Leader propagation speed and the final jump distance of 8 m long laboratory sparks

摘要: Abstract Vertical profile of the leader in long laboratory sparks was analyzed using high speed video photographs. Sparks were generated an 8 m gap sphere – plane electrodes with positive impulse voltage 250/2500 μs wave form. The spatial resolution frame camera 19.6 mm per pixel a time 50 μs. It found that average final jump distance five about 4 m and electric field region is 5 × 10 5  V/m varies from 1.3 × 10 4  m/s to 3.1 × 10 as it propagates toward ground. order 1.8 × 10  m/s. observations show there significant increase just before jump.