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The splitting and threshold currents of vacuum arc cathode spots in axial magnetic fields (AMFs) up to 220 mT are investigated experimentally. Measurements are made on electrodes of Cu and CuCr25 with electrode separations of 2 and 6 mm. The electrode diameter is 30 mm. All the experiments are conducted in a demountable vacuum chamber evacuated continuously by a turbo-molecular pump to a pressure of the order of 10−3 Pa. The spots are photographed using a high-speed digital camera with an exposure time of 2 μs. The AMF is applied by means of two permanent magnets placed symmetrically inside the chamber. The experimental results indicate that the splitting and threshold current decrease in the presence of AMF and tend to certain constant values when the field gets stronger. The splitting and threshold currents are considerably larger than Cu electrodes than those with CuCr25 electrodes. With increasing electrode separation, the splitting current decreases while the threshold current increases. Possible explanations are proposed to account for the experimental observations. [ABSTRACT FROM AUTHOR]

The dielectric recovery process is a crucial stage of current interruption in a vacuum circuit breaker (VCB). The postarc current is an important macroscopic electric characteristic of the dielectric recovery process, which has caused many concerns in the past few decades. In this paper, the postarc currents of VCBs with different types of contacts, such as butt contacts, axial magnetic field contacts, and transverse magnetic field contacts with different materials are measured with a high-resolution current-zero diagnostic system. Besides, the appearance of vacuum arcs is recorded using a high-speed camera in the experiments. The relationship between the arc memory effect and the postarc current is analyzed. What is more, the influence of the instability of the vacuum arc shape on the dispersion of postarc current is also studied. [ABSTRACT FROM AUTHOR]

A quench protection switch (QPS) is indispensable to protect the magnet coils from the damage of quench in a superconducting Tokamak. In this paper, a QPS based on artificial current zero is involved. The vacuum circuit breaker (VCB), which is driven by a high-speed electromagnetic repulsion mechanism, is used as the main circuit breaker (MCB). Two kinds of commercial vacuum interrupters (VIs), which have contacts generating axial magnetic field (AMF) and transverse magnetic field (TMF), respectively, are applied. The breaking current with an amplitude of 10~25 kA is generated by an LC oscillating circuit. The countercurrent with frequency in the range of 500–3000 Hz is provided by a commutation branch. The interruption performance of the two kinds of VIs under different breaking current and countercurrent frequencies is investigated. The experimental results indicate that the differences in interruption performance under the two types of contacts are increasing with larger frequencies of countercurrents. [ABSTRACT FROM AUTHOR]

The Robson drift phenomenon is a macroscopic reflection of the movement of a cathode spot (CS) in oblique magnetic field (OMF). Although it was discovered many years ago, its physical mechanism remains unclear. In this paper, the influence of OMF on the Robson drift of CS motion is simulated. A 2-D stepwise model of the movement of a single CS in OMF is established. It is assumed that the probability of generating a new spot in directions of Amperian force, anti-Amperian force, and directions perpendicular to Amperian force, is proportional to the magnetic pressure around the old spot. The drift angle and velocity of the CS in OMF are simulated. The simulation results show that the drift angle of the CS in OMF has liner relationship with the inclination angle of magnetic field, and it has no obvious relationship with the strength of the applied magnetic field and the amplitude of the arc current, which are in a good agreement with the experimental results. Besides, under the same angle of magnetic field, the velocity of spot motion increases linearly with the strength of OMF. Moreover, the simulation results show that the transverse magnetic field component has a much more predominant influence on the CS velocity than the axial magnetic field component, which are also in agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Fast interruption is vitally important in high-voltage direct current (HVDC) system to suppress the rapid increase of short current. In this paper, a multi-physics coupling simulation model of a high-speed electromagnetic repulsion mechanism (ERM) which is a part of HVDC breaker is proposed. The opening process with an electromagnetic buffer of ERM is investigated. The simulation results including forces, currents, displacements, and velocities are analyzed. Furthermore, a prototype of ERM is designed and developed. Results show that the efficacy of the proposed simulation methodologies is verified by the experimental results. The opening process of ERM could be divided into six stages. During an opening action, the impact of collision on the motion of ERM cannot be ignored. A good buffering effect can be achieved by reasonably setting the related parameters of the electromagnetic buffer. [ABSTRACT FROM AUTHOR]

