What steps are typically outlined in a transformer oil filtration procedure?

A typical procedure includes safety isolation, sampling and baseline tests, connecting a closed loop filtration skid, pre filtering particulates, vacuum dehydration to remove moisture and dissolved gases, degassing as needed, and fine filtration to target particle counts. Oil temperature and flow are controlled to improve moisture removal efficiency. After processing, confirm BDV, moisture, and sometimes DGA trending, then document results. Good procedures also include preventing air ingress, using clean hoses, and verifying seals and valves before returning to service.