Superconducting Fault Current Limiter Research Articles

Analysis of the DC Fault Current Limiting Characteristics of a DC Superconducting Fault Current Limiter Using a Transformer

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

Deployment of a Resistive Superconducting Fault Current Limiter for Improvement of Voltage Quality and Transient Recovery Voltage

This article presents a theoretical investigation of a resistive superconducting fault current limiter (R-SFCL) operating in a medium-voltage network. The considered power system presents a high level of fault current as well as a high transient recovery voltage. The simulation result shows that the R-SFCL not only limits the fault current to a desirable value, but also improves transient recovery voltage of circuit breakers by eliminating high-order harmonics generated by the opening of the circuit breaker.

Temperature and Resistance Profile on HTS Tape During Fault and Recovery in Modular SFCL Unit

A new modular configuration of resistive superconducting fault current limiter (SFCL) unit is developed to study the temperature and resistance profile on copper laminated 2G high-temperature superconductor (HTS) tape during fault and recovery at 77 K using a lab-scale resistive modular SFCL unit. The thermal characteristics and their transition behavior, i.e., the resistance profile on the HTS tape are investigated using five cycles of the fault of peak currents 1.8, 2.2, and 4 kA. The temperature of the HTS tape is measured during fault and recovery under load. The fault limiting characteristics are analyzed for various output voltages (20, 40, and 60 Vrms) across the modular SFCL unit. The resistance profile on the HTS tape is estimated analytically, which is compared with the experimental measurement of resistance. The recovery time is measured and it is correlated with the peak temperature on the HTS tape and the associated heat transfer in the liquid nitrogen bath. The study will be useful for developing a higher rating of SFCL using this modular configuration.

Superconductor fault current limiter effect on the performance of doubly-fed induction generators

<span>Between different wind turbine-generator configurations, one of the most accepted and highly regarded structures in the industry is the wind turbine with doubly-fed induction generator. The DFIG wind turbines are very sensitive to grid disturbances especially to voltage drop during grid faults due to relatively low power of the power converters. Fault in a power system causes voltage drop, current increase in stator and rotor coils, and over voltage in the DC shin. Several control methods have been proposed so far. A model based on power electronic instruments and superconductor theory, superconductor fault current limiter (SCFCL), has been proposed in this paper to improve domain and the attenuation time of the parameters under control such as voltage, current, and speed and voltage of the DC link against various types of faults (single-phase, two-phase, and three-phase). In addition to this, in order to compare the results with convectional models (crowbar) and study the innovation of the proposed model, a simulation of the system under two-phase fault and use of crowbar method to control the fault has been conducted using MATLAB-SIMULINK and also, the performance of the proposed method has been assessed. </span>

Experimental Study on the Performance Change of YBCO Tapes Under Repeated Overcurrent

Superconducting cables or fault current limiters may encounter short-circuit currents during operation. When experiencing multiple overcurrent cycles, the critical current degradation of yttrium barium copper oxide (YBCO) tapes may occur. The performance degradation of YBCO tapes under overcurrent is a gradual process. It may take dozens or hundreds of overcurrent or overheating pulses. To get a better understanding of this process, we explored the performance change of YBCO tapes under repeated overcurrent. A life characteristics test platform was established. The electromagnetic performance degradation of YBCO tape under 50 Hz sinusoidal ac operating conditions was investigated, taking the effect of the overcurrent amplitude and duration into account. Meanwhile, the relationship between the number of overcurrent cycles and the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation is proposed. The reason for this performance change is analyzed by comparing the 2-D current density distribution of the YBCO film before and after experiencing overcurrent. In addition, the U-I property and resistance variations of these tapes are presented. It is inferred that the cracking of the superconducting layer is the main cause of I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation. The experimental results provide meaningful references for the performance degradation of the YBCO tapes and related devices.

A Multifunction High-Temperature Superconductive Power Flow Controller and Fault Current Limiter

This article presents a novel high-temperature superconductive (HTS) power flow controller and current limiter (PFCCL), which limits fault currents and manages power flow in the intended transmission line. The proposed device includes series HTS reactors, HTS controlling dc coil, recovery resistive coil, and power electronic switches, which protects the microgrid from the upstream ac grid, short-circuit faults, and it controls the power flow between a microgrid and the upstream grid. Performance of the proposed PFCCL is mathematically analyzed, utilizing MATLAB and Maxwell software, and then validated by laboratory scaled-down experimental setup. It is shown that the simulation results are in fair agreement with the developed experimental laboratory setup results.

