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.

This paper presents the results of different optical diagnostic methods to investigate an anode plume which forms after the extinction of anode spot type 2. The formation of the anode plume is investigated by means of three high-speed cameras. Two high-speed cameras, positioned perpendicular to each other, are used to observe the general anode plume evolution. The third camera is connected to a spectrograph enabling the video spectroscopy. The arc is driven by a damped 50-Hz ac between Cu/Cr 75/25 butt contacts with a diameter of 10 mm. The emission coefficients for atomic and ionic Cu lines during anode plume formation are calculated. The inner part of the anode plume is dominated by atomic line radiation, whereas the outer part is dominated by the emission of singly charged ionic lines. The radiator density of the Cu I 510.55 nm is about 3x 10¹⁷ m⁻³ compared with a radiator density of Cu II of 9x 10¹³ m⁻³ at the same position inside the anode plume. A broadband absorption spectroscopy is used to determine the ground-state densities of Cu and Cr after the extinction of anode plume at current zero (CZ). The density of Cu I is about 1.5 times higher than Cr I at the same time around CZ. Moreover, near-infrared spectroscopy together with thermography is used to determine the anode surface temperature around CZ after the extinction of an anode plume. The central anode surface temperature varies from 1530 to 950 K within 20 ms after CZ.

Anode activity in high current vacuum arcs leads to the formation of various high current modes and transitions between them. Intense material evaporation during the anode spot mode and formation of a neutral vapour cloud during the anode plume mode modify the arc plasma properties and, hence, can have a crucial impact in applications, like e.g. reduction of interruption performance of switching devices. The influence of anode mode appearance on arc plasma parameters and on anode surface temperature was studied in detail by a novel optical diagnostic technique—intensified video optical emission spectroscopy. Employing advanced diagnostic methods, the ground state density, excitation temperature and pressure profiles close to the anode surface have been determined. For the anode plume mode, higher copper vapour pressure was found in the plume shell compared to its core. The copper ion density distribution shows a maximum outside of the plume shell. Consequently, a higher electrical conductivity in the surrounding area of the plume might be expected, i.e. the arc current flows around the plume rather than through it. Analysis of the temporal evolution of electrical and optical signals reveals that voltage jumps and drops during the mode transitions are accompanied by noticeable changes in the anode surface temperature. Thus, the formation of the anode plume leads to temperature lowering while the transition to the anode spot mode is accompanied by a temperature increase. In general, a clear correlation between electrode surface temperature and arc voltage in the case of constricted anode attachment is found. The results of this study give new insights into anode plume properties and consequences of anode mode transitions. Reversible mode transitions and correlations between arc voltage and anode surface temperature, as well as changes in the current path during anode plume mode, have to be considered as factors for optimization of electrode design and choice of materials for switching applications.

The switching behavior of gas-filled contactors was investigated using a model switch. High-speed imaging and spectroscopy provided information regarding the characteristics of the arc plasma. The impact of external magnetic fields, fill gas, fill pressure, and current amplitude was investigated. The most important factor, influencing the switching behavior for currents below 100 A, is provided by external magnetic fields, which increase arc voltage and arc instability considerably. The observed changes of the side-on profiles of the characteristic emission lines indicate changes in particle densities and arc temperature.

This work investigates the transient anode temperature and plasma parameters considering the electrode movement and the arc expansion. A transient self-consistent model is established using the dynamic mesh approach. Two cases with different maximum arc currents, representing various anode activity, have been studied. The simulations predict significant changes in spatial distribution of species densities, electron temperature and anode surface temperature in case with the anode spot formation. Furthermore, the influence of opening velocity on the plasma parameters has been studied numerically. The model was validated by comparison with experimental data for anode surface temperature as well as spectrally filtered arc images. Results of this comparison are presented and discussed.

The contribution presents an insight in the variety of modern optical diagnostic methods based on the use of high-speed cameras (HSCs). Those methods provide the information about the arc dynamics and, in addition, can be used for the analysis of spatiotemporal evolution of species densities, determination of temperature of the arc column plasma, and of the electrode surface temperature. Application examples are given for high-current vacuum arcs, which are characterized by pronounced anode activity (various high-current anode modes). The properties of switching arcs are presented for typical switching conditions, i.e., arc initialization by the separation of CuCr contacts during the ac operation in the current range 1–30 kA.