiter (SFCL). The SFCL has the advantage that the fault current can be quickly limited within 1/4 cycle immediately after the fault occurrence without affecting the power system since its impedance is zero in a normal time. However, the application of SFCL affects the operation of the over-current relay (OCR) due to the reduced fault current such as trip time delay. The trip time delay of OCR was reported to be suppressed by using SFCL's voltage component in previous studies. In this paper, the impedance compensation method was suggested to exclude the effect of SFCL on OCR. To prevent OCR from the influence of SFCL, the component that can exclude the impedance of SFCL was considered to be added to the characteristic formula of OCR. In addition, the effect of correcting this characteristic equation was analyzed by constructing a power distribution system using PSCAD / EMTDC. [ABSTRACT FROM AUTHOR]

Nonlinear Quasi-zero stiffness (QZS) mechanisms were studied to overcome the weakness of linear isolators. This paper presents an integrated design of the QZS mechanism. First, various types of QZS vibration mechanisms are analyzed and a generalized model for QZS mechanisms is derived. The generalized model consists of two main parts: link and horizontal spring. The motion equation of the QZS mechanism is a Duffing equation with nonlinear stiffness. Based on the generalized model, the design problem of the QZS mechanism is converted into the kinematic design of a link element. For simplicity, the link is generalized with a cam-roller mechanism. The integrated design approach shows that the QZS mechanism can have desired QZS characteristics with properly designed cam geometry. [ABSTRACT FROM AUTHOR]

ABSTRACT In this work, we propose a 1.9-GHz CMOS power amplifier using 0.18-µm RF CMOS technology. The amplifier operates in switching mode. To enhance the dynamic range of the switching mode amplifier, we propose a structure for the power stage in which a current source is used. In low-output power regions, the current source operates in the saturation region to limit the current flowing through the power stage of the amplifier and, hence, to enhance the dynamic range. Conversely, in high-output power regions, the current source operates in the triode region to minimize the parasitic resistance induced by the transistor and, hence, to maximize the maximum output power. We designed a power amplifier to prove the feasibility of the proposed structure using the current source. From the measured results, we successfully verify the feasibility of the proposed topology. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1886-1891, 2014 [ABSTRACT FROM AUTHOR]

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]

Abstract: The flux-lock type superconducting fault current limiter (SFCL) can quickly limit the fault current shortly after the short circuit occurs and recover the superconducting state after the fault removes. However, the superconducting element comprising the flux-lock type SFCL can be destructed when the high fault current passes through the SFCL. Therefore, the countermeasure to control the fault current and protect the superconducting element is required. In this paper, the flux-lock type SFCL with an isolated transformer, which consists of two parallel connected coils on an iron core and the isolated transformer connected in series with one of two coils, was proposed and the short-circuit experimental device to analyze the fault current limiting and the recovery characteristics of the flux-lock type SFCL with the isolated transformer were constructed. Through the short-circuit tests, the flux-lock type SFCL with the isolated transformer was confirmed to perform more effective fault current limiting and recovery operation compared to the flux-lock type SFCL without the isolated transformer from the viewpoint of the quench occurrence and the recovery time of the SFCL. [Copyright &y& Elsevier]

Abstract: In this paper, the transformer type superconducting fault current limiter (SFCL) with two triggering current levels was suggested and its current limiting characteristics were analyzed. The structure of the suggested transformer type SFCL with two triggering current levels largely consists of two parts. One is the transformer with two magnetically coupled coils, which correspond to the primary winding and the secondary one connected with one high-T C superconducting (HTSC) element. The other is third coil, or, another secondary winding with one HTSC element, which is wound on the same iron core together with two coils. This suggested transformer type SFCL can limit the fault current by generating its limiting impedance with two different amplitudes, which are dependent on the initial amplitude of the fault current in case of the fault occurrence. To confirm the usefulness of the proposed SFCL, the current limiting tests of the SFCL according to the fault angle, one of the effective fault conditions to affect the amplitude of the initial fault current, were carried out and its effective limiting operations were discussed. [Copyright &y& Elsevier]

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]

