Gas insulated transmission lines (GIL): ready for the real world

Gas-insulated transmission lines (GIL) are a further development of the tubular conductor intended for long distances and are especially suitable for connecting conurbations to centers of power supply. They are also as "invisible" as ordinary power cables as well as having a number of other advantages. The first mixed-gas-insulated power transmission line in the world successfully completed its field trials with an endurance test in early 1999. The most important aim in the further development of tubular conductors for long distance power transmission was to reduce costs so that they can be used economically over distances of up to several kilometers. This has now been achieved. The system costs of the gas-insulated transmission lines developed by Siemens are now only a factor of 8 or 10 above those of overhead power lines down from a factor of 30. Now the GIL has reached the order of magnitude to be accepted by utilities if an overhead line must be brought underground. The basis of this reduction in costs was the adaptation of installation techniques similar to those used in laying pipelines. The simplification and standardization of individual components, and the use of a sulfur hexafluoride (SF/sub 6/) and nitrogen (N/sub 2/) gas mixture. In the past, pure SF/sub 6/ has been the most widely used gas for tubular conductors, most of which have been incorporated into substations.