Question

A three-phase star connected synchronous generator is rated at 1.5 MVA and 11kV. The armature effective resistance and synchronous reactance are 1.2 $\Omega$ and 25 $\Omega$ respectively (per phase). The percentage voltage regulation for a load of 1.4375 MVA at 0.8 power factor lagging is _______.

• A. 21.14

Answer 1

The correct option is A 21.14

$\text{Given,}V=\frac{11\times {10}^3}{\sqrt{3}}=6350.853\text{V}$
$R=1.2\Omega$,

$jX=j25\Omega$

$|I|=\frac{1.4375\times {10}^6}{3\times 6350.853}=75.45A$

$I=75.45\angle -{36.87}^{\circ }$

$E=6350.853+(1.2+j25)(75.45\angle -{36.87}^{\circ })$

$=7693.807\angle {10.898}^{\circ }V$

$\text{Voltage regulation}=\frac{|E|-|V|}{|V|}=\times 100$

$=\frac{7693.807-6350.853}{6350.853}\times 100=21.14\%$