Calculator Inputs
Enter transformer design and operating data to estimate no-load loss, copper loss, stray loss, total loss, efficiency, yearly wasted energy, and cost.
Example Data Table
| Input Parameter | Example Value | Unit |
|---|---|---|
| Phase Type | Three Phase | - |
| Transformer Rating | 500 | kVA |
| Primary Voltage | 11000 | V |
| Secondary Voltage | 415 | V |
| Load Percentage | 75 | % |
| Power Factor | 0.90 | - |
| Core Loss | 1200 | W |
| Total Stray Loss at Full Load | 350 | W |
| Primary Resistance | 1.85 | Ω |
| Secondary Resistance | 0.0028 | Ω |
| Operating Temperature | 75 | °C |
| Energy Price | 0.14 | per kWh |
Formula Used
Single phase: I = (kVA × 1000) / V
Three phase: I = (kVA × 1000) / (√3 × V)
Rhot = Rref × [1 + α × (Top − Tref)]
Pcu = Iprimary2Rprimary,hot + Isecondary2Rsecondary,hot
Pstray = Pstray,full × Load Fraction2 × Harmonic Factor
Ptotal = Pcore + Pcu + Pstray
η = Output Power / (Output Power + Total Loss in kW) × 100
This method reflects the normal engineering assumption that no-load loss stays nearly constant with voltage held near rated value, while copper and stray losses vary approximately with the square of load current.
How to Use This Calculator
- Choose single-phase or three-phase operation.
- Enter the transformer rating, primary voltage, and secondary voltage.
- Provide expected operating load percentage and power factor.
- Enter known core loss from nameplate data, design data, or test reports.
- Fill in winding resistances at a known reference temperature.
- Set operating temperature and resistance temperature coefficient for the conductor.
- Add the expected full-load stray loss and harmonic multiplier for distortion effects.
- Enter annual operating hours and energy price for cost analysis.
- Press the calculate button to show the result panel above the form.
- Use the export buttons to save the result summary as CSV or PDF.
Frequently Asked Questions
1. What losses are included here?
The calculator includes core loss, copper loss in both windings, and stray load loss. It then combines them into total loss, efficiency, yearly energy waste, and yearly loss cost.
2. Why does copper loss change with temperature?
Winding resistance rises as conductor temperature rises. Since copper loss depends on current squared multiplied by resistance, hotter windings create higher loss for the same load current.
3. Why is load percentage important?
Load percentage directly changes current. Copper and stray losses are modeled with the square of load fraction, so moderate load changes can shift total loss significantly.
4. When should I adjust the harmonic factor?
Increase the harmonic factor when the transformer feeds nonlinear loads, such as drives, rectifiers, or large electronic equipment. Harmonics raise extra eddy and stray losses beyond the basic sinusoidal estimate.
5. Is core loss always constant?
Core loss is treated as nearly constant when applied voltage stays close to rated voltage and frequency remains stable. Large voltage or frequency changes require a more detailed magnetic loss model.
6. Can I use test report values?
Yes. No-load test data is ideal for core loss, and short-circuit or load test data can help estimate load loss. Using measured values usually improves practical accuracy.
7. What does loss per kVA tell me?
Loss per kVA helps compare transformers of different sizes on a normalized basis. Lower values usually indicate better loss performance for similar rating and application conditions.
8. Why is annual loss cost useful?
Annual loss cost translates thermal and electrical inefficiency into money. It supports equipment selection, retrofit evaluation, cooling review, and payback studies for premium-efficiency transformer designs.