Diffuse Arc Mode Research Articles

Optimizing the Opening Velocity for a Vacuum Circuit Breaker With Cup-Type Axial Magnetic Field Contacts

This article extends the quantitative method of optimizing the opening velocities for a vacuum circuit breaker (VCB) with cup-type axial magnetic field (AMF) contacts. The material of the AMF contact is Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> . We define v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> as the initial opening velocity over half the full contact gap and v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as the average velocity over the full contact gap of 20 mm. We optimize v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> using the transition of anode-discharging modes, of which we combine the footpoint mode and anode spot mode into a large-gap high-current (LGHC) mode. The experiment shows that v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> should be higher than a threshold velocity v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1_th</sub> , which corresponds to a peak critical contact gap d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1_th</sub> for the transitions of an intense arc mode into a diffuse arc mode, in high-current interruption. The higher v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> is than v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1_th</sub> , the faster the intense arc mode evolves into the diffuse arc mode. This helps successfully interrupt the short-circuit current in a short arcing time. Another threshold velocity, v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2_th</sub> , corresponds to the maximum critical contact d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">II_th</sub> for the formation of an LGHC mode in the second arc current half-wave. A high v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> design needs v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> to be lower than v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2_th</sub> . The lower v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is than v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2_th</sub> , the better the VCB avoids the LGHC mode in high-current interruption. This helps interruption over a long arcing time. We propose an intelligent opening and breaking operation for VCBs with cup-type AMF contacts, whereby the VCB opens with different opening velocities according to the short-circuit current level.

Experimental Determination of the Current Constriction Characteristics at the Anode of AMF Vacuum Arcs

Before the formation of the anode spot, the anode current constriction is considered as a result of current constriction on the cathode surface and in the arc column. The objective of this paper is to quantitatively determine the current constriction characteristics by experiments at the anode of vacuum arcs under an axial magnetic field (AMF). In this paper, the radial distribution of the anode current density in a diffused vacuum arc was determined quantitatively by a novel method of four types of split-anode contacts, with various diameters of the central areas. The vacuum arc was in the diffuse arc mode with the arc current ranging from 6-to 14-kA rms. An external AMF was applied at 74 mT. The results indicate that the radial distribution of the anode current density $j_{z}$ is in the form of the three-parameter equation, $j_{z}=aj_{A}e^{(-br\wedge 2)}+c$ , where $j_{A}$ is the average current density on the whole anode surface, $r$ is the radius of the anode contact, and the value of constants $a$ , $b$ , and $c$ depends on the arc current. Moreover, the results reveal the constriction characteristics of the anode current density in high-current vacuum arcs subject to the AMF, which was quite uneven in the radial distribution of the anode current density in the diffuse arc mode. Finally, under various arc currents, the constriction characteristics of the anode current density reveal similar patterns. The current density mainly constricted in the central region, in which the diameter might be only one-third of the whole diameter of the anode contact.

Effect of six pure metals cathode on constricted characteristics of high-current vacuum arcs subject to axial magnetic field

The objective of this paper is to quantitatively determine the effect of the six pure metals cathode on the constricted characteristics of high-current vacuum arcs subject to axial magnetic field (AMF). To measure the current density in anode surface, a butt-type split-contact with four axisymmetrical areas was selected as the anode, with the material of CuCr25. A plate contact was selected as cathode, under six pure metals material, including Cu, W, Mo, Fe, Cr, Al, respectively. The experimental arc current was 10 kA (rms) at 50 Hz. The opening velocity was 2.0 m s−1. The currents of the four areas in the anode surface were measured using four Rogowski coils situated outside the vacuum chamber. An external uniform AMF of 74 mT was applied during the experiment. The observed arc modes were recorded by a high-speed CCD video camera. The experimental results indicate that, in the diffuse arc mode, the cathode materials effect the constricted characteristics of the vacuum arcs. The vacuum arc column with the cathode of W and Mo constricted more severe than that in Cu, Fe, Cr and Al. For the cathode of Cu, Fe, Cr and Al, the uneven distribution of anode current density was mainly at the previous stage before the current peak. After the current peak, the difference of the average current density between the central area to other three periphery areas reduced continually. However, for the cathode of W and Mo, the uneven distribution of anode current density maintained during the whole arcing time. Moreover, the influence of the six pure cathode contacts on the constricted characteristics mainly focused on the spreading angle of the plasma jet and the numbers of the jet sources in the cathode surface. With a greater number of cathode spots, the distribution of the arc current density should be more uniform.

