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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]

Lightning protection near the fan is the key point of lightning protection in wind farm, which affects the safe and effective delivery of wind power resources. At present, the three-phase multi-gap arrester installed on a base tower behind the collector can cooperate with the zinc oxide arrester to reduce the system failure caused by the arrester failure. However, the chopped wave generated by the multi-gap arrester when it acts is transmitted to the fan box transformer along the line, which may threaten the insulation of the transformer winding. Based on the above problems, this paper builds a simulation model on ATP to analyze the impact of wave clipping of multi-gap arrester on the insulation of fan transformer windings, considers the conventional installation mode and the limit installation mode of multi-gap arrester, and calculates that the wave clipping overvoltage generated by multi-gap arrester after being struck by lightning in two cases is the impact on the insulation of fan transformer. Through the simulation analysis, it is found that the higher the amplitude of the lightning current, the larger the amplitude of the overvoltage generated by the truncated wave, the steeper the wave head, and the greater the threat to the insulation of the fan box. The damage degree of round lightning is less than that of counter lightning. When a multi-gap arrester is installed in a collector tower, the 100 kA lightning current may destroy the insulation of the fan box transformer winding and require additional protective measures. It is recommended that the multi-gap arrester be installed from the next pole tower of the collector tower in the wind farm. [ABSTRACT FROM AUTHOR]

The control strategy of a distributed photovoltaic (PV) power generation system within a microgrid consists of an inner-loop controller and an outer-loop controller. The inner-loop controller is divided into two types, namely, the maximum power point tracking (MPPT) control strategy and DC bus voltage support strategy. Switching between these two control strategies results in issues such as DC bus overvoltage, system oscillations, or even PV system failure. An improved droop control strategy with a novel inner-loop controller is proposed, incorporating an output power derivative regulator. The control system unifies MPPT and DC bus voltage support strategy without switching the controller structure. A simulation model is built to validate the effectiveness of the proposed control strategy, and the results show that the ripple of DC bus voltage decreases by more than 60%. [ABSTRACT FROM AUTHOR]

The impact of the topological formation of wind farms upon the lightning induced overvoltages injected into the grid was not covered earlier in literature. However, this topic is highly important to be investigated to allow the usage of the most reliable topology against lightning strikes. For such reason, the paper investigates this point with consideration of most damaging cases as lightning strikes to multi-blades. The testing used ATP software for four main topologies, radial, single-sided ring SSR, double sided ring and star topology. The features defining the similarities in response and the variance range between these topologies were recorded and analyzed. The multi-blade strikes gave an expected increase of 15% to 100% in the injected overvoltage to the grid for all topologies. The star topology showed the most reliable performance by allowing the least injected overvoltage to the grid. The percentage of reduction in the magnitude of the injected overvoltages reached 50.78%, 66.07% and 89.04% for SSR, DSR and star topology respectively with respect to radial topology. Recommendation was provided for design engineers to consider star topology during design phase in terms of more reliable lightning protection. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The grid‐connected photovoltaic plants (GCPVPs) encounter various types of anomalies during fault occurrence in the main grid. During a fault occurrence on the grid side, the voltage of the point of common coupling (PCC) drops, causing the DC connection voltage to become too high for power balancing. This high DC voltage may damage the inverter and DC link equipment, which necessitates a reliable control scheme with low voltage passage requirements. These requirements, which obligate the GCPVP to remain connected to the main grid during abnormal conditions are generally known as low voltage ride‐through (LVRT). Herein, a developed LVRT method in the control approach that injects maximum rated current during a sag is proposed to rectify the shortcomings in single and multi‐inverter grid topologies. The proposed approach utilizes a current limiter combined with a DC braking chopper to guarantee the GCPVP's continuous participation in the power supply. Different scenarios including low and high power generations as well as two‐phase and three‐phase severe faults to the ground are considered. The results show that the proposed approach not only improves the performance in the single‐inverter system but also remedies the defects aggravated in the case of a GCPVP with several inverters. [ABSTRACT FROM AUTHOR]

