Resistive Superconducting Fault Current Limiter Research Articles

Breakdown Phenomena in Liquid Nitrogen Under Synchronized Transient Boiling and Impulse Voltage

Resistive superconducting fault current limiters constitute a promising solution for high voltage networks. During the resistive current limitation, transient overvoltages and heat dissipation occur on superconducting tapes, inducing fast boiling of surrounding liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). An experimental system reproducing the fast transient heating of a tape electrode, synchronized with a high voltage impulse is described. Breakdown voltages measurements in both polarities are carried out versus synchronization delay, pressure (0.10 to 0.40 MPa), temperature (77 K and 65 K). Breakdown voltages show complex variations with these parameters. More insight is obtained from the recording of pre-breakdown phenomena (streamer). The size of vapor bubbles has a large and counter-intuitive influence on streamer initiation: the smaller bubbles, the lower inception voltage. Subcooling LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (by decreasing temperature and/or increasing pressure) sometimes has a beneficial influence (quenching of negative streamer propagation), but deleterious effects can be as well observed in other circumstances (by favouring positive streamer initiation).

Performance Analysis of Resistive Superconducting Fault Current Limiter Using LN2and GHe Cooling

Large-scale electric aircraft is a disruptive technology to address the environmental impact of air travel. Fault current limitation is crucial to realise the safety and reliability of the electric aircraft, in particular for large-scale electric aircraft using DC distribution network. This paper investigates the behavior of the resistive SFCL under different cryogenic cooling systems including liquid nitrogen and helium gas circulation cooling systems for the electric aircraft DC distribution network. Electromagnetic and thermoelectric models were used to predict the characteristics of resistive SFCL. The simulation results demonstrate that it is promising to design resistive SFCL using liquid nitrogen cooling as well as helium gas circulation cooling systems, which offer flexibility for SFCL cryogenic cooling system for electric aircraft applications.

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.

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).

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.

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.

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.

Rezistif Süperiletken Arıza Akımı Sınırlayıcı MATLAB-Simulink Modeli ve Uygulaması

Günümüzde, nüfus artışı, yerleşim yerlerinin ve endüstriyel alanların genişlemesi ve teknolojinin gelişmesiyle birlikte elektrik tüketiminde önemli bir artış görülmektedir. Buna paralel olarak üretim kapasitelerinin de artması ile elektrik güç sistemlerinde çeşitli sebeplerle meydana gelen arızaların sebep olduğu yüksek akım seviyeleri, sistemdeki elemanlar için tehlikeli durumlar oluşturmaktadır. Arıza akımlarının sınırlandırılması, bu akımların zorlayıcı termal, dinamik ve elektromanyetik etkilerinden sistemin ve sistem elemanlarının korunmasını sağlar. Bu çalışmada, modern arıza akımı sınırlandırma yöntemlerinden biri olan Rezistif Süperiletken Arıza Akımı Sınırlayıcıların (R-SFCL) yapısı ve çalışma prensibi incelenmiştir. Ayrıca, bir R-SFCL tasarımı yapılmış ve oluşturulan deney sisteminde arızalar gerçekleştirilerek elde edilen gerçek veriler ile MATLAB/Simulink’de gerçekleştirilen simülasyon sonuçları karşılaştırılmıştır.

Impact of superconducting fault current limiters on Delayed Current Zeros in industrial power systems

Electric power systems may exhibit fault currents with high asymmetry when generators are close to large motors and loads. In this condition and depending on the fault inception instants, the fault current waveforms may present Delayed Current Zeros (DCZ). During transient studies, in some cases, breakers do not see the current zero-crossing for several cycles. Indeed, if the breaker opens just after a transient when the current has not reached steady-state and may be offset by a slow exponentially decaying DC component, then, the breaker will fail to open as the current will not cross zero within the interruption time. Here, the main concern associated with DCZ is however related to the interruption of the circuit breakers on a current wave crossing zero. At this moment, the interruption is accompanied of an electrical arc having the potential to damage equipment. Resistive superconducting fault current limiters (r-SFCL) are a known solution to reduce the magnitude of short-circuit current in electrical systems. It is a versatile technology that can tackle both fault and stability issues in aging and modern power grids alike. As a side benefit, it may also address the DCZ problem. The present work aims at investigating the impact that an r-SFCL may have on DCZ and, in particular, its ability to eliminate this issue altogether. To that end, a r-SFCL based on an existing design was modeled using the consolidated thermal–electrical analogy. This approach has proven to be fairly accurate to model the transient behavior of the superconducting device. Here, the case study simulates a solid short-circuit at the terminal of a generator in a specific bus, simulating an industrial power system, that includes a circuit breaker, a motor load, and a r-SFCL. The electromagnetic transient computations were carried out considering load and no-load conditions with and without the r-SFCL. Eight scenarios were considered, showing that r-SFCLs can actually address DCZ in addition to limit the fault level.

