Zero-sequence Current Research Articles

Assessment of the spectral energy of zero-sequence currents in protected feeders with the presence of single-phase to ground fault in the isolated network

Subject of research: methods of relative measurement of higher harmonics for detecting a faulty feeder with a single-phase ground fault. Purpose of research: evaluation of sensitivity of the methodology of faulty feeder search using wavelet transform. Object of research: distribution networks of 6(10) kV. Main results of research: the level of higher harmonics does not affect the performance of the technique, regardless of the point of the fault and the harmonic composition of the load, the damaged connection is the highest value of the spectrum energy.

Optimized design of a fault-tolerant 12-slot/10-pole six-phase surface permanent magnet motor with asymmetrical winding configuration for electric vehicles

This paper presents a comprehensive methodology for optimizing the design of a 12-slot/10-pole permanent magnet (PM) motor with a six-phase winding configuration tailored for electric vehicles (EVs). The design aims to enhance motor performance under both healthy and fault conditions. While the single neutral configuration offers superior torque during faults, it also introduces zero sequence currents and additional space harmonics, which can lead to increased torque ripple that is difficult to control. This study addresses these challenges through innovative machine design optimization. The optimization process begins with sizing equations to establish an initial design. K-means clustering techniques are then employed to identify distinct loading points that accurately represent the full EV driving cycle, effectively minimizing computational power requirements. Following this, the Full Range Minimum Loss (FRML) strategy is applied to determine optimal current profiles across these loading points, significantly reducing copper losses. Finally, a multi-objective optimization approach is utilized to minimize torque ripple, enhance average torque, and optimize machine losses. The results demonstrate substantial improvements in torque and reduced ripple, validated through experiments conducted with a 2 kW lab-scale motor. This integrated approach not only ensures a robust and efficient motor design but also enhances fault tolerance, making it well-suited for advanced EV applications.

СИСТЕМА "АЛЬТРА" ДІАГНОСТУВАННЯ СТАНУ ІЗОЛЯЦІЇ ЕЛЕКТРИЧНОЇ МЕРЕЖІ ТА ЗАХИС-ТУ ЇЇ ВІД ОДНОФАЗНИХ ЗАМИКАНЬ

One of the problems in an electrical network with an isolated (compensated) neutral is the selective determina-tion of a damaged element during a single-phase earth fault. Taking into account the negative impact of single-phase earth faults on the equipment of electrical networks with an isolated or compensated neutral, as well as improving the electrical safety conditions of people and animals, it is necessary to install selective protections with the of turning off of damaged element. Selective operation of protections against such damage can be en-sured on the basis of the analysis of zero-sequence currents, phase voltages and zero-sequence voltage of the bus section from which these feeders are powered. As operational experience has shown, selective operation of pro-tection against single-phase earth faults in such networks can be ensured only with the use of digital devices. The work considers the "Altra" system, designed for diagnosing the state of insulation, protecting feeders of 6-35 kV from single-phase earth fault, recording analog and binary signals of electrical installations. Altra digital protec-tion simultaneously covers up to 28 feeders, which provides comprehensive protection against single-phase earth faults of all substation feeders. The working algorithm of the developed protection against single-phase earth faults is based on the analysis of the transient process immediately after the occurrence of damage, which provides selective identification of the damaged feeder both in networks with an isolated neutral and in networks with a compensated. The system organizes the recording of oscillograms of emergency processes and infor-mation about damage by "Altra" devices, followed by their transfer to the dispatcher's automated workplace. This makes it possible to carry out a detailed analysis of accidents and diagnose the insulation of the electrical net-work.

Faulty section location method for high impedance grounding fault in resonant grounding system based on discrete Fréchet distance

When a High Impedance Fault (HIF) occurs in a resonant grounding system, the differentiation of the current flowing upstream and downstream of the fault point is inconspicuous due to the weak electrical signal. This paper proposes a faulty section location approach based on Discrete Fréchet Distance (DFD) to address this issue. Initially, taking the zero-sequence current as the characteristic quantity, the instantaneous value of the zero-sequence current at each sampling point and its previous sampling moments are accumulated to amplify the fault signal, and furthermore to obtain the cumulative waveform of the zero-sequence current at each monitoring point. The DFD values between the cumulative waveforms of zero-sequence currents flowing through each section are also calculated. For a branchless section, if the Coefficient of Variation (CV) of the DFD in each section does not exceed the threshold value, it is identified as an end-of-line fault, otherwise, the section with the maximum DFD is identified as a faulty section. For a section with branches, the branching coefficient is calculated to determine whether it is a faulty section or not. Finally, MATLAB/Simulink simulation results and field-recorded data demonstrate the validity and robustness of the approach under various fault conditions, despite the connection of Distributed Generators (DGs).