When the electric locomotive pantograph is dropping, the interruption of pantograph catenary contact causes electromagnetic oscillation and arcing. The frequent arc burning that occurs due to charge accumulation results in the amplitude of overvoltage increasing gradually, posing a threat to locomotive high-voltage equipment. However, the physical mechanisms and characteristics of overvoltage are still unclear. This paper proposes a simulation model of operating overvoltage due to a dropping pantograph based on the pantograph–catenary arc and variable capacitance. Distributed RLC electromagnetic oscillation is considered, which allows the real-time calculation of arc resistance and capacitance. Under the same working conditions, the error between the simulation and test results is less than 4.0%, which proves the credibility of the model. The variation law of overvoltage under different dropping speeds or catenary phases was investigated, which shows the max amplitude is 298.20 kV and steepness is 2096.80 kV/μs at 0.30 m/s speed. The waveform shows the characteristics of high amplitude and high steepness, similar to very fast transient overvoltage (VFTO). There is a sinusoidal relationship between the catenary phase and overvoltage amplitude. The closer the catenary phase to 90°, the higher the overvoltage amplitude. The research has important guiding significance for the overvoltage formation mechanism of a traction power supply system and the insulation coordination design of high-voltage equipment. [ABSTRACT FROM AUTHOR]

The nonlinear resonance between the saturated inductance of a transformer and capacitance of the switching device in a substation induces overvoltages and overcurrents. The voltage transformer experience 2–4 pu overvoltages due to the different modes of nonlinear resonance. Though many overvoltage suppression circuits are being proposed, the transformer does not have a single suppression circuit against all modes. A memristor-based suppression circuit has been proposed already for the fundamental (periodic) mode of ferroresonance. In this paper, an aperiodic mode of ferroresonance has been addressed with same memristive circuit along with meminductive circuit. A subharmonic mode of ferroresonance overvoltage of 3.13 pu has been induced in a (400 kV/ √ 3 )/(110 V/ √ 3 ) CVT model according to IEC 61869 -5 standards. The primary current got increased from 23.3 mA to 1.56 A and has subharmonic frequency components. A meminductor circuit is proposed as a suppression circuit against ferroresonance for a Substation CVT. A gas discharge lamp T8 Philips 18 W with low-frequency magnetic ballast emulated peculiar pinched hysteretic characteristics of a memristor. The relation between charge and flux termed as memristance of the memristor circuit is used to mitigate the nonlinear resonance oscillations. A mutator circuit for mitigation requirement has been connected to the lamp model to emulate meminductor characteristics. The mitigation performance shows that the meminductor circuit dominantly recovers the secondary voltage of CVT in 0.188 s with a reduction of 1/3rd, 1/5th, and 1/7th harmonic components by 35.4%, 78.15%, and 90.41%, respectively. [ABSTRACT FROM AUTHOR]

Current research on overvoltage in trains can be divided into field tests and circuit simulations. The circuit simulation study focuses on the overvoltage amplitude distribution, the oscillation frequency of the main operating overvoltage is also an important characteristic, and the amplitude and frequency characteristics of the overvoltage need to be considered in the study of its suppression method. However, there is currently limited research on the frequency distribution of overvoltage. To provide guidance for the study of overvoltage suppression in the operation of the main circuit breaker, a new simulation model of train operating main break overvoltage is proposed based on the three-dimensional structure of the car body, high-voltage cables and rails. The model is used to simulate the transient overvoltage characteristics of the high-voltage cable core and each car body during the operation of the main circuit breaker, and the distribution of the overvoltage in each car body is obtained. The simulation results show that the maximum overvoltage amplitude during the operation of car 1 is 6.10 kV, while it is the smallest for car 4. The overvoltage amplitudes of cars 1 to 4 are all above 1 kV, and it was found that there are two main oscillation frequencies of the main overvoltage during the operation of the car body, which are 0.70 MHz and 1.30 MHz. Furthermore, the accuracy of the distribution characteristics and spectral characteristics of the train operating main break overvoltage is verified by static tests on the existing trains, and the test data show that the simulation results are extremely accurate in terms of overvoltage amplitude distribution, and the error between simulation and test does not exceed 5% in terms of amplitude, except for car 4. In terms of spectral characteristics, both simulation and experiment have two main oscillation frequencies, which can be considered consistent between simulation and experiment. Therefore, it can be concluded that the simulation model based on the three-dimensional structure has the ability to simulate the characteristics of operating overvoltage with high accuracy and provides guidance for overvoltage suppression research. [ABSTRACT FROM AUTHOR]

