Current Breaking Research Articles

Visualization of the Field Penetration at the Shielding Current Break and Its Restoration in the Pulse Magnetized YBCO Ring

The Hall scanning method was used to measure the distribution of the trapped magnetic field above the melt grown high temperature superconducting (YBCO) ring at various modes of the pulsed field magnetization. The scan detects the ring’s sector with a small trapped magnetic field after pulse with a short duration (14 ms) of sufficient amplitude (μ0На > 0.86 T). The residual field in the entire ring hole is also very low. Under these conditions of magnetization, the screening current is observed to break down in a certain region of the ring. This sector of the current break (SCB) arises as the result of the local overheating and the destruction of superconductivity. But in the rest (larger) part of the ring, the trapped magnetic field is significant since high current densities remain due to its weak heating. If descending time of the magnetizing field is increased from 7 ms to sufficiently large values > 100 ms, then the SCB has time to cool and the irregularity of the trapped magnetic field in the SCB disappears.

Low-Cost HVdc Circuit Breaker With High Current Breaking Capability Based on IGCTs

DC circuit breaker plays an important role in the reliability of HVdc system, but the large number of expensive press-pack insulated-gate bipolar transistors (IGBTs) is used at present, which is a serious impediment to HVdc development. Thus, the low-price integrated gate commutated thyristor (IGCT) becomes a promising alternative device. This letter presents a low-cost HVdc circuit breaker with high current breaking capability based on IGCTs. The topology and principle of the proposed HVdc circuit breaker are introduced at first. Then, the parameter design is analyzed. A scaled-down test successfully demonstrates the high current breaking capability of 15 kA. In the end, the cost comparison shows that this scheme can achieve 61.8% cost reduction of the commutation branch.

Tuning the dynamics of magnetic droplet solitons using dipolar interactions

Magnetic droplets are dissipative magnetodynamical solitons that can form under current driven nanocontacts in magnetic layers with large perpendicular magnetic anisotropy. Here, we extend the original droplet theory by studying the impact of the dipolar interactions on the dynamics of droplet solitons. By varying the thickness of the free layer of a spin torque nano-oscillator, we systematically tune the internal field of the free layer to investigate the dynamics of droplet solitons. Our numerical results show that increasing the free layer thickness increases the droplet threshold current, decreases the droplet frequency and diameter, enlarges the current hysteresis and also modifies the structure of the droplet. The Oersted field of the current breaks the phase coherency and deteriorates the stability of the droplet in free layers with larger thicknesses. Moreover, our findings show a simple relation to determine the impact of the free layer thickness on the droplet nucleation boundaries. Our study presents the missing brick on the physics behind magnetic droplet solitons, and further illustrates that magnetic droplets in thinner layers possess more promising characteristics for spintronic applications and enable devices with higher speed of operation.

A new, established approach to managing misbehavior: system justification theory

PurposeThe status quo for managing deviant workplace behavior is underperforming. The current research offers a new approach for scholars and managers in approaching these misbehaviors. Namely, we outline how system justification theory, which holds that people are motivated to rationalize and justify the systems—including workplaces—to which they belong even when those systems disadvantage them or others, offers value in explaining and addressing the prevalence of such misbehaviors and contemporary failures in managing them.Design/methodology/approachThis conceptual research explores the situated role of onlookers to patterns of workplace misbehavior, like harassment. We explore existing scholarship on why and how onlookers respond to such actions, including cultural elements, and draw parallels between those accounts and the foundational concepts of system justification theory to demonstrate an unrealized theoretical overlap valuable for its immediate applications in research.FindingsThe current paper establishes clear links between system justification theory and efforts to manage misbehavior, establishing system justifications as freezing forces in the culture of a workplace that must be unfrozen to successfully implement strategies for managing misbehavior. Further, we describe how organizational onlookers to misbehavior are subject to system justifications, which limit prescribed means of stopping these patterns of wrongdoing.Originality/valueVery limited organizational scholarship has utilized system justification theory, despite calls for such applications. Given the existing shortcomings in scholarship and management approaches to workplace misbehavior, the current research breaks from the status quo and offers an established theory as a new way to approach these misbehaviors.

