Gas insulated transmission lines-successful underground bulk power transmission for more than 30 years

Gas insulated transmission lines (GIL) are a means of bulk electric power transmission at extra high voltage. GIL consists of tubular aluminium conductors encased in a metallic tube that is filled with a mixture of sulphur hexafluoride and nitrogen gases for electrical insulation. Since the first installation of GIL in 1975, second generation GIL has been developed that is more economically viable and its design optimised both for installation and operation. Where GIL is installed in combination with gas insulated switchgear (GIS), compact solutions can be delivered in order to supply large amounts of electric power to meet the high demand of large cities and industry. These new possibilities can mitigate power flow problems, reduce the risk of failure of electrical transmission systems and enable the installation of optimum solutions regarding technical, economical and environmental aspects.