Positive Voltage Polarity Research Articles

Evolution from a guided-streamer mode to a continuous-discharge mode in an atmospheric pressure argon plasma jet

Atmospheric pressure plasma jet (APPJ) has attracted much attention due to its versatile applications in various fields, which normally operates in either a guided-streamer mode or a continuous-discharge mode. In this paper, temporal evolution is observed from the guided-streamer mode to the continuous-discharge one in an argon APPJ excited by a sinusoidal voltage. Waveforms of voltage and current indicate that the voltage applied to the electrode is distorted severely from the ideal sine. For the guided-streamer mode, there is only one discharge pulse per half voltage cycle. For the mode transition or the continuous-discharge mode, there is only one discharge composed of a pulse and a hump per half voltage cycle. Fast photography implemented for the mode transition reveals that both the discharges in the positive and the negative voltage polarities evolve from the guided-streamer mode to the continuous-discharge one. In the guided-streamer mode of the mode transition, the discharge behaves as a positive streamer in the positive voltage polarity, while a negative streamer in the negative voltage polarity. In addition, the mode transition only occurs in a range of dissipated power and gap width. Based on optical emission spectroscopy, temporal evolutions of the mode transition are investigated for excited electron temperature, electron density, and field strength. Moreover, their spatial distributions along the argon stream are studied at different time instants. These results are of great importance for the discharge dynamics of APPJ.

Effect of nitrogen/oxygen ratios on surface charge distributions generated by repetitive surface dielectric barrier discharges

Studies on the dielectric surface parameters and dielectric barrier discharges (DBD) characteristics considering the influence of gases in DBD on the surface charge distribution are scarce. Thus, to overcome this research gap, this study measured the potential distributions of AC-driven surface DBD in oxygen (O2), synthetic air and nitrogen (N2) as background gases using the Pockels effect. The results showed that the patterns of the filamentary discharges generated during the positive voltage polarity phase differed depending on the O2 ratio. In addition, the electrostatic repulsion forces between the residual charge and the newly created filament were analysed from the measured potential distribution and the greatest effect was observed in air, rather than in N2 and O2. The potential distribution was transformed into a charge density distribution and compared with the discharge luminescence in air and N2. The results showed that the shape of the filament tip differed between the charge density and discharge luminescence only in the case of air, which was attributed to the effect of attachment reactions on the formation of residual charge. The measurements showed that in a surface discharge, similar to the case in a volume discharge, the photoionisation and ionisation coefficients significantly affected the geometrical properties of the discharges.

Partial discharge characteristics of peek utilized in press-pack IGBT under DC voltage

Modular multilevel converters (MMCs) have been utilized in solid-state transformers (SSTs). With the increasing demand in high-voltage power module in MMC-SST, press-pack IGBTs are very promising. The poly-ether-ether-ketone (PEEK) frame is utilized in the submodules of press-pack IGBT to withstand the high voltage. The electric field simulation in this paper reveals that electric field concentrates on the surface of the PEEK frame. Thus, the surface partial discharge characteristics under direct current (DC) voltage is investigated by the developed test bench. The results show that surface partial discharge model of PEEK sample has polarity effect. Under positive and negative polarity voltage, the average discharge quantity, maximum discharge quantity and discharge repetition rate of the PEEK sample all increase with the voltage amplitude. Moreover, the front time of the surface partial discharge waveform reaches 20 ns, and its frequency spectrum is concentrated in range of 10–20 MHz.

Propagation of a pulsed nanosecond discharge on a water surface in non-symmetrical configuration, and comparison with the symmetrical configuration

