LEC HOME > HVDC Technology


HVDC electricity transmission is a proven technology with successful projects in operation around the world. Although the vast majority of power is transmitted via high-voltage alternating current (AC) lines, there are applications and situations where HVDC technology is preferred or even required. HVDC systems provide unique benefits and solutions in specialized circumstances, including underwater transmission applications such as the Lake Erie Connector.


A high-voltage direct current (HVDC) transmission system consists primarily of a converter station where high-voltage alternating current from the existing transmission system is converted to high-voltage direct current, transmission cables that connect the converter stations and transmit the HVDC power, and a converter station on the other end of the transmission cables that converts the power from direct current to alternating current for delivery back into the grid.

Electricity transmitted in this fashion can be moved in either direction and precisely controlled. HVDC cables can traverse long distances and may be installed overhead, underground, in water, or buried in lake or ocean beds.


  • Cables longer than approximately 25 miles (40 km) usually require HVDC transmission because inductive and capacitive elements of AC cables cause resistance and losses, limiting their maximum useful length.
  • HVDC lines have significantly lower losses than comparable AC lines.
  • HVDC transmission systems can move considerably more power than an AC system over the same size line.
  • HVDC systems help prevent the transmission of faults between connected AC grids and can serve as a system “firewall” against cascading faults.
  • Higher efficiency and lower losses reduce the total amount of power that must be generated. For an HVDC link with submarine cables, such as the Lake Erie Connector, there will be an energy loss of less than 3% in total, including cable and converter station losses.


Demand for HVDC transmission is increasingly markedly. In the past forty years, HVDC transmission links with a total capacity of 100 gigawatts (equivalent to the capacity of 100 large power plants) were installed. Another 250 gigawatts are projected to be added in this decade.