Brush Discharges Research Articles

On the pulse shape of discharge currents

Current pulse shapes of brush discharges from insulator surfaces and capacitive spark gap discharges were recorded on a fast oscilloscope and the data obtained fitted to assumed mathematical expressions by computer. The surface discharges were photographed using high sensitivity film, and their Lichtenberg figures made visible by a thin layer of Lycopodium. The geometry of a surface discharge depends on the radius of the discharging object. The number of foot-points of the discharge decreased with increasing radius; a sphere of 125 mm diameter caused one single foot-point, and a sphere of 25 mm diameter caused up to ten foot-points. The branching did not in any case occur at the surface of the electrode. The total current flow was concentrated to one single stem of at least five millimetres length. Resistances and linear energy densities of the surface discharges were calculated to be in the range of 1–4 kω and 3–40 μJ/mm respectively, whereas the capacitive discharges would have resistances of 1–90 ω and a linear energy density of 200–900 μJ/mm. The authors propose a new concept model for the discussion of the incendivity of electrostastic discharges.

Systems for electrostatic evaluation in industrial silos

AbstractWhile a primary strategy for avoiding ignition during silos filling lies in control of the ignition energy of the suspension, it may also be possible to control the energy of on‐bed brush discharges created during filling. Two instrument systems are described for investigations in operational, full‐scale process equipment. A discussion is made of the effective energies of brush discharges, the effects of process variables on static, and types of charge neutralizer that have been used or proposed. The instrument systems allow pragmatic, in‐plant evaluation of the effects of process variables and the benefits of any charge neutralizer system that is used.

Charge relaxation in powder beds

Many plastic powders become highly charged during mixing or transport operations. When such powders are stored in hoppers or silos, strong electric fields are established which can lead to hazardous dust-igniting electrostatic discharges. The most serious hazard is apt to occur during or shortly after filling operations. Thus, realistic risk assessment of ignnition probabilities requires solution of a transient electroquasistatic field problem, where both filling of the vessel with charged powder and simultaneous charge relaxation and/or brush discharge to the vessel walls are taken into account. A one-dimensional model of a filling silo with continuous charge relaxation is proposed. The problem is solved numerically using finite difference equations in time and space. The temporal solution is divided into the filling period and the relaxation period (after filling stops). The solutions for electrostatic field and surface charge demonstrate how various parameters influence the electrostatic discharge hazard. The ratio of filling time to charge relaxation time T is the most important of these paramweters. For T⪢1.0, the hazard is decreased because the charge relaxes to the conducting walls as soon as the powder is deposited in the vessel.

Some characteristics of liquid-to-metal discharges involving a charged “low risk” oil

Liquids possessing electrical conductivities greater than about 10 pS m −1 may be classified as “low risk” as regards hazardous levels of charge accumulation when loaded into grounded containers. The same liquids, when loaded into insulating containers, may give rise to liquid-to-metal discharges that are incendive either to vapor or to finely-dispersed oil mist in the vapor space. Using both theoretical and experimental approaches some characteristics of these discharges are evaluated in terms of measurable parameters; empirical ignition test data are employed to help establish safety criteria. When identifying “bad actors” in terms of tendency to static ignition it is recommended that both the liquid vapor pressure and the incidence of high negative charging levels be considered. In the present study, a negatively charged test oil produced energetic positive brush discharges accompanied by surface streamers. Positively charged oil yielded negative brush discharges which did not penetrate to the surface or produce surface streamers. The negative brushes carried an order-of-magnitude lower charge and were shown to be non-incendive during empirical ignition tests. Ignition of paraffin vapor by negative oil discharge occurred for surface potentials above 25 kV. High flash-point oil mists were ignited at surface potentials of about 60 kV, this being limited principally by the representative mist droplet diameter and the mist concentration in the discharge region.

Ignition of gas/air mixtures by discharges between electrostatically charged plastic surfaces and metallic electrodes

In a series of experiments it has been established that brush discharges from plastic surfaces are able to ignite the following gases and vapors: Propane, butane, 2,2-dimethylpropane, diethylether, acetone, ethylalcohol, acetic acid ethylester and mixtures of alkanes.With propane/air/nitrogen mixtures, which exhibit slowly increasing minimum ignition energies as a function of the additional nitrogen content, the equivalent energy of brush discharges was determined. For discharges between an electrode of 35 mm radius and a charged plastic surface of 0.13 m2, a value of 3.6 mJ has been obtained.

