The current pulses characteristics of the negative corona discharge in SF_(6)/CF_(4)mixtures

This paper presents the results of numerical investigation of the current pulses characteristics in SF_(6)/CF_(4)mixtures for the negative point-plane corona discharge.The pressure and the temperature of gas mixtures are 0.4 MPa and 300 K,respectively.The CF_(4)content varies from20%to 80%.The 2D axisymmetric geometry with point-plane electrodes is investigated,and the three drift-diffusion equations are solved to predict the characteristics of the negative corona discharge.In addition,Poisson’s equation is coupled with the above three continuity equations to calculate the electric field.In order to calculate the electron impact coefficients,including the Townsend ionization and attachment coefficients,as well as the mobilities and diffusion coefficients for electrons,the two-term Boltzmann equation is solved.The characteristics of three ionic species at five stages of the first current pulse in 60%SF_(6)-40%CF_(4)and20%SF_(6)-80%CF_(4)mixtures are selected to discuss the development mechanism of current pulses.Moreover,the reduced electric field strengths at the corresponding time instants are presented to help understand the discharge process.The current waveform and the total number of three species are compared in all the cases to analyze the effects of the CF_(4)content on the discharge.The reduced electric field strength is also helpful in understanding the effects of CF_(4)content.When the CF_(4)content increases to 80%,the discharge is more intensive and the pulse frequency also increases.

Numerical simulation and experimental validation of a direct current air corona discharge under atmospheric pressure

Air corona discharge is one of the critical problems associated with high-voltage equipment. Investigating the corona mechanism plays a key role in enhancing the electrical insulation performance. An improved self-consistent multi-component two-dimensional plasma hybrid model is presented for the simulation of a direct current atmospheric pressure corona discharge in air. The model is based on plasma hydrodynamic and chemical models, and includes 12 species and 26 reactions. In addition, the photoionization effect is introduced into the model. The simulation on a bar-plate electrode configuration with an inter-electrode gap of 5.0 mm is carried out. The discharge voltage- current characteristics and the current density distribution predicted by the hybrid model agree with the experimental measurements. In addition, the dynamics of volume charged species generation, discharge current waveform, current density distribution at an electrode, charge density, electron temperature, and electric field variations are investigated in detail based on the model. The results indicate that the model can contribute valuable insights into the physics of an air plasma discharge.

Temperature field at time of pulse current discharge in metal structure with elliptical embedding crack

Theoretical analysis is made on the temperature field at the time of pulse current discharge in a metal structure with an elliptical embedding crack. In finding the temperature field, analogy between the current flow through an elliptical embedding crack and the fluid flow through a barrier is made based on the similarity principle. Boundary conditions derived from this theory are introduced so that the distribution of current density and the temperature field expressions can be obtained. The study provides a theoretic basis to the applications of stopping spatial crack with electromagnetic heating.

Investigation of cyclohexane catalytic degradation driven by N atoms from N_(2)discharges

The effect of N_(2)discharge products on cyclohexane degradation over a MnO_(2)/γ-Al_(2)O_(3)catalyst has been evaluated by feeding N_(2)discharge products to the catalyst using a specially designed dielectric barrier discharge reactor.At a reaction temperature of 100℃,the cyclohexane conversion increased from 2.46%(without N_(2)discharge products)to 26.3%(with N_(2)discharge products).N-and O-containing by-product(3,4-dehydroproline)was found on the catalyst surface using gas chromatograph-mass spectrometry identification,in which C=N–C and C=N–H bonds were also confirmed from x-ray photoelectron spectroscopy analysis results.Operando analysis results using diffuse reflectance infrared Fourier transform spectroscopy revealed that N atoms can react with surface H_(2)O possibly to NH and OH reactive species that have reactivities to promote CO oxidation to CO_(2).The mechanism of N-atom-driven cyclohexane degradation to CO and CO_(2)is proposed.

Numerical simulation of a direct current glow discharge in atmospheric pressure helium

Characteristics of a direct current （DC） discharge in atmospheric pressure helium are numerically investigated based on a one-dimensional fluid model. The results indicate that the discharge does not reach its steady state till it takes a period of time. Moreover, the required time increases and the current density of the steady state decreases with increasing the gap width. Through analyzing the spatial distributions of the electron density, the ion density and the electric field at different discharge moments, it is found that the DC discharge starts with a Townsend regime, then transits to a glow regime. In addition, the discharge operates in a normal glow mode or an abnormal glow one under different parameters, such as the gap width, the ballast resistors, and the secondary electron emission coefficients, judged by its voltage-current characteristics.

