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It is crucial for the successful application of high-temperature superconducting (HTS) power transformers that they are able to survive under abnormal operations, such as a short-circuit fault. Modeling, based on the design of a four-winding three-phase HTS power transformer, suggests severe boiling will occur on the surface of the winding during a short-circuit fault and will jeopardize the turn-to-turn insulation of the HTS power transformer. In this paper, a turn-to-turn insulation breakdown experiment platform involving the introduction of boiling on the surface of electrode has been built. Nomex 410 paper, one of the candidates for turn-to-turn insulation in the design of the HTS power transformer, was tested. The characteristics of dielectric strength of Nomex 410 in three different thicknesses (0.13, 0.18, and 0.25 mm) have been investigated, without boiling, as well as under different boiling situations, in an open bath of liquid nitrogen. The voltage application methods applied during both experiments test the electrical breakdown of Nomex 410 under a dynamic situation. The experiment results show that when under film boiling, compared to the test results for nucleate boiling, the dielectric strength of Nomex 410 paper decreases by approximately 38% of the value when no boiling is involved. Moreover, it is verified that the presence of an electric field accelerates the heat transfer between the liquid nitrogen and the heated electrode. [ABSTRACT FROM PUBLISHER]

DC fault protection is the bottleneck that restricts the development of modular multilevel converter based high voltage direct current (MMC-HVDC) system. Superconducting fault current limiters (SFCL) is an ideal protection device that can significantly limit short circuit current and enhance the fault tolerance ability of MMC-HVDC system. At present, several topologies of SFCLs have been proposed, but there is no systematical study of their current-limiting characteristics in MMC-HVDC. This paper studies the development process of DC short-circuit faults in MMC-HVDC system, and analyzes its demand for fault current limiting. Then, resistive type, saturated iron core type and hybrid type SFCL are modeled and their limiting effect of critical fault current under DC pole-to-pole fault is tested. By comparison, the current-limiting characteristics of three types of SFCL are concluded. Results show that resistive SFCL has best performance in steady state, while saturated iron core SFCL has best performance in transient state. The current-limiting characteristic of hybrid type SFCL is between the other two types. [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]

In the family of the High-Luminosity LHC high order correctors, the skew quadrupole was the most critical magnet as three assemblies with different solutions were needed to meet the design specifications. This paper summarizes the prototyping phase of the magnet, discussing the observed nonconformities, the subsequent root cause analyses, and the adopted solutions. A first-hand experience showed us the importance of adopting rigorous quality assurance methods for the electrical insulation, aimed at the early defect detection, and implementing a consistent measurement-to-simulations chain for the optimization of the coils mechanical support. The improvements discussed in the paper are integrated into the final magnet design for the series production of six skew quadrupole correctors. [ABSTRACT FROM AUTHOR]

The high temperature superconducting (HTS) cable has shown promising prospects in megacities for the advantages of high transmission power density and low loss. However, when HTS cable is working on grid, various kinds of faults may cause irreversible damage, resulting in the failure of reclosing. In this paper, the resistive superconducting fault current limiter (R-SFCL) is introduced into the power system to cooperate with the HTS cable, so as to reduce the potential damage caused by fault current. Firstly, the equivalent circuit models are established, and then transient response of HTS cables under fault condition is analyzed, the recovery time of HTS tapes are used to define the design of R-SFCL. Finally, the operating reliability of HTS cable has been evaluated and measures about adaptive reclosing times were proposed under different fault currents. [ABSTRACT FROM AUTHOR]

This paper studies the current limiting behavior based on an air-core high-temperature superconducting transformer (HTST) and a group of inductor–capacitor series resonant limiters. The air-core HTST is composed of four same double-pancake type high-temperature superconducting coils made up of Bi-2333/Ag tape, and both of primary and secondary windings include two series superconducting coils. It plays the roles of inductive fault current limiting and transformation impedance; in addition, the magnetic flux saturation can also be avoided. Meanwhile, the inductor and capacitor series with the secondary winding of the air-core HTST in series resonance state are the conventional devices. The influence of them on the circuit can almost be ignored, because they are in series resonant state in normal operation. While the fault current appeared in the primary circuit, it will be limited by the impedance of the air-core HTST and the inductor without quench (the inductor and capacitor would quit the series resonant state). According to the preliminary experiment carried out in our laboratory, this superconducting current limiting module can operate as expected, and its behavior is satisfactory. [ABSTRACT FROM AUTHOR]

