COMBINATION OF EMISSION-SPECTROSCOPY AND FAST IMAGERY TO CHARACTERIZEHIGH-VOLTAGE SF6 CIRCUIT-BREAKERS

To investigate the break phenomenon in high-voltage SF6 circuit breake rs, a novel experimental approach combining spectroscopy and imagery f or measuring electron density, temperature and are geometry is present ed. Images of the are were taken using a narrow band optical filter, a nd spectra of the entire are and in the same spectral region were reco rded simultaneously. We report tests both on this method and on the av ailable literature data and the results obtained on two different circ uit 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 a t 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 fr om the corresponding Images. The results thus obtained compare favoura bly with and show less scatter than those of the conventional Boltzman n diagram method. They also agree with numerical simulations. During t he extinction phase, copper lines between 510 nm and 522 nm radiating at lower temperatures were selected for similar measurements. The imag es reveal that either a filament-like am or well isolated hot gas pock ets 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. T he hot gas pockets could be used as a tracer for flow velocity measure ments.