How is testing of transformer oil insulation carried out?

Oil insulation testing combines field screening and laboratory analysis. Field checks often include on site moisture screening, BDV testing, and visual inspection for color and particles. In laboratories, the program typically includes moisture by Karl Fischer, acidity, interfacial tension, dissipation factor, resistivity, inhibitor content, particle count, and DGA for fault gases. DGA is commonly referenced to standards like ASTM D3612 methods. Sampling quality is critical: clean bottles, flushing of valves, and avoiding air bubbles to keep results representative and actionable.