Fault Current Level Research Articles

Fault current limiters: a case study of protection and operational continuity for FPSOs

The Floating Production Storage Offloading offshore (FPSO) has been employed in the oil and gas exploration at the Brazilian pre-salt fields. Due to the increasing production capacity of process plants and consequently its power demands, FPSO power systems are experiencing higher fault current levels, which can present peak values of almost 200 kA in the medium voltage circuit. One solution to keep fault currents within safe values for the new electrical installations is to split the main switchgear busbar in two parts interconnecting them with a pyrotechnic device (PD). However, this typical fault current limiter (FCL) imposes operational restrictions to the FPSO; when the PD is triggered, the production of barrels is severely reduced. This work proposes two alternative FCLs to mitigate this problem: a Pyrotechnic Device (PD) associated with a parallel Air-Core Reactor (ACR) and a resistive Superconducting Fault Current Limiter (r-SFCL). As described in this manuscript, both alternatives allow full operation of the FPSO even after its actuation. The simulation model used to reproduce the transient behavior of two FCLs and the power system of typical FPSO was developed in the software Alternative Transients Program. The results show that the alternatives can limit the fault current below the main switchgear supportability limit, improving the reliability of FPSO’s production.

A novel solution for fault current suppression in transmission systems based on fault current splitters

To mitigate the threat from increasing fault current level in high-voltage transmission systems, a “dredging theory” based on the fault current splitter (FCS) was proposed to help the over-duty circuit breaker clear the fault. However, detailed practice of this theory is not fully studied. This paper investigates the feasibility of suppressing the fault current by FCSs from the perspectives of operation and planning. The operating scheme of FCSs is firstly qualitatively analyzed, and an iterative formula is derived to calculate the fault current in a system including multiple FCSs. Furthermore, the voltage sag caused by FCSs is evaluated by the Specified Computer Business Equipment Manufacturer Association (SCBEMA) curve and is minimized by the proposed optimization model considering maximum fault current limitation. A repeat-searching particle optimization (RSPSO) algorithm is developed to solve the model efficiently. This solution is validated to be effective and acceptable through two case studies.

Assessment of Cable Length Limit for Effective Protection by Z-Source Circuit Breakers in DC Power Networks

This paper introduces groundbreaking research on how to assess the Cable Length Limit (CLL) to ensure effective protection by Z-source Circuit Breakers (ZCBs) in DC power networks. It has been revealed that the line parameters of power cables have a significant impact on the cutoff performance of ZCBs. The question of assessing the CLL has been raised as an unsolved problem. In this paper, a method of CLL assessment is proposed based on physical models and simulation tests. To verify the proposed method, two studies were performed to assess the Cable Length Limits depending on fault levels and power delivery levels, respectively. The ZCB parameters were specified for a simulation testing system for a 5 MW distribution line feeder. The effectiveness of ZCB protection was tested in groups of simulation tests with various impacting quantities, i.e., cable lengths, fault current levels, and power delivery levels. The effective cable lengths for the ZCB to detect and successfully interrupt a faulty branch in the DC network were assessed and analyzed. The testing results prove that the CLL decreases along with a decreasing fault current level, as well as an increasing power delivery level. Based on data analysis, an equation was derived to calculate the effective length of the ZCB for DC lines, and the equation can be used to generate new CLL curves for various load-power requirements. This study could increase the reliability of a ZCB’s response to a fault in DC transmission and distribution lines. It could also help power system designers/operators to maintain reliable protection with ZCBs in DC power system networks.