Dual Buffer Layers for Developing Electrochemical Metallization Memory With Low Current and High Endurance

In this letter, the dual buffer layers of AgInSbTe (AIST) and monolayer defective graphene (DG) are introduced into amorphous carbon (a-C)-based electrochemical metallization (ECM) type memristor. The advantages of promoting Ag dissolution and localizing cation diffusion region of AIST and DG layers can effectively suppress the well-known current overshoot issue and break the current-retention dilemma. Compared with its counterpart without buffer layer (Ag/a-C/Pt), the device with dual buffer layers (Ag/AIST/DG/a-C/Pt) presents excellent resistive switching (RS) performance, such as lower forming voltage with reduced overshoot current, smaller parameter fluctuations, and better cycling endurance. More importantly, the nonvolatile RS with low operation current of 10 μA and remarkable endurance (> 3.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cycles) is realized, which is among the best of reported a-C-based ECM memories. Benefit from the low operation current, the device also shows the capacity of multilevel memory with six nonvolatile resistance states through regulating the compliance current.

FREIO DE FOUCAULT APLICADO À MEDIÇÃO DE POTÊNCIA EM TURBINA EÓLICA SAVONIUS / EDDY BRAKE APPLIED TO POWER MEASUREMENT IN WIND TURBINE SAVONIUS

In this work is proposed the design of a dynamometer based on Foucault's Current Break for the evaluation of torque and power provided by a Savonius wind turbine model in a wind tunnel. The applied measurement system is of the open source type using the Arduino platform. For the reaction force metering a load cell with converter and amplifier H711 was used as well as a photoelectric sensor with resolution of one pulse per turn for the rotation measurement. Equations available in the literature were used to estimate the wind turbine performance parameters for the dynamometer sizing. The wire applied for magnetic flux generation in the coils is AWG24, to support an electrical current rating of 0.5 A and a voltage of 1.0 V. The coils size are 3.1 cm of diameter and 3.0 cm of length. Two coils were applied in order to satisfy the wind turbine demand. As a result, the dimensional characteristics of an eddy current brake able to measure a power of up to 0.5 W, generated by a Savonius wind turbine, were obtained, with uncertainty of measurement about 0.01 W, being adequate for the analyzed turbine.

СПОСОБИ ПІДВИЩЕННЯ ККД І ПОКРАЩЕННЯ ОСНОВНИХ ХАРАКТЕРИСТИК DC/DC ПЕРЕТВОРЮВАЧІВ ІЗ ПОЗДОВЖНІМ КЛЮЧЕМ

The results of the study of three new variants of DC/DC-pulse converters (DCC) with a longitudinal transistor switch are presented. It is established that the creation of conditions in which there is no sharp break of the DCC input current, leads to a smooth change in voltage on its switch and to minimize the range of variation of this voltage, which is accompanied by reduced power losses on the switch and improved power quality at the DCС input and output. It is shown that the creation of such conditions is implemented using two-winding chokes and an input buffer node. Exact and approximate analytical expressions are presented that describe the processes in such converters, which are in good agreement with the results of computer simulation. The most acceptable ways to control the switches of DCC-1...DCC-3 were found out. Recommendations for the use of DCC -1... DCC-3 are given. References 11, figures 1, table 1.

New DC Solid-State Circuit Breaker With Natural Charging Operation

Recently, with the development of renewable energy such as solar power and wind power, the dc grid has garnered attention and the dc circuit breakers essential to the dc grid have been actively studied. The dc solid-state circuit breaker (dc SSCB) can quickly break the fault current within 1 ms compared with a mechanical circuit breaker, which does the same in several tens of milliseconds. The previous thyristor dc SSCB cannot naturally charge the commutation capacitor for fault current breaking, and thus its control of operation is complicated. Thus, this article proposes a new thyristor dc SSCB, which can naturally charge the commutation capacitor without complicated switching operation. It can not only perform the fast breaking of fault current, but also the operating duties of reclosing and rebreaking. The operating characteristics of the proposed dc SSCB are verified by the experimental results.

Research on the Postarc Sheath Growth Process Considering the Plasma Motion and Distribution

In this article, the sheath growth of the vacuum circuit breaker and its initial conditions of the calculation are introduced. The images of cathode spots distribution and waveforms of postarc current under different frequencies are obtained by medium- to high-frequency current breaking experiments. The quantitative relationship of $D$ and $di/dt$ with the variation of current frequency $f$ and current amplitude $I_{m}$ is obtained by fitting the data. The reasons for the change of postarc current parameters are reasonably explained by the analysis of equivalent circuit and plasma movement process. Combined with the continuous transition model (CTM) and its initial calculation conditions, the influence of the cathode spots distribution diameter $D$ and $di/dt$ after the current zero crossing on the sheath growth is analyzed. An initial postarc plasma density calculation model which is suitable for each current frequency is proposed which makes the calculation of the sheath growth more accurate, especially when applied to medium- to high-frequency current conditions.

