Green Line will use state-of-the-art high voltage direct current (HVDC) technology used in scores of applications worldwide for many decades. HVDC has long been the preferred technology for moving bulk power over long distances. There are more than 20 underwater cables operating around the world at lengths of up to 360 miles and at water depths of up to 1000 meters (3,300 feet). In the United States, submarine HVDC cable systems are becoming preferred solutions to reliability, portfolio diversity, and resource needs of highly urbanized power markets. The underwater cable systems connect the urban markets with better supplied and more fuel-diverse areas.
HVDC systems have a demonstrated history of very high reliability. The technical characteristics of HVDC technology, including overload capabilities and controlability, can be beneficial to overall system operations and reliability. HVDC lines can improve the stability of AC systems, including increasing the stability of parallel AC lines. They are capable of sharing spinning reserves and supplying peak load power.
An HVDC line is fully controllable in its ability to react quickly to frequency of AC system oscillations and to be controlled independent of AC system variations or in response to AC system conditions. Additional benefits of controllability include reactive power control and support of AC voltage, frequency control, limitation of short circuit current, and transmission at reduced voltage.