Electrical treeing characterisation of nanocomposite blends

In this work thermoplastic polymeric blends based on Low Density Polyethylene (LDPE) and Ethylene Vinyl Acetate (EVA) have been studied. The blends have been prepared by twin screw compounding. In order to obtain different nanocomposite materials, montmorillonite and silica fillers have been considered. These two fillers are characterised by different aspect ratios: the first having a lamellar structure while the second one presenting a spherical shape. The morphology of the prepared blends has been assessed by means of chemical physical analyses. Electrical treeing tests have been performed on suitable specimens. The tree inception voltage has been determined to evaluate both the effect of the filler and the good adhesion of the needle to the nanostructured sample material. During the tests, partial discharges have been acquired by means of a Phase Resolved Partial Discharge Analyser (PRPDA). The evolution of the parameters relevant to the partial discharges activity has been monitored in order to identify the tree growth morphology. Furthermore life models have been defined putting in relation the obtained lifetime values, relevant to the specimen total breakdown, and the change of parameters directly obtained by the Partial Discharges (PD) detection.