pp 1–12 | Cite as

Quantification of Kraft paper ageing in mineral oil impregnated insulation systems through mechanical characterization

  • I. A. Carrascal
  • C. Fernández-Diego
  • J. A. Casado
  • S. Diego
  • I. Fernández
  • A. Ortiz
Original Paper


Power transformers use Kraft paper, thermally upgraded Kraft and other polymeric papers (ex. Nomex) as the main solid insulation between the winding conductors. Dielectric oil used in transformers as an insulating and cooling fluid typically has an operating temperature range of 60–90 °C. These service temperatures can cause slow degradation of both the oil and the insulating paper winding, with a loss of mechanical and dielectric properties. In this sense, this work analyzes paper degradation through Young’s Modulus, yield stress, rupture strength and strain under ultimate strength. An accelerated thermal ageing of the paper in mineral oil was carried out at temperatures of 110, 130 and 150 °C over different periods of time, in order to obtain information on the kinetics of the ageing degradation of the paper. The evolution of the mechanical properties and micro mechanisms of paper failure are analysed as a function of temperature and ageing time. Finally, the results obtained are compared with the traditional method of degradation analysis, based on the degree of polymerisation measurement.


Kraft paper Power transformer Thermal ageing Degradation Tensile test Degree of polymerisation 



The authors are grateful for the funding received to carry out this work from the State Scientific and Technical Research and Innovation Plan under the DPI2013-43897-P Grant Agreement, financed by the Government of Spain.


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© Springer Science+Business Media B.V., part of Springer Nature 2018

Authors and Affiliations

  1. 1.LADICIM (Laboratory of Materials Science and Engineering), School of Civil EngineeringUniversity of CantabriaSantanderSpain
  2. 2.Electrical and Energy Engineering Department, School of Industrial and Telecomunications EngineeringUniversity of CantabriaSantanderSpain

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