Electrical and pyrometric measurements of the decay of the anodetemperature after interruption of high-current vacuum arcs andcomparison with computations

Vacuum arcs of up to 20-kA peak current were investigated. The surface temperature of the anode area melted during the anode spot mode was determined by pyrometry and the evaluation of thermionic currents. The measurements confirm the computations of heating and cooling of the anode, taking into account heat conduction melting/solidification, and evaporation. Pyrometrically obtained temperatures agree well with theory. This gives confidence in the heat conduction model and also shows that the boiling temperature was reached during arcing. Another method evaluates currents of a milliampere value after arcs of several kiloamperes and postarc currents of amperes. Experimental observation (e.g., loading of the shield surrounding the contacts) and theoretical analysis of the interfering effects support the idea that the currents measured are due to thermionic emission     

大电流下多棒极型真空触发开关电弧特性

提出了一种多棒极型真空触发开关（TVS）,利用3对棒形电极的特殊结构来增大主触头间的燃弧面积,从而有效地提高TVS通流能力。结合真空电弧电压实验,阐述了多棒极型TVS在不同的大电流等级下的电弧发展变化过程。电弧电压的变化表现了多棒极型TVS中多通道并联燃弧及其在各通道之间的电弧转移过程,从而使得真空电弧维持在扩散态。由此开发的TVS样品实现了225 kA的峰值电流,单次转移电荷量45 C。     

Initiation of Arcing at a Plasma-Wall Contact

Conditions for the initiation of arcing in a plasma-wall contact were studied experimentally. Arcing could only be initiated by applying a bias voltage producing a net ion current to the wall. Results obtained show that crucial parameters for the initiation of arcing are the wall material, surface contaminations, the voltage across the plasma-wall sheath, and the total current to the wall. The current density was found to have no significant influence on arcing. For fixed surface conditions, arcing can be described by initiation characteristics. Also characteristics of the burning arc were determined 5 ?s after initiation. The arc operates with voltages and currents lying between the initiation characteristic and the burning characteristic. This result can be interpreted in terms of a nonstationary mechanism of the cathode spot.     

Anode Phenomena in Triggered Vacuum Gaps

Arc voltage - current characteristics and threshold current densities occuring during the formation of anode spots in triggered vacuum gaps are reported. Single pulses of 1.65 ms arcing time, which correspond to switching surge currents, are used in the study with copper and aluminum anodes. The threshold values are 1.75 times the values reported earlier using the longer, 8 mis, arcing time. They are found to depend upon the duration of arcing time as well as upon electrode material, surface conditions, electrode size and contact separation. Lateral inhomogenity in the electrode geometry appears to reduce the threshold value by promoting early formation of anode spots.     

Cold-hollow-cathode arc discharge in crossed electric and magnetic fields

A crossed-field cold-hollow-cathode arc is stable at low working gas pressures of 10⁻²–10⁻¹ Pa, magnetic-field-and gas-dependent arcing voltages of 20–50 V, and discharge currents of 20–200 A. This is because electrons come from a cathode spot produced on the inner cathode surface by a discharge over the dielectric surface. The magnetic field influences the arcing voltage and discharge current most significantly. When the plasma conductivity in the cathode region decreases in the electric field direction, the magnetic field increases, causing the discharge current to decline and the discharge voltage to rise. The discharge is quenched when a critical magnetic field depending on the type of gas is reached. Because of the absence of heated elements, the hollow cathode remains efficient for long when an arc is initiated in both inert and chemically active gases.     

On the mechanism of liquid metal electron and ion sources

The mechanisms of electron and ion generation from Taylor cones of liquid metals are discussed. In the case of electron emission the vacuum arcing mechanism of Swanson and Schwind, which accounts for the observed high current repetitive pulsing is briefly reviewed. For ion emission mechanisms from onset to the high current regime are proposed. It is concluded that at onset ions are generated exclusively by field desorption. A theory to account for the observed emitter heating is advanced, and it is concluded that high currents result from field ionization of thermally evaporated atoms. It is shown that space charge becomes important even at very low ion currents and'is instrumental in providing stabilization in all regimes of ion emission.     

Submillimeter laser interferometry with pyroelectric image recording

The interferometer with a submillimeter laser and standard pyroelectric TV camera for visualization of interference fringe pattern is described. Problems typical for the development of such interferometer are solved by choosing of a proper arrangement and a mutual spacing of its elements with respect to laser. The interferograms of a teflon wedge and an arcing plasma are presented as an example.     

