Air Breakdown Research Articles

Mechanisms of air breakdowns for aluminum conductors steel reinforced wire-wire gaps induced by propane jet flames

In recent years, events of transmission line tripping caused by wildfires have occurred frequently in many mountain areas. In order to understand the mechanism of such events, an experimental system for simulating breakdown discharge processes of model wires induced by a simulated fire source is designed. In this experiment, propane jet flame (somewhat like eruptive fires in real wild fires) is used as a simulated flame source. By setting three different gas flow rates and five different wire-wire gaps, discharge breakdown behaviors and characteristics between two ACSR (aluminum conductors steel reinforced) segments in propane flames with three flame zones are explored. The influences of these different factors on the breakdown characteristics and mechanisms of wire-wire air gaps are analyzed. Results show that breakdown voltages increase almost linearly with the increase of wire-wire gaps in continuous zone of the flames for three gas flow rates. For a short wire-wire gap like 5.0 cm, the pilot discharge channels can be formed more easily, stably and completely under a lower voltage and weaker external ionization environment. The propane jet flame conditions are complex and affected by multiple actions like initial jet force (affected by gas flow rate), temperature distribution, soot particle, ion wind. As a result, local electric field will be distorted, a streamer channel is established dependently in different cases. These factors play individual, competitive or synergistic roles at the same time in breakdowns of real ACSR wire-wire gaps.

An Advanced Strategy to Enhance TENG Output: Reducing Triboelectric Charge Decay.

The Internet of Things (IoT) is poised to accelerate the construction of smart cities. However, it requires more than 30 billion sensors to realize the IoT vision, posing great challenges and opportunities for industries of self-powered sensors. Triboelectric nanogenerator (TENG), an emerging new technology, is capable of easily converting energy from surrounding environment into electricity, thus TENG has tremendous application potential in self-powered IoT sensors. At present, TENG encounters a bottleneck to boost output for large-scale commercial use if just by promoting triboelectric charge generation, because the output is decided by the triboelectric charge dynamic equilibrium between generation and decay. To break this bottleneck, the strategy of reducing triboelectric charge decay to enhance TENG output is focused. First, multiple mechanisms of triboelectric charge decay are summarized in detail with basic theoretical principles for future research. Furthermore, recent advances in reducing triboelectric charge decay are thoroughly reviewed and outlined in three aspects: inhibition and application of air breakdown, simultaneous inhibition of air breakdown and triboelectric charge drift/diffusion, and inhibition of triboelectric charge drift/diffusion. Finally, challenges and future research focus are proposed. This review provides reference and guidance for enhancing TENG output.

Lightning Initiation as a Consequence of Natural Thundercloud Evolution. Part 3. Streamers and Transition from Streamers to a Leader Channel

This article presents the final part of the study devoted to description of the authors’ scenario of lightning initiation in a thundercloud, the first two parts of which are presented in [1, 2]. The first part shows that consideration of the electron detachment from negative ions results in that the air breakdown field reduces by 15–30 %. This partially simplifies but does not solve the problem of lightning initiation in a thundercloud, the maximum electric fields in which are approximately an order of magnitude lower than the dielectric strength of air. The second part describes the transition from millimeter corona discharges to decimeter-scale regions of elevated ionic conductivity, which becomes possible if the spatiotemporal frequency of corona discharges arising due to collisions (nearly collisions) of hydrometeors exceeds a quite moderate value of 0,1 m-3s-1. In turn, the regions of elevated ionic conductivity give rise to positive streamers. The article presents the lightning initiation process final stage, at which streamers oriented by the large-scale electric field are combined into a single plasma network, inside which a hot leader channel is generated. It is shown that, for the transition from streamers to a lightning leader seed to occur, a potential difference between the boundaries of the zone of a strong intracloud field is to exceed 3 MV. The article ends with a general conclusion summarizing the trilogy results.

