Question

State the working principle of a transformer and mention the energy losses occurring in it.

Hint:

The principle is mutual induction between two coils on a common core; think about the four heat/energy drains: copper, eddy current, hysteresis, and flux leakage.

Answer 1

Step 1: Working principle.
A transformer works on the principle of mutual induction. When an alternating current flows in the primary coil, it produces a continuously changing magnetic flux. This changing flux links with the secondary coil (through a common soft-iron core) and induces an alternating e.m.f. in it.

Step 2: Turns relation.
The induced e.m.f. is proportional to the number of turns, so
\[ \frac{E_s}{E_p} = \frac{N_s}{N_p} \]
where \( E_p, E_s \) are primary and secondary voltages and \( N_p, N_s \) are the numbers of turns.

Step 3: Energy losses in a transformer.
1. Copper loss: heat produced as \( I^2R \) in the resistance of the primary and secondary windings.
2. Iron (core) loss: made of (a) eddy current loss due to induced currents in the core, reduced by using a laminated core, and (b) hysteresis loss due to repeated magnetisation and demagnetisation of the core, reduced by using soft iron.
3. Flux leakage loss: some magnetic flux of the primary does not link with the secondary.
4. Humming (magnetostriction) loss: energy lost as sound and vibration of the core.
\[\boxed{\text{Principle: mutual induction; losses: copper, iron (eddy + hysteresis), flux leakage, humming}}\]