Dielectric Performance of Biodegradable Ester Insulating Oils Under High-Voltage Transient Stress: A Study Based on Partial Discharge Measurements

Abstract

The search for sustainable solutions in the electrical sector has driven the use of biodegradable insulating fluids, such as esters, as alternatives to petroleum-derived mineral oils. This study experimentally evaluates the dielectric performance of two esters (one natural and one synthetic) under high-voltage transient stresses that simulate lightning strikes. A total of 40 standard lightning impulses (± 5 0 ~ k Vpeak) were applied to a prototype with an insulation system impregnated with each fluid. Partial discharge measurements were performed before and after the tests, in accordance with IEC 60270. In both cases, the apparent charge of partial discharge levels remained below 100 pC, the limit established for transformers rated up to 72.5 kV, indicating that there was no significant dielectric degradation. The results demonstrate that the esters tested offer good dielectric performance and provide additional environmental benefits, including biodegradability and a lower ecological impact. Therefore, esters are a technically viable and sustainable alternative for high-voltage insulation systems. (c) 2026 IEEE.