Question

A 200 kVA, 480 V, 50 Hz, Y-connected synchronous generator with a rated field current of 5 A was tested, and the following data were taken:

• A. 1.04 $\Omega$ and 0.5 $\Omega$
• B. 0.2 $\Omega$ and 1.02 $\Omega$
• C. 1.02 $\Omega$ and 0.2 $\Omega$
• D. 0.5 $\Omega$ and 1.04 $\Omega$

Answer 1

The correct option is B 0.2 $\Omega$ and 1.02 $\Omega$

The generator described above is Y-connected, so the direct current in the resistance test flows through two windings
$2R_A=\frac{V_{DC}}{I_{DC}}$

$R_A=\frac{10}{2\times 25}=0.2\Omega$

Internal generated voltage,
$E_A=V_{phO.C}=\frac{V_T}{\sqrt{3}}$
$E_A=\frac{540}{\sqrt{3}}=311.77V$

The short circuit is equal to line current, since generator is Y-connected,
$I_{A,SC}=I_L=300A$

$\frac{E_A}{I_A}=Z_s=\sqrt{R^2+X_s^2}$

$X_S=\sqrt{{\left(\frac{311.77}{300}\right)}^2-(0.2{)}^2}$

$X_S=1.02\Omega$