Transformer oil, a critical component for insulation and heat dissipation, degrades over time due to a combination of chemical, physical, and electrical factors, compromising the transformer’s performance and safety. One of the primary causes is Oxidation, which occurs when the oil reacts with oxygen in the air. This reaction is accelerated by high temperatures (above 60°C), moisture, and catalytic elements like copper or iron (from winding conductors or core laminations). Oxidation produces acidic by-products (such as carboxylic acids) and sludge, which lower the oil’s dielectric strength and increase its viscosity. Acidic compounds also corrode the transformer’s metal components (windings, core, and tank), while sludge clogs cooling systems, reducing heat dissipation efficiency and leading to further overheating.

　　Moisture Contamination is another major factor in oil deterioration. Moisture can enter the transformer through faulty gaskets, breathers (if desiccants are saturated), or during maintenance (e.g., improper oil filling). Even small amounts of water (as low as 50 ppm) significantly reduce the oil’s insulating properties—water molecules ionize under high voltage, increasing conductivity and the risk of partial discharge or arcing. Moisture also accelerates oxidation and hydrolyzes ester-based oils (used in some modern transformers) into acidic compounds, further degrading oil quality.

　　Electrical Stress from high voltages or partial discharges also contributes to oil degradation. Under electrical stress, oil molecules undergo dissociation (a process called “electrolysis”), producing free radicals that react with oxygen to form peroxides and acids. Partial discharges, which occur in areas of high electric field intensity (e.g., around damaged insulation), generate heat and ozone, both of which accelerate oil oxidation and break down hydrocarbon chains into smaller, more volatile compounds. These compounds can further contaminate the oil, creating a cycle of degradation.

　　Additionally, Mechanical Contamination (dust, dirt, metal particles) from manufacturing, maintenance, or wear of internal components can scratch the oil’s insulating film and act as catalysts for oxidation. Metal particles (e.g., copper or iron filings) increase electrical conductivity and promote the formation of sludge. To mitigate oil deterioration, transformers are equipped with oil filters, breathers with desiccants, and temperature control systems. Regular oil testing (measuring acidity, moisture content, dielectric strength, and dissolved gas levels) is also essential to monitor quality and schedule oil regeneration or replacement.

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