Search

Reverse breakdown in Cu(In,Ga)Se2 (CIGS) solar cells can lead to defect creation and performance degradation. We present pulsed reverse-bias experiments, where we stress CIGS solar cells with a short reverse voltage pulse of ten milliseconds and detect the electrical and thermal response of the cell. This way, we limit the duration of the reverse stress, allowing us to study the initial stages of reverse-bias defect creation in CIGS solar cells and modules. Our results show that permanent damage can develop very fast in under milliseconds. Furthermore, we find the location of defect creation as well as the susceptibility to defect creation under reverse bias depends strongly on whether the cell is encapsulated or not, where encapsulated cells are generally more robust against reverse bias.

Microservice platforms have brought many advantages to support the deployment of light-weight applications at both near the edge and data centers. Still, their suitability to support telecommunication and vertical services beyond the network edge is far from being a reality. On one hand, their flat networking approach does not support the establishment of link-layer connectivity among the different components of telecommunication and vertical services (e.g., access points, routers, specific-purpose servers, etc.) due to their reliance on high-level APIs. On the other hand, their networking approach has not been designed to operate over ad hoc networks built by the resource-constrained devices that may be available beyond the network edge. This can lead to suboptimal behaviors for the delivery of data traffic between microservices. This article presents the results of a research collaboration between Universidad Carlos III of Madrid and Telefónica: L2S-M. Our solution provides a programmable data plane that enables the establishment of on-demand link layer connectivity between microservices on ad hoc networks. This solution has the flexibility to execute different algorithms to build traffic paths between microservices, as well as to react against temporary link breakdowns, which could be present in these types of networks. The article presents a proof of concept for a functional validation of L2S-M, using an aerial ad hoc network deployed at 5TONIC Laboratory in collaboration with Telefonica. The validation results showcase the proper operation of L2S-M as a networking service for microservice platforms in ad hoc networks, including its ability to reconfigure the programmable data plane when link disruptions occur. This article has been supported by the TRUE5G (PID2019-108713RB681) project funded by the Spanish National Research Agency (MCIN/AEI/10.13039/5011000110) and by the H2020 FISHY Project (Grant agreement ID: 952644).

The influence of a non-uniform electric fields (a cylindrical capacitor) on the combustion of liquid droplets of such hydrocarbons as benzene, hexane, and methanol, which are characterized by different soot formation degrees, is experimentally studied. It is shown that the applied field can both increase and decrease the fuel mass burning rate depending on the field polarity (direction) and the fuel type. The hysteresis phenomena – the flame lift-off from the droplet and the droplet coverage with flame – and their dependence on the field properties, are described., Експериментально дослiджено вплив неоднорiдного електричного поля (цилiндричний конденсатор) на горiння вуглеводневої краплi бензолу, гексану, або метанолу, для яких притаманний рiзний ступiнь утворення сажi. Показано можливiсть як збiльшення, так I зменшення масової швидкостi горiння в залежностi вiд полярностi (напрямку) поля I виду палива. Описано гiстерезиснi явища у процесi зриву або охоплення краплi полум’ям в залежностi вiд величини поля.

The effect of 20 MeV electron radiation on the lifetime of the silicon carbide power MOSFETs was investigated. Accelerated constant voltage stress (CVS) was applied on the pristine and irradiated devices and time-to-breakdown ( T BD ) and charge-to-breakdown ( Q BD ) of gate oxide were extracted and compared. The effect of electron radiation on the device lifetime reduction can be observed at lower stress gate-to-source voltage ( V GS ) levels. The models of T BD and Q BD dependence on the initial gate current ( I G0 ) are proposed which can be used to describe the device breakdown behaviour. peerReviewed

A lateral power device with complementary homogenization field structure (C-HOF) is proposed and experimentally proved in this letter. The C-HOF is formed by introducing a P-type metal insulator semiconductor (P-MIS) on the N-MIS. The complementary P/N-MIS and the PN junction between them ensure the homogenized field ${E}_{\text {hof}}$ distributions and the high breakdown voltage ${V}_{\text {B}}$ in higher doping. Based on the C-HOF mechanism, experiments were performed, which demonstrated that a significantly increased N-drift doping dose up to 6.8 $\times \,\,10^{{12}}$ cm−2 can be realized in the C-HOF device. A measured low specific on-resistance ${R}_{ {{\scriptscriptstyle \text{ ON}}},\text {sp}}$ of 19.7 $\text{m}\Omega \cdot $ cm2 was observed in the C-HOF device under a ${V}_{\text {B}}$ of 426 V, realizing a high figure of merit $FOM = {V}_{\text {B}}^{{2}}/{R}_{ {{\scriptscriptstyle \text{ON}}},\text {sp}}$ of 9.21 MW/cm2 and a reduction of 42.8% when compared with the theoretical value of the triple RESURF technology under the same ${V}_{\text {B}}$ .

This work demonstrates a trench isolated lateral double-implanted MOSFET (LDMOS) on Si-face in 4H-silicon carbide (SiC). A device $\vphantom {_{\int _{}}}$ where ${L}_{\textit {ch}} = 0.8\,\,\mu \text{m}$ and ${L}_{d} = 12\,\,\mu \text{m}$ shows an ${R}_{ \mathrm{\scriptscriptstyle ON},\text {sp}}$ of 22.9 $\text{m}\Omega $ cm2 at a ${V}_{\text {GS}}$ of 20 V and a breakdown voltage (BV) of 1100 V, corresponding to a high BV2/ ${R}_{ \mathrm{\scriptscriptstyle ON},\text {sp}}$ of 55.5 MW/cm2. Devices that have different ${L}_{\text {ch}}$ , ${L}_{\text {JFET}}$ , ${L}_{d}$ , and P-top dose values are measured in order to investigate the effects of geometry on the static performance. Operations at 150 °C are measured to evaluate the temperature performance. Gate charge waveforms are also measured in order to include the switching performance in the evaluation. The ${R}_{ \mathrm{\scriptscriptstyle ON}} \times {Q}_{G}$ and ${R}_{ \mathrm{\scriptscriptstyle ON}} \times {Q}_{\text {GD}}$ values are calculated as 17.7 and $9.0~\Omega $ nC, respectively, which are promising for power-integrated circuit applications.

