Space charge accumulation in undersea HVDC cables as function of heat exchange conditions at the boundaries – water-air interface

Transmission lines with undersea HVDC cables are an interesting technological solution for the supply of electrical energy to islands. The accumulation of space charge inside the dielectric layer of a HVDC cable is one of the most important element to consider in its design and during operation. The formation of space charge is due to various factors including the high dependence on the temperature of the electrical conductivity of the insulation and the establishment of a thermal gradient under load conditions. This research is focused on the space charge accumulation phenomenon around a section of a HVDC cable half dipped in water and half in air. Due to the high difference in thermal conductivity between the conductor and the insulation, the axial conduction of heat near the interface can play an important role in locally increasing the thermal gradient. The main goal of this research is to evaluate the impact of this phenomenon in the alteration of the electric field distribution. This study has been carried out by means of a 2-D thermal and electrical model of a HVDC cable developed in time domain in Matlab®. The results show the establishment of an electrical field peak near the water-air interface due to an increased thermal gradient in this area.