Optical Spectra Analysis for Transformer Insulation Exposed to Thermal and Electrical Stresses

Abstract

Assessment of transformer oil condition reflects its aging extent, which is crucial for their reliable long-term operation. Several techniques have been proposed to assess the condition of transformer oil. Among these techniques, optical spectroscopy proved to be an effective and reliable technique. Herein both Photoluminescence (PL) and Ultraviolet-visible (UV-Vis) spectroscopies were applied to assess the condition of transformer oil exposed to both electrical and thermal stresses with a prim focus on electrical stresses. The accelerated electrical aging system was designed and built to generate arcing faults. Then, an operating voltage was selected to be 70 kV based on withstanding voltage measurements of the fresh oil sample. The investigated electrically and thermally aged oil samples were prepared with different aging levels. After that, both PL and UV-Vis spectra were obtained for electrically and thermally aged samples. It was found that electrical aging caused a shift in the intensity of PL spectra. While the thermally aged ones broaden the PL spectra to longer wavelengths. Regarding UV-Vis spectra, thermal aging affects both the absorbance and wavelength as the maximum absorbance level was increased, and the spectra were shifted to a longer wavelength with aging. Concerning electrical aging, arcing stresses caused a significant change in the absorption level with the aging extent.