TRANSFORMER - : A transformer is a static device which transfers electrical energy from one circuit to another circuit without a change of frequency. Transformer worke on electromagnetic induction principle. 
The primary wi di g draws a small amount of alternative current of instantaneous value called the exiting current,from the voltage source with posutive direction as indicated on the diagram. The exiting current establishes flux in the core. all of which is assumed confined to the core there is no leakage of flux Consequently, the primary winding has flus linkage.
The transformer which dilivers energy at a higher voltage level then it source voltage level then it is called step - up transformer. When the voltage of delivered energy of a transformer is less than its primary voltage than, it is called step- down transformer.
A transformer has no moving parts parts, si it is called static device, therefore it requires minimum repair and maintenance cost. its efficiency is much higher when compared to other apparatus.
CONSTRUCTION - : A single phase transformer consists of primary and secondary windings put on a magnetic core. Boyh windings are magnetically connected but not electrically. Magnetic core is ised to confinr flux to certain path. A winding and winding connected on load side is called secondary winding.
Transformer cores are made from thin laminated sheets of high grade silicon steel. Since, the laminated reduce eddy current loss and silicon steel reduces hysterisis loss. There are basically two type of transformer cknstruction, the core type and shell type.
WORKING PRINCIPLE OF TRANSFORMER - :
Transformer consists of two inductive and colis which are electrically separated but magnetically linked through a path of low resistance. If one coil is connected to a source of ternative voltage, an alternative flux is setup in the laminated core, most of which is linked with other coli in which is produce mutually - induced emf (according to Faraday's law of electromagnetic induction E=M. dI/dt)
If the second coil circuit is closed, a current flows i it and so, energy is transferred (entirely magnetically) from the first coil to second coil.
EMF EQUATION OF TRANSFORMER - :
As per Lenz 's law the positive of this emf oppose the positive current direction and is shown by (+ve) and (-ve) polarity marks on the diagram. According to kirchoff law.
V==E(winding has zero resistance)
E1/E2=N1/N2
E1/N1=E2/N2=K
EMF PER TURN IN PRIMARY=EMF PER TURN IN SECONDARY
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