Physical Limits on HVDC Voltage
There appears to be a 3200 or 3400km 1.1MV link (??? +/- 1.1 MV?) capable of carrying 12GW, in China, recently commissioned. Mentioned on this Wiki page : scroll down to Zhundong-Wannan.

This is a significant distance because it could (just : Shannon to Gander) span the Atlantic, or potentially carry near-peak generation from one timezone to cover peak consumption in another, which might prove at least as lucrative as a north-south link carrying power from a sunny climate to a cloudier one.

The first graph on this page suggests that a +/-400kv DC link carrying 1.2 GW could operate around 90% efficiency up to 1500 km, so 80% for a larger capacity 3000km link would seem conservative.

Press release on one of the "transformers" used here.

To carry 1 TW, you would need 80 of these links, or perhaps, fewer of whatever comes next.