Characteristics Of Vacuum Arc Research Articles

Study on the vacuum arc characteristics between novel straight slot transverse magnetic contacts with auxiliary slots on the back

The motion stability of the vacuum arc between TMF contacts significantly affects the breaking capacity of vacuum switches. The vacuum arc movement can be effectively controlled by slots on the TMF contacts to provide the necessary driving force. However, the necessary cross-slot movement of the arc affects its stability. In this paper, a novel straight-slot transverse magnetic field (SSTMF) contact structure with additional auxiliary slots on the back is proposed to improve current distribution and avoid stagnation at the contact center. The simulation analysis was conducted on the force acting on the arc at different positions and the magnetic field distribution between the contacts. Additionally, the arcing experiments were performed in a demountable vacuum chamber for both novel and traditional SSTMF contacts. The SEM analyses were carried out for the contacts after the experiments. Combined with simulation and comparative experimental results, it is verified that the auxiliary slots can improve the control and driving effect on the arc. This can provide ideas and references for future contact design and improve the breaking performance of vacuum circuit breakers.

Numerical Simulation and Experimental Investigation of the Influence of Gap Distance on Vacuum Arc Characteristics Between TMF Contacts

Numerical Simulation and Experimental Investigation of the Influence of Gap Distance on Vacuum Arc Characteristics Between TMF Contacts

Characteristics of Intermediate Frequency Vacuum Arc Under Different Breaking Speeds

Characteristics of Intermediate Frequency Vacuum Arc Under Different Breaking Speeds

Study on the microspot splitting characteristics of pulsed cathodic vacuum arc

The intense pulsed current superimposed on direct current arc discharges can promote arc spot splitting and reduce macroparticle ejection. In this study, the effects of different arc parameters including peak current, magnetic fields, pulse frequency and duty cycle on spot splitting characteristics for the pulsed cathodic arc discharge, as well as mechanisms involved in microspot formation, are investigated. The results show that under the effect of periodic micro-explosive emissions, the micro-spot splitting at the peak of the pulse displays a multi-stage annular expansion phenomenon, and its expansion radius increases with the increaseing peak current; the increasing transverse component of the arc source magnetic field gradually changes the microspot splitting pattern from annular expansion to arc-shaped expansion; the plasma motion after the micro-explosion requires a period of time to “accumulate force.” In addition, an increase in pulse frequency leads to a gradual reduction in the range of the microspot splitting, in which the microspots are in a relative aggregation state; an increase in duty cycle, leads to an instability in the continuous motion of the microspots after the splitting in the peak period. This causes some of the microspots to merge, exhibiting a trend similar to the direct current arc.

Study on structural parameters of cup-type axial magnetic contacts on gap magnetic field and arc characteristics

The axial magnetic field (AMF) plays a crucial role in maintaining the diffusion of vacuum arcs within contact gaps, making it a key component in vacuum breaking systems. To enhance contact surface utilization, a novel vacuum cup-type AMF contact was designed, featuring a stronger axial magnetic field at the edge and weaker at the centre. Through Ansys Maxwell 3D simulations, the designed contact increased the effective utilization area by 18 %. Experimental analysis demonstrated that, compared to traditional contacts, the designed contact exhibited lower arc voltage and significant arc diffusion. Ablation of the designed contact was more concentrated at the edge, with scanning electron microscope (SEM) images revealing four microscopic morphologies: overlapping craters, bright metal droplets, various-sized flakes, and fine particles. Energy dispersive spectrum (EDS) analysis provided insights into the cathode surface's elemental composition and droplet growth. Additionally, the study explored the influence of different slotting parameters on vacuum arc characteristics, including contact plate configurations, cup bottom slotting, and cup wall tilt, focusing on the arc initiation stage, arc voltage rise, and arc shape transition.

Study on arc characteristics and influencing factors of cup-shaped axial magnetic field contact at different gap distances

The cup-shaped axial magnetic field (AMF) contact, integral to high-voltage vacuum interrupters, undergoes innovation by enhancing the slotting rotation angle of the cup wall. This adjustment significantly amplifies the gap magnetic field, promising breakthroughs in handling long-gap arcs within high-voltage vacuum interrupters. Comprehensive vacuum arc experiments were conducted on cup-shaped AMF contacts with varying slotting rotation angles at different gap distances. The research meticulously analysed the evolution of vacuum arc characteristics under diverse breaking currents. Scanning electron microscope (SEM) images of the cathode surface unveiled three distinctive microscopic morphologies: particle gullies, pore platforms, and particle platforms. Notably, the chromium content corresponding to these morphologies exhibited a progressive increase. Integrating the surface distribution of copper and chromium, the study proposed a plausible cathodic erosion mechanism. Extending the investigation, the research delved into the influence of the iron core, contact diameter, and slot number on vacuum arc characteristics, which expected to provide reference for the application of the cup-shaped AMF contact in high voltage vacuum interrupters.

