Answer: High-voltage Alternating Current (HVAC) and High-voltage Direct Current (HVDC) are the two primary methods for transmitting electrical power. The key difference lies in the type of current used.

• HVAC is the more common method, especially for short to medium distances and within established grids. Its infrastructure is simpler and generally less expensive to build initially. However, HVAC systems experience reactive power losses and are less efficient over long distances due to factors like the skin effect and Ferranti effect.

• HVDC is a more efficient solution for long-distance bulk power transmission and for connecting asynchronous grids (grids with different frequencies). While the initial cost of converter stations is higher, HVDC lines have lower transmission losses, require fewer conductors, and can be loaded to their thermal limit without stability issues. This makes HVDC the more economical and efficient choice for very long overhead lines and submarine cables.