To investigate the effect of the nano-second consecutive impulse voltage（NCIV）on breakdown position distribution on conditioned contact surface of a conditioned vacuum interrupter

a CCD camera and a commercial 12 kV glass enveloped vacuum interrupter（VI）with an observing window on its shield were employed to analyze the effects of NCIV amplitude and frequency on the distribution of breakdown positions under different contact gaps. Results show that the breakdown position distribution on contact surface follows the Gaussian probability density distribution when the contact gap is broken down under NCIV stress. The breakdown positions concentrate in the center of the contact surface. The breakdown positions tend to uniformly distribute on contact surface with increasing impulse voltage frequency. However

a higher amplitude of the impulse voltage results in a more concentrative distribution. The larger the contact gap is

the more concentrative the breakdown position distribution becomes. Moreover

the non-parallelism of the contact surfaces has a significant influence on the distribution of breakdown positions on the contact surface. Greater non-parallelism of the contact surfaces leads to more concentrative distribution of the breakdown positions

and the concentration point tends to the side with smaller contact edge gap.