End Life Behavior of Ester Liquids in High‐Voltage Transformers

In this chapter, behavior of ester liquids are reported with an aim to understand the generation of decay particle (colloidal and soluble/dissolved particles) with aging. Thermal aging of oils is carried out as per ASTM D1934 in presence of cellulose and copper with aging history at elevated temperatures followed by analysis of colloidal and soluble particles. The aged and treated oils are characterized using diagnostic characterizations. The evolution and influence of colloidal and soluble decay contents for esters fluids and mineral oils are reported. The effect of colloidal particles on degradation of ester liquids is negligible, while degradation in mineral insulating oils is majorly governed by the colloidal particles. In addition, the potential of fuller's earth filtration for ester liquids is reported at different concentrations and different testing temperatures.