Why is filtration of transformer oil required during maintenance?

Maintenance filtration restores dielectric strength and cooling capability by removing water, gases, and contaminants introduced by aging, leaks, or handling. It helps prevent internal discharge and reduces thermal stress by keeping cooling paths clean. Filtration can also stabilize oil chemistry by reducing polar compounds and sludge precursors. After repairs or tank opening, filtration is essential because moisture ingress can occur rapidly. Many utilities use filtration as a standard step in outage work to bring oil back within acceptance limits before re energization and to improve long term reliability.