Streamer Propagation Research Articles

The polarity effect of nanosecond voltage pulses on the propagation of streamers in a point-to-plane gap filled with air

The results of experimental studies of the effect of polarity on the streamer velocity at various voltage amplitudes are presented. In the experiments, nanosecond voltage pulses were applied across an 8.5 mm point-to-plane gap filled with air at a pressure of 100 kPa. The formation of positive and negative streamers has been experimentally studied using a HSFC-PRO four-channel ICCD camera and a Hamamatsu C10910-05 streak camera. Waveforms of voltage and discharge current pulses were also recorded. The propagation velocity of streamers was estimated by streak images. It was found that a negative streamer crosses the gap faster than a positive one. This is most likely due to the presence of runaway electrons with the negative polarity of a pointed electrode. The experiment showed that runaway electrons are generated before the formation of a negative streamer. Runaway electrons can preionize the gas in the gap.

Formation of combustion wave in lean propane-air mixture with a non-uniform chemical reactivity initiated by nanosecond streamer discharges in the HCCI engine

The propagation of combustion wave, which is formed as a result of impact of a filamentary pulsed periodic non-equilibrium discharge on a mixture that is not ignited by only compression in the HCCI engine, has been simulated. The discharge for a short time locally activated the mixture in the engine cylinder at a certain crankshaft rotation angle at the compression stage. The approach to evaluation of the temperature and composition in the region activated by high-frequency corona discharge has been proposed. Multi-pulse and multi-channel nature of discharge was accounted for in our model. The densities of chemically active species produced during streamer propagation were found using two-dimensional axially symmetric fluid model. The obtained composition and temperature in the activated zone were the initial conditions for modeling the propagation of combustion wave along the cylinder radius in 1D approximation. Special terms were included in equations responsible for the compression along the axis of cylinder to mimic the real change in pressure in cylinder. The calculations were performed for a lean C3H8-air mixture, which is characterized by the presence of low-temperature heat release (LTHR) stage, and intermediate and high temperatures heat release (ITHR and HTHR) stages. It was shown that the ignition timing in activated zone depends on the specific energy input into the streamer channel, the radius of activated region coupled with the volume fraction of activated region treated by discharge, and the moment of discharge initiation relative to the top dead center (TDC). The speed of combustion wave, the occurrence of auto-ignition in the end gas and transition to combustion, accompanied by “knocking” or strong pressure fluctuations are largely determined by the moment of discharge initiation and the specific energy input. The significant effect of discharge is explained by the stimulation of oxidation kinetic mechanisms at LTHR and ITHR stages.

Blocking streamer development by plane gaseous layers of various densities

Streamer interaction with gaseous layers of various densities is numerically simulated in ambient air on the basis of a two-dimensional fluid model. It is shown that rarefied layers are greater obstacles to streamer propagation in comparison with dense layers. When intersecting a low-density layer, the streamer tends to initiate a radial ionization wave, which screens and weakens the electric field both on the axis in the layer and behind it. As a result, it is difficult to form a secondary streamer behind the low-density gas layer. A streamer interacting with a high-density layer also can initiate a radial ionization wave, which develops in undisturbed air along the outer surface of the layer. The streamer can overcome a high-density layer at not-too-high values of the layer thickness. The effects of the streamer polarity, layer thickness and density on the streamer interaction with the layer are studied. It is shown that the discharge gap with a thin low-density layer behaves like a diode in which streamer discharges of negative polarity can pass through the gap, while discharges of positive polarity are blocked.

Impact of different packing beads methods for streamer generation and propagation in packed-bed dielectric barrier discharge