Enabling Aqueous Processing for Low/No-Cobalt Lithium-Ion Battery Cathode Active Materials

Industrially, lithium-ion battery cathodes are manufactured through a wet slurry mixing and coating process. There is great interest in replacing the presently-used N-methyl-2-pyrrolidone (NMP) solvent with water due to the cost and toxicity associated with NMP. In this study, the modifications made to the active materials as a result of water exposure were studied and two materials, LiMn2O4 (LMO) and LiNi0.8Co0.15Al0.05O2 (NCA), were assembled in high-performing aqueous-processed cathodes for the first time.Five cathode active materials were the subject of this study: LiCoO2 (LCO), LiFePO4 (LFP), LMO, NCA, and LiNi0.5Mn0.3Co0.2O2 (NMC532). All materials exposed to DI water exhibited rapid increases in pH over the first 10 min, with stable pH values ranging from 9.0 (LFP and LMO) to 12.5 (NCA). Given that the protective aluminum oxide layer on the current collector breaks down at a pH of 8.5, corrosion is predicted for all materials, with NCA being the most extreme case. Pristine samples of the same five materials were submerged in water for 24 h, then the moisture was dried in a vacuum oven. The crystal structures of these materials (henceforth referred to as the wetted samples) were evaluated using X-ray diffraction and compared with pristine samples. No changes were observed in the crystal structure of any material as confirmed by Rietveld refinement. X-ray photoelectron spectroscopy was used to evaluate the changes of the surface composition of each wetted and pristine material.Based on inductively coupled plasma-mass spectrometry results, the amount of Li and transition metal leaching in water was found to be independent of time in excess of 1 h, and the amount of Li leaching in water for NCA was found to be five times that of NMC532 and more than 30 times that of the other materials. As a result, using a traditional aqueous slurry formulation (active material, carbon black, emulsion binder, carboxymethylcellulose thickener) resulted in a severely cracked and unusable NCA cathode. By including high-molecular weight polyacrylic acid (PAA), the adhesion of the cathode was restored. Half coin cells of this PAA-processed and an NMP-processed NCA cathode were constructed using punches with 1.7 mAh·cm-2 areal capacity and a charge and discharge rate of C/3 between 3.0-4.3 V. The initial capacity of the PAA-processed NCA cathode was slightly lower (176.3 mAh·g-1 to 185.2 mAh·g-1), though it did exhibit better capacity retention through 100 cycles (84.2% to 78.1%).

De la unidad suramericana a la fragmentación regional: contradicciones en la UNASUR a partir de las políticas de los gobiernos lulistas y las tensiones con las clases dominantes

Este artículo propone abordar las contradicciones y los problemas de fragmentación regional que surgieron en el seno de la UNASUR a partir de las políticas promovidas por los gobiernos lulistas en Brasil. Desde un diseño metodológico cualitativo que recupera el material de entrevistas a informantes clave, junto con el análisis de documentos y fuentes oficiales, se abordan las tensiones que se sucedieron a escala regional a partir de la reconstrucción de algunas de las principales políticas del Estado brasileño en relación a Suramérica. Reflexionamos en torno a las problemáticas vinculadas con la fragmentación que se produjo luego del impulso inicial que los procesos de integración tuvieron. Desde la singularidad de la UNASUR, se plantean nuevos interrogantes a la luz de su parálisis actual. Estos nos permiten visualizar por un lado, algunos de los avances en materia de integración regional que la UNASUR propició. Y por otro lado, las problemáticas subyacentes que persistieron durante su funcionamiento hasta su reciente freno, en un nuevo ciclo de las políticas integracionistas.

Transport Coefficients of Air - PMMA Mixtures Thermal Plasmas

The transport coefficients of Air - PMMA mixtures thermal plasmas is important to estimate the performances of cutting of the electrical arc in this gas by a circuit breaker. In this paper, Air - PMMA mixtures thermal plasmas dynamical viscosity, thermal and electrical conductivities coefficients are calculated in a temperature range from 5000K to 30000K. The calculations are made by supposing thermodynamic equilibrium at pressure of 1 bar to 10 bar. The results of the calculations show the influence of the initial proportion of PMMA but also that of the pressure on the mixture plasma transport coefficients. As the efficiency of the breaking of the electric current by the circuit breaker depends closely on the thermal and electrical characteristics of the extinguishing medium, this extinguishing medium should have a high thermal conductivity and an electrical conductivity varying rapidly with temperature. The plasma of the mixture constituted by 80% of air and 20% of PMMA presents at first sight best characteristics for the breaking of electric current. It has the highest thermal conductivity peak among the plasmas of the mixtures studied.