Cathode-constriction and column-constriction in high current vacuum arcs subjected to an axial magnetic field

The influence of the applied axial magnetic field on the current density distribution in the arc column and electrodes is intensively studied. However, the previous results only provide a qualitative explanation, which cannot quantitatively explain a recent experimental data on anode current density. The objective of this paper is to quantitatively determine the current constriction subjected to an axial magnetic field in high-current vacuum arcs according to the recent experimental data. A magnetohydrodynamic model is adopted to describe the high current vacuum arcs. The vacuum arc is in a diffuse arc mode with an arc current ranged from 6 kArms to 14 kArms and an axial magnetic field ranged from 20 mT to 110 mT. By a comparison of the recent experimental work of current density distribution on the anode, the modelling results show that there are two types of current constriction. On one hand, the current on the cathode shows a constriction, and this constriction is termed as the cathode-constriction. On the other hand, the current constricts in the arc column region, and this constriction is termed as the column-constriction. The cathode boundary is of vital importance in a quantitative model. An improved cathode constriction boundary is proposed. Under the improved boundary, the simulation results are in good agreement with the recent experimental data on the anode current density distribution. It is demonstrated that the current density distribution at the anode is sensitive to that at the cathode, so that measurements of the anode current density can be used, in combination with the vacuum arc model, to infer the cathode current density distribution.

High-Current Vacuum Arc Mode Transition of a Horseshoe-Type Axial Magnetic Field Contact With Long Contact Gap

The objective of this paper is to determine the high-current vacuum arc mode transition diagram of a horseshoe-type axial magnetic field (AMF) contact with long contact gap. Drawn arc experiments were carried out in an $L$ – $C$ discharging circuit. Horseshoe-type contacts with contact material of CuCr50 and contact diameter of 120 mm were arranged in a demountable vacuum chamber. Full contact gap was 60 mm. The experiment current level ranged from 4 to 40 kA, stepped by 4 kA. Prospective arcing time was set as 2, 5, and 9 ms, respectively. The evolution of vacuum arc behavior was observed using a high-speed camera. Nonsynchronous evolution phenomenon of twin parallel arc columns was observed. With current level ranged from 24 to 40 kA, the maximum nonsynchronous duration transiting from small-gap constricted column mode to diffuse column mode, from diffuse column mode to diffuse arc mode, and from diffuse arc mode to multicathode-spot arc mode were 0.98, 1.09, and 1.55 ms, respectively. The nonsynchronous duration in various vacuum arc modes was determined as well. Summarizing all arc mode transition points in the experiment, a vacuum arc mode transition diagram of the horseshoe-type AMF contact was proposed. Boundary of uncontrollable arc region was determined, which could provide criteria of maximum arcing contact gap design. Besides, an effective arcing region was defined according to distribution of AMF and arc behaviors, in which AMF on the contact surface plane was higher than 75%Baxial–max.

Effect of an axial magnetic field and arc current on the anode current density in diffuse vacuum arcs