Due to the increasing speed of high-speed trains, the grounding system faces new challenges. When the relative motion between the train and the track occurs, the phenomenon of ground backflow will be intensified, resulting in the rise of train body potential, the abnormity or even damage of bearing and ground carbon brush, insulation joint, on-board sensors and other problems. In view of the existing problems of grounding reflux and train body potential of high-speed trains and the failure of twodimensional model of high-speed train grounding system to simulate and analyze the potential of the left and right sides of the same axle based on radial parameters, it is necessary to conduct a more perfect three-dimensional modeling of the integrated grounding system of high-speed trains. In order to suppress the grounding current and reduce the potential of the vehicle body, optimized analysis of the grounding mode and grounding parameters of the grounding system is conducted. In this paper, based on the measured data and theoretical analysis of the impedance and inductance parameters of the train body as well as the actual size parameters of the train body by the RCL tester, the three-dimensional circuit model of the integrated grounding system of the high-speed train is completed respectively from the aspects of traction transformer, overhead contact line, on-board transformer of high-speed train, high-voltage cable and train body under the premise of fully considering all the influencing factors. At the same time, combined with the dynamic grounding reflux test of the train passing under the on-line condition and the static overvoltage test of the high-speed train raising the pantograph and closing the VCB, the simulation results are compared with the measured results to verify the reliability of the three-dimensional model. Finally, based on the threedimensional simulation model, the radial parameters of the docking system and the three-dimensional distribution of the protection grounding and working grounding are optimized. After optimization, the ground current flowing through the protection grounding of the train is reduced to different degrees, and the distribution becomes more uniform. Meanwhile, the potential of the train body is maintained within the safety limit. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Electrochemistry is the property of Journal of Electrochemistry Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background and Objectives: Modeling and simulation of electric railway networks is an important issue due to their non-linear and variant nature. This problem becomes more serious with the enormous growth in public transportation tracks and the number of moving trains. Therefore, the main aim of this paper is to present a simple and applicable simulation method for DC electric railway systems. Methods: A train movement simulator in a DC electric railway line is developed using Matlab software. A case study based on the practical parameters of Isfahan Metro Line 1 is performed. The simulator includes the train mechanical movement model and power supply system model. Regenerative braking and driving control modes with coasting control are applied in the simulation. Results: The simulation results of the power network are presented for a single train traveling in both up and down directions. Results manifest the correctness and simplicity of the suggested method which facilitates the investigation of the DC electric railway networks. Conclusion: According to the results, the train current is consistent with the electric power demand of the train. But the pantograph voltage has an opposite relationship with its electric power demand. In braking times, the excess power of the train is injected into the electrical network, and thus, overvoltage and undervoltage occur in the overhead contact line and the substation busbar. Therefore, at the maximum braking power of the train, the pantograph voltage reaches its maximum. The highest amount of fluctuation is related to the substation that is closest to the train. As the train moves away from the traction substations, the voltage fluctuations decrease and vice versa. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Engineering Technology is the property of Editorial Department of Electric Power Engineering Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Computer Measurement & Control is the property of Magazine Agency of Computer Measurement & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Microgrid inverters (MGIs) employing gate turn-off thyristor (GTO) technology are used in both gridtied and off-grid microgrids (MGs), where they are essential for controlling power flow and maintaining system stability. The ability of GTOs to withstand high voltages and currents is crucial in power conversion systems that require substantial power levels. GTOs in voltage source inverters (VSIs) are used to convert DC electricity from renewable energy sources, such as photovoltaic (PV) systems, wind turbines or energy storage systems, into AC power that is suitable for use in MGs. An MG’s GTO switch failure (GSF) in three-phase (3Ph) VSI can result in several issues, such as diminished power production, safety issues, unstable voltage and frequency, loss of grid connection, overcurrent or overvoltage situations, and operational downtime. Minimizing the impact of such issues on MG operations requires careful maintenance, monitoring, and fault detection techniques. An approach to determine GSF in a PV systemconnected 3Ph VSI for the MG application is demonstrated in this study. To identify GSF, a Fast Fourier Transform (FFT) based analysis of the 3Ph VSI’s output current signal has been conducted. [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]

