Current Breaking Research Articles

A Novel Forced Resonant Mechanical DC Circuit Breaker by Using Auxiliary Oscillation Switch for Zero-Crossing

A low-cost mechanical circuit breaker (MCB) is an important solution in the field of dc breaking. However, the zero-crossing points in the breaking process of the existing MCBs are either insufficient in number or slow in generation, which limits the breaking performance of MCBs. This letter proposes a novel forced resonant MCB (FR-MCB). A large number of zero-crossing points can be generated in a short time by utilizing a resonant circuit and a power electronic-based auxiliary oscillation switch. Thus, the FR-MCB can exhibit more reliable and faster breaking performance while maintaining the low cost. After the detailed analysis of current oscillation and breaking process in the FR-MCB, a prototype experiment of up to 10 kV/8 kA is conducted to verify its feasibility.

Comparison of algorithms for predicting plasma physical parameters of SF6–Cu mixtures at local thermodynamic equilibrium state via machine learning

In order to study the arc process of the SF6 circuit breaker during the current breaking process, it is necessary to calculate the physical parameters of the arc discharge plasma. However, the calculation of plasma physical parameters is very difficult and complicated and generally requires solving dozens of differential equations. Based on the machine learning method, this paper constructs a learning prediction model of physical property parameters in a local thermodynamic equilibrium state without solving a large number of differential equations so as to perform a rapid prediction of physical property parameters in other scenarios based on the existing physical parameter database. This paper uses the support vector machine, K-nearest neighbor algorithm, gradient boosting regression, decision tree, and random forest algorithm to predict and calculate the thermodynamic parameters and transport characteristics of SF6 at different pressures and temperatures. At the same time, this paper also predicts and calculates the parameters of the SF6–Cu mixed gas at different mixed concentrations. The results show that the machine learning algorithm can predict and generate consistent gas property parameter data, indicating that the model has good generalization performance. Finally, by comparing the error measures of the prediction results of various algorithms, the algorithm suitable for predicting the physical parameters is found to improve the prediction accuracy.

Mapping the abrasion on Sederhana Beach, Muara Gembong, Bekasi, West Java province for the coastal mitigation purpose

Sederhana Beach is located in the waters of Muara Gembong, Bekasi Regency, West Java Province, northeast part of Jakarta Bay. The observation data in 2018 showed the morphology of the damaged coast and the massive fallen mangrove vegetation. Loss of land and mangrove populations has a major impact on the economic and environmental aspect. How to mitigate the impact of abrasion? This study aims to map the type of sediment, sediment distribution and its depositional environment, to obtain a correlation with the type and direction of currents causing abrasion. The results would become the base for determining the appropriate actions to overcome further abrasion, in an integrated coastal area planning program. Seabed sediments were taken using a grab sampler, megascopic descriptions and analysis of the depositional environment off sediments were held on site. The results are plotted onto a map, to determine the distribution of sediments. Sediment types found are: coarse sand, clay, sandy clay, medium-fine sand, and silt. 75% of the study area is: scattered sandy clay, mostly covering the coastline to the north. This is a common phenomenon because the mainland of research location is dominated by mangrove vegetation. The Coarse sand took 20% of the research location. An interesting phenomenon is: the coarse sand reaches the coast directly adjacent to the mangroves, where 5% of silt is found outside this coarse sand zone. The presence of coarse sand on the shoreline with mangrove vegetation indicates that the main current that triggers abrasion is longshore current, moving parallel to the coastline, namely northeast - southwest. So, the recommended steps that can be taken in mitigating further abrasion at Sederhana Beach is the construction of a current breaking structure that is perpendicular to the coast line