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]

Saturated iron-core superconducting fault current limiters (SISFCL) are becoming increasingly well known for their effective and reliable current limiting capabilities. The device is capable of producing very low impedance during normal operation and substantially high impedance during fault. Its ability of changing impedance can be attributed to the change of magnetic state of the ferromagnetic core of the device from saturation to unsaturation. The SISFCL employs a dc source to maintain the saturated state of the core for normal operation with the help of a superconducting coil. The high ac ampere turns during fault not only bring the core to unsaturation, but also cause alarmingly high voltage to develop across the dc source. Hence, the protection of the dc source is of great concern as the high voltage is capable of destroying the source and additionally, force the superconducting material to quench. In this paper, the SISFCL is analyzed using the finite element method and the field suppression method of dc source protection is discussed and shortcomings are pointed. The novelty of the paper lies in the use of shorted winding for the improved performance of the field suppression system. For the finite element method (FEM) analysis, the ANSYS Maxwell 2D software is utilized. [ABSTRACT FROM PUBLISHER]

The medium voltage direct current (MVDC) is a promising direction of future shipboard power system (SPS). However, one of the main limitations encountered in its development is the fault isolation of DC side. This paper reveals the evolution process of short-circuit fault in typical MVDC SPS through equivalent circuit and transient simulation. Based on the analysis of protection needs, a superconducting current-limiting switch (SCLS) topology is proposed, which includes one superconducting coupled coil and two DC circuit breakers (DCCBs). The models of SCLS is built on MATLAB/Simulink and the current limiting principle and current sharing principle of SCLS are verified. The results show that the SCLS has effective current limiting performance and fault clearing effect. [ABSTRACT FROM AUTHOR]

DC fault is one of the most important and critical challenges for stable operation of DC microgrids. Resistive type superconducting fault current limiter (R-SFCL) is an ideal protective solution to limit DC fault current. However, the effect of only using SFCL may further deteriorate the DC bus voltage stability. This paper first analyzes the effect of R-SFCL on DC microgrid under different operation modes and different fault locations, and then presents a coordinated control method of SMES-battery hybrid energy storage system (HESS) and SFCL in ground fault. This method can not only reduce the fault current level but also regulate the DC bus voltage. Finally, the comparative study is conducted in PSCAD/EMTDC, the feasibility and superiority of the proposed method is verified. [ABSTRACT FROM AUTHOR]

Most industrial technologies are automated by sensitive electric parts such as programmable logic controllers(PLCs) and magnetic contactors which are required high power quality. The voltage sags occur in the non-faulted power distribution feeders during the fault duration. Therefore, voltage causes economic losses in the production process of various companies. To solve the fault current and the voltage sags, the superconducting fault current limiter (SFCL) is in the spotlight. The SFCL where was located on starting point of the feeder improves the reliability of the facility by reducing the fault current. In addition, it compensates the voltage sags on the bus-bar. In this paper, evaluating the voltage sags based on fault location in the power distribution system with the SFCL through PSCAD/EMTDC simulation. Next, the expected the voltage sags frequency is predicted by the reliability analysis technique of the power distribution system. The expected voltage sags frequency of the power distribution feeder is compared with before and after the application of the SFCL. [ABSTRACT FROM AUTHOR]

Short-circuit faults are inevitable in split-winding transformers with stabilizing windings, and the resulting transient electromagnetic force may cause detrimental damages to the equipment. This paper focuses on a comprehensive analysis of the characteristics of the split-winding transformer with stabilizing windings under different short-circuit faults. In this regard, a FEM based on a field-circuit coupled approach is proposed. Also, a SFFZ10-88000-kVA split-winding transformer with stabilizing windings is used as a prototype to investigate its transient performances with both full-crossing and half-crossing conditions under different short-circuit faults. The symmetrical component method is presented to compute short-circuit currents to compare with the simulation ones, and a prototype test model is established to verify the correctness of the proposed method. The results reveal that the axial forces exerted on the winding in half-crossing short-circuit faults are generally larger than those in full-crossing short-circuit faults. Moreover, there is a considerable short-circuit force in the stabilizing winding in cases of a single-phase earthed fault and a two-phase earthed fault and there is no current in the stabilizing winding under other short-circuit fault cases. The numerical modeling approach dealt with in this paper is expected to be useful in the design of the split-winding transformer with stabilizing windings. [ABSTRACT FROM AUTHOR]

