Oil in the transformer can be contaminated due to a number of factors such as; ageing, overheating, oxidation, faults in the transformer design, etc. Any one of these factors or combination will result in the built up of potentially harmful contaminants which could potentially destroy the transformer by shortening its useful operating life. If the transformer oil are diagnosed to have an unacceptable quantity of contaminants such as acids, sludge, moisture and dissolved gases, prompt treatment of the oil is required to prevent accelerating the deterioration of the transformer itself. Note that damage inflicted on a transformer cannot be reversed (unless it is stripped down and refurbished totally), but prompt and proper treatment of the contaminated oil can stop or at least slow down the deterioration process.



Oil treatment options currently available are as follow



Filtration will remove most free water (includes some dissolved water) and some trapped solid matter. It has major weaknesses. As the oil in the transformer is not treated chemically, it does not solve the sludge problem. More importantly, the process cannot remove dissolved oxidation by-products (like dissolved gases and acids) in the oil.


Transformer Oil Regeneration (TOR)


This basically involves three distinct processes; heating, absorption (reclamation) and vacuuming. The oil goes through the heating process which transforms the oil in the transformer into solvent for the sludge/oxidized by-products from the tank and solid insulation. Essentially, the heated oil dissolves such contaminants which otherwise the oil at normal temperature is unable to do so. The next process involves the removal of acids, sludges and other contaminants from the oil via the reclamation process. Finally, vacuuming removes moisture and gas in the oil.


Comparison between method of corrective oil work

Oil Filtration / Purification
Oil Regeneration
Oil Change

Removes Moisture, Particulate Materials, Free Water, Visible Sludge and Gasses from the insulating oil in the transformer unit.

Removes all contaminants from the insulating oil, transformer core and sludge formed onto the transformer unit.

Replaces Oil with new oil. (Filtration of the new oil prior to putting it into the transformer
unit is advised to ensure the oil replaced is low in moisture content.)

Primarily performed when Moisture is high

Performed when oil testing shows insulating oil is deteriorated.

Performed when oil testing shows insulating oil is deteriorated.

Partial removal of contaminants

Comprehensive removal of contaminants

Partial removal of contaminants.

(During oil change, there will be residue contaminated oil in the transformer oil and the contaminated oil is also absorbed by the solid insulation. Sludge formed onto the internal surface will not be removed during oil change.)

Lower cost than the other methods.

(Cost of filtration / purification, mobilisation cost)

Lower cost than oil change.

(Cost of regeneration, mobilisation cost)

High cost relative to the other method.

(Costly purchase of new oil, recommended filtration of oil, mobilization cost)

Environmentally Friendly – Oil recycled

Environmentally Friendly – Oil recycled

Environmentally Unfriendly – Oil disposal required.