Power transmission with HVDC at voltages above 600 kV

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 6000 MW for distances above 1000 km, Furthermore the use of 800 kV as transmission voltage will be achievable within the near future with a limited amount of development work. None of the AC equipment, auxiliary equipment or control and protection will be affected by the increase of DC voltage. Also most of the DC equipment is easily modified for 800 kV, such as thyristor valves and DC filter capacitors. However, equipment without resistive DC grading, like bushings and converter transformers, need additional R&D and verification. Also station external insulation and line insulation must be carefully considered. In order to meet the demands, ABB has started an R&D program with the goal to develop and test equipment needed for 800 kV HVDC