The Dependence of the Air Blast Arc Characteristics on Electrode Position

The effect of the position of the upstream electrode on the characteristics of the air blast arc in a converging-diverging nozzle is investigated using a simple one-dimensional model. It is found that altering the upstream electrode position affects the pressure gradient between the electrode and the nozzle throat. The pressure gradient in this region determines to a large extent the arc area contraction rate as the arc current decreases to zero and, therefore, the interruption capability of the arc after current zero. Moreover, the upstream electrode position affects the arc diameter in the steady and transient states throughout the whole arc length. It is found that radial turbulent cooling need not be incorporated into the model to explain the experimental results. However, turbulent radial cooling, if present, is found to enhance the interruption capability of the arc by a large factor.     

Pressure Transients in a Model Gas-Blast Circuit Breaker Operating at Extra High Current Levels

Test results for model circuit breakers operating at high current levels and with large diameter nozzles show evidence of pronounced pressure transients although the circuit breaker nozzle is not severely blocked. The magnitude and duration of these transients are sufficient to affect the arc properties and hence influence arc control during the peak current phase and to influence arc extinction at current zero. However, despite their inherent importance there exists only limited information concerning such pressure variations. The purpose of this contribution is to identify the nature and sources of the transients, to establish typical thresholds for the onset of the transients, and to determine the influence of different operating conditions upon the transients. Measurements of pressure and thermal mantle variations are used in conjunction with an electrical analog model of the aerodynamic test facility to show that the pressure transients arise not only from arc generated flow impedance effects but also aerodynamic resonances. The resonant pressure transients are shown to be pronounced during the high current phase even below the thermal blocking threshold. Above the threshold, excitation of negative increment resonance following current peak produces depressed pressures during the current-zero period which may lead to a deterioration in circuit breaker performance. Higher frequency resonances also occur and become more pronounced with electrode wear. Activation of such resonances is symptomatic of axisymmetric arc instabilities which also may cause a deterioration in performance.     

Correlation of the Radially Integrated Properties of Gas Blast Arc Discharges

Extensive experimental results for the properties of the arc thermal region and local electrical conductances have been reported in the literature for both peak current and current zero phases of orifice air flow arcs. The present paper is concerned with interpreting these results in terms of boundary layer integral analysis concepts. "Characteristic area" and "shape factor" values are presented for orifice flow arcs and methods of correlating these parameters for different arcing conditions are examined. The results show that within experimental accuracy unique relationships exist between various shape factors and correlation parameters, over a wide range of arcing conditions including the current zero period of an ac waveform. The resulting correlation curves, therefore, form the basis for predictive calculations of arc behavior under different gas blast conditions. Finally, an illustration is presented of the manner in which the shape factor correlations may be used for determining the relative importance of various fundamental processes during the current zero period of a gas blast circuit breaker arc.     

Mechanisms for Temperature Decay in the Freely Recovering Gas Blast Arc

Energy loss mechanisms for the extinguished gas blast arc channel in free recovery are defined and their comparative magnitudes are explored for both N2 and SF6 gases. The arc channel temperature decay rate is found to follow at least two time constants: one corresponding to the transit time of the channel gas and the other to a later period. In addition, the influence of the gas pressure and of the initial conditions of the arc channel and the surrounding hot gas mantle at current zero on the decay rate of the channel temperature are investigated.     

强流脉冲电弧作用下石墨电极蒸发特性

气体开关电弧的热侵蚀作用是电极损耗的主要成因。石墨电极在电弧作用下发生蒸发并在多次放电后有明显的质量损耗,改变了开关内的气体环境和电极间距,导致开关动作可靠性降低。为研究石墨电极在脉冲电弧冲击下的侵蚀特征,基于开关电弧瞬态扩散特征和石墨材料参数,在弧根区域建立了电弧-电极能量耦合模型,得到了等离子体-固体区域的传热特性。考虑石墨电极的相变特征,计算瞬态热作用下石墨电极的加热范围以及临界相变点,研究瞬态电弧热冲击作用下的石墨电极相变机制。研究结果表明,电弧-电极界面热流主要集中在电弧接触面中心,电弧沉积的能量密度最高可达109 W/m2,石墨在电流上升初期基本处于加热状态,在能量积聚作用下,石墨转变为升华状态,传热强度随半径急剧衰减,蒸发区域略小于电弧半径。通过实验记录了5种开关工况下石墨电极烧蚀形貌和质量损失情况,结果表明,电极质量损失与电弧沉积在电极表面的能量线性相关,近似为0.015 mg/J。研究了电弧关键参数对电极质量损失速率的影响,为延缓电极损耗提供数据支撑。     

Behavior of Sustained High-Current Arcs on Molten Alloy Electrodes during Vacuum Consumable Arc Remelting

