Cooling Class (ONAN/ONAF/ODAF)
Standardized codes describing transformer cooling methods: O=Oil, N=Natural, A=Air, F=Forced, D=Directed flow.
Cooling classes define heat dissipation from core and copper losses. IEC 60076 uses four-letter code: internal medium (O=Oil, G=Gas, A=Air); circulation (N=Natural, F=Forced, D=Directed); external medium (A=Air, W=Water); external circulation (N/F).
Common: ONAN (simplest, natural convection); ONAF (fans for higher capacity); OFAF (pumps+fans for large power transformers); ODAF (directed flow, most efficient).
Affects temperature rise and rated capacity. Multiple stages allow different capacity levels.
QDTB selects optimal cooling based on rating and conditions. ONAN preferred for high-altitude performance.
Related Products
Related Terms
Temperature Rise
The temperature increase of transformer components above ambient at rated load, a key design parameter.
Hot-Spot Temperature
The highest temperature within transformer winding insulation, determining aging rate and loading capability.
Power Transformer
A large transformer (>10 MVA) used in transmission networks for stepping voltage between system levels.
More Terms Starting with “C”
CCC Certification
China Compulsory Certification (3C mark) required for electrical equipment sold in the Chinese domestic market.
CE Certification
Conformite Europeenne marking required for electrical equipment in the European Economic Area.
Core Loss
Power dissipated in the transformer magnetic core due to hysteresis and eddy currents, also called iron loss or no-load loss.
Copper Loss
Power lost as heat in transformer windings due to electrical resistance, proportional to the square of load current.
More in “Design & Engineering”
Altitude Derating
The reduction in transformer capacity and insulation performance required at high altitudes where air density is lower.
Faraday Shield
An electrostatic shield between transformer windings blocking capacitive coupling of high-frequency noise.
Leakage Reactance
Reactance from magnetic flux not linking both windings, a major component of transformer impedance.
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