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A three-dimensional (3-D) model for multispecies vacuum arc considering ionization and recombination process has been built in this article. With the model, the arc behaviors and species characteristics subjected to actual spatial magnetic fields of cup-shaped axial magnetic field (AMF) contact and transverse magnetic field-axial magnetic field (TMF-AMF) contact are investigated and compared. Furthermore, the validity of the model is verified by comparing with the experiments. Simulation results show that contact structures affect the species distributions of the arc by changing magnetic field and current density distributions. More triple charged ions are generated through ionization under higher electron temperature so that the triple charged ions gather where current constricts. The heat flux density is large in the current contraction region, where the contribution from triple charged ions is large as well. Spatial magnetic field distribution affects the Lorentz force acting on ion components. The force distribution is relatively uniform and the species are subject to inward force on the arc edge under cup-shaped AMF contact. For TMF-AMF contact, the double charged ions are subject to the force pointing to the TMF contact arms, whereas the triple charged ions are subject to the force pointing to the arc center. In addition, the consideration of arc species can improve the accuracy of the simulation results of the heat flux distribution, leading to a good agreement of the erosion condition between experiments and simulation. [ABSTRACT FROM AUTHOR]

As a special phenomenon under transverse magnetic field (TMF) contacts, vacuum arc rotation deserves more attention. In this article, rotation characteristics of three typical TMF contacts, i.e., swastika-type, cup-shaped, and double-TMF contacts, are systematically studied. According to arc images, recorded by a high-speed camera, physical terms related to arc rotation such as rotation duration and rotation speed are clearly defined. The magnetic field and Lorentz force are calculated and the force balance of the moving arc is analyzed. On this basis, the effects of arc ignition mode, peak current, and contact type on arc rotation are investigated. Arc voltage noise as well as arc splashing outside caused by rotation is also discussed. The results show that the duration from ignition to rotation in two-point arc ignition (TPAI) mode is usually the shortest because of the rapidest constructed column formation. As the peak current increases, arc rotation becomes easier. Due to stronger TMF, the arc under double-TMF contacts has the longest rotation duration and the highest rotation speed. [ABSTRACT FROM AUTHOR]

The objective of this article is to investigate the effect of contact material on the formation and transition of high-current anode spots and anode plumes. A series of experiments are carried out in a demountable vacuum chamber at three current levels of 3, 4, and 6.5 kA. Plate contacts made of CuCr30 and CuCr40 with a diameter of 10 mm are adopted. Arc images are captured by a high-speed camera and synchronized with measurements of the arc current and voltage. The experimental results show that the three typical anode discharge modes, namely footpoint, anode spot type 1, and anode spot type 2, are formed at a smaller gap distance as the experimental current increases, and this tendency is independent of the contact material. The arc voltage is higher and the anode spot appears earlier and lasts longer under the CuCr40 contact than under the CuCr30 contact. As a result, the footpoint is formed at a smaller gap distance, whereas anode spot type 2 is formed at a larger gap distance. As a special anode discharge mode, an anode plume usually occurs between anode spot type 2 and arc current zero in various shapes at different locations on the anode surface. The anode plume of the CuCr40 contact appears at a larger gap distance and the corresponding threshold current and accumulated arc energy are also larger. Due to a stronger anode activity, the anode plume lasts a longer time under the CuCr40 contact than under the CuCr30 contact. [ABSTRACT FROM AUTHOR]

Modeling and numerical simulation is an important tool for the research of the physical mechanisms of the vacuum arc (VA). Compared with the experiments of the VA, numerical simulation is more efficient and economical. Axial magnetic fields (AMFs) are also the most popular control technology in vacuum interrupters and other application fields. First, the model of VA was reviewed from a relatively simple zero-order one to 2-D one, and then a 3-D one, which gives us a more comprehensive understanding of VA. Second, the influence of spatial distribution of magnetic fields on VA behavior is also studied. VA behavior under different commercial AMF contacts was simulated and compared based on 3-D magnetohydro-dynamic model. Influence of the radial slots and magnetic field generated by adjacent phase and bus bar on arc characteristics has been reviewed. Third, the VA modeling with active anode is reviewed and discussed. Anode vapor can cool arc plasma, and leads to changed distribution of current density and plasma parameters. Model and simulation technology of anode activity have also been reviewed in this paper, from 1-D, 2-D, to 3-D, and then the deformation of anode melting pool is considered. Deformation of anode melting pool will make anode temperature more reasonable. Finally, the challenge and research direction of VA modeling is also given and discussed. [ABSTRACT FROM AUTHOR]

