Showing papers on "Electric discharge published in 1999"

Design features for electric communication.

Abstract: How do the communication discharges produced by electric fish evolve to accommodate the unique design features for the modality? Two design features are considered: first, the limited range of signaling imposed on the electric modality by the physics of signal transmission from dipole sources; and second, the absence of signal echoes and reverberations for electric discharges, which are non-propagating electrostatic fields. Electrostatic theory predicts that electric discharges from fish will have a short range because of the inverse cube law of geometric spreading around an electrostatic dipole. From this, one predicts that the costs of signaling will be high when fish attempt to signal over a large distance. Electric fish may economize in signal production whenever possible. For example, some gymnotiform fish appear to be impedance-matched to the resistivity of the water; others modulate the amplitude of their discharge seasonally and diurnally. The fact that electric signals do not propagate, but exist as electrostatic fields, means that, unlike sound signals, electric organ discharges produce no echoes or reverberations. Because temporal information is preserved during signal transmission, receivers may pay close attention to the temporal details of electric signals. As a consequence, electric organs have evolved with mechanisms for controlling the fine structure of electric discharge waveforms.

Thermal processes in a streamer discharge in water

Abstract: The propagation features of a streamer discharge in water have been investigated. Based on the experimental data obtained in the study of water discharges in a nonuniform electric field, due propagation of streamers is explained as the evaporation of water at the tip of the streamer and around it. The energy balance in the process of the streamer propagation is calculated for a sub-microsecond discharge in distilled water. It is shown that the energy released in the pre-breakdown process is sufficient to evaporate the liquid in the streamer channels. Similar velocity of the streamer propagation in both tap and distilled water substantiates negligible effect of ionic current density onto the streamer propagation process. These estimations, based on experiment, have relevance to the discussion of the nature of the dielectric breakdown of water.

Electrical discharge diamond grinding of high speed steel

Abstract: A combination of two machining processes (i.e., a hybrid process) has a potential to improve process performance. This paper reports on experimental investigation of the electrical discharge diamond grinding process that combines mechanical grinding with electrical discharge machining. In this process, the workpiece is simultaneously subjected to heating, by electrical sparks bridging the gap between the metallic wheel bonding material and the work, and abrasion by diamond grains. The effect of current, voltage, pulse-on-time and duty factor on the grinding forces and the material removal rate while machining high speed steel workpiece, are investigated. The spark discharges facilitate grinding by thermally softening the work material in the grinding zone, and consequently decreasing the nromal force. It is observed that the material removal rate increases with an increase in current and pulse on-time, while it decreases with an increase in voltage and duty factor. These independent parameters ar...

Plasma-assisted boriding of industrial components in a pulsed d.c. glow discharge

Abstract: The influence of process parameters on plasma-assisted boriding of ferrous materials in a BCl3–H2–Ar atmosphere has been investigated. The elimination of pores in steel substrates is largely influenced by the discharge potential for a fixed BCl3–H2–Ar mixture. The electrical discharge is characterised by the belt of optical emission spectroscopy. Non-porous boride layers have been applied for oil pump drive gears which were then wear tested. The results show excellent wear protection properties of boride layers produced in a plasma-assisted process.

Properties of plasmas generated by electrical breakdown in flames

Abstract: Properties of electrical discharge in flames and influence of plasma electrons on gas neutrals are investigated by making use of the ionization cross section of air. An analytical expression of air ionization rate is obtained from tabulated data of the ionization cross section of oxygen and nitrogen, and is compared with air ionization rate measured with the applied electric field. The influence of gas temperature on electrical discharge properties is investigated by making use of electron energy gain in the electric field. Electrical breakdown occurs whenever ionization of neutrals dominates the electron attachment of oxygen molecules. It is found that the breakdown electric field in flames is inversely proportional to the flame temperature Tg, thereby easily generating plasmas in flames. A swarm of low-energy electrons in flames would allow a significant population of electronically excited states of flame molecules to be formed. The analysis shows that the electronic excitation of flame molecules may a...

Method and apparatus for initiating, directing and constricting electrical discharge arcs

Abstract: A method and associated apparatus for initiating and guiding an electrical discharge arc. This method preferably comprises the steps of: providing a laser beam through a predetermined gas comprising molecules amenable to vibrational excitation by a laser beam so as to cause vibrational excitation of the molecules and to define a beam path in a direction of desired electrical discharge; and propagating an electrical discharge arc so as to intersect the beam path, whereby the electrical discharge arc is directed along the beam path.