PMIA (Poly-m-phenylene isophthalamide) is an ideal substitute for traditional cellulose paper in oil-immersed paper insulating scenarios. This paper studies the partial discharge characteristics of oil-immersed laminated PMIA. According to the $\mathrm{q}{-}\varphi$ scatter diagram, discharge quantity and discharge phenomenon, the partial discharge process of PMIA is divided into 3 stages: creeping discharge, co-existence discharge and pre-breakdown. The micro-structure and chemical components of damaged PMIA are presented. The carbon trace, functional groups, carrier trap characteristics and residual insulation strength in different stages of partial discharge are studied. This paper provides a theoretical basis for the application of PMIA in electrical insulation.

Dissertação de mestrado integrado em Engenharia Informática, The procedural generation of geometry within the space of computer graphics has been a topic of study for quite some time, benefiting from a more unpredictable brand of randomness. Similarly, the exploration of lighting as a phenomenon within virtual space has been a field of study of comparable age. Despite its age and early adoption, there is a surprising lack of research in emulating the phenomenon of lighting past its interactions with the world. Most implementations of procedurally generated lightning within video games are based on randomized data trees. When part of the skybox, 2D meshes or textures are randomly selected from a pre-made pool. There are, however, methods based entirely on the dielectric breakdown model, using approximations to solve a Laplacian equation. This dissertation aims to present an alternative approach to the randomized and procedural generation of lightning bolts based on the Space Colonization algorithm. While the algorithm was first conceived for use in botanical applications, modeling the growth of biological structures, the similarities between the results produced by the dielectric breakdown model and botanic modeling algorithms coupled with the visual likeness of a lightning bolt and certain trees, made for solid groundwork upon which to establish this unique approach. As such, this work largely aims to be a first step into this particular realm, showing Space Colonization as a suitable algorithm for this specific purpose. That being said, a large portion of time was spent iterating, modifying and experimenting with ideas that were either discarded or adapted, an effort primarily dedicated towards controlling and stifling the possible growth of branches in ways beyond the reduction of attractors. The original algorithm was altered, focus put especially on the creation of a singular channel at a time, mixing discoveries from previous research with the work done on manipulating Space Colonization. Instead of the venation patterns observed with the original work, the stifling of any growth means that each node has a chance, when created, of sprouting a branch and each branch is, in turn, a different, modified instance of the same underlying concept providing an additional level of control. Effort was equally placed on showcasing different properties inherent to a lightning strike, such as its iterative construction when descending from its origin. In the rendering section, along with recreating the bloom and glow effect seen in previous works, effort was put into recreating the strobing observed in capturing slow-motion footage of lightning bolts with special detail given to this. In addition, parameters were joined with a waypoint system to allow for a great degree of freedom when generating new bolts., A geração iterativa de geometria no contexto de computação gráfica é um tópico de estudo à já algum tempo apesar de usado em apenas contextos específicos, um ramo que benefícia de um tipo de aleatoriedade imprevisível. Similarmente, a exploração de relâmpagos como um fenómeno em espaço virtual é uma faceta de idade comparável. Apesar disto, o foco quando tratando relâmpagos tem caído marioritariamente nos seus efeitos após impacto. Estudos têm sido conduzidos no âmbito de mitigar o dano causado por estes em fuselagem de aeronaves e analizar o impacto de trovoada em estruturas críticas. No entanto, existe uma falta de investigação sobre a emulação deste fenómeno barra as suas interações com o mundo. A maioria das implementações iterativas em video jogos são baseadas em árvores de dados. Quando fazem parte do cenário, são marioritariamente meshes ou texturas 2D selecionas aleatoriamente de um conjunto. Existem, no entanto, métodos baseados num modelo de colapso elétrico usando apróximações a uma equação de Laplace. Esta dissertação tem como foco apresentar uma alternativa para a geração aleatória e iterativa de relâmpagos baseada no algoritmo de Space Colonization. Apesar deste algoritmo ter sido concebido para uso botânico, modelando o crescimento de estruturas biológicas, as similaridades entre os resultados obtidos pelo modelo de colapso elétrico e estes algoritmos de modelagem, quando considerados com a semelhança entre certos relâmpagos e árvores, constroem uma fundação sólida para o tópico. Neste âmbito, este trabalho é um primeiro passo que tem o intuito de mostrar a capacidade do algoritmo de Space Colonization em simular relâmpagos. Dito isto, uma grande porção do tempo de desenvolvimento dobrou-se sobre a iteração modificação e experimentação de ideias que foram discardadas ou adaptadas, um esforço primariamente dedicado em controlar o crescimento de ramos sem reduzir o número de atratores. O algoritmo original foi alterado, focando especialmente na criação de um único canal e fazendo uso de conhecimento prévio, oriundo de trabalho e investigação feita sobre manipulação de Space Colonization. Em vez de padrões de venação, observados no trabalho original, o impedimento de qualquer crescimento significa que cada nodo tem uma probabilidade, quando criado, de dar origem a um ramo e que cada ramo é uma instância diferente e modificada do mesmo conceito, algo que cria um nível de controlo mais profundo. Um esforço extra foi, também, realizado com o intuito de mostrar todas as propriedades diferentes, inerentes a um relâmpago tal como a construção iterativa durante a sua travessia. Na parte de renderização, foram recriados efeitos de brilho e bloom vistos em trabalhos prévios. Foi também dada especial atenção à recriação do efeito estroboscópico observado durante a análise de imagens em câmera lenta, algo que se tornou no foco principal desta parte. Adicionalmente, a adição de parâmetros foi conjugada com um sistema de pontos que dá um grau superior de liberdade ao utilizador.