The objective of this paper is to measure the effect of an axial magnetic field (AMF) BAMF and arc current on the anode current density in diffuse vacuum arcs. The experimental geometry included a split anode and a butt-type cathode, both with a diameter of 60 mm. The anode surface was divided into a central area and three symmetrically disposed peripheral annular areas. The central area of the split anode had a diameter of 20 mm. The contact material was CuCr25 (25% Cr). The arc current IARC ranged from 4 to 14 kA (rms) at 50 Hz. The opening velocity was 2.4 m/s. The currents of the four areas on the anode contact were measured using four Rogowski coils situated outside the vacuum chamber. An external uniform AMF BAMF ranging from 0 to 110 mT was applied during the experiment. The observed arc modes were recorded by a high-speed charge-coupled device video camera. The experimental results quantitatively reveal that the current density distribution on the anode surface in the diffuse arc mode was not uniform but concentrated in the central area. The current density in the central anode area at the current peak JPeakArea I decreased with increasing BAMF following a power law. For BAMF of 0–110 mT and IARC of 4–14 kA, JPeakArea I = (2.2 IARC + 0.069 IARC2) BAMF−0.22, where JPeakArea I is in A/mm2, BAMF is in mT, and IARC is in kA. Moreover, the current distribution was uneven in the three peripheral areas.

Anode Current Density Distribution Measurements for Different Vacuum Arc Modes Subjected to Axial Magnetic Field

We report our measurements of anode current density distributions for different modes in vacuum arc discharge using a split-anode and a cup-shaped axial magnetic field cathode configuration system. The modes investigated included the diffuse arc and anode spot. The anode surface was divided into four regions: one central region and three symmetrical-disposed peripheral annular-arc regions. Three different-sized central regions were selected with diameters of 12, 18, and 20 mm. The contact material was CuCr25 (25% Cr). The arc current in the tests ranged from 6 to 14 kA (rms) at 50 Hz. The opening velocities were 1.8 and 2.4 m/s, respectively. The currents of the four areas on the anode contact were measured by four Rogowski coils situated outside the vacuum chamber. The experimental results show the current density distribution in different arc modes. For the diffuse arc mode with arc currents of 6 and 8 kA (rms), the average current density in the central region at current peak ranged from 8.5 to 15.9 A/mm $^{2}$ . The anode spot current density ranged from 31.9 to 37.7 A/mm $^{2}$ , estimated from the current density in the eroded region caused by the anode spots covering the entire central region of diameters 12 and 18 mm, at currents of 12 and 14 kA, respectively, regarded as the lower limit current density of the anode spot. Moreover, the dependence of the current density distribution on opening velocity in diffuse arcs was slight. For the anode spots, the current density distribution with higher opening velocity was more concentrated.

Design of a Dynamic Magnetic Field Steered Cathodic Arc Source in Arc Ion Plating

In this work, a dynamic arched magnetic field steered arc source was deigned by virtue of Finite Element Method (FEM) calculation. The magnetic field was produced by two main electromagnetic coils so that the magnetic field can be adjusted with the help of the two currentI1and I2,whereI1is the current to the internal coil mounted coaxially in a magnetic yoke generating a static arched magnetic field to confine the cathode spots and I2is the current to the external coil mounted coaxially outside the above yoke adjusting the position of the vertex of arch. Base on the results of simulation, it was found this design enable the sweeping of the arc spots on the target surface by means of adjusting the ratio of current (I1/I2) , and cause the arc distribute evenly on the cathode surface in the diffuse arc mode transferred from the constricted arc mode. The effects of the target thickness and current ratio on the configuration and intensity of dynamic arched magnetic field were investigated. The optimized operating modes was proposed and discussed.

Influence of Gap Distance on the Arc Behaviors of Slot Type Axial Magnetic Field (AMF) Electrode

In this paper the influence of gap distance on arc behaviors of slot type AMF electrode was investigated by a high-speed charge couple device (CCD) video camera at different gap distance of 10 mm and 20 mm respectively. The arc kept in diffuse arc modes while the amplitude of arc current reached 22.0 kA at gap distance of 10 mm. With the gap distance of 20 mm, the concentration of arc column near anode occurred while the amplitude of arc current was 14.0 kA. With the amplitude of arc current increasing, the duration time of the concentration of arc column near anode also increased at the same gap distance.

