The importance of particle dispersion in electrical treeing and breakdown in nano-filled epoxy resin

Siyuan Chen, Simon Rowland, James Carr, Malte Storm, Kwang-Leong Choy, Adam J Clancy

Research output: Contribution to journalArticlepeer-review


The addition of nano-fillers has been widely proposed as a method to enhance the dielectric properties of high voltage polymeric
insulation, though there are mixed reports in the literature. Here the potential of silica nano-particles to extend the time to failure
specifically through resistance to electrical tree growth in epoxy resin is determined. The benefit of silane treating the nano-particles
before compounding is clearly established with regard to slowing tree growth and subsequent time to failure. The growth of trees
in needle-plane samples is measured in the laboratory with loadings of 1, 3 and 5 wt% nano-filler. In all cases the average times to
failure are extended, but silane treatment of the nano-particles prior to compounding yields much superior results. The emergence
of a pronounced inception time before tree growth is also noted for the higher-filled, silane-treated cases. The average time to
failure of silane-treated 5 wt% filled material was 28 times that of the unfilled resin. The improvement in performance between
the nanocomposites with untreated and treated fillers is attributed to fewer agglomerations and improved dispersion of the filler in
the treated cases. Measurements of Partial Discharge (PD) indicated significant differences in PD patterns during the growth of
trees in the treated and untreated cases. This distinction may provide a quality control method for monitoring materials. In
particular, long periods in which PDs were not measured were observed in the silane-treated cases. Visual imaging of tree growth
in the unfilled material allowed the changing nature of the tree from fine to tree to dark tree to be observed as it grew. Corresponding
PD measurements suggest the dark tree is gradually becoming conductive, and that growth of maximum PD measured is dependent
on the relative rates of the growth of the tree and its carbonization. X-ray computer tomography identified significant differences
in average tree channel diameters (a reduction from 2.8 μm to 2.0 μm for 1 wt% and 3 wt% cases). This implies that in addition to
tree length changes, evaporated tree volumes also change and may explain the change in partial discharge characteristics observed.
Original languageEnglish
JournalInternational Journal of Electrical Power & Energy Systems
Publication statusAccepted/In press - 19 Jan 2021


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