Oil physical treatment

Friday March 17th, 2017

Insulating oil within electrical equipment in operation is subject to deterioration/contamination, mainly because of the surrounding conditions. This contamination continuously reduces the dielectric properties of the fluid thereby increasing the probability of failure.

The physical treatment (also called physical decontamination) of oil, a more beneficial process than replacing it, aims to eliminate any contaminants in the insulating liquid (water, solid particles, dissolved gas), returning them to the range indicated by industry regulations and guidelines (IEC, CENELEC, CIGRE, etc.) and to prevent potential damage caused for example by the progressive accumulation of water in solid insulation with the formation of gas bubbles and electric discharges.

Take a look to the standards about ``water content in oil``

Estratto "water content" da tab. 5 della IEC 60422 ed. 4-2013

Operating modes

Sea Marconi performs exclusive physical treatments in terms of operating modes and safety thanks to its treatment units (DMU – Decontamination Modular Unit) equipped with advanced monitoring and control systems capable of operating up to 24 hours a day.

The mobile units (designed and produced by Sea Marconi) aspire the oil within the transformer, decontaminate it and then pump it back into the appliance. Each time that the oil flows through our treatment plant, the oil is heated, dehumidified, degassed, and filtered.
It combines a closed circulation process with never emptying the transformer (even partially), which is a very important aspect.

Besides restoring the parameters of the oil to the range indicated by regulations, Sea Marconi’s physical treatment allows one to completely remove contaminants deposited on the internal parts of the transformer and on the bottom of the casing by using the oil flow within the transformer.

Open to see the details of the activities

The service includes the following activities:

  • Transport before/after of specialized technicians, treatment units (DMU), equipment, reactants and disposable objects from the Sea Marconi office to the sites of the transformers;
  • The Hydraulic and electrical installation and set up of the mobile depolarisation units (DMU)
  • Sampling, analysis and diagnosis (Deosvision®) before treatment (if any);
  • Physical decontamination treatment (degassing and dehydration in a vacuum);
  • Monitoring the treatment parameters;
  • An oil change for transformers in service (if necessary);
  • Level and vent controls;
  • Replacement of desiccant salts in silica gel;
  • Sampling, analysis and diagnosis (Deosvision®) at the end of the process;

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  • Removal of any water and physical contaminants from the oil
  • Restoration of the oil’s dielectric properties

and of course all the benefits that come with using Sea Marconi treatments:

Operational safety

due to never emptying the transformer and using decontamination units (DMU), a process created by Sea Marconi equipped with an advanced monitoring system, 24 hour a day automatic safety is provided

Environmental safety

since the physical treatment avoids both the replacement, disposal, transfer and handling of enormous amounts of oil that can still be used, and the risks associated with handling contaminated oil

The treatment units' small dimensions

mean they are operational even under extreme logistical constraints (e.g . in bunkers, and mines)

Functional recovery of oil and transformers

by means of the unique closed-loop operating mode

Reference and regulatory compliance

IEC 60422 Ed.4 2013

Strong case studies

with a total of 300 pieces of decontaminated equipment amounting to approx. 2,500 tons of oil physically decontaminated (data for 2017 only)


Property Method Test Maximum
rated voltage (kV)
< 72,5 between 72,5 and 170 > 170
Dissolved Water (mg/kg) IEC 60184 < 20,00 < 15,00 < 10,00
Discharge Voltage (kV) IEC 60156 > 50 > 60 > 70

Supplementary worksheet


Sea Marconi Treatments vs Oil replacement (354.1 KiB)

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