Streamer Propagation Velocity Research Articles

Modeling of streamer dynamics in helium plasma jets driven by modulated voltage pulses

The results of simulation of guided streamers driven by modulated voltage pulses are presented. It is shown that, in qualitative accordance with recently obtained experimental data, modulation of the applied voltage can lead to oscillations of the streamer propagation velocity and provide stepwise character of streamer propagation. A comparison of streamer characteristics upon application of modulated and constant voltages, showing the effects of modulation on plasma jet characteristics, is given.

Stepwise propagation of a guided streamer along a DBD helium plasma jet fed by biased oscillating voltage

A stepwise propagation of a guided streamer along a helium atmospheric pressure plasma jet driven by a dielectric barrier discharge was recorded. To feed the plasma jet, we used a power supply generating an output voltage signal consisting of a superposition of 41.6 kHz bipolar square pulses and 300 kHz oscillating signals. At a positive half a period of the output voltage signal, a step-by-step propagation was observed for the ionization wave along the plasma jet. The streamer head stops with the decrease in voltage in the first cycle of oscillations and then restarts its motion at the voltage front of the next cycle of a voltage oscillation. The streamer propagation velocity and plasma jet length are likely to be controlled by varying the gas flow rate, bias voltage, voltage rise rate, frequency of oscillations in the pulse, and other parameters.

Regularly-swelling plumes generated in atmospheric pressure argon plasma jet excited by a biased sinusoidal voltage

Far different from conical plumes, regularly-swelling plumes are generated in an atmospheric pressure argon plasma jet excited by a biased sinusoidal voltage at low frequency. Depending on the polarity of bias voltage, the plumes with periodic swells can be solid or hollow. Results indicate that discharge initiates once per voltage cycle, which appears in the negative and positive half cycles for the solid and hollow plumes, respectively. By fast photography, it is found that streamers are involved propagating downstream of the argon flow for the two plumes. Transversely, the streamer diffuses for the solid plume, while it propagates only in the flow periphery for the hollow plume. Due to a high field, intense discharges near the nozzle provide the following swell positions with active species, which can remarkably enhance the discharges there and induce the swells. This formation mechanism of periodic swells is verified through investigating the distance of two adjacent swells as a function of gas flow rate and driving frequency. Moreover, spatial distributions of excited electron temperature and streamer propagation velocity are qualitatively explained based on the mechanism.

Near-surface electron transport and its influence on the discharge structure of nanosecond-pulsed dielectric-barrier-discharge under different electrode polarities

We perform a systematic numerical investigation of the nanosecond-pulsed surface dielectric-barrier-discharge evolution under different electrode polarities. For both positive and negative electrode polarities, two discharge strokes take place corresponding to the leading edge and the trailing edge of the nanosecond voltage pulse. During the first discharge stroke, the positive streamer propagates along the dielectric surface accompanying a thin plasma sheath layer, while the negative streamer stays attached to the dielectric surface. The resultant propagation velocity of the positive streamer is found to be faster than that of the negative streamer. During the second discharge stroke, a plasma sheath layer forms between the negative streamer and the dielectric surface due to the electrons drifting away from the near-surface region, while the sheath layer between the positive streamer and the dielectric surface fades away due to the electrons drifting toward the dielectric surface. For both positive and negative electrode polarities, it is revealed that a strong downstream body force is generated when the plasma sheath layer exists, due to the high net charge density and strong electric field in the near-surface sheath layer.

Effects of photoionization characteristics on parameters of positive streamers

Results of simulations of positive streamers obtained with the use of variable photoionization coefficient are presented. It is shown that a reduction of photoionization coefficient can lead both to growth and to a decrease of streamer propagation velocity. Streamers move slower in the case of the reduction of the amount of produced photons, at an unchanged length of absorption of ionizing photons. If a reduction of photoionization coefficient is caused by addition to the gas of an admixture that absorbs ionizing photons and thus shortens their absorption length, the streamer velocity is greater than in the absence of admixtures.

