The dehydration system can remove about 10 liters of water. Absorption time, and so the efficiency of the device, varies depending on the hydration level (water content) and the transformer’s operating temperature.

• Applied to a device with a hydration level of 4% in the cellulose, and operating at high temperatures in a particularly humid environment, the system reaches saturation in about 6-9 months.
• Applied on a device with a hydration level of 1% in the cellulose, and operating at 50 ° C, the TRASEC CL3A system can last up to 24 months before saturation.
• On a new, dry appliance (hydration < 0. 5%), the system can last up to 5 years before saturation.

The oil suction pipe is connected to the lower part of the case or to the oil’s required cooling circuit; the delivery pipe is connected to the upper part of the case or the required cooling circuit.

The dehydrating device absorbs the water dissolved in the oil until it is saturated. The cartridges can be inserted with two sensors to measure the concentration of capacitive equivalent water dissolved (CL3AM).

After reaching the saturation point, the cylinders containing the molecular sieves must be replaced and sent to be regenerated. Sea Marconi staff or the user himself can replace the cylinders. During regeneration, the weight of the molecular sieves is compared to their original weight (dry material); the weight difference corresponds to the amount of absorbed water.

Essentially water within a transformer derives from two sources; either external, due to a damp environment or internal, due to thermal deterioration of the papers (hydrolysis).Therefore water can be dissolved within the oil or, more seriously, be absorbed into the solid isolation (papers) with an increasing probability of thermal damage, and bubble formation moving on to partial, low energy (D1) and high energy discharges (D2).

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.

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.

Activities in details

• 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;

• 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:

Supplementary worksheet

Sea Marconi has developed the Deosvision service for analysis and diagnosis, which is aimed at preventing the catastrophical failure of electrical equipment linked to critical issues,
In fact, it is very similar to what happens in clinical diagnostics, as one can monitor the health status of the transformer by analyzing a sample of oil taken from it and then make the subsequent diagnosis.

Deosvision involves the following steps:

1. Sending the client a kit to sample the fluid
2. Extracting the sample from the transformer and sending it to the Sea Marconi laboratory
3. Completeing the required laboratory analysis
4. Issuing the diagnostic report, which clearly highlights both the problems identified, and the course of action to take.

Based on the investigation’s aim Sea Marconi can suggest a specific diagnostic package (with a series of targeted analysis), for example to know the state of health of a transformer at a specific point in its life cycle (LCM) or to identify/expand on a particular critical “disease” that the oil or transformer has.

Below are the main packages:

• Sampling of oil, and even more so of papers, must be carried out by qualified operators according to protocols and procedures
• laboratory analyses must be carried out using methods set by reference standards, as guaranteed by accredited laboratories
• actions to prevent the “Water in the transformer (paper and oil)” criticality, namely the dehumidification and internal transformer inspections must be carried out
  • using technologies that are safe and fit to meet the requirements of BAT and BEP
  • using staff with specific skills and training
  • relying on operators able to demonstrate an extensive application case history and able to certify interventions carried out with quality assurance (ISO 9001)

For the definition of action priorities and choice of countermeasures, it is necessary to diagnose whether the criticality originates internally (paper degradation) or externally (atmospheric influences).

If the origin of the moisture is internal (degradation of paper and oil) the countermeasures are:

Physical treatment,
Physical treatment, in the first instance to be performed off-load and subsequently on-load (transformer under load). This activity can be aided by applying dehumidifying cartridges

Direct dehydration (cycle B).
Direct dehydration of the transformer (papers) consists of heating the windings through circulating the oil.

Then there are other techniques, some of which require handling of the transformer. These techniques require that the transformer be opened and treated, in some cases through drying of the nucleus in autoclave, in other cases using appropriate solvents (derivatives of aviation kerosene). These modes, which are far more expensive, are taken into consideration when, in addition to the water problem, there are other electromechanical criticalities which require replacement of parts or in any case extraordinary maintenance of the transformer.

If the origin is external, it is necessary to identify air inlet points and restore the seals. If necessary, it is advisable to change the drying salts, and consider increasing the amount or geometry of the container to increase the drying power.

The presence of water in the paper and oil system inside the transformer can be an extremely critical condition, especially when the criticality reaches an “extremely wet insulation” level (Table A1, IEC 60422, page 42), causing unreasonable risks of electrical failure.

Table A.1 – Guidelines for interpreting data expressed in per cent saturation – IEC 60422 ed. 4-2013

This condition cannot be resolved with physical treatment of the oil alone, which would reduce water in the oil but not in the papers. The phases of energisation of the transformer at low temperature with sudden load are particularly critical. In these cases, water bubbles are very likely to form.

The life cycle management strategy is to avoid the formation of water in the oil-paper system as much as possible. Although it is impossible to eliminate this criticality, it can be prevented or mitigated through appropriate operational practices (e. g. analytical control of oil and indirectly of papers, oil treatment, load profile management, cooling of the machine). If the transformer belongs to a family of equipment affected by failure for the same criticality, ad hoc operating practices can be defined that optimise the various critical factors (e. g. by installing dehydrating cartridges).

Monitoring symptomatic indicators (see symptoms above). If the first symptoms of criticality appear, such as a high content of water in the oil, it is recommended that the frequency of analyses be increased in order to monitor trends.

