Flashover voltage of alumina ceramic contaminated by metal vapor in vacuum interrupters

We have discussed the influence of metal vapor contamination for ceramic surface of vacuum interrupters (VIS) on surface flashover characteristics. Firstly, using the metal vapor emission fmm CuCr contacts, we produced disk-shape alumina (A1₂0₃,) ceramic samples with surface resistivity (p) of 10²-10^{15 Ω, and measured their surface flashover voltages. It was identified that lightening impulse flashover voltage decreased as p reduced and that both the conditioning effect and scattering of the flashover voltage became small when pwas below 1012 Ω. Secondly, we produced two types of VIS, with CuCr spiral contacts and CuCr axial magnetic field contacts respctively, to conduct forty times of short-circuit current interruptions with 20-40 kArms. It was specified that p f o r the ceramic of the VI with spiral contacts reduced down to 104 Ω, and that breakdown vokage between terminals of the VI also decreased. pand breakdown voltage for the VI with AMF contacts did not decreased.}