Non-thermal plasmas produced by pulsed nanosecond discharges at atmospheric pressure are of great interest for fundamental as well as technological and environmental applications due to their high reactivity. When generated in air in contact with water, these discharges induce many physical and chemical phenomena at the interface, including pattern formation. Although the patterns generated in symmetrical configuration have been extensively studied, those produced by asymmetrical discharges are not well characterized. In this study, we report the propagation dynamics of a nanosecond discharge produced in air in contact with water using electrodes mounted in parallel direction relative to the water surface (i.e. asymmetric configuration). The influence of the high voltage polarity and water electrical conductivity on the discharge pattern is investigated using fast imaging and electrical diagnostics. The obtained results demonstrate that under positive voltage polarity, plasma dots are produced along the ionization front. These dots have been previously observed in symmetrical configuration; however, their propagation velocity is greater in asymmetrical configuration, particularly in front of the anode. Under negative polarity conditions, a homogeneous emission pattern is observed, except in the area in front of the cathode, where dots are detected in the ionization front. Based on this data, the E-field threshold beyond which plasma dots are formed is estimated to be ∼5 × 108 V m−1. Overall, the results reported herein provide a fundamental understanding of plasma-water interactions.

Corona discharge ozonizers with vacuum coatings and their use for processing agricultural products

At present the majority of ozonizers in the world are manufactured on the basis of a barrier discharge. But the special ceramic electrodes used for such ozonizers are highly sensitive to humidity and pollution of the air supplied to the device. Typically, these devices use cartridges to filter and dehumidify the air. In this research, corona discharge ozone generators were used due to sufficient energy efficiency and ease of implementation of this method of ozone synthesis from oxygen-containing gases. The results showed that that coatings with a thickness of up to 3-5 μm made it possible to create a layer on the electrode surface that protects against oxidation or has a conductive oxide that maintains the operability of the point electrode. Furthermore, In the system of electrodes of the point-plane type, a voltage of positive polarity was applied to the point electrode. The initial voltage applied to the discharge gap was 14–15 kV. As the surface properties of the samples changed, the voltage had to be reduced to avoid spark breakdown.

PLLA scaffolds with controlled surface potential and piezoelectricity for enhancing cell adhesion in tissue engineering

The effect of the surface potential of biomaterials on cell attachment and development in regenerative medicine is still an unexplored area driving many regeneration processes, especially in piezoelectric bone tissue. Within this study, we electrospun poly(l-lactide) scaffolds constructed of fibers with either higher (−600 mV) or lower (−300 mV) surface potential, which is controlled by applied voltage polarity during their production. Interestingly, this way, the piezoelectric performance of PLLA fibers can be enhanced. The direct measurement of the PLLA fiber surface potential using Kelvin probe force microscopy (KPFM) showed a good correlation with the zeta potential analysis. The piezoelectricity of PLLA fibers was verified with piezoresponse force microscopy (PFM), indicating that it can be enhanced by applying the positive voltage polarity to the nozzle during electrospinning. Importantly, the cell adhesion assay showed a significant effect of the higher surface potential of PLLA fibers on osteoblasts behavior and creating a favorable bioelectric microenvironment. We observed enhanced initial adhesion of cells in the first 5 h with no additional effect of surface potential on proliferation, morphology, or collagen production. It was demonstrated that electrospun PLLA fibers with tunable surface potential and piezoelectricity are excellent for constructing bone tissue engineering scaffolds.

Conducting ferroelectric domain walls emulating aspects of neurological behavior

The electrical conductivity of lithium niobate thin film capacitor structures depends on the density of conducting 180° domain walls, which traverse the interelectrode gap, and on their inclination angle with respect to the polarization axis. Both microstructural characteristics can be altered by applying electric fields, but changes are time-dependent and relax, upon field removal, into a diverse range of remanent states. As a result, the measured conductance is a complex history-dependent function of electric field and time. Here, we show that complexity in the kinetics of microstructural change, in this ferroelectric system, can generate transport behavior that is strongly reminiscent of that seen in key neurological building blocks, such as synapses. Successive voltage pulses, of positive and negative polarity, progressively enhance or suppress domain wall related conductance (analogous to synaptic potentiation and depression), in a way that depends on both the pulse voltage magnitude and frequency. Synaptic spike-rate-dependent plasticity and even Ebbinghaus forgetting behavior, characteristic of learning and memory in the brain, can be emulated as a result. Conductance can also be changed according to the time difference between designed identical voltage pulse waveforms, applied to top and bottom contact electrodes, in a way that can mimic both Hebbian and anti-Hebbian spike-timing-dependent plasticity in synapses. While such features have been seen in, and developed for, other kinds of memristors, few have previously been realized through the manipulation of conducting ferroelectric domain walls.