The combination of plasma and catalyst can better promote the gas reaction for plasma catalysis. We used a two-dimensional particle-in-cell/Monte Carlo collision model to study the relationship between plasma behavior and dielectric beads with five different packing beads methods in a packed-bed dielectric barrier discharge in nitrogen gas at atmospheric pressure. The electron density, electric field, excitation rate, and ionization rate are calculated with different packing beads methods. As a result, either a change of the bead size or removing one bead can induce distinct features for plasma formation and streamer propagation. The electric field is enhanced near the beads and plates, resulting in a large tangential component to the dielectric surface, which gives rise to surface ionization waves (SIWs). The plasma streamer is generated between bead 1 and 2, then propagates to bead 4 and develops itself by surface SIWs along the bead 4 surface, yielding highest and uniform plasma density there with five packing beads. A positive streamer is generated after removing bead 2, and a volume discharge is developed for removing bead 4, asymmetric SIWs are induced with a smaller size of bead 4 while it becomes almost symmetric with a larger size of bead 4 for removing bead 5. The uniform and maximum ionization rate take place on the bead 4 surface, indicating the importance of bead 4 for packing. Moreover, the SIWs and positive streamers give rise to the highest plasma concentration due to the maximum ionization rate on the surfaces of the beads.

FINITE ELEMENT MODELLING FOR ELECTRIC FIELD DISTRIBUTION AROUND POSITIVE STREAMERS IN OIL

Electric field distribution of positive streamers during propagation was determined with the finite element method by using COMSOL multiphysics. Modelling was performed at 210 kV and 270 kV. The geometrical shape of streamers was modelled with cylinder and sphere for the case of 210 kV while a growing cylinder was used for streamer propagation at 270 kV. In addition, a spherical model was used for determining the correlation between streamer branching and the electric field. It is obtained from the simulation results that the 2nd mode streamers has the electric field at channel tips of about 0.1 MV/cm while 8.3 MV/cm was received for the 4th mode streamers. The simulation results also reveal that the shielding effect resulting from streamer branching significantly reduces the electric field at the channel tips, and the shielding effect disappears with the angle a between channels is about 30o-60o depending on the size of streamer envelope. The hypothesis on correlation among velocity, streamer branching and electric field is suggested.

Investigation on the streamer propagation in atmospheric pressure helium plasma jet by the capacitive probe

In this letter, the streamer propagation in the atmospheric pressure helium plasma jet with a floating electrode nozzle driven by the kHz AC power supply is investigated. The current signal induced by the space charges and the mean propagation velocity of the guided ionization waves are measured by the capacitive probe method in the discharge region. The space charges in the guided ionization waves are found to increase with the applied voltage, which enhances both the electric field near the streamer head and the propagation velocity. The applicability of the streamer mechanism to the propagation of the guided ionization waves is validated by this electrical diagnostic method.

Indirectly Measured Ambient Electric Fields for Lightning Initiation in Fast Breakdown Regions

AbstractWe report a new approach to measure indirectly the ambient thunderstorm electric fields in fast positive breakdown regions. For a given geometry of the discharged fast breakdown region, we show that there is a minimum ambient electric field required to produce a given charge moment change. We apply this approach to the fast breakdown measurements for two events reported by Rison et al. (2016, https://doi.org/10.1038/ncomms10721) and find that the average ambient electric field in the discharged region is at least V/m at the 9.5 km initiation altitude of these events. This electric field is close to the runaway electron avalanche electric field and to the critical field for positive streamer propagation. These measurements provide a meaningful starting point for more detailed analyses or simulations of what occurs inside the fast breakdown process that is responsible for the initiation of at least some lightning discharges.

Positive streamers: inception and propagation along mineral-oil/solid interfaces

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.

Breakdown and streamer behavior in double-layer oil-paper insulation under impulses of varying front time

The breakdown and streamer behavior in double-layer oil-paper insulation under impulses of varying front time were investigated in this study to determine the prebreakdown process in oil-paper insulation. The relationships between front times and breakdown characteristics were investigated and impulse-polarity-dependent variations were observed. The complete impulse breakdown process and precise role of front time were assessed as per streamer initiation and streamer propagation based on emitted light signals and shadow images. The re-initiation of streamers in non-first oil gaps was determined to be the key factor in breakdown as-dominated by applied voltage and space charge accumulation. The initiation and propagation times of streamers were observed to find that the streamers tend to propagate at phases with higher voltage amplitude as front time increases, which facilitates streamer re-initiation and thus decreases the breakdown voltage. Equivalent applied voltages during streamer propagation were further calculated to quantitatively investigate the effect of front time on streamer propagation.

