Discharge Current Measurements Research Articles

Electroaerodynamic thrusters: Influence of a freestream on the current, ionic wind, and force produced by a DC corona discharge

In the past few decades, atmospheric plasma propulsion has sustained a growth of interest. Recent studies have demonstrated the feasibility of light air-breathing plasma-propelled aircraft near ground level. Typically, corona discharge actuators are employed. Yet, the effects of the freestream velocity on the discharge current, ionic wind, and thrust must be characterized. The present study focuses on a wire-to-cylinder and a wire-to-airfoil actuators in a wind tunnel in a co-flow configuration. Discharge current and PIV (particle image velocimetry) measurements were used to determine both the differences between the two collecting electrodes and the aforementioned effects of the freestream velocity. The measured current follows the modeling already reported in the literature with a linear increase of the current with the freestream velocity. Besides, an interaction occurs with the charge density between the electrodes, which strengthens the rise of the current with the velocity as the voltage increases. In the study, the charge density increases linearly with the voltage with a slope of 0.75 mC/m2/kV for both collectors. However, the airfoil collector results in a higher current than the cylinder at the same voltage. The local velocity increases in three main regions thanks to the ionic wind. With both actuators, a higher velocity was captured with actuation on the upper and lower surfaces of the collectors. With the cylinder, the interelectrode region experiences a notable rise in velocity as well. In all cases, the air velocity downstream of the actuators is increased by the actuation. The ionic wind is usually less than 1 m/s (around 0.3–0.5 m/s on average) and its effect on the incoming flow decreases when the velocity increases up to 10 m/s. The force was calculated in control volumes around the actuators. For both actuators, the electroaerodynamic (EAD) force is governed by the current, and at constant current, the same EAD force is obtained with the two collectors. Yet, the force decreases with the drag of the collector, leading to a cancellation of the thrust when the drag exceeds the EAD force. At the maximum current tested in the study, the cylinder collector cancels the thrust at around 3 m/s of freestream against 5 m/s with the airfoil, showing that this type of propulsion is currently only applicable to low-speed aircraft.

Rotational and vibrational temperatures of transient atmospheric glow plasma

Plasma ignition can significantly improve the efficiency and performance of combustion devices through the enhancement of combustibility limits. Investigating plasma development for fundamental experimental flame conditions (i.e. spherical flame experiments) can provide insight into how plasma thermalizes the combustible mixture and, therefore a better understanding of flame development in future experimental studies. This study observed an ignition system designed to produce spherical flames in quiescent gas inside a constant-volume combustion chamber. Rotational and vibrational temperature measurements of dry atmospheric air glow plasma are reported. Measurements were taken for a transient discharge with currents less than 0.5 A. The electrode wire geometry and discharge variation resulted in an ellipsoid-shaped kernel and plasma region with an abnormal glow discharge. The measured temperatures were compared to the conductive thermal kernel boundary observed with Schlieren imaging. Maximum rotational and vibrational temperatures of 3000 K and 10 000 K, respectively, were observed near the anode electrode for a 0.5 A current. The temperature decreased with the axial distance from the anode, while a constant temperature was observed in the radial direction. Lower currents resulted in a smaller temperature, with minimum measured rotational and vibrational temperatures of 1500 K and 5000 K, respectively. The results were compared with available experimental literature and the variation observed was a result of the transient nature, which resulted in hysteresis in temperature vs discharge current measurements.

Pulse length dependence of a reactive high power impulse magnetron (HiPIMS) discharge

The pulse length dependence of a reactive high power impulse magnetron sputtering (HiPIMS) discharge with a tungsten cathode in an argon+oxygen gas mixture gas was investigated. The HiPIMS discharge is operated with a variable pulse length of 20–500 µs. Discharge current measurements, optical emission spectroscopy of neutral Ar, O, and W lines, and energy-resolved ion mass spectrometry are employed. A pronounced dependence of the discharge current on pulse length is noted while the initial discharge voltage is maintained constant. Energy-resolved mass spectrometry shows that the oxygen-to-tungsten (O+/W+) and the tungsten oxide-to-tungsten (WO+/W+) ion ratio decreases with pulse length due to target cleaning. Simulation results employing the SDTrimSP program show the formation of a non-stoichiometric sub-surface compound layer of oxygen which depends on the impinging ion composition and thus on the pulse length.

