The dynamic velocity of long positive streamers observed using a multi-frame ICCD camera in a 57 cm air gap

The streamer propagation plays an important role in long air gap discharge. In this paper, a multi-frame intensified charge-coupled display (ICCD) camera was used to observe the long positive streamers in a 57 cm air gap. The propagation process of the 20–30 cm long streamers was captured, and the velocity variation in a single streamer was analysed. When applying a +210–290 kV lightning impulse voltage on a rod–plane gap with three different tips, the velocity of a streamer decreases from 8.3 ± 2.7 mm ns−1 at the ignition stage to 0.4 ± 0.1 mm ns−1 at the later stage. The influence of the applied voltage and the electrode size was obtained and analysed. Higher voltage amplitude and larger electrode size lead to a greater velocity. In addition, the relationship between the velocity and the background electric field is discussed here, and the experimental results are compared with an analytical model of different parameters. (paper)