The quench protection switch (QPS) is an indispensable component ensuring the safety of the magnet coils of a superconducting Tokamak when a quench happens. In this paper, the second commutation process of a QPS based on artificial current zero is investigated. In this process, the current, which has already transferred from the bypass switch to the main circuit breaker, is forced to commutate from the vacuum circuit breaker (VCB) to the discharge resistor by the countercurrent. An LC oscillating circuit is applied to generate oscillating current to simulate the direct current near its peak which is about 20 kA. The countercurrent with frequencies of 500 and 1000 Hz is provided by a commutation branch. The equivalence of the experimental interrupting process compared with the practical situation is analyzed. Two kinds of vacuum interrupters of the VCB are used in experiments. One kind is equipped with contacts generating transverse magnetic field, and axial magnetic field contacts are used in another one. The experimental results indicate that the initial process of the vacuum arc before injecting the countercurrent has crucial impacts on the interruption performance. The countercurrent with the frequency of 500 Hz is easier to interrupt the current than the case of 1000 Hz. [ABSTRACT FROM AUTHOR]

The residual axial magnetic field (AMF) at current zero, which is caused by large \mathrmdi/\mathrmdt during the forced current-zero stage of DC interruption based on the technique of artificial current zero, has a significant influence on the interruption performance of the vacuum circuit breaker. In this paper, a model of AMF contacts system is developed by finite-element-analysis software Ansys. The eddy current induced in the contacts system is also analyzed by an equivalent circuit. The influence of the frequency of countercurrent and the characteristics of saturable reactor, which results in the change of \mathrmdi/\mathrmdt before current zero, are investigated. The results demonstrate that the frequency of countercurrent has a significant influence on the residual AMF at current zero. The residual AMF decays exponentially after current zero with a time constant independent of the countercurrent frequency. The residual AMF can be reduced by using a saturable reactor. The effect of a saturable reactor depends mainly on the duration of the low \mathrmdi/\mathrmdt stage before current zero. [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]

In this paper, the influence of an external transverse magnetic field, in parallel with the cathode surface, on the ignition probabilities of a cathode spot (CS) in the Amperian and retrograde directions is developed assuming that the ignition probability of a new CS is proportional to the magnetic pressure around the old one. Furthermore, both stepwise and statistical models are established to simulate the random and retrograde motions of a single CS of vacuum arc, assuming that the 2-D motion of the CS in the $xy$ plane is equivalent to the synthesis of two independent 1-D movements along the $x$ - and $y$ -axis, respectively. With both models, the random and retrograde motions of a single Cu CS are simulated step by step and statistically, respectively. It was found that stepwise simulation results agree well with the statistical results, and they are also consistent with the relevant experimental results. The difference in retrograde motion velocity between the present stepwise model and that assuming that a new CS can be ignited in any direction around the old one is discussed. [ABSTRACT FROM PUBLISHER]

In this paper, the relationship between the external transverse magnetic field (TMF) and the ignition probability of new cathode spot in different directions is developed assuming that the ignition probability of a new cathode spot is proportional to the magnetic pressure around the old one. Furthermore, a method is established to simulate the 2-D motion of a cathode spot step-by-step. With this approach, stepwise simulations of the 2-D retrograde motion of a single Cu cathode spot are carried out in a large range of flux density of TMF ( Bem ). Simulation results indicate that, if the self-generated magnetic field Bsm exceeds the applied magnetic field Bem , i.e., B\textrm {em}\le B{sm} , there is a linear relationship between the velocity of the retrograde motion and Bem , in certain range of Bem , after which the velocity of the retrograde motion increases slowly and nonlinearly with further increase of B\textrm {em} . This phenomenon agrees well with relevant experiment results. In the linear stage, the dependence of velocity constant on the spatial step and the temporal step of the motion of cathode spot is investigated as well. Moreover, when Bem>Bsm , the velocity of cathode spot decreases with the increase of B\textrm {em} , even the macroscopic motion is still in the retrograde direction. This effect might also contribute to the reversal of cathode spot motion from the retrograde direction to the Amperian direction at strong TMF besides the predominant effect of the deflection of arc column toward the Amperian direction. [ABSTRACT FROM PUBLISHER]

