Some investigations on slow and fast arc voltage fluctuations for contact materials proceeding in various gases and direct current

Arc voltage fluctuations are studied, taking into account the excitation and ionization potentials of both contact materials and gases. The parameters of the experiments are: the contact material (Au, Ag, . . .) and the environment (air, N₂, He, Ar . . .), electrical (50 V, 0.1 to 3 A DC), and mechanical (opening speed 1 to 50 cm/s) parameters. The accurate voltage values of the consecutive arc plateaus included in arc phases are determined by statistical measurements and voltage histograms. Each of these voltage plateaus is attributed to a specific combination of contact metal ionization potential and excitation metastable levels of the surrounding gases. The fast Fourier transform analysis of arc voltage samples shows that the maximum of the spectrum of these fluctuations corresponds to a frequency which is as high as 60 MHz in the metallic phase and only a few megahertz in the gaseous phase