Pulsed Electric Breakdown and Destruction of Granite

Abstract: There are various methods of rock drilling and demolition. Recently, a method utilizing pulsed power technology has appeared. This method is based on the difference of the dynamic breakdown field strength of liquid and solid dielectrics. The applicability of this method was examined using a very hard rock–granite. The features of the rock destruction have been studied. The X-ray computer tomography was used to confirm the penetration of the electrical discharge into the rock. Well-resolved marks of the electric discharge channel could be observed using this technique. Destruction effectiveness was examined for various experimental conditions. The volume of the rock destroyed in a shot and the energy consumption in the destruction process are dependent on the generator voltage. The distance between electrodes has the optimum value for a given voltage.

Analysis of the N2O dissociation in a RF discharge reactor

Abstract: In situ diagnostic measurements and reactor modelling are used to study the N2O dissociation by radio frequency (RF) discharges. Measurements are undertaken at 0.5 and 1 Torr gas pressure with a RF power density varying from 4.2 to 35.7 mW cm-2. The reactor modelling involves an electrical discharge model coupled to hydrodynamic and mass transfer models. Only an electrical discharge model accounting for the negative ion conversion from O- to NO- and the subsequent electron detachment allow a good coherence between the measured and predicted power densities. The electron-N2O dissociation cross sections are first fitted in the present work and then the corresponding dissociation rates, obtained from the electrical model, are used in the mass transfer model which includes eight species (N2O, N2, O2, NO, NO2, N, O(3P) and O(1D)). The corresponding results are in good agreement with the experimental ones related to the production of N2 and O2 and the consumption of N2O. Furthermore, the reactor model results show that N2 and O2 are the most abundant products (>1014 molecules/cm3) at 1 Torr.

Plasma pinch high energy with debris collector

Abstract: A high energy photon source. A pair of plasma pinch electrodes are located in a vacuum chamber. A working gas which includes a noble buffer gas and an active gas chosen to provide a desired spectral line. A pulse power source provides electrical pulses at voltages high enough to create electrical discharge between the electrodes to produce very high temperature, high density plasma pinch in the working gas providing radiation at the spectral line of the active gas. An external reflection radiation collector-director collects radiation produced in the plasma pinches and directs the radiation in a desired direction. In a preferred embodiment the active gas is lithium and the buffer gas is helium and the radiation collector-director is coated with the material used for the electrodes. A good choice for the material is tungsten. In a second preferred embodiment the buffer gas is argon and lithium gas is produced by vaporization of solid or liquid lithium located in a hole along the axis of the central electrode of a coaxial electrode configuration. Other preferred embodiments utilize a conical nested debris collector upstream of the radiation collector-director.

Oil removal from iron surfaces by atmospheric-pressure barrier discharges

Abstract: An atmospheric-pressure dielectric barrier discharge plasma is used for oil removal from iron surfaces. The first results show that oiled iron surfaces cleaned in liquid solvent or by an atmospheric-pressure dielectric barrier discharge plasma in oxygen provide the same X-ray photoelectron spectra to high sensitivity, indicating an efficient oil-removal effect of the plasma.

Light Emission from Pt during High‐Voltage Cathodic Polarization

Abstract: Light emission from cathodically polarized Pt electrodes was investigated at cell voltages up to 200 V in aqueous electrolyte solutions. The emission of light was observed when intense cathodic polarization caused the temperature of the Pt electrodes to exceed the boiling temperature of the electrolyte. A thin vapor layer was formed at the metal‐electrolyte interface in which a high electric field ionized vapor molecules to generate a plasma state. The emission of light was caused by the glow discharge at relatively low cell voltages and by the spark discharge at high cell voltages. The spectra of the emitted light were assigned to the constituents of the electrolyte solution, electrode material, and gaseous hydrogen evolved at the electrode. © 1999 The Electrochemical Society. All rights reserved.

Method and device for surface treatment with a plasma at atmospheric pressure

Abstract: Method for creating an electric discharge in an initial gas which is at atmospheric pressure and lies between two exciting electrodes, comprising applying a supply voltage to the two electrodes which is an AC voltage whose amplitude and frequency are adapted in order to maintain (1) at least a portion of the components of the gas in the excited state, and/or (2) the presence of electrons, between two successive half-cycles of the supply voltage.

