The spectral and spatial characteristics of three-dimensional radiation transfer across an arc column of 0.08 m long, typical in high-voltage gas blast circuit breakers, has been studied in detail. The arc column under study corresponds to an instantaneous current of 15 kA in SF6 gas at a pressure of 10 bar. Our results show that to calculate the radiative flux divergence (as a volumetric energy source), only a segment of the arc column of 0.024 m in thickness needs to be considered to attain an accuracy of better than 90%. Photons with a frequency lower than 21015 Hz (150 nm in wavelength) can travel a considerable distance (> 0.02 m) with an intensity attenuation factor of 0.2-0.8. Above 21015 Hz, only photons from the continuum spectrum can travel up to 0.015 m and line emission is absorbed within a distance of typically 0.0005 m, i.e. the arcing gas is optically thick to these photons. The gas within a cross-section of the arc column can be divided into a net emission core and a net absorption zone. 55% - 75% of the radiation emitted from the core is reabsorbed. The starting position of the net absorption zone sits within the temperature interval of 75% to 80% of the maximum temperature on the axis. The quantitative information from this work is expected to serve as baseline data for developing improved approximate models for radiation transfer calculation in SF6 switching arcs.
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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