Construction of a Transformer

                                                         Construction of a transformer

• The most important parts of a transformer are the winding and the core 
• However for the large capacity transformers, some other parts such as suitable tank, conservator, Buchholz relay bushings, breather, explosion vent etc, are also used alongwith the core and winding.
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• Laminated steel core
•       The material used for the construction of the transformer core is silicon steel. It is used for the high permeability and low magnetic reluctance. due to this the magnetic field produced in the core is very strong 

                The core is in the form of stacks of laminated thin steel which are electrically isolated from          each other. The core is assembled in such a way. that the assembly provides a continuous path            for the magnetic flux, with a minimum air gap.

                                                                   Transformer Tank

•      The whole assembly of large size transformer is placed in a sheet metal tank. Inside the tank the assembly of the transformer is immersed in oil which acts as an insulator as well as a coolant 

     The oil will take out the heat produced by the transformer winding and core and transfer it to the surface of the transformer tank.

                                                                  Function of transformer oil

•       The construction of the transformer should be such that the heat generated at the core and at the winding should be removed efficiently.
• Moreover in order to avoid the insulation deterioration. the moisture should not be allowed to creep into the insulation.
• Both these objectives can be achieved by immersing the built uo transformer in a closed tank filled with non inflammable insulating oil called transformer oil.
• IN order to increase the cooling surface exposed to ambient, tubes or fins are provided on the outside of tank walls. 

                                                                  Conservator

• In large transformer, some empty space is always provided above the oil level. This space is essential for letting the oil expand or contract due to the temperature changes.
• When the oil temperature increases, it expands and the air will be expelled out form the conservator. Whereas when the oil cools, it contracts and the outside air gets sucked inside the conservator. This process is called as the breathing of the transformer.
•  However, the outside air which has being drawn in can have the moisture content. When such an air comes in contact with the oil, the oil will absorb the moisture content and loses its insulating properties, to some extent. This can be prevented by using a Conservator.

The conservator is a cylindrical shaped air tight metal drum placed on the transformer tank. The conservator is connected to the tank by a pipe

                                                                 Breather

• The apparatus though which breathing of the transformer takes place is called as "Breather"

The air goes in or out through the breather . To reduce the moisture content of this air, Some drying agent such as silica gel or calcium chloride is used in the breather. The dust particles present in the air are also removed by the breather .

                                                               Buchholz Relay

• There is a pipe connecting the tank and conservator . On this pipe a protective devise called Buccholz relay mounted.
• When the transformer is about to be faulty and draws large currents, the oil becomes very hot and decomposes.

During this process different types of gases are liberated. The Buchholz relay get operated by these gases and gives an alarm to the operator. If the fault continues to persist. then the relay will trip off the main circuit breaker to protect the transformer.

                                                              Explosion vent

• An explosion vent or relif valve is the bent up pipe fitted on the main tank.
• The explosion vent consists of a glass diaphragm or aluminium foll. When the transformer becomes faulty, the cooling oil will get decomposed and various types of gasses are liberated. 
• If the gas pressure reaches a certain level then the diaphragm in the explosion vent will burst to release the pressure.
• This will save the main tank from getting damaged.