Numerical Simulation of Low Current Vacuum Arc Supersonic Flow

Based on a two-dimensional axisymmetric magneto-hydrodynamic （MHD） model, low current vacuum arc （LCVA） characteristics are studied. The influence of cathode process under different axial magnetic fields and different anode radii on LCVA characteristics is also simulated. The results show that the influence of both cathode process and anode radii on LCVA is significant. The sign of anode sheath potentials can change from negative to positive with the decrease of anode radii. The simulation results are in part verified by experimental results. Especially, as the effect of ion kinetic energy is considered, ion temperature is improved significantly; which is in agreement with experimental results.     

Simulation of the Effect of a Metal Vapor Arc on Electrode Erosion in Liquid Metal Current Limiting Device

The effect of arc plasma on electrode erosion in a liquid metal current limiter(LMCL)is studied.Based on a simplified two-dimensional magnetohydrodynamic model,the elongated GaInSn metal vapor arc and its contraction process in a liquid metal current limiter are simulated.The distributions of temperature,pressure and velocity of the arc plasma are calculated.The simulation results indicate that the electrode erosion is mainly caused by two high temperature gas jet flows arising from the pressure gradient,which is a result of the non-uniform arc temperature distribution.The gas flows,which act as jets onto the electrode surface,lead to the evaporation of the electrode material form the surface.A redesign structure of the electrode is proposed and implemented according to the analysis,which greatly increased the service life of the electrode.     

Influence of Gap Distance on Vacuum Arc Characteristics of Cup Type AMF Electrode in Vacuum Interrupters

The greenhouse effect of SFe is a great concern today. The development of high voltage vacuum circuit breakers becomes more important. The vacuum circuit breaker has minimum pollution to the environment. The vacuum interrupter is the key part of a vacuum circuit breaker. The interrupting characteristics in vacuum and arc-controlling techniue are the main problems to be solved for a longer gap distance in developing high voltage vacuum interrupters. To understand the vacuum arc characteristics and provide effective technique to control vacuum arc in a long gap distance, the arc mode transition of a cup-type axial magnetic field electrode is observed by a high-speed charge coupled device （CGD） video camera under different gap distances while the arc voltage and arc current are recorded. The controlling ability of the axial magnetic field on vacuum arc obviously decreases when the gap distance is longer than 40 ram. The noise components and mean value of the arc voltage significantly increase. The effective method for controlling the vacuum arc characteristics is provided by long gap distances based on the test results. The test results can be used as a reference to develop high voltage and large capacity vacuum interrupters.     

The Discharge Development and Arc Modes in Vacuum at A Long Gap Distance in Vacuum Interrupters

The influence of an arc current on the discharge development and the arc modes of a single coil type axial magnetic field （AMF） electrode were investigated by a high-speed charge couple device （CCD） video camera in a long gap distance of 40 mm. The distribution of the axial magnetic field of the single coil type AMF electrode was computed. By computational results, the single coil type AMF electrode could generate higher axial magnetic flux density than the slot type AMF electrode. It was found that the single coil type AMF electrode could perform better than the slot type AMF electrode with the same designing parameters. And the development of the arc modes experienced diffuse mode, constricted but unstable mode, and constricted and stable mode with the amplitude of the arc current increasing. The correlation between the vacuum arc and the noise components of arc voltage was investigated too. The interruption capability could be known in a practical commercial vacuum interrupter by the test results in a demountable vacuum interrupter （DVC） with a electrode diameter of 50 mm and a gap distance of 40 mm.The test results could provide reference to design the high voltage vacuum interrupter adopting the single coil type AMF electrode.     

Motion and Splitting of Vacuum Arc Column in Transverse Magnetic Field Contacts at Intermediate—Frequency

Arc motion and splitting of vacuum arc at intermediate frequency（400-800 Hz） were investigated under transverse magnetic field（TMF）.The experiment was performed on cup-type TMF contacts with contact diameter of 40 mm and a contact gap of 4 mm in a single-frequency circuit.With high-speed photography we characterized the arc appearance at different arc currents from 3.3 kA-rms to 10 kA-rms at intermediate frequencies.As arc current increases from3.3 kA-rms to 10 kA-rms the arc appearance changes obviously.When current value is 3.3 kArms（current frequency 400-800 Hz）,there is almost no splitting arc;when the current exceeds5 kA-rms（current frequency 400-800 Hz）,the arc rotates at a speed above 20 m/s,accompanied by an observable splitting arc.The splitting arc could be observed at different frequencies and the arc-voltage had no noises when splitting occurred.The motion direction and the velocity of arc column were studied.Finally,the formation of a split arc was discussed.     

Simulation Research of Magnetic Constriction Effect and Controlling by Axial Magnetic Field of Vacuum Arc

Based on magnetohydrodynamic (MHD) model of vacuum arc, the computer simulation of vacuum arc was carried out in this paper. In the MHD model, mass conservation equation, momentum conservation equations, energy conservation equations, generalized ohm‘s law and Maxwell equation were considered. MHD equations were calculated by numerical method, and the distribution of vacuum arc plasma parameters and current density were obtained. Simulation results showed that the magnetic constriction effect of vacuum arc is primarily caused by the Hall effect. In addition, the inhibition of axial magnetic field (AMF) on constriction of vacuum arc was calculated and analyzed.     

