Anode Spot Mode Research Articles

2-D Dynamic Excitation Temperature of Cu+ Under Diffuse Mode in Vacuum Arc

Cu I (Cu neutrals) excitation temperature is usually measured by researchers while analyzing vacuum arcs (ignited by CuCr electrodes). Since ions may have information that neutrals do not have, measuring Cu II (Cu <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{+})$</tex-math> </inline-formula> might reveal some new features of the vacuum arc. In this article, Cu II excitation temperature is measured by observing seven Cu II lines. Measurement results show the existence or not of a Cr component in a vacuum arc can greatly change the 2-D distribution pattern of Cu II excitation temperature (researchers suggest no influence on Cu I); from a “flat” shape changes to a “columnar” or a “bowl” shape (related to gap length). However, the Cr ratio in CuCr electrodes does not cause a noticeable difference both in Cu II excitation temperature value and in 2-D distribution shape. In the case of CuCr electrodes, before the arc mode change to anode spot mode, a new phenomenon occurs under diffuse mode; as the arc current grows higher than a critical value under a certain length of the gap, the temperature starts to drop in the area near the anode surface, forming a temperature valley. This temperature valley can be interpreted as a local increase in Cu II density. The local ion eruption caused by the Cr component might be a trigger or a pre-process for arc mode changing to anode spot mode.

Duration of Anode-Spot Mode Type 2 and Plume Mode in High-current Vacuum Arc

Duration of Anode-Spot Mode Type 2 and Plume Mode in High-current Vacuum Arc

Numerical simulation and experimental investigation of transient anode surface temperature in vacuum arc

In this paper, the spatial-temporal evolution of the anode temperature in the vacuum arc during the formation of an anode spot is investigated by numerical simulation and experiments. A transient self-consistent model is established to calculate the arc parameters and the anode temperature. The simulations predict that the maximum anode temperature always occurs after the current peak. Ion density and atom density at the anode side increase significantly during the formation of the anode spot. In the anode spot mode, more evaporated anode material comes into the arc column, leading to higher plasma temperature around the spot. The anode vapor can reduce the energy flux from the plasma to the anode center, providing more uniform anode temperature distribution and correspondingly smoother plasma parameter distributions in the vicinity of the anode center. In addition, a higher Cr fraction in the electrodes can result in a higher anode temperature. Near-infrared spectroscopy and high-speed camera thermography are used to study the anode temperature experimentally in order to verify the simulation results. A reasonable agreement was found.

Electron and Neutral Density Distributions of Vacuum Arcs Under Anode-Spot Mode

Electron and Neutral Density Distributions of Vacuum Arcs Under Anode-Spot Mode

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.

Modeling of vacuum arc plasmas in anode spot or anode plume mode taking into account multiple ion components

This work investigates the arc behaviors with CuCr25 electrodes considering anode vapor using a magneto-hydro-dynamic model. Different kinds of components are considered including ions (Cu and Cr) with different charge numbers, electrons, and atoms (Cu and Cr). The effect of the anode sheath is also considered. The density distributions of these components are analyzed and compared with the experiments during the anode spot mode and the anode plume mode. Simulation results show that the anode vapor can enter the arc column forming a cool and poorly conducting region (i.e., neutral atom vapor area, NAVA) under high anode temperature. Atoms and single-charged ions mainly gather near each electrode. The highest double-charged ion density can be seen in front of the NAVA. Triple-charged ion density is negligibly low and reaches its maximum where the electron temperature is high. Cr is more likely to be ionized to a higher ionization level compared with Cu. Our results agree with experimental measurements of density distributions of different components and plasma temperature.

Study of vacuum arc behavior under anode spot and anode plume modes

Anode spot (AS) and anode plume (AP) phenomena are widely observed in vacuum arc experiments and are related to anode melting and evaporation under strong heating from the arc column. Anode vapor will then strongly influence the arc column through ionization-recombination and energy exchange among atoms, ions, and electrons. This work investigated the characteristics of the vacuum arc with AS or AP using the two-dimensional magnetohydro dynamic model. Formation of the AS and AP modes was studied and analyzed using numerical simulation. Friction forces between ions and atoms were also taken into account. Simulation results show that anode vapor expansion depends on the pressure balance between the anode jet and cathode plasma. Higher anode temperature produces a larger neutral atom vapor area (NAVA), which was dominated by neutral atoms. Inside the NAVA, ion and electron temperatures were low in the AS and AP mode due to ionization and energy exchange. Electric conductivity in this area was also so low that the location of the maximal current density was near the edge of the anode instead of the anode center. The asymmetric appearance of an AP was mainly caused by the asymmetric anode temperature distribution with respect to the AS center. Qualitative comparisons show that the simulation results are consistent with the experimental results.

