Arc Core Research Articles

A study of three-dimensional natural convection in high-pressure mercury lamps—I. Parametric variations with horizontal mounting

A three-dimensional numerical model utilizing curvilinear coordinates and an efficient solution method has been used to investigate natural convection in horizontal, high-pressure mercury-vapor arctubes. For horizontal arcs, convection velocities are predominantly transverse to the arc axis. The associated upward bowing of the arc column results in non-uniform heating of the quartz wall which can substantially degrade the performance of the modern horizontal metal halide lamp. This investigation shows how the design parameters of the arctube, such as the mercury pressure, the curvature of the curved arctube, the offset electrode distance, and the electrode insertion length affect the temperature distribution in the arctube. Qualitatively, a downward curved arctube can move the hot arc core downward, and offset electrodes can improve temperatures near the ends of the arctube. The evolution of the design improvement of a 400 W high-pressure mercury lamp with the aim of centering the arc and having isotherms conform to the wall is achieved through better quantitative understanding of the transport characteristics.

Time dependence of nonequilibrium in the Hg resonance level in an AC arc plasma

The time-dependent behaviour of the degree of excitation non-equilibrium in the low lying 6 3P 1 resonance level of mercury at the arc core during half a period of a 50-Hz ac mercury arc plasma has been experimentally determined. The population density of this levels is less than the calculated one assuming equilibrium conditions and it exhibits a modulation out of phase with that of the high lying 6 3D 2 level and in phase with the electron temperature.

Optical diagnostics of SF6 high-current discharges

Results of optical investigations of SF6 high-current arc plasmas are presented. The experimental arrangement allowed measurements at arc currents up to 2.6 kA and at discharge pressures up to 100 kPa. The dependence of the electron density of the arc plasma on these parameters and the laser wavelength were determined using a Michelson interferometer and a Mach-Zehnder interferometer. Besides these measurements, the temperature in the arc core was determined using spectroscopic methods and the diameter of the arc was measured using an image converter camera. The results of the measurements were compared with calculated data supposing local thermodynamic equilibrium. It can be shown that there is a good agreement between the experimental and theoretical results and those of other authors.

Impact of anode evaporation on the anode region of a high-intensity argon arc

Experimental studies of a free-burning, high-intensity argon arc operated at 800 Torr with a solid, molten, or resolidified copper anode demonstrate that the cathode region is not affected by Cu vapor from the anode. Also Cu vapor concentrations in the arc core (beyond 1 mm from the anode surface) are negligible. In contrast, there is a strong effect of the Cu vapor on the anode region of the arc. The arc fringes become electrically conducting due to the presence of Cu vapor, resulting in a flattening of the current density distribution and a corresponding drop of the temperature in the arc core. At the same time, the overall arc voltage shows a slight drop (<1 V). In the case of the resolidified anode, the overall arc voltage increases, which seems to be associated with the distribution of the stagnation flow in front of the anode due to a dip in the center of the anode.

Two-temperature modeling of the free-burning, high-intensity arc

In this paper a two-temperature model (Te &amp;gt;Th) is applied to a free-burning, high-intensity, atmospheric pressure argon arc. With appropriate boundary conditions and nonequilibrium thermodynamic and transport properties, solutions of the conservation equations are obtained for the entire arc, except for the electrode sheath regions. Significant temperature discrepancies between electrons and heavy particles are found in the arc fringes. The elevated electron temperatures in the arc fringes lead to a rearrangement of the current density distribution which, in turn, has some effect on the temperature as well as on the velocity field in the arc core. Comparisons of the results of this study with spectrometric temperature measurements show better agreement than with results based on a one-temperature model.

Optical Observation of Self-Gas-Flow in GCB

The generation of self gas flow in a model SF6 gas circuit breaker without puffer action is observed by high speed photography, shadow photography using a Q-switch ruby laser and time-and space-resolved spectrography. The model breaker is specially designed for observation of gas flow in all the spaces from the cylinder to the exhaust space. The results of the observations are Icompared with a free burning arc and show that the self gas flow to the arc in the breaker reduces the diameter of the arc, and raises the temperature of the arc core. This model breaker interrupts the current of 3 kArms with a transient recovery voltage of 2 kV/μsec, though the pressure rise of the cylinder is less than 0.3 x l05 Pa.

Studies of the anode region of a high-intensity argon arc

This paper is concerned with experimental and analytical/numerical studies of the anode region of an atmospheric pressure argon arc in a current range from 100 to 300 A. The arc arrangement allows unobstructed viewing of the entire anode region, including the anode itself, and it is also suitable for simulating short as well as long arcs. Depending on the flow situation in the anode region, two different types of stable arc roots are observed. The diffuse anode arc root, characterized by a strong flow impinging on the anode surface, is well known from free-burning, short arcs. The second type reveals a more or less vevere constriction in front of the anode, caused by the entrainment of gas into the arc, resulting in an anode jet. Measurements of the induced flow at the cathode of such an arc show a linear increase of the induced mass flow rate with increasing current. This correlation can be confirmed by a simple analysis. A fast-scanning, computer-controlled system has been used for spectrometric measurements of the temperature distribution for both modes of anode arc roots, assuming local thermodynamic equilibrium (LTE) in the arc. The maximum temperatures in the arc core compare favorably with calculated temperature distributions of the constricted mode. The calculated isotherms, however, show a substantial shift which is probably due to the chosen boundary conditions at the end of the constrictor tube.