Development of the fast arcing protection for ECRH system on the HL-2A tokamak

1 Introduction A series of engineering tests and physical experiments,including ECRH[1],was carried out on the HL-2A tokamak in 2005.A fast arcing protection system[2] was developed to ensure operating of ECRH facilities[3],especially the gyrotron,against arcing in the transmission line.     

HL-2A装置电子回旋打火保护系统设计

电子回旋打火保护系统由打火弧光探测器、A/D转换单元和逻辑处理单元组成。弧光探测器响应时间小于2μs,A/D转换单元和逻辑处理单元响应时间小于1μs。打火保护系统输出保护信号关断各供电电源的响应时间小于20μs。     

一种矩形波导打火检测装置的设计

介绍了一种矩形波导打火检测电路,分析了打火探测点的选取和光敏器件的选择。理论分析及计算的结论是:在矩形弯头波导窄壁中间选择了一个小孔作为打火探测点,选择光电二极管SFH250V作为光敏器件。以SFH250V为核心器件,设计了一种打火探测及故障快速锁存电路,主要解决了微弱光信号的探测问题,解决了微弱光电流信号的转换及放大问题,同时设计了打火故障判断及故障信号输出电路。实验表明,该装置可以有效地捕获较微弱的打火故障信号。     

Experimental and numerical studies of arc restrikes in low-voltagecircuit breakers

This paper is devoted to the study of the arc restrike phenomenon in low-voltage circuit breakers. We focused our interest on the type of arc restrike that can be described as a sudden reignition in the arcing contact region while the arc was situated in the quenching chamber a few tens of microseconds before it occurs. Our experimental investigations have established that the critical arcing contact region is still crossed by a so called residual current on the order of several amperes. A gas temperature around 4200 K was derived from electrical measurements in this region before the arc restrike occurrence, We also demonstrate that the restrike takes place through the growth of the remaining current of several amperes in the arcing contact region. A numerical approach was carried out with a two-dimensional hydrodynamic code in order to simulate the gas behavior in the arcing contact region before and during the arc restrike phenomenon. The same temperature as the measured one is calculated just before the restrike. It is demonstrated that the current density appears to be the most sensible quantity. A critical value of 5 A/cm² was calculated     

The computation of axisymmetric, supersonic nozzle arc usingadaptive grids

The computational difficulties associated with an arc burning in an axisymmetric supersonic nozzle are mainly caused by the region (known as the boundary) surrounding the are core within which temperature changes rapidly. When the arcing current decreases, this boundary collapses rapidly towards the axis. An adaptive grid scheme based on the temperature gradient is used to solve the dynamic are conservation equations in the computational domain. A direct grid adaptive scheme relates the solution in the computational domain to that in the physical domain without interpolation. Numerical results are compared with the experimental results as well as other numerical solutions obtained respectively by using a uniformly distributed, fixed grid system in the physical domain and by the solution adjusted method. A good agreement is achieved     

Suppressing Arcing Phenomenon for MW/MMW CCTWT

The arcing phenomenon is easy produced for high power coupled cavity traveling wave tube (CCTWT) in MW/MMW because of higher operating voltage and electric field in electronic gun region of tube. Pre-breakdown phenomenon before arcing and the reasons of leading arcing are analyzed. The effects of cathode performance for arcing in the tube are emphatically discussed. Some approaches for reducing the arcing are proposed. It is shown that arcing phenomenon in CCTWT is effectively suppressed.     

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介绍了HL-2A装置电子回旋共振加热系统打火保护装置的改进。在改进设计过程中,实测了2类光电转换模块、4种型号的运算放大器芯片,定量测量了防自激电容的性能。选择了GGOE-2型光电转换器件,OPA128LM型运算放大器,确定了防自激电容为30pF。制作了30个原型机,满足了2009年HL-2A装置的要求。实验测得响应时间平均值为1.2μs,较改进前方案的小。此弧光探测器能够在不同强度的本底光和复杂电磁环境下稳定工作。     

Estimation of Post-Arc Neutral Vapor Density in the Gap Volume Generated by Evaporating Macroparticles in a Diffuse Vacuum Arc

This paper presents a mathematical model of calculations of the density of atoms evaporated from macroparticles in a diffuse vacuum arc. The influence of the initial temperature, diameter, and average velocity of the droplets, as well as the kind of the cathode metal on vapor density in the volume surrounding the electrodes was investigated. Both the initial density and the decay of vapor density were calculated for Cu and Cd electrodes following the extinction of the arc. The calculated densities constitute the basis for evaluating the influence of evaporating droplets on the development of electrical breakdown in a vacuum gap after arcing.     

