All transformer fluids oxidize
In non-free breathing transformer applications (transformers where ambient air and oil are not in continuous, direct contact for extended time periods), oxidation is not an issue as fluid exposure to the atmosphere is minimal.
Even in a free-breathing transformer, or with intermittent exposure (as experienced in a transformer that leaks), oxidation takes years.
Different fluids oxidise differently
Each fluid type oxidizes differently and the byproducts of oxidation may affect the performance of a transformer. As such, varied laboratory oxidation stability tests have been developed to be used as control tests for evaluating the relative oxidation stability of dielectric fluids in a laboratory environment; but they are not intended to simulate operational performance within a transformer. The in-application differences between mineral oil and natural esters are as follows:
- The byproducts of mineral oil oxidation form substances that precipitate from the fluid. In application, the long-term effect could be sludge formation on surfaces within the transformer, and will yield less efficient heat transfer.
- The byproducts of natural ester oxidation form oligomers (larger molecules) that stay in solution. In application, the long-term effect could be a slight increase in the fluid viscosity, but no sludge formation, and no impact to dielectric strength or dielectric performance.
Nearly 20 years of proven performance
In non-free breathing transformers, there is no concern about the oxidation stability of natural ester transformer oils. They have been formulated to meet IEC and IEEE standards for oxidation stability, while also achieving best-in-class environmental properties.
Natural ester oil has performed effectively in millions of transformers across the globe for over 20 years. This application experience includes:
- True free-breathing transformers and LTC’s
- Sealed transformers and transformers retrofit with bladders in the conservators, including units with incorrectly installed bladders
- Five-year large volume and thin film oxidation studies, supported with numerous laboratory tests conducted over extensive time periods, which verify natural ester fluid’s performance in application
Even though the rate of oxidation is faster than mineral oil, the time required to oxidise thin films is typically long enough to allow normal maintenance procedures (lasting days through to a few weeks) to be used during transformer repairs (when the components are outside the transformer, or the exposed transformer tank has been emptied). Simple ‘good housekeeping’ handling steps and recommendations minimise the potential for any issues.
Natural ester oil stability has been proven to be sufficient for real life application at most climate conditions and maintenance practice throughout the world. Within a transformer, oxidation stability is not a limiting factor. Contact our dielectric fluids team to help you incorporate natural ester transformer oil into your power and distribution transformer fleets.