Current self-limitation in a transverse nanosecond discharge with a slotted cathode

A high-voltage transverse pulsed nanosecond discharge with a slotted hollow cathode was found to be a source of high-energy （few kV） ribbon electron beams. Conditions for the formation and extinction of electron beams were experimentally studied in discharges in helium at pressures of 1-100 Torr. It was found that interaction of fast electrons with a non-uniform electric field near the slotted cathode led to limitation of the magnitude of the discharge current. A physical model was developed to describe the discharge current self-limitation that was in satisfactory agreement with the experimental results. Some technical solutions that are expected to increase the upper current limits in transverse nanosecond discharge are discussed.

Circle Points Discharge Tube Current Controller

Circle points discharge tube current controller is a new type device to limit the output of high voltage discharge current. Circle points uniform corona discharge to form air ionization current in the discharge tube. On the outside, even if the discharge electrode is spark discharging or the two discharge electrodes are short circuited, the air ionization current in the tube remains within a stable range, and there is no spark discharge. In this case, when the discharge current only increases slightly, the requirement to limited current is obtained. By installing the controller at a discharge pole with a small power but high voltage supply, we can realize the shift between the continuous spark line discharge and corona discharge. This provides a new simple device for spark discharge research and is a supplement to the Townsend discharge experiment.

A superhigh discharge capacity induced by a synergetic effect between high-surface-area carbons and a carbon paper current collector in a lithium–oxygen battery

This paper invesitages the synergetic effect between high-surface-area carbons, such as Ketjan Black(KB) or Super P(SP) carbon materials, and low-surface-area carbon paper(CP) current collectors and it also examines their influence on the discharge performance of nonaqueous Li–O2cells. Ultra-large specific discharge capacities are found in the KB/CP cathodes, which are much greater than those observed in the individual KB or CP cathodes. Detailed analysis indicates that such unexpectedly large capacities result from the synergetic effect between the two components. During the initial discharges of KB or SP materials, a large number of superoxide radical(O·-2) species in the electrolytes and Li2O2 nuclei at the CP surfaces are formed, which activate the CP current collectors to contribute considerable capacities. These results imply that CP could be a superior material for current collectors in terms of its contribution to the overall discharge capacity.On the other hand, we should be careful to calculate the specific capacities of the oxygen cathodes when using CP as a current collector; i.e., ignoring the contribution from the CP may cause overstated discharge capacities.

Plasma Current Sheath Motion in Coaxial Plasma Discharge

In this paper experiments and theoretical treatments [1] on 1.5 KJ coaxial plasma discharge device have been carried out to show, plasma current sheath, PCS, motion in coaxial plasma discharge by studying: the effect of nitrogen gas pressure in the range from 1 to 2.2 Torr and the axial position of PCS along the coaxial electrodes on the modification factor, actual drive parameter, PCS curvature and shape (thickness). Also the dynamics of PCS along the coaxial electrodes due to the combination effect of induced azimuthal and axial magnetic fields induction has been detected experimentally by using a magnetic probe technique.

Study on influencing factors of ion current density measurement in corona discharge of HVDC transmission lines

The ground level ion current density produced by corona discharge in high voltage direct current(HVDC)transmission lines can reflect the operation status of the lines,but the distorted electric field at the edge of the Wilson plate seriously affects the measurement results of ion current density.In order to measure the ground level ion current density accurately and directly,a new reduced scale wire-plate experimental device in which the Wilson plate is flush with the grounding plate is designed.The influence of protective annulus width and the height of the Wilson plate from the grounding plate on ground level ion current density are studied.In addition,the differences between the micro-current galvanometer method and the sampling resistance method in the measurement of ion current density are compared.Finally,the ground level ion current density distributions of unipolar and bipolar HVDC transmission lines are measured.The results show that the edge effect of the Wilson plate can be neglected when the width of protective annulus is less than 2 mm,and the ion current density is nonlinear with the height of the Wilson plate from the grounding plate.Moreover,the internal resistance of the digital voltmeter seriously affects the measurement results and it is necessary to correct the results.Finally,at the same applied voltage,the ground level ion current density in the negative conductor region is higher than that in the positive conductor region.

