Arc motion and gas flow in current limiting circuit breakers operating with a low contact switching velocity

Arc motion in low voltage (240 VAC) high current (10/sup 3/-10/sup 4/A.) current limiting-circuit breakers is dominated by arc root mobility. The mobility is influenced by the gas flow and gas composition in the contact region, but there is little experimental data on these effects. New pressure and spectral data measurement during arc movement are presented using a flexible test apparatus and an arc imaging system. These measurements are used to investigate gas flow characteristics in the arc chamber. The chemical and physical phenomena occurring during the arc motion are discussed. The combination of optical and spectral data provides new insight into the arc motion. The influences of arc chamber material, contact material, and contact opening speed, are investigated to improve arc control for a low contact opening velocity.     

The energetics of gas flow and contact erosion during short circuit arcing

The processes governing the movement of short circuit arcs in circuit breakers are complex and variable and the detailed understanding of these processes is incomplete. This paper presents a new approach to our understanding of the short circuit arcing process by concentrating on the bulk thermal behavior and energetics of the arcing and gas flow during contact opening. It is shown how considerations of the arc power and the heating and vaporization of the contact material can be used to examine the flow of gas through the arc chamber and the erosion of contact material. Experimental data from a flexible test apparatus and arc imaging system along with measurements of pressure and arc current and voltage are used as the basis of the analysis. It is demonstrated how the air initially present in the arc chamber will be rapidly expelled from the arc chamber to leave an arc burning in the products of contact volatilization. Data on mass and volume flow rates are presented as well as estimates of the gas velocity in the contact region. These data provide information on the nature of the gas flow in the arc chamber as well as contact erosion during the arcing process. Arcing conditions of interest are short circuit faults (10/sup 3/-10/sup 4/ A) in low voltage (220-380 VAC) circuit breakers.     

Three-dimensional-simulation of arc motion between arc runners including the influence of ferromagnetic material

The behavior of the moving electric arc in low-voltage switching devices is determined by the complex interactions of magnetic forces, current flow, gas flow, heat conduction, and radiation. In this paper three-dimensional simulations of arc motion between parallel arc runners are presented, which consider all these interactions. These simulations are carried out with a computational fluid dynamics (CFD) finite volume code. Based on earlier simulations by Frank Karetta the magnetic field, expressed as vector potential formulation, is now treated by the same type of general transport equations as the other processes, which allows the direct implementation into the CFD package used. This enables one to include the effect of ferromagnetic material in the arc chamber, such as ferromagnetic flux concentrators or steel splitter plates. Typical simulation examples are presented for different design details.     

保护气体对接头形貌及熔滴过渡的影响与模拟

为了研究保护气体流量对复合焊接接头形貌及熔滴过渡的影响，采用5mm厚的高强钢板材进行了激光电弧复合焊接试验的理论分析和实验验证，获得了不同气流量下的焊缝形貌以及焊接过程中电弧和熔滴图像。结果表明，随着保护气体流量的增大，焊接熔深先增大后减小；当保护气体流量在25L/min，焊接熔深达到最大；且焊缝的铺展性较好，飞溅较少；保护气体流量通过影响熔滴过渡的形式，对熔滴过渡频率产生影响；随着气流量的增大，熔滴过渡频率减小，且在25L/min时，熔滴过渡频率较稳定；采用FLUENT软件对气流量进行数值模拟，气流量越大，保护气体流速越大，在工件表面的作用面积减小。该研究结果为实际工程应用中选择保护气体流量制备高质量的焊缝奠定了基础。     

Composition and transport properties of SF6and their use in a simplified enthalpy flow arc model

The equilibrium composition of SF6was calculated for temperatures from 1000 to 45 000°K and for pressures from 1 to 16 atm. The usual thermodynamic functions and transport properties were also computed. Considering the arc column in axially flowing gas as a plasma generator, the power balance and momentum conservation equations are formulated and solved with certain simplifying assumptions. The solution gives the developing flow and electrical parameters as a function of distance along the nozzle. Arc voltages are predicted which agree with available data. Clarification is given on two processes contributing to dielectric recovery: axial sweeping away of the arc channel, and its conductance decay by thermal diffusivity, during the current fall approaching current zero.     

