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The combined insulation interface of a high-voltage cable and accessories is the weakest part of a cable system. In this paper, the parameters of the dielectric constant, thermal conductivity, and elastic modulus of cross-linked polyethylene (XLPE) and silicone rubber (SIR) are obtained experimentally. On this basis, the model of a specific type of 110 kV cable and prefabricated insulation joint is established. A simulation of the electric–thermal–stress coupling field in the presence of typical defects in the main insulation–inner semi-conductive (SEMI) shielding layer (XLPE/SEMI interface) and the main insulation–silicone rubber insulation layer (XLPE/SIR interface) is studied. The simulation results show that at the XLPE/SIR interface, the electric field distortion caused by bubble defects reached 20.17 kV/mm, and the temperature rose to 56.15 °C. The effect of air-gap defects on the interface is similar to that of bubble defects. In addition, the semi-conductive impurity defects induced an increase in temperature to 56.82 °C and an increase in stress to 0.32 MPa. At the XLPE/SEMI interface, the electric field distortion induced by bubble defects was 19.98 kV/mm, and the temperature rose to 61.72 °C. The electric field distortion caused by metallic and semi-conductive defects was 8.44 kV/mm and 8.64 kV/mm, respectively. This study serves as a reference for the fault analysis and the operation and maintenance of cable accessories. [ABSTRACT FROM AUTHOR]

The contact morphology change caused by high-current ablation will seriously affect the electric field distribution in the interrupter chamber, which in turn affects the closing prebreakdown arc duration, indicating that the prebreakdown arc duration can be used as one of the indicators to measure the contact ablation state. A circuit breaker simulated ablation test platform was established, and the voltage and current signals, electromagnetic field signals, and vibration signals in the process of circuit breaker closing were measured, and the closing prebreakdown duration was calculated. The results show that under the same size of the ablation current, with the ablation of the contacts, the closing prebreakdown duration shows an overall trend of increasing and then decreasing, and the larger the ablation current is, the larger the change in the closing prebreakdown duration is. At the same time, simulation verification was carried out, and the results show that the electric field distortion on the surface of the static arc contact inside the arc extinguishing chamber is the largest, and the ablation of the contact will further increase the degree of distortion of the electric field inside the arc extinguishing chamber. As the degree of ablation increases, the prebreakdown moment of the circuit breaker closing is advanced, and the prebreakdown duration increases. [ABSTRACT FROM AUTHOR]

The insulation of high-voltage direct-current (HVDC) cables experiences a short period of voltage polarity reversal when the power flow is adjusted, leading to sever field distortion in this situation. Consequently, improving the insulation performance of the composite insulation structure in these cables has become an urgent challenge. In this paper, SiC-SR (silicone rubber) and TiO2-SR nanocomposites were chosen for fabricating HVDC cable accessories. These nanocomposites were prepared using the solution blending method, and an electro-acoustic pulse (PEA) space charge test platform was established to explore the electron transfer mechanism. The space charge characteristics and field strength distribution of a double-layer dielectric composed of cross-linked polyethylene (XLPE) and nano-composite SR at different concentrations were studied during voltage polarity reversal. Additionally, a self-built breakdown platform for flake samples was established to explore the effect of the nanoparticle doping concentration on the breakdown field strength of double-layer composite media under polarity reversal. Therefore, a correlation was established between the micro electron transfer process and the macro electrical properties of polymers (XLPE/SR). The results show that optimal concentrations of nano-SiC and TiO2 particles introduce deep traps in the SR matrix, significantly inhibiting charge accumulation and electric field distortion at the interface, thereby effectively improving the dielectric strength of the double-layer polymers (XLPE/SR). [ABSTRACT FROM AUTHOR]

Electric field distortion caused by space charge accumulation is one of the challenges in the development of insulating liquid immersed converter transformers and battery energy storage. This paper studies the impact of temperature and moisture content on field distortion in synthetic ester through an improved computational model incorporating the time-development permittivity of insulating liquid, and the test results indicated highly accurate simulation results of electric field distribution can be produced compared with the previous model. Charge mobility and charge density in synthetic ester were extracted from frequency dielectric spectroscopy test results, which were then used to calculate field distortion by the developed computational model. Simulation results indicated that the field distortion in synthetic ester decreases with temperature due to the enhanced permittivity caused by space charge accumulation, while it increases with moisture content due to the increased charge density from the dissociation of water. [ABSTRACT FROM AUTHOR]

The lock-on effect of the gallium arsenide photoconductive semiconductor switch (GaAs PCSS) at repetition rate aggravates the current crowding and electric field distortion, which significantly increases the risk of switch damage or even failure. Therefore, it is of great significance to investigate the carrier transport and the heat generation mechanism for improving the performance and longevity of GaAs PCSS in lock-on mode. The internal physical process of an opposed-electrode GaAs PCSS at low optical energy and strong electric field is analyzed and discussed by experiment and simulation. A device-circuit hybrid simulation is employed to investigate the transient electric field, carrier concentration, and lattice temperature distribution within the GaAs PCSS in lock-on mode. The device temperature exhibits a positive correlation with the applied bias electric field, resulting in a peak temperature of 1037.25 K at an electric field of 38 kV cm−1. The temperature distribution within the GaAs PCSS indicates a greater possibility for thermal breakdown and damage near the electrodes. [ABSTRACT FROM AUTHOR]

Using the AC electric field to induce the orientation of nonlinear conductive fillers in composites is an effective solution for alleviating electric field distortion in power modules. However, the mechanism by which the electric field affects the filler dynamic characteristics and the composites' electrical properties remains unclear. In this paper, the correlation between the microscopic dynamic processes of fillers and the macroscopic current amplitude was analyzed. The results show that the current increases rapidly (0 ∼ 173 s) and then slowly (173 ∼ 869 s) at 600 V mm−1, influenced by the rotation and attraction processes of the fillers. This demonstrates that the orientation stops at about 869 s and the filler orientation state is a key factor in determining the dielectric properties. Secondly, the global orientation evaluation index D for the filler network was proposed, which can also derive the minimum time and energy loss required for preparation. Finally, the impact of different filler orientations on the composites' conductivity was investigated. In the low electric field stress region, with the average carrier jump distance decreasing from 150.23 to 109.71 nm as the D increases from −0.93 to −0.05. On this basis, materials with nonlinear conductivity gradient distribution can be easily prepared. Before optimization, the electric field stress of the power module at the triple point was 35.79 kV. This composite can reduce the value to 15.42 kV, a decrease of 56.9%, while maintaining good electric field uniformity. [ABSTRACT FROM AUTHOR]

