Average Streamer Channel Field Strength in Pressurized Synthetic Air at Lightning Impulse Voltage Stress

To design gas insulated switchgear filled with pressurized synthetic air, it is important to understand the discharge behavior. The streamer expansion is limited by the average streamer channel field strength. The polarity dependent behavior of the average streamer channel field strength in pressurized synthetic air at lightning impulse voltage stress was investigated in this study. To achieve this, streamers in a strongly nonuniform field created by a needle placed in a uniform and weakly nonuniform background field were optically recorded by a streak camera. This approach was novel compared to previous studies. The results for the average streamer channel field strength were similar at different degrees of homogeneity of the background field. The positive streamer channel field strength with 0.5 kV/mm is independent of the streamer length and increases as a function of pressure to the power of 1.5. The negative streamer channel field strength scales inversely proportional to the streamer length and increases linearly with pressure. For streamer expansions longer than 40 mm, the negative channel field strength is comparable to literature values at 0.1 MPa with 1.0 kV/mm.