Superconducting Fault Current Limiter Research Articles

Study of Resistive SFCLs for Transient Stability Enhancement of Paralleled Synchronous and Virtual Synchronous Generators in Weak Grid

Regarding a paralleled synchronous generator (SG) and virtual synchronous generator (VSG) system connected to a weak grid, the transient stability should be given more concern. This paper proposes applying resistive superconducting fault current limiters (R-SFCLs) to boost the paralleled SG-VSG system's transient stability while meeting the current limitation requirement (CLR). Firstly, the theoretical modeling is carried out, and the influencing mechanism of the grid strength on the transient stability is clarified. Then, the functions of the R-SFCLs to the paralleled system are analyzed, and the parameter design guidelines for the R-SFCLs are stated. Time-domain simulations are implemented in MATLAB, and a detailed comparison of using the R-SFCLs and the additional torque control for the paralleled system is made. From the simulations, the proposed approach offers a more significant stabilization effect. It outperforms the additional torque control to decrease the unbalanced power, eliminate the power angle oscillation, and handle the short-circuit fault with a longer duration for the paralleled system. The viability and appropriateness of the proposed approach are well confirmed.

진공도에 따른 절연파괴 분석에 관한 연구

This study focuses on investigating the dielectric breakdown characteristics of high-temperature superconducting (HTS) coils, which are increasingly used in various applications such as superconducting cables, superconducting fault current limiters (SFCLs), and superconducting particle accelerators. The research aims to understand how electrical breakdown, induced by high electromotive force and local quenching, can weaken the dielectric stability of HTS magnets. The dielectric experiments were conducted under different vacuum conditions and gaseous helium conditions, and an empirical formula for the electrical insulation design of HTS magnets was developed. Finite element method (FEM) analysis was also performed to simulate various conditions that may cause electrical breakdown, confirming that breakdown could occur at turn-to-turn and layer-to-layer of HTS magnets. As a result, it was confirmed that the magnitude of the induced electromotive force or quench voltage that could cause electrical breakdown of the HTS magnets under various insulating medium conditions such as gaseous nitrogen (GN2), gaseous helium (GHe), and vacuum was deduced.

Impact of Copper Stabilizer Thickness on SFCL Performance with PV-Based DC Systems Using a Multilayer Thermoelectric Model

Utilizing renewable energy sources (RESs) to their full potential provides an opportunity for lowering carbon emissions and reaching a state of carbon neutrality. DC transmission lines have considerable potential for the integration of RESs. However, faults in DC transmission lines are challenging due to the lack of zero-crossing, large fault current magnitudes and a short rise time. This research proposes using a superconducting fault current limiter (SFCL) for effective current limitation in PV-based DC systems. To properly design an SFCL, the present work investigates the effect of copper stabilizer thickness on SFCL performance by using an accurate multilayer thermoelectric model. In the MATLAB/Simulink platform, the SFCL has been modeled and tested using different copper stabilizer thicknesses to demonstrate the effectiveness of the SFCL model in limiting the fault current and the impact of the copper stabilizer thickness on the SFCL’s performance. In total, four different thicknesses of the copper stabilizer were considered, ranging from 10 μm to 80 μm. The current limitation and voltage profile for each thickness were evaluated and compared with that without an SFCL. The developed resistance and temperature profiles were obtained for various thicknesses to clarify the mechanisms behind the stabilizer-thickness impact. An SFCL with an 80 µm copper stabilizer can reduce the fault current to 5.48 kA, representing 71.16% of the prospective current. In contrast, the fault current was reduced to 27.4% of the prospective current (2.11 kA) when using a 10 µm copper stabilizer.