Design, Construction, and Testing of a Desktop Superconducting Series Reactor Toward the Grid Installation of a Prototype Unit

A desktop superconducting series core reactor (SSR), made from Yttrium barium copper oxide (YBCO) tape, serves as a precursor to a scaled-up, grid-connected prototype unit. The SSR is intended as an alternative to the traditionally employed technologies, including superconducting fault current limiters, when managing fault levels on the electrical power grid. The philosophy of connecting a prototype SSR at a grid-connected research site is first presented before the focus shifts to the desktop SSR. The desktop SSR is a development step before the prototype unit, as it will confirm design construction methodologies and functionality. The desktop SSR is compared to both the fault limiting performance and power consumption of a copper reactor of similar geometry. It was found that the SSR reduced the impact of the applied fault, comparably to the air core reactor (5.9% variance), and was more than four times more energy efficient. Another significant advantage of the SSR would be the significantly reduced footprint required in a typical substation yard.

Research on Delamination Damage of YBCO Tape Under DC Impact Based on Hilbert–Huang Transform

The short-circuit fault current on the dc side affects the operation safety of the multiterminal flexible HVdc transmission system seriously. The resistance-type superconducting fault current limiter (RSFCL) has received extensive attention in limiting the dc impact current because it has fast response speed and zero impedance at steady state. YBCO tapes are susceptible to delamination damage under large dc impact and it will affect the operation of RSFCLs. However, the existing methods of distinguishing the delamination damage of YBCO tape need an extra observation or testing after dc impact. These methods cannot meet the requirements for monitoring and protection when RSFCLs coming into use in the power system. In this article, the Hilbert-Huang transform (HHT) is used to analyze the delamination damage of YBCO tapes under dc impact to avoid extra observation and testing. The dc impact test on the YBCO tape sample is carried out and the test data are obtained. HHT is applied on the joule thermal power waves (TPWs) of the YBCO tape samples obtained from the dc impact test as the input signal. Hilbert spectrums and instantaneous energy spectrums (IEs) of the TPW signals are calculated and the difference between IEs of TPW signals of intact samples and delaminated samples is shown and explained. The feasibility of IEs of TPW signals can be as a monitoring target to avoid the stratification damage of YBCO tapes. The proposed method may aid in the on-load monitoring on RSFCLs and provided a new tack for related research.

High-Frequency Impulse Modeling and Longitudinal Insulation Analysis of Bifilar Superconducting Coil

Bifilar coil is one of the most applicable structures used for resistive-type superconducting fault current limiter. However, the turn-to-turn (longitudinal) insulation of the bifilar coil under lightning and switching impulse is rather different from the conventional pancake coil. The longitudinal insulation is characterized as the distributed circuit of the coil under high-frequency excitation, and the capacitance, inductance, and resistance parameters are solved by finite element model. The influence of those resistance, inductance and capacitance (RLC) parameters on the accuracy of the model is analyzed, and two samples of one bifilar pancake coil and two series connected bifilar coils are fabricated for high-frequency impulse voltage testing. The experimental results are consistent with the simulation results. The initial voltage distribution and impulse response of two samples are calculated under standard lightning impulse. In the initial voltage distribution calculation, the interturn channels of one bifilar coil and two series-connected bifilar coils are subjected to a maximum voltage of 1 and 0.5 times the lightning impulse voltage.

