Instability criteria at interface regions of spherical cavities in solid dielectric cable

Charge formation and the associated electric field distribution is described for a spherical cavity embedded in solid dielectric cable are treated analytically. This model is useful for understanding the high-voltage breakdown process in dielectric materials. Emphasis is placed on understanding the role of various phenomena at the cavity interface. The effects of space charge, discharge, polarization, and charge relaxation are considered. The analysis is based electrically on Poisson´s equation and, kinematically on the diffusion transport mechanism. The interaction between the gaseous plasma in the cavity and the dielectric surface is critical. The prebreakdown mechanism at the gaseous/dielectric interface is linked to the argument (Kν×r₂). Kν is a degrading factor related to the dynamic interaction between partial discharge and the dielectric surface, and r₂ is the cavity size. Dielectric instability at the interface increases with r₂ and decreases inversely with Kν. Instability implies degradation at the interface due to local field enhancement