Fault Current Research Articles

Enhanced Non-Communication-Based Protection Coordination and Advanced Verification Method Using Fault Impedance in Networked Distribution Systems

In recent years, the networked distribution system (NDS), which is normally connected to the distribution line (DL), was actively studied as the topology of the future distribution system for reasons such as improving supply reliability, improving line utilization, and increasing the capacity of distribution generators (DGs). However, the NDS creates new issues in terms of protection coordination because of its bidirectional power flow and fault current flow. The issues associated with conventional protection schemes in the NDS include malfunction of protective devices due to bi-directional fault currents and failure of protection coordination due to communication failures between protective devices. When applying a conventional protection method in the NDS, the protection schemes become complicated, and there is a risk of protection coordination failure due to communication failure between protective devices. To solve this problem, this paper proposes an effective and innovative non-communication-based protection algorithm for protection coordination in the NDS. The proposed protection algorithm utilizes fault impedance characteristics, which allow not only determination of whether a fault occurred, but also the ability to identify the exact fault point. Therefore, the proposed method is expected to be sustainably utilized and contribute to developing protection schemes and devices in various system topologies and scenarios in the future. Additionally, this paper addresses the overall concept of hardware-in-the-loop simulation (HILS) and directly verifies the proposed protection algorithm using HILS. Therefore, this study establishes a sustainable foundation for future research on protection coordination using HILS.

A Fault Current Limiter Self-Adapting Activation Strategy for Flexible HVDC System Based on Fault Severity Assessment

In the flexible HVDC system, fault current limiters (FCLs) need to be configured to reduce the rising rate of fault current. However, the FCL configured according to the bipolar near-end metallic short-circuit faults may cause the fault current to be unnecessarily over-suppressed and consume equipment life. This study develops a method to activate FCLs of the flexible HVDC system adaptively to follow changes in fault severity. Based on analyzing the relationship between the fault current and the transition resistance at the initial moment of the fault, a method to predict the fault condition based on the single-ended instantaneous information is proposed, which realizes the fault severity assessment. Considering mutual coupling of FCLs action sequences, a fast action sequence generate (FASG) method of FCLs based on fault current limiting contribution is proposed, which realizes the coordination between multi-terminal FCLs without communication. A FCL self-adapting activation strategy (SAAS) for flexible HVDC systems based on fault severity assessment and FASG is constructed. This strategy matches the severity of the fault by adjusting the FCL action sequence, improving the current limiting effect of severe faults and the life of FCLs. The accuracy of the SAAS is validated on a scaled-down two-terminal system in the laboratory and the simulation.

PWM Voltage-Based Modeling for PM Machines With Interturn Short Circuit Fault Considering the Effect of Drives

This paper presents a novel analytical fault model based on PWM voltage rather than ideal sinewave phase voltage for permanent magnet (PM) machines with inter-turn short circuit fault. This model is important because PM machines are usually driven by the pulse width modulation (PWM) inverter. In addition, main contributors to the accuracy of the fault model such as (i) the cables between the inverter and the machine, (ii) the precision of the rotor position estimation and (iii) the inverter, in particular the metal-oxide semiconductor field-effect transistors (MOSFETs) have been considered. Therefore, this developed model can fully account for the effects of PWM harmonics and accurately predicts the machine's behaviors (particularly the fault current) under fault conditions considering the effect of the drives. This has rarely been studied in the literature as most existing fault modelling methods adopt sinewave phase voltage as inputs, which cannot account for the PWM harmonics in the fault currents. However, the investigations in this paper showed that the PWM harmonic component could be close to 25% of the fundamental component in the fault current, and hence cannot be neglected. The accuracy of the proposed fault model has been validated by a series of experimental tests.

