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. A 400 kVA transformer has an iron-loss of 2 kW and the maximum efficiency at 0.8 power
factor occurs when theload is 240 kW. Calculate the maximum efficiency on full-load at 0.71
power-factor lagging.?
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. A 400 kVA transformer has an iron-loss of 2 kW and the maximum effic...
Given data:
- Transformer rating (S) = 400 kVA
- Iron-loss = 2 kW
- Load at maximum efficiency (Pmax) = 240 kW
- Power factor at maximum efficiency (cosφ) = 0.8

Calculations:
1. Calculate the copper losses:
- Full-load copper losses = Iron-loss = 2 kW
2. Calculate the full-load apparent power (Sfull) using the formula:
\[S_{full} = P_{full} / cosφ\]
\[S_{full} = 240 kW / 0.71\]
\[S_{full} ≈ 338.03 kVA\]
3. Calculate the full-load efficiency (ηfull) using the formula:
\[η_{full} = P_{full} / (P_{full} + Iron-loss + Copper-losses)\]
\[η_{full} = 240 kW / (240 kW + 2 kW + Copper-losses)\]
4. Calculate the copper losses at full-load:
\[Copper-losses = S_{full}^2 - Iron-loss - P_{full}\]
\[Copper-losses = 338.03^2 - 2 - 240\]
\[Copper-losses ≈ 113.93 kW\]
5. Substitute the value of copper losses in the efficiency equation to find the full-load efficiency.

Result:
The maximum efficiency on full-load at 0.71 power-factor lagging is calculated using the above steps.
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. A 400 kVA transformer has an iron-loss of 2 kW and the maximum efficiency at 0.8 power factor occurs when theload is 240 kW. Calculate the maximum efficiency on full-load at 0.71 power-factor lagging.?
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