Switching Arc Energy Limitation Approach for LV Circuit Breakers

This paper presents an experimentally verified approach to deriving switching arc energy limitations for low-voltage (LV) circuit breakers (CBs). Air-insulated contactors equipped with additional vacuum-insulated (VI) arcing contacts were tested for AC and DC current interruption efficiency, respectively. In the study, the contact arrangements of reed relay VI contact switches of low current breaking capacity combined with air-insulated contactors were examined. Tests were performed on selected LV CBs inductively loaded for LV power network rated voltages. A comparative analysis of the arc energy resulting from various arc time durations recorded during the switching-off operation was performed. Using a variety of either basic CB air-insulated contact systems or combined contact systems, a practical assessment of the proposed idea for enhancing the arc quenching efficiency was undertaken. As a result of the implementation of the proposed idea, the arc burning duration time was indicated as being hundreds of times shorter. In most cases, a complete arc reduction was achieved. Moreover, the resulting arc energy dissipation during the breaking operation was substantially minimized. Consequently, a significant increase in the total current breaking capacity of the tested CBs was achieved.

Research on the current-zero period of vacuum arc interruption and equivalent model of post-arc gap

In this paper, the current breaking experiments of vacuum interrupter are conducted and the waveforms of voltage and current are obtained. The results show that there is current instability phenomenon when the value of is low and the value of instability-initiation current decreases as the value of increases. The number of voltage spikes will also decrease and irregular oscillation will weaken. According to the experimental results and theoretical analysis, the ‘memory characteristic’ of plasma is proposed and a new mathematical model of post-arc initial plasma density is estabilished which will provides a new method for the calculation of the sheath growth. The equivalent circuit model of post-arc gap is established to analyze the transient recovery voltage. The equivalent parameters in the circuit are obtained by the calculation of sheath growth and plasma density and verified by comparison with measurements. Through the comparison of experimental results between the axial magnetic field (AMF) contact and the butt contact, the effects of AMF on post-arc plasma density and sheath growth are analyzed. The results show that AMF can make the post-arc plasma density higher and the sheath growth slower.

Magnetic Energy Release, Plasma Dynamics, and Particle Acceleration in Relativistic Turbulent Magnetic Reconnection

Abstract In strongly magnetized astrophysical plasma systems, magnetic reconnection is believed to be the primary process during which explosive energy release and particle acceleration occur, leading to significant high-energy emission. Past years have witnessed active development of kinetic modeling of relativistic magnetic reconnection, supporting this magnetically dominated scenario. A much less explored issue in studies of relativistic reconnection is the consequence of three-dimensional dynamics, where turbulent structures are naturally generated as various types of instabilities develop. This paper presents a series of three-dimensional, fully kinetic simulations of relativistic turbulent magnetic reconnection (RTMR) in positron–electron plasmas with system domains much larger than kinetic scales. Our simulations start from a force-free current sheet with several different modes of long-wavelength magnetic field perturbations, which drive additional turbulence in the reconnection region. Because of this, the current layer breaks up and the reconnection region quickly evolves into a turbulent layer filled with coherent structures such as flux ropes and current sheets. We find that plasma dynamics in RTMR is vastly different from its 2D counterpart in many aspects. The flux ropes evolve rapidly after their generation, and can be completely disrupted by the secondary kink instability. This turbulent evolution leads to superdiffusive behavior of magnetic field lines as seen in MHD studies of turbulent reconnection. Meanwhile, nonthermal particle acceleration and the timescale for energy release can be very fast and do not depend strongly on the turbulence amplitude. The main acceleration mechanism is a Fermi-like acceleration process supported by the motional electric field, whereas the nonideal electric field acceleration plays a subdominant role. We also discuss possible observational implications of three-dimensional RTMR in high-energy astrophysics.

