HVDC is much better than anything else for long distance transmission. But the gain is because of the high voltage part, not the DC one.
The one thing that pushes people into DC is that phase synchronization is a huge problem on high voltage. So, for indirect reasons, DC gets to be the winner right now.
“But the gain is because of the high voltage part, not the DC one.“
What do you mean by that? My understanding is the HVDC lines are still lower V than an AC line (the Soviet even had 500lV lines), and therefore DCs advantages are no coupling to ground, no Z reflections and ability to connect to any grid.
> Most HVDC links use voltages between 100 kV and 800 kV.
By contrast, high voltage AC lines are around 10kV to (very rarely) 100kV. AC presents some more problems to high voltage than just phase synchronization (so even two point lines are DC), but the gains come mostly from the HV part, and AC is avoided because it doesn't play well with HV, reverting the gains.
The one thing that pushes people into DC is that phase synchronization is a huge problem on high voltage. So, for indirect reasons, DC gets to be the winner right now.