# If the no-load voltage of a 3-phase, 440 V, 50 Hz alternator is 495 V, then its voltage regulation is:

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If the no-load voltage of a 3-phase, 440 V, 50 Hz alternator is 495 V, then its voltage regulation is:

1. 12.5%
2. 10.5%
3. 34%
4. 10%

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Correct Answer - Option 1 : 12.5%

Concept:

The voltage regulation of an AC alternator is,

Percentage voltage regulation $= \frac{{{E_{g0}} - {V_t}}}{{{V_t}}} \times 100$

Eg0 is the internally generated voltage per phase at no load

Vt is the terminal voltage per phase at full load

Voltage regulation indicates the drop in voltage from no load to the full load.

There are three causes of voltage drop in the alternator.

• Armature circuit voltage drop
• Armature reactance
• Armature reaction

The first two factors always tend to reduce the generated voltage, the third factor may tend to increase or decrease the generated voltage. The nature of the load affects the voltage regulation of the alternator.

Calculation:

Given that

Eg0 = 495 V, Vt = 440 V

Now percentage voltage regulation can be calculated as

Percentage voltage regulation $= \frac{{{495} - {440}}}{{{440}}} \times 100$

Percentage voltage regulation = 12.5%