Influence of high altitude on streamer discharge mechanism of sphere–plane gaps under positive switching impulse

Abstract China’s energy resources and load centers are unevenly distributed, and many extra-high voltage and ultra-high voltage projects pass through high-altitude regions, posing challenges for air-gap insulation. Understanding streamer behavior in high-altitude conditions aids in optimizing insulation design for power systems. This paper conducts positive switching impulse discharge experiments on sphere–plane gap with electrode radii of 0.15–0.45 m and a gap distance of 2 m at 2100 m altitude. The critical inception voltage, boost time delay, and statistical time delay are analyzed combining the photoionization model. The effects of electrode size and atmospheric pressure on statistical time delay are studied with the critical volume model. The evolution law of the discharge channel is explored from the perspective of microscopic particle reactions using a one-dimensional streamer–leader discharge model. The results show that critical inception voltage of streamer increases with electrode radius but decreases with lower air pressure. Both boost time delay and statistical time delay increase with larger electrode sizes. The combined effects of critical volume and internal field strength make the field strength’s influence on statistical time delay more significant. The fact that E / P remains consistently higher under low-pressure conditions compared to standard atmospheric pressure indicates that negative ions have a shorter lifetime at low pressure, making it easier for free electrons to be released, thereby promoting earlier streamer inception at high altitudes. The micro particle number density during the development of streamer in high-altitude environments is lower than that at lower altitudes, and the discharge channel requires more time to absorb energy to maintain discharge development. These findings provide theoretical support for high-altitude discharge studies and are significant for insulation design and protection of high-voltage equipment.