Needle-plate Electrode Configuration Research Articles

Numerical study on staggered needle-plate electrode configuration for improved particulate matter collection in electrostatic precipitator

The electrostatic precipitator (ESP) utilizes corona discharge to effectively separate particles from polluted air. The arrangement of electrode is a crucial role in achieving higher efficiency. Needle discharge electrodes can generate concentrated corona discharge at lower applied voltages. In this study, a staggered needle-plate electrode configuration was presented to expand the domain for particle charging, and thereby improve collection efficiency. A three-dimensional model was established to describe the multi-physics phenomenon in the ESP. The ion charge distribution, electric field, and particle collection efficiency were investigated under various conditions. The staggered model showed an average ion charge density that was 20% higher than that of the aligned arrangement. Particles introduced via staggered model acquired higher charge and showed improved collection efficiency across inflow velocities of 0.5 to 1.5 m/s and particle diameters of 0.1 to 50 μm. In the staggered model, particles predominantly escaped near the sidewall of the ESP.

Electric partial discharges in biodegradable oil-based ferrofluids: A study on effects of magnetic field and nanoparticle concentration

This paper presents an experimental study of partial discharge activity in ferrofluids based on biodegradable transformer oil and iron oxide nanoparticles. Three ferrofluid samples with low, medium and high nanoparticle concentrations are employed in the research. The basic ferrofluid characterization is followed by a partial discharge experiment exposing the ferrofluids to a high voltage in a needle-plate electrode configuration. The analysis confirms that the apparent charge and number of discharges decrease with increasing nanoparticle concentration. These findings are interpreted with reference to the well-recognised electro-hydrodynamic streamer model. The charge trapping by nanoparticles hinders the ionization and discharge development. The study also focuses on the partial discharge activity in the ferrofluids under the action of a static magnetic field acting perpendicularly to the electric field. A decreasing trend in the number of discharges due to the magnetic field is revealed. A qualitative explanation is provided based on the field-induced cluster formation and charge mobility reduction. The presented experiment and the discussed findings may be valuable for practical application of the ferrofluid in high voltage equipment with a special need for partial discharge suppression.

Soap bubbles deformation in non-uniform electric field and corona discharge

The paper presents the process of soap bubble development in a strong and highly non-uniform electric field obtained using a needle-plate electrode configuration. Bubbles ca. 43 mm in diameter were investigated in a point-plane electrode system with a 30 mm air gap and potential difference up to 14 kV The work includes a qualitative description of the observed phenomena as well as their quantitative evaluation. It was found that the polarity of the applied voltage has a significant effect on the behavior of the bubble in such electrode configuration. It was observed that changes in bubble height and width for positively charged bubbles are more than two times greater than for negatively-charged ones. The formation of a dimple at the top of the bubble caused by the ionic wind was also observed.

The Effect of Voltage Pulse Shape on the Discharge Characteristics in the Packed Bed Reactor under Air and Nitrogen

In this paper, the packed bed dielectric barrier discharge (DBD) with needle-plate electrode configuration is presented to study the effects of electrical parameters, such as pulse duration and pulse rising and falling time, on discharge characteristics under air and nitrogen. The waveforms of the voltage and the discharge current, discharge evolution images, and the emission spectral of N2 (C3Пu → B3Пg) and N2+ (B2Σu+ → X2Σg+) are collected to investigate the discharge current, as well as the spatial distribution of the discharge modes and the reactive species in the packed bed reactor specifically. It is found that the pulse duration and pulse rising and falling time can regulate the discharge current. Firstly, increasing the pulse duration and the pulse rising and falling time can both increase the discharge duration. Secondly, the peak value of the discharge current has an obvious increasing trend with the pulse duration. Finally, the discharge start time can be delayed by increasing the pulse rising and falling time. A bright discharge channel is distributed at the top of the reactor, while the discharge is diffused at the bottom of the reactor. The generation of N2+ (B2Σu+) tends to depend on the existence of the streamer channel, and N2 (C3Пu) can be generated in the entire discharge area. In addition, the discharge operated in pure nitrogen can reach higher current values, a stronger discharge intensity, and longer existence time for the reactive species than in the air.

