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

Vertical profile of the leader in long laboratory sparks was analyzed using high speed video photographs. Sparks were generated in an 8 m gap of sphere – plane electrodes with positive impulse voltage of 250/2500 μs wave form. The spatial resolution of the high speed frame camera was 19.6 mm per pixel with a time resolution of 50 μs. It was found that the average final jump distance of five sparks was about 4 m and the average electric field in the final jump region is about 5 × 105 V/m the leader speed varies from 1.3 × 104 m/s to 3.1 × 104 m/s as it propagates toward the ground. The average leader speed of the leader was in the order of 1.8 × 104 m/s. The observations show that there is a significant increase in the leader speed just before the final jump.