A Midel oil transformer uses synthetic ester oil as insulation and coolant, ideal for fire-sensitive or eco-friendly installations. GlobeCore systems process these ester oils by drying and filtering them, preventing degradation.

An important point when maintaining a transformer filled with MIDEL fluid is that ester-based dielectric liquids should not simply be treated as direct substitutes for conventional mineral transformer oil. Their physical and chemical properties influence both the behavior of moisture inside the transformer and the way the fluid should be evaluated during maintenance.
Natural ester fluids, for example, have a much higher affinity for water than mineral oil. This means that moisture distribution between insulating fluid and cellulose insulation can be significantly different. A comparatively high moisture concentration in the ester does not necessarily indicate the same insulation condition that an equivalent value would suggest in a mineral-oil transformer. Maintenance decisions should therefore be based on the characteristics and limits applicable to the specific dielectric fluid rather than on mineral-oil reference values.
Fluid condition should also be assessed as a combination of several parameters. Moisture content, dissolved gases, dielectric properties, particulate contamination, and changes in the fluid caused by thermal and oxidative aging can provide a much more reliable indication of transformer condition when evaluated together. Trending these parameters over time is particularly valuable, because gradual changes may reveal emerging problems before they affect transformer reliability.
Another practical consideration is contamination during servicing. Mixing an ester fluid with residual mineral oil or causing ingress of moisture and particles through hoses, tanks, pumps, or processing equipment can alter the properties of the dielectric system. For this reason, maintenance equipment should be clean, compatible with the fluid being processed, and operated under the conditions that minimize unnecessary exposure to ambient air.
The maintenance program should ultimately be based on the actual condition of the fluid rather than on a fixed assumption that ester-filled transformers require the same treatment intervals and acceptance criteria as mineral-oil units. Proper sampling, laboratory analysis, condition trending, and fluid purification when required can help preserve both the dielectric fluid and the transformer’s solid insulation.
For a practical example of how these principles apply specifically to MIDEL eN 1204 natural ester dielectric fluid, including its characteristics, purification process, and post-treatment parameters, this article provides useful additional information: https://globecore.com/oil-processing/midel-en-1204-natural-ester-dielectric-fluid-purification/.