A three-level temperature curve for power cables aging failure rate estimation incorporating load cycling Mojtaba Gilvanejad 1,2 , Hossein Askarian Abyaneh 1 * ,† and Kazem Mazlumi 3 1 Department of Electrical Engineering, Amirkabir University of Technology, 424 Hafez Street, Tehran, 15875-4413, Iran 2 Transmission and Distribution Research Center, Niroo Research Institute, End of Shahid-Dadman Blvd, Shahrak-e-Gharb, Tehran, Iran 3 Electrical Engineering Department, University of Zanjan, Daneshgah Blvd, PO Box 313, Zanjan 45371-38111, Iran SUMMARY Useful lifetime of power cables and related aging failure rates mostly depends on thermal stresses that they experience because of the loss-resulted heat inside the cable in normal or abnormal currents of the network. Knowing the real values of the cable aging failure rate is a key point, and the network operators should enable to estimate the related aging failure rates of their network cables. The already provided methods for cable transient temperature estimation require several different inputs as well as cable installation con- figuration data that are difficult to collect for operators. Hence, in this article, an artificial neural network– based approach is applied for estimation a cable maximum temperature, which serves a certain daily load curve. The artificial neural network only requires four inputs that are easy to provide. An experimental equa- tion is then used for estimating the cable minimum temperature, and finally, a three-level temperature curve is formed for cable aging failure rate estimation. The life fractions lost during each level of the predicted temperature curve are evaluated by resorting to an already existing combined electrothermal life model held for cable insulation. This method uses the life model and the probabilistic failure model to predict the failure rate of power cables for a future period. The results show that failure rate estimations are in good accordance with exact results, remarking that the estimated three-level stepwise curve of cable temperature is a good approximation of cable thermal transients during cyclic loads. Copyright © 2012 John Wiley & Sons, Ltd. key words: power cable; three-level temperature curve; aging failure rate; load cycling 1. INTRODUCTION In the competitive and uncertain context of the deregulated electricity market, distribution utilities are pushed on one hand towards the improvement of power quality and on the other hand towards the reduction of costs. In this respect, a decrease in the expenses associated with the maintenance and replacement of failed components is particularly desirable because it can be accomplished through a reduction in component failure rate, which also has a positive effect on power quality [1]. The failure rates of components are not constant values, as they depend on various independent factors such as intrinsic factors (age of the equipment, manufacturing defects and size of conductors), external factors (plant growth, animals and weather) and human error factors (vehicular accidents, repair crew mistakes and vandalism) [2]. In the case of high voltage alternating current (HVAC) cables, failure rate reduction is made possible in principle by the fact that they are usually designed neglecting load cycles and assuming conserva- tively the temperature at the conductor–insulation interface to be constant and equal to its rated (design) value, that is, the maximum permissible temperature for continuous operation of the chosen insulation. Hence, the life estimation of HV power cables at the design stage is commonly performed irrespectively *Correspondence to: Hossein Askarian Abyaneh, Department of Electrical Engineering, Amirkabir University of Technology, 424 Hafez Street, PO Box 15875-4413, Tehran, Iran. † E-mail: askarian@aut.ac.ir Copyright © 2012 John Wiley & Sons, Ltd. INTERNATIONAL TRANSACTIONS ON ELECTRICAL ENERGY SYSTEMS Int. Trans. Electr. Energ. Syst. 2013; 23:853–866 Published online 16 July 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/etep.1664