Electrical Breakdown of Oil-Impregnated Pressboard under AC and DC Voltages Ramp

In this work, we present an experimental study on electrical breakdown, also called dielectric failure on a material widely used as insulation in oil transformers and other equipment. This material is pressboard paper impregnated with insulating oil. The breakdown tests are carried out under three types of voltage and for several voltage rise speeds. Dielectric breakdown is a random phenomenon, many tests are carried out on a large number of samples and the results obtained have been subjected to statistical processing. The material is cut into square plates of 7.5 cm in length from a set of plates 2 m² in length and 500 µm in thickness. Prior to the tests, the samples were conditioned in a desiccator with silicone gel for at least 24 hours in order to eliminate any presence of moisture. Then they were impregnated with Borak22 insulating oil for at least one week. The tests consist of placing the sample concerned between two cylindrical bronze electrodes and applying a voltage ramp at constant speed until breakdown. After failure, the value of the breakdown voltage is taken. These tests are carried out in the laboratory at room temperature. However, we have tried to reproduce the same conditions for all the tests. These various tests relate to the effect of the form and the rate of rise of the applied voltage on the dielectric strength of the pressboard paper impregnated with Borak22 insulating oil. Two measuring devices were used, and the tests were carried out under three voltage forms: sinusoidal alternating current, continuous positive polarity, and continuous negative polarity, and at eight different voltage ramp speeds: 0,69; 1,07; 1,4; 1,89; 2,38; 2,94; 3,28 and 4,17 kV/s. For each measurement point, 35 samples of pressboard paper are used and tested. A total of 840 results were obtained and processed using the two-parameter Weibull statistical model. In order to validate this model, these results are subjected to a Kolmogorov-Smirnov adequacy test and are framed by 95% confidence bands. The maximum likelihood method is used for the estimation of the Weibull parameters and the smoothing of the experimental points. The results of the statistical tests on the breakdown voltage measurement points obtained confirm the use of the two-parameter Weibull model. The evolution of the nominal breakdown voltage as a function of the voltage ramp of the three forms of applied voltage gives three properties of the same form, which is akin to the letter 'S'. The breakdown voltage first increases linearly for low speeds, then increases and takes an exponential form for medium speeds, then tends towards a certain saturation for high speeds. The breakdown voltage under the DC voltage ramp is higher than the voltage obtained for the AC voltage ramp and are higher under negative polarity voltage than those under positive polarity voltage.

White electroluminescence from cross relaxation-free CaSiO3:Tb3+ film on silicon wafer and its concentration dependent white-color tunability

A full-color white light source is continuously required for general lighting applications. Herein, the white electroluminescence (EL) from Tb3+-singly doped CaSiO3 (CSO) thin film on a silicon substrate has been reported for the first time. The EL device has a metal-oxide-semiconductor (MOS) structure which consists of two CSO and SiOx oxide layers on silicon wafer. Above the threshold voltage in AC power, it shows a full-color white EL spectrum with two dominant emission groups of ultraviolet-blue and green-red peaks from the f-f intra-transition of Tb3+ ions without the cross-relaxation effect in the four blue peaks which suffers from their severe cross-relaxation quenching in its photoluminescence spectrum. It is attributed to the strong electric field splitting (Stark effect) which prevents the resonance energy transfer due to energy perturbation. With increasing Tb3+ concentrations, the blue bands get more dominant along with increasing the threshold voltage. Furthermore, we demonstrate the EL-voltage transient behavior with a large hysteresis in a positive voltage polarity.

