Name: Energy Losses in a Transformer
Uploaded: 2019-07-19
Duration: 8 min 12 s
Description: There are different types of energy losses in a transformer. This video explains those losses in detail and also talks about the efficiency of ideal and prac...

Question

With the help of labelled diagram, describe the principle, construction and working of a transformer.

Accepted Answer

The transformer is a device that transfers electric energy from one alternating-current circuit to one or more other circuits, either increasing (stepping up) or reducing (stepping down) the voltage.

Principle: It works on the principle of mutual induction i.e., if two coils are inductively coupled then on the flow of an alternating current in one coil an alternating induced emf is also produced in the other coil.

Construction :

It consists of two coils, a primary coil $P$ and a secondary coil $S$ , wound on a laminated soft iron core. Alternating current input supply is connected to the primary coil and the output voltage is obtained across a load joined in secondary coil circuit.
The transformer is of the following two types:
(i) Step-up transformer, in which the number of turns in $S$ coil is more than in $P$ coil so as to obtain a high alternating output voltage.
(ii) Step down transformer, in which the number of turns in $S$ coil is less than in $P$ coil

Theory and Working:

When an alternating emf/voltage source is applied across the $P$ coil, the input current and, hence, the magnetic flux through the coil keeps on changing with time. The changing magnetic flux gets linked up with $S$ coil through the iron core, which in turn produces induced voltage across the secondary coil.

The induced emf in $P$ coil is :

$ε_{p} = - N_{p} \frac{{dϕ}_{B}}{dt}$ [where $N_{p}$ = Total number of turns in P coil]
and instantaneous value of induced emf in $S$ coil,

$ε_{s} = - N_{s} \frac{{dϕ}_{B}}{dt}$ .

For an ideal transformer| $ε_{p}$ = input voltage $V_{p}$ and $ε_{s} = V_{s}$ = output voltage obtained across the secondary coil. Then,
$ε_{s} ε_{p} = V_{s} V_{p} = N_{s} N_{p}$ .
Again for an ideal transformer input power = output power
$V_{p} I_{p} = V_{s} I_{s}$ .

It can be shown that input and output alternative voltages are in mutually opposite phases.

With the help of labelled diagram, describe the principle, construction and working of a transformer.

Important Questions on Alternating Current

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