Small Discharge Gap Research Articles

Nanosecond Current Waveforms With Small Discharge Gaps Over Polyimide Films

Nanosecond Current Waveforms With Small Discharge Gaps Over Polyimide Films

Nanosecond Current Waveforms with Small Discharge Gaps in Needle-Plane Electrode over Three Kinds of Polymer Film

Nanosecond Current Waveforms with Small Discharge Gaps in Needle-Plane Electrode over Three Kinds of Polymer Film

Failure behavior of dielectric films for peaking capacitor subjected to surface flashover under nanosecond pulses

The flashover failure and damage of polypropylene (PP) and polyester (PET) films under nanosecond current pulses were experimentally investigated. A nanosecond pulse current test platform was established to study the flashover characteristics, performance degradation, and structural damage of dielectric films under repeated nanosecond current pulses. The accumulation and emission of surface charge influenced by field distortion and trap distribution were analyzed to clarify the mechanism by which the flashover voltage increases linearly with gas pressure at low pressure and saturates at high pressure. The significant effects of pulse energy, gas pressure, and discharge gap on film damage behavior were investigated. The damage pattern of PP and PET films includes surface deformation, reduced flash-voltage tolerance, molecular chain breakage, and group shedding. The damage of PP films is manifested as fine furrows, while PET corresponds to mountainous bumps. With the increasing number of discharges, the breakdown voltage of PP films decreased significantly, while the flash tolerance performance of PET films was more stable. Under the conditions of high pulse current amplitude, small discharge gap, and low air pressure, the damage degree of the film intensifies, which is characterized by severe destruction to the molecular structure and a significant decrease in flashover withstand voltage. Polymer films, flashover, nanosecond current pulses; performance degradation; microstructural damage.

Field parameters investigation of CO2 splitting in atmospheric DBD plasma by multi-physics coupling simulation and emission spectroscopy measurements

CO2 dissociation in DBD plasma was thoroughly studied by combining dissociation experiments, multi-physics coupling simulation and in-situ emission spectroscopy measurements. Evolution of spatial–temporal distributions of key field parameters such as discharge mode, electron density (Ne), electron temperature (Te), intermediate concentration and reaction rates were analyzed in depth, to uncover the underlying reaction mechanism. The specific energy input (SEI) had a large impact on CO2 conversion and energy efficiency, and there was a trade-off between plasma power and gas flow rate. The highest CO2 conversion was achieved a maximum of 15.5% at SEI = 177 J·cm−3 in this work. Meanwhile, the spectrum shows that there was a large amount of CO2+, CO, O, and O2 in the plasma. In addition, we proposed and validated a reduced CO2 splitting plasma chemistry set to explore the field parameter and key reactin rates distributions. According to the multiphysics modelling, the discharge gap greatly affected the discharge form of DBD, which will subsequently influence CO2 splitting. In discharge gap > 1.75 mm formation of discharge channels remarkably decreased, and an over small discharge gap (δg < 1.25 mm) would restrain the electric field range, causing shorter motion path of charged particles and less free electrons, both of which hindered the conversion of CO2. A thinner dielectric layer can promote CO2 conversion, due to the reduction in breakdown field strength and increase of high-energy electrons. Electron impact reactions (e + CO2 → CO + O−, e− + CO2 → CO + O + e−), reactions of the excited CO2* (CO2 + CO2* → CO2 + CO + O, CO2*+O → CO + O2) mainly contributed to the CO2 dissociation.

Partial Discharge Current Measurements With Small Discharge Gaps Over Polyimide Film

Partial discharge (PD) characteristics obtained with small gaps are very important to determine the PD resistance of polymers in power equipment. Particularly, PD characteristics of polymers used in small-sized power equipment, such as the power module of an electric vehicle instead of a gasoline engine, have become very important. Among polymer insulating materials, polyimide (PI), which is widely used for circuit mounting, is selected as our target insulating film sample. To understand PD mechanisms in depth, we measure nanosecond PD pulse current waveforms instead of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varphi $ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${q}$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${n}$ </tex-math></inline-formula> characteristics, which have been the mainstream of PD studies. Although numerous studies have used the amount of PD charge integrated from the PD pulse current, few studies have measured the high-speed nanosecond PD pulse current itself, which is easily buried in noise. In this study, we measure PD waveforms under an ac peak voltage of 2000 V and more at 50–1000 Hz to clarify the waveforms to understand low-voltage PD characteristics. The electrode system is a simple needle-plane electrode with small discharge gaps of 0, 75, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$150 ~\mu \text{m}$ </tex-math></inline-formula> . The current direction from the high-voltage electrode to the PI film is determined as a “positive current.” We found that the positive current magnitude is almost twice the negative one, whereas the negative current forms have almost half the duration time of that of the positive ones at almost all applied voltage frequencies. The waveform difference between positive and negative pulse indicates charge origin difference as electrons and ions. This study contributes to the understanding of PD mechanisms.

