Study on arc mode and shape transformation in the arc motion stage between transverse magnetic field contacts

Transverse magnetic field (TMF) contacts drive the vacuum arc moving along the contact surface by producing a magnetic field perpendicular to the arc current flow, which makes the arc energy distribute uniformly and prevents the contact from serious ablation due to local overheating. The characteristics of arc motion between the TMF contacts directly determine the surface temperature distribution and contact erosion. Also, it is closely related to the breaking ability of the contacts. In this paper, the arc motion between spiral‐type contacts was recorded by a high‐speed camera. By analysing the arc voltage and arc images, the characteristics of arc shape transformation in the motion stage under different currents were studied. At the same time, the influence of arc duration and arc characteristics before the motion stage on the arc motion is discussed. It is found that the arc behaviour before the motion stage did influence the shape transformation and range of arc rotation. After entering the motion stage, there was always a rapid transformation process of the arc shape and the arc would return to where it first became constricted after a short movement. After a continuous movement, it might rotate in a small region where the arc stagnated before the motion stage. In addition, the arc behaviour was also related to its duration. When the opening time was varied from 2 to 5 ms, the arc velocity decreased. Meanwhile, it was more likely that multiple transformations of the arc aggregation degree occurred.     

Investigation on arc characteristics in cup-shaped contacts with different structure for transverse magnetic field vacuum circuit breaker

The cup-shaped transverse magnetic field (TMF) contacts contain radial components and tangential components in the TMF generated when the current is interrupted. The tangential force generated by the radial magnetic field component drives the vacuum arc to rotate, and the tangential magnetic field component generates a radial force that causes the vacuum arc to move radially outward. In this paper, in order to study the influence of the arc force direction on the arc characteristics, the influence of the contact structure parameters such as the inclination of the inner wall on the arc force direction is simulated, and the breaking tests of different levels of current are carried out on the contact with different structure parameters. It is found that the direction of the Lorentz force has a significant effect on the breaking characteristics of the current, and the tangential and radial force components have varying degrees of influence on the motion characteristics of the arc during the start process and the metal droplet splashing.     

Investigation of unstable motion characteristics of vacuum arc cathode spots between transverse magnetic field contacts

With the improvement of the current level of power grids, the requirements of the opening level of the vacuum switches are also increasing. Vacuum arc cathode spots provide steam and electrons and, to a certain extent, determine the opening capacity of the vacuum switch. In this paper, a vacuum arc cathode spot research platform based on the de-mountable vacuum chamber is constructed. The characteristics of the vacuum arc cathode spots under the transverse magnetic field (TMF) contacts are assessed by a high-speed charge coupled device. The experimental results show that the cathode spot diffusion process can be divided into three processes through cathode spot distribution, arc voltage and current: initial diffusion stage of cathode spots, unstable motion stage of cathode spots, and extinguishing stage. The motion mode of cathode spots during unstable motion stage can be divided into cathode spots group stagnation (CSGS) to multi-cathode jet (MCJ) switch mode, cathode spots group motion (CSGM) to MCJ switch mode, CSGM mode, and MCJ mode. The effects of peak current and contact diameter on unstable motion mode were analysed.     

Influence of bias magnetic field on the vacuum arc in double‐break vacuum circuit breakers