The mechanisms governing electric field and partial discharge (PD) under stress cone dislocation remain unclear. This study employs the finite element method to explore the relationship between the electric field, externally applied voltage, and length of dislocation. Subsequently, the correlation between voltage and electric field is determined. The relationship between voltage and PD is established through PD tests conducted under stress cone dislocation conditions. By considering the influence of voltage, the association between the electric field and PD is established, revealing the mechanism of PD initiation by electric field distortion in joints. The findings suggest that the lifetime and reliability were increased by wrapping semi‐conductive self‐adhesive tape around the exposed cross‐linked polyethylene (XLPE) insulation layer. The electric field at a specific location is approximately proportional to the applied voltage. However, the slope is influenced by the composite insulation interface and the radial distance of the copper conductor. When crossing the interface between the XLPE insulation layer and the accessory insulation layer, the slope decreases significantly. The threshold for electric field PD is determined by examining the electric field distribution and the PD inception voltage during testing. When the voltage is sufficiently high, significant electric field distortions can occur at multiple points in the joint, potentially leading to concurrent PDs at several locations. [ABSTRACT FROM AUTHOR]

The present article provides a comprehensive analysis of the aging phenomenon of transformer insulation and the corresponding changes in insulation performance that occur over time. The present manuscript outlines diverse insulating materials that are employed in transformers, the fundamental aging mechanism of the insulation, the function of space charges in the aging of the insulation, and various simulation methodologies utilized for diagnosing the insulation status of the transformer. The primary focus of this paper is to examine the various numerical techniques employed in modeling and analyzing the aging characteristics of transformer insulation. The mechanisms underlying the accumulation of charge and distortion of electric fields in insulation are explained through the utilization of numerical modeling techniques. This paper focuses on understanding the mechanism of insulation aging, thereby facilitating the optimization and maintenance of insulation performance throughout its operational lifespan. [ABSTRACT FROM AUTHOR]

The presence of core–shell nanowire diminishes the distribution distortion of local electric field and also obstructs the flow of charge carriers. Polymer composite with fibrous structure demonstrates the improved polarization, and this work sheds a light on the energy loss related to the interface of polymer film for application of next-generation dielectric capacitor. [Display omitted] The development of polymer film with large electrical displacement is essential for the applications of lightweight and compact energy storage. The dielectric diversity at interface of polymer composite should be addressed to realize the film capacitor with high energy density and dielectric reliability. In this work, poly(vinylidene fluoride- co -chlorotrifluoroethylene) (P(VDF-CTFE)) nanocomposite was incorporated by core–shell nanowire with covalent organic framework (COF) outer coating to alleviate the dielectric mismatch at interface. After the preparation of Ag nanowire through polyol reduction, polyaniline (PANI) and COF layers were sequentially deposited to construct core–shell Ag@polyaniline@covalent organic framework (Ag@PANI@COF) nanowire. According to the unique core–shell architecture, the COF framework is utilized to suppress the remanent polarization while high electrical displacement is preserved by the center Ag nanowire. The maximum energy density of 25.0 J/cm3 at 425 MV/m is obtained in 0.1 wt% stretched Ag@PANI@COF/P(VDF-CTFE) nanocomposite. The presence of core–shell nanowire depresses the distribution distortion of electric field and the diffusion of charge carriers under high field. This work demonstrates an effective method to develop the polymer film with large electrical displacement, and sheds a light on insightful exploration of interfacial polarized mechanism in polymer dielectric composite. [ABSTRACT FROM AUTHOR]

Since the discovery of two-dimensional electron gas at the LaAlO3/SrTiO3 interface, its intriguing physical properties have garnered significant interests for device applications. Yet, understanding its response to electrical stimuli remains incomplete. Our in-situ transmission electron microscopy analysis of a LaAlO3/SrTiO3 two-dimensional electron gas device under electrical bias reveals key insights. Inline electron holography visualized the field-induced modulation of two-dimensional electron gas at the interface, while electron energy loss spectroscopy showed negligible electromigration of oxygen vacancies. Instead, atom-resolved imaging indicated that electric fields trigger polar distortion in the LaAlO3 layer, affecting two-dimensional electron gas modulation. This study refutes the previously hypothesized role of oxygen vacancies, underscoring the lattice flexibility of LaAlO3 and its varied polar distortions under electric fields as central to two-dimensional electron gas dynamics. These findings open pathways for advanced oxide nanoelectronics, exploiting the interplay of polar and nonpolar distortions in LaAlO3. Understanding two-dimensional electron gas at the LaAlO3/SrTiO3 interface to electrical stimuli remains incomplete. Here, the authors reveal that the lattice flexibility of LaAlO3 and its varied polar distortions under electric fields as central to 2DEG dynamics. [ABSTRACT FROM AUTHOR]

Barium titanate (BaTiO3, BT)/poly (vinylidene fluoride, PVDF) composites containing 0%–50% of ceramic filler volume fraction were fabricated by spin‐coating method, and it was shown that the permittivity of BT/PVDF composites increased with the addition of ceramic filler. In order to enhance the interfacial bonding between the two phases, the surface modification treatment of BT ceramic particles was carried out using different mass fractions of γ‐Aminopropyl‐triethoxysilane (KH550). The results indicated that the dielectric properties of the modified composites were enhanced. The dielectric constant of the BT/PVDF composite with 10 vol.% ceramic filler treated with 1 wt.% KH550 is 20.3, which is twice as much as pure PVDF. A model of BT/PVDF dielectric composite was employed by using COMSOL Multiphysics to simulate and analyze the effects of filler particle size, volume fraction, and degree of dispersion on the properties of composite dielectric films from the perspective of microstructural. Calculated results show that the addition of ceramic particles triggers local electric field distortion, which affects the dielectric properties of the composites. Meanwhile, the degree of dispersion of the filler also affects the breakdown resistance of the composite material, when the filler is uniformly dispersed, the local electric field is reduced, which effectively enhances the breakdown resistance of the material. Finite element simulation analyzes the macroscopic dielectric properties from a microstructural point of view, which is beneficial for further understanding of ceramic‐polymer composites. Highlights: The dielectric properties of the polymer matrix were enhanced by doping BT.The KH550 can enhance the dispersion of BT particles in the PVDF.The surface‐modified BT improved the dielectric properties of the composite.COMSOL simulation confirmed the effectiveness of the interface modification. [ABSTRACT FROM AUTHOR]

The aging of cable insulation presents a significant threat to the safe operation of cables, with space charge serving as a crucial factor influencing cable insulation degradation. However, the characteristics related to space charge and conduction current behavior during thermal aging remain unclear. This study focused on the thermal aging of cross-linked polyethylene (XLPE) material and utilizes a combined pulse electro-acoustic (PEA) and conduction current testing system to analyze the space charge and conduction current characteristics in the sample under varying electric fields and temperatures. The average charge density, short-circuit residual electric field, electric field distortion rate, and conduction current were studied. The findings indicate that the space charge in the samples following thermal aging is predominantly governed by the injected charge. The amorphous region of XLPE decreases, while the cross-linking degree increases after aging, thereby facilitating charge carrier migration within the sample and reducing the generation of charge carriers through thermal pyrolysis. The minimum temperature required for charge injection is reduced by thermal aging. Furthermore, modifications in conduction current, residual electric field, and average charge density indicate that thermal aging has the potential to alter the microstructure and trap characteristics of XLPE. This study provides empirical evidence to elucidate the underlying mechanism of cable insulation aging. [ABSTRACT FROM AUTHOR]

