Investigations on reclaimed oil performance through measurement of the relative free radical content

Abstract

The accelerated thermal ageing process was organized to compare the performance of oils before and after being subjected to oil reclamation. New mineral oil of the same brand was used as a base line measurement for evaluating the performance of the reclaimed oil with and without inhibitor. Samples consisting of oil, paper and metallic catalysts including zinc, copper, aluminum, and iron were aged at 115 °C in an air circulating oven for 250, 500 and 750 hours. A free radical reagent, 2.2 diphenyl-1-picrylhydrazyl (DPPH), was used to determine the relative concentration of free radicals in the oil samples. Key ageing indicators, namely free radical scavenging activity (RSA), relative content of dissolved decay products (DDP), turbidity, total acid number (TAN), interfacial tension (IFT), dielectric dissipation factor (DDF), and absolute water content for oil, and low molecular weight acids (LMA), and tensile index (TI) for paper, were measured regularly. It was found that the performance of the reclaimed oil is definitely better than the non-reclaimed oil, and is highly likely competitive with new mineral oil with the same brand. The results show that after a long run of the ageing process, RSA and DDP of the reclaimed oil without inhibitor are respectively more and less than that of the new oil. In addition, slower reduction of TI of paper aged in the reclaimed oils corroborates the theory that the paper degradation in a transformer can be reduced through oil reclamation.