Construction:- 

Transformer consists of pramary and secondary winding wound around a ferromagnetic core.

The winding and the core are separated by insulator.

Core:-

The material used for constricting the core should have following properties.

  1. High permeability and low reluctance.
  2. Generally the core is made of silicon steel or more specifically CRGO steel
The core consist of thin silicon steel lamination riveted and having thickness of .35mm at 50 HZ.

If we reduces thickness of lamination eddy current losses reduced.

Cross section of core:-

The cross section of smaller transformer is rectangular.

For large transformer circular cross section is preferred as compare to rectangular cross section.

The cross section area of circular core is less than rectangular core so volume of core reduced and core loss reduced.

Types of transformer winding:- 

Core type transformer:-

In core type transformer low voltage winding is placed near the core and high voltage winding is wound over low voltage winding such a construction is called concentric winding.

In concentric winding the outer winding or high voltage winding is away from the core so leakage is higher.if high voltage is placed inside then inner insulation layer needs to be increase which increase the cost and overall diameter due to which copper requirement is also increase.

If high voltage winding is placed in outside then taps can be provided by which different voltage level can be obtain.

Shell type transformer :- 

In shell type transformer each part of high voltage winding is sandwich between two part of low voltage winding and hence it is called as sandwich winding.

The direction of flux of the two coil should be opposite to each other according to len'z law and hence both carry current in opposite direction.

There is better coupling between low and high voltage winding in shell type transformer so leakage is reduced.

Transformer insulation:-

The entire transformer is placed in a tank which is filled with oil and the oil has two purpose to act as a collent in order to extract heat produced by transformer.

It provide insulation along with insulated conductor.

Bushing:- 

Bushing is used to prevent connection of transformer wire to the transformer tank otherwise the current carried by the winding will flow through the tank and will not enter transmission line.

For transformer above 36kv bushing is either oil filled or capacitor type.

Conservator and breabreather:- 

The transformer tank is completely filled with oil but some space is left free for air.

When oil is heated oil expands and volume of air  is reduced due to which air must be leaving the tank through the vent pipe and similarly when oil cooler down it contract and volume of air is increase which happen by air flowing in transformer through vent pipe.

The air coming into the transformer should not contain moisture otherwise dielectric strength of oil reduced so silica gel is placed in vent pipe which absorbs moisture.

The pushing out and exhaust air from atmosphere is called breathing of transformer.

Conservator is air tight cylindrical drum which is partially filled with oil and prevent oil from coming in contract with air.

When air rapidly expands due to fault it rushes toward conservator and when it contract it come back from conservator to the tank.

Conservator is mounted above transformer tank.