Cathode spots (CSs) dynamics in the initial expansion stage of high-current triggered vacuum arc and the influence of axial magnetic field (AMF) was investigated experimentally. Experiments were conducted with butt contacts in a demountable vacuum chamber. Images of CSs were photographed with a high-speed digital camera with exposure time of 2 \(\mu \) s. The uniform and constant AMF in the intercontacts region was supplied by external magnetic field coil. In high-current triggered vacuum arc, CSs expanded across the cathode surface in basically a ring-shaped pattern. Experimental results showed that the expansion ring consisted of group CSs (GCSs) and individual CSs at the beginning of the expansion process. The GCS moved outward faster than individual CS. Research results indicated that an AMF could reduce the tendency of formation of GCS. The effect of local plasma and global plasma, which could be significantly influenced by AMF, on the motion pattern and distribution of CSs in the initial expansion stage was investigated. [ABSTRACT FROM PUBLISHER]

The expansion speed of cathode spots (CSs) in the initial expansion stage of high-current triggered vacuum arc was investigated experimentally. Experiments were conducted with butt contacts in a demountable vacuum chamber. Images of CSs were photographed with a high-speed digital camera with exposure time of 2 \mus. The uniform constant axial magnetic field (AMF) was supplied by an external magnetic field coil. The combined influence of contact gap of 2–10 mm and AMF of 0–70 mT on CSs expansion speed in the initial expansion stage was mainly investigated. Investigation results indicated that the variation of contact gap could influence the CSs expansion speed by changing the plasma density inside the cathode arc root in two ways: loss of arc plasma and constriction of arc column. AMF could weaken these two effects caused by the variation of contact gap. In addition, experimental results indicated that there existed a critical current for a given AMF. If the arc current peak was less than the critical current, the given AMF could inhibit the arc column constriction effectively both at contact gap of 8 and 10 mm, which could maintain the dependence that CSs expansion speed increased with contact gap; otherwise, the constriction of arc column played a major role in the influence on CSs expansion speed. In this case, the CSs expansion speed was lower at contact gap of 10 mm than that at 8 mm. [ABSTRACT FROM AUTHOR]

In this paper, the influence of an axial magnetic field (AMF) on the expansion speed of cathode spots (CSs) in the initial expansion stage of high-current triggered vacuum arc is investigated experimentally in a demountable vacuum chamber. Butt contacts with contact plate material of oxygen-free high-thermal-conductivity Cu and CuCr25 were used in experiments. Images of CSs are photographed with a high-speed digital camera with an exposure time of 2 \mus. The uniform constant AMF in the intercontact region is supplied by external magnetic field coil. Experimental results indicate that, in an arc stabilized by AMF, CS expansion speed also increases with the increase of di/dt, which is the same as that in arc burning freely. In addition, quasi-quantitative analysis of the experimental results show that the bending and lengthening of CS motion trajectory in AMF are not sufficient to explain the decrease of CS expansion speed with AMF. Another reason might be related to the inhibitory effect of AMF on the loss of arc plasma, which could also contribute to the decrease of CS expansion speed. [ABSTRACT FROM AUTHOR]

This paper analyzes how removing oxide layer on metal surface by vacuum arc could be a green substitute for the traditional acid-washing and mechanical cleaning technique widely used in the metallurgical industry, which is harmful to the environment. In this paper, the effects of vacuum arc on removing oxide layer on the surface of carbon-steel tubes, which were used as the cathode, is investigated experimentally. External coils are used to generate transverse magnetic field (TMF) driving cathode spots to rotate on tube surface. Experiments are conducted in a vacuum chamber with Ar as the protection gas under different TMF flux densities. Arc images are captured by a high-speed digital camera with an exposure time of 2 \mus. The influence of transverse magnetic flux density on the characteristics of arc and descaling effect is mainly investigated. [ABSTRACT FROM AUTHOR]