Resistive superconducting current limiter (RSFCL) is a focus in the development of current limit technology, especially in the field of ac transmission. It has a significant effect of limiting current. However, the traditional double-wound noninductive pancake coil has an inevitable drawback. Due to its special structure the flashover would occur easily during the fault in high-voltage environment. That would make the SFCL working in an uncontrolled state. So, novel coil structures or connection modes are demanded to meet the protection of voltage source converter-based high voltage direct current. In this paper, the magnetic distribution of different flux coupling connection modes of the coils is analyzed through the simulations based on continuous pancake coil. A flux coupling type SFCL with pancake coils is designed and fabricated. The limitation process of the SFCL coils is analyzed through simulations and experiments in millisecond level. The parallel current sharing characteristics of the coils are researched through experiments in different impulse current. Meanwhile, a continuous pancake coil is made to study the series voltage sharing features of the coil. The result of this paper has certain guiding significance in the design of dc RSFCL. [ABSTRACT FROM AUTHOR]

Due to the high costs and difficulties to make the short-current experiment of large power transformers, it is critical to do the electromagnetic force analysis of the transformer windings through finite element software. Research in this paper establishes the analysis model of a 50000 KVA/110 KV three phase power transformer. In previous studies, short-circuit impedance is seldom evaluated for its effect to the accumulated effect of the electromagnetic force. A novel approach with considering of the short-circuit impedance is proposed to simulate the accumulated deformation. Short-circuit current is applied to this model, testing the electromagnetic forces of the transformer windings. Results of the research is significant to the evaluation of winding deformation state. [ABSTRACT FROM AUTHOR]

The superconducting fault-current limiter (SFCL) has been effective in coping with large fault currents and is expected to be largely applicated in the power system to solve the problem of increasing fault-current level in power grid nowadays. However, the coordination between SFCLs and traditional power system devices such as protective relaying has not been researched enough. This paper studies the influences of the resistive-type SFCL on the incremental power frequency relay of the transmission lines. The resistive SFCL is simulated by using thermal-electric analog method. A model of a 220-kV transmission system with the incremental power frequency relay element was built and simulated with the SIMULINK MATLAB software. Three compensation methods to eliminate the negative effects of the integration of SFCL are proposed and compared. Finally, numerical simulation tests have demonstrated the correctness and validity of theoretical analyses. [ABSTRACT FROM AUTHOR]

Rooftop transformer-less photovoltaic inverters (TLPVIs) have the potential to inject a very small dc current into the distribution network. The dc current quantity can be very high in a residential power distribution system where several TLPVIs are installed. Distribution transformers (DTs) supplying power to the customers in the networks can be adversely saturated with this high dc current accumulated from the small dc current injected by individual TLPVI. In this paper, a systematic investigation is carried out on the dc current injection potential of commercially available TLPVIs. Furthermore, the influence of this aggregated dc current on the DTs are analyzed through modelling, simulation, and laboratory testing. A three-phase three-leg transformer is used to analyze the effects of the high dc injection from the TLPVIs. A finite element analysis is carried out in COMSOL Multiphysics environment to explore the dc current injection effect. The results show that the injected dc current from TLPVIs highly affect the DTs and a solution is needed to overcome this challenge before the problem spreads widely and causes a barrier to the growth of the integration of renewable resources to the power grids. [ABSTRACT FROM AUTHOR]

This thesis presents a new type topology structure of superconducting solid fault current limiter (SSFCL). A group of academic researches on the new type topology structure of SSFCL are briefly performed. First, this paper reasonably analyses the hysteresis control mode of SSFCL and determines the superiority of its application. Then, the mathematical simulation model of SSFCL is built and the reliability of SSFCL is verified by simulation. By comparing the simulation results of SSFCL, solid fault current limiter, and superconducting fault current limiter, the conclusion can be drawn that the SSFCL is more stable and more effective on controlling the increase rising rate of a short-circuit current. [ABSTRACT FROM AUTHOR]

