Sequence Components Of Currents Research Articles

A Novel High-Impedance Fault Detection Technique in Smart Active Distribution Systems

Identification of high impedance fault (HIF) is important in smart active distribution systems (SADSs). The existing protection methods fail to detect HIF, as HIFs have peculiar fault current characteristics. However, if HIFs are left undetected, they result in severe fire hazards and arcing. The paper proposes a novel fault detection indicator that utilizes the differential energy associated with the positive sequence current components during faults. IEEE-13 bus and IEEE-34 bus system is used for simulation in Real Time Digital Simulator (RTDS). The results show that proposed technique accurately identify HIFs and perfectly discriminates the transients due to HIFs, non-linear loads and voltage and reactive power compensation devices. Furthermore, it differentiates HIFs from other switching transients like capacitor or load switching events. Other factors, like transformer inrush currents, effect of noise and sampling rate are also considered to ensure the accuracy and reliability of the proposed method. Moreover, the practical feasibility of the proposed method is also experimentally validated.

The Current Sequence Components Extraction for Dual Synchronous Rotation Frame Current Control in Unbalanced Grid Conditions

The Current Sequence Components Extraction for Dual Synchronous Rotation Frame Current Control in Unbalanced Grid Conditions

Deep neural networks based method to islanding detection for multi-sources microgrid

One of the significant issues in the field of microgrids is their islanding, where in many cases, the lack of awareness of microgrid islanding can lead to interference in the protective and control functions of the microgrid. Therefore, the accurate detection of microgrid islanding is of utmost importance. In this article, a method based on deep neural networks is presented. The proposed approach utilizes terminal parameters of microgrid resources, such as sequence current components, voltage, and other parameters, to detect islanding. Various operational states of the microgrid are simulated offline as standard test cases, and the parameters of each of them are recorded for later use. These data are then used to extract statistical features using discrete wavelet transform. Subsequently, the extracted features are fed into deep neural networks for training, and the training and evaluation results demonstrate an accuracy of over 99% for the proposed method in terms of precision and reliability. Furthermore, the accuracy of the proposed method is compared with some similar approaches for islanding detection.

Localization of HIFS in primary distribution networks using voltage and current sequence components

In the power system protection when a conductor accidentally makes contact with a highly resistive medium, a HIF problem arises. Because of their lowest current amplitude and incredibly varied features, the HIF are challenging to detect. To detect the fault type this work proposes Support Vector Machine (SVM) classifier and Convolution Neural Network (CNN) classifier to localize the detected fault based on the trained statistical features attained from current and voltage sequence components at distribution feeders. The weight parameters of the SVM classifier and the CNN classifiers are tuned by a novel Hybrid AqSea Optimization Algorithm. The performance of the presented HIFD method is compared to assess proficiency. The adopted model at 70 % learning attains an accuracy of 93 %, which is 0.89 %, 7.69 %, 4.60 %, 1.21 % and 30.37 %, better than the previous models like SVM, SVM + GWO, SVM + DFA, SVM + AQO, SVM + SOA, and Aqsea + SVM, respectively.

Theory and simulation analysis of parallel operation after main transformer replacement

As one of the most important main equipment in the power system, the safe and stable operation of transformer plays a vital role in ensuring the reliability of power supply. Because the three-phase parameters of the main transformer are not the same, the parameters of each phase and the three-phase load of the power grid are also different, resulting in a certain degree of asymmetry between the three-phase current and voltage of the transformer during normal operation. There will be negative sequence and zero sequence current components. The degree of asymmetry is generally small for the high-voltage power grid, but it has a large impact on the low-voltage side of the main transformer. In this paper, the parameters of two main transformers in a substation are quite different, but when they need to run in parallel, whether they can run in parallel, what are the conditions of parallel operation, these problems have been studied in theory and simulation. The results show that the two main transformers can be operated in parallel under suitable conditions. The actual operation result of a substation’s main transformer is normal, which further verifies the correctness of theoretical calculation and simulation.