A Tuning-free Fault Detection Method for Distribution Network Based on PMU Data and Random Matrix Theory

The increasing penetration of renewable energy sources has significantly altered the fault characteristics of distribution networks with distributed generators (DGs). The fault current is limited as the emerging solar plants normally connect to the grid via inverters. And the operating patterns of the system have become more diverse and complex. The traditional pre-tuned protection and fault detection methods are facing substantial challenges. This paper proposes a centralized fault detection scheme based on the random matrix theory (RMT) that utilizes synchronous phasor data from the distribution-level phasor measurement unit (PMU). Firstly, data normalization and resampling techniques construct the operating state matrix (OSM). Then the mean spectral radius (MSR) is calculated and used for fault detection without the complex tuning according to the operation state of the system. Finally, the faulty section is determined by comparing the features from different sub-group of the PMUs according to the topology partition. A multi-feeder distribution network is modeled in PSCAD and used to verify the proposed method.

Power electronic transformers in wind power generation systems

Power electronic transformers (PET) have received extensive attention due to their advantages of compensating reactive power, improving power quality, limiting fault current, and reducing the number of traditional transformer materials. At present, it is also an important research topic to replace conventional power frequency transformers in wind power generation systems. This paper first analyzes the topology of the primary circuit of the power electronic transformer. Several common PET topologies are introduced, and their advantages and disadvantages are analyzed. The module cascade topology and modular multilevel topology are mainly introduced, and the topological circuit diagram is given. The paper also comprehensively introduced the research status quo of wind power generation systems based on the interface of PET, permanent magnetic wind turbines and dual-feed fan wind turbines. The traditional structure of the permanent magnet synchronous generator (PMSG) system and the doubly fed induction generation (DFIG) system is shown. Finally, the problems in PET and the future development direction are summarized.

Fault identification and classification algorithm for high voltage transmission lines based on a fuzzy-neuro-fuzzy approach

ABSTRACT Traditional techniques are used for fault location detection in high-voltage transmission lines that mostly depend on traveling waves and impedance-based techniques suffer from large errors owing to the intricacy of fault modeling for various types of faults. Although single-line to ground faults are dominant in high-voltage transmission lines, fault resistance as well as fault inception angle might distort the current fault detection techniques. In addition, other types of faults exist and that raises the need to develop an accurate fault detection technique to minimize the recovery time. The current paper introduces a fuzzy and neuro-fuzzy algorithm to detect, analyze, and locate different faults taking place in high-voltage transmission lines. A MATLAB Simulink Model is used for analyzing different fault cases; fault detection and classification are done by the Fuzzy Interface System (FIS), while fault location detection is done using the Adaptive Neuro-Fuzzy Interface System (ANFIS). The introduced algorithm is evaluated via the Mean Square Error (MSE) technique. The results showed full success in detecting and identifying different fault types, with a 0.0042 validity performance factor for fault location detection using ANFIS.

Incorporating Modern Fault Ride-Through Standards into the Short-Circuit Calculation of Distribution Networks.

Modern fault ride-through (FRT) standards in many countries require distributed generators to remain connected for a specified period during the fault by providing reactive current, to support voltage and prevent a massive renewable outage. As a result, short-circuit current is not constant, but it varies depending on the current and disconnection order of distributed generators (DGs). This time-varying short-circuit current complicates the estimation of the time it will take for an overcurrent relay or fuse to trip. The existing short-circuit calculation algorithms usually assume that the fault current is constant throughout the whole period of fault. This assumption may result in incorrect conclusions regarding the tripping time of protective devices in networks with high renewable penetration. This paper incorporates modern FRT standards into the fault analysis by considering the influence of fault current variations on the protective devices (relays, fuses), significantly increasing the accuracy of the estimated tripping time. Simulations carried out in a 13-bus and the IEEE 8500-node network indicate that the traditional short-circuit calculation approaches may miscalculate the tripping time of protective devices, with deviations up to 80 s, when applied to networks complying with modern FRT standards.

