Air Arc Research Articles

Arc Cooling Mechanisms in a Model Circuit Breaker

Axially blown electric arcs in a model circuit breaker are investigated by electrical measurements and fast imaging with a high-speed camera for visualizing the arc structure. Parameters for a dynamic conductance model (known as the “black-box model” in the arc literature) are extracted from the electrical measurements for currents between a few tens of amperes and a few kiloamperes. The model is used for the prediction of the conductance-dependent cooling power and arc relaxation time, as well as the voltage-current characteristics of the arcs in our system. In order to work out the relevance of the different cooling mechanisms, an alternative and more physically based dynamic model for axially blown arcs is incorporated. It turns out that convective cooling predominates turbulent heat conduction and radiation cooling in the region of validity of the model. The result is consistent with the observed strong dependence of the cooling power on the flow conditions that are controlled by the blow-gas pressure and the geometry. Furthermore, the comparison between air and SF6 arcs indicates a considerable dependence of the conductance-cooling relation on the gas type.

Power balance at a copper electrode submitted to a non-stationary electric arc in air. Measurement of the amount of liquid metal created and modeling of the heating

In this paper, a measurement of the total amount of liquid metal created by an electric arc in air is made for copper anodes and cathodes. This amount is compared with usual erosion for the same experimental conditions for various values of the electrode gap (3–10 mm). It appears that the amount of liquid is ten times greater than the erosion for copper cathodes and may be fifty times greater for copper anodes. A method using experimental results and a numerical simulation of the thermal phenomena occurring in the electrode during the arc heating is then used to assess the characteristics of the power flux brought by the electric arc to the copper electrodes. It was found that about 80% of the energy received by the electrodes was conducted in the solid phase and that about 20% of this energy was used to melt or vaporize the electrode material. The power surface density brought to the electrodes was found in the range 4.6 × 10 8 –1.9 × 10 9 W/m 2 for the cathode and in the range 6.4 × 10 8 –1.1 × 10 10 W/m 2 for the anode.

Multi-time electron density imaging over arc discharges around the current zero point

Framing Shack–Hartmann type laser wavefront sensors were developed for obtaining time evolutions of two-dimensional electron density images over single SF6 and air arc discharges with decaying arc currents. An SF6 arc discharge showed initial drastic shrinking of the diameter of the filamentary arc column and subsequent rapid electron density reduction from 1023m−3 to less than 1021m−3 around the point of arc extinction. On the other hand, an atmospheric arc discharge around the current zero had almost constant electron densities of 1021–22 m−3 regardless of the presence or absence of the arc current. A current-basis study showed that the observed constant electron densities could be residual ones surrounding the arc column with electron densities of 1020 m−3 and contributing less to the arc current.

Experimental study of opening arcs in air of AgNi contacts

In the area of DC, power supply is made for resistive circuits which can contain elements with an inductive behaviour. This latest has an important effect on the transition phase that is favourable to the appearance of an electrical arc. The objective of this work is to have deeper knowledge on the arc’s characteristics in the air. These characteristics are arc duration, arc energy, mass loss and surface degradation. Arc duration and mass loss increase with decrease of opening speed and increase of current. Mass loss for an inductive load is almost ten times greater than for a resistive one. The microscopic analyses show a more intense degradation with decreasing opening speed, due to a higher arc density. The inductance’s effect was clearly observed on arc energy, on mass transfer and on arc duration. It is necessary to consider these effects in the contacts’ design in DC to insure safety and reliability.

Characteristics of DC discharge in a wire-cylinder configuration at high ambient temperatures