Investigation of the influence of opening speed on vacuum arc under transverse magnetic field

The objective of this paper is to investigate the vacuum arc characteristics on transverse magnetic field (TMF) contacts at different opening speeds. Experiments are carried out at different opening speeds. The experimental current ranges from 7 to 16 kA (peak current) at approximately 50 Hz. The contact material is CuCr30. The results show that increasing the opening speed increases the expansion speed of the arc after ignition. A higher opening speed increases the gap distance at which an anode spot occurs and reduces the duration of the instability stage, and it also reduces the duration of the motion stage. The arc motion can be optimized by adjusting the opening speed. The moment of contacts separation has no obvious influence on the gap distance at the transition of the arc mode. When the arc ignites between the arms, it expands slowly. This phenomenon is analyzed by a finite element method. The simulation results show that the ignition position influences the current direction, which influences electromagnetic force of the arc. The radial electromagnetic force is smaller when the arc ignites between the arms, causing a stagnation of the arc.

Determination of the critical contact separation length for DC interruption in a vacuum subject to an external transverse magnetic field

The objective of this work is to experimentally determine the critical contact separation length Lcritical for DC interruption in vacuum under an external transverse magnetic field (TMF), according the interruption behaviors and vacuum arc characteristics. L is defined as the separation length at the instant of TMF application. Lcritical is the critical and the minimal necessary separation length of the contacts for a successful DC interruption in vacuum. A pair of Helmholtz coils was used to generate the external TMF. A high-speed camera was used to record the vacuum arc appearance. The experimental results quantitatively determine Lcritical for DC vacuum interruption under a certain DC and the external TMF. When the DC ranged from 100 to 500 A under an external TMF of 30 mT, Lcritical ranged from 2.1 to 3.7 mm and did not show linear variation. Second, the extinguishing time of DC vacuum interruption te at various currents significantly increased in a similar pattern under decreasing L in the range of 0.3–1.6 ms. The decrease in L mainly increased the duration of the stable stage and had little apparent influence on the duration of the unstable stage of the DC vacuum arc. Third, the physical mechanism determining Lcritical in DC vacuum interruption under a TMF could be explained from two aspects: the expansion of the vacuum arc column and the diffusion of the metal plasma. In successful DC vacuum interruption, Lcritical should be large enough for the formation and expansion of the “C”-shaped arc column, and enough space should be available for the diffusion of the metal plasma.

Comparative study of the microspot splitting characteristics of direct-current and pulsed cathodic vacuum arc

Ejection of macroparticles is an inherent and unavoidable characteristic of cold cathode arc discharges. The size of the cathode arc spot's melt pool is closely related to the emitted particle size, and existing studies mostly indicate that motion velocity of arc spots can be heightened primarily by magnetic fields, thereby reducing the ejection of macroparticles. However, scant consideration has been given to avoid the fundamental nature of arc spot current concentration discharge by exploring the phenomenon of arc spot splitting. In this paper, microspot splitting characteristics of direct current and pulsed cathodic vacuum arc were compared and analyzed to investigate the effect of pulsed discharges on the arc spot's internal structure, splitting, and kinematic characteristics. The results showed that pulsed arc discharges emit a dense, highly ionized plasma flow which impacts the relatively thin positive charge layer instantaneously during the peak pulsed period. This then produces a highly ionized plasma region, while also promoting an effect by which the arc spot is split into multiple microspots. Additionally, the degree of dispersion resulting from microspot splitting is positively correlated with the ratio of the plasma flow density to the concentration of the positive charge layer at the moment of microexplosion. Therefore, the microspot splitting effect of a second-order pulsed arc is weaker than that of a first-order pulsed arc. Moreover, the splitting characteristics indicated a trend toward the progressive splitting state of the direct current cathode arc. When the peak current of the single-order pulsed arc was increased from 100 to 400 A, the particle refinement effect on the surface of the CrN coating became much more evident compared to the effect of a 200 A arc in the direct current mode. And upon reaching a peak current of 500 A (and up to 600 A), the number of splits did not increase linearly due to the continuous increase in the discrete degree of microspot splitting and concurrent decrease in microspot stability. This resulted in relatively high individual microspot currents, while some relative macroparticles still appeared on the coating surface.

