Anode and cathode arc root movement during contact opening at highcurrent

This paper presents experimental research into the behavior of short circuit break arcs ignited between opening contacts. The investigation is applied to arc chamber geometries commonly used in miniature circuit breakers (MCB). The movement of the anode and cathode roots are individually plotted from optical data, allowing the relative motion to be compared. The effect of a range of MCB configurations on the arc root motion has been investigated. The experiment was configured so that the fixed contact was always the cathode. The results show that the two are roots do not move away from the contact region simultaneously. Often the cathode root moved off the fixed contact and away from the contact region before the anode root commutated from the moving contact. The delay in anode root commutation leads to a delayed cathode root movement. These events are explained in terms of arc root emission processes     

Arc root mobility on piezoelectrically actuated contacts in miniature circuit breakers

A novel contact opening mechanism has been developed using a piezoelectric actuator to open the contacts in a low contact opening velocity circuit breaker. The arc control on the contacts is critical for successful current interruption (10/sup 3/-10/sup 4/ A) in low voltage (<250V) devices. Previous work has shown how arc root commutation from the contact region into the arc chamber is affected by arc chamber materials, contact materials and the gap behind the moving contact for contact velocities between 1ms/sup -1/ and 10ms/sup -1/. This work is extended using a commercially available piezoelectric actuator to open the contacts. Contact opening speeds are assessed and the arc root mobility is characterized under this operating regime. A flexible test apparatus and solid-state high-speed arc imaging system are used to gather data on the arc root during the opening of the contacts. New experimental results are presented on the anode and cathode root velocity and arc root motion in an arc chamber with piezoelectrically actuated contact opening. These results can be used to improve the design of high current low voltage circuit breakers suitable for piezoelectric actuation.     

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     

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.     

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     

Polymeric arc chamber walls influence on AgW/AgC contact resistance

Contact resistance was measured after arcing for AgW moving against an AgC stationary contact pair in an arc chamber, Contact resistance, measured at five different current levels over the range of 2 kA_p to 22 kA_p, was compared using two different arc chamber wall materials, ceramic and polyester, to determine if gases evolved from the polyester during arcing produced contaminants on the contact surface causing a resistance increase. When compared to results using ceramic walls, polyester walls did not show any statistical difference in contact resistance. However, increased chamber pressure, resulting from ablation of the polyester walls, was measured; scanning electron microscope (SEM) photographs and energy dispersive spectroscopy (EDS) surface mapping measurements showed the change in resistance, for both wall materials, was due to a depletion of silver from the contact surface at mid-range arcing currents and redeposition of silver at higher arcing currents. Discussions include the effect of arc temperature on contact resistance and the various gases, generated by the ablation of the polymer walls, on resistance and arc chamber pressure     

基于辐射电磁波监测技术的断路器开断性能研究

断路器在开断电流时,当触头两端的电压高于触头间灭弧介质的击穿电压时,动静触头将发生击穿,产生开关电弧,并激发空间高频的电磁波向外辐射。向空间辐射的高频电磁波信号与灭弧气体特性、机械特性及绝缘结构等多种因素相关,反映着断路器的开断能力。本文仿真计算了断路器辐射电磁波的过程,建立试验研究平台,测量对比了全新触头和退役触头开断过程中辐射电磁波的波形,开展了基于辐射电磁波监测技术的高压断路器开断性能研究。研究结果表明:随着触头表面烧蚀程度的增加,断路器开断性能下降,更容易发生电弧重燃,燃弧时间相对于全新触头会有明显的增加,同时对外辐射电磁波的持续也增多,辐射电磁波的持续时间可以作为判定断路器开断性能的判据。本文的研究内容为辐射电磁波监测技术在断路器开断性能的评估提供了技术参考与依据。     

Arc motion and wave propagation in arc chambers with lateral chinks

The effect of lateral chinks on shock wave propagation and arc motion in simplified arc chambers with parallel arc runners were investigated both experimentally and theoretically. Pressure transients were recorded at different positions of the arc chamber. The current supply was symmetric with respect to the arc in order to minimize the effect of the self-blast field on the arc; an external transverse blast field was applied. The arc motion was observed opto-electronically. To describe the arc region, the previously developed slug model was applied. The wave propagation along the arc chamber was treated as spatially one-dimensional. Mass and energy losses due to the chinks were taken into account. Both for shock wave propagation and arc motion good agreement between theoretical predictions and experimental data was obtained with low computational effort. It turned out that narrow chinks favor fast arc motion on parallel arc runners.     

