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GIL is installed to provide grid system expansion near the Frankfort Airport, resulting in lower losses than that of cables or overhead lines.
When the transmission system operator (TSO) Amprion (formerly RWE TSO) started planning further development of the extra-highvoltage (EHV) transmission system in the German state of Hesse, the expansion plans for the Frankfurt Airport had to be taken into account. The existing 220-kV overhead transmission lines that are routed in close proximity to the area scheduled for new runway had to be under-grounded for a distance of about 1 km (0.62 miles).
Also forming part of the power-supply system expansion in the Frankfurt region was the plan to convert the existing Kelsterbach transformer substation, situated directly alongside the Autobahn and opposite Frankfurt Airport, from 220 kV to 380 kV for integration into the existing 380-kV transmission network. Amprion had already installed the new 380-kV compact gas-insulated switchgear (GIS). The 380-kV GIS was commissioned in 2007 replacing the 220-kV outdoor installation. Interconnection to the 380-kV system is scheduled for completion by mid-2010.
Amprion, faced with the problem of under-grounding the existing 220-kV transmission line, considered two alternative solutions, conventional underground cables versus gas-insulated line (GIL). The TSO decided to install a GIL that will be connected via bushings on the transmission line terminal tower. The GIL that will be directly buried in a similar manner to installing a pipeline, terminating at the remote end with connection to 380-kV switchgear in Kelsterbach substation.
GIL Technology
The tubular conductor of a GIL, which is of coaxial construction, consists of an aluminum conductor enclosed in an aluminum tube. The tube is filled with an insulating gas mixture consisting of 80%...