If EXPERIMENTAL SETUP
In this paper, we specially designed four VIs to
understand the standard lighting impulse voltage
breakdown characteristics of vacuum interrupters with
contact gaps 10 to 50mm and compare the inflence of
three different contact parameters on the breakdown
characteristics of VIs with contact gaps 1O�50mm. The
three contact parameters are contact radius of curvature
2mm and 6mm, contact surface roughness 1.6 I m and
3.2 I m, and contact diameter 60mm and 75mm as
shown in Table.I. The electrodes of the four VIs were
shown in Fig.I. The contact material of the four VIs
was CuCr40. The thickness of the electrodes was I5mm.
The contact gap was IO�50mm.
The breakdown voltage characteristics were
measured in vacuum interrupters at a pressure of IO-sPa.
The vacuum interrupters were put into a porcelain
envelope with SF6 gas as an externl insulation. And the
SF6 pressure i the porcelain envelope was O.25MPa.
The contact gap was adjusted up to 50mm through a
gap spacing adjuster. Dielectric tests were carried out
by up-and-down method [7] and 11 was set as �4kV.
The occurrnce of a breakdown was determined by
observing the voltage waveforms on a digital
oscilloscope.