Citation: Yaqoob, Y.; Marzuki, A.; Lai, C.-M.; Teh, J. Fuzzy Dynamic Thermal Rating System-Based Thermal Aging Model for Transmission Lines. Energies 2022, 15, 4395. https://doi.org/10.3390/ en15124395 Academic Editor: Gianfranco Chicco Received: 5 May 2022 Accepted: 8 June 2022 Published: 16 June 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article Fuzzy Dynamic Thermal Rating System-Based Thermal Aging Model for Transmission Lines Yasir Yaqoob 1 , Arjuna Marzuki 2, * , Ching-Ming Lai 3 and Jiashen Teh 1, * 1 School of Electrical and Electronic Engineering, Universiti Sains Malaysia (USM), Nibong Tebal 14300, Malaysia; mianyasir888@gmail.com 2 School of Science and Technology, Wawasan Open University, George Town 10050, Malaysia 3 Department of Electrical Engineering, National Chung Hsing University (NCHU), 145 Xing Da Road, South District, Taichung 402, Taiwan; pecmlai@gmail.com * Correspondence: jiashenteh@usm.my (J.T.); arjunam@wou.edu.my (A.M.) Abstract: Electricity demand has surged over the last several years and will persist in the future. Increased transmission loads cause transmission lines to operate much closer to their security limits, leading to thermal and mechanical stress and thus affecting the transmission reliability and thermal aging. Accordingly, monitoring the conductor temperature over time is critical to identifying power transmission networks that may need extra attention and perhaps maintenance. This paper presents a fuzzy thermal aging model for transmission lines equipped with a fuzzy dynamic thermal rating system based on the IEEE 738 standard. In this framework, the ampacity of the transmission line was calculated. The conductor temperature was computed with the back-calculation method by considering the fully loaded transmission line. The estimated conductor temperature was employed to determine the corresponding conductor fuzzy loss of tensile strength, i.e., the fuzzy annealing degree of the conductor based on the Harvey model. Additionally, a tensile strength loss cost profile is provided. Simulation and numerical results indicate that the proposed framework is robust against various operating conditions of the parameters considered in the study and provides crucial information for managing transmission assets and transmission network operation. Keywords: fuzzy dynamic thermal rating systems; transmission line; thermal aging; annealing; loss of tensile strength 1. Introduction The electricity demand is increasing faster than the transmission capacity. Thus, to meet the energy demand, electric power networks are continuously evolving [1]. Power networks can be improved by integrating more renewable power sources without com- promising overhead conductors. Power utilities need to adopt new and flexible network- enhancement approaches that improve power transfer capabilities while avoiding or defer- ring investments in major assets [2]. The objective of such developments is to transform conventional power networks into smart systems that can accommodate various types of ever-growing energy demands. Considering the aforementioned scenarios, realizing the maximum capacity of existing transmission lines is one of the cost-effective and sustainable approaches to improving the transfer capacity of transmission systems [3]. Therefore, dynamic thermal rating (DTR) is recognized as one of the most promising and effective solutions for congested transmission lines [4]. It improves the overall reliability and provides greater flexibility during load shedding [5,6]. Following the implementation of DTR with demand-side management, the load demand transforms from fixed to dynamic and gains active response capacity. This allows the power system and power equipment to operate safely by controlling flexible resources on the load side [1,7]. Dynamic thermal rating with storage technologies and management systems could also improve the reliability and utilization of electric Energies 2022, 15, 4395. https://doi.org/10.3390/en15124395 https://www.mdpi.com/journal/energies