User-Defined Dual Setting Directional Overcurrent Relays with Hybrid Time Current-Voltage Characteristics-Based Protection Coordination for Active Distribution Network

With the penetration of renewable energy sources based distributed generation (RES-DG) in the distribution network (DN), the operating time of protection relays becomes a major concern to avoid the mis-coordination and nuisance tripping of RES-DG. It is due to the bidirectional flow of current, variance in the fault current level, i.e. high fault current in case of Squirrel cage induction generator (SCIG) based RES-DG, and low fault current for an inverter-based RES-DGs. This paper proposes a novel User-defined dual setting direction overcurrent relay with hybrid time current-voltage (UDDOR-TCV) characteristics to intensify the proposed scheme’s flexibility without any communication assistance for radial DN. The proposed model is formulated in a constrained non-linear optimization fashion and solved with the MINLP solver of general algebraic modelling system(GAMS) software to determine the optimal relay settings. The propounded protection scheme is simulated on IEEE-33 bus radial distribution system and a local 40-bus system hosting the multiple SCIG and PV based RES-DGs at optimal locations. Detailed numerical studies are carried out to show the performance of the proposed scheme. 66.848% and 68.26% reduction in relay operation time with zero mis-coordination is achieved with SCIG-WTG case and PV-units case for the IEEE-33 bus system and a similar reduction in operation time is 68.937% and 66.563% for Local-40 bus system. Moreover, the relays numbers are reduced by 32.692% and 39.7% for IEEE-33 and Local-40 bus systems, respectively, due to the forward/reverse characteristics capability of the proposed UDDOR-TCV. The performance of the proposed scheme is also evaluated on IEEE-8 bus meshed DN. The results are compared with the existing protection schemes in recent literature.

Fault Detection and Protection Schemes for Distributed Generation Integrated to Distribution Network: Challenges and Suggestions

The use of distributed generation has received wide attention due to low maintenance costs, reduced transmission line losses and network congestion, as well as minimal impact on climate change and global warming. However, the distributed generation integrated to the distribution network introduces various protection problems that cannot be solved by conventional protection systems. These obstacles include the bi-directional power flow and the variation in the fault current level during the topology change. Thus, appropriate fault detection and protection scheme are strongly recommended to increase safety and reliability of the distributed network. This paper presents a comprehensive overview of the distributed network fault detection and protection strategies incorporated with distributed generation. This review also investigates the various fault detection approaches concerning types, communication methods, operation mode, constraints and benefits. Additionally, numerous island detection techniques are explored, focusing on generation types, parameters, cost and advantages. Moreover, the review outlines the various protection schemes highlighting categories, operation, constraints, strength and shortcomings. The key issues and challenges are discussed along with selective proposals for future research. All the highlighted viewpoints of this research will hopefully be beneficial to power system engineers and researchers for the advancement of distributed network fault and protection strategies for suitable operation and management of future distributed generation systems.

Enhancing Distance Protection of Long Transmission Lines Compensated With TCSC and Connected With Wind Power

Thyristor controlled series compensation (TCSC) is widely used in long transmission lines to mainly improve power transfer capability. However, TCSC produces complicated impedance that negatively affects distance protection operation. The wind energy generation system produces additional complexity to the distance protection performance due to the variation of wind speed and fault current level. This paper proposes an integrated scheme to change adaptively the settings of the Mho distance protection by shifting the relay characteristics considering the bad impacts of TCSC, wind power and fault resistance. The proposed scheme achieves its main stages starting from fault detection, until relay tripping decision procedure including online estimation for preliminary fault location, impedance of TCSC and fault resistance using limited communication requirements. By extensive MATLAB simulations, the performance of the proposed scheme is examined compared with the conventional Mho relays under different fault locations, fault inception angle, fault resistance, different wind power penetration, different wind speeds and different TCSC firing angles. The achieved results ensured that the proposed scheme improves significantly Mho distance relay operation and avoids under-reaching and over-reaching problems irrespective of the large shunt capacitance along the transmission line, and also without identifying the parameters of TCSC such as the capacitance, the inductance or the firing angle.

