Transformer Cooling Fans

Transformers work to either ‘step up’ or ‘step down’ an incoming power supply. This is done by a precise relationship between the number of turns on the primary and secondary coils. Put simply, a transformer converts energy at one voltage level to energy at another voltage level.

Rosenberg transformer cooling fansTransformers do not have any moving parts but they do suffer losses, these are called either ‘copper losses’ or ‘iron losses’. Copper loss is the electrical power lost in heat as a result of circulating the currents around the transformers copper windings. Hysteresis, or Iron loss, is the lagging of the magnetised iron molecules within the core. The magnetised iron molecules are responding to the alternating magnetic flux generated by the AC input current. This lagging (or out-of-phase) condition is due to the fact that it requires power to reverse magnetic molecules; they do not reverse until the flux has attained sufficient force to reverse them.

The higher the capacity of the transformer, the higher the losses and resultant heat generation.  This means the temperature of the windings and the core increase. Thus, an effective cooling technique needs to be implemented. We outline our supplier, Rosenberg’s, transformer cooling fans below.

Heat generated in dry transformers must be dissipated over the surface of the coil. A combination of centrifugal and axial fans are ideally suited for this purpose. Our fans for transformer cooling help to remove the dissipated heat and, simultaneously, use the ambient air (air from outside the transformer) to cool down the transformer.

The following advantages result from efficient transformer cooling with fans:

  • Higher peak loads can be achieved
  • Improved transformer efficiency
  • Increase the power of the transformer
  • Longer life of components due to the constant distribution of temperature

Centrifugal Fans for Transformer Cooling

Both centrifugal and axial can work together as per the diagram. In this case, a centrifugal fan is pulling warm air down, extracting it away from the transformer whilst an axial fan provides cool supply air. There can be multiple configurations like this depending on the air volume and pressure requirements.

Centrifugal fans particularly suit compact transformer units with high pressure losses through the cooling coils, as this demands a higher pressure development from the fan than larger units. There will be a similar total air flow requirement in both sizes of transformer as the heat generation will be alike.

Our supply partner, Rosenberg’s DKNR centrifugal fans with free running impellers:

  • are available sizes 250-630 (impeller diameter)
  • benefit from an aluminium impeller with diffuser to improve the efficiency
  • are highly suitable for cooling of transformers in systems with increased pressure losses

Axial Fans for Cooling Transformers

Axial fans are suited to larger transformer units with lower pressure loss as they require a lower pressure fan. They will provide a similar air flow to centrifugal fans but at a lower pressure development.

Rosenberg’s AKSD / AKFD axial fans:

  • are available sizes 450-1000 (blade diameter)
  • benefit from efficient, sickle-shaped blades made out of aluminium with very low noise characteristics
  • are designed for a wide range of transformer cooling applications


To find out more about fans for transformer cooling or other applications, enquire here or call 01782 349 430.


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