Negative Corona Research Articles

Influence of negative corona discharge on the Zeta potential of diesel particles.

Electrical agglomeration as a pretreatment means can reduce the exhaust particle number concentration of diesel engine. The charge of particle is an important factor affecting the coagulation process. Therefore, an experiment was carried out to study the charging characteristic of diesel particles. Zeta potential for diesel particle was used to represent the charged state and the charge of particles could be calculated according to the value of Zeta potential. Influences of various factors on the charge of particle were investigated by changing the charged voltage, internal temperature of charging zone, and the load of engine. Experimental results show that the increase of charged voltage can improve the charge and the absolute value of diesel particles. With increase of charging zone temperature, corona inception voltage declines and the charge of particle increases. The load of engine has a positive effect on the charge of particles which reaches its peak at full load.

Dependence of inter-electrode gap separation on the Positive and Negative Pin-Grid Plasma Corona Discharge

In this work, both positive and negative corona discharge of pin-grid geometrical configuration was studied and the necessary modification of the general law of corona discharge was proposed. The current-voltage measurements were performed at room temperature and at different inter electrode separations. The variation of dimensional constant K and corona inception voltage Vo with pin-grid separations S were subjected into the general law of corona discharge using the least square fitting method in Log-Log scale. The relationship between corona current and different voltage (V-Vo) was investigated to find the acceptable value of exponent n. The least square fitting for all variations of corona parameters was based on the highest R-square value of obtained straight lines for individual measurements. It was found that value of exponent n for both polarities is larger compared to the empirical formula proposed previously for the general law of corona discharge.

Effect of electric diesel particulate trap on particulate emission characteristics of light-duty diesel engine

Based on the principle of corona discharge and electrostatic adsorption, an electric diesel particulate trap (EDPT) with high-voltage negative corona electrode structure was designed. The effect of EDPT on particulate emission characteristics of light-duty diesel engine was investigated based on engine bench test platform. The results show that at the external characteristics operating point of the engine, the trapping efficiency of EDPT for particulate number (PN) is 98.4%, and the trapping efficiency for particulate mass (PM) is 95.0%. With the increasing of exhaust flow, the trapping efficiency of EDPT for PN and PM both decreases slightly. At the load characteristics when engine speed is 1800 r·min−1, the trapping efficiency of PN and PM by EDPT are 98.9% and 95.1%, and the trapping efficiency does not change significantly with the increase of load and temperature. The effects of EDPT and DOC (Diesel oxidation catalyst)+diesel particulate filter (DPF) device on engine backpressure and particulate trapping efficiency are compared. The results show that the effect of using EDPT on engine exhaust backpressure is much lower than DOC+DPF, and the trapping efficiency for PN and PM is lower than that of DOC+DPF. From the perspective of trapping efficiency and device size, EDPT is more suitable for the exhaust gas treatment of construction machinery, agricultural machinery and factory fixed source diesel engines.

Novel particle-based model of negative corona in oxygen for investigation on emission of electromagnetic waves

In recent years, the ultrahigh frequency (UHF) partial discharge (PD) measurement technique has gained more attention as an effective approach towards condition monitoring of power transformers. In this contribution, a novel model for the simulation of negative corona, based on particles' movement, is presented and implemented in COMSOL Multiphysics. Unlike existing models of PD, this model aims at an accurate representation of the phenomenon from an electromagnetic (EM) viewpoint. Following a discussion on the theoretical fundamentals of PD, the model containing the mechanisms and processes that occur during the PD phenomenon and lead to propagation of EM waves is discussed. Subsequently, simulation results are analyzed and previously ambiguous properties of negative corona are interpreted and some efforts are done to validate the theory using experimental measurement.

