A three-phase 50 Hz star-connected synchronous generator has $X_s = 5\,\Omega$/phase (resistance negligible). It delivers rated current at 0.8 pf lagging with terminal voltage $V_t = 11\,\text{kV}$ (line). The excitation EMF $E_f$ per phase is approximately:

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Electrical Engineering QUESTION #2156

Question 1

$7{,}351\,\text{V}$✔️
$6{,}350\,\text{V}$
$8{,}660\,\text{V}$
$9{,}100\,\text{V}$

Correct Answer Explanation

$V_{ph} = \frac{11000}{\sqrt{3}} \approx 6350\,\text{V}$. Using $E_f = \sqrt{(V\cos\phi)^2 + (V\sin\phi + IX_s)^2}$ with rated current and 0.8 lag pf gives $E_f \approx 7351\,\text{V}$.

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