Hollow needle-to-plate electrical discharge at atmospheric pressure

Abstract: Ecological applications dealing with the cleaning of flue gases, the decomposition of volatile hydrocarbons and the destruction of toxic pollutants require, in order to reach high efficiency, the use of non-thermal plasma sources. Typical sources of such non-equilibrium plasmas are barrier discharge, direct current (DC) or alternating current (AC) gliding arc, pulsed or DC corona and DC atmospheric pressure discharge stabilized by a fast gas flow (APD-GFS). In case of APD-GFS the gas flows in a rectangular channel, the top wall of which serves as the anode and the multi-needle cathode is built into the bottom wall of the channel. In order to prevent the transition to a spark and to stabilize this type of discharge the velocity of the gas should be about 100-200 m s-1 or the discharge current must be limited. To avoid the problem connected with the acceleration of the primary (polluted) gas at such a velocity, the external flow of the primary gas around the needle electrodes can be superimposed by a flow of a secondary gas through the needles. Thus the primary gas need not be accelerated to high velocity and in order to stabilize the discharge a relatively small amount of a secondary gas supplied through the needle is required. This work is therefore focused on the study of the DC APD-GFS in hollow needle-to-plane geometry. The basic electrical characteristics, magnetic noise and integral emission spectra of this type discharge with the flow of nitrogen or air through the needle are given.

NO removal in a photo-triggered discharge reactor

Abstract: This paper presents the first study of a new type of reactor, the so-called photo-triggered reactor, for gas cleaning by non-thermal plasmas. Compared to the classical discharges used for this application, it allows the production of large volumes of uniformly excited plasmas without filamentary structures and glow to arc transition. Experimental and modellization studies of a 50 cm3 photo-triggered reactor have been performed. Chemical efficiency and specific energy consumption for NO removal in N2/O2/NO mixtures have been determined. It is shown that the NO removal efficiency is a sensitive function of the input energy but does not depend on the initial reduced electric field, (E/N)0, for values higher than 200 Td. Depending on mixture composition, NO destruction efficiencies between 30 and 100% are achieved in only one shot with energetic costs in the range 15 to 50 eV per removed NO molecule (22-75 g [NO] kW-1 h-1) for input specific energy lower than 150 J l-1. Moreover, in dry air, an ozone production efficiency as high as 64 g [O]3 kW-1 h-1 (28 eV mol-1) is obtained, demonstrating the excellent capability of the photo-triggered discharges to produce large amounts of atoms and radicals which in turn can reduce or oxidize the pollutant molecules. All these results point out the effectiveness of the photo-triggered discharges to homogeneously produce large volumes of plasma which could be efficiently used for gas cleaning applications.

Factors affecting the glow-to-arc transition at the cathode of an electric discharge at atmospheric pressure

Abstract: The glow-to-arc transition has been studied in an electric discharge at atmospheric pressure. Although this transition is a cathode effect, the cathode and the positive column have both been seen to affect the current at which the transition occurs. If the cathode is relatively small, the discharge passes through the abnormal glow region before the glow to arc transition takes place. If the cathode is sufficiently large, increasing the current causes the positive column to contract and the transition takes place directly from the normal glow without passing through the abnormal region. The oscillation phenomenon is explained in terms of the Steenbeck minimum principle and related to the power dissipated at the cathode root, which decreases when the glow changes to an arc. If the power dissipated at the cathode in the arc regime is insufficient to sustain electron emission the arc will revert to a glow. Variation of the slope of the load line alters the frequency of oscillation of the glow-to-arc transitio...

Driving circuit of plasma display panel, its driving method and plasma display panel device

Abstract: PROBLEM TO BE SOLVED: To widen the selecting width of an electric discharge and to obtain a driving method without a luminance nonuniformity by executing driving by means of a keeping pulse which is provided with a first voltage value for executing the first electric discharge during a half period and the second voltage value for executing the second discharge. SOLUTION: Electric discharge is executed by the combination of (Vs-Vs), (Vs-Vk) and (Vk-Vk) by giving an intermediate voltage being a second voltage value (Vk) though the voltage to be discharged is given only by the first voltage (Vs) in a conventional manner. That is, a cell itself discharges electricity by freely selecting the discharge voltage in accordance with its own electric discharge characteristic. Therefore, the cell executing discharge by Vs and the cell executing discharge by Vk exist, a light emission waveform L becomes the one for emitting light twice in the half period of the keeping pulse as the whole cell, first discharge is executed by the first voltage value Vs and the second one is executed by the second voltage value Vk so that the luminance nonuniformity owing to the dispersion of the electric discharge voltage is reduced. COPYRIGHT: (C)1999,JPO