Comparative Analysis of Partial Discharge Detection Features Using a UHF Antenna and Conventional HFCT Sensor

This article presents a design of ultra-high frequency (UHF), ultra-wide band (UWB) antenna used for partial discharge (PD) detection on high voltage and medium voltage power system equipment. The proposed UHF antenna has a working frequency band of 1.2GHz-4.5GHz, covering a total bandwidth of 3.3GHz with a return loss less than -10dB in the entire antenna’s operating frequency. The computer simulation technology (CST) Microwave Studio software was used to design, simulate and optimize the proposed antenna. Upon simulation and optimization process, the antenna prototype was fabricated on the FR-4 substrate of 1.6 mm thickness and dielectric permittivity of 4.4. This antenna has a compact size of 100mm x100mm.The radiating patch and the ground plane of this antenna are made of annealed copper whose thickness is 0.035mm. The simulations and measurement results for the proposed antenna are in a good agreement, and the return loss of this antenna is less than -10dB with voltage standing wave ratio, VSWR, < 2 within the frequency range of interest. The proposed antenna performance in PD sensing is compared with a commercial high-frequency current transformer, HFCT. To validate the sensitivity performance of the designed antenna, experimental PD measurements were carried out by using an epoxy slab inserted between two parallel plates electrode model, in order to generate surface discharge on the insulator, and using a needle-plate electrode configuration to generate corona discharge in transformer oil. Based on PD measurement results, it was shown that the designed antenna has a high sensitivity, which make it a suitable candidate for UHF partial discharge monitoring on high voltage and medium voltage power assets.

Boosting Electrically Actuated Manipulation of Water Droplets on Lubricated Surfaces through a Corona Discharge.

Controllable liquid transportation is of great value in various practical applications. Here, we experimentally demonstrate a method of actuating high-speed droplet transport with large manipulation controllability on lubricated surfaces using a corona discharge generated by a simple needle-plate electrode configuration. Linear motion of droplets is realized with a maximum velocity of 30 mm/s. Factors affecting the velocity of these droplets are analyzed systematically, and the mechanism of droplet transport is explained. The lubrication film flow induced by charge deposition is shown to be the dominating factor in the droplet manipulation controllability. The new method presented here opens a new path of high-performance manipulation of liquid droplets by controlling the lubrication liquid film flow with charge deposition.

Effect of Temperature on Creeping Flashover Voltage of Nanofilled Oil-Pressboard Insulation

Creeping flashover (surface discharge) at oil-pressboard interface is considered a serious failure of the insulation system in power transformers. In this paper, creeping flashover voltage at oil-pressboard interface using the concept of nanofluids is experimentally evaluated. The creeping flashover test is carried out using a needle-plate electrode configuration considering 5 mm gap spacing. Three different types of nanofiller (CuO, MgO and ZnO) with different concentration levels (0.05, 0.1, 0.2 g/l) are used for enhancing oil-pressboard creeping flashover voltage. The effect of temperature on creeping flashover voltage is experimentally studied for all nanofiller types at the adopted concentration levels. The considered temperatures are room temperature (30°C), 50 °C, 80 °C and 120 °C. These temperatures are considered to study their effect on creeping flashover voltage taking into consideration a wide range of transformer loading. Average of ten creeping flashover voltages is investigated for all studied conditions. Also, Weibull distribution is used for analyzing the creeping flashover voltages at 10% and 50% probabilities for the studied conditions. Finally, interpretations of the obtained results are presented through a proposed mechanism.

Autonomous Self-Healing of Electrical Degradation in Dielectric Polymers Using In Situ Electroluminescence

Summary Dielectric polymers are ubiquitous as electrical insulation in electrical power systems and electronic devices. Electrical treeing is typically regarded as an irreversible degradation process of dielectric polymers subjected to high electric stresses, which significantly limits their lifespan and endangers the reliability of electronics and electrical power systems. Here, we report self-healing polymers consisting of microcapsules that are capable of completely restoring the dielectric properties as a direct response to electrical tree degradation. We design the microcapsules with a relatively higher dielectric constant than polymer matrix to guide the propagation of electrical trees. The electroluminescence generated in situ during electrical treeing of polymers triggers crosslinking of the healing agents released from the capsules to repair the electrically damaged areas under ambient conditions. Notably, the breakdown strength of the mended region is largely enhanced upon healing, which was initiated at different locations. The integration of autonomous healing capability into dielectric materials opens new avenues to smart polymers for electronics and energy applications.

