Study on the contamination rate of mineral oil in natural-ester retrofilled transformers Articles uri icon

publication date

  • August 2023

start page

  • 1641

end page

  • 1648


  • 4


  • 30

International Standard Serial Number (ISSN)

  • 1070-9878

Electronic International Standard Serial Number (EISSN)

  • 1558-4135


  • The 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.


  • Electronics
  • Industrial Engineering


  • contamination rate; dielectric response; iodine index; kraft paper; natural ester (ne); oil-paper insulation; relative permittivity; retrofilled transformer