Application of an improved ultraviolet spectrophotometry technology for the determination of antioxidants in natural ester liquids

It is well known that the acidity of aged natural ester liquids is much higher than that of conventional mineral oil, which might result in the corrosion of metal components and hydrolysis of insulating paper. Ageing of ester liquids highly depends on the consumption of antioxidants. Traditional detection methods for antioxidants in natural ester, i.e., spectrophotometry and thin-layer chromatography, relies on the titrations between carboxyl in antioxidants and alkaline reagents. Faster and simpler detection technology is necessary for the practical ageing assessment of transformers filled with natural ester liquids. In this paper, an accelerated thermal aging experiment was designed for soybean oil, FR3 vegetable oil and mineral oil, and oil samples with different aging degrees were obtained by accelerated thermal aging experiment. And then, antioxidants in oil samples detected using spectrophotometry technology. Ultraviolet spectrophotometry is simpler and has a wider spectral range in the determination of antioxidants. The results show that the consumption of oxidizer is different for the oil samples with different aging degrees, and the absorbance of UV spectrum is also different. It is confirmed that ultraviolet spectrum is an effective method for the determination of consumption of antioxidants in natural esters.