Passive Island Detection Method Based on Positive Sequence Components for Grid-Connected Solar–Wind Hybrid Distributed Generation System

This paper presents the development and practical implementation of a new passive island detection method for grid-connected hybrid distributed generating systems. The method employs positive sequence voltage and current components at the point of common coupling. The product of the difference in positive sequence voltage and the difference in positive sequence current is used to produce the Islanding Detection Index (IDI). Islanding is identified when the IDI magnitude surpasses a predefined threshold over a predefined delay time. Even in the case of a zero power mismatch condition, the proposed method can identify the islanding condition in under 70 msec. Its effectiveness is validated under various operating circumstances. It provides excellent stability against various non-islanding situations, avoiding unwanted tripping. The suggested method also has the advantages of being simple and inexpensive to implement, having no adverse effects on output power quality, not requiring a classifier, not being system-dependent, and working regardless of the quantity and type of distributed generation connected to the utility grid. The obtained detection timings were compared to those previously reported in the literature, confirming the proposed approach’s superiority. The suggested work utilizes the OPAL-RT real-time hardware-in-loop environment and MATLAB/Simulink.

A Novel Proposed Algorithm to Enhance the Overcurrent Relays’ Performance in Active Distribution Networks

This research addresses two topics: the first is the optimal coordination of overcurrent relays (OCRs), which has recently become a major challenge to ensure reliability and speed of relays’ operation, and the second is a modified circuit added to the OCR to vanquish the barriers caused by the ever-increasing participation of distributed energy resources (DERs), at a lower cost. For robust and reliable OCRs coordination, various types of optimization techniques are frequently used to find optimal OCRs settings in distribution networks (DNs). In this study, the improved wild horse optimization (IWHO) algorithm is used as a novel metaheuristic method for solving optimization issues in coordination of OCRs in a distribution network, for the first time. This technique is used to determine the optimal time multiplier setting (TMS) and optimal pickup setting (PS) of OCRs in order to minimize the overall operating time. The results of the proposed algorithm are compared with those obtained from other recent metaheuristic techniques. The obtained TMS and PS settings of each relay show the effectiveness of the proposed IWHO technique in terms of accuracy and speed in a medium scale radial network configuration. To replace the costly mitigation methods employed in the DN comprising DER, a simple circuit was proposed to be added to the OCR. Using the angle’s sign of positive sequence current component (PSCC) of fault current solely, this proposed circuit can detect the fault direction and assist the OCR in making the correct decision in fault detection and clearing with high penetration of DERs. IEEE-33 bus electrical power system has been used to validate the newly proposed protective solutions.

Enhanced Control Strategy Based on Virtual Impedance Loops to Achieve the Sharing of Imbalance and Harmonic in 3-Phase 4-Wire Isolated Microgrids

An improved distributed control strategy for imbalance and harmonic sharing in 4-leg droop controlled power converters for 3-phase 4-wire isolated Microgrids is presented in this letter. The proposed control scheme improves a previous one proposed by some of the authors of this letter in the sense that both negative and zero current sequence components are independently controlled. A numerical comparison between the previous method [1] and the presented in this letter shows that, for the studied case, the negative sequence powers shared among the 4-leg converters using the method [1] are: 1638 VA, 2309 VA, 1760 VA, 2610 VA and 1344 VA (these powers are unequally shared). In contrast, with the improved method, all of these powers are equally shared at 1945VA, showing the effectiveness of the proposal. Similar behaviour was verified for zero-sequence powers, which, for the method [1], varied from 1588 VA to 2547 VA, while the proposed approach produced equal sharing of zero-sequence powers (2072 VA) among all the converters.

