Why is transformer oil cleaning required during maintenance cycles?

Oil cleaning removes water, gases, and particles that degrade dielectric strength and cooling performance. Moisture lowers BDV and accelerates paper aging, while particles can create local electric stress and trigger partial discharge. Dissolved gases and oxidation byproducts can indicate active faults or ongoing chemical degradation. Cleaning, typically via dehydration and fine filtration, restores BDV and reduces the risk of insulation failure. In many cases it is a cost effective way to extend service life without oil replacement, especially if the base oil is still chemically stable and acidity remains within acceptable limits.