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.

DESCARGAS EN CONTACTO CON LÍQUIDOS: CARACTERIZACIÓN ELÉCTRICA DEUNA DESCARGA CORONA PULSADA

The large number of works published in recent years on non-thermal discharges in (and in contact with) liquids, shows the growing interest in this particular field of electric discharges due to the large number of technological applications. In particular, one of the fastest growing emerging applications is the treatment of water, both for its purification and for its activation, with a view to carrying out the indirect treatment of food and seeds with non-thermal discharges; without the addition of chemicals. In this work, the experimental characterization of a corona discharge in contact with water operating in a pulsed regime is presented. A flat-wire type geometry was used with the flat electrode immersed in water. The discharge was powered through a pulsed capacitive type source, capable of providing a periodic train ofhigh voltage pulses (∼15 kV) with short duration (∼100 ns), with a repetition frequency of 40 pulses/s. The results of discharge voltage and current measurements are reported and discussed for different operating conditions, and the instantaneous power and energy dissipated in the generated plasma are inferred. Photographs in the visible with long exposure times of the pulsed discharge are also shown

Wide-bandgap fluorides/polyimide composites with enhanced energy storage properties at high temperatures

In advanced electronics and electrical power systems, polymer dielectric capacitors are favored for their high power density and great reliability. However, the low energy density at high temperatures constrains their use in emerging applications. To address this vital issue, herein, a novel calcium fluoride (CaF2) nanoparticle with a wide bandgap (∼12.1 eV) and moderate permittivity (∼10.0) is prepared by a simple direct precipitation method and then introduced into the polyimide (PI) matrix. The incorporation of the CaF2 nanoparticles increases the permittivity and reduces conduction loss simultaneously. Consequently, at 150 ℃, the PI film with 3 vol% CaF2 exhibits enhanced discharged energy density and breakdown field of 2.68 J cm−3 and 455.4 MV m−1, respectively. Besides, the composite shows a higher power density of 0.36 MW cm−3 and a faster discharge speed of 2.09 μs at 150 ℃ than that 2.93 μs of biaxially oriented polypropylene (BOPP) measured at 85 ℃. Notably, CaF2 nanofiller, as a deep trap, captures injected charges and alleviates the local electric distortion, as revealed by finite element simulation and thermally stimulated discharge current (TSDC) measurement. This work proposes a novel fluoride nanofiller to rationalize the energy storage improvement of high-temperature composites with potential wide application.

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

Cylindrical electrodes for neutralization of insulating flowing particles

This paper is aimed at studying charge neutralization of flowing particles using a DC corona discharge. The efficiency of two electrodes configurations, namely cone-grid and coaxial cylinder, was experimentally studied. The influence of electrode placement in the middle or at the end of a lab-scale canalization installation is highlighted. Surface potential distribution and charge measurements showed that both configurations can lead to excellent neutralization rates, of around 99%, depending on electrode voltage and placement. The performances of the cone-grid configuration were found to vary according to the electrode placement. Conversely, the coaxial configuration is more stable and, practically, placement independent. A theoretical calculation of required corona discharge to perfectly neutralize charges is also presented. The obtained formula was experimentally verified showing a good agreement between calculation and measurement. Furthermore, the influence of charged particles on the corona discharge when crossing the coaxial electrode is highlighted through discharge current measurement and electric field calculation using finite element software. The charged particles were found to alter the electric field distribution and discharge current resulting in the electric field increase near the wire and his decrease near the grounded cylinder. Therefore, the charged particles act as a dielectric barrier that can affect the discharge current.

Guidelines for the Characterization of the Internal Impedance of Lithium-Ion Batteries in PHM Algorithms

This article aims to describe the most important aspects to consider when using the concept of internal impedance in algorithms that focus on characterizing the degradation of lithium-ion (Li-ion) batteries. The first part of the article provides a literature review that will help the reader understand the concept of electrochemical impedance spectroscopy (EIS) and how Li-ion batteries can be represented through electrochemical or empirical models, in order to interpret the outcome of typical discharge and/or degradation tests on Li-ion batteries. The second part of the manuscript shows the obtained results of an accelerated degradation experiment performed under controlled conditions on a Li-ion cell. Results show that changes observed on the EIS test can be linked to battery degradation. This knowledge may be of great value when implementing algorithms aimed to predict the End-of-Life (EoL) of the battery in terms of temperature, voltage, and discharge current measurements. The purpose of this article is to introduce the reader to several types of Li-ion battery models, and show how the internal impedance of a Li-ion battery is a dynamic parameter that depends on different factors; and then, illustrate how the EIS can be used to obtain an equivalent circuit model and how the different electronic components vary with the use given to the battery.