Generally, the peak amplitude of the fault current after the fault occurrence depends on the transient component of the fault current, which is determined by the fault condition such as the fault angle. In the suggested flux-lock type superconducting fault current limiter (SFCL), the fault current of the lower peak amplitude causes the only high-TC superconducting (HTSC) element connected in series with one of two coils comprising the flux-lock type SFCL to be quenched, which the fault current can be limited by the lower limiting impedance of the flux-lock type SFCL. On the other hand, the fault current with the higher peak amplitude makes another HTSC element connected with the third winding to be quenched after the HTSC element connected in series with one of the SFCL's two coils is quenched, which contributes to the higher limiting impedance of this SFCL. Therefore, the effective fault current limiting operation of the flux-lock type SFCL can be performed by generating the SFCL's limiting impedance in proportion to the peak amplitude of the fault current. To confirm the current limiting operation of the proposed flux-lock type SFCL, the short-circuit tests of the flux-lock type SFCL using its third winding according to the fault angle were carried out and its effective fault current limiting operations were discussed. [ABSTRACT FROM AUTHOR]

The hybrid superconducting fault current limiter (SFCL) can be constructed to perform either first half cycle limiting operation or first half cycle non-limiting operation through rearrangement of the SFCL's components. Especially, the first half cycle non-limiting operation of the hybrid SFCL is expected to be preferred for the protection coordination with the protective device. However, if the components of the hybrid SFCL with the first half cycle non-limiting operation is designed with improper parameter, the hybrid SFCL can result in the continuous conduction of the fault current into the high-TC superconducting (HTSC) element after the fault occurs, which can sometimes bring about the destruction of the HTSC element comprising the hybrid SFCL. In this paper, among the components to affect the operational characteristics of the hybrid SFCL, the current limiting characteristics of the hybrid SFCL with the first half cycle non-limiting operation due to the resistances of HTSC element and the current limiting resistor (CLR) were investigated. Through the short circuit tests, the stable current limiting operation of the hybrid SFCL with the first half cycle non-limiting operation was confirmed to be performed by designing the resistances of both the HTSC element and the CLR to be larger values. [ABSTRACT FROM AUTHOR]

In this paper, we describes how to coordinate between recloser and fuse in power distribution system with superconducting fault current limiters (SFCL). The recloser and fuses are the main overcurrent protective devices in power distribution system. Universally, to protect against permanent faults, fuses are installed on overhead feeder laterals and the reclosers as a backup protection against temporary faults remove many unnecessary outages. Here, the recloser is set to trip using TCC curve for a temporary fault before any of the fuses can melt. If the fault is a permanent fault, the fuse has to melt just before the last delay trip of the recloser. However, the application of a resistive SFCL in power distribution system affects the recloser- fuse operation and coordination as decreased fault currents. In case that when a permanent fault occurs, the recloser could be locked-out after the last delay trip before the fuses operate. [ABSTRACT FROM AUTHOR]

In this paper, the effects on the protective coordination of a superconducting fault current limiter (SFCL) with the protective devices were analyzed. The SFCL has been noticed as the best solution to limit fault current effectively, which has continuously increased due to the expansion of the power facilities for the increased power demand. However, the application of the SFCL in the power system affects the protective coordination of the existing protective devices and can deviate their operation time from the original one. Therefore, the studies on the protective coordination considering the introduction of the SFCL are necessary prier to its installation. [ABSTRACT FROM AUTHOR]

Since the hybrid superconducting fault current limiter (SFCL) to solve the problems such as the larger volume of the superconducting components and the slow recovery time after the fault is removed has been developed, the plans to apply the hybrid SFCL into the real electrical power grid have been reported. Especially, the discussion for the protection coordination between the existing protective devices due to the introduction of the hybrid SFCL is more required together with the review from the whole viewpoint of the power system. In this paper, the experimental devices to simulate the operation of the hybrid SFCL as well as the protection coordination between the protective devices such as the over-current relay (OCR) were constructed and the protection coordination of the hybrid SFCL with the protective devices was analysed through the experiments. Through the analysis on the experimental results, among the various components comprising the hybrid SFCL, the current limiting resistor (CLR) was confirmed to affect the protection coordination between the OCR and the hybrid SFCL and the method to keep the protection coordination between the hybrid SFCL and the protective devices was discussed. [ABSTRACT FROM AUTHOR]