Stick‐Type Discharge Triboelectric Nanogenerator with Amplified Output Using a Conductive Spring

As technology develops over time, energy‐harvesting methods that generate sustainable energy have been highlighted worldwide. In energy harvesting, triboelectric nanogenerators (TENGs) have several advantages, such as a simple design, high efficiency, low cost, and accessibility. Although they are applied in various fields, TENGs have limitations regarding the low current output on the microampere scale due to a high surface charge, leading to air breakdown and field emission. In addition, TENGs are implemented under vacuum pressure with high mechanical input frequency to overcome the limitation. Nevertheless, the developed TENGs still retain critical problems, such as the inability to make packaging systems and device damage. This paper reports on the stick‐type discharge (SD) TENG that can provide an amplified current with outstanding durability by applying a conductive spring to solve the problem. Consolidating a dynamic electrode with an accumulated surface charge and low curvature spring and emitting a high electric field generate a milliampere current scale through electrons to flow directly with exceptional mechanical endurance. Thus, a multi‐SD‐TENG comprising four SD‐TENGs and a portable holder powers a warning light in daily life through a shaking motion.

Development and Discharge Characteristics of Surface Tracking on the Interface Between the PD Suppression Coatings Outside of Stator Winding Slots

During the operation of high voltage (HV) motors, the end-winding surface can be contaminated by oil or dust, resulting in a type of intense discharge: surface tracking, which gradually develops into phase-to-phase or phase-to-ground faults. To improve our understanding of the development process and characteristics of surface tracking on the end-winding, an accelerated aging test was performed on 10-kV stator coils to induce surface tracking under electrical and oil contamination stresses. To understand the evolution of surface tracking, the partial discharge (PD) was collected and the characteristics of the corresponding phase-resolved PD (PRPD) patterns and pulse sequence analysis (PSA) patterns were analyzed. Combined with finite element analysis (FEA) simulations, the development process of surface tracking was interpreted. It is established that the electrical field of a dry band with high resistivity on the contamination is much higher than other contaminated areas via FEA simulation, causing the electrical breakdown of the adjacent air and discharge. Such continuous and intense discharges finally leave on the end-winding surface a carbonized channel, forming a tree-like structure. This article presents the results of changes in PRPD patterns and PSA patterns during different stages, together with the surface potential distribution after tracking generation. The research of this article is devoted to providing a reference for PD monitoring and fault diagnosis of HV motors.

A database of near-field head-related transfer functions based on measurements with a laser spark source

This paper presents a database of near-field head-related transfer functions (HRTFs) of an artificial head, measured at four distances (0.2, 0.3, 0.4 and 0.5 m), with 49 positions recorded at each distance, for a total of 196 measurement points. The HRTFs were recorded using an acoustic pulse created by a laser-induced breakdown of air (LIB), which realizes a close to ideal, massless, monopole sound source. While the LIB produces a high amplitude pressure pulse, the amplitude decays toward low frequencies, which introduced a low frequency limit of about 200Hz for this particular setup. Thus, a spherical head model based on the analytical expression for scattering by a rigid sphere was fitted to the measured data, and used to extend the low frequency range of the measurements. A brief evaluation of the processed dataset was undertaken, considering interaural time and level differences. The measured and processed database, as well as the low frequency extension procedure are made publicly available to support future research into nearby sound localization, and virtual/augmented reality applications.

Discharge characteristics of positive and negative polarity streamers with submillimeter gap based on fractal theory

In order to study the characteristics of streamer discharge in sub-millimeter gap, an experimental system and an image acquisition system of positive and negative polarity streamer discharge in the gap of 100–500 μm at atmospheric pressure are built, and the initial breakdown voltages and breakdown images of positive and negative polarity streamer discharge in a gap range of 100–500 μm are collected, and the fractal dimension of the experimental discharge images is calculated by Matlab. The experimental analysis shows that the air breakdown discharge in the gap range of 100–500 μm still conforms to the stream theory, and the polarity effect between the breakdown voltage of positive and negative streamers and the fractal dimension of the discharge image is obvious. The influence of space charge and photoionization on the meandering degree and coverage of the discharge channel in stream theory increase with the increase of the gap, and jump at 300 μm. The fractal simulation of positive and negative streamer discharge with a gap of 500 μm is established by using WZ (Wiesmann-Zeller) model based on fractal theory in Matlab. It is found that the development probability index <i>η</i> is inversely proportional to the fractal dimension, and that the <i>η</i> is smaller in positive streamer than in negative streamer under the same discharge condition.

