Cable tunnels are widely used in large and medium-sized cities along with the continuous increase of urban power load and the economic and environmental development demand of power system.The adjacent magneticthermal effect is one of the most important factors affecting the permitted current rating of power cable lines.In order to investigate the influence of cluster laying on cable current rating quantitatively

this paper presents case studies of110 kV and 220 kV cable lines

which are laid in two typical arrangements of flat and trefoil formations.The permitted current ratings of cable clusters are calculated under different tunnel temperature

cable phase spacing

circuit spacing and circuit number.It is shown that ventilation affects the temperature distribution in the tunnel remarkably

and it is the most influential factor for cable’s permitted current rating.Three single-core cables in trefoil formation will be less influenced by other factors than those in flat formation

so the trefoil formation is preferred.Three phases of single-core cables in untouching trefoil formation will have a higher permitted current rating than those in touching trefoil formation

but the untouching trefoil formation occupies more space.For installation of a multi-circuit cluster in tunnel

the spacing design must strictly obey the regulations

and about 15 percent current rating reduction should be considered for the low or medium voltage power cables in cluster laying.