Technical Problems Associated with Developing HVDC Converter Stations for Voltages above 600 kV

This paper reviews the technical problems anticipated in the design construction and operation of HVDC converter stations in the voltage range ± 600-1200 kV. It is based on a literature review and discussions with experts from manufacturers and utilities. It concludes that 800 kV is a clearly feasible voltage step with existing knowledge, 1000 kV is practicable with further research effort, but that 1200 kV is unlikely to be economically feasible without a technological breakthrough. The principal problems identified are: 1) The behaviour of external insulation in bad weather, especially in polluted situations 2) Transformer insulation Controlled gas insulation 3) Surge arrester limitations Methods of controlling overvoltages.