Oil ages during the operating life of a transformer. By performing oil reclamation, where the oil is passed through an absorbent, the oil can be reinserted into the transformer in a new state.
Oil is a natural material that ages due to the operating environment and transformer properties. Through oil sampling and analysis, the condition of the oil can be inferred. Aged oil demonstrates a higher concentration of oxidation and acids.
Oil reclamation or oil regeneration is a process whereby oil is processed to achieve a significant condition improvement, aimed at being as close to “as new” as possible, by removing the aging products. The processing is performed while a transformer is in service to achieve maximum effectiveness with minimum impact on on-site operations. The oil affects the insulation in the transformer, and the insulation affects the oil; hence the condition of the oil impacts the expected life of the transformer.
The modern reclaiming technology with the reactivation of the absorbent makes it economically feasible to use much more active absorbent material. Typically 5-10 times more absorbent is used compared with the old conventional systems. This leads to a much better cleaning effect on the paper and to the excellent long-term stability of the reclaimed oil.
For some transformers, there is data available for up to 10 years after reclamation. The data shows very little change in acidity and color after 10 years of operation since the oil was reclaimed.
To prevent excessive production of acids due to oil degradation, it is recommended that the oil be reclaimed before it is severely degraded. Low molecular weight acids migrate into the paper insulation and become much harder to remove than from the oil.
The essential elements of the online reclamation technology are that the absorbent is automatically reactivated after each cycle and that the transformer remains in operation. The reactivation allows for using much more active absorbent than with the classical type of reclaiming plants, where the Fullers' earth needs to be replaced frequently and thereafter disposed of. The final step is to restore the inhibitor content.