Numerical Overcurrent Power Relay Enhancement Based on Integrated Discrete Wavelet Transform

As electrical power demands increases, the need for advanced protection relays has surged as a vital element in the power distribution system. That is, to ensure the continuity of power supply and eliminate abnormal faulty status, relays with different types and functions play a major role in electrical power system operation and protection as will. In the power system, current variation faults may accrue for many reasons, which may harm power system components, load, and jeopardize human safety. However, in now a day digital current relay, a large number of samples are collected and processed in order to continuously monitor and detect faults. This large amount of samples needs a bigger storage data real state and longer time to compile, optimization is needed to improve current relay reliability and accuracy with much fewer samples. Therefore, as this work aim toward optimizing the current relay, a substantial algorithm is needed for better current waveform analysis. As a result, the Wavelet transform algorithm with its wide spectrum feature of waveform analysis and decomposition process will be used as an enhancement tool. Using MATLAB/Simulink, a simulation, the unique characteristics of Wavelet transform (de-noising, mining, and decomposition) will be implemented into the modern numerical current relay to test the ability to advance fault detection based on less number of current waveform data. As this evaluation was compared with a typical conventional numerical overcurrent relay, a promising result in terms of less response time and compiling process was achieved.

A Study on a Communication-Based Algorithm to Improve Protection Coordination under High-Impedance Fault in Networked Distribution Systems

The rising demand for stable power supply in distribution systems has increased the importance of reliable supply. Thus, a networked distribution system (NDS) linked with individual lines is being adopted, gradually replacing the radial distribution system (RDS) currently applied to most distribution systems. Implementing the NDS can lead to various improvements in factors such as line utilization rate, acceptance rates of distributed power, and terminal voltages, while mitigating line losses. However, compared with the RDS, the NDS can experience bidirectional fault currents owing to its interconnected lines, thereby hindering protection coordination, which must be addressed before the NDS can be implemented in real-world power systems. Due to the characteristics of NDS, the reverse fault current is relatively small. However, this phenomenon becomes more severe when the high impedance fault (HIF) occurs. In this paper, the malfunction of protective devices during the HIF is directly verified and analyzed in the NDS. As a result, when the HIF occurs, the issue of the reverse protective device malfunctioning worsens because of a reduction in fault current and a failure in direction detection. To solve this issue, this work proposes a communication-based protection algorithm. Through the comparative verification of the proposed algorithm and the conventional protection method, protection coordination can be secured in the case of an HIF without new devices. It must be highlighted that the proposed method does not affect the settings of the protective device and provides a cost-effective and efficient solution since this algorithm is added independently to the existing relay.

Multi-target fault ride-through strategy for transformerless MMCs under asymmetric grounding faults in AC/DC hybrid distribution networks

In AC/DC hybrid distribution networks (HDNs), when asymmetric grounding faults occur, transformerless multiterminal modular multilevel converters (MMCs) should achieve three key targets of fault ride-through (FRT): 1) limiting the unbalanced fault currents; 2) injecting currents to support grid voltages in case of disconnection from grids; and 3) eliminating the zero-sequence circulating currents (ZSCCs) from fault networks through MMCs to nonfaulted networks. However, in medium voltage-level HDNs, the line impedances are mainly resistive-inductive, and traditional current injection methods are no longer effective. Moreover, in neutral nondirect grounding networks with multiple AC voltage levels, the voltages of nonfaulted phases rise, and it is difficult for MMCs to achieve fault current control. To solve the above issues, this manuscript proposes a multi-target FRT strategy. First, negative-sequence current controllers are used to eliminate the negative-sequence fault currents. Then, to support the positive-sequence voltages of grids, optimal and suboptimal active-reactive current references based on the line impedance ratios are proposed. To help transformerless MMCs with low modulation indices eliminate zero-sequence circulating currents, two zero-sequence voltage compensation modes and an improved zero-sequence current eliminator are proposed. Finally, the proposed fault current control is verified in MATLAB/Simulink.