Fault Line Selection of Small Current Grounding System Research Based on Zero Sequence Circuit Current Phase

Abstract This paper investigates fault line selection in small current grounding systems, focusing on the zero sequence current phase characteristics. Small current grounding systems, prevalent in medium voltage distribution networks, face challenges in fault detection due to minimal fault currents during single status phase grounding faults. Traditional methods relying on manual line switching and zero sequence voltage monitoring are inefficient and can induce overvoltage. This study categorizes fault line selection techniques into three approaches: steady-state fault information, transient information, and modern signal processing technology. The analysis of zero sequence currents in non-grounded systems reveals that fault line zero sequence currents equal the sum of system capacitive currents, flowing opposite to those in non-fault lines. Additionally, transient signal analysis shows that these signals provide more robust information for fault detection. MATLAB simulations validate the theoretical models, demonstrating that zero sequence current direction and amplitude effectively identify fault lines. The results confirm the efficacy of combining steady-state and transient signal analyses for accurate fault line selection, contributing to enhanced safety and reliability in power distribution networks. This research offers practical insights and tools for engineers, improving fault management and reducing potential economic losses in small current grounding systems.

Explainable Deep Learning Approach for High Impedance Fault Localization in Resonant Distribution Networks Considering Quantization Noise

ABSTRACTIn addressing the quantization noise challenge in high impedance fault (HIF) localization within resonant distribution networks, we propose a cutting‐edge, explainable deep learning approach that significantly advances existing methods. This approach utilizes differential zero‐sequence voltage (DZSV) and zero‐sequence current (ZSC) and introduces a novel “Vague” classification to improve localization accuracy by effectively managing quantization noise‐distorted signals. This approach extends beyond the conventional binary classification of “Fault” and “Sound,” incorporating a multi‐scale feature attention (MFA) mechanism for enriched internal explainability and applying gradient‐weighted class activation mapping (Grad‐CAM) to visualize critical input areas precisely. Our model, validated in an industrial prototype, exhibits unparalleled adaptability across various environmental conditions, including environmental noise, variable sampling rates, and triggering deviations. Comparative analysis reveals that our approach outperforms existing methods in managing diverse fault scenarios.

Fault Handling and Localization Strategy Based on Waveform Characteristics Recognition with Coordination of Peterson Coil and Resistance Grounding Method

To address challenges in locating high-impedance grounding faults (HIGFs) and isolating fault areas in resonant grounding systems, this paper proposes a novel fault identification method based on coordinating a Peterson coil and a resistance grounding system. This method ensures power supply reliability by extinguishing the fault arc during transient faults with the Peterson coil. When a fault is determined to be permanent, the neutral point switches to a resistance grounding mode, ensuring regular distribution of zero-sequence currents in the network, thereby addressing the challenges of HIGF localization and fault area isolation. Fault calibration and nature determination rely on recognizing neutral point displacement voltage waveforms and dynamic characteristics, eliminating interference from asymmetric phase voltage variations. Fault area identification involves assessing the polarity of zero-sequence current waveforms attenuation during grounding mode switching, preventing misjudgments in grounding protection due to random initial fault angles and Peterson coil compensation states. Field experiments validate the feasibility of this fault location method and its control strategy.

Cascade model predictive control strategy for medium voltage flexible interconnected systems with arc suppression capability under single phase grounding fault

The distribution network faces problems such as diversified electricity demand and difficulty in ensuring power quality. At the same time, complex working environments often lead to brief single-phase ground faults, resulting in zero sequence currents in the distribution network. The flexible interconnection system of medium voltage distribution network plays an important role in balancing loads and providing electrical reliability. This article uses a three-phase four-wire converter as a flexible interconnection device, injecting zero sequence current into the neutral point through the fourth bridge arm. Simultaneously, a novel control strategy for medium voltage flexible interconnected systems based on cascaded model predictive control is proposed. The simulation and experimental results demonstrate the effectiveness of the proposed control strategy, which comprehensively achieves power mutual benefit, neutral point displacement voltage suppression, and active arc suppression during single-phase grounding faults in flexible interconnected systems.