Study on the discharge mechanism and EM radiation characteristics of Trichel pulse discharge in air

The Trichel pulse stage is an unstable stage of negative corona discharge that can also involve electromagnetic (EM) radiation signals. In this paper, the discharge mechanism and radiation characteristics of the Trichel pulse are studied in the needle-plate electrode configuration. The Trichel pulse current and its EM radiation signals are measured at different applied voltages. The results show that Trichel pulse discharge changes from the random pulse stage to the continuous pulse stage as the applied voltage increases. During these different stages, the normalized shape of the Trichel pulses remains unchanged, while the frequency of the EM radiation generated by the discharge remains unchanged. The discharge mechanism and EM radiation characteristics of the Trichel pulse are theoretically analyzed in the different stages. Both the positive ion sheath and the negative ion cloud play key roles in the formation of the Trichel pulse. The EM radiation signal is generated by the rapidly changing Trichel pulse current, and the Trichel pulse current waveform determines the characteristics of the EM radiation signal.

Spatiotemporal characteristics of nanosecond pulsed discharge in an extremely asymmetric electric field at atmospheric pressure

In this paper, high resolution temporal-spatial diagnostics are employed to research the optical characteristics of nanosecond pulsed dielectric barrier discharge in needle-plate electrode configuration. Temporal-spatial distributions of discharge images, the emission intensities of optical emission spectra, and plasma vibrational and rotational temperatures are investigated. By analyzing the evolution of vibrational and rotational temperatures in space and time dimensions, the energy distribution and energy transfer process in plasma are also discussed. It is found that a diffuse structure with high density plasma concentrated in the region near the needle tip can be presented in nanosecond pulsed discharge, and an obvious energy transfer from electronic energy to vibration energy can be observed in each discharge pulse.

Hydroxyl Radicals and Hydrogen Peroxide Formation at Nonthermal Plasma–Water Interface

This paper investigated hydroxyl radicals and hydrogen peroxide formation under a needle-plate electrode configuration using positive-polarity dc discharges generated in air, nitrogen, and helium. The discharge mode in air and nitrogen was found to change above ultrapure water; initially, a nanosecond pulse discharge was observed, transitioning to a diffuse discharge due to the increasing conductivity of the water. The discharge in helium was a nanosecond pulse discharge and the repetition rate increased with increasing water conductivity. It was found that hydroxyl radicals contribute to 7%, 78%, and 70% of hydrogen peroxide formation when using the ultrapure water in air, nitrogen, and helium, respectively. It is suggested that hydroxyl radicals are formed by water reactions with energetic positive ions and the neutral particles, such as N2+, He+, O, H, and HO2. Part of hydrogen peroxide is directly formed from atoms and radical reactions with water in nitrogen and helium, while oxygen reactions are heavily involved for hydrogen peroxide formation in air. A fluorophotometry method, using terephthalic acid, was used to directly quantify the formation of hydroxyl radicals and compared with the tert-butanol method.

Numerical Study of Pulsed Dielectric Barrier Discharge at Atmospheric Pressure Under the Needle-Plate Electrode Configuration**supported by National Natural Science Foundation of China (No. 11405022)

In this paper, we study the characteristics of atmospheric-pressure pulsed dielectric barrier discharge (DBD) under the needle-plate electrode configuration using a one-dimensional self-consistent fluid model. The results show that, the DBDs driven by positive pulse, negative pulse and bipolar pulse possess different behaviors. Moreover, the two discharges appearing at the rising and the falling phases of per voltage pulse also have different discharge regimes. For the case of the positive pulse, the breakdown field is much lower than that of the negative pulse, and its propagation characteristic is different from the negative pulse DBD. When the DBD is driven by a bipolar pulse voltage, there exists the interaction between the positive and negative pulses, resulting in the decrease of the breakdown field of the negative pulse DBD and causing the change of the discharge behaviors. In addition, the effects of the discharge parameters on the behaviors of pulsed DBD in the needle-plate electrode configuration are also studied.

The mechanism of electrical treeing propagation in polypropylene

Growth property of electrical treeing is an important parameter to evaluate the insulation performance of a polymer. The complex non-uniform state of aggregation structure determines the electrical treeing growth in polypropylene (PP), a typical semi-crystalline polymer. In this paper, the electric treeing resistance property experiments for PP as well as the PP sample with nucleating agents are carried out. Effects of crystal shape, crystallinity, and crystalline structure on the electrical treeing growth characteristics in PP and PP with nucleating agents have been analyzed using polarized light microscopy (PLM) and differential scanning calorimetry (DSC). Thermodynamic and dynamic mechanisms of electrical treeing propagation are represented respectively by the thermodynamically driven action of phase interfacial free energy and the discharge-avalanche theory, demonstrating the essential role of electric field distribution in electrical treeing growth. According to physical properties of crystalline phase and amorphous phase in semi-crystalline materials, a computational model of interior electric field distribution has been established to simulate local electric field distribution in the polymer material under needle-plate electrode configuration, and used to analyze the characteristics of electrical treeing channel growing along the grain boundary in semi-crystalline materials. Inhibition effects of crystalline structure changed due to the nucleating agents on electrical treeing growth along the electric field direction are investigated.

