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Due to the erratic switching phenomenon of the Si avalanche bipolar junction transistor (ABJT) in the Marx bank circuit (MBC), an explanation of the leakage current trigger mode in the overvoltage state with a lack of displacement current is proposed. There are random switching properties (i.e., switching or non-switching) in the ABJT with emitter–base shorted, triggered by a voltage ramp to the overvoltage state temporarily with dV/dt rate close to 0 V/ns. The experimental conditions and characteristics of erratic behaviors are summarized. The optical visualization of the current channel in an erratic switching state is obtained, and the corresponding physical model of the leakage current trigger mode is established. It shows that the switching event occurs with the change in the position of the conductive channel. The process of emitter electron injection is caused by the leakage current in the overvoltage state instead of the displacement current. Meanwhile, the intensity of this trigger mode is weak, and the instability of the leakage current may cause the failure of switching. The study of erratic switching is of great significance for the working reliability of MBCs and failure analysis of ABJTs. The proposed explanation is validated by the agreement between the simulation results and the experimental observations. [ABSTRACT FROM AUTHOR]

Renewable energy‐based distributed generation presents new challenges for power inverters, requiring greater flexibility, reliability, cost‐effectiveness, and efficiency. Impedance source network‐based inverters (INIs) are an attractive option for addressing some of these issues since they provide a single‐stage power conversion structure with buck‐boost capability, allowing them to manage shoot‐through conduction on the inverter arms. However, some INI topologies based on magnetic coupling, such as those of the Y‐source impedance network family, have problems related to overvoltages at the power switches because of the presence of unwanted leakage inductances in the coupled‐inductor windings. The insertion of the regenerative and passive LCD snubber in the impedance network circuit is a solution to mitigate this problem, but there is currently a lack of a clear and concise methodology to design its components, which hinders a wider adoption of this solution in different types of INI. This paper presents a comprehensive and analytical design for determining LCD snubber components. This study was carried out with the quasi‐Y‐source inverter, but the same methodology can be extended to other types of INI based on the Y‐source network. [ABSTRACT FROM AUTHOR]

Oxygen mobility was studied by oxygen isotopic exchange on three electrodes used in Solid Oxide Electrolyser Cells under polarization (La0.8Sr0.2MnO3 (LSM), La0.6Sr0.4Co0.2Fe0.8O3‐δ (LSCF) and La2NiO4+δ (LNO)). The rate of the surface and the bulk mechanisms for oxygen mobility is depending on the type of conductivity (electronic conduction or mixed ionic and electronic conductivity). It is shown that a one oxygen atom exchange is dominant for the surface path whereas a two oxygen atoms mechanism dominates for the bulk path. The rate constant for the bulk path is much higher than the one for the surface path by two orders of magnitude. Additionally, polarized oxygen isotopic exchange revealed that electrode overvoltage increases significantly the rate constant for the surface path, whereas its impact on the bulk path is negligible. [ABSTRACT FROM AUTHOR]

The single switch resonant circuit can generate high-voltage pulses using only one switch, however, when the switch is turned off at a positive resonant current, a turn off overvoltage is generated, which damages the switch. To solve this problem, the RCD (Resistance Capacitance Diode) snubber circuit is paralleled with the switch or the RD (Resistance Diode) freewheeling branch is paralleled with the primary side of the trans- former. However, under high voltage pulse conditions, the loading characteristics and effects of the two overvoltage suppression circuits under different loads are still unclear. This study compares and analyzes the overvoltage suppression mechanism, parameter selection basis, overvoltage suppression effect and the components power loss of the two circuits. The results show that the overvoltage of the power supply switch with RD branch is proportional to the leakage inductance current and the resistance R of the branch. If R is larger, its overvoltage coefficient is larger than that of the power supply with RCD absorption circuit. And if R is smaller, the components power loss is large. In a high voltage pulse power supply, the capacitance of the RCD snubber circuit does not need to discharge the power. Due to the limitation of leakage inductance, when the resonant pulse circuit is short-circuited, the current is not too large to burn the switch. When driving the capacitive dielectric barrier discharge, the current can be reversed automatically to achieve zero current shutdown. [ABSTRACT FROM AUTHOR]

Electrical power systems represent an immense source of electromagnetic radiation spanning a wide frequency range, encompassing low-frequency, transient states, and high-frequency emissions. The radiation poses a significant self-pollution challenge for electric and electronic devices situated in close proximity to these systems. The present article aims to address this research, and provides a comprehensive review of the electromagnetic effects and pollution at differences frequency's ranges encompassing power systems network. In the context of the low-frequency range, the computation of electric and magnetic fields is conducted using quasi-static principles. To validate the behavior at high frequencies due to power line currents, Schelkunoff's approach is employed. Additionally, transient electromagnetic fields are analyzed using an exact analytical method. The results of computer simulations are compared with previously published and measured data for low-frequency regime and transient overvoltage conditions, verifying their consistency. Additionally, high-frequency results are presented and corroborated through the utilization of a numerical electromagnetic code (NEC-4). These analyses underscore the valuable role of computer-based calculations in examining the electromagnetic environment of power system networks. [ABSTRACT FROM AUTHOR]

Power grid modernization is often associated with new projects that imply the transmission network expansion, where transient overvoltages related to energization maneuvers must be studied in advance using suitable tools that consider the transmission line characteristics. Switching transient analysis is one of the options to deal with this phenomenon, but statistical switching analysis is the preferred tool to carry out multiple simulations. As opposed to existing works, this paper proposes a comprehensive approach for the statistical switching in double-circuit transmission lines based on existing transmission infrastructure that requires the installation of double-line circuits or resizing the existing ones. The switching sequence of circuit breakers based on distribution functions are discussed in detail, which are generalized using different standard deviations. Pre-insertion resistors and shunt reactors are also considered in this methodology, enabling practical results related to the calculation of the basic insulation level. All these aspects combined permit to establish the minimal requirements for the insulation coordination in double-circuit transmission lines from a practical standpoint. To showcase the method's practicality, the switching analysis of a 300-km double-circuit transmission line is conducted using the EMTP/ATP simulation package. Energization maneuvers with pre-insertion resistors and shunt reactors are studied, considering the transmission line operation at 230 and 400 kV, concluding that the minimal requirement of protection against transient overvoltages must be around 1.35 p.u. [ABSTRACT FROM AUTHOR]

