The basic purpose of any transformer is to fill the gap of voltage requirements from one end to the another. While the transformer does this, in the process losses are witnesses in windings and the core of the transformer. The distribution transformer manufactures in India agrees that these losses tend to escalate with a rising capacity and heat dissipation of the transformer. Conversely, the losses are converted into heat which needs to be cool down. So the basic question that arises is how can we cool the transformers for proper heat dissipation?
How to Cool the Transformer?
Basically, there are two ways of cooling the transformer:
The first way is that heat gathered in the windings and the core of transformers is transferred by the coolant which is circulating inside the transformer to the tank walls and later it is dissipated to the nearby medium.
The second way is to use the first technique along with transferring the heat to the inside the transformers as well.
The kind of technique which should be incorporated depends upon the type of applications, the size of the transformer, it’s capacity, whether it is dry type distribution transformers or oil cooled distribution transformers, or if it’s electrical distribution transformers or power distribution transformers and the current working condition of the transformer.
In oil-cooled transformers, the coolant used is oil and the heat dissipation takes place by transferring it to the oil surrounding and the windings to the walls of the tank and finally heat is dissipated to surrounding air through convection and radiation.
Methods of Cooling of Transformer in oil-type transformers:
Based on the coolant used the cooling methods can be classified into:
- Oil Natural Air Natural (ONAN)
- Oil Natural Air Forced (ONAF)
- Oil Forced Air Natural (OFAN)
- Oil Forced Air Forced (OFAF)
Oil cooling transformer:
Oil Natural Air Natural (ONAN)
It is suitable for transformers pertaining to at last 30MVA. Since heat is taken from inside of the transformer and then heat is taken away by surrounding air it is known as Oil Natural Air natural method. The heat produced in windings and core of the transformer is transferred to oil by the procedure of conduction. The oil which is in contact with the surface when heats up pass to the top and get replaced by the cooled oil from the bottom. As a result, the heated oil transform its heat to the tank walls of the transformer by convection and conversely, heat moves to the surrounding air by radiation and convection as discussed above.
Oil Natural Air Forced (ONAF)
In this method, external connectors like elliptical tubes or radiator separators from the tank of transformers are adopted by cooling it with air blast that’s produced by fans. The fans are automatically switched on if the temperature rises beyond the optimum levels. Since heat is transferred to the transformer tank by heated oil, hollowness in tanks is some so that air is consistently blown to dissipate the heat. Hence, the transformer cools rapidly up to five to six times if natural means we’re used.
Oil Forced Air Natural (OFAN)
In this method, the heat is taken away by copper coil sue to the circulation of water inside the coil. However, the drawback is that since water is used if it enters the transformer it can contaminate the oil.
Oil Forced Air Forced (OFAF)
This method is very similar to Oil Natural Air Natural (ONAN) as fans are switched on automatically during high loads as it helps in cooling the oil. In case loads are less, then fans are switched off. It is a highly efficient method and the most flexible method. It is widely used in transformers pertaining to ratings of above 30MVA.