Pre-breakdown to stable phase and origin of multiple current pulses in argon dielectric barrier discharge

We report on the results of numerical models of the(i)initial growth and(ii)steady state phases of atmospheric-pressure homogeneous dielectric barrier discharge in argon.We employ our new inhouse code called Py DBD,which solves continuity equations for both particles and energy,shows exceptional stability,is accelerated by adaptive time stepping and is openly available to the scientific community.Modeling argon plasma is numerically challenging due to the lower speeds of more inertial ions compared to more commonly modeled neon and helium,but its common use for plasma jets in medicine makes its modeling compelling.Py DBD is here applied to modeling two setups:(i)the exponential growth from natural electron-ion seeds(onset phase)until saturation is reached and(ii)the multiple current pulses that naturally appear during the steady state phase.We find that the time required for the onset phase,when the plasma density grows from 10^(9)m^(-3)to 10^(17)m^(-3),varies from 80μs at 4.5 k V down to a fewμs above 6.5 k V,for voltage frequency f=80 k Hz and gap width d_(g)=0.9 mm.At the steady state,our model reproduces two previously observed features of the current in dielectric barrier discharge reactors:(1)an oscillatory behavior associated to the capacitative character of the circuit and(2)several(N_(p))current pulses occurring every half sinusoidal cycle.We show that the oscillations are present during the exponential growth,while current pulses appear approaching the steady state.After each micro-discharge,the gas voltage decreases abruptly and charged particles rapidly accumulate at the dielectric boundaries,causing avalanches of charged particles near the reactor boundaries.Finally,we run a parametric study finding that N_(p)increases linearly with voltage amplitude V_(amp),is inversely proportional to dielectric gap d_(g)and decreases when voltage frequency f increases.The code developed for this publication is freely available at the address https://github.com/gabersyd/PyDBD.

Origin of Initial Current Peak in High Power Impulse Magnetron Sputtering and Verification by Non-Sputtering Discharge

A non-sputtering discharge is utilized to verify the effect of replacement of gas ions by metallic ions and consequent decrease in the secondary electron emission coefficient in the discharge current curves in high-power impulse magnetron sputtering （HiPIMS）. In the non-sputtering discharge involving hydrogen, replacement of ions is avoided while the rarefaction still contributes. The initial peak and ensuing decay disappear and all the discharge current curves show a similar feature as the HiPIMS discharge of materials with low sputtering yields such as carbon. The results demonstrate the key effect of ion replacement during sputtering.

Modeling Rogowski Coils for Monitoring Surge Arrester Discharge Currents

Rogowski coils(RCs)are widely used to measure power or high frequency currents based on their design.In this paper,two types of RCs that are circular(traditional)and cylindrical shapes wound using wire covered by varnish are constructed.This construction is carried out to be suitable for monitoring the discharge current of the surge arrester installed in the distribution system.Concerning high frequency RC modeling for both types considering transfer function is introduced.Self-integrating for both types is attained.Therefore,the experimental tests using function generator for both coils are carried out to identify the parameters of the transfer function representing the introduced model.The measured signals for current and induced voltages are denoised for the parameter identification process.The denoised process is achieved using the MATLAB code‘wdenoise’while the parameters are estimated using the system identification toolbox.Verification of the proposed model is achieved using experimental results for the two coils.The sensitivity of the two coils is investigated based on the induced output voltage.The application concerning the two coils for monitoring the discharge current of the surge arrester is done.The results confirm the accuracy of the introduced RC model,as well as the performance of the cylindrical shape,is better than the traditional one.The simulation is carried out using MATLAB and ATPDraw programs.

Research on corona discharge suppression of high-voltage direct-current transmission lines based on dielectric-film-covered conductor

Corona discharge suppression for high-voltage direct-current(HVDC)transmission lines at line terminals such as converter stations is a subject that requires attention.In this paper,a method based on a conductor covered with dielectric film is proposed and implemented through a bench-scale setup.Compared with the bare conductor,the corona discharge suppression effect of the dielectric-film-covered conductor under positive polarity is studied from the composite field strength and ion current density using a line-plate experimental device.The influences of film thickness and film material on the corona discharge suppression effect are investigated.The charge accumulation and dissipation characteristics of different film materials are also studied.The results show that the conductor covered with dielectric film has excellent ability to inhibit corona discharge.The ground-level composite field strength of the conductor covered with dielectric film is lower than its nominal field strength,and its ion current density is at the nA m^(−2) level.The corona threshold voltage can be promoted by increasing the film thickness,but the ability to inhibit corona discharge becomes weak.The larger the surface electric field strength,the more charge accumulated,but the faster the charge dissipation rate.Compared with polyvinyl chloride film,cross-linked polyethylene film has stronger charge accumulation ability and slower charge dissipation rate,which can better restrain the corona discharge of HVDC transmission lines.

An improved analysis method of constant-current charge/discharge curves and its application to nickel hydroxide electrode

The derivative of charge and discharge curves (d t /d E vs E plot) can be used to describe the charge and discharge process more exactly. The d t /d E ? 獷 plots of nickel hydroxide electrode at different charge/discharge rates and intermittent discharge experiment are discussed. Though the d t /d E ? 獷 plot is affected by many factors, it clearly has intrinsic relation with the nature of active material such as conductivity and thermodynamic potential of active material, which changes with the state of charge. The d t /d E—E plot can also be applied to other electrochemical active materials, especially to those having several phases during charge or discharge.

