Dynamic propagation velocity of positive streamer in a 3 m air gap under lightning impulse voltage

Streamer is an important stage in the initiation of gap discharge. In this work, we used an 8-frame intensified charge coupled device (ICCD) camera to capture the streamer development process when the lightning impulse voltage of 95%–100% U50% was applied in a 3 m rod-plate gap, and the streamer velocity was analyzed. By analyzing the observations, the streamer velocity is defined as three stages: rapid velocity decline (stage 1), rapid velocity rise (stage 2) and slow velocity decline (stage 3). The effects of electrode shape, applied voltage, gap breakdown or withstand on streamer velocity were analyzed. The electrode with a larger curvature radius will result in a higher initial velocity, and a higher voltage amplitude will cause the streamer to propagate faster at stage 3. Gap withstanding or breakdown has no obvious effect on streamer velocity. In addition, the experimental results are compared with the previous results and the statistical characteristics of the primary streamer discharge were discussed.