Streamer characteristics of dielectric natural ester-based liquids under long gap distances

Natural esters, as the renewable resources, offer excellent physiochemical and dielectric properties such as the fire-resistance, high biodegradability and satisfactory dielectric breakdown performance. Thus, natural esters are selected as the insulation and heat dissipation medium for electrical equipment. However, the electrical performance of natural esters with different structures under the long gap and higher electrical stress needs further evaluations. In this paper, streamer propagation of various natural esters under the long gap and higher electrical stress were observed optically. The influence of voltage polarity, liquid types and gap distances on streamer characteristics of natural esters were analyzed. Results show that the maximum propagation velocity of streamer in natural esters is greater than that in the hydrocarbon liquids. Breakdown voltage of natural esters under negative polarity is much higher than that under positive polarity for the same gap distance. Among all the natural esters concerned, the camellia liquid demonstrates slower streamer velocity and slight greater lightning breakdown voltages for the positive and negative polarity. The lower content of unsaturation triacylglycerol molecules in camellia liquid contributes to the inhibition of ionization and streamers propagation. Results would be valuable reference for the design, manufacture and operation of the electrical equipment filled with natural ester.

Effect of Nanoparticle Morphology on Pre-Breakdown and Breakdown Properties of Insulating Oil-Based Nanofluids.

Nanoparticles currently in use are challenged in further improving the dielectric strength of insulating oil. There is a great need for a new type of nanoparticle to promote the application of insulating oil-based nanofluids in electric industries. This paper experimentally investigates the effect of nanoparticle morphology on pre-breakdown and breakdown properties of insulating oil-based nanofluids. The positive impulse breakdown voltage of insulating oil can be significantly increased by up to 55.5% by the presence of TiO2 nanorods, up to 1.23 times that of TiO2 nanospheres. Pre-breakdown streamer propagation characteristics reveal that streamer discharge channels turn into a bush-like shape with much denser and shorter branches in the nanofluid with TiO2 nanorods. Moreover, the propagation velocity of streamers is dramatically decreased to 34.7% of that in the insulating oil. The greater improvement of nanorods on the breakdown property can be attributed to the lower distortion of the electric field. Thus, when compared with nanospheres, pre-breakdown streamer propagation of nanofluid is much more suppressed with the addition of nanorods, resulting in a greater breakdown voltage.

Characteristics of a Pulse-Periodic Corona Discharge in Atmospheric Air

Pulse-periodic corona discharge in atmospheric air excited by applying a voltage pulse with a subnanosecond or microsecond rise time to a point electrode is studied experimentally. It is shown that, at a voltage rise rate of dU/dt ~1014 V/s, positive and negative ball-shaped streamers with a front velocity of ≥2 mm/ns form near the point electrode. As dU/dt is reduced to 1010−1011 V/s, the streamer shape changes and becomes close to cylindrical. The propagation velocity of cylindrical streamers is found to be ~0.1 mm/ns at dU/dt ~ 2 × 1010 V/s. It is shown that the propagation direction of a cylindrical streamer can be changed by tilting the point electrode, on the axis of which the electric field strength reaches its maximum value. It is established that, for the negative polarity of the point electrode and a microsecond rise time of the voltage pulse, a higher voltage is required to form a cylindrical streamer than for the positive polarity of the point electrode.

The effect of temperature on pulsed positive streamer discharges in air over the range 292 K–1438 K

The effect of temperature on pulsed positive streamer discharges in air is measured by comparing atmospheric-pressure, high-temperature discharges with low-pressure, room-temperature discharges at the same air densities n and discharge voltages. Both discharges have the same reduced electric field E/n, so the differences between the two discharges only depend on the temperature, which is varied from 292 K to 1438 K. Temperature affects the discharge pulse energy most significantly; at 1438 K, the energy of an atmospheric-pressure discharge pulse is approximately 30 times larger than that of the corresponding 20.5 kPa, room-temperature discharge. Temperature also affects the shapes of the streamers when K, but no significant effect is observed for K. There is also no significant temperature effect on the spatially integrated intensity of N2(C–B) emission. However, temperature strongly affects the ratio of the integrated emission intensity to the discharge energy. No effect of the temperature is observed on the propagation velocity of the primary streamer or on the length of the secondary streamer.