When double‐break vacuum circuit breakers (VCBs) interrupt the fault current, the series arc will generate their individual magnetic fields in different breaks. The magnetic field in one break will influence the arc in another break if the magnetic field is strong enough or the two breaks are very close. In this case, an interactive magnetic field effect happens. This field is also called the bias magnetic field (BMF). BMF can cause anode erosion and affect the performance at current zero. The distribution of BMF and the optimal configuration of the double‐break VCBs were obtained by the electromagnetic field simulation using the Ansoft Maxwell software. Based on the simulated magnetic field data, in the experiments, the interaction between the series vacuum arcs in double‐break VCBs was equivalent to the interaction between a single vacuum arc and the magnetic field generated by a Helmholtz coil. A high‐speed CMOS camera was used to record the trajectory of the vacuum arc plasma under different BMFs with different types of contacts. The results show the BMF can increase the arc voltage, and the arc becomes unstable. When the BMF becomes stronger, the arc voltage increases, and the arc becomes more unstable. In addition, for different types of contacts, the development process of the arc and the influence level are different under the same BMF. For a Wan‐type transverse magnetic field (TMF) contact or strong BMF, metal sputtering is evident and anode erosion becomes serious. For a cup‐type axial magnetic field (AMF) contact, the influence of BMF on the series arc plasma in double‐break VCBs is less than that of the Wan‐type TMF contact. The results of this work may be helpful for the design of compact double‐break VCBs.     

The Investigation of Copper-Chromium Contacts in Vacuum Interrpters Subjected to an Axial Magnetic Field

The characteristics of a vacuum arc between CuCr contacts under an axial magnetic field have been investigated. Test samples were made of CuCr contacts, and the arcing voltage was measured. The arcing voltage of the CuCr contacts under an axial magnetic field is lower than that of pure copper contacts by 10-20 V. From the measurement of the post-arc current and interruption test results, it was found that the arc concentrates and a part of the electrode melts at a rather low current, but that the electrode melting does not affect the interrupting capability. Also, the insulation characteristics were measured. With respect to voltage conditioning, high-current conditioning improved the breakdown voltage by 50 percent for a 20-mm gap and by 100 percent for a 3-mm gap. These test results show that CuCr contacts, used with axial magnetic fields, are promising for use in high-voltage and high-power vacuum interrupters.     

Visualization and characterization of high-current diffuse vacuumarcs on axial magnetic field contacts

We have investigated the behavior of drawn vacuum arcs for several designs of axial magnetic field (AMF) contacts using high-speed digital photography and arc voltage measurements, As the peak current was increased, a gradual transition occurred in the arc appearance from a multiple cathode-spot arc to the high-current diffuse mode, and then to a high-current diffuse columnar mode. Two relatively simple models based on the literature are used to explain the results. The first is an empirical criterion for using the arc voltage behavior to determine the maximum arc current for which an AMF geometry can produce a high-current diffuse mode from the initial bridge column arc. The second model predicts the highest arc current that can be forced into a fully diffuse mode for given values of the AMF and the contact arcing radius. The predictions of these models are compared to our experimental and analytical results     

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。     

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     

Contact temperature and erosion in high-current diffuse vacuum arcson axial magnetic field contacts

We have investigated the surface heating effects of drawn vacuum arcs for several industrial designs of axial magnetic field (AMF) contacts, using near infrared (IR) photography of the Cu-Cr arcing surfaces with an image-intensified charge-coupled device (CCD) camera and an IR pyrometer. This enables detailed contact temperature mapping immediately after a half-cycle of arc current. The very homogeneous temperature distribution observed at current zero stands in contrast to the visually nonhomogeneous high-current diffuse arc, which was studied in separately reported experiments using high-speed digital photography and arc voltage measurements. The peak temperature at current zero increased relatively linearly with the peak current I_P, and reached well beyond the melting range. We combine the temperature maps with a heating model to determine the thermal sheath thickness after arcing and its dependence on I_P. The results suggest that near the interruption limit of AMF contacts, the interaction of the stable high-current arc with the anode and cathode is dominated by processes induced by flowing liquid metal, which redistributes the heat input from the axially concentrated arc over most of the contact surface. Furthermore, the flow of liquid metal off the cathode and anode faces contributes to the overall contact erosion     

