Resistive-type Fault Current Limiter Research Articles

Experimental and Simulation Study of Resistive Helical HTS Fault Current Limiters: Quench and Recovery Characteristics

Resistive type fault current limiters (SFCLs) have attracted lots of attention from research interests and engineering applications, due to their self-triggering, fast and effective fault current limitation ability. Fast recovery of SFCL after quench is highly attractive, yet still remains challenge when recover with load compared to recovering without load. We investigated the dependence of recovery time of a helical SFCL coil on the ratio of prospective current over critical current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pros</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> . A multilayer simulation model was built in MATLAB/Simulink to investigate the electro-thermal behavior of SFCL coil during a fault and recovery period, and the model was validated by experimental results. Quench simulations were carried out under different I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pros</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , ranging from 15 to 119 and in different recovery conditions including recovery with load condition and recovery without load condition, while keeping the fault duration of 100 ms. We observed that the SFCL coil reached 85 K and 195 K at the time when the fault was cleared, in the quench tests with I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pros</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> = 15 and 119, respectively. SFCL coil recovered without load in 0.5 s to 10 s, depending on the ratio of I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pros</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> .

Fault current limiter of VSC-HVDC systems using variable resistive bridge controller

This paper proposes a fuzzy logic controller (FLC) based variable resistive bridge type fault current limiter (VR-BFCL) to minimize the impact of faults on voltage source converter high voltage direct current (VSC-HVDC) systems. FLC for VR-BFCL is developed to dynamically insert the appropriate current limiting resistance during contingencies to maintain the fault currents within the acceptable limit. The proposed controller effectively provides variable duties to generate and insert controllable resistance in the system based on fluctuation of direct current (DC) link voltage and point of common coupling (PCC) voltage. The efficacy of the proposed controller is justified through simulations work for balanced and unbalanced faults. The results demonstrate that oscillations in PCC voltage and DC link voltage can be maintained within the acceptable range by controlling fault current through the insertion of the appropriate resistance. It is also found that the proposed controller outperforms the existing method.

Pareto optimal allocation of resistive‐type fault current limiters in active distribution networks with inverter‐interfaced and synchronous distributed generators

AbstractTo efficiently reduce the fault currents of active distribution networks (ADNs), this paper proposes a novel methodology for Pareto optimal allocation of resistive‐type fault current limiters (R‐FCLs). The proposed approach enables to simultaneously optimize the number, location, and size of the R‐FCLs in the ADNs with inverter‐interfaced and synchronous distributed generators (DGs). The sensitivity analysis is introduced to rank candidate locations, and a constrained multiobjective function is created to minimize the cost of the R‐FCLs and the fault currents of the ADNs. An improved multiobjective particle swarm optimization (MOPSO) algorithm and a multiobjective artificial bee colony (MOABC) algorithm are designed to obtain the Pareto optimal solution set. The proposed approach is verified using the modified IEEE 33‐node and 69‐node distribution systems, where both centralized and dispersed access of DGs are considered. The numerical results demonstrate that: (a) The fault currents in all nodes of the two testing systems are limited to the permissible levels using the least capital cost of the R‐FCLs, and (b) the improved MOPSO outperforms the MOABC to achieve a better Pareto front and decrease the number of iterative computation. In consequence, the feasibility and superiority of the proposed approach are well validated.

Design and Development of a 220-kV Resistive-Type Fault Current Limiters Based on 2G-Coated Conductors

The resistive-type superconducting fault current limiter (R-SFCL) is simple in configuration, near zero impedance at normal state, and can be quickly triggered by the fault current. So, it is a possible solution to suppress the fault current in the power grid. In this paper, the design and development of a 220-kV R-SFCL were reported. The core component of it is a module constructed by 128 bifilar coils. The bifilar coils are connected in series and parallel to form the module according to the application requirements. The bifilar coils are made of 12-mm-wide steel-stabilized 2G tapes, while 16 bifilar coils are connected in parallel to form a sub-module and 8 sub-modules are connected in series to form the module. For this fault current limiter, 10.75-km 2G tapes are used in total, and the resistance of the R-SFCL module is 4.5 Ω at 300 K. Besides, the half-size sub-module and the cryogenic insulation support (CIS) are developed and tested.

