Search Results (269)

For the precise description of gas physical processes in high-voltage direct current (HVDC) transmission, an advanced and robust numerical framework for the simulation of transient particle densities in the course of corona discharges is developed in this work. The aim is the scalable and consistent modeling of the space charge density under realistic conditions. The core component of the framework is a discontinuous Galerkin method that ensures the conservative properties of the underlying hyperbolic problem. The space charge density at the electrode surface is imposed as a dynamic boundary condition via Lagrange multipliers. To increase the numerical stability and convergence rate, a homotopy approach is also integrated. For the experimental validation, a measurement concept was realised that uses a subtraction method to specifically remove the displacement current component in the signal and thus enables an isolated recording of the transient ion current with superimposed voltage stresses. The experimental results on a small scale agree with the numerical predictions and prove the quality of the model. On this basis, the framework is transferred to hybrid HVDC overhead line systems with a bipolar design. In the event of a fault, significant transient space charge densities can be seen there, especially when superimposed with new types of voltage waveforms. The framework thus provides a reliable contribution to insulation coordination in complex HVDC systems and enables the realistic analysis of electrohydrodynamic coupling effects on an industrial scale. Full article

This study investigates the behavior of spark discharges under various environmental conditions to simulate aspects of early-stage lightning dynamics, with a focus on their spectral characteristics, propagation, and ionization behavior. In a laboratory setting, spark discharges generated by a Tesla coil operating with high-frequency alternating current (AC) were analyzed under varying air humidity and water surface conductivity. Spectral analysis revealed that the discharges are dominated by the second positive system of molecular nitrogen N₂ (2P) and also exhibit the first negative system of molecular nitrogen ions N₂⁺ (1N). Notably, the N₂ (2P) emissions show strong peaks in the 350–450 nm range, closely matching spectral features typically associated with corona and streamer discharges in natural lightning. Environmental factors significantly influenced discharge morphology: in dry air, sparks exhibited longer and more branched paths, while in moist air, the discharges were shorter and more confined. Over water surfaces, the sparks spread radially, forming star-shaped patterns. Deionized (DI) water, with low conductivity, supported wider lateral propagation, whereas higher conductivity in tap water and saltwater suppressed discharge spread. The gap between the electrode tip and the surface also affected discharge extent and brightness. These findings demonstrate that Tesla coil discharges reproduce key features of early lightning processes and offer insights into how environmental factors influence discharge development. Full article

Phased-array ultrasonic transducers using sol–gel composites face challenges in terms of polarization uniformity when using conventional corona poling. Pb(Zr, Ti)O₃ (PZT)/PZT composites with a thickness of 25 µm were fabricated on 3 mm thick titanium substrates, and the samples were poled by AC poling, DC poling, and corona discharge poling at RT. It was found that the polarization direction could be controlled by the voltage off-phase angle. When poling was performed with a voltage off-phase angle of 90°, applied voltage of 200 V (rms), 10 cycles, and frequency of 1 Hz, average values and standards of measured piezoelectric constant d₃₃ of −35.1 ± 0.8 pC/N and ultrasonic sensitivity of 11.4 ± 0.1 dB were obtained. Furthermore, the AC-poled samples demonstrated smaller variations in d₃₃ and ultrasonic sensitivity compared with the corona-poled samples, and higher values of d₃₃ and ultrasonic sensitivity compared with the DC-poled samples, indicating the potential of AC poling for PZT/PZT sol–gel composites with large areas. Full article

A laboratory-scale wire plate wet electrostatic precipitator was designed and constructed to investigate the particle enhancement and capture characteristics of electrostatically charged droplets in continuous atomization mode. A comparison was made between different types of wet electrostatic precipitation mechanisms for particle removal, and the change mechanism of gas ionization mode under the action of charged droplets was analyzed. Experimental investigations were conducted on the effects of electrospray on corona discharge “ionic wind”, as well as the force mechanism, agglomeration effect, and removal stability of particles under the synergistic action of electrostatic atomization and an electric field. The results demonstrated that electrospray mode could enhance the interaction between droplets and particles, promote the coagulation and accumulation of fine particles, increase their diameter to larger sizes that are easier to capture, and achieve high particle collection efficiency with significantly reduced water consumption while maintaining high corona current and particle capture effectiveness. Full article

