Investigating the Effects of Altitude (Air Density) on the HVDC Breakdown Voltage of Rod-Plane Air Gaps

This paper is on a study of altitude correction factors on short air gap DC breakdown voltage. Tests were conducted on small rod-plane air gaps in a pressure vessel. The air gaps used varied between 100 mm and 300 mm in length and pressure was drawn in the pressure vessel to give relative air densities as low as 0.53. The pressure was drawn from an ambient pressure of about 835 mbar. The range of pressures used made it possible to simulate relative air densities corresponding to altitudes of 1700 m to 4500 m. The results obtained showed a decrease in breakdown voltage as pressure decreased, but only up to a threshold point beyond which an increase in breakdown voltage at very low pressures was observed. The results were corrected using IEC 60060-1 and were also compared to predicted…