The results of measurements of the radiation power of a vacuum (p-' 10-4 Pa) arc in the near infrared, visible and ultraviolet regions of the spectrum (200 nm < ? < 1100 nm) are presented. The arc burned on industrial AMF-electrodes with a diameter of 55 mm. The material of the electrodes was the CuCr30 composition. The arc was fed by a current pulse in the shape close to half of the industrial frequency sine wave (f = 50Hz). The radiation was output through one of the side windows of the vacuum chamber. The window was made of quartz KU-1. The radiation receiver was a silicon photodiode with a diameter of 1.2 mm, located outside the vacuum chamber on an axis intersecting with the axis of symmetry of the discharge in the center of the interelectrode gap. The signal from the photodiode was taken through an amplifier and recorded on an oscilloscope. Considering the spectral sensitivity of the diode, two series of measurements were made: measurements without a filter and through a ZhS-10 yellow filter that cuts off radiation with ? < 400 nm. The results obtained made it possible to analyze the dependence of the radiation power on the arc current at different stages of its development. The results showed that at high currents in the developed vacuum arc with anodic activity (eroding anode), a significant part (up to 15%) of the power released in the arc is transferred by radiation.

The radiation of a vacuum arc was measured in the spectral region 200nm ≤ λ ≤ 1100 nm. The arc was initiated in the center of the cathode by ignition discharge, by breaking the current in the auxiliary circuit, and was fed by the rectangular current pulse with a duration of 10 ms. The contact gap was fixed at 4mm, the butt D=30mm CuCr30 contacts were used. The arc was stabilized by an external uniform axial magnetic field. Radiation was removed through KU-1 quartz window of the vacuum chamber. The radiation detector was a silicon photodiode 1.2 mm in diameter located outside the vacuum chamber on an axis intersecting the axis of symmetry of the discharge at the center of the interelectrode gap. The signal from the photodiode was taken through an amplifier and recorded on an oscilloscope. The measurements were made in a range of currents from 10 kA to 25 kA, which corresponds to a mean current density in the developed discharge of 1.5 kA/cm 2 ≤ j ≤ 3.5 kA/cm 2 . Considering the type of the spectral sensitivity of the diode, two series of measurements were made - measurements without a filter and through a ZhS-10 filter that cuts off radiation with λ ≤ 400nm. The results obtained made it possible to analyze the dependence of the radiation power on the arc current at different stages of the development of the arc. The results showed that at high current densities in the developed vacuum arc with anodic activity, a significant part of the power is transferred by radiation.

This article presents the results of the investigation of high-current vacuum arcs (HCVAs) on axial magnetic field (AMF) contacts at an average opening speed of 2 m/s and the comparison of the obtained results with similar results received earlier at a lower average opening speed of 1 m/s. We compared the voltage oscillograms and the current-voltage characteristics (CVCs), as well as the arc development process of the discharges at different opening speeds. The discharge was ignited by opening the contacts in a demountable vacuum chamber and was fed with the half-sine current pulse of 10 ms in duration. For analyzing the arc development processes, high-speed video recording of the arc column and the cathode surface was conducted throughout the entire current pulse. We discovered that the process looks similar for both the investigated contact speeds: a discharge is initiated at one or more points and covers the entire contact surface in a few milliseconds. Only quantitative differences are observed due to a higher arc voltage and, accordingly, energy input at a higher speed of contact movement. The CVC of the developed arc in both cases turned out to be linear in a wide range of currents. The analysis of the CVC showed that, in the developed arc, the ratio of the resistance of the column to its length does not depend on the length of the gap and the opening speed of the contacts. Thus, we can assume that the plasma parameters in the column change little with an increase in the current and in the opening speed of contacts. This assumption is supported by the results of a discussion of the literature on the CVC of HCVAs.

