Development of polymeric insulating materials for HVDC cables using additives: evidence from a multitude of experiments using different techniques

The main objective of the present paper is to shed more light on the multiple effects of the incorporation of certain additives into LDPE (low density polyethylene) on some of the properties of the doped material relevant to its use as an insulating material for HVDC cables. In the present work, the effects of two additives on DC insulation resistivity, DC breakdown strength, space charge accumulation under DC conditions, polymer structure and morphology were investigated using different techniques. Results of a multitude of experiments are presented and discussed. It is concluded that, although the incorporation of the additives may lead to certain beneficial effects such as the reduction of space charge density in the polymer and the improvement of the dependence of the DC insulation resistivity on temperature and electric field, yet the DC breakdown strength as well as the DC insulation resistivity itself may be reduced. It is also shown that the incorporation of the additives have a significant effect on the morphology of the doped material.