KEPCO decided to apply the HTS FCL and cable in real substation in 2009. This is the first commercial demonstration case and starting point of the HTS equipment in South Korea, even though this is not a general perfect commercialization. For a successful application on this commercialization preliminary, it is quite important to design the HTS-FCL specification with regard to the current status of the application site (for example, the existence of NGR (Neutral Grounding Reactor), 3-winding low% impedance and so on). This paper evaluates the necessary and sufficient design specifications of the 22.9 kV HTS-FCL to fulfill the real power system conditions. It investigates the detailed design criteria, short circuit capacity, FCL impedance, protection scheme, fault limiting type and other design parameters to learn the real status of ICHEON substation which will be using the HTS- FCL. [ABSTRACT FROM AUTHOR]

In this paper, an inductor-type superconducting fault current limiter (I-SC FCL) in the dc power system is proposed to combine the benefits of an inductor and a superconductor. I-SC FCL minimizes the power burden on a superconductor and maximizes the cutoff performance. The inductor delays the rise of the fault current, and the superconductor limits the maximum value of the fault current. Then, they serve together to protect the circuit before the circuit breaker comes into play. The fault currents, limited by an inductor and a superconductor, are introduced into the mechanical dc circuit breaker (M-DCCB). M-DCCB could perform stably due to low power consumption. Analysis of the cutoff characteristics is carried out using the EMTDC/PSCAD program. As a result, the maximum value of the fault current is limited to approximately 2.6 times lower than the previously proposed M-DCCB. Additionally, a low power is burdened on I-SC FCL due to the delay part. [ABSTRACT FROM AUTHOR]

The fast-response energy compensating feature from a superconducting magnetic energy storage (SMES) device is favored for suppressing instantaneous voltage fluctuations, while the self-triggering current limiting feature from a superconducting fault current limiter (SFCL) suits to suits to achieve automatic load protections in the electric vehicle (EV) charging stations. This paper investigates a new DC voltage quality enhancing scheme by using a combined superconducting power technology employing SMES and SFCL devices. Preliminary simulations demonstrate the feasibility of this SMES-SFCL-based voltage quality improver to avoid the voltage fluctuations during the EV load transients and suppress the fault current effectively during the short circuits simultaneously. [ABSTRACT FROM AUTHOR]

As medium voltage dc-based (MVDC) technology is widely considered in the shipboard integrated power system (IPS), the short fault protection of shipboard IPS is urgent. This paper suggests resistive type superconducting fault current limiter (R-SFCL), flux-coupling type SFCL (FC-SFCL), and a hybrid type SFCL (H-SFCL) alleviate fault current and improve the transient behaviors of shipboard MVDC IPS. All of these SFCLs are installed at the DC line. When pole to pole short fault occurs, resistive and inductive components play roles in current limiting. To evaluate these SFCLs and choose one for the system, theoretical analysis, simulation verification and experiments are done. According to the current limiting and economic cost index, H-SFCL is preferable in these SFCLs. [ABSTRACT FROM AUTHOR]

A rapiddevelopment of the permanent magnetic synchronous generator (PMSG)-based offshore wind farm has been witnessed in the past decade. To prevent the offshore wind farms from being disconnected during a fault, many countries have proposed specification requirements for the fault ride-through (FRT). Traditional FRT scheme Chopper circuit for PMSG needs to consume all the mismatching energy and the impulse current is too high during the fault, which will even affect the safe of the PMSG. In this paper, the superconducting fault current limiter (SFCL) is applied to enhance the ability of the FRT in the PMSG-based offshore wind farm. In the proposed scheme, the resistive SFCL can reduce the energy consumption and improve the working performance of the Chopper circuit by absorbing the power of the grid-side converter (GCS) during the fault. An offshore wind farm model is built through PSCAD/EMTDC software. The comparison simulation results validate the feasibility of the proposed scheme. [ABSTRACT FROM AUTHOR]