Pores form inside the ZnO varistor during the sintering process, especially in the edge area. The pore defects frequently lead to breakdown of the varistor. In this study, a simulation model was developed to calculate the electric field and energy density within the varistor. The presence of edge pores resulted in the distortion of the electric field and uneven energy distribution, causing a decrease in the energy capacity of the varistor. Combining the simulations with the results of impact energy tolerance tests on varistors, the mechanism of varistor failure induced by edge pores was revealed. To enhance the energy capacity of varistors, a repair medium with high permeability was developed herein. By employing a secondary sintering method, new grains were grown within the open pores at the edge of the varistor, improving the energy capacity of the varistor from 600 to 1000 A for a 2 ms square wave. Moreover, the mismatch between coefficients of thermal expansion was addressed. This work helped clarify the effects of edge defects in varistors, and a strategy for enhancing their energy capacity was demonstrated. [ABSTRACT FROM AUTHOR]

Hill fires, a sort of ultra-natural disaster that poses a severe threat to the safe and stable operation of transmission lines, have become more frequent in recent years. Currently, the modeling research on the transmission line gap electric field distortion under hill fire conditions does not consider the synergistic effect of charged particles and ash particles, which would lead to the imperfect gap electric field distortion mechanism. Herein, a coupled multi-physics field simulation model of electric, thermal, fluid, chemical field and particle motion was constructed to analyze the electric field distribution and particle motion. Compared to the related simulation models, this study improves the simulation accuracy by around 407% by optimizing the structure and parameters of the simulation model. The FEM software COMSOL Multiphysics simulation results show that the percentage of ash entering the examined region of the AC conductor was 34.1% higher, and the percentage of connected ash was 45% higher, increasing the likelihood of gap breakdown compared to the DC conductor; the charge of ash (10−14 to 10−11) is significantly less than the saturation charge of ash (⩾10−3). Therefore, the charged particles change the motion characteristics of the ash primarily through the electric field force and dielectrophoresis force, while the ash-induced distortion of the electric field affects the spatial distribution of the charged particles, eventually, the background electric field undergoes significant distortion by the synergistic effect of the two. The results examine the inherent mechanism of gap electric field distortion at the microscopic level, which can provide theoretical support for understanding the transition phase of transmission line gaps from insulation to break down under hill fire conditions. [ABSTRACT FROM AUTHOR]

It is found that the polarity reversal phenomenon occurs in the nanosecond pulse breakdown experiment. Two-dimensional axisymmetric particle-in-cell/Monte Carlo collisions' calculation is used to observe energetic electrons at positive nanosecond pulse voltage in atmospheric air and compared with previous calculation results under negative polarity in an attempt to explain the polarity reversal phenomenon. During the evolution of the positive polarity discharge, the difference in spatial net charge distribution leads to distortion of the electric field, which makes the electric field in the area of the ionization channel head very high, exceeding the threshold at which electrons can enter the high-energy state. The simulation results show that although electrons travel in the opposite direction to the ionization channel, energetic electrons can also be generated during the positive polarity discharge's evolution, which may differ from what some researchers expected. However, it is also found that the maximum energy of energetic electrons under positive nanosecond pulse voltage is lower than that under negative nanosecond pulse voltage (only about 1/4). This may be mainly because in the case of positive polarity, the energetic electrons in the head of the ionization channel will move to the low-field intensity region inside the ionization channel and cannot be accelerated continuously. However, it must be pointed out that in the case of positive polarity, energetic electrons still contribute significantly to the rapid breakdown of the air gap. This study provides a deeper understanding of the physics of nanosecond pulse discharge. [ABSTRACT FROM AUTHOR]

Cellulose insulating paper is widely used in the power industry for its good electrical insulating properties. Moisture sharply increases its conductivity, which directly leads to the weakening of insulation performance and greatly increases the risk of subsequent electric field distortion and insulation breakdown. This paper focuses on the microscopic mechanism of moisture changing the characteristics of charge transport in cellulose insulation and attempts to reveal the related conductivity mechanism. To achieve this purpose, microscopic and macroscopic perspectives are integrated and several simulation and experimental methods are utilized comprehensively. The molecular dynamics simulation results showed that most water molecules in damped cellulose were individually and uniformly adsorbed on the hydroxyl groups by hydrogen bond, and the quantum chemistry computation results showed that the lowest unoccupied molecular orbital more appeared on the water molecule and the corresponding density of state increased. Then, experimentally, it was confirmed that the trap energy level decreased by the thermally stimulated current method. On this basis, the promotion effect of moisture on charge transport is predicted and verified by polarization and depolarization current methods. As the moisture content increased, more charge carriers escaped from the trap by hopping and participated in long-range continuous charge motion. Therefore, after dampness, the current of cellulose insulating paper increased exponentially with the increase in electric field strength, which was consistent with the hopping conductivity mechanism. [ABSTRACT FROM AUTHOR]

Space charge accumulation in polymer dielectrics may lead to serious electric field distortion and even insulation failure during long-term operations of power equipment and electronic devices, especially under conditions of high temperature and direct current electric stress. The addition of nanoparticles into polymer matrices has been found effective in suppressing space charge accumulation and alleviating electric field distortion issues. Yet, the underlying mechanisms of nanoparticle doping remain a challenge to explore, especially from multi-dimensional composite insights. Here, a two-dimensional bipolar charge transport model with consideration of interface zones between organic/inorganic phases is proposed for the investigation into space charge behaviors of nanodielectrics. To validate the effectiveness and feasibility of the model, pulsed electroacoustic experiments are performed on epoxy/nano-MgO composites with different doping ratios of nanoparticles. Experimental observations match well with simulation anticipations, i.e., higher doping ratios of nanoparticles below the percolation threshold exhibit better capabilities to inhibit space charge accumulation. The deep traps (∼1.50 eV) generated in the interface zones are demonstrated to capture free charges, forming a reverse electric field in the region adjacent to electrodes and impeding the space charge migration toward the interior of the composite. This model is anticipated to provide theoretical insight for understanding space charge characteristics in polymer nanodielectrics and computing charge dynamics in extreme conditions where experiments are challenging to perform. [ABSTRACT FROM AUTHOR]

Long-term operation of high voltage direct current at elevated temperatures can result in the accumulation of surface charges in DC gas-insulated transmission line (GIL) insulators. Such a phenomenon leads to localized electric field distortion, increasing the risk of surface discharge. The analysis of interaction behaviors between surface charge and space charge at interfacial domains of GIL insulators is a complex task, which requires a comprehensive understanding of physical mechanisms of the gas–solid interface charging. In this work, a two-dimensional bipolar charge transport and interaction (2D BCTI) model is established, with the consideration of both surface and space charge dynamics. Pulsed electroacoustic tests and surface potential measurements are conducted on DC GIL insulator materials under different electrical-thermal coupling conditions. Experimental results exhibit great consistency with the predictions from the 2D BCTI model. The local accumulation of space charge near interfaces has certain effects on surface potential distribution, which in turn influences charge injection behavior from electrodes. In comparison to traditional surface charge simulation models, the consideration of space charge–surface charge interaction behaviors proves to be essential for estimating the polarity and amplitude of surface potential distribution. This model holds promise for assessing charge characteristics in electrical equipment where direct measurement is challenging. [ABSTRACT FROM AUTHOR]

