HVDC Power Transmission

In which circumstance, HVDC transmission line has advantages over the HVAC transmission line? Prove that a HVDC line with two conductors transmit same amount of power as transmitted by HVAC line with three conductors of same size. What type of power electronic converter is used in HVDC line and why?

Why is HVDC transmission preferred over HVAC transmission for transport of large power over a long distance? Perform a mathematical analysis to compare power transfer capacities of these lines.

Make a mathematical comparison between HVAC and HVDC lines to justify line conductor saving in HVDC line.