Characterization of a high current pulsed arc using optical emission spectroscopy

Abstract : In this paper, we present the investigation realized on an experimental setup that simulates an arc column subjected to the transient phase of a lightning current waveform in laboratory conditions. Optical emission spectroscopy is employed to assess space- and time-resolved properties of this high current pulsed arc. Different current peak levels are utilised in this work, ranging from 10 kA to 100 kA, with a peak time around 15 mu s. Ionic lines of nitrogen and oxygen are used to determine the radial profiles of temperature and electron density of the arc channel over time from 2 mu s to 36 mu s. A combination of 192 N II and O II lines is considered in the calculation of the bound-bound contribution of the absorption coefficient of the plasma channel. Calculations of the optical thickness showed that self-absorption of these ionic lines in the arc column is important. To obtain temperature and electron density profiles in the arc, we solved the radiative transfer equation across the channel under an axisymmetric assumption and considering the channel formed by uniform concentric layers. For the 100 kA current peak level, the temperature reaches more than 38 000 K and the electron density reaches 5 x 1018 cm(-3). The pressure inside the channel is calculated using the air plasma composition at local thermodynamic equilibrium, and reaches 45 bar. The results are discussed and utilised to estimate the electrical conductivity of the arc channel.