Multi-feature fusion-based TCA-WKNN cross-sensor fault diagnosis method for dynamic weighing

The outstanding performance of current machine-learning fault diagnosis methods is mainly attributed to the availability of a large amount of labeled training data. However, in practical dynamic weighing systems, the high costs and variability of operating conditions limit the availability of reliable training data, hampering engineering fault diagnoses in dynamic weighing systems. To address this issue, this study proposes a novel cross-sensor fault diagnosis method based on multi-feature fusion using a transfer component analysis (TCA)-weighted k-nearest-neighbor (WKNN) network. Using this method, time- and frequency-domain features are extracted from a laboratory-simulated set of fault data with small batches of real operational data. Source and target domain features are fused, and TCA is applied to map the source and target domain samples to a latent space using kernel functions to reduce the distribution differences among the samples. Finally, the WKNN is employed as a metric learner to enhance small-sample data matching and classification to improve diagnostic accuracy. The results show that with three samples per support set, the proposed method achieves a diagnostic accuracy of 93.33%. Compared with other approaches, the proposed method exhibits stronger generalizability for diagnostic knowledge transference from sensor to dynamic weighing failure data, effectively improving precision in on-site small-sample environments and reducing sample imbalances.

Communication-less adaptive directional overcurrent protection strategy considering islanded mode detection in active distribution networks

The integration of distributed energy resources (DERs) in electric distribution networks originates the Active Distribution Networks (ADNs). The presence of DERs introduces challenges to conventional protection schemes due to bidirectional power flows and variations in fault current magnitudes; furthermore, the connection and disconnection of DERs result in multiple ADN operating modes (OMs), deteriorating the effective operation of protective relays. Considering the above, this document presents an adaptive protection strategy to address the challenges related to the variable nature of the ADN operation. The main contribution of the proposed approach is accurate islanded mode detection without requiring communication links, enabling fault detection in all ADN operating modes. The protection strategy maintains directional overcurrent relays' coordination using local voltage and current measurements to continuously estimate the Thevenin equivalent, fault currents, and adaptive coefficients.Relay coordination is maintained through tests conducted on a modified IEEE 34-bus feeder, considering several OMs, fault types, and locations. A comparison between the proposed adaptive protection strategy and a conventional overcurrent scheme shows that relay operating time is better in 100% of the analysed cases for the former strategy. On the other hand, the maximum errors in the fault current estimation using the Thevenin equivalent parameters are between 0.05% to 2.6% for all of the analysed operating modes when compared with the true fault current magnitudes. Finally, the adequate results validate the potential of the proposed communication-less protection strategy for modern protective relaying applications.

Fuzzy current analysis-based fault diagnostic of induction motor using hardware co-simulation with field programmable gate array

Introduction. Presently, signal analysis of stator current of induction motor has become a popular technique to assess the health state of asynchronous motor in order to avoid failures. The classical implementations of failure detection algorithms for rotating machines, based on microprogrammed sequential systems such as microprocessors and digital signal processing have shown their limitations in terms of speed and real time constraints, which requires the use of new technologies providing more efficient diagnostics such as application specific integrated circuit or field programmable gate array (FPGA). The purpose of this work is to study the contribution of the implementation of fuzzy logic on FPGA programmable logic circuits in the diagnosis of asynchronous machine failures for a phase unbalance and a missing phase faults cases. Methodology. In this work, we propose hardware architecture on FPGA of a failure detection algorithm for asynchronous machine based on fuzzy logic and motor current signal analysis by taking the RMS signal of stator current as a fault indicator signal. Results. The validation of the proposed architecture was carried out by a co-simulation hardware process between the ML402 boards equipped with a Virtex-4 FPGA circuit of the Xilinx type and Xilinx system generator under MATLAB/Simulink. Originality. The present work combined the performance of fuzzy logic techniques, the simplicity of stator current signal analysis algorithms and the execution power of ML402 FPGA board, for the fault diagnosis of induction machine achieving the best ratios speed/performance and simplicity/performance. Practical value. The emergence of this method has improved the performance of fault detection for asynchronous machine, especially in terms of hardware resource consumption, real-time online detection and speed of detection.

