What compounds are formed in mineral oil as oxygen inhibitors are depleted over time?

As oxygen inhibitors in mineral oil break down over time, they lead to the formation of acids and sludge. This process occurs due to the oxidation of the oil, which starts to produce byproducts that contribute to the degradation of the oil's quality. The acids formed can lower the pH of the oil, potentially leading to corrosion of equipment and other problems in a substation setting. Sludge is the result of various degradation processes, including the precipitation of contaminants and degradation products, which can settle in the system and cause operational issues like clogging filters or affecting the circulating oil. Therefore, the production of acids and sludge significantly impacts the performance and longevity of mineral oil used in electrical equipment.