Partial Discharge Current Measurement with Small Discharge Gap over PI, PET, and PEN Films

Partial Discharge Current Measurement with Small Discharge Gap over PI, PET, and PEN Films

The differential analysis for temperature distribution diagnostics of arc current-carrying region in sheet slanting tungsten electrode inert gas welding with the electrostatic probe

Abstract An electrostatic probe differential analysis method is used to diagnose the arc current-carrying region of the sheet slanting tungsten electrode. Based on the local thermal equilibrium condition and energy transition model with charged particles collision, the temperature distribution in the current-carrying region of different welding process parameters is solved by saturated ion current. The results show that the temperature distribution range in the width direction of sheet slanting tungsten electrode expands, the arc high-temperature region shifts integrally, and the temperature in the thickness direction of sheet slanting tungsten electrode would be symmetrical. The guide effect of the hypotenuse of sheet slanting tungsten electrode for arc current and the inertia drag effect of arc would mainly change the temperature distribution. The variation of the inclination angle of the hypotenuse of sheet slanting tungsten electrode will aggravate the shift of the arc high-temperature region. The larger inclination angle will enhance the guiding effect, and then the inertia drag effect would be in a dominant position with a smaller inclination angle. With the increase of welding current, both the arc stiffness and the guiding effect would be intensified, the latter should make the arc high-temperature zone shift to the position with a small discharge gap.

Investigation of toluene removal by DC discharge with MgO/NiO/Ni cathode under different operating parameters

The degradation of toluene by DC discharge has been evaluated in a multi-wire-plate reactor with MgO/NiO/Ni (MNN) cathode and compared with a normal discharge with Ni cathode. The effects of various operating parameters, including the position distribution of wire electrodes, discharge gap, gas flow rate and toluene initial concentration have been systematically investigated. Morphological characterizations demonstrate that in addition to the normal discharge around the wire electrodes, extra discharge also occurs on the MNN cathode surface which is mainly concentrated in the vertical corresponding region of the wire electrodes and diffuses to both sides. The position distribution of two wires influences the total discharge current. It is because that it affects not only the discharge around the wire electrode, but also the discharge on MNN cathode surface. Beside, a wire–wire spacing of 25 mm in discharge reactor with MNN cathode is optimized due to a relative large discharge current. A small discharge gap between wire electrode and cathode contributes to the improvement of toluene degradation and mineralization and it is optimized of 15.3 mm. The effects of discharge power, gas flow rate and toluene initial concentration and the interactions between these parameters on toluene removal performance by discharge with MNN cathode are investigated using Box–Behnken design (BBD). The analysis of variance (ANOVA) is employed to evaluate the significance of the independent variables and their interactions. The results show that the initial concentration plays the most important role in determining the toluene removal efficiency, while discharge power is the most significant factor affecting the energy efficiency in this discharge process.

Detection of trace heavy metals using atmospheric pressure glow discharge by optical emission spectra

In this Letter, atmospheric pressure glow discharge based on a small discharge gap is excited by sine AC voltage in air on purpose of detecting trace heavy metal elements in solid samples, which makes the detection limits of trace heavy metal elements reach tens μg/kg. The waveforms of voltage and discharge current, discharge images, plasma gas temperature, and optical emission spectra are obtained to discuss the feasibility of atmospheric pressure glow discharge on detection of trace heavy metals. The formation mechanism of optical emission spectra and the strong emission intensity of heavy metal elements show that energetic electrons and excited metal atoms are easily generated by atmospheric pressure glow discharge. The effects of applied voltage and discharge gap on atmospheric pressure glow discharge are discussed to acquire the optimal experimental conditions. And a smaller discharge gap and applied voltage can restrain the transition from glow discharge to arc discharge. Besides, the limits of detections of Cu and Cd are about 0.0241 and 0.0318 μg/g, respectively, by using atmospheric pressure glow discharge with an applied voltage of 3.8 kV, discharge gap of 3.5 mm, and driving frequency of 10 kHz.