Statistical analysis of induced magnetic fields on oil-impregnated insulation pressboards

Electrical insulation materials are highly exposed to electrical network-based electric and magnetic fields in power systems. In electrical fields, electrical insulation materials are prone to breakdown and cause failure. A transformer failure which is related to pressboard insulation may lead to total breakdown and hence system malfunction in a total manner. In this study, a test setup is used to conduct discharge tests for pressboards in different thicknesses where main interest is originated magnetic fields on the pressboards. These tests are fulfilled with spherical and rod electrodes in transformer oil where magnetic field sensors are used to acquire discharge-based magnetic field data. By investigating high-voltage stresses with different levels, possible breakdown voltage of a pressboard is predicted and statistically analyzed. In addition to magnetic field measurements, discharge current measurements are taken; however, contrary to conventional studies, this study assesses magnetic field data which are dependent on the thickness of pressboard insulation. For different voltage levels (13 kV and 22 kV for different stress levels), magnetic field measurements and current waveforms are obtained by using magnetic field sensors and high-speed oscilloscope. Magnetic field time series signals are subjected to wavelet analysis, and wavelet coefficients are obtained. Rather than utilizing time series current signals or time series magnetic field signals, wavelet coefficients of magnetic field signals are taken into consideration as a novel approach. These coefficients are processed by multifractal analysis, and finally, the integrity of the pressboard is determined as in proper mode (no failure) or in breakdown mode.

Ionic wind produced by a DC needle-to-plate corona discharge with a gap of 15 mm

The goal of the present study is to better understand the electrohydrodynamic (EHD) phenomena occurring in 15 mm gap point-to-plate corona discharges supplied by positive and negative DC voltages, and to link them to the discharge regime. For that, discharge current measurements have been conducted and a 20 kHz Particle Image Velocimetry system has been used to characterize the ionic wind produced by the discharges. The main results are as follows: (a) the Townsend’s law can always correctly interpolate the experimental I–V characteristics of a negative corona, even in presence of Trichel pulses, (b) in the case of a positive streamer discharge, the current does not follow the Townsend’s law as it evolves in Vk with k = 4 in the present study, (c) Indeed, the discharge current becomes higher than the Townsend’s law when the glow-to-streamer regime transition occurs, (d) the ionic wind is unsteady, more especially in the case of a positive corona for which it seems that its velocity is pulsed at the same frequency than the streamer one, (e) when the positive high voltage is switched on, a strong streamer occurs at the end of the voltage rising (t = 25 µs for +6 kV), resulting in an over-velocity region upstream the head of the ionic wind jet that progresses in quiescent air toward the plate, (f) the topology of the time-averaged ionic wind is fully different compared to the one observed in a previous study where the gap was equal to 25 mm, (g) in the case of a negative corona, the ionic wind velocity is nearly constant in the electrode gap, (h) in the case of the positive corona, the results are even more surprising since the velocity is minimum at the tip and increases when one approaches the grounded plate, indicating that there is a significant space charge remained by the streamers in the second half of the inter-electrode region, (i) generally speaking, this study highlights that the spatio-temporal characteristics of the EHD force and the resulting ionic wind depend on the distribution of the space charge between both electrodes, the latter being linked to the voltage polarity, the discharge regime and the electrode gap.