Effect of dielectric material on bipolar nanosecond pulse diffuse dielectric barrier discharge in air at atmospheric pressure

In this paper, dielectric plates made by ceramic, quartz and polytetrafluoroethylene (PTFE) respectively are employed to generate low gas temperature, diffuse dielectric barrier discharge plasma by using a needle-plate electrode configuration in air at atmospheric pressure. Both discharge images and the optical emission spectra are obtained while ceramic, quartz and PTFE are used as dielectric material. Plasma gas temperature is also calculated by comparing the experimental emission spectra with the best fitted spectra of N2 (C3Πu→B3Πg 1–3) and N2 (C3Πu→B3Πg 0–2). The effects of different pulse peak voltages and gas gap distances on the emission intensity of N2 (C3Πu→B3Πg, 0–0, 337.1nm) and the plasma area on dielectric surface are investigated while ceramic, quartz and PTFE are used as dielectric material. It is found that the permittivity of dielectric material plays an important role in the discharge homogeneity, plasma gas temperature, emission spectra intensity of the discharge, etc. Dielectric with higher permittivity i.e., ceramic means brighter discharge luminosity and stronger emission spectra intensity of N2 (C3Πu→B3Πg, 0–0, 337.1nm) among the three dielectric materials. However, more homogeneous, larger plasma area on dielectric surface and lower plasma gas temperature can be obtained under dielectric with lower permittivity i.e., PTFE. The emission spectra intensity and plasma gas temperature of the discharge while the dielectric plate is made by quartz are smaller than that while ceramic is used as dielectric material and bigger than that when PTFE is used as dielectric material.

Experimental research of diffuse bi-directional pulsed dielectric barrier discharge plasma

A bi-directional nanosecond pulsed power supply is employed to generate diffuse dielectric barrier discharge in N2 using needle-plate electrode configuration at atmospheric pressure. Both discharge images and optical emission spectra of diffuse bi-directional nanosecond high-voltage pulsed dielectric barrier discharge are successfully recorded under severe electromagnetic interference. The diffuse performance of the discharge at different electrode gap distances is observed. The effects of pulse peak voltage, pulse repetition rate, electrode gap distance, He addition, and O2 addition on the optical emission spectra are investigated. The main physicochemical processes involved are discussed.

Optical study of diffuse bi-directional nanosecond pulsed dielectric barrier discharge in nitrogen

In this study, a bi-directional high voltage pulse with 20 ns rising time is employed to generate diffuse glow-like dielectric barrier discharge plasma with very low gas temperature in N 2 using needle-plate electrode configuration at atmospheric pressure. Both the diffuse nanosecond pulsed dielectric barrier discharge images and the optical emission spectra of the discharge are recorded successfully under severe electromagnetic interference. The effects of pulse peak voltage, pulse repetition rate, and the concentrations of Ar and O 2 on the emission intensities of NO (A 2Σ → X 2Π), OH (A 2Σ → X 2Π, 0-0), N 2 (C 3Π u → B 3Π g, 0-0, 337.1 nm), and N 2 + (B 2Σ u + → X 2Σ g +, 0-0, 391.4 nm) are investigated. The effects of the concentrations of Ar and O 2 on the discharge diffuse performance are also studied. It is found that the emission intensities of NO (A 2Σ → X 2Π), OH (A 2Σ → X 2Π, 0-0), N 2 (C 3Π u → B 3Π g, 0-0, 337.1 nm), and N 2 + (B 2Σ u + → X 2Σ g +, 0-0, 391.4 nm) rise with increasing pulse peak voltage, pulse repetition rate, and the concentration of Ar, but decrease with increasing the concentration of O 2. The main physicochemical processes involved are also discussed.