Pareto Optimal Allocation of Flexible Fault Current Limiter Based on Multi-Objective Improved Bat Algorithm

With the sustainable growth in the integration of distributed generation units in the distribution network, the probability of the fault current level exceeding the rating of existing components increases. Cascaded H bridge fault current limiter is widely used in the power grid due to its advantage in inhibiting surge current flexibly. In order to equilibrate the objective functions of its cost, fault current mitigation effect, and the weighted load reliability index, a novel methodology is proposed to simultaneously optimize the location and size of the limiters in the distribution network. Therein, the sensitivity factor considering the Monte Carlo fault simulation model is introduced to reduce the search space and rank candidate locations referencing the actual conditions. And then, according to the candidate locations and considering different conflicting objective functions, a multi-objective improved bat algorithm is employed to obtain the Pareto optimal solution set. Also, life cycle cost and net present value are introduced to construct an economic model to access the scheme costs and service life. The proposed approach is verified using the modified IEEE 33-bus distribution systems with DGs and IEEE 30-bus Benchmark system. The results demonstrate that the proposed method exhibits higher efficiency in finding optimum solutions and provides a new economic configuration idea for the practical engineering application.

Asymmetrical fault current calculation method and influencing factors analysis of droop-controlled inverter

Since the fault dynamic of droop-controlled inverter is different from synchronous generators (SGs), protection device might become invalid, the fault overcurrent may damage power electronic device and threaten the safety of microgrid. Therefore, it is urgent to conduct a comprehensive fault analysis of the inverter to guide the design of protection schemes. However, due to the complexity of droop control, existing literatures have simplified asymmetric fault analysis of droop-controlled inverter to varying degrees. Therefore, accurate fault analysis of droop-controlled inverter is needed. In this paper, by analyzing the control system, an accurate fault model is established. Based on this, a calculation method for instantaneous asymmetrical fault current is proposed. Besides, the current components and current characteristics are analyzed. It is found that fault current are affected by control loops, fault type, fault distance and nonlinear limiters. In particular, the influences of limiters on the fault model, fault current calculation and fault current characteristics are analyzed. Through detailed analysis, it is found that dynamics of control loop cannot be ignored, the fault type and fault distance determine fault current level, and part of the limiters will totally change the fault current trend. Finally, calculation and experimental results verify the correctness of proposed method.

Analysis of Signal Processing Techniques for High Impedance Fault Detection in Distribution Systems

High Impedance Faults (HIFs) occur by the contact between an energized conductor and a high impedance surface. Due to the low fault current level, HIFs cannot be detected by conventional protection and there is no fully efficient solution to this problem. HIF detection methods often extract metrics using signal processing techniques, such as Fourier Transform, Wavelet Transform, Stockwell Transform, and Mathematical Morphology. However, these techniques are applied under specific conditions, which hinders comparative and critical analyses among them. Therefore, this paper presents a critical review of HIF detection methods based on the aforementioned techniques, and also shows a detailed investigation of the performance of the metrics commonly used with them. To do this efficiently, the authors proposed a set of assessment indices based on the ratio between the metrics’ characteristics and another one based on the repeating of the metrics features. The proposed indices revealed that some of these metrics fail to distinguish HIF from other typical occurrences in power distribution systems, and their performances are negatively affected by the fault location and by the existence of noise in the measurements. Additionally, the results showed a need to specify system conditions in which any HIF detection technique is valid.

Ensemble empirical mode decomposition‐based differential protection scheme for islanded and grid‐tied AC microgrid

This study presents a differential protection scheme based on ensemble empirical mode decomposition (EEMD) for AC microgrid. The fault current level is significantly lower during the islanded operation of a microgrid, which leads to the malfunction of the traditional over-current protection scheme. The proposed differential protection scheme uses the spectral differential energy of the first intrinsic mode function extracted from the decomposition of the current signal using EEMD for effective fault detection in the AC microgrid. The proposed EEMD-based differential protection scheme is validated on 10 bus and modified IEEE 34-bus AC microgrid test systems during various shunt faults. Moreover, the performance of the proposed EEMD-based differential protection scheme is evaluated under high fault impedance scenarios. The simulation results reveal that the proposed differential protection scheme can effectively detect the faulty line in an AC microgrid during seamless islanded and grid-tied operations.

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.

