Superconducting Fault Current Limiter Research Articles

Design and Performance Analysis of a Saturated Iron-Core Superconducting Fault Current Limiter for DC Power Systems

A saturated iron-core superconducting fault current limiter (SI-SFCL) can significantly limit the magnitude of the fault current and reduce the stress on circuit breakers in direct current (DC) power systems. The SI-SFCL consists of three main parts: one magnetic iron-core, one normal conductive primary coil (CPC), and one superconducting secondary coil (SSC). This paper deals with the design options for the coil system of the SI-SFCL and confirms their operating characteristics through a physical experiment. The electromagnetic characteristics and operational features of the SI-SFCL was analyzed by a 3D finite element method simulation model. The design of the SSC was based on shape, wire types, required fault current limit and protection aspects. In the CPC, the bobbin was designed based on material selection, cost, structural design, and the effects of the SI-SFCL on the fault current limit. Based on these simulation results, a laboratory-scale SI-SFCL was developed, specifically fabricated to operate on a 500 V, 50 A direct current (DC) power system. In the experiment, the operating characteristics of each coil were analyzed, and the fault current limit of the SI-SFCL according to the operating currents of the SSC and bobbin design of the CPC were confirmed. Finally, the cost analysis of the SI-SFCL with the proposed design options of the coil system was implemented. The results obtained through this study can be effectively used to large-scale SI-SFCL development studies for high-voltage direct current (HVDC) power systems.

Current limiting tests of a prototype 160 kV/1 kA resistive DC superconducting fault current limiter

High voltage direct current (HVDC) transmission technology has begun to play a great role in power transmission industry over the last decade. However, short-circuit fault seriously threatens the safety of an HVDC network. In order to reduce the fault current level of an HVDC network, utilizing a superconducting fault current limiter (SFCL) was proposed by researchers and engineers worldwide. Recently, Guangdong Grid Company of China Southern Power Grid, Co. has led a project to develop a 160 kV/1 kA resistive type DC SFCL. As a middle-step objective, a 160 kV/1 kA laboratory prototype has been developed. Due to a facility with an adequate capacity for testing such DC equipment is practically inaccessible, the current limiting performance of the prototype cannot be tested with a straightforward current limiting experiment. In practice, effectual alternative methods have to be adopted. Since the AC half-wave impact method requires less equipment and cost than the DC impact method, we took on an AC half wave impact current method to evaluate the current limiting function of the prototype alternatively. In this paper, we report the procedures and results of these tests.

Current density distribution in resistive fault current limiters and its effect on device stability

The increase of current uniformity along of a Resistive type Superconductor Fault Current Limiter (R-SFCL) in the design of this type of limiters is well perceived as an important issue. The non-uniform distribution of current in R-SFCL only increases the current in some superconducting regions, as a result, in the fault conditions, only certain parts of the superconductor undergo a phase change that increases the heat pressure in those areas and causes the breakdown and destruction of the device. In this paper, the current density distributions in common patterns used in R-SFCs constructions have been simulated and investigated. To this end, an effective model is proposed for R-SFCL to achieve the highest uniformity of current and harmonic phase change over superconductors compared to other patterns. The simulation results in the Ansys Maxwell Software advocate the appropriate and satisfying performance of the proposed model.

Static Synchronous Compensator and Superconducting Fault Current Limiter for Power Transmission System Transient Stability Regulation Including Wind Generator

Static Synchronous Compensator and Superconducting Fault Current Limiter for Power Transmission System Transient Stability Regulation Including Wind Generator

Analysis of Superconducting Fault Current Limiter 6 kV/0.14 kA

Analysis of Superconducting Fault Current Limiter 6 kV/0.14 kA

Design Considerations on a Resistive Superconducting Fault Current Limiter

Design Considerations on a Resistive Superconducting Fault Current Limiter

Analysis on Double Quench and Instantaneous Power of SFCL Using Two Magnetically Coupled Windings According to Winding Direction

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

Improvement of the Transient Stability of a 14-bus Network Using a Superconducting Fault-Current Limiter SFCL

This study presents a new strategy for implementing the superconducting fault current limiter SFCL in order not only to limit short - circuit currents but also to improve the stability of electrical networks in the presence of faults. The calculation of the impedance that the limiter must introduce into the test network at the moment of the failure is obtained from a three-dimensional computation code, developed and implemented under MATLAB environment where the formulation in magnetic vector potentials A and scalar potential Electric V is adopted to solve the electromagnetic problem and the heat diffusion formulation is adopted also to solve the thermal problem. The coupling is ensured by an alternating algorithm and the numerical resolution of the problem is ensured by the method of the finite volumes in its three-dimensional version in order to avoid certain problems of numerical convergence linked to the strongly nonlinear character of the problem to be solved. The modeling of the network tests will be made by PSAT under the environment MATLAB.

