A Systematic Comparison of Intense-Mode Vacuum Arc Between CuCr and AgWC Electrode by Using Various Optical Diagnostics

The objective of this article is to determine the anode surface temperature during and after current zero (CZ) with single and dual vacuum arc columns. Both the alternating current (ac) and pulsed direct current (dc) waveforms were applied with a peak value of 5–16 kA. A butt-type electrode and a horseshoe-type electrode were utilized to generate single and dual vacuum arcs. In the draw arc experiment, three spectrometers with working wavelengths of: 1) 200–1000 nm; 2) 880–1700 nm; and 3) 1600–2400 nm, a fast thermography camera, and two high-speed cameras were used for optical analysis. Based on the experimental results, it was certified that spectroscopic analysis with the Planck fitting procedure is an effective method to determine the anode surface temperature after CZ. The most preferable wavelength of the spectrometer in anode temperature determination was 800–1900 nm. The temperatures of anode spot 1, anode spot type 2, and footpoint mode were 3200–3300, 3800–4000, and 3000–3100 K, respectively. Two kinks appeared in the anode temperature cooling curve. The corresponding temperature was the liquidus temperature of the electrode material and the melting point of copper. Besides, two hot areas on the anode surface were observed for the horseshoe-type electrode. The anode temperature tended to be homogeneous at about 0.8 ms after CZ.

Anode melting and crater formation significantly affect interruption of high-current vacuum arcs. The primary objective of this paper is to theoretically investigate the mechanism of anode surface crater formation, caused by the combined effect of surface heating during the vacuum arc and pressure exerted on the molten surface by ions and electrons from the arc plasma. A model of fluid flow and heat transfer in the arc anode is developed and combined with a magnetohydrodynamics model of the vacuum arc plasma. Crater formation is observed in simulation for a peak arcing current higher than 15 kA on 40 mm diam. Cu electrodes spaced 10 mm apart. The flow of liquid metal starts after 4 or 5 ms of arcing, and the maximum velocities are 0.95 m/s and 1.39 m/s for 20 kA and 25 kA arcs, respectively. This flow redistributes thermal energy, and the maximum temperature of the anode surface does not remain in the center. Moreover, the condition for the liquid droplet formation on the anode surfaces is developed. The solidification process after current zero is also analyzed. The solidification time has been found to be more than 3 ms after 25 kA arcing. The long solidification time and sharp features on crater rims induce Taylor cone formation.

It is important to obtain the information on the neutral metallic vapor during the arcing period for a better understanding of vacuum arc interruption process. In this work, the objective is to experimentally study the two dimensional distribution of copper vapor during arcing. A reverse current was injected at specific time points to force the 45 Hz sinusoidal arc current to be extinguished in a short time, avoiding the interference of intensive arc self-radiation. Meanwhile, the plane laser-induced fluorescence (PLIF) using a pulse laser with a central wavelength at 324.8 nm was adopted to excite the metallic vapor, and a iCCD camera recorded the distribution of the vapor from the induced fluorescence. In the experiments, a pair of cup-shaped axial magnetic field (AMF) contacts were used. The material was CuCr50 and the peak amplitude of the arc current was 3 kA. It is found that the peak value of the metallic vapor density occurred at about 8 ms while the current peak occurred approximate 3 ms in advance, and the highest density value can achieve up to 2.3×1020m-3. It is also found that the metallic vapor mainly accumulated on the anode surface under AMF during the arcing period, which became obvious when the current begins to drop.

