Current rating of an airduct transmission line

A possible design is described for a 230 kV duct line incorporating three tubular conductors supported in a duct 2.5 m in diameter with air at atmospheric pressure as the dielectric. Thermal models have been developed to facilitate the computation of temperature and current rating. With the duct line completely buried, it is found that the duct/soil-interface temperature is the limiting feature on current-carrying capacity, whereas, with the duct water cooled, or situated above the ground surface, the conductor temperature is limiting. For buried systems, the rating is only adequate, but with above-ground installation or intense water cooling of the buried duct, currents of the order of 10000 A may be achieved.