Direct Current Gas-Insulated Transmission Lines

The technology behind dc power transmissions shows an ever-increasing usage worldwide. Predominantly installed in remote areas, the use of overhead transmission lines is reasonable. Today, dc transmission technology is entering a new era, where rather densely populated areas are being firmly looked at with the desire of nonvisibility transmission lines. DC gas-insulated transmission lines (DC GIL) provide a powerful solution for underground installations. The acclaimed reliability of ac gas-insulated technology has, in turn, further initiated changes in the development of DC GIL. Driven by the German Energy Policy (“Energiewende”), additional north-south power transmission corridors are essential for power transmission of wind energy from the north and photovoltaic from the south, based on the required availability of energy. The DC GIL uses an aluminum conductor and enclosure pipes of high cross sections for rated currents of up to 5000 A and a voltage rating of ±550 kV. The assembly and installation technique of DC GIL is highly automated with the mobile factory and the friction stir welding process for fast and safe jointing of aluminum pipes. Development results and the state of the art are explained in this contribution.