Integration of superconducting fault current limiter with solid-state DC circuit breaker

The onboard direct current (DC) system in electric aircraft could face a severe fault current, which is tens of times the nominal current in a short-circuit fault. It is critical to limit the fault current and clear the fault within a few milliseconds to prevent any damage to the DC system. A protection method using a resistive superconducting fault current limiter (SFCL) with a solid-state DC circuit breaker (SSCB) to manage the DC short-circuit fault is proposed and experimentally verified. A bifilar SFCL coil prototype with two types of connection to achieve low and high inductance is designed and tested, which reduces the fault current considerably from 2000 A to below 1000 A. The performance when integrating the low and high inductance SFCL with a solid-state DC circuit breaker are investigated. It is found that when integrating the SFCL with the SSCB, a high voltage is induced across the high inductance SFCL during current interruption tests. In terms of reliability and durability, the low inductance SFCL is preferred to integrate with the SSCB. The experimental results show that the low inductance SFCL can be an effective solution to protect the DC system from severe fault currents and then SSCB can rapidly and reliably interrupt the fault current at 1000 A.© 2017 Elsevier Inc. All rights reserved.

Improved Recovery Time and Voltage Stability for Resistive Superconductor Fault Current Limiters

Fault current levels occurring in power systems force the breaking capacities of the breakers. In the power system elements, the generator, transformer, cables, etc., are exposed to the dangerous effects of fault current until the breaker clears the fault. Various limiting methods have been developed to eliminate this adverse situation in recent years. One of these methods is Superconducting Fault Current Limiters (SFCL). With the discovery of High-Temperature Superconductors (HTS), SFCL's Resistive type has become more popular. Resistive SFCL (R-SFCL), based on the non-linear resistance property of superconducting materials, limits the fault within the first half period. However, it cannot provide such a fast response after the fault. The time required to regain the superconducting state after the fault is the recovery time. For R-SFCL manufacturers, recovery time is a design parameter that must be kept short. This study examines limiting performance, recovery time, and voltage stability with the dynamic model created using MATLAB/Simulink. With the shunt breaker method proposed in the study, the recovery time was shortened, and the voltage stability improved.

Resistive SFCL Integrated Ultrafast DC Hybrid Circuit Breaker for Subsea HVDC Transmission Systems

High voltage direct current (HVdc) power transmission systems do not encounter any natural zero crossing unlike the ac systems, and hence, the dc circuit breakers employed should be fast-acting and reliable to ensure safe operation. Circuit breakers (CBs) that have fast response time with lower energy loss dissipation are required for subsea HVdc transmission systems. This article investigates the performance of various CB topologies, including ultrafast coupled inductor hybrid CB (CIHCB) topology without and with the integration of resistive-type superconducting fault current limiter (R-SFCL) for a 100-kV, 100-MW HVdc transmission systems. It is found that the addition of R-SFCL with 1.7-ms response time decreases the peak current through the breaker and, hence, the power dissipated in the CB during short-circuit fault conditions. Thus, the rating of CB can be significantly decreased with the proposed topology. Furthermore, a comparison of power loss in CIHCB with the existing topologies, such as mechanical CB, resonant CB, and HVdc-hybrid CB, are also presented in this article.

Limitation Analysis of 1st and 2nd Generation Superconductors used in Resistive Superconductor Fault Current Limiters

Fault currents in power systems force valuable power system elements thermally, dynamically, and electromagnetically until the arc disappears. Installation elements that can withstand fault currents or damage existing components require a high cost. Installing components that withstand fault currents and the damage of fault currents to existing components are costly. Resistive Superconducting Fault Current Limiter (R-SFCL), one of the modern limiting methods, increases the safety and sustainability of the system by eliminating these risks. In this study, a dynamic model was created in MATLAB/Simulink for 1G and 2G HTS used in R-SFCL, and their response to single phase-to-ground fault was observed. According to the simulation results, the most advantageous HTS type for R-SFCL was determined. The fault current level, limitation rate, resistance and temperature values, and response times were compared in terms of limiting performance.

Demonstration of a Three-Dimensional Current Mapping Technique Around a Superconductor in a Prototype of a Conventional Superconducting Fault Current Limiter

Here, we describe a three-dimensional (3-D) current mapping technology developed for a superconductor using an array of Hall sensors distributed around it. We demonstrate this in a prototype similar to a conventional resistive superconducting fault current limiter (SCFCL). By calibrating the Hall sensor voltage, we can directly measure the distribution of the currents in the superconductor and the shunt. Using pulsed measurements, we measure the fractions of current distributed between the superconductor and shunt resistor parallel combination when a fault-like condition is mimicked in the system. Using the Hall array measurements, we generate a real-time 3-D map of local average current distribution around the superconductor used in our prototype of SCFCL. Our measurements show that even for currents less than the critical current a nonuniform current flow pattern exists around the superconductor, which we have used in the prototype. The capability of real-time, 3-D monitoring of the average local current distribution offers a way for the early detection of instabilities like hotspots developing in a superconductor. We discuss the use of this technique to not only show how it offers early detection and protection against instabilities developing in the superconductor, but also how it offers an added flexibility, namely, a user-settable fault current threshold.