The key obstacle in integrating high-voltage direct current (HVDC) point-to-point networks into meshed multiterminal HVDC networks (MTDC) is the absence of dc circuit breakers (DCCBs), which can timely and reliably isolate the faulty HVDC network from the MTDC. In this paper, a novel hybrid-type superconducting DCCB model (SDCCB) is proposed. The SDCCB has a superconducting fault current limiter (SFCL) located in the main line, to limit the fault current until the final trip signal to the SDCCB is given. After the trip signal, insulated-gate bipolar transistor (IGBT) switches located in the main line will commutate the fault current into a parallel line, where dc current is forced to zero by combination of IGBTs and surge arresters. DC fault current behavior in MTDC and fundamental requirements of DCCB for MTDC were described, followed by an explanation of the working principles of the SDCCB. To prove the viability of the SDCCB, a simulation analysis demonstrating SDCCB current interruption performance was done for changing the intensity of dc fault current. It was observed that the passive current limiting by SFCL caused significant reduction in fault current interruption stress for SDCCB. Furthermore, fundamental design requirements for SFCL, including the effect of SFCL quenching impedance on SFCL voltage rating and energy dissipation capacity, were investigated. Finally, advantages and limitations of the SDCCB were highlighted. [ABSTRACT FROM PUBLISHER]

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]

DC system protection is more challenging than that for AC system due to the rapid rate of rise of the fault current and absence of natural current zero-crossing in DC systems. Superconducting fault current limiter (SFCL) in DC systems is a promising technology to reduce the fault current level and the rate of rise of the fault current, and also SFCLs have no resistance during normal operation. In this paper, the behaviors of an SFCL coil are investigated under both low impedance and high impedance fault conditions in DC systems. In the low impedance fault condition system, the SFCL coil performs effective limitation of the fault current level under different prospective fault current levels. The application of SFCLs with limited inductance in the DC system can be a potential solution to effectively suppress the fault current under low impedance short-circuit faults. The SFCL coil under the high impedance fault condition can only limit the prospective fault current when it is much higher than the critical current of the coil. [ABSTRACT FROM AUTHOR]

If the inductive superconducting fault current limiter (I-SFCL) cannot maintain its current-limiting capacity before the dc fault is isolated, it will lead to a secondary fault in the dc system, and cause an impact on the system primary equipment. Therefore, the study of sustainable current-limiting capability is an important aspect in the dc SFCL researches. In this paper, the sustainable current-limiting capability of a saturation-based dc I-SFCL prototype was discussed in details. Through the dc current-limiting performance experiments, it is found that the sustainable current-limiting capability of this type of SFCL has a negative correlation with its reverse saturation degree, which can be affected by the design parameters. The influence factors of reverse saturation were first analyzed through the mathematical model of this prototype. Afterward, combined with the experiments, the sustainable current-limiting capability of the proposed dc I-SFCL is fully explored by changing the coil current and the number of turns, which offers a reference for parameter design of I-SFCL in the future engineering application. [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]

The objective of this paper is to propose a dc current interruption technology for railway dc traction systems, consisting of a dc vacuum circuit breaker with a superconducting fault-current limiter (SFCL). To this end, a 1.5-kV dc circuit breaker prototype is designed, involving a dc vacuum circuit breaker and a resistive-type SFCL serially connected. The dc vacuum circuit breaker is developed with a commutation circuit to generate a reverse injection current, and the resistive-type SFCL is composed of yttrium barium copper oxide superconducting tape. An LC current source tested the 1.5-kV prototype, showing that, when the precharged capacitor voltage is 1.5 kV, the prospective current is 47 kA increasing at a rate of 9.4 A/μs. The SFCL limits this current to ~3 kA (peak value), and then, decreases the current to 2 kA after 6 ms, followed by successful clearance via the dc vacuum circuit breaker. The proposed 1.5-kV circuit breaker will successfully clear short-circuit faults up to 47 kA by first limiting the prospective current and then interrupting it. [ABSTRACT FROM AUTHOR]

Wind energy resources are accounting for an ever-greater portion of the many nations' generation portfolios to address global climate change concerns and reduce carbon dioxide (CO2) emissions. Increasing the role of wind in the power generation mix, however, presents significant operational challenges in ensuring the grid security and power quality due to the inherent resource variability. This paper addresses the integration of large-scale wind resources into the grid through DC lines incorporating SMES coil: Doubly-Fed Induction Generator (DFIG) type wind power plant linked by line-commutated HVDC with and without SMES is investigated using PSCAD/EMTDC for various operating scenarios. The study demonstrates the effectiveness of applying SMES coil in the DC line for mitigating the wind power intermittency and for improving its dispatchability and quality. Enhanced robustness for AC and DC faults due to the SMES coil and its benefits are also discussed. [ABSTRACT FROM PUBLISHER]