Vacuum interrupter is widely used in the medium-voltage power system. Controlling the arc by the magnetic field is an effective method to improve the breaking capacity. The transverse magnetic field (TMF) forces the constricted arc to rotate to reduce local overheating. In this paper, three kinds of TMF contacts, which are Swastika-type contact, cup-shaped contact, and double-TMF contact that combines Swastika-type and cup-shaped contacts coaxially, are investigated in a demountable vacuum chamber with a high-speed camera. The arc voltage and current are also recorded. The experiments were conducted with circuit currents from 5 to 20 kA (root mean square) with a frequency of 50 Hz. There are four current levels in the experiment, which are 5, 10, 15, and 20 kA, and at least three tests are taken for each current level. The results showed that under low current (I = 10 kA), the arc of the three TMF contacts did not rotate. Under high current (I = 20 kA), it was observed that the arc of Swastika-type and double-TMF contacts rotated in the gap. The arc speed of double-TMF contacts is higher than that of Swastika-type contacts. The cup-shaped contacts have the highest arc voltage and noise among the three TMF contacts. The Swastika-type contacts were eroded most seriously. The simulation results show the force distribution of the arc on different locations. The resultant force makes the arc rotate counterclockwise. [ABSTRACT FROM AUTHOR]

Using magnetic fields to control the vacuum arc is a major way to improve the breaking capacity of vacuum interrupters. Besides the single transverse magnetic field (TMF) and single axial magnetic field (AMF), new type of TMF-AMF contact and TMF-TMF contact structures have been put forward to control the vacuum arc in recent years. In this paper, three different structural contacts are used in the experiments. The arc evolution was captured by an high-speed digital video camera, and at the same time, the arc current and arc voltage wave were recorded. The experiment was conducted under current ranging from 5 to 20 kA (root mean square) and 10 mm of gap distance. There are 12 current shots performed on one contact design. There are four current levels in the experiment which are 5, 10, 15, and 20 kA, and three tests are taken for each current level. The results showed that for TMF-AMF contacts, under low current (I = 5 or 10 kA), the arcs of the two kinds of contacts both kept diffused and rotating. Under high current (I = 20 kA), the arc of the TMF-AMF contact with six slots was constricted and rotated on the plate, and the melting was uniform and slight. As for the eight-slot contacts, the arc was constricted but did not rotate which resulted in significant melting in the local region. As for TMF-TMF contacts, the result is similar under low current, while the arc was constricted and rotated quickly on the inner plate under high current. The simulation results show that when the arc core is located on the outer plate; the total Lorentz force is near zero. When the arc core is located on the inner plate, the direction of total force is counterclockwise. [ABSTRACT FROM AUTHOR]

