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Microparticles produced by high current vacuum arcs significantly reduce the insulation performance of vacuum interrupters. The objective of this paper is to observe the generation and dynamics of microparticles during the arcing and post-arcing period, and to further reveal the possible effects of particles during interruption of a high current va...
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... This behavior has been studied in our previous paper. 40 ...
The multibreak vacuum circuit breaker uses multiple short gaps to interrupt the fault current, greatly improving the dielectric strength, and is a viable method to realize high-voltage interruption. The metal vapor distribution near the current zero is crucial for the dielectric recovery process in the multibreak vacuum circuit breaker. Due to the complicated dielectric construction and the interaction between the breakers, the vacuum arc inevitably deviates from the axisymmetric distribution during the interruption process. The traditional diagnosis method limited to 0D or 1D is not sufficient to study the real distribution of metal vapor near the current zero. To address these issues, we developed a planar laser-induced fluorescence method to measure the 2D distribution of copper vapor near the current zero by detecting 510.6 nm fluorescence intensity. The results indicate that for the butt contacts, the copper vapor is diffused in the gap of the high-voltage break and aggregated on the cathode surface of the low-voltage break. The axial magnetic field and transverse magnetic field affect the 2D copper vapor distribution and eliminate the inconsistency, which is achieved by affecting the motion of charged particles and the ionization-recombination process. Furthermore, the copper vapor density exhibits a positive dependence on the arc current, and the magnetic field impacts the density increase rate and distribution mode.
... Molten droplets are inevitably splashing in the arc erosion process of electrical contacts. In addition to high fire risks, the ejection of molten droplets not only increases the probability of surface flashover accidents and induces arc interruption failure by changing the electric field distribution [28][29][30][31], but also produces adverse effects on the reliability and lifecycle of contacts [32,33]. Many researches were performed to reveal the arc erosion characteristics of electrical contacts, as described next. ...
Arc duration and erosion characteristics of cables are closely related to electrical fire hazards. In this study, the arc duration and arc erosion characteristics of copper and aluminum core cables were explored. The main erosion modes of copper core cable with mica insulation (HC0) and aluminum core cable with PI insulation (HA0) were determined. Results show that several large molten droplets with diameters of 5±0.5mm would drip down from the molten pool on the cable end during arcing of HC0, but the molten droplets are adhered to the molten pool and do not drip down during arcing of HA0. We concluded that the differences in melting energy and oxide film between copper and aluminum are the main reasons for this phenomenon. Besides, the molten pool can be formed on the cable end as the insulation is heatproof, which plays a vital role in prolonging the arc duration of cables. The arc duration of cables with heatproof insulation is longer than those with common insulation. This means that the cables with heatproof insulation have higher fire hazards from the perspective of arc duration. To further understand the influence of molten pools on arc duration, an arc duration model was developed based on energy balance, which is beneficial in determining the arc duration of cables with heatproof insulation in electrical fire accident investigation.
... In addition, a hot metallic particle produced from the anode is considered in this model, and the diameter of this metallic particle is set to 500 lm based on previous experimental observations. 18,19 Furthermore, the metal vapor atoms evaporated from the metallic particle will interact with the plasma jet, and the resulting ...
... At the same time, under the influence of the arc force, the crater starts to flow and may release metallic particles into the gap. 18 When the metallic particle leaves the anode, they have the same temperature as the anode surface. However, the energy injected into the anode by the vacuum arc is not uniform, 36 so the surface temperature of the anode is not the same everywhere, which causes metallic particles to leave the anode at different temperatures. ...
... 22 However, the appearance of metallic particles also brings uncertainty to the vacuum arc. In our previous experiments, 18,19 it can be observed that the generation and movement of metallic particles are random. Therefore, in this section, the metallic particle is placed at several different positions to investigate its influence on the plasma jet. ...