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     

CO2激光-MAG电弧复合焊接过程中熔滴受力及过渡特征研究

以5.0mm高强钢板为试验材料,进行了CO2激光与金属活性气体(MAG)电弧复合焊接试验。通过高速摄像和熔滴的受力分析研究了激光能量、电弧能量、光丝间距对复合焊接过程中熔滴过渡特征的影响。结果表明,激光的加入稳定了电弧,降低了射滴过渡的临界焊接电流值,由于激光对电弧的引导和压缩作用,改变了熔滴内电流线分布及电磁收缩力的大小及方向,进而影响了熔滴过渡特征。同时激光匙孔中喷射出大量的金属蒸气产生反作用力,改变了熔滴原来的受力状态,使熔滴过渡模式发生改变。随着焊接电流的增加,电弧变得更加稳定,能量更加集中,等离子体流力成为熔滴过渡的主导力。光丝间距的大小影响了熔滴过渡的频率,在光丝间距为4mm时熔滴频率最大。     

Arc structure, arc motion, and gas pressure between laterallyenclosed arc runners

Arc motion along parallel arc runners tightly enclosed by lateral walls was investigated experimentally, both with and without an exhaust barrier at the outlet. High speed movies (33 000 frames/s) were taken and the gas pressure was measured at several locations along the path of arc motion. The measurements show how both arc shape and motion depend on the parameters arc length (5-15 mm) and exhaust constriction. In many cases both arc shape and arc motion were influenced by a plasma volume forming a “nose” in front of the arc next to one of the electrodes. Spontaneous formation of an anode spot and/or a cathode spot in front of the arc may ignite a parallel current path and initiate a commutation process. The plasma volume in front of the arc is less significant at low electrode distance, high arc current, high blast field, and in more realistic chamber geometries with an exhaust barrier. Cold gas shock waves hitting the arc strongly influence both arc motion and shape. Simulation of arc motion may be a helpful tool in order to save expensive experiments when designing low voltage miniature circuit breakers. The high speed movies showed that the arc motion is sometimes strongly influenced by commutation processes requiring a very complex arc model     

Turbulence controlled high-power arcs with different electron and gas temperatures

Experiments with high-power arcs interacting with a sonic high-pressure gas flow suggest an energy dissipation mechanism much more effective than thermal conduction and radiation. It is shown that the arc behavior is almost completely controlled by turbulence phenomena. By means of a phenomenological turbulence theory, an expression for the turbulent heat conductivity is derived which is used to solve the energy balance. The static arc voltage and the temperature profiles calculated for currents up to 50 kA and pressures of some 100 N/cm²(≈ 10 atmospheres) depend on a characteristic turbulence length that is determined by comparison with the experiments. For radially blasted arcs with a length of a few centimeters, this turbulence length is shown to be constant over a wide range of current and pressure but varying with the arc geometry. The high energy dissipation leads to arc voltage gradients that may attain several kilovolts per centimeter. Such high gradients imply deviations from local thermal equilibrium, especially at smaller currents. For such a case, the solution of the energy balance requires the calculation of nonequilibrium plasma composition and transport properties for plasmas with different electron and gas temperatures. Numerical calculations have been performed for nitrogen.     

铝合金CO2激光电弧复合焊保护气体影响研究

为了研究保护气体对铝合金CO2激光-熔化极惰性气体保护电弧复合焊的焊缝成形和熔深等的影响,采用不同流量的He和Ar混合保护气体在5052铝合金板上进行激光-熔化极电弧复合焊工艺试验的方法,进行了理论分析和实验验证,取得了焊缝成形、熔深、焊接电压等数据。结果表明,复合焊时采用单He气会造成熔化极惰性气体保护焊的电弧电压增大,电弧稳定性变差,从而影响铝合金CO2激光-熔化极惰性气体保护焊复合焊的熔深,少量的Ar气加入有利于改善焊缝表面质量和稳定电弧,提高焊缝熔深的效果,当V(Ar):V(He)=5:25时,熔深最大,但He气中加入大量的Ar气会降低焊缝熔深,甚至抑制激光深熔焊接;当采用纯Ar气作为保护气体时,虽然焊缝成形美观,但焊缝熔深很小。这一结果对铝合金CO2激光-熔化极惰性气体保护电弧复合焊焊缝成形质量分析具有较好的理论和工艺指导意义。     

Potential gradient measurements in argon-nitrogen mixtures using a wall-stabilized arc†

The potential gradient in wall-stabilized atmospheric pressure arcs in argon, nitrogen and argon-nitrogen mixtures has been measured over the current range 5 to 40 A.