IDSN: A one-stage interpretable and differentiable STFT domain adaptation network for traction motor of high-speed trains cross-machine diagnosis

A surge of transfer fault diagnosis techniques has been proposed to guarantee the safe operation of traction motor systems. However, existing efforts highly depend on the availability of fault data in source domain, which is rare in practice due to the regular maintenance. Fortunately, self-customized testbeds provide an opportunity to easily obtain fault data, assuming that the simulated data can be utilized to monitor the real-world traction motor systems via the cross-machine diagnosis method. Besides, current deep learning-based cross-machine fault diagnosis methods suffer from the poor physical interpretability and the troublesome hype-parameter selection. To tackle aforementioned issues, a one-stage Interpretable and Differentiable STFT cross-machine dual-driven adaptation Network (IDSN) is proposed. In IDSN, a new paradigm termed interpretable differentiable STFT layer is devised, where a derivable coefficient is introduced to adjust pivotal parameters of STFT such as window length by the gradient descent. Prominently, it is a plug-and-play module, which can be embedded into the arbitrary typical network without conflict. Besides, a novel adaptive trade-off coefficient is developed to tackle the weight matching of the domain discrepancy metric. Finally, to ensure the reliability and effectiveness of cross-machine diagnosis, a concise yet valid smoothed joint maximum mean discrepancy is proposed, which simultaneously promotes intra-class compactness and inter-class separability. The results of experiments confirm that the proposed IDSN outperforms the state of the art.

Transient research on distribution networks incorporating superconducting cables utilizing field–circuit coupling method

High temperature superconducting (HTS) cable represents a promising solution for fulfilling the power demands of cities with large loads and high density. However, due to their connection to the distribution network, HTS cables are vulnerable to fault currents exceeding ten times their rated current, which poses a serious threat to both the safety of the cable and the operation of the grid. Considering the highly nonlinear nature of superconducting conductivity, this study develops a field–circuit coupling model to investigate the transient characteristics of distribution networks incorporating superconducting cables (DNSC). Firstly, a finite element model based on the two-dimensional H formulation was built to calculate the electrical and thermal parameters of the HTS cable. Subsequently, an equivalent circuit model of the distribution network was employed to estimate the short-circuit currents. Communicating via a co-simulation server, the superconducting cable current and distribution network impedance were updated in each step. Further, based on an actual DNSC system in Shenzhen, China, the highest quenching temperature of the cable and the maximum fault current of busbars were assessed. Finally, by integrating current limiters into the system, the withstand capability of the cable and busbars was determined, which indicates that the improved protection configuration can effectively suppress fault currents and ensure safe operation. Successfully applied to an actual distribution network, the co-simulation model utilizing the field–circuit coupling method addresses the challenges of solving highly nonlinear and time-varying systems, enabling transient analysis and protection research for the integration of superconducting devices into the conventional grid.

A fuse‐based DC circuit breaker with vacuum interrupter enhanced by an external transverse magnetic field

AbstractDue to the increasing power system capacity, the interruption of large fault currents has gradually become a major challenge in power systems. At the moment, such currents are interrupted mainly via circuit breakers based on the method of active current commutation. However, these types of circuit breakers tend to be costly and oversized. One possible alternative—a fuse‐based circuit breaker with current commutation process enhanced by an external transverse magnetic field (ETMF)—is proposed by the authors. Its main advantage lies in the fast current commutation achieved by an ETMF‐enhanced three‐stage increase of the vacuum arc voltage. The study of the current commutation process is mainly represented by the authors, and the influencing factors of the current commutation—contact opening speed and ETMF current—are discussed. At last, the proposed circuit breaker is verified by an experiment, whose results show that a short‐circuit current of 42 kA can be interrupted within just 2 ms.

