Novel Grafted Additives for Space Charge Mitigation in Extruded HVDC Cable Insulation

The need for HVDC systems is increasing worldwide. For extruded HVDC cables, the need for increasing both the operation voltage and temperature necessitates the development of novel insulation materials, e.g. polypropylene (PP) based blends. A crucial part in the development of future HVDC cable insulation is the mitigation of space charge accumulation under high field stresses. One promising method for this could be polar additivation of the insulation matrix. The aim of this paper is to study the influence of polymeric grafted additives on the material and dielectric properties of PP based insulation materials. With low concentrations of iPP additives grafted with maleic anhydride and polar amines the relative change in total TSDC charge is in the range of -13 to -70% in comparison to the PP blend reference. With higher concentrations (up to 2.5 wt-%), the impact can be even higher. According to the space charge measurements made by utilizing PEA method, the field enhancement factors (FEF) for some of the studied additives are below 10%. The results indicate that the additives can be used as space charge mitigating additives in extruded PP-based HVDC cable insulation. These additives offer promising performance for further HVDC insulation development. The most promising additives will be taken to pilotscale level and extended dielectric characterization for further HVDC insulation material development and optimizations.