The statistical and formative times for breakdown at a polymer-oil interface

The average statistical time and formative time associated with breakdown across a polymer-oil interface have been extracted from experimental time-to-breakdown data, gathered using a non-uniform electrode geometry designed to promote surface discharges. Five polymer materials of relevance to the designers of pulsed-power systems have been considered: polypropylene; LDPE; UHMWPE; Rexolite; and Torlon. It has been assumed that the temporal distribution of breakdowns can be described using the approach developed by von Laue, and the validity of this approach is discussed within the paper. The materials were clearly separated in terms of the statistical component of the overall time to breakdown, with Torlon showing the shortest average statistical time (~17 ns), and Rexolite the longest (~54 ns). However, the derived formative times were shorter for Torlon and Rexolite than for the other materials; PP, LDPE, and UHMWPE have similar formative times, at ~350-400 ns.