Heat is generated during the operation of a transformer due to ohmic losses (I2R losses) in the winding and core. The removal of heat from the transformer is called transformer cooling. In this article, we will learn different ways to cool a transformer.
Types of Transformer Cooling Methods
Depending upon the type of transformer, transformer cooling methods are as follows.
For Dry type transformers, the transformer cooling methods are
- Air Natural (AN) cooling
- Air Blast (AB) cooling
These methods are also known as air type cooling of the transformer.
For Oil immersed transformers, the transformer cooling methods are
- Oil Natural Air Natural (ONAN) cooling
- Oil Natural Air Forced (ONAF) cooling
- Oil Natural Water Forced (ONWF) cooling
- Oil Forced Air Natural (OFAN) cooling
- Oil Forced Air Forced (OFAF) cooling
- Oil Forced Water Forced (OFWF) cooling
These methods are also known as oil immersed type cooling of the transformer.
Air type cooling of the transformer
1. Air Natural (AN) cooling
This type of cooling is used in dry type transformers. The cooling of transformers is accomplished through the use of the natural circulation of air around the transformer. In this method, the external surface is sufficient to dissipate the heat produced due to losses in the transformer. In general, this type of cooling is sufficient for low voltage, small transformers up to a few kVA (5-10kVA) in size.
2. Air Blast (AB) cooling
This type of cooling is also used in dry type transformers. In this method, a continuous blast of filtered cool air is forced through the core and windings in order to provide cooling to the transformer. External fans and blowers are used to produce the air blast. The use of this method of cooling is only permitted on transformers whose voltage rating does not exceed 25 kV.
Oil immersed type cooling of the transformer
1. Oil Natural Air Natural (ONAN) cooling
This type of cooling is used in oil immersion type transformers. In this method, the heat produced in the transformer is transferred to the oil. Heat causes oil to become lighter and rise to the top, replacing it with cool oil from the bottom of the tank. As the oil circulates through the tank, the heat from the oil is transferred to the walls. By means of radiation and convection, the heat is transferred to the surrounding atmosphere. As a result, the oil becomes cold and falls to the bottom. Therefore, the natural circulation of oil is maintained.
Note: There is no use of a fan in ONAN cooling.
2. Oil Natural Air Forced (ONAF) cooling
This type of cooling is also used in oil immersion type transformers. This type of cooling utilizes forced air to cool the cooling elements of the transformer immersed in oil.
3. Oil Natural Water Forced (ONWF) cooling
This type of cooling is also used in oil immersion type transformers. This type of cooling utilizes forced water to cool the cooling elements of the transformer immersed in oil. A water pump is used in this cooling.
4. Oil Forced Air Natural (OFAN) cooling
In this method of cooling, an oil pump is used to circulate the oil in the transformer. In this way, heat is transferred to the oil. The heat from the oil is then transferred to the walls of the tank. As a result, heat is transferred to the surrounding by radiation and convection. There is no use of a fan in this type of cooling.
5. Oil Forced Air Forced (OFAF) cooling
In this method of cooling, an oil pump is used to circulate the oil in the transformer. In this way, heat is transferred to the oil. Then it utilizes forced air to cool the oil. There is the use of a fan in this type of cooling.
6. Oil Forced Water Forced (OFWF) cooling
In this method of cooling, an oil pump is used to circulate the oil in the transformer. In this way, heat is transferred to the oil. Then it utilizes forced water to cool the oil. A water pump is used in this cooling. This method actually uses an external water heat exchanger.