Self-Healing of Active Distribution Networks by Accurate Fault Detection, Classification, and Location

The power system self-healing concept needs accurate and reliable fault detection, classification, and location (FDCL). This research proposes a novel and robust FDCL approach for distribution networks (DNs) in proportion to self-healing requirements. The proposed algorithm utilized a discrete wavelet transform (DWT) to decompose the measured current and zero sequence current component of only one terminal (substation) to detect and classify all fault types with the identification of the faulted phase (s). The fault location is achieved by integrating DWT and support vector machine (SVM). The data for training were extracted using DWT and collected, and then SVM was trained to locate the faulted section. The simplicity of the applied approach, ignoring DG’s data that is merged into the system, reduced training data and time, ability to diagnose all fault types, and high accuracy are the most significant contributions. The proposed techniques are tested on IEEE 33 bus DN with two distributed generation (DG) units, which are simulated in MATLAB. The simulation results demonstrate that the proposed methods give more accurate and reliable results for diagnosing the faults (FDCL) of various fault sorts, DN size, and resistance levels.

Stator Fault Detection and Faulty Phase Identification in Network/Inverter-fed Induction Machines using Negative Sequence Current Component

This paper proposes a non-invasive negative sequence impedance-based technique to detect stator turn-to-turn faults (STTFs) and dentify the related faulty phase at early stages based on the tracking the magnitude and angle variations of the negative sequence current component generated due to STTFs. To extract these indicators, a simplified steady-state negative sequence equivalent circuit of the induction motor is used. To neutralize the effect of various produced disturbances by the inherent non-ideal construction of the machine and also unbalanced feed voltage to the STTF diagnosis, they will be estimated and removed from the main obtained component. It is shown experimentally that the introduced technique is independent of mechanical loading level (load variations) and is applicable for network or inverter-fed motors as well. Online fault detection and faulty phase identification, as the most important goals of the protection plan, are accessible by defining an appropriate threshold for the magnitude and allowable range of angle variation of the introduced criterion, respectively. The performance of the method is evaluated by simulation as well as multiple experimental tests. The experimental results have shown that from the sensitivity point of view, even weak faults are detectable by such a technique. Also, the obtained tests showed that such technique is robust, reliable and secure in the face of unbalanced voltage sources and load level variations. In addition, the performance of this method for the inverter-fed mode showed that the related sensitivity will be increased in such a condition.

A Missing Data Tolerant Wide-Area Back-Up Protection Scheme for Transmission Network

The proposed scheme develops a missing data tolerant wide area back-up protection scheme for power transmission network with fewer PMUs. The scheme assumes division of power system into different coherent groups. The fault detection index (FDI) is used to detect a fault in the system network using active power transfer and angular difference between voltages of connected areas or summation of negative and zero sequence current components in each area. The faulted area is then identified by change in area-current (CAC) using current contribution towards each area and finally, the faulted line is identified for the respective faulted area using distance to fault (DF) index. The scheme is extensively tested on a New-England 39-bus system for several fault and stressed scenarios considering all PMU data available and PMU data loss at some of the buses. For this, the PMUs are deployed at less than half number of system buses. The maximum response time of the proposed scheme is approximately 260 ms which is well within the third zone operation time of distance relays for back-up protection. The test results including the comparative assessment with existing schemes indicate that the proposed scheme can be a potential candidate for enhancing the performance of the wide-area back-up protection in the transmission network.

DC‐link low‐frequency current and voltage ripple analysis in multiphase voltage source inverters with unbalanced load

Inverter's performance and operating mode may be negatively affected by inverter input (dc-link) current and voltage ripple. It is a common experience that even theoretically balanced loads with perfectly balanced supply voltages, such as multiphase ac motors supplied by pulse-width modulation (PWM) inverters, in practice show a certain degree of current unbalance, in the range of a few percent, which introduces a low-frequency instantaneous power oscillation. This reflects in current and voltage low-frequency ripple on the dc-link inverter side (i.e. at the double-fundamental frequency). A possible method to analyse this matter is through the symmetric sequence components. In particular, based on the first negative current sequence component and by considering the equivalent dc-link impedance calculated at the dominant double-fundamental frequency, the amplitude of the corresponding dc-link voltage ripple component is calculated in this work for a general multiphase load. Finally, the design of the dc-link capacitor in multiphase inverters is proposed considering requirements referred to the double-fundamental dc voltage ripple. The feasibility of the proposed developments has been verified for three-, five- and seven-phase inverters by both numerical simulations and comprehensive experimental tests, always showing a good matching.

