Cooling Methods of Transformer

Cooling Methods of Transformer

A transformer is a static device used to transfer the electrical energy from one voltage level to another voltage level. As we have seen in the construction of the transformer, it consists of two windings; primary winding and secondary winding. These windings placed on the core of the transformer. In this article, we will discuss different cooling methods of Transformer.

Why Cooling Methods Required in Transformer?

In the transformer losses, the main losses are core loss and copper loss. The core loss occurs in the core of transformer and copper loss occurs in the winding of the transformer.

These losses appear in the form of thermal energy and increase the temperature of the transformer. therefore, it is necessary to dissipate heat from the transformer for reliable operation and long life.

If the heat is not dissipated properly, the insulation of the transformer may get damages. Hence, it is essential to control the temperature of the transformer within permissible limits.

The coolant used for the transformer is,

  • Air
  • Mineral oil (Transformer oil)

The transformer which used air as a coolant, that transformer known as dry type transformer. And the transformer which used oil as a coolant, that transformer known as an oil-immersed transformer.

There are several methods for cooling of the transformer. Out of these methods, the choice of method depends on the size, rating, type of application and type of condition obtaining at the site where it installed.

Cooling Methods of Transformer

With the use of air and oil, there are several methods as listed below.

1) Air Cooling

  • Air Natural

2) Oil Cooling

  • Oil Natural Air Natural (ONAN)
  • Oil Natural Air Forced (ONAF)
  • Oil Forced Air Forced (OFAF)

3) Oil Immersed Water Cooling

  • Oil Forced Water Forced

Let’s explain all the methods in detail.

1) Air Natural

This method used for a small rating of the transformer and not recommended for a large transformer. In this method, the ambient air used for cooling the transformer.

2) Oil Natural Air Natural (ONAN)

This method used for the transformer up to the rating of 50 MVA. This is the simplest method of cooling of the transformer up to this rating.

In this method, the transformers fitted with a panel radiator for oil natural circulation.

3) Oil Natural Air Forced (ONAF)

In this method, panel type radiators are provided with cooling fans. The fans are switched on during heavy loads only.

Oil Natural Air Forced (ONAF)
Oil Natural Air Forced (ONAF)

The above figure shows the Oil Natural Air Forced method of cooling.

The forced air produced by the fans takes away heat from the surface of the radiator and provides better cooling than natural air.

The rate of heat dissipation in this method is good compared to the Oil Natural Air Natural (ONAN) method. This method used for the transformer rating up to 75 MVA.

4) Oil Forced Air Forced (OFAF)

In this method, the oil forced to circulate within the closed-loop of the transformer tank by means of oil pumps.

The oil circulated through coolers. The coolers have cooling fans to exchange heat from oil to air.

Oil Forced Air Forced (OFAF)
Oil Forced Air Forced (OFAF)

The above figure shows the method of Oil Forced Air Forced (OFAF)

Heat dissipation in this method is faster than Oil Natural Air Natural (ONAN) and Oil Natural Air Forced (ONAF) methods. This method used for transformer rating up to 75 MVA.

It is a compact system and occupies less space compared to the other two methods.

5) Oil Forced Water Forced (OFWF)

In the same weather condition, the ambient temperature of the water is less than the atmospheric air. Therefore, the water is a good heat exchanger compared to the natural air.

In this method, the heat exchanged from oil to water. And both oil and water circulated in a closed path through the radiator.

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