Brush Discharges Research Articles

Electrostatic charging of material webs in production machines and how to eliminate it

The elimination of electrostatic charges, especially on material webs is critical to preventing ignition hazards and personal injury hazards in industry. The use of discharge bars (called “ionizers”) is an important method for eliminating electrostatic charges.The possibility of electrostatic discharge in a production machine is real. The metrological detection of charges on material webs is also discussed and the special phenomenon of a super brush discharge is described. A useful arrangement for active ionizers is described and justified.

Parameters Influencing Space Charge Density in Vessels by Spraying Water

Spraying water in vessels generates electrostatically charged clouds of droplets. If the resulting space charge density is sufficiently high, brush discharges to conductive earthed parts may occur. In vessels where potentially explosive atmospheres might occur, the prevention of hazardous space charge density is required. This work gives an overview of all the relevant parameters that influence the space charge density. For this purpose, own measurements are presented and compared with knowledge from the literature. The measurements have been carried out with earthed vessels and nozzles built of conductive material. To take the state of the art into account, pump pressures of up to 2500 bar have been used. The result of this work provides support for dimensioning vessels and water spraying techniques to minimize the risk of ignition hazards due to brush discharges of the electrostatically charged clouds of droplets.

RESEARCH AND EVALUATION OF THE METHOD OF ACTIVATION OF THE GAS FLOW FOR ALLOYING WITH GASEOUS NITROGEN"

Increasing the strength of steels and improving their operational qualities is one of the main tasks contributing to solving the issue of reliability, durability of parts and structures. Alloying, including nitrogen, occupies a special place among the large number of ways to improve the properties of steels.
 Nitrogen, as an alloying element, has been known for a long time, and its sufficiently high content in the atmosphere makes nitrogen even more attractive to technologists. However, it has limited solubility in iron alloys, especially with a high content of other components.
 There are various methods of gas activation, but in order to ensure relatively low energy costs and having positive experience of works on electric high-voltage activation of oxygen, it was proposed an option of activation by creating an electric brush discharge.
 The research was carried out on a physical bench that simulates the section of the lance at the outlet for the supply of activated gas when using different types of closed-type discharge devices. The devices differed by the arrangement of one of the electrodes: with a submerged non-insulated electrode and a protruding almost completely insulated electrode. The effect of purge gas pressure and arc length (distance between electrodes) on the efficiency of the nitrogen-containing gas flow ionization process (using air as an example) was analyzed. It was established that when using a discharge device with a submerged electrode, the current strength that forms the activated gas has a quadratic function on the distance between the electrodes with a maximum at a distance of about 15 mm and a purge gas pressure of 0.25—0.3 MPa. With a further increase in pressure, the visible discharge disappears and the current decreases.
 When using a discharge device with a protruding electrode, much higher indicators of the strength of the ionized current were obtained while maintaining a visual discharge even at high pressures of the purging gas (0.6MPa). At the same time, the current strength increases with an increased discharge distance — with the highest values at low blow-by pressures. That is, the version of the discharge device with a protruding electrode is more promising from the point of view of activation of the nitrogen-containing gas stream.

Study on the Path and Thermal Characteristics of the Spark Discharge Between Ice and Electrode Gap

The corona-to-spark transition is a fundamental discharge process between the ice and electrode gap, the first step of a partial arc formation on the ice-covered insulators. This article set up a calibrated Schlieren system synchronized with electrical signals to study the primary process and characteristics of the corona-to-spark transition between ice and electrode gap. The Schlieren system is calibrated by a Plano lens and verified with a thermocouple; a series of experiments are set up to obtain the discharge process’s voltage, current, and temperature in the time domain. A vibration–translational model is proposed to quantitatively explain the influence of discharge path on the thermal–electrical characteristics. It is found that the brush discharge appears only in the air, which promotes the temperature rise during the corona-to-spark transition and makes the discharge’s air path have the highest temperature. The findings in this article will provide a basic understanding of the corona-to-spark transition characteristics between the electrode and ice gap.

