Subject: Re: Bubbles
Date: Fri, 13 Jun 1997 19:30:49 -0700 (PDT)
From: "Edward V. Phillips" <ed-at-alumni.caltech.edu>
"Speaking from experience with run-in-air LDPE rolled caps, main thing
is heating at any favourable corona spots (foil edges) wnich seems
to actually "crack" or decompose the plastic. "
The transformer design whizzes at Hughes Aircraft, where I
used to work, were of the opinion that almost all high-voltage
capacitor (or insulation, for that matter) capacitor failures when
operating on AC were due to corona discharge in voids, followed
by deterioration of the dielectric and ultimate failure. In other
words, exactly in agreement with your observation. One way they
used to check the quality of the impregnation was to bring the voltage
up and listen for radio noise due to corona! High noidr = potential
failure. Make that high noise!!!