What are the advantages of HVDC transmission over HVAC?

HVDC advantages include: lower losses for long distances (break-even around 500-800km overhead, 50km submarine), no reactive power issues or skin effect, asynchronous interconnection capability (connect grids at different frequencies), precise power flow control, smaller right-of-way (two conductors vs three), and no stability distance limit. Disadvantages are expensive converter stations and difficulty in tapping intermediate points. HVDC is used for long-distance bulk power and submarine cables.