Influence of the surrounding medium on the dielectric strength measurement of LLDPE/clay nanocomposites

This paper evaluates dielectric breakdown measurements according to the ASTM D149-09 standard for various specimen thicknesses and surrounding media. This study was performed on LLDPE/nanoclay with three different surrounding media. Pre-breakdown partial discharge activity was monitored and the electrical field in the breakdown area was computed by FEM modeling. It was observed that the variations of the dielectric breakdown values from the neat polymer to the nanostructured polymers strongly depends on the surrounding medium, a situation which could lead to non-valid conclusions if appropriate care is not taken to select the optimal experimental procedure. Also, the results underscore the influence of the pre-breakdown partial discharge gas generation on the electrical field distribution and the influence of the surrounding medium degradation. To conclude, the ASTM D149 Standard shows a lack of normalization in terms of the surrounding medium parameters and the sample thickness, even though a certain amount of normalization is needed in order to compare breakdown results from one experiment to the other and to improve the understanding of the solid dielectric breakdown phenomena.