Intense Corona Research Articles

The Discharge Preceding the Intense Reillumination in Positive Leader Steps Under the Slow Varying Ambient Electric Field

AbstractUnder the slow varying ambient electric field, positive leader propagation exhibits steps characterized by intense reilluminations and abrupt elongations. These steps are currently not well understood. In this work, we investigate these steps in laboratory atmospheric discharges, using a high‐speed video camera and a synchronized electrical parameter measurement system. The discharge, emitting weak light and preceding the intense reillumination, is discovered. This finding suggests that the leader channel actually restarts and extends forward before the intense reillumination, which deepens our understanding of the dynamic process of the positive leader step. The discharge before the intense reillumination contributes to the corona inception from the electrode, leading to the intense reillumination of the leader channel and the emergence of an intense corona streamer burst from the leader tip.

Abrupt Elongation (Stepping) of Negative and Positive Leaders Culminating in an Intense Corona Streamer Burst: Observations in Long Sparks and Implications for Lightning

AbstractProperties of positive and negative leaders developing in air gaps ranging from 4 to 10 m that were subjected to 100/7,500‐μs voltage impulses were examined using a two‐frame, high‐speed video camera with image enhancement. Abrupt extension (stepping) that culminated in a bright and structured corona streamer burst was observed for both negative (expected for the “classical” stepping process) and positive (expected for the so‐called restrike process) leaders. Selected high‐quality images of five negative and four positive leaders with pronounced corona streamer bursts are presented here. The morphology of corona streamer bursts was essentially independent of polarity. Streamer bursts exhibiting nearly spherical symmetry were observed. For the four positive leaders, the newly added channel sections (steps) were almost straight and had lengths ranging from about 50 to over 120 cm. For the five negative leaders, most of the steps were curved and their 2‐D lengths were some tens of centimeters. It is generally thought that positive leaders in both long sparks and lightning extend continuously or exhibit optically unresolvable steps whose length is comparable to the leader tip size (1 cm or less) and that for sparks only when the absolute humidity is relatively high (>10 g/m3 or so) or voltage rise time is relatively long (around 1 ms or more) can larger steps occur. In this study, both modes of propagation for different branches of the same positive leader were observed.

Impact of mist and acidic fog on polymer insulator samples exposed to corona discharges

Corona resulting from the metallic parts of the transmission line insulators and hardware has proven to be the potential factor in inducing the degradation of polymer insulators. Corona activity is found to increase substantially during the foul weather condition (rain, fog/mist, hoarfrost), which further promotes the ageing of polymer insulators. Present work investigates the possible corona activity under fog/moist condition and its effects on the long term performance of polymer insulators in service. The spread of corona generated plasma is observed to be different under fog condition than in normal air condition. The concentrated streamers that are originated from the corona electrode during fog condition are believed to damage the polymer shed material locally and more intensely. This was confirmed by the scanning electron microscopy and Fourier infrared spectroscopy analysis carried out on the treated polymer samples, which showed more damage on the corona treated under fog than on the samples treated under normal air condition. Further TGA and EDAX studies have shown that loss of ATH occurs on the sample due to intense corona activity.

Variable Cross-Section Cylinder-Type Corona and Combined Corona–Dielectric Barrier Discharge Precipitators for Fly-Ash Particles

This article is aimed at evaluating three designs of cylindrical-type electrostatic precipitators that might be installed at the output of household boilers in order to reduce the pollution due to burning wood or fossil fuels. The first design is the “standard” precipitator, which consists in a thin copper wire (0.16 mm in diameter), coaxial with a cylindrical aluminum cylinder, 345 mm in length, of constant radius (20 mm). The second and third designs, equipped with a similar wire electrode, are characterized by the same global length, but are divided into three sections, two having the same cross-section as the “standard” precipitator, while the third section, 20 mm in length and located between them, has a smaller radius (11.5 mm). The reduction of the diameter in this central section of the precipitator is done by introducing an aluminum ring, covered by a sleeve made of either aluminum (design #2) or polyvinyl chloride (design #3). Together with the modification of the conditions for mechanical collection of particles, the more intense corona (design #2) or dielectric barrier discharges (design #3) generated in these sections of reduced diameter contribute to a significant increase of precipitation efficiency.

