High Voltage Direct Current (HVDC) underground and submarine cables transport high power loads over long distances with minimal losses. They have been in commercial use since the 1950’s.
Today, HVDC land and submarine cables can carry medium and high power (100 MW up to 1,000 MW) with voltages up to +/- 600 kV over distances above 50 km. They are a core technology to build Europe´s backbone power transmission lines, both on land and out at sea.
HVDC transmission has mainly been used in submarine applications, either connecting offshore wind farms to land or transmitting high electrical power over long distance through the sea. From 1996 to 2015 some 8,000 km of high and extra-high voltage DC submarine cables have been installed globally. Looking into the future, notably submarine interconnectors will play a crucial role in creating Europe´s extra high voltage power grids.
Today, HVDC cables are increasingly used for land transmission projects as higher power loads need to be transported over long distances towards centres of power consumption. When compared with AC systems fewer cables need to be used, HVDC underground cables benefit from narrower trenches both during construction and operation. HVDC underground cables are compatible with HVDC overhead technology and can be combined in sensitive areas.
Today, two HVDC cable technologies are installed:
- Single core mass impregnated or self-contained fluid filled (SCFF) cables:
|This type of cable is currently the most used. It has been in service for more than 40 years, has proven highly reliable and can be provided by European manufacturers at voltages up to +/- 500 kV and 1400 A DC which corresponds to a maximum pole rating of 660 MW (in service) and bipole rating of 1320 MW. Conductor sizes are typically up to 2500 mm2.|
- Cross linked polyethylene (XLPE) cables:
|XLPE cables are only used in Voltage Source Converters applications that allow to reverse the power flow without reversing the polarity.
To date this technology is in service at voltages up to +/- 320 kV and 800 MW up to 1000 MW, with voltages up to +/- 600 kV now qualified for use.
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