If Midel ester fluids have high acid levels, how do I recondition my fluid?


Mineral oil: aging by-products are short chain acids, water soluble can catalyse paper degradation.

MIDEL fluids: aging by-products are longer chain acids, not harmful to paper insulation.

Because of hydrolysis (the consumption of H2O and production of non-water-soluble long-chain acids) MIDEL fluids can have higher in service acid numbers than mineral oil.

However, being longer chain the acids produced will not dissolve in water and will stay dissolved in the ester. The shorter chain acids from mineral oil are water soluble, will transfer to the paper and catalyse the aging of the solid insulation.

Common transformer oil processing techniques

MIDEL fluids can be processed using common equipment used for mineral oil. Materials and processes, including reconditioning (via degassing) and regeneration (using Fuller’s earth) can be applied to MIDEL fluids.



CIGRE White Paper: Experiences in Service with New Insulating Liquids – Working Group A2.35

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Retrofilling transformers with ester fluids