Positive Streamer Propagation Research Articles

Investigation of positive streamers in CO2: experiments and 3D particle-in-cell simulations

Abstract We investigate the propagation of positive streamers in CO2 through 3D particle-in-cell simulations, which are qualitatively compared against experimental results at 50 mbar. The experiments show that CO2 streamers are much more stochastic than air streamers at the same applied voltage, indicating that few electrons are available in front of the streamer head. In the simulations, we include a photoionization model for CO2. The computational results show that even a small amount of photoionization can sustain positive streamer propagation, but this requires a background electric field close to the critical field. When we compare streamers in CO2 and in air at the same applied voltage, the electric field at the streamer head and the electron density in the streamer channel are higher in CO2. We discuss the uncertainties in CO2 photoionization and provide an estimate for the quenching pressure, which is based on the radiative lifetime of emitting states and the collision frequency of the gas. Furthermore, a criterion for self-sustained streamer growth in CO2 is presented and compared against simulation results.

Mechanisms of charge-induced surface discharge under positive impulse voltages

Abstract Charge-induced surface flashover is a critical factor leading to insulation failures in high-voltage direct current gas-insulated equipment, and the underlying mechanisms are still unclear. In the present study, the typical surface charge distributions are first summarized. Then, the impact of charge polarity and position on surface discharge characteristics in ambient air is studied, and the surface charge dynamics during multiple discharge processes are also focused. Comparative studies of the charge-induced surface discharge are conducted in SF6, and the effect of the gas atmosphere is discussed. The results indicate that the repulsive effect of deposited positive charges significantly inhibits the positive streamer development by reducing the electric field. The acceleration of negative charges on positive streamer propagation is the result of two competitive mechanisms: the enhancement of the electric field and the neutralization with positive charges in the streamer channel. In the multiple discharge process, positive streamers develop along the gap of positive streamer channels from the previous discharge. When the last discharge is intense enough, back discharges may occur along the pattern of the deposited positive channels from the previous discharge. The effects of the deposited charges on the surface discharge process are consistent in air and SF6. These findings will be advantages in improving the insulation reliability of gas-insulated equipment.

A 3D kinetic Monte Carlo study of streamer discharges in CO2

We theoretically study the inception and propagation of positive and negative streamers in CO2 . Our study is done in 3D, using a newly formulated kinetic Monte Carlo discharge model where the electrons are described as drifting and diffusing particles that adhere to the local field approximation. Our emphasis lies on electron attachment and photoionization. For negative streamers we find that dissociative attachment in the streamer channels leads to appearance of localized segments of increased electric fields, while an analogous feature is not observed for positive-polarity discharges. Positive streamers, unlike negative streamers, require free electrons ahead of them in order to propagate. In CO2 , just as in air, these electrons are supplied through photoionization. However, ionizing radiation in CO2 is absorbed quite rapidly and is also weaker than in air, which has important ramifications for the emerging positive streamer morphology (radius, velocity, and fields). We perform a computational analysis which shows that positive streamers can propagate due to photoionization in CO2 . Conversely, photoionization has no effect on negative streamer fronts, but plays a major role in the coupling between negative streamers and the cathode. Photoionization in CO2 is therefore important for the propagation of both positive and negative streamers. Our results are relevant in several applications, e.g. CO2 conversion and high-voltage technology (where CO2 is used in pure form or admixed with other gases).

Effects of SF6 mixing ratio on DC positive streamer propagation in SF6/N2 gas discharge under a nonuniform electric field

Effects of SF6 mixing ratio on DC positive streamer propagation in SF6/N2 gas discharge under a nonuniform electric field

The influence of individual evaluation of electron‐impact ionization, attachment, and photoionization rates on positive streamer propagation

AbstractThis study evaluates the individual effects of electron‐impact ionization, attachment, and photoionization on streamer propagation to provide a deeper understanding of the streamer propagation mechanism and useful knowledge to obtain the best set of input data for verification and validation studies. The results show that streamers with higher electron‐impact ionization rates have higher propagation velocities and lower electric fields, while those with higher attachment rates have slower propagation velocities and higher electric fields. Streamers with higher photoionization rates have lower electric fields at the head, but the velocity remains largely unaffected. The effects of different rates of ionization, attachment, and photoionization have been analyzed using an analytical solution called the diameter‐speed relation.

On propagation of positive and negative streamers in air in uniform electric fields

Recently published results of numerical simulations of positive and negative streamers propagating in uniform applied electric fields in air are analyzed in the framework of an analytical approach. It is shown that obtained approximate relations between the streamer radius, velocity and length, depending on the value of applied electric field, are in reasonable agreement with the computational data.