An improved arc model for vacuum arc regarding anode spot modes

This paper introduces an improved arc model for vacuum arcs. In this model, the impact of different high-current anode modes is considered. An existence diagram for different high-current anode modes including footpoint, anode spot type 1 and type 2 is determined using emission spectroscopy, high-speed camera, and electrical measurements. During transition from diffuse to the high-current mode the arc voltage will be affected due to high evaporation rate, which can affect dielectric recovery of vacuum interrupter. Conventional arc models cannot trace the corresponding sudden changes in the arc voltage during the transition to anode spot type 2. Therefore, different areas of discharge modes are determined based on the threshold current and gap length for AC 50 Hz and cylindrical contacts made of CuCr7525. The physical parameters of the arc, e.g. the arc temperature, contact geometry and material is considered as implicit parameters in the existence diagrams. The boundaries of the areas are used as a user-defined library in EMTP-RV for a new electric arc model. The voltage behavior of the arc can be predicted well in a larger range of peak currents by the results. The validity of the model is also investigated for AC 100 Hz and pulsed DC 10 ms.

Influence of arc-melted cathode layer depth on vacuum insulation

It is well known that after current interruptions, a fine Cu-Cr melted layer is formed on the electrode surface, and the vacuum insulation between electrodes is improved. However, the influence of the depth of the arc-melted layer on the vacuum insulation is still not clear. The objective of this paper is to determine the influence of the depth of the arc-melted layer of the cathode on the vacuum insulation. A 12 kV vacuum interrupter with a pair of rod-plane electrodes was designed. A DC current source was applied to the vacuum interrupter, and the rod electrode was chosen as the anode. A drawn vacuum arc in the anode spot mode was used to generate melted layers with different depths on the rod electrode. The arcing time was controlled to 0, 10, 46 or 73 ms. Then, the vacuum gap was adjusted to 1 mm to measure the basic lightning impulse breakdown voltage. Standard positive-polarity 1.2/50 μs lightning impulses were applied by a basic up-down method, in which the rod electrode was the cathode. Experimental results revealed that the breakdown probability followed a Weibull distribution when the breakdown voltage reached saturation. The 50% breakdown voltage U50 with arcing times of 0, 10, 46 and 73 ms was 55.6, 73.3, 75.5 and 77.9 kV, respectively. Next, a cross section of the rod electrode was analyzed using an electron microscope, and the average depths of the arc-melted layers were 0, 5, 35 and 65 μm at current arcing times of 0, 10, 46 and 73 ms, respectively. The depth of the arc-melted layer varied approximately linearly with the arcing time. The U50 values of the vacuum gaps with the arc-melted layers were significantly larger than that without a melted layer but very close to each other for all arc-melted layer depths. Thus, the melted layer did improve the breakdown voltage, but the depth of the arc-melted layer had little influence on the breakdown voltage.

Anode modes in vacuum arcs: Update

This paper discusses the seven different anode discharge modes which can occur in a vacuum arc. These modes are diffuse arc (low current, with or without anode sputtering), footpoint and plume (intermediate current), plus anode spot (two types), and intense arc (high current). The plume and Type 2 anode spot modes may occur just for certain materials, since they have been seen only with CuCr electrodes. Descriptions of the various spot modes are presented, based primarily on experimental results. The effects of external magnetic fields on anode modes are briefly stated. Arc column modes are also discussed, but only as they correspond to anode modes.

Optical and Electrical Investigation of Transition From Anode Spot Type 1 to Anode Spot Type 2

This paper presents differences between anode spot type 1 and type 2 and the discharge conditions for a transition from anode spot type 1 to type 2 are investigated by means of optical and electrical measurements. The transition from the diffuse mode to the high-current anode modes (footpoint, anode spot type 1, and anode spot type 2) is studied with respect to spatial and temporal distributions of different ionization levels of Cu lines, voltage–current waveforms, transferred charge, and aspect ratio. The driving current pulse was applied by a high-current generator which corresponds to a pulsed dc of 10-ms duration. Spectral lines of Cu I, Cu II, and Cu III are analyzed for various anode modes using a combination of an imaging spectrograph and a high-speed camera. The results show that during the formation of the anode spot type 2, the intensity of all lines change noticeably. Significant differences are found, for example, in the spatial structure of Cu III lines in the anode spot modes. A jump in the arc voltage corresponding to the time of intensity changes appears at the transition from anode spot type 1 to type 2. The impact of transferred charge, instantaneous current, and aspect ratio on the formation of the anode spot type 2 is also investigated. The transition from anode spot type 1 to type 2 is dominated by the ratio of electrode diameter to gap length. The formation of an anode plume is always observed after extinction of anode spot type 2 and before current zero.