This paper presents an adaptive adjustment of thresholds for diagnosing the insulation status of medium-voltage power cable joints and triggering the emergency alert before insulation breakdown. The principle of this method is based on the decrease in the discharge phase along with insulation degradation. First, the initial threshold is evaluated by the end of the partial discharge (PD) data, so that it can classify the insulation status as about to fail. In addition, the adaptive adjustment of thresholds can trigger the emergency status alert earlier and even effectively test the samples where initial thresholds cannot trigger the emergency alert. The proposed method does not need the definition of the state class, unlike machine learning. The performance of the different adjustments is estimated using two types of PD quantities: average discharge and fractal of the n-q-φ pattern. The latter effectively triggers the emergency status alert in all test samples before insulation breakdown. The residual time after the emergency alert, related to maintenance, is also studied and compared.

A 2-D analysis of OFF-state breakdown characteristics of AlGaN/GaN HEMTs with a high- ${k}$ passivation layer is performed as a function of gate-to-drain distance ${L} _{\text {GD}}$ . The relative permittivity of the passivation layer $\varepsilon _{\text {r}}$ is changed from 1 to 60, and ${L} _{\text {GD}}$ is changed from 1.5 to $10~\mu \text{m}$ . It is shown that, in all cases with different ${L} _{\text {GD}}$ , the breakdown voltage ${V} _{\text {br}}$ increases as $\varepsilon _{\text {r}}$ increases. When a deep-acceptor density in an Fe-doped buffer layer ${N} _{\text {DA}}$ is $10^{{17}}$ cm $^{-{3}}$ and the gate length is $0.3~\mu \text{m}$ , ${V} _{\text {br}}$ is determined by buffer leakage current at $\varepsilon _{\text {r}} \ge30$ before impact ionization dominates. Hence, ${V} _{\text {br}}$ is similar at ${L} _{\text {GD}} =3$ – $10~\mu \text{m}$ , and the increase rate in ${V} _{\text {br}}$ from ${L} _{\text {GD}} = 1.5\,\,\mu \text{m}$ is about 50% even at $\varepsilon _{\text {r}} =60$ . However, when ${N} _{\text {DA}}$ is $2\times 10^{{17}}$ cm $^{-{3}}$ , ${V} _{\text {br}}$ is determined by impact ionization of carriers even at $\varepsilon _{\text {r}} \ge30$ because the buffer leakage current is reduced. ${V} _{\text {br}}$ becomes about 500, 930, 1360, and 1650 V for ${L} _{\text {GD}} =1.5$ , 3, 5, and $7~\mu $ m, respectively, at $\varepsilon _{\text {r}} =60$ . These voltages correspond to gate-to-drain average electric fields of about 3.3, 3.1, 2.7, and 2.3 MV/cm, respectively. Particularly, for short ${L} _{\text {GD}}$ , the electric field profiles between the gate and the drain are rather uniform. However, in the case of ${L} _{\text {GD}} = 10\,\,\mu \text{m}$ , ${V} _{\text {br}}$ is about the same as that (1650 V) of ${L} _{\text {GD}} = 7\,\,\mu \text{m}$ , suggesting that the electric field at the drain edge of the gate becomes a critical value before the high electric field region extends to the drain enough. This may be a limitation to increase ${V} _{\text {br}}$ by using a high- ${k}$ passivation layer in this case. However, it can be said that, to improve ${V} _{\text {br}}$ further at long ${L} _{\text {GD}}$ , such as $10~\mu \text{m}$ , the combination of field plate or using a higher $\varepsilon _{\text {r}}$ material may be effective because both of them decrease the electric field at the drain edge of the gate.

The development of lightning protection standards for petrochemical processing and storage facilities has progressed significantly over the past 20 years. Standard requirements have become more stringent and prescriptive. Understanding of the development and propagation of lightning has grown with the advent of 3D-detection systems. This is part 1 of a three-part primer on lightning protection systems (LPSs) for petrochemical production, storage, and processing facilities. Part 1 covers the basic science behind lightning strikes and the history of lightning research, protection systems, and models of attachment. The purpose of this article and this primer series is to update the design and operating engineer?s knowledge of lightning protection at petrochemical facilities and to increase worker and equipment safety in these facilities.

In this paper we consider phase-field model which describes electric breackdown process in solid dielectrics. The presented model extends the earlier presented one. The derived model includes energy conservation equation, accounts for nonisothermal effects (e.g., Joule heating) and consistently describes energy transformation during breakdown channel propagation. The consistent derivaton of the model is performed in the context of rational thermomechanics framework and M. Gurtin theory of microstresses and microforces.

Lift (or elevator) breakdowns cause huge inconveniences to city dwellers and affect more than 80% of Singapore's residents who live in high-rise apartments. Unfortunately, lift maintenance today is either preventive (e.g., follows a fixed cycle based on statistics) or reactive (the faults are fixed after they happen).

Silver niobate AgNbO3 ceramics have been regarded as a promising lead-free material for energy storage applications. In present work, pure and fine AgNbO3 powders were successfully fabricated via the hydrothermal method using AgNO3 as the raw material. It is found that the reaction products show strong dependence on the molar ratio of NH4HF2:AgNO3:Nb2O5, pH value and reaction time. Pure AgNbO3 powders were obtained when the process conditions are 3NH4HF2:2AgNO3:xNb2O5 with x≤0.85 or yNH4HF2:2AgNO3:1Nb2O5 with y = 4–5, pH = 5 and reaction time t ≥ 10 h. Benefitting from the hydrothermal synthesised AgNbO3 powders, AgNbO3 ceramics with fine-grain of ∼3.4 μm were obtained. The fine-grain leads to increased electric breakdown strength Eb up to 250 kV/cm, which is the highest among the pure AgNbO3 ceramics to our best knowledge. The further enhancement in Eb and recoverable energy density could be highly anticipated if the antiferroelectric phase could be stabilized.

