Insulating oil decaying assessment by FTIR and UV-Vis spectrophotometry measurements

The most easily accessible and efficient way to determine the transformer condition is to use the insulating oil as diagnostic medium. Practical experiences have shown that more than 70% of incipient failures can be detected through oil tests. To meet pressing needs of power industries, fast, inexpensive and reliable laboratory testing procedures are necessary. In this contribution, oil samples aged in laboratory condition were monitored with traditional diagnostic methods - i.e., interfacial tension (IFT) and total acid number (TAN) - and alternative techniques based on spectral analysis, using Fourier Transform Infrared (FTIR) and Dissolved decay products (DDP) assessed by spectrophotometer. From the obtained results, the sensitivity and reliability of each method in monitoring step-by-step the decay products formation are analyzed and discussed. It is shown that ratio of DDP to FTIR transmittance measurements at 1710 cm^-1 might be possibly be used as index for assessing the degradation of transformer oil.