A rotating arc gas pump for circuit breaking and other applications

A rotating arc circuit breaker is described which uses an auxiliary current source to generate the magnetic field for driving the arc. Test results obtained using optical fiber measurement systems have shown that there are three main arcing phases. Initially the arc rotates at an essentially constant but low velocity, subsequently its velocity oscillates between this and much higher values, and finally the are plasma may become diffuse in nature. Test results obtained with dielectric strength probes have indicated that a unidirectional flow of arc heated gas is generated. The flow is away from the moving contact of the interrupter so promoting good dielectric strength in this critical contact region. The combination of the optical fiber and dielectric probe results indicates two possible modes of gas pumping represented, respectively, by a fan and a piston-type action of the arc. Simplified analytical models for both modes are developed with predictions obtained showing good agreement with the experimental results. Discussion of experimental results suggests that the transition from oscillatory velocity changes to diffuse arcing represents an important parameter for scaling the geometries of future interrupters and arc heaters     

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.     

The Interaction of Vacuum Arc Ion Currents with Axia I Magnetic Fields

We summarize a series of experiments in which we measured the distribution of ion currents leaving the interelectrode region of a vacuum arc with Cu electrodes. Ion currents were collected by an arrangement of cylindrical collectors surrounding the arcing space. A Helmholtz coil arrangement surrounding the arcing chamber generated the axial magnetic field. Arc currents ranged from 70 to 2400 A dc.     

HL-2M装置5 MW中性束加热束线离子源放电室研制

为了给HL-2M装置建设一条5 MW中性束加热束线,开展了中性束加热用热阴极弧放电离子源放电室的研制。这条中性束束线包含4套80 kV/45 A/5 s离子源,放电室的设计指标为850 A/5 s。首先采用CST软件中的电磁工作室对特定几何结构的放电室会切磁场进行了模拟计算,得到了会切磁场分布,验证了会切磁场布局的合理性。针对放电室加工工艺和实验过程中局部拉弧等问题,对放电室结构进行了不断改进。放电室侧壁由40列会切磁体改为7圈环形磁体,阴极灯丝结构从灯丝板结构最终改为陶瓷可伐结构,并且在放电室和加速器之间增加了陶瓷屏蔽。在阴极板结构放电室和阴极陶瓷可伐结构放电室内都获得了正常的弧放电。最终定型的放电室采用周边7圈环形会切磁体和陶瓷可伐结构。在定型的放电室内达到了5 MW中性束束线离子源弧放电的指标。弧放电时间接近5 s,最大弧放电电流达到1 000 A。     

The High Current Metal Vapor Arc Column between Separating Electrodes

We observed metal vapor arcs between separating electrodes in a demountable vacuum chamber using high speed photography. The peak values of the ac arc current half-wave ranged from 5 kA to 67 kA. Determination of the arc appearance as functions of arc current and electrode gap revealed that the arc can assume various types of columnar forms when the current at the instant of electrode separation exceeds 7 kA. The duration of the columnar arcing forms is influenced by axial magnetic fields differently for different field strengths. The graphical representation of the results allows prediction of the most probable arc appearance for a given set of operating parameters. A qualitative explanation of the various arc appearances on the basis of balances between magnetic and kinetic pressures is provided.     

纵磁结构真空灭弧室电磁场及电弧运动特性

为了了解纵向磁场下的电弧运动过程,建立了真空灭弧室的3维仿真模型。采用PIC模拟方法对12 kV灭弧室内的电磁场、电弧运动特性进行计算仿真。通过改变触头间距、屏蔽罩尺寸和触头开槽宽度,研究了灭弧室内的电场、磁场分布;对不同触头间距下随时间变化的电弧运动过程和触头表面的电弧分布情况进行了模拟计算。计算结果表明:在真空灭弧室中适当设置屏蔽罩,可有效改善灭弧室内的电场分布;触头铜基上的开槽宽度对磁场会产生影响,宽度越大,磁场强度越大。     