Stator Faults Detection on Induction Motors Using Harmonic Sequence Current Components Analysis

In this paper we propose a strategy for detecting interturn short circuits on stator windings of three-phase induction motors (IM). The strategy is based on an analytical model that includes a stator fault in any of the phase windings considering the h-th harmonic in the supply voltage. To find the adequate model, we propose an equivalent electrical circuit of the IM in steady state, considering each sequence component. The proposed strategy allows the detection of an interturn short-circuit fault by monitoring the fifth-order harmonic component. We present simulation and experimental results for the faulty IM and different operating conditions. In the laboratory tests, we use a programmable power supply in order to synthesize distorted and unbalance voltages. Also, the windings of a three-phase IM have been modified to generate stator faults and validate the proposed model. The results show that the sustained increase of the fifth-order harmonic of positive-sequence current is a good indicator of the fault severity.

Current limiting strategy for grid-connected inverters under asymmetrical short circuit faults

Grid-connected inverter plays an essential role as an interface between energy resources and the power grid. The performance of the inverters is adversely affected by the grid disturbances such as imbalances and asymmetrical short circuit faults. Then, it is necessary to enhance the functionality of the inverter under such conditions. This paper proposes an unbalance current limiting strategy for grid-connected inverters under asymmetrical short circuit fault conditions. In the proposed current limiting strategy, two main features are included: (i) second-order harmonic elimination from instantaneous active power injected into the grid, and (ii) reactive current injection according to the grid code demand. In the proposed current limiting strategy, proper positive and negative sequence current components are calculated, by which the aforementioned goals are achieved. Furthermore, to be compatible with the well-known control structure of the power converters, the current references are obtained in the form that is applicable with the commonly-used double-synchronous-references-frame control structure. To verify the effectiveness of the proposed method, the behavior of the current limiting strategy is examined by simulation of an asymmetrical short circuit fault condition in a test system. In the simulation, both the transient response upon fault occurrence and steady-state of fault condition are considered and analyzed. Furthermore, the simulation results are supported by experimental test results, verifying the effectiveness of the proposed strategy.

Stator Winding Fault Diagnosis Method Based on Dc Side Current of Inverter

This paper analyzes the influence of the fundamental negative sequence component of the grid voltage on the output voltage of the variable frequency power supply, and points out that the fundamental negative sequence component of the grid voltage will not generate the fundamental negative sequence current component in the stator current of the induction motor, so when the stator winding fault is diagnosed, the influence of the negative sequence voltage of the grid does not need to be compensated. Based on the characteristic that the fundamental negative sequence current component in the stator current is converted into two times of the inverter output frequency component in the DC side current of the inverter, a stator fault diagnosis method based on the DC side current of the inverter is proposed. The method of connecting the short-circuit resistance between the two phases of the motor is used to simulate the nonmetallic short-circuit fault of the stator coil. The experimental results show that this method does not need to compensate the negative sequence voltage, and only needs to collect one current signal, and the algorithm is relatively simple, which is a simple and effective method.

Enhanced Performance of Charging Stations via Converter Control Under Unbalanced and Harmonic Distorted Grids

This article proposes a new control structure for grid-interfaced converters to enhance ancillary services from emerging electric vehicle (EV) charging stations (CS) under unbalanced and distorted grid conditions. Compared to existing methods, the proposed control structure is relatively simple yet effective for both regulating powers and minimizing harmonics under unbalanced and distorted grid conditions. A simple direct predictive control methodology is proposed where the positive fundamental component of currents is controlled for power regulation while other negative sequence or harmonic current components are set to zeros. Consequently, the charging station operation is enhanced with efficient ancillary services to the electric grid. The novelty originates from a simple predictive control structure in an <i>abc-</i>natural frame without adding any decoupled or separated current-component controllers. Comparative studies on both Matlab&#x002F;Simulink platform and OPAL-RT-based real-time system among proportional integral (PI) control, finite predictive control, and the proposed method are conducted to verify the efficacy of the proposed structure. The comparative results show that the control structure improves the control performance and significantly enhances the support for the local loads under unbalanced, harmonic distorted grid conditions.

