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

Arc voltage fluctuations with control of the main experimental parameters are studied, taking into account the excitation and ionization potentials of both contact materials and gases. The actual parameters of the experiments are the contact material (Au, Ag, etc.), and the environmental (air, N₂, He, Ar, etc.), electrical (50 V, 0.1-3 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 histogram drawings. Each of these voltage plateaus is attributed to a specific combination of contact metal ionization potential and excitation metastable levels of the surrounding gases. It has been found that each phase can enclose more than one plateau, such as in helium where the two last plateaus occur in gaseous phase, while in ambient the metallic phase is constituted by the two earlier plateaus. According to the plateau attribution, arc phase duration could be the sum of the corresponding plateau durations. Moreover, during each plateau, fast potential fluctuations occur. The fast Fourier transform (FFT) 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