Achieving high-efficiency triboelectric nanogenerators by suppressing the electrostatic breakdown effect

Maximizing TENGs’ energy cycle by analyzing the dynamic charge transfer process and suppressing air breakdown.

Spatiotemporal Plasma-Particle Characterization of Dry Aerosols Using Nanosecond, Femtosecond, and Filament Laser-Produced Plasmas.

The ability to rapidly characterize dry aerosols in air using laser-induced breakdown spectroscopy (LIBS) with femtosecond laser pulses promises advancement towards real-time atmospheric sampling and standoff capabilities. Of particular interest is the ability to apply LIBS in the context of low-particle loaded environments where discrete particle interactions must be observed within the sampling volume of the laser-produced plasma (LPP). In this study, dry nanoparticles in suspension are generated from a standard solution and sampled in air using Q-switched nanosecond (ns-) pulses, short-focus (SF) femtosecond (fs-) pulses, and filaments. Short time-gated plasma images are captured to observe spatially and temporally varying discrete plasma-particle interactions, which is shown to influence early air breakdown behavior and subsequent plasma evolution. Along with images, photo-multiplier tube (PMT) measurements are conducted where strong spatiotemporal dependencies are exhibited by the collected emission signal on particle proximity and plasma expansion behavior. Finally, conditional analysis is performed on LIBS measurements to determine associated sampling probabilities and filter out spectra with poor or absent emission peaks with an adaptive threshold algorithm.

Characterization of CdTe Thin Films Using Orthogonal Double-Pulse Laser-Induced Breakdown Spectroscopy

Orthogonal reheating double-pulse laser-induced breakdown spectroscopy (LIBS) was applied to the elemental analysis of CdTe thin film samples. Films were grown through nanosecond pulsed laser ablation over silicon and glass substrates. The analysis was performed by applying a 266 nm pulsed laser devised to minimize sample damage. Re-excitation was conducted using a nanosecond laser emitting at 1064 nm that induced air breakdown 1 mm above the target. Emission enhancement was investigated as a function of both time acquisition delay and inter-pulse delay. The plasma temperature and electron density calculations made showed that the double-pulse scheme produced higher temperature values and a longer plasma duration than single-pulse LIBS. The self-absorption coefficient of the lines was determined from the measured ablated matter, plasma volume and collected spectra. The results of the double-pulse LIBS configuration showed a significant increase in emission intensity, reducing the self-absorption effect. In addition, the relative concentration of the thin films was determined for both experimental schemes. The calculated elemental values for the double-pulse configuration coincide with those expected and are more accurate than those obtained using a single laser.

Lightning Initiation as a Consequence of Natural Thundercloud Evolution. Part 2. Pre-Streamer Stage

The article presents the second part of the authors’ lightning initiation scenario, which is a continuation of the study [1]. In the first part it was shown that, if the detachment of electrons from negative ions is taken into account, the air breakdown field reduces by 15–30 %. This partially simplifies but does not solve the problem of lightning initiation in a thundercloud, the maximum electric fields in which are approximately an order of magnitude lower than the dielectric strength of air. This article addresses the lightning discharge inception scenario pre-streamer stage. It describes how a series of corona discharges that occur during collisions (nearly collisions) of hydrometeors seeds the cloud with decimeter-scale regions having increased ionic conductivity. The electric field at the poles of these regions enhances to a level necessary for positive streamers to appear. It is shown that, for a transition from millimeter-scale corona discharges to decimeter- or meter-scale streamers to occur, a spatiotemporal frequency of corona discharges on hydrometeors higher than 0,1 m-3s-1 is required, which may well be achieved in a typical thundercloud. The final stage, at which streamers oriented by the direction of a large-scale electric field are combined into a single plasma network, within which a hot leader channel forms, will be described in the coming part of the study.

