Types of Transformer

 

Depending upon the type of construction of transformer are classified into two types:-

1.     Core-type transformer

2.     Shell-type transformer

Core Type transformer:-

In core type transformer, the coils are wound around the two limbs of a rectangular magnetic core. Each limb carries one half of the primary winding and one half of the secondary winding so as to reduce leakage reactance. The LV winding is wound on the inside nearer to the core while HV winding over the LV winding away from the core in order to reduce the amount of insulation material is required

          

                                                                                                                            

NOTE:-

HV winding= High voltage winding

LV winding= Low voltage winding

Shell type transformer:-

In shell type transformer, the coils are wound on the central limb of a three limb core. The entire flux  passes through the central limb consequently, the cross-sectional area of the central limb is twice of that of each of the side limbs.

             .                                                                                                                                                                                                                                                                                                                                                                                                                          HV winding

                                                                                                               
                                                                                                                                                                                                                                                                                                                                                                                                     Fig:- Shell type transformer

Difference between core type and shell type transformer:-

Core type transformer	Shell type transformer
1.     The windings surround the core	1.The core sorrounds the windings.
2.     There are two limbs.	2.There are three limbs.
3.     The flux is equally distributed in both limbs.	3.The central limb carry the whole flux and side limbs carries the half of the flux.
4.     Losses is more.	4.Losses is less.
5.     It is used for power and distribution transformer	5.It is used for small transformer.

 

Transformer Construction

 The single elements of a transformer consists of two coils or windings having mutual inductance and a laminated steel core.

                                                     In all type of transformers, the core is constructed of laminated steel sheets assembled to provide a continous magnetic path with a minimum air gap included. The steel used is of high silicon content, to reduce hystresis  loss and the core is laminated to reduce eddy current loss.

                                                In order to mount the coil windings, the individual laminated steel sheets are stamped or punched out from larger steel sheets and into strips formed of thin steel resembling the letters E, L, U, and I.

Working Principle of Transformer

 

When an alternating voltage V1 is applied to the primary, an alternating flux phi is setup in the core. The alternating flux links both the windings and induces EMF’s E1 and E2 in them according to faraday’s laws of electromagnetic induction. The EMF E1 is termed as primary emf and EMF as E2 is termed as secondary emf.   

Mathematically,

                    

E1=-N1 (dphi/dt)                         and                  E2=-N2 (dphi/dt)

i.e. E2/E1 = N2/N1

hence,

E2/E1 = N2/n1 = V2/V1 = I2/I1

NOTE:-

1.   1.  The transformer action is based on the faraday’ laws of electromagnetic induction.

2. 2. There is no electrical connection between the primary and secondary. The ac power           transformer from primary to secondary through magnetic flux.

    3.There is no change in frequency i.e. output power has the same frequency as the               input power.

Faradays law of electromagnetic induction

 

When the magnetic flux linking a conductor or coil changes an EMF is induced in the conductor. If the conductor or coil forms a complete loop a current will flow in it. This phenomenon is called Electromagnetic induction.

First law:-

When the magnetic flux linking a conductor or coil changes an EMF induced is in it.

Second law:-

The magnitude of EMF induced in a conductor or coil is directly proportional to the rate of flux linkages.

        Mathematically

                   E=-N (d phi/dt)       where,

                                                N=no. of turns

                                                            (d phi/ dt)=rate of change of flux linkage

The minus sign on the RHS represents lenz’s law state that the induced current will flow in such a direction so as to oppose the cause that produces it.                                      

                              

Transformer

                                                                 TRANSFORMER

Introduction:- A transformer is a static device used either for raising or lowering the voltage of an AC supply with a corresponding decrease or increase in current. It essentially consists  of two winding the primary and secondary wound on a common laminated magnetic core. The winding connected to the AC souurce is called primary winding and one connected to load is called secondary winding.

                            The total sum of magnetic line of force is called magnetic flux(phi).

                              

 

                         Fig :- Single phase Transformer                     

V1=Input Voltage

V2=Output voltage

E1=EMF induced in primary winding

E2=EMF induced in secondary winding

N1=Number of turns in primary winding

N2=Number of turns in secondary winding