VIDEOCONFERENCING FOR SPEAKING ASSESSMENT MEDIUM: ALTERNATIVE OR DRAWBACK?

The urgency of technology integration has arisen due to the current pandemic break. With a sudden shift from conventional learning to virtual learning, less proper preparation on utilizing the technology integration may occur. The present study aimed at unraveling the perception and obstacles faced during the implementation of videoconferencing as a speaking assessment medium. By applying qualitative research with a snapshot case study design in a vocational education institution, this study gained the data through questionnaires, focus group discussion, and an interview. As a result, the majority of the students perceived negatively toward the implementation of videoconferencing as a speaking assessment medium. These negative reactions occurred due to the nervousness and anxiety along the online speaking assessment process. Moreover, the obstacles faced, such as bad internet connection, technical problems, and surrounding disturbance, also contributed an impact on students’ language production and the sound heard by the students during the online speaking assessment. From the results of the present study, the application of videoconferencing as a medium in assessing students’ speaking ability needs to be reappraised to preview its function whether it can be used as an alternative way or it contributes a drawback effect during the assessment process.

A New Active Thyristor-Based DCCB With Reliable Opening Process

Replacing expensive IGBT with thyristor to design dc circuit breaker (dcCB) is attracting attention recently due to its advantages in terms of low investment and low conduction loss. However, due to the half-controlled characteristic of thyristor, the existing thyristor-based dcCBs (T-CBs) cannot be actively turned off. As a result, the opening process is not fully controllable and reliable. In this letter, a simple active T-CB (AT-CB) topology is proposed. The proposed AT-CB can interrupt both fault current and operation current actively, and the current breaking process is fast, reliable, and fully controllable. Moreover, the proposed AT-CB can be improved to be bidirectional without increasing the conduction loss, and the topology remains simple. Parameters design principle and operation process of AT-CB are presented. Scaled-down experiment verified the effectiveness of the proposed solution.

Study of Arc Parameters of AC Relays Operating under Distorted Supply Voltage Conditions

The paper presents a procedure for measuring and analyzing the switching arc parameters occurring in air-insulated low voltage (LV) relays operating in distorted supply voltage conditions. The main purpose of the research was the analysis of the switching arc duration and its energy affecting the current breaking capacity of the selected LV current interrupters (CI). The performed study and simple statistical analysis enabled the determination of the main factors and their impact level on parameters of the switching arc that comes about during switching-off operation. Experimental tests executed for various shapes of the supply voltage but similar RMS (Root Mean Square) and THD (Total Harmonic Distortion) values and for various breaking moments of the load current allowed recognition of the decisive factors for estimating the tested relay’s switching-off capacity. Tests stand combined with dedicated software developed in the frame of the research, permiting fast calculation of the arc parameters based on a large number of recorded diagrams.

An experimental analysis of DC magnetic blowout high-speed circuit breakers’ parameters

High-speed circuit breakers (HSCB) used in DC circuits are one of the basic elements of overload, short-circuit and electric shock protection. Such breakers are used in transport (trams, trolleybuses, subways and railways) in electric power supply facilities and in vehicles. The performance and capability of limiting the current depend on the HSCB design and solutions applied in it. The circuit parameters, particularly its inductance also affect the performance. Additionally, each DC breaking in the RL circuit is accompanied by overvoltages whose level depends on the circuit parameters and breaker design. The paper discussed the process of direct current breaking by magnetic blowout high-speed circuit breakers and factors that affect the HSCB performance, i. e. opening time and arcing time. The influence of the circuit parameters and HSCB design on the value of arc voltage is outlined. The results of laboratory tests of 4 types of high-speed circuit breakers produced in Europe are presented. The test results were used to analyze the effect of current changes in the short circuit on the time of current breaking and the value of switching overvoltages – arc voltage. The results of simulation of the short-circuit breaking in the RL DC circuit made at the rate-of-rise of current in the circuit are presented. Based on the tests and simulations, the current breaking times, values of arc voltage generated in this process and arc energy that is acquired and dissipated by the arc chamber are determined. The objective of the tests and simulations was to answer the question whether it is possible to turn off direct current quickly without generating high arc voltage values – overvoltages in the circuit and how di/dt changes should be formed by a high-speed circuit breaker to achieve the shortest possible time with the lowest possible arc voltage and its lowest energy

Research on the Multiphysics Field-Circuit Coupling Model of Press Pack IGBT Considering the Application of Hybrid HVDC Breakers

