During the operation of the transformer, the oil undergoes an aging process, a result of the request for temperature increase, oxygen action and contact with materials in its constitution, such as metals (copper and iron). As a consequence, it occurs to the deterioration of the insulating properties of the oil.
In addition, by-products from IMO degradation lead to the acceleration of the degradative process of solid insulation and the formation of sludge. The process that governs the oxidation of hydrocarbons is the mechanism of peroxidation, leading to the formation of hydroperoxides.
After formation of these compounds, many oxidation by-products are formed, which differ according to the species that gave rise to them. The by-products formed, also called intermediates, are alcohols, aldehydes and ketones, which, in the presence of oxygen, generate carboxylic acids.
Because of their polar and acid nature, carboxylic acids are aggressive agents to the insulation paper and other materials present in the transformer. The insoluble, acidic sludge deposits on the windings, damaging the transfer of heat from the copper to the oil, increasing the temperature of the insulating paper and attacking it chemically.