Electric arc furnace controller

Abstract: An electric arc furnace includes a container for receiving metal, an electrode spaced apart from the container, and an electrical power source coupled to the electrode and the container for generating an electrical discharge between the electrode and the container for melting the metal in the container. The arc furnace includes a flicker controller for reducing flicker induced in the power source by the electric arc furnace. The flicker controller consists of a switch electrically connected between the power source and the electrode, and a control system coupled to the switch. The switch includes a gating input for controlling a conduction interval of the switch, and the control system applies gating signals to the gating input for maintaining a magnitude of reactive current flow through the arc furnace substantially constant.

Discharge surface treating electrode and production method thereof

Abstract: In an electrode for electric discharge surface treatment used in electric discharge surface treatment for forming a hard coating on the surface of a treated material through the energy by generating electric discharge between the electrode and the treated material, a TiC powder (11) which is metal carbide and a TiH2 powder (12) which is metal hydride are mixed and heating treatment is performed after compression molding and hydrogen in the TiH2 powder (12) is desorbed to make a Ti powder (13) and a practical electrode (10) for electric discharge surface treatment having moderate strength and crumbliness as well as safety is formed.

Discharges in combined transformer oil/paper insulation

Abstract: Discharge signatures and breakdown levels have been recorded for combined transformer oil/impregnated paper insulation subjected to AC high voltage. Different electrode geometries have been studied, varying from the point-plane gap to a semi-homogeneous sphere-plane configuration. At high moisture levels discharge activity was monitored at an average electric field below 1 kV/mm, with breakdown occurring 6 kV/mm. Characteristic discharge patterns were identified for corona, wedge, void and creeping discharges, but depend strongly on applied voltage, time and moisture content of the insulation.

Controller of wire electric discharge machine

Abstract: A controller of a wire electric discharge machine monitoring a change in thickness of a workpiece and a current density in real time, promoting a machining speed by preventing occurrence of disconnection of a wire electrode even when the change in the thickness is caused in the workpiece and improving a dispersion in a machining enlargement amount. A machining distance calculating device outputs a signal at each progress of machining by a predetermined distance Δx. A main pulse number storing device counts a main pulse number for discharge machining outputted from a main pulse generator during a time period of the signal. A thickness calculating device calculates the thickness from a reference main pulse number in machining a reference thickness, the main pulse number stored to the main pulse number storing device and the reference thickness at each reception of the signal. The calculated thickness, further, a machining current, the machining speed and a machining current density are displayed. A discharge pause time control device changes a pause time period of voltage applied to the wire electrode and the workpiece in accordance with a thickness change rate and adjusts the machining current density such that no change is caused before and after the change in the thickness.

Method and device for detecting the rectification effect that occurs in a gas discharge lamp

Abstract: Method for detecting the rectification effect in at least one gas discharge lamp (10) and electronic ballast for operating at least one gas discharge lamp, which recognises the appearance of the rectification effect in the gas discharge lamp (10). In order to be able to detect the appearance of the rectification effect in the gas discharge lamp (10) simply and with high sensitivity there is monitored the current (i 1 ) flowing via a primary winding (7A), connected parallel to the gas discharge lamp (10), of a heating transformer (7A-C) or a parameter (i 2 , u 3 ) dependent upon this current (i 1 ) , and in the event that a predetermined limit value is overshot the presence of the rectification effect in the gas discharge lamp (10) is determined.

Resonant square wave fluorescent tube driver

Abstract: A driver (10) produces a current to generate traveling waves of voltage for low levels of illumination and an arc voltage for high levels of illumination through a gas discharge lamp (50). At the low illumination levels the traveling waves of voltage are produced in a manner so as to increase the current in the lamp at a controlled rate so that the increase in current can be stopped by an optical or ionization feedback loop (80) when the lamp reaches the glow discharge region, after the Townsend discharge region (B) and before the arc discharge region (D). Without careful control of the rate of the current increase, the desired current level can easily be overshot or undershot. Also, the feedback is critical given the varying nature of the impedance of gas discharge lamps. The process is repeated at selected intervals to produce a desired average level of illumination. The nature of the traveling waves assists the direction of ion acceleration toward the walls of the lamp (50), allowing the lamp to be brought to the glow discharge region (C) without damage to the cathode filaments (250a, 250b).

