Switching Impulse Discharge Characteristics of Ultra-High Altitude Sphere-Plate Air Gaps

The insulation design of power equipment in ultra-high altitude areas faces severe challenges, especially in valve halls where equipment is densely arranged and the structure is complex, which imposes higher requirements on the insulation performance of air gaps. Currently, there are many studies on rod-plate gaps, but they are not applicable to grading spheres and grading rings. This paper conducts research on the switching impulse discharge characteristics of a 1m sphere-plate air gap under different pressures and obtains a correction formula. The results show that the altitude of this experiment ranges from 232 to 4500 m, the discharge voltage ranges from 804.0 kV to 483.1 kV, the standard deviation ranges from 8.2 to 16.3, and the relative standard deviation ranges from 1.0 to 3.0%. Pressure has an impact on the flashover voltage of air gaps. Generally speaking, as the pressure decreases, the U50 of the air gap also decreases. Under standard atmospheric pressure, the influence coefficient of pressure on the discharge voltage is 0.94.