Resistivity of REBCO tapes in overcritical current regime: impact on superconducting fault current limiter modeling

A detailed knowledge of the resistivity of high-temperature superconductors in the overcritical current regime is important to achieve reliable numerical simulations of applications such as superconducting fault current limiters. We have previously shown that the combination of fast pulsed current measurements and finite element analysis allows accounting for heating effects occurring during the current pulses. We demonstrated that it is possible to retrieve the correct current and temperature dependence of the resistivity data points of the superconductor material. In this contribution, we apply this method to characterize the resistivity vs. current and temperature of commercial REBCO tapes in the overcritical current regime, between 77 and 90 K and in self-field conditions. The self-consistency of the overcritical resistivity model is verified by comparing DC fault measurements with the results of numerical simulations using this model as input. We then analyze by numerical simulation to what extent using the model instead of the widely used power-law model affects the thermal and electrical performance of the tapes in the practical case of a superconducting fault current limiter. A remarkable difference is observed between the measured overcritical current resistivity model and the power-law resistivity model . In particular, the simulations using the power-law model show that the device quenches faster than with the overcritical resistivity model. This information can be used to optimize the architecture of the stabilizer in superconducting fault current limiters.

10 kV AC test verification of the high temperature superconducting fault current limiter with bias magnetic field

Under the support of the China State Grid Corporation Science and Technology Project, a set of 10 kV superconducting fault current limiter (SFCL) with bias magnetic field including a high temperature superconducting a low inductance unit, a double split reactor, a fast breaker and its control system is designed and assembled in Hushitai high voltage center of Electric Power Research Institute of State Grid Liaoning Electric Power Co., Ltd. The 10 kV dedicated test including high voltage test, phase to phase short circuiting fault test, quench resistance measurement, quench recovery time measurement were performed in December 2019. The fault current distribution and voltage test results during the phase to phase short-circuit fault of the SFCL are presented and analyzed. Test results indicate that current limiting resistance of SFCL unit is about 1.21 Ω within 10 ms fault time. Those results meet the design requirement.

Flashover characteristics of vacuum interrupters in liquid nitrogen and its comparison with air and transformer oil for the superconducting switchgear applications

Liquid Nitrogen Insulated metal enclosed Switchgear (LNIS) is a new type of power switchgear system. It uses liquid nitrogen (LN2) as coolant, insulation and arc quenching medium. LNIS mainly consists of resistive type superconducting fault current limiter (R-SFCL), LN2 isolator switch and Vacuum circuit breaker (VCB). Vacuum interrupters (VIs) are used in combination with magnetic actuator to operate as VCB in LNIS. This paper deals with the surface flashover investigations of VI in LNIS. For fair comparisons, two types of standard manufacturing, 12 kV, VI modules, namely; Smooth type and Umbrella type, were selected and tested in open air, transformer oil (also known as Hydro-treated Light Naphthenic Distillate) and LN2 environments under the standard lightning impulses, i-e positive and negative. Therefore, a total of 12 comparisons have been reported in this paper. Up and down method has been followed and Statistical analysis have been done for all types of tests. Weibull and Box & Whiskers plots reveal some important results with accumulated probabilities from 0% to 100% Flashover voltages (FOVs), the most important be the critical FOV, also known as 50% Flashover voltages (U50). The results reveal that, for Air tests, the 12 kV smooth type VI has a U50 range of 109–121 kV and Umbrella type is 98–123 kV. In transformer oil tests, the 12 kV smooth type VI has a U50 range of 161–164 kV and Umbrella type is 161–168 kV. In addition, For LN2 tests, the 12 kV smooth type VI has a U50 range of 232.5–282 kV while Umbrella type is 256–260 kV respectively. The 200 shoots survival tests were also done on three smooth type and 3 umbrella type VI bottles. Electrical distribution simulations were carried out to compare the experimental results with the simulation results. All types of tests were done at least 200 times or when the results became stable. It was also observed that the FOVs gets higher after 100 tests due to conditioning process. Lastly, it was observed that Umbrella type VIs are more suitable for LNIS applications because of its mechanical toughness and overall higher range of FOVs. The results documented in this paper will play an important role in designing the overall structure of LNIS. VI manufacturing companies are expected to take advantage of these findings for their design of VIs in Air, Transformer Oil and LN2 environments because the literature lacks such results about VIs until now.

