A study on the depletion effects of insulating oil preservation additives in power transformers

Power transformers utilise solid and liquid-oil insulators as the insulation system against the dielectric stresses between the internal parts. The insulation system itself is a core component of the transformer and ageing thereof is mainly dependent on the condition of the insulation system. During operation of the power transformer, chemical reactions occur internally between materials and compounds, whereby some of these reactions are detrimental to the insulation system and the overall transformer health. Mineral insulating oil comprise of several compounds and additives that are essential in preserving the transformer against ageing. This paper focuses on inhibitor and passivator additives employed in mineral insulating oil in power transformers. These additives deplete over time and require careful monitoring and replenishment to ensure sustained transformer health. An ongoing challenge in protecting power transformers against premature ageing lies with a lack of understanding of the causes of additive depletion as well as the depletion rates. Although, there is a basic understanding of normal depletion of the additives, the major factors that influence depletion and the extent of these effects are not yet fully comprehended. The presented study reviews research on additive depletion rate and factors that affect depletion of those additives, with the aim of explicating the related knowledge gaps and determining key aspects of future research focus towards addressing the aforementioned challenge.