Analysis of reverse fault current regarding the impact of transformer core types on the two most common winding connections of distributed energy resources in distribution systems

As many DERs with solid grounding are connected to the distribution system, unwanted reverse fault current is generated during a single-line-to-ground fault. Therefore, it often causes protection problems such as protection blinding and sympathetic tripping. To ensure reliable protection coordination between protective devices, fault current should be calculated accurately. Although three-limb core transformers are utilized for DERs for economic and spatial reasons, the conventional method that assumes five-limb core transformers for DERs is still used to calculate fault current. The zero-sequence impedance of a three-limb core transformer is often unknown. For this, a methodology for evaluating the zero-sequence impedance according to the core-type of transformer is presented with IEC 60076-8 standard. Then, a methodology for evaluating fault current is proposed considering the impact of DERs, loads, and transformer core types. The proposed methodologies are used for a comprehensive analysis of fault current discrepancies according to the core-type of transformers. The results indicate that significant discrepancies exist in fault current evaluated with five- and three-limb core transformers. Therefore, to accurately calculate the fault current, utility engineers should use the proper zero-sequence impedance of three-limb core transformers instead of five-limb core transformers.

Stray Currents in Livestock Farming: Electrical Diagnosis in Farms

For several years, farmers have been questioning the effects of electromagnetic fields and stray electrical currents on the health of their animals. Observing changes in behavior or a decline in livestock productivity, farmers suspect that electrical installations on or near the farm may be responsible. Indeed, these systems can generate fault currents or stray currents, some of which may pass through the animals, affecting their well-being and productivity. To identify the origin and address this issue, an electrical diagnosis can be performed. In this study, diagnostics were carried out in eleven bovine farms considered “healthy”. These measurements included earth resistance equipment insulation resistance, continuity, leakage currents, as well as contact and step voltages, with some farms presenting non-conformities. This study will better understand the potential links between electrical installations and animal well-being, correlate the results of this study with those obtained in diagnostics conducted on farms experiencing such concerns and implement appropriate preventative and corrective measures.

Effect of Shunt Resistor Value on the Performance of Resistive Superconducting Fault Current Limiters

Resistive-type superconducting fault current limiters (r-SFCLs) have generated great interest for research and technical applications. This is attributed to their superior features, which include self-action, fast response, and simple operation. In low line impedance systems, r-SFCLs are seen as a viable protective mechanism for limiting high-magnitude fault currents. However, overcurrent caused by faults results in an increased temperature of the r-SFCL, possibly damaging the coils. Thus, the r-SFCL must be appropriately engineered to protect it while still allowing for effective fault current limitation. To achieve this goal, an appropriately sized shunt resistor must be used. Adding a shunt resistor benefits the r-SFCL in several ways, from lowering its maximum temperature to speeding up its recovery. Additionally, the shunt resistor protects the r-SFCL from excessive surges in temperature by giving the current an alternative path to flow down, thus saving it from further damage. A multilayer thermoelectric model was developed to examine the thermoelectrical behavior of the r-SFCL coil throughout a fault occurrence and the subsequent recovery period using three shunt resistors ranging from 4 to 16 Ω. MATLAB®/Simulink was used as the simulation platform in this study. The dependence of the current limitation capability and the voltage profile on the shunt resistor value was studied compared to the basic case without an r-SFCL. Increasing the shunt resistor value led to an enhanced ability to limit fault currents, although at the cost of higher temperatures and a longer recovery time. This study also presents guidance for optimizing the design parameters of r-SFCLs.

Enhancement of low-voltage ride-through capability for virtual synchronous generators based on virtual impedance voltage control

Virtual Synchronous Generator (VSG)-based grid-forming converters (GFC) increasingly serve as interfaces between renewable energy resources and the power grids with high penetration. Although the emulation of the characteristics of Synchronous Generator (SG) enables GFC to provide virtual inertia and oscillation damping under the VSG control, it remains challenging to replicate the short-circuit behaviors of SGs under the grid voltage sag/recovery conditions. The existing technologies are limited and lack full functionalities in terms of power synchronization, overcurrent suppression and capability of dealing with asymmetric grid-faults. This paper presents a Virtual Impedance Voltage Control (VIVC) strategy to enhance the fault-ride-through capability of the converter under a variety of fault conditions. In the case of asymmetric faults, a negative-sequence current control is performed to mitigate the negative-sequence voltages and achieve the grid current balance. The fault current is restrained and the power synchronization is improved by the virtual reactance without oversizing the GFC. The simulation and experimental results validate the effectiveness of the proposed control strategies.