HL-2A装置电子回旋系统弧光探测器的改进

介绍了HL-2A装置电子回旋共振加热系统打火保护装置的改进。在改进设计过程中,实测了2类光电转换模块、4种型号的运算放大器芯片,定量测量了防自激电容的性能。选择了GGOE-2型光电转换器件,OPA128LM型运算放大器,确定了防自激电容为30pF。制作了30个原型机,满足了2009年HL-2A装置的要求。实验测得响应时间平均值为1.2μs,较改进前方案的小。此弧光探测器能够在不同强度的本底光和复杂电磁环境下稳定工作。     

Separation of spiral contacts and the motion of vacuum arcs at highAC currents

A framing camera is used to photograph the vacuum arc between separating spiral-petal vacuum interrupter contacts. The rupture of the molten bridge between the contacts first leads to a high-pressure, transient arc column. This arc motion can become constricted for several milliseconds before it goes diffuse as the current decreases to zero. The current through the spiral contacts produces a magnetic field perpendicular to the arc column, which forces the arc to move outward and run along the periphery of the petals. Several vacuum arc modes occur during the half-cycle of high current arcing. Movies, gap-current curves, and arc voltage traces are used to study the development of the arc motion and how it is affected by the contact structure. This information is used to generate arc appearance diagrams in which the arc form and motion are correlated to instantaneous values of current and gap for a wide range of peak currents. Appearance diagrams are shown for two ranges of opening delay from current onset     

新型筒状双层闪络板等离子体枪

提出了新型筒状双层闪络板等离子体枪及其驱动电路的设计方案。枪内层接脉冲高压,均布160个电弧点,每个电弧点由中心焊盘及填充TiH2粉末的外围凹槽组成,TiH2粉末用硅酸钠粘接于凹槽中;通过100Ω电阻连接每个高压焊盘与接地端,电极间隙中产生等离子体。通过放电实验得出:当由3 kV,20μF电容器驱动时,脉宽为1.5μs、幅值约150 A的电流通过枪,产生的等离子体密度为1013~1014cm-3,存在时间0.5μs,等离子体定向速率达到5 cm/μs。实验证明:该闪络板等离子体枪可靠性强,可重复产生均匀等离子体。     

Vacuum interrupter model based on breaking tests

In this paper, a model will be presented of a HOLEC-made commercially available vacuum interrupter. This model can he used to determine the breaking capacity under various current switching conditions. It will be shown how the model is derived from switching tests in a synthetic test circuit. The measured data consist mainly of short circuit currents, arc voltages, TRV's, and arcing times from which other important information like, e.g., the critical arc energy and the amount of transferred electric charge can be determined. The calculated results obtained by the theoretical model and the measured data will be shown in various graphs. Furthermore, derating curves of this type of vacuum interrupter and a comparison between different types of electrode configurations will be presented     

Time-Resolved Laser Doppler Measurements in the Underexpanded Jet of a Model Gas-Blast Circuit Breaker under Arcing Conditions

A differential laser Doppler system has been used in conjunction with a self-triggered oscillographic raster display system for measuring particle concentrations and flow velocities in a model gas-blast circuit breaker. The flow velocities have been correlated with particle size to enable extrapolation to be made to determine the true plasma flow velocity. The results have been deconvoluted to take account of lateral movements of the arc column. The measurements have been taken with air as the host arcing medium and a flow through a 25-mm-diameter orifice sustained by an upstream pressure of about 7 bar (downstream pressure 1 bar). The arc was sustained by sinusoidal cuffents of peak values 3 and 8 kA and a frequency of 85 Hz. These two currents corresponded to conditions when the model circuit breaker successfully and unsuccessfully interrupted the arc-sustaining current, respectively. The results show that in the case of the 8-kA arc, the flow pattern is severely distorted from that under nonarcing conditions, suggesting that this is a contributory reason for the poorer perfonnance of the model circuit breaker at this higher current level.