Transformer cooling methods

As a result of transformer action, both the core and the coil of the transformer become hot. The method used to compress the heat generated by the transformer or to keep the transformer cool is called the cooling system of the transformer.

Transformer cooling methods (transformer cooling class)

1. Natural calling,
2. calling by the winds associated with the high-pressure system,
3. calling itself submerged oil,
4. oil-immersed in cooling water stressful,
5. stressful oil submerged by air cooling, 
6. oil-immersed forced oil-cooled transformer

Transformer cooling requirements (transformer cooling necessity)

During the operation of an electric machine, various types of losses are expressed in the form of heat These losses are copper loss of welding, friction loss, and various types of mechanical parts, etc.

When the heat caused by different types of losses is not at normal temperature, the efficiency of the mentioned machine decreases, and over time the machine can be severely damaged.

In the case of a transformer, this heat must be properly affected and confined to normal temperature. For this, the transformer is cooled in different ways.

This increases the efficiency of the transformer and can function normally.

Transformer cooling methods are described (cooling of transformers)

1. Normal Calling: (Natural calling)

The heat generated between the small transformer and the instrument transformer spreads throughout the transport system and cools naturally in the radiation system.

This method is usually used to cool transformers of low KVA rating The heat that enters the body of the transformer is then cooled by exposure to air.

2. High pressure added Calling by air: (forced air cooling transformer)

In this method, the cold air blowing through the bottom of the transformer is introduced by the blower.

As a result, the cold air flows through the core and the coil, exits through the top, and cools the transformer as it travels and carries the heat of the coil.

This is done in densely populated areas where there is a risk of accidents due to oil exploding.


3. Immersed in oil Self Calling: (oil immersed self-cooled transformer or ONAN )

In this method, the core of the transformer and the coil are immersed in complete insulation oil. The number of iron tubes or pipes attached to the outside of the tank of such a transformer is always filled with the transformer coil.

When the transformer core and coil are heated at full load, the oil heats up and becomes light and rises. This hot light oil enters the pipe and the cold heavy oil of the pipe enters the transformer tank. 

The hot oil in the pipe then cools down in contact with the air and flows downwards, so that the cores, coils, and pipes flow naturally. As a result, the transformer cools itself with the help of oil 

4. Oil-pressurized water cooling: (oil immersed forced water-cooled transformer or ONFW)

In this system, the core and coil are immersed in oil, and a copper tube coil is placed in the hot oil on top of the transformer. Coldwater flowed through the pipe at high pressure from the outside.

When cold water flows through the tube, the tube cools As a result, the hot oil around the tube cools down and the hot oil from the bottom rises to the top.

The biggest drawback is that if the copper tube is perforated in any way, there is a good chance that the entire oil in the transformer will be contaminated.

5.Cooling by pressure air immersed in oil: (oil immersed forced air-cooled transformer or ONAF)

The surface area is increased by using Prince in the body of such a transformer. These fins are filled with hot oil and cold air from outside is given over the Prince tube or radiator at very high pressure.

Many electric fans are usually used around the transformer outside for this purpose This measure is usually taken in the case of large transformers

6. Immersed in oil Cooling by pressurized cold oil: (oil immersed forced oil-cooled transformer)

This method is similar to the method described above, but instead of cold water in a copper tube, a national cold oil used by the transformer is pumped through the abdomen.

If for some reason the pipe is perforated, there is no possibility of oil contamination.

It is not commonly used as it is an expensive and complex system.

Symbol of transformer cooling system


The full name is Oil Natural Air Natural, meaning this type of transformer oil will be cooled by normal air pressure. The oil will not be used in any other cooling process.

This process usually cools the small distribution transformers


The full name is Oil Natural Air Sports, meaning such transformers will be cooled by oil pressurized air. This is why electric fans are used in this process

These fans are placed at the bottom of the transformer If necessary, the fans are turned on and cooled by the pressurized air Large power transformers have this system


The full name is Well Force Airport, which means that such transformers will be cooled by oil and pressurized air. Larger power transformers have this system.

Transformer oil and its properties: - (oil used in transformer)

Transformer oil: - (transformer oil is)

The oil used in the transformer to keep it cool, This is called transformer oil It is basically mineral oil Mineral oil is treated and made suitable for use The main name of this oil is "Pyranol''. Another function is transformer  coil to increase the insulation between the and the tank

transformer oil properties (transformer oil quality)

Extremely high-quality resistance must be complete

Must have high dielectric power

There will be no sludge

There will be no sediment

Must be less adhesive

It will not evaporate easily

Water vapor must be free 

There can be no floating matter

Must be free from acids, alkalis, and sulfur

It will have less viscosity and less tendency to freeze

Must be combustible

Oil flush point should not be below 160C

Oil fire point should not be below 200C

The relative importance of the oil should be 0.85

FAQ Question in Transformer cooling methods

Q1.  What is the sledding of the transformer?

When the oil of the transformer comes in contact with air, it reacts with oxygen and breaks down the oil molecules to form sediment. This is called sledding.

Q2. Where is the problem of water cooling of the transformer?

The biggest problem is that the copper pipe is perforated or cut. Then the water in the copper pipe mixed with the transformer oil can cause a fatal accident.

Q3.What is the flush point of transformer oil?

The temperature at which the oil floats and catches fire is called the flash point. Its temperature should not be below 160C.

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