Abstract In the present work, the characteristics of direct-current (DC) discharge in a wire-cylinder configuration at an ambient temperature range of 350–850 °C were studied by analyzing photographs of the discharging process and the corresponding V – I characteristics, with the aim of facilitating the application of plasma technology in the fields of energy and the environment. The influences of the ambient temperature, the inter-electrode gap, the gas medium and the cathode material on the DC discharge were investigated. The corona-onset threshold voltage (COTV) and the spark-breakdown threshold voltage (SBTV) decrease as the ambient temperature increases, and the SBTV decreases more rapidly. Increasing the inter-electrode gap enlarges the difference between the SBTV and the COTV. After spark breakdown, in an air atmosphere, glow discharge is more likely to take place under conditions of high ambient temperatures or small inter-electrode gaps. The values of the SBTV in different atmospheres have the following relation: air ≈ O 2 > CO 2 . At an ambient temperature range of 350–850 °C and in an atmosphere of N 2 , glow discharge and arc discharge occur successively as the output voltage of the power supply is increased, while in an atmosphere of O 2 and CO 2 , only corona and arc discharge are successively observed. In an air atmosphere, when the inter-electrode gap is 29 mm, corona, glow and arc discharge occur successively with increasing output voltage when the ambient temperature is 850 °C, while only corona and arc discharge appear when the temperature is 350–750 °C. When the inter-electrode gap is 5 mm in an air atmosphere, corona, glow and arc discharge occur successively in an ambient temperature range of 350–850 °C. The cathode material has a minor influence on the COTV and a more significant influence on the SBTV. In a device using a cathode with a low work function, the SBTV is low, and the power to maintain arc discharge is small.

Low-cost synthesis of single-walled carbon nanotubes by low-pressure air arc discharge

We have demonstrated firstly an easy and low-cost approach to synthesize single-walled carbon nanotubes (SWCNTs) by direct current arc discharge in low-pressure air with Ni/Y as catalysts. Experimental results show that the as-synthesized SWCNT diameter is in the range of 1.29–1.62nm and the SWCNTs show higher oxidization temperature than those synthesized by helium arc discharge. Our findings support that oxygen in air is transformed to CO during the arc discharge process, resulting in the fact that the real buffer gas in our experiments is the N2–CO mixed gas. This synthesis strategy enables the cost down of SWCNTs and paves the way toward large-scale applications of SWCNTs.1

Characteristics of the Arc Voltage of a High‐Current Air Arc in a Sealed Chamber

SUMMARYThe effect of the arc voltage on various factors of design and control was investigated for high currents in order to develop design guidelines for circuit breakers. In this study, the dependence on such factors, namely, the current, arc length, electrode surface area, and internal pressure of the arc voltage, was evaluated quantitatively. As a result of the evaluations, it was estimated that the arc voltage near the electrode surface rises linearly with the arc current and the power −0.8 of the surface area, and that the voltage in the arc column rises as the 0.3 power of the pressure increase. We confirmed the validity of the estimated voltage characteristics by comparison with the generated voltage in an actual arc‐extinction chamber. The characteristics of the estimated voltage can provide effective guidelines for the design of arc extinguishing chambers. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(1): 34–42, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22487

Influence of the Splitter Plates on the High Current Air Arc in Low Voltage Circuit Breaker

Influence of the Splitter Plates on the High Current Air Arc in Low Voltage Circuit Breaker

Characteristics of Arc Voltage for High-Current Air Arc under Arrangement of Deion Plates and Approach to Improving Availability of the Plates

In this study, (i) effect of deion plates on arc voltage and (ii) appropriate arrangement of the plates were investigated in order to develop a design guide of a circuit breaker which is able to interrupt fault current (> several kA). As for evaluation (i), improved effect on arc voltage under arrangement of the plates were evaluated quantitatively in association between arc voltage and the design factors which are current, arc length, internal pressure and number of the used plates. As the result, it was found that arc voltage rises 19.2V by number of split arc between the plates and electrical field in arc rises about 3V/mm under high internal pressure above 0.2MPa-g. Experimental formula constituted by the design factors for estimation of arc voltage was developed on the basis of the improved effect on the voltage. Since the formula is able to estimate actual arc voltage with a margin of error within about 7%, it would be provided as effective guidelines to design arc extinguishing chambers. As for evaluation (ii), dependences of the availability of used plates on electromagnetic force to drive arc were evaluated. As the result, it is found that the plates are used effectively by exerting above a certain electromagnetic force (e. g., above 5N in case of 5kA) on the arc between the electrode and the plate. Therefore, the improvement of magnetic design near the electrodes, especially the movable electrode, or the arranging enough space to drive the arc between the electrode and the plate would be improved availability of the used plates.

