Effective streamer discharge control by tailored nanosecond-pulsed high-voltage waveforms

Pulsed streamer discharges submerged in water have demonstrated potential in a number of applications. Especially the generation of discharges by short high-voltage pulses in the nanosecond range has been found to offer advantages with respect to efficacies and efficiencies. The exploited plasma chemistry generally relies on the initial production of short-lived species, e.g. hydroxyl radicals. Since the diagnostic of these transient species is not readily possible, a quantification of hydrogen peroxide provides an adequate assessment of underlying reactions. These conceivably depend on the characteristics of the high-voltage pulses, such as pulse duration, pulse amplitude, as well as pulse steepness.A novel electrochemical flow-injection system was used to relate these parameters to hydrogen peroxide concentrations. Accordingly, the accumulated hydrogen peroxide production for streamer discharges ignited in deionized water was investigated for pulse durations of 100 ns and 300 ns, pulse amplitudes between 54 kV and 64 kV, and pulse rise times from 16 ns to 31 ns. An independent control of the individual pulse parameters was enabled by providing the high-voltage pulses with a Blumlein line. Applied voltage, discharge current, optical light emission and time-integrated images were recorded for each individual discharge to determine dissipated energy, inception statistic, discharge expansion and the lifetime of a discharge.Pulse steepness did not affect the hydrogen peroxide production rate, but an increase in amplitude of 10 kV for 100 ns pulses nearly doubled the rate to (0.19 ± 0.01) mol l−1 s−1, which was overall the highest determined rate. The energy efficiency did not change with pulse amplitude, but was sensitive to pulse duration. Notably, production rate and efficiency doubled when the pulse duration decreased from 300 ns to 100 ns, resulting in the best peroxide production efficiency of (9.2 ± 0.9) g kWh−1. The detailed analysis revealed that the hydrogen peroxide production rate could be described by the energy dissipation in a representative single streamer. The production efficiency was affected by the corresponding discharge volume, which was comprised by the collective volume of all filaments. Hence, dissipating more energy in a filament resulted in an increased production rate, while increasing the relative volume of the discharge compared to its propagation time increased the energy efficiency.

Understanding pre-breakdown phenomena in natural ester insulating oil is crucial for ensuring the safe operation of electrical insulation systems. Meanwhile, Air bubbles may occur as a typical defect in power transformer oil under the effect of thermal stress or the local electrical field. These bubbles are subject to exposure to a high electric field, and this will in turn influence the pre-breakdown phenomena. To evaluate the impact of bubble on streamer propagation, based on electro-hydrodynamic model, a numerical model of natural ester insulating oil with air bubbles is constructed by introducing plasma chemical reaction into the model. The model takes into account the ionization process of gas molecules inside bubbles, laying the foundation for studying bubble-triggered streamer discharges. In addition, Finite element method was used to simulate the streamer discharge in natural ester insulating oil containing bubbles, and the influence of bubble size on the streamer branching behavior was analyzed. Simulating results show that the streamer propagation is dependent on the bubble size, especially the interface contact position between the bubble and the natural ester insulating oil.

Streamer discharge plays a central role in the electrical breakdown of matter in high electric fields, both in nature and in applied technology. This tutorial provides an intuitive introduction to the physics of streamer discharges using a fluid modeling approach. The fundamental mechanisms governing streamer inception, propagation, and interaction are demonstrated under representative electrode configurations and electric field conditions. Both positive and negative streamers are examined under uniform and nonuniform background fields. Temporal evolutions of key parameters, such as charge density, electric field, and propagation velocity, are analyzed to build a physical understanding of streamer dynamics. The relationships among streamer velocity, electron drift velocity, and diffusion velocity are analyzed to elucidate the self-consistent dynamics of the discharge front. The influence of humidity is also explored to demonstrate the environmental effects on discharge behavior. Under nonuniform electric fields, the development of the conduction and displacement currents and the morphological differences between positive and negative streamers are clarified. Finally, the interaction between oppositely charged streamers is analyzed, revealing how the electric field distribution at their heads determines the streamer interaction behavior. This tutorial integrates physical reasoning and numerical visualization to build an accessible foundation for understanding streamer discharge physics.