Non-Linear Control for Variable Resistive Bridge Type Fault Current Limiter in AC-DC Systems

This paper proposes a non-linear control-based variable resistive bridge type fault current limiter (VR-BFCL) as a prospective solution to ease the effect of disturbances on voltage source converter-based high voltage DC (VSC-HVDC) systems. A non-linear controller for VR-BFCL has been developed to insert a variable optimum resistance during the inception of system disturbances in order to limit the fault current. The non-linear controller takes the amount of DC link voltage deviation as its input and provides variable duty to generate a variable effective resistance during faults. The VSC-HVDC system’s real and reactive power controllers have been developed based on a current control loop where direct axis and quadrature axis currents are used to control the active and reactive power, respectively. The efficacy of the proposed non-linear control-based VR-BFCL solution has been proved with balanced as well as unbalanced faults. The results confirm that the oscillations in active power and DC link voltage have been significantly reduced by limiting the fault current through the insertion of an optimum effective resistance with the proposed control technique. The real time digital simulator (RTDS) has been used to implement the proposed approach. The performance of the proposed non-linear control based VR-BFCL is compared with that of traditional fixed duty control.

Experimental and numerical transport AC losses in a four-strand Roebel cable bifilar stack

REBCO Roebel cables are promising candidates for bifilar coils (or non-inductive coils) in large scale high temperature superconducting resistive type fault current limiters (SFCLs), as they enable large current-carrying capability in conjunction with low AC loss. Here we report transport AC loss measurement results in two Roebel cable bifilar stacks (RBS) with different vertical spacing between the turns assembled from a straight 4/2 (four 2 mm width strands) Roebel cable. We also report two-dimensional finite element method AC loss simulation results using the H-formulation in the RBSs, in two parallel bifilar stacks (TPBS) which have the same geometrical dimensions as the RBS with 0.284 mm spacing (g) but have unequal current distribution between the conductors composing the stacks, and in an equivalent bifilar stack (EBS) comprising four 4 mm wide conductors while keeping identical vertical geometrical dimensions with the RBS with g = 0.284 mm but has unequal current distribution between the conductors. We show that the measured transport AC loss values in the RBS with g = 0.284 mm are approximately one fifth of those in the parent straight 4/2 Roebel cable due to cancellation of the perpendicular magnetic field components in the bifilar stack, and also show the AC loss in RBSs increases with increasing g. We then show the calculated transport AC loss values in the RBS with g = 0.284 mm are approximately one third of the values in the TPBS and EBS when It,turn/Ic0,cable > 0.6, where It,turn is the current amplitude for upper or lower turn of the bifilar stacks and Ic0,cable is nominal Ic value for the 4/2 Roebel cable. We numerically demonstrate that the result is caused by flux flow loss in the inner conductors in the TPBS and EBS due to unequal current distributions in conductors. Roebel cables show clear advantage over simple vertical stacks for SFCL applications in terms of AC loss.

Comparative study on the fastest effective fault limitation for stabilized and stabilizer-free high Tc superconductors

The fastest effective fault limitation is one of the selection criterion of high Tc superconductors (HTS) for resistive type fault current limiter (R-SFCLs) application. In the present work, we have given a comparative DC & AC performance study on HTS tapes with and without stabilizer. At first, we have investigated the temperature dependent DC resistivity of the SS stabilized Bi2223 based conductor, Cu (50 µm substrate) and SS (75 µm substrate) stabilized YBCO based coated conductors (CCs) and compared with the stabilizer free YBCO based CC (50 µm and 100 µm substrate). We have studied the DC transport properties (E–I) of the stabilized and stabilizer-free tapes to obtain flux-flow resistance before reaching normal state, critical current and ‘n’ factor at 1 µV/cm criterion. Further, the 1st peak limitation, response time and resistance attained during fault limitation have been compared for AC over-current pulses of 1.5 kA for 100 ms duration. The aforesaid measurements helped us to select a suitable high Tc superconductor for fastest effective fault limitation to be used in R-SFCL application.

FCL Effect of DC Superconducting Cables in Unsteady State

DC superconducting cables for railway systems connected between substations have been developed. If the length of the superconducting cable is long enough, the superconducting cable is expected to have an effect of a resistive type fault current limiter (FCL) by the transition of the superconducting state and the normal state due to overcurrent than the critical current. Therefore, the simulation model of a direct current system with superconducting cables was constructed and the behavior of a superconducting cable was analyzed. And, there is a possibility of deterioration of critical current in a superconducting cable due to the aging and unexpected stresses since a superconducting cable is assumed to operate for long term. Then, the behavior of a deteriorated superconducting cable in the unsteady state was also analyzed. The analyzed results suggest that the 3000-m-long superconducting cable has the FCL effect and the temperature distribution assuming operation at liquid nitrogen does not affect the FCL effect. Furthermore, influence of the local deterioration, which has a potential to damage a superconducting cable in the unsteady state, could be estimated using this constructed model.

