Space charge injected via interfaces and tree initiation in polymers

Space charge can be measured non-destructively as a standard practice now. It has been long suspected that space charge might be critically involved in local dielectric breakdown or tree initiation. It is widely accepted that space charge is formed under dc stress in dielectrics. The author demonstrated a hypothetical space charge-dominant model for tree initiation in 1979 in Japanese and in 1991 in English, and proposed that charge can be accumulated inside polymer dielectrics near the divergent high field region even under ac stress. The model consists of a charge injection and extraction process, a charge trapping and space-charge forming process, a polymer scission process due to high energy injected and extracted electrons, an oxidation process, an electric field enhancement process, and a tree initiation process. The author explains his hypothetical space charge dominant model for tree initiation, various relevant phenomena and data that could prove the validity of the model, tries to interpret several recently discovered phenomena with his model, and reevaluates it as compared with modern concepts for tree initiation