About Transformer Calculator
A transformer changes AC voltage in proportion to the turns on its windings, so the turns ratio is primary voltage divided by secondary voltage. Full-load current follows from the apparent power rating: I = kVA × 1000 ÷ V for single phase and I = kVA × 1000 ÷ (√3 × V) for three phase, using line voltage. The figures describe an ideal transformer and ignore losses, impedance, and inrush current.
How to use Transformer Calculator
- Fill in "Phases", "Rating", "Primary voltage" and "Secondary voltage".
- The result appears below and updates as you type.
- Copy the result with the copy button, or download it as a file where that is offered.
Questions about Transformer Calculator
Why are transformers rated in kVA and not kW?
Winding heating depends on current and voltage, not on the power factor of the load. The same transformer can deliver different real power in kW depending on the load, so the rating uses apparent power in kVA.
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