HVDC grids stability improvement by direct current power system stabilizer

High-voltage direct current breaker is among the essential components of high-voltage direct current grids. Such a breaker generally needs a direct current reactor to reduce the fault currents rate. However, direct current reactors have destructive effects on the multi-terminal high-voltage direct current grid dynamic stability, and in such a system, despite the variety of controllers, the system dynamics are highly sensitive to the operating point. Therefore, additional damping control will be needed. This paper proposes a modification to be applied to the traditional droop controller of high-voltage direct current grids to cope with the influence of these large reactors, improving the direct voltage stability and decreasing power variations in the transient events by introducing a direct current power system stabilizer. The proposed method for direct voltage control has been investigated through the analytical model of the system. Stability improvement has been studied following the application of the proposed method by investigating zeros, poles, and frequency response analysis. Moreover, a method is proposed for optimal design and optimal placement of direct current power system stabilizer. The system analysis and time-domain simulations demonstrate a decent damping improvement attained by the proposed method. All simulations and analytical studies are conducted on Cigré DCS3 test high-voltage direct current grid in MATLAB/Simulink.

Prospects of regenerative current breaking in DC circuit breaker topology

Due to the stunning advancement of power electronics, DC power system is getting immense attention in the field of research. Protection and hereafter the protective devices for the DC power system application are two vital areas that need to be explored and developed further. Designing a protective device such as DC circuit breaker possesses a lot of challenges. The main challenge is to interrupt a current which does not have a natural zero crossing like AC current has. In addition, energy is stored in the network inductances during normal operation. Instantaneous current breaking is opposed by this stored energy during circuit breaker tripping, hence, all the DC circuit breaker topologies proposed in literature use snubber network, nonlinear resistor to dissipate this stored energy as heat during the current breaking operation. However, it is possible to store this energy momentarily and reuse it later by developing an improvised topology. In this paper, the prospects of energy recovery and reuse in a DC circuit breaker was studied and a new topology with regenerative current breaking capability had been proposed. This new topology can feed the stored energy of the network back into the same network after breaking the current and thus can improve the overall system efficiency.

Prospects of regenerative current breaking in DC circuit breaker topology

Prospects of regenerative current breaking in DC circuit breaker topology

Kick-induced rectified current in a symmetric nanoelectromechanical shuttle

We have studied the rectified current in a geometrically symmetric nano-electromechanical shuttle with periodic kicks and sinusoidal ac bias voltages. The rectified current is exactly zero under the geometrical symmetry which is generated by the electrons transferred from source to drain electrodes through the movable shuttle. We investigate the nonzero rectified currents through the symmetric shuttle with regular motion of which the time-translational symmetry is broken. The motion of the shuttle, moreover, becomes chaotic with the same mechanism of the kicked rotor and generates the scattered current as increasing kick strength. We point out that the time-translational-symmetry breaking of the instantaneous current is an important role of manipulation of the rectified current.

Capillary‐gravity solitary waves on water of finite depth interacting with a linear shear current

AbstractThe problem of two‐dimensional capillary‐gravity waves on an inviscid fluid of finite depth interacting with a linear shear current is considered. The shear current breaks the symmetry of the irrotational problem and supports simultaneously counter‐propagating waves of different types: Korteweg de‐Vries (KdV)‐type long solitary waves and wave‐packet solitary waves whose envelopes are associated with the nonlinear Schrödinger equation. A simple intuition for the broken symmetry is that the current modifies the Bond number differently for left‐ and right‐propagating waves. Weakly nonlinear theories are developed in general and for two particular resonant cases: the case of second harmonic resonance and long‐wave/short‐wave interaction. Traveling‐wave solutions and their dynamics in the full Euler equations are computed numerically using a time‐dependent conformal mapping technique, and compared to some weakly nonlinear solutions. Additional attention is paid to branches of elevation generalized solitary waves of KdV type: although true embedded solitary waves are not detected on these branches, it is found that periodic wavetrains on their tails can be arbitrarily small as the vorticity increases. Excitation of waves by moving pressure distributions and modulational instabilities of the periodic waves in the resonant cases described above are also examined by the fully nonlinear computations.

