Anode Temperature Evolution in a Vacuum Arc With a Blackbody Electrode Configuration

Copper film deposition and anode temperature measurements in a vacuum arc with tungsten anode

Anode temperature distribution and coating characteristics in a Hot Refractory Anode Vacuum Arc with an asymmetric anode

The objective of this paper is to compare the electron temperature and electron density in diffuse vacuum arc mode and anode spot mode. The experiment was based on the butt type copper electrodes, with contact diameter D=40mm, and gap distance g=10mm. The vacuum arc was ignited by a needle tungsten electrode, which was embedded in the cathode. A high-voltage pulse with a rise time of 8ns, and aptitude of 24kV was applied on the needle electrode. The arc current varied from 2.8kA to 7.5kA (rms). The arc current was measured by Hall sensor and the arc voltage was measured by Tektronix P6015A, respectively. The arcing process was recorded by a high-speed charge-coupled device (CCD) video camera. The emission intensities of the interelectrode plasma of the vacuum arc were collected by an optics spectrograph. The Bolzman plot method was used to calculate the electron temperature and the Saha equation was used to determine the electron density of diffuse vacuum arc mode and anode spot mode. The electron temperature was 1.09eV in diffuse arc mode and it was 1.22eV in anode spot mode. The electron density was increased from 7.6 × 1015/cm3 to 2.1 × 1015/cm3 when the arc mode changed from diffuse arc mode to anode spot mode.

A kinetic one-dimensional model of ultra short (10 microns) vacuum arc was developed to research the vacuum arc near-anode region and the influence of anode plasma on the cathode attachment selfconsistently. The kinetic model is a model of 1D3V PIC/DSMC type. The model takes into account the main types of elastic and inelastic collisions of particles in the plasma as well as evaporation and thermo-field electron emission from the both electrodes. The model has three task parameters: cathode temperature, anode temperature, and voltage drop applied to the gap. The plasma state in the gap, current density, and energy fluxes density to the electrodes are the outcome of the model. The calculations have shown that the anode temperature variation strongly influences both the plasma column parameters and the cathode attachment. It was shown, that at the ratio T a /T c ∼ 1 (T a , T c -anode and cathode temperature) the plasma in the gap changes the direction of motion, so the conventional arc transits to the anodic arc.

A new technique for investigating the recovery period is described. A rectangular pulse of arc current is used and a probing voltage impulse is applied to the decaying arc channel at varied delay times after current interruption. The method has certain advantages over the normal a.c. method of testing.Reignition-voltage/time curves are presented for different conditions of electrode material, gas, gap length, arc current, arc duration and reignition polarity, with gas pressures at or near atmospheric. Observations are also made on the dynamic characteristics of the electrical discharge following reignition.Polished-copper and polished-tungsten electrodes require a reignition voltage of 355 volts within 3 microsec after current interruption for arc currents of 20 amp and less. Pipped-copper, pipped-tungsten, mild-steel, aluminium and graphite electrodes show continuing emission of electrons after current interruption to a varying degree, with corresponding reduction of the reignition voltage.The reignition phenomena are markedly affected by the polarity of the reignition. The arc anode normally attains a higher temperature than the cathode, so that continuing thermionic emission of electrons is more prevalent. Thus reignitions of reverse polarity from the original arc discharge tend to be lower than those of the same polarity.Different gases recover electric strength in the order: sulphur hexafluoride, carbon dioxide, oxygen, air, nitrogen and argon.

The electrical contact erosion of a relay directly depends on the arc energy. The arc duration is proportional to the arc energy. Thus, the dc arc duration has an important effect on the life and the reliability of a relay. Most studies of dc arc have concentrated on the influence of the contact opening velocity that is a mean value, or a constant, on arc duration and arc energy. This paper emphasizes the influence of the contact breakaway initial velocity on arc duration. Here, the contact breakaway initial velocity is the velocity of the moving contact at the moment of the moving contact breaking away from the stationary contact. According to the experimental model designed, the waveforms of arc voltage and arc current are measured in a resistive load circuit and an inductive load circuit The relationships between the contact breakaway initial velocity and the molten metal bridge duration (abbreviated to the bridge duration), metallic phase arc duration, gaseous phase arc duration, and the total arc duration are analyzed. It is proved that increasing the contact breakaway initial velocity from 0.08 m/s to 0.3 m/s leads to decreases in the bridge duration, metallic phase arc duration, gaseous phase arc duration, and the total arc duration.