Experimental study on positive corona discharge characteristics in plane-single/double earthed rods air gaps under negative DC voltage

In order to analyze the corona discharge characteristics at the grounding object tip under the thundercloud electric field environment, scaled simulation test has been conducted on corona discharge in the plane-single/double earthed rods air gap. Five gap configurations with three different grounding rods were built during experiments. Factors as rod tip curvature, voltage and gap configuration have been considered in detail. Corona voltage, corona current and the number of ultraviolet photons were all recorded. The grounding rod tip curvature radius can affect corona discharge processes at grounding rod tip. With increasing applied negative DC voltage, five typical corona processes of dark discharge, burst streamer corona, periodic streamer corona, glow corona and brush discharge occurred at conical and spherical grounding rod tip (r=0.75cm), but under d=5cm and d=10cm no glow corona and brush corona appeared at spherical grounding rod tip (r=1.25cm). It is much easier for grounding rod tip with smaller curvature to form glow corona phenomenon. The mean value Iav of periodic streamer corona current pulse amplitude decreases with grounding rod tip curvature radius, while the mean corona current pulse width and pulse interval increases. For grounding rod with conical tip, there is little difference of average current pulse amplitude between periodic streamer corona and brush corona; for grounding rod with spherical tip (r=0.75cm), the mean value Iav of brush corona pulse amplitude increases to 3595.8 μA which has increased by a factor of about 36. The photon number at conical grounding rod tip is larger than that at spherical grounding rod tip at low voltage but the relation reverses as the applied voltage exceeds a critical value. The shielding effect of two grounding rods in plane-double rods air gaps increased with spherical grounding rod curvature radius and decreases with the lateral gap distance between two grounding rods.

Basin-Type Spacer for DC-GIL—Part I: Surface Charging and Discharging Behaviors

In this study, a downsized direct current (dc)-gas-insulated transmission line (GIL) model is applied to investigate the surface charging and discharging characteristics of the basin-type spacer in 0.1-MPa SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> and air. Under a low electric field, the surface charge accumulation is dominated by the bulk conduction of the spacer. As the charging voltage increases, gas ionization occurs in the localized strong electric field, taking over the dominant position. In 0.1-MPa SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas, flashovers typically develop along the convex surface of the spacer under both positive and negative voltages because the homo-charge accumulation induced by brush discharges on the concave surface aggravates the electric field distortion at the convex side. In air, the dc flashovers have the polarity effect. Under the negative voltage, the flashover development is similar to that in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas. But for positive polarity, the space charge region of positive polarity intensifies the electric field ahead of the corona region, thus promoting the air-gap breakdown at the concave side of the spacer.

Expansion characteristics of a discharge column in an electrode–ice gap

When modeling the propagation of an electric discharge on an ice-covered insulator, the diameter and temperature of the discharge column are vitally important. This paper studies the thermal expansion characteristics of a discharge column occurring after electrode–ice gap breakdown both experimentally and theoretically. It is found that the air part of the discharge channel expands faster and has a higher temperature and larger diameter than the surface part. To provide a quantitative explanation of this phenomenon, a physical model is established based on the gap breakdown process, discharge channel heat conduction, and molecular thermal relaxation theory. The results of theoretical calculations show that the experimentally observed differences in discharge column thermal expansion characteristics result from the heating effect of brush discharge and from differences in heat conduction around the column.

Experimental Study on Thermal Characteristics of DC Arc Formation between Ice-Electrode Gap

The partial arc is a destructive discharge phenomenon for HVDC insulators under icing conditions, leading to flashover incidents. This study sets up a calibrated Schlieren system to examine the DC arc's thermal characteristics on an ice surface. The theoretical analysis shows that the plasma component changes significantly between 2000 K to 2882 K, which is the characteristic temperature of arc formation. Experimental results show that the temperature characteristics in the time domain depend on the discharge stages. A temperature jump appears at the spark discharge and then increases exponentially with the leakage current during the arc formation. However, the temperature in the corona and brush discharge is almost unchanged. Results also show that higher water conductivities increase the spark temperature and promote arc formation, but do not affect corona and brush discharge, which take place in the air gap. In the arc channel, the gas near the core comprises molecules, atoms, electrons, and ions, while the gas in other regions is mainly composed of neutral molecules. This study provides findings that might enhance our basic understanding of the ice surface's partial arc formation process.

