Abstract
To clarify factors influencing the conditioning effect brought by repetitive breakdowns of a vacuum gap, changes of electrode surface conditions before and after 500 breakdowns caused by impulse voltage application has been investigated. Changes of prebreakdown current characteristics has been also investigated. Electrode material used was copper. Electrode surfaces were analyzed by the X-ray photoelectron spectroscopy (XPS). The XPS analysis revealed that electrode surfaces were completely cleaned by repetitive breakdowns. Prebreakdown characteristics were classified into 3 patterns;(1) displacement current alone, (2) field emission current as well as the displacement current, (3) explosive current increase. The patterns (1) and (3) were observed mainly at the early stage of repetitive breakdowns, while the pattern (2) was at the later stage. It has been concluded that the breakdown mechanism alters during conditioning by repetitive breakdowns.