Binder-Free 3D Integrated Ni@Ni3Pt Air Electrode for Zn-Air Batteries.

Developing an air electrode with high efficiency and stable performance is essential to improve the energy conversion efficiency and lifetime of zinc–air battery. Herein, Ni3Pt alloy is deposited on 3D nickel foam by a pulsed laser deposition method, working as a stable binder‐free air electrode for rechargeable zinc–air batteries. The polycrystalline Ni3Pt alloy possesses high oxygen‐conversion catalytic activity, which is highly desirable for the charge and discharge process in zinc–air battery. Meanwhile, this sample technique constructs an integrated and stable electrode structure, which not only has a 3D architecture of high conductivity and porosity but also produces a uniform Ni3Pt strongly adhering to the substrate, favoring rapid gas and electrolyte diffusion throughout the whole energy conversion process. Employed as an air electrode in zinc–air batteries, it exhibits a small charge and discharge gap of below 0.62 V at 10 mA cm−2, with long cycle life of 478 cycles under 10 min per cycle. Furthermore, benefitting from the structural advantages, a flexible device exhibits similar electrochemical performance even under the bending state. The high performance resulting from this type of integrated electrode in this work paves the way of a promising technique to fabricate air electrodes for zinc–air batteries.

Machining Performance Characteristics of Inconel 718 Superalloy Due to Hole-Sinking Ultrasonic Assisted Micro-EDM

Inconel 718 superalloy is widely used in aerospace industries for fabrication of the various components for aircraft engine because of its high strength at elevated temperature. It is an extremely difficult-to-machine material due to its work hardening nature and poor thermal conductivity. Creating micro-holes of high precision in this material is beyond the capability of conventional twist drill due to its low thermal conductivity. Micro-electrical discharge machining (micro-EDM) is a well-established process for the machining of any electrically conductive hard and brittle material, but due to very small feature size and narrow discharge gap, removal of debris becomes difficult, causes arcing and short-circuiting. In order to solve this problem, authors indigenously developed an innovative ultrasonic-assisted micro-EDM setup for workpiece vibration. The machining performance characteristics of Inconel 718 superalloy was studied using the developed setup in sinking configuration in terms of material removal rate (MRR), tool wear rate (TWR) and hole taper ([Formula: see text]) considering the effect of ultrasonic power, gap current, pulse on time and pulse off time. It was observed that higher ultrasonic power was more suitable for higher MRR, lower TWR and [Formula: see text]. It was also found from the results that 3 A gap current at 6[Formula: see text][Formula: see text]s pulse on time was appropriate for better MRR and 12[Formula: see text][Formula: see text]s pulse on time was more appropriate for low TWR and [Formula: see text]. The scanning electron microscope (SEM) analysis of created micro-holes was also performed with and without ultrasonic vibration to ensure the quality as well as accuracy.

Virtual Signal-Based Pulse Discrimination in Micro-Electro-Discharge Machining

Owing to the contaminations in the small discharge gap of micro-electro-discharge machining (μEDM), generation of nonuniform nature of discharge pulses is more significant than in macro-EDM. To address the contribution in material removal of workpiece by each of these pulses, a pulse discriminating (PD) system which discriminates them into contributing and noncontributing types is generally used. Developing a PD system in μEDM is a time-consuming process that requires an availability of continuously running machine. Such requirement could be eliminated if virtual signals, similar to the actual once, are made available and provided continuously to the PD system developer. An innovative idea of generating such virtual signals, based on ni multisim, is, therefore, proposed and a robust PD system based on these signals is developed and validated. The strategy for discriminating the pulses in various types is developed through virtual instrumentation in ni labview. The robustness is validated in terms of its applicability over a wide range of parametric settings, acquisition length, and time.

