Screening of suitable random copolymer polypropylene blends for HVDC cable insulation

Polypropylene (PP) based thermoplastics offer an interesting alternative over cross-linked polyethylene (XLPE) for extruded HVDC cable insulation. In this study, a set of PP random copolymer-based blends are screened by dielectric characterizations (dielectric breakdown strength, space charge, thermally stimulated depolarization current (TSDC), polarization/conductivity) in order to find the most promising blend systems for HVDC cable insulation. Moreover, thermomechanical properties of the PP blends are evaluated to ensure suitability for cable insulation applications. The blends show similar or slightly improved breakdown strength but clearly lower field enhancement factor in space charge measurements when compared to a fully degassed XLPE reference material. The TSDC measurements reveal the possibility to optimize the trapping behavior by varying the blend composition. Thus, the best blend formulations offer promising performance for further HVDC insulation development. After this screening phase, the best blend alternatives will be taken to pilot-scale production level with sample extrusion and for further HVDC insulation material development and optimization.