Researches on the transformer oil-based nanofluids to determine its suitability for replacing the conventional liquid insulation has been consistently happening for more than a decade. Yet, to prepare an optimum blend of transformer oil-based nanofluid with the stability compliance and superior breakdown (BD) characteristics is still a key issue to be addressed. So to achieve the higher BD voltages (BDVs) with good stability, the nanoparticle and surfactant weights dispersed in the oil should be optimised to at least possible critical levels. In this work, dielectric BD characteristic of mineral oil dispersed with TiO(2) nanoparticle and surfactant cetyl trimethyl ammonium bromide (CTAB) is been studied with the applied AC and DC high voltages, which is termed as titania-based transformer nanofluid (TTNF) for this study. Series of TTNF samples were synthesised with different weights of TiO(2) nanoparticle and CTAB, and the partial discharge inception voltage, AC and DC BDV were experimented to ascertain the optimum concentration level. Results show that the AC and DC BDV enhanced up to 36.23 and 43.07%, respectively, for the TTNF prepared with 0.00562 wt% of TiO(2) and its 1% weight of CTAB, which was stable for around eight weeks.

Electric breakdown of a thin film of polypropylene is accompanied by emission of the electromagnetic radiation pulse of about 400 ns duration with a spectrum consisting of three main frequencies. A relationship between the electric resistance of the breakdown channel and observed radiation spectrum is explained.

Competency assessment is a complex problem that has been approached from multiple perspectives but remains a work in progress. This paper presents a new competency assessment model accompanied by a computational assistant that guides its implementation. The model covers seven phases of an evaluation process, beginning with the definition of the competency and ending with the feedback of evidence provided from the teacher to the students. In each phase, the assistant provides suggestions to the teacher, which are obtained through text analysis algorithms and improve as information is added. The model was validated through pre and post-test study requiring the participation of a group of university teachers. The results indicate that with the use of the model, the time invested by the teacher in evaluation tasks is reduced, the clarity and completeness of the process improves, and an integrated evaluation of generic and specific competences is achieved.

Trends in the studies of mineral oil (MO)-based nanofluids (NFs) show that most of the conducted works have focused only on the thermal and dielectric properties but few numbers on the ageing performance. In the present study, ZnO NF, in combination with cellulose insulation experienced accelerated thermal ageing at 120 °C for 20 days to study the ageing performance and it was compared with that of MO–cellulose insulation. The deterioration rate of cellulose was evaluated through tensile strength, breakdown voltage (BDV) and dielectric dissipation factor properties. Whereas oils deterioration was evaluated through BDV, interfacial tension, kinematic viscosity, acidity and colour. The results demonstrate that for cellulose aged in NF (NFIP), the tensile strength and BDV are 3 and 6.9% higher, respectively; than those aged in MO. For aged oils, NF exhibits higher values of the viscosity and acidity by 3 and 33.3%, respectively, than MO. The BDV of NF is superior to that of MO in the initial ageing period, after that; it shows a lesser reduction tendency with ageing. The most important observation from this study is that despite this increment of ageing indicators for NF, it could improve the anti-ageing properties of cellulose insulation.

Repetitively pulsed gas volume and dielectric surface discharges have gained growing attention because of peculiar and exciting physics phenomena, high efficiency, high reactivity, and potential to obtain conventionally unachievable plasma properties. Nevertheless, incomplete understanding of fundamental mechanisms renders the repetitively pulsed discharge far less predictable and controllable, where the inherent memory effect and the discharge mode transition are universal challenges. In this topical review, the authors will explore the macroscopic characteristics of the gas gap breakdown and the surface flashover, state-of-the-art mechanisms and dominant agents of discharge memory effects, operation regimes and transitions of the discharge mode, and how waveform parameters affect the pulsed discharge properties. Challenges and potential approaches for further understanding the memory effect and the discharge mode transition in the repetitively pulsed discharge are discussed.

Polymer nanocomposites with improved dielectric permittivity and high breakdown strength are extremely desirable for the flexible electronic devices and power systems. The compatibility of fillers and polymer matrix is important in determining the dielectric and breakdown strength properties. The core–shell structure concept is useful to improve the compatibility of fillers with polymer matrix. Herein, an organic thermoplastic urethanes (TPU) polymer shell was successfully grafted on the surface of barium titanate (BaTiO(3), BT) and such a TPU shell improved the permittivity and breakdown strength of TPU@BT/PVDF polymer nanocomposites greatly. The permittivity of TPU@BT/PVDF nanocomposites with 12 wt% fillers at 10^2 Hz was up to 13.5, which was 1.5 times higher than that of pure poly(vinylidene fluoride) (PVDF). The improvement of the dielectric properties could be attributed to the enhanced interfacial polarisation between BT nanoparticles and TPU shell. Besides, the compatibility of BT nanoparticles and PVDF matrix was improved after the introduction of TPU shell. Accordingly, a highest breakdown strength value about 373 MV/m was obtained for the TPU@BT/PVDF nanocomposites with 7 wt% fillers. The core–shell strategy could be extended to a variety of inorganic fillers to improve the dielectric and breakdown strength properties of polymer nanocomposites.

High-voltage direct current (HVDC) and high-voltage alternating current (HVAC) cables are the most important equipment for high-voltage, large-capacity and long-distance power transmission. Electrical tree is a pre-breakdown phenomenon leading to failure of insulation materials, and it is the major issue that threatens the safe and stable operation of HVDC and HVAC cable systems. This study summarises and analyses the achievements in the research of electrical tree for HVDC and HVAC cables. The initiation mechanisms of the electrical tree, including Maxwell electro-mechanical stress, charge injection–extraction, charge trapping and electroluminescence theories, are elaborated for fully understanding the electrical degradation process in insulation materials. Then, the influences of the high electric field, high temperature and mechanical stress on electrical tree behaviours are discussed, and the relationship between charge transport and the electrical tree is analysed and illustrated. The suppression methods of the electrical tree are put forward by introducing inorganic and organic additives into insulation materials, and the suppression mechanisms are presented from the viewpoints of the structure-property and microscale–macroscale relationships. Recently, the electrical tree research studies are focused on the high-precision of initiation models, high-dependence of multi-physical fields and high-efficiency of suppression methods. The achievements provide theoretical support for improving the electrical performance of insulation materials, while it is a practical problem to explore their application feasibility in HVDC and HVAC cable.