Numerical modeling of positive streamer propagation in alternative natural ester and traditional naphthenic oil under sub-microsecond pulsed voltages

In this paper, a two-dimensional axisymmetric numerical model of streamer discharge in alternative natural ester liquid and conventional naphthenic oil under a positive sub-microsecond impulse voltage is proposed. The model is based on the charge drift-diffusion approximation in a divergent electric field. Simulation shows that streamer propagation in naphthenic oil is divided into two stages: stage I with a small streamer velocity of 0–0.91 km s−1 and stage II with a rapidly rising streamer velocity up to 213 km s−1. In natural ester, the streamer velocity gradually slows down from 4.84 km s−1 to 2.11 km s−1. The electric field at the head of the streamer in natural ester ranges from 2.4 × 108 V m−1 to 2.5 × 108 V m−1 during propagation, which is visibly lower but more consistent than that in naphthenic oil (3.5 × 108 V m−1 to 8.4 × 108 V m−1). It is revealed that the different streamer features within the two types of oil are caused by the different competition between the Laplacian electric field and space charge effect at the streamer head. For streamer propagation in naphthenic oil, stage I is dominated by the Laplacian electric field whereas stage II is dominated by the space charge effect. In natural ester, the whole streamer propagation is dominated by the Laplacian electric field. Further, it is indicated that the streamer head consists of two specific discharging regions, i.e. the front region of the streamer head which guides new space charge accumulation and the back region of streamer head which guides density reduction of accumulated space charge. The expansion of the streamer tunnel is caused by the alternating space charges in these two regions. The work in this paper provides a theoretical reference for the practical application of alternative transformer liquids.

The influence of humidity on positive streamer propagation in long air gap

A 2D numerical simulation of the positive streamer properties was performed in 9–12 cm plane-to-plane air gaps for various pressures and water vapor contents. It was shown that an increase in air humidity leads to hampering the streamer development and to increasing the average critical electric field required for bridging the discharge gap. The effect of humidity was most profound at atmospheric pressure and decreased with decreasing pressure. The influence of water content on the streamer properties was explained by a decrease in the streamer channel conductivity due to dissociative recombination of electrons with positive hydrated ions and enhanced three-body electron attachment to O2 molecules. The calculated critical electric field and streamer velocity in humid air gaps were compared with available experimental data.

Numerical Simulation of the Positive Streamer Propagation in N₂ Under Nanosecond Pulse Voltage

Numerical Simulation of the Positive Streamer Propagation in N₂ Under Nanosecond Pulse Voltage

Radiation Phenomenon Due to Streamers of Sprites

An upper atmospheric phenomenon i.e., sprites can be thought to be mainly caused by the propagation of positive corona streamers. This research presents the formulation for the calculation of radiation power received from the propagating corona streamers responsible for the origination of the sprites. The produced magnetic field variation using the calculated electromagnetic radiation power is found to be similar with the previous observation-based research work.

Effect of Profiled Surface on Streamer Propagation and the Corner Effect

Streamer behavior near dielectric surfaces is an important characteristic of gas-solid electrical insulation systems. This paper presents the numerical study on the propagation of positive streamers along dielectric surface with different roughness and shape in ambient air. Each surface is designed to have different roughness but the same streamer propagation length to exclude the effect of elongated profiled surface on the streamer. So other factors that involved in streamer propagation on profiled dielectric surface could be analyzed. When streamers propagate to the corner on a surface with concaves, the radius of streamer increases and the electric field in front of the streamer decreases. The phenomenon is called corner effect. With the increase of roughness, the radius of the streamer becomes larger and the electric field in front of the streamer becomes smaller at the corner. Meanwhile, the increase of the roughness results in an inhibition on the streamer development. Moreover, it is found that the streamer accelerates when it descends on the slope and decelerates when ascending. When the streamer propagates on a dielectric surface with convexities, the streamer development is also impeded. However, the variations of streamer radius and electric field at the corner show different trend as that in a concave.

