HVDC power transmission

A high-voltage direct current (HVDC) electric power transmission system uses direct current (DC) for the transmission of electrical power instead of the more common alternating current (AC). It allows efficient electricity transmission across long distances and supports offshore wind farm integration, particularly for large, distant offshore farms where underwater AC cabling is not feasible.
Latest technology developments made smaller HVDC systems economical and introduced advantages such as fully controllable four-quadrant operation for independent, flexible active and reactive power control, flexible AC voltage control, contribution to network fault currents to support weak AC networks and the ability to black-start shut-down networks. Most HVDC links today run on voltages between 320 kV and 800 kV, but there are also installations up to 1100kV with transmission capacity of up to 12GW.