High torque ripple can be observed with a 6/4 variable flux reluctance machine (VFRM). In order to minimize the torque ripple in VFRMs, this paper presents a harmonic injection method for 6/4 VFRMs with an open-winding configuration. By analyzing the impact of harmonics on VFRMs, the method involves detecting the third harmonic using a first-order low-pass filter (FLPF). Subsequently, the extracted harmonics are controlled and shifted to counteract the voltage harmonics in both inverters without inducing phase imbalance or overvoltage. With the proposed method, the torque ripple can be significantly reduced by about 50% under load conditions. The effectiveness of the harmonic injection method is validated through a prototype VFRM. [ABSTRACT FROM AUTHOR]

This paper introduces a Fuzzy Logic Controller designed for an on-load tap changer within medium voltage distribution systems with bulk penetration of Distributed Energy Resources. As the on-load tap changer remains one of the most essential forms of voltage regulation in medium voltage distribution networks, improving its operation is a cost-effective response to the emerging voltage violations caused by intermittent generation during the early stages of the energy system transformation. Software-in-the-loop simulations were conducted to validate the effectiveness of the proposed algorithm compared to the conventional methods. A modified CIGRE Medium Voltage Distribution Network Benchmark in European Configuration was modelled while the controller code developed in Python 3.12 was running on a PC, both coupled in a real-time closed-loop environment. The analyses showed that the proposed algorithm managed to reduce overvoltage from 7.02% to 4.85% in the benchmark network, thus demonstrating that the algorithm is efficient and ready for on-field implementation. [ABSTRACT FROM AUTHOR]

The paper is devoted to the development of a device for protecting facilities with turn-to-turn insulation, namely transformers and wind generators in order to increase the reliability of operation of electrical power systems, renewable energy installations and energy storage systems. The paper presents the results of experimental studies of the parameters of a prototype frequency-dependent device, as well as an assessment of the effectiveness of suppression of high-frequency surge voltages by the proposed device. The results of four groups of measurements are shown, which were compared with each other and with the results of previously showed computer simulations. The high efficiency of the proposed device when influencing the slope and amplitude of short high-frequency transients is shown. It is indicated that the parameters proposed earlier in the simulation allow the device to be used effectively. A brief analysis of alternative methods and means of protection is provided, and the prospects for using the device as protective equipment for wind power plants are also considered. [ABSTRACT FROM AUTHOR]

Ferroresonance in power networks is a dangerous phenomenon, which may result in overcurrents and overvoltages, causing damage to power equipment and the faulty operation of protection systems. For this reason, the possibility of the occurrence of ferroresonance has to be identified, and adequate methods need to be incorporated to eliminate or reduce its effects. The aim of this paper is to evaluate the effectiveness of ferroresonance damping in auxiliary power systems of high-voltage substations by selected damping devices. Laboratory experiments, the results of which created bases for the development of models of selected damping devices, are presented. These models were used to simulate the effectiveness of ferroresonance damping in an auxiliary power system of a 220/110 kV substation in the EMTP-ATP program. The analyses showed that control systems with different algorithms of operation are used in damping devices. This knowledge is important when selecting parameters and settings of the applied damping devices for a given network and the disturbances in it. The presented research results have proved the effectiveness of commercially available damping devices, provided their parameters are correctly coordinated with the settings of the power system protection. [ABSTRACT FROM AUTHOR]

8/20 µs lightning pulse current generators (LPCG) used in testing surge arresters require a laborious production process that needs a high budget. An easily repairable, portable, and affordable test system with a maximum energy of 2.9 kJ and a voltage level of 24 kV that can alter its parameter values was described in this work. Simulation and experimental studies were carried out to investigate the effects of the resistor and coil elements in the Pulse Current Generator (PCG) circuit on the amplitude, front, and tail time of the pulse current. Most components of the experimental system were created using 3D printing technology with polylactic acid (PLA) material. The production costs were significantly reduced, according to equivalent pulse generators. Tests at different pulse currents and voltage levels were performed with the experimental system. Power capacitors may often fail due to overvoltage, switching, and partial discharge reasons. The high voltage (HV) power capacitors used in the pulse generator introduced in the study were obtained with the help of low voltage capacitor stacks. As a result, a less expensive, high-capacity capacitor system that is easily and quickly repairable in case of failure was achieved. [ABSTRACT FROM AUTHOR]

In order to improve the immunity and speed tracking performance of active inverters in resonant overvoltage flexible suppression under load variation, parameter perturbation, and other uncertainties, a current control strategy of a resonant overvoltage flexible grounding device based on a cascading linear-nonlinear active disturbance rejection controller is proposed in this paper. First, the mathematical model of the flexible device considering load disturbance and parameter mismatch is established. Second, a cascade of linear and nonlinear extended state observers is designed to estimate and compensate the uncertain disturbance of the system in real time. The former linear extended state observer ensures the stability of the system under large disturbance, and the latter nonlinear extended state observer further improves the estimation accuracy of the disturbance by using the nonlinear mechanism. Finally, the flexible grounding system based on PI control and cascaded linear-nonlinear active disturbance rejection control (CL-NLADRC) is simulated and compared. Compared with PI control, NLADRC, and CLADRC, the current drop of the proposed CL-NLADRC during loading is 0.03 kA, which is 81.1%, 85.7%, and 73% of the three, respectively, and the regulation time is 13 ms, which is 82%, 75%, and 18.7% shorter than the three, respectively. The speed increase during load shedding is 93.5%, 80.5%, and 74.3% of the three, and the adjustment time is shortened by 80%, 73%, and 28%, respectively. The superiority of the proposed method is verified. [ABSTRACT FROM AUTHOR]

