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Transformer oils: Oil regeneration
Energo-Complex, basing on ARRAS-MAXEI company technology, introduced to the range of its services regeneration of electro-insulating oils.

The process of oil regeneration consists in solid particles filtration, separation of polar particles with the use of absorbent material, vacuum drying and degassing. The decisive factor of the whole cycle is the physicochemical process of oil purification passing through the adsorption column, created by the Fuller clay. Column sorption, during one cycle can regenerate the decuple of the sorbent’s mass. The regeneration process using Fuller clay has been well known for many years. However, previously the filtration element, sorbent was a DISPOSABLE element and the oil saturated clay had to be utilized.

A breakthrough in the use of regeneration technology came with the introduction of sorbent reactivation process. Thanks to the new technology, the sorbent can be used up to 300 times without a deterioration of the filtering properties.

Oil aging evaluation:
  • Acid number - the most important parameter describing the oil aging. Acids resulting from the oxidation process cause the corrosion of metals, accelerated degradation of cellulosic insulation. Oxidation products are insoluble sludge and sediments, which reduce heat dissipation from the active parts of the device.
  • Loss factor tan δ - a value that indicates the presence of impurities as well as polar and ionic particles dissolved in oil.
  • Resistivity - the resistivity volume depends on the water content, impurities and on the degree of oxidation of the tested oil. This is the auxiliary parameter that facilitates the evaluation of the loss factor.
  • Surface tension - on the basis of this parameter’s value you can determine the presence of even very low polar substances concentrations, arising during the oil aging process.

Oil regeneration stages:
  • During the regeneration process, the oil flows through a standard oil processing device model MAS 6000, and through the regenerative unit REGEN 6C with the efficiency 2000 up to 3000 l/h.
  • After the saturation of sorbent with decomposition products (8 hours treatment) the flow of oil through the regeneration columns is cut off and starts the process of and the sorbent reactivation. Reactivation takes about 8 hours. The cooling process of the columns takes another 8 hours.
  • The process of oil degassing and dewatering can be continued in the meantime.
  • After the regeneration of oil, natural inhibitors removed during the process, are supplemented with synthetic inhibitor in an amount of 0.3 to 0.5% of the oil weight.


Exemplary results of oil regeneration for different transformer unitsbased on the acid number:

Comparative table:

ParameterMethodOld oilNew oilThe regenerated oil
Breakdown voltage (kV / 2,5 mm)IEC 60156~ 20> 70> 70
Acid number (mg KOH / g)IEC 60296 / 82~ 0,2< 0,03< 0,01
Water content (mg / kg)IEC 60814> 10< 10< 10
Loss factor tan δ at 90°C (%)IEC 60247~ 10< 0,3< 0,4
Surface tension (mN / m)ISO 606295~ 25> 40> 50
Resistivity at 90°C (GΩm)IEC 60247~ 1> 150> 150

Measurement and comparative analysis of oil showed that the regenerated oil has a comparable performance with new oil.

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