The insulation status of oil-impregnated paper (OIP) bushings directly indicates their operational condition. Damp defects constitute the primary factor contributing to the deterioration of oil-paper insulation. In this paper, the overall moisture distribution of capacitor cores with three damp defects (steady-state, transient, anzd tail moisture damp defect) and its effect on the electric field were studied. A moisture diffusion model for OIP bushing was established based on Finite Element Method (FEM) software, and it was also verified by moisture diffusion experiments. Then, the overall moisture distribution of the capacitor core under three damp defects was investigated. The findings indicate significant variation in the overall moisture distribution of the capacitor core influenced by factors such as aluminum foil and temperature. Furthermore, the relative permittivity of the oilimpregnated paper was computed. Subsequently, the impact of various moisture-induced defects on the electric field was determined. Simulation results unveiled distortion in the electric field of each electrode within the capacitor core. Specifically, the electric field of the zero electrode increased, while that of the outermost electrode decreased in all three damp defect scenarios. The conclusions drawn can thus be used for intelligent operation and condition assessment of OIP bushings. [ABSTRACT FROM AUTHOR]

The advanced Gas Insulated Switchgear/Gas Insulated Lines (GIS/GIL) transmission equipment serves as an essential physical infrastructure for establishing a new energy power system. An analysis spanning nearly a decade on faults arising from extra/ultra-high voltage discharges reveals that over 60% of such faults are attributed to the discharge of metal particles and dust. While existing technical means, such as ultra-high frequency and ultrasonic sensing, exhibit effectiveness in online monitoring of particles larger than sub-millimeter dimensions, the inherent randomness and elusive nature of micron-nano dust pose challenges for effective characterization through current technology. This elusive micron-nano dust, likely concealed as a latent threat, necessitates special attention due to its potential as a "safety killer". To address the challenges associated with detecting micron-nano dust and comprehending its intricate mechanisms, this paper introduces a micron-nano dust adsorption experimental platform tailored for observation and practical application in GIS/GIL operations. The findings highlight that micron-nano dust's adsorption state in the electric field predominantly involves agglomerative adsorption along the insulator surface and diffusive adsorption along the direction of the ground electrode. The pivotal factors influencing dust movement include the micron-nano dust's initial position, mass, material composition, and applied voltage. Further elucidation emphasizes the potential of micron-nano dust as a concealed safety hazard. The study reveals specific physical phenomena during the adsorption process. Agglomerative adsorption results in micron-nano dust speckles forming on the epoxy resin insulator's surface. With increasing voltage, these speckles undergo an "explosion", forming an annular dust halo with deepening contours. This phenomenon, distinct from the initial adsorption, is considered a contributing factor to flashovers along the insulator's surface. The physical mechanism behind flashovers triggered by micron-nano dust is uncovered, highlighting the formation of a localized short circuit area and intense electric field distortion constituted by dust speckles. These findings establish a theoretical foundation and technical support for enhancing the safe operational performance of AC and DC transmission pipelines' insulation. [ABSTRACT FROM AUTHOR]

Polypropylene (PP) receives significant interests because of environmental friendship and excellent insulation. The development of PP cables depends heavily on the semi-conductive shielding layers that match the PP insulation layers. In this paper, propylene–ethylene copolymer (POP) is used to toughen the PP-based shielding layer. The effects of POP content (40 parts, 50 parts and 60 parts) on the electrical and mechanical characteristics are investigated. Further, the interface matching characteristics and toughening mechanism of the shielding layer are explored. According to the experimental findings, owing to the growth in POP content, the distribution of carbon black (CB) particles becomes more uniform, and the surface roughness decreases from 52.7 nm to 14.7 nm. When the POP content is 60 parts, the charge injected into the insulation layer is the least, which is 0.643 × 10−7 C, and the maximum electric field distortion decreases to 11.4 kV/mm. All three POP content shielding layers maintain a low resistivity at high temperatures (110 ℃, 80 Ω·cm). Besides, as the POP content increases, the toughness of PP-based shielding layer is improved and the elongation at break of POP-60 semi-conductive shielding layer reaches 420%. This research paves a new way for the development of semi-conductive shielding layer of PP cables. [ABSTRACT FROM AUTHOR]

To achieve exceptional recyclable DC cable insulation material using thermoplastic polypropylene (PP), we have introduced the organic polar molecule styrene-maleic anhydride copolymer (SMA) into PP-based insulation materials following the principles of deep trap modification. PP, PP/SMA, PP/ethylene-octene copolymer (POE), and PP/POE/SMA insulating samples were prepared, and their meso-morphology, crystalline morphology, and molecular structure were comprehensively characterized. The results indicate that SMA can be uniformly dispersed in PP with minimal impact on the crystalline morphology of PP. The DC electrical properties of the materials were tested at temperatures of 30, 50, and 70 °C. The findings demonstrate that the introduction of SMA can improve the DC properties of the material in both PP and PP/POE. The thermal stimulated depolarization current results reveal that SMA can introduce deep traps into the material, thereby improving its DC properties, which is in agreement with the quantum chemical calculation results. Subsequently, a bipolar carrier transport model was employed for coaxial cables to simulate the space charge distribution in the insulation layer of the four sets of insulation samples as well as the actual cable in service. The results highlight that SMA can significantly suppress space charge in PP and PP/POE systems, and it exhibits excellent electric field distortion resistance. In summary, the results illustrate that SMA is expected to be used as an organic deep trap modifier in PP-based cable insulation materials. [ABSTRACT FROM AUTHOR]

With the concept of environmental protection is deeply popular, the power cables change from traditional thermosetting cross‐linked polyethylene (XLPE) cables to low‐carbon, environmentally friendly, recyclable polypropylene (PP) cables and the semi‐conductive shielding layer that matches the insulation layer for PP cables is highly valued. In this paper, LDPE is replaced with PP in the formulation of shielding layer of commercial XLPE cables. The physicochemical and electrical properties of PP/EVA/CB (PP‐based) and LDPE/EVA/CB (LDPE‐based) shielding layers were compared. The effect of interface matching characteristics on the electric field distortion was analyzed by finite element simulation software. The experimental results show that the volume resistivity of the shielding layers all tend to rise with the increasing temperature, but the resistivity of the PP‐based shielding layer has a smaller fluctuation. The PP‐based shielding layer has a smoother surface, while the space charge injected into the PP insulation layer is the lowest, about 0.433 × 10−7 C. Compared to the LDPE‐based shielding layer/insulation layer, the PP‐based shielding layer/insulation layer has a 50% reduction in interfacial electric field distortion rate. This work is an essential reference for the development for PP cables and their shielding layer selection. [ABSTRACT FROM AUTHOR]

