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The use of ultra high voltage direct current (UHVDC), i.e. voltages above the highest in use, 600 kV, has been found to be economically attractive for power blocks up to 6400 MW for distances above 1000 km. Several utilities in China, India and Brazil are at present planning for the use of 800 kV as transmission voltage. In order to meet the demands, ABB has been running an R&D program with the goal to develop and test equipment needed for 800 kV HVDC. The R&D work has focused on equipment connected to the pole voltage, with special attention to converter transformers, bushings and external insulation. Due to the large amount of power transmitted by these transmission systems, special attention must be given to reliability and availability. Thus a thorough review of equipment, station layout, control and protection and auxiliary systems has been done.