Pole-to-pole fault characteristics in VSC-HVDC transmission system with a resistance-inductance type superconducting fault current limiter

Pole-to-pole fault characteristics in VSC-HVDC transmission system with a resistance-inductance type superconducting fault current limiter

Critical Current Degradation in HTS Tapes for Superconducting Fault Current Limiter under Repeated Overcurrent

Superconducting fault current limiters (SFCL) can be an alternative to conventional devices limiting short-circuit currents in power systems. SFCL use high-temperature superconducting tapes of the second generation (HTS 2G) in SFCL, which, after reaching the characteristic critical current of the tape, go into the resistive state (quenching), limiting the short-circuit current. The critical current determines the moment of activation of the SFCL. Therefore, its value should not change during the operation of the device due to repeated limitation of short-circuit currents. The constancy of the critical current is a prerequisite for proper cooperation with the power system protection devices. Multiple quenching can cause microdamage in the superconducting layers responsible for lowering of the value of the critical current of the HTS tapes. The article presents the research results on the degradation processes of 2G HTS tapes intended for the construction of SFCL due to the action of prospective short-circuit currents with values exceeding the critical current of the tested tapes. The decrease in the value of the critical current of the HTS tape as a result of multiple transitions to the resistive state was investigated. The amount of energy emitted during the test current pulse of 0.2 s duration was determined. The limitation values of the voltage drop on the tape, which does not cause accelerated degradation processes, were defined. The microstructural tests of cross-sections of new HTS tapes subjected to prospective short-circuit currents were performed.

Parametric design method and application study of a 160‐kV resistive‐type DCSFCL in a three‐terminal flexible DC transmission system

AbstractThe intermittent access of renewable energy sources leads to a significant increase in fault short‐circuit currents in power grid. DC superconducting fault current limiters (SFCL) can limit short‐circuit currents in flexible DC transmission systems, which work in combination with direct current circuit breaker (DCCBs) to protect the grid system effectively. However, for the parameter design of DC superconducting fault current limiter (DCSFCL), it is difficult to balance the economics of the device and its adaptability to different fault situations. In this paper, a cross‐mapping design methodology for the DCSFCL is proposed and applied in the Nan'ao flexible DC transmission project, China. A cross‐mapping method is designed combining the critical parameters of DCSFCL and the system parameters. A three‐terminal simulation model of the flexible DC transmission system is constructed through MATLAB/Simulink and the design process of DCSFCL parameters is introduced. A cyclic calculation approach is proposed for the design of DCSFCL parameters through three fault conditions of the power system. Meanwhile, impact current short‐circuits test and artificial ground short‐circuit test were conducted on the prototype. Test results show that the designed DCSFCL meets the requirements of practical applications.

Impacts of a Flux-coupling SFCL on the overcurrent protection for distribution system with infeed

With the rapid development of distribution system and the integration of distributed generations, the increasing fault current is threatening electrical equipment of the power grid. The superconducting fault current limiter (SFCL) is an effective solution to dealing with the large fault current in the distribution network. In this work, the characteristics of the current limiting impedance of the flux-coupling SFCL is presented. The impacts of the flux-coupling SFCL on the overcurrent protection for distribution system with and without infeed is analyzed. Furthermore, a simulation model of a real 10 kV distribution system with a flux-coupling SFCL is built to verify the analysis. This work is of significance to the coordination between a flux-coupling SFCL and the overcurrent protection for distribution system.

The Structural and Electromagnetic Comparative Analysis of the Bifilar-Meander-Type Winding Method of Superconducting DC Circuit Breaker

As the utilization of DC systems increases worldwide, the importance of DC cutoff technology is increasing. We proposed a hybrid DC cutoff technology combining an SFCL (superconducting fault-current-limiter) and a mechanical DC circuit breaker. This model can perform a fault-current-limiting operation through the quenching of the SFCL and a breaking operation through an artificial cutoff zero point of a mechanical DC circuit breaker. In particular, the SFCL is responsible for the growth of the initial fault current according to the DC characteristics. As the DC system’s supply and demand increase, the DC system’s capacity also increases. Therefore, the fault-current-limiting capability of the SFCL should be increased according to the increasing DC system breaking capacity. The fault-current-limiting capability can be increased by increasing the superconducting wires used in the SFCL. Current commercially available SFCLs use bifilar-helical-type and bifilar-spiral-type winding methods. These have the disadvantage of increased volume with increased capacity. To compensate for these disadvantages, we proposed a bifilar-meander-type winding method. In this paper, a new bifilar-meander-type winding method was introduced. In addition, the structural and electromagnetic parts of the existing winding method and the bifilar-meander-type winding method were compared and analyzed for differences. The program used for this analysis is the electromagnetic analysis Maxwell program. As a result, it was confirmed that the bifilar-meander-type winding method is superior to the conventional bifilar-helical and bifilar-spiral types.

