Characterization of Bi-Layer XLPE/EPDM and PP-Blend/EPDM Insulations for HVDC Cable Accessories

This paper focuses on the characterization of different formulations of bi-layer insulation materials Cross-linked Polyethylene (XLPE)/ Ethylene Propylene Diene-Monomer (EPDM) and Polypropylene (PP)-blend/EPDM for High Voltage Direct-current (HVDC) cable accessories including joints and terminations in the framework of the European project HEU NEWGEN. Two principal grades of EPDM terpolymer having low and higher diene content were selected for this study. These were combined with two main HVDC insulation materials, i.e., XLPE and a novel binary polypropylene (PP) random copolymer blend. The combinations yield four bi-layer insulation sets. Results show that XLPE/EPDM (with low diene content) shows continuous and smooth morphological interface, low Thermally stimulated depolarization current (TSDC) peaks, low charging current, and minor space charge accumulation compared to other specimens. However, the mean breakdown strength is significantly reduced in all specimens compared to that of the relevant cable insulation i.e. (XLPE or PP blend).