Flashover Characteristics of 500kV Insulators under Positive Short-tail Wave Impulse

The $U_{50 \%}$ and volt-time characteristics of insulators are crucial models for lightning protection of transmission lines. Since negative lightning predominates in natural thunderstorms, the voltage across insulator during back flashover is characterized by the rapidly decaying positive short-tail wave. Therefore, it is necessary to further investigate the flashover characteristics of different material insulators under the various short-tail wave pulses and establish accurate flashover criteria. Experiments have provided the flashover criteria for 500 kV insulators under positive short-tail wave pulses, offering a basis for accurately assessing the lightning withstand level of transmission lines. By comparing the experimental results of glass insulators and composite insulators, the influence of material properties and altitude on flashover characteristics has been analyzed. It is found that there are significant differences in the discharge paths of insulators made from different materials, while the effect of material on the flashover characteristics is relatively small, with $U_{50} \%$ differing by only $\mathbf{2. 7 \%}$. Regarding the impact of altitude, by adopting different standards for the calibration of $U_{50 \%}$ and breakdown voltage of volt-time characteristics, it is determined that under short-tail wave conditions, the test values at high altitudes, after calibration using the g-parameter method and IEC 60071-2 standard, showed significantly reduced discrepancies compared to those from plain areas.