Experimental investigation on “glow flow” phenomenon during current-zero period between transverse magnetic contacts

The inter-electrode state of the transverse magnetic field contact during the current-zero period is determined by the evolution of the arcing process. It has an important effect on whether the vacuum switch can be successfully broken. In this paper, a series of contacts were subjected to arcing and fixed gap distance experiments. The results show that a special inter-electrode phenomenon (glow flow) appears during the current-zero period when the current exceeds the threshold for the transition from diffused to constricted state of the vacuum arc. The mechanism behind the formation of this phenomenon was elucidated through an analysis of multiple sets of experimental results. It is found that the inter-electrode phenomenon arises from the disruption of the equilibrium process between the pressure from the arc column plasma and the anode vapor flux on the near-anode side at the current-zero. The copper vapor falls and is ionized by collisions with heat-emitting electrons. The experimental results and theoretical analysis also show that this phenomenon has a time interval with the reignition phenomenon. When this phenomenon is intense to a certain degree, the reignition will occur with high probability. The observation and theoretical analysis results of this paper are relatively consistent with the research results of other scholars, which can help to improve the vacuum arc characteristics and interrupting mechanism. This can provide a basis for improving the arc extinction performance of the vacuum switch.

Simulation Analysis and Experimental Investigation of the Iron-Core Cup-Shaped Transverse Magnetic Field Contact

The transverse magnetic field (TMF) contact uses self-generated TMF to drive the arc movement and has been widely used in the field of vacuum breaking. An iron-core cup-shaped TMF contact was designed by adding an iron core and changing the parameters of the cup wall based on the structure of the traditional cup-shaped TMF contact to optimize the gap magnetic field distribution of the cup-shaped TMF contact and improve the force characteristics of the vacuum arc. From the aspects of simulation and experiment, the gap magnetic field characteristics, arc force, and vacuum arc characteristics of the iron-core cup-shaped TMF contact were studied. The simulation analysis model of the iron-core cup-shaped TMF contact was established by COMSOL Multiphysics software, and the gap magnetic field characteristics and arc force were analyzed. Compared with the traditional cup-shaped TMF contact, the tangential electromagnetic force on the arc is increased by 30%, and the radial electromagnetic force is reduced by 36%. The arcing processes of the iron-core cup-shaped TMF contact and the traditional cup-shaped TMF contact were analyzed through experiments. The results show that the iron-core cup-shaped TMF contact has a faster arc movement speed, longer movement duration, and less metal droplet splashing.

Experimental investigation of vacuum arc characteristics subject to axial magnetic field contacts with different ratios of diameter to gap distance

In this study, to investigate vacuum arc characteristics under different diameter-to-gap distance ratios (D/g), experiments are conducted on axial magnetic field (AMF) contacts with varying D/g. The peak current value ranges from 15 to 35 kA. The experimental results show that the ability of AMF contacts to control the arc decreases with D/g. Furthermore, the 2/3 coil contact can control the arc under long gap distances, whereas the cup-shaped contact cannot effectively control the arc under long gap distances. The arc energy and noisy period duration decrease with increasing D/g. The arc voltage of the 2/3 coil contact at the peak moment is always the lowest compared to the cup-shaped contact and the 1/2 coil contact, and the arc voltage of the 2/3 coil contact at the peak moment has an approximate power function relation with D/g. The simulation results show that the AMF distribution changes from saddle shape to bell shape with decreasing D/g. The 2/3 coil contact is more suitable for high-voltage vacuum interrupters (VIs), while the cup-shaped contact is more suitable for medium-voltage VIs.