The earlier experimental setup for the study of a multi-streamer single pulse sliding discharge was supplemented by a photoelectric system for recording streamer radiation with a time resolution of 1.5 ns. Measurements of streamer delay and propagation velocity in Ne of atmospheric pressure at two supply voltage polarities were performed. The results showed that during each discharge pulse, regardless of its polarity, streamers of two types propagate across the gap in opposite directions. The first ones, primary streamers, start from a high-voltage electrode and move to a grounded electrode. The other type of streamers, reverse streamers, propagate in the opposite direction from a grounded electrode only after primary streamers have reached it. The experiments were carried out using voltage amplitude of 3 and 3.5 kV applied to plane-parallel electrodes on an alumina ceramic substrate with a rectangular discharge area of 9.5×11.6 cm2 in size. The total delay time range of the streamers was up to 2500–2700 ns and their motion velocity up to (3.5−5.6)×107 cm/s, depending on the discharge voltage and polarity. The dependence of delay time and velocity of the streamers' head motion on their position in the gap is presented. A qualitative explanation of the primary streamer characteristics is proposed, while the obtained experimental data are not sufficient for a similar explanation with respect to reverse streamers. The presented results are significant for studying the physical mechanisms of counterpropagating surface streamer/ionization wave dynamics, while the experimental methodology allows recording their spatiotemporal evolution in the gap.

The non-thermal, chemically active plasma is one of the promising technologies for the removal of the hazardous environmental pollutants. Pulsed streamer discharges in atmospheric pressure gases have received a great deal of interest for many years. It is very important to know the propagation mechanism of streamer discharges in order to improve the energy efficiency of pulsed discharge systems. In the present work, a Blumlein generator that has a pulse width of 100 ns was used to investigate the streamer discharge propagation. The propagation images in a coaxial reactor were taken by a streak camera for both positive and negative polarities of the applied voltage. From the results, primary and secondary streamers were observed propagating from the inner wire electrode to the outer cylinder electrode, and the maximum propagation velocity of the streamer head were 0.6 - 1.2 mm/ns in the range of 43 - 93 kV of the absolute value of the applied voltage. The propagation velocity of the positive streamer was faster than that of the negative polarity. The electric field at the wire electrode for streamer onset was 12 MV/m for the positive streamer and 20 MV/m for the negative streamer.

In this research, the dynamics of double-head streamer discharge initiation, propagation, interaction and breakdown in the air under different pressure values were presented. The double-head streamer discharge dynamics were analysed within a plane-to-plane electrode configuration. That was done through many aspects proposed, such as electron density, electric field, space charge density and streamer propagation speed. The simulation performed using ‘COMSOL Multiphysics’ is based on the finite element method and was carried out with the fluid model. The fluid model describes the movement of particle concentrations using partial differential equations (PDEs) together with Poisson’s equation; Poisson's equation and charge concentrations determine the electric field distribution in space. According to the results, as the pressure increased from (1, 2 and 3atm), the evolution time of the streamer increased from (0.563 to16.29ns) with the same breakdown voltage of 19kV. This means that the double-head streamer discharge developed faster with the decrease in pressure.

The effect of the electron distribution in front of thecathode-directed streamer head on the characteristics of the dischargeitself has been analysed in this paper. Both the process of gasphotoionization in front of the streamer head and the effect of spatiallyuniform `background' pre-ionization have been taken into consideration. Itis shown that the substitution of the actual photoelectron distribution infront of the streamer head for uniform `background' pre-ionization makesit possible, by the variation of this parameter, to attain the coincidenceof some characteristics of the streamer discharge (streamer velocity,conduction current, electron distribution in the streamer head andchannel), not allowing for coincidence of all the characteristicssimultaneously in this case. The analytical model that allows us, with theuse of the known streamer head potential, to obtain associated values ofthe head radius and peak electric field strength has been proposed andverified.

