Cooling methods of transformer:
One of the major electrical machine in distribution system is power transformer.while operating transformer at high power ratings we experience heat comes from I²R losses of copper,hysteresis & eddy current losses.we need to reduce this heat in transformers for efficient operation.In electrical power transformer we use different cooling methods of transformer to eliminate heat quickly.
Transformers can be divided in two types as
(i) dry type transformers and
(ii) oil immersed transformers.
Different cooling methods of transformers are:-
For dry type transformers
1.Air Natural (AN)
2.Air Blast(AB)
For oil immersed transformers
1.Oil Natural Air Natural (ONAN)
2.Oil Natural Air Forced (ONAF)
3.Oil Forced Air Forced (OFAF)
4.Oil Forced Water Forced (OFWF)
There are different methods of cooling depends on transformer type.here at Learnelectrical.net Everything explained below.
Dry Type Transformers Cooling Methods:-
Cooling method for Air Natural or Self Cooling (AN):-
This method uses atmospheric air as cooling medium.heat will be dispersed in air automatically.It is used for small rating transformers(ratings 1.5-3 MVA).
Air Blast(AB) Cooling Method:-
In large transformers, cooling by natural air is difficult.in this process transformer located above the air chamber and a blast of compressed air is forced on core and winding with the help of blowers or fans.
Cooling Methods for Oil Immersed Transformers:-
Oil Natural Air Natural (ONAN) Cooling Of Transformer:-
This method is used for oil immersed transformers.in this heat transferred from winding to oil in conventional way.heated oil flow in tubes of radiator,radiator will be cooled by natural air flowing between the radiator.the oil in transformer keeps circulating due to natural convection and dissipating heat in atmosphere due to natural conduction.
Oil Natural Air Forced (ONAF) Cooling Of Transformer:-
In oil forced air natural cooling system of transformer, the heat dissipation is accelerated by using forced air on the dissipating surface but circulation of the hot oil in transformer tank is natural convectional flow. In this method, the tank is made hollow and compressed air is blown into the hollow space to cool the transformer. The oil circulating inside takes heat to the tank walls.
In oil forced air natural cooling system of transformer, the heat dissipation is accelerated by using forced air on the dissipating surface but circulation of the hot oil in transformer tank is natural convectional flow. In this method, the tank is made hollow and compressed air is blown into the hollow space to cool the transformer. The oil circulating inside takes heat to the tank walls.
Oil Forced Air Forced (OFAF) Cooling Of Transformer:-
In the external heat exchanger the compressed air is blasted with the help of fans to cool is the oil.Here the Oil and Air both are applied forcefully, but the hot oil follows a specific route for flowing. Convection channels are made closer to the winding of the transformer and the transformer oil is passed through those channels.
Oil Forced Water Forced (OFWF) Cooling Of Transformer:-
In this method forced water flow is used to dissipate hear from the heat exchangers. The pressure oil is kept higher than water so oil mixes with water in case of leakage but water dose not mix with oil. Due to this method, smaller transformer size is sufficient as it is not necessary to employ water tubes inside the transformer tank.
These are the most used electrical transformer cooling methods,which are efficient to cool major types of transformers.
