Technical support in transformers

The power transformers are the most important equipment in a substation and its construction usually takes into consideration a life expectancy of 40 years, however the accessories connected to it do not always have the same longevity.

Therefore, the concern with the process of predictive and preventive maintenance in order to increase the operational reliability of the transformers, as well as seeking to control its lifetime, while resulting in savings of maintenance costs and shorter unavailability of the machine being a valuable business asset management of a substation. And in part the work of maintenance staff is to ensure that the transformer accessories remain in perfect working order, with the measurement accuracy, or with the performance of fire alarms.

Diagnosis, prognosis and expertise on the state of a transformer

The transformers are vital components in a transmission system. The work to maintain this equipment in reliable operating conditions depends largely on system for measuring oil temperature and winding. It is known that high temperatures cause accelerated aging in transformers and their measurement limits the increased load of the transformers.

Sampling of oil and processing of physical-chemical and chromatographic analysis

• The first big step towards a predictive maintenance system passes through the transformer periodic testing (physical and chemical analysis) to the insulating oil.
Through the results, is allowed to the Maintenance Manager to take the necessary corrective measures to maintain the operability of equipment.
In comparison to the overall maintenance costs and the risks associated to the absence thereof, the testing costs are very insignificant.

• When we speak about oil samples it must be to approached environmental issues with high caution, which should be of extreme rigor when we are in presence of dielectric oils, which by its use can easily be contaminated with foreign elements, highly toxic, including PCBs (polychlorinated of Biphenyl).

• Until recently, it was often to come across with transformers contaminated with insulating oil , PCBs above 50 ppm, due to poor market practices and the fact that about 35% of equipment in use in Portugal are contaminated (pure or diluted ). In order to identify and remove all equipment by the end of 2010, was drafted legislation, Decree-Law 277/99 of 23 July and Decree-Law 72/07 of 27 March.

• We guarantee screening of PCBs through the simple use of the KIT Clor-N-Oil Dexsil of 50, that it is a useful tool in achieving the general objectives of the Decree-Law 277/99 of 23 July ,which considers a contaminated equipment when the concentration of PCBs in the insulating fluid is greater than 50ppm.

Filtration, dehumidifying and degassing of the insulating oil

The presence of the insulating oil in a transformer has a dual function of dielectric and heat transference agent, for that must possess certain basic properties such as:
• Dielectric strength enough to withstand the stresses for its capacity to move and heat transfer is not disadvantaged;
• Must possess good oxidation resistance to ensure a long service life.
• The oil deterioration begins after the established contact with the equipment, ie, from the first minute in which the oil is placed inside the transformer, is influenced by the following factors:
• Presence of oxygen;
• High temperatures;
• Presence of moisture and metals act as catalysts for oxidation reactions.
• Initially in oxidation are formed soluble products in hot oil, but insoluble in cold oil, and may precipitate in the cooler parts of the equipment.

In advanced stages of oxidation are formed lees that may be insoluble even in hot oil, by depositing on the active part (core and walls of the tub) of the transformer. Besides damaging the circulation of heat and change the dielectric oil, the formation of these products accelerates aging of the paper, shortening the life of the transformer.

Thus, it is essential to improve the control and monitoring of results in the form of laboratory tests, the state oil, mainly to moisture, since the temperature of the active part is lower than the oil, there will be migration moisture in oil for an active and vice versa.

In the case of repackaging these oils and / or replacement thereof, should be a drying of active part in order to prevent the water (core, windings and the inner walls of the tub) migrate back to the oil.

Passivation of Oil Insulating

“During 2004 and early 2005, the occurrence of failures in over a dozen transformers of 500kV voltage class from various manufacturers (ABB, AREVA, Siemens and Toshiba), and concluding, after internal inspection, that the attack on covers the top of the winding interturn short sulfur cause the formation of copper sulphate, abruptly changing the dielectric strength of insulating paper, we need to determine the mechanism of failure and develop methods to diagnose and prevent the process . ”
(Cigré Set in Brazil, III Workshop of Chemistry & Environment, Belém – Pará – Aug / Sep 2006)”.