Spectral computed tomography (CT) enables improved tissue characterization, although virtually all research has focused on contrast-enhanced examinations. We hypothesized that changes in myocardial tissue related to acute myocardial infarction (AMI) might potentially be identified without the need for contrast administration using electron density (ED) imaging. This retrospective observational study involved a small series (n = 15) of patients admitted to our institution with a first AMI without signs of hemodynamic instability and identification of a culprit vessel with invasive coronary angiography during the same admission, who also underwent a noncontrast, low-dose chest CT using a dual-layer spectral CT scanner. Images were assessed in search of dark areas with low density on ED imaging, and the mean percentage ED relative to water (%EDW) was calculated. Using a qualitative approach, ED assessment enabled the identification of 11/15 (73%) affected coronary territories, with a sensitivity of 73% (95% CI: 45; 92%) and a specificity of 87% (95% CI: 69; 96%). AMI segments showed significantly lower ED values than the remote myocardium (103.8 ± 0.8 vs 104.3 ± 0.6 %EDW, P < 0.0001), and a threshold below 103.9 %EDW had a sensitivity of 66% and specificity of 79% for the identification of AMI. In a control group of patients without a history of cardiovascular disease, none had areas with focal reduction of ED following the shape of the myocardial wall. In our preliminary series, ED imaging showed the potential to enable the identification of myocardial tissue changes related to AMI without iodinated contrast requirement.

An electrical circuit with an applied voltage of dc 50 V and a current flow of 3.3 A is shut out by a pure Ag contact, a pure Pd contact, and three types of AgPd alloy contacts. The distributions of the metal vapor and the metal vapor density near the cathode of the long-term arc were measured. It was found that the arc duration was long if the vapor density of Ag atoms in the arc column during the later half of the discharge was high. Also, the distribution shape of the metal vapor at an Ag contact arc was axially symmetric with respect to the arc column during the later half of the discharge. In the case of Pd contact arc, the distribution was axially asymmetric. In the AgPd contact arc, the vapor of Ag atoms and Pd atoms is concentrated around the axis of the arc column in any of three alloy contacts during the later half of the discharge. The distribution of Pd atoms is shifted to the axially symmetric form as a characteristic of the Ag contact arc. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(2): 30–38, 1998

The arc between the vacuum transverse magnetic field (TMF) contacts is driven by the TMF generated by contacts to move at high speed. The motion characteristics of the arc determine the key parameters, such as contact surface temperature and metal vapor density during the arcing process, which are closely related to the breaking capacity of the vacuum switch. Under the conditions of different gap distances, the motion characteristics of the vacuum arc during the arcing process are significantly different. In this article, a magnetohydrodynamic (MHD) simulation model is established by the method of modeling and simulation, and the variation characteristics of plasma parameters during the movement of the vacuum arc under different gap distances are studied. The results show that with the gap distance increasing, the maximum electron temperature in the center of the arc column increases and the position gradually approaches the anode, and the average moving speed of the arc first increases and then decreases. At the same time, experiments are carried out on the vacuum contacts in the checkable vacuum interrupter to analyze the influence of the gap distance on the arc motion and arc shape changes, and the simulation results are verified. The research in this article shows the influence of the variation of the gap distance on the arc motion characteristics, which provides a theoretical basis for designing contacts with better breaking capacity.

The distribution and dissipation of neutral atoms are crucial for understanding the dielectric recovery process after interrupting direct current (DC) vacuum arcs. This article aims to investigate the dissipation of copper atoms after a forced extinction of the vacuum arc experimentally, adopting the plane laser-induced fluorescence method. The change in the 2-D distribution of copper atoms with time is presented. The results show that the magnetic fields, the axial magnetic field (AMF), and the transverse magnetic field (TMF) have a limited effect on the initial density of copper atoms. For both the AMF and the TMF, the copper atom densities at current zero (CZ) vary in the range (6– $8) \times 10^{17}\,\,\text{m}^{-3}$ when 3-kA vacuum arcs are forced to 0 in 0.2 ms. Contrary to the TMF case, in the AMF case, the evaporation on the anode after the CZ results in long-existing atoms near it. Consequently, the atom density of the TMF decays faster than that of the AMF, which indicates that a vacuum interrupter with the TMF contacts has a better performance when interrupting a DC load. The difference between the two magnetic fields originates from the arc control patterns. Namely, the AMF tends to keep vacuum arcs in a stable mode, which is unfavorable for a DC interruption; on the contrary, the TMF drives the vacuum arcs to move at high velocities resulting in faster dissipation of copper atoms after the CZ. In addition, the composition proportion of CuCr contacts has a limited effect on the diffusion of copper atoms when a low-vacuum arc is interrupted.