Currently, various light-emitting diode (LED) lighting systems are being developed because LEDs are one of the most used lighting sources for work environments, buildings, homes, and public roads in terms of some of their applications. Similarly, they have low energy consumption, quick responses, and excellent optimal performance in their operation. However, these systems still need to precisely regulate lighting, maintain stable voltage and current in the presence of faults and disturbances, and have a wide range of operations in the event of trajectory changes or monitoring tasks regarding the desired voltage and current. This work presents the design and application of two types of robust controllers (structure-at-infinity control and geometric control) applied to an LED driver using a buck converter. The controllers aim to follow the desired trajectories, attenuate disturbances at the power supply input, and compensate for faults in the actuator (MOSFET) to keep the capacitor voltage and inductor current stable. When comparing the results obtained with the two controllers, it was observed that both present excellent performance in the presence of constant disturbances. However, in scenarios in which variable faults and path changes are implemented, the structure-at-infinity control method shows an overimpulse of output voltage and current ranging from 39 to 42 volts and from 0.3 to 0.45 A, with a margin of error of 1%, and it can generate a failure in the LED driver using a buck converter. On the other hand, when using geometric control, the results are satisfactory, achieving attenuating constant disturbances and variable faults, reaching the desired voltage (40 v to 35 v) and current (0.3 to 0.25 A) with a margin of error of 0.05%, guaranteeing a system without overvoltages or the accelerated degradation of the components due to magnetic conductivity. [ABSTRACT FROM AUTHOR]

For producing hydrogen from renewable energy, a proton exchange membrane water electrolyzer (PEMWE) is an appealing method offering higher current density and purity of generated hydrogen than other electrolyzers. However, this technique should be further developed to have higher efficiency for utilization. The main issue on reducing the PEMWE performance is the management of generated oxygen bubbles near the reaction site. They persist near the reaction site, inhibit the water supply, and significantly reduce the reaction efficiency. Therefore, how oxygen bubbles are removed from the reaction site should be optimized, however, the mechanism of transport phenomena of oxygen bubbles through the porous transport layer (PTL) has not been clarified. Therefore, in this study, an original cell was developed which allowed us to observe bubble movements inside PTL with a high-speed camera, and the effects of PTL wettability on the oxygen bubble movement were investigated. The PTL wettability drastically affected the PEMWE performance and bubble movement, and hydrophobic PTL reduced the PEMWE performance. The oxygen bubbles tended to stay inside hydrophobic PTL, which might cause lower PEMWE performance. [Display omitted] • Oxygen mass transport was studied in a proton exchange membrane water electrolyzer. • Oxygen bubble movement was observed inside operating PEMWE. • Wettability largely affected PEMWE performance, facilitating bubble removal from PTL. • Mass transport overvoltage is discussed with three factors. • Drying ionomer is one candidate for mass transport overvoltage. [ABSTRACT FROM AUTHOR]

To achieve the transient overvoltage suppression of doubly fed induction generator (DFIG) terminals and the point of common coupling (PCC) in the wind farm (WF), an adaptive overvoltage control strategy based on data‐driven approach is proposed. Firstly, the PCC reactive power demand and DFIG overvoltage threshold are derived, respectively. Secondly, three regression models are developed through surface fitting to determine three variables: the maximum overvoltage of each DFIG, the PCC maximum overvoltage, and the reactive power demand of each DFIG. Subsequently, the K‐means clustering method is adopted to group all DFIGs, and then the reactive power requirement of the PCC is proportionally distributed to each group of DFIGs. Lastly, a coordinated control strategy of DFIGs and static var generator (SVG) is designed based on the values of three regression models, which can adaptively adjust the reactive power absorbed by each DFIG and SVG. In particular, the de‐load control is adopted to enlarge the maximum reactive power capacity of DFIG. The simulation results show that the proposed control strategy can timely and effectively restore the transient overvoltage of the wind farm to the normal range during the gird failure, ensuring the stable operation of the wind farm. [ABSTRACT FROM AUTHOR]

In order to further improve the defect detection capability of gas insulated switchgear and avoid equipment faults, broadband current array sensing system is designed to simultaneously monitor the system status such as partial discharge, relative dielectric loss, and power frequency overvoltage. The dynamic model of the system is analysed, and based on which, the system state equation is obtained meanwhile fault observer is designed, and the system stability criterion under H∞ condition is calculated. The reliability of the system under different packet loss rates is verified based on cloud models, and the principle of using appropriate electromagnetic compatibility to prevent packet loss rates below 50% is proposed. [ABSTRACT FROM AUTHOR]

In recent years, linearization technology for nonlinear devices has become a hot topic in many fields. In this study, a linear voltage divider based on metal oxide arresters was designed by combining linearization technology and electrical measurement technology to solve the objective problems of online voltage monitoring. These problems include high difficulty in equipment installation, low measurement accuracy, and poor economic benefits. Based on a summary of linearization theory, the sufficient and necessary conditions for the linearization of the voltage divider were deduced in detail. The relevant circuit simulations were conducted, along with voltage divider experiments under power frequency AC voltage, operating overvoltage, and lightning overvoltage. The results revealed that the voltage divider was able to realize linearized measurements and meet the relevant standards of online voltage monitoring. The measurement errors were concentrated in the transition region between the pre-breakdown region (small current region) and the breakdown region (nonlinear region) in the volt–ampere characteristic curve. The main influencing factor of errors was the consistency of the nonlinear characteristics of the high- and low-voltage arms of the voltage divider. The voltage divider designed in this study can be applied in many scenarios, such as power plants, substations, high-voltage electrical equipment manufacturing plants, and high-voltage laboratories. [ABSTRACT FROM AUTHOR]