The potential gradient was measured by four methods which were found to agree to within 3%. The values obtained were found to be a function of the state of the surface of the discs forming the arc channel and independent of the gas flow rate in the range l·-9·0 1/min.

The results demonstrate that the effect of a small trace of nitrogen in argon is much greater than that of a small trace of argon in nitrogen. For example, at 26 A 5% nitrogen in argon increases the potential gradient by ～30%, while 5% argon in nitrogen reduces it by ～ 3% from the pure argon and pure nitrogen values, respectively.

A simple two zone arc model is used to explain the results. This model indicates that the arc in argon entirely fills the channel for currents greater than 5 A. However, when nitrogen is added a central core is formed whose diameter decreases as the nitrogen concentration is increased, the current being kept constant.     

316L不锈钢激光-钨极惰性气体复合焊接工艺研究

为了进一步提高316L不锈钢的可焊性,采用Rofin Sinar 5kW快轴流CO2激光器和Miller钨极惰性气体(TIG)焊机,对3mm厚316L不锈钢进行了一系列CO2激光-TIG电弧复合焊接工艺试验,研究了激光功率、电弧电流、热源间距等工艺参数对焊缝成形的影响规律。在激光功率大于2.5kW时,会产生小孔效应,其对复合焊接熔深影响显著;而当电弧电流小于150A时,焊接熔宽与两热源的热输入关系密切,当电流大于150A时,仅电弧电流是焊接熔宽的决定性因素;热源间距存在一个最佳值2mm~3mm,此时,焊接熔深可提高1.46倍~2.54倍。研究结果表明,复合焊接提高了316L不锈钢的可焊性。     

The process of arc splitting between metal plates in low voltage arc chutes

The behavior of arcs in low voltage switching devices is affected by several interactions. For studying simple arrangements of arc runners without metallic splitter plates ("deion plates") a three-dimensional simulation system has already been developed. It takes into account the plasma fluid dynamics, the current flow within the electrodes and the plasma, and the magnetic field generated by both currents. In order to model the arc splitting process simulations with an insulating barrier were done in a first step. For the simulation of the splitting process between metallic deion-plates the simulation model has to be extended. In experiments including high-speed movies it is shown that this process is a continuous transition of current flow from the still undivided arc to the new arc roots formed on the metal plates. A new simulation model representing the roots by a thin layer of current-dependent resistivity is discussed and simulation results are compared with switching experiments.     

A real-time prediction model of electrode extension for GMAW

This paper presents the development of an electrode extension model for the gas metal arc welding process based on the process voltage. The full dynamic model for the electrode extension is derived by combining a dynamic resistivity model with the voltage model. The electrode extension model was found to be represented mathematically by a nonlinear, time-varying, second-order ordinary differential equation. This model can be used in through-the-arc sensing and arc length control systems. To experimentally verify the model, the process dynamics were excited by a continuous sinusoidal variation of arc current. Using a constant current power source with the electrode positive, sinusoidal perturbations of variable amplitude were superimposed on the current to allow direct measurement of changes in electrode extension, arc length, and total voltage. A high-speed video system was used to capture the experimental electrode extension dynamics. The model was verified by comparing the frequency response of the model to the frequency response of the real process. Agreement between the simulations and the experimental results was found to be very good. The accuracy of this model was found to be approximately /spl plusmn/0.6 mm, which is considered to be suitable for process control applications.     

New Catalytic Proportions for Syntheses of SWNT Bundles （Ropes） and Its Characterization

The single-walled carbon nanotube（SWNT） bundles and ropes have been prepared by using the anode are discharge plasma to evaporate the graphite rods which contain Fe, Co and Ni powders as catalyst in He atmosphere. Many purifying methods are used for the products. It indicates that the synthesis of SWNTs has been greatly affected by the preparation parameters of catalyzer, the buffer gas and its pressure, the arc current intensity, etc. The optimal condition for preparing SWNTs in our case has been proposed. The forming mechanism of the SWNTs bundles and ropes is also studied qualitatively. The evaporated single graphite sheet tends to reduce its active energy.     