In this paper, the interaction between the vacuum arc plasma jet and the hot metallic particle near current zero was investigated by numerical simulation. A vacuum arc plasma jet model was developed using the hybrid simulation method, in which electrons were considered as a massless fluid, while heavy particles such as atoms and ions were modeled as particles. In this model, the effect of the evaporation of metal atoms from the metallic particle was considered. Additionally, the Monte Carlo collision method was used to model inelastic collisions between electrons and heavy particles. The simulation results demonstrate that the metallic particle blocks the plasma jet, causing an asymmetric and nonuniform distribution in the plasma jet. Furthermore, some of the evaporated atoms from the hot metallic particle are converted into Cu ¹⁺ ions by ionization collisions with electrons. The drift velocity of Cu ¹⁺ ions coming from the ionization of metal vapor is much lower than that of highly energetic ions emitted from the cathode spot, making it difficult for them to be completely dissipated as soon as possible during the extinguishing phase. Moreover, the presence of a hot metallic particle causes an increase in the density of plasma in its surroundings, which increases the probability of arc reignition in the post-arc phase.
... They also observed particles spontaneously generated by high currents flowing through an open fixed gap [32]. Our previous work [33] also focused on particles produced by high currents and found that hot particles stemming from the sputtering of liquid metal, which may provide metal vapor to invoke late breakdowns. However, the majority of particles generated in capacitive interruptions originate from the mechanical rupture of the cold-welding area, which are irregularly shaped, have low temperatures and large sizes (up to several millimeters). ...
... In most cases, the glowing of particles cannot be observed. According to our previous direct observation [33], if particles were generated or heated by a higher interrupting current over several kilo-ampere, they may keep melting and glowing for a while. Otherwise, particles are hard to heat to a high-temperature luminous state. ...
Post-arc breakdowns of vacuum circuit breakers during capacitive operation can be possibly caused by particles. In this work, we experimentally observe the generation and dynamics of particles in capacitive interruptions and their resultant effects on post-arc breakdowns. We further constructed a synthetic test circuit for the capacitive current switching and adopted the laser-shadow technique to observe the dynamics behaviors of particles, formed by different electrode materials and inrush currents. CuCr10 electrodes tend to generate particles with high probability and quantity, owing to their weak refractoriness and lower mechanical strength. Furthermore, we find that the higher inrush current facilitates the formation of particles. Additionally, under the influence of recovery voltages and variable charges, particles show complex and diverse dynamic behavior, such as bouncing, oscillating, levitating, lifting, and rotating. Essentially, all particles relevant to breakdowns moved at a low speed (below 0.5 m/s), besides, almost all non-sustained disruptive discharges and restrikes are concerned with the particles closed to electrodes under near-peak recovery voltage. Therefore, we think neither energy accumulation nor high-speed bombardment of particles can explain post-arc breakdowns, conversely, the joint effect of particle-induced field enhancement and resulting field electron emission is responsible for breakdowns.
... In high-current arc mode, the anode becomes active in the sense that it emits microparticles and vapour into the plasma [10][11][12][13]. Wang et al. [14] observed the process by which microparticles were produced from the anode using the lasershadow technique and proved that these microparticles were closely related to the long-delayed breakdown. Just as the active anode, the cathode is active too in high-current arc mode. ...
... In addition, experimental results of [37] show that the decay time of anode material of CuCr50 was longer than that of anode material of CuCr25 at the same arc current. Simulation results of [14] show that it is the size rather than the temperature that is a greater determinant of temperature decay. And we infer that large Cr particles could become hot spots which keep copper above melting point to continuously produce microparticles. ...
Microparticles are an inevitable component of vacuum arcs. This paper focused on the dynamics of microparticle and erosion behavior in high-current vacuum arcs. The arc was sustained with AC 110 Hz between two butt CuCr alloy contacts with a diameter of 10 mm. An in situ microparticle diagnostic system suitable for vacuum arcs was developed. Three sources of microparticles were observed and the corresponding motion characteristics were obtained by our method. The influence of current and Cr content on erosion characteristics was investigated. The results indicate that the increase of Cr content contributes to inhibiting production of microparticles when the current is small. CuCr30 has the best effect of suppressing microparticle production among the three tested alloy materials under large current. The work of this paper helps with the understanding of microparticle behavior in high-current vacuum arcs and may provide a path for the design of a vacuum electrode.