Design, Verification, and Protection Setting of Superconducting Fault Current Limiter for a 10 kV Power Network

Design, Verification, and Protection Setting of Superconducting Fault Current Limiter for a 10 kV Power Network

Enhancing transient stability of power systems using a resistive superconducting fault current limiter

The electricity demand keeps increasing with development and time, which leads to the need to install more generating units in the grid. Therefore, the fault current levels will rise above the limits of the electrical equipment, particularly when the electric grid becomes meshed and interconnected with neighboring networks. Consequently, the electrical equipment needs to be replaced or use a method that will decrease the fault current to be within the permissible boundaries. The existing solutions such as neutral impedance, current limiting reactor (CLR), and bus splitting have negative impacts on the electric grid. The superconducting fault current limiter (SFCL) appears to be a promising solution. In this paper, the resistive SFCL is proposed to enhance the stability of the interconnected power system. The two-area system is used as a case study for the interconnected power system. Also, the optimal value and locations of the resistive SFCL are analyzed. The results show that the system will remain stable without tuning the power system stabilizer (PSS).

Quenched Flux-Coupling Superconducting Fault Current Limiter Scheme and Its Electromagnetic Design Method.

In order to solve the problem of excessive short-circuit current in the present power system, a fault current limiter has become a new type of power device with high demand and is one of the current research hotspots. The flux-coupling type superconducting fault current limiter (FC-SFCL) generates a current-limiting impedance through decoupling superconducting parallel inductance based on the circuit breakers' fractional interruption. The principle is simple, and the impedance is low during normal operation. It can directly use the existing circuit breaker to open a short circuit that is much higher than its own breaking capacity. Thus, it can be used for large-capacity fault current limiting and effective failure breaking. This paper focused on exploring and studying the implementation scheme of practical products of FC-SFCL. Considering that the quenched-type parallel inductance can limit the first peak value of the fault current, a quenched-type improvement scheme was proposed. Then, an electromagnetic design method based on the simplified calculation of the number of parallel tapes was proposed, which simplified the design process and reduced the design difficulty of the quenched FC-SFCL. Taking a 10 kV/500 A/5 kA quenched prototype as an example, its electromagnetic design was completed, and the performances of the non-quenched and quenched schemes were compared. The results showed that, compared to the non-quenched structure, the technical economics of the quenched one were more prominent, and it can be used preferentially for engineering prototypes. This study about the scheme of the quenched FC-SFCL and its electromagnetic design method is useful for promoting the implementation of the current limiter engineering prototype.

Voltage Sag Mitigation Effect Considering Failure Probability According to the Types of SFCL

The development of industrial technology is based on electronic devices that are sensitive to power quality. Thus, the demand for high-quality and reliable power supplies is increasing. Voltage sag results in severe problems in the manufacturing process of power quality-sensitive industrial loads. When a fault occurs in a multi-ground power distribution system, the magnitudes of the fault current and voltage sag in the faulted and nonfaulted feeders become high. Hence, installing a superconducting fault current limiter (SFCL) is an effective method of compensating for fault current limitation and voltage sag. This study evaluates the effects of improving the magnitude, duration, and frequency of the voltage sag according to the type of SFCL used. First, a fault in the power distribution system is analyzed using PSCAD/EMTDC, a power system simulation software, according to the fault current-limiting element (CLE) and the type of SFCL. Second, the expected voltage sag frequency caused by a feeder fault in the power distribution system is assessed. Finally, the voltage sag improvement effect according to the CLE and the type of SFCL are compared. The trigger-type SFCL with a resistor as a CLE has been evaluated and found to be effective in improving voltage sag.

