While HVAC is the traditional and most common method for power transmission over shorter distances, HVDC is increasingly favored for long-distance and submarine power transmission. Here are the main differences:

• Efficiency and Losses: HVDC systems have significantly lower power losses over long distances, making them more efficient. This is because DC transmission only involves active power, whereas AC transmission includes both active and reactive power, which contributes to higher losses.

• Number of Conductors: A three-phase HVAC system requires three conductors, while a bipolar HVDC system requires only two conductors. This reduces the amount of conductor material needed and simplifies tower design.

• Asynchronous Connections: HVDC links can connect two AC power grids that are not synchronized or have different frequencies, which is not possible with HVAC. This is a crucial advantage for integrating diverse regional grids.

• Right-of-Way (ROW): HVDC lines require a narrower ROW compared to equivalent HVAC lines, which is beneficial in densely populated or environmentally sensitive areas.

• Cost: While HVDC converter stations at each end of the line are expensive, the lower cost of the transmission line itself over long distances can make the total project cost lower than an HVAC alternative.