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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 Kp 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 (Kp = 0.98-0.99), because the line must be de-energized each time a phase is damaged.