Search Results (61)

Nanocrystalline material provides an opportunity to improve the wideband performance of inductive current transformers and enables the possibility of ensuring their transformation accuracy for distorted and sinusoidal current from 50 Hz up to 20 kHz. Introduced in the year 2023, the standard IEC 61869-1 defines optional wideband accuracy classes for inductive current transformers with the WB2 class extension for harmonic frequencies up to 20 kHz. In this paper, design requirements in order to develop high accuracy 0.1-WB2 class wideband inductive current transformers compliant with the standards IEC 61869-1/2 are presented. It is shown that the main emphasis and design difficulties in ensuring high transformation accuracy still concern the lowest frequency of wideband operation—the fundamental component. However, it is of high importance that in order to obtain the highest possible wideband transformation accuracy of inductive current transformer for the low order higher harmonics, we ensure the lowest possible self-distortion of secondary current by minimalization of the load of its secondary winding is achieved—it should operate close to the short circuit conditions. Therefore, the low-power inductive CT should be designed and used for measurements in the power grid, as they will ensure the highest wideband transformation accuracy. Full article

This paper analyzes the power quality in a 400 kWp grid-connected solar photovoltaic system with storage (BESS), considering standards IEEE Std 519TM, IEEE Std 1159TM, and IEC 61000-4-30. For system analysis, a photovoltaic array model is developed. Neplan-Smarter Tools software is used for model validation, and experimental measurements are performed on the actual photovoltaic system, recording total harmonic distortion (THDi/THDv). A class B power quality monitor was used to measure three-phase electrical variables: current, voltage, power, power factor, and THD. The THD level was generated at an energy level below 20% of the rated power, resulting in high THDi. The recorded THDv remained below 2.5%, which means that its value is limited by the IEEE 519 standard. When the BESS was connected to the PCC grid, the voltage level remained regulated, and the electrical system appeared to be stable. This paper contributes a methodology and procedure for measurement and power quality assessment, allowing for THD identification and enabling designers to configure better designs and energy system protections when integrating solar photovoltaic energy into an electrical distribution network. Full article

Large amounts of high-quality data are required to train artificial intelligence (AI) models; however, curating such data through human intervention remains cumbersome, time-consuming, and error-prone. In particular, erroneous annotations and statistical imbalances in object detection datasets can significantly degrade model performance in real-world autonomous driving scenarios. This study proposes an automated pruning framework and quality assurance strategy for 2D object detection datasets to address these issues. The framework is composed of two stages: (1) noisy label identification and deletion based on labeling scores derived from the inference results of multiple object detection models, and (2) statistical distribution whitening based on class and bounding box size diversity metrics. The proposed method was designed in accordance with the ISO/IEC 25012 data quality standards to ensure data consistency, accuracy, and completeness. Experiments were conducted on widely used autonomous driving datasets, including KITTI, Waymo, nuScenes, and large-scale publicly available datasets from South Korea. An automated data pruning process was employed to eliminate anomalous and redundant samples, resulting in a more reliable and compact dataset for model training. The results demonstrate that the proposed method substantially reduces the amount of training data required, while enhancing the detection performance and minimizing manual inspection efforts. Full article

The new revision of the main instrument transformer standard, IEC 61869-1:2023, premiered requirements for the performance of instrument transformers in terms of transfer accuracy at higher frequencies. Five accuracy class extensions were introduced to establish an explicit performance level. Each of the extension levels has a distinct bandwidth and accuracy performance associated with it. While these requirements are mainly aimed at non-conventional instrument transformers, the hypothesis of this paper is that conventional high-voltage instrument transformers can have a performance conformant to the above-mentioned requirements. Specifically, the focus of this paper will be on open-core inductive voltage transformers, which inherently exhibit an improved frequency response in comparison to their conventional closed-core counterparts. The main aim of this paper is to present a relevant transformer model based on a lumped parameter equivalent diagram. This model considers the actual mutual coupling (both capacitive and inductive) of the transformer windings. The model is created in EMTP software, and the output yields a frequency response characteristic of the transformer. The model will be validated with test results obtained through measurements on actual 123 kV, 245 kV, and 420 kV inductive voltage transformers. Full article