Recently, there has been a significant increase in the integration of distributed energy resources (DERs) such as small-scale photovoltaic systems and wind turbines in power distribution systems. When the aggregated outputs of DERs are combined, excessive reverse current may occur in distribution lines, leading to overvoltage issues and exceeding thermal limits of the distribution lines. To address these issues, it is necessary to limit the output of DERs to a certain level, which results in constraining the hosting capacity of DERs in the distribution system. In this paper, coordination control methodologies of DERs are developed and executed to mitigate the overvoltage and overcurrent induced by DERs, thereby increasing the hosting capacity for DERs of the distribution system. This paper proposes three coordinated approaches of active and reactive power control of DERs, namely Var Precedence, Watt Precedence, and Integrated Watt and Var Control. The Var and Watt Precedence prioritizes reactive power for voltage (Q–V) and active power for current (P–I) to address network congestion, thereby enhancing hosting capacity. Conversely, the Integrated Var and Watt Precedence propose a novel algorithm that combines four control indices (Q–V, P–V, Q–I, and P–I) to solve network problems while maximizing hosting capacity. The three proposed methods are based on the sensitivity analysis of voltage and current to the active and reactive power outputs at the DER installation locations on the distribution lines, aiming to minimize DER active power curtailment. Each sensitivity is derived from linearized power equations at the operating points of the distribution system. To minimize the computation burden of iterative computation, each proposed method decouples active and reactive power and proceeds with sequential control in its own unique way, iteratively determining the precise output control of distributed power sources to reduce linearization errors. The three proposed algorithms are verified via case studies, evaluating their performance compared to conventional approaches. The case studies exhibit superior control effectiveness of the proposed DER power control methods compared to conventional methods when issues such as overvoltage and overcurrent occur simultaneously in the distribution line so that the DER hosting capacity of the system can be improved. [ABSTRACT FROM AUTHOR]

This article proposes a modular system for prosumer installations composed of photovoltaic (PV) panels and energy storage (ES) integrated with the low voltage (LV) network through a common 4-wire AC/DC inverter. The novel idea is a control strategy for the inverter in which additional functionalities are incorporated. Apart from transmitting an active power generated by the PV source, the same inverter is used to manage energy generated by the PV and to compensate for the current unbalance, harmonics (including subharmonics and interharmonics) and reactive power of the prosumer loads. As a result of the algorithm operation, the currents flowing to the prosumer installation are sinusoidal, symmetrical and purely active, which results in voltage balancing and improving voltage waveforms at the point of common coupling (PCC). In this way, with the widespread use of this solution among prosumers, the impact of the prosumer installation on the distribution network is minimized, and power quality (PQ) disturbances such as unacceptable voltage rises, voltage unbalance and harmonics are avoided. The presented approach may be a solution to the problems network operators face nowadays due to the uncontrolled connection of PV sources. The proposed modular system is also beneficial for the prosumer as the instances of unacceptable overvoltage and, consequently, shutdowns of prosumer installations are reduced. The features of the proposed method are shown in relation to other means applied for PQ improvement in the networks with distributed generation. A principle of the control and the involving algorithm for the inverter is presented. The efficiency of the control strategy was tested in a simulation developed in the PSCAD/EMTDC program. The results of simulations are presented, and the proposed solution is concluded. [ABSTRACT FROM AUTHOR]

Commutation failures in high-voltage direct current (HVDC) transmission systems often occur within inverter stations, posing challenges to the safe and consistent operation of HVDC transmission projects. This paper examines data gathered from a wide-spectrum transient electromagnetic voltage monitoring apparatus. The findings uncover a notable correlation between transient AC bus voltage disturbances, stemming from faults, and the occurrence of commutation failures in HVDC transmission systems. Leveraging this correlation, we propose a commutation failure mitigation strategy for HVDC systems centered around AC bus voltage disturbances within inverter stations. Through fault validation simulations conducted across three HVDC transmission systems, our strategy demonstrates effective suppression of commutation failure incidents within HVDC transmission projects. [ABSTRACT FROM AUTHOR]

The finite number of pixels in a silicon photomultiplier (SiPM) limits its dynamic range to light pulses up to typically 80% of the total number of pixels in a device. Correcting the non-linear response is essential to extend the SiPM's dynamic range. One challenge in determining the non-linear response correction is providing a reference linear light source. Instead, the single-step method used to calibrate PMTs is applied, based on the difference in responses to two light sources. With this method, the response of an HPK SiPM (S14160-1315PS) is corrected to linearity within 5% while extending the linear dynamic range by a factor larger than ten. The study shows that the response function does not vary by more than 5% for a variation in the operating voltage between 2 and 5 V overvoltage in the gate length between 20 and 100 ns and for a time delay between the primary and secondary light of up to 40 ns. [ABSTRACT FROM AUTHOR]

The accurate measurement and the investigation of electromagnetic transients are becoming more important, especially with the increasing integration of renewable energy sources into the power grid. These sources introduce new transient phenomena due to the extensive use of power electronics. To achieve this, the measurement devices must have a broadband response capable of measuring fast transients. This paper presents a capacitive electric field sensor-based measurement system to measure transient overvoltages in high-voltage substations. The concept and design of the measurement system are first presented. Then, the design and concept are validated using tests performed in a high-voltage laboratory. Afterwards, two different calibration techniques are discussed: the simplified method (SM) and the coupling capacitance compensation (CCC) method. Finally, three recorded transients are evaluated using the calibration methods. The investigation revealed that the SM tends to overestimate the maximum overvoltage, highlighting the CCC method as a more suitable approach for calibrating transient overvoltage measurements. This measurement system has been validated using various measurements and can be an efficient and flexible solution for the long-term monitoring of transient overvoltages in high-voltage substations. [ABSTRACT FROM AUTHOR]

The induced voltages and overvoltages generated by lightning are one of the main causes of unscheduled outage of the electric power system, which compromise the energy supply of thousands of consumers. In view of the constant climatic changes and the consequent increase in the incidence of lightning, studies aimed at understanding, characterizing, and estimating the induced caused in distribution lines by indirect lightning have revealed even more their need in order to develop procedures to protect against these disorders. In this context, the present research focuses on the presentation of the main aspects related to the incidence of lightning and the appearance of induced voltages, for further analysis of the main analytical and numerical methods for estimating the induced voltages by indirect lightning. As a result, from a critical and comparative analysis of these methods and their models, requirements and limitations for application in studies of estimation of the voltages induced by indirect lightning in distribution systems were raised. [ABSTRACT FROM AUTHOR]