Studies on the combination of RSFCLs and DCCBs in MMC-MTDC system protection

The high rate of rise and large amplitude of a dc fault current in MMC-MTDC system make its interruption difficult for DC Circuit Breakers (DCCBs). In order to tackle this issue, this paper proposes a combined operation of a Resistive-type Superconducting Fault Current Limiter (RSFCL) and a DCCB. By analyzing the fault current in a symmetrical monopole MMC-MTDC system, the effectiveness and necessity of adding a resistive type fault current limiting device into the system after fault is established. With detailed modeling of the RSFCL and DCCB including the quench and recovery processes of the RSFCL, their combined operation is investigated. The influence of different parameters, such as the maximum quench resistance of the RSFCL, the insertion time of the energy absorption branch in the DCCB, and the quench and recovery process of RSFCL, on the fault clearing process are investigated in detail. The effectiveness of the combined operation is verified by extensive simulations in PSCAD/EMTDC. The results indicate that the combination of RSFCLs and DCCBs can obtain a suppression rate of at least 25% on the peak value of the fault current. Besides, the energy that DCCBs need to absorb in their arresters has been reduced by more than 60%, and the total fault clearing time is also reduced. Furthermore, all the converters remain unblocked, making the fast recovery of MMC-MTDC system possible through DCCBs reclosing. It is concluded that the combination of RSFCLs and DCCBs provides an effective solution to handle short circuit faults in MMC-MTDC systems.

Optical fibre sensing for fast hotspot detection in SFCLs

The health monitoring of superconducting fault current limiters (SFCL) is important for their large-scale exploitation in HVDC grids protection. The intrinsic non-homogeneity of critical current along the superconductor length can cause localized points of heating, called hotspots, in the SFCL device which can lead to device damage. In this paper we propose to use an extremely simple and cost-effective technique based on all-fibre Mach-Zehnder interferometers for hotspot detection in SFCLs, where the measurement arm of the interferometer is integrated with the SFCL and the reference arm remains in ambient. The system only consists of a laser, two optical fibre couplers and a photo detector. By studying the acquired interference patterns, even singular hotspots within the entire conductor length, can be informed in few milli-seconds, which is the fastest and most sensitive demonstration to the best of our knowledge that meets the SFCL requirement for fast hotspot detection.

Magnetization Characteristics Due to Fault Angle of Transformer Type SFCL with Two Isolated Secondary Windings

In this paper, a transformer type superconducting fault current limiter (SFCL) with two isolated secondary windings was fabricated to increase the current limiting capacity. As the magnetization current increased due to the large transient fault current immediately after the fault, the magnetization force variation, the operating range of the flux linkage, and the voltage region variation were compared at fault angles of 0° and 90°, respectively. The short-circuit test analyzed the current limiting operation, power consumption, and energy consumption characteristics according to the fault angle immediately after the fault occurrence. The results showed that the fault angle of 0° could limit the fault current much more than the fault angle of 90°. In addition, it was confirmed that the magnetization force variation, the operating range of the flux linkage, and the voltage induced in the primary winding were all much larger at the fault angle of 0° than at the fault angle of 90°.

A novel sensitivity analysis for optimal design of superconductive fault current limiter in microgrids

Several studies concluded that installing superconductive fault current limiters (SFCLs) at generators’ sides in microgrid systems (MGSs), at the secondary side of each transformer in the system, at each load or at the location with most fault occurrences improve both the reliability and the stability of the system. However, increasing the number of SFCLs in the system leads to an increase in the cost. This paper intents to find the optimal locations and size of SFCLs to improve the stability and the reliability of the studied MGS during a faulty condition by protecting transformers in the system from tripping. The number of SFCLs should be less than the number of transformers which leads to less cost of the initial installations. In order to achieve this goal, this paper presents a novel sensitivity analysis inside a multi-objective optimization method to find the best solution for the optimal location and size of the SFCLs. A line outage distribution factor sensitivity analysis method is utilized to investigate the effect of line outage on the entire system. Also, the effects of each location in the system have been taken into consideration in this study. The results in this paper prove the robustness of the proposed approach which enhances the stability and reliability of the power network while minimizing the required impedance and number of SFCLs.

