Question 307: AC fundamentals

Question

The core used in transformers are laminated to

Accepted Answer

Laminating the core in transformers is primarily done to
reduce eddy current losses in the core
.
Explanation
When an alternating current (AC) flows through the primary coil of a transformer, it creates a changing magnetic field. This changing magnetic field induces currents known as eddy currents in the core material, according to Faraday's law of electromagnetic induction. These eddy currents circulate within the core perpendicular to the magnetic flux lines and can cause undesired heating, leading to energy losses.
To mitigate these losses, the core is laminated. Lamination involves stacking thin sheets of magnetic material, each insulated from the other by a thin layer of insulating material (such as varnish or oxide layer). This reduces the size of the eddy current loops, which in turn decreases their intensity and thus the power wasted as heat.
The reduction in eddy current losses due to lamination can be understood by considering the formula for the power loss due to eddy currents:
$$ P_{	ext{eddy}} = \frac{B_{	ext{max}}^2 f^2 t^2 V}{6 ho} $$
Where:
$ P_{	ext{eddy}} $ is the power loss due to eddy currents,
$ B_{	ext{max}} $ is the maximum magnetic flux density,
$ f $ is the frequency of the AC current,
$ t $ is the thickness of each lamination,
$ V $ is the volume of the core, and
$ ho $ is the electrical resistivity of the core material.
By reducing the thickness $ t $, the eddy current power losses $ P_{	ext{eddy}} $ are significantly reduced, which is why lamination is an effective strategy.
Hence, the correct answer is:
Option D: reduce eddy current losses in the core.

Answer

increase the magnetic field.

Answer

increase the level of the magnetic saturation of the core.

Answer

reduce the residual magnetism in the core.

Answer

reduce eddy current losses in the core.

AC fundamentals

The core used in transformers are laminated to

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