Phenomena in a molten bridge between electrical contacts at the stage preceding vacuum arc ignition and their influence on the arc duration are investigated using a mathematical model and experimental data. Two models of a bridge are considered and compared. The first model is based on the representation of a bridge as a melting filament between contact surfaces, while the second one describes bridging as extension of a liquid metal drop between contacts. The initial conditions for the temperature fields of electrical contacts at bridging start are formulated taking into account heat transfer in solid contacts before bridging. Evolution of a bridge during contact opening, its length, radius, time and coordinates of bridge rupture at boiling temperature are evaluated depending on electrical current, opening velocity and parameters of contact materials. The above mentioned mathematical model enables estimatation of the density of metal vapors in contact gap just after bridge explosion, which is responsible for vacuum arc ignition and maintenance at the initial stage of arc burning. It was found that bridge duration and anode arc duration is interrelated. There exists a critical contact gap, which becomes too large to support the power capacity required for the maintenance of extending zones of anode melting and evaporation. If the length of a bridge exceeds this critical gap, then the anode arc phase could be not appearing at all. On the contrary, if the bridge length is negligible or if the bridge does not appear at all, then duration of anode arc phase is maximal.

A high-current vacuum arc subjected to an axial magnetic field is maintained in a diffuse status. With an increase in arc current, the energy carried by the arc column to the anode becomes larger and finally leads to the anode temperature exceeding the melting point of the anode material. When the anode melting pool is formed, and the rotational plasma of the arc column delivers its momentum to the melting pool, the anode melting pool starts to rotate and also flow outwards along the radial direction, which has been photographed by some researchers using high-speed cameras. In this paper, the anode temperature and melting status is calculated using the melting and solidification model. The swirl flow of the anode melting pool and deformation of the anode is calculated using the magneto-hydrodynamic (MHD) model with the volume of fraction (VOF) method. All the models are transient 2D axial-rotational symmetric models. The influence of the impaction force of the arc plasma, electromagnetic force, viscosity force, and surface tension of the liquid metal are all considered in the model. The heat flux density injected into the anode and the arc pressure are obtained from the 3D numerical simulation of the high-current vacuum arc using the MHD model, which gives more realistic parameters for the anode simulation. Simulation results show that the depth of the anode melting pool increases with an increase in the arc current. Some droplets sputter out from the anode surface, which is caused by the inertial centrifugal force of the rotational melting pool and strong plasma pressure. Compared with the previous anode melting model without consideration of anode deformation, when the deformation and swirl flow of the anode melting pool are considered, the anode temperature is relatively lower, and just a little more than the melting point of Cu. This is because of liquid droplets sputtering out of the anode surface taking much of the energy away from the anode surface. The azimuthal velocity of the anode melting pool for arc current 12.5 kA root-mean-square (rms) is larger than that for 17.5 kA (rms), which is likely to be caused by the thinner liquid layer, and also a smaller melting pool mass of 12.5 kA.

Low frequency AC transmission systems exhibit extensive application prospects in scenarios such as long distance offshore wind power transmission and have garnered significant attention in developing eco-friendly power systems. Compared with conventional 50 Hz AC systems, low frequency systems demonstrate prolonged short-circuit current duration with distinct vacuum arc characteristics. Consequently, this study conducts numerical analyses of arc evolution dynamics and anode thermal processes in 20 Hz vacuum interrupters to evaluate the applicability of standard 50 Hz vacuum circuit breakers under low frequency conditions. Results reveal that reduced frequency alters the coordination between arc current and contact gap, intensifying arc constriction during later arcing stages for 20 Hz vacuum arc, thereby elevating the plasma parameters, including pressure, temperature, and current density. Under specified conditions, namely 60 mm contact diameter, 2.0 m/s contact opening speed, and 10 kArms short-circuit current, the peak anode heat density reaches 5.2 × 108 W/m2 for 20 Hz arcs, exceeding the maximum value of 50 Hz with 4.1 × 108 W/m2 by 26%. The 20 Hz arc anode further maintains elevated temperatures for extended duration, attaining a peak center temperature of 1795 K, which is 64% higher than the 50 Hz value of 1095 K. These findings provide theoretical guidance for designing low frequency vacuum interrupters.