This paper assesses and analyses the effects of superconducting fault current limiter (SFCL) installed in power distribution system on voltage sags. First of all, resistor-type SFCL is modeled using PSCAD/EMTDC to represent the quench and recovery characteristics based on the experimental results. Next, typical power distribution system of Korea is modeled. When the SFCL is installed in various locations from the starting point to end point of feeders, improvement of voltage sag is evaluated using the Information of Technology Industry Council (ITIC) curve of customer's loads when a fault occur. Finally, future studies needing to apply SFCL to power distribution system are presented [ABSTRACT FROM AUTHOR]

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]

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]

The flux-lock type high-Tc superconducting fault current limiter (SFCL) has different fault current limiting characteristics according to the winding direction between coil 1 and coil 2. In this paper, the fault current limiting characteristics and the resistance of high-Tc superconducting (HTSC) element in the flux-lock type SFCL without the 3rd winding due to the winding direction were analyzed based on the equivalent circuit with the magnetization branch. In addition, we investigated the fault current limiting characteristics of it along the number of turns of coil 2 with the fixed number of turns of coil 1 through the fault current limiting experiments. In case that coil 1 was wound to the same winding direction as coil 2, or, subtractive polarity winding, the more the number of turns in coil 2 for the fixed turns of coil 1, the higher the resistance of HTSC element and the limited line current. On the other hand, the additive polarity winding case, which coil 1 was wound to the reverse winding direction of coil 2, showed the opposite operational characteristics to the case of the subtractive polarity winding. The experimental results for each winding direction were well coincided with the analyzed ones from the equivalent circuit. [Copyright &y& Elsevier]

In this paper, we showed that the third winding of the flux-lock type high-Tc superconducting fault current limiter (HTSC-FCL) could be operated as the damping coil to suppress the saturation of the iron core during a fault period. This third winding of the HTSC-FCL was installed to apply the magnetic field into HTSC element simultaneously after a fault happened. To confirm it, the hysteresis characteristics of an iron core of the flux-lock type HTSC-FCL were investigated from the equivalent circuit of a saturable transformer including the nonlinear magnetizing characteristic. Due to the magnetic coupled structure of the flux-lock reactor together with the third winding, the iron core of the flux-lock type HTSC-FCL could be restrained from saturation during a fault period. Through the analysis for the fault current limiting characteristics and the hysteresis ones obtained from the experimental results, the fault current limiting level as well as the saturation of the iron core of the flux-lock type HTSC-FCL with the third winding could be more improved than that of the flux-lock type HTSC-FCL without the third winding. [Copyright &y& Elsevier]

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]

Superconducting flux flow transistors with a micron channel (3 μm) have been fabricated based on the flux flow by the inductively coupled plasma (ICP) etching technique. For a channel of superconducting vortex flow transistor (SFFT) with the high-Tc superconducting characteristic in YBaCuO, the proper ICP etching conditions were an ICP power of 700 W, r.f. power of 150 W, pressure in chamber of 5 mTorr, and mixing rate of etching gas for Ar:Cl2, 1:1. The sample etched by ICP produced smoother morphology than by H3PO4 etchant, while it made little difference with a sample by non-aqueous etchant, Br. The transresistance of an SFFT etched by the ICP technique was below 0.1 Ω at an Ibdy of 40 mA. Output resistance was below 0.2 Ω. It is expected that the transresistance can be improved by decreasing the thickness of the link and introducing the multi-link structure. [Copyright &y& Elsevier]

DC faults cause severe disruption in not only the DC system but also the AC system because the fault current is very large and rapidly increases. The DC circuit breaker used to separate the DC faults from the power system is still being researched, but it is very expensive due to the use of multiple power semiconductors to interrupt a large fault current in a short time. However, if the quench characteristic of a superconductor is used, the amplitude of fault current can be reduced. Therefore, it is possible to effectively interrupt a large fault current even if a relatively cheap mechanically passive DC circuit breaker is used. In the current study, a superconducting hybrid DC circuit breaker is proposed, and the limiting characteristics of each element are analyzed. By using two superconducting elements, the quench occurs sequentially twice according to the magnitude of the fault current, and the current-limiting reactor and resistance are used. If a current-limiting reactor is used in the DC system, the fault current rises slowly at the beginning of the fault, and the use of resistance can reduce the magnitude of the fault current. The inductance of the current-limiting reactor and resistance parameter settings of the hybrid DC circuit breaker was analyzed by the step-changing case method, and the interrupting characteristic of the DC circuit breaker was improved. [ABSTRACT FROM AUTHOR]