In order to improve the breaking capacity of contacts, it is very important to find a better contact material. In this paper, the triggering experiments of plate contact with different materials are studied to investigate the characteristics of vacuum arc. The current range is from 1 to 9 kA (rms). The gap distance is selected as 3 and 5 mm. The arc appearance and the behavior of cathode spots are captured by high-speed camera with an exposure time of $2~\mu \text{s}$. The surface topography of contacts after experiments is evaluated by scanning electron microscope. The arc current and arc voltage are measured at the same time by Rogowski coil and high-voltage probe. The diameter of the contact is 25 mm. There are seven kinds of materials (CuCr10, CuCr25, CuCr30, CuCr40, WCu10, WCu30, and CuW–WC) conducted in this paper. Compared with the experimental results, the arc of WCu alloy distributes more evenly on the contact plane with many bright cathode spots. The small gap distance makes the burning point more fixed. The arc of CuW–WC is unstable. During the arc trigger moment to the arc stable burning stage, the radial diffusion velocity of WCu10 cathode spot is the lowest with about 25% of CuCr10. CuCr10 alloy has the worst melting resistance. WCu alloy has good melting resistance and bad toughness. The toughness of CuW–WC is even worse. Under the low current, CuCr30 might be preferred for vacuum interrupters from the cathode spots’ radial diffusion speed, arc appearance, and erosion result. When the current increasing, the arc can easily spread to the entire surface of WCu contact, and WCu10 would be the prefer material with the diffusion arc and good erosion resistance. [ABSTRACT FROM AUTHOR]

In the interrupting process of a three-phase vacuum interrupter, there exists a transverse magnetic field (TMF) in the interelectrode region, which is produced by adjacent phases. The deflection of the vacuum arc caused by TMF will affect the interrupting process of vacuum circuit breakers. In this paper, the vacuum arc characteristics considering the action of TMF produced by adjacent phases is simulated based on a steady 2-D asymmetrical magnetohydrodynamic model. The simulation results show that the vacuum arc will swing around and is especially obvious at the smaller current moments near current-zero during one ac half-cycle, because of the changed direction of TMF produced by adjacent phases. This kind of swing phenomena can also be observed in the electrode erosion of unsuccessful interruption. At the moments near current-zero, axial magnetic field is relatively weaker, while TMF generated by adjacent phases is relatively stronger, therefore, the offset phenomenon of plasma parameters is more significant. Compared with smaller diameter electrode arc, larger diameter electrode has larger arc deflection distance, while its value of plasma parameters is much smaller. [ABSTRACT FROM AUTHOR]

The motion of cathode spots plays a crucial important role in removing oxide layer on a metal surface by vacuum arc. In this paper, the characteristics of the motion of a single cathode spot on metal surface with oxide layer are investigated experimentally. Experiments are conducted in a detachable vacuum chamber. A hollow copper anode with a hole of 10~\text mm \times 10 mm is used in order to observe the 2-D motion of the cathode spot. The motion of the cathode spot during the descaling process is photographed by a high-speed digital camera with an exposure time of 2~\mu \texts . Experimental results indicate that there are slow motion and fast motion of the cathode spot during descaling process, and the slow motion is the basic characteristic in most of the descaling time. The probability distribution of the cathode spot’s displacement and resident time, the average velocity, and the movement parameter S^2/t are analyzed quantitatively. The results indicate that with the increase of gap distance or the decrease of oxide layer thickness, the cathode spot becomes more active. [ABSTRACT FROM PUBLISHER]

Anode material seriously influences the characteristics of vacuum arc and further affects the performance of medium-voltage vacuum switches when the interruption current is high. There are many materials used for electrode manufacture, and different materials are selected for different switches. For a pure metal, its performance usually cannot satisfy the actual requirement. To improve switch’s performance, an alloy is usually used as an electrode material. In this paper, thermal processes of six kinds of metal anodes (including pure metal and alloy anodes) are simulated and researched. The physical parameters of the pure metals all come from experiment results directly or are fitted by the experimental data. The physical parameters of the CuCr alloys are derived from Cu and Cr parameters. Two kinds of temperature calculation methods are used, which are called melting and solidification model and equivalent specific heat method, respectively. Simulation results show that W and Mo anodes have the higher temperature than Cu, Cr, CuCr25, and CuCr50 anodes. A pure Cr anode has the largest melting width and highest saturated vapor pressure and evaporation energy. A Cu anode has the biggest melting depth. A W anode has the smallest melting width and depth. Axial temperature gradient is related to the thermal conductivity, and the Cr anode has the largest axial temperature gradient. The thermal characteristics of CuCr25 and CuCr50 anodes are located between the pure Cu and Cr anodes. There are two melting points appearing in the results of CuCr alloys, and between the two melting points, the alloy anodes are in solid–liquid mixture state. [ABSTRACT FROM PUBLISHER]