Vacuum consumable arc remelting is a casting process carried out in a vacuum with the aim of remelting the consumable electrode in such a way that the new ingot has improved chemical and physical homogeneity. The power which causes the melting is supplied by a vacuum arc burning between the electrodes. In order to determine the furnace partitions of electrical power and current, experiments were conducted on molten-faced round electrodes. The quasi-steady melt rate was determined for both horizontally opposed 15-cm-diameter Ni electrodes and for vertically suspended 40-cm-diameter Inconel 718 electrodes. The cathode thermal power is directly proportional to the melt rate which, for the horizontally opposed electrode experiment, agrees to within 10 percent with the Ni breaker switch calorimetry measurements and with predictions from retarded potential analyzer plasma data. However, for the vertically suspended electrode experiments, the measured thermal power at the cathode is 50 percent higher than for nickel. When CO is introduced into the vertical alloy electrode system and electrode gap is increased, the cathode thermal power is reduced by approximately 50 percent. Furthermore, the electrode position measurements and observation of the ingot surface suggest that a concentrated arc is formed under these conditions.     

Investigations of the Arc Burning in the Water Vapour Atmosphere

The functions of thermal conductivity α(T) and electrical conductivity σ(T) for water vapour, within the temperature intervals 7700–8000 K and 2000–3500 K, were calculated. These calculations were performed by using the UHLENBUSCH'S method and the empirical one. Calculations were based on experimentally determined electric field strength as a function of the arc current and radial temperature distribution in the central zone and in the surrounding of the arc burning in water vapour atmosphere.     

Metal vapour transport in a FXR discharge

Streak photographs of the axial motion of vapourized anode and cathode materials in a flash X-ray (FXR) discharge correlated with the time derivative of the discharge current (dI/dt) indicate that clouds of vapourized metal are formed outside the electrode surfaces during the first significantdI/dt dip, i.e. during the pinching of the discharge column. The anode cloud propagates towards the cathode with a velocity of (1–1.5)×10⁶ cm/sec and reaches the cathode cloud at current zero. This means that the discharge current is not entirely carried by a metallic arc until after the first current zero. The metal vapour propagation is discussed in relation to existing theories.     

Influence of ambient pressure on the performance of an arc discharge plasma actuator

The arc discharge plasma actuator (ADPA) has wide application prospects in high‐speed flow control because of its local heating effect and strong disturbance. In this paper, the influence of ambient pressure, which ranges from 3 to 20 kPa, on the performance of a two‐electrode ADPA is investigated by a schlieren system. The duration of the arc heated region, as well as its area, is extracted by image processing. As the ambient pressure increases, different flow field evolutions occur. The duration of the ADPA heated region increases with the ambient pressure. The maximum duration reaches 1185.3 µs at 20 kPa. The velocity of the discharge‐induced blast shock wave first decreases gradually and then remains at 345 m/s for all air pressures. The blast shock wave has a higher velocity at lower pressures when it is freshly produced. A maximum blast shock wave velocity of 582 m/s is observed at the pressure of 7 kPa. The arc heated region is not sensitive to ambient pressure, but the deposited energy from the arc increases when the pressure increases.     

Plasma density decay of vacuum discharges after current zero

In vacuum circuit breakers the post-arc current caused by the remaining ions and electrons in the contact gap is an indication of the residual ionization and its decay. It coincides with the formation of a positive space charge sheath in front of the new cathode, which grows toward the new anode. In a vacuum test chamber an arc (1.5-15 kA RMS) is drawn between high current electrodes of the spiral type. At different times after current zero a transient recovery voltage is applied across a separate pair of high voltage electrodes. In contrast to real circuit breakers, where the transient recovery voltage reappears between the arcing contacts, this separation allows the study of residual plasma free from the thermal stress and melting on the contact surfaces. From the post-arc current across these electrodes, in comparison with a mathematical model of sheath growth, the density of the charge carriers can be evaluated. Such values and their temporal decay are presented     

Characterizing and modeling the free recovery and constrained recovery behavior of a polyurethane shape memory polymer

In this work, tensile tests and one-dimensional constitutive modeling are performed on a high recovery force polyurethane shape memory polymer that is being considered for biomedical applications. The tensile tests investigate the free recovery (zero load) response as well as the constrained displacement recovery (stress recovery) response at extension values up to 25%, and two consecutive cycles are performed during each test. The material is observed to recover 100% of the applied deformation when heated at zero load in the second thermomechanical cycle, and a stress recovery of 1.5 MPa to 4.2 MPa is observed for the constrained displacement recovery experiments.After performing the experiments, the Chen and Lagoudas model is used to simulate and predict the experimental results. The material properties used in the constitutive model - namely the coefficients of thermal expansion, shear moduli, and frozen volume fraction - are calibrated from a single 10% extension free recovery experiment. The model is then used to predict the material response for the remaining free recovery and constrained displacement recovery experiments. The model predictions match well with the experimental data.     