Miniature, metal 3D-printed, multiplexed electrohydrodynamic gas pumps

We report the design, fabrication, and experimental characterization of the first additively manufactured, miniature, metal multi-needle ionic wind pumps in the literature. The pumps are needle-ring corona diodes composed of a monolithic inkjet binder-printed active electrode, made in stainless steel 316L, with five sharp, conical needles, and a thin plate counter-electrode, made in copper, with electrochemically etched apertures aligned to the needle array; by applying a large bias voltage across the diode, electrohydrodynamically driven airflow is produced. The influence of tip multiplexing and tip sharpening on the ion current, airflow velocity, volumetric flow rate, and kinetic conversion efficiency of the pumps was characterized under different interelectrode separations, counter-electrode aperture diameters, and applied bias voltages, while triggering a negative corona discharge. At the optimal operating bias voltage (7.4 kV), the as-printed five-needle ionic wind pumps eject air at 2.66 m s−1 and at a volumetric flow rate of 316 cm3 s−1 –a twofold larger than the flow rate of an as-printed single-needle device and with 35% higher efficiency (i.e. 0.27%). Using a two-step electropolishing procedure, the needles of the active electrode can be uniformly sharpened down to 83.4 μm average tip diameter, i.e. about one quarter of their as-printed dimension (∼300 μm). Operated under the same conditions, the electropolished five-needle pumps eject air at 3.25 m s−1, i.e. 22% higher speed compared to the as-printed devices, with the same kinetic conversion efficiency. A two-module model was built in COMSOL Multiphysics, consisting of a three-species corona discharge module and a gas dynamics module, to gain insights into the operation of the pumps and to determine trends for increasing device performance. The electrohydrodynamic (EHD) body force calculated using this model has the same periodic behaviour of the Trichel pulse current. A time-dependent EHD body force analysis was performed, and the stabilized forces averaged over a multiple of the Trichel pulse period were used to predict the large-timescale airflow. The EHD force from the corona simulation can be rescaled to calculate the flow at different bias voltages, greatly reducing the simulation time, and making possible to systematically study the relevant parameters and optimize the design of the air pump. The experimental data agree with the simulation results and the reduced-order modelling.

Strengthening of Paper Materials Under the Action of Unipolar Corona Discharge by Increasing the Level of Interaction Between Cellulose Fibers

The mechanical properties of bag paper before and after processing in a field of a unipolar (negative) corona discharge are investigated. It is shown that the modification of bag paper leads to its strengthening: absolute punching resistance, breaking stress, breaking length, tensile stiffness, tearing resistance in the longitudinal (machine) and transverse directions increase. The strengthening of the material is explained by the increased interfiber interaction due to an increase in the potential of the double electric layer on the surface of the fibers under the action of charge carriers injected into the paper volume during processing in a unipolar corona discharge.

Experimental study on pulse characteristics of negative corona discharge in SF6/N2 gas mixtures under DC voltages

Corona discharge, an inevitable phenomenon, may lead to insulation degradation, threatening the safe and reliable operation of gas-insulated power equipment. The pulse stage is a complex but usual discharge process in corona discharge. In this paper, we investigate the pulse characteristics of negative corona discharge in a needle-to-plane electrode configuration in SF6/N2 gas mixtures under DC voltages. With an increase in mean current, a stage transition phenomenon from the Townsend stage through the pulse stage to the breakdown stage is observed. The variation in pulse amplitude and pulse time characteristics at the pulse stage is analyzed. In addition, the effects of gas pressure, gap spacing, and N2 content on onset voltage and pulse characteristic parameters, including pulse time parameters and the pulse repetition rate, at the pulse stage are presented. The results show that the current pulses mainly exhibit an irregular distribution of small amplitude. The pulse time parameters are not affected by gas pressure, gap spacing, or N2 content at pressures higher than 0.1 MPa. The pulse repetition rate decreases with an increase in gas pressure and N2 content but is only weakly affected by gap spacing, ranging from 1 kHz to dozens of kHz.

Polarity effect of corona discharge poling for sol-gel composite-based ultrasonic transducers

Corona discharge was produced in air atmosphere by applying positive and negative high voltage to a needle to investigate the poling effects for two kinds of sol-gel composite materials, Pb(Zr, Ti)O3(PZT)/PZT and Bi4Ti3O12 (BiT)/PZT. Concerning piezoelectric constant d33, only polarity was different. The samples poled by negative corona discharge showed superior temperature durability above certain temperatures even though no significant difference was observed regarding ultrasonic performance characteristics such as center frequency, 6 dB frequency bandwidth. When the pulse voltage supplied by pulser/receiver increased, that difference starting temperature decreased and negative corona poling effect increased. Negative corona discharge poling was effective to improve thermal durability of sol-gel composite ultrasonic transducers when normal pulser/receiver with negative excitation pulse voltage was used for measurements.

