What steps are followed in a power transformer oil filling procedure?

A typical procedure aims to keep oil dry and avoid introducing air. Common steps include draining or isolating old oil as required, evacuating the tank under vacuum, filtering and degassing new or processed oil, and filling under vacuum or with a sealed system to prevent moisture pickup. During filling, technicians monitor oil level, temperature, and leak points, then allow settling and de aeration. After filling, they sample oil for BDV, moisture, and sometimes DGA baseline, verify conservator and breather operation if present, and confirm protection devices and gauges function correctly.