A new approach for Micro-WEDM control based on Real-Time estimation of material removal rate

This paper describes a new approach for controlling a micro wire electrical discharge machining (μ-WEDM) process. In this approach, the relative feedrate of electrodes was controlled based on the real-time estimation of material removal rate and the identification of the workpiece height. An assisted vibration was applied to the workpiece, eliminating the limitation of a small discharge gap. This allows the electrode to be moved continuously, which cannot be performed in conventional WEDM. To verify the efficiency of the system, two workpieces with different shapes were used. For one workpiece, the height was varied linearly, whereas for the other, the height was varied non-linearly. The discharge current, discharge voltage, and number of discharge pulses were measured using current and voltage probes. The signal was uploaded to a computer through data acquisition devices, and a LabVIEW program was developed to estimate the feedrate and control the stages. The experimental results showed that the developed system worked effectively, with high machining stability and efficiency.

Microplasmas ignited and sustained by microwaves

The challenges and benefits of microwave-induced microdischarges are reviewed. Transmission lines, resonators and surface wave launchers may be used for coupling microwave power to very small plasmas. Fortunately, microplasmas are typically much smaller than the wavelength of microwaves, and the electromagnetic problem may be treated electrostatically within the plasma. It is possible to trap electrons within small discharge gaps if the amplitude of electron oscillation is smaller than the plasma size. Typically occurring above 0.3 GHz, this condition results in lower breakdown fields than are required by direct current or radio frequency systems. Trapping of electrons also decreases the electrode potential to only tens of volts and makes the plasma density invariant in time. The steady-state microplasma produces electron densities of up to 1015 cm−3 in argon but the electrons are not in equilibrium with the low gas temperatures (500–1000 K). Microwave discharges are compared with other forms of microplasma and guidelines for device selection are recommended. Scale-up of microplasmas using array concepts are presented followed by some exciting new applications.

Enhancing the ammonia to hydrogen (ATH) energy efficiency of alternating current arc discharge

In order to enhance the ammonia to hydrogen (ATH) energy efficiency, systematic study was carried out with atmospheric pressure alternating current arc discharge reactor (using a pair of stainless steel (SS) tube electrodes). Results showed that, using small-diameter SS tube electrodes with small discharge gaps forced more ammonia molecules to go through the effective plasma volume and obtained high electrodes temperature. Adopting low discharge frequency increased the discharge time, the effective plasma volume and the electrode temperature. These changes can enhance both the gas-phase plasma decomposition and the electrode-surface catalytic decomposition of ammonia. Insulating the reactor significantly increased the electrode temperature in small-diameter reactor, so as to enhance the electrode-surface catalytic decomposition of ammonia. In large-diameter reactors, however, the electrodes temperature increased less rapidly and more ammonia bypass of the effective plasma volume occurred. A 12.5 mol/kW h ATH energy efficiency was reached when ammonia was completely converted under the conditions of electrode diameter 3 mm, electrode gap 4 mm, discharge frequency 5 kHz, reactor diameter 8 mm, NH3 flow rate 150 ml/min and input power 48 W. The ATH energy efficiency was further enhanced under similar conditions when incomplete ammonia conversion was allowed.

Study on Surface Modification of GaN by Atmospheric Microplasma

GaN is widely studied and developed as a material for new application in power electronic devices or as an emitter of various colors of light. GaN is usually formed by nitriding GaAs and grown on the sapphire substrate with a high dislocation density. For this dislocation, microchannel epitaxy or regrowth of GaN is required to reduce dislocations. Recently, plasma treatment has been used for interface treatment, regrowing of GaN crystal, and nitridation process of GaAs. GaN surface was treated by atmospheric-pressure microplasma using Ar and N2 as process gases and powered by ac and pulsed-power supplies. Microplasma is atmospheric-pressure nonthermal plasma and a type of dielectric barrier discharge which has a small discharge gap and requires relatively low discharge voltage of only about 1 kV. Modifications of the surface were observed after the treatment, and they depend on the gas process, treatment time, and power supply. The surface was analyzed before and after the treatment using X-ray photoelectron spectroscopy analysis and atomic force microscopy.

Spatial and Temporal Distribution of Microplasma in Small Discharge Gaps

Emission spectra were measured by the use of an intensified charge coupled device (ICCD) camera and a spectrometer to which was attached a fiber optic. Photographs of microdischarges were taken using a microscope, a digital camera, and an ICCD high-speed camera. A self-made fiber optic with a 100-μm diameter was used in order to have an accurate measurement of a small part of the microplasma discharge. A negative-pulse Marx generator was used to energize the electrodes. Experiments were carried out at atmospheric pressure in Ar and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ar mixture. The discharge voltage was a negative pulse, the rise time was 100 ns, and the width was 1 μs at 1 kHz. The electrodes used had 3-mm hole diameter, and the discharge gap was set at 100 μm. Microplasma was measured in different points along the discharge gap. The spatial and temporal distribution showed characteristics that suggested the microplasma formation and its evolution across the discharge gap.