Effects of Nanoparticle Materials on Prebreakdown and Breakdown Properties of Transformer Oil

In order to reveal the effects of nanoparticle materials on prebreakdown and breakdown properties of transformer oil, three types of nanoparticle materials, including conductive Fe3O4, semiconductive TiO2 and insulating Al2O3 nanoparticles, were prepared with the same size and surface modification. An experimental study on the breakdown strength and prebreakdown streamer propagation characteristics were investigated for transformer oil and three types of nanofluids under positive lightning impulse voltage. The results indicate that the type of nanoparticle materials has a notable impact on breakdown strength and streamer propagation characteristics of transformer oil. Breakdown voltages of nanofluids are markedly increased by 41.3% and 29.8% respectively by the presence of Fe3O4 and TiO2 nanoparticles. Whereas a slight increase of only 7.4% is observed for Al2O3 nanofluid. Moreover, main discharge channels with thicker and denser branches are formed and the streamer propagation velocities are greatly lowered both in Fe3O4 and TiO2 nanofluids, while no obvious change appears in the propagation process of streamers in Al2O3 nanofluid in comparison with that in pure oil. The test results of trap characteristics reveal that the densities of shallow traps both in Fe3O4 and TiO2 nanofluids are much higher than that in Al2O3 nanofluid and pure oil, greatly reducing the distortion of the electric field. Thus, the propagations of positive streamers in the nanofluids are significantly suppressed by Fe3O4 and TiO2 nanoparticles, leading to the improvements of breakdown strength.

Characteristics of streamer propagation along the insulation surface: Influence of air pressure and humidity

Most of the UHV transmission lines passed the high altitude and high humidity area. It was necessary to study the influence of air pressure and humidity on characteristics of flashover along the insulation surfaces. In the three-electrode arrangement, the characteristics of streamer propagation in air alone and along the silicone rubber surface were measured at Shenzhen, Kunming, and Yangbajing, respectively. The data of the streamer ‘stability’ propagation field and velocity were measured at the different air pressure and humidity. Empirical equations were presented expressing the effects of the air pressure and humidity on the streamer ‘stability’ propagation field and velocity. Furthermore, the variation of the streamer ‘stability’ propagation field and velocity with air pressure and humidity was analysed. The test results showed that the streamer stability propagation field was in proportion to air pressure or humidity. Under the same electric field, the streamer propagation velocity was in inverse proportion to air pressure or humidity. Therefore, it was easier for streamer propagation in the lower air pressure or humidity. Furthermore, the effect of the humidity and air pressure on stability fields of streamer propagation along silicone rubber surface was larger than that in air alone.

The influence of bremsstrahlung on electric discharge streamers in N2, O2 gas mixtures

Streamers are ionization filaments of electric gas discharges. Negative polarity streamers propagate primarily through electron impact ionization, whereas positive streamers in air develop through ionization of oxygen by UV photons emitted by excited nitrogen; however, experiments show that positive streamers may develop even for low oxygen concentrations. Here we explore if bremsstrahlung ionization facilitates positive streamer propagation. To discriminate between effects of UV and bremsstrahlung ionization, we simulate the formation of a double headed streamer at three different oxygen concentrations: no oxygen, 1 ppm O2 and 20% O2, as in air. At these oxygen levels, UV-relative to bremsstrahlung ionization is zero, small, and large. The simulations are conducted with a particle-in-cell code in a cylindrically symmetric configuration at ambient electric field magnitudes three times the conventional breakdown field. We find that bremsstrahlung induced ionization in air, contrary to expectations, reduces the propagation velocity of both positive and negative streamers by about 15%. At low oxygen levels, positive streamers stall; however, bremsstrahlung creates branching sub-streamers emerging from the streamer front that allow propagation of the streamer. Negative streamers propagate more readily forming branching sub-streamers. These results are in agreement with experiments. At both polarities, ionization patches are created ahead of the streamer front. Electrons with the highest energies are in the sub-streamer tips and the patches.

Characteristics of streamer propagation along insulation surface: quantitative influence of permittivity and surface properties

An investigation into the quantitative influence of permittivity and surface properties on characteristics of streamer propagation along insulation surface was presented. In the three-electrode arrangement, the variation of the streamer stable propagation electric field and streamer propagation velocity along the dielectric materials was measured through three photomultipliers. The measured dielectric materials were consisted of two different dielectric materials with the thickness of 5 mm piled by the side of each other. The influence of the permittivity (the capacitive effect) and the surface properties on the characteristic of streamer propagation along the surface of dielectric materials were obtained by varying the ratio of two material volumes. The streamer propagation velocity and electric field for streamer stable propagation along two combinations of nylon and PTFE, silicone rubber and PTFE were measured, respectively. The conclusion was that the surface properties of dielectric materials had large effect on streamer propagation. Furthermore, surface properties of silicone rubber were most unfavorable for streamer propagation in the three dielectric materials.