Vacuum arc characteristics of an AMF–TMF composite contact with fixed AMF contacts under different opening velocities

The objective of this paper is to determine the vacuum arc characteristics of a novel axial magnetic field (AMF)–transverse magnetic field (TMF) composite contact under different opening velocities. The AMF–TMF composite contact consists of a pair of outer fixed AMF contacts and a pair of inner movable TMF contacts. Drawn arc experiments were carried out in an L–C discharging circuit with this composite contact system to observe the differences in the arc development process under different opening velocities. The opening velocity of the inner movable contact was set to 1.3, 1.8, and 2.3 m/s. The arc current was up to 20 kA rms. In the experiments, the arc behavior was recorded using a high-speed camera. The arc current of each contact and the arc voltage were measured. Then the arc characteristics, including the arc current transfer characteristics, diffused arc duration, and mental droplet distribution before zero current, were quantitatively analyzed. Furthermore, magnetic field calculation was carried out to explain why the arc characteristics are different under different opening velocities. Experimental results show that with an increase in the opening velocity from 1.3 to 2.3 m/s, the diffused arc duration before zero current increases from 1.05 to 1.75 ms when the cathode is on the fixed side and increases from 1.30 to 1.90 ms when the anode is on the fixed side. In addition, the quantity of mental droplets between contacts before zero current is less with high opening velocity. It indicates stronger short-current breaking capacity under higher opening velocity. From the simulation results, it can be seen that during the arcing period, more current transfers to the fixed AMF contact under higher opening velocity and generates a stronger AMF. It could explain the earlier diffusion of the vacuum arc column under higher opening velocity.

A Relationship Between Vacuum Arc Characteristics and Short-Circuit Current Interrupting Capability at Minimum Arcing Times

The study is to explore a relationship between vacuum arc characteristics and short-circuit current interrupting capability of a fast vacuum circuit breaker (FVCB) at a minimum arcing time. Both a short-circuit current interruption test and an arc mode transition observation test were carried out to explore the relationship. Firstly, an FVCB with ceramic enclosure vacuum interrupter (VI), in which a pair of axial magnetic field (AMF) contacts were arranged, was operated with three different opening speeds to interrupt short-circuit currents. A Weil synthetic circuit provided short-circuit currents of 20, 30, and 40 kA, and a transient recovery voltage (TRV) of 92 kV/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$120~\mu \text{s}$ </tex-math></inline-formula> for the short-circuit current interruption capability experiment. Then, the arc mode observation experiment was carried out under the same conditions as the short-circuit current interruption capability experiment, except for two differences, that is, a glass enclosure VI without a shield was used for observing the arc with a high-speed camera, and the other point was that only the short-circuit current was applied and no TRV was applied. Experimental results showed that the increase in the opening speed resulted in a decrease in the minimum arcing time, the critical arc extinguishing gap, and the critical arc diffusion time, but led to an increase in the maximum arc column diameter. In contrast, the increase in the short-circuit current would increase the minimum arcing time, the critical arc extinguishing gap, the critical arc diffusion time, and the maximum arc diameter. The diffusion of the arc column is essential but not sufficient for the successful interruption. The contact gap plays a significant role. On the one hand, a larger contact gap promotes arc diffuse. The arc diffusion can decrease the contact surface temperature and the local particle density at current zero. On the other hand, a larger gap distance leads to a smaller electric field intensity between fixed and moveable contacts, which reduces the breakdown probability during the postarc dielectric recovery. The critical arc energy density for a successful interruption of the FVCB in short arcing times was obtained to range from 0.54 to 1.01 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times \,\,10^{8}$ </tex-math></inline-formula> J/m3.

Investigation of Vacuum Arc and Erosion Characteristics of Spiral TMF Contacts With Different Materials

The transverse magnetic field (TMF) can drive the arc to rotate, to reduce the erosion of contact. In this article, TMF contacts of six commonly used materials (CuCr10, CuCr30, CuCr50, WCu10, WCu30, and CuW-WC) are investigated by experiments at the current of 5, 10, and 15 kA. Experimental results show that the contact material has a significant impact on the arc, the arc on CuCr materials rotates, and shows noisy voltage, while the arc on WCu hardly rotates and exhibits a stable arc voltage because of staying in the diffuse mode. Though the erosion of CuCr contacts is more severe than WCu contacts, the results of breaking operations also indicate that CuCr contacts outperform WCu contacts, where CuCr10 contact has a lower breaking capacity than CuCr30 and CuCr50. Moreover, the steel support disk of the interrupter contacts plays a role in the reignition of the arc after a half-cycle of current which is obvious from the erosion of the disk and from records of the arc appearance.