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.     

Erosion and contact resistance performance of materials for slidingcontacts under arcing

In our previous work, we have investigated copper sliding switching contacts for automotive power applications. In order to improve their reliability, we have studied in this present paper, alternative materials to copper such as silver based materials (Ag, AgSnO₂, AgC, and AgCNi). Their performance was evaluated by measuring mass variations and contact resistance stability during sliding. The contacts are operated in a test machine during 50000 sliding operations, under inductive loads which produce long arcs, or under lamp loads which produce a short arc. In most cases, we have seen a significant wear of the anode compared to the cathode. We believe that the wear process for the sliding contact is the abrasion of the track by a rough contact surface. This roughness is produced and renewed by material transfer because of arcing. Regarding this wear, we show the medium performance of Ag and Cu contacts, while the worst performance is obtained with AgC and AgCNi, which make these latter materials unsuitable. Regarding contact resistance, we have measured low values <1 mΩ for AgC, AgCNi, and Ag. With AgSnO₂ and Cu contacts, the resistance ran reach high values, especially with an inductive load, which make these latter materials unsuitable. Concerning the effect of operating parameters, we show that polarity may emphasize the already poor performance of a high wear anode by disturbing the sliding motion. In addition, contact force and shape size are found to act on material performance: low force and large shape (cylinder) reduce wear and enhance resistance whereas high force and small shape increases wear and lowers contact resistance     

The unusual electrical erosion of high tungsten content, tungstencopper contacts switching load current in vacuum

The electrical erosion of high tungsten content, tungsten-copper (7-10 wt.% Cu) was investigated. The contacts were placed in a vacuum interrupter envelope with a background pressure of about 10^-6 torr. The contacts switched one half cycle of 60 Hz current per operation. The polarity of the current was changed on each operation. Six contact pairs were investigated. Each pair was subjected to an ever-increasing number of operations: 1 K, 5 K, 10 K, 20 K, 40 K, 50 K, and 60 K. The contact erosion was inferred by measuring the linear position of the moving contact terminal. On completing the electrical testing, the vacuum interrupters were dismantled and the contact surfaces were observed. Unlike the previous work on Ag-WC (50 wt.% Ag) and Cu-Cr (75 wt.% Cu), the W-Cu contacts showed a localized build up of erosion products on the contact surfaces even beginning at 1 K operations. The experiments were repeated switching a unidirectional current i.e., the contacts remained at the same polarity throughout the experiments. Here an anode pip and a cathode crater were formed immediately. The difference in the topographies of these contacts is discussed in terms of the metallographic analysis of the deposits on the contacts, the erosion deposits on the shields surrounding the contacts and the expansion of the vacuum arc     

In-situ vacuum-sealed lateral FEAs with low turn-on voltage andhigh transconductance

We have fabricated a new lateral field emitter array, in-situ vacuum-sealed, which exhibits a low turn on voltage and a high transconductance value without any additional vacuum sealing process. The vacuum-sealed lateral FEA (VLFEA) is encapsulated during the fabrication process, so that field emission characteristics can be measured without any additional vacuum environments. Experimental current-voltage (I-V) characteristics show that the anode current is field emission current obeying the linearity of the Fowler-Nordheim (F-N) plot. The experimental turn-on voltage of about 9 V is in good agreement with the extracted one from the F-N plot. In order to verify the integrity of the vacuum sealed micro-cavity, we have measured the anode current of the VLFEA both in a high vacuum chamber and in an atmospheric environment and found that the structure is well sealed. The anode currents as a function of gate voltage of the Mo-sealed VLFEA are analyzed and transconductance is extracted. The experimental results show that the VLFEA has superior field emission characteristics, such as low turn-on voltage and high transconductance, and does not require any additional troublesome vacuum sealing     

Vacuum arc ion currents and electrode phenomena

Properties of dc vacuum arcs between copper electrodes are studied in both a vacuum interrupter and a metal walled arc chamber. Maximum ion currents of ∼8 to 20 percent of the arc current (100 to 3000 A) are drawn from the diffuse arc plasma when the bounding metal wall or shield is biased negative. This maximum ion current is a fundamental arc property independent of wall diameter, anode diameter, and electrode spacing. The geometric dependence of the wall ion current, together with observations of isotropic vapor and ion emission from the cathode, indicates that the cathode regions adjacent to the cathode spots are the predominant sources of ionization for the plasma. Assuming single ionization, 55 percent of the vapor leaving these regions is ionized. Starvation phenomena in the anode region remote from the cathode spots lead to anode voltage drop and anode spot formation. Post arc currents reveal a mean ion speed during arcing of ≈8×10⁵cm/s. This mean speed may be acquired in the cathode region by acceleration from a potential maximum.     

