The characteristics of negative corona discharge and radio interference at different altitudes based on coaxial wire-cylinder gap

The corona discharge from transmission lines in high-altitude areas is more severe than at lower altitudes. The radio interference caused thereby is a key factor to be considered when designing transmission lines. To study the influence of altitude on negative corona characteristics, an experimental platform comprising a movable small corona cage was established: experiments were conducted at four altitudes in the range of 1120-4320 m, and data on the corona current pulse and radio interference level of 0.8-mm diameter fine copper wire under different negative voltages were collected. The experimental results show that the average amplitude, repetition frequency and average current of the corona current pulse increase with increasing altitude. The dispersion of pulse amplitude increases with increase in altitude, while the randomness of the pulse interval decreases continuously. Taking the average current as an intermediate variable,the relationship between radio interference level and altitude is obtained. The result of this research has some significance for understanding the corona discharge characteristics of ultra-highvoltage lines.

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.

Introduction to investigations of the negative corona and EHD flow in gaseous two-phase fluids

Research interests have recently been directed towards electrical discharges in multi-phase environments.Natural electrical discharges,such as lightning and coronas,occur in the Earth＇s atmosphere,which is actually a mixture of gaseous phase（air） and suspended solid and liquid particulate matters（PMs）.An example of an anthropogenic gaseous multi-phase environment is the flow of flue gas through electrostatic precipitators（ESPs）,which are generally regarded as a mixture of a post-combustion gas with solid PM and microdroplets suspended in it.Electrical discharges in multi-phase environments,the knowledge of which is scarce,are becoming an attractive research subject,offering a wide variety of possible discharges and multi-phase environments to be studied.This paper is an introduction to electrical discharges in multi-phase environments.It is focused on DC negative coronas and accompanying electrohydrodynamic（EHD） flows in a gaseous two-phase fluid formed by air（a gaseous phase） and solid PM（a solid phase）,run under laboratory conditions.The introduction is based on a review of the relevant literature.Two cases will be considered：the first case is of a gaseous two-phase fluid,initially motionless in a closed chamber before being subjected to a negative corona（with the needle-toplate electrode arrangement）,which afterwards induces an EHD flow in the chamber,and the second,of a gaseous two-phase fluid flowing transversely with respect to the needle-to-plate electrode axis along a chamber with a corona discharge running between the electrodes.This review-based introductory paper should be of interest to theoretical researchers and modellers in the field of negative corona discharges in single-or two-phase fluids,and for engineers who work on designing EHD devices（such as ESPs,EHD pumps,and smoke detectors）.

Effects of temperature and discharge parameters on ozone concentration of negative corona discharge

The relationship of the ozone generation and the heating power, corona wire surface temperature, discharge electrode and netting electrode was studied during the negative corona discharge. The experimental results showed that the ozone concentration reduced with applied voltage decrease. With heating power increase, the ozone concentration of unit current decreased at exponential rate and it almost change no longer over 0.40 W. Under given temperature, the lower the applied voltage was, the smaller the ozone concentration was; while under given applied voltages, only over 11 kV could decrease with the surface temperature increase. The ozone concentration decreased with the lengthening of corona wire, and could reduced to 10 ppb under experimental condition of 14.2 kV; it also decreased with the shortening of wire diameter, and could decrease 67% at best in the given condition. Moreover, it decreased with the increasing size of netting electrode mesh. At the anion current of 1.65 μΑ, the ozone concentration of 5.0×5.0 cm 2 is only 41% of that of 3.3×3.3 cm 2.

Characteristics of water volatilization and oxides generation by using positive and negative corona

The physical and chemical properties have significant differences for the positive and negative charged particles generated by discharge.In this work,a positive and negative corona discharge system was established,and two discharge reactors for charged particles restraining and acting were designed by a needle electrode covered with a quartz tube and a plate electrode filled with water.The corona discharges happened within the needle-plate electrodes were excited by a positive and negative high voltage source,and the characteristics of both water volatilization and oxides generation were examined within influence of the distances of both quartz tube inside and outside.The results show that the characteristics of both the water volatilization and oxides generation can be affected by the distances of both quartz tube inside and outside.When the distances of tube inside were increased from 5.00 to 13.00 mm,the water volatilizations decreased under negative corona,and increased firstly and declined immediately under positive corona.The maximum value of the water volatilization appeared in the distances of tube inside with 6.00–8.00 mm.In addition,the concentrations of the HNO_(x) and H_(2)O_(2)in treated water decreased with increasing the distances of tube inside.Moreover,with increasing the distances of tube outside from 4.00 to 14.00 mm,the change trends of both the water volatilizations and oxides presented the same as the distances of tube inside,and the maximum value of the water volatilization and oxides appeared in the distance of tube outside with about 9.00 mm.Overall,the positive corona can generate more water volatilizations and oxides in water than negative corona,and non H_(2)O_(2)can be produced by negative corona.The results reflect the difference between positive and negative corona interaction with water,which can provide reference for plasma application.

Corona with Streamers in Atmospheric Pressure Air in a Highly Inhomogeneous Electric Field

The paper presents research data on positive and negative coronas inatmospheric pressure air in a highly inhomogeneous electric field. Thedata show that irrespective of the polarity of pointed electrodes placed ina high electric field (200 kV/cm), this type of discharge develops via ballstreamers even if the gap voltage rises slowly (0.2 kV/ms). The start voltageof first positive streamers, compared to negative ones, is higher andthe amplitude and the frequency of their current pulses are much lower:about two times and more than two orders of magnitude, respectively.The higher frequency of current pulses from negative streamers provideshigher average currents and larger luminous areas of negative coronascompared to positive ones. Positive and negative cylindrical streamersfrom a pointed to a plane electrode are detected and successive dischargetransitions at both polarities are identified.

Review on ionization and quenching mechanisms of Trichel pulse

Trichel pulse is a kind of pulsed mode in negative DC corona discharge,which has attracted significant attention because of its considerable applications in industry.Over eighty years,plenty of effort including simulations and experiments has been spent to reveal the ionization and quenching mechanisms of Trichel pulse.By revisiting and summarizing the basic characteristics and well-accepted ionization and quenching mechanisms,this review provides a basic understanding and the current status of Trichel pulse.