Question

The transformer core is laminated so as to:
$(a)$ Increase the secondary voltage
$(b)$ Make it tight and strong
$(c)$ Reduce the energy loss due to eddy current
$(d)$ Make it light weight

Answer 1

Hint: In this question use the concept that whenever a current flows through the conducting core of the transformer, it gives rise to an electric field and thus in turn it gives rise to a changing magnetic field. As a magnetic field is composed of magnetic flux so whenever there is a fluctuation in current the magnetic lines of forces linked with the core changes and thus the flux associated changes, to oppose this changing flux a back emf is induced in the coil and thus eddy currents are formed. Eddy current leads to losses in the core, this will help approaching the solution of this problem.

Complete step-by-step solution -

The core is designed such that no current flows through it.
But the core is a conducting loop that experiences a changing magnetic field due to variation in the flux of the core of the transformer induced by some small amount of current called Eddy current.
As these currents interfere with the efficiency of the transformer while transferring energy from primary coil to secondary coil.
The eddy current causes energy to be lost in the form of heat (as the core heated due to these currents), so we have to minimize these currents.
So one of the very best and widely used methods is lamination of the core while laminating the core the eddy current loss is not completely eliminated but reduced to minimum value.
The equation for eddy current loss is given as:
\[{P_{{\mathbf{e}}\;}} = {\text{ }}{{\text{K}}_{\mathbf{e}}}\; \times {\text{ }}{{\text{B}}_{{\mathbf{max}}}}^{\mathbf{2}}\; \times {\text{ }}{{\text{f}}^{\mathbf{2}}} \times \;{\text{ }}{{\text{t}}^{{\mathbf{2}}\;}} \times {\text{ v}}\], where
\[{P_{{\mathbf{e}}\;}}\] = eddy current loss (W)
${K_e}$ = eddy current constant
B = flux density (Wb/m2)
f = frequency of magnetic reversals per second (Hz)
t = material thickness (m)
V = volume (m3)
So doing laminations the thickness and volume of the core reduced so that eddy current loss also reduced.
Hence the core of the transformer is laminated so that eddy current loss can be minimized.
So this is the required answer.
Hence option (C) is the correct answer.

Note – This lamination is actually not done over the transformer coil in fact each transformer coil is protected by silicon sheet lamination, then all these are combined together in a certain configuration and this combination actually forms the core of the transformer.