Due to the economic and environmental concerns associated with fossil fuels, many government and private organizations are progressively shifting towards the integration of solar farms with Utility Grids. However, these systems are facing insulation failure issues due to internal and external transient overvoltage’s, in which their shape, magnitude, and duration are unpredictable, and consequently, the insulation stress also becomes unpredictable. To ensure the safety and integrity of the system against any transient overvoltage event, it is important to carry out an insulation coordination analysis. The primary goal of this research work is to achieve this optimization in an economically viable manner, ensuring both operational stability and cost-effectiveness in the design of electrical equipment like surge Arresters. The research work presented in the literature does not fully evaluate all International Electrotechnical Commission (IEC) overvoltage classes as specified in the insulation coordination standards for Utility Grids integrated with solar farms. Therefore, this research paper investigates the impact of various transient and switching overvoltage conditions, as defined in the IEC 60071.4 Insulation Coordination Standard at the Solar and Utility Grid Electrical power system using PSCAD 4.6/EMTP Software. Five distinct simulation scenarios were developed to assess the systems’ resilience against insulation stress events. The proposed system was also examined with and without the application of a lightning surge arrester. Full article

The mechanism underlying intestinal fibrosis, the main complication of inflammatory bowel disease (IBD), is not yet fully understood, and there is no therapy to prevent or reverse fibrosis. We evaluated, in in vitro cellular models, the ability of different classes of drugs currently used in IBD to counteract two pivotal processes of intestinal fibrosis, the differentiation of intestinal fibroblasts to activated myofibroblasts using CCD-18Co cells, and the epithelial-to-mesenchymal transition (EMT) of intestinal epithelial cells using Caco-2 cells (IEC), both being processes induced by transforming growth factor-β1 (TGF-β1). The drugs tested included mesalamine, azathioprine, methotrexate, prednisone, methylprednisolone, budesonide, infliximab, and adalimumab. The expression of fibrosis and EMT markers (collagen-I, α-SMA, pSmad2/3, occludin) was assessed by Western blot analysis and by immunofluorescence. Of the drugs used, only prednisone, methylprednisolone, budesonide, and adalimumab were able to antagonize the pro-fibrotic effects induced by TGF-β1 on CCD-18Co cells, reducing the fibrosis marker expression. Methylprednisolone, budesonide, and adalimumab were also able to significantly counteract the TGF-β1-induced EMT process on Caco-2 IEC by increasing occludin and decreasing α-SMA expression. This is the first study that evaluates, using in vitro cellular models, the direct antifibrotic effects of drugs currently used in IBD, highlighting which drugs have potential antifibrotic effects. Full article

Power quality measurements are essential to monitor, analyse and control the operation of smart grids within power systems. This work aims to develop and calibrate a PQ network analyser. As the penetration of non-linear loads connected to power systems is increasing every day, it is essential to measure power quality. In this sense, a power quality (PQ) analyser is based on the high-speed sampling of electrical signals in single-phase and three-phase electrical installations, which are available in real time for analysis using wireless Wi-Fi (Wireless-Fidelity) networks. The PQAE (Power Quality Analyser Embedded) power quality analyser has met the calibration standards for Class A devices from IEC 61000-4-30, IEC 61000-4-7 and IEC 62586-2. In this paper, a complete guide to the tests included in this standard has been provided. The Fast Fourier Transform (FFT) obtains the harmonic components from the measured signals and the window functions used reduce spectral leakage. The window size depends on the fundamental frequency of, intensity of and changes in the signal. Harmonic measurements from the 2nd to 50th harmonics for each phase of the voltage and each phase and neutral of the current have been performed, using the Fast Fourier transform algorithm with various window functions and their comparisons. PQAE is developed on an open-source platform that allows you to adapt its programming to the measurement needs of the users. Full article

