Steady Arc Research Articles

Low current arc modes of short length and time: a review

Until the middle of the 20th century the electric arc was known solely as a steady, self sustaining gas discharge phenomenon requiring certain minimum values of current and voltage, depending on the electrode material and the gas environment. Special investigations on material transfer in contacts switching low direct currents, however, revealed step by step that there were certain till then unknown unstable arc modes appearing in extremely short electrode gaps only but requiring minimum current and voltage values distinctly lower than those of the classical steady arc discharge in air. Low current break arcs have to pass one or more of these transient modes whether or not they may eventually attain the steady gas arc mode.

Production of fullerenes and single-wall carbon nanotubes by high-temperature pulsed arc discharge

Fullerenes and single-wall carbon nanotubes (SWNTs) have been produced for the first time by the high-temperature pulsed arc-discharge technique, which has developed in this laboratory. Fullerenes are identified quantitatively by high-performance liquid chromatography (HPLC), and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations reveal a significant amount of production of bundles of SWNTs in soot. The pulse arc production of fullerenes and SWNTs favors the high-temperature (⩾1000 °C), long pulses (⩾1 ms) and a heavy rare gas such as Ar or Kr as a buffer gas. We have found that fullerenes and SWNTs have complementary relationships in their early stage of production. The details of the pulsed arc discharge have been obtained by observing the transition from the pulsed arc discharge to the steady arc discharge while increasing the pulse width.

Investigation of the properties of an anodic vacuum arc

An anodic vacuum arc deposition device is described that provides a steady arc discharge obtained after ignition in vacuum, which is sustained by metal vapor emitted at a consumable anode. The anode is formed by winding evaporent wire around a tungsten anode; Al was used for evaporation. The preliminary properties of Al arc plasma generated by the anodic vacuum arc are investigated in the current range between 15 and 40 A. Electron temperatures were measured in the range 0.4–0.8 eV and electron density within 10 15–10 17/m 3 at 25 A arc current. Trace anodic element contents in the coatings deposited using two different methods of ignition were investigated with Rutherford Back-scattering Spectrometry. A suitable method of ignition is discussed with respect to the W content in the deposited films.

Experimental observations of steady anodic vacuum arcs with thermionic cathodes

Stationary plasma discharges have been investigated in a high vacuum ambient (background gas pressure <10/sup -2/ Pa), with an externally heated cathode and a consumable hot evaporating anode. With various anode materials like chromium or copper, and electrode separations between 0.5 and 3 mm, the nonself-sustained discharge operates with DC arc currents in the range of 220 A. The waveform of the arc voltage is strongly influenced by the magnetic field of the cathode heating current, and arc voltages between a minimum of 3 V and a maximum exceeding 100 V have been observed. The voltage-current characteristics (V/sub CC/) and the influence of the electrode separation have been measured separately for the minimum and the maximum of the arc voltages and show a different behavior. The metal plasma expands into the ambient vacuum toward the walls of the vacuum vessel and offers a macroparticle free deposition source of thin films. The arc voltage can be varied by external manipulations of the arc discharge, and the mean ion energy of the expanding metal plasma shows a linear dependence of the mean arc voltage.

High-pressure hypervelocity electrothermal wind-tunnel performance study and subscale tests

The feasibility of a Mach 10 to 20, high pressure electrothermal wind tunnel was assessed. A heater based on a continuous high power electric arc discharge capable of heating air to temperatures above 10,000 K and pressures of 15,000 atm is the key element of this wind tunnel. Results of analytical study indicate that the facility is capable of simulation conditions suitable for hypervelocity airbreathing propulsion testing up to Mach 16. In this case simulation was limited by pressure containment, high nozzle throat heat flux rates, and chemical freezing in the nozzle. The high total pressure capability improved the recombination chemistry in the facility nozzle as chemical equilibrium prevailed to the freezing point. Steady arc discharges were observed with liquid nitrogen flowing into the arc chamber during tests based on the two millisecond test facility. The measured steady pressure in the arc chamber was 4559 psi, which is two times greater than maximum total pressure obtainable in conventional arc heaters.