Optimum Resistive Type Fault Current Limiter: An Efficient Solution to Achieve Maximum Fault Ride-Through Capability of Fixed-Speed Wind Turbines During Symmetrical and Asymmetrical Grid Faults

This paper proposes an optimum resistive type fault current limiter (OR-FCL) as an efficient solution to achieve maximum fault ride-through (FRT) capability of fixed-speed wind turbines (FSWT) during various grid faults. In this paper, a dedicated control circuit is designed for the OR-FCL that enables it to insert an optimum value of resistance in the FSWT's fault current's path for improving transient behavior of the FSWT. The optimum resistance value depends on fault location and prefault active power. The control circuit of the proposed OR-FCL is capable of calculating the optimum resistance value for all the prefault conditions. By using the proposed control circuit, the FSWT can achieve its maximum FRT capability during symmetrical and asymmetrical faults, even at zero grid voltage. Analysis is provided in detail to highlight the process of calculating the optimum resistance of the OR-FCL. Moreover, the effect of the resistance value of the OR-FCL on the FRT behavior of FSWT is investigated. To show the efficiency of the proposed OR-FCL, its performance during various operation conditions of the FSWT is studied. It can be proved that each operation condition needs its own optimum resistance value, which can be obtained by using the proposed control circuit during the fault to achieve the maximum FRT capability of the FSWT. Comprehensive sets of simulations are carried out in PSCAD/EMTDC software and the results prove the effectiveness of the proposed approach.

Low voltage ride-through enhancement of DFIG-based wind turbine using DC link switchable resistive type fault current limiter

Doubly-fed induction generator (DFIG)-based wind turbines utilise small-scale voltage sourced converters with a limited overcurrent withstand capability, which makes the DFIG-based wind turbines very vulnerable to grid faults. Often, modern DFIG systems employ a crowbar protection at the rotor circuit to protect the rotor side converter (RSC) during grid faults. This method converts the DFIG to a squirrel cage induction generator, which does not comply with the new grid codes. The recent grid codes need wind turbines to stay connected to the utility grid during and after power system faults, especially in high penetration level of wind power. Furthermore, the crowbar switch is expensive. This paper proposes a novel DC-link switchable resistive-type fault current limiter (SRFCL) to improve the LVRT capability of the DFIG. The proposed SRFCL is employed in the DC side of the RSC. The SRFCL solves crowbar protection activation problems and eliminates subsequent complications in the DFIG system. The proposed SRFCL does not have any significant impact on the overall performance of the DFIG during normal operation. Whenever the fault, whether symmetrical or asymmetrical, occurs, the SRFCL not only limits rotor over-currents but also prevents rotor speed acceleration and restricts high torque oscillations even during zero grid voltage, as recommended by some grid codes. To prove the effective operation of the SRFCL on the RSC fault current limitation, analytical analysis is performed in each switching interval. The proposed approach is compared with the crowbar-based protection method. Simulation studies are carried out in PSCAD/EMTDC software. In addition, a prototype is provided to demonstrate the main concept of the proposed approach.

Can Resistive-Type Fault Current Limiter Operate in Cryogen-Free Environment?

Superconducting fault current limiters are unique devices that offer fast response to fault without need of an external triggering system. Therefore, they are interesting for industrial use, although their price is high. The principle of the resistive fault current limiter is based on the steep current-voltage characteristic of superconductors. When the current rises over the critical one, voltage on the superconductor rises steeply, and this mechanism blocks the increase of the current. Simultaneous appearance of voltage and current during this limiting period of operation generates a substantial amount of heat that is dissipated in the superconducting wire causing a rapid increase of its temperature. In this contribution, we further develop the idea that, during a limiting period, there is only a small difference between cooling by liquid nitrogen and adiabatic conditions. Using this approach, one can think about a current limiter free from a liquid coolant using a cryocooler. In this contribution, we discuss main differences in cooling conditions and test the idea on a short sample of the high-temperature superconductor REBCO conductor. We compare the behavior of identical samples cooled to the same temperature by liquid nitrogen and conduction cooled. If the realization can be achieved, the huge benefit would be an FCL with a tunable triggering current via its operating temperature.