Photoionization model for streamer propagation mode change in simulation model for streamers in dielectric liquids

Radiation is important for the propagation of streamers in dielectric liquids. Photoionization is a possibility, but the effect is difficult to differentiate from other contributions. In this work, we model radiation from the streamer head, causing photoionization when absorbed in the liquid. We find that photoionization is local in space (μm-scale). The radiation absorption cross section is modeled considering that the ionization potential (IP) is dependent on the electric field. The result is a steep increase in the ionization rate when the electric field reduces the IP below the energy of the first electronically excited state, which is interpreted as a possible mechanism for changing from slow to fast streamers. By combining a simulation model for slow streamers based on the avalanche mechanism with a change to fast mode based on a photoionization threshold for the electric field, we demonstrate how the conductivity of the streamer channel can be important for switching between slow and fast streamer propagation modes.

A two-dimensional air streamer discharge model based on the improved Helmholtz equation at low temperature and sub-atmospheric pressure

In this paper, an efficient boundary condition is applied to solve the photoionization rate, and a two-dimensional numerical simulation is carried out for the development and propagation of an air streamer at low temperature and sub-atmospheric pressure. The results show that the new boundary condition improves the calculation accuracy, but the influence of photoionization on the streamer discharge process is not obvious. The discharge current in the development of streamer discharge is defined, and the corresponding expression of the positive and negative streamer discharge current is given. The influence of the electric field exceeding the threshold value on the discharge process is preliminarily introduced. In the process of discharge, only the propagation velocity of the streamer is obviously higher than that of normal temperature and pressure, and the trend of the other parameters is basically the same as that described in the previous paper. The above results give us a deeper understanding of the discharge characteristics under low temperature and sub-atmospheric pressure, which has certain significance for the development of aviation and high voltage engineering.

Discharge Enhancement Phenomenon and Streamer Control in Dielectric Barrier Discharge with Many Pores

The surface and volume discharge enhancement phenomena and streamer propagation direction control in catalytic pores are significant for the plasma catalytic degradation of pollutants. In this work, we use a two-dimensional particle-in-cell with Monte Carlo collisions model to explore the effect of lateral voltage on streamer enhancement and streamer propagation control for different driving voltages in pores of various shapes, sizes, and numbers. The driving voltage is applied to the top of the device, while the lateral voltages are applied at the left and right sides of the device. The surface and volume discharge enhancement phenomena become more significant and streamer propagation is more restricted within a narrow channel as the lateral voltage (with the same values on the left and right sides) increases from −5 kV to −30 kV for a fixed driving voltage of −20 kV. In this case, both the volume and surface discharges are intensive, leading to highly concentrated plasma species in a narrow channel. Moreover, the streamer propagates in a straight direction, from top to the bottom plate, with the lateral voltage added on both sides. The streamer propagation, however, deviates from the center and is directed to the right side when the lateral voltage is applied to the left. Our calculations also indicate that increasing the number or size of the pores enhances both the volume and surface discharges.

Computation of Streamer Propagation Characteristics of Y-type Composite Insulator Under Contaminated Condition

Insulators are a vital part of the power system and play an important role in electrical insulation and mechanical support. Nowadays, long rod composite insulators are used in UHV transmission lines. I type, II type and V type are the commonly used insulators. Y type insulators are the new type of compact polymeric insulator, which is the combination of both I and V type. The performance of the insulators under abnormal conditions is essential for the reliability of the power system. Streamer criteria is used to study the streamer propagation criteria under abnormal condition. In this paper a part of work done is presented in a 765kV Y type insulator and 11kV insulator. For 11kV insulator the design is verified by evaluating the streamer criteria under abnormal condition. For 765kV Y type insulator, electric field distribution along different possible paths were studied.

Pre-Breakdown Streamer Propagation and Positive Lightning Breakdown Characteristics of Palm Oil Impregnated Aged Pressboard

This paper presents the investigation on the breakdown characteristics and pre-breakdown streamer propagation of Palm Oil (PO) impregnated aged pressboard under positive lightning impulse voltages. The experimental work was carried out under a non-uniform field with needle-plane electrodes configuration. The streamer stopping length and breakdown voltage of 2 types of refined, bleached, and deodorized palm oil were examined in the presence of new and aged pressboards. The pressboard was placed in parallel to the needle-plane electrode at a gap distance of 50 mm. The lightning breakdown voltage was applied to the samples based on 1 shot per step rising voltage method under positive polarity as per IEC 60897. The presence of impregnated pressboard in both PO slightly increases the 50% positive lightning breakdown voltages. PO impregnated pressboards have lower 50% positive lightning breakdown voltages than MO. After subjected to ageing, the positive lightning breakdown voltages for PO and MO impregnated pressboards decrease. In the presence of aged pressboard, the streamers in PO generally propagate further than MO at the same voltage level.

