Question

In a single-phase transformer, the core is laminated primarily to reduce:

• A. Copper loss
• B. Hysteresis loss
• C. Eddy current loss
• D. Friction loss

Hint:

Core losses (iron losses) consist of two parts:
1. Eddy current loss: Reduced by laminating the core (using thin sheets).
2. Hysteresis loss: Reduced by choosing a high-permeability magnetic material with a narrow hysteresis loop, such as silicon steel (CRGO).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks for the primary technical reason for constructing the magnetic core of a transformer using thin laminated sheets instead of a single solid block of iron.

Step 2: Key Formula or Approach:
Eddy current loss (\(P_e\)) in a magnetic core is given by the formula:
\[ P_e = K_e \cdot f^2 \cdot B_m^2 \cdot t^2 \cdot V \] where:
- \(K_e\) is a constant dependent on the material.
- \(f\) is the frequency of the magnetic field.
- \(B_m\) is the maximum magnetic flux density.
- \(t\) is the thickness of each individual lamination sheet.
- \(V\) is the volume of the magnetic core.

Step 3: Detailed Explanation:

• A time-varying magnetic flux induces electromotive forces (EMFs) inside the iron core of a transformer because iron is an electrical conductor.

• These induced EMFs produce circulating electrical currents inside the core, known as eddy currents.

• Because the core has electrical resistance, these eddy currents cause \(I^2 R\) power losses that are dissipated as heat, lowering transformer efficiency.

• From the eddy current loss equation, we see that losses are proportional to the square of the lamination thickness (\(P_e \propto t^2\)).

• By constructing the core from thin, insulated laminations, the path of the circulating eddy currents is broken into small, isolated segments. This increases the effective resistance of the eddy current paths.

• This reduction in lamination thickness drastically minimizes eddy current power losses in the core.

Step 4: Final Answer:
The core is laminated primarily to reduce eddy current loss.