Transformers play a critical role in the power industry by stepping voltage up or down. However, during operation, transformers generate heat in their windings and core. If this heat is not removed, the transformer could overheat, lose efficiency, or even fail.
That’s why cooling methods are so important. Cooling ensures safe, reliable, and long-term operation. Let’s explore the main cooling types, their principles and features.
1. Dry-Type Transformer Cooling
Dry-type transformers use air instead of oil for insulation and cooling.
(1) Natural Air Cooling (AN)
Principle: Heat is released naturally into the air through convection and radiation.
Features:
- Simple, low cost, easy to maintain
- Less efficient
- Best for small-capacity transformers
(2) Forced Air Cooling (AF)
Principle: Fans are added to force air circulation, improving heat dissipation.
Features:
- Higher efficiency
- Suitable for medium-capacity transformers
- Consumes extra power and requires fan maintenance
2. Oil-Immersed Transformer Cooling
In oil-immersed transformers, the windings and core are submerged in insulating oil, which transfers heat to the tank walls and then to air or water.
(1) Oil Natural Air Natural (ONAN)
Principle: Oil circulates naturally, transferring heat to the tank walls, then to the air.
Features:
- Reliable, simple, cost-effective
- Used in small and medium transformers
- Limited cooling capacity
(2) Oil Natural Air Forced (ONAF)
Principle: Same as ONAN, but with fans to force air circulation.
Features:
- Higher cooling efficiency
- Widely used for medium and large transformers
- Consumes extra energy
(3) Oil Forced Air Forced (OFAF)
Principle: Oil pumps circulate oil, and fans cool radiators.
Features:
- Very efficient
- Used for large-capacity transformers
- More complex and costly
(4) Oil Forced Water Forced (OFWF)
Principle: Oil pumps move oil through a water cooler, and cooling water carries heat away.
Features:
- Extremely efficient
- Suitable for very large transformers
- Requires water supply and higher maintenance
3. Cooling Code System
Cooling methods are often described using four-letter IEC codes (e.g., ONAN):
- First Letter: Internal medium (O = oil, A = air, W = water)
- Second Letter: Internal circulation (N = natural, F = forced)
- Third Letter: External medium (A = air, W = water)
- Fourth Letter: External circulation (N = natural, F = forced)
4. Industry Insight from TAILI ELECTRIC
At TAILI ELECTRIC, we design and manufacture distribution transformers and switchgear for different markets. From experience, we see that:
- ONAN and ONAF are the most common solutions for distribution projects in Asia and Africa.
- For critical infrastructure and data centers, OFAF and OFWF are often preferred due to higher safety margins.
- Selecting the right cooling method is not only about technology—it must also consider climate, project size, and maintenance conditions.
TAILI ELECTRIC – Powering a Safer World
