COOLING OF TRANSFORMER - ELECTRICAL ENCYCLOPEDIA

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COOLING OF TRANSFORMER


In this article we will study about the Cooling and Methods of cooling is a transformer.
In rotating machines like motors and generators ,cooling fans are provided . When the machine rotates, the fan causes the circulation of air and hence provides necessary cooling.
But as we know, transformer is a static machine and cooling is difficult. When transformer is working some heat is always produced due to copper losses.

The removal of heat from the winding of transformer is called the Cooling of Transformer.

Cooling is important for every machine whether it is an engine, transformer or computer etc.
Cooling increases the efficiency of the machines.
Same is true for Humans also, suppose you are made to work at temperature above 40 degree celsius, it would a very tough condition for you.
Therefore, some means are taken to avoid the high temperature of the winding . The different methods of cooling of transformer are ;

TYPES OF COOLING OF TRANSFORMER

Cooling of transformer depends upon the type of transformer whether it is an oil immersed transformer or a dry transformer.

For Dry type Transformer
Dry type Transformer are the transformer which does not have any liquid like oil or silicone in it. Such transformers are used upto lower voltage rating and in areas which are having high moisture content.
Such transformers have following methods of cooling.

1. Air Natural Cooling.
2. Air Blast Cooling.

1. Air Natural Cooling-  This cooling is used for small transformer upto voltage rating of 10 to 15 kV. In this method , only natural circulation of air without using any fan, blower etc is used for cooling.
The surface area of the core and  transformer winding is increased to dissipate the heat generated.
Fins are made on the body of transformer similar to that in an engine to increase it's surface exposure area.
Fins are provided on the main tank of
transformer to increase it's surface exposure.


2. Air Blast Cooling- We can say that it is the type of artificial cooling because the forced air is used for cooling purposes.
In this method, transformer is placed over an air chamber and air is maintained at a sufficient pressure with the help of blowers. The air is forced through core and winding of transformer.
Air Blast Cooling with fan provided.

Use of this method of cooling is preferred for the transformer installed in the substation located in thickly populated areas, where oil is considered as fire hazard.

For Oil Immersed Transformer
Oil Immersed Transformer are used for higher voltage ratings. In such transformers, core and winding of transformers are immersed in the "transformer oil", hence it's name.
Cooling methods used in such transformers are:

1.Oil immersed Natural Cooling.
2. Oil immersed water Cooling.
3. Oil immersed air Blast Cooling.
4. Forced Oil Immersed Natural Cooling.

1. Oil Immersed Natural Cooling- In this system, only transformer oil is used for cooling as well as insulation purposes. The oil takes away the heat from core and winding and gives it to the tank surface ,from where the air takes away the heat.
Transformer is filled with oil for cooling.
Oil Immersed Natural Cooling.

To make this system more effective, the surface area of tank is increased . Due to the heat produced by transformer, the oil circulates through pipes, tubes and tanks. The hot oil, being lighter in weight and it goes up and hence natural circulation of oil takes place.

2. Oil Immersed Water Cooling- This is the another method of cooling for the transformer of ratings above 500kVA.
Heat produced in the main tank is taken away by the transformer oil. To dissipate the heat more fastly from the oil to the surrounding , radiator spiral pipes are provided. Water is circulated through these pipes .It absorbs the heat from the oil. Water itself becomes hot and thus reducing  the temperature of the oil, which in turn reduces the transformer's temperature.
Oil Immersed Water Cooling.

But in this method there is always a risk of leakage of water through the pipes. Even a small leakage of water can increase the moisture content of the oil.

3. Oil Immersed Air Blast Cooling- In this method of cooling, the core and winding is immersed in the oil and in addition to this ,air is forced over the surface with the help of fans and blowers.
Broadly speaking, this method is the combination of Oil Immersed Natural Cooling and Air Blast Cooling.

4. Forced Oil Immersed Natural Cooling- In this method of cooling, the core and winding are immersed in the transformer oil as usual. As well as the oil in the main tank is circulated with the help of motor driven pump. This pump forces the oil in the main tank and circulates in it.

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