Experimental Investigation on the Vacuum Arc Behaviors of the Axial Magnetic Field (AMF) Electrode with Single Coil Structure

In this paper, the influence of arc current on vacuum arc behaviors of a new AMF electrode with single coil structure was investigated at long gap distance of 40 mm. A high-speed charge couple device (CCD) video camera was used to observe the arc behaviors. Two groups of arc modes were featured: 1) diffuse arc modes including multi-cathode spots arc, high current diffuse arc and high current diffuse column arc. 2) constricted arc modes including anode plasma jet with local concentration of many cathode spots and group of cathode spots (APJS), anode plasma jet with local concentration of many cathode spots, anode and cathode plasma jets (APJ), and intense arc mode. The vacuum arc behaviors under different amplitude of arc current were researched.

Transition mode of the vacuum arc in an axial magnetic field: comparison of experimental results and theory

The transition mode for drawn vacuum arcs in an axial magnetic field (AMF) occurred over a few milliseconds during the evolution from the initial bridge column arc to the diffuse arc mode. This dynamic period of arc evolution could be studied using a diffuse column arc model for the behavior of individual cathode spot jets burning in parallel with a high-current arc column. The model calculated a critical arc voltage, above which the sign of the anode sheath for the individual spots changed from negative to positive with respect to the inter-contact plasma. In this case, the individual jet could continue burning only if the anode supplied B significant fraction of its near-anode plasma. This change could hinder the existence of individual cathode spot jets outside the column. Experimental observations of the transition mode showed that when the arc voltage exceeded the critical voltage, the arc was in one of two modes. The lint mode consisted of a central column with few or no cathode spots outside the column, and the second involved the appearance of some cathode spots outside the column. When the arc voltage dropped below the critical voltage, the arc converted into a high-current diffuse mode. The diffuse column model can be used to explain the observed transition mode behavior. Cathode spots could freely burn over the cathode surface when the arc voltage was less than the critical voltage because of the change in sign of the anode sheath. This could divert current out of the arc column, thereby lowering the magnetic pinch pressure on the column and causing it to collapse. The theoretical predictions of the critical voltage agreed well with the observed transition to a high-current diffuse mode for AC currents ranging from 5-28 kA rms and axial magnetic field strengths from 2.5-7.5 mT/kA.

Modeling the effects of an axial magnetic field on the vacuum arc

A quantitative two-dimensional model of a vacuum arc in an applied magnetic field is presented. For the particular case, a uniform axial magnetic field B/sub Z/, it provides a unified condition for the two regimes of arc voltage versus B/sub Z/, i.e. ? the steeply falling voltage branch (low B/sub Z/), and the slowly rising voltage branch (high B/sub Z/, which characterizes the diffuse arc mode). The transition to the high-B/sub Z/ regime is complete when the average mixing distance of the individual expanding cathode-spot plasma jets, measured from the cathode plane, is equal to the contact gap length. The model also predicts the observed smooth transition and minimum arc voltage between the two branches, and the independence of the are voltage on the arc current in the high-B/sub Z/ regime. Calculated results are found to be in good agreement with reported experimental data from several independent investigations over a wide range of gap, B/sub Z/ and arc current I/sub ARC/.

Characterization of an atmospheric pressure plasma generated by a plasma torch array

Based on a capacitively coupled electrical discharge scheme, it is demonstrated that an array of plasma torches can be lit up simultaneously to form a dense plasma layer in the open air by a single ac power source. The number of torches is only limited by the power handling capability of the source. The measured v–i characteristic of the discharge indicates that the torch is operating in the diffuse arc mode. Experiments have been performed to explore the effect of the plasma torches on the propagation of microwaves in an X-band rectangular waveguide by passing the plasma of the torches through holes in the top and bottom walls of the waveguide. The results show that the plasma torches can effectively attenuate microwaves. The wave–plasma interaction process is also analyzed numerically. The plasma parameters deduced from the theoretical model, by matching the numerical results with those of experiments, are shown to agree well with the experimental measurements.