Due to the increase in DC load and DC Power generation, the need for DC power system is emerging. Accordingly, FRT (fault ride through) and LVRT (low voltage ride through), which are related regulations for renewable energy sources, have been enacted, and operation algorithms of each converter are required for this. However, the operation of the converter according to LVRT regulations causes DC voltage fluctuations. In the current study, DC voltage fluctuation is suppressed through converter control of DC-linked battery. The controller was designed from the relational equation between DC voltage and instantaneous power of battery. The pattern of DC voltage fluctuations to the output of the PV (photovoltaic), which is a DC power generation source, was confirmed, and voltage fluctuation suppression was verified by applying the designed converter cooperation algorithm and controller. [ABSTRACT FROM AUTHOR]

In this paper, a superconducting fault current limiting breaker (SFCLB) using flux coupling with a tap changer is suggested and its effective fault current limiting and breaking characteristics due to the winding method using its tap changer are analyzed. The suggested SFCLB using flux coupling, which consists of the SFCLB using flux coupling with a tap changer, mechanical switch and driving coil, can perform the circuit-breaking function without external driving power after the fault current limiting operation. To examine the suggested SFCLB's operation, the small scale SFCLB using flux coupling was fabricated and alternative current (AC) short-circuit experiments due to the winding method using the tap changer of the SFCLB were executed. From the experimental results, a lower fault current limiting rate and faster breaking time in the case of a SFCLB with a series connection could be obtained compared to one with a parallel connection. [ABSTRACT FROM AUTHOR]

Recently, studies on connecting distributed generation (DG) to power distribution systems through DC links have been actively conducted. When a fault in feeder of this power distribution system occurs, a voltage dip can happen in the grid. In order to prevent voltage dips, there are several solutions such as the application of a superconducting fault current limiter (SFCL). If a SFCL with a larger impedance is applied, the voltage dip of the grid is effectively prevented. However, this action can bring about the malfunction or the delayed operation of the over-current relay (OCR) due to the decreased fault current, which causes another problem of protection coordination between the protective relays. On the other hand, if the impedance of the SFCL is too low, excessive reactive power is supplied by the fault ride-through (FRT) regulation and the active power is reduced. This causes an active power imbalance on the DC link and increases the DC link's voltage. As previous solutions to prevent the rise of DC links' voltage, the deloading method and the application of a chopper resistor have been suggested. In this paper, a technique called active power tracking control (APTC), was proposed to suppress the rise of DC links' voltage. Case studies considering the impedance of SFCL in the constructed power distribution system were carried out, and the rise of DC links' voltage could be effectively suppressed without any significant delay in the operation of the OCR. This study is expected to solve both the voltage dip of the grid and the rise of DC links' voltage when distributed generation is connected to a grid. [ABSTRACT FROM AUTHOR]

The penetration of wind turbine generators onto the grid has grown worldwide at unprecedented rates in recent years. This raises the concern that the tripping of wind turbine generators could potentially cause system collapses. To alleviate these concerns, wind turbine generators need to maintain connection with the grid when a grid fault occurs. This has provoked many countries to adopt low-voltage ride-through (LVRT) for wind turbine generators. The LVRT is the capability of wind turbine generators to maintain connectivity during certain periods of voltage sag. The wind turbine generators should be connected to the grid to support fault recovery. Also, wind turbine generators must provide reactive power according to the grid voltage sag. Therefore, much research has been focused on enhancing LVRT capability. To enhance LVRT capability, this paper proposes the application of a superconducting fault current limiter (SFCL) in the system. The fault current was suppressed and the voltage sag was improved through the application of the SFCL. By improving the voltage sag, the wind turbine generator and the grid were able to maintain a connection. However, suppression of the fault current can cause a problem in the overcurrent relay (OCR) trip time delay. The trip time delay was solved by OCR resetting. Through a power system computer-aided design/electromagnetic transients including DC (PSCAD/EMTDC), the enhancement of LVRT capability and improvement of the trip delay was confirmed. [ABSTRACT FROM AUTHOR]