Impact of Different Vacuum Interrupter Properties on High-Current Anode Phenomena

This paper presents the impact of current waveform and frequency on the formation of high-current anode phenomena in a vacuum interrupter experiment. Different waveforms including the alternative current pulses of 50, 180, and 260 Hz and direct current pulses of 5 and 10 ms are compared. The impact of different opening times and contact speeds on the high-current anode mode formation is investigated. The results show that both instantaneous current and total transferred charge are important in the formation of high-current anode modes. Therefore, the arcing time has a strong influence. Two types of anode spot modes with different electrical and optical characteristics are also observed. The transitions between different high-current modes are examined systematically, resulting in existence areas dependent on threshold current and gap length. The latter are determined for different contact materials including Cu, CuCr7525, and CuCr50 and different contact diameters.

Video Spectroscopy of Vacuum Arcs During Transition Between Different High-Current Anode Modes

This paper presents spectroscopic results of high-current anode phenomena in a vacuum arc discharge between CuCr electrodes. AC (alternative current) 50-Hz and 10-ms pulsed dc (direct current) are applied as interrupting current. Time and space resolved optical emission spectroscopy (video spectroscopy) is used to examine the temporal and spatial distribution of different atomic and ionic copper lines. During the transition from low-current mode to different high-current modes, including footpoint, anode spot, and intense arc mode, the intensity of Cu I, Cu II, and Cu III line radiation is examined near the anode, the cathode, and in the interelectrode gap. The results show that during the formation of anode spot and intense mode the intensity and the distribution of all lines change noticeably in the different spectral regions. In fact, higher ionization states represent the arc dynamics behavior during transition to high-current anode modes. Significant differences have been found, for example, in the spatial structure of Cu II and Cu III lines in the anode spot mode. The results for Cu I lines indicate an active role of atoms together with the ions in different charge states in high-current anode modes. The impact of threshold current and transferred charge of the formation of high-current anode modes in case of ac and pulsed dc is also investigated regarding the intensity of copper lines near the anode.

An Opening Displacement Curve Characteristic Determined by High-Current Anode Phenomena of a Vacuum Interrupter

A vacuum interrupter reaches its interruption limit once high-current anode phenomena occur. In order to increase the interrupting capability of vacuum interrupters, extensive research work has been done which included consideration on the contact geometry, contact material, and magnetic field in order to avoid the formation of high-current anode phenomena. However, an opening displacement curve characteristic of a movable contact should be another contributor to the formation of high-current anode phenomena. The objective of this paper is to propose an opening displacement characteristic that is determined by high-current anode phenomena of a vacuum interrupter. Butt-type contacts were used in the test vacuum interrupters and the contact diameters were 12 mm and 25 mm, respectively. The contact materials were microcrystalline CuCr25 and nanocrystalline CuCr25, respectively. Two different opening velocities were tested which were 1.1 m/s and 2.0 m/s, respectively. In the tests, the arcing time was adjusted from ~ 1 ms to 10 ms at each velocity. Test results showed that each type of vacuum interrupter has its own anode discharge diagram which is irrespective of the opening velocities. Based on each anode discharge diagram, an opening displacement curve can be proposed in order to avoid the regions of an intense arc mode and an anode spot mode. With the proposed opening displacement curve, high-current anode phenomena have less of an impact on the arcing period, which is expected to improve the interrupting performance of the vacuum interrupter.

Anode mode in cathodic arc deposition apparatus with various cathodes and ambient gases

The anode mode of a vacuum arc in a cathodic arc deposition apparatus was observed as a function of ambient gas pressure ranging from 0.01 to 300 Pa. The chamber (400 mm in diameter and 600 mm in length) made of stainless steel (SUS304) acted as the anode. The arc was operated at a relatively low constant current of 50 A. The cathode materials used were Al, Ti, Fe, Ni, and Cu, and ambient gases were He, Ne, Ar, H 2, N 2, O 2, and CH 4. The principal results are as follows. (1) As the pressure was increased, the anode mode changed from diffuse-arc to footpoint to plane luminous to anode-spot mode. (2) The anode mode and resultant arc voltage increase were strongly dependent on gas species, and weakly on the cathode material. (3) Comparing diatomic and polyatomic (H 2, N 2, O 2, and CH 4) with mono-atomic molecule gases (He, Ne, and Ar), the onset pressure of the anode mode transition in the former was lower, the arc voltage higher, and the footpoints more numerous, smaller, and clearer. Both the dependence of the ambient pressure and the influence of the cathode materials and gas species on the anode mode changes were explained by the ion deficiency theory.

