“…Nevertheless, electrical techniques do not always provide adequate effectivity, sensitivity, and reproducibility because moisture, which reversibly migrates between the paper and the oil with changes in the transformer operating temperature [20], has a dominant effect on most of the measured electrical properties [16]. Therefore, in addition to traditional methods, alternative methods, including UV-Vis spectroscopy, turbidity, near-infrared (NIR) spectroscopy, FT-IR spectroscopy [21][22][23][24][25], and differential scanning calorimetry (DSC) [26], have also been continuously explored as effective diagnostic tools to assess transformer oil quality. For these reasons, we utilized UV-Vis spectroscopy and FT-IR spectroscopy in this study.…”