Medium-voltage (MV) distribution networks that are spread through larger territory and threatened by extreme weather conditions are sometimes formed by very long underground cable lines. In such circumstances, a significant amount of capacitive reactive power flow can be generated. If, concurrently, there is low power demand in the network, it can result in significant reverse reactive power flows and voltage rise issues. This paper proposes a general approach for analyzing and mitigating voltage rise issues and demonstrates it using an example of a real distribution network that operates under the described conditions. Previous studies that dealt with this problem did not include the allocation of multiple shunt reactors in a larger distribution network, modeling a high number of lines that create reverse reactive power flows, and modeling the main distribution transformers, which are the locations where voltage rise predominantly occurs. In this paper, we demonstrate that precise allocation and placement of multiple shunt reactors in a fully modeled, larger distribution system, including transformer models, can reduce reverse reactive power flows, thereby improving voltage in the distribution system. If hourly control of the power factor from the distributed generation unit is also implemented, the voltage can be further improved. [ABSTRACT FROM AUTHOR]

Copyright of Southern Energy Construction is the property of Southern Energy Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Featured Application: The proposed surge arrester is applied to a DC GIS in an offshore wind farm converter platform, significantly reducing the space the equipments take up by up to 95%, which performs well especially in the new power system. The employment of a multi-column parallel connection is intended to enhance the energy absorption capability and reliability of surge arresters. However, the disparity in reference voltage between each varistor column and the uneven current distribution may result in a reduction in performance or even failure of the surge arrester. The objective of this study is to investigate the spiral structure of a ±550 kV DC gas-insulated switchgear (GIS) parallel arrester and its influence on the current distribution characteristics. This research develops a model of a ±550 kV DC GIS arrester and performs an in-depth theoretical analysis using multi-physics field simulations. Subsequently, a ±66 kV miniature prototype is constructed, and the accuracy of the theoretical analysis and simulation results is validated by experiments, validating the effectiveness of the proposed method. This study calculates the self-generated inductance in the spiral structure of ZnO varistors using simulations. The influence of the self-generated inductance on the current distribution of the multi-column arrester when absorbing energy is further investigated. The results indicate that the self-generated inductance of the spiral structure can reduce the current deviation factor by 28–65%. This research provides a novel approach to improving current equalization in the parallel surge arresters of DC GISs for offshore wind power converter platforms. [ABSTRACT FROM AUTHOR]

In the paper problem of power supply unbalance voltage states with the same Voltage Unbalance Factor (VUF) value for power converters is tackled. This factor is being used to assess the quality of power supply. There are many sources of voltage unbalance phenomenon such as system asymmetries and uneven distribution of demand throughout phases. Based on literature three unbalance states are presented: lines overvoltage, lines undervoltage and phase angle asymmetry. VUF value alone cannot provide information on the type of voltage unbalance state. Moreover, the same VUF percentage can be obtained for different amount of unbalanced phases. In this paper simulation experiments were conducted in order to obtain data of rectifier output voltage during different unbalance states with same VUF. Ripple, mean value and frequency components of said voltage were used in order to detect and categorise power supply voltage unbalance. Such approach does not require complex power quality measuring tools as power supply unbalance can be initially diagnosed using single voltage sensor. [ABSTRACT FROM AUTHOR]

