Electric field inside a gas cavity formed at a solid-solid dielectric interface stressed with HV impulses

Interfaces between solid dielectric materials may exhibit lower breakdown strength compared to that associated with bulk breakdown of solid materials. A reason for such reduction is the presence of gas cavities which are formed at the interface. When the solid-solid interface is subjected to impulsive electrical stress, the enhanced electric field inside cavities may result in the development of initial (partial) discharges. This may ultimately lead to breakdown across the interface, resulting in the catastrophic failure of the entire insulation system. Therefore, it is paramount to understand the field distribution and ionisation processes within interfacial cavities, such that the behavior and strength of the insulation system can be fully predicted. The present paper considers a gas-filled cavity formed between poorly-conducting solids, subjected to a transient external electric field. The corresponding boundary value problem is defined and analytically solved, obtaining closed form solutions for the electric field distribution inside and around an isolated cavity. Results from model validation and intra-cavity field enhancement are presented, as well as brief discussion of other possible applications and future model extensions.