Energies 2022, 15, 3408. https://doi.org/10.3390/en15093408 www.mdpi.com/journal/energies Review A Review of Aging Models for Electrical Insulation in Power Cables Maninder Choudhary 1,2, *, Muhammad Shafiq 1 , Ivar Kiitam 1 , Amjad Hussain 3 , Ivo Palu 1 and Paul Taklaja 1 1 Department of Electrical Power Engineering and Mechatronics, Tallinn University of Technology, 12616 Tallinn, Estonia; muhammad.shafiq@taltech.ee (M.S.); ivar.kiitam@taltech.ee (I.K.); ivo.palu@taltech.ee (I.P.); paul.taklaja@taltech.ee (P.T.) 2 Department of Electrical Engineering, Sir Syed University of Engineering and Technology, Karachi 75300, Pakistan 3 Department of Electrical Engineering, American University of Kuwait, Kuwait City 15453, Kuwait; ghussain@auk.edu.kw * Correspondence: machou@taltech.ee Abstract: Electrical insulation is an integral part of power components. The aging of electrical insu- lation is an undeniable fact that limits the operational lifetime of power components. Apart from regular aging, abnormal stresses and the development of defects are real threats because of their contribution in accelerating the aging rate and thereby leading to a premature failure of the power components. Over the decades, various studies have been carried out to understand the aging be- havior of electrical insulation mainly considering electrical and thermal stresses. Similarly, a num- ber of mathematical (aging) models have been developed based on the theoretical and experimental investigations and evidences. However, a dependable formulation of the models that can provide more practical estimation of the insulation degradation profile has not been achieved yet. This paper presents a comprehensive review of the aging models considering single and multistress conditions. Further, the paper discusses possible challenges and barricades averting the conventional models to achieve a suitable accuracy. Finally, suggestions are provided that can be considered to improve the modeling approaches and their performance. Keywords: electrical insulation; power cables; insulation degradation; aging models; partial dis- charge 1. Introduction While air provides the withstanding capability of 3 kV/mm between two conductors, the use of dielectric material increases this withstanding capability to the required voltage levels. In addition to increased electrical breakdown strength, the materials must be able to meet thermal and mechanical performance requirements [1]. Keeping performance in view, the reliability, cost, and environmental impacts are the major considerations during the insulation design of the components [2]. The operational lifetime of the power com- ponents depends on the reliability of the dielectrics. Insulation aging is a looming issue in all types of power components [3]. However, aging becomes more critical at medium or high-voltage operation as compared to low-voltage applications. During a survey of Stockholm, out of 1392 total failures, 263 were due to power transformers, 435 failures were caused by cables, and overhead lines were responsible for 20 failures where electri- cal insulation was considered as a significant cause of these failures [4]. Sudden failure of grid equipment can cause unplanned power outages, leading to huge economic and op- erational loss to customers and utilities. A better understanding of the aging behavior and its progression can help to foresee the incoming failures of critical network components, which in turn reduces the associated losses and interruption of the industrial, commercial, and social processes. Citation: Choudhary, M.; Shafiq, M.; Kiitam, I.; Hussain, A.; Palu, I.; Taklaja, P. A Review of Aging Models for Electrical Insulation in Power Cables. Energies 2022, 15, 3408. https://doi.org/10.3390/ en15093408 Academic Editor: Pawel Rozga Received: 15 April 2022 Accepted: 2 May 2022 Published: 6 May 2022 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims in published maps and institu- tional affiliations. Copyright: © 2022 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (http://crea- tivecommons.org/licenses/by/4.0/).