Poly(vinylidene fluoride-trifluoroethylene) (PVTF) nanoparticles coatings with electrically heterogeneous microdomains were engineered to mimic the natural electromechanical microenvironment of bone tissue, offering a novel strategy to enhance osteogenesis. Through a biphasic solvent phase separation method, PVTF nanoparticles (NPs) were synthesized and spin-coated onto substrates, followed by melt-recrystallization to achieve high β-phase crystallinity. The substrates were then subjected to corona poling, a process involving high-voltage corona discharge to electrically polarize and align the molecular dipoles. Structural and electrical characterization revealed tunable microdomain surface potentials and piezoelectric coefficients, correlating with enhanced hydrophilicity. Notably, microdomain potential—produced by controlled polarization—was shown to directly regulate cellular responses. In vitro studies demonstrated that a corona-poled PVTF NP coating significantly improved bone marrow mesenchymal stem cell (BMSC) proliferation and early osteogenic differentiation. This work establishes a surface electropatterning approach and highlights the critical role of electrical heterogeneity in bone regeneration, offering a novel strategy for bioactive biomaterial design. Full article

Although oily sludge is an industrial waste and difficult to separate, its calorific value can still reach 6000 cal/g, thus possessing significant recycling value. This study compares various types of non-thermal plasma for refining oily sludge. The pre-treatment technology utilized filtration combined with solvent extraction to extract the oil portion from the oily sludge. Subsequently, two types of non-thermal plasma, DC streamer discharge and dielectric plasma discharge, were used to crack and activate the oily sludge under different operating conditions. The fuel compositions and properties of the refined fuel treated by two types of non-thermal plasma were compared. The elemental carbon and oxygen of the oily sludge after treatment in a direct DBD plasma reactor for 8 min were 1.96 wt.% less and 1.38 wt.% higher than those of commercial diesel. The research results indicate that the pre-treatment process can effectively improve the refined fuel properties. After pre-treatment, the calorific value of the primary product from the oily sludge can reach 10,598 cal/g. However, the carbon residue of the oily sludge after pre-treatment remained as high as 5.58 wt.%, which implied that further refining processes are required. The streamer discharge plasma reactor used a tungsten needle tip as a high-voltage electrode, leading to a rather small treated range. Corona discharge and arc formation are prone to being produced during the plasma action. Moreover, the addition of quartz glass beads can form a protruding area on the surface of the oily sludge, generating an increase in the reacting surface of the oily sludge, and hence an enhancement of treatment efficiency, in turn. The direct treatment of DBD plasma can thus have a wider and more uniform operating range of plasma generation and a superior efficiency of plasma reaction. Therefore, a direct DBD type of non-thermal equilibrium plasma reactor is preferable to treat oily sludge among those three types of plasma reactor designs. Additionally, when the plasma voltage is increased, it effectively enhances fuel properties. Full article

This study conducted experiments and simulations to examine the DC corona-generated space charge characteristics and understand the performance of high-voltage direct current (HVDC) transmission lines. In experimental studies, various gradient temperatures are tested on a standard model of the potential HVDC transmission line in Southern Africa using an indoor corona cage. Initial tests on the single-line model of aluminium TERN conductors measured the DC corona inception voltages (CIVs) as the ambient temperature increased from 25 °C to 42 °C. A daylight ultraviolet corona camera (CoroCam8) has been used for measurements and visualisation; the measurements record temperatures for positive and negative direct current (DC) voltages. Experimental investigations are supplemented by simulations utilising the finite element method (FEM)-based software COMSOL Multiphysics. Following the creation of 3D models of the corona cage and potential conductor arrangement, the electric field distribution on the surfaces of the conductors was examined. The CIV observations and modelling findings determine the setups’ corona inception electric field strengths. The study effectively integrated experimental data from a corona cage with FEM models to assess DC corona properties across different air temperatures thoroughly. The inception voltage levels of corona are significantly influenced by ambient temperature and the space charge generated by corona. The outcomes of the discussion will inform the design of the proposed HVDC transmission line in Southern Africa. Full article

Terahertz (THz) antennas are among the critical components required for enabling the transition to sixth-generation (6G) wireless networks. Although research on THz antennas for 6G communication systems has garnered significant attention, a standardized antenna design has yet to be established. This study introduces the modeling of a full-metal transverse slotted waveguide antenna (TSWA) for 6G and beyond. The proposed antenna operates across the upper regions of the V-band and the entire W-band. Designed and simulated using widely adopted full-wave analysis tools, the antenna achieves a peak gain of 17 dBi and a total efficiency exceeding 90% within the band. Additionally, it exhibits pattern-reconfigurable capabilities, enabling main lobe beam steering between 5° and 68° with low side lobe levels. Simulations are conducted to assess the power handling capability (PHC) of the antenna, including both the peak (PPHC) and average (APHC) values. The results indicate that the antenna can handle 17 W of APHC within the W-band and 3.4 W across the 60–160 GHz range. Furthermore, corona discharge and multipaction analyses are performed to evaluate the antenna’s power handling performance under extreme operating conditions. These features make the proposed TSWA a strong candidate for high-performance space applications, 6G communication systems, and beyond. Full article