Influence of discharge polarity on streamer breakdown criterion of ambient air in a non-uniform electric field

Streamer breakdown of atmospheric air with non-uniform dc electric field in a needle-to-plate electrode configuration is studied using a semi-analytic model and experimental measurements. A high voltage (either positive or negative) is applied to a hollow needle with outer diameter and inner diameter separated from a planar ground electrode by a gap distance of 0.1–1.4 cm. Breakdown voltages are recorded for both positive and negative discharge polarities. Empirical relations between the critical avalanche size for streamer breakdown and the gap distance are proposed. Using these empirical relations, a semi-analytic model based on Meek’s criterion for streamer breakdown is developed to accurately predict the measured breakdown voltages. It is found that for (or d 0.5 cm at one atmosphere) streamer breakdown of ambient air occurs at a lower applied voltage for a positively biased needle compared to that with a negatively biased needle, referred as the polarity effect. For breakdown is attained at a lower applied voltage with a negatively biased needle compared to that with a positively biased needle, and breakdown mode transits from the polarity effect to the so called inverted polarity effect.

Lightning Initiation as a Consequence of Natural Thundercloud Evolution. Part 1. The Role of Detachment in Reducing the Critical Air Breakdown Field

Direct measurements show that the maximum values of electric fields measured in thunderclouds are approximately an order of magnitude lower than the air breakdown (ionization threshold) field. At first glance, this means the impossibility of electron avalanches to form and, as a consequence, the impossibility of a lightning discharge to occur. This circumstance puts the question about the lightning origin physical mechanism on a par with the most amazing mysteries of the nature. For more than half a century of research, several mechanisms have been proposed to solve this problem, among which two main lines can be distinguished. The first group of approaches focuses on the possibility of a streamer or a system of streamers to initiate from the surface of one or several hydrometeors, while the second one interprets lightning initiation as a consequence of the runaway electrons breakdown emerging from the interaction between high-energy cosmic rays and the atmosphere. There are also hybrid scenarios that combine both the ideas. However, in view of certain limitations, none of the proposed approaches has been recognized as the final solution to the problem. The article describes a fundamentally new lightning initiation mechanism that develops sequentially on several spatiotemporal scales. The scenario proposed shows how a series of corona discharges occurring during collisions of hydrometeors seeds the cloud with decimeter-scale elevated ionic conductivity regions, the electric field at the poles of which increases to the level necessary for positive streamers to appear. At the next stage, multiple streamer discharges oriented by the direction of a large-scale electric field are combined into a single plasma network, within which a hot leader channel is formed. The mechanism discussed effectively utilizes small-scale and mesoscale electric field fluctuations arising in a thundercloud and can be implemented if the spatiotemporal frequency of corona discharges, accompanying collisions and near collisions of hydrometeors, and the potential difference between the strong intracloud field zone boundaries exceed 0.1 m-3s-1 and 3 MV, respectively. In contrast to alternative approaches, the proposed lightning initiation scenario can be implemented under the conditions of a typical thundercloud without the need to involve any external auxiliary factors. The study results are presented in three parts. This article gives an introductory part, which sets the general context of the narrative and determines the study aims, and describes the role the detachment of electrons from negative ions plays in the air breakdown field reduction. The authors' lightning initiation scenario based on the results described in the present paper is given in two subsequent publications.