Study of Resistive Superconducting Fault Current Limiters for Stability Improvement of VSG-Controlled Multiple Microgrid Clusters

Multiple microgrid (multi-MG) clusters based on virtual synchronous generator (VSG) control can preferably incorporate renewable energies. Nevertheless, the power angle stability (PAS) of VSG–controlled multi-MG clusters is easy to be influenced by grid faults. In this paper, resistive superconducting fault current limiters (R–SFCLs) are introduced to deal with this PAS problem. It is designed to install the R-SFCLs at the point of common coupling (PCC) of each MG in the clusters. The transient stability mechanism based on power balance and swing equation is analyzed to clarify the impacts of the R-SFCLs. Through MATLAB, a simulation model of three VSG-controlled MGs with R-SFCLs is built, and different fault scenarios are imitated for checking the performance behaviors of the R-SFCLs. From the simulation results, the R-SFCLs can visibly suppress the overcurrent inrush and assist the MGs in the clusters to fulfill the fault-ride through (FRT). Moreover, the energy dissipation of the R–SFCLs is calculated, and an improved power balance property is obtained in the multi-MG clusters to alleviate the power-angle fluctuations. Consequently, the effectiveness of the R–SFCLs on reducing the relative power angle variation is demonstrated, and the transient stability of the multi-MG clusters withstanding the three-phase faults is favorably enhanced.

Numerical Study on the On-Grid Performance of Superconducting Cable Cooperated With R-SFCL

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.

Formation of Hot Spots in Coated Conductors During Static and Dynamic DC Loading

High voltage DC transport at long distances represents an opportunity for wider use of superconductors. In particular, the second generation of high temperature superconductor tapes produced in form of coated conductors (CC) offers a unique solution for protecting a high-capacity connection against fault currents. In the resistive superconducting fault current limiter (R-SFCL), the CC tape would emerge as a substantial resistance in case of overcoming its critical current, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> . Non-uniformity of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> along the CC length is a common issue requiring attention. Because of highly nonlinear current/voltage dependence, the spot with critical current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_cmin</i> < <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> could transform into the hot spot with rapid rise of local temperature. Due to its small dimension, it would not create an observable voltage at the device terminals, thus may escape attention of a quench detection system. We have investigated the mechanism of hot spot creation at the DC currents between <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_cmin</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> , and the analytical formulas have been derived predicting the limits of stable operation. Now we extend the analysis to the case of the limitation event, when for a fraction of second the current exceeds also the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> . It is desirable that the temperature rise happens along all the conductor length, leading to a quick reduction of transported DC. Numerical modelling has been utilized to analyze such an event, and a simplified analytical model has been developed to predict the range of currents causing the formation of hot spots.

Numerical Simulation of Thermal Stabilization Used in HTS Tapes for SCFCL Application

Resistive superconducting fault current limiters (R-SCFCL) are novel devices which implement high-temperature superconducting (HTS) tapes. Unfortunately, the tapes in as-delivery state cannot withstand higher electric fields and thus high temperatures during a quench event, so they must be modified by a thermal stabilization layer. Detailed thermal finite-element (FE) analysis was carried out using the finite element modeling software (FEM SW) ANSYS, to investigate the heat transfer in ( <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</b> ) high-heat capacity materials applied on the HTS tapes, as well as in (2) the HTS tapes themselves. The individual models differ in materials of thermal stabilization, thicknesses and geometry configuration. Their thermal behavior was investigated under different quenching temperatures. Numerical simulations proved that epoxy composite filled with 20 vol.% of SiC particles as a filler in form of 100 μm thick overlayer coating is a promising high-heat capacity material, suitable for the thermal stabilization of HTS tapes in R-SCFCL application.

Limiting Characteristics of Capacitor Discharge Current of MMC-Based System Using the SFCL on Short Circuit

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.

Fault protection of multiterminal HVDC networks: Impact of inductance

Multiterminal Voltage Source Converter (VSC) High Voltage Direct Current (HVDC) networks are developing rapidly worldwide, especially in China with urgent needs of long-distance power transmission. Currently, the interrupting capacity of available DC circuit breakers (DCCBs) is a key obstacle to the development of multiterminal VSC HVDC networks. Superconducting fault current limiters (SFCLs) can compensate for the limitation of DCCBs. Conventionally, a resistive SFCL is regarded as essential and sufficient, while an inductive one is less related and optional. However, pure resistance cannot effectively suppress the rising rate of fault current at the very early stage of a fault, resulting in unnecessary blocking of the converter. Adequate inductance is required for such SFCLs to curb rapidly increasing fault currents within the first few milliseconds, which is critical to DCCBs to isolate fault without interrupting other DC transmission lines. In this paper, we compared and analyzed the performances of SFCLs with different resistances and inductances in a four-terminal VSC HVDC network using PSCAD/EMTDC software. The results indicate that even resistance and inductance show different current limiting effects, but they are both necessary to realize effective SFCL function for multiterminal VSC HVDC networks. The outcomes of this paper are of significance in FCL design for multiterminal VSC HVDC networks.