Search Results (18)

In electrical power systems, shunt reactors control excess reactive power, keeping voltage levels within acceptable limits. As shunt reactors play a crucial role in the operation of electrical systems, it is essential to ensure the use of modern and fast protection schemes for these devices. Furthermore, protection functions must be capable of identifying various fault conditions, including critical operating situations such as turn-to-ground and turn faults, involving only a few short-circuited turns. This paper proposes a comparative evaluation of protection schemes commonly employed by manufacturers to meet the requirements of different grid codes. Thus, the investigation encompasses restricted earth fault, directional, differential, and distance functions. The latter is typically cited as a backup protection function. To support the analyses conducted, an electrical power system with shunt compensation was modeled in the ATPDraw software version 7.3. Through this platform, various internal fault conditions were simulated, encompassing turn-to-ground and turn faults. This facilitated the analysis of the influence of parameters such as the leakage factor value and the number of short-circuited turns. Additionally, external fault conditions were evaluated, including cases involving Current Transformer (CT) saturation. Full article

In a rail transit system, there is a constant leakage of current from the subway rails to the earth, and these stray currents have complex propagation paths and a wide range of influence. Since no stray current collection devices are installed at subway depots, some of the stray current leaking from the mainline will converge at the depot, seriously corroding the structural reinforcement and buried metal of the station, thereby jeopardizing the normal operation of subway trains and passenger safety. In this paper, a field-circuit coupling method is proposed to analyze the current leakage and distribution law of the subway mainline and depot. It is found that the failure of the gauge block at the mainline will trigger the maximum leakage of rail current. Additionally, it is observed that the stray current distribution at the depot is mainly influenced by the operating status of the one-way conduction device (OWCD) and the change of rail potential. These results validate the applicability and effectiveness of the field-circuit coupling method proposed in this paper and provide new technical support for the study of stray current leakage distribution in subways. Full article

This paper investigates the issue of leakage current at the transmitter in the Dynamic Wireless Power Transfer (DWPT) system for electric vehicles and puts forward a novel bilateral resonant compensation topology structure based on the conventional LCC-S architecture. Based on the LCC-S framework, a circuit model was developed for traditional (unilateral)/bilateral resonant compensation topologies. The Fourier series voltage-to-earth expansions for the power supply rail were deduced for both topologies. Subsequently, the voltage-to-earth waveforms for the power supply rail were obtained by utilizing the Fourier series expansions of the voltage-to-earth and the corresponding circuit simulation models. The results demonstrate the efficacy of the bilateral resonant compensation topology in mitigating higher-order harmonics of the voltage to earth on the power supply rail by effectively suppressing the distortion in the leakage current and minimizing its conduction. The effectiveness of the double-ended resonant compensation topology in suppressing leakage current conduction has been verified through experimental tests and waveform comparisons of the voltage to earth and leakage current on the power supply rail under two different topologies. Through experimental testing, during which the unilateral/bilateral resonant compensation topologies were compared, an analysis was conducted on the waveforms of the voltage to earth and leakage current of the power supply rail. The results verified the effectiveness of the bilateral resonant compensation topology in mitigating the conduction of leakage current. This study provides empirical evidence supporting the use of the bilateral resonant compensation topology for suppressing leakage current in power rail applications. Full article

Under the premise of using the solid-phase method to pre-sinter Bi₂O₃ and Sb₂O₃ into BiSbO₄ as a substitute for equal amounts of Bi₂O₃ and Sb₂O₃ in the formula, the effects of co-doping with In(NO₃)₃, Al(NO₃)₃, and Y(NO₃)₃ on the microstructure and electrical properties of ZnO varistors were studied. The experimental results show that with an increase in In³⁺-doped molar concentration, the leakage current of the ZnO varistor shows a rapid decrease and then a slow increase trend. However, the nonlinear coefficient is the opposite of it. With the combined effect of the rare earth element Y³⁺, the average grain size is significantly reduced, which leads to an increase in the voltage gradient. At the same time, a certain amount of doped In³⁺ and Al³⁺ is dissolved into the grains, resulting in a decrease in grain resistance and thus a low level of residual voltage. The varistor with 0.6 mol% In³⁺, 0.1 mol% Al³⁺, and 0.9 mol% Y³⁺ doping ratios exhibits excellent overall performance. The nonlinear coefficient is 62.2, with the leakage current being 1.46 µA/cm² and the voltage gradient being 558 V/mm, and the residual voltage ratio is 1.73. The prepared co-doped ZnO varistors will provide better protection for metal oxide surge arresters. Full article