Airmass analysis of the processes driving the progression of the Indian summer monsoon

AbstractThe Indian summer monsoon is a vital source of water and a cause of severe impacts for more than a billion people in the Indian subcontinent. The INCOMPASS project investigates the mechanisms driving its onset and progression through an observational field campaign supplemented by high‐resolution numerical simulations for the 2016 season using UK Met Office models. A 4.4 km resolution convection‐permitting limited‐area model simulation (driven at its boundaries by a daily‐initialised global model) is used in this study, and verified against observations, along with short‐lead‐time operational global forecasts. These data show that the monsoon progression towards northwest India in June 2016 is a non‐steady process, modulated by the interaction between moist low‐level southwesterly flow from the Arabian Sea and a northwesterly incursion of descending dry air from western and central Asia. The location and extent of these two flows are closely linked to midlatitude dynamics, through the southward propagation of potential vorticity streamers and the associated formation of cyclonic circulations in the region where the two airmasses interact. Particular focus is devoted to the use of Lagrangian trajectories to characterise the evolution of the airstreams and complement the Eulerian monsoon progression analysis. The trajectories confirm that the interaction of the two airstreams is a primary driver of the general moistening of the troposphere associated with monsoon progression. They also indicate the occurrence of local diabatic processes along the airstreams, such as turbulent mixing and local evaporation from the Arabian Sea, in addition to moisture transport from remote sources. In summary, this combined Eulerian–Lagrangian analysis reveals the non‐steady nature of monsoon progression towards northwest India. This process is driven by the interaction of different airmasses and influenced by a synergy of factors on a variety of scales, such as midlatitude dynamics, transient weather systems and local diabatic processes.

Characterization of a novel volume-surface DBD reactor: discharge characteristics, ozone production and benzene degradation

Surface dielectric barrier discharge (SDBD) is very efficient for the production of reactive species to degrade gaseous pollutants, but the streamer propagation only along the dielectric surface limits the gas treatment capacity. In our experiments, an additional ground electrode pasted on a dielectric was arranged over the surface electrode to form a hybrid volume-surface DBD (V-SDBD) configuration for enlarging the spatial distribution of discharge plasma. The current waveforms, discharge images and power measurements indicate that the V-SDBD configuration produced more steamer channels and induced the development of discharge filaments towards the air gap, leading to more production of ozone and higher benzene degradation efficiency compared to SDBD configuration. At the conditions of 16 kV applied voltage, 2.8 mm air gap spacing and 1 l min−1 air flow rate, the ozone concentration and benzene degradation efficiency of V-SDBD configuration were 3.45 times and 2.15 times that of SDBD configuration, respectively, which may be contributed to the enhanced electric discharge and the enlarged spatial plasma distribution in V-SDBD device compared to SDBD device.

Effect of electric field uniformity on positive streamer and breakdown characteristics of transformer liquids

Streamer development in liquid has different dominant mechanisms under uniform and divergent electric fields, respectively initiation and propagation. This paper presents a study on the influence of electric field uniformity on the pre-breakdown and breakdown characteristics of transformer insulating liquids. Streamers were investigated experimentally in different needle-plane non-uniform field and plane-needle-plane semi-uniform field configurations under standard positive lightning impulses. For the same gap distance, streamers under non-uniform field propagate with a more side-branched structure whereas streamer propagation under semi-uniform field is more constrained to the axial direction. Field enhancement factor was used to indicate the degree of inhomogeneity of the field configuration. Streamers in fields with higher field enhancement factors occupy larger areas. As field enhancement factor reduces, the streamer withstanding probability distribution gets closer to the breakdown probability distribution and hence the breakdown happens at a lower normalized voltage level. Furthermore, a transition phase from a propagation-dominated to an initiation-dominated process of streamer development was evident as the field enhancement factor decreases. The field enhancement factor at which this transition happens was quantitatively derived. It is 54.1 for the investigated mineral oil under positive lightning impulses.