The ignition power of brush discharges — experimental work on the critical charge density

The properties of brush discharges were studied and ignition experiments were made for determination of the ignition power of brush discharges. At the ignition experiments a n-pentane — air mixture was used. Large PVC plates were charged in a corona discharge and discharged with spherical electrodes of varying diameter. The ignition probability was determined for negatively charged plates. No ignition was obtained with a positive charge on the plates.The experimental results are compared with similar experiments made by other authors. A method for estimation of the critical charge density for ignitions is suggested.

Natural organic atmospheric aerosols of terrestrial origin

Particulate matter in the atmosphere is a major source of contamination, having an impact upon visibility, health, and even climate. These aerosols are predominantly of natural origin. A minor component, the anthropogenic organic aerosol, has been studied extensively because of its relation to smog. Much less is known about the far more abundant natural organic aerosol. Estimates of the annual global production rate of the latter range between 75 and 1000 million metric tons. In contrast, the corresponding rate for man‐made organic aerosol is only between 0.2% and 17% of the natural rate. Thus the natural organic aerosol production rate is exceeded greatly only by that of natural sea‐salt aerosol and possibly by that of natural nitrate. By far the largest proportion of the natural organic aerosol is derived from vegetation by means of a photochemical reaction of its vapors, a process which is observed as haze formation. This reaction of olefins has been studied extensively and is believed to be identical with that involved in smog production by anthropogenic olefins. In fact, the resultant products in the two cases are virtually indistinguishable, although minor differences do exist. An additional possible source for natural organic aerosols is the release of waxy particles from the tips of pine needles by means of electrical brush discharge from clouds. Yet other small amounts come from biological cellular debris and possibly even from volcanos. The role of natural organic aerosols in condensation and precipitation has been studied. Claims for the effectiveness of organic aerosols as ice‐forming nuclei have been made. Natural organic aerosols have been suggested as possible sources of petroleum and of humus in the ground. Biodegradation mechanisms for this result have been considered. If it is verified, the impact upon pollution control strategies would be considerable.

Entladungen infolge elektrostatischer Aufladung in großen Lagersilos

AbstractDischarges resulting from electrostatic charging in large storage silos. A very high electrostatic charge can be generated on pneumatic transport of non‐conducting dusts or granular materials. Charge accumulation in this way can lead to discharges of different kinds and energy density. If elimination of ignition sources is adopted as a means of avoiding explosions and fires, the ability of these discharges to cause ignition must first be examined. The conditions leading to spark and brush discharges and so‐called lightning flashes in large‐volume silos are discussed. Their ability to ignite flammable dust/air mixtures is estimated with the aid of calculations. Furthermore, measures are also discussed for avoiding the occurrence of potentially igniting discharges in solids/air mixtures.

A general saturation curve for an ionization chamber filled with nitrogen at pressures up to 8 atmospheres

A plane parallel ionization chamber, which was designed to permit high collecting fields to be applied to the layer of ionized gas without introducing local field concentrations which might tend to produce brush discharges, was used. By interchanging the insulating spacing rings, six different electrode spacings could be obtained, ranging from 3 to 13 mm. Irradiation was from a 2000 Ci 60Co source, the dose rate being varied by moving the chamber to different distances from the source.

Barley leaf tip damage resulting from exposure to high electrical fields

Barley leaves in point to plane electrode configuration were exposed to high electrical fields. The amount of tip damage was observed for various voltages and exposure times. Damage appears to be due exclusively to I2 Rt energy dissipated in the leaf. The damaging current is comprised of contributions from brush discharge and corona glow. Ozone and other corona byproducts contribute little or nothing to the tip damage.

