AC Electrical Characteristics of Polypropylene for Eco-friendly Thermoplastic Power cable

While previous studies have primarily focused on macroscopic physical defects such as voids and contamination, the influence of chemical defects — specifically residual catalyst species originating from the polymerization process — has been less explored. These trace inorganic residues may act as ionic impurities or localized charge transport sites, potentially enhancing conduction loss and initiating dielectric degradation under AC electric fields.

In this study, the effect of catalyst residues on the AC dielectric properties of polypropylene was systematically investigated. Two commercial-grade PP resins were synthesized using large-scale polymerization reactors: a standard-residue resin and a low-residue counterpart produced using a modified catalyst system designed to minimize residual species. To isolate the effect of catalyst purity, both materials were compounded with identical additive packages and processed under identical conditions prior to electrical characterization.

The experimental results indicate a correlation between catalyst residue content and dielectric performance. While the relative permittivity of the two materials remained essentially unchanged due to their comparable molecular structure and density, the dielectric loss tangent of the low-residue polypropylene showed a substantial reduction compared with the standard grade, particularly at elevated temperatures. This behavior is attributed to the suppression of thermally activated ionic conduction associated with residual catalyst species. In addition, AC breakdown testing demonstrated not only an increase in characteristic breakdown strength but also a notable improvement in Weibull shape parameter, indicating enhanced insulation reliability and reduced statistical variability. These findings underscore the importance of controlling catalyst-derived impurities and support the potential of high-purity polypropylene as a reliable and environmentally sustainable alternative to XLPE for next-generation power cable insulation systems.