Steady-state thermal analysis of a 400 kV-cable through joint

Temperature distributions in a 400kV through joint and associated cable, as used in directly buried transmission circuits, are obtained for natural cooling and various forms of artificial cooling. The joint, rather than the cable, is seen to limit the current rating for all forms of cooling. With the higher ratings resulting from artificial cooling, the joint limitation becomes more severe. In all the cases considered, including the use of water jackets around the glass-fibre box surrounding the joint, the conductor temperature at the centre of the joint is above 85°C when the rating is decided by the cable alone. A thermal resistivity of the soil of 120degCcm/W, and a maximum coolant-temperature rise of 20degC are assumed. Investigation into joint power factors in the. range 0.004¿0.008 shows a large temperature dependence with natural cooling, but small dependence with artificial cooling.