Grid converters play a central role in renewable energy conversion. Among all inverter topologies, the current source inverter (CSI) provides many advantages and is, therefore, the focus of ongoing research. This review demonstrates how CSIs can play a pivotal role in ensuring the seamless conversion of solar-generated energy with the electricity grid, thereby facilitating stable and reliable integration. This study extensively investigates various categories of single-stage CSI photovoltaic inverters, categorizing them into two-level, three-level, and multi-level architectures. Furthermore, these inverters are classified based on construction attributes, power factor, and total harmonic distortion values to assess their compliance with the standards, such as IEEE 1547 and IEC 61727. This review also delves into diverse control strategies for seamless grid integration. This comprehensive assessment serves as a resource for researchers in the field, enabling them to effectively choose the most suitable CSI for their specific applications. Additionally, it offers a quick reference point to steer research endeavors toward refining the integration of CSIs within photovoltaic systems. Full article

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. Full article

This article reviews the progress in developing ZnO-V₂O₅-based metal oxide varistors (MOVs) using powder metallurgy (PM) techniques. The aim is to create new, advanced ceramic materials for MOVs with comparable or superior functional properties to ZnO-Bi₂O₃ varistors using fewer dopants. The survey emphasizes the importance of a homogeneous microstructure and desirable varistor properties, such as high nonlinearity (α), low leakage current density (J_L), high energy absorption capability, reduced power loss, and stability for reliable MOVs. This study investigates the effect of V₂O₅ and MO additives on the microstructure, electrical and dielectric properties, and aging behavior of ZnO-based varistors. The findings show that MOVs with 0.25–2 mol.% V₂O₅ and MO additives sintered in air over 800 °C contain a primary phase of ZnO with a hexagonal wurtzite structure and several secondary phases that impact the MOV performance. The MO additives, such as Bi₂O₃, In₂O₃, Sb₂O₃, transition element oxides, and rare earth oxides, act as ZnO grain growth inhibitors and enhance the density, microstructure homogeneity, and nonlinearity. Refinement of the microstructure of MOVs and consolidation under appropriate PM conditions improve their electrical properties (J_L ≤ 0.2 mA/cm², α of 22–153) and stability. The review recommends further developing and investigating large-sized MOVs from the ZnO-V₂O₅ systems using these techniques. Full article

Utility grid-tied photovoltaic (PV) installations are becoming a typical component of the current electrical energy grid. The adoption of transformerless inverters has recently changed the topology of these systems. Despite being small, inexpensive, and effective, transformerless inverters have a recurring leakage current issue. Numerous studies are being conducted to improve its performance and bring the leakage current down to acceptable levels. The studies propose three tracks for addressing the leakage current problem of transformerless PV systems: the control technique, the inverter modulation, and the inverter topology. This study applies the model-free predictive control (MFPC) technique to a grid-connected NPC 3-φ transformerless converter powered by a PV panel. An LCL filter connects the transformerless inverter to the grid. The system model considers the grid filter components and the internal impedance of the utility grid. The proposed system’s discrete model is established before describing the MFPC controller’s algorithm. The suggested system is simulated in MATLAB using the MFPC and a standard PI current controller with SVPWM modulation. According to the simulation’s findings, the MFPC controller performs best regarding current spectrum, THD, and earth leakage current. Additionally, MFPC-based systems are more efficient than those that use PI controllers. Full article