Vacuum circuit-breakers (VCBs) are commonly used in emerging mechanical DC circuit-breakers. The electrical performance of VCBs in DC interruption duties has been extensively investigated, but basic physics such as the excitation temperature of plasma species, electron/vapor densities and emission of droplets in such applications were rarely reported. In this paper, we focus on how the short high frequency (HF) current pulse affects erosion of electrodes as well as generation of flying droplets by using laser shadow photography. Spectroscopy was adopted to obtain spectra and calculate the excitation temperature of CuI. Shack–Hartmann wavefront sensors were applied to measure neutral and electron density, in tests where di/dt, breaking current and the direction of the injected HF current varied. Indeed, the in-phase injection of the HF current caused an intense arc, but the pulse was too short to make either the cathode or anode melt. Since the plasma is in a nonequilibrium state, the excitation temperature of CuI is relatively low. Electron densities in different tests all approach similar values right before current zero. Neutral densities show strong fluctuation and independence on instantaneous current.

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.

The excitation temperature of the high-current vacuum arc was measured based on the intensity ratio of two Cu I spectra of 510.6 and 515.3 nm. Diffuse mode vacuum arcs with the peak current of 2 kA, igniting between 5-mm gap, 10-mm phi electrodes, Cu100, Cu80Cr20, and Cu50Cr50 wt.% contacts were measured by a multiple-imaging optical system and high-speed video camera. It turns out that the excitation temperature was almost evenly distributed in the gap. The excitation temperature at the current peak depended on the electrode material and took higher in the order of Cu100, Cu80Cr20, and Cu50Cr50. The excitation temperature was also measured by a spectroscopic approach, and it showed the same tendencies as the measurement using multiple-imaging optical systems and a high-speed video camera. The current decreasing phase of dc interruption was simulated by using semiconductor switches at the peak of ac 50-Hz current, and as a result, the current zero with a decreasing ratio of 30 A/μs was realized. The excitation temperature for the Cu100 electrode decreased with the decreasing current, whereas those for Cu80Cr20 and Cu50Cr50 increased. This difference suggests that developing direct current vacuum circuit breakers needs the optimization of the electrode materials, current waveform, and plasma parameters in the gap.

Pulmonary ground-glass nodules (GGNs) are increasingly being detected as manifestations of early lung cancer. However, conventional computed tomography (CT) images may fail to clearly show small lesion details, particularly in the case of small, low-density GGNs, which are often difficult to observe. Limited evidence suggests that dual-layer spectral detector CT (SDCT) electron density imaging (EDI) improves the visualization of ground-glass opacities (GGOs) and increases the detection rate of mixed GGNs (mGGNs). This study aimed to evaluate the clinical value of SDCT EDI reconstruction images in detecting pulmonary GGNs by comparing them with conventional CT images of different reconstruction slice thicknesses. The SDCT data of 27 patients with GGNs, including pure GGNs (pGGNs) and mGGNs, were included in both the EDI and conventional CT groups. The images were reconstructed using thin 1 mm, 3 mm minimum intensity projection (MinIP), and 5 mm maximum intensity projection (MIP). Two radiologists, each with over 10 years of experience, subjectively assessed the morphological signs and image quality of the lesions. Additionally, the clinical value of the images was evaluated by another 20 thoracic surgeons and radiologists through a six-item questionnaire. The results showed that lobulation (P<0.001), spiculation (P=0.029), tumor-lung interface (P<0.001), and solid components (P=0.003) was significantly more prominent in electron density (ED) images. Conversely, the vacuole sign (P=0.016) was more apparent in conventional CT images. Neither the pleural indentation sign (P=0.429) nor the vessel crossing sign (P=0.227) showed statistically significant differences between the groups. The subjective image quality of lung structures study found that image noise suppression and artifact reduction were significantly greater in ED images (P<0.001). Conventional CT images demonstrated sharper visual reproduction of lung parenchyma, lung vessels and fissures, lung-thorax wall, and the pleuro-mediastinal border (P<0.001). In clinical evaluations of the value of conventional CT and ED reconstruction images, ED images showed significant advantages in defining the tumor-lung boundary, confirming solid components, measuring the size and solid portions, making a definitive diagnosis, choosing treatment options, increasing confidence in treatment decisions, facilitating multidisciplinary consultations, and reducing time (P<0.001). SDCT EDI is an effective method for the differential diagnosis of benign and malignant GGNs. It provides clearer image features, particularly in terms of the lobulation and the tumor-lung interface and solid components, helping radiologists and thoracic surgeons to make more accurate diagnostic and treatment decisions.