To confront reaction described, NYNAS, manufacturer of insulating oil, developed and recommended the use of a “passive” that is the Tolutriazol-based additive, known commercially as “NYPASS.”

Cosmanlux provides Passivation services.

Maintenance cleaning of the microswitches

Also known as switch, OLTC (On Load Tap Changer), CDC, load switches are devices used in conjunction with voltage transformers to vary the transformation ratio of these without using the service processor exit.

However, there are some switches that operate only out of power, ie, it is necessary to disconnect the transformer so that ratio be changed.
These devices operate mechanically, by changing the connection of the windings of the transformer according to the request of an operator. This request can be supply by means of a remote, power through local control or manually by a crank.

Exceeding the maintenance intervals jeopardizes the safe operation of the switch load and transformer. The key aspects to be considered for a proper predictive maintenance, undergoes:
• Monitor systematically the visual aspect of the silica, since it influences the quality of insulating oil on the switch;

• Because the outer parts of the switch, such as the head of the switch, relay protection and the drive motor, are subject to changing weather conditions, there is the need to carry out full and keeping these components;

• In the main and auxiliary contacts arcs are generated, causing carbonization of the insulating oil and wear contacts. The determination of wear and / or replacement of these contacts may only be subject to analysis during the inspection of key load (within the switch body • microswitches) at this time, is normal to replace fully the insulating oil;

• Some mechanical parts such as springs and brake blockers, are subject to mechanical wear and tear. Measurements and any replacements of these mechanical parts are needed and the switch just made during the inspection of cargo;

Surface treatment of the tub, conservative and radiators

For each work done on site, we suggest to our clients, according to the specific needs of each transformer, with or without the complete dismantling of its mechanical components, cleaning and degreasing, mechanical cleaning to St2/St3 areas with corrosion, sanding general of the surfaces (to remove non-adherent paint and opacities of the rest, application of at least one coat of epoxy primer 80 ? aluminum and applying two layers of 50 ? finishing.

• Status of preparation

• Final Status

Replacement of joints and / or crossings

• Before the replacement and subsequent assembly, the crossings must be perfectly dry and should be cleaned with alcohol or similar agent. The gaskets must be carefully placed and their attachments tightened in order to achieve good sealing.
The crossings must be fitted one at a time, to reduce the possibility of penetration of moisture into the transformer.
When necessary, for greater safety during the assembly of the crossings, shall be used proper devices for lifting and handling themselves.

Elimination of oil leaks, by welding

• Depending on the type of leakage, fissure or pore, and depending on the accessibility of it, can be viewed as potential remedies, the application of liquid metal or performance of the new weld.

Electrical measurements (transformation ratio, insulation resistance and dielectric strength of oil)

• We own properly equipment and calibrated for the testing of possible and necessary work.

Installation, maintenance, repair and replacement of equipment control and protection

• Our maintenance team ensures that the transformer accessories will continue in perfect working order, with the measurement accuracy, condition or actions of the alarms and reliable.

Maintenance of control cabinets and fans

• A perfect operation of the forced ventilation system is critical to a transformer, that request in previously established and calculated tests, to be automatically triggered. It becomes necessary, the application of predictive maintenance of the transformer, check the operating status of the entire set of existing equipment in the control and their fans.

Maintenance of transformer stations

• Electric Power Systems, which are part of Production, Transportation and Electricity, are linked together to the fact that constitutes a single “infinite network”.
This means that service quality, depends not only on how it is made to Operation of the EDP, but also of incidents at electrical customers of EDP and the method of operation thereof.
According to current legislation, all customers supplied from a private Transformation Station must have a Technical Responsible for Operation of electrical installations.
Cosmanlux has a responsible team with technical experience in providing maintenance services to a transformation station.

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