Fuzzy Fault Detection for Permanent Magnet Synchronous Motor

In the transition to automated and automatic manufacturing an urgent problem is to increase the reliability of mobile robots (MR) and their drives, creation of devices to monitor the technical characteristics of MR, diagnose and predict the remaining resource. Inspite of the high relevance of the diagnosing MR drives problem, there are no generally accepted methodology for diagnosing MR drives, criteria for selecting methods, parameters and volumes of diagnostics at present. An unsolved problem, related to the diagnosis of MR drives and the prediction of their residual life remains, is the development of methods that allow to carry out of automatic complex multiparametric diagnostics and prediction of the residual life using artificial intelligence methods. Effective fault detection and diagnosis can improve the reliability of the MR drive and avoid costly maintenance. In this paper a fault detection scheme for synchronous motors with permanent magnets based on a fuzzy system is proposed. The sequence current components (positive and negative sequence currents) are used as fault indicators and are set as input to the fuzzy fault detector. The expediency of the proposed scheme for determining of various types of faults for a synchronous motor with permanent magnets under various operating conditions is simulated using the SimInTech software.

Sequence component direction element based on power frequency variation

Unlike the relatively stable network structure of the transmission and distribution network, under the new distribution network, resulting in errors in the impedance tuning of the fault directional element, misjudgment of the fault directional element, and a decrease in sensitivity. For this reason, this paper proposes a sequence component adaptive fault directional element based on power frequency variation. The sequence impedance amplitude is calculated through the measured values of the voltage sequence component and the current sequence component of the relay location. Then the phase angle of the setting impedance is determined according to various sequence components in the system. It improves the problem that the setting impedance of power frequency distance directional element is greatly affected by the amplitude and phase angle fluctuation of distribution system impedance and line impedance. The reliability and stability of the sequence component adaptive fault directional element based on the power fresquency variation are verified by Matlab simulation.

Frequency‐adaptive complex‐coefficient filter‐based control for grid‐integrated PV system

This work deals with a frequency-adaptive complex-coefficient filter-based control for three-phase grid supportive double-stage photovoltaic (PV) system. This control eliminates harmonic components, DC offset at unbalanced loads and robust against phase frequency shift and on utility grid voltage disturbances. It uses harmonic-free positive sequence current components to generate sinusoidal reference currents without amplitude scaling. Moreover, tuning of parameters is not required due to the absence of gain parameters. This system responds quickly to balance the grid currents under unbalanced load currents, mitigates load current harmonics while feeding active power to the distribution network. The presented topology has enhanced the voltage source converter (VSC) utility, particularly in the absence of PV array generation, thus, VSC payback period is reduced. The PV dynamic term is utilized to enhance VSC input voltage profile, to avoid overshoots and undershoots in grid currents, and to mitigate transients in PV array current under varying irradiance. The behaviors under dynamic state and steady state of the presented system are validated under varying irradiance, load currents unbalance and grid voltage disturbances through simulated and test results. The power quality concerns are addressed, by achieving harmonic contents in grid currents below to 5% in accordance to the IEEE-519 standard.

Protection of transformer due to external fault between two voltage levels using overvoltage protection and sequence component of currents

The main role of the transformer protection is based on satisfying fast and reliable relay to isolate the power transformer from the grid with minimum damage. Also, to avoid the mal-operation of the protection system during different operating conditions. This paper presents a simple method to protect the power transformer due to the short circuit between two different voltage levels that may be produced when two overhead transmission circuits with different voltages intersect with each other. This leads to the failure of all equipment on the lower voltage especially the power transformer due to the resulting overvoltage. The proposed methodology depends on the combination between the sequence components of the currents from both sides of the transformer. Moreover, it uses the voltage measurements of the lower voltage side to detect the resulting overvoltage. The magnitude and phase angle of current measurements are computed using Fast Fourier Transform (FFT). The modelling and simulation of the fault between high-and medium-voltage are carried out using PSCAD/EMTDC program. The results reveal the accuracy, security and the applicability of the proposed methodology.