Based on a steady-state 3-D magnetohydrodynamic (MHD) model, the high-current vacuum arc (HCVA) under combined effect of actual magnetic field (MF) and external transverse MF (ETMF) is simulated. The actual MF is generated by cup-type axial magnetic field contact system commonly used in commercial vacuum circuit breakers. The ETMF may cause the deflection of arc column, which is the main reason of the contact deflected erosion. According to some experimental results, the electron temperature in HCVA is assumed to be uniform and equal to 3 eV. Therefore, the MHD model is simplified by neglecting the electron energy equation to improve the simulation efficiency. With the three conservation equations (mass, momentum, and energy) of ion flow coupling solved, the spatial distributions of some flow parameters can be obtained. The influence of all three components of the MF is inserted by solving the magnetic transport equations sequentially. Proper boundary conditions are set on the cathode and anode side, which separated the cathode spots mixing region and anode sheath region from computation domain, respectively. Under the influence of the ETMF, the deflection of the plasma flow can be predicted, which may be helpful to understand the mechanism of the contact deflected erosion. [ABSTRACT FROM PUBLISHER]

In this paper, high-current vacuum arc (VA) breaking experiments in vacuum interrupters were conducted using two kinds of high-capacity (larger diameter) axial magnetic field (AMF) electrodes with contact gap distance changing from 10 to 40 mm. Triggering arc mode and fixed gap distance were adopted. Experimental results showed that during the initial diffusion stage, the arc voltage of high-current VA got a peak value. The change in high-current VA appearance would also affect the curve of arc voltage. With the increase of contact gap distance, the voltage of high-current VA increased and the VA near the anode appeared contracted, and its shape was changed from cylinder to cone. In the shorter gap distance, for cup electrodes, the plasma jets mix with each other and the arc column appears like a bright cone, whereas for coil electrodes, the plasma jets are clear and the column appears like a cylinder, and the transfer of arc appearance affects arc voltage distribution. Moreover, arc twist and rotation often occur under longer gap and higher current, which is due to the larger radial magnetic field component generated by AMF coils, and arc voltage appeared high-frequency and high-amplitude noise, and ultimately resulted in the distortion of the arc current in the current experimental conditions (lower charging voltage of capacitor). [ABSTRACT FROM PUBLISHER]

Trigatrons have been widely used in many fields. However, the performance of trigatrons typically degrades as operational time increases. Among many influence factors, electrode erosion is a primary cause of trigatrons failure. In this paper, the peak current and pulsewidth of trigatrons are in the order of kiloampere (kA) and microsecond (\mus) , respectively, with an electrode size in the order of millimeters (mm). The discharge images show that the arc appearance looks filamentary in shape during the early period of the discharge. As the discharge process progresses, the arc expands and moves radially to the side surface of the anode. Simultaneously, electrode erosion experiments are conducted on the trigatrons in an atmospheric environment. Experimental results show that the erosion level becomes more serious with an increase of gap distance and discharge current. The weight loss of Mo and W electrodes with erosion times are very close to a linear distribution, however, weight loss rate of W-Cu electrodes increases more dramatically with an increase of erosion times. The erosion of WCu electrode is more pronounced than Mo and W electrodes the volume erosion rate of W is smaller than Mo, but the mass erosion rate of W is higher than Mo. Many cracks always appear on the W and Mo electrode surfaces, which are due to frequent and intensive interaction between the expansion and shrinkage of the electrode material. [ABSTRACT FROM PUBLISHER]

In this paper, a transient 3-D model of the anode activity in a high-current vacuum arc (HCVA) was established. The melting, flow, evaporation, and solidification of the anode material were included in this model. Based on this model, the thermal and flow process of the anode in an HCVA under axial magnetic fields was simulated and analyzed. Simulation results showed that the maximum anode temperature appeared near 7 ms. The maximum rotational velocity and melting radius appeared near 9 ms. This meant that the anode was still in the melting, flow, and evaporation status near current zero moment, which was easier to cause reignition of vacuum interruption. Through 3-D modeling and simulation, a more visualized anode process can be understood. In the future, unsymmetrical anode phenomena will be researched and analyzed by this 3-D model. [ABSTRACT FROM PUBLISHER]