Analysis of the characteristics of microwave-enhanced laser-induced atmospheric air plasma and ablation plasma for Al target

The investigation and comparison of air plasma generated directly in the absence as well as in the presence of solid target along with microwave enhancement were reported. The plasma characteristics including emissions, size, duration, and temperature were measured using high-speed camera, optical emission spectroscopy, and temperature approximation through spectral fitting. The laser energy required for ablation is much lower than the air breakdown energy but, the minimum energy density for air and alumina breakdown is inversely proportional to the focal lengths. The size and volume of the air plasma generated by the microwave and ablation plasma interactions were less than those of the microwave-enhanced laser-induced air plasma but was similar with standard laser-induced air plasma. When comparing the plasma lifetimes, both air plasmas (with and without a solid target) exceeded the duration of the microwave pulse input (approximately 1 ms). As the plasma lifetime is a function of electron density, shorter lifespan with the target ∼1500 ± 150 µs compared with the lifetime of the plasma without the target at ∼1800 ± 150 µs were observed. Similar results were observed for the time-series measurements of the OH and N2 second positive (N2PS) molecular emissions. OH and N2PS were not observed within the first 300 µs in the presence of the solid target; these air plasma components were only generated as a “by-product” of the microwave and ablation plasma. The rotational and vibrational temperatures were approximated by spectral fitting of simulated OH and N2PS spectra and the experimentally acquired spectra. The microwave increased the vibrational temperature in a constant rotational temperature during the expansion of the air plasma. The same trend is observed with the presence of the alumina target.

Heterogeneous CPU-GPU Accelerated Subgridding in the FDTD Modelling of Microwave Breakdown

Microwave breakdown is crucial to the transmission of high-power microwave (HPM) devices, where a growing number of studies have analyzed the complex interactions between electromagnetic waves and the evolving plasma from theoretical and analytical perspectives. In this paper, we propose a finite-difference time-domain (FDTD) scheme to numerically solve Maxwell’s equation, coupled with a fluid plasma equation for simulating the plasma formation during HPM air breakdown. A subgridding method is adopted to obtain accurate results with lower computational resources. Moreover, the three-dimensional subgridding Maxwell–plasma algorithm is efficiently accelerated by utilizing heterogeneous computing technique based on graphics processing units (GPUs) and multiple central processing units (CPUs), which can be applied as an efficient method for the investigation of the HPM air breakdown phenomena.

Theoretical boundary and optimization methodology of contact-separation triboelectric nanogenerator

Triboelectric nanogenerators (TENGs) have exhibited great potential as the promising energy harvesters in recent decades. To obtain superior output performance, advances in materials science and engineering technology have been applied to promote the surface charge density and energy output. In this work, the mathematical derivations have been developed to derive the theoretical boundary under the air breakdown restriction for contact-separation mode TENGs. Through the optimization of limitation equations, mathematical relations were deduced between the output evaluation metrics and TENGs’ design including the structural and material factors. In addition, methodologies for output performance enhancement were proposed, from which an optimized model possessing 10 μm silicone rubber as the dielectric layer exhibits 2.85 mC/m2 in surface charge density and 1.12 mJ in energy output under 2 cm separation distance. This work provides systematical analysis and comprehensive predicts for the theoretical boundary of TENGs’ capability, which gives guidance on the design and optimization for high-performance TENGs.

Power Generation by a Double-Sided Tape.

A novel contact-separation triboelectric generator concept is proposed in this study, which is composed of a double-sided tape with acrylic adhesive material and a metalized polyester (PET/Al) film (an aluminum layer coating on one side). The proposed concept is very cost-effective and easy to fabricate compared to existing triboelectric nanogenerators (TENGs), which require special equipment and sophisticated procedure to build. The strong bonding nature of acrylic adhesive on the tape induces a significant charge when contacting. The peak power generation depends on the induced pressure at the impact. During the separation phase, the air breakdown between triboelectric layers allows most existing electrons to flow back from the ground due to rapid charge removal at the interface. A higher voltage can be generated when the PET is interfaced with the double-sided tape compared to the Al-acrylic configuration because of the effect of triboelectric series and a Schottky barrier formation for electrons at the tape-Al interface during contact. A double-electrode configuration with an assembly of Al/PET-tape-PET/Al significantly improved the performance, in which a 21.2 mW peak power is achieved compared to 7.6 mW in the single-electrode design with tape-PET/Al assembly when excited at 20 Hz in a shaker test. This double-electrode triboelectric generator can power 476 LEDs with an active area of 38 mm × 25 mm. Moreover, a direct power of a 650 nm laser diode was demonstrated. In summary, the proposed triboelectric generator concept using tacky materials shows the potential for higher-energy harvesting via triboelectrification and advances the state of the art by offering low cost and easy fabrication options. It is expected that such newly proposed triboelectric generators are able to meet power requirements in many engineering applications.

