Space charge injected via interfaces and tree initiation in polymers

Space charge is a recent hot topic in the field of electrical insulation, since it can be measured nondestructively as standard practice. It has been suspected long 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 charge injection and extraction, charge trapping and space-charge forming, polymer scission due to high energy injected and extracted electrons, oxidation, electric field enhancement, and finally tree initiation. The author will explain his old hypothetical space charge dominant model for tree initiation, various relevant phenomena and data that could prove the validity of the model, try to interpret several recently discovered phenomena with his model, and re-evaluate it as compared with modem concepts for tree initiation.