Investigation on Aging of Paper and Liquid insulation during Overload Test of Natural Ester Immersed Transformer

Natural-ester dielectric liquids (vegetable‑oil based triglycerides) are now widely adopted in distribution and increasingly in power transformers, driven by their high fire point, biodegradability, and compatibility with sealed designs specified in IEC 62770 (2024), which formalizes acceptance tests and application constraints for unused natural esters. Beyond safety and sustainability, the fluid’s higher water solubility and propensity for hydrolysis shift the moisture equilibrium away from cellulose, promoting “in‑oil” water migration and consumption; this mechanism is consistently associated with slower paper depolymerization and extended solid‑insulation life compared to mineral oil systems. Long‑duration CIGRE and academic studies further show improved cellulose preservation in…