The Influence of Diethylaniline and Toluene on the Streamer Propagation in Cyclohexane between a Point-Plane Gap under Positive Impulse Voltage Stress

Liquid insulation is used in high voltage equipment such as power transformers as both dielectric medium and coolant. Breakdown in liquid insulation tends to be governed either by streamer initiation under more uniform fields, or by streamer propagation under more non-uniform fields. A model streamer propagation study, which screens the effectiveness of additives based on cyclohexane and mixtures with diethylaniline (DEA) and toluene, is presented in this paper. The effect of additives, at different concentrations, on streamer propagation velocity in cyclohexane under an applied lightning impulse voltage of positive polarity is studied. Cyclohexane (ionisation potential 9.88 eV) was chosen because, being a hydrocarbon, it shares similarities with the constituents of common insulating liquids. Previous studies have also shown how, in general, the addition of additives of lower ionization potential than the bulk liquid can slow down streamer propagation in insulating liquids. A point-plane electrode configuration of 70 mm gap with a 5 μm tip radius is used and subjected to an applied positive polarity impulse of 1.2/50 μs. A high velocity imaging system is also used to capture streamer images to validate a Time-To-Breakdown (TTB) measurement approach used in inferring approximate streamer velocity. The DEA (ionisation potential 6.98 eV) was found to be an effective additive to slow down positive polarity streamers in cyclohexane in the applied voltage range (≈220–280 kV peak) in concentrations above approximately 0.33% (by volume). Toluene (ionisation potential 8.82 eV) was found not to significantly slow down streamers in cyclohexane, even at 10% concentration, for the same voltage range. This is postulated to be due to the fact that toluene does not have a low enough ionisation potential (with respect to that of the cyclohexane) to change the streamer branching characteristics sufficiently during propagation.

Interleaved Boost Integrated Flyback Converter for Power Factor Correction in Brushless DC Motor Drive

The scope of this research is to manage the speed of Permanent Magnet Brushless DC Motor Drive (PMBLDCMD) for various less capacity applications. In the circuit, a 1ϕ AC power is given to Diode Rectifier and the converted DC supply is given to condenser, which leads to abnormal pulsating current. Because of this pulsating current, the power quality disturbances arise at the supply point. Hence, the PMBLDCMD requires Power Factor Correction (PFC) converter for many household and profitable applications. The rotors of PMBLDCMD are driven by 3ϕ voltage source inverter (VSI), which performs electronic commutation. The range of PFC converter for feeding PMBLDCMD has high emphasis on the power quality (PQ) norms, cost and performance of controllers. The proposed converter requires very less components, which imposes less stress, low ripple and less power loss with positive voltage polarity. The chopper is used to correct the power factor. Various chopper layouts like buck boost Converters and boost converters with single switch are used. The mostly used regulated structures for PFC converters govern the current with continuous conduction technique and to govern the potential differential tracker using discontinuous conduction method (DCM). The processes like examining, modelling and governing of PFC converters are applied for upgrading the quality of power in AC supply.

Bridgeless Isolated Positive Output Luo Converter Based High Power Factor Single Stage Charging Solution for Light Electric Vehicles

In this article, a high-power factor ac–dc conversion system based on bridgeless isolated positive output Luo converter is demonstrated for light electric vehicles charging. Unlike conventional bridgeless Luo converters, the presented topology ensures positive voltage polarity at its output and incorporates a minimum component count over the universal supply voltage range of 85 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RMS</sub> to 265 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RMS</sub> . Meanwhile, the volume of magnetic components and the charger's cost are reduced by considering a discontinuous inductor current mode (DICM) design. To accomplish desired charging profile of the battery, a simple control incorporating few sensing devices and single gate drive circuitry, is utilized. It is noteworthy that, the single stage bridgeless structure of the presented topology with DICM design considerably reduces conduction and switching losses of the charger. Finally, the presented topology is designed and modeled through MATLAB environment, and its efficacy is tested through a prototype in the laboratory environment. The critical test results at various operating conditions are demonstrated to verify design and control objectives of the charger. A brief comparative analysis with existing solutions, is presented to justify the effectiveness of the presented solution.

Impulsive Breakdown of Mineral Oil and Natural and Synthetic Ester Liquids When Containing Varying Levels of Moisture