Experimental study on electrostatic discharges from a metal protrusion inside a silo during continuous loading of polypropylene powder

In this study, the electrostatic discharges from a metal protrusion existing inside a conical-cylindrical silo during continuous loading of polypropylene powders (PP, 3 to 4 mm) were experimentally investigated. A pilot-scale silo connected to a pneumatic powder transport facility was used while all parts were electrically grounded. The metal protrusion used in this study had a diameter of 4 cm. The silo was continuously loaded with PP powders at a mass flow rate of 0.68 kg/s to a total mass of approximately 800 kg. An image intensifier unit was used to observe the electrostatic discharges generated from the metal protrusion, and a current probe attached to an oscilloscope was used to measure the discharge amount (Q [nC]). As for the results, a multiplicity of small electrostatic discharges (brush discharges) from the protrusion was observed. The electrostatic discharge from the protrusion during PP powder loading clearly developed at the 391 s mark, when approximately 270 kg of the powder had been loaded. In addition, a difference was observed in the electrostatic discharges before and after the protrusion was embedded in the accumulated powder. That is to say, after the metal protrusion was embedded in the accumulated powder, the electrostatic discharges were stronger than when the protrusion was not embedded. As well, the Q after the immersion of the metal protrusion in the accumulated powder was several times larger than that when the protrusion was out. Strong broad bulk surface discharges clearly appeared after the protrusion was fully immersed in the powder.

Complete Prevention of Contact Electrification by Molecular Engineering

Summary Electrostatic charges are easily generated on surfaces during contact electrification. Although these invisible charges have emerged as a new dimension in mediating the functions of surfaces, such as energy conversion, liquid transport, reactivity, and adsorbability, the accumulation of charges on surfaces can also pose many undesirable consequences. Despite notable progress, existing approaches in engineering antistatic surfaces suffer from limitations such as the need to modify bulk materials or for delicate control of patterning on surfaces that rely on the neutralization of generated charges. Herein, we report a general toolbox for designing antistatic coatings by leveraging on chemically heterogeneous components with electron-donating and electron-accepting functions, i.e., N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and 1H,1H,2H,2H-perfluorooctyl trimethoxysilane, to molecularly engineer the surface potential to achieve an electrostatic homogeneity and completely prevent charge generation. Our approach is general, which allows the facile fabrication of antistatic coatings on various materials, even flexible and curved, with good re-writability and transparency.

Experimental study on the effect of metal protrusions inside silos on electrostatic discharges

This paper experimentally introduces the electrostatic discharges generated from metal protrusions inside a silo during the loading of powders. An industrial-scale pneumatic powder transport facility including a silo and approximately 400 kg of polypropylene powder (PP, 2–3 mm in size) were used for this test. The PP powder loading speed was approximately 0.38 kg/s. Six different diameters (D: 1 cm to 6.3 cm) of metal protrusions were used. The metal protrusions were attached to the silo wall using a 30 cm support rod that was electrically grounded. The height from the accumulated PP powder to the protrusion in the silo varied from 10 cm to 50 cm. An image-intensifier unit was used in order to observe the electrostatic discharges generated from the metal protrusions and a current probe attached to an oscilloscope was used in order to measure the current of the discharges. As for the results, electrostatic discharges (such as brush discharges) from protrusions during the loading of PP powders were clearly observed. Specifically, the electrostatic discharge was the strongest in this paper when the diameter of the protrusion was 4 cm and the height from the accumulated powder was 30 cm. As an important finding, the value of the discharge amount was affected to a greater extent by the maximum discharge current. The maximum charge amount of electrostatic discharges generating from the metal protrusions in all of the test conditions was −122 nC, which is twice as high as the threshold for electrostatic risk assessment in the liquid painting process. These results suggest that, in the chemical process, sensitive powders with MIEs of less than 4 mJ, powders wetted with solvents, and the solvents themselves must be carefully handled, as these kinds of powders may be ignited by brush discharges. In order to prevent and reduce electrostatic accidents, it is important to make sure that no external material enters the silo.