The erosion and thermal states at current zero for the axial magnetic field (AMF) electrodes after high-current vacuum arcs (HCVAs) were studied at an average opening speed of 2 m/s. The results obtained are compared with similar results received earlier at an average opening speed of 1 m/s. The discharge was ignited in a demountable vacuum chamber by opening the contacts and was fed with the half-sine current pulse of 10 ms in duration. To determine the thermal state of the surface of the electrodes at zero current, a Phantom MIRO M310 high-speed video camera with a Carl Zeiss 100 mm F2 lens was used. In addition, the surface of the electrodes after the arc exposure was photographed by a Canon camera. The study showed that at the same current an increase of the opening speed leads to an increase in the thermal effect on the electrodes. Besides, the work revealed that at high opening speed (HOS) the process of appearances of erosion traces on the cathodes and, especially, on the anodes, is significantly different. The estimations made in the work showed that the difference in erosion traces on the anode is associated not only with an increase in the thermal effect but also with a change in the momentum transferred to the anode by cathode jets due to jets relaxation in the interaction with the secondary anode plasma in a long arc.

Using a silicon photodiode, we have performed measurements of the power emitted by a vacuum arc in the UV and visible spectral ranges. Measurements have been carried out upon stabilizing the arc by an axial magnetic field in high-current modes with developed anodic activity. The power of radiation emerging from the arc through the side surface is measured. The results obtained show that, when analyzing the energy balance of a high-current vacuum arc, the radiation must be taken into account.

It is shown that high-current vacuum arcs accompanied by partial melting of the cathode surface and its droplet erosion can generate, in addition to the well-known droplets formed immediately in the cathode spot (first type droplets), a second component of erosion. The liquid part of the cathode surface can emit droplets with significantly different sizes and velocities, which may be called second type droplets. The mechanisms of the formation of first and second type droplets are also substantially different.

The aim of this paper is to compare the state of anode surface of different AMF contact systems during arcing and after arc extinction. Arcs were ignited by opening of electrodes and were fed by sine half-wave current pulses with durations of 10 ms. CuCr electrodes were used. We performed investigations in the range of arc currents from successfully interrupted ones up to the levels of guaranteed failure (limiting interrupted current) if the transient recovery voltage was applied. The measurements were implemented by a high-speed Phantom M310 video camera equipped with a Carl Zeiss 100/2 macro lens. We studied the anode surface state during the arcing using the set of neutral density filters. We found that at currents close to the limiting interrupted current, most of the anode surface melts. Liquid metal is squeezed out of the axial area and an annular crest is formed. The crest splashes out and breaks into separate jets. The jets are broken up into fragments, from which droplets separate. The anode surface temperature distribution just after current zero was obtained by comparison of the results of anode surface filming and the results of calibrated band-lamp filming in identical conditions. We carried out the filming using an interference filter (775 nm). The effect of reflection from electrodes was evaluated using mathematical simulation. The temperature distribution of the anode surface is highly non-uniform. The temperature of the most heated fragments of the anode surface increases with increasing current and reaches 2000 K with the limiting interrupted current. However, the size of these fragments is small, substantially less than the length of the interelectrode gap. They cannot create the vapor concentration in the entire gap up to the opposite electrode sufficient to provide the Townsend breakdown of the gap when the transient recovery voltage is applied. The analysis of the obtained results suggests that droplets, and hence, the phenomena on the surface that lead to their appearance play an important role in the breakdown process in the investigated contact systems at extreme currents.

The aim of the work is analysis of current-voltage characteristics (CVCs) of vacuum arc for the high-current pulse. The arc was ignited by the opening of the electrodes and was fed with half-sine current pulse of 10-ms duration. CuCr axial magnetic field (AMF) contacts were used. Investigations for each contact system were performed in the range of arc currents up to the levels of guaranteed failure when transient recovery voltage (TRV) applied. Oscillograms of current and arc voltage were compared with the results of high-speed video. We propose a method for compact presentation of video filming in the form of Xt-diagrams. It is shown that analysis of CVCs allows determining the ignition character and duration of arc development stage. Correlation between durations of arc development and magnetic field setting has been found. We have found out that the nature of the ignition does not affect the state of the developed arc in the investigated contact systems. We conclude that neither voltage oscillograms nor CVCs can determine the onset of evaporation from anode, and the very presence of evaporation from anode is observed also at currents that are significantly below failure ones and is not a failure criterion.

