Ester-based insulating liquids are considered today for electrical insulation in medium and high voltage transformers. The main advantages expected are their non-toxicity, excellent biodegradability, and fire resistance. Esters can be either of natural origin or synthetic. In this work, we present a study of prebreakdown and breakdown properties at high voltage and large gaps in several natural and synthetic esters, and a comparison with the well-know mineral transformer oil. This study is focused on the study of streamer propagation in large gaps up to 10cm. Compared to mineral oil, the transition to fast streamers in esters occurs at much lower voltage. Measurements also show no difference between esters, whatever their origin, viscosity, etc. From these results, it appears that the properties of esters are less favorable for very high voltage insulation than in mineral oil: once triggered, streamers are able to propagate very quickly to breakdown at lower voltage. In consequence, esters show a lower resistance to fast transients such as the standard lightning impulse.
Polymers typically have intrinsic thermal conductivity much lower than other materials. Enhancement of this property may be obtained by the addition of conductive fillers. In this research, epoxy nanocomposites with exfoliated graphite nanoplatelets are prepared and characterized. The chosen approach requires no surface treatment and no sophisticated equipments allowing one to produce composites on a pilot scale. A significant increase of the thermal conductivity with the increasing of the graphite fillers content is nevertheless observed on 4 mm thick specimens. Our results viewed in the latest scientific findings suggest that the choice of resin is an important parameter to move towards composite materials with high thermal conductivity.
A 2-D ceramic nanostructure was successfully processed out of nanolamellar 312 MAX phase ternary carbide and titanium silicon carbide via a simple shear-induced delamination method and was incorporated in an epoxy matrix, so as to improve the bulk properties of the polymer.
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