Monitoring Aging of Natural Ester Insulating Fluid using Supercritical Fluid Chromatography-Mass Spectrometry (SFC-MS)

Petroleum-based mineral oils have been used in transformers to provide cooling and insulation. However, there are increasing concerns over the persistence and impact of petroleum-based oils on the environment due to their resistance to biodegradation. Natural ester-based oils are considered to be sustainable alternatives, as they are biodegradable and possess improved fire safety properties compared to mineral oils. Here, supercritical fluid chromatography-mass spectrometry (SFC-MS) is used to study the chemical composition of natural ester oils and their behavior when subjected to aging experiments. Under the applied aging conditions detectable amounts of hydrolysis products (free fatty acids and DAGs) are evident in the aged samples. Furthermore, SFC-MS can also be used to simultaneously monitor the presence of other oil components, such as antioxidants.