Development of water pipe cooling system for power cables in tunnels

A full-size test line was constructed to study the water pipe cooling system for a bulk-power transmission line installed in a tunnel. Based on the test data and their analysis, a technique for designing the system has been established. The results have indicated an effective layout of the cooling pipes in the tunnel, and have validated the accuracy of the computer models to determine thermal characteristics of the tunnel system. An efficient control method to operate the cooling system according to the load changes of the cables was developed. The chosen layout is shown to be more effective than the dispersed layout because it accelerates the air convection and makes the air temperature more uniform. Furthermore, the thermal convection resistance between the tunnel wall and the air is reduced. It was also verified that the air temperature distribution along the vertical shaft could be predicted by thermal convection analysis. This cooling system is scheduled to be applied to a 154 kV power cable line in 1990