A hybrid circuit breaker consists of a series-connected vacuum- and SF6 interrupter. The vacuum interrupter has the function to withstand very steep-rising transient recovery voltages, whereas the SF6 interrupter is stressed with the peak of it. Full scale tests are described of a 145-kV prototype, which is subjected to short-line faults based on 63 kA. During these tests, current through the breaker and voltages across both interrupters were monitored with a high-resolution measurement system. It is shown that the principal idea works correctly. From measured results, it is demonstrated that the interaction between the two arcs of completely different physical nature has a positive effect on the interruption: Immediately before current zero, the SF6 arc assists the vacuum arc to interrupt, whereas after current zero, the vacuum arc assists the SF6 arc in the recovery against the recovery voltage. From the analysis of the measurements, it becomes clear that high values of post arc current (up to 30 A) have (at least initially) a positive effect on the breaker performance. Detailed modeling of the interaction of arc-arc and arc-circuit is described, showing a good agreement with the measured results. The model is used to predict the voltage distribution across both interrupters when other (capacitive) voltage grading is applied in the design than present during the tests.

The breaking capacity of a medium voltage (MV) rotary SF6 load break switch (LBS) can be improved by incorporating permanent magnets into the stationary contacts. The magnetic field is intended to blow the switching arc root towards a recessed space at the stationary contacts thereby preventing reignition of the arc after current zero. Making and breaking tests of load current 630 A were performed comparing the switching performance of load break switches equipped without a permanent magnet, with a ferrite and with a neodymium magnet. The impact of different polarity arrangements of the magnets in the three phases is also considered and analysed. In order to understand the arc behaviour caused by the effect of permanent magnet, arcing times and arc voltage were measured and evaluated. The results show that the arc voltage depends on the direction of the electromagnetic force, which is determined by the phase current direction but also by the polarity of the magnets. When the force is directed towards the recessed space at the stationary contacts, the arc voltage is notably higher than in the case where the arc is blown in the opposite direction. The higher arc voltage is a reliable indication that the length of the arc is increased, which significantly reduces the risk of both thermal and dielectric breakdowns after the first current zero. The consequences are noticed first in the reduction of the number of missed current zeroes and second in shorter minimum arcing times. An adverse arrangement of the magnet polarity in the three phases increases the number of missed current zeroes.

Anode activity is critical in high-current vacuum arcs in vacuum interrupters. If the anode temperature gets too high, an evaporation of metal vapor from an anode melting pool may lead to a formation of anode spots, which would lead to a failure of current interruption of vacuum interrupters. The input energy from an arc column to an anode surface is adjusted by an anode sheath. The objective of this paper is to develop a numerical simulation model of the anode sheath of vacuum arc by using a Particle-in-Cell method. A low-current case and a high-current case of arcing are simulated. The physical parameters of electrons and ions are obtained from magnetohydrodynamic simulations, and are set at the simulation boundary of the current model. The sheath thickness is 2∼4 Debye length, and the anode potential fall is about 1.5∼3 V for both case. It is found that the acceleration of ions by electric field in the anode sheath is more significant for the high-current case. This also adds to the energy flux into the anode surface.

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.