This paper presents the results of short-circuit tests with a 22.9 kV hybrid superconducting fault current limiter (SFCL) on the KEPCO test grid. The hybrid SFCL we used for the test had suffered from lots of field tests including a long term operation and it is still in working order. We have already proved that the SFCL showed high reliability as well as feasibility through a long term operation and short-circuit tests performed before. In this paper, we tried to study a dynamic characteristics of the same SFCL on the distribution power grid through short-circuit tests with a circuit breaker and a reclosing relay. An artificial fault generator (AFG) was used to generate fault currents in the KEPCO power test center. The two objectives of the tests are (1) verifying a precise reaction of the SFCL to reclosing operation and (2) a study for protection coordination with SFCL. The test results showed that the SFCL worked precisely with a fast recovery of the superconducting elements when we applied a one-time reclosing operation with the interval of 0.6 second. We also suggested a proper manipulation of the coordination of the protection system in distribution networks with the SFCL in the paper. [ABSTRACT FROM PUBLISHER]

In this paper we present a new arrangement implementing a novel self-limiting transformer. We have developed a 1-phase model. We used a 3-limb transformer for one phase and we surrounded 2 limbs of the three, the primary and the secondary coils, with a common perfect closed YBCO loop. In this way we could realize the active magnetic short circuit which gives a new possibility for novel applications. Its operation is based on the principle of the magnetic flux conservation in a closed loop. This is a well-known physical law but so far not applied in this way. We used perfect closed YBCO wire loops with parallel turns. The paper presents the results of our experiments and opens new advanced applications of the perfect YBCO loops made of HTS wire. We considered the efficiency and significance of the perfect closed loop made from YBCO wire. [ABSTRACT FROM AUTHOR]

The dc fault current has a high amplitude and a fast rising speed, therefore with regard to the hybrid dc circuit breaker, it is hard to meet the requirement of a high breaking capacity while maintaining economically efficient. The SI-SFCL can prevent the speed of the fault current from rising too fast, and ensure the current remains under the interrupting capability of the dc circuit breaker, so the couse of the SI-SFCL and the dc circuit breaker is an effective solution for fault clearing in dc grids. In this paper, the current-limiting requirement of the DCCB is given, and a simplified equivalent circuit of the active SI-SFCL is proposed, based on which the matching between the electrical parameters of the active SI-SFCL and the dc circuit breaker is studied. Parameter constraint and the protection voltage range of the active SI-SFCL are given. Finally, the conclusion on the matching between the electrical parameters of the active SI-SFCL and the DCCB is verified by MATLAB/Simulink. [ABSTRACT FROM AUTHOR]

Mainly used in ac grids, resistive-type superconducting fault current limiters may be still more interesting for dc systems due to their capability to reduce high short circuit currents appearing in case of dc cable fault. This limiter reduces the breaking capability, speed, and energy requirements of the required dc circuit breaker allowing the implementation of electromechanical breakers for fault current interruption. These breakers have lower breaking capability, on-load losses, and investment costs in comparison with hybrid circuit breakers based on power electronics. This paper presents a technical and economic analysis of a superconducting fault current limiter used in a radial three-terminal high voltage dc grid to protect a cable link. Based on simulation studies using an electromagnetic transient program, an effective system protection will be demonstrated with special attention to the continuity of power flow through healthy parts of the grid. [ABSTRACT FROM PUBLISHER]

This paper presents the design of a 10 kV, 200 A resistive type superconducting fault current limiter prototype. Several one-meter long YBCO coated conductors prepared by Shanghai Jiaotong University are used to build the current limiting module. Each module has 2 tapes connected in parallel to reach 400 A rated current (Ic of each tape is 150 A \sim 200 A) and 6 tapes connected in series to withstand 700 \sim 800 V voltage drop. A series of tests and measurements have been carried out to investigate the performance of the fault current limiting module. Short circuit test of the module has been performed on a specially designed transformer which is able to withstand large current on the secondary side. The power capacity of the lab allows performing the test up to 40 V and a few thousand Amperes. The whole process of a fault, including fault occurring, current limiting, circuit breaker opening and superconductors recovery, has been tested and the current and voltage of YBCO tapes are monitored. The current limiting module is tested with different shunt resistors to demonstrate its ability to vary its limited current. [ABSTRACT FROM PUBLISHER]

