Effect of Additive Concentration on the Dielectric Properties of Extruded HVDC Cable Insulation

In the future HVDC networks, the operational fields and temperature will also set new challenges for the insulation materials. One solution for the next-generation HVDC cable insulation material could be polypropylene (PP) based blends instead of state-of-the-art cross-linked polyethylene (XLPE). Under high DC field stress, mitigation of space charge accumulation in extruded HVDC cables is a necessity. A promising method for space charge mitigation in cable insulation material could be adding grafted additives into insulation matrix, e.g. maleic anhydride grafted PP (PP-g-MAH). This paper studies the effects of different concentrations (0.5 wt-% to 8.0 wt-%) of grafted maleic anhydride in PP cable insulation material by investigating their material and dielectric properties. No significant changes in morphological characteristics are observed with PP g MAH contents up to 8.0 wt-%. According to TSDC and PEA measurements, effective space charge mitigation is not yet achieved at 0.5 wt-%, whereas the optimal concentration could be in the range of 1.0-5.0 wt -%. Additives increase the short-term DC breakdown strength (BDS) in comparison to the reference material, but the concentration does not have significant effect on the BDS. However, the additivated PP blends have remarkably higher BDS than DC XLPE.