Auroral Audibility

A comprehensive compilation of reports on auroral sounds ranging from the 16th century to the present have been made. The reports have been evaluated for their accuracy and catalogued according to their locations which range from 55° to 70° geomagnetic latitude. A detailed study showed that significant correlation exists between sunspot cycles, magnetic character figures, and the reports of auroral sound. The duration, quality, and possibly accompanying effects such as odor have been carefully examined. In determining a theoretical explanation, we have considered the psychological effect, tinnitus, meteorological effect, direct transmission, infrasonic waves, emission of radio waves in the audio region, direct perception of electromagnetic radiation, and electric field pressure effect. In considering the direct conversion of electrical energy to sound energy through electrostriction we considered two models, an isothermal and an adiabatic model. Calculations from these models showed that the electric fields are insufficient for producing audible sounds. Our final conclusion is that a fraction of the most intense auroras have associated electric fields which produce induced fields at ground level and that these induced fields in dry, calm weather lead to brush discharges which are audible.

Folded-path atmospheric-pressure CO2laser

A folded-path transversely excited atmospheric-pressure CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser utilizing shower or brush discharges is described. The output pulse has an initial peak 0.4 μs wide followed by a tail <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-3 \mu</tex> s long. A peak power of 0.2 MW with 4.4 percent efficiency is obtained. By rotating one of the mirrors of the resonator the tail is eliminated, yielding a pulse 0.2 μs wide of the same peak power.

The theory of the high frequency brush discharge.

The theory of the high frequency brush discharge.

Hochfrequente Fackelentladung als Spektralquelle

Summary The brush discharge induced by a rectified high-frequency source on a nickel point can be used as a spectral source if it is supplied with an atomized solution of the sample through a co-axial stream of air. The sensitivity of this source is compared with that of the flame for thirteen elements. The uniformity of the source was tested for BaCl 2 and found to be satisfactory.

Transition from Glow to Arc Discharge

I HAVE suggested1 a mechanism to account for the occurrence of long electrical discharges in electric fields which are only of the order of one per cent of those generally believed2,3 necessary to cause sparkover. In the case of the leader stroke of the lightning discharge, the integrated lateral corona currents from the channel ultimately reach values of the order of thousands of amperes4, so that the characteristics of the channel must be those of the electric arc, though the discharge must start as a brush or glow discharge. This consideration led me to suggest that the steps in the initial leader stroke represent the transition of successive lengths of the channel from glow to arc conditions, and that a self-propagating discharge is initiated by this transition.

The use of Geiger-Müller Counters for Locating Radium and for Measuring Gamma-Ray Intensities

THE development of Geiger-Müller counters to a state of good reliability has provided a new order of sensitivity and facility with which weak sources of gamma rays and x-rays can be detected and measured.Combined with extraordinary sensitivity, counters are rugged, stable, simple to operate, and the results of measurements made with them lend themselves to easy interpretation. Geiger-Müller tube counters are not particularly new instruments. They were invented in 1928 by Professor H. Geiger and W. Müller,1 as an outgrowth and great improvement of the Geiger counter, or point counter, which had been in use for many years for counting alpha particles. Since their invention, tube counters have been adapted to a large variety of uses in physical laboratories. They have, indeed, become one of the physicist's most powerful tools for measuring weak radiations. Three general types are now in use: (1) gamma-ray counters, suitable for measuring gamma rays, x-rays, and cosmic rays; (2) photo-electric quantum counters, which combine the characteristics of photo-cells and counters, and are used for measuring weak ultra-violet light, and (3) particle counters, for measurements of alpha, beta, and H particles. Of these forms, there are various mechanical modifications, made to meet the requirements of particular problems.2 The present paper deals with counters of the first type, which we have used for locating radium and for making gamma-ray measurements during the last two years. I. Construction and Principle of Operation of Counters A counter apparatus consists of: the counting tube (counter), an amplifier, usually employing radio tubes, a recording device for registering the number of discharges of the counter, and a suitable source of (negative) high voltage for the counting tube. The negative voltage is usually between 500 and 1,500 volts, depending on the kind of counter used. The principle of operation of a GeigerMüller counter (G-M counter) is explained by reference to Figure 1. A wire, W, is stretched along the axis of a hollow metal cylinder, F, enclosed in a glass tube. After suitable treatment of the. electrode surfaces, the tube is filled with a suitable gas, usually at about 1/10 atmospheric pressure, and sealed off. A negative voltage, V, is applied to the cylinder-electrode (cathode); the wire (anode) is connected through a small condenser, C, to a vacuumtube amplifier, A (or a string electrometer), and through a high resistance, R, to ground. The value of V is adjusted so that it is nearly enough to cause a brush discharge between the electrodes. When in this sensitive state, any ray, Q, passing through the tube and liberating one or more ions in F, initiates a small gas discharge between the electrodes.

