Effect of Graphene Coating on Space Charge Characteristic of XLPE and Semiconductive Layer at Different Temperatures

DC cross-linked polyethylene (XLPE) power cables are being used recently for HV/EHV applications, the reliability of which is claimed to be significantly affected by space charge accumulation in the insulating material. Many methods have been provided for limiting the injection and accumulation of space charge. In the paper, three kinds of specimens with graphene coating applied on a sandwich composed of XLPE and semiconductive layer were made. Space charge distribution of specimens was measured at 10 kV/mm and 40 kV/mm under room temperature and 60 °C. The measurement results show that positive charges are injected and accumulate in reference XLPE specimen. Negative charge accumulates in XLPE, and the quantity of positive charge injected from anode is significantly reduced, when graphene is coated on the semiconductive side. Little space charge is injected into XLPE coated with graphene, and positive charge accumulates near the interface between XLPE and electrode, which lowers electric field near the anode. Graphene layer introduced deeper trap distribution, thus making difficult negative charge injection from the cathode into XLPE.