Assessment of regenerated oil through accelerated thermal ageing experiments

Laboratory-based accelerated thermal ageing experiments were conducted in order to compare the performance of oils before and after being subject to oil regeneration. Three commercially available new mineral oils were used as a benchmark for the performance of the regenerated oil. Samples consisting of oil, paper and copper were aged at 120 °C under sealed conditions for a period of up to 63 days. Key ageing indicators, namely Total Acid Number (TAN) and moisture for oil, and moisture, Low Molecular Weight Acids (LMA), and Tensile Index (TI) for paper, were measured regularly. It was found that the performance of the regenerated oil is better than that of the non-regenerated oil, and is also comparable to that of other new mineral oils. Slower reduction of TI of paper aged in oil after regeneration compared to paper aged in oil before regeneration conforms to previous findings that oil condition plays a role in determining the ageing rate of paper, and supports the premise that oil regeneration can slow down paper degradation in transformers.