This article reports and discusses the results of impulse breakdown study of different insulating liquids under highly divergent electric field conditions. Samples of a natural ester (Envirotemp FR3), a synthetic ester (MIDEL 7131), and a naphthenic mineral oil (Shell Diala S4 ZX) at different levels of relative humidity were exposed to HV impulses with a nominal 7- $\mu \text{s}$ rise time and 150-kV peak voltage of both positive and negative polarity. A strong dependence of the breakdown voltage and time to breakdown of the investigated dielectric liquids was observed with respect to the polarity of the applied HV impulses. It was shown that the FR3 natural ester liquid has a higher dielectric strength when exposed to positive impulse than when under negative impulse stress. The opposite breakdown behavior was observed for the synthetic ester MIDEL 7131 and the naphthenic oil Shell Diala S4 ZX which exhibited lower breakdown voltage under positive energization as compared with the negative energization. The breakdown voltage and prebreakdown time obtained in the present tests of the naphthenic oil, Shell Diala S4 ZX, lie between that of the ester liquids irrespective of impulse polarity. It has been established that no statistically significant variations exist in the breakdown parameters (breakdown voltage and time to breakdown) of the studied dielectric liquids as their relative humidity is increased under either impulse polarity. The obtained results will help in coordination of practical applications of low environmental impact dielectric fluids in power and pulsed power systems and components.

Photo electric properties during streamer-to-leader transition in a long positive sphere–plane gap

In this work, a combined photoelectric detecting system is established using devices such as a photomultiplier, an electric field sensor based on optoelectronic integration, and a high-speed camera. The system is used to measure the instantaneous optical power, spatial electric field strength, and optical image during discharge of a 3-m-long sphere–plane gap under standard switching surge voltage of positive polarity. The test results show that the initial streamer of the 3-m-long sphere–plane gap can be divided into strong and weak ionization according to the rate of rise of optical power and electric field strength. Within the dark discharge period in the sphere–plane air gap, the intensity of the spatial electric field slightly jumps when the streamer-to-leader transition is completed, with an increase of about 162.59 kV/m. It is proposed to take the time when the intensity of the spatial electric field jumps in the dark discharge period as the criterion for the streamer-to-leader transition. The measured duration ta of the streamer-to-leader transition is calculated according to instantaneous optical power and spatial electric field strength. Based on the thermodynamic equilibrium equation, a Gallimberti simulation model for this streamer-to-leader transition is established. The duration ts for completing the streamer-to-leader transition is obtained according to the quantity Q of injected electric charges. By comparing the measured duration ta with the calculated duration ts of the streamer-to-leader transition, the rationality of the criterion is verified. The research results provide a basis for establishing an improved model for the inception of a leader in a long air gap.

Magnonic crystal-semiconductor heterostructure: Double electric and magnetic fields control of spin waves properties

The main features of the spin wave band structure formation and manipulation in the magnonic crystal – semiconductor layered heterostructure have been studied. We demonstrate possibility of double electric and magnetic control of band gap characteristics within the spectra of propagating spin waves. It is shown that in the magnonic crystal- semiconductor heterostructure, when a positive polarity voltage is applied to the semiconductor layer, the band gap in the spin-wave spectrum shifts to the low-frequency region, while for the negative polarity the band position is practically not changed. We show also that as the magnitude of the applied magnetic field is increased the shift of the band gap is decreased. Our results show the possibility of integration of magnonics and semiconductor electronics on the base of proposed structure.

How pulse polarity and photoionization control streamer discharge development in long air gaps

A 2D approach is used to simulate the properties of positive and negative streamers emerging from a high-voltage electrode in a long (14 cm) air gap for standard pressure and temperature. The applied voltage varies from 100 to 500 kV. To reveal the influence of photoionization, the calculations are made for various rates of seed electron generation in front of the streamer head. The difference between the properties of positive and negative streamers is associated with the different directions of the electron drift ahead of the streamer head. As a result, the peak electric field at the streamer head and the streamer velocity are higher for positive voltage polarity. The average electric field in the negative streamer channel is approximately twice that in the positive streamer channel, in agreement with available measurements in long air gaps. It is shown that photoionization in front of the streamer head is important not only for the development of strong positive discharges, but for the development of strong negative discharges as well. An increase in the photoionization rate increases the propagation velocity of the positive streamer and retards the propagation of the negative streamer.

