Technology
Green Line will deploy state-of-the-art 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.
Examples of other HVDC submarine cable systems deployed in the United States include the 660 MW Neptune Regional Transmission System between New Jersey and Long Island; the 330 MW Cross Sound Cable between Long Island and Connecticut; the 400 MW TransBay Cable across San Francisco Bay, and the 660 MW Hudson Transmission Project now under construction beneath the Hudson River between New Jersey and Manhattan.
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 controlability include reactive power control and support of AC voltage, frequency control, limitation of short circuit current, and transmission at reduced voltage.
ENVIRONMENTALLY BENIGN
The submarine portion of the Green Line cable measures less than a foot in diameter. Thus disturbance of the ocean floor during installation is minimized to a narrow width. Terrestrial segments of Green Line, where overhead lines are most cost-effective, will take advantage of already disturbed existing rights-of-way in order to minimize clearing of new right-of-way. Further, overhead DC lines require a much narrower right-of-way than AC lines carrying the same amount of power.
Converter stations located at the each end of the transmission line are simple low-rise buildings whose exterior can be designed to be compatible with the surrounding area. Neptune’s Sayreville, New Jersey converter station includes a clock tower. Associated electrical switch yards appear to similar to commonly observed electrical substation.