Compare the performance of natural ester with synthetic ester as transformer insulating oil

Natural and synthetic esters are considered as potential candidates to replace mineral oil in power transformers. However, there is comparatively less experience on usage of ester-based insulating liquids in large power transformers. The high reliability and safety level required for large power transformers lead to careful assessment of the use of ester as the insulating liquid in these units. Therefore, this study assesses the ageing behavior of the dry pressboard insulation immersed in a commercially available natural ester and a synthetic ester through accelerated ageing experiment. At different stages of ageing, oil conditions are analyzing by measuring acidity value, 2-furaldehyde (2-FAL) concentration and kinematic viscosity. Dissolved Gas Analysis (DGA) is also performed to assess the degradation of both pressboard and oil. Moreover, the change of AC breakdown strength of natural and synthetic ester due to mixing with mineral oil (new and aged) is analyzed. This paper reveals that pressboard ageing in both types of oils associates with dissolved 2-FAL and CO₂+CO concentration in oil. It has been observed that there is different gassing behavior between natural and synthetic ester due to thermal ageing. This paper reveals that, the AC breakdown strength of both types of ester used in this study decline due to mixing with mineral oil.