The study of the ground tip corona discharge is an important part of the lightning strike mechanism and lightning warning research. Because the characteristics of the corona charge distribution are difficult to observe directly, simulation research is indispensable. However, most of the previous models have been unipolar models, which cannot reflect the characteristics of the tip corona discharge under electric field reversal during real thunderstorms. Therefore, the development of three-dimensional positive and negative corona discharge models is of great significance. In this study, a three-dimensional corona discharge numerical model considering the polarity reversal process of the electric field was developed with or without a wind field and simulated the tip corona discharge characteristics under this reversal. The reliability of the model was verified by comparing the observed results. Compared with the unipolar corona discharge model, this model could effectively evaluate the impact of the first half-cycle corona discharge on the second half-cycle opposite-polarity corona discharge and invert the spatial separation distribution characteristics of different polar corona charges released in both cycles under the influence of wind and the spatial electric field distribution characteristics generated by the corresponding corona charges. Comparing unipolar corona discharges under the same wave pattern and amplitude of the background electric field, it was assumed that the unipolar corona discharge occurred in the half cycle after the polarity reversal of an electric field, and there was also an opposite-polarity corona discharge process before it. Due to the influence of the first half cycle, the background electric field required for a corona discharge was smaller, and the corona current was generated earlier, but the end time was equivalent. At the same time, due to the neutralization effect of positive and negative corona charges, the peak value of the total corona charge in the second half cycle was significantly smaller than that of the unipolar model. At different building heights, the peak difference in the corona current and the peak difference in the corona charge between the two models increased linearly with an increase in height. It could be seen that this model had better simulation results and wider application value. Full article

Restrike frequently occurs during the positive leader development of long-air-gap discharges. At present, however, its detailed physical process and mechanism remain unclear. To investigate the physical mechanism of restrike, experiments were conducted in a 6 m rod–plate air gap under positive impulses with a wavefront time of 1 ms, and the process of restrike was observed during discharge. Our experimental results showed that significant luminescence appeared at the tip of the leader channel for a relatively long time during the discharge relaxation process before restrike occurred, and the luminescence became increasingly intense as the applied voltage increased until restrike occurred. By analyzing the composition of the charged particles inside the leader channel, we inferred that, during the relaxation process, the positive ions inside the leader channel migrate toward and concentrate in the leader channel tip as the applied electrical field increases, and the concentration of positive ions at the leader channel head distorts and enhances the local field, which then induces streamer corona discharge, leading to the luminescence of the leader channel. The observations, evidence, and discussion presented herein could provide a valuable reference for more effectively understanding the physical mechanism of restrike. Full article

The effect of low-temperature plasma treatment on the surface properties of thermoplastic starch film (TPS) was investigated. The surface layer (SL) modification of polymeric materials is mainly carried out to improve wettability and adhesive properties and to increase surface cleanliness. TPS was modified in an air atmosphere under either atmospheric or reduced pressure. The process parameters for modifying the SL of TPS were determined based on wettability assessment using a goniometer, geometric structure using scanning electron microscopy (SEM), and the degree of oxidation (O/C ratio) using X-ray photoelectron spectroscopy (XPS). Additionally, the effect of plasma treatment on TPS film sterilization was investigated. Full article

Electrified transportation is calling for insulation design criteria that is adequate to provide elevated levels of power density, power dynamics and reliability. Increasing voltage levels are expected to cause accelerated intrinsic and extrinsic aging effects which will not be easily predictable at the design stage due to a lack of suitable modeling. Designing reliable insulation systems would require finding solutions able to control accelerated aging due to an unpredictable increase of intrinsic stresses and the onset of extrinsic stresses as partial discharges. This paper proposes the concept of reliability redundancy for the insulation design of aerospace electrical asset components, which is also validated at lower-than-standard atmospheric pressure. The principle is that extrinsic-aging-free design might be achieved upon determining the aging stress or abnormal service stresses distribution and being sure that aging will not generate conditions that can incept extrinsic aging (partial discharges) during operation life. However, such information is never, in practice, fully available to insulation system designers. Hence, especially in critical applications such as electrified aircraft, aerospace, and combat ships a further level of reliability should be added to a partial-discharge-free design, which can consist of the use of corona-resistant materials and/or of life models able to consider the accelerated aging effect of partial discharges (or any other type of extrinsic-accelerated aging factor). Innovative life modeling considering both extrinsic and intrinsic aging stresses, insulating material testing to estimate model parameters, and a metric for quantifying the extent of corona (or partial discharge) resistance can lead to establishing feasibility and limit conditions for optimized or fully reliability-redundant design. It is shown in the paper that if an extrinsic-aging-free design is not feasible, and it is therefore replaced by a redundant design, a further level of reliability redundancy can be provided by effective condition monitoring plans. Full article