Based on a 2-D magnetohydrodynamic model, high-current vacuum arcs (HCVAs) under axial magnetic fields (AMFs) with consideration of current density distribution at the cathode are simulated and analyzed. The current density distribution at the cathode used in the simulation is obtained by processing the image of cathode spots from experiments. In order to study the influence of current density distribution at the cathode on vacuum arc characteristics, HCVA is simulated under two kinds of current density distribution at the cathode. Then, for HCVA simulation in a half-sinusoidal period, the current density distribution at the cathode and the AMF delay are both taken into account. The simulation results show that the nonuniform current density at the cathode makes the values of the arc plasma parameters in the interelectrode region larger and their radial distribution more nonuniform than the uniform current density at the cathode. The more uniform current density at the cathode and the stronger AMF at the moments in the second 1/4 cycle make the values of the arc plasma parameters in the central region smaller and their radial distribution broader than those in the first 1/4 cycle. In addition, the simulation results will also be compared with the experimental results. [ABSTRACT FROM AUTHOR]

Removing an oxide layer on a metal surface by vacuum arc has been preliminarily used in the metallurgical industry as an environment-friendly substitutor for the traditional acid-washing technique. In this paper, the influence of protection gas pressure on descaling process is investigated experimentally. Arc images taken by a high-speed digital camera indicated that the descaling rate was closely related to the motion pattern of cathode spots in different gas pressures. The decrease of descaling rate with the increase of gas pressure could be partly attributed to the formation of cathode-spot group and its less mobility at high gas pressure. The influence of gas pressure on the power density of cathode spot was also analyzed. It seemed that higher gas pressure would lead to the decrease of the ratio of power input into the cathode spot to the total arc power, which could also contribute to the decrease of the descaling rate. [ABSTRACT FROM PUBLISHER]

Experiments on a drawn vacuum arc with forced current zero, which was formed by injection of a countercurrent with a frequency of 1 kHz, were conducted in a detachable vacuum chamber. The prospective peak main current was 3.5 kA. Arc characteristics were investigated with the aid of a high-speed digital camera with an exposure time of 2 \mu\s. In this paper, the influence of axial magnetic field (AMF) distribution and anode material on the evolution of vacuum arc in the initial expanding stage is mainly investigated. Three types of electrodes were used in the experiments. One of them was simple electrodes with butt contact plates, and the other two types were specially designed electrodes generating a conventional bell-shaped AMF profile and a saddle-shaped AMF distribution, respectively. OFHC copper and WCu10 were used as anodes for the electrodes with bell-shaped AMF. The appearance of vacuum arc in the forced current-zero stage is also investigated. [ABSTRACT FROM AUTHOR]

Based on a 3-D steady magnetohydrodynamic model, the high current vacuum arc subjected to a realistic spatial magnetic field generated by the cup-type contacts was simulated. The influence of the realistic spatial magnetic field profile on plasma's rotation behavior was analyzed. The distribution of the azimuthal velocity on anode side under realistic spatial magnetic field profile was quite different from that under uniform axial magnetic field. [ABSTRACT FROM PUBLISHER]

The anode melting in high-current vacuum arcs leads to the increase of metal vapor and liquid droplets around current zero and even the interruption failure. In our recent experiments of the cup-shaped axial magnetic field (AMF) contacts, an obvious clockwise swirl flow of the liquid copper was detected on the anode surface. However, if an additional external AMF which is reverse to the AMF generated by the contacts was introduced, the rotation direction of the liquid copper swirl flow on the anode surface could reverse to anticlockwise. These phenomena indicate that AMF has great influence on the performance of anode melting and its swirl flow. [ABSTRACT FROM AUTHOR]