Transient temperature rise of tunnel for power cables

A computation method has been developed for predicting the temperature of a tunnel during an arbitrary year (e.g. 30 years hence), taking into account the thermal capacity of the soil and the annual load variation. The results showed that, if the depth of burial of the tunnel is great, the thermal time constant for soil temperature elevation is large, and thus 30 years or more are required to reach saturation. Moreover, if the annual load variation is not taken into account, then a considerable overestimate may occur. In order to ascertain the validity of these theoretical results, measurements along an actual power line were performed, and the results so obtained agree well with the theoretical values for both short (approximately one week) and long (approximately three years) periods