Fault classification in power system distribution network integrated with distributed generators using CNN

Fault detection is the critical stage of the relaying system and their successful completion in minimum time is expected for fault clearance. With the increasing usage of distributed generators (DGs) in a distribution network, the conventional relaying methods are becoming inappropriate due to changing fault current levels. This paper presents a deep learning algorithm i.e. Convolutional Neural Network (CNN) customized for fault classification in the distributed networks integrated with DGs. This is first time that CNN has been used for fault detection using raw and sampled-data of three-phase voltage and current signals of various fault classes and no-fault class. The 10-fold cross-validation is used to demonstrate the performance of the proposed model in terms of different metrics such as accuracy, sensitivity, specificity, precision, and F1 score. The proposed model has attended an average 10-fold cross-validation accuracy of 99.52% for all the tested fault cases. This featureless proposed method has been compared with conventional approaches from literature and has shown better performance in terms of accuracy and computation burden. Further, a similar fault study is conducted on a mixed transmission line and distribution network with PV as DG using the proposed method and found performance accuracy of 99.92% and 99.97%, respectively.

HVDC Grid Fault Current Limiting Method Through Topology Optimization Based on Genetic Algorithm

Limiting fault current level of high-voltage direct current (HVDC) grid is conducive to reduce the cost of current limiting devices and to relieve the stringent time constraints on protection, but the main concentrations are focused on pole-to-pole fault, while few attentions have been paid to pole-to-ground fault, especially in symmetrical mono-pole dc grid. This article proposes a pole-to-ground fault current limiting method through topology optimization, which is implemented in three steps. The influence factors of pole-to-ground fault current in symmetrical mono-pole HVDC grid are clarified in the first step, which is based on the detailed state space model of dc grid. And the fact that the topology of dc grid influences fault current a lot is confirmed. In the second step, a simplified index is proposed based on the above theoretical analysis, thus the fault current level of each topology can be estimated in a simple and efficient way. At last, to limit the pole-to-ground fault current level, the genetic algorithm is used to optimize the dc grid topology. The optimization results of studied cases indicate that the mesh structure or ring structure is recommendable for dc grid in term of fault current limiting.

A Robust Adaptive Overcurrent Relay Coordination Scheme for Wind-Farm-Integrated Power Systems Based on Forecasting the Wind Dynamics for Smart Energy Systems

Conventional protection schemes in the distribution system are liable to suffer from high penetration of renewable energy source-based distributed generation (RES-DG). The characteristics of RES-DG, such as wind turbine generators (WTGs), are stochastic due to the intermittent behavior of wind dynamics (WD). It can fluctuate the fault current level, which in turn creates the overcurrent relay coordination (ORC) problem. In this paper, the effects of WD such as wind speed and direction on the short-circuit current contribution from a WTG is investigated, and a robust adaptive overcurrent relay coordination scheme is proposed by forecasting the WD. The seasonal autoregression integrated moving average (SARIMA) and artificial neuro-fuzzy inference system (ANFIS) are implemented for forecasting periodic and nonperiodic WD, respectively, and the fault current level is calculated in advance. Furthermore, the ORC problem is optimized using hybrid Harris hawks optimization and linear programming (HHO–LP) to minimize the operating times of relays. The proposed algorithm is tested on the modified IEEE-8 bus system with wind farms, and the overcurrent relay (OCR) miscoordination caused by WD is eliminated. To further prove the effectiveness of the algorithm, it is also tested in a typical wind-farm-integrated substation. Compared to conventional protection schemes, the results of the proposed scheme were found to be promising in fault isolation with a remarkable reduction in the total operation time of relays and zero miscoordination.

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.

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.

