Modelling the impulsive breakdown characteristics of sub-mm to mm spheroidal voids

Solid insulation is widely used in power and pulsed power systems. In the past, great attention has been paid to gas-filled voids found in solid dielectrics within the context of partial discharges for power equipment, such as high voltage cables. However, it is equally important to consider the effect of such voids on the degradation of solid insulation within pulsed power systems. Discharge activity within gas-filled voids, or across cavities at solid-solid interfaces, can potentially threaten equipment longevity and durability. Therefore, the transient ionization processes initiated inside these voids, particularly under fast-rising impulsive energization, are of great importance. Yet, the additional complexities of transient stress compared to steady-state conditions typically render classical steady-state breakdown models inapplicable, and necessitates a different approach for the impulsive regime. In this work, an approach for the breakdown voltage and time-to-breakdown estimation of spheroidal air-filled voids, subjected to fast-rising high voltage impulses has been developed. The proposed model links the time-dependent electric field developed within a spheroidal void to gas ionization and breakdown criteria, allowing the estimation of the formative time-to-breakdown and breakdown voltage of the void. This study investigated the effects of dV/dt on estimated void breakdown parameters, and the approach may be of use for the further characterization of solid insulation under impulsive energization, aiding in the future development of novel insulation technologies for current and future pulsed power systems.