Protection schemes using resistive‐type superconducting fault current limiters with mechanical DC circuit breakers in MMC‐MTDC grids

The cooperative characteristics of resistive superconducting fault current limiters (R-SFCLs) and DC circuit breakers (DCCBs) have been investigated with regard to the fault clearing in modular multilevel converter (MMC)-based multiterminal direct current (MTDC) grids. However, research is lacking in complete protection solutions that combine R-SFCLs and mechanical DCCBs while considering the backup protection and the effect of R-SFCLs on the fault characteristics of MMCs. This study investigates a fault current breaking scheme that includes primary and backup protection. Moreover, the fault characteristics of MMCs with R-SFCLs are analysed, and the fault transient process is divided into three stages. Then two fault current limiting schemes with R-SFCLs located at the converter output or the line are proposed. These two protection schemes are applied to the DC test system, verified and compared. The results show that in both schemes, the size of the designed R-SFCL should be generally a few tens of Ω. These R-SFCLs maintain the converters unblocked until the primary breakers or backup breakers interrupt the fault currents, and the M-DCCBs are only required to break several kA currents. After a fault occurs, the system will restore within 200 ms for primary protection or 250 ms for backup protection.

Simulation and visualization experiment on the liquid nitrogen boiling behaviors during the quenching and recovery process of YBCO tapes

The resistance Superconducting Fault Current Limiter (RSFCL) using YBCO tape is supposed to be of great potential in the high voltage power grids. The fast recovery rate after quenching is the safety guarantee of the electric system to prevent the subsequent fault current shocks. However, the transient heat transfer and local boiling bubble behaviors of liquid nitrogen (LN2) highly affecting the recovery rate are seldom revealed, especially for the disc structure RSFCL with tiny channels. In this work, the boiling heat transfer characteristics during the quenching and recovery process of a YBCO tape in LN2 bath were studied. A 3-D CFD model based on a local part of a typical RSFCL with disc structure was first built to reveal the transient heat transfer coefficient, cooling curve, gas phase volume and temperature distribution that cannot be measured in experiments. The visualization experiment for verification and observation on bubble distribution was conducted with a high-speed camera. Results show that the boiling bubbles generate immediately as quenching starts, film boiling can form quickly within in 0.035 s on the tape surface. The bubble motion behaviour is severely affected by the layout of the Teflon framework. The bubbles detachment from the upper surface of the tape is more frequent than that from the lower surface of the tape, causing inhomogeneous temperature distribution along the tape. Since the recovery is mainly under the film boiling with small heat flux, even a single YBCO tape needs about 2.5 s to return to 77.7 K from 162 K, which means it is impossible to reclose the YBCO tape within 2 s after the quenching cutting off, especially for practical large RSFCL systems with longer recovery time. Besides, there are bubbles still remaining in the system after 5 s when the temperature has recovered to 77.7 K. The remaining gas would change the dielectric field and induce a risk of electric breakdown under the next large impulse current, which should be considered in the safe operation of RSFCL.

An Iterative and Cost-Based Approach for Optimal SFCL Allocation in Fault Level-Constrained Meshed Networks

In this article, an allocation method for superconducting fault current limiter (SFCL) to reduce the exceeded short circuit current within the breaking capacity of the circuit breakers (CBs) is proposed. A cost-based allocation method is advised because of the high cost of SFCL depending on its type. In this article, the multiple parameters such as number, impedance size and type of the SFCLs in meshed networks are determined by defining a cost function for SFCL and using a new hybrid genetic algorithm and sensitivity analysis (HGASA) optimization. The proposed method is based on gradual (step by step) adding the multiple SFCLs in various points of the network during the iterative-based process to optimal SFCL allocation with the least economic costs in fault level-constrained meshed networks. A sensitivity index based on the average decrease of fault current is proposed to reduce the search space and to improve the efficiency of the algorithm. Also, since the different types of SFCLs have different behavior in fault current mitigation, they are analyzed and considered in this article. IEEE 30-bus test system is chosen to evaluate the accuracy and efficiency of the proposed method.

R-Q curve based evaluation method for current-limiting performance of DC R-SFCL in high voltage DC system

The current-limiting performance of the dc resistive-type superconducting fault current limiter (dc R-SFCL) is vital to the reliability in the high voltage dc current (HVDC) transmission system. It is expensive and difficult to utilize the discharging process of the precharged dc capacitor to evaluate the current-limiting performance. In this paper, a R-Q curve based evaluation method for current-limiting performance of dc R-SFCLs in dc system is proposed, which replaces the dc impulse experiment with ac impulse experiment. A ± 160kV dc SFCL prototype is designed by Guangdong Power Grid Co., Ltd., and tested to acquire the experimental heat accumulation Q and the experimental R-Q curve. Accordingly, the mathematical model consistent with the prototype is built in PSCAD. Finally, a fault condition is simulated in dc system to verify the feasibility of the R-Q curve based evaluation method. It is shown that the proposed method has superior properties in simplifying the testing platform, reducing the test requirements and costs, and providing reference for precise modeling of SFCLs.