A beam monitor system is being developed for the cool storage ring (CSR) external-target experiment (CEE) at the Heavy Ion Research Facility in Lanzhou (HIRFL). The beam monitor is required to measure the lateral position of each beam particle with spatial resolution less than 50 m and with beam rates up to 1 MHz. As the beam intensity increases, the build-up of slow-moving positive ions created from the ionization of the detector gas by the beam leads to a significant distortion of the nominal electric field in the drift region. In this work, simulation studies of the beam monitor are performed, in particular the space charge effect and the correction strategy. It shows that the space charge at the nominal drift electric field of 700 V/cm modifies the electric field in the sensitive volume by roughly 5 in both the drift and transverse directions. The distortion on the measured position is up to 0.35 mm in the 5 region of the beam profile. The expected spatial resolution of 500 MeV/u U ion is 34.5 m considering the pixel noise of 400 and the 100 m 1 mm pixel size of the charge sensor chip in the selected gas mixture. [ABSTRACT FROM AUTHOR]

Body movements are known to play an active role in sensing. However, it is not fully understood what information is provided by these movements. The Peter's elephantnose fish, Gnathonemus petersii , sense their environment through active electrolocation during which they use epidermal electroreceptors to perceive object-induced distortions of a self-produced electric field. The analysis of electric images projected on their skin enables them to discriminate between three-dimensional objects. While we know the electric image parameters used to encode numerous object properties, we do not understand how these images encode object shape. We hypothesized that 'movement-induced modulations' (MIMs) elicited by body movements might be involved in shape discrimination during active electrolocation. To test this, we trained fish to complete a shape discrimination task in a two-alternative forced-choice set-up, and then manipulated the space available to individuals for scanning movements to see whether this led to a change in their discrimination performance. We found that if enough space was available, fish were very good at discriminating objects of different shapes. However, performance decreased when the space was reduced so that scanning movements were impaired. Our study demonstrates the importance of body movements for gaining complex environmental information such as object shape through active electrolocation. Movement can enhance perception by allowing the extraction of certain kinds of information. Similar observations have been made in other animals using different senses, suggesting that the core principles of sensory-motor integration might be valid for various sensory modalities. • Animals can move their bodies to improve perception of their environment. • G. petersii can use movement for shape recognition during active electrolocation. • Discrimination performance worsened as space around the objects was restricted. • Response times and movement behaviour also changed as space was reduced. • Parallels with active sensing strategies observed in animals with different senses. [ABSTRACT FROM AUTHOR]

Plasma-assisted conversion of ethane (C2H6) can produce value-added chemical building blocks using green electricity. Here we employ a simple packed-bed coaxial dielectric barrier discharge (DBD) reactor to convert C2H6 at mild operating conditions unattainable by conventional thermocatalysis. Ethylene (C2H4), acetylene (C2H2), and methane (CH4) are the main products along with small fractions of C3 and C4 hydrocarbons. Interestingly, the C2H4 selectivity is primarily correlated to C2H6 conversion, dominated by electron dissociation and recombination reactions irrespective of the dielectric properties of the packed bed material (SiO2, Al2O3, ZrO2, TiO2, and BaTiO3), packing material size, supplied power, and C2H6 concentration. While a distortion of the electric field and discharge propagation results in varying dissipated power as materials change, the C2H4 energy yield remains constant. The particle size appears to affect conversion mainly due to pressure alterations. Pd/SiO2 catalyst can change the selectivity, favoring saturated species by expending hydrogen. [ABSTRACT FROM AUTHOR]

Crystallization kinetics in ZrO 2 -modified glass-ceramics, (35- x)Na 2 O–5K 2 O–40Nb 2 O 5 –20SiO 2 - x ZrO 2 (x = 0, 1, 3, 5, 10 mol%), is analyzed by crystallization activation energy E c and kinetic parameter k . A large kinetic parameter k of 1.657 × 1025 is found for the sample with x = 1, which indicates a high tendency toward crystallization. NaNbO 3 is formed as the major phase, and its crystallinity changes significantly by the addition of ZrO 2. It is found that the dielectric permittivity and maximum polarization are affected by crystallinity. Large domains are formed, and a relaxation process appears at high frequencies. In addition, the breakdown strength (BDS) is affected by the strong electric field distortion rather than the resistance in this system. Complex impedance analysis shows that resistance decreases with the addition of ZrO 2. The electric field distortion of the glass-ceramics is simulated by COMSOL. A low interfacial polarization activation energy E a of 0.821 eV is achieved by the addition of ZrO 2. The maximum pulse power density reaches 90 MW/cc at 350 kV/cm for the sample with x = 10, and the pulse energy density attains 0.91 J/cm3 at 300 kV/cm for the sample with x = 1. Light transmittance is achieved because of the low crystallinity and the disappearance of cristobalite SiO 2 in the Na 2 O–K 2 O–Nb 2 O 5 –SiO 2 glass-ceramics. [ABSTRACT FROM AUTHOR]

Developing polymer dielectrics with a low dielectric loss but high dielectric permittivity (ε′) and breakdown strength (Eb) is steadily expected for applications in microelectronic and electrical industries. In this study, to elevate the overall dielectric properties of molybdenum (Mo)/poly(vinylidene fluoride) (PVDF), an insulating polystyrene (PS) shell was first constructed on the Mo's surface through a suspension polymerization, and then the core-shell Mo@PS particles were compounded with the host PVDF. The PS shell's influence on the dielectric performances of the composites was explored in terms of the filler concentration, diverse shell thicknesses and frequency. Compared with neat Mo/PVDF, the Mo@PS/PVDF composites present immensely restrained loss and conductivity owing to the insulating PS interlayer stopping the physical contact among Mo powder and wonderfully constraining the long-range charges migration. More importantly, the integrated dielectric performances can be efficaciously tuned and optimized via engineering the PS shell's thickness because the PS shell not only bolsters the interfacial interactions, but also alleviates the local electric field distortion and concentration subsequently leading to boosted Eb. Analyzing the dielectric results via the Havriliak-Negami expression theoretically illustrates the underlying polarization mechanism in the composites. The resulting Mo@PS/PVDF composites owing high ε′ and Eb coupled with fairly low loss, present prospective applications in electrical power systems. [ABSTRACT FROM AUTHOR]

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The movement of metal particles in the electric field of the DC gas-insulated transmission line (GIL) may cause local electric field distortion on the surface of the spacer, which seriously affects the operation stability of the GIL. In this paper, based on a ±320 kV GIL platform, the movement characteristics of metal particles (aluminum blocks, aluminum wires, aluminum balls) inside the GIL are studied. The suppression effect of particle activity for particle trapping and surface coating are experimentally studied in DC electric field. The relationship between particle trap porosity and particle suppression effect are discussed and verified with experiments. The research results show that under negative voltage, the minimum take-off voltage of metal particles in ±320 kV GIL is −190 kV, which is far lower than the steady-state operating voltage of GIL. Once the spherical and blocky particles take off, they will continue to reciprocate rapidly between the conductors. When the block particles are close to the spacer, they might be attracted and adsorbed on the surface of the spacer. Metal wires after taking off tend to show 'firefly' movement near the high-voltage conductor. The coating has a significant effect on increasing the take-off electric field of metal particles. It is verified that the traditional AC GIL particle trap is not effective in inhibiting particles in DC voltage. The suppression of the DC GIL particle is positively related to the porosity of the particle trap to a certain extent. The conclusions of this paper can be reference for the development of future stable and reliable DC gas-insulated equipment. [ABSTRACT FROM AUTHOR]