Runaway electrons in diffuse gas discharges

The paper provides a review of research data showing the role of runaway electrons in gas breakdowns and diffuse discharges in an inhomogeneous electric field at a pressure of 0.01–1.2 MPa. From the data presented the reader can grasp the idea of how such discharges develop at negative and at positive voltage polarity, what setups and conditions are best suited to detect runaway electron beams, and what factors influence their amplitude, duration, and energy. Also analyzed are the streamer mechanisms of diffuse discharges and the generation of runaway electrons in high-pressure gases in an inhomogeneous electric field. The review is supplemented with respective diagrams and with images captured at high resolution to trace the plasma dynamics of nanosecond gas discharges from early prebreakdown stages till their final diffuse appearance.

Relaxation characteristics of ion jet formed across the short air gap in the cone–sphere electrode under positive polarity DC voltage

The research into the development of discharge under positive polarity voltage across the short air gap is of great significance to improve insulation of electrical equipment. By establishing a photoelectric joint detection system, this study observed phenomena in short air gaps before, and the period of breakdown. By utilising a photomultiplier tube and a Rogowski coil, the optical and current signals were obtained. Moreover, through z-type Schlieren system and high-speed digital camera, relaxation images of ion jet formed across cone–sphere electrodes were obtained. Through comparison and analysis, the discharge of short air gap was divided into three stages: initial corona, strong corona and streamer breakdown. On the basis of this, the relationship between optical and current signals was compared by assessing characteristics of the ion jet in each stage. Also, the relaxation characteristics of an ion jet were analysed. The results showed that ion jets appeared in the initial corona stage, while relaxation channel of the ion jet was formed and the channel fluctuated in the strong corona stage. In the streamer breakdown stage, the process of expansion, constant fluctuation and breakdown appeared; the amplitudes of corona current signals and optical signals in these three stages constantly increased.

Ionization wave propagation in an atmospheric pressure plasma multi-jet

The atmospheric pressure multi-plasma jet produces an array of individual plasma jets which originate from the branching of a single ionization wave (IW). The use of arrays of such plasma jets could enable treatment of larger surface areas than is possible with a single plasma jet. In this paper, we discuss results from a combined experimental and two-dimensional modeling investigation of the behavior of IWs in an atmospheric pressure plasma multi-jet device. In this multi-jet, a rare gas is flowed through a tube having a line of holes, producing gas jets into the ambient from each of the holes. A primary ionization wave (PIW) propagates through the tube which launches a series of secondary ionization waves (SIWs) propagating out each hole through the plumes of the individual gas jets. The propagation of the SIWs is more intense using a positive polarity voltage pulse due to the higher electric field at the ionization front. The diameter of the holes determines the delay of the SIW after passage of the PIW past the hole, with smaller holes resulting in larger delays. The larger delay results from a smaller view angle for photoionization outside the tube from photons originating in the PIW. Higher helium flow rates result in a greater tendency for SIW propagation because the air concentrations in the individual gas jets outside the tube are lower and so the electron temperature is higher. The interaction between SIWs is primarily electrostatic, and is a sensitive function of geometric parameters including proximity of ground planes and the spacing between the holes through which these SIWs emerge.

Electrical discharge drilling of granite with positive and negative polarity of voltage pulses

Electrical discharge drilling is a promising method that allows for the reduction of the costs of well drilling in hard rocks including the energy costs. This paper describes experimental drilling of a well in granite. The well has the diameter of 340 mm and the depth of 15 m, and transformer oil was used as the drilling fluid. In order to study the characteristics of the drilling process and drill string stability we used two drill bits with the interelectrode gaps of 40 mm and 70 mm and applied pulse voltage of positive and negative polarity to the drill bit electrodes. The results are as follows. Increasing the inter-electrode gap has allowed us to reduce the energy costs while increasing the drilling rate, but it has slightly reduced the lifetime of the drill string insulation. The polarity of the voltage pulse has no effect on the penetration rate. At the same time, in the case of negative pulse polarity, the electrical stability of the drill string insulation is higher than that for the positive one. For the 70 mm inter-electrode drill gap, the specific energy consumption and energy input per unit length of the inter-electrode gap are lower while the performance of a single pulse is greater. In this paper we are also discussing the peculiarities and prospects of industrial implementation of electrical discharge drilling. In addition to increasing the overall reliability of the drill string and pulse power source, it is necessary to find suitable insulation material with high flashover resistance in water-based mud.