Combination of emission spectroscopy and fast imagery to characterize high-voltage SF6 circuit breakers

To investigate the break phenomenon in high-voltage SF6 circuit breakers, a novel experimental approach combining spectroscopy and imagery for measuring electron density, temperature and are geometry is presented. Images of the are were taken using a narrow band optical filter, and spectra of the entire are and in the same spectral region were recorded simultaneously. We report tests both on this method and on the available literature data and the results obtained on two different circuit breaker models. For the high-current phase (I = 2 kA to 10 kA) we chose to study the well isolated 624-641 nm fluorine lines radiating at elevated temperatures, expected to be Tn the range 15 000-20 000 K. With electronic densities higher than 10(17) cm(-3) the Stark effect, as the predominant line broadening mechanism, yields a direct relation between plasma conditions and the measured spectrum. Corrections for eventual self-absorption were applied with the are geometry deduced from the corresponding Images. The results thus obtained compare favourably with and show less scatter than those of the conventional Boltzmann diagram method. They also agree with numerical simulations. During the extinction phase, copper lines between 510 nm and 522 nm radiating at lower temperatures were selected for similar measurements. The images reveal that either a filament-like am or well isolated hot gas pockets are present during extinction. The measured temperature was still high even a few hundred microseconds before ultimate extinction. This result is fully compatible with computations of the cooling process. The hot gas pockets could be used as a tracer for flow velocity measurements.