Uniform and stable reactivity of atmospheric pressure plasmas is a prerequisite for most applications in fields ranging from materials' surface processing, environment protection, to energy conversion. Dielectric barrier discharges (DBDs) are among the most promising plasmas to satisfy these requirements. However, the unpredictable and uncontrollable transitions between discharge modes, the limited understanding of the DBD ignition and extinction processes, and the complexity of plasma chemistries and reactions with admixture gases restrict their adoption in industry. Here, we report a practically relevant and elegant solution based on using customized nanosecond (ns) pulse excitation and precise addition of oxygen to an Ar flow. The effects of ns pulses and oxygen on the uniformity and reactivity of the DBD are investigated via quantifying the gap voltage Ug and the discharge current Ig from the current–voltage measurements and quantitative discharge imaging. The electron density, ne, is estimated with Ug and Ig. With increasing Ug, more electron avalanches are ignited and overlap, which facilitate ne, Te, and discharge uniformity, while high Ug induces excessive electrons generated with high ionization rates, resulting in the distortion of the space electric field and reduced stability and uniformity. A small amount of added oxygen favors the production of electrons. Overdosed oxygen molecules capture electrons causing a drop in ne and Te and couple with the effect of the electrical field resulting in the filamentary discharges or complete plasma extinction. The mechanism of the effects of ns pulses and oxygen addition on the uniformity and reactivity of plasmas is based on the electrical measurements and discharge image analysis and is cross-validated by optical emission spectra measurements and the ratio of the Ar intensities' calculations as indicators of the variation in ne and Te. The results in this work contribute to the realization and controllability of uniform, stable, and reactive plasmas at atmospheric pressure. [ABSTRACT FROM AUTHOR]

In the design and manufacturing of epoxy resin insulation components, complex structures can be achieved through multiple pours, thereby forming the structure of interface of laminated epoxy resin. This type of interface structure is often considered a weak link in performance which can easily accumulate charges and cause electric field distortion. However, research on the interlayer interface of epoxy resin has received little attention. In this study, epoxy samples with and without interlayer interfaces were prepared, and the space charge accumulation characteristics and trap characteristics of the samples were analyzed via pulsed electro-acoustic (PEA) and thermally stimulated depolarization current (TSDC) methods. The experimental results indicate that the Maxwell–Wagner interface polarization model cannot fully explain the charge accumulation at the interface. Due to the influence of the secondary curing, the functional groups in the post-curing epoxy resin can move and react with the partially reacted functional groups in the prefabricated epoxy resin layer, resulting in a weak cross-linking network at the interface. With the increase in temperature, the molecular chain segments in the weak cross-linked region of the interface become more active and introduce deep traps at the interface, thereby exacerbating the accumulation of interface charges. In addition, due to the influence of interface polarization and weak cross-linking, the ability of the interface charges to cause field strength distortions decreases with the increase in applied field strength. This research study can provide a theoretical reference for the interfacial space charge transport characteristics of epoxy-cured cross-linked layers and provide ideas for regulating interfacial cross-linking to suppress interfacial charge accumulation. [ABSTRACT FROM AUTHOR]

The insulating properties of polypropylene (PP) film play a very important role in the operating status of direct current (DC) support capacitors. Charging and discharging currents in PP film under high DC electric fields and temperatures correspond to charge transportation and accumulation, which significantly influence the electrical insulating properties of PP. In this paper, we have comprehensively studied the dependence of charging/discharging currents in PP film on time, electric field (150–670 kV/mm), and temperature (40–120 °C). The results showed that the charging current increased by almost an order of magnitude from 150 kV/mm to 670 kV/mm and exhibits a steep increase with temperature above 80 °C. The discharging currents are about 10 times less than the corresponding charging currents. Carrier mobility varies little with the electric field and becomes slightly larger with an increase in temperature. The quantity of the accumulated charges was calculated by the integral of the charging and discharging current differentials and showed a significant increase with the electric field and temperature. The corresponding electric field distortion becomes larger above 80 °C compared to 20–60 °C. Both electric field and temperature have an important effect on PP film and capacitors based on charge transport and accumulation and their electric field distortion. This study is innovative in that it combines the operating status of DC support capacitors with traditional methods to research synthetically charged transport mechanisms of PP film. The findings are meaningful for understanding the insulation failure mechanisms of PP film and capacitors under complex stresses. [ABSTRACT FROM AUTHOR]

The partial discharge in the converter transformer will cause the carbonization of the insulating paper. The high concentration of free carbon particles generated from the insulating paper during the operation of the converter transformer will cause partial discharge, which will aggravate the insulation performance deterioration. For the bi‐directional interaction of carbon particles and partial discharge, the mechanism of insulating paper carbonization caused by partial discharge and the effect of carbon particles on the dielectric strength of oil paper are studied. In this paper, we construct a simulation system of amorphous cellulose to study the carbonization mechanism of insulating paper from the microscopic level. Furthermore, we build a DC voltage experimental platform to carry out partial discharge damage tests of oil‐paper insulation models and to measure the changes in the breakdown voltage with different carbon particle concentrations and diameters. The results show that partial discharge speeds up the cleavage rate of cellulose, generates low molecular hydrocarbon gas and water molecules, and the carbon atoms rearrange into PAH‐like molecules with aliphatic side chains. The surface of the insulating paper will carbonize, then form free carbon particles after peeling off. Afterward, the carbon particles in insulating oil accumulate in the high electric field area and attach to the insulating paper, which will cause electric field distortion and reduce the dielectric strength of oil‐paper insulation. With the increase of carbon particle concentration and diameter, the breakdown voltage of oil‐paper insulation decreases gradually. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Antiferromagnetic spintronics exploits unique properties of antiferromagnetic materials to create new and improved functionalities in future spintronic applications. Here, we briefly review the experimental efforts in our group to unravel spin transport properties in antiferromagnetic materials. Our investigations were initially focused on metallic antiferromagnets, where the first evidence of antiferromagnetic spin-transfer torque was discovered. Because of the lack of metallic antiferromagnets, we then shifted towards antiferromagnetic Mott insulators, where a plethora of transport phenomena was found. For instance, we observed a very large anisotropic magnetoresistance, which can be used to detect the magnetic state of an antiferromagnet. We also observed reversible resistive switching and now provide unequivocal evidence that the resistive switching is associated with structural distortions driven by an electric field. Our findings support the potential of electrically controlled functional oxides for various memory technologies. [ABSTRACT FROM AUTHOR]

The aim of the work was to simulate the residual stresses and distortion of an electric arc welding with tungsten electrode and gas shielding of a hypoeutectoid steel, using the finite element method, the microstructural transformations and taking into account the effect of the filler material, an element little studied in the specialized literature that focuses more on autogenous welds. The modelling was divided into two stages: one thermal simulation and another structural simulation. The thermal-dependent properties of an ASTM A210 Gr. A1 steel and an ER - 70S6 wire were used. The spots were analyzed in the thickness of the plate and at different lengths of the weld center. The results obtained were similar to those reported in the literature. The maximum stresses were tensile. The most important values of total distortion were found at less than 20 mm from the weld center. Above this length, they are practically nil. A marked difference between longitudinal and transverse residual stresses was found in the molten zone. [ABSTRACT FROM AUTHOR]