Finite Element Based Comparative Analysis of Positive Streamers in Multi Dispersed Nanoparticle Based Transformer Oil

The dispersion of dissimilar nanoparticles (NPs) in transformer oil (TO) has a major impact on fast propagating positive streamers. This work investigates the positive streamer dynamics in TO modified by dispersing both Fe3O4 and Al2O3 NPs at a homogenous concentration. The hydrodynamic drift diffusion model of positive streamer evolution and propagation are solved using the commercial software package COMSOL Multiphysics. The impact of multiple NPs (MNPs) has been analysed for streamer propagation, electric field intensity, electron density, and space charge density of modified TO. MNPs successfully reduce streamer propagation velocity by 50%, 17%, and 37.5% comparing to pure oil, Fe3O4 based nanodielectric fluids (NDFs), and Al2O3 based NDFs, respectively. The spatial distribution of electron density reveals the loss of electrons from the ionization region until the saturation of NPs. A comparative study demonstrates that MNPs significantly alter the streamer dynamics and augment the dielectric strength of TO compared to individual NPs.

Computational study of simultaneous positive and negative streamer propagation in a twin surface dielectric barrier discharge via 2D PIC simulations

The propagation mechanisms of plasma streamers have been observed and investigated in a surface dielectric barrier discharge (SDBD) using 2D particle in cell simulations. The investigations are carried out under a simulated air mixture, 80% N2 and 20% O2, at atmospheric pressure, 100 kPa, under both DC conditions and a pulsed DC waveform that represent AC conditions. The simulated geometry is a simplification of the symmetric and fully exposed SDBD resulting in the simultaneous ignition of both positive and negative streamers on either side of the Al2O3 dielectric barrier. In order to determine the interactivity of the two streamers, the propagation behavior for the positive and negative streamers are investigated both independently and simultaneously under identical constant voltage conditions. An additional focus is implored under a fast sub nanosecond rise time square voltage pulse alternating between positive and negative voltage conditions, thus providing insight into the dynamics of the streamers under alternating polarity switches. It is shown that the simultaneous ignition of both streamers, as well as using the pulsed DC conditions, providing both an enhanced discharge and an increased surface coverage. It is also shown that additional streamer branching may occur in a cross section that is difficult to experimentally observe. The enhanced discharge and surface coverage may be beneficial to many applications such as, but are not limited to: air purification, volatile organic compound removal, and plasma enhanced catalysis.

Simulation of positive streamer propagation in an air gap with a GFRP composite barrier

The puncture of glass fibre reinforced polymer (GFRP) laminate is a primary damage pattern of wind turbine blades due to lightning strikes. A numerical simulation model of positive streamer propagation in a needle-to-plate air gap with a GFRP laminate is established to investigate the breakdown mechanism of GFRP laminate. The model not only considers the dynamics of charged particles in the air and the composite laminate, but also the current continuity at gas–solid interfaces. The simulated streamer discharge pattern and the surface streamer length are in good agreement with the observation results. The distributions and evolutions of the electron number density, electric field, and surface charge densities during streamer propagation are obtained. It is found that the enhancement of the electric field on the GFRP laminate is caused by the rapid deposition of positive and negative space charges on the GFRP laminate after a secondary streamer incepts on the lower surface of the GFRP laminate. The effects of the applied voltage, relative permittivity, and thickness of the GFRP laminate on the electric field on the GFRP laminate are investigated. The obtained results could assist in further understanding of the mechanism of GFRP wind blade breakdown due to lightning strikes.

Cerman: Software for simulating streamer propagation in dielectric liquids based on the Townsend–Meek criterion

We present a software to simulate the propagation of positive streamers in dielectric liquids. Such liquids are commonly used for electric insulation of high-power equipment. We simulate electrical breakdown in a needle–plane geometry, where the needle and the extremities of the streamer are modeled by hyperboloids, which are used to calculate the electric field in the liquid. If the field is sufficiently high, electrons released from anions in the liquid can turn into electron avalanches, and the streamer propagates if an avalanche meets the Townsend–Meek criterion. The software is written entirely in Python and released under an MIT license. We also present a set of model simulations demonstrating the capability and versatility of the software.

Positive and negative streamer propagation in volume dielectric barrier discharges with planar and porous electrodes

AbstractThe spatiotemporal dynamics of volume and surface positive and negative streamers in a pin‐to‐plate volume dielectric barrier discharge is investigated in this study. The discharge characteristics are found to be completely different for positive and negative streamers. First, the spatial propagation of a positive streamer is found to rely on electron avalanches caused by photoelectrons in front of the streamer head, whereas this is not the case for negative streamers. Second, our simulations reveal an interesting phenomenon of floating positive surface discharges, which develop when a positive streamer reaches a dielectric wall and which explain the experimentally observed branching characteristics. Third, we report for the first time, the interactions between a positive streamer and dielectric pores, in which both the pore diameter and depth affect the evolution of a positive streamer.