Assessing the Role of Photon Processes in Facilitating Radio Frequency Breakdown of Air at Atmospheric Pressure in Millimeter Gaps

The behavior of the breakdown electric field versus gap lengths (in the 1–5-mm range) and at different frequencies in the 1–80-MHz span, has been studied numerically at atmospheric pressure. Unlike previous studies of radio frequency (RF) breakdown, the role of photon-emission processes is explicitly included and shown to be important for large-area electrode configurations. Numerical analysis based on Monte Carlo calculations is used to predict the breakdown thresholds. The simulations embed a statistical photon transport model, based on random selections of emission angles and times from excited atoms, as well as photoemission from the electrodes. Simulation results compare well with experimental data from our group, but only with the inclusion of photon processes. Though both photoemission and photoionization are included in the breakdown physics, the former is identified as the dominant process. The frequency behavior of breakdown fields is also assessed with the inclusion of photons, and the results reveal a U-shaped trend with increasing values for smaller gaps.

A Mutual Boosting Self-Excitation Hybrid Cell for Harvesting High Entropy Energy at 32% Efficiency.

Triboelectric nanogenerators (TENGs) and dielectric elastomer generators (DEGs) are potentially promising energy conversion technologies, but they still have limitations due to their own intrinsic characteristics, including the low energy output of TENGs caused by the air breakdown effect, and external polarization voltage requirement for DEGs, which severely limit their practical applications. Herein, coupling TENG with DEG is proposed to build a mutual beneficial self-excitation hybrid generator (named TDHG) for harvesting distributed and low-quality mechanical energy (high entropy energy). Experimental results demonstrate that the output charges of this TDHG are enhanced by fivefold of that of the conventional charge-excitation TENG, and continuous operation of DEG is also realized by simple mechanical triggering. More importantly, owing to the high peak power contributed by TENG and the long output pulse duration guaranteed by DEG, the TDHG realizes a much higher energy conversion efficiency of 32% in comparison to either the TENG (3.6%) or DEG (13.2%). This work proposes a new design concept for hybridized energy harvester toward highly efficient mechanical energy harvesting.

Hydroxyl Spectroscopy of Laboratory Air Laser-Ignition

This work investigates spatial and temporal distributions of hydroxyl, OH, in laser-plasma in laboratory air at standard ambient temperature and pressure. Of interest are determination of temperature and density of OH and establishment of a correlation of molecular OH emission spectra with shadow graphs for time delays of 50 to 100 μs, analogous to previous work on shadow graph and emission spectroscopy correlation for cyanide, CN, in gas mixtures and for time delays of the order of 1 μs. Wavelength- and sensitivity-corrected spatiotemporal data analysis focuses on temperature inferences using molecular OH emission spectroscopy. Near-IR radiation from a Q-switched laser device initiates optical breakdown in laboratory air. The laser device provides 6 ns, up to 850 milli Joule, pulses at a wavelength of 1064 nm, and focal irradiance in the range of 1 to 10 terawatt per centimeter-squared. Frequency doubled beams are utilized for capturing shadow graphs for visualization of the breakdown kernel at time delays in the range of 0.1 to 100 μs. OH emission spectra of the laser plasma, spatially resolved along the slit dimension, are recorded in the wavelength range of 298 nm to 321 nm, and with gate widths adjusted to 10 μs for the intensified charge-coupled device that is mounted at the exit plane of a 0.64 m Czerny-Turner configuration spectrometer. Diatomic OH signals occur due to recombination of the plasma and are clearly distinguishable for time delays larger than 50 μs, but are masked by spectra of N2 early in the plasma decay.