Power: HVDC for the long run: High-voltage de transmission may be a viable alternative to ac transmission for long-distance routes

High-voltage d.c. transmission has proved a promising competitor to conventional extra-high-voltage a.c. transmission under several conditions-where long transmission distances from generation to load centers exist; where asynchronous ties are required; or where underground or underwater cables of considerable length are necessary. Now, developments are underway on higher-voltage overhead lines and cables, higher rated converters, more versatile controls, d.c. breakers, improved sensors, and compact substations that will permit HVDC to play an ever-greater role in future power transmission.