Three‐phase ac choppers feature output voltage amplitude controllability and enable more compact system realizations compared to autotransformers. For the practical realization advantageously standard power transistor with unipolar voltage blocking capability such as MOSFETs can be employed as a naturally resulting offset voltage between the grid and the input‐stage starpoint ensures purely positive power transistor voltages. This offset voltage is, however, not strictly defined and may drift to higher voltage values, resulting in high power transistor voltage stresses and finally a potential overvoltage breakdown. Traditionally, the offset voltage drift is prevented by introducing discharge resistors across the input‐stage capacitors which, however, results in substantial ohmic losses. This paper analyzes the offset voltage formation in ac choppers and proposes a novel clamping modulation scheme which ensures a strictly defined and minimum time‐varying offset voltage without need for discharge resistors. Theoretical analyses and circuit simulations are finally experimentally verified with a 400 V (rms, line‐to‐line) 50 Hz grid connected three‐phase buck‐boost ac chopper with 3 kW rated power. [ABSTRACT FROM AUTHOR]

This paper is about the development and demonstration of a motor drive for e-transport applications based on an innovative hybrid Si-SiC dual switching frequency interleaved buck–boost Y-inverter and a single-rotor Halbach machine. In particular, the focus is the implementation of the required discontinuous inverter modulation scheme, input voltage feed-forward and motor currents feedback control loops, as well as over-voltage, over-current, and over-temperature protections, using an off-the-shelf commercial hardware platform enabling straightforward Simulink-environment programming of all parts, while ensuring the high switching frequency capability required by wide-band-gap semiconductors. Experimental results showed good inverter efficiency, transient dynamic response to load changes, input voltage regulation, and fully functional protection capability, validating the proposed approach as a powerful option for reducing system development time and cost. [ABSTRACT FROM AUTHOR]

Abstract Constrained by the AC voltage amplitude modulated by a modular multilevel converter‐based static synchronous compensator (MMC‐STATCOM), its reactive power output may be subject to oscillations under grid contingencies, posing a threat to the grid stable operation. To solve this problem, this paper proposes a variable DC voltage (VDCV)‐based reactive power enhancement scheme for MMC‐STATCOM. In this scheme, a novel variable DC voltage control is designed, which can increase the DC voltage in a transient state for relaxing the constraint of the AC voltage amplitude modulated by MMC‐STATCOM and improving its reactive power output capability (RPC). At the same time, to make full use of the improved RPC of MMC‐STATCOM, a VDCV scheme also proposes an optimisation algorithm of its reactive current‐AC voltage droop coefficient using the established reactive power model of the MMC‐STATCOM. Based on small signal modelling and analysis, the key parameters of the proposed VDCV scheme are optimised. The performance and reactive power enhancement of the VDCV scheme is evaluated through the hardware‐in‐the‐loop experiment under grid disturbances.

Abstract The grid‐connected photovoltaic plants (GCPVPs) encounter various types of anomalies during fault occurrence in the main grid. During a fault occurrence on the grid side, the voltage of the point of common coupling (PCC) drops, causing the DC connection voltage to become too high for power balancing. This high DC voltage may damage the inverter and DC link equipment, which necessitates a reliable control scheme with low voltage passage requirements. These requirements, which obligate the GCPVP to remain connected to the main grid during abnormal conditions are generally known as low voltage ride‐through (LVRT). Herein, a developed LVRT method in the control approach that injects maximum rated current during a sag is proposed to rectify the shortcomings in single and multi‐inverter grid topologies. The proposed approach utilizes a current limiter combined with a DC braking chopper to guarantee the GCPVP's continuous participation in the power supply. Different scenarios including low and high power generations as well as two‐phase and three‐phase severe faults to the ground are considered. The results show that the proposed approach not only improves the performance in the single‐inverter system but also remedies the defects aggravated in the case of a GCPVP with several inverters.