Vacuum arc plasmas with a deuterium-saturated metal cathode are used for producing accelerated deuterium ion beams in neutron tubes. Here we present research results on the mass-charge state of such plasma with a zirconium cathode containing up to 40 at% of deuterium, on the ion velocity distribution, and on the fraction of deuterium ions in the plasma at different arc durations and currents. Also discussed are issues regarding the increase in the fraction of deuterium ions in vacuum arc plasmas.

A 3D thermal hot refractory anode vacuum arc (HRAVA) anode problem was developed and numerically solved by the finite-difference method. The heat flux from the plasma to an asymmetric anode with a slanted front surface in a HRAVA was determined using a three-dimensional numerical model for the heat flow in the anode and anode temperature measurements. The effective anode voltage (defined as the total heat flux to the anode divided by the arc current) was ∼7.0–7.5 V for the range of gaps and arc currents 5–18 mm and 125–225 A, respectively. The effective anode voltage increases slightly (∼2–3%) with the arc current increasing from 125 to 225 A. The effective anode voltage decreases (∼6–7%) with gap distance increasing from 5 to 18 mm. The heat flux to the asymmetric anode was strongly asymmetric with the maximum at the anode apex. The calculated heat flux density at the apex was up to 3 times higher than at the anti-apex.

As the main source of the vacuum arc plasma, cathode spots (CSs) play an important role on the behaviors of the vacuum arc. Their characteristics are affected by many factors, especially by the magnetic field. In this paper, the characteristics of the plasma jet from a single CS in vacuum arc under external axial magnetic field (AMF) are studied. A multi-species magneto-hydro-dynamic (MHD) model is established to describe the vacuum arc. The anode temperature is calculated by the anode activity model based on the energy flux obtained from the MHD model. The simulation results indicate that the external AMF has a significant effect on the characteristic of the plasma jet. When the external AMF is high enough, a bright spot appears on the anode surface. This is because with a higher AMF, the contraction of the diffused arc becomes more obvious, leading to a higher energy flux to the anode and thus a higher anode temperature. Then more secondary plasma can be generated near the anode, and the brightness of the ‘anode spot’ increases. During this process, the arc appearance gradually changes from a cone to a dumbbell shape. In this condition, the arc is in the diffuse mode. The appearance of the plasma jet calculated in the model is consistent with the experimental results.

ZnO nanoparticles were successfully synthesized by arc discharge using two difference electrodes, i.e., a zinc anode and a graphite cathode, which were submerged in de-ionized water. Gas mixture of oxygen and nitrogen was continuously supplied through holes in the cathode, while the arc was initiated by applying electrical current between the electrodes. Consequently, zinc anode was vaporized and reacted with oxygen to form ZnO nanoparticles. The effects of synthesis parameters, which are anode speed, arc current, water temperature and oxygen concentration in the gas mixtures on characteristics of ZnO nanoparticles were investigated and reported. Electron microscopy showed that the products are semispherical and ellipsoid particles with the average size of 20-50 nm. Optical characterizations indicated blue photoluminescence emission which corresponds to Zn interstitial defects of ZnO and leads to reduction in the band gap of the products. The photocatalytic activity of the as-prepared ZnO nanoparticles was evaluated via methylene blue (MB) degradation. The results showed that not only the particle size and surface area affects photocatalytic activity of the synthesized ZnO but also the intrinsic defect on the surface.

The objective of this work is to determine the arc transformation characteristics of the high current vacuum arcs with fixed contacts under combined magnetic fields. A novel TMF-AMF combined contact consisted of a pair of outer fixed cup-shaped AMF contact and a pair of inner moving cup-shaped TMF contact. The vacuum arc characteristics include the arc transformation characteristics, vacuum arcing behavior and the arc voltage. The arc current in the tests varied over a range from 0 to 30 kA at 50 Hz. The contact material was CuCr25 (25% Cr). A high-speed charge coupled device video camera was used to record the vacuum arc appearance. The experimental results show that the vacuum arc can transform from inner TMF contacts to the outer fixed AMF contacts successfully, which can reveal the effective function of the inner TMF contacts and the outer fixed AMF contacts, respectively. Moreover, the experimental results reveal that the current flew through the outer fixed contact was limited. The arc current mainly flew through the inner contact. When the fixed lower contact was cathode, the current transformed to the fixed contact more early, due to the moving characteristic of the cathode spot. This results will promote the application of the combined magnetic fields contacts.

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.