Monitoramento da degradação térmica de óleo mineral isolante de transformador utilizando espectroscopia de absorção e fluorescência UV-Vis

Abstract

In this study we verify the potential of the UV-Vis absorption and fluorescence techniques to monitor the degradation of the insulating mineral oil (IMO) used in transformers depending on their heating. Measurement and analysis of contour maps (excitation - emission) were taken from samples of new and regenerated insulating mineral oils diluted and undiluted in hexane after systematically heating and bringing them back to room temperature. Absorption spectra were also obtained from diluted samples. The mentioned measurements were performed to monitor the degradation of new and regenerated insulating mineral oil undiluted samples in order to verify the applicability of the techniques without prior sample preparation. The results showed that the values of absorption and fluorescence underwent systematic changes starting at about 150 °C, temperature at which oil degradation becomes more pronounced. Similar absorption and fluorescence behaviors for both new and regenerated oils were observed, indicating that this simple optical approach may be used for continuous monitoring of oil quality, regardless of its source. The possible mechanisms responsible for the changes are also discussed, and the effect of the geometry of the experimental setup of the fluorescence measurements was investigated as well. The results provide the basis for the development of portable, simple and potentially inexpensive devices, able to check the insulating mineral oil quality in laboratories and remote environments without the need of any prior preparation of the sample.