Impact of CLSI Break Point Changes Over the Past Decade on Antimicrobial Susceptibility in Gram-Negative Bacteria

Background: Over the past decade, the CLSI has updated susceptibility break points for several antimicrobial agents. The purpose of this study was to evaluate the impact of these changes against gram-negative bacteria at our academic medical center. Methods: In this retrospective, IRB-approved study, we collected consecutive, nonduplicate clinical isolates of Enterobacter cloacae, Escherichia coli, Klebsiella aerogenes, K. oxytoca, K. pneumoniae, and Pseudomonas aeruginosa for the past decade (2010–2019) at our academic medical center and 3 adult ICUs. Susceptibility testing was performed using the BD Phoenix automated system. For these isolates, susceptibilities for 7 β-lactams (aztreonam, ceftriaxone, ceftazidime, cefepime, piperacillin/tazobactam, ertapenem, and meropenem) and 2 fluoroquinolones (levofloxacin, ciprofloxacin) were calculated based upon CLSI break points in 2010 and current CLSI break points in 2020. Any change >5% in susceptibility was deemed significant for this analysis. Results: In 17.5% of Enterobacteriales isolates tested, at least 1 antimicrobial demonstrated significant decline. Ertapenem was the most commonly affected antimicrobial (45% of the isolates) followed by ceftriaxone (35%) and cefepime (25%). Susceptibilities of aztreonam, ceftazidime, and meropenem were not affected for any of the Enterobacteriales. The most common organism demonstrating a significant impact on change in susceptibility among the Enterobacteriales was E. cloacae (41.7% of the time) followed by E. aerogenes (20.8%), K. oxytoca (12.5%), K. pneumoniae (8.3%) and E. coli (4.2%). Most of the impact was observed hospital-wide (33.3%), followed closely by the MICU (28.6%), the NSICU (23.8%) and the CVICU (14.3%). For P. aeruginosa, the impact of the antimicrobial break-point changes on susceptibility was more pronounced than the Enterobacteriales. Overall, 93.8% of the time there was a significant decline in antimicrobial susceptibility. Each antimicrobial (ciprofloxacin, levofloxacin, meropenem, and piperacillin/tazobactam) demonstrated a significant decline in susceptibility hospital-wide and in each ICU except for the susceptibility of meropenem in the NSICU. Conclusions: Changes in break points had a significant impact on the susceptibility of all antimicrobials for P. aeruginosa at our institution, both hospital-wide and in the adult ICUs. Although the impact was less for the Enterobacteriales, ertapenem, ceftriaxone, and cefepime demonstrated significant susceptibility changes, especially with E. cloacae. Understanding and evaluating the impact of the break-point changes may lead to changes in empiric therapy in other institutions.Funding: NoDisclosures: None

Numerical modelling of alongshore variability in waves and wave-driven currents during the morphodynamic change of a laboratory beach

A non-hydrostatic phase-resolving numerical model (SWASH) is used to investigate the wave-driven nearshore hydrodynamics corresponding to new observations from a three-dimensional physical model in a wave basin. In the physical model, waves from a passing storm are simulated by varying the energy and duration of waves generated by a paddle over time and the beach morphology is surveyed in high spatial-resolution using a 3D laser scanner after each segment of the storm. An oblique incident wave angle introduces spatially variability in wave energy along the beach and results in morphologic differences during the storm, with active transport of beach sand by the wave-driven circulation. SWASH is validated using wave and current observations at each stage of the storm, indicating low root-mean-squared errors between model results and wave measurements, where the high-resolution model is able to predict wave shoaling, breaking and generation of the alongshore current. Model-data agreement is not as high for the velocity, suggesting spatial variability in bottom friction and horizontal mixing, and evolution of the bed in the physical model, could explain the differences. The detailed numerical model results indicate that the alongshore current is generated by wave breaking in the nearshore zone, and it increases in speed across a wider surf zone for increasing wave energy during the storm. This is associated with a bottom shear stress that exceeds the critical bed shear stress, with the potential to initiate motion and transport sediment in agreement with the experimental observations.