Superconducting fault current limiters (SFCLs) are emerging as an alternative to limit fault current in AC and DC power systems. SFCLs can perform faster current limiting operation and automatic fault current detection and recovery, regardless of the type of fault. In this paper, a laboratory-scale prototype SFCL was fabricated and analyzed for its magnetization characteristics due to the magnetizing current according to the change of the number of windings in pairs. This bridge type SFCL consists of two windings and two high-Tc superconducting (HTSC) elements on one iron core. When the number of windings of the two coils were changed in pairs, the variation of the induced voltage and Joule losses due to the magnetizing current, magnetic flux in each winding, and power losses for the bridge type SFCL were compared with each other. Through comparative analysis, it was confirmed that the size of the number of turns should be considered to reduce the power losses of SFCL while effectively limiting the fault current during the fault cycle. [ABSTRACT FROM AUTHOR]

Low-voltage direct current (LVDC) systems have been increasingly studied as new efficient power systems. However, existing studies have primarily focused on power conversion designs, control, and operation, and research on ground configurations of LVDC systemsis insufficient. Consideration of the installation criteria of protective equipment and grounding systems is crucial because ground configurations in general households for end users are highly associated with the risk of human electrocution. Therefore, we investigate a mid-point grounding system using capacitors to ensure electrical safety in a mono-polar LVDC system that a general end user can directly experience in a household. MATLAB/Simulink is used to analyze the fault characteristics of the mid-point grounding system using capacitors by considering the effects of DC on the human body based on the International Electrical Code (IEC). Consequently, this paper suggests the minimum required values of the capacitors and resistors to operate the DC residual current detector (DC RCD), and the operation of the DC RCD was confirmed. By confirming the applicability of DC RCD in a household LVDC system with a mid-point grounding system using capacitors and resistors, unnecessary power loss in a mid-point grounding system and electrical accidents, such as electric shocks and fires, could be minimized. [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]

• A bridge type superconducting fault current limiter (SFCL) with two high-temperature superconducting (HTSC) elements using flux-coupling is proposed to reduce the influence of short-circuit accidents. • A laboratory-scale prototype SFCL was fabricated and short-circuit test was conducted. • The power consumption and the accumulated energy were compared and analyzed according to the winding current when the number between N 1 and N 2 coil changed during the fault period. • The operating range of the flux linkage and the variation of the magnetizing force area were compared according to the magnetizing current. • The usefulness of the proposed SFCL was confirmed through analysis of the fault current limiting operation characteristics and the energy consumed by the simultaneous quench of two HTSC elements. A bridge type superconducting fault current limiter (SFCL) with two high-temperature superconducting (HTSC) elements using flux-coupling is proposed to reduce the influence of short-circuit accidents. A laboratory-scale prototype SFCL was fabricated and short-circuit test was conducted. The power consumption and the accumulated energy were compared and analyzed according to the winding current when the number between N 1 and N 2 coil changed during the fault period. In addition, the operating range of the flux linkage and the variation of the magnetizing force area were compared according to the magnetizing current. The usefulness of the proposed SFCL was confirmed through analysis of the fault current limiting operation characteristics and the energy consumed by the simultaneous quench of two HTSC elements. As a future study, we will apply this modified bridge-type SFCL model to a direct current (DC) distribution system. First, after establishing a DC short circuit accident test environment, this SFCL is constructed in front of the DC load and the fault occurrence resistor to measure and analyze the DC fault current limiting characteristics. [ABSTRACT FROM AUTHOR]

We have been focusing on the preparation of superconducting flux flow sensor (SFFS) for use of constructing highly sensitive thermal detectors. In this research, SFFS with five channel (5 μm/l channel) has been fabricated based on the flux flow using high temperature superconducting thin films by the ICP etching technique. We have designed a bolometer based on the temperature dependence of the kinetic inductance of a superconducting flux flow thin film. This paper examines the fabrications and flux flow resistance and thermometer responses of the highly sensitive sensor constructed of a thin YBCO film. It has also been suggested that they will be applicable to a new type of flux flow sensor. [Copyright &y& Elsevier]