Evaluation of AC axial magnetic fields needed to prevent anode spots in vacuum arcs between opening contacts

The influence of AC axial magnetic (AM) fields on the development of half-cycle drawn vacuum arcs is described. A Helmholtz coil provided an independent AC AM field B/sub ax//sup ac/ in the opening gap between flat profile, butt type, Cr-Cu contacts. For peak arc currents I/sub p/ up to 20 kA, critical AM fields B/sub crit//sup ac/ were determined, which prevented anode involvement. The dependence of B/sub crit//sup ac/ on I/sub p/ is compared with the analogous dependence using constant AM fields B/sub ax//sup DC/. These results extend the usefulness of the B/sub crit/ parameter to the design of contact structures for producing self-generated AM fields from the AC arcing current. A similar direct transition to the high-current diffuse arc mode can be maintained over the half-cycle without an imposed B/sub ax/ if I/sub p/>

Experimental investigations into the arc properties of vacuum interrupters with horseshoe electrode, four pole electrode, and their applications

By using ferromagnetic material around electrodes to generate strong nonuniform magnetic fields, vacuum arcs can be kept in well-defined diffuse mode or multiple arc mode. As a result, the arc voltage is low and stable, the current is confined in certain areas, and high interrupting ability and small size are achieved. The different arc modes for different electrodes, the arc voltage versus arc current for flat electrodes, horseshoe, and four-pole electrode, and the vacuum arc distribution are measured. The criteria of choice of electrode diameter and electrode distance are given. >

低電流真空アーク放電の拡散アークモードからフットポイントモードへの移行

低電流真空アーク放電の拡散アークモードからフットポイントモードへの移行

Study of recovery phenomena in a high-current pulse-triggered vacuum switch

The recovery capacities of a triggered vacuum switch after the crossing of a 25- mu s high-current pulse were investigated. The recovery time is less than 100 mu s. An experiment was conducted with several electrodes with different gaps, and the influence of an axial magnetic field on the switch was studied. A diffuse arc mode was achieved, making possible a commutation power as high as 10/sup 9/ VA. >

Wall ion current in high-current vacuum arcs

Ion currents collected at the metal wall connected to the cathode in a high-current (2 to 20 kA) vacuum arc are experimentally studied. Arcs are burned by exploding a Cu wire between a 60 mm diameter anode and a 30 mm diameter cathode made of various materials in a demountable chamber. The wall draws a larger ion current from a Cu cathode than from a Zn cathode and a smaller current than from a Mo cathode. The anode melting is caused for an 8 kA arc in a 4 mm gap between the Cu anode and the Mo cathode. A high-speed movie shows that the diffuse-arc mode appears in the same gap configuration between the Cu anode and the Zn cathode up to 15 kA. The anode-mode transition is found to occur when the collected ion current attains a certain value independent of the cathode material. The behaviour of the wall ion current associated with the ion generation between the anode and the arc plasma is briefly discussed, proposing a new idea for modelling the anode spot formation.

Time- and Spatially Resolved Spectroscopy of the Plasma State Prior to and during Anode-Spot Formation in High-Current Vacuum Arcs

The emission of numerous lines was measured from a vacuum arc between an Al cathode and Cu anode in which the diffuse, anode-spot, and intense arc modes are observed during a single pulse. An increase in Cu emission and a decrease in Al emission are observed at the transition to the anode-spot mode, and increases in both Al and Cu emission are observed at the transition to the intense-arc mode. Spatial profiles of the excited-state density and Boltzmann-distribution temperatures could be obtained at several positions in the gap. The results show not only a clear correspondence between arc voltage and the arc appearance during different arc modes, but also distinctly different spectral emission properties and droplet behavior.

Visual observations on the high−current transition from the constricted to the diffuse MPD arc mode

High−speed movies of the continuous change through the high−current transition region from a retrograde constricted MPD arc discharge to a diffuse MPD discharge have been obtained. The occurrence of the high−current diffuse discharge is governed by the behavior of the cathode spots with increasing current and magnetic field. Besides obtaining a relatively uniform discharge distribution between the electrodes with the diffuse arc mode, three other important properties are that (1) the retrograde moving cathode spots distribute uniformly over the cathode when the uniform discharge is obtained, (2) the arc voltage decreases, and (3) the arc voltage noise is greatly reduced.