Performance analysis of alternate liquid dielectrics for power transformers

In this work mineral oil, natural ester, synthetic ester and a mixture of mineral oil and synthetic ester have been subjected to accelerated thermal stressing in presence of copper and cellulose. All these samples were subjected to 110°C, 150 °C, 170 °C and 200 °C thermal stressing for different test durations. Thermal degradation of the samples has been monitored continuously with UV Spectroscopy and visual inspections. Additionally interfacial tension of mineral oil and mixture oil has been monitored under the same test conditions to observe the miscible performance of the fluids. It has been found that the degree of degradation is less with synthetic esters than other samples. Interfacial tension and visual observations revealed less sludge formation in synthetic esters. Furthermore, aged insulation paper has been analyzed using X- ray diffraction technique to find the degradation rate of cellulose in various insulating fluids. It has been found that the rate of degradation is low in synthetic ester and performance of mixed oil is better than mineral oil.