For medium and high voltage drives, the three-level converter has better technical and economical performances than the two-level converter. Permanent magnetic brushless DC (BLDC) motors are widely used due to their simple control, low-resolution requirement of the position sensor, and high power density. The power switching devices in the non-conducting phase are blocked all the time when the two-phase conduction mode is used. Serious overvoltage of the inner power switching device occurs, which triggers the overvoltage alarm or causes system failure. In this paper, the overvoltage mechanism of the inner power switching device is analyzed in detail, and a mixed conduction mode containing a three-phase conduction mode in the first stage and a two-phase conduction mode in the second stage is proposed. The speed threshold for the switching of the two control modes is designed to suppress overvoltage in the starting stage and to reduce the loss of the converter at high speeds. The effectiveness of the overvoltage suppression and system safety of the proposed mixed conduction mode are verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

In this study, a concentration overvoltage model that focuses on describing variable-temperature operating condition properties for PEMFCs is established. Sensitivity analysis and a quantification study of oxygen transport resistance are carried out based on the oxygen transport resistance model and measurement data. By analyzing the influence of temperature on cathode oxygen transport resistance, the key structural parameters of the cathode oxygen transport resistance models are estimated, and the parameter modification method of fuel cell limiting current density under variable temperatures is proposed. Based on the polarization curve test experiments under variable-temperature conditions, it is demonstrated that the newly developed concentration overvoltage model reduces the relative error of simulation for a low Pt loading fuel cell in the high current region by 2.97% and 10.06% at 60 °C and 80 °C, respectively. The newly established concentration overvoltage model of a PEMFC solves the problem that the parameter of limiting current density is set without considering the influence of fuel cell temperature fluctuation, which leads to the poor simulation accuracy of the concentration overvoltage model in the high current region. [ABSTRACT FROM AUTHOR]

The insulated core transformer (ICT) power supply is widely employed in electron beam accelerators (EBAs) due to its high power, heightened efficiency, and stable operation. However, the segmented-core structure of the ICT power supply increases magnetic leakage, which leads to it adversely affecting the consistency of the output voltages in the rectifier stages. Currently, numerous studies focus on stage voltage compensation, including turns compensation, capacitor compensation, dummy primary winding compensation, and full-parameter compensation. This paper presents a unified simulation model and an improved gradient-based genetic algorithm, which can also optimize the parameters of the four compensation methods. Based on this, the performance of the power supply using the four compensation methods under different ICT energy levels and power supply requirements is studied, and the selection suggestions are given. This work fills the gap in the performance comparison and application research of various compensation methods. [ABSTRACT FROM AUTHOR]

The phase‐locked loop (PLL) is a critical control module applied in the control system of renewable energy sources (RESs) to synchronize with the grid voltage. When a fault occurs, the dynamic response process of the PLL will generate a phase locking error, resulting in a mass of harmonic components in the fault current of the PV inverter, which further poses challenges to transformer differential protection. To address the challenges posed by the phase locking error in practical engineering applications, this paper proposes an improved scheme that uses a digital computer algorithm to record and store the pre‐fault voltage and introduces the limiting coefficient. Firstly, the memory voltage is used to eliminate the phase locking error of the PLL, thereby mitigating harmonic distortion in the fault current of the RESs and ensuring the reliability of the transformer differential protection. In addition, the limiting coefficient is introduced to eliminate the effect of the increased amplitude of the fault current caused by the memory voltage. The voltage reference value of the inverter is multiplied by an appropriate limiting coefficient k and then output to the physical system. Finally, the effectiveness of the proposed scheme is verified by MATLAB/Simulink simulation. [ABSTRACT FROM AUTHOR]

A comparison of measurements of voltage transformer (VT) voltage ratio and phase displacement was performed between the National Center for High Voltage Measurement (NCHVM), China and the National Measurement Institute (NMI), Australia, with two voltage transformers provided by the NCHVM being used as the travelling standards. Voltage ratios of the 10 kV/100 V transformer measured by the two institutes differed by less than 5 μV/V and the phase displacement by less than 6 μrad, while voltage ratios of the (110/√3 kV)/100 V transformer differed by less than 16 μV/V and 13 μrad. These results confirmed that measurement results of the two institutes agreed within detailed measurement uncertainties evaluation. The comparison further enhances the confidence in both methods, which are widely used for calibration of voltage transformers in the electricity industry. [ABSTRACT FROM AUTHOR]

At the S-300 facility (2 MA, 400 kV, 100 ns), the generation of ultra hard X-rays was observed upon magnetic compression of cylindrical nested aluminum arrays with a linear mass of ~350 μg/cm, consisting of aluminum wires with a diameter of 15 μm. At the final phase of compression, a compact pinch is formed, consisting of a large number of hot spots arranged along the axis. This phase is accompanied by the emission of soft X-rays with a duration of ~10 ns. Simultaneously with the soft X-ray pulses, ultra hard X-rays with an energy exceeding 450 keV were detected. Ultra hard X-rays were measured with scintillation detectors shielded with lead 20–70 mm thick. The main cause of overvoltage on the plasma column appears to be sausage instability. [ABSTRACT FROM AUTHOR]