Dynamic Measurements of the Current Distribution in the Foot of an ARC Propagating Along the Surface of an Electrotype

Measurements of the arc current distribution obtained for pertinent flashover conditions are reported. A new experimental technique for measuring the distribution of the current in the foot of the arc as it progresses at the surface of an electrolyte is described. Results indicate a sharp current density gradient at the forward edge of the arc foot and a low gradient in a region extending a few centimeters behind. These results are compatible with conformal mapping of the current streamlines, provided that account be taken of a current in the electrolyte which flows parallel to the arc current. This parallel current was measured, in the electrolyte throughout the entire length of the arc during flashover. A propagation model is also proposed which stresses the importance of this asymmetrical shape of the current distribution in the continuous regeneration of the arc channel in the forward direction. An average current density of ~2 A/cm2 was measured, although a peak current density of ~30A/cm2 was measured in the arc core. These results and the formulation of the proposed model are compared with those reported in the literature.

Experiments on Arc Perturbation in Turbulent Gas Flow

AbstractElectric arcs burning in a strong, turbulent, axial nitrogen gas flow are studied. Time‐resolving (framing) picture series of the arc and its deformations are taken through the quartz tube channel wall. Individual perturbations like kinks exist under strong, turbulent flow conditions. They move with constant acceleration in the direction of the cold gas flow. The temperature of the arc core is disturbed at the position of these disturbances, too. This shows up most distinctly, if the decay of the arc after short‐circuiting is studied, as has been done additionally.

Two-temperature modeling of an arc plasma reactor

In this paper a two-temperature plasma model is established and applied to the injection of cold gases into an atmospheric-pressure, high-intensity argon arc. The required nonequilibrium plasma composition and the non-equilibrium transport properties are also calculated. The results show that the arc becomes constricted at the location of gas injection due to thermal and fluid dynamic effects of the injected cold flow. Enhanced Joule heating in the constricted arc path raises the electron as well as the heavy-particle temperatures. This temperature increase resists, via secondary effects, the penetration of the cold gas into the hot arc core which behaves more or less as a “solid body” as far as the injected flow is concerned. The temperature discrepancy between electrons and heavy particles is most severe at the location of cold flow injection, a finding which may have important consequences on chemical reactions in an arc plasma reactor.

Investigations on the radially free full circle arc

An argon arc, burning between two horizontal, plane-parallel, insulating plates, is bent circularily by an external and its own magnetic field. Except for the small electrode zone, one gets a stationary radially free full circle arc for experimental investigations of magnetohydrodynamic and thermodynamic effects under well defined conditions. The local temperature distributions in the arc cross-section are detected spectroscopically as functions of the arc current and the arc radius or curvature, respectively. By means of the basic equations of conservation of energy, mass, and charge and the known transport properties of argon at atmospheric pressure, the mass flow field in the arc is evaluated. In the arc core it follows the direction of the Lorentz force radially outward counter-balancing the tendency of the curved arc to move inwards thermodynamically. Due to the symmetry to the centre-plane of the arc chamber and the vanishing net flow for the whole system, the gas flow has to stream back in the cold outer arc zones, thereby forming a double whirl. By reasons of the experimental arrangement even a quadruple whirl occurs. Additionally the evaluation yields the specific radiationu(T) of argon being compared with results in the recent literature.

Two-Temperature Modeling of the Anode Contraction Region of High-Intensity Arcs

In this paper, an analytical model for a two-temperature plasma (Te > Tg) is established which is suitable for dealing with arcflow interactions induced by the arc itself. This model is applied to the anode contraction region of high-intensity argon arcs taking the interaction of anode and cathode jets close to the anode into account. The complete set of conservation equations describing the mass, charge, momentum, and energy transport of a two-temperature plasma with temperature-dependent transport properties is solved numerically by an interative finite-difference method using appropriate boundary conditions. Results for an atmospheric-pressure argon arc indicate that the temperature discrepancy between electrons and heavy particles is very pronounced in the arc fringes and in the regions close to the anode, while the departure from kinetic equilibrium becomes insignificant in regions in which the temperature exceeds 12 000 K (i.e., in the arc core). The computed temperature fields of the heavy particles in the anode contraction region resemble the observed arc appearance which clearly shows the interaction of anode and cathode jets in front of the anode.

Investigation on Gas Flow of Puffer-Type Gas Circuit Breaker Based on Observation of Arc and Pressure Measurement

Energy balance of gas blasted arc was investigated by arc observation, and power loss radially conducted from arc core was evaluated. Based on the experiment, a method which gives better approximation of gas blasted arc was shown.

