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Question

What will be the eddy current loss if the supply frequency of a transformer becomes double?

This question was previously asked in
RRB NTPC 2024 Undergraduate CBT 1 Question Paper (29-Aug-2025) (Shift 1)
The correct answer is

Four times

Eddy current losses in a transformer are proportional to the square of the supply frequency and the square of the magnetic flux density. The formula for eddy current loss is given by:

\(P_e = K f^2 B^2 t^2\)

where:

  • \(P_e\) is the eddy current loss
  • \(K\) is a constant that depends on the material properties and geometry of the core
  • \(f\) is the supply frequency
  • \(B\) is the magnetic flux density
  • \(t\) is the thickness of the lamination

If the supply frequency (\(f\)) is doubled, while other factors remain constant, the eddy current loss will change as follows:

Original loss: \(P_{e1} = K (f)^2 B^2 t^2\)

New loss with doubled frequency: \(P_{e2} = K (2f)^2 B^2 t^2 = 4 K (f)^2 B^2 t^2 = 4 P_{e1}\)

Therefore, the eddy current loss will become four times its original value.

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Similar Questions

  1. Which power loss is assessed by open-circuit test on transformer?

Important Questions from Transformer Core Losses

  1. The lamination thickness of a rotor should be selected from _______ to minimize the eddy current loss.

  2. Which power loss is assessed by open-circuit test on transformer?
  3. Eddy current loss in a transformer can be reduced by _________.

  4. Stray load-losses in a motor vary according to square of the load current; are caused by the leakage flux induced by load currents in laminations and account for 4% to 5% of total losses. What is the way to reduce these losses?

  5. The core loss of a single phase, 230/115 V, 50Hz power transformer is measured from 230 V side by feeding the primary (230 V side) from a variable voltage variable frequency source while keeping the secondary open circuited. The core loss is measured to be 1050 W for 230 V, 50 Hz input. The core loss is gain measured to be 500 W for 138 V, 30 Hz input. The hysteresis and eddy current losses of the transformer for 230 V, 50 Hz input are respectively

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