#
**Transformer**

Basic Working of Transformer
E.M.F Equation of transformer
Voltage Transformation ratio (K)
## Introduction

A transformer is a static piece of apparatus by means of which electric power in one
circuit is

** transformed** into electric power of the same frequency in another circuit.
It can

** raise** or

** lower** the voltage in a circuit but with a corresponding

** decrease or increase in current** .

It has an input side (primary) and an output side (secondary). Electrical energy applied to the
primary is converted to a

** magnetic field** which in turn, induces a current in the secondary which
carries energy to the load connected to the secondary. The energy applied to the primary must
be in the form of a

** changing voltage** which creates a constantly

** changing current** in the primary,
since only a

** changing magnetic field** will produce a current in the secondary.

In brief, a transformer is a device that

** (a)** transfers electric power from one circiut to another.

** (b)** it does so without a change of frequency.

** (c)** it accomplishes this by electromagnetic induction and

** (d)** where the two circuit are in mutual inductive influence of each
other.

In its most basic form a transformer consists of :

** (1)**A

** primary coil** or winding.

** (2)**A

** secondary coil** or winding.

** (3)**A

** core** that supports the coils or windings.

It consist of

** two inductive coils** which are electrically separated but magnetically linked through a
path of low reluctance. If one coil (primary) is connected to source of

** alternating voltage** ,
an

** alternating flux** is set up in the laminated core, most of which is linked with the other
coil in which it produces mutually-induced e.m.f. (according to

** Faraday's Laws of
Electromagnetic Induction**) . If the second coil (secondary) circuit is closed, a current
flows in it and so electric energy is transferred (entirely magnetically) from the first
coil to the second coil.

Let

** N1** = No. of turns in primary

** N2** = No. of turns in secondary

** Øm** = Maximum flux in core in webers = Bm x A

** f** = Frequency of a.c. input in Hz.

The

** flux increases** from it's

** zero** value to maximum value

** Øm** in one quarter
of the cycle i.e. in

** 1/4 f** second.

Therefore, r.m.s value of e.m.f./turn = 4.44 Øm volts

Now, r.m.s value of induced e.m.f in the whole primary winding

= ( induced e.m.f. / turn ) x No. of primary winding

** E1** =

** 4.44 f N1Øm ** -------------------

**(i)**
Similarly,

** r.m.s.** value of e.m.f. induced in secondary is,

** E2** =

** 4.44 f N2Øm ** -------------------

**(ii)**
From the above equations (i) and (ii), we get

(i) If

** K > 1** , then the transformer is called

** step-up** transformer.

(ii) If

** K < 1** , then the transformer is called

** step-down** transformer.