The article presents the results of research in the field of limiting the effects of overvoltages and improving the conditions for the self-extinguishing of transient faults in medium voltage networks with earth fault current compensation. The aim of the research was to estimate the level of overvoltages generated by an earth fault during re-ignition of the electric arc and to assess the possibility of reducing them by increasing the attenuation of the earth fault circuit. The results of the conducted tests show that to increase the attenuation, which ensures a significant effect of limiting such overvoltages, it is enough to change the way of operation of the devices forcing an additional active component of the earth fault current (AWSCz/ACFA). In Poland, such devices are commonly used to improve the effectiveness of earth fault protection. It was also found that the proposed solution enables accurate tuning of the Petersen coil in networks with natural asymmetry of earth capacitances. Therefore, changes in the operation of AWSCz/ACFA devices may have a beneficial effect on the limiting the effects of repeated ignitions during earth faults and, at the same time, enable the accurate tuning of the Petersen coil and increase its ability to extinguish arc-fed faults. Research and theoretical analysis of the issue were carried out on the basis of data characterizing the parameters of the earth fault circuits of the real 15 kV network. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The paper considers the use of a solid discharger with a cathode localized enhancement of electric field working together with an opening switch of an inductive storage to form a quick-rising current pulse in a low-impedance load. The physical factors bringing to an increase in pulse sharpening efficiency are specified. The discharger geometry variant is proposed. The technique for a determination of its parameters depending on the experimental requirements and conditions is described. The paper presents the results of the experiments on a stationary facility demonstrating a possibility to generate the current pulses with a rise front ∼100 ns in the inductive loads ∼10 nH. The obtained results allow giving a recommendation to use this type of dischargers to form multi-megaampere current pulses with submicrosecond rise front (up to ∼100 ns) for the inductive energy storages and, in particular, for the explosive magnetic (magnetocumulative) generators, in the circuits with low-impedance loads. [ABSTRACT FROM AUTHOR]

The commutation failure is the most prevalent fault in line‐commutated converter based high‐voltage direct current systems, which may result in transient overvoltage on the sending‐side system. Overvoltage level evaluation has become a crucial task for power industries to assess the tripping risk of large‐scale wind turbines and implement effective stability control measures. In this paper, a derivation of the mathematical relationship between the reactive power consumed by the rectifier and AC voltage is presented firstly, along with an analytical expression for the peak value of transient overvoltage. Secondly, decision tree (DT) model is adopted to extract the mapping relationship between transient overvoltage and massive electrical quantities of power grids. The common DT algorithm is transformed by modifying the error weight assignment, which reflects the error tolerances for different actual overvoltage regions. On this basis, an overvoltage analysis method integrating the model‐driven and data‐driven techniques is proposed, and the improved DT algorithm is applied to fast error correction, enhancing the interpretability of regression prediction results. Case studies were performed in the simulation system of Northwest China local power grid with transient overvoltage problems, and the simulation results verified the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The DC side fault of the high voltage DC transmission system based on modular multilevel converters high voltage DC (MMC-HVDC) is easily affected by the double influence of AC transient electrical quantity infeed and overvoltage and overcurrent, seriously threatening the safe operation of the power grid. Aiming at the problem above, a fault suppression strategy in dual mode of isolation and current limiting is proposed. Based on the half-bridge-full-bridge hybrid MMC, the fault transient mathematical model considering AC feed and sub-module switching feed is analyzed. AC isolation module with double conduction self-resistance structure and current-limiting control module is constructed, which can be adaptively adjusted to the system's direct current parameters. The ±500 kV double-ended hybrid MMC system model is established to verify the scheme's effectiveness. In addition, the influence of high AC modulation parameters on the suppression effect is investigated. PSCAD/EMTDC simulation results show that AC active and reactive power feed-in peaks are reduced by 388.69 MW and 119.82 Mvar, respectively, under dual-mode control. The peak value of DC overvoltage and overcurrent is reduced by 1211.53 kV and 22.5 kA, respectively, the fault self-clearing time is shortened by 43 ms, and the fault suppression effect is remarkable. In the high AC modulation ratio operating state, the modulation parameters are positively correlated with the AC power feed and negatively correlated with the overvoltage and overcurrent of the DC system. The research results provide support for the fault protection scheme of the hybrid MMC flexible and direct power grid. [ABSTRACT FROM AUTHOR]

Ferroresonance, as an undesirable disturbance, leads to significant overvoltage and distorted waveforms. This phenomenon can be highly damaging to voltage transformers and other parallel-connected equipment and can entail catastrophic consequences. This paper aims to design and study a solid-state ferroresonance-suppressing circuit (SSFSC) to protect voltage transformers (VTs) together with other parallel-connected equipment in wind generation systems from the adverse effects of the ferroresonance phenomenon. The proposed structure consists of low-voltage circuits, including power IGBTs. The excellent performance of the proposed SSFSC in suppressing ferroresonance overvoltage in wind generation VTs has been authenticated by analyses conducted utilizing a wind generation system model. In order to validate the performance of the proposed SSFSC, detailed analytical studies and time-domain simulations have been carried out employing a MATLAB/Simulink environment. The results verify that the proposed SSFSC can effectively suppress ferroresonance phenomena in VTs and mitigate their accompanying overvoltages with a high operational speed. [ABSTRACT FROM AUTHOR]

