Energy
Transformer Efficiency Calculator
Calculate transformer efficiency, copper loss, total loss and annual energy loss from transformer rating, load and loss data.
Used to convert between real power and apparent power at the operating load.
Also called core or iron loss. Use manufacturer test data where available.
Optional. Used to estimate annual transformer energy loss.
Transformer Efficiency
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Estimated efficiency at the entered transformer load and power factor.
Transformer loading
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Output power
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No-load loss
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Copper loss at actual load
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Total transformer loss
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Input power
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Transformer efficiency
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Annual energy loss
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Method:
Transformer loading fraction is:
Load Fraction =
Actual kVA ÷ Rated kVA
Copper loss varies approximately with current squared:
Copper Loss at Load =
Full-Load Copper Loss ×
(Load Fraction)²
No-load or core loss is treated as approximately constant while the transformer remains energized.
Total transformer loss is:
Total Loss =
No-Load Loss + Copper Loss
Output real power is obtained from the actual load and power factor.
Transformer efficiency is:
Efficiency =
Output Power ÷
(Output Power + Total Loss) × 100
If operating hours are entered:
Annual Energy Loss =
Total Loss × Operating Hours
This calculator assumes balanced operation and uses rated full-load copper loss as the reference winding-loss value.
Real transformer losses can also include stray-load losses, auxiliary cooling power, harmonic effects and temperature-dependent winding resistance. Manufacturer test data should be used for detailed performance assessment.