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Transformer Cooling Methods: Brief Explanation

Cooling of transformers is a process where the heat generated is treated back to a safe value. The cooling of transformers is done through various methods. 

The primary reason for transformer heat up is the loss of eddy current, iron, copper loss, and hysteresis. Out of all the major reasons behind the transformer’s heating up is the copper loss known as I2R loss.

And so it is evident for the need for a solution for the same.

Transformer Cooling Methods

 Transformers can be parted into two kinds:

 (i) dry-type transformers and (ii) oil-immersed transformers

Keep reading the article on various methods to cool down the transformer. For the cooling of transformers, the below cooling methods are used.

  1. Air Natural (AN)
  2. Air Blast or forced (AF)
  3. Oil Natural Air Natural (ONAN)
  4. Oil Natural Air Forced(ONAF)
  5. Oil Natural Water Forced(ONWF)
  6. Oil Forced Water Forced(OFWF)

1. Air Natural (AN)

The circulation of natural air is used in this method. By the process of natural convection, the heated air is replaced by cold air. This method is used for cooling smaller output transformer to 1.5 MVA, Also known as the self-cooled method

2. Oil Natural Air Natural (ONAN)



One of the easiest methods of cooling the transformer. The oil that gets hot because absorbing heat flows into the transformer’s upper tank due to convection. And the cold oil takes its place; hot oil that moves into the upper tank is cooled down again. The oil in the tank cools down, goes and flows back into the radiators. For as much as there is a load on the transformer, this circulation of hot and cold oil occurs. Tubes and radiators are added to the tank to create a different surface so that quick dissipation can take place, helping the transformer cool down easily and quickly.

3. Oil Natural Air Forced(ONAF)


This method is used to cool the transformer up to the rating of 60 megavolts ampere. In this method, the air is naturally circulated to cool down through the convection process’s dissipation. The pressure of forced air is used to cool down the transformer. You can cool down the transformer faster if the tank’s area is increased, which will result in a heat dissipation level. The air’s high velocity is forcefully applied and makes the fans and blowers work more quickly and efficiently, making the cooldown faster.

4. Oil Natural Water Forced(ONWF)

In this method, immerse down the core transformer and the windings in the oil tank. Install a radiator outside the tank. The temperature will rise, and the oil will heat up and move upward. The heat is dissipated because of the convection generated, oil is passed through the radiator; the water gets pumped and passed through the heat exchanger for cooling of the oil.

5. Oil Forced Water Forced(OFWF)


This method is much simpler. Logically, the water temperature is lesser than air, so water is used instead of air in this method. The circulation of the oil happens through the radiators, through a water chamber. Their jets of cooling water are showered on to the pipes containing the hot oil. Heat is exchanged much faster, and the oil gets cooled much quicker. Thus making this method more effective.

I hope this article had your answers on how to cool down a transformer! Keep reading.

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