Development of calculation system for transient temperature rise of power cables in protection pipe

The allowable current of an underground power cable system is evaluated based on the temperature rise of a conductor. Generally the steady allowable current is evaluated based on saturated temperature rise, and the short-time allowable current is evaluated based on transient heat conduction only in one cable with approximate time constants. There is a relatively large tolerance. Therefore, an evaluation system for transient temperature rise of power cables in a protection pipe with actual transient load change is strongly required. It is effective if temperature rises of a protection pipe and a conductor in a cable are calculated individually and then subsequently added because heat capacity of soil is very large and that of the cable itself is relatively small. In this study calculation programs for a protection pipe and cable are developed and with these programs the evaluation system for underground power cable temperature is proposed. With this system, tolerance of the conventional method is evaluated and validity of this system is presented.