Voltage regulation calculator

Use the following calculator to calculate the Voltage regulation calculator to calculate voltage regulation precisely. Enter Vno-load and Vfull-load and click on calculate button.

Voltage regulation calculator

Enter No-Load Voltage
Enter Full-Load Voltage
Voltage regulation

Read more: Voltage regulation of transformer

Steps to use the voltage regulation calculator

  • Enter the no-load terminal voltage:
    • Let’s assume: 440 V
  • Enter the full-load terminal voltage:
    • Let’s assume: 550 V
  • Click the calculate button. You should get an output of 15.3%


Voltage regulation of a transformer can be defined as the change in the magnitude of the secondary voltage of a transformer when the load changes from full load to no load, assuming a constant primary voltage.

Formula for Voltage regulation calculator


  • Vno-load is the no-load voltage measured across the secondary terminals
  • Vfull-load is the voltage measured across the secondary terminal at full load.

Percent voltage regulation

Normally, voltage regulation is expressed as either per – unit or percentage of load voltage

Percentage voltage regulation formula

Example problem:

Consider a three-phase, star-connected alternator that is fully loaded at 0.8 lagging power factor. Below are the terminal voltage details:

  • The line voltage measured at the alternator terminals at full load: 440 V
  • The terminal voltage at no load with speed and field excitation being maintained constant: 520 V

Let’s calculate its voltage regulation for this alternator using the formula given above:


  • Voltage regulation = (520 – 440)/520 = 0.153
  • Percent voltage regulation = 0.1818 * 100 = 15.3%

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