Ester Fluids Face Moisture Challenges in Extreme Cold
Low temperatures can create a moisture-management challenge for ester-filled power transformers, according to Pierluigi De Horatiis, author of a September 2026 article published in Transformer Technology.
In The “Dual Nature” of Dielectric Esters, De Horatiis explains how cooling reduces ester fluids’ ability to retain dissolved water. Synthetic ester saturation limits fall from about 1,100 ppm at 20°C to 120 ppm at −20°C, the article reports. If fluid becomes oversaturated, water can separate and migrate towards solid insulation, potentially affecting dielectric performance during cold starts.
“As the temperature drops, the molecular kinetic energy decreases, and the hydrogen bonds become less effective at stabilizing the water molecules within the fluid matrix,” De Horatiis writes.
He also discusses low-temperature viscosity and cold-start precautions. For related background on moisture behaviour, see Effects of Water on Dissolved Gas Analysis.
Read the full article.