Central and External Cathode Operations in a Diverging-Magnetic-Field Electrostatic Thruster

The effects of hollow cathode position on thrust performances of a diverging-magnetic-field electrostatic thruster, which had a diverging magnetic field between a ring anode and a hollow cathode, were investigated. The hollow cathode was located in either a central or an external configuration. Based on the discharge current and direct thrust measurements, electrostatic and magnetic hybrid plasma acceleration was observed in the central cathode operation and even in the external cathode operation especially when magnetic field strength was less than 315 mT. However, the operating points were different: low discharge discharge current in the central cathode operation, and high discharge discharge current in the external cathode operation. This difference comes from electron-Hall parameter; the estimated electron-Hall parameter was about 50 in the central cathode operation, which was much lower than that of 3000 in the external cathode operation. By combining electromagnetic acceleration, the generated thrust can increase even with lower electron-Hall parameter operation. As a result, similar thrust performances were achieved in both cathode positions. Because of the hybrid plasma acceleration method, thrust density reached , which is comparable or even higher than that of the conventional electrostatic thrusters.

Ion source based on a circular anode layer plasma thruster.

A new version of pulsed ion source based on plasma thruster technology has been developed and tested. The ion source design uses a circular anode layer geometry in which the ion beam is extracted radially from the full circumference. The source has been tested for operation in argon, nitrogen, and air at a gas flow rate of up to 20 SCCM with discharge current and voltage measurements in low- and high-current modes. The source, having a simple design and open acceleration gap geometry for observation and photography, is suitable for the treatment of the inner surfaces of pipes and tubes.

Influence of discharge parameters on pulsed discharge of coaxial gun in deflagration mode

Coaxial gun can produce high-speed and high-density plasma jet and has some potential applications in many research areas such as space thruster, space debris impact simulation, nuclear fusion, and material processing. The coaxial gun is usually composed of a pair of coaxial cylindrical and hollow electrodes. The pulsed discharge of coaxial gun has two discharge modes, i.e., deflagration mode and pre-fill mode. Compared with the pre-fill mode, deflagration discharge mode can induce a plasma jet with few impurities, high collimation, and fast speed. In this paper, the effect of gas injection mass and discharge voltage on the discharge characteristic of deflagration mode are studied with electrical and optical diagnosis including the emission spectrum, plasma velocity and discharge current measurements. The experimental results show that when the gas injection mass is relatively low, such as 1.4 mg, many plasma clusters eject from the muzzle. As the gas flowing into the coaxial gun bottom increases, the plasma density increases and the jet velocity decreases. Eventually, when the gas injection mass increases to 2.6 mg, one cluster of plasma is found and ejects from the muzzle of the gun. In the discharge process, as a small quantity of gas flows into the bottom of the coaxial gun through the electromagnetic valve continuously, new current paths will be generated at the bottom of the coaxial gun and move forward. This results in the observation of multiple plasma jet at the exit of the coaxial gun. It is noted that the plasma densities are different for different gas mass flowing into coaxial gun bottom, but the currents have little effect in the first discharge half cycle due to the small plasma inductance in discharge circuit. Meanwhile, the plasma characteristics under different voltages with the fixed gas mass of 2.6 mg flowing into the coaxial gun bottom are experimentally measured. The results show that the plasma density and speed increase with voltage increasing, which is attributed to the stronger discharge current and larger self-induced Lorentz force. More neutral particles can be ionized into plasma with discharge voltage increasing, and the transport speed becomes faster under the enhanced force. In addition, the multiple ionization phenomena are observed again when the discharge voltage increases from 5 kV to 8 kV. This study provides an insight into how to better apply the coaxial gun discharge plasma to practical engineering field. The article further verifies the phenomenon of multiple discharges at the bottom of the coaxial gun by changing the charging capacitance and analyzing the magnetic probe signals.

Breathing modes in HEMP thrusters

HEMP thrusters develop breathing mode oscillations with frequencies in the 100 kHz range during stable operation in test facilities. The mechanism of those oscillations in the HEMP-T DM3a model, developed by Thales Deutschland GmbH, is investigated using a fully kinetic PIC-MCC simulation model. The formation and time evolution of a breathing mode are discussed. The consequences for stable thruster operation are outlined and the oscillation frequency is compared to a 0D predator–prey oscillation frequency estimate. A comparison with an experimental discharge current measurement of a breathing mode is discussed.

