Polymer nanocomposites are more and more researched and employed as dielectrics
in electrical power equipment. However, the bad dispersion and distribution of particles
are often reported to deteriorate the dielectric properties of polymer nanocomposites. In
most cases, researchers tend to use SEM/TEM images with imprecise descriptions to
describe these two factors, and there was still no clear relationship between their
quantified particle dispersion characteristics and dielectric properties of polymer
nanocomposites. This work is to, first, propose a combined quantification method to
estimate the dispersion and distribution of spherical/ellipsoidal particles/aggregates in
polymer nanocomposites based on SEM images of epoxy SiO2 nanocomposites. Based on
the proposed quantification method, epoxy nanocomposite with surface treated SiO2
shows overall better dispersion and distribution of particles/aggregates than those with
untreated ones. The presence of agglomerations would lead to the enhancement of
mobility of charge carriers and thus reduction of breakdown strength, which become
more obvious with the growth of filler loadings. It is found that, in AC breakdown tests,
dispersion and distribution of particles/aggregates show little influence on the reduction
of AC breakdown strength. However, those should be the main factor which influences
the DC breakdown strength in epoxy nanocomposites with a variation of filler loading
concentrations.