Monitoring the Sol and Gel in Natural Esters under Open Beaker Thermal Aging

The application of natural ester-based dielectric liquids for liquid-filled transformers is a topic of high concern for transformer owners and utilities. The potential advantages of being biodegradable, high flash point, good dielectric properties, and high moisture tolerance encapsulated natural esters to be a promising solution for transformer insulation systems. Several research reports are affirmative towards the usage of natural esters in transformers. Meanwhile, the poor oxidation stability of natural esters is a challenge that needs to be emphasized. Natural esters develop a polymerized aging product known as gelling under the influence of oxygen. Before gelling occurs, the first thing is to form sol in the bulk of the liquid that influences the liquid viscosity and further accelerates oxidation. Thus, in this paper, a natural ester is subjected to accelerated thermal aging to observe and understand the formation of sol. However, accelerated thermal stressing is continued till gelling is evident in the liquid. The changes in liquid absorbance with aging and the level after which sol is developed is reported. The changes in the viscosity of the natural ester with the formation of sol and gel are also reported. Further, the compositional changes of the liquid that are responsible for the formation of sol are reported using FTIR analysis. Finally, the breakdown failure rate of the completely gelled natural ester is reported to understand the influence of the gelling on the liquid breakdown strength