REOIL® Transformer
Oil regeneration plant

REOIL transformer oil regeneration plant regenerates aged transformer oils into like new condition fulfilling the requirement of IEC 60422 standard. REOIL transformer oil regeneration plants are built with variable capacity and sorbent reactivation capability. Plants are of stationary or mobile design and can work on offline or online transformers.

Description of oil regeneration process

Most power equipment is using transformer oil for its dielectric properties for cooling, insulating, and protecting the active parts. Transformer oils are highly refined oils that consist mainly of a mixture of hydrocarbons. Over time, oxidation byproducts start to form in the oil. Increases in oxidation byproducts result in the increase of acidity (neutralization number) and decrease the interfacial tension of the oil. At this stage, sludge starts to form, and oil is losing its dielectric properties because it is getting old. To prevent further deterioration of oil and possible damage to the active part of the transformer, oil needs to be regenerated. Oil regeneration equipment regenerates oil in steps.


At the inlet of the equipment, oil is filtered through a coarse filter to prevent any particles from entering the equipment. It is then heated to the desired temperature to elevate the regeneration effect.


After the oil has been heated, it enters the back section of the equipment. Oil is pumped trough the back section which houses columns with sorbent media. It is in this section where the oil is stripped of impurities and ageing byproducts.


Oil is then pumped trough a vacuum breaking valve into the degassing section where it is dehydrated and degassed. Treated oil is then pumped back to the transformer by the outlet pump.


After a given period, sorbent in the back section of the equipment achieves full saturation and is no longer able to regenerate oil.


At this stage, the sorbent needs to be reactivated (restored to its original state) to be able to regenerate oil again. Reactivation stage starts by draining the columns in the back section of saturated oil.


After the oil has been drained, a vacuum is created and maintained throughout the whole reactivation process in the back section.


Then by selective use of heating elements on the top parts of individual columns, the reactivation process is initiated. During the process, the impurities are removed from the sorbent which restores it to its original state.


This entire process can be repeated many times until the sorbent starts to lose its properties and needs to be replaced.

Technical characteristics of oil regeneration equipment

Oil regeneration equipment is sophisticated. Its inlet pump is a positive displacement rotary pump. The outlet pump is a centrifugal closed coupled high suction pump. For degassing the rotary vane, a vacuum pump and vacuum booster roots pump are used. For the reactivation phase, a rotary piston roots pump is used. All valves across the equipment are automatic ball valves, which are pneumatically controlled. Equipment is fully automatic, controlled by PLC logic and interfaced with a SCADA system. Numerous safety features are introduced throughout the unit to ensure the safety of the equipment as well as the operating personal. Aeration valves, overheating protection, and automatic level switches guarantee the safety of the equipment as well as its ability to identify a possible risk and to power down to prevent any accidents.

No. of columns Length (mm) Width (mm) Height (mm) Weight (kg) Oil flow (l/h) Piping (DN) Power (kW)
3 4600 2150 2150 6000 1000/6000 32 51
6 5200 2150 2150 7000 1000/6000 32 102
9 5800 2150 2150 8000 1000/6000 32 164
12 6400 2150 2150 9000 1000/6000 32 168

Performance values of oil regeneration equipment

The level of contamination differs from transformer to transformer. The ageing process, as well as the utilization of a transformer, make it difficult to determine when and how will oil age to the point that it loses its dielectric properties. Regardless of the level of contamination, oil regeneration always delivers the result required by the IEC 60422 standard for mineral insulating oils in electrical equipment. However, our REOIL regeneration technology goes one step further and significantly improves on the values required by the IEC 60422 standard, with the returning oil having properties almost identical to those put into the transformer for the first time.

Property (Unit) IEC 60422 Before regeneration After regeneration 10 years after regeneration
Breakdown voltage (kV/2,5 mm) >60 49 95 81
Dielectric dissipation factor at 90 °C <0,01 0,0823 0,0008 0,0029
Acidity (mg KOH/g) <0,03 0,15 0,010 0,018
Water content (ppm) <10 35 6 9
Interfacial tension (mN/m) >35 27 49 41

Fully automatic operation of the REOIL units is controlled by PLC while the operation is ensured by a SCADA system installed on a laptop.

REOIL plant uses highly effi cient, fast pneumatic control valves to ensure high reliability of operation throughout the lifetime of the plant.

The back section of the REOIL unit where regeneration columns house sorbent, which ensures that all properties of the oil are suffi ciently restored.