How Is a Transformer Filled and Degassed?
Quick answer — The tank is vacuum-dried, then filled with degassed, dry oil under vacuum to remove moisture, air and dissolved gases that would reduce the dielectric strength. A vacuum degassing plant heats and degasses the oil before it enters the tank, and the assembly is filled slowly to avoid trapping air. The final step is to verify the oil quality and top up.
How is a transformer oil-filled and degassed?
Why degas?
Air, moisture and dissolved gases in the oil lower the dielectric strength and accelerate aging. Removing them before the oil is in service is critical.
The process
The oil is heated and passed through a vacuum-degassing plant that removes water and gases, then fed into the vacuum-dried tank. Filling is done slowly and from a low point to displace air without trapping pockets.
Verification
After filling, sample the oil for breakdown voltage, moisture, and dissolved gas, and check the level and any leaks. The tank is often kept under a slight vacuum or nitrogen until sealed.
References & standards
- IEC 60296 (transformer oil)
- IEC 60076-1
Related
Related manufacturers
Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp
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Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.
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