The current study aims to develop polyvinyl chloride (PVC) nanocomposites with enhanced electrical and mechanical properties by incorporating titanium oxide (TiO(2)) nanoparticles within PVC chains. Different loading of nanoparticles and different nanoparticle surface states were considered. The surface states are unfunctionalised, functionalised using vinyl silane and functionalised using amino silane. The choice of a most suitable surface state was a critical factor that guarantees a good dispersion of nanoparticles and consequently enhances the compatibility between TiO(2) and PVC matrix. The process followed in the PVC/TiO(2) nanocomposites preparation, loaded with different wt.% of TiO(2) nanoparticles, was the solvent method. The dielectric properties measured here were the relative permittivity (ɛ(r)), dielectric loss (tanδ), breakdown strength (AC and DC under uniform field) and the internal partial discharges (PDs) within insulation cavity. All measurements have been performed under room temperature and at frequency ranged from 20 to 1.0 MHz. Furthermore, the mechanical properties of the samples like elongation, elasticity modulus and tensile strength were also studied. Vinyl silane showed better improvements in both electrical and mechanical performances compared to the amino silane, especially in cases of high weight fractions of TiO(2). This is because of the improvement in the PVC-TiO(2) interfacial region arise from the similarity of polarity and surface tension values of vinyl silane with that of PVC matrix and TiO(2) nanoparticles.

Na0.3Sr0.4Bi0.3TiO3 with various concentrations in La modified ceramic specimens were fabricated using a traditional die-press process. All the obtained NBT-ST-xLa ceramics exhibited a typical perovskite structure with a single phase, and the grain sizes were found to be uniform and fine. The electric breakdown strength of the sample after La doping increased significantly. In particular, the ceramic electric breakdown strength of x = 0.02 component reached 190 kV/cm, the stored energy density reached 1.67 J/cm3, and the efficiency was stable and greater than 80%. In addition, the ceramic with x = 0.02 La also exhibited an excellent temperature, frequency stability, and good fatigue resistance. More specific and detailed analysis were conducted in this study.

The time formative time lag (t f ) in the breakdown process of polymers on a nanosecond time scale is calculated. By reviewing the mechanisms related to breakdown of solid dielectrics, it is concluded that the avalanche breakdown mechanism is mainly responsible for the breakdown phenomenon of polymers on a nanosecond time scale, which is similar to the Townsend theory of gas breakdown under short pulses. In addition, the maximum functioning time of this theory is ascertained as 1 μs. When the time is longer than 1 μs, the thermal breakdown mechanism and other mechanisms begin to play the role. A formula to calculate t f for the avalanche breakdown mechanism is presented. This formula takes into account different factors that have an influence on t f , such as the dielectric size, type and purity. With this formula, it is calculated that t f for common polymers with a thickness ranging from 0.001-1 mm is about 0.01-100 ns. Experimental results in literatures were summarized to support the calculation results. The formative time lag is a key parameter to evaluate the pulse width effect on the electric breakdown strength on a nanosecond time scale.

Hexagonal boron nitride nanosheets (BNNSs) are two-dimensional nanomaterials with graphitic-like layered nanostructures, high surface areas, and large aspect ratios. Owing to their excellent thermal conductivity, electrical and mechanical strengths, BNNSs are emerging as multifunctional fillers in polymer dielectrics. In this article, the authors review the recent progress in the BN-containing polymer nanocomposites designed for high-performance film capacitors. While general synthetic approaches to BNNSs and polymer/BNNS nanocomposites are summarized, particular attention is placed on structure-property correlation and rational structural design of the composites with optimized dielectric properties and capacitive performances. In stark contrast to the polymer composites employing high dielectric constant fillers to enhance the electric displacement, a new design concept based on the utilization of BNNSs with a wide bandgap to impede electrical conduction and consequently improve breakdown strength and charge-discharge efficiency of the polymer composites, is highlighted. The significance of developing dielectric capacitors with desirable thermal conductivity and thermal stability to ensure their robust and efficient operation is emphasized. The merits and challenges regarding the existing polymer dielectrics containing BNNSs for energy storage are identified. An outlook for future research opportunities and engineering applications is also presented in this review.

In insulating liquid, a conductive particle becomes charged through the interaction with a conductor exposed to an applied field. Then, it migrates in the action of both electric field and fluid and causes the enhancement of local field when it is in proximity of the conductor with opposite polarity. The enhancement will lead to partial discharge (PD) and may even ignite full gap breakdown in special cases. This study reviews comprehensive researches relevant to these topics. In the first place, several theoretical methods about how to obtain the charges held by a conductive particle with known potential are introduced, so are experimental methods. Then, forces acting on the charged particle in liquid are classified, and its migration characteristics, as well as influential factors, are described. Subsequently, PD and breakdown mechanisms of liquid initiated by conductive particles are presented. The latter involves two cases: electric-field enhancement when the particle concentration is low and bridging phenomenon when it is high. At last, two important, but frequently ignored factors, i.e. dielectric barrier and oil flow, are highlighted, and the authors’ suggestions for future work are put forward.

This study presents the discharge process on rod–rod electrodes under oscillating lightning impulse voltage. For this purpose, a measurement system has been developed to record the discharge currents at both rod electrodes simultaneously and to photograph the spatial propagation of the discharges. The measurement results of the discharge process are shown for an air gap of [inline-formula] and for a superimposed frequency of [inline-formula]. Like the standardised lightning impulse voltage, three consecutive phases of discharge have been identified before a breakdown occurs. These are streamer discharge phase, channel transition phase and channel formation phase. The three phases are described, interpreted and their correlation is shown. On the basis of the oscillations, the discharge processes recur periodically if the momentary voltage is higher than the mean curve of the oscillating lightning impulse voltage. The streamer discharge emerges foremost at the positive rod electrode and propagates toward the grounded rod electrode. Its propagation depends on the voltage crest value. Arriving at the grounded rod electrode, the channel transition phase begins. There the discharge moves back to the positive rod electrode due to recombination and generation. Then the discharge constricts to the positive rod electrode, which forms a channel. Simultaneously, at the grounded rod electrode, a channel is also emerging. In each period, the channel will build up stepwise. The channel leads to the main discharge of the oscillating lightning impulse voltage.

