Question

A 1500 kVA, 11 kV, $3-\varphi$ star connected alternator has $R_{a}and{X}_{s}of1.2\Omega and24\Omega$ respectively.
The value of generated voltage (line) at a load of 1200 kW, unity pf is

• A. 6601.79 V
• B. 11434.64 V
• C. 3681.14 V
• D. 5493.16 V

Answer 1

The correct option is B 11434.64 V

$I_a=\frac{1200\times {10}^3}{\sqrt{3}\times 11\times {10}^3}=62.98A$

$V_{ph}=\frac{11000}{\sqrt{3}}=6350.85V$

$E_f=\sqrt{(V\cos \varphi +I_a{R}_a{)}^2+(V\sin \varphi +I_a{X}_a{)}^2}$

$=\sqrt{(6350.85+62.98\times 1.2{)}^2+(62.98\times 24{)}^2}=6601.79V$

$E\left(line\right)=6601.79\times \sqrt{3}=11434.64V$