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

The objective of this paper is to understand the standard lighting 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 mm and 60 mm, contact surface roughness 1.6 μm and 3.2 μm, and contact radius of curvature 6 mm 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. Negative polarity basic impulse level (BIL) voltage (1.2× 50μs) was applied by an up-and-down method. Experimental results revealed the breakdown probability distribution followed a Weibull distribution when the breakdown voltage saturated in the investigated contact gaps 10 to 50 mm. And 50% breakdown voltage U₅₀ depends on the contact gap d (10~50 mm), can be expressed by an equation U₅₀=kd^α, where α is a power exponent; k denotes a coefficient which is determined by experiments. Within the contact gaps 10 to 50 mm, U₅₀ of vacuum interrupter with contact radius of curvature 2 mm was significantly 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.