The novel design of an energy efficient superconductor-based series reactor for installation at a grid connected research site

This paper proposes the development of a superconducting series reactor (SSR) as an alternative to traditionally employed technologies and superconducting fault current limiters when managing fault levels on the electrical power grid. By utilizing superconducting tape, which has negligible resistance, in the construction of a series reactor, it is proposed that fault level mitigation could be achieved in a more energy efficient manner. Once constructed the SSR will be installed and tested at a grid-connected power engineering research site, and the proposed impact of this installation is firstly simulated using Reticmaster® power system simulation software. Design parameters for the prototype SSR are then calculated enabling the total cost of the modifications and prototype SSR to be determined. A desktop SSR was also constructed and tested as a pre-cursor to the prototype construction to confirm functionality and design and was found to be up to four times more energy efficient as the equivalent copper reactor. Finally, the calorimetric method of power loss determination was investigated and experimentally shown to be a viable alternative to the traditional electrical method of power loss determination. In the past, the relatively cheap cost of electricity in South Africa had favoured the installation of poor power efficiency devices that required a lower initial capital investment. With increasing energy costs and a focus on carbon emission reductions, the development of the SSR augurs a new era in power system engineering in which designs are proposed considering both total lifecycle costs and energy efficiency.&#x0D; &#x0D; Design proposal for the first superconducting power device in Africa&#x0D; Alternative to less efficient fault current management technologies currently employed&#x0D; Construction and testing of a desktop superconducting series reactor&#x0D; Verification of the calorimetric method for power loss determination.&#x0D;

Impact of Resistive Superconducting Fault Current Limiter and Distributed Generation on Fault Location in Distribution Networks

Resistive Superconducting Fault-Current limiters (r-SFCL) appear as a new attractive technology to address faults in power grids. Based on a new generation of superconductors, referred to as High-Temperature Superconductors (HTS), they could offer economical benefits compared to more conventional technologies. To understand their impact on the electrical networks, two models of r-SFCL, differing by their complexity, were built to conduct short-circuit analysis. Different fault locations in distribution networks were studied in the standard IEEE 13-node and 34-node test feeders. Both models were validated against experimental data and then cross-checked in the IEEE 13-bus distribution system to determine their relative accuracy when used in practical power grids. Subsequently, using the simplest electrical model of r-SFCL, the 34-bus test system incorporating Distributed Generation (DG) was used to analyze short circuits. It was found that the presence of r-SFCL increases the error of the fault location algorithm. However, it was also demonstrated that a single r-SFCL enables the incorporation of several additional DG in a distribution network by reducing the fault current level by at least 45% depending on its design characteristics and the number of added DG. Finally, an improved algorithm is presented. This algorithm takes into account the r-SFCL resistance in order to reduce the fault location error.

Analysis on Operational Characteristics of Double Quench Flux Lock Type Superconducting Fault Current Limiter

The superconducting fault current limiter (SFCL) which has many advantages is being chosen as an attractive method for limiting fault current. To upgrade the performance of the SFCL, various configurations are reported. Among them, the double-quench type SFCL has been studied in order to reduce the power burden of the high-temperature superconducting (HTSC) elements. The double-quench type SFCL which consists of the two HTSC elements and the normal resistance is a method to improve the performance of the HTSC elements. The design of the normal resistance in the double-quench type SFCL for the control of distributed fault currents on both HTSC elements to reduce the power burden is very important. However, the double-quench type SFCL is difficult to change the specification of the component depending on changing the power system. To improve the disadvantage on the double-quench type SFCL, this paper proposed the double-quench-flux-lock type SFCL which combine the double-quench type SFCL and the flux-lock type SFCL. The conventional flux-lock type SFCL which consists of an iron core, two coils, and the HTSC element could control the operation current and the impedance of the SFCL depending on the turn ratio between two coils. The operational characteristics of the flux-lock type SFCL could flexibly respond to changes in the power system. The double-quench-flux-lock type SFCL proposed in this paper was verified through PSCAD/EMTDC.