... The existing studies concluded that these phenomena could cause the exchange of energy and charge, and further trigger breakdown. Wang et al [14] combined the laser shadow technique and direct light emission and, consequently, observed that the incandescent particles with high temperature triggered breakdown after collision with the electrodes. ...
... Because of the image intensifier, ICCD can not only display particles distribution, but also obtain the relative intensity of the scattering light to reveal the evolution of particle accumulation and suspension. In addition, large particles can be observed clearly by the laser shadow technique [14] due to their remarkable shading light effects. Generally, an expanded collimated light spot obtained by adding one beam expander (GCO-2501) served as the background light, and subsequently the shadow graphics of particles were captured with a high speed camera (Photron FastCam-Mini_Ux) with temporal resolution of 25 µs. ...
Pulse-power technology has been widely used in inertial-confinement fusion, electron-beam accelerators, and the aeronautics and astronautics fields. However, particle contamination can reduce operational stability by altering the breakdown process. The objective of this paper is to study the effects of large numbers of metallic submicron particles on the breakdown characteristics. Particles were spontaneously generated via consecutive high-pulse-power breakdowns in compressed N2. In this paper, we adopted a plasma-diagnosis system that combines a laser scattering technique with laser shadow photography to detect particles originating from different materials. To distinguish the specific effects of particles, a double-electrode/double-pulse method was used to eliminate the unwanted effects of electrode erosion. After thousands of consecutive breakdowns, numerous particles were unexpectedly found to suspend and accumulate in the inter-electrode gap rather than fall to the bottom. These particles mainly stemmed from the anode and were identified as either metallic conducting nanoparticles or submicron particles. Furthermore, their density continuously increased and remained at a high level for a long time. This converted the insulating medium from a pure gas to a mixture with numerous metallic particles. In this case, the probability of breakdowns involving particles increased and their mean breakdown voltage showed a downward trend. According to our analysis of the field-enhancement process, these small particles alone can neither cause field emission nor trigger a microdischarge. However, their collective effects could be significant if they were involved in the breakdown channel.
... On the other hand, in the HCVA, the energy flow is injected into the anode by the contracted arc plasma, the temperature distribution of the anode surface will also have a radial distribution due to the radial distribution of the energy flow [23][24][25]. ...
In the arc-burning process of a high-current vacuum arc (HCVA), the metal particles (MPs) splashed from the active anode will have a significant influence on the plasma characteristics of the arc column. In this paper, the influence of varying MPs on the characteristics of HCVA are studied by establishing a HCVA model containing single or multiple MPs. The simulation results show that when the MPs vaporized metal vapor (MV) enters the interelectrode region and once the arc column plasma cannot ionize all atoms immediately, the ionization layer and the neutral atom vapor area (NAVA) will be formed in the adjacent region of the MPs. When the MP diameter and temperature increase, the number of vaporized metal atoms increases, so that the influence range of MV increases, and the area of ionization layer and the NAVA increases. In addition, when the arc current increases or the MPs are closer to the cathode surface, the greater the ion number density and ion pressure around the MPs are, the stronger the compression on the MV will be, resulting in the decrease of the area of ionization layer and the neutral atom vapor, and the increase of the net ionization rate of the ion number density. When multiple MPs exist in the interelectrode region at the same time, the MV from the MPs will affect each other. In the central region of multiple MPs, the density of MV becomes the largest, while the net ionization rate of ion number density is distributed in the periphery region of the MP group.
... For example, it was found in work [10], that Cu-45 %Cr material provides comparably the lowest cathode wear, while Cu-50 %Cr provides lowest anode wear. Moreover, it was concluded in [11] that it is much more difficultto form a melting pool on a Cu-Cr contact surface with a higher proportion of chromium. On the other hand, an increasing of Cr content leads to decreasing of interruption rate [12]. ...
The results of optical emission spectroscopy (OES) investigation of plasma of electric arc discharges in steadystate mode between Cu-Cr composite electrodes, manufactured at different sintered temperatures: 750, 850, 950 or 1050 °C, is presented. In particular, the impact of sintering temperature on erosion resistanceof such composite materials, which was determined in indirect manner by estimation of metal vapours content in the midsection of discharge gaps, is studied by the analysis of plasma parameters. These contents were calculated in assumption of local thermodynamic equilibrium (LTE) on the base of experimentally obtained radial distributions of plasma temperature and electron density.