МЕТОД АМПЛИТУДНОЙ МОДУЛЯЦИИ ВЫСОКОЧАСТОТНОГО КОРОННОГО РАЗРЯДА

Коронний розряд знайшов своє застосування в різних галузях науки і техніки. Коронний розряд, що протікає при високих частотах, застосовується для поверхневого легування металів і напівпровідників, для очищення газів від пилу в складі електростатичних фільтрів, для діагностики станів конструкцій. У статті наводяться результати дослідження з управління розрядом за допомогою амплітудної модуляції.

Characterization of negative corona plasma discharge reactor using point-to-plane electrode configuration in atmospheric pressure and its application in the treatment of woven natural silk

This research is aimed at obtaining the characteristics of negative corona plasma discharge with the presence and absence of woven natural silk and to figure out morphological alteration of woven natural silk by negative corona plasma discharge and water absorption characteristics of irradiated woven natural silk. The plasma reactor used employed multi point-to-plane electrode configuration using 100 electrodes. The reactor is connected to a high DC power supply with the point electrodes with spacing and the plane electrode varies from 0.6 to 3.0 cm. The silk sample has a dimension of (10 × 10) cm2. Plasma irradiations were performed with a varied duration that ranged from 5 to 30 minutes. Sample testing was performed using SEM and water drop test. SEM testing results also show damages on the fabric surface compared to non-irradiated fabric. Meanwhile, the water drop test results reveal that optimum absorption for woven natural silk is at a distance of 2.4 cm for 30-minute irradiation. These settings resulted in an average absorption time of 10.28 seconds, which is way faster than absorption for non-irradiated fabric, at 48.88 seconds.

Effect of Corona Discharge Plasma and Ozone on the Rate of the Photocatalytic Oxidation of Acetone and Benzene Vapors

The effect of negative corona discharge plasma on the rate of the photocatalytic oxidation (PCO) of acetone and benzene vapors is explored via an in situ IR spectroscopic study of the dynamics of the change in the composition of a gas–vapor system in a 404-L static reactor. The photocatalyst is Hombifine N titanium dioxide, exposed to the light of UV lamps at a wavelength of λ = 365 nm. The rate of the PCO of substrate vapor is compared to those of oxidation in corona discharge plasma, of dark oxidation by ozone (a byproduct of a discharge), of PCO in the presence of ozone, and of PCO upon simultaneous treatment of the medium by corona discharge plasma. It is shown that the rates of oxidation of different substrates, both in plasma alone and in an ozone-containing atmosphere, are much lower than that of PCO. In a corona discharge, however, the rate of PCO increases along with that of the oxidation in an ozone-containing atmosphere. Considerable accumulation of ozone in a gas mixture upon exposure to a discharge is detected only after 80–90% of the oxidized substrate is consumed. The order of the PCO of acetone with respect to ozone is determined. It is shown that plasma treatment substantially accelerates the PCO of benzene by greatly reducing the deactivation of the photocatalyst observed in the PCO of benzene without plasma.

Surface charge dissipation and DC flashover characteristic of DBD plasma treated epoxy resin/AlN nanocomposites

This paper presents the mechanism of the surface charge dissipation and flashover voltage of epoxy resin (EP) with nano aluminum nitride (AlN) composites enhanced by dielectric barrier discharge (DBD) plasma treatment in open air. Surface conductivity, surface potential decay (SPD), flashover voltage, Fourier transform infrared (FT-IR) and surface roughness were measured to evaluate the electrical and physicochemical properties of EP/AlN nanocomposite samples before and after the plasma treatments. It is found that surface conductivity is evidently increased with the increase of the plasma treatment time. Moreover, the SPD of the plasma treated samples after positive and negative corona charging are enhanced. However, the positive charge dissipation is influenced more significantly by the treatment. Both the positive and negative flashover voltage are improved after the plasma treatment, and the amplitude of negative flashover voltage is higher than the positive flashover voltage in each case. Physicochemical measurements show that the content of polar groups is improved after the plasma treatment, and the surface roughness is continuously increased with the increment of the plasma treatment time. The calculated trap distribution demonstrates that the amount of both shallow holes trap and shallow electron trap are increased after the plasma treatment. This investigation attributes the enhanced SPD and improved flashover voltage to the increased surface conductivity, the more amount of shallow traps and the improvement of the sample surface roughness.

