High Voltage Direct Current (HVDC) transmission lines use direct current as opposed to the alternating current which is used by the HVAC transmission lines. HVDC is used for bulk transfer of electricity across long distances and for direct point to point applications. Recently, it has begun to be used for shorter distances. HVDC voltages are in the 100kV to 800 kV range.
In comparison to HVAC, HVDC is more efficient and has 30 - 50% less line losses over long distances than HVAC. HVDC transmission lines do not require substations like HVAC transmission systems do, instead an HVDC converter substation is needed at each end of the transmission line.
In a typical overhead transmission line installation, HVDC uses a narrower right of way and smaller towers. Additionally HVDC cable can be more easily buried than HVAC and can be installed under water.
When comparing costs between HVDC and HVAC a 2022 feasibility study done by NextGen Highways found that buried HVDC is cost competitive to HVAC. The DOE notes that " converter stations required for HVDC deployment are expensive, however, with a breakeven distance of approximately 37 miles for submarine lines and 124 miles for overhead lines "