The phenomenon of high-frequency distortion (HFD) in the electric grids, at both low-voltage (LV) and medium-voltage (MV) levels, is gaining increasing interest within the scientific and technical community due to its growing occurrence and the associated impact. These disturbances are mainly injected into the grid by new installed devices, essential for achieving decentralized generation based on renewable sources. In fact, these generation systems are connected to the grid through power converters, whose switching frequencies are significantly increasing, leading to a corresponding rise in the frequency of the injected disturbances. HFD represents a quite recent issue, but numerous scientific papers have been published in recent years on this topic. Furthermore, various international standards have also covered it, to provide guidance on instrumentation and related algorithms and indices for the measurement of these phenomena. When measuring HFD in MV grids, it is necessary to use instrument transformers (ITs) to scale voltages and currents to levels fitting with the input stages of power quality (PQ) instruments. In this respect, the recently released Edition 2 of the IEC 61869-1 standard extends the concept of the IT accuracy class up to 500 kHz; however, the IEC 61869 standard family provides guidelines on how to test ITs only at power frequency. This paper provides an extensive review of literature, standards, and the main outputs of European research projects focusing on HFD and ITs. This preliminary study of the state-of-the-art represents an essential starting point for defining significant waveforms to test ITs and, more generally, to achieve a comprehensive understanding of HFD. In this framework, this paper provides a summary of the most common ranges of amplitude and frequency variations of actual HFD found in real grids, the currently adopted measurement methods, and the normative open challenges to be addressed. Full article

The evolution of smart grids has led to technological advances and a demand for more efficient and sustainable energy systems. However, the deployment of communication systems in smart grids has increased the threat of cyberattacks, which can result in power outages and disruptions. This paper presents a semi-supervised hybrid deep learning model that combines a Gated Recurrent Unit (GRU)-based Stacked Autoencoder (AE-GRU) with anomaly detection algorithms, including Isolation Forest, Local Outlier Factor, One-Class SVM, and Elliptical Envelope. Using GRU units in both the encoder and decoder sides of the stacked autoencoder enables the effective capture of temporal patterns and dependencies, facilitating dimensionality reduction, feature extraction, and accurate reconstruction for enhanced anomaly detection in smart grids. The proposed approach utilizes unlabeled data to monitor network traffic and identify suspicious data flow. Specifically, the AE-GRU is performed for data reduction and extracting relevant features, and then the anomaly algorithms are applied to reveal potential cyberattacks. The proposed framework is evaluated using the widely adopted IEC 60870-5-104 traffic dataset. The experimental results demonstrate that the proposed approach outperforms standalone algorithms, with the AE-GRU-based LOF method achieving the highest detection rate. Thus, the proposed approach can potentially enhance the cybersecurity in smart grids by accurately detecting and preventing cyberattacks. Full article

In this paper, a single-stage step-down power factor corrector without a full-bridge rectifier is developed, which is designed to operate in discontinuous conduction mode (DCM). In terms of control, the DCM has the advantages of simple control and easy realization, no slope compensation, zero current switching, and no diode reverse current. By sampling the output voltage and using the voltage-follower control to generate the necessary control force to drive the power switch, not only can the output voltage be stabilized at the desired value, but also the input current can be, as much as possible, in the form of a sinusoidal waveform and can follow the phase of the input voltage. Moreover, the harmonic distortion meets the requirements of the IEC6100-3-2 Class D harmonics standard, and, thus, the proposed rectifier is appropriate for the computer, computer monitor, and television receiver. Eventually, by means of mathematical deductions, simulations by PSIM version 9.1, and experimental results, the feasibility and effectiveness of the proposed circuit can be verified. Full article

Europe has initiated the transition process toward IE4 efficiency motor classes, setting an example for other regions to follow in adopting higher-efficiency motor standards. However, in some regions, the operating voltage may differ from the nominal voltage according to the IEC 60038-2009. Therefore, the performance of new technologies under conditions of voltage variations (VVs) must also be assessed. This study presents a comprehensive analysis of a 0.75 kW line-start permanent-magnet motor (LSPMM) under different VV magnitudes, including undervoltage and overvoltage, while considering different load conditions. The study incorporates technical, economic, statistical, and thermal analyses to obtain important indicators related to power consumption, efficiency, power factor, and temperature. This study provides valuable insights to specialists regarding the technical and economic impacts of voltage-magnitude variation on LSPMMs. Full article