Femtosecond laser filament guided negative coronas

We report on the experimental investigation of femtosecond laser filament guided negative coronas. When the coupling between the filament and negative corona was weak, the side fluorescence spectral analysis confirmed the existence of impact ionization although less effect on the filament length was observed. When the coupling was strong so that the negative corona was well connected with the filament, the filament guided coronas at the ends of laser filaments were observed. The newly generated negative coronas were confined around the filament axis, and no streamer-type of coronas guided by the filament was observed under conditions similar to those reported in the work of Wang et al. [Sci. Rep. 5, 18681 (2015)] although both could give rise to an elongation of the filament. A physical picture was proposed to understand the processes of the laser filament guided coronas.

The pulsed mode of negative DC corona in nitrogen at atmosphere pressure: Comparison with Trichel pulses in air

The pulsed mode of negative DC corona discharge in nitrogen at atmosphere pressure is investigated in needle–plate electrodes and compared with Trichel pulses in air. Current/voltage waveforms and time-resolved discharge pictures are recorded experimentally. It is found that the pulsed mode only appears in the presence of a large ballast resistor. The slope of pulsed mode time-averaged voltage–current curve is negative, in contrast to that of Trichel pulses. A transition of slope from negative to positive is tracked by increasing the oxygen fraction. The development of pulse discharge in nitrogen can be divided into three stages: (1) current raising stage, (2) current falling stage, and (3) charging stage. At stage 1, the current raises and forms a peak. The leading edge lasts for dozens of nanoseconds, similar to that of Trichel pulses in air. At stage 2, the voltage decreases monotonically, where a second hump can appear in the current waveform. Through intensified charge coupled device (ICCD) pictures and fluid model simulation, the hump is attributed to the further development of temporal glow discharge. The relative value and occurrence time of this hump are shown to be affected by a parallel capacitor, the space between electrodes, and the applied source voltage. At stage 3, the current remains constant, combined with a rise of gap voltage. Meanwhile, the stray capacitor is charged, which is analyzed by an equivalent circuit model. Through this experiment and simulation, we further clarify the mechanisms of pulses in nitrogen and differences between pulses in nitrogen and Trichel pulses in air.

Corona characteristics of aerial conductors under switching impulse voltages

Corona can be a major factor influencing the attenuation and deformation of switching surge transients. Experimental measurements of corona characteristics are needed for realistic simulations. This paper presents an experimental study of the corona characteristics of solid and stranded conductors under switching impulse voltages. The results include the corona inception voltage, the apparent change in the capacitance of the line conductor, a comparison of charge-voltage (Q-V) curves for positive and negative corona, and the effect of surface roughness. A theoretical corona model represented by an enlarged conductor diameter above inception voltage is proposed and compared with the experimental measurements.

Analysis of current characteristics of corona discharge in high voltage transmission

In order to study the current characteristics of corona discharge in high voltage transmission, the time-domain characteristics and volt ampere characteristics of corona discharge under different high voltage are tested and analyzed. The actual test results show that: in the whole process of corona discharge, with the increase of inter electrode voltage, the frequency of pulse current increases, and the duration of current remains unchanged; negative corona discharge is more likely to occur, and with the increase of voltage, the average current growth rate is higher than positive corona discharge. Under the same interelectrode voltage, the negative corona current is stronger than the positive one. The nonlinearity of equivalent resistance between positive corona discharge electrodes is stronger than that of negative corona discharge.

Effect of Corona Discharge on the Optical Properties of Thin-Film Cu–As2Se3 Structures

The effect that corona discharge has on holographic recording of diffraction gratings in a thin-film Cu−As2Se3 structure deposited on glass by thermal vacuum evaporation is studied. The use of negative corona discharge during holographic recording enhances the holographic sensitivity of the Cu−As2Se3 structure and the diffraction efficiency of inscribed gratings. Irradiation of the Cu−As2Se3 structure with actinic light results in photodarkening in the spectral region in which the structure exhibits a strongly absorption, while the region characterized by a weaker absorption becomes more transparent. The effect of photoinduced transparency is enhanced if samples are treated using positive corona discharge and with negative corona discharge the effect is weakened. The experimental results are explained qualitatively, assuming the diffusion of Cu+ ions into the As2Se3 layer.

