Voltage regulation is a measure of how much an alternator's output voltage changes from no load to full load, expressed as a percentage. It is calculated by taking the difference between the no load voltage and full load voltage, dividing by the full load voltage, and multiplying by 100. The example shows an alternator whose voltage rises from 3300V at full load to 3350V at no load, resulting in a voltage regulation of 1.5% at unity power factor. The regulation depends on the load power factor.

2. VNL - VFL
Voltage Regulation = × 100 %
VFL

3. Where:
VNL = No load voltage
VFL = Full load voltage

4. Example:
A three phase star connected alternator has an output voltage
of 3300 V at full load, with unity power factor. When the load is
removed and the excitation is unchanged, the voltage rises to
3350 V. Find the percentage regulation.

5. The change in voltage = 3350 – 3300 = 50 V

6. Therefore,
50 x 100
voltage regulation = = 1.5 % at unity power.
3300

7. Note: The regulation must also be referred to the load power
factor because these figures at any other power
factor would be different.