Transformer Voltage Regulation Calculator
Calculate regulation from measured no-load and full-load secondary voltage or estimate it from equivalent impedance and load power factor.
Enter transformer values
Voltage regulation
Positive values indicate secondary voltage reduction under load; negative values indicate a rise under the selected convention.
About this calculator
Calculate regulation from measured no-load and full-load secondary voltage or estimate it from equivalent impedance and load power factor.
The impedance method is an approximate first-order estimate at the specified load power factor. It does not model nonlinear loads, harmonics, temperature, taps, or transient voltage behavior.
Method and assumptions
Measured regulation = (no-load voltage − full-load voltage) ÷ full-load voltage × 100. The estimate mode uses R% × PF plus or minus X% × √(1 − PF²), adding the reactive term for lagging and subtracting it for leading power factor.
Ideal ratio and capacity arithmetic do not include winding losses, temperature rise, harmonics, load diversity, or equipment-specific limits unless stated in the input model.
FAQs
Does this determine a complete transformer installation?
No. It performs the displayed arithmetic only. Verify the transformer nameplate, manufacturer application data, connections, protection, conductors, and locally adopted requirements separately.
Can I use line-to-line voltage as winding voltage for every three-phase transformer?
No. Use the actual winding voltage or turns data. Three-phase line-voltage ratios depend on winding connections and are not always equal to individual winding turns ratios.
Sources
Ideal transformer relationships, entered nameplate and test values, and the calculation conventions described above.