Nature of convection-stabilized DC arcs in dual-flow nozzlegeometry. I. The cold flow field and DC arc characteristics

An experimental investigation of the steady-state low current air arcs in a dual-flow nozzle system is presented. The cold flow field with no arc was determined for various nozzle geometries, i.e. two- and three-dimensional and orifice nozzles, and nozzle pressure ratios. Supersonic flow separation and oblique and detached shock waves were observed in the flow field. Using a finite-element computer program, the Mach number contours were determined in the flow field for various nozzle-gap spacings and pressure ratios. In addition, the DC arc voltage and current measurements were made for an electrode gap spacing of ≈5.5 cm and current levels of I≈25, 50, and 100 A for the three nozzle geometries. The arc voltage and arc power increased rapidly as the flow speed increased from zero to sonic velocity at the nozzle throat. The shock waves in the converging-diverging nozzles resulted in a decrease in the overall resistance by about 15%     

Anode-Spot Formation and Motion of Vacuum Arcs

This paper reports about experimental investigations on high-current vacuum-arc phenomena, especially anode-spot formation, arc states, and motion. The presented work was stimulated by lack of information about the transition process from the diffuse low-current mode to the high-current mode characterized by anode spot(s). Optoelectronic measurements, streak photographs, high-speed movies, and correlated arc voltage/current records yielded remarkable results on power-frequency vacuum arcs. Three different high-current vacuum arc modes can be observed beyond a certain threshold current. Which mode appears depends mainly on the momentary electrode distance. The modes are characterized by different anode-spot behavior and interelectrode phenomena. The transition between different arc modes is continuous. The arc modes observed on ring electrodes producing a magnetic blast field are the same as those appearing on butt-type electrodes. Anode-spot formation is preceded by congregations of cathode spots and may be initiated by thermal overload of the anode surface opposite to these cathode-spot clusters.     

Gas Phase Emitter Effect of Thulium within Ceramic Metal Halide Lamps in Dependence on Frequency

The gas phase emitter effect within ceramic metal halide (CMH) lamps reduces the effective work function of the electrode material and, therewith, the electrode temperature. An investigation of the gas phase emitter effect of thulium (Tm) within CMH lamps seeded with Tm iodide (TmI3) is carried out. For this purpose, phase resolved images of the arc attachment and measurements of the electrode temperature, Tm atom and ion densities are performed in dependence on operating frequency by pyrometry and optical emission spectroscopy. Additionally, the influence of a sodium iodide (NaI) admixture is studied. The emitter effect is generated by means of a monolayer of Tm atoms on the electrode surface generated by a Tm ion current within the cathodic phase. It overlaps onto the anodic phase at higher frequencies of some hundreds of hertz. The reason is the finite life time of the monolayer, which is determined by the adsorption energy of Tm on the tungsten surface. Due to the low electric field strength in front of the anode and the mass inertia, the emitter ions and atoms remain in front of the anode. They retard the decay of the monolayer and with it the increase of the work function. Moreover, a comparison of a lamp seeded with TmI3 and sodium iodide (NaI) with a lamp seeded only with TmI3 illustrates a slight reduction of the electrode tip temperature caused by a higher Tm saturation vapour pressure and a higher Tm amount within the lamp filling. The influence of Na appears to be quite low. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Model for DC Interruption in Diffuse Vacuum Arcs

A theoretical model for current interruption in a diffuse vacuum arc with dc commutation is described. Before current zero the interelectrode plasma is modeled as an ion-neutral fluid through which electrons are flowing. After current zero a positive ion sheath grows into the plasma from the former anode, driven by the transient recovery voltage. Using the basic laws of conservation, the decay of the plasma during commutation is evaluated numerically, enabling the post-arc current, the electric field at the former anode, and the power input to this electrode after current zero to be calculated. For copper electrodes, with a commutation time of 30 ?s, the ion density and velocity at current zero are 23 percent and 35 percent of their respective steady state values. The calculated post-arc currents of tens of amps are in good agreement with experimental data. The post-arc data generated with this model can be used to study reignition mechanisms and the interrupting capability of different contact materials.     

Transport properties in an electrode vapour contaminated arc in air

The electrical and thermal conductivities of air contaminated with electrode metal vapour from copper electrodes has been measured up to 8200 °K at atmospheric pressure using a modified form of Maecker's wall stabilized arc with a stabilizing hole 5 mm in diameter. The results of the study are compared with those of an uncontaminated arc in air. Both the conductivities are much greater than those for uncontaminated arc in air. This is believed to be due to the increased electron density by virtue of the lower ionization potential of copper. Energy transport by radiation is neglected in this study.     

