Nanodielectrics for machine insulation

Abstract

Thanks to the development of nanotechnology, epoxy nanocomposites have been expected to be potential candidates to replace the base resin, due to their superior properties. However, the effects of nano-fillers have been controversial, in both positive and negative ways. There are two main factors, comprising of stoichiometry and the nature of interfacial areas of nano-sized fillers, which are expected to contribute to the final properties of epoxy nanocomposites. The chosen stoichiometry is important in determining the nature of the polymer network that forms. A stoichiometric formulation with the optimal chemical balance between reactants will introduce good performance. However, incorporation of nano-fillers with large interfacial areas into epoxy matrices may modify the cure behaviour of the system, through introducing additional chemical reactions between moieties on the nano-filler surfaces and reactants, thereby altering the rate and sequence of the possible chemical reactions that occur during curing. These effects change the chemical balance of the original base resin system. As a result, the nature of the cross-linked network that forms may be altered.
An investigation into the effects of stoichiometry and the nature of the interfacial surface of treated nanosilica particles of various sizes on properties of epoxy-based systems has been conducted, using the differential scanning calorimetry, space charge and ac breakdown measurements, and the dielectric spectroscopy. The introduction of nanosilica has induced changes in curing mechanisms and led to different impacts on systems of different resin stoichiometry. In addition, the investigation has revealed a key role of the characteristic interaction between the nanoparticle surface and the resin matrix in determining material properties, rather than the filler size. Weak interactions have produced negative impacts on material properties. The addition of nano-silica particles into conventional microcomposites has suggested the possible synergetic effects due to the presence of both nano and micro fillers.
Furthermore, the long-term performance of the unfilled epoxy and its nanocomposites has been explored. Open branch trees with the faster propagation rate have been observed in nanocomposites, compared to the unfilled epoxy. The material degradation during partial discharge activities has also been evinced using the confocal Raman microprobe spectroscopy.

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ORCID for A.S. Vaughan: orcid.org/0000-0002-0535-513X

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