Various overvoltage mitigation schemes were used in literature in suppression of switching overvoltages in wind farms. However, the evaluation of how the effectiveness of these mitigation techniques would vary with the change of the wind farm topology is still un-explored territory. The main aim of this paper is to study the effectiveness of four mitigation schemes while using SF6 circuit breaker namely; R–L smart choke, R–C snubber circuit, surge capacitor and pre-insertion resistor (PIR) were studied in four different wind farm topologies; radial, single-sided ring, double-sided ring and star topologies. The topologies were based on a real wind farm located in Zaafrana, Egypt. The results showed that R–L choke to be the most effective scheme for all topologies followed by PIR, R–C snubber and surge capacitor schemes respectively. Their percentage of reduction of overvoltage ranged from 62 to 84% for R–L choke, 33–67% for PIR, 8–25% for R–C snubber circuits and 4–15% for surge capacitors. Also, it was shown that the change of the wind farm topology didn't affect the order of effectiveness of the mitigation schemes such that R–L remained the most effective and surge capacitor the least effective for all topologies. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to model the dependences of the output voltage, temperature, current and electrical power dissipation of a voltage limiter based on a two-layer varistor–posistor structure on time and analysis the influence of operating modes and design parameters of such a limiter on these characteristics. Design/methodology/approach: The behavior of the limiting voltage, temperature and other parameters of the voltage limiter when an input constant overvoltage is applied is studied by the simulation method. The voltage limiter was a two-layer construction. One layer was a zinc oxide ceramic varistor. The second layer was a posistor polymer composite with a nanocarbon filler of PolySwitch technology. Findings: The output voltage across the varistor layer decreases and reaches some fixed value related to its breakdown voltage after applying a constant overvoltage to the structure over time. The temperature of the structure increases to some steady state value, while the current decreases significantly. The amplitude of the transient current pulse increases, its duration and energy of the transient process decrease with increasing overvoltage. An increase in the internal resistance of the overvoltage source can cause a decrease in the amplitude and an increase in the duration of transient currents. Originality/value: The ranges of values for the activation energy of conduction of the varistor layer in weak electric fields, the intensity of heat exchange between the structure under study and the environment are determined to ensure the stable operation of this structure as a voltage limiter. The results obtained make it possible to select the necessary parameters of the indicated structures to ensure the required operating modes of the voltage limiter for various applications. [ABSTRACT FROM AUTHOR]

The increase in distribution power demand and distributed generation may lead to a rise in power substation fault current levels. One possible solution to this problem is the use of a solid-state fault current limiter (SS-FCL). In this context, this paper proposes the concept of a bridge-type solid-state device switching an air-core reactor as an SS-FCL topology. The overvoltage protection system details are presented, along with an explanation of the fault detection algorithm control's principle. An experimental setup is designed to evaluate various events in addition to the short-circuit, such as load-steps, harmonic loads, motor startups, and transformer's inrush. Fault current is detected within one millisecond, with a total reduction of 42%. The overvoltage protection system clamped the peak voltage across the semiconductor switch and kept the dV/dt below the maximum stipulated. The load input tests showed a proper limiting operation and provided that the device is within the parameterization range. [ABSTRACT FROM AUTHOR]

The restrike of vacuum circuit breaker during the breaking process causes overvoltage and intensifies the insulation deterioration of high‐voltage equipment. To solve this problem, the vacuum breaker aging test method and the restrike characteristics are researched. A withstand voltage test platform of 40.5‐kV vacuum circuit breaker was established to obtain the effects of the contact spacing and loop and inrush currents of vacuum circuit breaker on the number of restrike, the wavefront steepness of the breakdown voltage, and the breakdown duration. The number of restrike during the breaking of vacuum circuit breaker decreased and the duration of the repeated‐breakdown arc increased with the increased contact spacing of vacuum circuit breaker. As the loop current of the test system increased, the number of restrike during the breaking of vacuum circuit breaker, the wavefront steepness of the breakdown voltage, and the duration of the restrike arc increased. As the inrush current amplitude increased during the closing of vacuum circuit breaker, the number of restrike and the duration of the repeated‐breakdown arc during the breaking of vacuum circuit breaker increased. The results provide a theoretical basis and data support for the preventive test of 40.5‐kV vacuum circuit breaker and the optimization of the withstand voltage test. [ABSTRACT FROM AUTHOR]

Renewable energy sources have a multifaceted impact on power grids, ranging from the reliability and quality of electricity to the selective impact on equipment. While renewables used to be distributed in distribution networks, now their capacity is commensurate with thermal power plants and their impact on the grid should not be underestimated. According to the statistics on the interruption of the bulk electric networks, one of the main reasons for emergency shutdowns of extra high-voltage power lines are single-phase short circuits. The problem of mathematical modeling of the limit modes in terms of static stability is very relevant to the design and operation of electric power systems (EPS). Calculations of limit modes have both an independent value and a component of other electrical engineering tasks related to ensuring the required level of reliability and cost-effectiveness of the operation of the united PS. Despite the great degree of development of issues of planning and control of electric modes, system accidents associated with unacceptable loads of network elements occur in the Ukrainian energy industry. Non-phase modes regularly occur in electric power systems, which can lead to an unacceptable load of intersystem network elements, which imposes significant restrictions on their throughput. Single-phase short circuits are more than 95% of other damage that occurs in the line. The use of single-phase auto reclose on the transmission lines allows disconnecting only the damaged phase for a short period of time and not the entire transmission line. This action preserves the transit of electricity along the line and prevents the violation of the stability of parallel operation. To achieve this, the current-free pause of the single-phase auto reclose should last as short as possible. On the other hand, an important task to be solved when using single-phase auto reclose is to choose the minimum duration of the current-free pause necessary for its success. The problem studied in this paper deals with the safety and correct operation of transmission lines (TS) of the Ukrainian bulk power system in special conditions (not predictable, changing due to frequent attacks). For a quickly changing configuration, the power grid uses switches, and in the case of ultra-high voltage, the TS needs to solve the problem of secondary arc currents and recovering stresses in the place of arc burning after its extinction. One of the methods of reducing secondary arc currents and recovering stresses in the place of arc burning after its extinction is the implementation of single-phase automatic reclosing (SPAR). The main theoretical result of the paper is a proposed mathematical model of a compensated power transmission line based on the use of matrix n-poles, which makes it possible to model in detail stationary power transmission modes, including the SPAR mode. The proposed mathematical model of three-phase power transmission has been created using phase coordinates and can be used for the analysis of complex asymmetric modes. The main practical result of the paper is physically interpreted simplified models of three-phase TS, which can be used for the study of resonant overvoltages and currents of the feeding arc in non-full-phase circuit SPAR. The conclusion that can be drawn from the obtained results points out which line lengths must take into account the influence of longitudinal asymmetry when choosing the inductive resistance, i.e., take into account the dependence of the mode parameters on the location of the damaged phase. The observed results show that the largest values of the multiplicity of overvoltages will take place in phase B. The novelty of the work is the developed technique that makes it possible to determine in advance, depending on the disconnected phase of the line, the values of the primary conductivities of the STC (static thyristor compensators) and the corresponding angles of control of the thyristor switches, which satisfy almost complete compensation of the secondary arc at any point of the line in the specific condition (hard) of the bulk power system operation. [ABSTRACT FROM AUTHOR]