Time-resolved imaging of positive pulsed corona-induced surface streamers on TiO2 and γ-Al2O3-supported Ag catalysts

We report the first instance of time-resolved imaging of surface streamers in air propagating on the surface of titanium dioxide (TiO2) and alumina (γ-Al2O3) beads at ambient temperature and atmospheric pressure. The propagation velocity of primary streamers was found to be dependent primarily on the applied voltage and the type of catalyst. The presence of Ag nanoparticles enhanced the propagation velocity of primary streamers in both TiO2 and γ-Al2O3. Some of the primary streamers passed through a partial discharge, which resulted in enhanced discharge intensity. Through successive steps, the partial discharge served as a staging point for primary streamers, and promoted their propagation toward the next catalyst bead. For a given configuration and catalyst, the velocity of the primary streamer was largely influenced by applied voltage and catalyst type. For a mesh-to-mesh reactor with Ag/ TiO2 catalyst, the primary streamer reached about 660 km s−1. Secondary streamers occurred with much slower velocities after the primary streamer had disappeared. In contrast to primary streamers, secondary streamer velocities were almost completely independent of the applied voltage on both TiO2 (150 ± 50 km s−1) and γ-Al2O3 (70 ± 10 km s−1). Detailed time-resolved imaging data on surface streamers can provide important insight into understanding and modeling plasma-catalysis, which can accelerate the progress of research and development in this area.

Characteristics of streamer propagation along insulation surface: influence of shed configuration

The reasonable shed configuration could improve flashover voltage of insulator and enhance the reliability of the overhead transmission lines. An investigation into the effect of shed configuration on streamer propagation along insulation surface was presented. In the three-electrode arrangement, the influences of the diameter, location, and combination of insulator shed on streamer propagation path, propagation probability, 'stability' field, together with velocity, were measured using three photomultipliers and an ultraviolet camera. The streamer propagated along smooth insulation surface with two propagation paths. That is 'fast' component propagating along the insulation surface and 'slow' component propagating in air. As a shed appeared on the insulation surface, the 'fast' propagation path was cut off, and the 'fast' component of streamer never reached the cathode. The 'slow' propagation path could bypass the shed, and the 'slow' component of streamer would cross the gap to reach the cathode. Furthermore, the electric field required for streamer propagation along the insulator with a shed was larger than along the smooth insulator. The electric field required for streamer stable propagation was in proportion to the diameter of shed. Under the same electric field, the streamer propagation velocity was in inverse proportion to the diameter of shed. The location of shed also had a great influence on the characteristics of streamer propagation. The more the shed was close to the initiation of streamer, the more difficult the streamer propagated along the insulator surface.

Fluid modeling of a high-voltage nanosecond pulsed xenon microdischarge

A computational modeling study of high-voltage nanosecond pulsed microdischarge in xenon gas at 10 atm is presented. The discharge is observed to develop as two streamers originating from the cathode and the anode, and propagating toward each other until they merge to form a single continuous discharge channel. The peak plasma density obtained in the simulations is ∼1024 m−3, i.e., the ionization degree of plasma does not exceed 1%. The influence of the initial gas pre-ionization is established. It is seen that an increase in the seeded plasma density results in an increase in the streamer propagation velocity and an increase in the plasma density obtained after the merging of two streamers.

Effect of Fe3O4 nanoparticles on positive streamer propagation in transformer oil

Fe3O4 nanoparticles with an average diameter of 10 nm were prepared and used to modify streamer characteristic of transformer oil. It was found that positive streamer propagation velocity in transformer oil-based Fe3O4 nanofluid is greatly reduced by 51% in comparison with that in pure oil. The evolution of streamer shape is also dramatically affected by the presence of nanoparticles, changing from a tree-like shape with sharp branches in pure oil to a bush-like structure with thicker and denser branches in nanofluid. The TSC results reveal that the modification of Fe3O4 nanoparticle can greatly increase the density of shallow trap and change space charge distribution in nanofluid by converting fast electrons into slow electrons via trapping and de-trapping process in shallow traps. These negative space charges induced by nanoparticles greatly alleviate the electric field distortion in front of the positive streamer tip and significantly hinder the propagation of positive streamer.