过滤管道磁场在改进真空弧沉积系统中的作用

在90°磁过滤管道和MEVVA源阴极之间加30～60V的正偏压可使磁过滤管道起到阴极弧放电第二阳极的作用.在此情况下,就磁过滤管道磁场对MEVVA源阳极-阴极和磁过滤管道-阴极两个回路弧放电和磁过滤管道等离子体传输效率的影响进行了实验研究.研究结果表明随磁过滤磁场升高,磁过滤管道和阴极之间的弧放电规模降低,系统的等离子体传输效率升高,但对MEVVA源阳极和阴极之间的弧放电规模影响不大.     

真空石墨加热器温度场数值模拟与分析

石墨加热器是测量球床堆芯等效导热系数实验的关键部件,加热器温度场对系统安全及数据准确性有重要影响。本文基于Fluent计算平台,分别采用DTRM模型、P1模型、ROSSELAND模型、DO模型对真空保护环境下的石墨加热器温度场进行数值模拟,确定适合真空保护石墨加热器温度场的计算方法并讨论石墨导热系数、表面发射率对温度场分布的影响。比较分析表明：DO模型计算得到的温度分布较为接近真实情况,导热系数小于35W/(m•K)时,最高温度对其敏感;导热系数大于35W/(m•K)时,其对加热体最高温度影响较小,最高温度较为稳定。     

Simulation to Predict Target Erosion of Planar DC Magnetron

Plasma properties in a planar DC magnetron system are simulated by a non-self- consistent particle method in two dimensions. Through tracing the trajectories of the energetic electrons in the specified electric field and the magnetic field, and treating the collision process by Monte Carlo method, the spatial profile of ionization events can be obtained conveniently. Assuming that the ions speed up from the ionization points and bombard the target with the energy at these points, and according to the Yamamura/Tawara method, the target erosion can be predicted. The magnetic field is calculated by the finite element method, and the electric field is estimated according to the self-consistent simulation and measured results. The influence of the time step size on the target erosion profile is analysed first to find a proper step size. Then the influence of electric field estimated on the erosion profile is discussed. The erosion profile may become narrower if the sheath thickness is increased. Finally, considering the dynamic erosion process, the erosion profile may get wider over time for the magnetron with shunt bar.     

Interruption Phenomenon in Intermediate-Frequency Vacuum Arc

In the condition of the 3 mm gap, experiments for 360 Hz intermediate-frequency vacuum arc are carried out in interrupters with the diameters being 41 mm and with the contact materials being CuCr50 and Cu-W-WC alloy respectively. The results indicate that the contacts material is closely related to the breaking capacity of the vacuum interrupters and characteristics of an intermediate-frequency vacuum arc. For contacts with the same diameter, the breaking capacity of CuCr50 is better than that of Cu-W-WC. When the current fails to be interrupted, the arcs overflow the gap and present irregular performances in the first half wave. Consequently a voltage spike appears. More macroscopic metal droplets can be seen in the arc column between CuCr50 contacts because of the lower melting point. It is observed that the droplet emission is much more severe during arc reignition than that in the first half wave. It is much more conspicuous that the high frequency arc voltage noises appear in Cu-W-WC contacts when the vacuum arcs reignite, for higher temperature and stronger electronic emission ability of Cu-W-WC contacts.     

Arc Behaviours in Vacuum Interrupters with Axial Magnetic Field Electrodes

To improve the limiting current interruption capability and minimizing vacuum interrupter with axial magnetic field （AMF） electrodes, it is significant to investigate the vacuum arc behaviours between the contacts. AMF distributions of the slot type electrodes were studied by both numerical analysis and experiments. Furthermore, the behaviours of vacuum arcs for different parameters of the slot type AMF electrodes were investigated by using high-speed CCD camera. The influences of gap distance, contact diameter and phase shift time between AMF and arc current on the vacuum arc were investigated. The results provide a reference for research and development of vacuum interrupters with slot type or other types of AMF electrode.     

Influence of Jet Angle and Ion Density of Cathode Side on Low Current Vacuum Arc Characteristics

In this study, the influence of the initial jet angles （IJAs） and ion number densities （INDs） at the cathode side on the low current vacuum arc （LCVA） characteristics is simulated and analysed. The results show that the ion temperature, electron temperature, ion number density, axial current density and plasma pressure all decrease with the increase of the cathode IJAs. It is also shown that LCVA can cause a current constriction for lower cathode IND, and the anode sheath potential is more nonuniform, which is mainly related to the nonuniform distribution of the axial current density at the anode side.     