Estimation of the energy released during propagating brush discharge

Propagating brush discharges are highly energetic and pose risks to the control and indicating equipment, hazardous atmosphere and human health. The nature of the PBD poses some difficulties, as one electrode, is non-conductive. Direct measurements of the voltage requires specialized equipment. Presented method uses voltage measurements on a low inductance RC circuit. PBD were also recorded with fast camera at 200 K pps. Some dependencies were observed, e.g. the energy released is usually higher for negative polarity. For chosen PVC test samples (0.2 mm thick), typical energies actually released to the atmosphere were between dozens and hundreds of mJ.

Study of a composite container with integrated barrier film considering electrostatic hazards in a propane and air flammable atmosphere

In this work the study of the possibility of potential electrostatic hazards is exposed in the case of a composite container for storage of propane gas with integrated barrier film made of insulating material intended to make the container impermeable. Charging/discharge tests were performed to evaluate the possible occurrence of brush discharges that can act as an ignition source for flammable propane/air mixture. The barrier film reduced the efficiency of surface charge dissipation but the values obtained are within published safety threshold values found in the literature.

Стендовое исследование особенностей электрофизической активизации газового кислородсодержащего потока

В работе изложены результаты стендовых исследований по оценке количества ионов (по величине силы ионного тока), формирующиеся при высоковольтной активизации газовых струй, содержащих кислород, при их подаче через кислородную фурму. Установлено, что в процессе активизации на срезе сопла фурмы образуется кистевой разряд, а внутри фурмы на электроде - тлеющий разряд, способствуют формированию в потоке газа заряженных частиц кислорода - ионов положительного и отрицательного знака, сила тока которых имеет ярко выраженную экспоненциальную зависимость от расстояния до источники их образования (электрода) независимо от давления газа или уровня содержания в нем кислорода. Выявлено, что углубление электрода на величину 10 мм способствует максимилизации значений ионного тока на близких расстояниях до среза сопла. А при активизации кислородного потока количество ионов на начальном участке струи в 4-5 раз больше, чем при активизации воздуха при одинаковом продувочном давления, что, вероятно, связано с количеством кислорода в продувочном газе, который превращается в ионы.

Energy released by brush discharges from the fabric with conductive fibres

Fabrics containing regularly spread conductive fibres introduced into their structure may storage an electric charge, what results in a characteristic surface potential distribution. The brush, electrostatic discharges may occur when the grounded conductive object approaches to the charged fabric surface. A simplified, charged fabric-grounded object model is proposed. A metal sphere as the conductive object and a synthetic fabric with conductive yarn (forming regular cells) are considered. The analytical model allows to connect the energy Wrel, that can be released during the discharge, with geometry of the fabric-object system. The model has led to the power type relation between the energy Wrel and the cell diameter of a.

Assessment of electrostatic discharges in insulating venting lines

In the field of protection against an explosion, every plant where flammable chemicals (liquids, gases, powders) are handled should build an explosion protection document. This document is a powerful tool to assess explosion management on the plant. Among other parts, it must include an ignition source analysis that assess the probability of explosion for every single place where a flammable atmosphere is expected.The ignition sources to be considered as listed in various standards such as the EN 1127-1 (Secteur interdisciplinaire de normalisation, 2012) and the IEC 60079-0 (IEC, 2012). The trickiest ignition sources are often static electricity and sometimes, the general measures that could be defined for a fully new plant are extremely difficult to implement on an existing plant.A common case deals with venting lines. Those lines are sometimes made of insulating plastics while a flammable atmosphere remains possible under normal operation. A strong charge build up can be generated on the inside surface of those lines and several hazards might happen. The charge build up in the inside part of the line will generate an electric field in its vicinity and will charge by influence the conductive parts that are not grounded. In that case, a spark discharges can occur in the working area. If a flammable atmosphere takes place at that point, an ignition could occur. The second main hazard would be a propagating brush discharge across the thickness of the venting line. In that case, an ignition of the vapours inside the pipes is possible.This presentation describes an experimental approach to measure the charge build up generated during the different process steps of one chemical firm. The results showed large differences depending on the process step and a hazard of propagating brush discharge was identified at some point.