... The existing studies concluded that these phenomena could cause the exchange of energy and charge, and further trigger breakdown. Wang et al [14] combined the laser shadow technique and direct light emission and, consequently, observed that the incandescent particles with high temperature triggered breakdown after collision with the electrodes. ...
... Because of the image intensifier, ICCD can not only display particles distribution, but also obtain the relative intensity of the scattering light to reveal the evolution of particle accumulation and suspension. In addition, large particles can be observed clearly by the laser shadow technique [14] due to their remarkable shading light effects. Generally, an expanded collimated light spot obtained by adding one beam expander (GCO-2501) served as the background light, and subsequently the shadow graphics of particles were captured with a high speed camera (Photron FastCam-Mini_Ux) with temporal resolution of 25 µs. ...
Spark gas switches (SGS) are widely used in various pulsed power applications where sulfur hexafluoride (SF6) is still dominant because of its excellent insulating performance. However, particle contamination generated by SF6 possesses some special properties that can greatly reduce the effectiveness of the gas switches. The objective of this paper is to study the effects of particles generated spontaneously by consecutive breakdowns of high-pulse-power SGS on the insulating performance in compressed SF6. A double electrode/double pulse method, coupled with laser scattering and laser shadow photography, is adopted to detect the particles and examine their specific roles in the breakdown process. Many large particles in SF6, of approximately 150 μm in diameter, are observed at about 80 milliseconds after a single breakdown. Furthermore, numerous particles gradually suspend and accumulate in the gap after consecutive breakdowns. Particles generated by SF6 can reach tens of micrometers in size. They have rough microtopography covered by abundant floccules, and contain rich electronegative elements: fluorine and sulfur. Moreover, particle-involved abnormal breakdowns in SF6 usually occur with nearly equal threshold and probability in spite of the increasing consecutive breakdowns, and conversely, the abnormal breakdowns in N2 appear more frequently and unsteadily with a high dispersibility. The analysis of field enhancement caused by these large metal-fluoride/sulfide particles shows that they can directly cause significant field emission (FE) due to their properties of surface-field enhancement and causticity. Such FE further triggers micro-discharge. Subsequently, this behavior eventually leads to abnormal breakdowns at a lower threshold.
... Compared with metal vapors, the considerable erosion volume via droplet ejections can cause severe mass loss and rugged surface morphology of the anode. This is even a critical challenge for the high-voltage switching devices: the generation of splashing droplets not only exacerbates the deterioration of the contact surface but also increases the probability of post-arc breakdown by changing the electrical field during the motion of the ejections, which leads to the failure of arc interruptions [18,19]. ...
Based on the in situ diagnostic system and the digital image post-processing technique, quantifications of the anodic erosion components and heat transfer efficiency for tungsten and the W80Ag20 material in arcs of argon, helium, and nitrogen were achieved. The leading vaporization of silver has been found to result in evidently lower anodic heat transfer efficiency and much smaller molten pools compared with those of the tungsten anode, but the intensive generation of silver vapor under the melt layer causes higher splashing erosion of the W80Ag20 anode. However, these characteristics can be strongly changed by the cathodic blowing, which leads to a much higher splashing erosion of tungsten anode but a lower erosion rate of W80Ag20 anode. Through the visualization of the erosion behavior and the post microanalysis of the anode surface, the possible driving mechanisms for the generation of the splashing droplet were discussed. The result indicates that the local high pressure caused by the vapor blasting during the bubble explosion plays a key role in the detachment of splashing droplets. Furthermore, as for the tungsten-based anode, the comparison of erosion behavior between the W80Ag20 anode and the previous-studied W70Cu30 anode makes it clear that increasing the temperature difference between the melting point of tungsten and the boiling point of the other material has the pros and cons. It is effective for the decrease of the anode erosion when the anode heat energy is relatively weak, while it can promote the splashing erosion when the liquid tungsten layer has been formed on the anode tip. These results are beneficial for the optimal design of the electrode system in circuit breakers.
