The trapped charge voltage during a gas insulated switchgear (GIS) disconnector operation significantly influences the characteristics of the very fast transient overvoltage (VFTO)

such as its amplitude and waveform

and in-depth study of its variation law is essential for accurately characterizing VFTO. Consequently

using an ultra-high voltage GIS as a prototype

we derived the relationship between trapped charge voltage

disconnector speed

and breakdown voltage polarity via mathematical description of repeated breakdown processes. An arc model for disconnector multiple restrikes

considering the polarity effect of gap breakdown voltage

was established

and its accuracy was verified by comparison with measured waveforms of the IEC typical test circuit. Based on this model

the influences of switch speed and polarity characteristics on trapped charge voltage variation laws were studied by simulation

and the impact of trapped charge voltage on VFTO waveform and amplitude during repeated breakdown was further analyzed. The results indicate that a higher operating speed leads to an elevated trapped charge voltage level

consequently resulting in an increased VFTO magnitude; trapped charge voltage exhibits different variation laws with the positive-to-negative breakdown voltage ratio

so the maximum VFTO during operation does not necessarily occur in the last opening or first closing breakdown. When the ratio is large

trapped charge voltage amplitude is small; when approaching 1

the most severe breakdown conditions may occur during both opening and closing operations. Thus

increasing the ratio can reduce the trapped charge voltage amplitude

and lower the VFTO level.