For long distance bulk electrical power transmission, HVDC transmission is far superior technology to AC systems for several reasons:
• the efficiency of HVDC is only limited by the design of the cable (both conductor and insulator) and the operating temperature.
• HVDC transmission can achieve very low transmission losses, using generated electrical energy more efficiently and making it very economical;
• for submarine power cables, HVDC avoids the heavy currents required to charge and discharge the cable capacitance each cycle;
• HVDC allows asynchronous AC grids or AC grids with different frequencies to be connected, improving the stability and economy of each grid;
• the power flow through an HVDC cable is fully controllable in either direction and has inherent overload capability that can be actively used for peak supply. This facilitates effective stabilisation of a network against disturbances due to rapid changes in power; and
• HVDC (particularly XLPE) cables are unobtrusive and environmentally friendly.