Despite successive transformer oil purification treatments, the oil always finishes by deteriorating and becoming acid and brown in colour. Beyond a certain acidity limit (index between 0.4 and 0.6 Mg KoH/gr depending on the voltage) there is a real danger since the breakdown voltage deteriorates quickly and requires a multiplication of dehydrating operations to keep it at an acceptable level. When this occurs purification is no longer sufficient and the oil must be either changed or regenerated.
The regeneration process is an economic and ecological alternative to the « refilling » process which consists in replacing the oil with new oil. Besides used oil recycling issues and the consumption of a high volume of generally fossil origin product (large transformers can contain up to 100T), the « refilling » method requires the extended halt of the transformer to be treated. This is not the case for regeneration which can be carried out with the transformer running, thereby avoiding shutting down the installation. Generation, which treats the oil in a loop on the transformer, also avoids the rises in acidity usually experienced within a few weeks of a « refilling » because of the used oil still contained in the insulation.
Oil regeneration is therefore an important treatment step to be carried out after purification treatment. The process passes the oil through resins (commonly know as « Fuller’s earth ») which especially absorb acidity thereby allowing the dielectric fluid to return to its original physical-chemical properties (acidity, colour, viscosity, resistivity, IFT, Delta tangent, resistance to oxidation, breakdown voltage, etc.). The service life of the fluid, and therefore of the transformer, is extended.
Previously this process was seldom used because the effectiveness of the fuller’s earth dropped quickly during prolonged use, and the cost of replacing it was significant, especially as the the cost of treating oil-saturated fuller’s earth had to be added to its purchase price.
Our new Reg’N process significantly reduces operating costs by making it possible to regularly re-activate the resins throughout the process to maintain their effectiveness. This reactivation process is achieved by self-combustion of the treated fluid within the resins using the oxygen from the air. This operation can be repeated over 300 times before the resins need to be replaced.
The combustion fumes are treated using activated carbon before being released. Other treatment systems without consumables will be proposed shortly.
The Reg’N system developed by ARRAS MAXEI once again offers great flexibility since we can propose either the complete treatment and regeneration unit, or only the regeneration module to be used behind an existing treatment system. The complete solution has the advantage of being more compact, but above all of being equipped with centralised totally built-in control/command to guarantee the automatic, reliable and completely safe operation of both treatment systems. This is strongly recommended if the option with the transformers running is chosen. The separate module solution makes it possible to switch to regeneration at a lower budget with an interconnection of the two installations but a less complete interaction and fewer functions.
The possible options are similar to those for oil treatment systems despite the fact that many items of equipment are included in the standard models.