Combinatorial Multi-Objective Optimization of SFCL and SMES for the Low-Voltage Ride-Through Fulfillment of Solid-State Transformer

To figure out the low-voltage ride-through (LVRT) problem of a solid-state transformer (SST), this paper proposes a methodology that combinatorically optimizes a resistive superconducting fault current limiter (SFCL) and a superconducting magnetic energy storage (SMES) unit. The goal of minimizing the capacities of the resistive SFCL and the SMES while achieving the LVRT of the SST is designed, and a multi-objective Pareto optimization is carried out. Firstly, the modeling of a three-stage SST with a resistive SFCL and a SMES is presented through theoretical analysis, and the SST's fault transient characteristics are analyzed. Then, the optimization scheme based on the improved non-dominated sorting genetic algorithm-II (NSGA-II) is elaborated. The proposed approach is verified in a typical SST connecting a 10 kV power distribution network and a 380 V electricity grid. Using MATLAB/Simulink and RT-lab real-time simulation platform, different tests are done to check the rationality of the optimal solutions. The results reveal that a satisfying LVRT for the SST is guaranteed while minimizing the ratings of the SFCL and the SMES, and getting a proper reactive current injection. Consequently, the validity and suitableness of the proposed approach are well confirmed.

Design and Experimental Investigation of Three-Phase Inductive Type Superconducting Fault Current Limiter based on Current Injection Method

Design and Experimental Investigation of Three-Phase Inductive Type Superconducting Fault Current Limiter based on Current Injection Method

Stability Enhancement of Grid-Connected Wind Power Generation System Using PSS, SFCL and STATCOM

The stability related issues may occur in a power system due to disturbances in generating or loading conditions, especially in the presence of distributed generation (DG) based on renewable energy resources (RERs). This paper proposes a novel strategy for the stability enhancement of a wind power generation system (WPGS) by using a combination of three devices, namely, a power system stabilizer (PSS), resistive superconductor fault current limiter (R-SFCL) and static synchronous compensator (STATCOM). The small signal (SS) stability of the test system is enhanced by selecting the best PSS type from the different types of PSS. An R-SFCL is used for improving the rotor angle and the frequency stability of the test system. Two indices, namely, transient stability index and sum of maximum deviations (SMD) index are introduced for determining the optimal locations of different sized R-SFCLs for increasing the rotor angle stability. The sensitivity index (SI) based on the power change between areas is applied for determining the optimal locations of different sized R-SFCLs for enhancing the frequency stability. Along with rotor angle and frequency stability, LVRT capability improvement of the wind farm using STATCOM is also considered. Finally, the combined effect of R-SFCL and STATCOM on the rotor angle and the frequency stability, for different fault locations, is also investigated for determining the optimal location of an R-SFCL in the presence of STATCOM. The results presented in the paper show that STATCOM affects both the number of feasible locations and the optimal locations that can be selected for different sized R-SFCLs for augmenting the rotor angle and the frequency stability of the system during faults. Moreover, it is pointed out that an optimal combination between the different sizes and the locations of R-SFCLs and STATCOM exists to enhance the overall stability of the test system under fault conditions.

Shielding Characteristics of Solenoidal Superconducting Screens Made From HTS Tape, for SFCL Applications

In the design and prototyping of an Inductive-Resistive Superconductor Fault Current Limiter (IR-SFCL), previously presented by the authors, superconducting screens made from BSCO bulk have been used for shielding the inductive stage of the device. This kind of screens has several problems as rigidity, brittleness, commercial dependence on size and high cost. In order to avoid such issues, replacing the bulk-type superconducting screens by screens made from high temperature superconducting (HTS) tape is proposed. Tapes are more flexible and allow to easily make screens with several sizes and configurations, and better behavior against temperature changes and dynamic effects. To select a suitable configuration for this type of screen, a preliminary study of the shielding capacity of screens with different configurations, made from tape, is presented. This study, as well as literature, led us to select the solenoidal configuration as the most suitable for our application. In this work, we study solenoidal screens built with independent concentric layers, each one made from non-insulated tape, and all in contact just by the Ag external cover of the tape. A test method has been developed, and screens with 1 to 10 solenoid layers have been tested to find out their shielding factor. The shielding mechanism (diamagnetism vs. induced currents) has been studied by measuring of the transport current generated in between the non-insulated solenoids. The low incidence of these currents in the magnetic shielding process of the superconducting tape screens is reported.

