Contact erosion during arcing is one of the main causes of electrical ageing of vacuum circuit breakers. The degree of contact erosion is controlled by the behaviours of cathode spots. Therefore, modification of cathode material and consequentially adjusting the cathode spot characteristics is of interest to mitigate contact erosion. In this paper, a simulation model of Molecular Dynamics (MD) is built to investigate the process of single cathode spot formation induced by the assumed leftover plasma ions. The heating factors of leftover plasma ions, back ions, and Joule heating, as well as the cooling effects of heat conduction, evaporation, and surface electron emission, are considered to achieve a self-consistent model. Based on simulation results, the influences of contact material characteristics on the process of cathode spot formation are discussed, such as the material type (copper, chromium and tungsten) and the crystal type (monocrystal and polycrystal). This work provides foundations for further analysis of cathode spot formation and studying of cathode spot dynamics for a complex alloy cathode.
Arc radiation-induced polymer nozzle ablation plays a crucial role in the operation of self-blast circuit breakers. Up to now, there is no study specifically on the spectral distribution of radiated power from a switching arc towards the nozzle surface and its implication to nozzle ablation. Three-dimensional radiation transfer calculation has been performed in this study for arcs burning in the mixture of C4F7N+CO2+PTFE, a gaseous environment that is under significant focus in the development of SF6 free switching technology to aim net-zero by the middle of this century.
Results show that photons from infrared to extreme ultraviolet (UV, up to 5×10^15 Hz) are emitted from the core of high current arcs. However, the high-frequency photons are mostly absorbed within the arc column, especially at the arc edge, and only photons up to 1.7×10^15 Hz (far UV, 7 eV) can penetrate the arc edge and cold gas and reach the nozzle surface. The spectral distribution of the radiative energy at different instantaneous currents (15 kA, 28 kA and 60 kA peak) and different locations of the nozzle is presented and compared in detail. The location of the radiation absorption zone at the arc edge and the radiative power reaching the nozzle wall as a function of the instantaneous current is, in particular, purposely considered.
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