Efficient fault ride-through scheme for three phase voltage source inverter-interfaced distributed generation using DC link adjustable resistive type fault current limiter

This paper proposes a DC link adjustable resistive type fault current limiter (AR-FCL) based-voltage source inverter (VSI) fault ride-through (FRT) capability improvement, which is new approach of using FCLs. Instead of using three phase FCLs in AC side of the VSI, just one single phase proposed AR-FCL is connected in series with DC side of the VSI. During normal operation, the AR-FCL does not have effect on the VSI performance. When fault happens, the AR-FCL limits AC side fault currents in faulty phases to safe area operation of semiconductor devices of inverter, and does not affect healthy lines. The desired limited fault current value can be achieved by discharging and charging of DC inductor using large resistance, which enters and retreats by turning off and on of the AR-FCL's semiconductor switch, respectively. The VSI does not require to change its control strategy from normal to fault mode operation. Consequently, wind-up and latch-up problems are smoothed. Analytical analysis is provided in each switching interval to highlight effectiveness of the AR-FCL on the VSI fault current limitation. The proposed FRT scheme is validated through both extensive simulation studies in PSCAD/EMTDC environment and three-phase experimental prototype for all symmetrical, asymmetrical, and transient faults.

Transient Stability Augmentation of PV/DFIG/SG-Based Hybrid Power System by Nonlinear Control-Based Variable Resistive FCL

This paper proposes three nonlinear controllers such as fuzzy logic controller (FLC), static nonlinear controller (SNC), and adaptive-network-based fuzzy inference system (ANFIS)-based variable resistive-type fault current limiter (VR-FCL) to augment the transient stability of a large-scale hybrid power system consisting of a doubly fed induction generator (DFIG)-based wind farm, a photovoltaic (PV) plant, and a synchronous generator (SG). Appropriate resistance generation of the VR-FCL during a grid fault to provide better transient stability is the main contribution of the work. The effectiveness of the proposed control methods in improving the transient stability of the hybrid power network is verified by applying both balanced and unbalanced faults in one of the double circuit transmission lines connected to the system. Simulation results show that the proposed FLC-, SNC-, or ANFIS-based VR-FCL are effective in improving the transient stability of the studied hybrid system. Moreover, all the proposed methods exhibit almost similar performance. Therefore, any of the methods can be chosen for the transient stability enhancement of the hybrid power system.

Controllable resistive type fault current limiter (CR-FCL) with frequency and pulse duty-cycle

In this paper a controllable resistive type fault current limiter (CR-FCL) is introduced. The CR-FCL inserts a pre-specified value of resistance based on a pre-defined function, by using a simple switching method, in series with the fault current path. When a fault occurs, a self turn off switch starts switching with a pre-specified frequency and duty cycle. By this switching pattern, the controlled value of resistance enters to the fault current path. So, the CR-FCL limits the fault current to the desired values. In addition, from transient stability point of view, by inserting the optimal resistance value, the CR-FCL is capable to enhance power system transient stability in a good manner. In fact, generation of the controllable resistance that depends on the duty cycle of the self turn off switch is the main idea of the CR-FCL. The variable duty cycle results the variable resistance and the fixed duty cycle results the fixed resistance. Analytical analyses of the proposed FCL are presented in details. Simulation results by power system computer-aided design/electromagnetic transients, including dc (PSCAD/EMTDC) software and corresponding experimental results are studied to validate the effectiveness of the CR-FCL. Considering error analyses, there is the good agreement between the simulation results and the experimental results.

Quench Distribution During an Overcurrent Fault Condition in Highly Homogeneous REBCO Coated Conductor

One of the most important factor for resistive-type fault current limiters is uniform voltage distribution under fault condition. Homogeneous distribution of I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and resistance of nonsuperconducting state in the longitudinal direction are essential for uniform quenching. Recently, we have succeeded in manufacturing the highly homogeneous superconducting RE BCO coated conductor. In this paper, we report the voltage distribution in our coated conductor under fault condition, at 50 Hz for a half cycle. The experimental results show that applied voltage, which is necessary to quench over the entire length of sample, depends on I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and normal state resistance on T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> .

Electrical-Thermal Coupled Finite Element Model of High Temperature Superconductor for Resistive Type Fault Current Limiter

A multi-physics finite element model of high temperature superconductors (HTS) is presented in this article. An electrical model based on a set of Maxwell's equations and E-J power law is used to solve the critical state of the superconductor. A heat transfer model is added to the electrical model to calculate the temperature distribution and therefore investigate the J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (T) dependence of the superconductor. The model is used to study the quench behavior of YBCO-coated conductors for the application of resistive type fault current limiters. Some numerical techniques are applied and assumptions are made to simplify the calculation and improve convergence. An equivalent heat transfer coefficient which is much larger than the normal heat transfer coefficient is applied to the region surrounding the superconductors. This equivalent coefficient represents the drastic heat exchange during the boiling of the liquid nitrogen. The cross-section of YBCO tapes is divided into several sub-domains. The temperature is assumed to be uniform in each sub-domain. This simplification significantly improves the convergence of model and still is able to keep a reasonable level of accuracy. The model is then able to simulate the whole process of YBCO tapes quenching and recovering to superconducting state. The numerical results are compared with the fault current experiments and excellent agreement is obtained.

