Regeneration of transformer oil

Oil regeneration is a process that eliminates or reduces soluble and insoluble polar contaminants from the oil by chemical and physical means. It requires special competence, equipment and experience.

Regeneration of moderate to high acidity oils will usually result in a lower oxidation resistance than the new oil.

Before performing a reclamation process, a laboratory feasibility test is recommended.


The regeneration process by percolation consists of three consecutive steps:

•  The oil taken from the transformer or from a storage tank is heated to a given temperature and circulated through a filter to eliminate the particles and suspended solids
•  It is then circulated through one or more percolating columns containing adsorbent, to eliminate soluble polar contaminants from the oil
•  Finally the oil is circulated through a physical reconditioning equipment to eliminate water and gases


The adsorbents used to regenerate the oil allow the non-polar components to pass through, but retain the polar contaminants or degradation compounds dissolved in the oil.

The whole art of oil regeneration consist in the choice of the adsorbent.

Experience has shown that it is usually necessary to pass the total volume of oil through the adsorbent columns at least three times. The final number of cycles will depend on the degree of initial contamination and the desired results.

During regeneration, a small portion of the oil (typically less than 5%) remains in the adsorbent material, thus some unused oil shall be used for topping-up the equipment at the end of the process. The adsorbent in the percolation columns during service becomes contaminated with used oil and solid contaminants, therefore the disposal or re-activation of the substance should be carried out.



Technical characteristicsRU 1
Oil flow rate [l/h]1000
Connection flange diameter [mm]DN 25
Number of percolation columns6
Weight [kg]3000
Neutralization number [mg KOH/g]< 0,03
Dielectric dissipation factor 90°C [%]< 1
Interfacial tension [mN/m]> 40
Adsorbent materialAA + FE
Adsorbent reactivationYes