Reillumination of submicrosecond pulsed corona-like discharges in water

Pronounced reilluminations can be observed for discharges that are generated in water by submicrosecond high-voltage pulses. This phenomenon can appear during the decrease of the applied voltage, depending on the pulse characteristics, especially fall times. The respective processes are expected to be crucial for optical investigations of discharge characteristics and also for applications. Accordingly, the development of individual corona-like discharges in water was investigated in a needle-to-plate geometry for their ignition by single rectangular high-voltage pulses with a duration of 100 ns. The pulse amplitudes of about 50 kV and adjusted pulse fall times of 20, 26, and 43 ns were used. Voltages, currents and light emissions were synchronized with subsequent images of individual discharge events. Two distinct stages, a propagation phase and a reillumination phase, were identified. The individual discharges expanded for all investigated fall times with the same velocity of (29 ± 2) km s−1. No significant differences of streamer morphologies and electrical characteristics were observed for the propagation phase. As the voltage began to decrease, light emissions first went through a minimum before increasing again. The following maxima were strongly dependent on fall times. Corresponding images showed that discharge channels were reilluminated within 6 ns. However, not all of the previously observed filaments reignited at once for longer fall times and instead single channels reilluminated subsequently. The development of reillumination can be explained from the external electric field in the electrode gap during the streamer propagation, which determines the head charge distributions at the discharge channel ends. This space charges generate an internal electrical field in the filaments resulting in the reillumination during the falling edge of the applied high-voltage pulse.

Correlation between electric field, current and photon emission in subsequent barrier corona microdischarges

We investigate single microdischarges (MDs) in a sinusoidally operated barrier corona discharge in air. For the voltage amplitude being applied, two subsequent MDs appear in the anodic pin half-cycle. The developments of these subsequent MDs were studied and presented in detail in a previous contribution [Jahanbakhsh et al., Plasma Sources Sci. Technol. 27, 115011 (2018)]. In the present study, the reduced electric field strength (E/n) values of the MDs are determined. In addition, the current pulses are synchronized, with a subnanosecond time resolution, to the spatiotemporally resolved light emission and E/n development of the MDs. It is proposed that the current pulse derivative maximum corresponds to the streamer head arrival on the cathode surface. Therefore, the derivatives of the current pulses are used to synchronize the light emission and current measurements. Based on this synchronization, spatiotemporally resolved light emissions at different positions are compared to the averaged current pulses. Considering the observed correlations, it is proposed that after the arrival of the streamer head on the dielectric (cathode) surface and bulk plasma formation, the ionization processes near the dielectric surface are the dominant source of electron current production. The determination of the E/n is based on the analysis of the time-correlated single photon counting results for the molecular states of the first negative and the second positive systems of nitrogen. The E/n increases during the streamer propagation in the gap, reaching its maximum value at the impact of the streamer on the cathode. The E/n values for the second group MDs are lower only in the vicinity of the dielectric surface, which can be attributed to the positive residual surface charges from the first group MDs.

Characteristics of spatiotemporal variations of primary and secondary streamers under pulsed-voltage in air at atmospheric pressure

A pulsed positive streamer discharge was simulated using a two-dimensional axisymmetric model to investigate the characteristics of primary and secondary streamers in air at atmospheric pressure and ambient temperature. The spatiotemporal variations of the reduced electric field and the electron density during propagation of the primary streamer were clarified, and their relationships with the applied voltage were discussed. The phenomenon of the secondary streamer was introduced according to the previously developed “attachment instability” theory, and the spatiotemporal variations of the net-attachment frequency were presented to validate the theory. The results indicated that variations in the reduced electric field and electron density can be approximately estimated by the theory even in conditions involving a pulsed voltage and non-uniform Laplacian field. Because the primary and secondary streamers have spatiotemporal characteristics related to the chemical reactivity in the streamer discharge, understanding these characteristics is valuable for the development of atmospheric-pressure plasma applications.