Reliability analysis and comparison of long-distance HVAC and HVDC power transmission lines

Double-circuit HVDC overhead power transmission lines rated at ±500 to 750 kV with self-supporting towers and a long current-boosting capacity are capable to assure a maximum performance coefficient K_p of 0.996 (per 1000 km) in terms of electric energy transmitted. Much promise for densely populated areas is offered by quadrupolar transmission lines, i.e. those with double-circuit towers, calling for a minimum-width right-of-way. HVAC lines of a 500 to 1150 kV rating are inferior to their ±500-750 kV counterparts as regards maneuverability, right-of-way width and performance coefficient (K_p = 0.98-0.99), because the line must be de-energized each time a phase is damaged.