Transformer Regulation Calculator
Calculate voltage regulation between no-load and full-load conditions.
About Transformer Regulation Calculator
Regulation is the voltage droop between no load and full load. It can be computed from measured voltages or predicted from the transformer’s percentage impedance and the load power factor, and the two should agree closely. Reactance dominates regulation at poor power factor, which is why a lagging load causes far more voltage droop than a unity-power-factor one of the same kW.
Formula
Transformer Regulation
Regulation % = (V_noload − V_fullload) ÷ V_fullload × 100 ≈ %R cos φ + %X sin φ
- %R
- Percentage resistance
- %X
- Percentage reactance
Worked example
With the default values below, Transformer Regulation Calculator returns Voltage Regulation of 3.750%. Change any input above and every figure here is recalculated in your browser.
Inputs used
- No-load secondary voltageminimum 0.01 V
- 415 V
- Full-load secondary voltageminimum 0.01 V
- 400 V
- Percentage resistanceaccepts 0–100 %
- 1.2 %
- Percentage reactanceaccepts 0–100 %
- 5 %
- Load power factoraccepts 0.01–1
- 0.85
Results
- Voltage Regulation
- 3.750%
- Regulation From Impedance Data
- 3.654%
- Voltage Drop on Load
- 15.00 V
- Percentage Impedance
- 5.142%
- Verdict
- Typical regulation for a distribution transformer
Step by step
- 1Values used
- 2Transformer Regulation
- 3Voltage Regulation= 3.750
- 4Regulation From Impedance Data= 3.654
- 5Voltage Drop on Load= 15.00 V
- 6Percentage Impedance= 5.142
- 7Verdict= Typical regulation for a distribution transformer
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Transformer Regulation calculated?
Regulation % = (V_noload − V_fullload) ÷ V_fullload × 100 ≈ %R cos φ + %X sin φ Regulation is the voltage droop between no load and full load. It can be computed from measured voltages or predicted from the transformer’s percentage impedance and the load power factor, and the two should agree closely.
Why does Transformer Regulation matter?
Reactance dominates regulation at poor power factor, which is why a lagging load causes far more voltage droop than a unity-power-factor one of the same kW.
What values do I need to enter?
This calculator takes 5 inputs: No-load secondary voltage, Full-load secondary voltage, Percentage resistance, Percentage reactance, Load power factor. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.