This paper describes a study on PEM balanced-pressure electrolysis in a batch process. For this purpose, a test bench is developed that enables electrolysis to be carried out at high pressure level. In this study, results up to a pressure level of 110 bar are shown. The focus is on the measurement of hydrogen crossover as a function of pressure and current density. An analysis is also conducted on the pressure dependence of the cell voltage. In addition, the catalyst coated membrane (CCM) is examined for ageing effects using SEM and EDX analysis. Taking the measurement results into account, a system model is created in order to determine the limits of balanced-pressure electrolysis in the batch process. • The hydrogen crossover is significantly lower in the batch process than in stationary operation. • For current densities >3 A cm−2, it was shown that the overvoltage decreases as a function of the pressure. • The EDX and SEM -analyses of the pressurised membrane show clear changes. • In the single-stage batch process, a maximum pressure of 140 bar can be achieved. [ABSTRACT FROM AUTHOR]

This study concerns the identification and interpretation of current and voltage signals during complex non-simultaneous disturbances in high-voltage overhead lines. It includes topics related to both the search for the optimal model of the system during complex disturbances as well as the analysis of the obtained results. The available EMT-like tools for the analysis of these phenomena are discussed. Models of high voltage overhead transmission lines are presented along with a discussion of their suitability for the study of electromagnetic transients during the analysis of complex non-simultaneous faults. Examples of transient waveforms of currents and voltages during non-simultaneous faults are presented, and the conditions for the occurrence of delayed current zero during short circuits in the system are discussed. The maximum values of the overvoltage factors and the conditions of their occurrence are described. Faults in transmission lines with various voltage levels suspended on the same supporting structures are discussed, together with an indication of the dangerous consequences of unusual intersystem faults. In the final part of the paper, the summary and recommendations for non-simultaneous fault studies are presented. [ABSTRACT FROM AUTHOR]

The paper presents the methods of assessing the technical condition of varistor surge arresters used in laboratory tests and in operation—performed without disconnecting the arresters from the network. The analysis of the diagnostic methods was supplemented with the results of the measurements of the leakage current of arresters coming directly from their production and used in the power industry. Among the available methods of evaluating the technical condition of arresters, mainly indicator solutions (temperature and operation counter) and the measurement of the selected parameters of the leakage current are used. In the latter, the method of determining the resistive component of the leakage current, determined on the basis of the analysis of the voltage and current waveforms, or only the arrester current, has become widespread. In this type of measurement, current clamps are used in the operation, and additionally, in voltage measurements, voltage transformers are used, where you have to take into account the fundamental, additional sources of errors discussed in the article. These errors and the dispersion resulting from the production technology may fundamentally hinder the proper assessment of the technical condition; hence, it is so important to properly recognize the listed basic sources of measurement uncertainty. In addition, the analysis should take into account three factors related to external conditions: temperature, the voltage applied to the arrester, and the content of higher harmonics in the supply voltage, for which appropriate methods have been provided to determine the active component of the leakage current for reference conditions. This article presents the results of the measurements of the leakage currents of surge arresters measured with various methods. [ABSTRACT FROM AUTHOR]

Capacitive equipment refers to its insulation design using the principle of capacitance of electrical equipment, mainly by a variety of different capacitive components in series. Most of the equipment in the substation is capacitive equipment. Once an insulation failure occurs, it will lead to extremely serious consequences. Monitoring grid overvoltage and insulation degradation of capacitive equipment is an effective means to ensure the stable operation of the power system. Therefore, in order to enhance the health management of capacitive equipment, including transformers, bushings, and current transformers, and to mitigate the risk of severe failures, it is imperative to conduct broad-spectrum frequency-domain online monitoring of overvoltages, dielectric losses, and partial discharge. However, the current monitoring work requires the utilization of multiple detection apparatuses. Aiming at the disadvantage that the existing inspection is not well integrated and requires a combination of multiple devices. This paper proposes a smart grid overvoltage identification system that utilizes partial discharge (PD) signals in correlation with dielectric loss detection. The system achieves synchronous detection of dielectric loss and high-frequency partial discharge by synchronously and in real-time acquiring four current signals from the power grid, enhancing the integration level of the hardware system. [ABSTRACT FROM AUTHOR]

Megatrends, such as the proliferation of distributed generation, electrification, and the appearance of aggregator companies, put the low voltage power grids under intense pressure. Since the network infrastructure developments cannot keep up with the trends, distribution system operators turned to alternative solutions. Smart grid assets, such as on-load tap-changing distribution transformers or serial low voltage regulators, are promising solutions. However, the energy transition cannot be handled with the network expansive on the distribution level. Control centers are predicted to expand to this voltage level in the near future, and distribution system state estimation could be an enabler of all functionalities. On the low voltage level, data scarcity is a great challenge in observability; therefore, research must focus on the creation of pseudomeasurements and integration of available data sources. This paper examines the inclusion of smart assets from the conceptual point to the application on two sites, based on data from operational environments, both with a pseudomeasurement and an integrated metering point approach. The results showed that integrating smart assets could considerably mitigate voltage fluctuations, and reduce estimation errors by two magnitudes on the low voltage network. [ABSTRACT FROM AUTHOR]

This review discusses the electrochemical principles involved in the recovery of metals from aqueous solutions and fused salt electrolytes. In this article we concentrate on electrolytic processing of different types of metals with an emphasis on the significant role of electrochemical principles together with free energy and activity in electrowinning and electrorefining of common and reactive metals. Based on discharge potentials, metals are classified into three categories with respect to their characteristics of deposition from aqueous electrolytes without hydrogen evolution, under hydrogen over-voltage, and only from fused electrolytes. [ABSTRACT FROM AUTHOR]