Desludging of the transformer

Friday March 17th, 2017

Sea Marconi has devised a service called desludging, for insulating liquids and transformers affected by a prolonged oxidation process with insoluble by-product deposits (sludge), aimed precisely at removing those deposits, consequently prolonging the thermal working life of the transformer.

Desludging has great effect on transformers. Thanks to this treatment insoluble deposits that have formed on the papers,  the bottom of the case and in the interstices of the transformer are removed. This leads to a considerable improvement in terms of thermal exchange and therefore an overall improvement to the state of the transformer.

In cases of “Corrosion caused by dissolution of metals (C4)” with an increase of dissolved copper in the oil, the metals act as a catalyst for oxidation accelerating oil deterioration and sludge formation.

The insoluble oxidation by-products (sludge) accumulate on the reels and on the papers reducing their heat exchange properties. The consequence is a significant increase in localized temperature and therefore quicker deterioration of the papers until their failure. This mechanism is explained by Arrhenius law which states that the reaction rate doubles every 6/8°C.
It is a similar phenomenon to the prolonged accumulation of fat in veins, causing an increase in local stress (with increased blood pressure) and reducing the life expectancy of the patient.

Operating mode

Sea Marconi’s extraordinary results are based upon its experience in the industry since 1968, the use of Decontamination Modular Units (DMU), designed and manufactured internally, and the formulation of specific reactants used depending on the operating scenario.

The DMUs are connected to the transformer via flexible hoses, after which the decontamination process is started: the insulating fluid circulates through the DMUs where it is rheated, degassed, dehumidified, and filtered and depolarised (through special patented reactants) to then returned to the transformer, which is never emptied, not even partially.

The oil’s closed circuit between the transformer and the DMU, which creates a constant flow of oil to the transformer, is one of the necessary conditions for this treatment to be effective, however a meticulous control of the oil’s process temperature must be made alongside it. In fact, it is only possible to solubilise the polar compounds at 75/80°C (the aniline point temperature) and thus remove them.. The oil acts as a solvent for the insoluble compounds deposited on the papers and on the bottom of the case, which after dissolving into the oil, are attacked by Sea Marconi’s depolarizing reactants.
If necessary, desludging can be helped by adding a small percentages of insulating oils with an aromatic base.

The desludging treatment is a complex operation which requires great skill, proven experience and specific intervention protocols in order to operate safely.

The process can be done safely thanks to

  • the controlled process temperatures,
  • the use of patented reactants that are not explosive or flammable,
  • the use of special piping (SpillGuard®) which can stop the process if there are any accidential leaks but also thanks to
  • a software control system able to check in real time that the process is taking place safely as well as guaranteeing quality, 24 hours a day even without the supervision of an operator.

The treatment is performed with the On-Load option, keeping the transformer in service, under tension and filled, i.e. without any loss of production (with international experience also in nuclear power stations and transformers up to 760 MVA and 500 KV).

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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);
  • Desludging treatment;
  • Treatment quality control with on site measurement kit SM-TAN;
  • 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;
  • Oil inhibition with antioxidant additive DBPC (if necessary), should the initial conditions of the oil be such as to arouse suspicion that the oil has lost resistance to oxidation


  • Removal of insoluble oxidation compounds (acids) in oil
  • 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

gis due to; using a solid patented reactants, low process temperature (80-100 ° C), the lack of emptying the transformer, the use of a decontamination modular unit (DMU) created by Sea Marconi and equipped with an advanced monitoring system, providing 24 hour a day automatic safety

The treatment units' (DMU) small dimensions

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

Functional recovery of the oil and transformers

thanks to the unique and effective characteristics of Sea Marconi’s processes, after the treatment the oil’s properties return to excellent

Reference regulation

IEC 60422 Ed. 4 2013

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