 Perform appropriate oil treatments in order to keep moisture low in the papers and in any case in order to avoid reaching the “wet insulation” condition (Table A. 1 – IEC 60422 ed. 4-2013).

Suggested actions include:

Physical treatment
This is a process performed on site, keeping the transformer in service (and under load) without having to empty it. The operation is carried out using a Modular Decontamination Unit (MDU) specifically created by Sea Marconi. The transformer is connected to the DMU by flexible hoses; the oil contaminated with DBDS is sucked from the lower part of the transformer and transferred into the DMU, which heats it, filters it, degasses it and dehumidifies it before pumping it back into the upper part of the transformer. This creates a closed loop which, every time the oil is circulated, is able to restore the values of the main physical parameters of the oil (water, gas, particles). (read more)

Application of cartridges for dehumidifying the transformer
This activity is accomplished by means of an apparatus which is placed on the transformer and operates continuously as a loop circuit under load and has columns with molecular sieves for selective adsorption of moisture and other polar compounds.

For breathing machines with conservator, it is advisable to periodically check the drying salts (read more)

It is recommended performing (and keeping updated) the dynamic inventory of transformers with indication of the markers (indicator) symptomatic of the “Water in the transformer (paper and oil)” criticality throughout all phases of the life cycle. It is also advisable to map the equipment in “wet” and “extremely wet” conditions.

Other than those using minerals, what are the preventive measures for electrical machines with insulating liquids?

With regard to natural ester oils and synthetic esters, the preventive actions are the same; however, it is advisable to choose countermeasures after careful assessment in terms of cost-benefit, cost-effectiveness and environmental impact (biodegradability and fire safety). For silicone oils in operation, the treatments recommended by the standard (IEC 60944:1988) are “vacuum treatment and filtration” and “molecular sieves and filtration”.

For diagnosis of the the “Water in the transformer (paper or oil)” criticality, Sea Marconi uses its own diagnostic metrics, namely:

visual signs on the transformer (and those from any internal inspection) are interpreted;

through analysis of the oil and papers (if available following internal inspection) the symptoms are identified and co-factors evaluated. One of these is undoubtedly the temperature, both sampling and ambient temperature. At the same time it is necessary to evaluate the degradation of the oil, the type of oil (between paraffins and naphthenics there are different degrees of solubility, which is even more evident for natural esters, which can reach solubilisation up to 10 times more than mineral oils ) and concentration and type of additives.

The limits recommended limits by IEC 60422 regarding oil in a just-filled transformer and before energisation are:

Sempre la stessa norma a pag. 28 indica i limiti raccomandati di acqua in olio per un trasformatore in esercizio:

Starting from the analytical results of the “water in oil” test, there are several methods (with different levels of precision) for evaluating the state of cellulose hydration, that is, the water absorbed by the papers. First of all, it is necessary to distinguish between direct methods, which involve the analysis of paper samples taken from internal inspection, and indirect methods, through mathematical formulas and diagrams.

Technical standard IEC 60422, for example, enables (see table below) estimation of the moisture conditions of the solid insulator (papers). To obtain this estimate, it is necessary to calculate (see formulas below) the saturation of the water in oil, that is, the maximum concentration of oil that can solubilise in oil at a certain temperature.

After calculating the water saturation in oil in percentage terms, using the table below (Table A. 1 – IEC 60422 ed. 4-2013) it is possible to obtain an estimate of the moisture of the papers: dry, slightly moist, moist, extremely moist.

the database is used to study family or subjective case histories (in the search, for example, for failures in twin machines);

 the factors of uncertainty, speed and evolution over time (trends) of symptomatic indicators are taken into consideration and monitored during the life cycle phases; for this purpose, it is important to disengage from the sampling temperature (which changes in relation to the operating profile), renormalising the analytical result of the water in oil at a temperature of 20 °C (seeIEC 60814]. This calculation is performed using the formula [put formula] pag. 13 (IEC 60422) with correction factor (see Fig. 1, page 41, IEC 60422).

 on the basis of assessment of these key factors, the specific criticality is classified according to type and priority, and type and priority of corrective actions are identified at the same time.

The specific symptom of the “Water in the transformer (paper and oil)” criticality is related to the presence of the following diagnostic indicators with typical values not compliant with those recommended by the IEC 60422 standard:

Water in oil (IEC 60814)

To these are added diagnostic indicators derived from insulating paper analysis (following any internal inspection and sampling):

DP, degree of polymerisation (IEC 450:1974)
Water in papers (IEC 60814)

There are also co-factors useful to complete the diagnostic framework (resulting from the oil analysis):

Acidity TAN (IEC 62021-1)
Particles (IEC 60970)

In cases of internal inspection of the transformer, signs of free water or drops of water can be observed mainly at the bottom of the casing and at the bottom of the transformer casing head. These are very dangerous because they are close to high voltage areas. Signs of rust or localised paint stripping can be observed in the same area. In the case of loss of casing seal, windings can sometimes also also show signs of water.

Should it be decided to carry out an internal inspection of the transformer, following a failure or in order to carry out a thorough inspection, it is strongly recommended to take samples of the insulating papers in accordance with relevant protocols and procedures. In particular, it is advisable to take papers from the top, bottom and middle of the both individual primary and secondary windings for each phase, taking multiple paper samples in areas with greater signs of criticality (see below).