978-1-6654-1221-6/21/$31.00 ©2021 IEEE Thermal Behaviour of Natural Ester Based Oil Used in Distribution Transformers Melissa I. Torregroza-Rosas Universidade Federal de Itajubá UNIFEI Mestrado em Engenharia Elétrica Itajubá (MG), Brazil melissatorregrozarosas@gmail.com Tales Cleber Pimenta Universidade Federal de Itajubá UNIFEI Itajubá (MG), Brazil Tales@unifei.edu.br Edgardo Arrieta-Martínez Heliuz SAS Barranquilla, Colombia earrieta@heliuz.co Jorge I. Silva-Ortega Universidad de la Costa, CUC. Departamento de Energía Barranquilla, Colombia Jsilva6@cuc.edu.co Abstract— This work compares the thermal behavior of a distribution transformer when using as dielectric liquid a mineral oil or natural esters. These cases have been analyzed using Finite Elements Method (FEM) at the software COMSOL Multiphysics® with a 3D-symmetrical model through the Heat Transfer in Solid module. The results of simulations show a higher values of maximum temperature in mineral oil submerged transformer than in natural ester, for the same operational conditions. Keywords—Natural Ester, Finite Elements Method (FEM), COMSOL Multiphysics®, Heat Transfer in Solid interface. I. INTRODUCTION As one of the core equipment of the power system, the safety and stability of a transformer is significant to the reliability and economy of the power system [1]. One of the most critical issues regarding the machine lifetime is the operating temperature range, this value affects directly to the degradation of transformer insulation system, which has always been considered “The weakness link” to the electrical machines. Therefore is required to add a cooling system inside the transformer. For small distribution transformer it is enough with ambient air but for large power transformers more efficient cooling is needed to ensure their performance [2]. Since 1892, the mineral oil (MO) is widely used as a cooling and dielectric medium, due to experiments that proved a better performance compared to other options, included vegetal oils. In addition, no other substance demonstrated be commercially successful. However, during the 70s were discovered the adverse health effects of PCB (Polychlorinated Biphenyls), which cobinated with the “Oil crisis”, obligated to the industry to explore alternatives to the mineral oil [3]. In this context, reappears the interest about natural esters based oils resulting in a patent registration in September 1999 by ABB, commercially known as BIOTEMP®. As mineral oil substitute in transformers, natural ester (NE) based oils had demonstrated several advantages, among which are [4] [5] [6] [7] [8]:  Environmental safety: According EPA (Environmental Protection Agency) vegetal oils are categorized like “Finally biodegradable” and “Easily biodegradable”. Additionally, for the aquatic toxicity, after to be retired oxidation inhibitor agent, results show “Zero toxicity” for the standard test.  More safety for people and physical facilities: Natural Esters have fire and flash point higher than mineral oils, making them liquids less inflammable for be used in transformers, according to Factory Mutual and Underwriters Laboratories.  Less aging and more useful life of insulation paper: Due to a superior saturation water boundary, between 5 to 8 times higher than mineral oils, solid isolation (cellulose paper) contents less humidity.  Higher thermal conductivity: This represents a faster heat transfer to the vegetal oil for be dissipated to environment. A higher thermal conductivity has been documented in the literature related, with thermal evaluation of natural esters, as higher oil temperature rise in transformers immersed in vegetable oil. This factor would suggest a lower useful lifespan than for transformers with mineral oil; however, given that paper degrades much slower in the presence of vegetable oil, due to a higher saturation water boundary, these transformers could have an equal or greater useful lifetime than those immersed in mineral oil [9]. The Finite Element Method FEM is a tool widely used to solve engineering and physics problems; it has taken a lot of recognition in recent years. This is due to the high degree of accuracy that this method is capable of achieving, as well as its capacity for modeling complex systems. This capacity made FEM a powerful tool than used with the correct parameters could save the costs of assembly of many experiments. Several authors has used the FEM for the thermal evaluation of transformers isolated with NE [10] [11]. The most analyzed topic related to this field are Hot Spots and Hotter Spots Temperature Locations, Temperature Distribution and Maximum Values (Oil, tank and paper), Thermal Behavior Effects on Isolation Paper Aging and others. In those cases, the MEF demonstrated high effectiveness to get results with low margin of error, good performance for simulate real situations and easy handling for the researchers. 2021 IEEE XXVIII International Conference on Electronics, Electrical Engineering and Computing (INTERCON) | 978-1-6654-1221-6/21/$31.00 ©2021 IEEE | DOI: 10.1109/INTERCON52678.2021.9532650 Authorized licensed use limited to: Corporacion Universitaria de la Costa. Downloaded on September 26,2021 at 16:53:52 UTC from IEEE Xplore. Restrictions apply.