Performance of biodegradable insulating oil under accelerated thermal ageing

Biodegradable insulation oils are gaining acceptable use in power transformers as alternative to the successfully petroleum-based oil. In general all insulation oils must be good as insulators and as well as being good heat exchange media. The ability of the insulation oil to remain physically and chemically stable under thermal stress defines the quality of the oil. Based on this expectation, this paper presents experimental result of study on physical and chemical changes in two commercial biodegradable insulation oils: palm-based Palm Fatty Acid Ester (PFAE) and soybean-based Envirotemp FR3 (FR3). Both were subjected to sustained thermal stress at 150 °C for period of 200 hours to induce accelerated ageing process. The breakdown voltage (BDV) and intrinsic viscosity of both oils are analyzed and presented in this study. Fourier Transform Infrared (FTIR) spectroscopy of the oils was investigated with the aim of studying the physical and chemical changes in the molecular structure of the oils that causes the BDV and viscosity result outcomes. The result shows that the BDV in both oils decrease in the same pattern while the viscosity of the FR3 increased by 10.38 % and the PFAE increased 34.25 % indicating that the PFAE degrades more than the FR3 when both oils are subjected to the same thermal conditions. The FTIR spectra showed significant changes in the peak positions which confirm the thermo-oxidative degradation of the oils.