Electrical Engineering

, Volume 101, Issue 3, pp 1007–1018 | Cite as

Investigation on thermal ageing impact on dielectric properties of natural ester oil

  • Soumya Thakur
  • R. SarathiEmail author
  • M. G. Danikas
Original Paper


Ester oils are evolving as next-generation transformer insulants, and it is essential to understand their characteristic variation upon thermal ageing. Corona inception voltage reduces with thermally aged ester oil under AC and DC voltages. The UHF signal generated due to corona discharge activity has energy content in the range 0.4–4 GHz. The magnitude and energy content of the UHF signal formed due to corona activity increases with thermally aged oil. Ionic mobility studies are carried out to understand the impact of thermal ageing on polarization and depolarization current, ion concentration, and ionic radius formed in the oil. Thermal ageing of ester oil leads to an increase in the ionic mobility of oil samples along with an increment in the ionic concentration. The conductivity of oil is observed to increase with ageing, accompanied by a reduction in ionic radii. The effect of voltage stress shows enhanced conductivity for thermally aged oil samples. Dielectric response spectroscopy exhibits higher loss and permittivity values for thermally aged oils. The physicochemical analysis shows a gain in viscosity, moisture content and turbidity, and a marginal loss in thermal conductivity due to the formation of new molecular species. UV analysis exhibits a significant redshift in the oil sample aged at a higher temperature.


Natural ester oil Thermal ageing Corona inception voltage Ionic mobility Dielectric response spectroscopy 



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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of Electrical EngineeringIndian Institute of Technology MadrasChennaiIndia
  2. 2.Department of Electrical and Computer Science EngineeringDemocritus University of ThraceXanthiGreece

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