药芯焊丝脉冲TIG电弧增材制造电弧特性研究

对药芯焊丝脉冲TIG电弧增材制造电弧特性展开研究。利用高速摄像拍摄不同熔敷层脉冲电流条件下的电弧与熔滴过渡图片,对高速摄像图片进行分析,发现焊丝熔化过程存在“滞熔”现象,导致熔滴过渡存在渣桥过渡与液桥过渡两种接触过渡方式,在脉冲峰值电流较小的50/100 A电流参数下,出现熔滴断续的渣桥过渡的频率最高。熔滴过渡影响电弧温度场与药粉成分在电弧中的分布,利用光谱诊断分析熔敷过程中在不同脉冲峰值电流与脉冲基值电流条件下电弧温度场及药粉成分在电弧中的分布。利用点阵法测量得到各点光谱数据,根据Boltzmann图法计算各点温度,将各点温度拟合得到完整电弧温度场,结果表明,焊丝从钨极轴线前（左）侧送入,吸收电弧热量并且对电弧有扰动作用,电弧前侧温度低于电弧后（右）侧,电弧前侧尺寸稍小于后侧;随着熔敷层数增加,降低峰值电流,电弧收缩,高温区面积相对减小,低温区面积相对增大。电弧最高温度区域出现在钨极下方1~2 mm的范围,大约为13 000~15 000 K,脉冲峰值电流越大则最高温度区域面积越大。在脉冲基值电流时期,由于电流小,电弧面积相比于峰值时期要小得多,焊丝与电弧相互作用减弱,电弧温度场基本关于钨极轴线对称分布。选择药芯焊丝中特有的Na元素的NaⅠ589.6 nm谱线对其分布点进行标记,拟合绘出不同脉冲峰值电流与基值电流下药粉元素在电弧中的分布情况,结果表明,电流越小,药粉运动高度越低,在不同的脉冲峰值电流下药粉均没有沾染到钨极上,在不同的脉冲峰值电流与脉冲基值电流下 Na元素均偏电弧后侧分布,说明焊丝自电弧前侧送入熔池后,在电弧前侧的电弧中没有出现药粉强烈的喷发现象,而是进入熔池进行冶金反应。接触过渡解决了碱性焊丝工艺性差的问题,电弧较为稳定,避免药粉喷发损伤钨极,熔敷过程稳定进行。     

Measurements of the behaviour of neutral atom density in a diffusevacuum arc by laser-induced fluorescence (LIF)

The method of laser-induced fluorescence was used to study the behavior of the absolute neutral vapor density of a diffuse vacuum arc on FeCu contacts. The local and temporal resolutions were 1 mm³ and 10 μs, respectively. The arc current had a sinusoidal shape of 5.8-ms duration with peak values of 90 and 510 A. It was found that the maximum densities of the iron and copper atoms are 1.2×10 ¹⁷ m^-3 and 7.5×10¹⁷ m^-3, respectively. During the arc the density was correlated with the current. At current zero the measured densities decreased to 10 ¹⁶ m^-3. After current zero, an exponential density decay with a time constant of about 100 μs was observed, indicating the recovery of dielectric strength after current zero. Measurements of the neutron iron vapor density at different spatial positions in the electrode gap reveal a nonisotropic distribution. From the measurements of the population distribution of the iron ground-state multiplet a ⁵D, the excitation temperature was derived. This temperature was low compared with the cathode spot temperature 2500-4000 K and decreased from 1600 K at the current maximum to 1000 K at current zero. The results indicate that the generation of neutrals is caused by flying evaporating metal droplets rather than by molten surface areas     

Dielectric recovery of copper chromium vacuum interrupter contactsafter short-circuit interruption

The recovery of a vacuum interrupter gap after short-circuit interruption was measured by application of an overshooting transient recovery voltage (TRV) several tens of microseconds after current zero. Copper chromium contact materials were employed varying in composition (25 and 50% chromium content), gas content, and production method. The gap failure was either pure dielectric or it was dominated by a significant postarc current. Therefore, postarc current phenomena were experimentally investigated focused on the relationship among the postarc current, the power frequency current amplitude, and the gap length. It was found that two postarc current maxima exist: the first strongly dependent on the power frequency current, and the second on the field strength. A correlation among postarc current facilitated failures, the ultimately dielectric recovery, and the erosion rate of the material was found. Strong indication is given that all of these effects are dominated by the metal vapor pressure rise given by the constricted rotating arc. A significant influence of the material properties can be drawn from these experiments, allowing a good estimation of the capability for short-circuit current interruption, thus providing a useful tool for material development