Insulation oil is an important dielectric in power devices, and many studies on mixed insulation oil have been conducted in recent years to improve the performance of insulation oils. To replace mineral oil directly, the authors previously developed a novel three-element mixed insulation oil successfully; the main parameters of which satisfy the IEC 60296-2012 standard for mineral oil. In the present study, the AC breakdown properties of insulation paper (pressboard) immersed by the new mixed oil and naphthenic mineral oil were compared. For both insulation oils, the increase in temperature cannot significantly reduce the breakdown strength of oil-immersed insulation paper (pressboard) at a low moisture content, and the increment of moisture content cannot reduce the breakdown voltage at a low temperature (25°C). The breakdown voltage decreases only when the two factors increase simultaneously. For the mixed and mineral oils, the AC breakdown voltage of oil-immersed paper (pressboard) with different thicknesses has significant difference. The mineral oil has a high breakdown voltage for the thin insulation paper, whereas the mixed oil has a high breakdown voltage when the thickness of the insulation paper (pressboard) exceeds 0.2 mm. This phenomenon is mainly caused by the breakdown field strength that varies with the increase of dielectric thickness and the different change trends of paper (pressboard) immersed with the mixed and the mineral oils. Moreover, the stack of thin multilayer insulation paper enables the mixed oil-immersed paper to have a higher breakdown strength than the mineral oil-immersed paper. For the AC breakdown voltage of oil-immersed pressboard with an oil-gap structure, the mixed oil is comprehensively superior to the mineral oil due to its larger relative permittivity.

Polypropylene (PP)-based nanocomposite is a promising insulation material for recyclable high-voltage direct current (HVDC) cables, where the coupling agent plays an important role. In this study, four silane coupling agents with different alkyl chain groups (methyl, propyl, octyl, and octadecyl) were used to surface-modify magnesium oxide (MgO) nanoparticles. The surface-modification effect on the electrical properties of PP/MgO nanocomposites was investigated. The results show that surface-modified nanoparticles introduce quantities of deep traps, whose quantity increases as the alkyl chain length increases. The similar tendency also occurs on DC volume resistivity. All these nanocomposites show remarkable space charge suppression ability and improved DC breakdown strength. Among them, the nanocomposites with octyl-modified MgO show the best electrical properties, which could be attributed to the introduction of a large quantity of deep traps. The work may give a reference for the selection of coupling agents in PP-based nanocomposite insulation material for HVDC cable.

In this study, a design, simulation, fabrication, and measurement of the TEM-TE11 mode converter antenna (MCA) like a pelican beak are investigated. The working frequency of the pelican beak-shaped MCA (PBMCA) is the frequency in the range of 3.9–4.6 GHz (700 MHz bandwidth). Due to increasing the antenna cross-section, the probability of the electrical breakdown dramatically reduces. Electrical breakdown may occur at very high power outputs of the electromagnetic sources. The power-handling capacity of the PBMCA is 829 MW, at the centre frequency. The antenna is simulated and measured at three frequencies. The simulation results are a good agreement with the measurement results.

Breakdown failure in insulation material is one of the key problems that threaten the safe operation of high-voltage direct current cable. In this work, the effect of boron nitride nanosheets (BNNSs) concentration, space charge and temperature on DC breakdown strength have been explored. Cross-linked polyethylene (XLPE)/BNNS nanocomposites were prepared by the melt blending method, and the basic characteristics of nanoparticles and composite were characterised. The experimental results indicate that DC breakdown strength of nanocomposite can be effectively improved when a small amount of BN nanosheet is doped into the matrix. The breakdown strength of the sample reaches the maximum value of 407.52 kV/mm when BNNS content is 0.5 wt%, which is about 33% higher than that of pure XLPE. Further, the effect of space charge on the breakdown of nanocomposites has been studied by pre-injecting charges. For the samples with different BNNS contents, all the breakdown strength present ascending trend when the polarity of the applied voltage is the same as that of the pre-injected charges. Besides, it can be found that the breakdown strength of the XLPE/BNNSs composite decreases significantly at 50°C, which is due to more charge accumulation at 50°C. It reaches 2.06 × 10 −8 C which increases by about 2.2 times than the room temperature.

Generation of hot spot in photovoltaic (PV) cells, under mismatch condition, is a reliability and safety issue associated with PV systems since its very early applications in satellites. Some of the solutions to this long-standing problem, proposed by the researchers in the past, were though effective in reducing the hot spot temperature, but were not accepted widely in commercial scale, because of design complexity and significant cost implications. The main aim of this paper is to present a novel hot spot mitigation circuit (HSMC), which effectively reduces temperature of the cells under mismatch conditions through a modified bypass arrangement, and thereby increase the reliability of the complete PV system. Special attention is paid to ensure that the proposed solution does not increase complexity of the bypass circuit to restrict its impact on the project cost and system reliability. Experimental investigation is carried out to quantify the comparative performance of the proposed HSMC vis-a-vis standard bypass circuit (SBC). Thermographic images revealed that temperature of the cells, under mismatch condition, reduced by up to 10.3 °C when protected by the proposed HSMC, while the temperature increased by 6 °C under protection of the SBC under same ambient and operating conditions.

The emergence of Industry 4.0 enhances the capabilities of predictive maintenance and paves the way for efficient and optimized maintenance operations. Until now, the technical implications of adopting predictive maintenance solutions in Industry 4.0 environments have been reported in various studies. However, the business perspective is usually not considered, although there are significant managerial barriers toward the 4th industrial revolution. In this article, we present the benefits, business opportunities, and managerial implications of predictive maintenance based upon our experience in the design, implementation, and deployment of related solutions.