This paper proposes automatic power changeover switch system applied superconducting fault current limiter (SFCL) of the Korea electric railway using 25 kV-AC Scott transformer. The electric railway needs neutral section to separate two different electrical power phase to m phase and t phase. While the train passes through the neutral section, the electrical power supply phase is changed over to other phase. And that time, the train must turn off the circuit breaker to avoid transient as ‘inrush-current’ and ‘arc’. These cause negative problems as speed decline of the train, a shorter life of the train circuit breaker. To improve the problems, the inrush current limitation method is proposed. In addition, we analysed the effect of proposed method using time-domain transient simulation software (PSCAD/ EMTDC). [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]

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]

Superconducting fault current limiters (SFCLs) may play an important role in power-dense electrical systems. Therefore, it is important to understand the dynamic characteristics of SFCLs. This will allow the behavior of multiple SFCLs in a system to be fully understood during faults and other transient conditions, which will consequently permit the coordination of the SFCL devices to ensure that only the device(s) closest to the fault location will operate. It will also allow SFCL behavior and impact to be taken into account when coordinating network protection systems. This paper demonstrates that resistive SFCLs have an inverse current–time characteristic: They will quench (become resistive) in a time that inversely depends upon the initial fault current magnitude. The timescales are shown to be much shorter than those typical of inverse overcurrent protection. A generic equation has been derived, which allows the quench time to be estimated for a given prospective fault current magnitude and initial superconductor temperature and for various superconducting device and material properties. This information will be of value to system designers in understanding the impact of SFCLs on network protection systems during faults and in planning the relative positions of multiple SFCLs. [ABSTRACT FROM AUTHOR]

We propose a high-temperature superconducting fault-current-limiting cable (SFCLC), which is a hightemperature superconducting cable with a fault-current-limiting function. The SFCLC is expected to achieve fault-current limitation by flux-flow resistance of a long cable length. Particularly, in this paper, we focus on E–I –T characteristics of a YBCO-coated conductor at the flux-flow region. Based on the obtained E– I–T characteristics, we develop a numerical model and investigate current-limiting characteristics of the SFCLC for different cable lengths and fault conditions into a model power system. [ABSTRACT FROM AUTHOR]

Among superconducting fault-current limiters (FCLs), the inductive type has some distinctive merits such as large design flexibility due to the turn ratio, isolation between a current-limiting device and a power transmission line, and low heat losses. This paper highlights the future perspective for an inductive-type superconducting fault-current limiter (LSFCL) by using an autotransformer (AT) in closed- and open-core schemes. These are considered technically feasible and economically viable alternative for the LSFCL in terms of compactness, efficient limitation, and lower alternating-current losses, which prove to be a construction cost-effective means of fault-current management. In the hybrid scheme, a diode-bridge-type SFCL is integrated with an AT-based LSFCL. The above is accomplished by advanced numerical techniques and, hence, simulation studies in a sample distribution system to realize the significant efficiency improvement of the superconductor-based technology. [ABSTRACT FROM AUTHOR]

Fault levels in electrical distribution systems are rising due to the increasing presence of distributed generation, and this rising trend is expected to continue in the future. Superconducting fault-current limiters (SFCLs) are a promising solution to this problem. This paper describes the factors that govern the selection of optimal SFCL resistance. The total energy dissipated in an SFCL during a fault is particularly important for estimating the recovery time of the SFCL; the recovery time affects the design, planning, and operation of electrical systems using SFCLs to manage fault levels. Generic equations for energy dissipation are established in terms of fault duration, SFCL resistance, source impedance, source voltage, and fault inception angles. Furthermore, using an analysis that is independent of superconductor material, it is shown that the minimum required volume of superconductors linearly varies with SFCL resistance but, for a given level of fault-current limitation and power rating, is independent of system voltage and superconductor resistivity. Hence, there is a compromise between a shorter recovery time, which is desirable, and the cost of the volume of superconducting material needed for the resistance required to achieve the shorter recovery time. [ABSTRACT FROM AUTHOR]