The propagation of the Ion-Flow Near the AC Transmission Lines

The series of physical processes contained in the corona layer is the source of space ions formed by the corona discharge of the high-voltage AC line. However, since these physical processes are difficult to calculate accurately and the corona layer thickness is usually small, the corona layer is ignored in the published literature on the corona discharge of the AC line, and the ions are considered to be emitted directly from the conductor surface. In this paper, the distribution area of the charged particles is divided into the corona plasma region and the unipolar drift region. A mathematical physical model of the photoionization and photoemission, which sustain self-sustaining discharge in the positive and negative half-cycle of corona plasma region of the AC conductor in dry air, are established. The influence of the ions generated in the previous cycle is also considered in the numerical simulation process. Finally, a complete microscopic physical model describing the corona discharge of the AC conductor under dry air is established. The validity of the physical model proposed in this paper is demonstrated by comparison with experimental results reported in the literature. Through the numerical simulation of the ion flow field of positive and negative half-cycle and the corona current, the physical process of the corona discharge around the AC line is better understood and analysed. Further positive and negative half-cycle charged particle motion and corona plasma regions were compared and analyzed. This work provides a brand new mathematical physics method for understanding and applying AC corona discharge.

FEM Simulation of Charge Accumulation Behaviours on Polyimide Surface in 10 kV Negative High-Voltage Corona Polarization Process

The study investigates behaviors of charge accumulation on an insulated surface from micro perspective via the numerical method. A coupling bridge between the micro-ion reaction system and the macroscopic multi-physical field was constructed by means of the electronic energy distribution function, which revealed the coupling mechanism in the process of corona charge. Moreover, it revealed the transport and accumulation mechanism of charge on the surface of insulating materials. 2D axisymmetric finite element model was built based on the multi-physical field coupling theory. 10 kV negative voltage was applied using a pin-plate electrode structure and polyimide film was taken as insulated surface to simulate the dynamic charge accumulation behaviors in the corona discharge process. The generation, migration and distribution laws of charged ions and electrons in different stages of corona discharge process were given. Charge distribution laws in different stages of charge process of polyimide were given and discussed. When corona discharge reached quasi-stationary state, the total charge number accumulated on the surface was at 10 -10 Coulomb order of magnitude, and the drift current was at 10 -7 ampere order of magnitude. An experimental platform was set up to test drift current and charge distribution under quasi-stable discharge state. The results show that the simulation results and the experimental data under quasi-stable state are consistent, thus indirectly verifying the correctness of the proposed numerical simulation algorithm and its simulation results.

Effect of Positive and Negative Corona Discharge Field on Vigor of Millet Seeds

To investigate the effects of corona discharge field treatment of different electric field strength with the different polarities on the vigor of millet seeds, the positive and negative corona discharge fields generated with arc-shaped prick electrodes and plate electrodes are different for millet seeds respectively. The treatment voltage was (2 × n kV, n = 1, 2. . .10) and the time treated was 2 min. The results showed that after treatment by the corona discharge field, the germination potential, germination rate, germination index and vigor index of millet seeds increased to different degrees compared with the control. The optimal treatment voltages of the positive and negative corona discharge field were 12 kV. Under the optimal treatment voltage, the germination indexes (germination potential, germination rate, germination index, vigor index) of millet seeds were significantly different from the control (p <; 0.01), and the millet seeds treated by the positive corona discharge field compared with the control group, the germination potential, germination rate, germination index and vigor index increased by 21.2%, 23.0%, 19.9% and 23.2% respectively. The germination indexes of the millet seeds treated by the negative corona discharge field increased by 29.1%, 28.5%, 26.9% and 32.1%. It was also found that under the same treatment voltage, the electrical conductivity of the leachates of the millet seed treated with the negative corona discharge field was lower than that of the positive, which indicated that the negative corona discharge field would repair the cell membrane more effectively. According to various indicators, it can be concluded that the negative corona discharge field treatment was better than the positive.