Temperature Evaluation of Protection Pipe with Diurnal Load Variation

The allowable current of an underground power cable system is evaluated on the basis of the temperature rise of a conductor. Generally, the steady allowable current is evaluated on the basis of saturated temperature rise. Because there is a large difference between the time constant of heat conduction in a cable and that in soil, loss factor (L_f) is generally used. However, when an allowable current is calculated using L_f, there is a possibility of overestimation, such as in a shallow laying case. We previously developed programs for evaluating the transient temperature rise of power cables in a protection pipe with actual transient load change. Using these programs, we can evaluate the overestimation due to L_f in this study. Among the cases we assumed to be normal, there occurred 5°C of overheating of a protection pipe and 3°C of overheating of a conductor.