There is increasing utilization of photovoltaic (PV) grid-connected systems in modern power networks. Currently, PV grid-connected systems utilize transformerless inverters that have the advantages of being low cost, low weight, a small size, and highly efficient. Unfortunately, these inverters have an earth leakage current problem due to the absence of galvanic isolation. This phenomenon represents safety and electrical problems for those systems. Recently, the H8 transformerless inverter was introduced to eliminate the earth leakage current. The present study proposes improving the performance of an H8 transformerless inverter using model predictive control (MPC). The inverter was supplied by PV energy and attached to the grid through an LCL filter. During system modeling, the grid weakness was identified. The discrete model of the overall system, including the PV panel, the boost converter, the H8 transformerless inverter, and the controllers, was derived. Then, the introduced H8 transformerless inverter system was simulated and analyzed by the Matlab/Simulink program. The proposed system response using MPC was tested under step disturbances in the PV insolation level. Moreover, the effect of the weak and strong grid operations was considered. The simulation results indicate that the MPC controller has better performance and high-quality injected power. Despite the excellent performance of the strong grid, the nearly weak grid performance is acceptable. Moreover, the Hardware-in-the-Loop (HIL) of the proposed system was implemented using the DSP target LaunchPadXLTMS320F28379D kit to validate the simulation results. Finally, the system performance under the parameter variations showed good robustness. Full article

We perform first-principles calculations to explore the electronic, thermodynamic and dielectric properties of two-dimensional (2D) layered, alkaline-earth hydroxides Ca(OH)${}_2$ and Mg(OH)${}_2$. We calculate the lattice parameters, exfoliation energies and phonon spectra of monolayers and also investigate the thermal properties of these monolayers, such as the Helmholtz free energy, heat capacity at constant volume and entropy as a function of temperature. We employ Density Functional Perturbation Theory (DFPT) to calculate the in-plane and out-of-plane static dielectric constant of the bulk and monolayer samples. We compute the bandgap and electron affinity values using the HSE06 functional and estimate the leakage current density of transistors with monolayer Ca(OH)${}_2$ and Mg(OH)${}_2$ as dielectrics when combined with HfS${}_2$ and WS${}_2$, respectively. Our results show that bilayer Mg(OH)${}_2$ (EOT∼0.60 nm) with a lower solubility in water offers higher out-of-plane dielectric constants and lower leakage currents than does bilayer Ca(OH)${}_2$ (EOT∼0.56 nm). Additionally, the out-of-plane dielectric constant, leakage current and EOT of Mg(OH)${}_2$ outperform bilayer h-BN. We verify the applicability of Anderson’s rule and conclude that bilayers of Ca(OH)${}_2$ and Mg(OH)${}_2$, respectively, paired with lattice-matched monolayer HfS${}_2$ and WS${}_2$, are effective structural combinations that could lead to the development of innovative multi-functional Field Effect Transistors (FETs). Full article

A new Single-sided Variable Flux Permanent Magnet Linear Machine with flux bridge in mover core is proposed in this paper. The flux bridge prevents the leakage flux from the mover and converts it into flux linkage, which greatly influences the performance of the machine. First, a lumped parameter model is used to find the suitable coil combination and no-load flux linkage of the proposed machine, which greatly reduces the computational time and drive storage. Secondly, the proposed machine replaces the expensive rare earth permanent magnets with ferrite magnets and provides improved flux controlling capability under variable excitation currents. Multivariable geometric optimization is utilized to optimize the leading design parameters like split ratio, stator pole width, width and height of permanent magnet, flux bridge width, the width of mover’s tooth, and stator slot depth at constant electric and magnetic loading. The optimized design increases the flux linkage by 44.11%, average thrust force by 35%, thrust force density by 35.02%, minimizes ripples in thrust force by 23%, and detent force by 87.5%. Furthermore, the results obtained by 2D analysis are verified by 3D analysis. Thermal analysis is done to set the operating limit of the proposed machine. Full article

As the physical size of MOSFET has been aggressively scaled-down, the impact of process-induced random variation (RV) should be considered as one of the device design considerations of MOSFET. In this work, an artificial neural network (ANN) model is developed to investigate the effect of line-edge roughness (LER)-induced random variation on the input/output transfer characteristics (e.g., off-state leakage current (Ioff), subthreshold slope (SS), saturation drain current (Id,sat), linear drain current (Id,lin), saturation threshold voltage (Vth,sat), and linear threshold voltage (Vth,lin)) of 5 nm FinFET. Hence, the prediction model was divided into two phases, i.e., “Predict Vth” and “Model Vth”. In the former, LER profiles were only used as training input features, and two threshold voltages (i.e., Vth,sat and Vth,lin) were target variables. In the latter, however, LER profiles and the two threshold voltages were used as training input features. The final prediction was then made by feeding the output of the first model to the input of the second model. The developed models were quantitatively evaluated by the Earth Mover Distance (EMD) between the target variables from the TCAD simulation tool and the predicted variables of the ANN model, and we confirm both the prediction accuracy and time-efficiency of our model. Full article

