The temperature rising characteristics of 275 kV cables and GILs in tunnels

Chubu Electric has a scheme to provide cooling systems for 275 kV cables and GILs in underground tunnels to cope with the increment of their transmission capacities in the years ahead. Various heat dissipation constants, such as thermal resistances, are used in designing the cooling systems. Since the thermal constants differ from route to route, it is important to grasp proper figures of the constants and utilize those in actual design to obtain appropriate systems. A study was conducted to offer an effective tool to determine temperatures in tunnels accurately by optimizing constants for a calculation model through analyzing chronological data on temperature-rise characteristics in some of the tunnels in service. An attempt was also made to clarify the air-cooling effects by natural ventilation in tunnels so that obtaining appropriated transmission capacities of the service facilities considering the effects became possible. This paper reports on the results of our study on these topics.