Reliable Fans for Transformer Cooling Applicatio

To ensure a reliable electricity supply, power transformers play a key role in the society and its infrastructure. This kind of system can be found in power plants and in the electricity grid in substations.

During operation of typically oil immersed transformers, losses occur in the tank and generate heat. These are concentrated in what is known as hot spots in the winding and significantly inhibit the service life of the transformer. Overheating of the winding would bring the system to a stop, which could result in a “blackout”.

According to studies by the University of Stuttgart, the service life of a transformer is reduced by a factor of 2 if the hot spot temperature increases by just 6 K. For decades mainly, axial flow fans have proved effective for use with powerful air-cooled transformers by using radiators or oil-coolers.

On a first view cooling seems simple. The hot oil (top oil temperature) flows by “natural” convection in an external radiator. The radiator basically is “naturally air cooled”, which is based on convection and radiation. This type of transformer is called ONAN (Oil Natural Air Natural).

But transformers with high power density and/or high ambient temperatures the heat dissipation will be insufficient by natural cooling methodology. The logical and simple way to improve the cooling capacity of a Transformer is to increase the air flow by using fans. Doing this we come to the most used power transformer types called ONAF (Oil Natural Air Forced).

But the cooling capacity of ONAF cooling systems depends on the local flow situations and temperatures in the radiator. Reliable cooling is a must to get the best performance from a Transformer, so the reliability of the fans used is of huge importance.

An ideal fan should:

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