Can high-voltage DC (HVDC) transmission offer advantages?
17.1 Yes, for very long distances. Undersea cables are DC, which avoids the problems of reactive power. There is an underground DC “Greenconnector” project between Italy and Switzerland. DC transmission lines need expensive (and large) converter stations at each end, so they tend to be for specialised use. There are overhead DC lines (on pylons), e.g. in Australia connecting to the Basslink undersea project, but residents object to them as they do to AC lines. 17.2 HVDC lines would create no AC EMFs, about which there are health concerns. The DC fields are considered more benign. 17.3 Recent communications with industry suggest that costs for HVDC cables depend strongly on the required capacity, as a result of costs for the converter stations which can be over 50 million each for capacity up to about 1,000 MW. For such a capacity, the cost would be around 0.4 million per km for overhead line (HVDC-OHL) or about 1.5 million per km underground (HVDC-UGC), in addition to the converter sta