Discrimination of arcing faults on overhead transmission lines for single-pole auto-reclosure

SUMMARY To block auto-reclosing operation for permanent earth faults on extra-high-voltage transmission lines, an accurate numerical algorithm is developed in this paper. The earth fault location and its nature (arcing or arc-less) are estimated, only using the sequence quantities of the local terminal and their harmonics. The proposed algorithm calculates the amplitude of arc voltage and compares it with a given threshold value; then, decision is made if it is transient or not. A square wave arc model is considered to represent the long electric arc in the free air. One main contribution of the algorithm is its independence from the remote terminal information such as phase difference and infeed current. The successful simulation results using the square wave and dynamic arc models show that this simple and powerful algorithm can be effectively utilized for implementing a single-pole auto-reclosing scheme. Copyright © 2012 John Wiley & Sons, Ltd.

Assessment of the Power Balance at a Copper Cathode Submitted to an Electric Arc by Surface Temperature Measurements and Numerical Modelling

The aim of this work is to improve the understanding of the heating of copper cathodes under the action of a nonstationary electric arc in air. An experimental method is proposed for the measurement of the surface temperature distribution just after a very fast arc-controlled arc extinction. The arc current intensity is about 60-70 A, and the arc duration is in the range of 2.5-5 ms. Different kinds of surface temperature distributions have been observed depending on the arc root behavior. The measurement of the temperature decrease after the arc extinction was used to estimate the cathode surface temperature just at the moment of arc extinction. Two-dimensional thermal modeling taking into account phase changes is used to estimate the power balance at the cathode surface and to propose a second estimation of the surface temperature at the point of arc extinction. The comparisons between experimental results and thermal modeling lead in the present experimental conditions to a volt equivalent at the cathode in the range 6.7-10.7 V, to a surface power density in the range0.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> - 2.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> W/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and to a maximum surface temperature in the range 850°C-1300 °C .

Numerical Study on Arc Plasma Behavior During Arc Commutation Process in Direct Current Circuit Breaker

This paper focuses on the numerical investigation of arc plasma behavior during arc commutation process in a medium-voltage direct current circuit breaker (DCCB) contact system. A three-dimensional magneto-hydrodynamic (MHD) model of air arc plasma in the contact system of a DCCB is developed, based on commercial software FLUENT. Coupled electromagnetic and gas dynamic interactions are considered as usual, and a thin layer of nonlinear electrical resistance elements is used to represent the voltage drop of plasma sheath and the formation of new arc root. The distributions of pressure, temperature, gas flow and current density of arc plasma in arc region are calculated. The simulation results indicate that the pressure distribution related to the contact system has a strong effect on the arc commutation process, arising from the change of electrical conductivity in the arc root region. In DCCB contact system, the pressure of arc root region will be concentrated and higher if the space above the moving contact is enclosed, which is not good for arc root commutation. However, when the region is opened, the pressure distribution would be lower and more evenly, which is favorable for the arc root commutation.

Magnetic field influence on pulsed air arc anode mass loss

Anode mass loss was studied in pulsed air arcs between two electrode pairs, 99.99% Ni/Ni and 99.5% Cu/Cu, in a transverse magnetic field. In both cases the anode mass loss decreased (by a factor of 2 for Cu and by a factor of 6 for Ni) when the magnetic field was increased up to 15–20 Oe and then remained approximately constant for Cu and decreased weakly for Ni. The observed dependences of anode mass loss were explained by the published behaviour of an arc motion in a magnetic field. The lattice parameter was decreased by the discharge treatment. The decrease was attributed to residual tensile stress produced on the arced surface. The lattice parameter of Ni increased with magnetic field, while for Cu it did not change substantially. The different behaviour is attributed to the magneto-plastic effect on magnetic Ni, which increases the plasticity with magnetic field.

201 外乱に強いプラズマ切断条件のパラメータ設計(OS2-1 デジタル設計・評価・製造システムI)

Air arc plasma cutting, which does not requires special orifice gas, is applicable to a wide range of small-to-medium-sized manufacturing industries because it is simple and economical. However, one of its limitations is that angular precision of the bevel produced by this method is inferior. Especially, when the cutting torch is combined to the simple automated machine, this kind of fault has occurred. The authors researched plasma cutting conditions for reducing sensitivity to noise factors in this case.