Investigation of surface discharges on different polymeric materials under HVAC in atmospheric air

Surface discharge on dielectric materials seriously restricts the performance of many electrical and electronic systems. Based on Pockels electro-optic effect, the surface discharge on polymeric insulating materials has been investigated under HVAC in Atmospheric Air. Different polymer materials such as polyimide (PI), polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF) films are employed. One single cycle of sinusoidal HVAC with peak value of 5 kV and duration time of 50ms is applied on a needle-plate electrode configuration and the applied voltage starts from the positive or negative half-cycle, respectively. During the development process of surface discharge on different materials, the dynamic observation of surface charge distribution is recorded in a cycle by a high speed camera. The experimental results show that there is significant voltage polarity effect observed, and the radius of negative charge distribution is smaller than that of positive charges. The positive charge density on PET and PI is lower than that on PVDF, which are closely related to the enhancement of electric field by permittivity and thickness of polymer films. Moreover, PI, PET and PVDF samples behave different surface charge distribution. Positive streamer channels on PI and PET are gradually growing into a snake-like pattern with voltage applying, and positive streamers on PVDF develop instantaneously and exhibit as a regular spoke-like pattern. The influence factors on different discharge patterns are discussed in the paper.

Production of atmospheric pressure diffuse nanosecond pulsed dielectric barrier discharge using the array needles-plate electrode in air

In this paper, a bidirectional high pulse voltage with 20 ns rising time is employed to generate an atmospheric pressure diffuse dielectric barrier discharge using the array needles-plate electrode configuration. Both double needle and multiple needle electrode configurations nanosecond pulsed dielectric barrier discharges are investigated. It is found that a diffuse discharge plasma with low gas temperature can be obtained, and the plasma volume increases with the increase of the pulse peak voltage, but remains almost constant with the increase of the pulse repetition rate. In addition to showing the potential application on a topographically nonuniform surface treatment of the discharge, the multiple needle-plate electrode configuration with different needle-plate electrode gaps are also employed to generate diffuse discharge plasma.

A diffusive air plasma in bi-directional nanosecond pulsed dielectric barrier discharge

In this study, a diffuse dielectric barrier discharge in air is generated by a bi-directional nanosecond pulsed power supply using a needle–plate electrode configuration at atmospheric pressure. Time-resolved spectra of N2(C 3Πu → B 3Πg, 0–0, 337.1 nm) for both positive and negative pulse discharges are recorded under severe electromagnetic interference. It is found that the lagged time of the photocurrent pulse compared with the voltage pulse in the negative pulse discharge is about 50 times longer than that in the positive pulse discharge at 16 kV pulse peak voltage and becomes shorter with an increase in pulse peak voltage. In addition, the gas temperature of the air plasma is determined to be approximately 395 K by measuring the optical emission spectra of the first negative band of , 0–0, 391.4 nm).

Scaling laws and internal structure for characterizing electrospun poly[(R)-3-hydroxybutyrate] fibers

Using chloroform/dimethylformamide (CF/DMF) co-solvent, electrospinning of poly[(R)-3-hydroxybutyrate] (PHB) solutions was carried out at ambient temperature. The effects of the applied voltage (V), flow-rate (Q), and solution viscoelastic properties on the Taylor cone, electrified jet, and fiber morphology were investigated. In addition, the electric field developed by the needle-plate electrode configuration was calculated using a finite element analysis to reveal the tip-to-collector (H) effect. Among the processing parameters (V, Q and H), it was found that Q played a key role in determining the jet diameter (dj) and electrospun fiber diameter (df), and scaling laws existed between them, i.e., dj–Q0.61 and df–Q0.33. The diameter reduction ratios of Do/dj (Do is the needle diameter) and dj/df were measured as 50–120 and 5–10, respectively; it suggested that major jet stretching took place in the straight electrified jet region, and further chain orientation could be gained by the subsequent process of jet whipping. By changing PHB concentrations from 5 to 15wt%, the solution viscosity (ηo) was increased from 100 to 4900cP, whereas the surface tension and solution conductivity remained unchanged; it provided a good model solution to exclusively reveal the ηo effect on the electrospinning process. Our results showed that the ηo-dependence of dj and df also followed simple scaling laws: dj–ηo0.06, and df–ηo0.39, with a prefactor depending on the processing variables, mainly the flow-rate. Regardless of the PHB concentrations used, the obtained PHB fibers showed a similar crystallinity fraction of ca. 0.63 and possession of major α-crystals together with a small amount of β-crystals with zigzag chain conformation.