Optical Sensing Techniques for Condition Monitoring of Transformer Insulation Material

Non contact optical sensing techniques—probing of surface flashover and probing of laser induced plasma, spectrally and temporally, were used to study the thermal ageing induced degradation of oil impregnated pressboard (OIP) insulation material of transformer. Optical probing of surface flashover discharge, gave parameter values comparable with, flashover discharge current measurements. Optical emission persistence time was increasing with ageing level of the insulation. Optical emission spectroscopy of impulse surface flashover gave atomic emissions from the copper sulphide contaminant, diffused in the OIP material due to ageing. Failed insulation samples showed larger Cu emission intensity. Optical emission intensity during AC, + DC and − DC flashover was used to indicate ageing and to identify initiation and arcing stages of surface flashover. Alternatively, laser induced breakdown spectroscopy (LIBS) indicated neutral Cu emission in the aged OIP material, indicating diffusion of Cu contaminants. Quantitative analysis was performed on OIP samples with surface deposited Cu and thermally aged specimen. A minimum detection limit of 4.5 µg/cm2 was achieved. LIBS plasma persistence time was identified as an alternative tool for understanding ageing level of OIP material of transformer.

Influence of annealing conditions on elastic and dielectric properties of P(VDF‐TrFE) copolymer and its composites

In this article, we report on investigation of wave attenuation and longitudinal velocity at ultrasonic frequency in P(VDF‐TrFE) composites with fillers of conductive carbon nanotubes (CNT). Large thermal hysteresis was observed in temperature dependences of both the ultrasonic velocity and attenuation. Moreover, the temperature dependences of the ultrasonic velocity and attenuation were shown to be sensitive to thermal cycling over the ferroelectric phase transition. In our knowledge, this is the first time when the effect of annealing on the ferroelectric phase in P(VDF‐TrFE) composites is investigated by means of ultrasonic spectroscopy. Obtained results are compared with data of dielectric spectroscopy, differential scanning calorimetry, as well as thermally stimulated discharge current measurements. An analysis of the impact of CNT fillers on the dipolar charge distribution in P(VDF‐TrFE)/CNT composites was performed by means of thermally stimulated discharge current measurements. POLYM. COMPOS., 40:1609–1618, 2019. © 2018 Society of Plastics Engineers

Discharge current measurements on Venera 13 & 14 – Evidence for charged aerosols in the Venus lower atmosphere?

Measurements of discharge currents on the Venera 13 and 14 landers during their descent in the lowest 35 km of the Venus atmosphere are interpreted as driven either by an ambient electric field, or by deposition of charge from aerosols. The latter hypothesis is favored (`triboelectric charging' in aeronautical parlance), and would entail an aerosol opacity and charge density somewhat higher than that observed in Saharan dust transported over long distances on Earth.

Enhanced pseudocapacitance from finely ordered pristine α-MnO2 nanorods at favourably high current density using redox additive

A flexible technique is developed using hydrochloric acid to modify the redox reaction between potassium permanganate and sodium nitrite in order to grow ultrafine α-MnO2 nanorods, hydrothermally. The nanorods grown were 10–40 nm diameters in range. Not any crack, fissure, imperfection or dislocation is observed in the nanorods suggesting it to be finely ordered. Structure, phase and purity of as developed nanorods were determined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Energy-dispersive X-ray spectroscopy. Peseudocapacitance of α-MnO2 nanorods was tested using a three electrode system. Considerably very high pseudocapacitance value of 643.5 F/g at 15 A/g current density was calculated from the galvanostatic discharge current measurement. Also excellent cyclability is observed with high retention of 90.5% after 4000 cycles. Highly uniform and confined morphology of the nanorods helps smooth the electron dynamics between electrode/electrolyte interfaces resulting in superior performance. Most importantly, the use of potassium ferricyanide as redox additive to KOH electrolyte was proved to be quite effective as it provides extra redox couple [Fe(CN)6]3−/[Fe(CN)6]4− which helps in further smoothening of electron transition thereby resulting in considerably superior pseudocapacitive performance.

平行円板電極のマイクロギャップ間の火花放電に対する火花抵抗則の適用性

Measurements of discharge currents due to the sparks between parallel disc electrodes with a micro-gap were conducted at charge voltages of 500 V and 4000 V in order to investigate the applicability of Rompe-Weizel's and Toepler's formulae, which reveals that the measured results agree well with those simulated by the Matlab for both the formulae in view of the corresponding “product of spark constant and spark length”.