The rise in renewable energy has increased the use of DC/AC converters, which transform the direct current to alternating current. These devices, generally called inverters, are mainly used as an interface between clean energy and the grid. It is estimated that 21% of the global electricity generation capacity from renewable sources is supplied by photovoltaic systems. In these systems, a transformer to ensure grid isolation is used. Nevertheless, the transformer makes the system expensive, heavy, bulky and reduces its efficiency. Therefore, transformerless schemes are used to eliminate the mentioned disadvantages. One of the main drawbacks of transformerless topologies is the presence of a leakage current between the physical earth of the grid and the parasitic capacitances of the photovoltaic module terminals. The leakage current depends on the value of the parasitic capacitances of the panel and the common-mode voltage. At the same time, the common-mode voltage depends on the modulation strategy used. Therefore, by the manipulation of the modulation technique, is accomplished a decrease in the leakage current. However, the connection standards for photovoltaic inverters establish a maximum total harmonic distortion of 5%. In this paper an analysis of the common-mode voltage and its influence on the value of the leakage current is described. The main topologies and strategies used to reduce the leakage current in transformerless schemes are summarized, highlighting advantages and disadvantages and establishing points of comparison with similar topologies. A comparative table with the most important aspects of each converter is shown based on number of components, modes of operation, type of modulation strategy used, and the leakage current value obtained. It is important to mention that analyzed topologies present a variation of the leakage current between 0 to 180 mA. Finally, the trends, problems, and researches on transformerless grid-connected PV systems are discussed. Full article

Due to the working condition of low-voltage cabling from the mining flameproof movable substation to the loads of the mining face being poor, it is easy to cause various external mechanical damages to the cable sheaths. Furthermore, a single-phase earth leakage fault or short-circuit fault can occur when the low-voltage cable sheaths are damaged, and electric sparks caused by these faults can lead to a gas explosion. As the gas detonation time caused by the above faults is usually more than 5 ms, the high-speed interruption solid-state switch which controls the cables must cut off the current within 3 ms. This requires the action time of the solid-state switch to be less than 1 ms, and at the same time, the sampling and calculation time of the relay protection must be less than 2 ms. Based on these problems, this paper proposes the use of a high-speed solid-state circuit breaker (SSCB) topology at the neutral point of transformer, and analyzes the conduction mechanism and shut-off mechanism of the current of the SSCB. It presents an ultra-high-speed algorithm based on pattern recognition of single-phase earth leakage fault protection, and an ultra-high-speed algorithm of short-circuit fault which is based on the rate-of-change of the current. Finally, through computer simulation experiments and semi-physical simulation experiments, the feasibility of the above three technologies is verified to ensure that when a single-phase earth leakage fault or short-circuit fault occurs in the low-voltage cable, the solid-state switch which is installed in the mining flameproof movable substation will cut off the current within 3 ms. Full article

Grid-connected photovoltaic (PV) systems are now a common part of the modern power network. A recent development in the topology of these systems is the use of transformerless inverters. Although they are compact, cheap, and efficient, transformerless inverters suffer from chronic leakage current. Various researches have been directed toward evolving their performance and diminishing leakage current. This paper introduces the application of a model predictive control (MPC) algorithm to govern and improve the performance of a grid-tied neutral-point-clamped (NPC) 3-φ transformerless inverter powered by a PV panel. The transformerless inverter was linked to the grid via an inductor/capacitor (LC) filter. The filter elements, as well as the internal impedance of the grid, were considered in the system model. The discrete model of the proposed system was determined, and the algorithm of the MPC controller was established. Matlab’s simulations for the proposed system, controlled by the MPC and the ordinary proportional–integral (PI) current controller with sinusoidal pulse width modulation (SPWM), were carried out. The simulation results showed that the MPC controller had the best performance for earth leakage current, total harmonic distortion (THD), and the grid current spectrum. Also, the efficiency of the system using the MPC was improved compared to that using a PI current controller with SPW modulation. Full article