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.     

Contact material and arc current effect on post-current zero contact surface temperature

Optical radiation measurements of contact surfaces were made after current-zero of a high-current (>10kA/sub p/) arc, to determine how much the contact surface temperature at and after current zero was affected by a change in contact material and arc current. Contact surface temperature was measured for different types of "typical" contact materials (AgW and AgC) commonly used in molded case circuit breakers (MCCBs). The average temperature at the contact surface was measured by using photodiodes in conjunction with a narrow band filters and long-range microscope. A 250-A rated MCCB was modified, with renewable chamber walls and contacts, and used as a test bed to insure that these results can be directly applied to MCCBs in the 125 to 250-A range. Uniform and repeatable arcing conditions were maintained by using an electronically timed capacitor bank source, timed contact part, and a well-maintained arc chamber. Along with other important engineering properties of the contacts (arc erosion, temperature rise), this data can be useful for selecting contacts for circuit breaker applications.     

A means of raising the threshold current for anode spot formation in metal-vapor arcs

Of the various processes occurring in an arc at high currents one of the most important with regard to application is the formation of an anode spot and the consequent melting associated with it. Vacuum arc devices depend for their operation on the formation of a high current transient metal-vapor arc. The limiting current in a particular design may be set by destructive melting at the anode. It is shown that it is possible to raise the threshold current for anode spot formation in a metal-vapor arc by suitably changing the electrode geometry. From a study of a few simple electrode geometries a set of guidelines has been evolved governing the choice of electrode geometry. As an illustration of the efficacy of these guidelines and the means of implementing them in practice it is shown how it is possible, with successive modifications of a coaxial-cylindrical electrode structure, to attain a peak current of 72 kA for a damped 60-Hz current wave without electrode melting.     

Make arc erosion and welding in the automotive area

A make arc has been investigated using a new testing apparatus. This apparatus which includes a piezo-translator, enables controlled bouncing to be studied at make under mechanical conditions similar to those encountered in automotive relays. Material transfer and welding tendency of silver, silver alloys and silver metal oxide contact materials have been studied under inductive, resistive and lamp loads at 14 V dc and 10-70 A. With all loads, anode to cathode material transfer has been observed. AgCdO, Ag and AgNi under lamp and resistive loads show the highest material transfer, as opposed to non doped and doped AgSnO₂ under inductive loads. This well known transfer is due to the anodic arc, which occurs during bounces when the gap between the contacts is shorter than ~5 μm, at the beginning and the end of the bounce. We have demonstrated that welding occurs at the beginning of the bounce, i.e. when the contacts begin to separate under arc, and not when the contacts close under arc at the end of the bounce. It was found that welding occurs mainly with Ag, AgCdO, AgZnO, AgFeRe, and AgFeO_x contact materials, and under high inrush current produced by lamp loads     

基于WVD-HT的SAR/ISAR多运动目标检测

本文提出和研究了基于Wigner-Ville分布(WVD)和Hough变换(HT)的合成孔径雷达(SAR)和逆合成孔径雷达(ISAR)对多运动目标成象的运动补偿新方法,给出了多运动目标检测、参数估算和运动补偿的主要步骤。理论分析、计算机和微波暗室模拟实验的结果表明,新方法对交叉项和噪声的抑制是有效的,它与单一的WVD法相比,提高了在噪声中对单个和多个运动目标检测及其参数估算的能力。     

Influence of electrical and mechanical parameters on contact welding in low power switches

A model switch has been developed to investigate the influence of kinetic parameters, as contact velocity and contact force, on contact welding under conditions prevailing in relays, micro switches etc. Both frequency and intensity of the statistically scattering weld forces increased with increasing arc duration and current. Pre-strike and bounce arcs show identical results under corresponding conditions. Both frequency and intensity of the statistically scattering weld forces initially increased and then decreased with increasing impact velocity. Increasing the static contact force hardly influenced the strength of the primary weld after impact but reduced or prevented weakening of the weld by a following bounce process. The results agree with the predictions of a mathematical model proposed. The configuration of the load circuit determining the actual arc current curve essentially influences the weld force values.