Comments on ’’Optical analysis of the interface between a moving arc and air at atmospheric pressure’’

Recent photographic and interferometric measurements, obtained by Mai et al., on an arc driven in air between parallel electrodes by a transverse magnetic field are examined. The interpretation, proposed by Mai, based on a continuous growth of a transition region in front of the moving arc is shown to be highly questionable. By contrast, the generally accepted existence of a double-vortex flow in the arc core is shown to account for the results.

Measurement of the temperature and flow fields of the magnetically stabilized cross-flow N2 arc

A straight, steady-state cross-flow arc is burning in an N2 wind tunnel. The arc is held in position by the balance of the Lorentz forces produced by an external magnetic field perpendicular to the arc axis and by the viscous forces of the gas flow acting on the arc column. The temperature field in the discharge is determined spectroscopically using the radiation of N I lines. Because of the lack of rotational symmetry an inversion method developed by Maldonado was used to determine the local emission coefficient from the measured integrated spectral intensity distributions across the arc in various directions. For known local temperature the mass flow field inside the arc may be evaluated from the convective term of the energy equation and the continuity equation. This is done by expanding the terms of these two equations around the point of the temperature maximum into Fourier-Taylor series and determining coefficients of the same order and power. The solution of the resulting set of algebraic equations yields the unknown coefficients of the mass flow. The flow field obtained by these calculations shows a relatively strong counterflow through the arc core. In the region for which the series expansion holds a partial structure pertaining to a closed double vortex can be recognized.

Study of the Arc and of the Interaction between Arc and Operating Mechanism in SF6 Puffer Breakers

The article deals with studies of the arcing performance of SF6 puffer breakers at currents of up to 80 kA and voltages of up to 200 kV, using an interrupter unit fitted with viewing windows. The studies are mainly concerned with the behavior of the arc at current zero and with restrike phenomena under various conditions. In addition to measurements of the electrical variables and the pressure variation, the tests cover the use of high-speed cameras, spectroscopic diagnostic methods, and schlieren methods. The density fields and flow fields derived from the latter are used to optimize the gas flow. On the basis of the breaker data and those of its operating mechanism a method for computing the essential variables, e.g., pressure, gas flow, back pressure, and contact travel, is developed. The variation of these parameters as a function of the interrupter data for various currents and with due allowance for the interaction between the arc and the operating mechanism must be known if the breaker design is to be optimized. The method uses simplified equations for the gas flow and the arc. The relationship between the gas data (e. g., density, enthalpy, speed of sound, electrical conductivity, and dielectric strength) and the temperature is taken into account by using approximation functions. The temperature of the arc core is matched to the test results.

Optical analysis of the interface between a moving arc and air at atmospheric pressure

The passage of a short magnetically driven arc in air has been recorded simultaneously by means of differential interferometry and phase-contrast photography. Correlation of these results with conventional high-speed photographs reveals an abrupt change in refractive index in the gas preceding the visibly luminous region of the subsonic arc. Midchannel flow calculations and scaling trends indicate the refractive change is due to a front of high-pressure air sustained primarily by molecular heat conduction from the arc core.

Gas blast nozzle flows with arc heating

The equations describing gas flow surrounding an electric arc in a converging-diverging nozzle are derived for the case where the gas temperature changes as a function of distance along the nozzle. It is shown that analytic solutions can be obtained if the temperature varies exponentially with the local flow Mach number. Only small temperature increases are needed near the nozzle throat to substantially modify the flow conditions from the usual adiabatic expansion. Under heating conditions which produce a strong axial temperature rise the theory predicts that the sonic point will move a considerable distance down stream from the nozzle throat. For short nozzles containing high current arcs, such as those used in gas blast circuit-breakers, this effect may be sufficient to restrict the entire flow outside the arc core to subsonic values.

Axial and radial heat transport in a high-temperature SF6 arc

Measured radial temperature profiles and electric fields in high-current (1-17 kA), supersonic (Mach 1.5) SF6 interrupter arcs are used to evaluate the axial (enthalpy and kinetic energy flux) and radial (conduction and radiation) components of the energy balance. The input power in the 20 mm upstream arc section considered varies from 0.5 to 6 MW and the copper impurity concentration from <or=2 to 20% in this current range. Axial losses are a maximum of 75% of the input at 9 kA. A significant fraction of the input at 17 kA is lost by optically-thin impurity line radiation. At 1 kA only 20% of the input can be attributed to convection and only approximately 1% to laminar thermal conduction. The low-current temperature profiles are characteristic of radiation-loss-dominated arcs. Evaluation of the effective radiation conductivity yields repeatable peaks at 13500 and 18500K corresponding to maximum emission of S and F atomic resonance line radiation. Resonance radiation escaping from the arc core is absorbed in the thermal zone by molecular species.

Measurement of density and temperature in an orifice arc

A method for measuring the species density and temperature in a high-current arc column subjected to a steep axial pressure gradient is described. The method has been used to determine the temperature variation in the thermal region surrounding the arc core so that estimates can be made, together with the additional knowledge of the gas velocity, of the axial enthalpy flow at various axial arc stations. These results have been used to confirm energy and momentum conservation for the arcing environment by Malghan (1975).