Streamer discharges in water, which are a pre-breakdown phenomenon caused by underwater discharge, have gained attention because of the development of plasma-based technologies for water purification and medical treatment. In this study, a single-shot pulsed negative high voltage of –18 to –21 kV with a rise time of 100 ns was applied to a needle electrode in ultrapure water, and streamers were continuously imaged using an optical system combining a high-speed video camera, a streak camera, and an ultra-high-speed camera with a microscope lens. These observations were synchronized with the applied voltage and the discharge current to investigate the effect of the discharge on streamer propagation. Negative streamers propagated with a velocity of 820 ± 50 m/s in the presence of pulsed currents, and 100 ± 20 m/s when pulsed currents were absent. The streak camera detected light emission when the pulsed currents appeared, and it was also observed that 1480 m/s pressure waves were generated during streamer propagation. Furthermore, we developed a simple new method of imaging weak density changes similar to those detected using the Schlieren method or Mach–Zehnder interferometer. This method simply involves inserting a pair of polarizing plates on the optical axis, so that the pressure waves can also be imaged in two-dimensional photographs. Our results indicated that the pressure waves were generated from the propagating streamer head when the pulsed currents appeared in the waveform. Analysis of temporal resolution with nano-second order clarified that the branching phenomenon occurred at different times resulting in the branching streamer propagation with different directions.

This paper reports the streamer discharge generation in different types reactor and evaluate the chemical efficiency. We have used point to plane electrode arrangement for generation of underwater discharge (UWD) and water surface discharge (WSD). We have also generated gas bubbling discharge (GBD) in water employing a point to mesh electrode arrangement. A magnetic compression pulsed power modulator able to deliver 25kV, 100Hz was used as a high voltage pulse source to initiate discharge in reactors.Chemical efficiency of streamer discharge plasma was evaluated in UWD, WSD and GBD reactors by measurement of hydrogen peroxide (H 2 O 2 ) from discharged water. The amount of H 2 O 2 indicates the formation of chemical species by discharge plasma in all reactors. In addition, orange II organic dye solution was treated as polluted water sample to understand the plasma chemical activity of streamer discharge generated in different reactors. The experimental results reveal that the chemical species formation and degradation of orange II dye was influenced by streamer discharge propagation in underwater, water surface and gas bubbling reactors depending on their physical processes. Highest production of H 2 O 2 was in UWD and faster degradation of orange II dye was in WSD.

This paper describes a correlation of partial discharge phase-resolved patterns with an optical imaging performed in a non-uniform electric field configuration. The influence of different dielectric barrier materials, placed on the plane electrode, on the discharge propagation and surface landing was investigated. The investigations were focused on the corona at positive polarity of AC high voltage. It was found that the initial positive corona stage is similar for all cases whereas the discharge propagation and surface landing strongly depends on the barrier material properties. The observed streamer discharge modes have been described by the geometrical measures such as stem length, stretch of a discharge profile on the dielectric barrier surface and an hemispherical envelope of discharge filaments. Since various dielectrics reveal different properties of charge accumulation and surface neutralization, the charge memory effect may be visible and can be related to the ability to create and sustain of additional electric field component. It may refer to subsequent discharges as well as to conditions faced at the voltage polarity reversal. The correspondence between different forms of phase-resolved patterns have been associated with the modes of streamer discharges observed by optical imaging. Presented methodology poses huge potential for both scientific investigations on underlying discharge phenomena as well as on the application in future diagnostic systems of HV insulation.