AC Loss and Contact Resistance of Resistive Type Fault Current Limiter Using YBCO Coated Conductors

Heat loss is one of the most important issues for resistive type superconducting fault current limiters (SFCL) built from YBaCuO-coated conductors. A newly designed 400 V SFCL module by Smart Grid Center, Shanghai Jiaotong University (SJTU) is tested and modeled in order to get a clear understanding of its characteristics of heat losses. Two main losses, including AC loss of superconducting tapes and the losses due to contact resistance inside the SFCL module are investigated. Experiments based on “electrical method” are set up to measure the AC loss at 77 K with lock-in amplifier conditions. Meanwhile, losses from the contact resistance are calculated by analyzing their V-I curve. To better understand the behavior of the AC loss in SFCL module and verify the accuracy of the experimental results, modeling analysis is performed by means of a 2-dimensional finite element modeling (FEM). Numerical results show that the results are very close to what we get from experimental method. Detailed results will be presented and the heat losses of 10 kV SFCL consisting of about 25 modules in series are going to be discussed.

Design and Test Results of a 1 MVA Resistive Type Fault Current Limiter

Abstract The 1 MVA resistive type single phase AC fault current limiter (FCL) was build and successfully tested by capacitors battery discharge. FCL rated voltage is 3.5 kV, current 250 Arms. The 240 m of HTS tape (type SF12100 by SupePower) was used for FCL production. The FCL consists of 8 bifilar coils each wound onto glass-fiber 70 mm diameter tube and connected in series. The HTS tapes were additionally stabilized with Cu laminated highly resistive foil. During the tests of separate FCL coils at 380 V an excellent limiting performance was observed. Tested FCL coil was switched off after 75 ms, the maximum temperature at the HTS tape was less then 230 K, the recovery time was about 5 s.

2 Dimensional Voltage Distribution Measurement of YBCO Thin Film during S/N transition

The process of the resistance generation in a YBCO thin film during the S/N transition used in resistive type fault current limiters has not been clarified completely. During the process, a thin film may be broken by overheat. Understanding the process of the resistance generation would lead to prevent thin films from this burnout. In this paper, the voltage distribution of a YBCO thin film during the S/N transition is measured by probes arranged 2 dimensionally on a thin film to understand how the normal transition area on a YBCO thin film expand. The voltage probes are placed in a matrix of 3 times 10 on a 30-by-210 millimeter YBCO thin film. A sinusoidal wave current whose amplitude is several hundreds ampere flows into the thin film connected with a parallel resistance. It is observed from these measurements that a narrow normal conducting state band vertical to the current appears first, and this band expands along the current. The critical current of the area on the thin film where the normal conducting state band appears first is the lowest along the thin film. This band is considered to have a great influence on the resistance generation of the YBCO thin film.

Analysis of Transient Stability Enhancement of LV-Connected Induction Microgenerators by Using Resistive-Type Fault Current Limiters

In this paper an analytical method by which the transient stability of an induction machine is maintained regardless of the fault clearance times is introduced. The method can be applied in order to improve the transient stability of a large penetration of low-voltage (LV) connected microgeneration that can be directly interfaced by single-phase induction generators within domestic premises. The analysis investigates the effectiveness of using resistive-type superconducting fault current limiters (RSFCLs) as remedial measures to prevent the microgenerators from reaching their speed limits during remote faults, and hence improving their transient stability. This will prevent unnecessary disconnection of a large penetration of LV-connected microgeneration and thus avoiding the sudden appearance of hidden loads, and unbalanced voltage conditions. The minimum required value of a resistive element of RSFCL for mitigating the transient instability phenomena of LV-connected microgeneration based on the system and connected machine parameters is determined. The analytical method has been validated by conducting informative transient studies by using detailed models of a small microwind turbine with constant mechanical output interfaced directly within residential dwellings by a single-phase induction generator, a transient model of resistive superconducting fault current limiter (RSFCL), and a typical suburban distribution network with residential loads. All the models are developed in the time-domain PSCAD/EMTDC dynamic simulation.