Space charge injected into a liquid dielectric by an electrode under an impulse voltage causes the electric field to be distorted, which affects the dielectric's insulation performance. In this study, the authors study the surface modification of three-electrode materials, namely aluminium, copper, and stainless steel, by sputtering of titanium dioxide (TiO 2 ) based on magnetron sputtering. The breakdown voltage of propylene carbonate and the surface morphology of the electrodes before and after modification were examined. Furthermore, the distribution of the space charge injected into the propylene carbonate from the different electrode materials was also measured based on the Kerr electro-optic effect. These results indicate that the breakdown voltage of propylene carbonate increased by 7, 4, and 9% after surface modification of aluminium, copper, and stainless steel, respectively. After sputtering of TiO 2 , micro-grooves on the surface of the three-electrode materials became smooth, and the surface roughness decreased, which changed the barrier height of the solid–liquid interface. The space charge injection mode of the three-electrode materials before and after surface modification was bipolar injection; however, the space charge injection amounts were markedly lower for the modified electrodes.

Motorway off-ramp is a main source of traffic congestion and collisions. Heavy diverging traffic and associated lane changing to off-ramp slows down the mainline traffic speed. When the off-ramp queue spills onto the motorway mainline, it may cause a major breakdown of the motorway capacity and a significant threat to the traffic safety. This paper proposes using Variable Speed Limits (VSL) to protect the motorway off-ramp queue to improve safety in congested diverging areas through microsimulation tests. To support timely activation of VSL in advance of queue spill-over, a proactive strategy is proposed based on off-ramp queue estimation and new arrival prediction in the near term. This process determines the estimated queue size on the off-ramp in the near-term, on which the decision to change speed limits is made. VSL can effectively slow down traffic as it is mandated and enforceable in Queensland, Australia. As a possible scenario, reduced speed limits could make drivers more attentive to the surrounding condition, and prepared for a sudden braking of the leading car. This paper analyses and quantifies this possible effect of VSL on traffic safety and efficiency using the microsimulation approach.

Breakdown mechanism in 0.25- μm gate length AlGaN/GaN-on-SiC iron doped high electron mobility transistors (HEMTs) with background carbon is investigated through the drain current injection technique. The measurement results reveal that it can be divided into two distinct stages according to the gate voltage levels. The first stage of the measured drain injected breakdown is mainly due to the initiation of the punchthrough process under the gate, and the second stage of breakdown is associated with the potential barrier between the unintentionally doped (UID) GaN and the Fe doped p-type GaN buffer layer which also has a higher carbon density. The electroluminescence (EL) results suggest that the first stage shows uniform punchthrough current flow, but localized leakage current flow associated with a snapback breakdown mechanism replaces the uniform punchthrough current flow and dominates the second stage. A 2D-TCAD simulation has been implemented and shows the current paths under uniform flow conditions.

Publisher Copyright: This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ The spatial sign covariance matrix (SSCM), also known as the normalized sample covariance matrix (NSCM), has been widely used in signal processing as a robust alternative to the sample covariance matrix (SCM). It is well-known that the SSCM does not provide consistent estimates of the eigenvalues of the shape matrix (normalized scatter matrix). To alleviate this problem, we propose BASIC (Bias Adjusted SIgn Covariance), which performs an approximate bias correction to the eigenvalues of the SSCM under the assumption that the samples are generated from zero mean unspecified complex elliptically symmetric distributions (the real-valued case is also addressed). We then use the bias correction in order to develop a robust regularized SSCM based estimator, BASIC Shrinkage estimator (BASICS), which is suitable for high dimensional problems, where the dimension can be larger than the sample size. We assess the proposed estimator with several numerical examples as well as in a linear discriminant analysis (LDA) classification problem with real data sets. The simulations show that the proposed estimator compares well to competing robust covariance matrix estimators but has the advantage of being significantly faster to compute.

Glass fibre composites are common materials used in high voltage applications as insulating materials that provide good structural integrity. The aim of this thesis is to develop a method of studying the failure in such materials by measuring the dielectric strength on micro- and meso- scale samples, consisting of single fibre filaments and fibre bundles respectively embedded in epoxy resin. To do this, a body of relevant knowledge has been amassed, which is complemented with finite element analysis giving detailed insight into the electric field distribution in the microstructure of fibre composites. A method of producing virtually defect free single fibre samples has been developed where a filament is hung down tubes and cast in epoxy resin. A similar method was developed for producing bundle samples, however this needs some slight correction in order to prevent exothermic reactions. The dielectric strength of these samples are measured by applying a continuously increasing voltage until discharge is recorded. To evaluate the method micro- and meso- scale samples were prepared of three different fibres and their dielectric strengths measured. This evaluation showed that the method can be used to measure a definitive lower bound in the dielectric strength of fibre composites. However, the method can not definitively determine the location of the discharge, which is necessary to verify conclusions about the materials properties. To progress the method, the dielectric strength of neat epoxy samples of the same dimensions as the fibre composite samples should be investigated. Increasing the tolerance of the measurement setup should also be investigated as this could help by increasing the power of the discharge leading to more severe damage in the material.

Drilling costs can be 80% of geothermal project investment, so decreasing these deep drilling costs substantially reduces overall project costs, contributing to less expensive geothermal electricity or heat generation. Plasma Pulse Geo Drilling (PPGD) is a contactless drilling technique that uses high-voltage pulses to fracture the rock without mechanical abrasion, which may reduce drilling costs by up to 90% of conventional mechanical rotary drilling costs. However, further development of PPGD requires a better understanding of the underlying fundamental physics, specifically the dielectric breakdown of rocks with pore fluids subjected to high-voltage pulses. This paper presents a numerical model to investigate the effects of the pore characteristics (i.e., pore fluid, shape, size, and pressure) on the occurrence of the local electric breakdown (i.e., plasma formation in the pore fluid) inside the granite pores and thus on PPGD efficiency. Investigated are: (i) two pore fluids, consisting of air (gas) or liquid water; (ii) three pore shapes, i.e., ellipses, circles, and squares; (iii) pore sizes ranging from 10 to 150 µm; (iv) pore pressures ranging from 0.1 to 2.5 MPa. The study shows how the investigated pore characteristics affect the local electric breakdown and, consequently, the PPGD process., Energies, 15 (1), ISSN:1996-1073

