Performance of alternative insulating liquids at low temperature

摘要

Alternative insulating liquids such as ester oils can be used in transformers when ecological aspects and extra fire safety are desired. These alternative dielectric fluids have some different physical properties such as higher viscosities or much higher water solubility than mineral oil. This contribution will show results from extensive investigations on natural and synthetic esters in comparison with one mineral oil. The AC breakdown voltage is determined for different low temperature points down to -35°C. Also different humidity levels of the oil have been investigated in order to check possible critical crystallization at very low temperature. Additionally slow natural and fast artificial defrosting of solidified natural ester is also evaluated. The results of the experiments are compared to mineral oil where possible. Finally suggestions for the safe operation of transformers at very low temperatures are presented.