The initial expansion process in a drawn vacuum arc and the influence of axial magnetic field (AMF) were investigated experimentally in a demountable vacuum chamber. Arc characteristics were investigated with the aid of a high-speed digital camera with an exposure time of 2 \mu\s . In a drawn vacuum arc, the arc sequence begins with the bridge column arc formed after the rupture of the molten metal bridge. This column evolves into the transition mode, which consisted of a central column with few or no cathode spots (CSs) outside the column, and then into the fully diffuse mode. Experimental results indicated that in transition mode arc, the expansion process could be characterized by the appearance of CSs outside the central column, and could be classified into two patterns, “slow” expansion and “quick” expansion according to the characteristics of the formation and motion of new CSs (conducting channels) outside the central column of arc. The influence of AMF and its distribution on the expansion process was also investigated. Investigation results indicated that AMF had two contrary effects, i.e., inhibiting effect and prompting effect, on the initial expansion stage of drawn vacuum arc. Furthermore, saddle-shaped AMF could encourage the arc transition into diffuse mode more effectively than bell-shaped AMF. [ABSTRACT FROM PUBLISHER]

The method of magnetic field calculation and its influence on simulating the motion of cathode spots (CSs) in a vacuum arc were investigated in this paper. A method based on coordinate transformation and magnetic field superposition principle was proposed. In this method, the influence of current passing through an electrode rod and a contact plate was taken into account. Comparison was made between the proposed method and two simplified methods which were on the basis of the Biot–Savart law. Moreover, simulation results of CS motion with magnetic field calculated by different methods were shown and compared. Investigation results indicated that current passing through the contact plate and electrode rod could significantly influence the magnetic field and thus influence the simulation results of CS motion. Furthermore, it was shown that the proposed magnetic field calculation method had higher calculation accuracy with acceptable consumption of calculation time. [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]

In the Special Issue, we are very pleased to present the expanded versions of selected papers from the 27th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV). It was held at the Xi’an Jiaotong-Liverpool International Conference, Suzhou, China, from September 18–23, 2016. [ABSTRACT FROM PUBLISHER]

This work investigates the dynamic characteristics of vacuum arc in the initial expansion process of a direct current (dc) circuit breaker. Based on the commercial cup-type axial magnetic field (AMF) contact, a 3-D transient magnetohydrodynamic (MHD) model is established. In the model, transient equations are used to study the transient characteristics of the vacuum arc. The effect of magnetic field hysteresis is also considered in the method. The dynamic mesh technique is adopted to simulate the electrode separation, which can make the simulation results more accurate. The simulation results show that, during the initial expansion process, with the increase in the current, the arc gradually expands in the electrode gap. The ion pressure, ion number density, axial current density, and energy flux density to the anode gradually decrease. Ion rotation can be observed under the influence of the magnetic field, and the rotation speed will increase with the increase in the current. Two different arc ignition positions are also compared. The result shows that igniting the arc at the contact center is more helpful to the success of the interruption of the dc circuit breaker. The appearance of the arc predicted by the model is consistent with the experimental results. [ABSTRACT FROM AUTHOR]

Much research has been done on the motion of low-current vacuum-arc cathode spots (CSs). The relationship between the motion velocity of CSs and the magnetic field, particularly the relationship between the direction of CS motion and the ratio of Bz/Bt, has been revealed. However, little investigation on the motion of CSs in high-current vacuum arcs has been conducted before. In this paper, the motion of CSs of high-current vacuum arcs under different axial magnetic fields was experimentally investigated. Simultaneously, calculation of the motion of CSs based on the empirical formula has been done, and comparison with experiments and analysis were given. Experiments were conducted in a detachable vacuum chamber with an arc current of 10 kA (root mean square). Images of CSs were photographed with a high-speed digital camera with an exposure time of 2 \mu\s. With computer-aided numerical processing, the spatial distribution of the CSs was obtained, based on which the magnitude and direction of the CS motion velocity were calculated, and the CS motion trajectories around the current peak were plotted. Results indicated that the properties of the CS motion in high-current vacuum arcs are similar to those in low-current vacuum arcs. [ABSTRACT FROM AUTHOR]