[Introduction] With the establishment of the energy Internet architecture mainly relying on new energies, HVDC transmission has become an important way of power transmission, power grids present a new characteristic of "strong DC and weak AC". Synchronous condensers have unique advantages in dealing with the issue of "strong DC and weak AC" by virtue of their dynamic performance such as fast reactive power response and strong voltage support capability. [Method] To study the application of synchronous condensers in HVDC works, this paper summarized the development of synchronous condensers, introduced the current development status of several major types of synchronous condensers in China, such as synchronous condensers for transforming thermal power units, new-generation large-capacity synchronous condensers, distributed synchronous condensers, analyzed the working principle and dynamic characteristics of synchronous condensers. Then the paper summarized the virtues of synchronous condensers when compared with other reactive power compensation devices such as SVC, the application scenarios, existing configuration strategies of large-capacity synchronous condensers and distributed synchronous condensers. [Result] Finally, a simulation model of DC transmission system with synchronous condensers is built on the PSCAD/EMTDC platform. The simulation verify the suppression capability of synchronous condensers for commutation failure at the sending end and transient overvoltage at the receiving end caused by commutation failure, as well as the dynamic reactive power compensation capability under lagging phase operation. [Conclusion] The analysis shows that synchronous condensers have adequate suppression of transient overvoltage and commutation failure and their reactive power response speed and dynamic reactive power support capability will not be affected by lagging phase operation, which contributes to their prospect of engineering application for steady-state compensation in converter stations.

AC submarine cable is an important component in AC transmission system of offshore wind farms. However, the issue of charging current limits its application in offshore wind power with long-distance and large-capacity. Taking HYJQF41-F290/500 kV single-core AC submarine cable as an example, the overvoltage distribution along the cable in different working conditions is analyzed, considering the long-distance and high-voltage transmission. The simulation model of the cable is established and its parameters are corrected firstly. According to the different compensation degrees of the shunt reactor, the capacity of the shunt reactor under the configuration scheme of single-end compensation and two-end compensation calculated out. Finally, based on the single-phase grounding fault, the closing and opening conditions in the high-voltage and long-distance wind farm models, and the distribution law of overvoltage along the submarine cable under different reactive power compensation schemes is tested by simulation. The results show that the maximum overvoltage of submarine cables appears in different positions with different compensation schemes. Based on this, the selection methods for high-voltage submarine cable and overvoltage in insulation level design of substation equipment are given out under different compensation schemes, which have certain guiding significance for engineering practice.

High-voltage direct current (HVDC) transmission is a crucial way to solve the reverse distribution of clean energy and loads. The line commutated converter-based HVDC (LCC-HVDC) has become a vital structure for HVDC due to its high technological maturity and economic advantages. During the DC fault of LCC-HVDC, such as commutation failure, the reactive power regulation of the AC grid always lags the DC control process, causing overvoltage in the AC sending grid, which brings off-grid risk to the wind power generation based on power electronic devices. Nevertheless, considering that wind turbine generators have fast and flexible reactive power control capability, optimizing the reactive power control of wind turbines to participate in the transient overvoltage suppression of the sending grid not only improves the operational safety at the equipment level but also enhances the voltage stability of the system. This paper firstly analyses the impact of wind turbine's reactive power on AC transient overvoltage. Then, it proposes an improved voltage-reactive power control strategy, which contains a reactive power control delay compensation and a power command optimization based on the voltage time series prediction. The delay compensation is used to reduce the contribution of the untimely reactive power of wind turbines on transient overvoltage, and the power command optimization enables wind turbines to have the ability to regulate transient overvoltage, leading to the variation of AC voltage, thus suppressing the transient overvoltage. Finally, the effectiveness and feasibility of the proposed method are verified in a ±800kV/5000MW LCC-HVDC sending grid model based on MATLAB/Simulink.

