Computational study on the positive streamer inception in air at high altitude

The streamer inception is the initial stage of long air gap discharges. In order to predict the breakdown voltage of long air gaps at high altitude of 4000 m and above, it is necessary to establish a computational model to identify the streamer onset voltage and the inception time-lag at low pressure. However, traditional critical volume method didn't consider the impact of air pressure. In this paper, the seed electron generation process due to the detachment of O-2(-) and its hydrated ions is simulated by considering different air pressure. Combined the computed generation rate of seed election and the critical volume method, a computational model for the streamer onset condition is proposed. The mean electric field for streamer onset and the distribution of inception time delay under different air pressure were calculated and compared with measured data. Finally, the impacts of air pressure on the streamer inception for different applied voltage waveforms and electrode curvatures are analyzed.