Monitoring Oxidation in Natural Ester Insulating Liquids Through FTIR Spectroscopy Analysis

This study investigates the thermal aging behavior of MIDEL eN1204, a natural ester-based insulating oil derived from rapeseed, using Fourier Transform Infrared (FTIR) spectroscopy as the primary analytical method. The oil samples were subjected to an intensive thermal aging process at 115°C for 1000 hours to replicate the long-term aging process that occurs in transformers. FTIR spectroscopy was employed to monitor shifts in key absorbance bands indicative of oxidative and hydrolytic degradation. The 1711 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> band, associated with carbonyl compounds, showed a significant increase in intensity, marking the oil's degradation. A differential normalization approach was introduced to enhance the detection of these aging effects. The results demonstrate the potential of FTIR spectroscopy to improve diagnostic processes of natural ester insulating liquids for maintaining transformer insulation systems.