Transformer oil service life is determined by oxidation, thermal stress, moisture ingress, and contamination with particles or dissolved gases from internal faults. High operating temperatures accelerate oxidation and form acids and sludge, which degrade dielectric strength and reduce cooling efficiency. Moisture and oxygen ingress, especially in poorly sealed breathers, raises water content and speeds paper insulation aging. Electrical discharges can generate gases and carbon particles that contaminate the oil. Regular testing, filtration, dehydration, and in some cases regeneration can extend oil life, but persistent faults will continue to degrade oil until corrected.
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