THERMAL ANALYSIS OF HIGH VOLTAGE UNDERGROUND POWER CABLES

Abstract

• In case of flat configuration of buried cables, the temperature of the middle cable is higher than the temperature of other two side cable. when the 3 cables touching each other the temperature of the middle conductor is 95.4 oC and the temperature of the side cable’s conductor is 92.5 oC. Calculations are done at spacing equals to 0.5 m, it is found that the temperature of the middle cable sheath reaches to 82.31 oC while the side one temperature is 78.8 oC. • In case of trefoil configuration, the temperature of the upper one is higher than the others, For Al conductor buried at 1.2m depth, the temperature of the upper cable is 100.8oC compared to the lower one which is 99.3 oC. • As the soil thermal resistivity increases the current carrying capacity of the cable decreases as the heat dissipation of the cable become more difficult. • Increasing cable laying depth, decreases the current carrying capacity of the cable. • As the spacing between the cables increase, the current carrying capacity of the cables will increase, For Al conductor the cable capacity is 842 A at 0.3 m spacing comparing with 950 A at 1.5m spacing between each two conductors. • Increasing of the ambient temperature has significant influence on the cable rating. • The dry soil resistivity decreases the cable rating regardless of the soil composition. Current carrying capacity of the underground cable at 1.2 0C.m/W thermal resistivity is 780 A for Al conductor and 960 A for Cu conductor. These values are increased to 920 A and 1250 A when the back-fill soil is reduced to 0.5 0C.m/W at wet soil. • Dynamic thermal model using IEC 60853-2 is used to investigate the thermal performance of the 220 kV cable.