Numerical study of low-current steady arcs

The development of a high-efficiency CW YLF laser doped with Er,Tm,Ho: and featuring a strongly focusing resonator that collects a high density of pump power on the active crystal is described. The emission is investigated at 2.06 microns and a tuning range both at liquid-nitrogen (77 K) and at dry-ice (210 K) temperature. The noise characteristics and the long-term power stability of the laser is studied with an eye to employing this source for high-resolution spectroscopy in the 2-micron wavelength region. The detection of several absorption lines of NH3 at low pressure is described. The output power of the laser as a function of the power impinging on the crystal for different transmission of the output mirror is illustrated. The best result obtained is 1.46 W output for 3.2 W of argon pump. The minimum threshold achieved is 3.5 mW with a 1-percent transmission mirror. It is concluded that it is possible to develop a highly efficient Ho:YLF laser featuring low noise and sufficient tunability for high-resolution spectroscopy in the 2-micron region.

Electromagnetic interference from discharge phenomena of electric contacts

The electromagnetic interference (EMI) from steady arc and showering arc electrical discharges was investigated. The experiment was carried out on Ag, Pd, and Ag-Pd alloy contacts under several circuit current conditions. Radiated noise levels were measured at frequencies up to 200 MHz. Experimental results show that the EMI levels from a steady arc, which is generally the phenomenon of the break of a noninductive circuit, are dependent on the composition of contact materials. The EMI levels from a showering arc, which is generally the phenomenon of the break of an inductive circuit, are independent of the composition of contact materials. The EMI from a steady arc is roughly inversely proportional to the frequency in the 0.1-10.0-MHz range, whereas in the 25-200-MHz range, the maximum level of EMI appears at about 70 MHz. The frequency characteristics of EMI from a showering arc are similar to those from a steady arc. The EMIs from these arcs exceed, in part, statutory limits.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Influence of arc discharge types on contact resistance of Ag‐Pd alloys

AbstractDifferent types of arc discharge, that is, steady arc, showering arc or no discharge (initial arc), occur at the break of contacts. These arcs are considered to cause not only contact erosion, but also to affect contact resistance. In this paper, the relation between arc‐discharge types and contact resistance is investigated on Ag, Pd and some Ag‐Pd alloy contacts with Pd content of 30, 50 and 70 wt% by using the automatic data acquisition system of newly developed contact resistance. The following can be made clear. Under no discharge and showering arc discharge, contact resistance is always low at any Pd content. However, under steady arc discharge, contact resistances of the contacts with Pd content more than 50 wt% remain low and those of Ag and of AgPd30 become high. From the results of the approximation of distributions of the measured contact resistances with Weibull distribution function, it can be stated that the calculated location parameter RO gives the approximate value of constriction resistance and the scale parameter Rα gives that of film resistance. On the other hand, the observation of contact surfaces reveals the relation between contact resistance and surface conditions. Also, the differences of arc duration or discharge voltage waveforms according to Pd content are recognized. They are considered to influence surface conditions or contact resistance. A physical model that describes these phenomena is proposed.

The anodic vacuum arc. I. Basic construction and phenomenology

A new type of vacuum arc is described, the anodic vacuum arc at low currents. This arc discharge is ignited in vacuum and generates a pure metal vapor plasma by evaporating anodic material, which continuously sustains the discharge. By proper construction of the electrodes a steady arc can be maintained at low currents (20–40 A). Basic electrode phenomena are the formation of cathode and anode spots. Metallic coatings produced by means of the anodic vacuum arc show promising features: the coatings are homogeneous, the deposition rates are high (8 nm/s for a 0.7-kW Al arc), and the thermal stress of the substrates being coated is low.

Influence of arc discharge types on contact resistance

AbstractThe state of the breaking contact can be steady arc, showering arc or no‐discharge depending on the circuit condition, even if the same current is cut off. These types of discharge are concerned not only with the wear of the contact, but also with the contact resistance. In this paper, using the automatic measuring instrument for contact resistance developed by the authors, the relation between types of arc discharge and the contact resistance is examined, mostly for the silver and palladium contacts. As a result, it is seen that the silver contact in steady arc condition has a fairly high contact resistance (50 ˜ 100 m Ω) with a large variance. On the other hand, the palladium contact in steady arc condition and the palladium and silver contacts in showering arc condition are relatively stable with low contact resistance. These properties are related to the erosion of contact surface by the arc. It is seen from the observation of surface by SEM that the contact resistance of the silver contact in steady arc is affected greatly by the surface film, while a metallic contact is maintained in the palladium contact. In the showering arc condition, both silver and palladium contacts maintain the metallic contact, with the measured contact resistance being in good agreement with the calculation by the theory of spreading resistance.

