Evaluation of Physicochemical and Dielectric Properties of Mineral Oil – Natural Ester Mixtures under various Ageing Conditions: Implications for Retrofilled Transformers

Retrofilling transformers with natural and synthetic esters has gained traction as a strategy to enhance the safety and performance of electrical systems because of the superior electrical and fire properties of esters. While prior studies have extensively analyzed the properties of fresh mineral oil - ester mixtures, they do not fully account for the aged conditions typical in retrofilled transformers, where mineral oil has undergone prolonged use and aging. This study investigates the dielectric and physicochemical properties of mineral oil and natural ester mixtures, including dielectric permittivity, dissipation factor, AC breakdown voltage, water content, and acidity. The findings provide valuable insight into the behavior of the liquid insulation of retrofilled transformers under various conditions, helping to optimize the retrofilling processes and improve transformer performance.