Decreasing Distribution Generation Effects on Grid Short Circuit Level Using Superconducting Fault Current Limiter Through Updating Relays Set-Points

Decreasing Distribution Generation Effects on Grid Short Circuit Level Using Superconducting Fault Current Limiter Through Updating Relays Set-Points

Analysis of key factors affecting the non-limiting state reactance of superconducting fault current limiter

With the rapid development of the power grid, the voltage level is getting higher, and the degree of interconnection is becoming stronger. As a result, the level of the short-circuit fault current of the power grid keeps increasing, which seriously threatens the security of the power grid. The saturated-core superconducting fault current limiter (SCSFCL) is a new type of current limiting device, which can effectively limit the short-circuit current without influencing the flexibility of the power grid. The non-limiting state reactance is very important to the normal operation of the power line protected by the SCSFCL, but there is little detailed analysis of the key factors affecting its non-limiting state reactance so far. In this paper, the effects of the height of AC coil, the turns of AC coil, the cross-section area of the iron core and the excitation of the DC coil on the non-limiting state reactance are analysed and verified by simulation with ANSYS Maxwell. Finally, the design suggestions are put forward, including the method of designing the DC excitation value of the superconducting coil and how the key factors affect the non-limiting state reactance.

A Resistance Model of Fault Current Limiting Coils Under DC Impact

The short-circuit fault current on the dc side affects the operation safety of the multiterminal flexible HVdc (MTDC) transmission system seriously. The resistance-type superconducting fault current limiter (RSFCL) has received extensive attention in limiting the dc impact current because it has a fast response speed and zero impedance at a steady state. At present, there are so many works on the simulations of RSFCLs but the error is relatively larger, which affects the design accuracy of RSFCLs. In this article, the characteristics of dc fault current limiters are studied. The resistance and other parameters of yttrium barium copper oxide (YBCO) samples under the dc impact are measured. The equivalent heat capacity and the equivalent heat dissipation of YBCO tapes are defined and calculated to analyze the heat transfer process of YBCO tapes under the dc impact. A modeling method based on the equivalent heat parameters is obtained. In addition, the thermal balance point during the dc impact is defined by that thermal power production and heat loss of the YBCO tape are equal to identify the credible boundary of the resistance curve. Finally, the correctness of the proposed method is verified by the experimental results of fault current limiter coils and compared with the R-Q fit model. This research aids in the simulation analysis and optimization design of dc RSFCLs.

Protective Coordination of the OCR with the Voltage Component in a Closed-Loop Power Distribution System with the FCL

Recently, the requirement of the electrical energy from the renewable source has been growing in the South Korea since government’s energy plan to generate the electrical power of 20% as renewable source. In addition, these renewable power plants have been constructed on not only the existing power plant’s side but also customer’s side. These changes in power distribution system cause the fault current to increase higher and to reverse the direction of the fault current. Variable countermeasures to reduce the fault current have been studied and the introduction of the superconducting fault current limiter (SFCL) in the power distribution system, one of them, has been actively reported. However, the installation of the SFCL can affect the power system protection because of the fault current’s decrease or increase, which depends on the construction of the power distribution system. Especially, the application of the SFCL in a closed-loop power distribution system can cause the delayed trip operation or the fast trip operation of the over-current relay (OCR), one of the representative protective devices widely used in a power distribution system. This change can influence on the existed protective coordination. In this paper, the OCR with voltage component, one of the methods to suppress its trip operation’s change in a power distribution system with a closed loop construction due to the application of the SFCL, was suggested and the protection coordination between the OCRs in a power distribution system with a closed loop was analyzed. It was confirmed that a simple using voltage component in the OCR could cause the trip variation of the reverse direction OCR in loop power system and it can be improved by matching the relaying voltage components.

Application of a novel approach of resistive‐type superconducting fault current limiter with a fast protection system in multi‐terminal direct current network

The key obstacle in the realization of Multi-terminal HVDC (MTDC) grids is the lack of existing commercial protection that a device can withstand the DC fault. Although different HVDC circuit breaker technologies have been investigated and demonstrators tested by manufacturers, the innovation of such devices to ensure a reliable protection system has not been proven yet due to the maximum braking capability limitation especially in MTDC grids. To this, a combination of Superconducting Fault Current Limiter (SFCL) technology with a fast DC circuit breaker could bring a solution to this bottleneck. In this work, a new application of an accurate model of resistive-type SFCL (rSFCL) considering both the electrical and thermal behaviors is proposed to work together with a proactive hybrid DC circuit breaker (PHCB) to fulfill the whole system protection. The viability of the proposed approach is verified under a worst DC fault case-scenario that imposed in a five-terminal MTDC meshed grid. The numerical analysis and simulations are carried out using (EMTP-rv®) software, while the obtained results show how significantly the proposed rSFCL can reduce the fault current and enhance the breaking capability. Also, a positive interaction has been observed between the rSFCL and PHCB in terms of design sizing and operation performance.