Processes in PE free volume and electrical tree initiation

Abstract

Processes taking place in the polymer free volume are very important in the initiation phase of electrical trees under ac stress. Electrons injected from the electrode are accelerated in the free volume (between 10 and 100 nm) and bombard the free volume wall to produce free radicals and break polymer chains. The type of gas in the free volume has a large effect on ac tree initiation. Under O2‐rich conditions, free radicals react with O2 and autoxidation begins. Autoxidation, a chain reaction with low activation energy, creates a large cavity in a short time, where discharge can occur. He or Ar atoms in the free volume are excited to metastable level by electron impact. Metastable atoms collide with the free volume wall and break polymer bonds with high efficiency, creating a cavity in a short time. © 1998 Scripta Technica, Electr Eng Jpn, 124(2): 8–15, 1998