The objective of this paper is to compare the state of cathode surface of different axial magnetic field (AMF) contact systems (CSs) during arcing and after arc extinction. The arcs were ignited by opening of electrodes and were fed by sine half-wave current pulses with a duration of 10 ms. Investigations were performed in the range of arc currents up to the levels of guaranteed failure. The measurements were done by a highspeed Phantom M310 video camera. The cathode surface state during arcing was studied using a set of neutral density filters. It was discovered that melting of a part of the cathode surface during arc burning takes place in high-current vacuum arcs. A changing relief in the form of hillocks and hollows forms on the melted surface. We found out that there are two components in droplet erosion of the cathode, when its surface is partially melted: in addition to droplets formed directly in the cathode spot (which can be called droplets of the first type), the liquid part of the surface also emits droplets (which can be called droplets of the second type) significantly different in their sizes and velocities. The formation mechanisms of droplets of the first and the second type are different. The cathode surface temperature distribution immediately after current zero was obtained by comparing the results of cathode surface filming to the results of calibrated band-lamp filming in identical conditions. Reflection of anode radiation from cathode surface was analyzed by mathematical simulation. The filming was carried out using an interference filter. We found that the distribution of the cathode surface temperature is substantially nonuniform. The axial region is the most heated. We conclude that in all investigated CSs with the same amplitude value of the current, the temperature of the most heated parts of the cathode surface is significantly lower than the temperature of the most heated parts of the anode surface. Analysis of obtained results shows that switching failure can be provoked by the cathode and by the anode processes depending on CS design.

The aim of the work is analysis of Volt-Ampere characteristics of vacuum arc for the high current pulse. The arc was ignited by the opening of the electrodes and was fed with half-sine current pulse of 10 ms duration. CuCr axial magnetic field contacts were used. Investigations for each contact pairs were done in the range of arc currents up to the levels of guaranteed failure when transient recovery voltage (TRV) applied. Oscillograms of current and arc voltage were compared with the results of highspeed video. It is shown that analysis of current-voltage characteristics allows to determine the ignition character and duration of arc development stage. Correlation between durations of arc development and magnetic field setting has been found.

The aim of this work is to compare the state of cathode surface of different AMF contact systems during arcing and after arc extinction. The arcs were ignited by opening of electrodes and were fed by half-sine current pulses with duration of 10 ms. CuCr electrodes were used. Investigations were performed in the range of arc currents from successfully interrupted ones by the contact system up to the levels of guaranteed interruption failure when transient recovery voltage was applied. The measurements were done by a high-speed Phantom M310 video camera equipped with a Carl Zeiss 100/2 macro lens. The cathode surface temperature distribution just after current zero was obtained by comparison of results of cathode surface recording and the results of calibrated band-lamp recording in identical conditions. Reflection of anode radiation from cathode surface was taken into account. The recording was carried out using an interference filter. The cathode surface state during arcing was studied using the set of dense neutral filters. Obtained results show the difference between the cathode and anode condition during arcing with the same currents. It was found that switching failure can be provoked by the cathode and by the anode processes depending on contact system construction.

The cathode attachment of a high-current vacuum arc on the fall of a current pulse was studied. Contacts generating an axial magnetic field were used. The revealed transformation of the attachment shape near zero current was explained quantitatively in a way that was in satisfactory agreement with experimental results.

Исследована катодная привязка сильноточной вакуумной дуги на спаде импульса тока. Использовались контакты, генерирующие аксиальное магнитное поле. Дано количественное объяснение обнаруженного изменения формы привязки вблизи нуля тока, которое показало удовлетворительное согласие с результатами эксперимента. DOI: 10.21883/PJTF.2017.20.45150.16932

Overheating of electrode surfaces during arc burning is considered to be the main reason of a breakdown after kiloampere arc extinction. The greatest interest in this connection is the most energy-loaded electrode-the anode. The aim of this paper is to measure the distributions of thermal radiation brightness of anode surface just after current zero for a range of arc currents from successfully interrupted levels up to the levels of guaranteed failure. The measurements allow us to determine the anode surface temperature distributions and trace the anode cooling. The measurements were done by a high-speed video camera Phantom M310 equipped with a Carl Zeiss 100/2 macro lens. The anode surface temperature distribution was obtained by comparison of the results of anode surface filming and the results of calibrated band-lamp filming in identical conditions. The measurements were done for CuCr 70/30 electrodes with a diameter of 64 mm generating axial magnetic field for the currents up to the interruption limit. The cooling was traced over the time interval, during which the absolute majority of breakdowns takes place at the TRV application for the given contact system.

