What precautions are required during transformer oil filling?

Use clean dry oil that meets specification, verify filtration and moisture levels, and keep the system closed to minimize air ingress. Ground equipment to prevent static, follow hot work controls, and use proper PPE. During filling, monitor vacuum level when vacuum filling is used, control flow to avoid foaming, and ensure vents and valves are correctly sequenced. After filling, check for leaks, verify oil level at correct temperature reference, and take post fill samples for moisture and BDV confirmation.