The computation of steady state arcs with mild nozzle — Wall ablation

The computation of steady state arcs with mild nozzle — Wall ablation

The computation of steady state arcs in nozzle flow

The computation of steady state arcs in nozzle flow

Arc damage of interelectrode insulators in MHD generators

The damage to interelectrode insulators on the anode wall of an MHD generator, resulting from magnetically driven arcs, has been studied experimentally and analytically. Recession rates of about 1-3 mm/s and damage widths of about 2-4 mm were measured for alumina, boron-nitride, and magnesia insulators at arc currents ranging from 7 to 83 A and at magnetic fields up to 1 T. The recession rate and damage width were affected by both the magnetic body force (IB) and the power dissipated in the arc. In general, boron-nitride performed best and alumina worst. A simple model of the steady arc and the heat transfer from the insulator predicted the damage parameters within a factor of 2. Damage from unsteady arcing can also occur and has not been addressed in detail. The relationship of the fault arc voltage-current characteristics to the width and spacing of electrode sections required for an MHD generator is presented.

The computation of steady state arcs with mild nozzle - wall ablation

The computation of steady state arcs with mild nozzle - wall ablation

Analysis of the wave forms of breaking arc of electrical contacts in air

The breaking arc wave forms have been observed by means of an oscilloscope in the range of applied voltages from 20 to 280 V and of amperages from 0.3 to 50 A for both dc and ac circuits of noninductive and inductive loads; the materials of contacts examined are silver, tungsten, and carbon. The equations to give the length, voltage, and current of the breaking arc are derived in terms of the applied voltage and current, minimum voltage and current necessary for a steady arc, breaking phase angle, phase angle between the applied voltage and current, angular velocity, and finally separating speed. The equations are found to be applicable for all materials irrespective of thermionic emission type or field emission (T-F emission) type.

Scaling Laws for Gas-Blast Circuit-Breaker Arcs during the High Current Phase

A steady state nozzle arc model based on the boundary layer integral method is established and scaling laws are derived. For affinely related nozzles, the solution is uniquely determined by a nozzle coefficient N, which is related to the stagnation conditions, the arc current, and the dimensions of the nozzle. Tests have been performed on nozzle arcs in air using two geometricaly similar nozzles at three stagnation pressures. A good agreement between theory and experiment is obtained which indicates that circuit-breaker arcs can be scaled. To avoid nozzle clogging, the nominal current density at the throat (I/At) should not exceed the highest permissible nominal current density at the throat. For all affinely related nozzles, this upper limit of current density at the throat is proportional to ?p0?t, where p0 is the stagnation pressure and Zt the distance of the throat from the nozzle entrance. The overal arc voltage exhibits the precurrent-zero static behavior as indicated by Browne's composite arc model.

The computation of steady state arcs in nozzle flow

The computation of steady state arcs in nozzle flow

Auroral NO concentrations?

Auroral NO chemistry is studied to determine the limits on [NO] and its production rate in steady auroral arcs. We conclude conservatively that the NO concentration cannot exceed 0.1[O2]. The precise value of this upper limit depends very sensitively on the relative yields of N(²D) and N(4S) in the reactions that are the major auroral sources of N atoms, and on the basis of the requirements of mid-latitude models for odd nitrogen, a value of 0.03[O2] is estimated. Plausible auroral [NO] enhancements are of the order of (3–6) × 108 cm−3 after 10³ s and (1–4) × 109 cm−3 after 104 for a steady IBC 2+ arc.

Miscellaneous arc devices

Abstract Steady arc discharges at about normal pressure exposed to magnetic fields and flows are studied. In particular, a cylindrical, wall stabilized arc and a free burning arc between fixed electrodes are considered and the different modes of operation are investigated. In a second section the transition of a wall stabilized straight arc into a helical shaped discharge is discussed. Finally phenomena occurring in an arc column under influence of a longitudinal magnetic field are reviewed.

Integral methods of analysing electric arcs: II. Examples

Two problems are considered in the present paper as examples of the integral method formulated in part I (the preceding paper). The first concerns arcs in uniform flow, and it is shown that the only form of steady solution, if the conductance shape factor is taken to be a function of power level, is the fully developed arc. A known solution of the full differential equations provides a test of the adequacy of the result. Free recovery is briefly discussed. The second problem concerns steady arcs in nozzles. With the assumptions of constant shape factors and negligible radiation, a simple model is derived which provides insight into behaviour as a nozzle-blocking condition is approached.