Montero, AndrésGarcía de Burgos, María BelénBurgos Díaz, Juan Carlos2023-10-232023-10-232023-08Montero, A., García, B., & Burgos, J. C. (2023). Study on the contamination rate of mineral oil in Natural-Ester Retrofilled transformers. IEEE Transactions on Dielectrics and Electrical Insulation, 30(4), 1641-1648.1070-9878https://hdl.handle.net/10016/38646The replacement of mineral oil (MO) by ester (retrofilling) is a practice used in power transformers to reduce fire and environmental risk. Although measures are taken to remove traces of oil on the paper, a certain amount of MO remains, which migrates over time. This article presents a study to evaluate the migration of MO from paper to ester using techniques such as the iodine value or the measurement of permittivity and dielectric losses.8eng© 2023 IEEE.Contamination rateDielectric responseIodine indexKraft paperNatural ester (NE)Oil-paper insulationRelative permittivityRetrofilled transformerresearch articleElectrónicaIngeniería Industrialhttps://doi.org/10.1109/TDEI.2023.3298314open access164141648IEEE Transactions on Dielectrics and Electrical Insulation30AR/0000033438