Distributed power generation and the ever-growing load demand have caused fault current levels to exceed the nominal rating of the power system devices, and fault current limiters are more needed. Superconducting fault current limiter (SFCL) forms an important category of current limiters. In this paper, a novel flux-based model for the inductive shield-type high-temperature SFCL is developed based on the Bean model. This model is employed to simulate the SFCL performance in a sample circuit. Utilizing the model, the signal characterization of the limited current is determined. A prototype laboratory scale SFCL has been fabricated with superconducting rings. Yttrium barium copper oxide powders have been used for superconducting ring production. The critical current density of fabricated rings has been measured with an innovative method based on application of a magnet device. The fabricated SFCL has been tested in a circuit by applying different types of faults. The related experimental results are recorded and compared with the model results. The results obtained based on the modeling shows full compatibility with the experimental results. [ABSTRACT FROM AUTHOR]

A laboratory prototype of 800 V/30 A active superconducting current controller (SCC) is developed. The SCC is composed of an air-core superconducting transformer and a compensation voltage source. Based on the principle of series voltage compensation, the SCC can limit the fault currents effectively during fault conditions. Besides, it can actively control the power flow of the transmission lines within a certain extent. Due to the characteristic of higher energy density and high power density, the supercapacitor module is adopted to compensate the dynamic power during controlling the system current. To evaluate the dynamic characteristic of the SCC, a series of experiments are carried out in the laboratory. This paper presents parts of the important test results, including the capability of voltage regulation of the compensation voltage source, and the characteristic of system current control in a simulated power system. [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]

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]

The addition of new generation capacity increases the fault current levels in power systems. New generation and transmission capacity additions can be limited by the fault current constraints in power systems. The superconducting fault current limiter (SFCL) has great potential as a special protection device to limit the fault current in the event of a fault in power systems. Installations of SFCLs can alter fault current levels in power systems, thereby influencing the power system planning. This paper presents fault current constrained decentralized optimal power flow (OPF) for generation system planning incorporating a SFCL. The numerical simulation results are presented to show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper analyses the effect of a superconducting fault current limiter (SFCL) on the optimal sizing of a wind-turbine generator system (WTGS), which is a representative renewable energy source. When the WTGS is connected to a radial distribution system, the level of fault current during a contingency is increased. This increased fault current can reduce the coordination time intervals (CTIs) between multiple overcurrent relays, which are an important factor in determining the optimal size of the WTGS. Moreover, the maximum capacity of WTGS is also restricted by the associated fault current level and CTIs in a power system. [ABSTRACT FROM AUTHOR]

The power grid, especially distribution grid, has been more complicated due to distributed generations (DGs) with renewable energy sources and the smart grid. The complexity changes two things in terms of a fault; higher prospective fault current and the temporal variation of sources and loads. To correspond to those remarkable changes, we propose a fault current controller (FCC) named “smart FCC.” The smart FCC consists of a superconducting coil with a freewheeling diode if necessary, four thyristors, and a control unit. Smart FCC can not only limit but also control the current when a fault occurs. The smart grid technology can provide so enough information that it is possible to estimate which level of limited current should be the best in the real-time situation of the grid. Based on a real-time calculation of optimal fault current using the smart grid monitoring technologies, this new device is always ready to adjust the fault current. In this paper, we introduce a concept of the smart FCC and prove the concept. Various topologies have been proposed and simulated. Finally, a case study on a distribution class of 22.9 kV smart FCC has been conducted based on a conceptional system design. [ABSTRACT FROM AUTHOR]

Superconducting fault current limiter (SFCL) is a promising novel electric equipment to reduce excessive fault current in electric power systems effectively. However, in practical application of this novel device into electric networks, SFCL could cause some unfavorable impacts on the electric power system. Especially, coordination between the SFCL and the recloser which has a conventional protection scheme is a major concern because it could cause severe reliability and stability problems in power systems. Several important characteristics of SFCL, which affects on a recloser operation scheme, are quenching phenomena, recovery from the quenching state, limiting impedance and its triggering time. Therefore, careful assessment of coordination issues with a recloser should be investigated to evaluate reliabilities of electric power system by installing SFCL into conventional power networks. This paper presents the impacts of SFCL on the recloser operation by considering various aspects of newly developed hybrid resistive SFCL into distribution systems in Korea. Consequently, it was deduced that conventional recloser scheme might be altered in order to meet the performance and requirements of hybrid SFCL into distribution electric power systems. [ABSTRACT FROM AUTHOR]