3-D Dynamic Simulation of the Initial Expansion Process of Vacuum Arc Plasma in DC Interruption

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.

Investigation on the arc root characteristics of vacuum arc between the iron-core cup-shaped transverse magnetic field contacts

The severity of the contact surface ablation determines the breaking capacity of the vacuum circuit breaker, and the interaction between the arc root and the electrode is the main cause of the contact surface ablation. The characteristics of the arc root determine the magnitude of the electromagnetic force received by the arc during the movement stage as well as the shape and speed of the arc movement. It will eventually affect the temperature of the contact surface and the ablation situation. This paper studied the arc root characteristics of high-current constricted vacuum arcs between the iron-core cup-shaped transverse magnetic field contacts and put forward the idea of using the ratio of cathode and anode arc root areas to quantitatively analyze the concentration of vacuum arc. The research on the arc root characteristics of the vacuum arc can help to improve the arc characteristics and arcing mechanism, and the proposition of the ratio can provide a new method for the study of constricted arc. This can provide a basis for improving the arc extinction performance of the switch, reducing the ablation of the contact material, and improving the contact life.

Vacuum Arc Evolution Characteristics in Low-Voltage DC Current Interruption Under Composite Transverse Magnetic Fields

Based on our novel dc vacuum interruption technology under composite transverse magnetic fields (TMFs), the arc voltage of dc vacuum arc can be effectively improved to interrupt the dc current. The objective of this work is to experimentally investigate the vacuum arc characteristics and their evolution in dc current interruption under composite TMFs. The composite TMFs were generated by both multipole permanent magnets and cup-type TMF contacts. The vacuum arc photos were recorded by a high-speed camera. The experimental results indicate that under these composite TMFs, the dc current could be successfully interrupted, which was closely related to the dc vacuum arc characteristics and their evolution. The experimental dc current and voltage were less than 500 A and 500 V. First, the evolution of the dc vacuum arc could be divided into Stable and Unstable stages, according to the characteristics of the arc voltage waveform. In the Stable stage, the dc vacuum arc might be stagnated, constricted, and rotated with a stable arc voltage of 20 V. In the Unstable stage, the dc vacuum arc was transferred to the outer periphery of the contact in the form of a ``C''-shape, and the arc voltage significantly increased higher than the supply dc voltage. Second, there was an Extinction Area in the middle of Area 4 under the composite TMFs, which made the dc vacuum arc always extinguish at this position. Third, repeated fluctuations of the arc voltage are caused by the formation and extinction of the ``C''-shaped arc. Finally, when the distance between the igniting area and Extinction Area increased, the duration of the Stable stage increased, while the duration of the Unstable stage decreased.

Vacuum arc characteristics of a new type of curved-surface contact for high-frequency forced interruption in aero applications

Aiming at the arc interruption problem in aviation 270 V DC power systems, this report proposed new contact types of vacuum interrupter contacts with curved surfaces for high-frequency forced interruption. The characteristics of vacuum arc behavior, high-frequency forced interruption capacity and contact surface ablation under curved contact with different structural parameters are investigated. The interruption ability, arc voltage characteristics and contact ablation of CuW80 and CuCr25 contact materials and their differential combinations were obtained. To select the optimal structural parameters of the curved contacts, a method based on the curvature of the electrode surface was proposed for high-frequency forced interruption under a short-gap vacuum arc. Experimental results show that a current of 4.8 kA can be interrupted at a commutation frequency of 20 kHz with a di/dt of 650 A/μs when the curvature of curved contacts is in a certain range.

Observed Oscillating Anodic Plasma Plume Phenomena in High Current Vacuum Arcs

The impact of current density on the anode attachment characteristics of high current vacuum arcs was investigated using high-speed imaging techniques. The current density determines the occurrence of attachment transition into an anode spot type 2. Electrodes were made of Cu/Cr 50%/50%. In combination with the adequate amplitude of current, the anode spot type 2 was accompanied by first observed oscillating anodic plasma plumes by the higher current densities. Resulting electrode overheating processes, which depend on the instantaneous power delivered, determine the formation of a plasma region in front of the anode. Image processing indicates that this region interacts actively with the cathode, displacing the radiation intensity region, and influencing the behavior of its arc spots. In addition, increased high-frequency contents on the measured voltage signals accompanied the observed oscillations of the anodic plume. An explanation through a double-layer effect for the anode spot type 2 is proposed.