Data transmission through a wireless network has faced various signal problems in the past decades. The orthogonal frequency division multiplexing (OFDM) technique is widely accepted in multiple data transfer patterns at various frequency bands. A recent wireless communication network uses OFDM in longterm evolution (LTE) and 5G, among others. The main problem faced by 5G wireless OFDM is distortion of transmission signals in the network. This transmission loss is called peak-to-average power ratio (PAPR). This wireless signal distortion can be reduced using various techniques. This study uses machine learning-based algorithm to solve the problem of PAPR in 5G wireless communication. Partial transmit sequence (PTS) helps in the fast transfer of data in wireless LTE. PTS is merged with deep belief neural network (DBNet) for the efficient processing of signals in wireless 5G networks. Result indicates that the proposed system outperforms other existing techniques. Therefore, PAPR reduction in OFDM by DBNet is optimized with the help of an evolutionary algorithm called particle swarm optimization. Hence, the specified design supports in improving the proposed PAPR reduction architecture. [ABSTRACT FROM AUTHOR]

To explore the influence of electrothermal aging on the properties of HVAC XLPE cable during its normal operation, two circuits of 110 kV XLPE cable were subjected to a combined electrothermal accelerated aging test for 180 days. The test voltage was set at 95 kV, and the test temperature was set at 90 °C. The constant temperature aging mode was adopted for one circuit, and the periodic thermal cycle aging mode was adopted for the other circuit. The dielectric property of the cable was diagnosed with dielectric spectroscopy measurement, and the thermal property was diagnosed with thermal parameters (thermal capacity and thermal resistance) measurement. Combined with Fourier infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) measurements, morphological changes in the insulation under different electrothermal aging modes were analyzed to construct the correlation with the dielectric and thermal properties. The results show that the short-term electrothermal constant temperature aging mode effectively enhances the dielectric and thermal properties of the cable by modifying spherulite morphology and migrating polar compounds; the short-term electrothermal cycle aging mode also enhances the thermal properties of the cable due to the drop in small polar compounds. However, different distributions of polar compounds and crystal interfaces in the insulation lead to extreme distortion in the electric field distribution. [ABSTRACT FROM AUTHOR]

The XY model of oil‐paper insulation connects the dielectric properties of oil, paper and oil‐paper system. Its equivalent circuit is the basis of the application of dielectric response technology in the state diagnosis of transformer oil‐paper insulation. To better apply the XY model to the study of the dielectric properties of oil‐paper insulation, the dielectric properties of the coaxial oil‐paper insulation system built in the laboratory, XY model and its equivalent circuits are compared. Then an improved circuit of XY model which can reflect the properties of the oil‐paper insulation more truly is proposed. The results show that there is no difference between the XY model and the coaxial model, and both can well characterize the oil‐paper insulation system. The two equivalent circuits of XY model, "Series to Parallel" circuit and "Parallel to Series" circuit, ignore the current tangential component and the electric field distortion in oil‐paper insulation, respectively, resulting in deviations from the XY model. By introducing a new branch C*XY, the improved circuit can reflect the tangential current and electric field distortion in oil‐paper insulation, which can be completely equivalent to XY model. In addition, there is a characteristic frequency point in the oil‐paper insulation system, where the dielectric loss factor tan δ of oil, paper and oil‐paper system are the same. There is no difference between the XY model and its two equivalent circuits at this point. The characteristic frequency is determined by the dielectric properties of oil and paper, and not affected by the insulation structure. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Multi-element detectable laser excited atomic fluorescence (LEAF) technique has been regarded as impressive progress in the analytical field because it possesses high sensitivity and overcomes the specific resonant wavelength constraint. However, a limited understanding of the universal signal enhancement mechanism restricts its further development and follow-up studies. In this study, experiments of LEAF are conducted to investigate the details of the ablation process, excitation process, and coupling behavior. Multi-element signals were dramatically enhanced with 1.49 mJ ablation laser energy at tip = 200 ns, and quantitative analysis with minimal destruction was obtained. Compared with the literature, the following new understandings are firstly proposed: (1) the ablated mass from the ablation process was plasma instead of just a plume, which was stimulated by an excitation laser; (2) photoexcitation contributes to the enhanced signal other than the electron thermal excitation supported by the fact that the signal gains its higher intensity when the re-excited plasma was less bright. That is, the multi-element excitation may relate to the atom energy-level distortion by the electric field. With the elucidation of key processes and mechanisms, there would be a much broader application for laser ablation-assisted ultraviolet LEAF due to its distinctive advantages. [ABSTRACT FROM AUTHOR]

The total electric field on the roof platform of buildings becomes a new and important indicator of the environmental assessment of HVDC projects. In this paper, the upper-stream finite element method is used to simulate and calculate the distribution characteristics of the total electric field on the roof platform of the flat-roofed building adjacent to an HVDC line, from the factors of material conductivity and three-dimensional structure. The results show that when the conductivity of the building is greater than 10−10 S/m, it can be regarded as an equipotential body with the ground. Therefore, when the field mill measures the electric field on the roof platform, the field mill can be connected to the building to achieve the purpose of grounding. Otherwise, additional appropriate grounding treatment is required. Moreover, the protrusions such as parapets and stairwells on the roof platform of the building have both distortion and shielding effects on the total electric field. The larger the area of the protrusions, the better the shielding effect, making the total electric field on the roof platform weaker. Therefore, when measuring the total electric field on the roof platform, to avoid the unpredictability of the measurement results of the field mill, the field mill should be arranged in the center flat area at least 2 m away from the protrusions. [ABSTRACT FROM AUTHOR]

The effects of uneven icing, number of icicles, inclination angle of icicle, ice pallets and arc ignition on the electric field are ignored for the two‐dimensional axisymmetric model of ice‐covered insulator. Therefore, a 3D simulation model was developed in this paper. The average electric field strength of air gap (Eav) and maximum field strength of icicle tip (Emax) were determined to characterize the influence of various factors on the electric field distortion degree. The results show that compared with the insulator without ice and with a dry ice, the supply voltage is almost entirely applied to all icicle air gaps for a wet ice‐covered insulator. Eav is independent of icicle diameter and icicle number but increases with the increment of icicle length and icicle inclination angle. Emax raises with the increase of icicle length, icicle number, icicle inclination angle and icicle diameter. As the source of electric field distortion, the ice pallets on the surface of the sheds rise the field strength of air gap. Based on the simulation analysis and natural icing test, the applied voltage is redistributed in the remaining air gaps when an arc occurs in the gap near the high‐voltage terminal, thereby causing the subsequent flashover. [ABSTRACT FROM AUTHOR]

