Positive Switching Impulse Discharge Performance and Voltage Correction of 1-m Rod-Plane Air Gap

Switching impulse discharge performance of air gaps at high altitudes, which is a fundamental in the extremely high voltage external insulation design, remains an unsolved key technology across the world. Due to the limited applicable range of “g” parameter method recommended by IEC Publication 60-1(1989), this paper aims to explore the relationship between positive switching impulse 50% discharge voltage $U_{50}$ of rod–plane air gaps and atmospheric parameters, and proposes two new voltage correction methods based on the parameter “g” and the atmospheric pressure ratio, respectively. The two methods have been proved by the experimental investigations carried out on 1-m rod–plane air gap both in the artificial climate chamber and at three spots of different high altitudes in this study. The results show that, if the additional influence of absolute humidity is considered, the positive switching impulse 50% discharge voltage $U_{50}$ of rod–plane air gaps is a power function of relative pressure and relative air density; the “g” parameter method in IEC Publication 60-1(1989) is not applicable to the regions with an altitude above 2000 m or the condition of $h/\delta>15\ {\rm g/m}^{3}$; compared with the correction method based on the “g” parameter method, the correction method based on relative atmospheric pressure has a wider applicable range and less error; when the absolute humidity increases 1 ${\rm g/m}^{3}$, $U_{50}$ varies within the range of 1.0%–1.15%.