A spectroscopic investigation of electrode material entrained into the extinguishing arc of SF6circuit breaker

Spectra of SF 6 circuit breaker arcs during the arc extinction phase following peak currents up to 53 kA have obtained in the wavelength range 510-517 nm. Copper emission lines and irregularly occurring tungsten emission lines from entrained contact material have been identified and the ratio of the number density of tungsten to copper atoms estimated from the line intensities. An approximate radial distribution of both copper and tungsten line intensities has also been obtained. The irregular occurrence of tungsten in the arc plasma column and the restricted extent of the tungsten line emitting cross section are both believed to be a consequence of the complicated evaporation processes associated with the copper-tungsten contact. An approximate correlation is shown to exist between the occurrence of tungsten line emission at the critical instant of current zero when current interruption is sought and a sharp deterioration in the current interrupting ability of the breaker. The implication of this is that the hitherto neglected presence of tungsten at current zero, as distinct from copper, contributes in combination with the already known effects of flow throttling and nozzle ablation in determining the extent of the degradation of circuit breaker performance.