Determination of the thermal endurance of transformer oil by structural analyses

Determination of the thermal endurance of transformer oil Nynas Lyra X was studied. The oil was exposed to thermal treatment at temperatures of 110, 120 and 130 °C for times ranging from 100 to 2400 hours. New methods for determination of material´s thermal endurance were searched. Attention was drawn to the group of structural analyses from which two methods were selected: Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The dissipation factor was also measured according to standard EN 60247 as a comparison test and for a determination of end-point criteria of all newly monitored observables. Infrared spectral band of low temperature inhibitor and the temperature of the first thermo-oxidative DSC peak were used for further evaluation. It has been shown that the both analysed observables are continuously changing along applied thermal treatment and hence meet essential requirements of IEC 60216 standards. End-point criteria of analysed observables were determined and Arrhenius diagrams were subsequently plotted. The proposed observables, as determined via structural analyses, provide promising alternatives to dissipation factor measurement.