The coming of Age of HVDC extruded power cables

High voltage DC (HVDC) transmission systems have the potential to transform major electrical grids; they can deliver very high powers over long distances with high efficiency and reliability. Cables are required for subsea and underground systems. Extruded cables - i.e. those with polymeric insulation - have been successfully used in AC applications for 40 years or more and have developed to overcome some of the early problems encountered with water and electrical trees. Such extruded cables have advantages in terms of manufacturing, maintenance and reliability over lapped paper and oil systems. Lessons have been learnt from early experiences with AC cables that may be useful in the development of DC cables. DC cables, however, also provide a new set of insulation challenges, primarily associated with the control of conductivity and space charge, which may lead to very high internal electric fields building up in the insulation. Techniques for measuring space charge and conduction are described and discussed in terms of how they might be used to quantify the state of a HVDC cable. Nanodielectrics are likely to play a part in the development of new materials for their insulation. With an understanding of the key processes to control, techniques to control them and new materials, manufacturers now seem keen to embrace extruded power cable technology for HVDC applications. The paper gives a personal perspective on the development of these cables and links it with the author's research over the last 30 years.