Press pack insulated gate bipolar transistor (PP IGBT) is suitable for the hybrid high voltage direct current (HVdc) breaker to clear the fault current of the flexible HVdc transmission system with its advantages of double-side cooling, short-circuit failure mode, and easy to connect in series. However, it should have the ability to transmit the fault current, which is up to five or six times of its rated current, within several milliseconds depending on the distances between two stations without external cooling system. The junction temperature of PP IGBT will increase sharply and it is not possible to be measured during that situation. Therefore, the accurate prediction of junction temperature is extremely important for the packaging design of PP IGBT according to its working condition. In this article, an electro-thermo-mechanical multiphysics field-circuit coupling model of PP IGBT, which is coupled with the electrical, thermal, and mechanical fields, is proposed to predict the collector current, clamping force, and junction temperature. The 3-D mechanical model is decoupled with the 1-D electro-thermal Cauer network model to simplify this multiphysics model without reducing its accuracy. Both the normal and worst working conditions are analyzed through this multiphysics field-circuit model.

A miniaturized wireless micro-heating strip integrated with an acrylate-composite temperature regulator for restenosis prevention

• This work presents aminiaturized wireless heating strip with novel temperature regulator forwireless hyperthermia treatment. • The proposed device employs an acrylate-based composite which is critical for achieving smooth regulation of temperature. • The resonant methodoffers high frequency selectivity and high efficiency in wireless heating. • The temperature regulator enables the capability of heating regulation in a passive manner, reducing the complexity of the device, and thus further facilitates the miniaturization of the device. This work proposes a miniaturized wireless heating strip designed for safe wireless hyperthermia treatment against restenosis. The proposed heating strip was designed to be inserted into a stent that can be deployed in a blood vessel using a typical catheter-based delivery system. The device consists of a micromachined LC-based resonator and a microheater with a temperature regulator (MHTR). The LC-based resonator was employed to achieve wireless resonant RF heating, with the embedded MHTR serving as an electric current breaker in the resonator circuit to maintain the strip’s temperature within a desired range. An acrylate-based composite was used as the key material of the MHTR for temperature sensing and electric-current breaking. The MHTR allows smooth heating regulation in a passive manner, reducing the complexity of the device, and thus further facilitates the miniaturization of the device. The frequency responses to temperature of devices with and without an MHTR were studied. The performance of devices immersed in physiological saline solution was also examined in detail. Wireless heating tests demonstrated that the proposed MHTR effectively maintained the device temperature at around 45 °C with an output RF power of 500 mW. The results indicate that the proposed device potentially offers safe and reliable hyperthermia treatment.

Persistent spectral graph.

Persistent homology is constrained to purely topological persistence, while multiscale graphs account only for geometric information. This work introduces persistent spectral theory to create a unified low-dimensional multiscale paradigm for revealing topological persistence and extracting geometric shapes from high-dimensional datasets. For a point-cloud dataset, a filtration procedure is used to generate a sequence of chain complexes and associated families of simplicial complexes and chains, from which we construct persistent combinatorial Laplacian matrices. We show that a full set of topological persistence can be completely recovered from the harmonic persistent spectra, that is, the spectra that have zero eigenvalues, of the persistent combinatorial Laplacian matrices. However, non-harmonic spectra of the Laplacian matrices induced by the filtration offer another powerful tool for data analysis, modeling, and prediction. In this work, fullerene stability is predicted by using both harmonic spectra and non-harmonic persistent spectra, while the latter spectra are successfully devised to analyze the structure of fullerenes and model protein flexibility, which cannot be straightforwardly extracted from the current persistent homology. The proposed method is found to provide excellent predictions of the protein B-factors for which current popular biophysical models break down.

Bridge‐type fault current limiter and hybrid breaker for HVDC grids applications

The fast raising nature of DC fault currents and sensitivity of high-voltage DC (HVDC) power converters to DC faults is critical protection issues. On the other hand, DC fault current does not meet zero; which causes DC to fault current breaking process become more challenging. Specifically, to protect HVDC grids against DC fault currents, the development of very fast breakers is crucial. This study proposes a DC fault current limiter and breaker, which is able to protect the HVDC system/grid in a very fast and safe manner. The main goal of this study is to enhance the performance of already in the market hybrid DC circuit breakersincluding the magnitude of fault current and breaker operation speed. In the proposed HVDC fault current limiter and breaker, the fault current is limited in two stages by an inductive and resistive current limiter, which drastically decreases the main breaker dissipated energy. The functionality of the proposed HVDC fault current limiter and breaker is mathematically analysed, and then verified by PSCAD and Matlab/Simulink. Finally, simulation results are validated by scaled-down laboratory examinations.