Research on fault line selection method based on steady state variables

When a single-phase ground fault occurs, the transient zero sequence current will significantly increase. So, it is possible to detect whether a single-phase grounding fault has occurred in the transmission line by calculating and comparing the amplitude of transient zero sequence current. Only when the amplitude of the zero sequence voltage under the steady-state power frequency is greater than the preset threshold can the line selection device be effectively and reliably started. The instantaneous value protection device can also be used to start first, and then, the steady-state amplitude of the power frequency can be compared as the verification object.

Research on the countermeasures of the single-phase-to-earth faults in flexibly grounded distribution networks

In a neutral, flexible, grounded distribution network, the phenomenon that a single-phase ground fault with high impedance connected in parallel with a low resistance can result in a relatively lower zero-sequence current flowing through the faulty feeder. This zero-sequence current can make it a challenge to use zero-sequence protection schemes to accurately identify and effectively protect the faulty feeder. In terms of the aforementioned challenge, based on the zero-sequence equivalent circuit of a single-phase-to-earth fault, this paper conducts an investigation on the phase difference between the zero-sequence current and the non-fault phase line voltage at power frequency in flexible grounding distribution network with different grounded conditions, both before and after the introduction of a parallel low-resistor connection. Subsequently, a criterion for selecting the faulty feeder is developed based on the observed phase difference characteristics following the implementation of the parallel low-resistor connection. Furthermore, a disposal strategy for single-phase-to-earth faults is formulated, which takes fault resistance estimation into account. To validate the proposed method, a simulation model of a flexible grounding distribution network is implemented with PSCAD/EMTDC. The effectiveness and reliability of this method in multiple scenes, including the initial fault conditions, sampling frequency, and distributed generation (DG), are proved through simulation results.

Application of a Centroid Frequency-Based Back Propagation Neural Network Fault Location Method for a Distribution Network Considering Renewable Energy Assessment

The distribution network is a crucial component of the power system as it directly connects to users and serves the purpose of distributing power and balancing the load. With the integration of new energy sources through distributed generation (DG), the distribution network has undergone a transformation from a single power radial network into a complex multi-source network. Consequently, traditional fault location methods have proven inadequate in this new network structure. Therefore, the focus of this paper is to investigate fault location techniques specifically tailored for DG integration into distribution networks. This paper analyzes how fault conditions impact the characteristics of single-phase grounding faults and extracts spectral feature quantities to describe differences in zero-sequence currents under various fault distances. This paper also proposes a fault location method based on centroid frequency and a BPNN (back propagation neural network). The method uses centroid frequency to describe the features of zero-sequence currents; to simulate the mapping relationship between fault conditions and spectral features, BPNN is employed. The mapping relationship differs for different lines and distribution networks. When a line faults, the spectral features are calculated, along with the transition resistance and fault closing angle. The corresponding mapping relationship is then called upon to complete distance measurements. This location method can be applied to various types of distribution lines and fault conditions with high accuracy. Even with insufficient training samples, sample expansion can ensure accuracy in fault distance measurement. We built a distribution network consisting of four feeders with different types and lengths of each line on Simulink and verified the effectiveness of the proposed method by setting different fault conditions. The results suggest that the method has a clear advantage over other frequency domain-based approaches, especially for hybrid lines and feeder lines with branches in distribution networks. Additionally, the method achieves a measurement accuracy within a range of 100 m.

Faulty line detection for cross‐line same‐phase successive ground faults in distribution network based on transient characteristics

AbstractCurrently, theoretical analysis of single‐phase grounding (SPG) faults in low‐current grounding systems has reached a high level of refinement, and the corresponding detection methods have matured. However, there is a significant lack of research on successive grounding (SG) faults, particularly in the area of detecting cross‐line same‐phase successive grounding (CSSG) faults in arc suppression coil grounding systems. To address these issues, a novel faulty line detection method based on transient characteristics of CSSG is proposed. Firstly, a transient equivalent circuit is established, and the characteristics of transient zero‐sequence current (ZSC) are theoretically analysed. Secondly, variational mode decomposition (VMD) is employed to extract low and high‐frequency information from intrinsic mode functions (IMFs). Subsequently, a fault initiation criterion based on kurtosis theory and the Teager‐Kaiser energy operator (TKEO) is proposed, which can accurately detect the occurrence time of secondary faults. Finally, a method for faulty line detection based on cross‐correlation distance (CCD) and transient energy (TE) is proposed. The results of PSCAD simulation under different conditions and field test affirm the accuracy of the analysis and the effectiveness of the proposed method.