真空电弧镀膜等离子体参数的测量

本文介绍了真空电弧镀膜（VAD）环境下用法拉第杯分析等离子参数的实验系统。利用该系统，着重测量了气压、电流等参数对离子能量的影响，以及离子能量在固定位置的角分布。由测量结果，讨论了VAD中的复合离子参数值（Ep），在100A、0．66Pa、偏压-100V下，典型的最大离子能量为75eV，到达工件Ep值为8286V／atom。     

Investigation of arcing effects during contact blow open process

A theoretical model has been developed to simulate the blow open process considering contact constriction force, contact spring force, and plasma pressure. Meanwhile, monochromatic high speed imaging technique has been used to characterize arc behavior, contact vapor distribution and determine contact blow open gaps. Modeling results are in good agreement with test results. The results show that plasma pressure has a significant effect at the initial arcing stage of a blow open process, but it decreases rapidly due to the increase of arc gap and the gas pressure equilibrium around moving contacts. The plasma pressure and the contact spring force (or applied magnetic force) basically determine the arcing time during the blow open process. However, contacts can be held open by plasma pressure till current zero if piston type arc chamber is employed. Higher contact spring force results in shorter arcing time, higher arcing current and more likely leads to contact weld. Due to the fact of arc pressure decreasing rapidly during the blow open process, the blow open contact gap is less than 2.5 mm for all the contactors tested at the blow open current level. The results indicate that larger allowed arc gap does not necessarily reduce contact weld possibility, since other factors such as arc motion and heat conduction through contacts also have strong influence on contact weld     

激光-MIG复合热源焊接熔滴过渡力学行为分析

针对激光等离子体和电弧等离子体共同作用下的熔滴过渡，根据气体动力学和静态力学平衡理论，对CO2激光-惰性气体金属弧焊(MIG)复合焊接过程中熔滴的复杂受力状态及其力源的产生与作用原理进行了深入分析。结果表明，一方面由于激光焊接过程中材料剧烈气化时产生的大量金属蒸气射流，对熔滴形成了巨大的反冲作用力，阻碍了熔滴过渡;另一方面，由于激光焊接产生的等离子体改变了原有惰性气体金属弧焊电弧等离子体形成路径，从而改变了原有焊接熔滴中的电流密度分布和流向而形成了一个新的复合电弧收缩力。两者综合作用降低了复合焊接熔滴过渡频率，破坏了焊接稳定性。在此基础上，进一步研究了焊接参数对金属蒸气反作用力、复合电弧收缩力等的影响规律，并采用数值分析的方法推导出了它们的数学描述;定量分析了复合热源作用下熔滴的受力机制，揭示了复合热源焊接过程中熔滴受力状态与焊接稳定性之间的内在关系。     

Discharge lighting brightens the night

As part of an historical study of streetlighting in London (UK), the article examines how the gas discharge lamps of 1930 indicated the way ahead but were not the complete answer. They needed special circuits, with an inductance to control the current and usually some way of producing a high voltage to strike the arc, but the higher efficiency compared with filament lamps made that worthwhile. The real problems facing designers and manufacturers of discharge lamps were materials. They needed materials for the arc tube and for the electrodes that would resist chemical attack from the hot ionized gases in the tube. In any event, the high-pressure mercury lamp and the sodium lamp were developed almost simultaneously. Today these lamps dominate street lighting as well as flood light applications     

基于FFT和电磁辐射的低压电弧故障检测

为了快速、有效地检测低压串联电弧,分别对电弧电流信号和电磁辐射进行了检测。对相同负载条件下的电弧电流和正常工作电流信号进行快速傅里叶变换,并以二者频域特性差异作为电弧故障检测的依据。结合简易环形天线接收到的电弧电磁辐射可以进一步提高电弧故障检测的正确率。最后,综合电弧电磁辐射和电弧电流的频域特性,提出了低压电弧故障检测算法。该方法运算量小,易于在嵌入式装置实现,对于电弧故障断路器的研制具有一定参考价值。