We investigated the development of high-current vacuum arc on the axial magnetic field contacts. The arc was initiated by opening of the contacts. We considered the processes during half wave of the industrial frequency current in the range of current from 0.1 to 1.2 of breaking capacity of the contact system. Using the high-speed video we investigated the time dependence of the plasma luminosity in the gap between the electrodes and the shape of luminous column. It has been shown, that high-current electrodes material evaporation has a notable effect on processes in the gap between the electrodes, but it doesn't cause contraction.

The paper presents detailed research of voltage oscillograms at opening contacts with currents 0.5-12 kA. The used copper-chromium electrodes 20 mm in diameter were sharpened to a weak cone to fix the contact location. The authors have developed the technique for quantitative analysis of the voltage oscillograms and have determined values of voltages and voltage derivatives describing various stages of transition to an arc: instability of the liquid metal bridge, the stage of bridge column arc (BCA) [1], as well as durations of these stages. Their studies of dependences of duration of various stages on the current have ascertained that, although destruction of a liquid bridge occurs at a random time moment, the duration of the transition process, including the stages of the bridge instability and BCA, is constant with satisfactory accuracy, for the given current and velocity of the contacts.

The paper presents the method for simultaneous determination of locations of vacuum arc attachments to the cathode and to the anode by high-speed photography. The method provides possibility to ascertain propagation direction of a cathode spot jet subjected to action of magnetic field. This method was used to examine single-spot vacuum arcs between Cu electrodes. The arc length was L = 8 mm, and the arc current was I = 65 A. The magnetic field had two independently varied components (axial component Bz ≤ 0.2 T and tangential one Bt ≤ 0.2 T). The accuracy of the jet angle determination was ±3 degrees. The measurement data show that the jet, which is normal to the cathode in the immediate vicinity of its surface, is turned parallel to the magnetic field at some distance ZB, which depends on magnetic field induction B and its inclination to the cathode surface. The experimental results are compared with calculation results found in literature.

In our previous work is shown that in the visual spectral region of radiation of the high-current vacuum arc with copper electrodes there is a spectral "window" that allows to register continuum radiation (including at high-current densities). This fact was used for elaboration of the method of determination of the electron density in the gap of high-current vacuum arc. The method was verified by comparison of the obtained results with known results received by different methods.

Measurements of spatial distribution of the intensity of radiation of different ionization sates of copper (CuI, CuII and CuIII) in a short (8 mm length) low-current vacuum arc with copper electrodes were carried out. The arc current I = 60 A = Is (Is - average current per cathode spot). That is, an arc with a single spot was investigated. The spatial and temporal resolutions are, respectively, 0.5 mm and 50 μs. Induction of the external axial magnetic field 0 ≤ B ≤ 0.1 T. The investigations showed that the state of the plasma and the shape of the channel of the short arc are determined not only by cathode process. In the near-anode region of the arc, changes take place both inside the channel and in the “coat” of low ionized plasma surrounding the arc. Interaction of high-speed ions of the cathode spot plasma jet with the anode forms a flow of atoms from that part of the surface to which the arc is attached. The atoms are ionized in the immediate vicinity of its surface. This increases the plasma concentration and decreases the average charge of ions in the near-anode part of the arc, in comparison with the average charge of the cathode spot plasma jet.

The high-current vacuum arcs (HCVA) with high average current densities in axial magnetic fields (AMF) Bn les 1.2T were studied. The typical V-shape of volt-tesla characteristic (VTC) has been shown to retain in strong AMF and at raising the current density to 3 kA/cm2; the quantitative parameters change, though. It has been confirmed the conclusion of Chaly et al. (1999) that, in strong AMF, the cathode attachment size for an arc in a quasi stationary state is defined by AMF induction and arc length. The quantitative comparison of VTC and voltage of a low-current arc under the action of magnetic field, inclined to the arc axis (Chaly et al., 2006), encounters difficulties arising in describing of HCVA as an aggregate of independent cathode jets at moderate values of AMF induction