Electrical tree initiation due to bombardment of metastable excited Ar

Abstract

Ac tree initiation voltage of Ar-impregnated LDPE is much lower than vacuum-degassed LDPE, and even lower than normal (air-impregnated) LDPE. Injected electrons are accelerated in polymer free volume. In Ar-impregnated LDPE, the hot electrons collide with Ar atoms in free volume and excite them to metastable level. Metastable atom can return to ground state after transferring the energy by collision with free volume wall. The energy transferred from metastable atom breaks polymer bond of free volume wall, and creates micro cavity in short time.