Customized converter for cost-effective and DC-fault resilient HVDC Grids

This paper presents a comprehensive study that aims to establish the meaningful range for the ratios of full-bridge cells to the total number of cells per arm, in which the performance of the mixed cells modular multilevel converter (MC-MMC) can be customized by trading the number of FB cells for high value features such as: resiliency to DC faults, reduced capital costs of DC circuit breakers (DCCBs) and running costs of the semiconductor, and continued operation. The MC-MMC design for particular ratio of FB cells to total number of cells per arm to achieve tailored features at system level is termed as an customized modular multilevel converter (CMMC). The primary motivation for the CMMC is to facilitate the use of low-cost and relative slow mechanical DC circuit breakers, with fault isolation times in the order of 8 ms to 12.5 ms. With these objectives to be achieved, interruption of power flows across the DC grid and surrounding AC grids must be minimized. It has been found that after certain ratios of FB cells to total cells per arm, the CMMC starts to exhibit current limiting mode, which helps to reduce DCCBs current breaking capacities and extend critical fault clearance times for remote converters from the fault point. Results of the pole-to-ground and pole-to-pole DC faults, semiconductor loss studies, and extended control range indicate that the presented CMMC is promising for future realization of DC grids.

Semi-supervised deep learning approach to break common CAPTCHAs

Manual data annotation is a time consuming activity. A novel strategy for automatic training of the CAPTCHA breaking system with no manual dataset creation is presented in this paper. We demonstrate the feasibility of the attack against a text-based CAPTCHA scheme utilizing similar network infrastructure used for Denial of Service attacks. The main goal of our research is to present a possible vulnerability in CAPTCHA systems when combining the brute-force attack with transfer learning. The classification step utilizes a simple convolutional neural network with 15 layers. Training stage uses automatically prepared dataset created without any human intervention and transfer learning for fine-tuning the deep neural network classifier. The designed system for breaking text-based CAPTCHAs achieved 80% classification accuracy after 6 fine-tuning steps for a 5 digit text-based CAPTCHA system. The results presented in this paper suggest, that even the simple attack with a large number of attacking computers can be an effective alternative to current CAPTCHA breaking systems.

Technical Assessment on Self-Charging Mechanical HVDC Circuit Breaker

High-voltage DC (HVDC) circuit breaker is the necessary equipment for multiterminal HVDC grids, which is a prospective power transmission method in the future. Therefore, the research about HVDC interruption ushered in an explosive development in recent years. The mechanical DC circuit breaker based on the precharged capacitor for current commutation and interruption is considered to be one of the most promising HVDC interruption solution. However, the commutation capacitor requires a complicated precharging circuit, especially in high-voltage applications, which brings a great challenge to the promotion of mechanical interruption solution. In this article, a novel self-charging mechanical HVDC circuit breaker is proposed. It utilizes the induced voltage generated by part of current limiting reactor to adaptively charge the commutation capacitor under different fault current conditions without extra auxiliary charging circuit. By investigating the influence of capacitance and inductance on the charging time and current commutation process, the optimized parameters are determined. Then, the breaking performance of proposed HVDC breaker under different rising rates of fault current is evaluated in a two-terminal HVDC system. Finally, a low-power prototype is developed to verify the feasibility of the proposed topology and an improved scheme for rated current breaking is discussed.

Melting Pattern of Vacuum Interrupter Contacts Subjected to High Inrush Currents at High Frequencies