Electric discharge machining apparatus

Abstract: An electric discharge machining apparatus including a first power source for applying machining voltage to a machining gap to generate an electric discharge, a second power source for applying voltage of equal to or lower than 20 V to the machining gap, a transistor switching bridge connected to both the workpiece and the tool electrode, a switch for selectively connecting one of the first and second power sources to the transistor switching bridge, a transistor controller for controlling on/off switching operation of the transistor switching bridge to alternatively change polarity of voltage being applied to the machining gap, a contact detector for electrically detecting the contact between the workpiece and the tool electrode when output of the second power source is applied across the machining gap, and an NC device which controls the switch so that the first power source is connected to the transistor switching bridge when the application of the machining power is required while the second power source is connected to the transistor switching bridge when detecting the contact by the contact detector is required.

Dynamics and correlated performance of a photo-triggered discharge-pumped HF laser using SF6 with hydrogen or ethane

Abstract: , has been performed in Ne/SF6/H2 and Ne/SF6/C2H6 mixtures. Parameters involved have been the storage line capacitance and the circuit inductance, the capacitors charging voltage, the RH-molecule type and partial pressure, and the X-ray dose for the preionization. High laser performance has been achieved with C2H6: an output energy up to 3 J corresponding to a specific energy of 9.6 J/l at an efficiency of 4.7%, which strengthens the advantage of the photo-triggering technique to energize high-power HF lasers. However the optimum performance achieved with H2, 5.75 J/l and 3.5%, are lower. It is shown, through a time-resolved study of the electrical discharge and spatial dynamics correlated to laser power and energy measurements, that discharge instabilities are responsible for the poor laser performance of the mixture with H2. These instabilities, which lead to arc development, are characteristics of the discharge in Ne/SF6. It is demonstrated for the first time that addition of a heavy hydrocarbon, such as C2H6, to that mixture induces the discharge stabilization so that the laser emission arises in a homogeneous active medium. This effect allows us to achieve better laser performance than with H2.

Light source using dielectric barrier discharge lamp, and power supply

Abstract: A dielectric barrier discharge lamp apparatus comprises a high-voltage A.C. power supply for an electrode that cooperates with discharge gas and an interleaving dielectric to produce an excimer by dielectric barrier discharge. The voltage waveform applied to the lamp includes a slow-varying period of time before reaching the firing potential toward another discharge after one complete discharge. The following condition is satisfied: 0.3 y x x y< = VF-VA.VA : the voltage at the end of one discharge, VB : the voltage at the end of the next discharge, and VF : the voltage at the end of the slow-varying period.

Incrementally preheating and lighting system for a discharge lamp

Abstract: A lighting system for a fluorescent lamp includes an inverter circuit having a pair of outputs between which is connected a resonant circuit of an inductor and a capacitor in series, with the discharge lamp connected in parallel with the capacitor. An inversely frequency dependent voltage is applied between the lamp electrodes according to a predefined resonance characteristic. During a preheat period, which precedes a lightup period during which the lamp is to be lit up with the commencement of an electric discharge between the lamp electrodes, the voltage is made lower in the first half than in the second, thereby averting the sudden flow of a large preheating current through the filamentary lamp electrodes.

Simulation of streamer discharges as finitely conducting channels

Abstract: This paper presents a two-dimensional simulation of positive streamers in air at atmospheric pressure in a quasi-uniform electric field. A streamer is assumed to consist of a hemispherical tip and a finitely conducting cylindrical channel with a constant axial potential gradient. The model predicts that E/sub g//spl sim/450 kV/m and the radius is r/spl sim/50 /spl mu/m in air at standard atmospheric conditions. Moreover, the estimated number of positive ions in the streamer head of stably propagating streamers, agrees with estimations based on more advanced streamer models. The model is used to predict the behavior of streamers in electrical discharges in a semiuniform electric field and good agreement is found between experiment and theory. The computer simulation of such a simplistic model could be applied to predict the behavior of streamer discharges in complex electrode arrangements, including dielectric surfaces.