How Are Dry-Type Transformers Cooled?
Quick answer — Dry-type transformers are cooled by natural air convection (AN) or forced air (AF) over the windings and core, with the heat carried away by the air through the insulated winding surface. They use AN for natural cooling and AF for forced air (fans) when the rating or ambient demands it, and the air must flow freely and the insulation (class B/F/H) sets the temperature limit.
How is a dry-type transformer cooled?
AN and AF
AN (air natural) is passive convection; AF (air forced) adds fans to raise the heat transfer, so the rated capacity can be higher for the same package — the dry-type equivalent of ONAN/ONAF.
Why it differs from oil
There is no oil, so the heat must leave through the surface of the windings by air. Cooling is less efficient than oil, so dry-type units are larger for a given rating and the insulation class sets the limit.
Improving cooling
Good ventilation, adequate clearances, a proper enclosure to keep airflow, and fans (plus a thermostat) control the temperature and maximise the rating.
References & standards
- IEC 60076-11 (dry-type)
- IEC 60076-2
Related
Related manufacturers
Prolec GE (GE Vernova) · Eaton · Virginia Transformer Corp · Delta Star · WEG Transformers USA · LS Electric America
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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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