Ways to more potent capacitors for high-voltage DC transmission technology based on polymer nanocomposites and blends

Abstract:
To evaluate possible improvements of thin film capacitors, biaxial oriented films based on nanocomposites of PP and hydrophobic silica as well as polymer blends of PP and ENC were investigated. Therefore, the films were produced on a pilot scale stretching line, metallized and wound to capacitors. On scanning electron microscope (SEM) images the PP/ENC blends showed a layer like structure and the particles a homogeneous distribution throughout the film. The morphology of the PP matrix investigated by differential scanning calorimetry (DSC) was comparable for all films. Additionally, the degradation by compounding and processing was investigated using high temperature gel permeation chromatography (HT-GPC). A pronounced reduction of the molecular weight was found for the nanocomposites, as the particles were added in an additional compounding step. The suitability of the compounds for an application as capacitor films was evaluated determining dielectric strength and voltage endurance of the films as well as the reduction in capacitance and the increase in loss factor of the capacitors during an endurance test based on IEC 61071. It was revealed that the degradation of the molecular weight determined by HT-GPC was the governing factor for all four parameters. Among the different compounds the blend of PP and ENC was the most promising as it showed low degradation and a better voltage endurance than the PP reference. Nanoparticles might still be a viable option, however the degradation during compounding has to be reduced significantly.