High-voltage direct-current transmission (HVDC)
Schematic representation of the current conversion stages for high-voltage direct-current transmission (HVDC) from the production point to the medium-voltage grid of the local supply system.
High-voltage direct-current transmission (HVDC) can also be used to span overland routes (overhead lines) with a length of 1,000 km (about 600 miles) or more and undersea routes (submarine cables) from a length of 60 km (about 40 miles) upwards more economically than with alternating current. Direct current has the advantage over alternating current that it does not cause eddy currents and can thus make use of the full cross section of the cable. Heat losses are lower because of the lower resistance for the same cross-section.
Incidentally: Power losses with AC voltage are higher under water than in the air or underground because with deep sea cables it is not possible to use compensating elements (coils, capacitors) against inductive and capacitive losses.
Information and ideas:
What were used as rectifiers in the past?
Using the source: https://de.wikipedia.org/wiki/Hochspannungs-Gleichstrom-%C3%9Cbertragung