AC Breakdown Characteristics of Air in Non-Uniform Electric Fields at Low-Pressure Conditions

With the development of the power grid at high altitudes, more and more transmission and transformation projects are being implemented at altitudes close to 5000 meters. As the altitude increases, the air pressure decreases, resulting in a decrease in the insulation performance of the air gap and requiring corresponding adjustments to the insulation structure of power equipment. This paper investigated the AC breakdown characteristics of air in non-uniform electric fields at pressures of 50~100 kPa. The relationship between maximum breakdown field strength and electric field non-uniformity factor at different pressures was analyzed. The applicability of streamer criterion in low-pressure air gap was also analyzed. The results show that the breakdown voltage increases with increasing pressure and electrode distance for different electrode radius. At the same air pressure, the maximum breakdown field strength increases with the decrease of the electrode radius. When the electrode radius
$r$
≥ 1.0 cm, the streamer criterion can accurately calculate the breakdown voltage of short air gaps at low pressures.