Lightning impulse voltage breakdown characteristics of vacuum interrupters with contact gaps 10 to 50 mm

The objective of this paper is to understand the standard lightning impulse voltage breakdown characteristics of vacuum interrupters with contact gaps 10 to 50 mm and how contact parameters influence the breakdown characteristics. The investigated contact parameters include contact diameter 75 and 60 mm, contact surface roughness 1.6 and 3.2 μ m, and contact radius of curvature 6 and 2 mm. Therefore we designed four high-voltage vacuum interrupters in the experiments. The vacuum interrupters were put into a porcelain envelope with SF₆ gas as an external insulation of the vacuum interrupters. The contact gaps can be adjusted manually up to 50 mm. Positive polarity lightning impulse voltage (1.2/50 μs) was applied by an up-and-down method. Experimental results revealed the breakdown probability distributions followed Weibull distributions when the breakdown voltage saturated within the investigated contact gaps 10 to 50 mm. Within the contact gaps 10 to 50 mm, U₅₀ of vacuum interrupter with contact radius of curvature 2 mm was higher than that of vacuum interrupter with contact radius of curvature 6 mm. And U₅₀ of contact roughness 1.6 μm was close to that of contact roughness 3.2 μm. U₅₀ of the contact diameter 60 mm was close to that of contact diameter 75 mm. And 50% breakdown voltage U₅₀ depended on the contact gap d (10-50 mm) for four interrupters, can be expressed by an equation U₅₀=kd^α, where a is a power exponent; k denotes a coefficient which can be determined by experiments. And under our experimental condition, power α lay in a range of 0.6-0.7 for the four vacuum interrupters. The breakdown phenomenon could be due to the micro-particles.