The formation and propagation of pseudo-filamentary dielectric barrier discharge in atmospheric air are investigated through a 2D fluid model. The discharge development can be divided into three stages: the volume streamer stage, the surface streamer stage, and the reverse discharge stage. The simulations show that the streamer head becomes wider and the electron density of the volume streamer head increases six times when the volume streamer interacts with the dielectric, and the volume streamer transforms into the surface streamer after the interaction. Compared with volume streamers, surface streamers have a smaller radius, a higher electric field, and a higher electron density. Furthermore, the parameters that may influence the discharge characteristics are also studied. It is found that a larger dielectric permittivity, a thinner dielectric, or a shorter voltage rise time leads to earlier inception of volume streamers, faster propagation of surface streamers, and higher current density. It is observed that the velocity of the surface streamer increases first, and then, decreases with the accumulated charges on the surface.

The vibrationally excited molecules play an important role in the plasma process. We numerically calculate the two-dimensional point-to-plane streamer propagation and the vibrational kinetics in atmospheric pressure dry-air (80% N 2 , 20% O 2 ) environment. The calculated streamer discharge characteristics, such as the mean streamer velocity and the streamer channel radius, show good agreement with an experimentally obtained results. The calculation shows that vibrational temperature for N 2 is higher than for O 2 and these two temperature have a different spatial distribution.

Axisymmetric two-dimensional (2D) simulation is often used in case of streamer discharge in atmospheric-pressure air. To validate the 2D simulation of streamer discharge, the simulation has to be compared with the measurement results. However, there is difficulty in performing the comparison because the streamer is not a 2D phenomenon but a three-dimensional phenomenon. In this study, a pseudo-2D axisymmetric single-filament pulsed positive streamer discharge was generated in atmospheric-pressure air and compared with our 2D simulation. The propagation, emission intensity, shape, and cathode current of the streamer were compared. The ozone density was also measured using laser spectroscopy and compared with the simulation because our simulation intends to simulate the dynamics of reactive species. The measurements and simulations exhibited some agreements and disagreements. The measurement also showed a cathode fall and other cathode phenomena, which were not considered in the simulation.

This paper presents an experimental characterization of the prebreakdown phenomena in liquid/solid interfaces. The characterization is devoted to the 2nd mode positive streamers initiated and propagated along interfaces of mineral-oil and solids with different chemical composition and physical properties. Polymers of low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) polyvinylidene fluoride (PVDF) and papers made of kraft paper and a kraft fibril paper (made from cellulosic micro and nano fibrils), lignin-free paper and paper with high lignin content (referred to as k107 kraft paper) are used as the solid to study their influence on the streamer inception and propagation. The streamers are initiated at the interface by applying steps of voltage to a point-plane electrode arrangement with a solid (dielectric barrier) into the gap. The solid is placed diagonal to the oil gap and near to the point electrode. Shadowgraphs, charge and light intensity recordings are obtained during the inception and propagation of the streamers. Thus, estimations of the streamer length, velocity, current and average charge, are also presented. A time delay has been observed before the initiation of the streamer. This delay is probably correlated to the initiation process and formation of the gaseous phase of the streamer near to the interface. The threshold propagation voltage of the 2nd mode streamers at mineral-oil/solid interfaces is shown to be independent of the interface. However, the inception voltage is highly influenced by the interface. Additionally, the observed characteristics of streamers propagation (e.g. current, length, velocity, etc) along the tested interfaces cannot be fully explained by a capacitive coupling effect (permittivity mismatch). This open a discussion for the possibility that properties of the solid such as chemical composition, wettability and surface roughness can influence the streamer propagation.

This work is devoted to the modeling of streamer discharge, propagation in liquid dielectrics (water) gap using the bubble theory. This of the electrical discharge (streamer) propagating within a dielectric liquid subjected to a divergent electric field, using finite element method (in two dimensions). Solution of Laplace's equation governs the voltage and electric field distributions within the configuration, the electrode configuration a point (pin) - plane configuration, the plasma channels were followed, step to step. The results show that, the electrical discharge (streamer) indicates the breakdown voltage required for a 3mm atmospheric pressure dielectric liquid gap as 13 kV. Also, the electric potential and field distributions shown agreement with the streamer growth, according to the simulation development time.