Modeling of Pulsed Direct-Current Glow Discharge

A self-consistent model was adopted to study the time evolution of low-voltage pulsed DC glow discharge. The distributions of electric field, ion density and electron density in nitrogen were investigated in our simulation, and the temporal shape of the discharge current was also obtained. Our results show that the dynamic behaviors of the discharge depends strongly on the applied pulse voltage, and the use of higher pulse voltages results in a significantly increase of discharge current and a decrease of discharge delay time. The current-voltage characteristic cMculated by adjusting secondary electron emission coefficient for different applied pulse voltage under the gas pressure of 1 Torr is found in a reasonable agreement with the experimental results.

A two-dimensional air streamer discharge model based on the improved Helmholtz equation at low temperature and sub-atmospheric pressure

In this paper,an efficient boundary condition is applied to solve the photoionization rate,and a two-dimensional numerical simulation is carried out for the development and propagation of an air streamer at low temperature and sub-atmospheric pressure.The results show that the new boundary condition improves the calculation accuracy,but the influence of photoionization on the streamer discharge process is not obvious.The discharge current in the development of streamer discharge is defined,and the corresponding expression of the positive and negative streamer discharge current is given.The influence of the electric field exceeding the threshold value on the discharge process is preliminarily introduced.In the process of discharge,only the propagation velocity of the streamer is obviously higher than that of normal temperature and pressure,and the trend of the other parameters is basically the same as that described in the previous paper.The above results give us a deeper understanding of the discharge characteristics under low temperature and sub-atmospheric pressure,which has certain significance for the development of aviation and high voltage engineering.

E-beam generation in discharges initiated by voltage pulses with a rise time of 200 ns at an air pressure of 12.5-100 kPa

The effect of air pressure(12.5,25,50,and 100 kPa)on the gen eration of runaway electron beams in a non-uniform electric field when applying voltage pulses(~35 kV)with a rise time of?200 ns has been studied.The results show that the discharge has various stages:streamer,diffuse,and spark.Initially,a wide streamer develops in the gap and a diffuse discharge is formed.A spark is formed u 100 ns after the breakdown.The current pulse of a supershort avalanche electron beam(SAEB)was measured with a collector at various pressures of air.Experiments show that there are two modes of generation of run away electrons.At an air pressure of 25-100 kPa,a single SAEB current pulse with a full width at half-maximum(FWHM)of 120-140 ps is observed.At the air pressure of 12.5 kPa,two current pulses of the electron beam are observed.FWHM of the first and second current pulses are ul40ps and u300 ps,respectively.The current pulse amplitude of the second electron beam is higher than that of the first one,but the electron energy is less.

Pressure Distribution Induced by Ionic Wind in Needle-to-water Corona Discharge

The negative DC corona discharge in air at atmospheric pressure was investigated in a needle-to-water system to obtain the pressure distribution of corona ionic wind.The deformation of water surface was measured and the distribution of wind pressure over the water surface was calculated.The effects of varying discharge parameters,such as applied voltage,gap spacing,tip radius of needle,and the shape of grounded electrode,on the wind pressure were studied.The measured wind pressure ranges from several Pa to several tens of Pa and up to 33 Pa over a small area;the pressure is comparatively large in the center and decreases quickly outwards.In the experiment system,a higher voltage on a 3 mm gap resulted in a stronger pressure of the ionic wind;around the onset voltage,using a needle with tip radius of 50μm obtained a larger wind pressure than using a needle with 100μm tip radius,but the latter one can produce larger pressure at higher voltages.Plus,the shape of the grounded electrode only influences the wind pressure a little.

Electro-hydrodynamic Simulation of Wire-plate Corona Discharge

To simulate the electro-hydrodynamics of wire-plate corona discharge at different voltages accurately,a simulation method,which relates the definite radius and initial velocity of a jet source to the amplitude of discharge voltage,is developed.Firstly,a model of the electro-hydrodynamics is established by the Matlab software using the governing equations discretized with the finite difference method.Secondly,the electric field strength and current density are simulated and the radius and initial velocity of a jet source at different voltages are determined.Finally,the discharge electro-hydrodynamics is simulated using the determined boundary conditions.Compared with using a conventional method,using the proposed method can obtain a wind velocity with smaller errors from the experimental and theoretical wind velocities: the errors between simulated wind velocity and its theoretical counter part at 45 kV and 50 kV decrease from 9% and 6.25% to 1.7% and 1.56%,respectively.Thus,the proposed method is feasible for the existing discharge models.