What steps are involved in transformer oil processing procedure?

A typical oil processing procedure includes heating and circulating the oil, coarse and fine filtration to remove particulates, vacuum dehydration to remove dissolved and free water, and vacuum degassing to reduce dissolved gases. The process may include adsorption or regeneration steps if acidity and sludge precursors are high. Operators control temperature, vacuum level, flow rate, and filter condition, then verify results with BDV, moisture, and sometimes gas content before returning the transformer to service.