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A transformer core is laminated to ____________
1. reduce hysteresis loss
2. reduce eddy current losses
3. reduce copper losses
4. reduce all above losses

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Correct Answer - Option 2 : reduce eddy current losses

Concept:

  • When an alternating magnetic field is applied to a magnetic material, an emf is induced in the material itself according to Faraday’s law of Electromagnetic induction.
  • Since the magnetic material is a conducting material, these EMF’s circulates current within the body of the material. These circulating currents are called Eddy currents. They are produced when the conductor experiences a changing magnetic field.
  • The process of lamination involves dividing the core into thin layers held together by insulating materials.
  • Due to lamination effective cross-section area of each layer reduces and hence the effective resistance increases.
  • As effective resistance increases, the eddy current losses will get decrease.

 

Eddy current loss in the transformer is given by:

Pe = KBm2. t2. f2. V Watts

Where;

K - coefficient of eddy current. Its value depends upon the nature of magnetic material

Bm - Maximum value of flux density in Wb/m2

t - Thickness of lamination in meters

f - Frequency of reversal of the magnetic field in Hz

V - Volume of magnetic material in m3

From the above formula, we conclude that the Eddy current loss is proportional to the square of the frequency.

Application:

Since the Eddy current loss is proportional to the square of the thickness of the lamination.

 The eddy current loss in a transformer can be reduced by decreasing the thickness of the laminations.

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