Characteristics of Arc Voltage of High-Current Air Arc in Sealed Chamber

Effect of arc voltage on different factor of design and control was investigated for high current in order to develop design guide of circuit breaker. In this study, dependences on these factors which are current, arc length, surface area on electrode and internal pressure of arc voltage were evaluated quantitatively. As a result of the evaluations, it was estimated that arc voltage near electrode surface rise linearly with arc current and the area on the surface to the power -0.8, and the voltage in arc column rise pressure increase to the power 0.3. We confirmed the validity of the characteristics of the estimated voltage by comparison with the generated voltage in an actual arc extinguishing chamber. The characteristics of the estimated voltage would be provided as effective guidelines to design arc extinguishing chambers.

Theoretical computation studies for transport properties of air plasmas

The thermophysical properties of arc plasma provide reliable micro-theoretical foundations and parameter inputs for the numerical simulation of the air arc discharge process. Based on the assumption of the local thermodynamic equilibrium, the computation of transport properties including electron diffusion coefficient, viscosity, thermal conductivity and electrical conductivity is performed by using the Chapman-Enskog method and expanding the sonine polynomial up to the third-order approximation (second-order for viscosity) in a pressure (0.120 atm) and temperature range (30040000 K) conditions which satisfy most thermal plasma modelling requirements. The most recent data on potential interactions and elastic differential cross sections for interacting particles are utilized to determine the collision integrals, resulting in more accurate and reliable values of transport properties than those given in the previous literature.

Surface temperature measurement of a copper anode submitted to a non-stationary electric arc in air

This work concerns the assessment of the surface temperature of copper anodes submitted to an electric arc in a non-stationary regime in air at atmospheric pressure. An infrared camera is used to measure the decrease of the surface temperature just after a very fast controlled arc extinction. Results are presented for different mean values of the arc current intensity (30, 70 and 130 A) with an electric arc duration in the range of 2–5 ms. The temperature decrease after the arc extinction allows an assessment of the surface temperature just at the moment of the arc switching off. In the present experimental conditions the mean temperatures reached for copper anodes are in the range of 750–1200 °C according to the arc current intensity values. Comparison between experimental results and a numerical modeling of the electrode heating allowed one to assess the surface power balance. The values for the volt equivalent are found about 12 V and the values for the surface power density are found to be near 2 × 109 W/m2.

High-Speed Imaging and Radiative Energy Measurements of a High-Current Pulsed Arc in Air

A high-current pulsed arc struck between a 100-mm electrode gap in open air was experimentally studied by time-resolved imaging. The arc was created by a discharge current with an amplitude of 10 kA and a duration of about 10 ms. A high-speed camera was used to investigate the dynamic behavior of the arc. The images extracted from the video show in particular strong interaction between the anode and cathode jets.

Simulation of Arc Splitting Process Considering Splitter-Plate Erosion

A 3-D simulation model of air arc plasma in a low-voltage circuit breaker, considering the production of iron vapor from splitter-plate erosion, is developed. The distributions of temperature and mass fraction of iron vapor are calculated. The simulation results indicate that the arc splitting process is strongly influenced by the presence of iron vapor from the splitter plate. Images of arc simulation results are presented.

New Static “AirArc” EMTP Model of Long Arc in Free Air

In this paper, long arcs in free air are investigated. A long arc was induced in the high-power test laboratory at FGH-Mannheim, Germany. From the recorded arc data, the features of the arc were derived and analyzed, including elongation effects associated with these arcs. Based on this analysis of a real arc, a new “AirArc” static arc model, including the length variations, was derived and incorporated into the Alternate Transients Program-Electromagnetic Transients Program software package in which it was simulated. The arc is modeled as a current-dependent voltage source with a characteristic-distorted rectangular voltage that elongates nonlinearly over time. Fault arcs are a significant source of harmonics that distort other voltages and currents in the network. The time-domain and spectral-domain features of the simulated arc are compared with those of the real arc. The assessment of transient processes during arcing faults was carried out using the discrete wavelet transform.