Correct Answer - Option 3 :
\(\frac{{{E_0} - V}}{V}\)
Voltage regulation:
Voltage regulation is the ratio of the change in terminal voltage to the rated voltage when the load is suddenly removed with the same excitation, same speed.
Voltage regulation = \(\frac{{{E_0} - V}}{V}\)
% Voltage regulation \( = \frac{{{E_0} - V}}{V} \times 100\)
Where E0 is the no-load voltage
And V is the rated terminal voltage
The range of voltage regulation of an alternator is 30-40%