Dynamic Characteristics of Positive Pulsed Dielectric Barrier Discharge for Ozone Generation in Air**supported by National Natural Science Foundation of China (Nos. 51366012 and 11105067), Jiangxi Province Young Scientists (Jinggang Star) Cultivation Plan of China (No. 20133BCB23008), Natural Science Foundation of Jiangxi, China (No. 20151BAB206047) and Jiangxi Province Higher School Science and Technology Landing Plan of China (No. KJLD-14015)

A comprehensive dynamic model consisting of 66 reactions and 24 species is developed to investigate the dynamic characteristics of ozone generation by positive pulsed dielectric barrier discharge (DBD) using parallel-plate reactor in air. The electron energy conservation equation is coupled to the electron continuity equation, the heavy species continuity equation, and Poisson's equation for a better description. The reliability of the model is experimentally confirmed. The model can be used to predict the temporal and spatial evolution of species, as well as streamer propagation. The simulation results show that electron density increases nearly exponentially in the direction to the anode at the electron avalanche. Streamer propagation velocity is about 5.26 × 104 m/s from anode to cathode in the simulated condition. The primary positive ion, negative ion, and excited species are O2+, O3− and O2(1Δg) in pulsed DBD in air, respectively. N2O has the largest density among nitrogen oxides. e and N2+ densities in the streamer head increase gradually to maximum values with the development of the streamer. Meanwhile, the O2+, O, O3, N2(A3Σ) and N2O densities reach maximum values in the vicinity of the anode.

A numerical study of species and electric field distributions in pulsed DBD in oxygen for ozone generation

A numerical model including 29 reactions and 11 species is developed to investigate the spatial-temporal distributions of species and electric field in oxygen parallel-plate positive pulsed dielectric barrier discharge for ozone generation. Electron energy conservation equation is coupled to electron continuity equation, heavy species continuity equation and Poisson's equation. The spatial-temporal distributions of species and electric field are obtained at electron avalanche and during streamer propagation. The results show the dominant positive ion, negative ion and excited species are O2+, O3− and O2(∑g+1), respectively. The average streamer propagation velocity is about 5.56 × 104 m/s. Overall electron density almost increases exponentially but with a violent oscillation in the vicinity of anode at electron avalanche. Electron density increases at first and then declines in the vicinity of anode and streamer channel during streamer propagation, and increases gradually in streamer head with the development of streamer, as well as reduces sharply to almost zero near cathode. Electron density almost remains constant in whole streamer channel at any one moment. Other species have a similar spatial-temporal distribution.

A computational modeling study on the helium atmospheric pressure plasma needle discharge**Project supported partly by the National Natural Science Foundation of China (Grant No. 11465013), the Natural Science Foundation of Jiangxi Province, China (Grant No. 20151BAB212012), and in part by the International Science and Technology Cooperation Program of China (Grant No. 2015DFA61800).

A two-dimensional coupled model of neutral gas flow and plasma dynamics is employed to investigate the streamer dynamics in a helium plasma needle at atmospheric pressure. A parametric study of the streamer propagation as a function of needle tip curvature radius and helium gas flow rate is presented. The key chemical reactions at the He/air mixing layer which drive the streamer propagation are the direct ionization via collision with electrons, the Penning effect being not so crucial. With increasing the gas flow rate from 0.2 standard liter per minute (SLM) to 0.8 SLM, however, the emissions resulting from reactive oxygen and nitrogen species change from a solid circle to a hollow profile and the average streamer propagation velocity decreases. Air impurities (backdiffusion from ambient air) in the helium jet result in a significant increase in the streamer propagation velocity. Besides, with decreasing the tip curvature radiusfrom 200 μm to 100 μm, the electron avalanche process around the near-tip region is more pronounced. However, the spatially resolved plasma parameters distributions (electron, helium metastables, ground state atomic oxygen, etc.) remain almost the same, except that around the near-tip region where their peak values are more than doubled.