Thermal Assessment of an Air-Filled Surface Trough for 400 kV Cables

Using a full-scale trough, temperature measurements around the cables and inside the trough yield an empirical formula for heat transfer from the central cable. This, together with assumed solar and wind quantities at the ground surface and the effective thermal resistance of the trough via the soil to ambient, yields the thermal resistance of the cable surface to ambient. Calculation of the current rating of the cables yields a value below the normal buried rating. It is concluded that the air-filled trough has no advantage over the sand-filled variety.