Drilling costs can be 80% of geothermal project investment, so decreasing these deep drilling costs substantially reduces overall project costs, contributing to less expensive geothermal electricity or heat generation. Plasma Pulse Geo Drilling (PPGD) is a contactless drilling technique that uses high-voltage pulses to fracture the rock without mechanical abrasion, which may reduce drilling costs by up to 90% of conventional mechanical rotary drilling costs. However, further development of PPGD requires a better understanding of the underlying fundamental physics, specifically the dielectric breakdown of rocks with pore fluids subjected to high-voltage pulses. This paper presents a numerical model to investigate the effects of the pore characteristics (i.e., pore fluid, shape, size, and pressure) on the occurrence of the local electric breakdown (i.e., plasma formation in the pore fluid) inside the granite pores and thus on PPGD efficiency. Investigated are: (i) two pore fluids, consisting of air (gas) or liquid water; (ii) three pore shapes, i.e., ellipses, circles, and squares; (iii) pore sizes ranging from 10 to 150 µm; (iv) pore pressures ranging from 0.1 to 2.5 MPa. The study shows how the investigated pore characteristics affect the local electric breakdown and, consequently, the PPGD process. ISSN:1996-1073

[EN] High power radio frequency (RF) breakdown testing is a subject of great relevance in the space industry, due to the increasing need of higher transmission power and smaller devices. This work presents a novel RF breakdown detection system, which monitors the same parameters as the microwave nulling system but with several advantages. Where microwave nulling-a de facto standard in RF breakdown testing-is narrowband and requires continuous tuning to keep its sensitivity, the proposed technique is broadband and maintains its performance for any RF signal. On top of that, defining the detection threshold is cumbersome due to the lack of an international standardized criterion. Small responses may appear in the detection system during the test and, sometimes, it is not possible to determine if these are an actual RF breakdown or random noise. This new detection system uses a larger analysis bandwidth, thus reducing the cases in which a small response is difficult to be classified. The proposed detection method represents a major step forward in high power testing as it runs without human intervention, warning the operator or decreasing the RF power automatically much faster than any human operator., This work was supported in part by the "Ministerio de Ciencia e Innovacion," Spanish Government, under Project PID2019-103982RB-C41, and in part by the European High RF Power Space Laboratory of the European Space Agency and Val Space Consortium for contributing with its installations, Laboratory co-funded by the European Regional Development Fund-A way of making Europe.

The degradation and breakdown of high-voltage XLPE cable insulation are usually followed by morphological and chemical changes. This paper presents the outcome of Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) tests on broken-down cables. Tests are conducted on several sample points of the broken-down cable at one of PLN’s substations. As a comparison, the tests are also applied to the unbroken-down part of the same cable roll the unbroken-down cable of another brand. Striking differences are obtained from the results of the tests. The experimental results show a higher absorption peak at the double bond area on the cable that breakdown indicates the high presence of the carbonyl group due to polymer oxidation. And the cable that is one roll with the cable that breakdown has a high oxidation index even though it is relatively new. This proves the lower quality of the cable that breakdown compared to the other brand.

Breakdown strength in uniform electric fields of N2O mixtures with CO2, N2, and O2 is measured under AC voltage stress, 300 kPa pressure, and electrode separation of 5 mm. The obtained results show the best synergism of 115% for N2O/CO2 30/70 mixture. For high electric strength of mixtures, a high fraction of N2O is beneficial, but is limited by the oxidizing power. Considering this limit, a N2O/CO249.1/50.9 mixture can be used with the electric strength 135% of synthetic air and 45% of SF6, respectively. ISSN:1070-9878 ISSN:1558-4135

In a growing number of applications, fast and localized pressure measurement in aqueous media is desired. To perform such measurements, a custom-made single-mode fiber-optic probe hydrophone (FOPH) was designed and used to measure the pressure pulse generated by laser-induced breakdown (LIB) in water. The sensor enabled sub-nanosecond pressure rise time measurement. Both the rise time and the duration of the shockwave were found to be shorter in the direction perpendicular to the breakdown generating laser beam, compared to the shockwave observed in the parallel direction. Simultaneous high-frame-rate imaging was used to qualitatively validate the novel hydrophone data and to observe the shockwave evolution. The measurements were performed also on pressure pulses emitted during the generation of miniature ( [Formula: see text] diameter) laser-induced bubbles at very small distances (down to [Formula: see text]), further demonstrating the capabilities of the small-size sensor and the ability to measure locally. The results improve understanding of LIB shockwave characteristics dependence on laser pulse energy and duration.

A heavily congested metro line is vulnerable to unexpected disruptions which often cause train delays and other negative impacts. This paper firstly proposes a train rescheduling optimization model in the case of the vehicle breakdown on a metro line. The objective of this optimization model is to minimize the deviation from the original scheduled timetable and the number of canceled train services. Moreover, the train timetable rescheduling (TTR) and the rolling stock rescheduling (RSR) problems are simultaneously considered in this paper. Efficient rescheduling strategies including flexible short-turning and adding backup trains are particularly formulated into the model. By introducing additional constraints and the big-M variable, the optimization model is further transformed into an integer programming (IP) model, which can be efficiently solved by CPLEX optimizer. Finally, a case study with the realworld data set of the Beijing Fangshan metro line is carried out to verify the effectiveness of the rescheduling model.

In this paper, two TDDB test structures of TSV, including Single-TSV and Dual-TSV, have been designed. In order to compare the availability between these two test structures, the electric field simulation and TDDB failure analysis have been carried out. The simulation results show that the Single- TSV is more prone to abnormal breakdown for its higher electric field between surface pads during TDDB test. On the contrary, the Dual- Tsvhas a greater probability of breakdown in the dielectric liner of TSV, because the maximum of electric field is located at the dielectric liner. The conclusion of TDDB failure analysis support the point of simulation. The Dual- Tsvhas better availability than the Single- TSV for the TDDB test of TSV. Furthermore, we discussed the guidelines for the design of TSV TDDB test structures.