Engineering
Transformer Efficiency Calculator
Estimate output and input real power, copper and stray losses at load, operating efficiency, derated capacity utilization, annual loss energy, and loss cost.
Load as a decimal fraction-
Delivered real output power-
Copper loss at entered load-
Stray load loss at entered load-
Core plus load-dependent losses-
Input real power-
Output divided by input power-
Operating efficiency minus requirement-
Derated real-power capacity at entered PF-
Output divided by derated real capacity-
Annual electrical loss energy-
Annual cost of modeled losses-
Losses as share of input-
Decision view
Transformer real-power and loss flow
Transformer real-power and loss flowApparent-power loading and power factor produce delivered real power; constant core loss and load-squared copper and stray losses bridge output to input power and annual loss cost.
Exact scenario comparisonOperating load (% of kVA rating) changes while all other entered assumptions remain constant.
| Operating load (% of kVA rating) | Load as a decimal fraction | Delivered real output power | Copper loss at entered load | Stray load loss at entered load | Core plus load-dependent losses | Input real power | Output divided by input power | Operating efficiency minus requirement | Derated real-power capacity at entered PF | Output divided by derated real capacity | Annual electrical loss energy | Annual cost of modeled losses | Losses as share of input |
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How to use Transformer Efficiency Calculator
- Enter nameplate kVA, load fraction, and power factor.
- Enter no-load and full-load tested loss components.
- Set derating, annual hours, energy price, and required efficiency.
Calculator guide
Understanding Transformer Efficiency Calculator
Transformer efficiency must reconcile delivered real power with constant core loss and load-dependent winding and stray losses at the entered load fraction.
Detailed calculation process
Detailed transformer loss and efficiency calculation
The default case bridges output power through each loss component to input power.
General formula: x=L/100P_o=SxPFP_cu=P_cu,r x^2P_s=P_s,r x^2P_loss=P_0+P_cu+P_seta=100P_o/(P_o+P_loss) Core loss stays constant at the operating point while copper and stray load loss scale with load fraction squared.
What each symbol means
Worked substitution with the default inputs
Adding the 7.825 kW loss to 675 kW output reproduces the 682.825 kW input used by the efficiency ratio.
Worked situations
Practical examples
- At half load, a modeled full-load copper loss becomes one quarter.
- Core loss remains constant while energized in this simplified operating point.
Better inputs
Useful tips
- Use tested loss data for the actual unit.
- Model materially different load periods separately.
- Include auxiliary cooling power when relevant.
Before relying on the result
Limitations and common mistakes
- Harmonics, voltage, frequency, and temperature effects are excluded.
- One operating load and power factor are modeled.
- Cooling-mode transitions and tap position require detailed analysis.
Reference
Key terms
- Core loss
- Approximate no-load loss present while the transformer is energized.
- Copper loss
- Winding I-squared-R loss modeled with load fraction squared.
- Power factor
- Real power divided by apparent power for the load.
Important note
Use manufacturer test values and applicable efficiency and loading standards for procurement or compliance.
Frequently asked questions
Why square load fraction?
Winding current follows load and resistive loss follows current squared.
Is efficiency based on kVA?
No. It uses real output power after applying power factor.
Does derating change losses?
Here it changes the capacity comparison only; a detailed thermal model is required to change loss behavior.