Study on Coordination of Resistive SFCLs and Hybrid-Type Circuit Breakers to Protect a HVDC System With LCC and VSC Stations

Directing at the robustness increase of a high voltage direct current (HVDC) system with line commutated converter (LCC) and voltage source converter (VSC), this paper proposes to coordinate resistive superconducting fault current limiters (SFCLs) and hybrid-type DC circuit breakers (HDCBs) for dealing with the DC line fault. The theoretical modeling of the SFCLs is presented, and the DC fault current characteristics are analyzed. Considering that the fault interruption involves multi-stages, the coordination of the SFCL and the HDCB in the LCC/VSC station is elaborated. Using PSCAD/EMTDC, the simulation model of a 320 kV HVDC system is built. Changing the SFCL size and the HDCB operation delay is simulated, and the performance indexes such as the fault current level, breaking time and dissipated energy are compared. The proposed coordination is verified to be very effective in handling the fault. Especially for the VSC station, it enables to visibly limit the fault current rising, shorten the transient voltage duration, and facilitate a significant decrease in the dissipated energy of the HDCB. For the LCC station, the proposed coordination can serve as a competitive backup to ensure a timely fault breaking. Consequently, the DC line fault is removed more rapidly and reliably.

Modeling and Simulation of a Saturated Core Fault Current Limiter Integrated in a Typical Distribution System Based on PSCAD Environment

Due to load increasing and generation extensions of the electrical networks, the fault current levels may be largely changed. So, the short circuit capacity may easily exceed the installed equipment interrupting capacity such as circuit breakers. Nowadays there are different methods for restoring the fault current normal values. The traditional methods in power utilities consider one of three options: (1) Replace installed equipment with higher rated equipment or, (2) Install series reactors or, (3) Replace the existing transformers with high impedance transformers. In this paper a Saturated Core Superconducting Fault Current Limiter (SCSFCL) will be presented as an efficient method for solving this problem so that replacing existing circuit breaker infrastructure can be avoided or postponed. This paper simulated the SCSFCL based on the PSCAD environment. An 11 kV West Delta Egyptian Distribution System in TANTA region is modeled as a typical system with the proposed simulated model of SCSFCL. The model parameters are adapted by the authors to restore the fault current levels as their values before the integration of the Distributed Generation (DG) units. The obtained results ensure that the model is easily used in other distribution systems. The results show also that the model performances can meet utility’s needs in mitigating fault current at all types of fault and different fault positions

Design of DC‐side fault current limiter for MMC‐HVDC systems: Safety of the MMC along with frequency stability

A high voltage direct current system based on the modular multi-level converter (MMC-HVDC) is introduced as a suitable device for transmission of bulk powers over long distances. A pole-to-pole DC-side fault is a significant challenge for the MMC-HVDC system. Three main problems are the appearance of voltage spikes following a fast DC fault current break up, frequency instability due to insufficient inertia (networks such as renewable energy-based systems) and destruction of anti-parallel diodes within the MMC due to the high fault current. This study proposes a novel method for limiting DC fault current, improving isolation of the three-phase AC system from the DC-side. The suggested design employs high power resistors as virtual load such that continuity in active power flow will be kept on. Further, this prevents frequency deviation from exceeding the allowable limits. Also, transient over-voltages will be limited which are coming from stray inductances linked with electromagnetic effects of fault current level. Simulations and design practical issues have verified the validity of the proposal by using MATLAB/Simulink.

Investigation of HTS cable impact on turbo‐electric aircraft performance

With significant interest in the use of high-temperature superconducting (HTS) components in electric aircraft, there is a need for novel modelling techniques that allow architecture-level studies of the electrical systems including HTS components. In this study, a simple electric network architecture, as proposed in the literature has been considered, which includes generators, dynamic propulsion load and cables. This electric network has been modelled considering conventional technology and using HTS cables by replacing the conventional copper cables, to evaluate the variations in the network performance. The network performance has been studied for the dynamically varying propulsion load, which is nearly equivalent to the aircraft load over the entire flight duration. Following this, electric faults have been applied at various locations, and the impact of HTS cables on the network fault levels has been evaluated. The fault current levels are compared using both conventional and HTS cables, due to the fault current limiting properties of the HTS cables, they are observed to offer lowered fault current values.