Observation of tungsten particles in vacuum arcs by laser induced fluorescence

We have clarified the relation between the decay of tungsten ion density in the vicinity of current zero and vacuum arc mode in high current period by using a laser induced fluorescence method in tungsten vacuum arcs of 60 Hz sinusoidal current with the peak value of 3.3, 6.7, and 9.8 kA. In the case of 6.7 kA, the arc mode was the anode spot mode. Because of the generation of the anode spot, the tungsten ion density near the anode was higher than near the cathode and the density near the anode was about ten times as high as the case of 3.3 kA which was the diffuse mode. In the case of 9.8 kA, which was the intense arc mode, the density near the anode was not significantly different from the case of 6.7 kA. The density near the cathode was higher than near the anode and tungsten ions were observed till about 30 /spl mu/s after current zero while they disappeared at current zero in the other cases.

Arc-discharge mode and interruption performance in vacuum switch tubes

Arc phenomena in vacuum switch tubes involving the transition mechanism of the arc-discharge mode, and the relations among the arc-discharge mode, the electrode material, the electrode configuration, and the interruption performance are investigated. It is suggested that the positive ion accumulation near the anode causes the anode-spot mode transition. The floating shield potential and the arc voltage are related to the interrupting ability for the arcs between unslotted flat electrodes and between spiral electrodes, respectively. Through these fundamental research activities, a new line of compact vacuum switch tubes and new types of vacuum circuit breakers carrying them have been developed. >

A Review of Anode Phenomena in Vacuum Arcs

AbstractThis paper discusses are modes at the anode, experimental results pertinent to anode phenomena, and theoretical explanations of anode phenomena.A vacuum are can exhibit five anode discharge modes: (1) a low current mode in which the anode is basically passive, acting only as a collector of particles emitted from the cathode; (2) a second low current mode that can occur if the electrode material is readily sputtered (a flux of sputtered atoms will be emitted by the anode); (3) a footpoint mode, characterized by the appearance of one or more small luminous spots on the anode (footpoints are generally much cooler than the true anode spots present in the last two modes); (4) an anode spot mode in which one large or several small anode spots are present (such spots are very luminous, have a temperature near the atmospheric boiling point of the anode material, and are a copious source of vapor and ions); and (5) an intense are mode where an anode spot is present, but accompanied by severe cathode erosion.The are voltage is relatively low and quiet in the two low current modes and the intense are mode. It is usually high and noisy in the footpoint mode, and it can be either in the anode spot mode. Anode erosion is low, indeed negative, in the two low current modes, and it is low to moderate in the footpoint mode. Severe anode erosion occurs in both the anode spot and intense are modes.The dominant mechanism controlling the formation of an anode spot appears to depend upon the electrode geometry, the electrode material, and the current waveform of the particular vacuum are being considered. In specific experimental conditions, either magnetic constriction in the gap plasma, or gross anode melting, or local anode evaporation can trigger the transition. However, the most probable explanation of anode spot formation is a combination theory, which considers magnetic constriction in the plasma together with the fluxes of material from the anode and cathode as well as the thermal, electrical, and geometric effects of the anode in analyzing the behavior of the anode and the nearby plasma.

Electrical and pyrometric measurements of the decay of the anode temperature after interruption of high-current vacuum arcs and comparison with computations

Vacuum arcs of up to 20-kA peak current were investigated. The surface temperature of the anode area melted during the anode spot mode was determined by pyrometry and the evaluation of thermionic currents. The measurements confirm the computations of heating and cooling of the anode, taking into account heat conduction melting/solidification, and evaporation. Pyrometrically obtained temperatures agree well with theory. This gives confidence in the heat conduction model and also shows that the boiling temperature was reached during arcing. Another method evaluates currents of a milliampere value after arcs of several kiloamperes and postarc currents of amperes. Experimental observation (e.g., loading of the shield surrounding the contacts) and theoretical analysis of the interfering effects support the idea that the currents measured are due to thermionic emission.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Theoretical analysis of the current and energy flow to the anode in the diffuse vacuum arc

The current energy flow to the anode in a diffuse vacuum arc is investigated using a simple multicathode-spot fluid description of the interelectrodic plasma. Decisive for the current constriction and the energy flow to the anode center is the space-charge sheath in front of the anode. This sheath not only determines the current-density distribution at the anode, but also may lead to a strong energy gain of the electrons before they reach the anode surface (in case the anode drop appears to be positive in the anode center). Numerical results are given and two possible scenarios for the transition from the diffuse to the anode-spot mode are discussed. >