Arc temperatures in a circuit breaker experiment from iterative analysis of emission spectra

Abstract

A switching-off process very similar to those in real high-voltage self-blast circuit-breakers is emulated in a model chamber to study the arc properties by optical emission spectroscopy. The arc is operated in a chamber filled with SF$_6$ between a pin-tulip contact system enclosed by a PTFE nozzle. Transparent windows in the chamber wall and a slit in the nozzle enable an optical investigation of the arc cross section less than one millisecond before current zero. The side-on radiance of a fluorine atom lines has been measured with an imaging spectroscopic system. Considering rotational symmetry of the arc the corresponding radial emission coefficients have been determined by Abel inversion. The radial temperature profiles are calculated from the emission coefficients including pressure measurements and the corresponding plasma composition. In contrast to previous studies, a specific iterative approach is proposed to consider the optical thickness of the plasma. A maximum optical thickness between 0.2 and 0.4 has been observed. Temperature profiles corrected for absorption effects show increasing maximum temperature in the arc axis with decreasing current towards current zero. The effect of the plasma composition on absolute arc temperatures is discussed. The temperature profiles can be used to validate CFD simulations of the switching-off process in the model chamber.