Electrically isolated propagating streamer heads formed by strong electron attachment

Streamer discharges occur in the early stages of electric breakdown of gases in lightning, as well as in plasma and high voltage technology. They are growing filaments characterized by a curved charge layer at their tip that enhances the electric field ahead of them. In this study, we analyze the effect of strong electron attachment on the propagation of positive streamers. Strong attachment occurs in insulating gases like sulphur hexafluoride (SF6) or in air at increased density. We use the classical fluid approximation with photo-ionization for streamers in ambient air, and we artificially increase the electron attachment rate where the field is below the breakdown value. This modification approximates air pressures above 1 bar at room temperature. We find that the streamer head can keep propagating even though the ionized channel loses its conductivity closely behind the head; hence, even if it is electrically isolated. We describe how, depending on the attachment rate, the streamer propagation in a constant electric field can be accelerating, uniformly translating, or stagnating.

Modelling of second mode positive streamer in cyclohexane by considering optimized electron saturation velocity

Experimental and modelling study of the pre-breakdown phenomenon in dielectric liquids, generally called ‘streamers’, is vital for the application of liquids in high voltage and power dense devices. Streamer is characterized into four modes by average propagation velocity, among which the second mode streamer is responsible for breakdowns at a wide range of gap distances and voltage levels. The stable propagation velocity of around 2 km s−1 is one of the key characteristics of the second mode streamer. The most recent study found that streamer branching is not the main reason for the stable velocity of second mode streamer as was assumed previously. Besides, one major drawback of the existing charge-drift model of the second mode streamer is the over-estimation of electron velocity, which leads to the much higher streamer propagation velocity in simulation than that observed in experiments. In this paper, restriction of streamer propagaiton velocity by using electron saturation velocity (ESV) is found to be the key reason for the stable propagaiton velocity of the second mode streamer. The charge-drift model is modified by considering different ESVs. It is found that reducing ESV from 30 km s−1 to 2.5 km s−1 in simulation can greatly constrain positive streamer propagation velocity from 4.15 km s−1 to 0.50 km s−1 in cyclohexane. When ESV is set to be 7.5 km s−1 in cyclohexane, the streamer propagation velocity in simulation increases from 1.59 km s−1 at 80 kV (below breakdown voltage) to 1.91 km s−1 at 100 kV (near to acceleration voltage), which closely matches the experimental observations.

Simulation of positive streamers in CO2 and in air: the role of photoionization or other electron sources

Positive streamer discharges have been studied and modelled extensively in air. Here we study positive streamers in CO2 with and without oxygen admixtures; they are relevant for current high voltage technology as well as for discharges in the atmosphere of Venus. We discuss that no efficient photoionization mechanism is known for gases with a large CO2 fraction, as photons in the relevant energy range are rapidly absorbed. Hence positive streamers can propagate only due to some other source of free electrons ahead of the ionization front. Therefore we study positive streamer propagation in CO2 with different levels of background ionization to provide these free electrons. The effect of replacing photoionization by background ionization is studied with simulations in air. Simulating streamers in background fields of 16 to 20 kV cm−1 at standard temperature and pressure within a gap of 6.4 cm, we find that streamer propagation is rather insensitive to the level of photoionization or background ionization. We also discuss that the results depend not only on the value of breakdown field and applied electric field, and on preionization or photoionization, but also on the electron mobility μ(E) and the effective ionization coefficient α eff(E), that are gas-dependent functions of the electron energy or the electric field.

Streamer propagation along a profiled dielectric surface

We investigate the propagation of positive streamers along a profiled dielectric surface in air at atmospheric pressure. Results from experiments and two-dimensional planar low-temperature plasma fluid simulations are presented and analysed. The test object consists of a disk-shaped high voltage electrode and a dielectric slab with 0.5 mm deep corrugations. The corrugated surface has a 47% larger surface area than the smooth reference surface. The experiments and simulations are performed at voltage levels that lead to either gap-bridging or arrested streamers. In both experiments and simulations, the streamers take a longer time to reach the ground electrode when propagating along the profiled surface than along the smooth reference surface. Also, arrested streamers stop closer to the high voltage electrode when a profiled surface is used. Streamers propagate closely along the surface profile in the simulations, which suggests that the observed surface profile effect is mainly a result of elongated streamer channels. Compared to the streamers propagating along the smooth surface, the elongated streamers on the profiled surface have less residual voltage at the streamer front to drive the streamer advancement.