Effect of Heat Exchange Transient Conditions With Moving Water-Air Interface on Space Charge Accumulation in Undersea HVdc Cables

Abstract

Power 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 issue to be considered in the design stage and during the operating conditions. The separation of space charge is due to several factors including the dependence on 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 in an HVDC cable immersed partly in water and partly in air. Due to the high difference in thermal conductivity between the conductor and the insulation, the axial heat conduction near the interface can play an important role in locally increasing the thermal gradient. The main goal of this research is to investigate the impact of this phenomenon on the electric field distribution. Moving cable-water-air interface is considered, with time varying sinusoidal law. 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.