Experimental investigation of current limiting characteristics for a novel hybrid superconducting fault current limiter (SFCL) with biased magnetic field

High temperature superconducting fault current limiter (SFCL) is widely considered as an effective protection for power system when the short-circuit fault currents occur. This paper proposes a novel design of a hybrid SFCL with biased magnetic field which has two-stage current limiting characteristics. This kind of SFCL limits the short current using non-inductive superconducting coil at the first stage, and then by the double-split reactor at the second stage, usually 10 ms later. The advantage of this type of SFCL is saving the amount of superconducting tapes, and it is especially attractive in large current and high voltage occasions. A prototype hybrid SFCL with biased magnetic field is designed and constructed in China Electric Power Research Institute (CEPRI) using YBCO coated conductor. A high speed Data Acquisition (DAQ) System based on LABVIEW is established to monitor and control the SFCL. The current limiting ratios for this prototype SFCL have been investigated experimentally under the operating temperature of 77 K. The experimental results show that the current limiting ratio reaches to 89.66% which validates the design and proves the potential application of this hybrid SFCL.

Investigation of a Modified Flux-Coupling-Type SFCL for Low-Voltage Ride-Through Fulfillment of a Virtual Synchronous Generator

To solve the low-voltage ride-through (LVRT) issue of a virtual synchronous generator (VSG) under severe grid fault, our research group proposes to use a modified flux-coupling-type superconducting fault current limiter (SFCL). In this study, the configuration structure of the VSG with the SFCL at the point of common coupling (PCC) is designed. The fault analytical circuit of the VSG is presented, and the functions of the SFCL are stated from the aspects of current restraint, voltage compensation, and energy dissipation. Using MATLAB/Simulink, symmetrical and asymmetrical faults are both simulated to assess the transient behaviors of the VSG, and the SFCL parameters are changed to clarify the quantitative effects. From the comparison results, the SFCL parameters are properly determined to provide favorable performance. The SFCL can visibly decrease the fault current of each phase within the permissible level, and facilitate the VSG to have a preferable voltage profile. Furthermore, the SFCL can positively stabilize the VSG by enhancing the power delivery, mitigating the frequency fluctuation and consuming the excess energy. A satisfactory LVRT operation is gained, and the efficacy of the SFCL on reinforcing the VSG robustness is validated.

Current limiting characteristics of a magnetic shielding type Superconducting Fault Current Limiter of REBCO pancake coils

Superconducting Fault Current Limiters (SFCLs) are installed in the electric power system, and expected to limit fault current and improve system stability. In this paper, we focus on the transformer magnetic shielding type SFCL made of REBCO wires. This SFCL limits fault current mainly with reactance for small fault current. When fault current gets larger, resistance component is added and a larger impedance is generated. In this time, we fabricated the transformer type SFCL composed of pancake coils and investigated the basic characteristics. The pancake coil type has the advantage that the amount of superconducting wire is less and the size of SFCL becomes smaller than solenoid coil type. As the results of experiment, it was confirmed that SFCL limits fault current with reactance and resistance properly. Regarding the current limiting impedance, it almost agreed with the designed value, and confirmed the current limiting operation as expected.

Fault Current Limitation Coordination of Multiple SFCLs in IEEE 14-Bus Test System

We have proposed the concept of “fault current limitation coordination” of multiple superconducting fault current limiters (SFCL) to be introduced in a future electric power grid. Using a simplified test system, the transients on fault current and internal phase angle of generators were analyzed by PSCAD/EMTDC and the modeling of resistive SFCL with a variable resistance as a function of both current and temperature at the recovery under load. In this paper, we extended the analyses to the fault current limitation coordination of multiple SFCLs in IEEE 14-bus test system. The effective coordination strategy on the introduction and operation of multiple SFCLs, e.g. introduction lines of SFCLs, operation parameters such as operating current, critical current and prospective fault current of each SFCL, was discussed and optimized for an arbitrary fault location in the test system.