Influence of Front Time on Long-Airgap Breakdown Voltage in High-Altitude Areas

As the altitude increases, air density decreases to cause a decrease in the air insulation strength. Test results in low-altitude areas indicate the significant impact of front time
$t$
(μs) on the characteristics of long-airgap discharge. Nevertheless, the impact of
$t$
on the breakdown voltage at high altitudes has yet to be studied. In this paper, impulse discharge characteristic tests for rod-plane gap were conducted at altitudes of 2500 m and 4300 m, with
$t \in [2,1000]$
. The rod-plane gap discharge characteristic curves are obtained, and the critical front time and 50% breakdown voltage in the two areas are determined. Subsequently, the influence of altitude on the discharge characteristics under critical wave and standard switching impulse wave is compared and analysed. Based on the experiments considering low altitude, 2500 m and 4300 m high-altitude areas, the applicability of the altitude correction method recommended by IEC 60 071 is analysed. Moreover, an improved altitude correction method is presented to adapt to wide waveform variations in high-altitude areas. These results provide fundamental data and support for the external insulation design approaches in power grids at high altitudes.