In real power system, when the three-phase short-circuit fault occurs, the vacuum arc in one phase will be influenced by the transverse magnetic field generated by neighbor phases and bus bars. This kind of effect is the main cause of the unstable arc and deflected erosion of contact plates, which leads to the failure of vacuum circuit breakers interruption. The objective of this paper is to get more insight into the influence of external transverse magnetic field (ETMF) on vacuum arc’s behavior. The experiments were conducted in a demountable vacuum chamber with pressure about 10^-4 Pa. The cup-type axial magnetic field contacts were used, whose material was pure copper and the diameter is 35 mm. The uniform ETMF in the arc region was generated by two parallel bulk permanent magnets. The experiments were conducted under different ETMFs (0, 15, and 25 mT) and current levels (1-, 2.5-, and 4-kA rms) with different gap distances (6, 8.5, and 11 mm). The videos of arc column were recorded by a high-speed charge-coupled device camera. Under the action of ETMF, the vacuum arc got deflected. Due to the retrograde motion of cathode spots and Ampere force acting on arc column, the deflection behaviors during three typical periods (that is, initial, peak value, and close-to-current-zero period) were different. Moreover, the deflection level of vacuum arc at current peak value moment was greatly impacted by ETMF and gap distance. Larger the ETMF and gap distance were, higher the deflection level at current peak value moment was. The simulation results of arc deflection based on magnetic-hydrodynamic model were in agreement with experimental results in trends. [ABSTRACT FROM AUTHOR]

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]

With a quasi-steady 3-D MHD model, time-dependent axial magnetic field vacuum arcs (AMFVAs) characteristics in commercial vacuum interrupters for half-wave interruption of power-frequency (50 Hz) current are simulated. In a current time-dependent simulation, the influence of AMF lagged from arc current is considered in the arc model. 3-D spatial distributions of many important plasma parameters and electrical characteristics in AMFVAs can be obtained, such as ion number density, ion temperature, electron temperature, plasma pressure, current densities along different directions (x, y, and z), electric fields strength along different directions, and so on. Simulation results show that there exists a significant spiral-shaped rotational phenomena in the AMFVAs and the rotational velocity at the moments (9, 8, 7, and 6 ms) after 5 ms (the current peak value moment) is always larger than that before 5 ms (1, 2, 3, and 4 ms) because of the lagged AMF. This kind of plasma rotational phenomena also can be observed by high-speed arc photographs. In the future, the asymmetric appearance in high-current vacuum arc will be simulated based on a 3-D model. [ABSTRACT FROM AUTHOR]

With the increase of interruption frequency of high-current vacuum arc (HCVA), the relaxation time of arc plasma is close to characteristic time of arc current and transient characteristics of vacuum arc plasma become more obvious. In this paper, based on a 2-D transient magneto-hydrodynamic model, HCVA under different interruption processes is simulated and analyzed. The simulation results of power-frequency (50 Hz) current show that transient simulation results are the same as those of the steady-state model, as characteristic time of current is much longer than relaxation time of plasma. For fast current drop stage in dc interruption process, simulation results show that higher frequency makes current drops faster and ion number density larger; besides, residual plasma density between electrodes at current-zero moment is higher, and interruption becomes more difficult. Finally, transient characteristics of high-frequency HCVA is also simulated and analyzed. Simulation results show that change curve of ion number density lagged behind current curve; higher ion number density in the second 1/4 cycle can lead to reignition more easily. [ABSTRACT FROM AUTHOR]

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]

The theoretical and experimental studies of cathode plasma jets in vacuum arc and the effect of magnetic field on them have been under way for several years. In this paper, different axial magnetic field electrodes were tested in a vacuum chamber, obvious individual cathode plasma jets were observed, and the cathode-jet inclination was also detected. Based on the numerical calculation of magnetic field in interelectrode region and the measurement of cathode-jet inclination in experimental results, it is proven that the inclination angle of composite magnetic field (the combination of the axial, the azimuthal, and the radial components) is consistent with the inclination angle of cathode plasma jets, which indicates that the cathode plasma jets in the arc column flow along the magnetic-field direction when the high-current vacuum arc is diffused or even constricted slightly. Meanwhile, it was also found that plasma jets far from the cathode surface mixed with each other and became ambiguous when the electrode gap increases to a certain distance. [ABSTRACT FROM PUBLISHER]

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]