不同水深下水下湿法焊接电弧引弧温度计算

水下湿法焊接技术近年来得到了广泛应用,但目前对水下湿法焊接引弧过程的物理本质的研究很少。首先搭建了水下湿法焊接电弧光谱诊断平台,同步采集不同水深条件下焊接过程中的电流、电压及光谱信号,对不同水深条件下水下湿法焊接引弧阶段进行界定,高速摄像机拍摄水下湿法焊接引弧过程以更直观观察引弧过程中电弧、气泡等水下动态变化。在此基础上,设置光谱仪延时,分别采集了引弧5,10,15,20及25 ms的光谱信号;改变水深条件,得到不同水深条件下引弧不同时刻的电弧光谱图。根据谱线选取原则综合分析,选取Fe元素作为计算水下湿法焊接引弧电弧温度的特征元素。引弧不同时刻均选取了五组数据,运用统计分析的方法对五组数据做平均化处理,以保证计算结果的准确性和可靠性。从Fe元素谱线中选取了五条合适的谱线作为计算水下湿法焊接引弧过程电弧温度的目标谱线,再利用玻尔兹曼图示法分别计算了不同水深条件下引弧不同时刻的水下湿法焊接电弧等离子体温度。结果表明：在相同水深条件下,引弧过程中电弧等离子体温度是随着引弧时间的不断增加而不断变化的,但其变化趋势并不是简单的线性增加,而是分别在引弧的不同时刻出现峰值;随着水深的增加,水下湿法焊接电弧等离子体的温度也随着上升,但其电弧温度的上升趋势开始变缓慢,40 m水深相对于20 m水深的电弧温度上升量要低于20 m水深条件下相对0.3 m水深条件下的电弧温度上升量。伴随着水深的增加,水下环境压力增大造成电弧进一步压缩,但压缩量有限。由于电弧被压缩,弧光的强度也增大。通过光谱分析的方法,从电弧物理的角度获悉水下湿法焊接引弧过程的物理本质,对认识电弧建立过程中微观击穿机理及实际生产中进一步提升引弧过程的稳定性提供了重要参考。     

Vacuum interrupter design based on arc magnetic field interactionfor horseshoe electrode

Computational methods for evaluating the complex magnetic field structure in axial magnetic field type vacuum interrupters based on horseshoe electrode geometry are demonstrated. Arcing behavior can only be understood by incorporating an arcing model. An essentially low-current arcing model is capable of predicting the high-current arcing behavior and can be used to optimize the contact structure     

Influences of travelling magnetic field on the dendritic structures of Sn–1.8Cd peritectic alloy during directional solidification

The effects of melt flow driven by a travelling magnetic field (TMF) on solidification structures of Sn–1.8 wt.% Cd peritectic alloy have been investigated numerically and experimentally. Numerical results indicate that the flow velocity at the solid–liquid interface under a downward TMF is smaller than that under an upward TMF. The experimental results show that the growth directions of dendrites are chaotic, and several crotches among the dendrites are observed at the solid–liquid interface in the case of no field. It is concluded from TMF results that the ordered growth of dendrites at two different directions occurs, and only one crotch among the dendrites appears at the solid–liquid interface. The location of the crotch gradually approaches the interface center with increasing magnetic field intensity (B≤10.3 mT). Moreover, the growth of high-order branches occurs at the crotch under a downward TMF. A simple model is established for explanation and it well corresponds to the experimental results.     

Arc erosion reduction on electrical contacts using transversecurrent injection

Electrical contact lifetime is often directly determined by arc erosion. A method for reducing are erosion was developed consisting of injecting from an external current source an additional electrical current flowing parallel to the contact surface. This method was examined in three are environments using the additional transverse electrical current with a density less than 1 A/mm²: 1) automobile ignition contacts; 2) pulsed air arc; and 3) low pressure (P=100 mTorr) arc in nitrogen, SEM and X-ray examination showed that application of a transverse current in a contact during arcing changed the phase composition and microstructure of the contact surface. Under optimal conditions, the microstructure which is formed is significantly more erosion resistant than without the transverse current injection