Objective The overvoltage caused by circuit breaker closing will aggravate the insulation aging of high voltage equipment when EMU (electric multiple units)passes neutral section. The research on the mechanism and influencing factors of overvoltage caused by circuit breaker closing provides significant theory for the insulation matching and equipment selection of EMU main circuit. Method Based on the EMU main circuit structure and the process of passing neutral section, the causes of overvoltage during breaker closing under normal operation is analyzed. In consideration of the special influence of vacuum circuit breaker closing bounce characteristics on overvoltage, a simulation model of EMU main circuit is established.By comparative study of the overvoltage characteristics of EMU main circuit breaker closing, the influence patterns of main circuit action time, parameters of EMU high voltage cable, parameters of catenary and equipment characteristics on overvoltage are obtained. Result & Conclusion In extreme conditions, the peak overvoltage is 2.39 times the peak power frequency voltage, close to 2.4 times the stipulated value in the "Testing specifications of high-speed electic multiple unit on completion of construction". The overvoltage generated in extreme conditions will affect the insulation performance of the EMU high voltage equipment, even leading to breakdown phenomenon. Therefore, it is necessary to adopt the phase controlling closing technology for the circuit breaker to close at the target phase, select the high voltage cable with small capacitance of unit distribution, improve the mechanical characteristics of the vacuum circuit breaker and other relevant preventive measures，and finally to effectively reduce the EMU closing overvoltage.

Abstract 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.

Integrating renewable energy generation with the conventional grid supports reduces carbon emissions in the atmosphere. Despite technical advancements in protection strategies, critical issues concerning renewable integration in microgrid structures require standardized solutions. The essential aspects that need to be concentrated during securing the grids are rapid fault interruption, false tripping and blinding of protection. This study proposes an innovative approach to enhance fault isolation speed through the implementation of a grid monitoring system (GMS) coupled with a fault identification method based on Kosaraju's algorithm. This algorithm operates on the principles of overvoltage and overcurrent detection. The study assesses the efficacy of this approach by examining its integration with a Z-source circuit breaker and conducting tests on different fault types within a 13-bus system. Real-time simulations using Opal RT software are employed to experimentally validate the proposed methodology, ensuring its efficacy in fault interruption and isolation. [ABSTRACT FROM AUTHOR]

Sequential recommender models should capture evolving user preferences over time, but there is a risk of obtaining biased results such as false positives and false negatives due to noisy interactions. Generative models effectively learn the underlying distribution and uncertainty of the given data to generate new data, and they exhibit robustness against noise. In particular, utilizing the Diffusion model, which generates data through a multi-step process of adding and removing noise, enables stable and effective recommendations. The Diffusion model typically leverages a Gaussian distribution with a mean fixed at zero, but there is potential for performance improvement in generative models by employing distributions with higher degrees of freedom. Therefore, we propose a Diffusion model-based sequential recommender model that uses a new noise distribution. The proposed model improves performance through a Weibull distribution with two parameters determining shape and scale, a modified Transformer architecture based on Macaron Net, normalized loss, and a learning rate warmup strategy. Experimental results on four types of real-world e-commerce data show that the proposed model achieved performance gains ranging from a minimum of 2.53 % to a maximum of 13.52 % across HR@K and NDCG@K metrics compared to the existing Diffusion model-based sequential recommender model. [ABSTRACT FROM AUTHOR]

Atmospheric pressure cold plasmas have recently been the subject of intense research and applications for solving problems in the fields of energy, environmental engineering, and biomedicine. Non-thermal atmospheric pressure plasma sources, with dielectric barrier discharges, plasma jets, and arc discharges, are non-linear power loads. They require special power systems, which are usually designed separately for each type of plasma reactor, depending on the requirements of the plasma-chemical process, the power of the receiver, the type of process gas, the current, voltage and frequency requirements, and the efficiency of the power source. This paper presents non-linear phenomena accompanying plasma generation in the power supply plasma reactor system, such as harmonic generation, resonance, and ferroresonance of currents and voltages, and the switching of overvoltages and pulse generation. When properly applied, this can support the operation of the above-mentioned reactors by providing improved discharge ignition depending on the working gas, thus increasing the efficiency of the plasma process and improving the cooperation of the plasma-generation system with the power supply. [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]

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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]