Influence of aged conductor surface conditions on AC corona-generated audible noise with a corona cage

Relatively few investigations have previously been made on the effects of surface conditions on corona-generated audible noise for the long-term aged ac conductors. In the present work these were investigated by means of comparing audible noise on typical aged conductors with that on new ones. The aged conductors from the ac power transmission lines had been in service for 12, 15 and 20 years, and their surface morphology, composition and roughness had been analyzed in our previous paper. A microphone and sound level meter was employed to measure the audible noise of the aged conductors in a small corona cage. As a result of the much intense corona discharge on the surfaces of the aged conductors, the audible noise of the aged conductors was much higher than the new conductors in dry condition. In wet condition, the corona discharge was found to be become more serious than the conductor in dry condition; hence, the audible noise was about 3 to 5dB stronger than that in dry condition.

Electrospraying of Water With Streamer Corona Discharge

The effect of electrospraying of water [electrohydrodynamic atomization (EHDA)] was studied in combination with dc streamer corona discharge as a possible method of biodecontamination of water. This effect was investigated under various voltages and water flow rates. The best conditions when the water spray was localized directly in the relatively stable and intense corona active region were reached at 8 kV and 8.3 μl/s. Images of EHDA with streamer corona discharge are presented.

Surface treatment and printing properties of dispersion-coated paperboard

Paperboard was coated on a pilot scale using aqueous dispersions of styrene–butadiene (SB) copolymers in order to improve its surface characteristics (including printability) and barrier properties with regard to the transmission of water vapour. Coating the paperboard with the dispersion in two steps gave a smoother surface with a remarkable increase in gloss. The printing properties of the smoother double-coated surface were slightly better than those of the single-coated surface. Paraffin wax added to the latex dispersion reduced the water vapour transmission rate (WVTR) but had a negative effect on the printability of the board. The effect of two commonly used surface treatment techniques (corona and plasma at atmospheric pressure) on the printing and barrier properties of dispersion-coated (containing wax) paperboard was evaluated. A fairly intense corona treatment led to an undesirable increase in the WVTR-value. A less intense corona treatment preserved the WVTR-value to a great extent, but the printability remained at an unsatisfactory level. With plasma treatment, the water vapour barrier was not impaired, and the printability of the plasma-treated dispersion-coated (wax-containing) substrate was good. It is suggested that a better result using corona treatment may be obtained by optimising the power and controlling the time between the treatment and the printing, although this was not investigated here.

Behaviour of conducting particles in corona-dominated electric fields

The motion of charged particles in electric fields can be harmful to gas-insulated apparatus, or may be used beneficially in several electrostatic technologies, such as printing, coating and separation of mixed granular solids. The theoretical analysis and the experimental data demonstrate the existence of numerous factors which determine the behaviour of a single conducting particle in corona-dominated electric fields. Various kinds of particles, spherical and cylindrical in shape, are studied. Several high-voltage electrode arrangements (point-plate, co-axial wire-cylinder) are employed, in order to generate intense corona discharges. The results ('lift-off' field, amplitude of motion) are compared to the previously studied cases of electric fields without space charge.

Pulse corona induced plasma chemical process: a horizon of new plasma chemical technologies

Abstract

A dust trapping system for rotary magnesite kilns

By reducing the gas velocity to 0.5–0.7 m/sec and thus increasing the time spent by the gas in the electrostatic precipitator to 14–20 sec, despite the formation of intense reverse corona we can obtain 99% purification of gas in the electrostatic precipitator, given optimum agitation of the precipitation electrodes and optimum electric supply, and provided that the kiln is firing a mixture containing not more than 50% caustic dust.

Ozone Resistance of Rubber Insulations

Abstract The results of experiments on the ozone and corona cutting of rubber high voltage insulation show that the relaxation of mechanical stress in the insulation plays an important role. Studies were made to establish the stress decay characteristics of various formulations based on natural rubber, SBR and butly rubber. A method was developed for correlating the stress decay and ozone resistance characteristics which permits the performance of bent samples of any formulation to be predicted at ozone concentrations up to 0.2%. Comparisons were made between the cutting in an intense corona discharge and that in high concentrations of ozone outside of the discharge. These comparisons show that the results of ozone tests at constant load together with stress relaxation tests may be used to predict the performance of rubber insulation in corona discharge. Tests were carried out in the products of corona discharge at pressures less than atomospheric. These tests lead to the conclusion that at very low pressures (ca. 1 mm Hg) cutting is caused not by ozone but by atomic oxygen. Compounds based on a variety of polymers were exposed to atomic oxygen and it was found that butyl rubber cuts rapidly in atomic oxygen while natural rubber, SBR, neoprene, and Hypalon do not. Antioxidants do not protect butyl rubber against cutting in atomic oxygen, but surface coatings were found to offer protection.