This paper proposes a novel phase-resolved partial discharge (PRPD) sensor embedded in a MV-class bushing for high-accuracy insulation analysis. The design, fabrication, and evaluation of a PRPD sensor embedded in a MV-class bushing aimed to achieve the detection of partial discharge (PD) pulses that are phase-synchronized with the applied primary HV signal. A prototype PRPD sensor was composed of a flexible printed circuit board (PCB) with dual-sensing electrodes, utilizing a capacitive voltage divider (CVD) for voltage measurement, the D-dot principle for PD detection, and a signal transducer with passive elements. A PD simulator was prepared to emulate typical PD defects, i.e., a metal protrusion. The voltage measurement precision of the prototype PRPD sensor was satisfied with the accuracy class of 0.2 specified in IEC 61869-11, as the maximum corrected voltage error ratios and corrected phase errors in 80%, 100%, and 120% of the rated voltage (13.2 kilovolts (kV)) were less than 0.2% and 10 min, respectively. In addition, the prototype PRPD sensor had good linearity and high sensitivity for PD detection compared with a conventional electrical detection method. According to performance evaluation tests, the prototype PRPD sensor embedded in the MV-class bushing can measure PRPD patterns phase-synchronized with the primary voltage without any additional synchronization equipment or system. Therefore, the prototype PRPD sensor holds potential as a substitute for conventional commercial PD sensors. Consequently, this advancement could lead to the enhancement of power system monitoring and maintenance, contributing to the digitalization and minimization of power apparatus. Full article

Regulating LED current and voltage is critical to maintaining a constant luminous flux in AC- or DC-powered LED lighting circuits. Today, users require constant current drivers that can provide a wide range of output voltages to drive different numbers of series-connected LED arrays. This work proposes an LED driver by combining an isolated SEPIC converter operating in the continuous conduction mode (CCM) and a modified Vienna rectifier. The proposed LED driver offers a single-switch control structure by adding a Vienna rectifier to the integrated SEPIC-FLYBACK converter. This driver structure provides many advantages over traditional bridge rectifier structures. The prototype circuit was tested in an 18 W continuous current mode (CCM) to verify its feasibility. As a result of the values obtained from both simulation and prototype circuit models, it has been shown to provide many of the following advantages: 95% high efficiency, high reliability, 4% low total harmonic distortion, 97% high power factor, and 70 V low switching voltage. This work meets class C 3-2 and IEC 61000 standards. Full article

This paper presents the evaluation of tested inductive CTs’ accuracy for distorted current harmonics in accordance with the optional accuracy class WB1 introduced by the new edition of the standard IEC 61869-1 published in the year 2023. The tests were performed in compliance with the interpretation sheet IEC 61869-2:2012/ISH1:2022. Therefore, the resistive and the resistive–inductive loads of the secondary winding of tested inductive CTs were used, as this was required for the given test conditions. The results indicate that the units designed for the transformation of a sinusoidal current of a frequency of 50 Hz ensure the high wideband transformation accuracy of the distorted current harmonics, as demanded by the power quality monitoring and distorted electrical power and energy requirements. The key to this is proper design using modern magnetic material(s) for the magnetic core and its oversizing in relation to the requirements for a given accuracy class defined for the transformation of sinusoidal currents with a rated frequency. Both tested inductive CTs with a rated primary current RMS value equal to 300 A, class 0.2 and 0.5, ensured compliance with the requirements of the WB1 wideband accuracy class. Full article

This paper presents the results of load capacity calculations for three-phase squirrel-cage induction motors supplied with distorted voltage with rotating harmonics. The calculations were made on the basis of a commonly used model of an induction machine. The difference from many papers is that the parameters of the equivalent circuit of each motor were precisely determined in terms of power losses in the motor. The load capacity of the motors was made dependent on the load power losses in the rotor cage. These losses were determined on the basis of short-circuit measurements of motors, made for frequencies equal to harmonic frequencies. Measurements and calculations were made for low-voltage squirrel-cage motors with rated powers of 4–65 kW and various efficiency classes. Calculations have shown that the calculated derating curves do not match the curves given in IEC 60034-17 and NEMA MG1. The differences are up to 15% for IE1 and IE2 motors and more than 50% for IE3 motors. Full article