Surface Modification of GaN Substrate by Atmospheric Pressure Microplasma

In this study, surface modification of GaN substrates by microplasma was investigated. Microplasma, which is an atmospheric pressure nonthermal plasma and a type of dielectric barrier discharge, was generated with a pair of electrodes that were covered with a dielectric layer and that faced each other at a small discharge gap under 100 µm with a spacer. Owing to small discharge gaps (0–100 µm) and to the assumed specific dielectric constant of εr = 104, a high-intensity electric field (107–108 V/m) could be obtained with a relatively low discharge voltage of only about 1 kV at atmospheric pressure. The GaN surface was treated with atmospheric pressure microplasma using Ar and N2 as process gases and powered by AC and pulse power supplies. Modifications of the surfaces were observed after the treatment and they depend on the gas process, treatment time, and power supply. The surface was analyzed before and after the treatment by X-ray photoelectron spectroscopy (XPS) analysis and Field-emission scanning electron microscopy (FE-SEM).

Development and Experimental Study of MWEDM Prototype

A Micro Wire Electrical Discharge Machining (MWEDM) prototype is developed for fabricating micro complex parts. It mainly includes granite basement, micro energy pulse generator, precise servo mechanics, detection and servo control system, constant tension winding systems. Experiments are done on the prototype. Experimental results show that: the peak current and pulse duration have obvious influence on surface roughness and machining time, and they also have an optimum value for the highest cutting speed. The servo reference voltage also influences the surface roughness and machining time. Utilizing micro wire electrode with diameter in 30m, the MWEDM can machine micro slot with minimum size of 38m, which proves that the discharge gap width can be controlled not more than 4um, and so small discharge gap is beneficial for part’s machining accuracy. All kinds of complex micro part (such as micro gear, micro bearing bracket, micro shaped holes, etc.) can also be machined by this prototype.

Basic Study of Bacteria Inactivation at Low Discharge Voltage by Using Microplasmas

Inactivation of microorganisms, such as <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Escherichia coli</i> , by exposure to a microplasma is experimentally investigated. A microplasma is an atmospheric-pressure nonthermal plasma. Microplasmas, which generate high-intensity electric fields, can be formed using relatively low discharge voltages (0.7-1.1 kV) across small discharge gaps (0-100 ?m). The key benefits of the practical application of exposure to a microplasma are as follows: 1) the low discharge voltage and 2) the simple apparatus because a vacuum enclosure is not required. Hence, the apparatus for generating a microplasma could be relatively small and inexpensive and could be integrated into a portable device. The ozone generated by a microplasma at a low power level was measured, although the specific power density of the microplasma was larger than that of large-scale conventional plasmas. The emission spectra of the microplasma discharge in N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was measured: 1) to confirm the UV light emission and 2) to identify the active chemical species generated by the microplasma discharge. The emission spectra was also measured with the presence of water droplets. The UV light from the microplasma discharge showed excited nitrogen molecules and OH radicals. In this paper, two cultures of bacteria, i.e., gram-negative <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Escherichia coli</i> HB101 and gram-positive <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Bacillus subtilis</i> JCB 20036 were the target microorganisms to be inactivated. In the experiments reported here, the number of bacteria decreased after microplasma treatment. The inactivation rate increases as the discharge voltage increases. <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Escherichia coli</i> is completely inactivated when air is used as carrier gas at a plasma discharge voltage of 1.05 kV. Using nitrogen as carrier gas, the highest inactivation rate is 77% at a discharge voltage of 1.15 kV. In addition, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Bacillus subtilis</i> is inactivated with a rate of 97% at 1.07 kV with air as carrier gas. Using nitrogen as carrier gas and a discharge voltage of 1 kV results in an inactivation rate of 70% of bacteria. The inactivation of microorganisms by microplasma may be due to several factors either individually or in combination of the following: 1) the excited molecules and ions; 2) ozone; 3) high electrical fields; and 4) UV light. The effect of active species such as OH radicals may also be important since all the bacteria were carried within a small water droplet in between the electrodes.