Spectral and spatial characteristic behaviour of three-dimensional radiation transfer in SF₆ switching arcs

Abstract

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 21015 Hz (150 nm in wavelength) can travel a considerable distance (> 0.02 m) with an intensity attenuation factor of 0.2-0.8. Above 21015 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.

Thermodynamic, transport, and radiation properties of HFO-1336mzz(E) mixtures as eco-friendly SF6 alternatives

“…The radiative spectra of the arc plasma consist of visible, ultraviolet, and near infrared regions. The spectrum from 10 12 to 10 16 Hz [33] is utilized in this work. Considering the line overlapping, instead of using the escape factor to calculate line absorption [34][35][36], the NEC is estimated with a line by line treatment [37,38] of the total discrete spectrum.…”

Frequency spectrum of radiation transfer in high voltage circuit breaker arcs for polymer nozzle ablation in C4F7N and CO2 gas mixture

“…Radiation transfer in a gaseous medium is governed by the radiation transfer equation (RTE) [5,28]. For switching arcs, the RTE takes its steady-state form as given in equation (1).…”

“…Radiation intensity and flux are defined in numerous sources e.g. [5,[26][27][28]. The total transferred energy by radiation can be calculated through the volume integral of the radiation flux divergence [31].…”

“…The thermophysical and transport coefficients for the gas mixture used in the simulation are from [24,25]. The temperature and pressure distribution samples have all the main characteristics of arcs in gas-blast circuit breakers although the discrete ordinates method (DOM) [5,26,27], which is used in the present work and explained more in section 3, is not coupled in arc simulation to obtain selfconsistent arc solutions. The radiation calculation domain in this work is cylindrical with a length of 0.05 m and a radius of 0.01 m following the findings in [5].…”

“…During the high current phase of the arcing process of a gas-blast circuit breaker, especially when the instantaneous current is well above 15 kA, photons with a wide range of frequency are emitted from the high-temperature core of the arc column where the gas temperature is above 20 000 K [4]. High-frequency photons can only travel a small distance before they are absorbed, while line spectral and continuum behave differently in the lower frequency range [5]. A considerable portion of the radiation from the arc core is re-absorbed at the arc edge where the arc temperature drops steeply in the transverse direction of the arc column from 20 000 K to 5000 K [6,7].…”