Influence of low amounts of nanostructured silica and calcium carbonate fillers on the large-area dielectric breakdown performance of bi-axially oriented polypropylene

Abstract

-Influence of low amounts (1.0-2.0wt-%) of nanostructured silica and calcium carbonate fillers on the largearea dielectric breakdown performance of bi-axially oriented polypropylene (BOPP) is analyzed. A multi-breakdown measurement method based on the self-healing breakdown capability of metallized film is utilized for the breakdown characterization in order to cover relatively large total film areas, thus leading to results of higher relevance from the practical point-of-view. The dispersion and distribution qualities of filler particles at the nanoscale are evaluated with transmission electron microscopy (TEM) imaging. Weibull statistical analysis suggests that the breakdown distribution homogeneity can be improved with both the filler types. The 1.0wt-% silica-BOPP composite also shows a shift of the weakest points towards higher dielectric strength in comparison to the neat BOPP. However, with increasing filler content, new failure modes are introduced into the nanocomposites, hence decreasing the overall breakdown performance in the >5% breakdown probability region in comparison to the un-filled reference BOPP film.

The Role of Film Processing in the Large-Area Dielectric Breakdown Performance of Nano-Silica-BOPP Films

“…As also discussed in [3], [4], Figure 2a clearly shows that an increase in silica content reduces the breakdown performance in the >5 % breakdown probability region in comparison to the unfilled reference BOPP but also leads to a concurrent improvement of the breakdown distribution homogeneity. Interestingly, the Weibull lines of the 1.0 wt-% SiO 2 -BOPP PNC and the unfilled BOPP intersect in the 5-10 % breakdown probability range with the 1.0 wt-% SiO 2 -BOPP PNC showing higher strength in the low probability region.…”

“…The film processing was conducted at the VTT Technical Research Centre of Finland and at a Brückner pilot film line in Denmark. As the total amount of studied compounds was over 25, a detailed listing of all the materials, processing parameters and film specifications is out of the scope of this paper and can be found from the related publications ( [3], [4], [7]). Only the essential aspects are summarized in the following.…”

“…Inclusion of low amounts (~1 wt-%) of permittivitymatching nanoparticles such as silica in a suitable polymer matrix has been shown to be a promising approach, and some improvements in the short-term dielectric strength and breakdown distribution homogeneity have been previously reported [2]- [4]. However, as the dielectric breakdown performance of polymer-based thin films is largely dependent on various processing-and material-related aspects [5], [6], a thorough understanding of the underlying factors and optimization of the film processing parameters are crucial in order to achieve improved breakdown strength in practical insulation systems.…”

“…A large-area multi-breakdown measurement approach based on the self-healing breakdown capability of metallized polymer films has been extensively applied for studying the breakdown properties, as it enables a large amount of breakdown data to be acquired from a relatively large total film area hence leading to a high statistical accuracy even at low breakdown probabilities. A detailed description and evaluation of the measurement method was recently given in [7] while studies exemplifying the large-area multi-breakdown characterization of various laboratoryscale, pilot-scale and commercial BOPP and BOPP-PNC films are presented in [3], [4], [8], [9].…”