In this study, the characteristics of the double quench and instantaneous power of a superconducting fault current limiter (SFCL) using two magnetically coupled windings were analyzed. In the proposed model of SFCL, two magnetically coupled windings are wound on the iron core and each winding is connected to one superconducting element. When a fault occurs, the SFCL can limit the fault current by the double quench occurrence of two superconducting elements. In order to analyze the influence of the winding direction on the fault current limiting characteristics of the proposed SFCL, two magnetically coupled windings were designed to allow the same and the reverse directions. From the simulated short circuit experiment, the currents and the voltages of two coupled windings and two superconducting elements were measured and the instantaneous power and the double quench occurrence were analyzed. It was confirmed from the experimental results analysis that the fault current limiting characteristics of the SFCL were more favorable in the reverse winding direction than in the same winding direction. [ABSTRACT FROM AUTHOR]

Recently, a lot of interesting research has been conducted to solve the fault current problem of the DC system. In long-distance transmission, DC transmission is more economical than AC transmission. The connection of power grids with a DC system can also better control the power flow and provide high stability. However, the control of the fault current in a DC system is more difficult to handle than in an AC system because the DC system does not make a zero point, unlike the AC system. In addition, there is a disadvantage, in that an arc occurs when a circuit breaker operates. In this paper, a new type of DC superconducting fault current limiter (SFCL) is proposed. This new type of SFCL is composed of two superconducting elements, a current limiting resistor/reactor (CLR), and a transformer. With the proposed SFCL, the DC fault current limiting experiments were performed and the DC fault current limiting characteristics of this SFCL due to the component of the CLR were analyzed. [ABSTRACT FROM AUTHOR]

A bridge type superconducting fault current limiter (SFCL) with simultaneous quench using two high-temperature superconducting (HTSC) elements and two coils was fabricated to analyze the fault current limiting characteristics. Before and after the fault occurrence, the current limiting operation and the voltage waveforms of each device were compared according to the change of the input voltage. We also analyzed flux linkages and instantaneous powers of the bridge type SFCL with simultaneous quench using flux-coupling composed of HTSC elements with different critical currents. During the fault period, the magnetization power area and the flux linkage's operating range variation due to the magnetizing current were compared with each other. [ABSTRACT FROM AUTHOR]

The effects of an atomic hydrogen (Hat) pretreatment of the catalyst layer on the low temperature growth of single-walled carbon nanotubes (SWCNTs) have been investigated using a modified catalytic chemical vapor deposition system. Well-defined and isolated individual Fe nanoparticles as a catalyst are successfully formed on the defects with high trapping energy which are created on the Al2O3 surface by Hat pretreatment, yielding highly dense SWCNTs. The pretreatment mechanism of Hat, compared to H2, is also discussed. It was also found that the quality of SWCNTs can be enhanced when Hat is flowed with CH4 during nanotubes growth at low temperature. In this case, the undesired carbon products and defects on catalyst seeds and nanotube walls can be selectively removed by Hat. Therefore it is essential to use Hat in the pretreatment stage for increasing catalytic activity and to keep the size of nanoparticles in the nm range. Hat can also be employed in growth stage for enhancing SWCNTs quality and density at low temperature. [ABSTRACT FROM AUTHOR]

Superconducting flux flow transistors (SFFT) was successfully fabricated by an inductively coupled plasma (ICP) etching technique. YBaCuO thin films on LaAlO3 substrate were patterned as a three-terminal device by a conventional wet etching method and the ICP system. The characteristics of a fabricated device were investigated by examining the I–V curves under various applied currents. The control current dependence of the transresistance was also measured. The SFFT with a channel fabricated by the ICP system showed a transistor-like characteristic over the liquid nitrogen temperature. [Copyright &y& Elsevier]

In this paper, direct current (DC) fault current limiting and interrupting operation of hybrid DC circuit breaker (DCCB) using double quench, which consists of DCCB, a series resonance circuit, power electronic switch, surge arrestor, two separated current limiting reactor/resistor, and two superconducting elements, were suggested. The suggested hybrid DCCB can perform the interrupting operation after twice or once DC fault current limiting operation according to DC fault current amplitude. To verify the effective operation of the suggested hybrid DCCB, the modeling for the components of DCCB, the surge arrestor, and the SCE was carried out and its DC operational characteristics were analyzed. Through the analysis of the modeling results for the suggested hybrid DCCB, the advantages of hybrid DCCB were discussed. [ABSTRACT FROM AUTHOR]