TECHNIQUE DE CONTRÔLE INTÉGRÉE OPTIMISÉE POUR VAUTOUR AFRICAIN POUR APPLICATION DE POMPE À MOTEUR À INDUCTION À ENROULEMENT OUVERT À ALIMENTATION PV

Open-end winding induction motors (OEWIM) have gained much attention, and they are used for solar photovoltaic (PV) fed pumping applications as a compromise alternative to multi-level inverters. Solar irradiance conditions further exacerbate the nonlinear control problem, resulting in significant loss of power and low reliability, which affects motor operation. To overcome these issues, this paper presents an optimized integrated control technique-based PV integrated three-level dual inverter fed Open-end winding induction motors for pumping application. An integrated African vulture optimization algorithm and scalar coupled pulse width modulation (AVO-SCPWM) based control techniques are proposed to extract the maximum power from the solar PV source and control the induction motor pump. Here, the AVO-based maximum power point tracking (MPPT) technique adjusts the modulation index (ma) by insolation and temperature. The proposed technique balances the zero-sequence current, reduces THD, and reduces the switching losses over the inverter. The proposed work is evaluated in MATLAB/Simulink software and compared with the existing conventional induction motor (IM), Conventional OEWIM Drive, and scalar decoupled PWM-based IM techniques under two climatic conditions. Thus, the simulation results demonstrate that the proposed technique accomplishes better than the existing techniques.

A ground fault location algorithm in double‐circuit transmission lines with T‐off connection to an industrial microgrid by using current and voltage phasors information of a single terminal

AbstractThe paper presents a ground fault location algorithm (GFLA) in double‐circuit transmission lines (DCTL) with a T‐off connection to an industrial microgrid (IMG) containing electric arc furnaces (EAF), renewable distributed generations (RDG), and static VAR compensator (SVC). The design presented utilizes the information on the current and voltage phasors of one side of the transmission lines (TL) during the fault period, and there is no need for the availability of information on the type of faulty phase(s) and even the faulty section. To find the exact location of the fault in this design, the voltage phasor equations governing the fault point in positive, negative, and zero‐sequence (PNZS) domains, the zero‐sequence current (ZSC) equation of the fault point, and the boundary condition equation of the fault point have been used. The simulation system is implemented in Simulink/MATLAB using accurate modelling of all network components. The algorithm has been tested and evaluated in different fault conditions, including various locations, phase types, phase‐to‐ground connection resistance, occurrence time, and microgrid (MG) operation modes. The successful results of various tests of the proposed design as well as the analysis of various sensitivities confirm the satisfying performance of the suggested algorithm.

Ground Fault in Medium-Voltage Power Networks with an Isolated Neutral Point: Spectral and Wavelet Analysis of Selected Cases in an Example Industrial Network Modeled in the ATP-EMTP Package

The paper presents some case spectral analysis of zero-sequence voltages and currents in an example industrial power distribution network. The network layout is based on typical power delivery networks in underground coal mines. Ground fault simulations have been made using an ATP/EMTP program. Due to the high environmental risks, the reliability of the protection relay operation related to their selectivity plays an important role. This paper tries to find the reasons for nonselective operation and unnecessary tripping in extensive mine cable networks, particularly with large power sources of higher-order harmonics. It was found that in transient states—due to the decaying oscillations occurring in complex RLC circuits—the results of short time measurements of the criterion values for ground fault protective relays can be overestimated (particularly for small values of ground resistance) and lead to nonselective tripping of a healthy cable line. Therefore, it might be advisable to increase the integration time used for measuring rms values. Also, if there is a significant level of higher harmonics in the industrial network generated by high-power converters, it should be noted that the higher harmonics of the ground fault current and currents measured by ground fault protection relays assume much higher values, which may also cause nonselective tripping. In this case, it may be advisable to use higher harmonic filters in the measuring circuits and to select a sufficiently high sampling frequency in the digital protective relays.