Design aspects of transmission voltage superconducting fault current limiters with YBCO tapes in China

The design progress of superconducting fault current limiter (SFCL) for transmission voltage is presented, with a focus on the results of recent key experiments that have led to a state-of-the-art high-voltage high-capacity super-conducting current limiting techniques: the resistive alternating current (AC) SFCL, saturated iron cores AC SFCL, and resistive direct current (DC) SFCL. The main driving factors for designing SFCL in these projects are the preparation of highperformance superconducting materials, the development of large-scale superconducting current limiting winding, system testing, and operation technology. Based on the authors’ experience with both AC and DC SFCLs, this paper focuses on the main design aspects of resistive SFCL at transmission voltage. The relationship between the hot spot caused by the inhomogeneity of long superconducting tape and the overall parameter selection is presented. In addition, the thermal calculation based on the current limiting resistance and a real-time current curve is also proposed for the parameter design of the current limiting winding.

A Power-Electronics Free Protection Device for Superconducting Electrical Propulsion Aircraft

Research into developing cryogenic protection devices for superconducting electrical systems is lacking. One of the few investigations was of cryogenic switches in the form of a solid-state circuit breaker (CB). It was reported that these breakers would take up nearly 40% of the superconducting electrical system mass and losses. This article designs a cryogenic switch, free of power electronics, whose conduction loss is only 4.1% of a comparable solid-state CB’s total loss. Protection considerations of a 1-kV/40-MW cryogenic system are referred to validate its application in a superconducting electrical powertrain. The designed cryogenic switch’s dc and ac interrupting ability were verified by experiments to interrupt 750-V/1500-A dc and 1-kV/6.3-kA ac, very close to the dc and ac limits of the proposed 40-MW Center for High Efficiency Electric Aircraft (CHEETA) system. For fault conditions, a noninductive pancake resistive superconducting fault current limiter unit was designed to help with the unacceptable fault current. The 750-V/10-kA prospective current was suppressed to 1.4 kA in 588 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> and interrupted by the switch in 12 ms. Cooperation of the cryogenic switch and superconducting fault current limiter shows potential in dealing with fault currents in future electric aircraft.

An electrical schematic solution for superconducting fault current limiter access to the power system

High-temperature superconducting current limiters (SFCL) can suppress the short-circuit current of the power grid effectively. The 220kV and 35kV SFCL have been applied and connected to the power system in China. The 500kV SFCL equipment has been developed through the prototype and has the conditions to access the power grid. In this paper, the possible fault conditions of SFCL and the electrical scheme for connecting to the power grid are studied. The low-temperature system of SFCL is the weak point of the equipment that is prone to failure. An electrical schematic solution is proposed according to the characteristics of the SFCL equipment. This solution has the advantages of high reliability, flexibility, and convenient operation and maintenance, and it can be applied to various voltage levels of the power system.

A Coordination Scheme for a Combined Protection System Considering Dynamic Behavior and Wind DGs Fault Ride-Through Constraints

• A proposed design of a hierarchical protection scheme is presented. • Protective devices are optimally coordinated based on fault current transients. • Hybrid superconducting fault current limiters are optimally allocated to keep coordination under synchronous and inverter-based wind DGs. • Ride-through capability of wind DGs is integrated into the fault current limiter sizing problem. • Changes of network topology and variation of detected fault current are considered. A combined protection system has multiple types of devices such as directional overcurrent relays, reclosers, and fuses to protect distinct areas in a DG-incorporated network. An approach for setting all protective devices to realize complete coordination of adjacent ones taking transient responses into account is presented. The participation of synchronous generator-based and/or inverter-based wind DGs can degrade protection coordination. So, a scheme for sustaining coordination by optimal hybrid superconducting fault current limiters is proposed. The scheme can cope with variation of network topology; and handles the change of fault current level perceived by the protection device under a given topology. Moreover, instead of the conventional steady-state models, more realistic dynamic models of relays, reclosers, DGs, and fault current limiter are used. As a serious operation problem, undesired tripping of wind DGs under fault condition can occur due to the sag of terminal voltage below certain limits defined by national and international standards. Therefore, the proposed scheme prevents this undesired tripping of wind DGs by integrating its ride-through capability constraints into the fault current limiter allocation problem. The proposed approach is applied to the IEEE 9-bus and 30-bus systems. Results confirm the efficacy of the proposed method.