One important aspect in capacitor switching concerns the high inrush current during the energizing of the capacitor. For vacuum interrupters, it is assumed that the modification of the contact surface due to high inrush currents has the highest impact on the current breaking performance. One peculiarity of capacitor switching is the high rate of switching operations easily achieving 1000 operations in a couple of years. Two vacuum breakers were therefore operated up to 1000 times in a simple test circuit simulating the making of high inrush currents. According to standards, peak and frequency of inrush currents are 20 kA and 4250 Hz for back-to-back capacitor switching, or around 5 kA and 400 Hz for single bank switching. The range of inrush currents was extended here to peak currents up to 60 kA and frequencies up to 24 kHz. Peak current and frequency have an important impact on radius and current density of the inrush current arc, and thus on the energy deposited under the arc roots. Under the conditions prevailing here, the whole surface of the contacts exhibits a uniform melting pattern with the depth of the solidified melt being less than 1 mm after 1000 operations. It is assumed that the arc moves on the contact surface driven by the radial magnetic forces generated by this kind of contact and distributes the arc energy all over the contact surface. The inrush current integral ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ICI</i> ) might be a measure of the available energy for contact melting or erosion. However, since the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ICI</i> has no relation to the arc current density, it is only representative for a particular melting pattern of the contact surface if frequency and peak inrush currents are varied in a limited range.

Surge Capacity Crisis and Mitigation Plan in Trauma Setting Based on Real-Time National Trauma Registry Data.

The objective of this study was to assess the current breaking point of crisis surge capacity of trauma services in Qatar and to develop a mitigation plan. The study utilized real-time data from the National Trauma Registry. Data was explored cumulatively by weeks, months and a year's interval and all trauma admissions within this time frame were considered as 1 'Disaster Incident.' A total of 2479 trauma patients were included in the study over 1 year. The mean age of patients was 31.5 ± 15.9 and 84% were males. The number of patients who sustained severe trauma which necessitated Level 1 activation was 16%. The emergency medical services (EMS) surge attained crisis of operational capacity at 5 months of disaster incident for priority 1 cases. Bed capacity at the floor was the first to reach operational crisis followed by the ICU and operating room. The gap in the surge for surgical interventions was specific to the specialty and surgery type which reached operational crisis at 3 months. The study highlights the surge capacity and capability of the healthcare system at a Level 1 trauma center. The identified gaps in surge capacity require several key components of healthcare resources to be addressed across the continuum of care.

HVDC Breaker Power Loss Reduction by Bridge-Type Hybrid Breakers

Several types of high voltage direct current (HVDC) breakers have been introduced and commercialized. Each of them has advantages and disadvantages. Among them, the hybrid HVDC breaker is highly successful. One of the most important concerns that the hybrid HVDC breaker has faced is high power loss throughout its fault current breaking process. The hybrid HVDC breaker comprises a high voltage bidirectional main HVDC breaker. A significant number of electronic switches need to be connected in a series where anti-parallel diodes are essentially embraced. During fault inception, a number of series solid-state switches and a number of series diodes dramatically increase the power loss of the main breaker. This study, firstly, studies the power loss of the hybrid HVDC breaker and later develops a structure of a full-bridge hybrid breaker (FBHB) to reduce the losses of the current structure both in the normal and fault protection states. In this paper simulations are done based on PSCAD. In addition to the analytical study and simulations, we show that the developed structure substantially decreases the amount of power lost during the normal operation and fault current breaking stage.

Research on dynamic handover decision algorithm based on fuzzy logic control in mobile FSO networks

Because of multiple advantages such as high bandwidth, high security, and flexible networking, the free space optical communication (FSO) has attracted more and more attention. However, the narrow beam of laser and the constrained access degree of optical node limit the development of mobile FSO networks, especially in the aspect of handover. In this paper, we propose a fuzzy logic control-based handover decision (FLC-HD) algorithm to ensure real-time and reliable communication. First, according to the predictive position and the motion information of mobile nodes obtained by the error correction extend Kalman filter algorithm, we obtain the received signal strength and the relative motion angles at next transmission. Second, we put forward the concept of threshold to ensure the completion of handover operations before the current link breaking. Third, the fuzzy logic control method is designed to select the optimal access point (AP) with three critical parameters, i.e., the received signal strength, the relative motion angles, and the access degrees of nodes. Simulation results show that the FLC-HD algorithm can improve the handover efficiency and relieve the ping-pong effect in mobile FSO networks.