The COVID-19 pandemic highlighted the urgent need for sustainable and scalable air disinfection technologies in HVAC systems, addressing the limitations of energy-intensive and chemically intensive conventional methods. This study developed and evaluated a pilot experimental installation integrating plasma chemistry and photocatalysis for airborne pathogen and pollutant mitigation. The installation, designed with a modular architecture to simulate real-world HVAC dynamics, employed a bipolar plasma ioniser, a TiO₂ photocatalytic module, and an adsorption-catalytic module for ozone abatement. Characterization techniques, including SEM and BET analysis, were used to evaluate the morphology and surface properties of the catalytic materials. Field tests in a production room demonstrated a 60% reduction in airborne microflora in three days, along with effective decomposition of ozone. The research also determined the optimal electrode geometry and interelectrode distance for stable corona discharge, which is essential for efficient plasma generation. Energy-efficient design considerations, which incorporate heat recovery and heat pump integration, achieved a 7–8-fold reduction in air heating energy consumption. These results demonstrate the potential of integrated plasma photocatalysis as a sustainable and scalable approach to enhance indoor air quality in centralised HVAC systems, contributing to both public health and energy efficiency. Full article

Voltage withstand tests on stator bars can cause destructive phenomena such as thermal breakdown and flashover discharge on the surface of the anti-corona layer. This study optimizes the anti-corona structure at a stator bar’s end to prevent such failures using a 120 MW water-cooled turbogenerator with a rated voltage of 15.75 kV. For a well-designed anti-corona system, the maximum potential gradient of the stator bar should be lower than the discharge intensity of air corona. In our design, the electric field intensity is maintained below 3.1 kV/cm, and the maximum surface loss in the anti-corona layer is limited to less than 0.6 W/cm². Additionally, the terminal voltage is kept lower than that of flashover voltage at rated conditions. Furthermore, the length of the anti-corona layer should be minimized. The optimization process involves determining the rotation angle of the stator bar, calculating the total length of the anti-corona layer, and analyzing the electric field and loss in the layer at different lengths. The results demonstrate that the optimized anti-corona design effectively reduces the risk of flashover and thermal failure, ensuring stable operation under rated conditions. This manuscript belongs to purely computational experiments. At present, the electrical machinery with 120 MW rated power grade is put into operation steadily. There is a growing requirement for anti-corona. In this manuscript, computing method is used to assist the anti-corona structure design. The electrical machinery insulation is improved by better anti-corona materials. Therefore, the service life of electrical machinery can be prolonged, which is significant in engineering. Full article

Human health is directly affected by indoor environmental quality, and researchers are still working on innovative techniques to remove several pollutants from indoor air, such as non-thermal plasma processes. The purpose of this paper is to investigate the mechanism of ozone production for air purification from volatile organic compounds (VOCs) using symmetric corona discharge. A numerical simulation is performed using COMSOL Multiphysics v.5.1. software based on an electrical and chemical model. The agreement between simulated current–voltage characteristics and experimental results is satisfactory. In addition, the distributions of the charged particle density, the electrical field, and ozone (O₃) particle density are illustrated in symmetric geometry. The role of key parameters in determining ozone stability for reducing VOCs from indoor air is determined to enhance air purification using corona discharges. A 45% reduction in voltage reduces the ozone generation rate by nearly 90%. The total amount of ozone decreases with a rise in the temperature. At higher temperatures, a reduction in ozone density is observed in the drift zone. In addition, the ozone generation rate is reduced by 40%, using 0.1 mm tungsten discharge wire instead of 0.2 mm. Using air (80% N₂) rather than pure oxygen in any commercial ozonizer produces lower ozone yields. Numerical results show significant findings indicating that ozone generation has a critical role in removing VOCs from indoor air. Full article