Summary
Isotopic monitoring adds a new dimension to transformer diagnostics by providing information that is not accessible through conventional chemical markers. In this work, we investigate the use of carbon isotopes and CO₂ isotopologue patterns as indicators of paper degradation in oilimmersed transformers and as inputs to predictive models for the degree of polymerisation (DP) of cellulosic insulation.
Read more Read lessAccelerated ageing tests were carried out with mineral insulating oil and thermally upgraded kraft paper (MIO+TUK) at 175, 185 and 195 °C, together with blank mineral oil (MIO) aged without paper. At selected ageing times, paper DP, furanic compounds, dissolved gases and
CO₂ isotopologue ratios were measured. Additional samples of oil and paper were analyzed by accelerator mass spectrometry (AMS) for radiocarbon (¹⁴C) and by isotope ratio mass spectrometry (IRMS) for bulk δ¹³C.
Radiocarbon results clearly separated biogenic from fossil carbon pools: unused and aged mineral oils showed pMC values below 1, whereas TUK paper exhibited values slightly above the modern oxalic acid standard. The aged oil in contact with paper displayed a small but measurable increase in ¹⁴C content, providing direct evidence that part of the carbon dissolved in the oil originates from cellulose. Bulk δ¹³C values further confirmed the isotopic contrast between oil and paper.
Furanic compounds (especially 5-HMF and 2-FAL) showed monotonic, approximately exponential relationships with DP when data from the three temperatures were combined. CO₂ isotopologue ratios (Pmz45/44, 46/44 and 29/28), derived from GC–MS signals at the CO₂ retention time, also evolved systematically with DP, reflecting the growing contribution of biogenic carbon from the degrading paper. Multivariate regression models that combine isotopic ratios, furanic compounds and selected DGA gases were able to reproduce experimental DP values with good accuracy in the range investigated. Paris Session 2026
August 23 to 28
Palais des Congrès, Paris, France
The results demonstrate that radiocarbon, bulk δ¹³C and CO₂ isotopologue patterns provide complementary and physically meaningful information on the involvement of cellulose in transformer degradation. Integrating these isotopic markers with established chemical diagnostics offers a promising route to more reliable assessment of paper condition and remaining life of power transformers.This work is being developed as part of the project number
PD-10737-124/2023 regulated by the National Electricity Agency (ANEEL).
Additional informations
| Publication type | Session Materials |
|---|---|
| Reference | D1_11399_2026 |
| Publication year | |
| Publisher | CIGRE |
| Country | Brazil |
| Study committees | |
| File size | 776 KB |
| Price for non member | 30 € |
| Price for member | 30 € |
Authors
WILHELM Helena - VEGOOR Brazil; FERNANDES Paulo - VEGOOR Brazil; MANNES Yorrannys - VEGOOR Brazil; SILVA Cassio - ARGO Brazil
Keywords
Liquid-immersed transformers, Life-prediction tool, Isotopic monitoring, Isotope-ratio analysis, Radioactive carbon analysis, Biogenic carbons