Application of the Wilson chamber to the study of spark discharge

The usual methods of investigating the problems related to the phenomenon of spark discharge may be classified into two kinds. The first is to measure the potential and current or their variations with respect to time, which may be called "electrical." By this means we know only the signals transmitted from the spark. The second method is optical, to which belong the photographic and spectrographic investigations as well as the method using a Kerr cell. These methods give us information on the spark itself, but they are confined to the problems accompanied with the emission of light. For observing a process of discharge that does not accompany any luminous phenomenon, the use of Professor Wilson's cloud chamber seems to be the only method suitable for the for the purpose at our present stage of knowledge. As a matter a fact, already in 1899 Wilson, using an expansion chamber of the earlier type, had investigated the formation of ion clouds by the positive and negative point discharges. Since then no communication seems to have been published on the formation of ion clouds by an electrical break-down process until recently, when the present authors and Snoddy and Bradley published independently the reports of their experiments of this subject. Several years ago one of the present authors, under the direction of Professor T. Terada, engaged, in a study concerning the form and structure of long electric sparks. He then succeeded, using a quartz-fluorite ions, in taking a photograph of the brush discharges immediately preceding the main spark. This preceding discharge is rich in ultra-violet light, and more complicated and extended in its form than the succeeding main spark, appearing as appendages to the luminous spark track. This result led him to look for the other form of discharge which cannot be photographed even with the quartz-fluorite lens. Then, on the suggestion of Professor T. Terada, he tried to take a Wilson photograph of ions produced by a spark, but did not succeed in obtaining a satisfactory one. Later on, in the course of conversation with Professor Wilson at Cambridge he was given a great deal of advice on this problem and decided to take up this subject again.

Current-voltage characteristics of high potential, direct current brush and glow discharges in air at atmospheric pressure

Current-voltage characteristics of high potential, direct current brush and glow discharges in air at atmospheric pressure

Spark Investigation by the Wilson Chamber

SEVERAL years ago, one of the present writers (U. N.) engaged in a study concerning the form of long electric sparks at the laboratory of the Institute of Physical and Chemical Research in Tokyo under Prof. Terada. We succeeded then, by using a quartz-fluorite lens, in taking a photograph of the brush discharge immediately preceding the main spark1. This preceding discharge is rich in ultra-violet light, and more complicated and extended in its form than the succeeding main spark, giving an aspect as appendages to the luminous spark track. This result led us to look for the other form of discharge which cannot be photographed even with the quartz-fluorite lens. The use of Prof. Wilson's cloud chamber is at our present stage of knowledge the only method suitable for observing a process of discharge that is not accompanied by any luminous phenomenon. We then tried, on the suggestion of Prof. T. Terada, to take a Wilson photograph of the ions produced by a spark, but did not succeed in obtaining a satisfactory one. Later on, in the course of conversation with Prof. C. T. R. Wilson at Cambridge, I was given a great deal of advice on this problem and decided to take up this subject again.

On the Rotation of Dielectrics in Electrostatic Fields and Related Phenomena

The rotation of a dielectric covered body, suspended between the poles of a Wimshurst machine, is investigated and found to be due to the accumulation of charge on the surface of the body, under the action of the brush discharge, and to the subsequent electrostatic repulsion of this charge. It is shown theoretically, in an appendix, that the rate of rotation is governed by the rate of decay of the surface charge, and is a maximum for a certain value of this rate of decay. The rotation of a chain hanging from an electrical machine into the dielectric layer of a Leyden jar (the inner conducting coating being removed) and similar electrostatic experiments are described, and shown to be due also to the superficial charging of a dielectric body, body, and depends upon the rate of decay of this surface charge. A similar explanation is shown to account for some other electrostatic phenomena.