High‐electrical‐strength polymer dielectrics are essential for advanced devices with high power and/or high integration densities and film capacitors with high energy‐storage densities. Key factors affecting the polymer dielectric electrical strength are deep‐level defect states, which lead to electron and hole accumulation. Numerous deep‐level defect states lead to charge accumulation in the polymer dielectric during operation, contributing to local electric field distortion and resulting in flashover or breakdown. In this work, first‐principles calculations and experiments reveal that VH (i.e., H vacancies) in the polymer dielectric molecular chain can create defect states deep in the bandgap. RCl (R = Li, Na, K) can be used for passivating the deep‐level polymer dielectric defect states. In addition, the passivation mechanisms are analyzed. The RCl cations can passivate deep‐level defect states into shallow‐level acceptor defect states because the RCl dipole moment regulates the deep‐level defect state energy. The RCl anions can passivate deep‐level defect states into shallow‐level donor defect states by forming a stable covalent bond between carbon and lone‐pair electrons. This work supports the design of high‐electrical‐strength polymer dielectrics. [ABSTRACT FROM AUTHOR]

The paper reports simulation results on the influence of a direct-current driven radial electric field on the emission characteristics; especially NOx and CO of a premixed methane/air laminar jet flame. A multi-physics computational model is developed in the OpenFOAM framework to simulate electric-field-coupled premixed combustion process. The computational framework consists of coupled species, momentum and energy conservation together with a Poisson's equation solver to resolve the electric field distribution. Electron and ion conservation equations are resolved to consider the ionic wind body force in the momentum conservation equation and the associated possible electric field distortion due to the space charge distribution. The simulations are conducted for a stochiometric and fuel rich condition and over a range of jet flow rates for a configuration representative of a test-scale experimental setup. The model predictions show that for an applied voltage of 50 kV, the flame structure changes significantly for both the stoichiometric and fuel rich conditions. The flame is stretched significantly by the electric field due to ionic wind. For the fuel rich condition, the ionic wind allows additional mixing of the fuel rich stream with the surrounding air and drastically altering the flame structure. The electric field was found to reduce the NOx emission significantly for both stoichiometric and rich conditions. Over the entire range of flowrate conditions, the stochiometric fuel-oxidizer mixture showed a decrease in maximum NOx by a factor of 1.6 in presence of electric field. For the fuel rich case, however as the flow rate is increased, the NOx reduction factor decreased from 12.0 to 1.6. For CO emissions, the presence of electric field reduces the concentration under fuel rich conditions and vice versa for the stoichiometric flame. The role of kinetics is analyzed and discussed. [ABSTRACT FROM AUTHOR]

Objective. Boag et al (1996) formulated a key model of collection efficiency for ionization chambers in pulsed radiation beams, in which some free electrons form negatively charged ions with a density that initially varies exponentially across the chamber. This non-uniform density complicates ion recombination calculations, in comparison with Boag's 1950 work in which a collection efficiency formula, f, was straightforwardly obtained assuming a uniform negative ion cloud. Boag et al (1996) therefore derived collection efficiency formulae f ′, f ″ and f ′″ based on three approximate descriptions of the exponentially-varying negative ion cloud, each uniform within a region. Collection efficiencies calculated by Boag et al (1996) using these formulae differed by a maximum of 5.1% relative (at 144 mGy dose-per-pulse with 212 V applied over a 1 mm electrode separation) and all three formulae are often used together. Here an exact solution of the exponentially-varying model is obtained. Approach. The exact solution was derived from a differential equation relating the number of negative ions collected from within some distance of the anode to numbers of ions initially located within that region. Using the resulting formula, f exp, collection efficiencies were calculated for a range of ionization chamber properties and doses-per-pulse, and compared with f, f ′, f ″ and f ″′ values and results from an ion transport code. Main results. f exp values agreed to 5 decimal places with ion transport code results. The maximum relative difference between f exp and f ″′, which was often closest to f exp, was 0.78% for the chamber properties and doses-per-pulse studied by Boag et al (1996), rising to 6.1% at 1 Gy dose-per-pulse and 2 mm electrode separation. Significance. Use of f exp should reduce ambiguities in collection efficiencies calculated using the approximate formulae, although like them f exp does not account for electric field distortion, which becomes substantial at doses-per-pulse ≥100 mGy. [ABSTRACT FROM AUTHOR]

High-Voltage Direct Current (HVDC) cable accessories are the key equipment to connect HVDC cables, and also the weak link in the cable system. In order to investigate the transport characteristics of space charge in cable joints, a two-dimensional axisymmetric cable joint model was established using the bipolar charge transport model, and its space charge and electric field distribution were analyzed through numerical simulation. Furthermore, the effects of the trap depth based on molecular chain displacement and temperature field on interface charge distribution of cable joint were compared with the basic model, respectively. The results show that the stress cone root and the top of the high-voltage shield are easy to accumulate space charges, which will lead to electric field distortion. The trap depth based on molecular chain displacement is larger than that of basic model at the insulation interface, which hinders the charge transport. The model without considering the effect of temperature field accumulates less charge, and the electric field and space charge at the stress cone root and the top of the high-voltage shield change gently with time. The above research results can provide a reference for the design and optimization of cable joints. [ABSTRACT FROM AUTHOR]

Gas discharge in heterogeneous porous dielectric (PD) is becoming a reliable and popular low-temperature plasma technique in surface modification and plasma catalysis. However, the exact breakdown characteristics in the PD are not well studied due to experimental and diagnostic limitations. In this paper, a fluid model is then used to simulate the gas breakdown characteristics in real PD. It is found that the breakdown will selectively occur in PDs. The spatial distribution of PD determines regions of local breakdown. Variations in pressure result in the rearrangement of breakdown probability in each region of PD so that breakdown regions will change. In order to explain the selective breakdown phenomenon, based on the assumption that a PD can be simplified into a network consisting of multiple tortuous capillaries, we developed a theoretical model of the breakdown in a capillary network. Three geometrical factors, i.e. capillary tortuosity, capillary radius, and line porosity, are taken into the model to account for the effect of electric field distortion and electron loss on the dielectric walls in the presence of PD. The calculated results explain the selective breakdown phenomenon occurring in the numerical simulation. This paper simulates the breakdown in a real PD and provides a quantitative theoretical model to analyze the geometrical effect of PD on the breakdown. This paper will also provide insights into the design of optimal parameters for porous dielectric discharge in surface modification and plasma catalysis. [ABSTRACT FROM AUTHOR]

We consider the scattering of metal colloids in aqueous solutions by an insulating circular post under the action of an AC electric field. We analyze the effects on the particle of several forces of electrical origin: the repulsion between the induced dipole of the particle and its image dipole in the post, the hydrodynamic interaction with the post due to the induced-charge electroosmotic (ICEO) flow around the particle, and the dielectrophoresis arising from the distortion of the applied electric field around the post. The relative influence of these forces is discussed as a function of frequency of the AC field, particle size and distance to the post. We perform numerical simulations of the scattering of the metal colloid by the insulating circular post flowing in a microchannel and subjected to alternating current electric fields. Our simulation results show that the maximum particle deviation is found for an applied electric field parallel to the flow direction. The deviation is also greater at low electric field frequencies, corresponding to the regime in which the ICEO's interaction with the post is predominant over other mechanisms. [ABSTRACT FROM AUTHOR]