Advancing high impedance fault localization via adaptive transient process calibration and multiscale correlation analysis in active distribution networks

Fault localization is crucial for ensuring stability, particularly in high impedance faults (HIF) characterized by low current levels and prolonged transient processes (TP). Existing methods predominantly analyze differences in the fixed-length transient waveform, potentially causing delays in triggering or failure in HIF scenarios. To address these challenges, a novel AI application paradigm for HIF localization was introduced, incorporating both adaptive TP calibration and multiscale correlation analysis. Based on 1D-Unet, the TP of the zero-sequence voltage (ZSV) can be adaptively calibrated to maximize the utilization of transient information. Subsequently, the differential zero-sequence voltage (DZSV) and transient zero-sequence current (TZSC) can be acquired to facilitate multiscale correlation analysis. Combined with a sliding window strategy, the micro correlation between DZSV and TZSC is articulated through the local correlation degree (LCD). The comprehensive correlation degree (CCD) between DZSV and TZSC is then formulated to realize fault feeder/ section localization at the macro level. The 1D-Unet model achieved a classification accuracy of 99.2 % for sample points in test datasets and showed robustness with an accuracy exceeding 93.5 % in the presence of 20 dB noise interference. When integrated with the well-trained 1D-Unet, the proposed approach underwent further validation using simulation data and field recordings. These tests confirmed the model's resilience to noise interference up to 20 dB and its efficacy across networks of diverse topologies, such as the IEEE-13 and 34-node distribution networks. Additionally, an industrial prototype applying this framework identified all fault conditions without false positives or omissions, outperforming existing methods under various fault scenarios, including those involving high impedance materials and different resistance levels across multiple feeders.

Analytical Torque Ripple Reduction Strategy for Flux Modulated Doubly-Salient Reluctance Motor Drives Based on ZSC Harmonic Regulation

Compared to the conventional doubly-salient reluctance motor (DRM) drives, the novel flux modulated DRM (FMDRM) drives can achieve a better overall torque performance due to the dc-biased sinusoidal current excitation. However, previous investigations only focus on the dc-biased and fundamental current components, and the contributions of current harmonics to the torque production are not clear. This paper proposes an analytical torque ripple reduction strategy for open-winding FMDRM drives based on zero-sequence current (ZSC) harmonic regulation. Firstly, the contribution of third-order ZSC harmonic to the electromagnetic torque is investigated together with the dc-biased sinusoidal current components. Secondly, an alternative torque component cancellation method is put forward, where the additional third-order ZSC is utilized to counteract the dominating part of the alternative torque generated by the dc-biased sinusoidal current for torque ripple reduction. Both the amplitude and initial phase angle of the additional third-order ZSC are calculated by the analytical equation of electromagnetic torque. Moreover, the corresponding three-dimensional current distribution is investigated to achieve the desired ZSC regulation. With the proposed scheme, the torque ripple can be effectively suppressed while maintaining high output torque capability and efficiency. Furthermore, experimental results are presented on a three-phase FMDRM prototype to verify the proposed strategy. <fn fn-type="other" id="fn3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> </fn>

Reduction of Zero Sequence Components in Three-Phase Transformerless Multiterminal DC-link based on Voltage Source Converters

This paper is focused on the analysis and reduction of zero sequence currents which appear in multiterminal DC links based on Voltage Source Converters (VSCs). A zero sequence current may flow between the VSCs due to the absence of the coupling transformer, in spite of this application is intended for three-phase three-wire system. The proposed solutions to mitigate this issue have been tested through simulation and experimental results.

Fuel cell inverters used for unbalance compensation in low voltage distribution systems

The aim of this paper is to evaluate the benefits that can be achieved by operating the connection inverters of the distributed energy resources as active power filters in LV distribution networks. The use of the future fuel cell inverters to compensate zero sequence currents, arising from unbalances among phases, can improve the efficiency of the distribution networks by means of reducing the total amount of losses. A common unbalanced load connected to a LV feeder where a FC inverter is present has been simulated. The reductions in the distribution power losses and compensation of zero sequence currents have been analyzed.

Zero-sequence controller requirements and comparison for a delta-CHB STATCOM under unbalanced operation

Delta-configured Cascaded H-Bridge (DCHB) topology is a suitable alternative for Static Synchronous Compensator (STATCOM) applications. However, under unbalanced voltage and/or current conditions, zero-sequence current needs to be injected to guarantee dc-link capacitor voltage balancing. The control loop of this zero-sequence current is analyzed in this paper, in order to determine the requirements that the implemented controller must fulfill. Considering these requirements, appropriate transient response and stability margin indicators are defined to quantify and evaluate the performance of different controllers that could be employed —Proportional-Resonant controller (PR), PR controller with delay compensation (PRd), and Vector Proportional-Integral controller (VPI) are proposed and analyzed for this application in this paper. Based on the defined indicators, the VPI is the most appropriate among the studied control techniques. Experimental results validate the analytical model of the controllers and their performance.