Foreword
Cooling method codes on transformer nameplates are often confusing for engineers and buyers. Today we explain ONAN, ONAF, OFAF and other cooling codes based on IEC 60076-2:2011, helping you choose the correct cooling type for 2500 kva 3 phase transformer and dry type distribution transformer.
1. 4-Letter Cooling Code Structure (IEC 60076-2:2011)
For liquid-immersed transformers, the cooling method is identified by a 4-letter code system:
1st Letter: Internal Cooling Medium
O: Mineral oil or synthetic insulating liquid with flash point ≤ 300°C
K: Insulating liquid with flash point > 300°C
L: Insulating liquid with non-measurable flash point
2nd Letter: Internal Circulation Mode
N: Natural convection circulation
F: Forced circulation by oil pump
D: Directed forced circulation (oil guided directly into windings and core channels)
3rd Letter: External Cooling Medium
A: Air
W: Water
4th Letter: External Circulation Mode
N: Natural convection
F: Forced circulation (fan or water pump)
2. Common Air Cooling Methods
ONAN – Oil Natural Air Natural
Internal: Oil natural circulation
External: Air natural convection through radiators
Features: No auxiliary equipment, simple structure, low maintenance
Application: Small distribution transformers
ONAF – Oil Natural Air Forced
Internal: Oil natural circulation
External: Forced air by cooling fans
Features: Fan interlock controlled by oil temperature
Application: Medium and large transformers, widely used in 2500 kva 3 phase transformer
OFAF – Oil Forced Air Forced
Internal: Oil forced circulation by oil pump
External: Forced air by fans
Features: High cooling efficiency, strong heat dissipation
Application: Large power transformers
ODAF – Oil Directed Air Forced
Internal: Directed forced oil circulation to core and winding hotspots
External: Forced air by fans
Features: Highest air-cooling efficiency, optimized material utilization
Application: Large and extra-large capacity transformers
3. Common Water Cooling Methods
OFWF – Oil Forced Water Forced
Internal: Forced oil circulation
External: Forced water circulation (oil-water heat exchanger)
Features: Ultra-high cooling efficiency; oil pressure must be higher than water pressure
Application: Large power transformers with water cooling system
ODWF – Oil Directed Water Forced
Internal: Directed forced oil circulation
External: Forced water circulation
Features: Top-level cooling performance
Application: Extra-high capacity power transformers
4. Cooling for Dry Type Distribution Transformer
A typical dry type distribution transformer mainly uses:
AN: Air Natural cooling
AF: Air Forced cooling
Most dry type distribution transformer supports AN/AF dual-mode cooling to improve overload capacity and operational stability.
About JINSHANMEN TECHNOLOGY CO., LTD
JINSHANMEN TECHNOLOGY CO., LTD mainly produces oil immersed power transformers, dry-type power transformers, oil immersed three-dimensional coiled power transformers, dry-type three-dimensional coiled power transformers, mining explosion-proof dry-type transformers, mining explosion-proof mobile substations, amorphous alloy power transformers, on load capacity regulating power transformers, locomotive dry-type transformers, as well as prefabricated substations, modular substations, wind energy box type substations, high and low voltage switchgear and other transmission and distribution equipment.
We provide standard ONAN / ONAF / OFAF cooling designs for 2500 kva 3 phase transformer and reliable cooling solutions for dry type distribution transformer for global customers.