What Is a Hermetically Sealed Transformer?
Quick answer — A hermetically sealed transformer has a fully sealed tank that does not breathe — the oil is contained and the headspace is kept as nitrogen or a vacuum or a sealed gas cushion, so moisture and air cannot enter. It is used for distribution transformers where low maintenance, a long life and no breather are wanted, and it is often oil-filled with a corrugated tank to absorb oil expansion.
What is a hermetically sealed transformer?
How it differs
Unlike a conservator-type unit that breathes, the sealed unit has no air ingress, so the oil stays dry and needs no breather. The tank expands and contracts (often via corrugations) to absorb the oil volume change.
Advantages
No moisture or oxygen ingress, lower maintenance, longer oil life and a compact design — used widely for distribution and pad-mounted transformers.
Considerations
The sealed design means the pressure can rise with temperature, so the tank and relief must be rated; the unit generally needs replacing rather than oil top-up.
References & standards
- IEC 60076-1
- IEEE C57.12.00
Related
Related manufacturers
Prolec GE (GE Vernova) · Eaton · Virginia Transformer Corp · Delta Star · WEG Transformers USA · LS Electric America
Related components
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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