Analysis of the effects of load cycling and thermal transients on polymer-insulated HVAC cable life

In the paper, a procedure for power cable life estimation in the presence of load cycles, accounting also for thermal transients, is proposed. Such procedure is based on Miner´s approach to life inference in the presence of time-varying stresses. Life fractions lost during each portion of a load cycle are calculated resorting to combined electrothermal life models holding for polymer-insulated cables subjected to voltage and temperature. Thermal transients that take place within cable thickness as load changes are evaluated by a simplified analytical expression for the temperature response of cable layers to current steps. The procedure is applied to high voltage ac EPR-insulated cables, subjected to a simple daily load cycle. The application shows that life is very sensitive to load cycles, as well as to thermal transients, that should be thus considered for accurate life inference of high voltage cables in the presence of load cycles.