核电站凝汽器仿真模型研究

凝汽器是核电站汽轮发电机组的主要设备之一,采用仿真手段研究核电站凝汽器的运行特性对于优化设计和运行、提高运行的安全性和经济性具有实际意义。本文以核电站中普遍采用的表面式单流程对分制凝汽器为研究对象,运用分布式热动力学的建模思想,考虑不凝结气体（空气）对换热特性的影响,建立了凝汽器的动态数学模型。通过仿真计算,得到不同控制参数阶跃情况下凝汽器的动态响应,仿真结果与实验结果符合良好,表明所建立的仿真模型正确、合理。     

Influence of Copper Vapor on Low-Voltage Circuit Breaker Arcs During Stationary and Moving States

The influence of copper vapor on the low-voltage circuit breaker arcs is studied. A three-dimensional （3-D） magnetohydrodynamics（MHD） model of arc motion under the effect of external magnetic field is built up. By adopting the commercial computational fluid dynamics （CFD） package FLUENT based on control-volume method, the above MHD model is solved. For the mediums of air-1% Cu and air-10% Cu, the distributions of stationary temperature, pressure, electrical potential and the arc motion processes are compared with those of a pure air arc. The copper vapor diffusion process in the arc chamber and the distribution of copper vapor mass concentration are also simulated. The results shows that the copper vapor has a cooling effect on the arc plasma and can decrease the stationary voltage as well. Moreover, the presence of copper vapor can decelerate the arc motion in the quenching chambers. The maximal copper vapor concentration locates behind the arc root because of the existence of a ＂double vortex＂ near the electrodes.     

Simulation of Vacuum Arc Characteristics Under Four Kinds of Axial Magnetic Fields and Comparison with Experimental Results

Based on a two-dimensional axisymmetric magnetohydrodynamic （MHD） model, the vacuum arc characteristics under four kinds of axial magnetic fields （AMFs） are ana...     

Investigation of Vacuum Arc Voltage Characteristics Under Different Axial Magnetic Field Profiles

Characteristics of the arc voltage under different profiles of axial magnetic field were investigated experimentally in a detachable vacuum chamber with five pairs of specially designed electrodes generating both bell-shaped and saddle-shaped mafnetic field profile. The arc column and cathode spot images were photographed by a high speed digital camera. The dependence of the arc voltage on arcing evolution is analyzed. It is indicated that the axial magnetic field profile could affect the arc behaviors significantly, and the arc voltage is closely related to the arc light intensity.     

Study of Distortion of a Vacuum Arc at a Long-Gap Distance

Experimental study of the long-gap distance vacuum arc distortion for three types of axial magnetic field (AMF) contacts, by using high-speed charge coupled device (CCD), is presented. The arc current was of a half-cycle sine wave with a frequency of 50Hz, produced by an L-C discharging circuit. The time of appearance and duration of vacuum arc distortion under three conditions were studied. It was found that the gap distance, current and diameter of the electrode affected the characteristics of vacuum distortion at a long-gap distance. Some characteristics of the vacuum arc at a long-gap distance was revealed and the experience and data for further investigation were provided.     

Distribution of Cathode Spots in Vacuum Arc Under Nonuniform Axial Magnetic Fields

Recent results on the distribution of vacuum arc cathode spots （CSs） in nonuniform axial magnetic field （AMF） are presented. Based on previous studies, we deem that two contrary influences of AMF, inward effect and outward effect, are attributed to CSs distribution. With this notion, we have analyzed the controlling effectiveness of nonuniform AMF on CSs distribution. Experiments were conducted in a detachable vacuum chamber with iron-style AMF electrodes. Images of vacuum arc column and the distribution of CSs were photographed with a high-speed charge coupled device （CCD） camera. Experimental results agreed well with the theoretical analysis.     

真空弧离子源引出束流在加速空间的分布

采用数码相机直接照相的方法来确定真空弧离子源引出束流在加速空间的分布。实验在动态真空实验系统中进行,系统真空度优于2×10-3 Pa。在离子源脉冲工作的条件下,采用数码相机拍摄到离子源引出束流在加速空间的积分图像,得到引出束流的幅亮度在拍摄平面上的相对分布,然后再通过Abel转换得到引出束流在加速空间的径向分布。实验结果表明:真空弧离子源引出束流近似高斯分布,离子源出口处的束流比靶入口处的束流强40%。     

Influce of Initial Opening Speed on Characteristics of a Drawn Vacuum Arc

Influence of the initial opening speed on the characteristics of drawn vacuum arcs for axial magnetic field(MF) vacuum interrupters (VIs) is studied using a high-speed charge- coupled device (CCD) camera. Two values of initial opening speed, 0.5 m/s and 1.5 m/s, were set to make a comparative study. The cup-type electrode was made of Cu-Cr (50%-50% in weight) with a diameter of 30 mm and a gap distance between electrodes of 10 mm. The results show that the transition time decreases by 0.5 ms when the initial opening speed increases from 0.5 m/s to 1.5 m/s at a peak current of 2.5 kA, while the transition time decreases by 1.0 ms when the initial opening speed increases from 0.5 m/s to 1.5 m/s at a peak current of 5.0 kA. The reason why the duration of the transition arc mode decreases is that the e®ect of electromagnetic force and Coulomb force among arcs is increased when the initial opening speed increases.