The development of DC+/-500 kV XLPE cable in consideration of the space charge accumulation

This paper introduces the findings of a detailed study on space charge behavior under DC voltage and the development of HVDC cable. Conventionally, Oil-filled (OF) and Mass Impregnated (MI) cables have been applied to DC transmission. However, OF cables have a limited span length due to the need for oil feeding equipment while MI cables have a limited transmission capacity due to their low allowable temperature. XLPE cables are not subject to these limitations, and are widely used for AC transmission. When a conventional AC XLPE is used under DC voltage, its DC withstand characteristic will decline due to space charge accumulation. We have therefore improved the polymer composition and developed a new insulation material for HVDC cable. The recent development of the Pulse-Electro Acoustic method (PEA) has made it possible to measure the space charge distribution in the insulation material. Using this method, electric charge and field distribution can be evaluated quantitatively. It has been possible to reduce the insulation thickness of DC+/-500 kV XLPE cable with an insulation design reflecting the findings of this evaluation. The long-term tests that were performed with the DC+/-500 kV XLPE cable have substantiated its adequate performance capability for practical use.