Filling velocity for the prevention of incendive brush discharges on a liquid surface

Filling velocity for the prevention of incendive brush discharges on a liquid surface

Fine particle removal by a two-stage electrostatic precipitator with multiple ion-injection-type prechargers

A novel two-stage electrostatic precipitator (ESP) with multiple ion injection type chargers and parallel collection plates was developed and shown to efficiently collect particles from the corrosive waste gas discharged from semiconductor and optoelectronic processes. Multiple carbon brush electrodes for the generation of ions were located outside of the main gas flow, but the injection of clean air and induced voltage between the outer and inner plates of the charging stage carried ions into the main gas flow; thus, gases and particles in the main flow did not corrode or contaminate the charger. The particle collection performance of the ESP was evaluated experimentally for 0.3 μm particles, PM (Particular matter) 10, and PM 2.5 by varying the application voltages to the charging stage, main gas flow rate, and distance of the carbon brush discharge electrode from the main gas flow duct. The novel ESP achieved particle collection efficiency of 89.5% and 99.5% at the best condition when the voltage was applied to only the charging stage and to both the charging and collection stages, respectively. The particle collection efficiency of the charging stage only and the two-stage ESP was characterized according to the corona discharge power and main flow rate based on Deutsch's collection theory. Also, a simplified 2D simulation results show that the electric field is very high not only near outer carbon fibers but also near the outer metallic electrode edge.

Effects of Mechanical Load and Ionizing Radiation on Glass

This paper develops an approach to investigation of a solid as an integral system whose fundamental properties are determined by the energetics of its structure. Addressing the subject from a unified viewpoint, we consider the formation, accumulation, and transformations of defects in silicate and aluminophosphate glasses, which emit electromagnetic waves in a wide frequency range as a result of cracking. It has been shown that electron irradiation causes spontaneous electrical discharges, whose magnitude depends on the electron energy and irradiation time. The discharges occur at surface defects. Brush discharges develop in a layer where charged particles are distributed. In a thin layer of a charged dielectric, we observe a breakdown effect. The electrical discharge concentrates at surface defects, which can be produced in advance. A discharge can be initiated by approaching a grounded metallic tip to a charged surface even some time after irradiation. A discharge, mechanical loading, cooling, or heating of glass is accompanied by not only a light burst but also electromagnetic emission (EME), which correlates well with a polymorphic transformation process, thermoluminescence, etc. Thus, the release of accumulated energy from unirradiated and irradiated inorganic glasses on heating and cooling is accompanied by pulsed EME, whose intensity depends on the energy stored in the material.

Experimental study on electrostatic charges and discharges inside storage silo during loading of polypropylene powders

As polymer powders have high resistivity, they can easily be charged due to the repeated collision and separation of particles along with particle-wall friction in a pneumatic conveying system. This study experimentally investigated the electrostatic charges and discharges inside a conical-cylindrical silo during the loading of polypropylene (PP, 2–3 mm) powders. The silo was continuously loaded with PP powders at 0.68 kg/s to a total mass of approximately 800 kg. To measure electrostatic charges of the PP powder being loaded into the silo, a Faraday cage with a cover was set at a distance of 50 mm from the center of the loading pipe inside the silo. To observe electrostatic discharges inside the silo, an image-intensifier unit was set on the windowpane of the silo roof. The results show that the charge-to-mass ratio of the loading PP powder remained at a constant value of approximately −12 μC/kg. The ring-shaped light, which is the electrostatic discharge, appeared clearly at the center of the silo approximately 7 s after initial loading. The diameter of the ring-shaped light grew larger as time passed after loading. This was because the diameter of the accumulated PP powders increased in the silo during the running time, meaning that electrostatic discharge occurred between settled PP powders and the grounded metal silo wall. Additionally, the electrostatic discharges during the loading of powder in this study were clearly observed and classified into three kinds of discharges: brush, linear, or broad bulk surface discharges.